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PDGFRβ regulates adipose tissue expansion and glucose metabolism via vascular remodeling in diet-induced obesity
Short running title: The role of PDGF-PDGFRβ in adipose tissue expansion
Yasuhiro Onogi1, Tsutomu Wada1, Chie Kamiya1, Kento Inata1, Takatoshi Matsuzawa1,
Yuka Inaba2, 3, Kumi Kimura2, Hiroshi Inoue2, 3, Seiji Yamamoto4, Yoko Ishii4,
Daisuke Koya5, Hiroshi Tsuneki1, Masakiyo Sasahara4, and Toshiyasu Sasaoka1
1Department of Clinical Pharmacology, 4Department of Pathology; University of Toyama, Toyama 930-0194, Japan
2Department of Physiology and Metabolism, Brain/Liver Interface Medicine Research Center, 3Metabolism and Nutrition Research Unit, Innovative Integrated Bio-Research Core, Institute for Frontier Science Initiative; Kanazawa University, Kanazawa, Kanazawa 920-8640, Japan
5Department of Internal Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa 920-0293, Japan
Corresponding author:
Toshiyasu Sasaoka, MD., Ph.D.
Department of Clinical Pharmacology, University of Toyama
2630 Sugitani, Toyama, 930-0194, Japan
Tel.: +81-76-434-7514, Fax: +81-76-434-5067
E-mail: [email protected]
Word count: 4,794
Number of figures: 8
References: 44
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Diabetes Publish Ahead of Print, published online January 25, 2017 Diabetes Page 2 of 45
Abstract
Platelet-derived growth factor (PDGF) is a key factor of angiogenesis; however, its role in adult obesity remains unclear. In order to clarify its pathophysiological role, we investigated the significance of a PDGF receptor β on adipose tissue expansion and glucose metabolism. Mature vessels in the epididymal white adipose tissue (eWAT) were tightly wrapped with pericytes in normal mice. Pericytes desorption from vessels and the subsequent proliferations of endothelial cells were markedly increased in the eWAT of diet-induced obese mice. Analyses with flow cytometry and adipose tissue cultures indicated that PDGF-B caused the detachment of pericytes from vessels in a concentration-dependent manner. M1-macrophages were a major type of cells expressing PDGF-B in obese adipose tissue. In contrast, pericyte detachment was attenuated and vascularity within eWAT was reduced in tamoxifen-inducible conditional Pdgfrb-knockout mice with decreases in adipocyte size and chronic inflammation. Furthermore, Pdgfrb-knockout mice showed enhanced energy expenditure. Consequently, diet-induced obesity and the associated deterioration of glucose metabolism in wild-type mice were absent in Pdgfrb-knockout mice. Therefore, PDGF-B-PDGFRβ signaling plays a significant role in the development of adipose-tissue neovascularization, and appears to be a fundamental target for the prevention of obesity and type 2 diabetes.
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Introduction
The physiological roles of the vasculature in adipose tissue have been attracting interest from the viewpoint of adipose tissue expansion and chronic inflammation (1,2). White adipose tissue (WAT) such as visceral fat possesses the unique characteristic of plasticity; its volume may change several fold even after growth depending on nutritional conditions. Enlarged adipose tissue is chronically exposed to hypoxia (3,4), which stimulates the production of angiogenic factors for the supplementation of nutrients and oxygen to the newly enlarged tissue area (5). Selective ablation of the vasculature in WAT by apoptosis-inducible peptides or the systemic administration of angiogenic inhibitors has been shown to reduce WAT volumes and result in better glucose metabolism profiles in obese mice (1,2,6). Regarding angiogenic factors, VEGF has been characterized in the most detail, and is known to play crucial roles in the neovascular development of adipose tissue with obesity (7-13).
PDGF-B is another growth factor and its homo-dimer activates an intracellular signaling cascade by binding to its receptor, PDGFRβ (14,15). It plays an essential role in fetal vascular development, and also contributes to wound healing and tumor growth via angiogenic actions in adults (16). PDGFRβ is almost restrictively expressed in perivascular mesenchymal cells, particularly in vascular smooth muscle cells and pericytes (14,15). Endothelial cells (ECs)-derived PDGF-B promotes the migration of pericytes to neovessels for maturation by covering blood vessels, and these pericytes regulate vascular permeability and sprouting (17). The systemic deletion of the Pdgfb or Pdgfrb gene results in a lack of pericytes in the vasculature and embryonic lethality with vascular dysfunction (15,18-20). However, it currently remains unclear whether the angiogenic effects of PDGF are involved in the mechanisms responsible for the development of adult obesity.
Therefore, we herein used tamoxifen-inducible conditional Pdgfrb-knockout mice in which PDGFRβ was deleted during adulthood without affecting vascular development in the fetal and growing periods for the selective ablation of Pdgfrb. These mice were fed a normal chow diet or high fat diet (HFD), and the effects of the Pdgfrb deletion on adipose tissue vasculature and glucose metabolism were investigated.
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Research Design and Methods
Materials
Human recombinant insulin was provided by Novo Nordisk Pharma Ltd. Antibodies and ELISA kits used in this study were listed in Supplementary Table 1. All other reagents of analytical grade not elsewhere specified were obtained from Sigma Aldrich or Wako Pure Chemical Industries.
Mice and metabolic analyses
All experimental procedures used in this study were approved by the Committee of Animal Experiments at the University of Toyama. Pdgfrbflox/flox mice on a C57BL/6 background were cross-bred with Cre-estrogen receptor transgenic mice (Jackson Laboratories). Their offspring, Cre-ERTM/Pdgfrbflox/flox, were orally administered tamoxifen at 9 weeks old (Cayman, 2.25 mg per 10 g body weight for 5 consecutive days) to produce conditional systemic Pdgfrb-knockout (Pdgfrb∆SYS-KO) mice, as shown in Fig. 1E (21, 22). To conduct experiments appropriately, Pdgfrbflox/flox littermates of the same age and sex were treated identically and used as controls (FL). Mice were housed on a 12:12-h light-dark cycle (lights on at 7:00) in a temperature-controlled colony room (23 ± 3°C) and were allowed free access to food and water. Mice were fed control PicoLab Rodent diet 20 (chow: 3.43 kcal/g, PMI Nutrition International) or 60 kcal% HFD (5.24 kcal/g, D12492, Research Diets Inc.) for 12 weeks, and physiological experiments were performed thereafter. Male mice were used in all experiments. The glucose tolerance test (GTT) and insulin tolerance test (ITT) were conducted after 6 h of fasting, as described previously (23,24). Body composition was analyzed with MRI images (MRmini SA; DS Pharma Biomedical, Osaka, Japan), as described previously (25,26).
Hyperinsulinemic euglycemic clamp
Hyperinsulinemic euglycemic clamp studies were performed after 7-8 days of recovery from cannulation, as described previously (27). During clamp studies, human insulin at 2.5 mU/kg/min was infused into mice with variable amounts of the 40% glucose solution to maintain blood glucose levels at 110 ± 20 mg/dL.
