Liver Glutamate Dehydrogenase Controls Whole Body Energy Partitioning Through

Page 1 of 43 Diabetes

Liver glutamate dehydrogenase controls whole body energy partitioning through

amino acid-derived gluconeogenesis and ammonia homeostasis

Melis Karaca1,2,*, Juliette Martin-Levilain1,2, Mariagrazia Grimaldi1,2, Lingzi Li1,2, Eva Dizin1, Yalin

Emre3, and Pierre Maechler1,2,*

1Department of Cell Physiology and Metabolism & 2Faculty Diabetes Center, University of Geneva

Medical School, rue Michel Servet 1, 1205 Geneva, Switzerland

3Department of pathology and immunology, University of Geneva Medical School, rue Michel Servet 1,

1205 Geneva, Switzerland

*Correspondence to: Melis Karaca [email protected] and Pierre Maechler

[email protected] ; phone: +41 22 379 55 54

Running title: Liver GDH and energy homeostasis

Word count: 4’248

Diabetes Publish Ahead of Print, published online July 12, 2018 Diabetes Page 2 of 43

Abstract

Ammonia detoxification and gluconeogenesis are major hepatic functions mutually connected through

amino acid metabolism. The liver is rich in glutamate dehydrogenase (GDH) that catalyzes the reversible

oxidative deamination of glutamate to α-ketoglutarate and ammonia, thus bridging amino acid to glucose pathways. Here we generated inducible liver-specific GDH knockout mice (HepGlud1-/-) in order to explore the role of hepatic GDH on metabolic homeostasis. Investigation of nitrogen metabolism revealed altered ammonia homeostasis in HepGlud1-/- mice characterized by increased circulating ammonia associated with reduced detoxification process into urea. The abrogation of hepatic GDH also modified energy homeostasis. In the fasting state, HepGlud1-/- mice could barely produce glucose in response to alanine due to impaired liver gluconeogenesis. Compared to control mice, lipid consumption in

HepGlud1-/- mice was favored over carbohydrates as a compensatory energy fuel. The changes in energy

partitioning induced by the lack of liver GDH modified the circadian rhythm of food intake. Overall, this

study demonstrates the central role of hepatic GDH as a major regulator for the maintenance of both

ammonia and whole body energy homeostasis.

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INTRODUCTION

The turnover of amino acids is characterized by the respective metabolisms of nitrogen and carbon

skeletons. Regarding nitrogen metabolism, the crucial steps are first the removal of the amino group from

in the form of ammonia (NH3) and second its detoxification into urea to prevent further accumulation of

+ the neurotoxic ammonium (NH4 ). The liver is the central organ of ammonia metabolism, while the

muscles and kidneys play a role in the inter-organ exchange and final ammonia disposal (1; 2). The liver

has a remarkable capacity to remove ammonia via both the high-capacity / low-affinity urea cycle, as well

as the low-capacity / high-affinity glutamine synthetase (GS) (3). Both of these ammonia removal

systems engage glutamate as an intermediary metabolite.

Glutamine serves, along with alanine, as a major non-toxic inter-organ ammonia shuttle in the body (2;

4). Glutamine is deamidated to glutamate by glutaminase (GLS), thereby generating ammonia. Alanine

aminotransferase (ALAT) catalyzes the transfer of an amino group from the donor alanine to the acceptor

α-ketoglutarate (α-KG), thereby producing pyruvate and glutamate. Then, glutamate is deaminated to α-

KG through glutamate dehydrogenase (GDH), releasing NH3 for urea synthesis. GDH is abundant in the

liver and is the only mammalian enzyme that catalyzes the deamination of an amino acid. Despite its

specificity for glutamate GDH, via the coupling to aminotransferase reactions, plays a key role in the

deamination of most amino acids.

Beside its role in nitrogen metabolism, the liver is also the major site for gluconeogenesis, which is a

fundamental process under metabolic challenging conditions, such as fasting or sustained physical

exercise (5-9). Primary carbon skeletons used for gluconeogenesis may derive from pyruvate, lactate,

glycerol, and amino acids. During fasting, glutamine and alanine account for 60 to 80% of the amino

acids released from the skeletal muscles and subsequently taken up by the liver (10). GDH represents an

essential link between amino acids and carbohydrates, channeling the carbon skeletons of several amino

acids into the tricarboxylic acid cycle for anaplerosis and the provision of gluconeogenic substrates (2;

11; 12). The importance of GDH activity is witnessed by the severity of disorders where GDH function is

altered (gain of function mutations), such as hyperinsulinism/hyperammonemia syndrome (13; 14).

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While our current knowledge points to liver GDH as a key player in nitrogen metabolism and amino acid-

derived gluconeogenesis, no study has challenged yet such an assumption by in vivo abrogation of GDH

in hepatocytes. Here, we generated inducible liver-specific GDH knockout mice in order to investigate

the role of liver GDH in metabolic homeostasis under both basal and energy challenging conditions. We

found that hepatic GDH was critical for maintenance of both ammonia and urea homeostasis, playing a

central role in the circadian rhythm of food intake and energy partitioning through alanine-induced

gluconeogenesis.

RESEARCH DESIGN AND METHODS

Mice

Glud1 floxed (Glud1lox/lox) mice (Glud1tm1.1Pma, MGI:3835667 (15)) were crossed with mice carrying the tamoxifen-dependent Cre-ERT2 recombinase coding sequence preceded by an internal ribosomal entry

site inserted in the 3 untranslated region of the serum albumin gene (16). The in vivo deletion of GDH in

hepatocytes (HepGlud1-/- mice) was induced at 8 weeks of age by subcutaneous implantation of tamoxifen pellets (Tamoxifen free base, 25mg/pellet - 21 day release - E-361; Innovative Research of

America) in male Glud1lox/lox mice carrying the Albumin-Cre-ERT2 construct and used for analyses 4 weeks later at 12 weeks of age, unless otherwise specified. Animals were maintained on a mixed

(C57BL/6J x 129/Sv) genetic background to avoid inbred strain-specific phenotypes. As control mice, we used Glud1lox/lox littermates in order to optimize standardization of the genetic background between the two groups. To rule out the possibility that the Albumin-Cre transgene used in the present study may have independently contributed to the metabolic phenotype, we studied in parallel cohorts of mice carrying the

Albumin-Cre transgene without floxed Glud1 littermates to investigate some metabolic parameters, revealing no effects of Albumin-Cre per se. Mice were maintained in our certified animal facility (12 hour x 12 hour light/dark cycle with 7 AM on and 7 PM off) according to procedures that were approved by the animal care and experimentation authorities of the Canton of Geneva (#1034-3615-1R).

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Expression by immunoblotting and immunofluorescence

Antibodies against GDH (100-4158, Rockland), actin (MAB1501, Millipore), glutaminase (ab200408,

Abcam), porin (ab34726, Abcam), G6Pase (developed by Dr G Mithieux’s laboratory, Inserm U855,

Lyon, France) and PEPCK-c (ab70358, Abcam) were used for immunoblotting experiments on whole

tissue extracts. For immunofluorescence, tissue sections were stained using antibodies against GDH and

glutamine synthetase (MAB302, Millipore) and bodipy dye (D3922, Molecular Probes) for lipid droplets.

Primary hepatocytes were labeled with MitoTracker Orange CMTMRos (M-7510, Molecular Probes) to

visualize mitochondria. Nuclei were stained either with DAPI or Hoechst (Molecular Probes). Detailed

protocols are described in the Supplemental Experimental Procedures.

GDH enzymatic activity

GDH enzymatic activity was measured in tissues collected in ice-cold saline before homogenization in 50

mM Tris/HCl pH 7.4, 0.5 mM EDTA, 1 mM ß-mercaptoethanol in glass potter. After 40 min

centrifugation at 8000 g, supernatants were assayed for enzymatic activity as previously described (17).

Determination of metabolic parameters

Blood, urine and tissue parameters were determined on samples collected from fed or overnight fasted

animals (18 hours fasting from 4 pm to 10 am). Specific measurements are described in detail in the

Supplemental Experimental Procedures.

