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Mitochondrial Aldehyde Dehydrogenase (ALDH2) Protects

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Mitochondrial Aldehyde Dehydrogenase (ALDH2) Protects Zhang et al. BMC Medicine 2012, 10:40 http://www.biomedcentral.com/1741-7015/10/40 RESEARCHARTICLE Open Access Mitochondrial aldehyde dehydrogenase (ALDH2) protects against streptozotocin-induced diabetic cardiomyopathy: role of GSK3b and mitochondrial function Yingmei Zhang1,2, Sara A Babcock2, Nan Hu2, Jacalyn R Maris2, Haichang Wang1 and Jun Ren1,2* Abstract Background: Mitochondrial aldehyde dehydrogenase (ALDH2) displays some promise in the protection against cardiovascular diseases although its role in diabetes has not been elucidated. Methods: This study was designed to evaluate the impact of ALDH2 on streptozotocin-induced diabetic cardiomyopathy. Friendly virus B(FVB) and ALDH2 transgenic mice were treated with streptozotocin (intraperitoneal injection of 200 mg/kg) to induce diabetes. Results: Echocardiographic evaluation revealed reduced fractional shortening, increased end-systolic and -diastolic diameter, and decreased wall thickness in streptozotocin-treated FVB mice. Streptozotocin led to a reduced respiratory exchange ratio; myocardial apoptosis and mitochondrial damage; cardiomyocyte contractile and intracellular Ca2+ defects, including depressed peak shortening and maximal velocity of shortening and relengthening; prolonged duration of shortening and relengthening; and dampened intracellular Ca2+ rise and clearance. Western blot analysis revealed disrupted phosphorylation of Akt, glycogen synthase kinase-3b and Foxo3a (but not mammalian target of rapamycin), elevated PTEN phosphorylation and downregulated expression of mitochondrial proteins, peroxisome proliferator-activated receptor g coactivator 1a and UCP-2. Intriguingly, ALDH2 attenuated or ablated streptozotocin- induced echocardiographic, mitochondrial, apoptotic and myocardial contractile and intracellular Ca2+ anomalies as well as changes in the phosphorylation of Akt, glycogen synthase kinase-3b, Foxo3a and phosphatase and tensin homologue on chromosome ten, despite persistent hyperglycemia and a low respiratory exchange ratio. In vitro data revealed that the ALDH2 activator Alda-1 and glycogen synthase kinase-3b inhibition protected against high glucose- induced mitochondrial and mechanical anomalies, the effect of which was cancelled by mitochondrial uncoupling. Conclusions: In summary, our data revealed that ALDH2 acted against diabetes-induced cardiac contractile and intracellular Ca2+ dysregulation, possibly through regulation of apoptosis, glycogen synthase kinase-3b activation and mitochondrial function independent of the global metabolic profile. Keywords: ALDH2, cardiac contraction, diabetes, GSK3b?β?, mitochondrial function Background others has revealed a rather singular role for ALDH2 in The mitochondrial isoform of aldehyde dehydrogenase cardioprotection against ischemic injury, arrhythmias (ALDH2) has been shown to play a pivotal role in the and alcoholism [2,3,5-7]. However, the role of ALDH2 metabolism of acetaldehyde and other toxic aldehydes in myopathic anomalies associated with metabolic disor- [1-4]. Ample evidence from our laboratory as well as ders, including diabetes mellitus, has not been eluci- dated. The prevalence of diabetes and associated heart * Correspondence: [email protected] diseases has been steadily increasing, particularly in 1Department of Cardiology, Xijing Hospital, Fourth Military Medical Asian countries, with approximately 50% of populations University, Xi’an, 710032, China carrying one copy of the mutant ALDH2 gene [4,8-11]. Full list of author information is available at the end of the article © 2012 Zhang et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Zhang et al. BMC Medicine 2012, 10:40 Page 2 of 17 http://www.biomedcentral.com/1741-7015/10/40 A plethora of studies have depicted significant contribu- hour dark circadian cycle with access to water and food tion from genetic variants, such as peroxisome prolifera- ad libitum. Five-month-old male FVB (used as wild-type) tor-activated receptors (PPARs), in the predisposition of and ALDH2 transgenic mice received intraperitoneal diabetes [12]; however, very few have examined the role injections of streptozotocin (STZ, 200 mg/kg). All mice of ALDH2 in the onset and progression of diabetes and were maintained for four weeks with free access to stan- its complications. Recent evidence revealed that ALDH2 dard laboratory chow and tap water before their blood polymorphism is closely associated with an increased glucose levels were monitored. Mice with fasting blood risk of diabetes [11] while experimental findings showed glucose levels > 13 