Cell and adipose tissue cultures
Bone marrow-derived macrophages (BMDM) were prepared, as described previously (4). 4
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Bone marrow cells were treated with 100 nM 4-hydroxytamoxifen (Cayman) to delete the Pdgfrb allele for 48 h, and differentiated into FL-BMDM and Pdgfrb-knockout-BMDM (KO-BMDM), respectively. In adipose tissue cultures, epididymal WAT (eWAT) isolated from lean 8-12-week-old male mice was cut into small pieces (approximately 3 mm × 3 mm), and cultured in serum-free DMEM. To obtain Pdgfrb-knockout tissue, adipose tissue pieces from Cre-ERTM/Pdgfrbflox/flox or Pdgfrbflox/flox control mice were incubated with 100 nM 4-hydroxytamoxifen for 48 h. These adipose tissues were treated with or without PDGF-BB (Life Technologies) for 24 h, and used for measurement of whole-mount immunofluorescence.
Measurement of immunofluorescence in sections and whole-mount adipose tissue
Immunofluorescence measurements were performed in accordance with previous methods with minor modifications (28). Sections (30 or 40 m slices) were obtained from the middle part of eWAT using cryostat (CM 3050S-IV, Leica Microsystems) and used in experiments of Figs. 3D, 3I, and Supplementary Fig. 4D. To measure whole-mount immunofluorescence, tissues were obtained from the tip region of eWAT, an active area for neoangiogenesis (29), incubated with fructose solution as an optical clearing agent to reduce the amount of light scattering in tissues (30), and then used in experiments of Figs. 3A and 3F. The immunofluorescent images were randomly taken by a confocal microscope (TCS-SP5, Leica Microsystems). Blood vessel areas, pericyte association levels, and PDGFRβ-like immunoreactivities in each mouse were measured with the ImageJ software (National Institute of Health), and the data were averaged.
Real-time PCR and Western blotting
The method used for real-time PCR and Western blotting was described previously (23). Primer sequences are listed in Supplementary Table 2.
Flow cytometry
The fractionation of the stromal vascular fraction (SVF) of eWAT was analyzed by FACSCant II and FACSAria II for cell sorting (BD Bioscience), as previously described (26,31). Data were analyzed by FACS Diva 6.1.2 (BD Bioscience) or FCS Express (De Novo Software).
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Measurement of energy consumption and locomotor activity
Oxygen consumption (VO2), production of carbon dioxide (VCO2), locomotor activity, and food consumption were measured with metabolic chambers (MK-5000RQ, Muromachi Kikai, Tokyo, Japan), as described previously (25,26).
Statistical Analyses
Data are expressed as the mean ± SE. P values were obtained by an unpaired two-tailed Student’s t-test between two groups and by 2-way ANOVA with Bonferroni’s test among groups composed of two genetic strains (knockout vs. FL) and two diets (chow vs. HFD). One-way ANOVA with Bonferroni’s test was used in Fig. 1C, 1D, 3H, 4C, 5C, and Supplementary Fig. 2E, and 4C. p<0.05 was considered significant.
Results
HFD-induced obesity was prevented in mice lacking Pdgfrb.
We initially characterized the tissue expression profiles of PDGF-B and its receptors in lean and obese C57BL/6J mice. The mRNA of Pdgfb was markedly increased in the WAT of mice by HFD feeding, but remained unchanged in the liver, muscle, and hypothalamus (Fig. 1A). The Pdgfrb tissue expression profile was almost the same as that of Pdgfb (Fig. 1B). WAT specific increase in the mRNA levels of Pdgfb and Pdgfrb appears to reflect the angiogenesis, since expression of Kdr, a marker of ECs, increased only in eWAT but not in the liver and skeletal muscle after HFD feeding (Supplementary Fig. 1A). The expression of Pdgfb markedly increased after 8 weeks of HFD feeding, and increased further thereafter (Fig. 1C). In contrast, the increase observed in the expression of Vegfa was more gradual and milder than that in Pdgfb (Fig. 1D). Serum PDGF-B levels slightly increased, whereas serum VEGF-A levels were not significantly affected by HFD feeding (Supplementary Fig. 1B and C). These results indicate that PDGF-B rather than VEGF-A was strongly produced in adipose tissue and acted in an autocrine and/or paracrine manner during the development of obesity in mice. To clarify whether the up-regulated expression of PDGF-B and PDGFRβ during the development of obesity is involved in adipose tissue expansion associated with impaired glucose metabolism, we investigated the influence of the deletion of Pdgfrb using a tamoxifen-inducible gene ablation system (21,22). The experimental protocol was illustrated
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in Fig. 1E. Pdgfrb∆SYS-KO and FL mice were divided into 2 groups and maintained on chow or HFD. Although the congenic systemic knockout of Pdgfrb resulted in embryonic lethality (18), Pdgfrb∆SYS-KO mice survived and grew normally (data not shown). PDGFRβ mRNA levels and protein expression in WAT, brown adipose tissue, the liver, and skeletal muscle were significantly lower in Pdgfrb∆SYS-KO mice than in FL mice, and the knockout efficacy of PDGFRβ did not differ during HFD feeding (Supplementary Fig. 1D-F). Body weights were similar between the two genotypes prior to the administration of tamoxifen. Nevertheless, body weights were lower in Pdgfrb∆SYS-KO mice than in FL mice under normal chow-fed condition (Fig. 1F). Furthermore, Pdgfrb∆SYS-KO mice were protected from body weight gain and the accumulation of subcutaneous and visceral fat under HFD conditions (Fig. 1F-I). However, no significant changes in lean mass and muscle mass in hind limbs occurred in either genotype (Fig. 1H, Supplementary Fig. 1G). Consistent with the changes observed in fat volume, fasted serum levels of leptin were significantly lower in Pdgfrb∆SYS-KO mice (20.8 ± 5.5 ng/mL) than in FL mice (47.1 ± 2.3 ng/mL) under HFD feeding condition. These results indicated that PDGFRβ signaling plays crucial roles in the regulation of fat accumulation.
Profiles of adipocytes in mice lacking Pdgfrb.
We analyzed the size of adipocytes in the eWAT of FL and Pdgfrb∆SYS-KO mice. Under HFD-fed conditions, adipocytes in eWAT were smaller in Pdgfrb∆SYS-KO mice than in FL mice (Fig. 2A-C). To clarify the direct effects of the deletion of Pdgfrb on adipocyte differentiation, we isolated embryonic fibroblasts from FL and Pdgfrb∆SYS-KO mice (FL- and KO-MEF), and compared their differentiation into adipocytes in vitro. Lipid accumulation was slightly higher in KO-MEF than in FL-MEF, although both were partial. Moreover, the mRNA levels of Adipoq were slightly higher, while those of Leptin and Pparg were significantly higher in KO-MEF (Supplementary Fig. 2A-C). On the other hand, mitogenic activity detected by MTT assay and analysis of insulin-stimulated Ki67 expression was lower in KO-MEF than in FL-MEF (Supplementary Fig. 2D and E). These results indicated that the lack of PDGFRβ in eWAT did not lead to reductions in body fat via the direct inhibition of adipocyte differentiation.
HFD-induced chronic inflammation in eWAT was attenuated in mice lacking Pdgfrb.