In vivo experiments

Body composition was assessed by an EchoMRI-700™ quantitative nuclear magnetic resonance analyzer

(Echo Medical Systems, Houston, TX). Metabolic parameters and physical activity were measured using

a LabMaster system (TSE Systems GmbH, Bad Homburg, Germany) at the Small Animal Phenotyping

Core Facility (University of Geneva, Geneva, Switzerland) under controlled temperature (22 ± 1°C) and

lighting (light on: 07.00-19.00 h). Energy expenditure and respiratory exchange ratio were determined by

indirect calorimetry, locomotor activity was recorded by an infrared frame, and food and water intake

were measured by highly sensitive feeding and drinking sensors. These parameters were measured in

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mice housed individually in Labmaster metabolic cages (TSE Systems GmbH, Bad Homburg, Germany).

Glucose and insulin tolerance tests were performed upon i.p. injection of D-glucose (2g/kg; Sigma-

Aldrich) after an overnight fast or insulin (0.75U/kg; Nova Rapid, Novo Nordisk) on fed mice. Glycerol,

pyruvate, alanine and glutamine challenge tests were performed upon i.p. injection of glycerol (2g/kg;

Sigma-Aldrich), sodium pyruvate (2g/kg; Sigma-Aldrich), L-arginine (2g/kg; Sigma-Aldrich) or L-

glutamine (2g/kg; Acros Organics) after an overnight fast. For ammonia and urea determination, blood

was taken from mice under anesthesia from abdominal aorta and portal, hepatic and renal veins. Detailed

procedures are given in the Supplemental Experimental Procedures.

Glucose production by primary hepatocytes and renal proximal tubule cells

Primary hepatocytes were starved for 6 hours in DMEM 5030 (without glucose, glutamine and pyruvate,

Sigma-Aldrich) for glycogen depletion. The medium was replaced by Krebs-Ringer-Bicarbonate-Hepes

(KRBH) buffer (140 mM NaCl, 3.6 mM KCl, 0.5 mM NaH2PO4, 0.5 mM MgSO4, 2 mM NaHCO3, 1.5 mM CaCl2, and 10 mM HEPES) alone (for basal condition) or KRBH containing 20mM alanine or

10mM glutamine (for stimulatory conditions) and cells were further incubated for 60 min in water bath at

37°C. The supernatant was stored at −20°C until assayed for glucose. Renal cells (200×103) were pre- incubated for 30 min at 37°C in silicone-coated glass tubes gassed with a mixture of O2:CO2 (95%:5%), in a shaking water bath containing KRBH buffer. Thereafter, the medium was replaced by 500 µl KRBH- containing 20mM alanine or 10mM glutamine cells were further incubated for 60 min at 37°C. The supernatant was stored at −20°C until assayed for glucose.

Statistics

Data are presented as means ± SEM. Statistical analyses were performed using GraphPad Prism 6 software, with one–way ANOVA when more than two groups of data were compared and with two-tailed student’s t–test when only two groups of data were concerned. We deemed the difference being significant when p < 0.05.

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RESULTS

Assessment of liver-specific GDH-knockout mouse, HepGlud1-/-

The in vivo deletion of GDH in hepatocytes was induced at 8 weeks of age by subcutaneous implantation

of tamoxifen pellets in Glud1lox/lox mice carrying the Alb-CreERT2 construct, giving rise to liver-specific

GDH-knockout mice (HepGlud1-/-) (Figure S1A). Four weeks after in vivo induction of recombination by

tamoxifen, deletion was successful and specific for the liver of HepGlud1-/- mice (<5% remaining of

immunoreactive GDH), GDH protein being preserved in non-hepatic tissues normally expressing the

Glud1 gene (Figure 1A; Figure S1B). Immunofluorescence of liver sections confirmed the deletion of

GDH in HepGlud1-/- hepatocytes (Figure 1B; Figure S1C). Accordingly, GDH enzymatic activity was

deficient in liver homogenates of HepGlud1-/- mice (-98%, p<0.01) (Figure 1C). Expression of liver GDH

was absent at least up to 50 weeks after tamoxifen implantation (Figure S1D). GDH ablation altered

neither the liver morphology nor the liver to body weight ratio of young and aged HepGlud1-/- mice

(Figure S2). Intracellular lipid distribution as well as mitochondrial morphology were not modified by the

hepatocyte-specific GDH deletion (Figure S3). Finally, plasma levels of ALAT and aspartate

aminotransferase (ASAT), measured as an index of the global liver health status, did not show differences

between control Glud1lox/lox and knockout HepGlud1-/- mice (Table S1).

Liver GDH controls ammonia detoxification into urea

We next examined the role of GDH in the fate of cellular ammonia by quantifying circulating ammonia

levels in the fed animals at different sites of the vasculature. Blood was collected from the same animal

from the portal vein (representing the “intestinal outflow” and about 85% of the “liver inflow”), the

abdominal aorta (representing the remaining 15% of the “liver inflow”), the hepatic vein (representing the

“liver outflow”) and the renal vein (representing the “renal outflow”) (18). Compared to control mice, the

absence of liver GDH resulted in a marked elevation of plasma ammonia levels at any of the sites.

HepGlud1-/- mice showed mild systemic arterial hyperammonemia (+59%, p<0.01), along with increased

portal venous ammonia (+51%, p<0.05) irrigating the liver (Figure 2A). The similar differences observed

between control and GDH null mice in aorta and in portal vein indicate that the intestine did not

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contribute to the higher ammonia levels in HepGlud1-/- mice (Figure 2A). Hepatic ammonia metabolism was not sufficient to normalize the hepatic vein ammonia levels in HepGlud1-/- mice, as revealed by the gap between control and HepGlud1-/- mice, even more pronounced in this compartment (+117%, p<0.01,

Figure 2A). Sampling from the hepatic vein revealed that control Glud1lox/lox livers were able to clear 49%

(p<0.01) of the portal ammonia, a clearance that dropped to only 27% (p=0.07) for HepGlud1-/- livers

(Figure 2A). The resulting increased hepatic ammonia output in HepGlud1-/- mice was further witnessed by the higher hepatic arteriovenous difference for ammonia (Figure 2B). Moreover, the absence of GDH in the liver resulted in an increase of ammonia concentrations in renal venous plasma (+154%, p<0.01,

Figure 2A). We also observed a higher magnitude of the renal arteriovenous difference for ammonia

(Figure 2B), indicating increased renal ammonia output as a consequence of liver-specific GDH deletion.

This observation was supported by increased GLS protein levels in kidney of HepGlud1-/- mice (Figure

S4A). Accordingly, we measured higher peripheral venous ammonia levels in HepGlud1-/- mice (+93%, p<0.001, Figure 2C). Finally, urine ammonia levels were higher in HepGlud1-/- mice when compared to controls (Figure 2D).

In normal conditions, the liver detoxifies ammonia by synthesizing urea, which is then released in the blood and excreted by the kidneys before its elimination through urine (3; 19). Peripheral venous urea levels were decreased in HepGlud1-/- mice (-35%, p<0.001, Figure 2E) due to reduced urea synthesis by the liver as shown by lower hepatic vein urea levels (-14%, p<0.05, Figure 2F). As a consequence, urea levels measured in urines of HepGlud1-/- mice were much lower than those of control mice (-45%, p<0.01, Figure 2G).

As glutamate is required for ammonia removal systems, we measured the activities of liver enzymes involved in glutamate handling. In the fed state, protein levels of GS and enzymatic activities of GS,

GLS, ASAT and ALAT were similar between control and HepGlud1-/- mice (Figure S4B-F). These data show that the lack of liver GDH was not compensated by other liver enzymes involved in glutamate handling.

Finally, glutamine and glutamate levels were similar in liver of HepGlud1-/- and control mice. However, aspartate levels were significantly decreased in HepGlud1-/- liver (Figure 2H). The process of urea cycle 8

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involves equimolar provision of NH3 and aspartate (20; 21). Thus, the limiting step for urea synthesis in

HepGlud1-/- mice could be the availability of aspartate required in the urea cycle, leading to decreased

liver clearance of ammonia into urea. Upstream of aspartate incorporation, the hepatic contents of the

urea cycle intermediates ornithine and citrulline were similar between controls and HepGlud1-/- mice

(Figure 2H), indicating that these intermediates were not rate limiting.

Altogether, this set of data shows that the specific deletion of GDH in the liver alters ammonia

homeostasis due to increased ammonia output and decreased detoxification into urea.

Liver GDH directs rhythms of feeding behavior and energy substrate utilization

HepGlud1-/- mice showed similar body weight and body fat versus lean mass distribution when compared

to Glud1lox/lox controls (Figure 3A-B). These parameters were conserved during lifetime (not shown).

