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. 2018 Apr;17(2):e12721.
doi: 10.1111/acel.12721. Epub 2018 Jan 31.

Ablation of PPARγ in subcutaneous fat exacerbates age-associated obesity and metabolic decline

Lingyan Xu  1   2 , Xinran Ma  1   2 , Narendra Kumar Verma  3 , Dongmei Wang  1   2 , Oksana Gavrilova  4 , Richard L Proia  1 , Toren Finkel  5 , Elisabetta Mueller  1   3
Affiliations

Ablation of PPARγ in subcutaneous fat exacerbates age-associated obesity and metabolic decline

Lingyan Xu et al. Aging Cell. 2018 Apr.

Abstract

It is well established that aging is associated with metabolic dysfunction such as increased adiposity and impaired energy dissipation; however, the transcriptional mechanisms regulating energy balance during late life stages have not yet been fully elucidated. Here, we show that ablation of the nuclear receptor PPARγ specifically in inguinal fat tissue in aging mice is associated with increased fat tissue expansion and insulin resistance. These metabolic effects are accompanied by decreased thermogenesis, reduced levels of brown fat genes, and browning of subcutaneous adipose tissue. Comparative studies of the effects of PPARγ downregulation in young and mid-aged mice demonstrate a preferential regulation of brown fat gene programs in inguinal fat in an age-dependent manner. In conclusion, our study uncovers an essential role for PPARγ in maintaining energy expenditure during the aging process and suggests the possibility of targeting PPARγ to counteract age-associated metabolic dysfunction.

Keywords: PPARγ; aging; metabolic decline; obesity; subcutaneous fat.

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Figures

Figure 1
Figure 1
Selective ablation of PPARγ in iWAT of aging mice via adenoviral delivery. (a–d) Analysis of 12‐month‐old control, PPARγ‐iWAT‐KO, and PPARγ‐iWAT‐KD mice. n = 6 per group. (a) Illustration of the strategy used to achieve modulation of PPARγ levels in iWAT via adenoviral delivery. (b) mRNA and (c) protein levels of PPARγ in iWAT. (d) mRNA levels of PPARγ in fat depots, liver, pancreas, and macrophages present in iWAT. Data are presented as mean ± SEM and *, p < .05; **, p < .01
Figure 2
Figure 2
PPARγ deficiency in iWAT of aging mice increases adiposity. (a–g) Analysis of 12‐month‐old control, PPARγ‐iWAT‐KO, and PPARγ‐iWAT‐KD mice. n = 6 per group. (a) Body weight; (b) fat mass; (c) lean mass; (d) adipose tissue weights; (e) tissue weights; (f) representative images of H&E staining of adipose tissues; (g) adipocyte sizes of iWAT and eWAT. Data are presented as mean ± SEM and *, p < .05; **, p < .01
Figure 3
Figure 3
Impaired glucose and lipid homeostasis in aging mice with PPARγ deficiency in iWAT. (a–d) Analysis of 12‐month‐old control, PPARγ‐iWAT‐KO, and PPARγ‐iWAT‐KD mice. n = 6 per group. (a, b, c) Insulin sensitivity measured by GTT and ITT and shown as area under the curve (AUC); (d) serum parameters including free fatty acids (FFA), total triglyceride (TG), and total cholesterol (TC). Data are presented as mean ± SEM and *, p < .05; **, p < .01
Figure 4
Figure 4
PPARγ is required for the maintenance of brown fat programs in iWAT of aging mice. (a–e) Analysis of 12‐month‐old control, PPARγ‐iWAT‐KO, and PPARγ‐iWAT‐KD mice. n = 6 per group. (a) Oxygen consumption normalized to lean mass (LM); (b) food intake; (c) total locomotor activity; (d) gene expression levels of white and brown markers in iWAT; (e) representative images of UCP1 staining in iWAT. Data are presented as mean ± SEM and *, p < .05; **, p < .01
Figure 5
Figure 5
PPARγ deficiency in iWAT of young and aging mice leads to distinct adiposity phenotypes. (a) Illustration of the strategy used to reduce PPARγ levels in the iWAT of young and aging mice via adenoviral delivery. (b) PPARγ mRNA levels; (c) weight of iWAT; (d) representative H&E images of iWAT and (e) adipocyte area in 2‐month‐old and 12‐month‐old mice injected with shRNA control (shCon) or shPPARγ (shPPARγ) adenoviruses. Data are presented as mean ± SEM and *, p < .05; **, p < .01
Figure 6
Figure 6
PPARγ preferentially regulates brown gene programs in inguinal fat of aging mice. (a) Heat map of white and brown gene transcripts in iWAT of 2‐month‐old (young) and 12‐month‐old (aging) mice with knockdown of PPARγ (shPPARγ) compared to control (shCon) (b, c) White and brown PPARγ gene targets in iWAT of 2‐month‐old (b) and 12‐month‐old (c) mice after PPARγ knockdown. (d) Chromatin IP at the aP2 promoter and at the Ucp1 enhancer in iWAT of 2‐month‐old (Young) and 12‐month‐old (Aging) mice. The β‐globin promoter was used as a negative control. Data are presented as mean ± SEM and *, p < .05; **, p < .01. n = 7–8 per group
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