We subsequently investigated chronic inflammation in eWAT. The results of immunostaining
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analyses demonstrated that CD11c+ macrophages were almost absent in the eWAT of both genotypes under chow-fed conditions (data not shown). In contrast, a cluster of CD11c+ macrophages around dead adipocytes, i.e., a crown-like structure (CLS), was prominent in the eWAT of control FL mice fed HFD. In addition, the infiltration of pro-inflammatory macrophages and CLS formation were markedly decreased in Pdgfrb∆SYS-KO mice (Fig. 2D and E). In accordance with these histological observations, flow cytometric analyses clearly showed that total macrophages in the SVF of eWAT were decreased in Pdgfrb∆SYS-KO mice on HFD. Furthermore, percentages of M1-macrophages defined by gating on CD11c+CD206- in CD45+F4/80+ cells were decreased, while those of M2-macrophages defined by gating on CD11c-CD206+ in CD45+F4/80+ cells were significantly increased in Pdgfrb∆SYS-KO mice (Fig. 2 F and G).
In analyses of mRNA expression in eWAT from control FL and Pdgfrb∆SYS-KO mice maintained on chow or HFD, no significant differences were observed in the expression levels of Vegfa, Adipoq, the adipogenic genes Pparg and Ppargc1a or lipolytic genes Lipe and Pnpla2 among the four groups (Fig. 2H). Regarding the hypoxic and inflammatory genes, the expression of Hif1a, Emr1, Itgax, Mrc1, Tnfa, and Ccl2 were significantly increased by HFD-feeding in FL mice, whereas the increasing effects were attenuated in HFD-fed Pdgfrb∆SYS-KO mice (Fig. 2H). The expression of Pdgfb in the eWAT of Pdgfrb∆SYS-KO mice was significantly lower than that of FL mice under HFD-fed condition (data not shown). These results indicated that HFD-induced chronic inflammation in eWAT was ameliorated in Pdgfrb∆SYS-KO mice.
We further investigated the direct effects of the Pdgfrb deletion on the macrophage inflammatory response in vitro. The expression of the macrophage differentiation markers Emr1, Itgax, and Mrc1 was similar between FL- and KO-BMDM (data not shown). Importantly, LPS-induced Tnfa expression was indistinguishable in both types of BMDMs (Fig. 2I). Therefore, the attenuation of chronic inflammation in Pdgfrb∆SYS-KO mice appears to arise from the amelioration of fat accumulation, rather than the deletion of Pdgfrb having a direct effect on macrophages.
Vascularity in eWAT was reduced in mice lacking Pdgfrb.
Since the formation of a neovascular network is necessary for the development of adipose tissue, we investigated the vascularity of eWAT in FL and Pdgfrb∆SYS-KO mice. The blood
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vessel area and number of branches were reduced by the deletion of Pdgfrb in chow-fed and HFD-fed conditions (Fig. 3A-C). The expression of VEGFR2, a vascular endothelial marker, was increased by HFD feeding in eWAT of FL mice, whereas no such increase was observed in Pdgfrb∆SYS-KO mice (Supplementary Fig. 3). We confirmed that PDGFRβ was predominantly expressed in the SVF, but not in mature adipocyte fraction (MAF) of eWAT, particularly in the perivascular cells of pericytes (Fig. 3D and E). These cells also stained well with CD13 and neural/glial antigen 2 (NG2), recognized markers of pericytes. PDGF-B is an angiogenic factor that promotes the recruitment of pericytes to neovascular ECs for maturation via the activation of PDGFRβ in pericytes (15). Therefore, we investigated the ratio of the pericyte (green, defined as CD13-positive cells) association with ECs (red) as an index of vessel maturation and the angiogenic condition in eWAT (Fig. 3F and G) as previously described (32, 33). Pericytes attached tightly along blood vessels (yellow) in FL and Pdgfrb∆SYS-KO mice under normal chow-fed condition. Importantly, we found that the attachment of pericytes was significantly reduced by HFD feeding in FL mice, indicating that these vessels were prone to vascular sprouting (33). To investigate the kinetics of HFD-induced pericyte behaviors, we measured the ratio of pericyte coverage in C57BL/6 mice fed HFD for various periods (Fig. 3H). Pericyte-uncovered vessels increased by HFD feeding depending on the loaded period. On the other hand, the HFD-induced decrease in the pericyte coverage ratio was not observed in Pdgfrb∆SYS-KO mice, and the ratio was similar to that in normal chow diet-fed FL mice (Fig. 3F and G). Interestingly, ECs with Ki67-stained nuclei were detected in some of the pericyte-uncovered areas in the eWAT of FL mice fed HFD (Fig. 3I). The flow cytometry-based quantitative analysis again demonstrated that the mean fluorescent intensity of Ki67 in ECs was lower in Pdgfrb∆SYS-KO mice than in FL mice (Fig. 3J). These results indicated that the HFD-induced detachment of pericytes from ECs and subsequent proliferation of ECs, relevant to angiogenesis, appeared to be suppressed by the deletion of Pdgfrb.
To directly investigate whether PDGF-B induces pericyte detachment from mature vessels, we cultured whole eWAT from lean mice and treated it with PDGF-B for 24 h (Fig. 4A and B). CD13-labelled pericytes closely associated with the PECAM1-stained vasculature in control tissues. The PDGF-B treatment caused their detachment from the vasculature in a dose-dependent manner (Fig. 4A-C). The vascular-detached pericytes were spindle-shaped due to the lack of close contact with vessels (Fig. 4B). In contrast, in cultured adipose tissue 9
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from Pdgfrb∆SYS-KO mice, where PDGFRβ-like immunoreactivity was lower than that from FL mice (Fig. 4D and E), PDGF-B-induced detachment of pericytes from the vasculature was significantly attenuated (Fig. 4F and G). These results indicated that a high concentration of PDGF-B around vessels facilitates the detachment of pericytes from mature vessels through PDGFRβ signaling and promotes vascular remodeling in adipose tissue.
HFD-induced increments in PDGF-B in adipose tissue originated from M1-macrophages.
To identify the cell types responsible for the marked increases observed in PDGF-B in obese adipose tissue, as shown in Fig. 1A, we initially analyzed the MAF and SVF separated from the eWAT of diet-induced obese mice. The expression of Pdgfb was significantly higher in the SVF than in MAF (Fig. 5A). To further clarify the cell types, we divided the SVF into CD45+F4/80+ macrophage and CD45-F4/80- non-leukocyte populations that included ECs and preadipocytes. In the lean state, the expression of Pdgfb was similar between the two populations. In contrast, its expression was markedly increased in the macrophage fraction with obesity (Fig. 5B). Since ECs are known to play important roles in the maturation of vessels by producing PDGF-B (15,17), we analyzed the content of ECs in SVF of eWAT from HFD-fed obese mice by different gating (Supplementary Fig. 4A and B). Expression of Pdgfb mRNA in the CD45-CD31+ ECs fraction was comparable to that in the CD45+F4/80+ macrophage fraction; however, most of the cells were in the CD45+F4/80- and CD45+F4/80+ fractions, and ECs were small component (only 1.1±0.1%) of total SVF in obese eWAT.