Remarkably, the absence of liver GDH modified the food intake profile. HepGlud1-/- mice exhibited a

shift in their circadian rhythm of feeding as they stopped eating earlier at night, before the end of the dark

cycle, and began eating earlier during the normal fasting daytime in the afternoon, way before the end of

the light cycle (Figure 3C; Figure S5). This was associated with a slight decrease in food intake over a

24h period (Figure S5). Whereas the spontaneous locomotor activity tended to be lower in HepGlud1-/-

mice compared to Glud1lox/lox controls (Figure S6), the energy expenditure was similar between the two

groups (Figure S7). The calculated VCO2/VO2 revealed a significant shift towards lower values in

respiratory exchange ratio (RER) pointing to differential energy substrate utilization (Figure 3D; Figure

S8). The calculated fat vs carbohydrate and protein oxidation (22) showed that, at the whole body level,

lipids were favored over carbohydrates and proteins as energy fuel in HepGlud1-/- mice compared to

control animals (Figure 3E-F).

The difference in feeding behavior between HepGlud1-/- and Glud1lox/lox mice did not affect the glycemia

measured either in the morning in the fed state or after an overnight (O/N) fasting-induced metabolic

challenge (Figure 4A). Even older (25-27 weeks of age) control Glud1lox/lox and knockout HepGlud1-/-

mice subjected to a 24h fast exhibited similar glycemia (3.8±0.3 and 4.6±0.3, respectively, n=5-6). The

first metabolic response to fasting is liver glycogenolysis. In the fed condition, deletion of GDH in the

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hepatocytes did not modify liver glycogen content that was efficiently restored upon feeding (Figure 4B);

without changes in the expression of glucokinase (assessed by immunoblotting, data not shown). Fasting-

induced depletion of liver glycogen was similar between HepGlud1-/- and Glud1lox/lox control animals, showing a rapid mobilization and near complete depletion (about 98% drop) already after 6h of fasting in both groups (Figure 4B). Upon energy need, reduced blood insulin levels promote lipolysis of fat stored as triglycerides in adipose tissue leading to the release of free fatty acids (FFA) used for ß-oxidation, ketogenesis, and reformation of triglyceride-rich lipoproteins in the liver. Plasma FFA levels in fed condition were similar in HepGlud1-/- and Glud1lox/lox control animals (Figure 4C). However, HepGlud1-/- mice showed lower circulating levels of FFA in the fasting state compared to controls (Figure 4C) despite similar insulin levels (Table S1). The fasting-induced ketone body production was preserved in

HepGlud1-/-mice (Figure 4D). Higher clearance of plasma FFA is in line with the preferential utilization of lipids as energy substrates in HepGlud1-/- mice.

Liver GDH is mandatory for alanine-induced gluconeogenesis

Glucose tolerance tests revealed normal glucose excursions in HepGlud1-/- animals (Figure 5A) and insulin tolerance tests showed similar peripheral sensitivity in HepGlud1-/- mice and Glud1lox/lox controls

(Figure 5B). Next, we investigated the gluconeogenic capacity of HepGlud1-/- mice by measuring the rise in blood glucose after intraperitoneal administration of substrates recruited in situations of energy imbalance, such as fasting. Administration of either glycerol or pyruvate, two GDH-independent gluconeogenic substrates, induced similar increases in blood glucose levels in both knockout and control mice (Figure 5C-D). Then we tested the GDH-dependent amino acids glutamine and alanine, two major substrates transported from the muscles during periods of active gluconeogenesis. Glycemia of control mice increased in response to both glutamine and alanine challenge (Figure 5E-F). Of note, the CreERT2 transgene per se did not affect the alanine response (Figure S9A). Remarkably, glutamine was able to increase glycemia in HepGlud1-/- mice, whereas the alanine response was markedly impaired in the absence of hepatic GDH (Figure 5F and Figure S9). This effect observed 4 weeks after recombination, i.e. at 12 weeks of age, was preserved in older mice 17 weeks after recombination (Figure S9B). Since the

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skeletal muscles may contribute to the supply of gluconeogenic amino acids to the liver, we assessed the

levels of such metabolites in both soleus and gastrocnemius muscles, revealing no major differences

between HepGlud1-/- mice and Glud1lox/lox controls (Figure S10).

We then measured plasma amino acids in fed and O/N fasted mice (Figure 6A-B and Figure S11).

Circulating glutamine levels were higher in fed HepGlud1-/- mice compared to Glud1lox/lox controls

(Figure 6A). Interestingly, plasma glutamine levels decreased following an O/N fasting in HepGlud1-/-

mice but not in control animals (Figure 6A), indicating an increased utilization of glutamine in HepGlud1-

/-mice. O/N fasting induced efficient clearance of plasma alanine in Glud1lox/lox control animals, which

was not the case in HepGlud1-/- mice (Figure 6B).

Whereas gluconeogenesis from glutamine takes place in the kidneys and the intestine, gluconeogenesis

from alanine and lactate is the key pathway in the liver (23). Thus, we tested the gluconeogenic capacity

of isolated primary hepatocytes and renal proximal tubular cells. In control hepatocytes, both alanine and

glutamine stimulation increased glucose production when compared to basal state (Figure 6C). On the

contrary, hepatocytes isolated from HepGlud1-/-mice failed to increase glucose production in response to

alanine and glutamine, both being GDH-dependent substrates (Figure 6C). In renal proximal tubule cells,

only glutamine could promote glucose production to similar extents in both groups (Figure 6D).

In agreement with these data, the O/N fasting induced a robust gluconeogenic adaptive response in livers

of Glud1lox/lox and HepGlud1-/- mice, as shown by increased PEPCK-c and G6Pase protein levels (Figure

S12). However, fasting-induced PEPCK-c upregulation was less efficient in liver of HepGlud1-/- mice

when compared to Glud1lox/lox controls (Figure 6E), not compensating for the impaired alanine-induced

gluconeogenic activity in the knockout animals. In fasting kidney, no differences of PEPCK and G6Pase

levels were observed between in Glud1lox/lox and HepGlud1-/- kidneys (Figure 6F and Figure S12A).

Consistently, both groups exhibited similar levels of amino acids in kidney extracts (Figure S12B).

Altogether, these data show altered gluconeogenesis in the liver of HepGlud1-/- mice.

DISCUSSION

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Urea synthesis and gluconeogenesis characterize some of the prominent liver functions, closely related to

each other through amino acid metabolism. On the one hand, deamination of the α-amino group of amino

acids produces ammonia, a toxic metabolite that is detoxified by its conversion into urea via the ornithine

cycle in the liver. On the other hand, carbon skeletons derived from deaminated amino acids are

preferentially converted into glucose by gluconeogenic enzymes. The present in vivo study, using a liver

specific GDH-deficient mouse, shows that hepatic GDH is central to ammonia homeostasis and

gluconeogenesis from amino acids. Regarding nitrogen metabolism, deletion of liver GDH triggered a

systemic rise in ammonemia due to decreased detoxification into urea and to increased ammonia output

(Figure 7A).

While GDH is found throughout the liver lobules, its activity increases from periportal to perivenous cells

(24). The bidirectionality of the GDH pathway in the liver has been confirmed by labelling experiments

(25-28). In periportal hepatocytes expressing the urea cycle enzymes, where deamination of much of the

amino acids takes place, GDH function is thought to be the deamination (29); whereas in perivenous

hepatocytes, where GDH levels are particularly high, GDH may produce glutamate needed for glutamine

synthesis via GS. In the liver, while the glutamate deamination through GDH supplies nitrogen to the urea

cycle in the form of ammonium, the reaction towards glutamate production may have multiple

consequences on the regulation of systemic ammonia detoxification. As formulated by Nissim et al. (30),

the formation of glutamate from ammonia may: (i) serve as a scavenger for excess of ammonia; (ii)

improve the availability of mitochondrial glutamate for the synthesis of N-acetyl-glutamate; and (iii) lead

to the formation of aspartate via the ASAT reaction. Consequently, increased N-acetyl-glutamate and

aspartate levels favor ammonia detoxification via urea synthesis. In HepGlud1-/- mice, hepatic aspartate levels were reduced and might have contributed to the incomplete conversion of ammonia to urea, pointing to the liver as the primary source of the excess ammonia measured in the knockout animals. Of note, an alternative route to urea production for clearance of ammonia from the body is exhalation.

Indeed, it was reported that excess ammonia not efficiently excreted out of the body may diffuse into the lungs and can be exhaled in breath (34). This has not been assessed in the present study and future studies

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with flux measurements might help delineating inter-organ ammonia turnover in the absence of liver

GDH.

