Adipose depot-specific upregulation of Ucp1 or mitochondrial oxidative complex proteins are early consequences of genetic insulin reduction in mice

Abstract

Hyperinsulinemia plays a causal role in adiposity tissue expansion. We have previously shown that mice with reduced insulin gene dosage have increased energy expenditure, but the tissue-specific molecular mechanisms involved in the effects of abrogated hyperinsulinemia have remained unclear. Herein we investigated the effects of genetically reducing insulin production on the abundance of oxidative mitochondrial complex proteins in liver, skeletal muscle, white adipose tissue and brown adipose tissue. To suppress insulin levels, we manipulated Ins1 gene dosage in mice lacking both Ins2 alleles to prevent compensation. Male Ins1+/+ or Ins1+/-littermates were fed either a low-fat diet (LFD) or a high-fat diet (HFD) for 4 weeks, starting at 8 weeks of age. As expected, HFD increased fasting hyperinsulinemia, and Ins1+/-mice had significantly lower circulating insulin compared with Ins1+/+ littermate controls. Fasting glucose and body weight were not significantly different between genotypes at any time over the 4 weeks of study. In liver and skeletal muscle, protein abundances reflecting complex I (Ndufb8), II (Sdhb), III (Uqcrc2), and V (Atp5a1) were not consistently different between groups. In mesenteric white adipose tissue, Ins1+/-mice had reduced abundance of Ndufb8 and Sdhb proteins. Ucp1 protein abundance was increased in the context of the HFD, and HFD alone had a dramatic inhibitory effect on Pparg protein levels. In inguinal white adipose tissue, Ins1+/-mice exhibited significant increases in all oxidative mitochondrial complexes measured, independent of diet. No changes in Ucp1 or Pparg protein, or Prdm16:Pparg association were found. While HFD increased the abundance of nuclear Sirt1, no effects on total Sirt3 protein levels were observed in this tissue. In brown adipose tissue, lowered insulin increased Sdhb protein levels that had been reduced by HFD. Ucp1 protein levels, Prdm16:Pparg association, and Sirt3 abundance were all increased in the absence of diet-induced hyperinsulinemia. Our data show that in young mice, reducing insulin upregulates oxidative proteins in inguinal fat without affecting Ucp1, while in mesenteric white fat and brown adipose tissue, reducing insulin upregulates Ucp1 in the context of HFD. Collectively, our results show that preventing hyperinsulinemia have depot-specific effects on adipose tissue metabolism and help explain the increased energy expenditure previously reported in Ins1+/-mice. Insulin is secreted from pancreatic β-cells in response to nutrient intake to regulate anabolism in multiple tissues. In addition to glucose homeostasis, insulin is a potent regulator of lipid homeostasis (42). Insulin signaling is required for glucose and lipid uptake into fat, as well as for the development and hypertrophy of adipocytes. Indeed, mice lacking insulin receptors in adipose tissue are protected against high fat diet and glucose intolerance (4, 34). Chronically elevated insulin levels are associated with obesity in human populations and preclinical models (2,3,7,27,31,39). Ph...

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Hyperinsulinemia in Obesity, Inflammation, and Cancer

“…Energy expenditure was increased, but there was no difference in measured food intake [20]. Follow-up studies identified upregulation of oxidative phosphorylation complex proteins and uncoupling protein 1 in white adipose tissue [114]. Templeman et al [30,115] made similar observations by modulating Ins2 gene dosage in mice without Ins1.…”

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“…CC-BY-NC-ND 4.0 International license perpetuity. It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted November 16, 2021. ; https://doi.org/10.1101/2021.11.11.468339 doi: bioRxiv preprint expenditure (10). The PPARγ-NcoR complex benefited vascular endothelium insulin resistance (11).…”