We next examined the expression of Pdgfb in macrophage subpopulations in the eWAT of obese mice (Supplementary Fig. 4C). The Pdgfb expression was apparently high in F4/80+CD11c+CD206+ macrophages; however, these cells were small component (only 0.3±0.1%) of total macrophages. In other fractions, CD11c+CD206- M1-macrophages are a major type of cells expressing Pdgfb. In addition, the expression of Pdgfb was gradually and preferentially increased in F4/80+CD11c+CD206- M1-macrophages, but not in F4/80+CD11c-CD206+ M2-macrophages in a time-dependent manner during HFD feeding (Fig. 5C), which appeared to correlate with pericyte detachment in the eWAT (Fig. 3H). Consistently, pericytes associated with vessels were further decreased around CLS areas compared to non-CLS areas in the obese adipose tissues (Supplementary Fig. 4D and E). These results suggested that the obesity-associated recruited M1-macrophages have a greater
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impact on the constitution of the high PDGF-B environment for vascular remodeling during adipose tissue enlargement.
HFD-induced ectopic fat deposition was reduced in mice lacking Pdgfrb.
We examined lipid metabolism in each genotype of mice. Fasted serum non-esterified fatty acid (NEFA), triglyceride (TG), and cholesterol levels were not different between Pdgfrb∆SYS-KO and FL mice on chow diet, but significantly lower in Pdgfrb∆SYS-KO mice than in FL mice on HFD (Supplementary Table 3). HFD-induced accumulation of triglyceride in the quadriceps muscle and liver was significantly reduced in Pdgfrb∆SYS-KO mice, when compared to that in FL mice (Fig. 6A and B). In accordance with hepatic lipid contents, the results of histological analyses revealed brighter hepatocytes and more abundant vacuolar changes in the livers of HFD-fed FL mice, whereas these features of hepatic steatosis were ameliorated in Pdgfrb∆SYS-KO mice (Fig. 6C). The hepatic expressions of lipogenic, β-oxidative, and gluconeogenic genes were significantly increased by HFD-feeding in FL mice, whereas most of the increasing effects were attenuated in Pdgfrb∆SYS-KO mice (Fig. 6D).
Energy metabolism was enhanced in mice lacking Pdgfrb.
Since HFD feeding did not cause ectopic fat accumulation in Pdgfrb∆SYS-KO mice despite reduction in adipose tissue expansion, we investigated whether energy metabolism was
enhanced in the mice. VO2 and VCO2 were higher both in the light and dark phases in Pdgfrb∆SYS-KO mice than in FL mice under both chow and HFD conditions (Fig. 6E and F). Locomotor activity was also significantly higher in Pdgfrb∆SYS-KO mice (Fig. 6G). Food intake was increased in the Pdgfrb∆SYS-KO mice, possibly to compensate for the increased energy expenditure (Fig. 6H). In the inguinal WAT of Pdgfrb∆SYS-KO mice, beige-related changes were not observed in the histological and RT-PCR analyses (Supplementary Fig. 5).
The HFD-induced impairment in glucose metabolism was prevented in mice lacking Pdgfrb.
We investigated alterations in glucose metabolism in Pdgfrb∆SYS-KO mice (Fig. 7A-D). Under chow-fed condition, glucose levels during GTT were significantly lower in Pdgfrb∆SYS-KO mice than in FL mice, while no differences were observed in insulin levels during GTT and glucose levels during ITT. HFD-induced glucose intolerance,
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hyperinsulinemia, and insulin resistance were more preventable in Pdgfrb∆SYS-KO mice than in FL mice. Hyperinsulinemic euglycemic clamp studies showed that the glucose infusion rate was markedly increased in Pdgfrb∆SYS-KO mice in association with increases in the disappearance of whole body glucose and the suppression of hepatic glucose production by insulin (Fig. 7E-G). We subsequently analyzed the insulin-induced phosphorylation of Akt in eWAT, the liver, and skeletal muscle of Pdgfrb∆SYS-KO mice (Fig. 7H). Phosphorylation levels were reduced in all of these tissues in FL mice fed HFD. Importantly, reductions in phosphorylation levels in each tissue were prevented in Pdgfrb∆SYS-KO mice fed HFD. These results suggested that the deletion of PDGFRβ prevented HFD-induced insulin resistance in eWAT, the liver, and skeletal muscle.
We examined whether the deletion of Pdgfrb improved obesity and glucose metabolism, even after the development of obesity. The tamoxifen-induced deletion of Pdgfrb after 8 weeks of HFD feeding significantly decreased body weight gain and ameliorated insulin resistance in Pdgfrb∆SYS-KO mice fed HFD (Supplementary Fig. 6). Thus, the deletion of PDGFRβ had a therapeutic impact on existing obesity and its related metabolic abnormalities in mice.
Discussion
WAT has a unique capacity for remodeling according to the energy status. Adequate angiogenesis is necessary for adipose tissue expansion because it enables the supplementation of nutrients and oxygen in newly enlarged areas. In the present study, we identified a distinguishing role for PDGF-B/PDGFRβ signaling in the regulation of the initiation on neovascular formation in WAT in diet-induced obesity. We found that obesity-associated increase in PDGF-B promoted the detachment of pericytes from mature vessels, which was correlated with proliferation of ECs in obese adipose tissue. In contrast, this detachment was attenuated and vascularity within WAT was reduced in Pdgfrb∆SYS-KO mice. In addition, energy metabolism was increased in the mice. These appeared to contribute to the decreases in adipocyte size and chronic inflammation in Pdgfrb∆SYS-KO mice even under HFD feeding conditions.
PDGFRβ is almost restrictively expressed in perivascular mural cells, and its signaling is
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known to be crucially involved in neovessel formation (14). Matured vasculature is covered with pericytes that are mobilized by PDGF-B secreted from ECs (34). The attached pericytes suppress the proliferation of ECs as well as the formation of new vascular branches (33-36); therefore, the detachment of pericytes from the vessel wall is considered to be the initial step in angiogenesis. In the present study, the ratio of pericytes attached to blood vessels was markedly decreased by HFD feeding in the eWAT of FL mice (Fig. 3). Our results strongly correlated with previous findings showing that the pericyte-to-EC ratio in adipose tissue was significantly lower in obese subjects than in lean subjects (37). Exogenous PDGF-B facilitated the detachment of pericytes from mature vessels via PDGFRβ signaling in tissue culture experiments (Fig. 4). In addition, some populations of ECs located at the site at which pericytes detached showed growth characteristics in obese adipose tissue (Fig. 3). Therefore, the vessels of obese adipose tissue may be anticipating vascular sprouting and angiogenesis. Since HFD-induced pericyte detachment was limited, HFD-induced angiogenesis and WAT expansion were attenuated in Pdgfrb∆SYS-KO mice. These results suggested that obesity-induced angiogenesis in WAT largely depends on PDGF-B-PDGFRβ signaling in pericytes.