In kidneys, GDH operates towards the deamination direction, thereby contributing at least to 25% of the

renal ammonia production (31), the main proportion being produced by the deamidation of glutamine by

the action of glutaminase. It was shown in rats that BCH-induced activation of GDH results in increased

ammonia production by the kidney (32). Under conditions of acidosis, a marked increase in glutamate

deamination was found, with the GDH pathway contributing to about half of the augmented ammonia

production (33). We did not find any upregulation of GDH protein or activity levels in the kidneys of

HepGlud1-/- mice. However, increased glutaminase levels in HepGlud1-/- mice led to higher renal

ammoniagenesis as measured by increased ammonia levels in the renal vein and urine.

We have previously reported the important contribution of GDH to brain energy metabolism (35; 36).

The liver being one of the major organs contributing to metabolic control, we have now examined the

putative importance of liver GDH for whole body energy homeostasis in the HepGlud1-/- mouse model.

While the body weight and body composition were similar between control and HepGlud1-/- mice, the

food intake profile as well as the respiratory exchange ratio were different between genotypes. In fact, the

deletion of GDH in the liver led to a modified body fuel recruitment in HepGlud1-/- mice with preferential

utilization of lipids over carbohydrates and proteins as energy substrates in the post-prandial state. GDH

participates to cataplerosis during periods of increased energy supply and to anaplerosis during periods of

increased energy demand feeding the TCA cycle (11). The reaction catalyzed by GDH links carbohydrate

to protein metabolism. At the whole body level, the metabolic shift to fatty acid metabolism seems to be a

compensatory mechanism for reduced carbohydrates/protein utilization in the absence of liver GDH and

the subsequent impaired hepatic glucose production (Figure 7B).

Fasting represents an important metabolic challenge. During fasting, the nutritional glucose supply

becomes progressively limiting, glucose production being maintained through glycogen breakdown

(glycogenolysis) and then de novo glucose synthesis (gluconeogenesis) upon starving conditions. Because

proteolysis is mainly responsible for the net production of gluconeogenic precursors, oxidation of fatty

acids is essential as an alternative pathway to prevent a rapid erosion of the protein mass (37; 38). The 13

Diabetes Page 14 of 43

contribution of glycogenolysis was similar in control vs knockout mice, while the lower circulating free fatty acid levels in HepGlud1-/- mice observed upon prolonged fasting was in line with increased fatty acid oxidation.

The importance of gluconeogenesis rapidly increases with the duration of fasting, exhaustion of the glycogen stores initiating starving conditions. When livers from fasted rats are perfused with a mixture of physiological gluconeogenic substrates at their normal plasma levels, amino acids account for over 50% of the glucose production (39). Most amino acids derived from proteins of the skeletal muscles are converted to alanine and glutamine and released in the circulation before their uptake and use by the liver and the kidney, respectively. Additionally, lactate and glycerol are used to similar extents by both gluconeogenic organs. In vivo challenge with various gluconeogenic substrates, as well as in vitro stimulation of primary hepatocytes isolated from control and HepGlud1-/- animals, showed that liver gluconeogenesis from amino acids was altered in HepGlud1-/- mice. Although alanine is primarily used by the liver, glutamine is used by the kidney for gluconeogenesis (23), while we did not observed compensatory glucose production in renal cells isolated from HepGlud1-/- mice. In the liver of HepGlud1-

/- mice, alanine-derived gluconeogenesis via ALAT was probably impaired because of shortage of ALAT

substrate α-KG resulting from the absence of GDH.

Interestingly, there was no compensatory increase of the gluconeogenic capacity of the kidney, as

indicated by similar levels of PEPCK-c and G6Pase. Furthermore, primary tubule cells isolated from

HepGlud1-/- mice did not enhance glucose output upon glutamine stimulation, showing that the kidney

did not compensate for decreased liver gluconeogenesis in our model. However, lower circulating plasma

glutamine levels in fasting HepGlud1-/- mice compared to controls indicate an increase in glutamine utilization, potentially contributed by intestine gluconeogenesis.

Overall, our data point to liver GDH as a key player in glucose and amino acid metabolism, participating to the control of the circadian rhythm of food intake. On the one hand, GDH regulates ammonia homeostasis. On the other hand, GDH contributes to whole body energy homeostasis, due to its role (i) in the metabolic shift between carbohydrates/protein oxidation versus fatty acid oxidation and (ii) in gluconeogenesis from amino acids. 14

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ACKNOWLEDGEMENTS

This work was supported by the State of Geneva, the Swiss National Science Foundation (#135704,

#146984 to P.M.), the Gertrude von Meissner and Schmidheiny Foundations (to M.K.) and Machaon

Foundation (to Y.E.).

We are grateful to Dr P Chambon and Dr D Metzger for sharing the SA-Cre-ERT2 mice (IGBMC,

Strasbourg). We thank Dr J Altirriba for his help with metabolic cages data analyses (University of

Geneva) and Dr R Martin-del-Rio and Dr J Tamarit-Rodriguez for plasma amino acid analyses

(Complutense University, Madrid). We thank G Chaffard, C Vesin and F Visentin for expert technical

assistance as well as Dr T Brun and Dr E Feraille for helpful discussions (University of Geneva). We

thank Dr J Ivanisevic and her team for amino acid analyses (University of Lausanne). We are grateful to

Dr G Mithieux’s laboratory (Inserm U855, Lyon) for sharing G6Pase antibody and in particular to Dr F

Rajas for helpful discussion.

M.K. and P.M. designed research; M.K., J.M.L., M.G., L.L., E.D., Y.E. performed research; M.K., Y.E.

and P.M. analyzed data; and M.K. and P.M. wrote the paper. PM is the guarantor of this work and, as

such, has access to all the data in the study: Part of the study was presented at the 52nd annual meeting of

the European Association for the Study of Diabetes (EASD, September 2016). The authors have no

conflict of interest to declare.

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REFERENCES

1. Wright G, Noiret L, Olde Damink SW, Jalan R: Interorgan ammonia metabolism in liver failure: the basis of current and future therapies. Liver international : official journal of the International Association for the Study of the Liver 2011;31:163-175 2. Aikawa T, Matsutaka H, Yamamoto H, Okuda T, Ishikawa E: Gluconeogenesis and amino acid metabolism. II. Inter-organal relations and roles of glutamine and alanine in the amino acid metabolism of fasted rats. Journal of biochemistry 1973;74:1003-1017 3. Haussinger D: Nitrogen metabolism in liver: structural and functional organization and physiological relevance. Biochem J 1990;267:281-290 4. Nurjhan N, Bucci A, Perriello G, Stumvoll M, Dailey G, Bier DM, Toft I, Jenssen TG, Gerich JE: Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man. J Clin Invest 1995;95:272-277 5. Rui L: Energy metabolism in the liver. Comprehensive Physiology 2014;4:177-197 6. Sharabi K, Tavares CD, Rines AK, Puigserver P: Molecular pathophysiology of hepatic glucose production. Molecular aspects of medicine 2015;46:21-33 7. Donovan CM, Sumida KD: Training improves glucose homeostasis in rats during exercise via glucose production. Am J Physiol 1990;258:R770-776 8. Burelle Y, Fillipi C, Peronnet F, Leverve X: Mechanisms of increased gluconeogenesis from alanine in rat isolated hepatocytes after endurance training. Am J Physiol Endocrinol Metab 2000;278:E35-42 9. Wasserman DH, Cherrington AD: Hepatic fuel metabolism during muscular work: role and regulation. Am J Physiol 1991;260:E811-824 10. Young VR: Nutrient interactions with reference to amino acid and protein metabolism in non- ruminants; particular emphasis on protein-energy relations in man. Zeitschrift fur Ernahrungswissenschaft 1991;30:239-267 11. Karaca M, Frigerio F, Maechler P: From pancreatic islets to central nervous system, the importance of glutamate dehydrogenase for the control of energy homeostasis. Neurochem Int 2011;59:510-517 12. Mallet LE, Exton JH, Park CR: Control of gluconeogenesis from amino acids in the perfused rat liver. J Biol Chem 1969;244:5713-5723 13. Stanley CA, Fang J, Kutyna K, Hsu BY, Ming JE, Glaser B, Poncz M: Molecular basis and characterization of the hyperinsulinism/hyperammonemia syndrome: predominance of mutations in exons 11 and 12 of the glutamate dehydrogenase gene. HI/HA Contributing Investigators. Diabetes 2000;49:667-673 14. Grimaldi M, Karaca M, Latini L, Brioudes E, Schalch T, Maechler P: Identification of the molecular dysfunction caused by glutamate dehydrogenase S445L mutation responsible for hyperinsulinism/hyperammonemia. Human molecular genetics 2017;26:3453-3465 15. Carobbio S, Frigerio F, Rubi B, Vetterli L, Bloksgaard M, Gjinovci A, Pournourmohammadi S, Herrera PL, Reith W, Mandrup S, Maechler P: Deletion of Glutamate Dehydrogenase in Beta-Cells Abolishes Part of the Insulin Secretory Response Not Required for Glucose Homeostasis. J Biol Chem 2009;284:921-929 16. Schuler M, Dierich A, Chambon P, Metzger D: Efficient temporally controlled targeted somatic mutagenesis in hepatocytes of the mouse. Genesis 2004;39:167-172 17. Carobbio S, Ishihara H, Fernandez-Pascual S, Bartley C, Martin-Del-Rio R, Maechler P: Insulin secretion profiles are modified by overexpression of glutamate dehydrogenase in pancreatic islets. Diabetologia 2004;47:266-276 18. Ghallab A, Celliere G, Henkel SG, Driesch D, Hoehme S, Hofmann U, Zellmer S, Godoy P, Sachinidis A, Blaszkewicz M, Reif R, Marchan R, Kuepfer L, Haussinger D, Drasdo D, Gebhardt R, Hengstler JG: Model-guided identification of a therapeutic strategy to reduce hyperammonemia in liver diseases. Journal of hepatology 2016;64:860-871 19. Adeva MM, Souto G, Blanco N, Donapetry C: Ammonium metabolism in humans. Metabolism: clinical and experimental 2012;61:1495-1511

