Calorie restriction prevents diet‐induced insulin resistance independently of PGC‐1‐driven mitochondrial biogenesis in white adipose tissue

Abstract

Calorie restriction (CR) exerts remarkable, beneficial effects on glucose homeostasis by mechanisms that are not fully understood. Given the relevance of white adipose tissue (WAT) in glucose homeostasis, we aimed at identifying the main cellular processes regulated in WAT in response to CR in a pathologic context of obesity. For this, a gene‐expression profiling study was first conducted in mice fed ad libitum or subjected to 40% CR. We found that the gene network related to mitochondria was the most highly upregulated in WAT by CR. To study the role that increased mitochondrial biogenesis plays on glucose homeostasis following CR, we generated a mouse model devoid of the coactivators peroxisome proliferator‐activated receptor ³ coactivator 1 (PGC‐1)α and PGC‐1β specifically in adipocytes. Our results show that mice lacking PGC‐1s in adipocytes are unable to increase mitochondrial biogenesis in WAT upon CR. Despite a blunted induction of mitochondrial biogenesis in response to calorie deprivation, mice lacking adipose PGC‐1s still respond to CR by improving their glucose homeostasis. Our study demonstrates that PGC‐1 coactivators are major regulators of CR‐induced mitochondrial biogenesis in WAT and that increased mitochondrial biogenesis and oxidative function in adipose tissue are not required for the improvement of glucose homeostasis mediated by CR.—Pardo, R., Vila, M., Cervela, L., de Marco, M., Gama‐Pérez, P., González‐Franquesa, A., Statuto, L., Vilallonga, R., Simó, R., Garcia‐Roves, P. M., Villena, J. A. Calorie restriction prevents diet‐induced insulin resistance independently of PGC‐1‐driven mitochondrial biogenesis in white adipose tissue. FASEB J. 33, 2343–2358 (2019). http://www.fasebj.org

Calorie Restriction and SIRT1 Overexpression Induce Different Gene Expression Profiles in White Adipose Tissue in Association with Metabolic Improvement

“…Importantly, regardless of the effects on the mRNA levels of brown adipocyte‐specific genes, we did not find any detectable UCP1 protein in WAT of CR and Sirt1‐Tg mice, suggesting that browning of WAT was negligible. These finding agree with similar studies demonstrating the absence of WAT browning in response to CR, both in rodent and humans, [ 17,51 ] and indicate that thermogenic beige adipocytes do not contribute to the improvement of glucose homeostasis observed in CR and Sirt1‐Tg mice.…”

“…Nevertheless, the increase in the levels of Ucp1 mRNA did not translated into detectable levels of UCP1 protein in subcutaneous WAT of CR‐treated mice (Figure 3B, Supporting Information), suggesting that the appearance and physiological impact of beige adipocytes in response to CR is negligible, in agreement with previous reports. [ 17 ] Opposed to CR, SIRT1 overexpression appeared to have a minor impact on the expression of genes encoding for mitochondrial proteins. Although mRNA levels for most of the mitochondrial genes were, in general, mildly reduced, changes did not reach statistical significance (Figure 5C).…”

“…For instance, it has been shown that adipose‐specific knockout mice simultaneously devoid of PGC‐1α and PGC1β co‐activators, considered as ubiquitous master regulators of mitochondrial biogenesis, [ 40 ] exhibit blunted mitochondrial biogenesis and oxidative capacity in WAT in response to CR but retain their full capacity to improve whole body and tissue‐specific insulin sensitivity when subjected to a caloric restricted regime. [ 17 ] Similarly, muscle‐specific knockout for PGC‐1α normally respond to CR by improving glucose homeostasis despite their inability to mount a proper mitochondriogenic response. [ 41 ] These findings suggest that the activation of the transcriptional program aimed at increasing mitochondrial mass and cellular oxidative capacity is not an essential process by which CR improves metabolic status.…”

“…The activation of the transcriptional program related to mitochondrial biogenesis in WAT, which appears to be also turned on in other tissues, [9,27,28] is a hallmark of CR. [17,29,30] Although not exempt of controversy, [31] it has been suggested that by increasing mitochondrial biogenesis CR would improve mitochondrial efficiency, leading to a reduction of ROS production while maintaining ATP generation. The improved functional efficiency, with the consequent relieve of oxidative stress, has been proposed as a key process by which CR exerts beneficial effects on health.…”

Enhancing Glycolysis Protects against Ischemia-Reperfusion Injury by Reducing ROS Production

“…Protein extracts from H9C2 cells were prepared in RIPA homogenization buffer (20 mmol/L Tris-HCl pH 7.5, 150 mmol/L NaCl, 1 mmol/L Na 2 EDTA, 1 mmol/L EGTA, 1% Nonidet P-40), containing protease and phosphatase inhibitors. Thirty-five micrograms of protein were subjected to electrophoresis in a 10% polyacrylamide gel and transferred to a PVDF membrane and probed against specific antibodies to detect NDUFB9 (ab106699, Abcam, Cambridge, UK), COXIV (#4844, Cell Signaling Technology, Danvers, MA, USA), α-Tubulin (11H10, Cell Signaling Technology), mTOR and p-mTR (#2983 and #2974, respectively from Cell Signaling Technology), Akt and p-Akt (#9272 and #2965, respectively, from Cell Signaling Technology) as previously described [45].…”