PDGF-B derived from ECs has been reported to promote the proliferation of pericytes and/or their recruitment to blood vessels (14,38), whereas excessive PDGF-B derived from implanted tumor cells induced the recruitment of pericytes to tumor cells from neovessels (38, 39). Thus, pericytes are considered to be recruited according to the concentration gradient of PDGF-B. We found that Pdgfb mRNA levels were similar between CD45-F4/80- populations and CD45+F4/80+ macrophages in the eWAT of lean mice, whereas they selectively increased in F4/80+CD11c+CD206- M1-macrophages in the eWAT of obese mice (Fig. 5). Although ECs expressed Pdgfb mRNA, there were few ECs in SVF of the obese adipose tissue (Supplementary Fig. 4B). Based on these results, we provide a putative model for explaining the regulation of WAT expansion by angiogenesis in obesity through PDGF-B/PDGFRβ signaling, as described in Fig. 8: PDGF-B produced by ECs appears to recruit pericytes toward the vessel walls to maintain the mature vascular system in the lean state. Under HFD feeding conditions, excessive amount of PDGF-B is produced by infiltrated M1-macrophages in obese WAT. It may cause the detachment of pericytes from vessels via PDGFRβ signaling, i.e., an initial step in neovascular sprouting. The adipose-tissue angiogenesis may help the WAT expansion, because vascular remodeling 13
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enables the tissue to store abundant amounts of fuel provided by HFD. Therefore, suppression of the PDGFRβ signaling may inhibit the detachment of pericytes from vessels within WAT and the tissue expansion, as observed in Pdgfrb∆SYS-KO mice fed HFD. However, it remained unclear whether the M1-macrophage-derived PDGF-B directly causes the detachment of pericytes from vessels and whether these events, if any, can sufficiently promote adipose tissue expansion. Further study is required to determine the causal relationship.
M2-macrophage plays a principle role in angiogenesis, since it locates in the vicinity of vessel branch and promotes angiogenesis by releasing pro-angiogenic factors, such as VEGF (40). In the present study, we found that M1-macrophage is a major source of PDGF-B in obese adipose tissue (Fig. 5). Although the Pdgfb mRNA was also highly expressed in the CD11c+CD206+ macrophage, this subpopulation was almost negligible in the obese adipose tissue (Fig. 2G, Supplemental Fig. 4C); therefore, the functional significance of this type of macrophage remained to be clarified. Infiltration of M1-macrophage was also observed in the liver and muscle and contributes to the development of chronic inflammation in obesity (41,42); however, we did not detect any increase in the expression of Pdgfb by HFD feeding in the liver and skeletal muscle of mice (Fig. 1). These results suggested that adipose tissue-specific environment, such as abnormal production of adipokines or hypoxia, promotes the production of PDGF-B in M1-macrophage in diet-induced obese mice. M1-macrophage may contribute to vascular remodeling in adipose tissue via PDGF secretion under obese conditions, whereas M2-macrophage may contribute to the development or maintenance of vascular system under physiological conditions.
Tamoxifen is widely used to generate inducible conditional transgenic mice; however, several recent studies have concerned its influences on the adipocyte biology (43,44). In particular, acute adipocyte death and transient reduction of body weight have been observed during the tamoxifen treatment, although body weight was recovered by de novo differentiation of adipocytes after the treatment (43). In addition, tamoxifen has been reported to induce browning of subcutaneous fat (44). In the present study, we administered tamoxifen to all groups of mice, including FL mice, to conduct the experiments under the same condition. Body weight was not acutely changed during 5 days of tamoxifen treatment except in Supplementary Fig. 6 where tamoxifen was administered to obese mice. Moreover,
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we did not observe any histological feature of browning or increase of browning gene transcripts, such as Ucp1, in the inguinal WAT of both FL and Pdgfrb∆SYS-KO mice (Supplementary Fig. 5). Thus, the influence of tamoxifen on metabolism in mice appeared to be negligible in the present experimental condition, although we cannot completely rule out the possibility that some phenotypes of Pdgfrb∆SYS-KO mice might be affected by the treatment of tamoxifen especially under the obese condition.
In obese adipose tissue, VEGF-A is mainly produced by mature adipocytes, and promotes obesity-associated angiogenesis for the supply of oxygen and nutrients to hypoxic areas (11). Adipocyte-specific VEGF-A knockout mice have dysfunctional adipose tissue with reduced vascular density (11). Thus, the obesity-associated production of VEGF-A in adipose tissue is crucial as the homeostatic machinery. In contrast, the present results indicated that PDGF-B was mainly produced by adipose tissue macrophages in obesity, particularly by proinflammatory M1-macrophages that infiltrated into the expanding tissues (Fig. 5). Therefore, it is possible to speculate that PDGF-B mediates pathological adaptation in obese adipose tissue. In this regard, the excess exposure of PDGF-B from infiltrated M1-macrophages to pericytes promotes inappropriate angiogenesis in obese adipose tissue, which may facilitate the further infiltration of immune cells (5), resulting in a disturbance in adipose tissue homeostasis.
The functional relationship between adipose-tissue neovascularization and energy expenditure in obesity is somewhat complicated. The Pdgfrb∆SYS-KO mice exhibited the limited adipose neoangiogenic capacity and enhanced energy metabolism; however the primary mechanism responsible for reducing adiposity in the mice remains unknown. In addition, it is still unclear whether the observed changes in the adipose tissue vasculature of Pdgfrb∆SYS-KO mice were due to primary effects of the Pdgfrb deletion or secondary effects of the lack of weight gain. Previous studies demonstrated that treatments with angiogenic inhibitors or anti-neovascular peptide not only inhibited adipose tissue enlargement but also enhanced energy metabolism, possibly by compensatory mechanism for maintaining energy homeostasis (1,2,6). Therefore, we consider that insufficient expansion of adipose tissue, the main organ for energy storage, due to suppressed angiogenic activity might enhance energy metabolism in Pdgfrb∆SYS-KO mice via unknown compensation pathways. Further studies are needed to clarify the precise underlying mechanism.
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In conclusion, the present study demonstrated that the systemic deletion of Pdgfrb inhibited neovessel formation in WAT, reduced fat accumulation and chronic inflammation in visceral adipose tissue, and improved whole body glucose metabolism in association with decreased ectopic fat deposition in the muscle and liver of diet-induced obese mice. We documented the distinct role of PDGF-B-PDGFRβ signaling in the development of adipose-tissue neovascularization accompanied by diet-induced obesity. Based on these favorable effects, we consider the suppression of PDGF-B-PDGFRβ functions to be a valuable approach for preventing obesity and type 2 diabetes.
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Acknowledgments.
Y.O. performed most of the experiment, designed the experiment, wrote the manuscript, and contributed to discussion. T.W. conceived and designed the experiment, researched data, wrote the manuscript, and contributed to discussion. C.K., K.I., T.M., Y.Ina., K.K., and H.I. researched data, and contributed to discussion. S.Y. and D.K. contributed to discussion. Y.Ish. and M.S. produced and provided Pdgfrb∆SYS-KO mice and contributed to discussion. H.T. and T.S. designed the experiments, wrote the manuscript, and contributed to discussion. T.W. and T.S. are the guarantors of this work and, as such, had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. All authors critically reviewed the manuscript.
The authors thank Drs. S. Fujisaka, Y. Nishida, and K. Tobe at the First Department of Internal Medicine and Drs. M. Ikutani and Y. Nagai at the Department of Immunobiology and Pharmacological Genetics, University of Toyama for their technical advice regarding flow cytometry; Drs. S. Watanabe, and K. Fujita at the Division of Nutritional Biochemistry, Institute of Natural Medicine, University of Toyama for their technical advice regarding lipids analysis; and Ms. T. Matsushima at the Department of Pathology, University of Toyama for her excellent technical assistance.