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20. Meijer AJ, Lamers WH, Chamuleau RA: Nitrogen metabolism and ornithine cycle function. Physiol Rev 1990;70:701-748 21. Yang D, Hazey JW, David F, Singh J, Rivchum R, Streem JM, Halperin ML, Brunengraber H: Integrative physiology of splanchnic glutamine and ammonium metabolism. Am J Physiol Endocrinol Metab 2000;278:E469-476 22. Bruss MD, Khambatta CF, Ruby MA, Aggarwal I, Hellerstein MK: Calorie restriction increases fatty acid synthesis and whole body fat oxidation rates. Am J Physiol Endocrinol Metab 2010;298:E108-116 23. Stumvoll M, Meyer C, Perriello G, Kreider M, Welle S, Gerich J: Human kidney and liver gluconeogenesis: evidence for organ substrate selectivity. Am J Physiol 1998;274:E817-826 24. Maly IP, Sasse D: Microquantitative analysis of the intra-acinar profiles of glutamate dehydrogenase in rat liver. J Histochem Cytochem 1991;39:1121-1124 25. Cooper AJ, Nieves E, Coleman AE, Filc-DeRicco S, Gelbard AS: Short-term metabolic fate of [13N]ammonia in rat liver in vivo. J Biol Chem 1987;262:1073-1080 26. Cooper AJ, Nieves E, Rosenspire KC, Filc-DeRicco S, Gelbard AS, Brusilow SW: Short-term metabolic fate of 13N-labeled glutamate, alanine, and glutamine(amide) in rat liver. J Biol Chem 1988;263:12268-12273 27. Brosnan JT, Brosnan ME, Charron R, Nissim I: A mass isotopomer study of urea and glutamine synthesis from 15N-labeled ammonia in the perfused rat liver. J Biol Chem 1996;271:16199-16207 28. Nissim I, Brosnan ME, Yudkoff M, Brosnan JT: Studies of hepatic glutamine metabolism in the perfused rat liver with (15)N-labeled glutamine. J Biol Chem 1999;274:28958-28965 29. Brosnan ME, Brosnan JT: Hepatic glutamate metabolism: a tale of 2 hepatocytes. The American journal of clinical nutrition 2009;90:857S-861S 30. Nissim I, Horyn O, Luhovyy B, Lazarow A, Daikhin Y, Yudkoff M: Role of the glutamate dehydrogenase reaction in furnishing aspartate nitrogen for urea synthesis: studies in perfused rat liver with 15N. Biochem J 2003;376:179-188 31. van de Poll MC, Soeters PB, Deutz NE, Fearon KC, Dejong CH: Renal metabolism of amino acids: its role in interorgan amino acid exchange. The American journal of clinical nutrition 2004;79:185-197 32. Treberg JR, Clow KA, Greene KA, Brosnan ME, Brosnan JT: Systemic activation of glutamate dehydrogenase increases renal ammoniagenesis: implications for the hyperinsulinism/hyperammonemia syndrome. Am J Physiol Endocrinol Metab 2010;298:E1219-1225 33. Schoolwerth AC, Nazar BL, LaNoue KF: Glutamate dehydrogenase activation and ammonia formation by rat kidney mitochondria. J Biol Chem 1978;253:6177-6183 34. Hibbard T, Killard AJ: Breath ammonia levels in a normal human population study as determined by photoacoustic laser spectroscopy. Journal of breath research 2011;5:037101 35. Karaca M, Frigerio F, Migrenne S, Martin-Levilain J, Skytt DM, Pajecka K, Martin-del-Rio R, Gruetter R, Tamarit-Rodriguez J, Waagepetersen HS, Magnan C, Maechler P: GDH-Dependent Glutamate Oxidation in the Brain Dictates Peripheral Energy Substrate Distribution. Cell reports 2015;13:365-375 36. Frigerio F, Karaca M, De Roo M, Mlynarik V, Skytt DM, Carobbio S, Pajecka K, Waagepetersen HS, Gruetter R, Muller D, Maechler P: Deletion of glutamate dehydrogenase 1 (Glud1) in the central nervous system affects glutamate handling without altering synaptic transmission. J Neurochem 2012;123:342- 348 37. Cahill GF, Jr.: Starvation in man. The New England journal of medicine 1970;282:668-675 38. Cahill GF, Jr.: Fuel metabolism in starvation. Annual review of nutrition 2006;26:1-22 39. Exton JH, Park CR: Control of gluconeogenesis in liver. I. General features of gluconeogenesis in the perfused livers of rats. J Biol Chem 1967;242:2622-2636

Diabetes Page 18 of 43

FIGURE LEGENDS

Figure 1. Assessment of liver-specific glutamate dehydrogenase (GDH)-knockout mouse, HepGlud1-

/-. (A) Liver-specific GDH knockout was controlled by immunoblotting and compared to non-liver tissues

collected from control (Glud1lox/lox) and liver-specific Glud1 knockout HepGlud1-/-mice. Brain extracts from constitutive GDH brain knockout CnsGlud1-/- mice served as a negative control for GDH expression. Actin served as loading control. Immunoblots are representative of 4 independent preparations. (B) Representative maximal projections of confocal images of liver cryosections from

Glud1lox/lox control and HepGlud1-/- mice co-stained for GDH (red), glutamine synthetase (GS, green) and nuclei (DAPI, blue) (n=5). (C) Enzymatic oxidative activity of GDH measured in tissue extracts of

Glud1lox/lox control (CTL) and HepGlud1-/- (LKO) mice using glutamate as substrate (n=6). Values are means ± SEM. **p<0.01, Glud1lox/lox control vs HepGlud1-/- mice.

(n=6-8). (B) Hepatic and renal arteriovenous differences for ammonia in Glud1lox/lox control and

HepGlud1-/- mice (n=8). A, arterial; RV, renal vein; HV, hepatic vein. (C) Retro-orbital sampling allowed quantification of peripheral venous ammonia levels (n=8). (D) Urine ammonia levels (n=6-8). (E)

Peripheral venous, (F) hepatic vein and (G) urine urea levels in Glud1lox/lox control and HepGlud1-/- mice

(n=7-9). (H) Liver content in amino acids (n=5-6). All values are means ± SEM. *p<0.05; **p<0.01;

***p<0.001, control vs HepGlud1-/- mice.

(RER as VCO2/VO2) measured over 3 consecutive periods of 24h composed of night and day time

(n=12). 18

Page 19 of 43 Diabetes

(E) Extrapolated fat and (F) carbohydrate & protein oxidation represented over a 24h period

corresponding to the mean of three consecutive periods of 24h composed of night and day time (n=12).