mM were deemed diabetic [17]. reduced ALDH2 expression and activity associated with ALDH2 activity was measured in 33 mM sodium pyro- oxidative stress and cardiac dysfunction in diabetes [13]. phosphate containing 0.8 mM NAD+,15μMpropionalde- These observations are somewhat consistent with the hyde and 0.1 mL protein extract. Propionaldehyde, the notion that inactive ALDH2 promotes hyperglycemia substrate of ALDH2, was oxidized in propionic acid, while [9], while genotypes of ALDH2 can modify diabetes risk NAD+ was reduced to NADH to estimate ALDH2 activity. irrespective of alcohol intake [14]. To this end, this NADH was determined by spectrophotometric absorbance study was designed using a unique murine model to at 340 nm. ALDH2 activity was expressed as nanomoles examine the impact of ALDH2 overexpression in the NADH per minute per milligram of protein [18]. pathogenesis of diabetic cardiomyopathy and the under- lying cellular mechanism(s) involved. Recent evidence Serum free fatty acid, plasma insulin and blood glucose from our group has revealed a pivotal role for the essen- levels tial survival factor Akt and its downstream signaling Plasma free fatty acids were measured three hours after molecules, including glycogen synthase kinase-3b mice were denied access to food using a Free Fatty Acid (GSK3b), PPAR (mTOR) and the forkhead transcrip- Assay Kit (Cayman Chemical, MI, USA). In brief, mouse tional factor in ALDH2, in cardioprotection against blood samples were centrifuged at 2000 × g for 15 minutes alcoholism and ischemia-reperfusion [3,7,15]. To better at 4°C. An excitation wavelength of 530 nm and an emis- elucidate the interplay between these signaling cascades sion wavelength of 590 nm were used to detect the quan- and mitochondrial function in diabetes and/or ALDH2- tity of free fatty acids. Plasma insulin levels were measured induced cardiac responses, we scrutinized apoptosis and using a mouse insulin ELISA kit from Diagnostic System mitochondrial integrity, including mitochondrial mem- Laboratory (Webster, TX, USA). Fasting (overnight) and brane potential, as well as cell signaling of Akt, GSK3b, postprandial (two hours after re-feeding following the mTOR and Foxo3a in wild-type FVB and ALDH2 trans- overnight fasting) blood glucose levels were determined genic mice with or without the induction of experimen- using a glucometer (Accu-ChekII, model 792, Boehringer tal diabetes. Given that Akt signaling is under the Mannheim Diagnostics, Indianapolis, IN, USA) [17]. negative control of phosphatase and tensin homologue on chromosome ten (PTEN) in a wide variety of disease Metabolic measurement conditions, including myocardial hypertrophy, heart fail- Indirect calorimetry and total physical activity were ure and preconditioning [16], we monitored pan protein measured in light (10 a.m.) and dark (10 p.m.) phases expression and phosphorylation of PTEN. To evaluate if using the Comprehensive Laboratory Animal Monitor- ALDH2 affects myocardial morphometric and functional ing System (Oxymax/CLAMS; Columbus Instruments, anomalies in diabetes through any potential effect sec- Columbus,OH,USA).Volumeofoxygenintake(VO2), ondary to global metabolic alterations, we scrutinized volume of Carbon Dioxide exhaled (VCO2), the RER whole body metabolism, including the respiratory (VCO2/VO2) and physical activity were measured. All exchange ratio (RER), and total physical activity as well the parameters were measured every 10 minutes for six as plasma levels of free fatty acid, insulin and glucose hours during daytime and six hours during nighttime. (fasting and postprandial) in control and diabetic mice. Result recorded in the first and last half hour was not be used. For simplicity, only the RER is presented with- Methods out displaying original data from VO2 and VCO2 [19]. Experimental animals, experimental diabetes and ALDH2 activity Echocardiographic assessment All animal procedures were approved by our Institutional Cardiac geometry and function were evaluated in Animal Care and Use Committee at the University of anesthetized mice using a two-dimensional guided M- Wyoming (Laramie, WY, USA). Production of ALDH2 mode echocardiography (Sonos 5500; Phillips Medical transgenic mice using the chicken b-actin promoter was System, Andover, MA, USA) equipped with a 15-6 MHz as described previously [5]. All mice were housed in a linear transducer. Left ventricular (LV) wall thickness temperature-controlled room under a 12 hour light-12 and diastolic and systolic dimensions were recorded Zhang et al. BMC Medicine 2012, 10:40 Page 3 of 17 http://www.biomedcentral.com/1741-7015/10/40 from the M-mode images. Fractional shortening was cal- velocities of shortening (+dL/dt) and relengthening
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