Funding.
This research was supported by the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) grants 24591318 (to T.W.), a grant from the Japan Diabetes Foundation (to T.S. and T.W.), Takeda Science Foundation (to T.W.), Suzuken Memorial Foundation (to T.W.), The Hokuriku Bank Grant-in-Aid for Young Scientists (to T.W.), Research Grant from Mitsubishi Tanabe Pharma Corporation (to T.W.), The Murata Science Foundation (to T.W), Foundation for Growth Science (to T.S.), and Sasakawa Scientific Research Grant (to Y.O.).
Duality of Interest. No potential conflicts of interest relevant to this article were reported.
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Figure Legends
Figure 1
Systemic Pdgfrb knockout mice exhibited resistance to diet-induced obesity. Mice were fed a chow diet or high-fat diet (HFD) from 8 weeks old. A,B: Influences of HFD feeding on mRNA levels of Pdgfb (A) and Pdgfrb (B) in various tissues of mice at 22-24 weeks old (n = 4-6 per group). C, D: The time course of changes in the mRNA levels of Pdgfb (C) and Vegfa (D) during HFD feeding (n=4-6 per group). E: Protocol of tamoxifen administration and HFD feeding. At 9 weeks old, tamoxifen was administered to both Cre-ERTM/Pdgfrbflox/flox and Pdgfrbflox/flox mice to obtain Pdgfrb∆SYS-KO mice and their tamoxifen-treated control (FL) mice. Each genotype of mice was divided into 2 groups and fed chow or HFD. In vivo analyses of metabolic phenotypes were performed from 21 to 25 weeks of age, and then the mice were killed for tissue sampling. F: Changes in body weight in FL and Pdgfrb∆SYS-KO mice during chow or HFD feeding. G,H: Representative images of MRI (T1-weighted image, G), and the estimated volumes of subcutaneous (SubQ) fat, visceral fat, and lean mass, assessed by MRI imaging (H). I: Tissue weights at 23-25 weeks old. Data are represented as the mean ± SEM. n=6-10 per group. *p<0.05 and **p<0.01. Hatched symbols: chow-fed FL mice, dotted symbols: chow-fed Pdgfrb∆SYS-KO mice, open symbols: HFD-fed FL mice, closed symbols: HFD-fed Pdgfrb∆SYS-KO mice. eWAT: epididymal white adipose tissue, iWAT: inguinal white adipose tissue, BAT: brown adipose tissue, S. M.: skeletal muscle. ND: not detectable.
Figure 2 Suppressive effects of the Pdgfrb deletion on adipocyte enlargement and chronic inflammation in white adipose tissue in diet-induced obese mice. A: Representative hematoxylin and eosin (H&E) staining of eWAT of control (Pdgfrbflox/flox, FL) and Pdgfrb∆SYS-KO mice. Scale bar, 200 m. B: Frequency distribution of the adipocyte areas of eWAT of FL and Pdgfrb∆SYS-KO mice fed chow (upper) and HFD (lower). C: Mean area of adipocytes (n=4-8 per group). D: Representative images of eWAT immunostained with the anti-CD11c antibody. Scale bar, 200 m. E: The number of crown-like structures (CLS). n=6-8 per group. F,G: Flow cytometric analysis of the SVF in eWAT of HFD-fed mice. The number of macrophages (F) gated on CD45+ or CD45+F4/80+ (left) and the percentage of
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total cells (right), and the number of subpopulation of macrophages (G) gated on CD11c-CD206-, CD11c+CD206-, CD11c-CD206+, or CD11c+CD206+ (left) and the percentage of adipose tissue macrophages (ATM) in the SVF of eWAT (right) were analyzed (n=6-7 per group). The inset shows the same data of CD11c+CD206+ subpopulation at different y-scale. H: The mRNA expression of genes in eWAT. n=4-10. I: Tnfa mRNA levels after the 3-h stimulation with LPS (0 or 1 ng/mL) under serum starvation for 4 h in BMDMs derived from FL (open column) and Pdgfrb∆SYS-KO mice (closed column). n=6-8 per group. Data represent the mean of three independent experiments. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05 and **p <0.01. Hatched symbols: chow-fed FL mice, dotted symbols: chow -fed Pdgfrb∆SYS-KO mice, open symbols: HFD-fed FL mice, closed symbols: HFD-fed Pdgfrb∆SYS-KO mice.
Figure 3 Effects of the Pdgfrb deletion on vascularity in white adipose tissue in mice. A-C: Changes in vascularity in eWAT of control (Pdgfrbflox/flox, FL) and Pdgfrb∆SYS-KO mice fed chow and HFD. The tip region of eWAT was used for vascular imaging. A: Representative vasculature of whole-mount eWAT. Blood vessels were visualized with anti-PECAM1 immunostaining. Scale bar, 500 m. B,C: Quantitative vessel area (B) and numbers of vessel segments (C) analyzed with low-power field microscopy. To this end, total PECAM-1-stained area and numbers of branches of vessels on each microscopy (10X objective) were measured and averaged. n=4 per group. D: Perivascular cells (pericytes: PCs) in the eWAT of lean control (FL) mice were co-stained with anti-CD13 (green) and anti-PDGFRβ (cyan, left panel) or anti-NG2 (cyan, right panel) in cryosections of eWAT. Blood vessels were visualized with anti-PECAM1 immunostaining. Scale bar, 50 µm. E: The mRNA expression levels of Pdgfrb in the MAF and SVF of eWAT in C57BL/6J mice. F: Representative whole-mount immunofluorescence images. Epididymal WAT of control (Pdgfrbflox/flox, FL) and Pdgfrb∆SYS-KO mice fed chow and HFD was stained with anti-PECAM1 (red: ECs) and anti-CD13 antibodies (green: PCs). Scale bar, 200 m. G: The percentage of PCs associating with blood vessels in panel F. H: Changes in the percentage of PCs associated with blood vessels in eWAT from C57BL/6 mice during HFD feeding. n=4-5 per group. I: Representative immunofluorescence images stained with Hoechst (blue, nuclei), anti-Ki67 24
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(white), NG2 (green), and PECAM-1 (red) in eWAT of HFD-fed FL mice. Scale bar, 100 m. J: The mean fluorescence intensity (MFI) of Ki67 in PECAM1+ cells gated on CD45- in SVF of eWAT from HFD-fed FL and HFD-fed Pdgfrb∆SYS-KO mice. n=6-11 per group. Blood vessel areas (A,B) and pericyte associations (F-H) were measured with the ImageJ software. Data are represented as the mean ± SEM. *p<0.05 and **p<0.01. Hatched symbols: chow-fed FL mice, dotted symbols: chow-fed Pdgfrb∆SYS-KO mice, open symbols: HFD-fed FL mice, closed symbols: HFD-fed Pdgfrb∆SYS-KO mice.