All values are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice.

Figure 4. Lipid utilization is favored in HepGlud1-/-mice. (A) Plasma glucose levels in fed and

overnight (O/N) fasted Glud1lox/lox control and HepGlud1-/- mice (n=13-16). (B) Liver glycogen content

(the inset shows the 6h and O/N fasting condition with adjusted scale), (C) Plasma free fatty acids and

(D) Plasma ß-hydroxybutyrate concentrations in fed and overnight fasted Glud1lox/lox control and

HepGlud1-/- mice (n=6-8). All values are means ± SEM. *p<0.05, control vs HepGlud1-/- mice. #p<0.05;

##p<0.01; ###p<0.001, fasting vs fed condition of corresponding genotype.

Figure 5. Alanine-induced gluconeogenesis is altered in HepGlud1-/- mice. (A) Glucose tolerance test

(2g/kg) and (B) insulin tolerance test (0.75U/kg) with corresponding AUC in Glud1lox/lox control and

HepGlud1-/- mice (n=6-8). (C-F) Blood glucose levels in response to (C) glycerol challenge (2g/kg; n=8-

9), (D) pyruvate challenge (2g/kg; n=11-13), (E) glutamine challenge (2g/kg; n=10-13) and (F) alanine

challenge (2g/kg; n=19-22) with corresponding AUC in Glud1lox/lox control and HepGlud1-/- mice. IP,

intra peritoneal; TT, tolerance test; AUC, area under the curve. All values are means ± SEM. ***p<0.001,

control vs HepGlud1-/- mice.

-/- Figure 6. The kidney of HepGlud1 mice does not compensate for altered liver gluconeogenesis. (A)

Plasma glutamine and (B) alanine levels measured in fed and overnight (O/N) fasting conditions (n=7).

Glucose production by (C) primary hepatocytes and (D) renal proximal tubule cells isolated from control

Glud1lox/lox (CTL) and HepGlud1-/- (LKO) mice in response to alanine and glutamine stimulations

compared to incubation in basal medium (n=3-6). Immunoblotting for (E) liver and (F) kidney GDH,

PEPCK-c and G6Pase in HepGlud1-/- mice compared to Glud1lox/lox controls in overnight (O/N) fasting

state. All values are means ± SEM. *p<0.05, ***p<0.001, control vs HepGlud1-/- mice in the same fed or

fasting state. &&p<0.01, fasting vs fed condition of corresponding genotype. #p<0.05, amino acid

stimulation compared to basal condition of corresponding genotype. §p<0.05, glutamine stimulation

compared to alanine stimulation of corresponding genotype. 19

Diabetes Page 20 of 43

Figure 7. Scheme depicting the consequences of GDH deletion in the liver. (A) Ammonia metabolism

in HepGlud1-/- mice in fed condition. (B) Energy metabolism in HepGlud1-/- mice in fasting condition.

Pathways and metabolites increased in HepGlud1-/- mice are shown in green while the decreased ones are in red.

Page 21 of 43 Diabetes

Figure 1. Assessment of liver-specific glutamate dehydrogenase (GDH)-knockout mouse, HepGlud1-/-. (A) Liver-specific GDH knockout was controlled by immunoblotting and compared to non-liver tissues collected from control (Glud1lox/lox) and liver-specific Glud1 knockout HepGlud1-/-mice. Brain extracts from constitutive GDH brain knockout CnsGlud1-/- mice served as a negative control for GDH expression. Actin served as loading control. Immunoblots are representative of 4 independent preparations. (B) Representative maximal projections of confocal images of liver cryosections from Glud1lox/lox control and HepGlud1-/- mice co-stained for GDH (red), glutamine synthetase (GS, green) and nuclei (DAPI, blue) (n=5). (C) Enzymatic oxidative activity of GDH measured in tissue extracts of Glud1lox/lox control (CTL) and HepGlud1-/- (LKO) mice using glutamate as substrate (n=6). Values are means ± SEM. **p<0.01, Glud1lox/lox control vs HepGlud1-/- mice.

190x254mm (96 x 96 DPI) Diabetes Page 22 of 43

Page 23 of 43 Diabetes

Figure 2. Lack of GDH in HepGlud1-/- livers alters ammonia handling. (A) Plasma ammonia levels were measured in the same mice at different sites: aorta (arterial), renal vein, hepatic vein and portal vein (n=6- 8). (B) Hepatic and renal arteriovenous differences for ammonia in Glud1lox/lox control and HepGlud1-/- mice (n=8). A, arterial; RV, renal vein; HV, hepatic vein. (C) Retro-orbital sampling allowed quantification of peripheral venous ammonia levels (n=8). (D) Urine ammonia levels (n=6-8). (E) Peripheral venous, (F) hepatic vein and (G) urine urea levels in Glud1lox/lox control and HepGlud1-/- mice (n=7-9). (H) Liver content in amino acids (n=5-6). All values are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice.

190x254mm (96 x 96 DPI)

Diabetes Page 24 of 43

Figure 3. Altered food intake and early recruitment of lipids in HepGlud1-/-mice. (A) Body weight and (B) body composition showing lean and fat mass distribution in Glud1lox/lox control and HepGlud1-/- mice measured by EchoMRI (n=9). (C) Non-incremental food intake and (D) Respiratory exchange ratio (RER as VCO2/VO2) measured over 3 consecutive periods of 24h composed of night and day time (n=12). (E) Extrapolated fat and (F) carbohydrate & protein oxidation represented over a 24h period corresponding to the mean of three consecutive periods of 24h composed of night and day time (n=12). All values are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice.

190x254mm (96 x 96 DPI)

Page 25 of 43 Diabetes

Figure 4. Lipid utilization is favored in HepGlud1-/-mice. (A) Plasma glucose levels in fed and overnight (O/N) fasted Glud1lox/lox control and HepGlud1-/- mice (n=13-16). (B) Liver glycogen content (the inset shows the 6h and O/N fasting condition with adjusted scale), (C) Plasma free fatty acids and (D) Plasma ß- hydroxybutyrate concentrations in fed and overnight fasted Glud1lox/lox control and HepGlud1-/- mice (n=6-8). All values are means ± SEM. *p<0.05, control vs HepGlud1-/- mice. #p<0.05; ##p<0.01; ###p<0.001, fasting vs fed condition of corresponding genotype.

190x254mm (96 x 96 DPI)

Diabetes Page 26 of 43

Figure 5. Alanine-induced gluconeogenesis is altered in HepGlud1-/- mice. (A) Glucose tolerance test (2g/kg) and (B) insulin tolerance test (0.75U/kg) with corresponding AUC in Glud1lox/lox control and HepGlud1-/- mice (n=6-8). (C-F) Blood glucose levels in response to (C) glycerol challenge (2g/kg; n=8-9), (D) pyruvate challenge (2g/kg; n=11-13), (E) glutamine challenge (2g/kg; n=10-13) and (F) alanine challenge (2g/kg; n=19-22) with corresponding AUC in Glud1lox/lox control and HepGlud1-/- mice. IP, intra peritoneal; TT, tolerance test; AUC, area under the curve. All values are means ± SEM. ***p<0.001, control vs HepGlud1-/- mice.

190x254mm (96 x 96 DPI)

Page 27 of 43 Diabetes

Figure 6. The kidney of HepGlud1-/-mice does not compensate for altered liver gluconeogenesis. (A) Plasma glutamine and (B) alanine levels measured in fed and overnight (O/N) fasting conditions (n=7). Glucose production by (C) primary hepatocytes and (D) renal proximal tubule cells isolated from control Glud1lox/lox (CTL) and HepGlud1-/- (LKO) mice in response to alanine and glutamine stimulations compared to incubation in basal medium (n=3-6). Immunoblotting for (E) liver and (F) kidney GDH, PEPCK-c and G6Pase in HepGlud1-/- mice compared to Glud1lox/lox controls in overnight (O/N) fasting state. All values are means ± SEM. *p<0.05, ***p<0.001, control vs HepGlud1-/- mice in the same fed or fasting state. &&p<0.01, fasting vs fed condition of corresponding genotype. #p<0.05, amino acid stimulation compared to basal condition of corresponding genotype. §p<0.05, glutamine stimulation compared to alanine stimulation of corresponding genotype.