Figure 4
Changes in pericyte localization in cultured eWAT by an exogenous PDGF-BB treatment. A-C: Representative images of cultured eWAT stained with anti-CD13 (green) and anti-PECAM1 (red) antibodies (A,B) and counter staining with Hoechst (B). Scale bar, 50 µm. The lower panels show a magnified view of the white squares in the upper image. B: Representative high-magnification images in tissues treated with 1 µg/mL PDGF-BB for 24 h. C: Percentage of pericytes associating with blood vessels analyzed under low-power field microscopy. n=6 per group. D-G: The influence of deletion of PDGFRβ on the PDGF-BB-induced changes in pericyte localization. Representative images of PDGFRβ (green)-positive cells (D) and mean fluorescence intensity of PDGFRβ-positive signals (E) to determine the knockout efficiency in whole-mount cultured eWAT from Cre-ERTM/Pdgfrbflox/flox (KO-eWAT) and control mice (FL-eWAT) after treatment with 100 nM 4-hydroxytamoxifen (4-OHT) for 48 h. n=3 per group. F: Representative images of whole-mount eWAT from KO-eWAT and FL-eWAT stained with anti-CD13 (green) and anti-PECAM1 (red) antibodies after treatment with 100 ng/mL PDGF-BB for 24 h. Scale bar, 100 µm. G: The percentage of pericytes associated with blood vessels in panel F. n=9-11 per group. Data represent the mean of independent experiments. Data are represented as the mean ± SEM. *p<0.05 and **p<0.01.
Figure 5 Identification of cell types strongly expressing Pdgfb in the eWAT of mice fed HFD. Mice were maintained on HFD from 8 weeks of age. A: mRNA levels of Pdgfb in the MAF and SVF isolated from the eWAT of C57BL/6J mice at 22 weeks old. B: The mRNA levels of
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Pdgfb in CD45-F4/80- non-leukocyte populations and CD45+F4/80+ macrophages of the SVF from eWAT in FL mice before (Lean) and after (Obese) HFD feeding for 12 weeks. C: The time course of changes in the mRNA levels of Pdgfb in F4/80+CD11c+CD206- (closed columns) and F4/80+CD11c-CD206+ cells (open columns) obtained from eWAT of C57BL/6J mice fed HFD for indicated times. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. n=5-6 per group. *p<0.05 and **p<0.01.
Figure 6 Deletion of systemic Pdgfrb reduced ectopic lipid accumulation in diet-induced obese mice. Chow-fed FL mice (hatched columns), chow-fed Pdgfrb∆SYS-KO mice (dotted columns), HFD-fed FL mice (open columns), and HFD-fed Pdgfrb∆SYS-KO mice (closed columns) were used. A,B: Total lipid content in the skeletal muscle (SM) (A) (n=6-9 per group) and the liver (B) (n=4-8 per group). Lipids were extracted by the method of Bligh-Dyer. Triglyceride contents among the total lipid content were measured using a triglyceride kit and normalized with each wet tissue weight. C: Representative H&E staining in the liver. Scale bar, 200 m. D: mRNA levels in the liver. n=4-8 per group. E-H: Parameters of energy metabolism. Oxygen consumption (E), carbon dioxide production (F), locomotor activity (G), and daily food intake (H) were measured in mice at 19-21 weeks old by a metabolism measuring system. n=6-9 per group. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05 and **p<0.01.
Figure 7 Deletion of systemic Pdgfrb improved glucose tolerance and insulin sensitivity in mice. Chow-fed FL mice (hatched symbols), chow-fed Pdgfrb∆SYS-KO mice (dotted symbols), HFD-fed FL mice (open symbols), and HFD-fed Pdgfrb∆SYS-KO mice (closed symbols) were used. A,B: Blood glucose (A) and insulin levels (B) during the glucose tolerance test (GTT) (n=8-10 per group). C: Insulin tolerance test (ITT) (n=6-9 per group). aP<0.05: chow-fed FL vs. chow-fed Pdgfrb∆SYS-KO mice bP<0.05: chow-fed FL vs. HFD-fed FL mice. cP<0.05: HFD-fed FL vs. HFD-fed Pdgfrb∆SYS-KO mice. D: Glucose area under the curve (AUC) in
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GTT (A) and ITT (B). E-G: Hyperinsulinemic-euglycemic clamp study in HFD-fed mice at 22 weeks old. Glucose infusion rate (GIR, E), glucose disposal rate (Rd, F), and the percentage suppression of hepatic glucose production (HGP, G) in FL and Pdgfrb∆SYS-KO mice under the 6-h fasting condition were examined. n=6 per group. H: Representative western blotting images and quantitative results of insulin-induced Akt phosphorylation in eWAT, the liver, and skeletal muscle of FL and Pdgfrb∆SYS-KO mice at 24 weeks old. n=4-5 per group. Tissue samples were isolated 5 min after an intravenous injection of insulin (1.0 U/kg body weight) under the 6-h fasting condition. Data are represented as the mean ± SEM. *p <0.05 and **p<0.01.
Figure 8 A conceptual model of vascular remodeling and adipose tissue expansion in adult obesity. Proinflammatory M1-macrophages increase along with adipose tissue expansion. They produce high levels of PDGF-B, and promote the detachment of pericytes from mature vessels, thereby making vessels prone to sprouting. Consequently, adipose-tissue angiogenesis continues with tissue enlargement.
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F4/80+ CD11c+ CD206- + - + F4/80 CD11c CD206 Page 33 of 45 Diabetes
Figure 6
A B C FL Pdgfrb∆SYS-KO
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Figure 7
A B C GTT ITT
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300 b ∆SYS HFD (ng/mL) Pdgfrb -KO b a c 1 100 200 c c c a 50 c 100 a
Insulin Insulin 0 Glucose (mg/ Glucose Glucose (mg/dL) Glucose 0 0 0 60 120 0 15 30 0 60 120 Time (min) Time (min) Time (min)
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(A.U.) 0.5 ( 0.5 ( 0.5 pAkt/Akt pA pA 0 0 0 Insulin - + - + - + - + - + - + - + - + - + - + - + - + Chow HFD Chow HFD Chow HFD FigurePage 35 8 of 45 Diabetes The Schema of Adipose Tissue Expansion
Lean Pericyte PDGFRb+ cell
Recruitment DETACHMENT
PDGF - B
M1- macrophages
ANGIOGENES I S Obese Diabetes Page 36 of 45
Supplementary data
PDGFRβ regulates adipose tissue expansion and glucose metabolism via vascular remodeling in diet induced obesity
Yasuhiro Onogi1, Tsutomu Wada1, Chie Kamiya1, Kento Inata1, Takatoshi Matsuzawa1, Yuka Inaba2, 3, Kumi Kimura2, Hiroshi Inoue2, 3, Seiji Yamamoto4, Yoko Ishii4, Daisuke Koya5, Hiroshi Tsuneki1, Masakiyo Sasahara4, and Toshiyasu Sasaoka1
1Department of Clinical Pharmacology, 4Department of Pathology; University of Toyama, Toyama 930 0194, Japan, 2Department of Physiology and Metabolism, Brain/Liver Interface Medicine Research Center, 3Metabolism and Nutrition Research Unit, Innovative Integrated Bio Research Core, Institute for Frontier Science Initiative; Kanazawa University, Kanazawa, Kanazawa 920 8640, Japan, 5Department of Internal Medicine, Kanazawa Medical University, 1 1 Daigaku, Uchinada, Ishikawa 920 0293, Japan
1
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Supplementary data
Supplementary Table 1. The list of antibodies used in the present study.