190x254mm (96 x 96 DPI) Diabetes Page 28 of 43

Page 29 of 43 Diabetes

Figure 7. Scheme depicting the consequences of GDH deletion in the liver. (A) Ammonia metabolism in HepGlud1-/- mice in fed condition. (B) Energy metabolism in HepGlud1-/- mice in fasting condition. Pathways and metabolites increased in HepGlud1-/- mice are shown in green while the decreased ones are in red.

190x254mm (96 x 96 DPI)

Figure S1 Diabetes Page 30 of 43 A

Control mice : Glud1lox/lox Alb-CreERT2 KO mice : HepGlud1-/- (tamoxifen pellet implanted at 8 weeks of age)

tamoxifen - + + - + GDH

actin

tissue Brain Liver

C Glud1lox/lox Control HepGlud1-/-

GDH + GS

50µm 50µm

Glud1lox/lox HepGlud1-/- tamoxifen at 8 weeks + + + -

GDH

actin

tissue Liver Brain Page 31 of 43 Diabetes

Figure S1. Validation of HepGlud1-/- mouse model. (A) Sketch of the generation of HepGlud1-/- mice. (B) Immunoblotting for liver GDH showing deletion after tamoxifen implantation in Alb-Cre ERT2 Glud1lox/lox mice only compared to Alb-Cre ERT2 and Glud1lox/lox controls also implanted with tamoxifen. No recombination was observed in the absence of tamoxifen in Alb-Cre ERT2 Glud1lox/lox mice. Brain extracts from constitutive CnsGlud1-/- mice served as a negative control for GDH expression. Actin served as loading control. Immunoblots are representative of 3 independent preparations. (C) Representative maximal projections of confocal images of liver cryosections from Glud1lox/lox control and HepGlud1-/- mice co-stained for GDH (red) and glutamine synthetase (GS, green), a marker of pericentral hepatocytes (n=5). (D) Immunoblotting for GDH in liver of Glud1lox/lox control (n=5) and HepGlud1-/- (n=7) aged mice (41 to 58-week- old), i.e. up to 50 weeks after tamoxifen implantation. Livers from Glud1lox/lox and Alb-Cre ERT2 mice implanted with tamoxifen served as positive control. Brain extracts from constitutive CnsGlud1-/- mice served as a negative control for GDH expression. Actin served as loading control. Figure S2 Diabetes Page 32 of 43

A Young Old (12 to 25-week-old) (41 to 58-week-old)

Glud1lox/lox Control 200mm 200mm

100mm 100mm

HepGlud1-/-

200mm 200mm

100mm 100mm

B Glud1lox/lox Control HepGlud1-/-

6 # # # # #

ratio (%) ratio 4

Liver to 2 weight

body 0 Young Old (12 to 25- (41 to 58- week-old) week-old)

Figure S2. Histomorphology and liver to body weight ratio are preserved in HepGlud1-/-mice. (A) Representative Hematoxylin + Eosin staining on liver paraffin sections from young (12 to 25- week-old) and aged (41 to 58-week-old) Glud1lox/lox control and HepGlud1-/- mice (n=5). (B) Liver to body weight ratio in young (12 to 25-week-old) and aged (41 to 58-week-old) Glud1lox/lox control and HepGlud1-/- mice (n=12-15). Values are means ± SEM. ## 0.01, ###p<0.001, young vs old mice of corresponding genotype. Figure S3 Page 33 of 43 Diabetes

A Glud1lox/lox Control HepGlud1-/-

50µm 50µm

Bodipy + DAPI

B Glud1lox/lox Control HepGlud1-/-

20µm 20µm

Mitotracker + Hoechst

Figure S3. Cellular characteristics of livers deleted for GDH. (A) Representative maximal projections of confocal images of liver cryosections from Glud1lox/lox control and HepGlud1-/- mice co-stained with bodipy for lipid droplets (green) and DAPI (blue) (n=5). (B) Representative maximal projections of confocal images on cultured live primary hepatocytes isolated from Glud1lox/lox control and HepGlud1-/- mice stained with mitotracker for mitochondria (red) and Hoechst for nuclei (blue) (n=5). Diabetes Page 34 of 43

Table S1. Plasma parameters. Plasma parameters from Glud1lox/lox control and HepGlud1-/- mice (n=5-16). All values are means ± SEM.

Plasma values Glud1lox/lox Control LiverGlud1-/-

ALAT - fed (U/L) 65.5 ± 10.74 50.40 ± 5.51

ASAT - fed (U/L) 300.25 ± 125.82 254.00 ± 49.63

Creatinine - fed (µmol/L) 27.77 ± 1.41 27.08 ± 1.29

Insulin - fed (pg/mL) 3511.6 ± 369.2 3972.8 ± 636.8

Insulin - O/N fasting (pg/mL) 1696.3 ± 435.6 2381.5 ± 513.9 Figure S4 Page 35 of 43 Diabetes

A B Liver lox/lox Glud1-/- Kidney Glud1lox/lox HepGlud1-/- Glud1 Hep Glutaminase GS Porin Porin

Glud1lox/lox Control HepGlud1-/- C D 2.0 0.8 per min per activity 1.0 0.4 nmol g of protein) of g 5 per Liver GS x10 (

0.0 (U/L) Liver GLS activity 0.0

E F 4.0 1.6

3.0 1.2

2.0 0.8

1.0 0.4

0.0 0 Liver ALAT activity (U/L) Liver ASAT Liver ASAT (U/L) activity

Figure S4. Lack of liver GDH does not affect other glutamate-associated enzymes of HepGlud1-/-mice. Immunoblotting for (A) kidney glutaminase and (B) liver glutamine synthetase (GS). Enzymatic activities for (C) liver GS, (D) liver glutaminase (GLS), (E) liver aspartate amino transferase (ASAT) and (F) liver alanine amino transferase (ALAT) of Glud1lox/lox control and HepGlud1-/- mice (n=6). All values are means ± SEM.

vs day , 001 . 0 p< . genotype corresponding of time night

###

± SEM means are values All . ) 12 (n= . mice 1 Glud Hep vs control , 001 . 0 ***p< ; 05 . 0 *p< .

- / -

during represented also and h 24 of periods h 24 of period a over as well as time night and day

mice 1 Glud Hep of intake Food . 6 S Figure consecutive 3 over recorded intake food Incremental .

- / -

D2 14:26 D2 11:06 D2 07:46 N2 04:26 N2 01:06 N2 21:46 D1 18:26 D1 15:06 D1 11:46 D1 08:26 N1 05:06 N1 01:46 N1 22:26 N1 19:06 D3 17:06 D3 13:46 D3 10:26 D3 07:06 N3 03:46 N3 00:26 N3 21:06 D2 17:46

24h 0

Food intake intake Food

(g/kg)

100 intake (g/kg) Food 200

* 100 * * *

* 300

Day

Night *

400 0

Food intake Food intake * * * * * 500

# * * * *

# * (g/kg) #

# 100 600

Day 3 Day 3 Night Day 2 Day 1 Day 1 Night

* * * 2 Night * 150

* 200

Hep Glud1

- / -

Control Glud1

lox lox/

Figure S5 Figure

Diabetes Page 36 of 43 of 36 Page Figure S6 Page 37 of 43 Diabetes Glud1lox/lox Control -/- 40000 HepGlud1 A Night 1 Day 1 Night 2 Day 2 Night 3 Day 3

4000

* 30000

3500 *

* # * 20000 # # 3000 # # #

2500 (Counts) 10000

2000 * Total movements Total * 0

1500 Night Day 1000 * 30000 500 20000

Total movements (Counts)movements Total 0 10000 (Counts) 0 Total movements Total

N1 19:06 N1 22:26 N1 01:46 N1 05:06 N1 08:26 D1 11:46 D1 15:06 D1 18:26 D1 21:46 N2 01:06 N2 04:26 N2 07:46 D2 11:06 D2 14:26 D2 17:46 D2 21:06 N3 00:26 N3 03:46 N3 07:06 D3 10:26 D3 13:46 D3 17:06 D3 24h

B 15000

* 1200 *

* 1000 * 10000 # #

# #

* # #

800 * 5000 (Counts)

600 * Fine movements 0 400 Night Day 200 10000

Fine movements (Counts)Fine movements 0 5000 (Counts)

3000 25000 2500 * 20000

15000 2000 * # # 10000 # # 1500 #

Ambulatory 5000

1000 * 0

movements (Counts) movements

* * Night Day 500 0 15000 10000 Ambulatory movements (Counts)Ambulatory movements

5000 N1 19:06 N1 22:26 N1 01:46 N1 05:06 N1 08:26 D1 11:46 D1 15:06 D1 18:26 D1 21:46 N2 01:06 N2 04:26 N2 07:46 D2 11:06 D2 14:26 D2 17:46 D2 21:06 N3 00:26 N3 03:46 N3 07:06 D3 10:26 D3 13:46 D3 17:06 D3 0 24h movements (Counts) movements Diabetes Page 38 of 43

Figure S6. Locomotor activity of HepGlud1-/-mice. (A) Total movements composed of (B) fine and (C) ambulatory movements recorded over three consecutive periods of 24h and also represented during day and night time as well as over a period of 24h (n=12). All values are means ± SEM. *p<0.05; **p<0.01, control vs HepGlud1-/- mice. ##p<0.01; ###p<0.001, day vs night time of corresponding genotype. Figure S7 Page 39 of 43 Diabetes

Glud1lox/lox Control HepGlud1-/-

Night 1 Day 1 Night 2 Day 2 Night 3 Day 3 25

30 # * 20 # # # # 15

25 * 10 expenditure 20 5

(Kcal/h per kg) (Kcal/hper 0

Energy Night Day

(Kcal/h per kg) (Kcal/h per 15 Energy expenditure 20 10 15 10 expenditure 5 N1 19:06 N1 22:26 N1 01:46 N1 05:06 N1 08:26 D1 11:46 D1 15:06 D1 18:26 D1 21:46 N2 01:06 N2 04:26 N2 07:46 D2 11:06 D2 14:26 D2 17:46 D2 21:06 N3 00:26 N3 03:46 N3 07:06 D3 10:26 D3 13:46 D3 17:06 D3

(Kcal/h per kg) (Kcal/hper 0

Energy 24h

Figure S7. Energy expenditure of HepGlud1-/-mice. Energy expenditure recorded over 3 consecutive periods of 24h and also represented during day and night time as well as over a period of 24-h (n=12). All values are means ± SEM. *p<0.05, control vs HepGlud1-/- mice. ##p<0.01; ###p<0.001, day vs night time of corresponding genotype. Figue S8 Diabetes Glud1lox/lox ControlPage 40 of 43 HepGlud1-/- A Night 1 Day 1 Night 2 Day 2 Night 3 Day 3

6000 5000 * # # # 4000 # # 5500 kg)

kg) 5000 3000 *

4500 VO 2000 4000 1000 (ml/h per (ml/h ml/h per ml/h ( 3500 0 2 3000 Night Day VO 2500 5000

2000 kg) 2 2500 VO (ml/h per (ml/h N1 19:06 N1 22:26 N1 01:46 N1 05:06 N1 08:26 D1 11:46 D1 15:06 D1 18:26 D1 21:46 N2 01:06 N2 04:26 N2 07:46 D2 11:06 D2 14:26 D2 17:46 D2 21:06 N3 00:26 N3 03:46 N3 07:06 D3 10:26 D3 13:46 D3 17:06 D3 0 24h

B 5000 6000

kg) # * 4000 # 5500 * 2 # # # #

kg) 5000 3000 *

* VCO 2000

per 4500

* *

4000 * per (ml/h 1000 *

(ml/h

* 0 3500 * 2 3000 Night Day 5000 VCO 2500 kg)

2000 2 2500 VCO

(ml/h per (ml/h

) # # C 2 1.0 # # #

1.1 0.8 #

/VO

* * 2

) *

* 0.6

2 * *

* * * * *

1.0 * * * * * * *

* * * * *

* 0.4

/VO *

2 * *

* * * 0.9 * * * * 0.2

0.8 RER (VCO 0.0 Night Day

0.7 ) 2 RER (VCO 1.0 p = 0.06

0.6 /VO 2 0.5

N1 19:06 N1 22:26 N1 01:46 N1 05:06 N1 08:26 D1 11:46 D1 15:06 D1 18:26 D1 21:46 N2 01:06 N2 04:26 N2 07:46 D2 11:06 D2 14:26 D2 17:46 D2 21:06 N3 00:26 N3 0.0 RER (VCO 24h Page 41 of 43 Diabetes

-/- Figure S8. Energy substrate utilization of HepGlud1 mice. (A) VO2 (B) VCO2 and (C)

respiratory exchange ratio (RER as in Fig. 3D with higher resolution time) measured as VCO2/VO2 recorded over 3 consecutive periods of 24h and also represented during day and night time as well as over a period of 24h (n=12). All values are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice. ##p<0.01; ###p<0.001, day vs night time of corresponding genotype. Figure S9 Diabetes Page 42 of 43

A IP Alanine challenge

14 # * 12 # * # * *# /L) 10

mmol 8

6 1000 Glud1lox/lox Control 4

Glycemia ( Alb-CreERT2 Control 500 *# 2 AUC *# HepGlud1-/- 0 0 0 30 60 90 120 Time (min)

B IP Alanine challenge

16 Glud1lox/lox Control 14 -/- 12 HepGlud1 10 * mmol/L) * ( 8 6 * 4

lycemia 2 G 0 0 30 60 90 120 Time (min)

Figure S9. Alb-Cre ERT2 transgene does not contribute to the phenotypic response to alanine of HepGlud1-/-mice. Blood glucose levels in response to alanine challenge (2g/kg) measured (A) in Glud1lox/lox control, Alb-Cre ERT2 control and HepGlud1-/- mice (n=9-22) 4 weeks after tamoxifen treatment and (B) in Glud1lox/lox control and HepGlud1-/- mice (n=5-6) 17 weeks after tamoxifen treatment. IP, intra peritoneal; AUC, area under the curve. All values are means ± SEM. *p<0.05; **p<0.01, Glud1lox/lox control vs HepGlud1-/- mice. ##p<0.01, Alb-Cre ERT2 control vs HepGlud1-/- mice. Figure S10 Page 43 of 43 Diabetes

A 6 Glud1lox/lox Control 50 -/- 45 acids HepGlud1 ) 5 40 4 35 amino * 30 protein * 3 25 * * 20 2 15 content in content

(µmol/g of(µmol/g 1 10 * * 5

Soleus 0 0 Ala Gln Glu Gly

B 8 45 acids Glud1lox/lox Control 7 40 HepGlud1-/-

) 35

amino 6 30 5 * 25 protein 4 20 *

content in content 3 * * * 15 2 10 (µmol/g of(µmol/g 1 5 * 0 0 Ala Gln Glu Gly Gastrocnemius

Figure S10. Concentrations of amino acids in skeletal muscles. Soleus muscle (A) and

gastrocnemius muscle (B) contents in amino acids in non-fasted mice (n=5-6). All values

are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice. Figure S11 Diabetes Page 44 of 43

A 700 lox/lox Fed Glud1 Control HepGlud1-/- 600

500 (µmol/L)

400 acids 300 amino 200 * * 100 *

Plasma * * * * 0 Asp Glu Ser His Gly Thr Arg Tau Tyr Val Phe Ile Leu

B 900 O/N fasting 800

700

(µmol/L) 600

500 acids 400

amino 300

200

Plasma 100

0 Asp Glu Ser His Gly Thr Arg Tau Tyr Val Phe Ile Leu

Figure S11. Circulating amino acid levels in HepGlud1-/-mice. Plasma amino acids were measured in (A) fed and (B) overnight (O/N) fasting conditions (n=7). All values are means ± SEM. *p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice. Figure S12 Page 45 of 43 Diabetes

A Glud1lox/lox HepGlud1-/- Liver Fed O/N fasting Fed O/N fasting PEPCK-c G6Pase Porin

Kidney Fed O/N fasting Fed O/N fasting PEPCK-c G6Pase Porin

B 12 55 lox/lox Glud1 Control 50

acids 10 HepGlud1-/-

) 45 40 8 35 amino

protein 30 6 25 4 20 15 content in content

(µmol/g of (µmol/g 2 10 * * * * 5 0 * 0 Kidney Ala Gln Glu Gly

Figure S12. Both control and HepGlud1-/-mice are able to induce liver and kidney

gluconeogenesis upon overnight fasting. Immunoblotting for liver and kidney PEPCK-c and

G6Pase (A) in Glud1lox/lox control and HepGlud1-/- mice in overnight fasting state compared to fed

state. Kidney contents in amino acids (B) in non-fasted mice (n=5-6). All values are means ± SEM.

*p<0.05; **p<0.01; ***p<0.001, control vs HepGlud1-/- mice.