Ar Hamster: Armenian Hamster, SCB: Santa Cruz Biotechnology, CST: Cell Signaling Technology, JIR: Juckson ImmunoResearch, FC: flow cytometry, WB: western blotting, IHC: immunohistochemistry, IF: immunofluorescence.
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Supplementary data
Supplementary Table 2. The list of primers used in the present study.
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Supplementary data
Supplementary Table 3. Serological parameters of mice on fasting condition.
Serological parameters of mice on normal chow (Chow) or high fat diet (HFD) feeding for 14 16 weeks under 6 h fasting condition were assessed. Data are represented as the mean ± SEM. n = 6 10 per group. Statistically significance was defined p<0.05 obtained by 2 way ANOVA with Bonferroni’s tests for multiple comparisons. *p<0.05 and **p<0.01 compared to Chow FL. †p<0.05 and † † p<0.01 compared to HFD FL. NEFA: nonesterified fatty acid.
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Supplementary data
Supplementary Figure 1 Relevance of the PDGF B/PDGFRβ system in white adipose tissue to metabolic changes in diet induced obese mice. Mice were divided into normal chow diet (Chow) or high fat diet (HFD) group at 8 weeks old. A: The mRNA levels of Kdr in the major target tissues of insulin when mice were 22 24 weeks old. n=4 6 per group. B, C: The time course of changes in the serum levels of PDGF B (B) and VEGF A (C) during HFD feeding. n=4 6 per group. D, E: The protein (D) and mRNA levels (E) of PDGFRβ in various tissues of FL and Pdgfrb SYS KO mice fed Chow. Tamoxifen was administered at 9 weeks old, and mice were sacrificed at 23 24 weeks old. Tubulin was used as a loading control. n=4 9 per group. F: mRNA levels of Pdgfrb in various tissues of FL and Pdgfrb SYS KO mice. Mice (9 weeks old) were treated with tamoxifen, and maintained on HFD. The mice were sacrificed after 2 weeks or 14 weeks of HFD feeding. n=4 7 per group. G: Hind limbs mass of FL and Pdgfrb SYS KO mice were analyzed by MRI imaging. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05, and **p<0.01. Hatched columns: chow fed FL mice, dotted columns: chow fed Pdgfrb SYS KO mice, open columns: HFD fed FL mice, closed columns: HFD fed Pdgfrb SYS KO mice. A.U.: arbitrary unit, eWAT: epididymal white adipose tissue, iWAT: inguinal white adipose tissue, BAT: brown adipose tissue, S. M.: skeletal muscle.
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Supplementary data
Supplementary Figure 2 Differentiation and proliferation assay in mouse embryonic fibroblast (MEF) derived from FL and Pdgfrb SYS KO mice. Mouse embryonic fibroblasts were obtained from embryo cross bred Pdgfrbflox/flox mice and Cre ERTM/Pdgfrbflox/flox mice on embryonic day 13.5 14.5. Cells were differentiated into adipocytes by the standard protocol of 3T3 L1 adipocyte differentiation by treatment with differentiation medium for 60 h and medium containing insulin and 100 nM 4 hydroxytamoxifen for 48 h. A, B: Representative Oil red O staining of MEF (A) and lipid accumulation levels in MEF (B) at 8 days after adipocyte differentiation. Lipid levels were compared by measuring the optical density of the extract at 490 nm after Oil red O staining. n=3 per group. Scale bar, 50 m. C: The mRNA levels of adipocyte differentiation markers in MEF at 8 days after adipocyte differentiation. Data represent the mean of three independent experiments. D: Cell proliferation activity was determined by MTT assay on 7 day in vitro. n=8 14 per group. E: MEF were serum starved for 13 h, and stimulated with various concentration of insulin for 24 h. Then insulin induced Ki67 expression was determined by real time PCR. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05, and **p<0.01.
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Supplementary data
Supplementary Figure 3 Changes in the levels of vascular endothelial cell marker in the eWAT of mice fed HFD. Tamoxifen was administered to FL and Pdgfrb SYS KO mice fed chow and HFD at 9 weeks old. Protein levels of VEGFR2, an endothelial marker, in eWAT of mice at 23 25 weeks old were analyzed by western blotting. Tubulin is used as a loading control. n=6 11 per group. Data are represented as the mean ± SEM. **p<0.01.
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Supplementary data
Supplementary Figure 4 Components of cells expressing Pdgfb in the eWAT of mice fed HFD. A,B: Cell populations and mRNA expression of Pdgfb in each population. SVF from eWAT of HFD fed obese mice were separated into CD45 CD31+ endothelial cell fraction, CD45 CD31 other non leukocyte fraction, CD45+F4/80+ macrophage fraction, and CD45+F4/80 other leukocyte fraction. The mRNA expression of Pdgfb in each fraction (A) and the content rate of each cell population (B) are shown. n = 4. C, Macrophages in SVF from eWAT of HFD fed mice were separated into CD11c CD206 , CD11c+CD206 , CD11c CD206+, and CD11c+CD206+. The mRNA expression of Pdgfb in each fraction was examined. D,E: Pericyte associations with vessels in CLS area and non CLS area of obese adipose tissues were determined. Control mice were fed HFD from 8 weeks old to 20 weeks old (n =6). Representative immunofluorescence images of eWAT with anti F4/80 (cyan: macrophage), anti NG2 (green: PCs), and anti PECAM1 (red: ECs) antibodies are shown (D). Scale bar, 100 m. The percentage of PCs associating with blood vessels in CLS area (18 area) and non CLS area (except for CLS area in the same slide, 7 area) are determined (E). The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05.
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Supplementary data
Supplementary Figure 5
Histological and quantitative gene expression analyses in inguinal white adipose tissue (iWAT) from FL and Pdgfrb SYS KO mice fed chow diet. 24 week old mice were used. A: Representative H&E staining of iWAT. Scale bar, 500 m. B: mRNA levels of thermogenesis related genes in iWAT. n=6 per group. The mRNA expression was normalized to Rn18s and expressed as a fold change with the values for control. Data are represented as the mean ± SEM. *p<0.05. Hatched columns: chow fed FL mice, dotted columns: chow fed Pdgfrb SYS KO mice.
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Supplementary data
Supplementary Figure 6 Therapeutic effects of the tamoxifen induced conditional deletion of systemic Pdgfrb on body weight changes and insulin sensitivity in diet induced obese mice. Mice were maintained on HFD from 8 weeks of age. A: Changes in body weight in Pdgfrbflox/flox (FL) and Cre ERTM/Pdgfrbflox/flox mice on HFD feeding. Each mouse was administrated tamoxifen for 5 consecutive days to delete Pdgfrb 8 weeks after the initiation of HFD feeding. B: Blood glucose levels in ITT 18 weeks after the initiation of HFD feeding. Data are represented as the mean ± SEM. n=6 7 per group. †p<0.1, *p<0.05, and **p<0.01. Open circles: HFD fed FL mice, closed circles: HFD fed Pdgfrb SYS KO mice.
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