Autophagy In Adipocytes Research Articles

Cinnamaldehyde ameliorates STZ-induced diabetes through modulation of autophagic process in adipocyte and hepatic tissues on rats

Type 2 diabetes mellitus is a worldwide public health issue. In the globe, Egypt has the ninth-highest incidence of diabetes. Due to its crucial role in preserving cellular homeostasis, the autophagy process has drawn a lot of attention in recent years, Therefore, the purpose of this study was to evaluate the traditional medication metformin with the novel therapeutic effects of cinnamondehyde on adipocyte and hepatic autophagy in a model of high-fat diet/streptozotocin-diabetic rats. The study was conducted on 40 male albino rats, classified into 2 main groups, the control group and the diabetic group, which was subdivided into 4 subgroups (8 rats each): untreated diabetic rats, diabetic rats received oral cinnamaldehyde 40 mg/kg/day, diabetic rats received oral metformin 200 mg/kg/day and diabetic rats received a combination of both cinnamaldehyde and metformin daily for 4 weeks. The outcomes demonstrated that cinnamaldehyde enhanced the lipid profile and glucose homeostasis. Moreover, Cinnamaldehyde had the opposite effects on autophagy in both tissues; by altering the expression of genes that control autophagy, such as miRNA 30a and mammalian target of rapamycin (mTOR), it reduced autophagy in adipocytes and stimulated it in hepatic tissues. It may be inferred that by increasing the treatment efficacy of metformin and lowering its side effects, cinnamaldehyde could be utilized as an adjuvant therapy with metformin for the treatment of type 2 diabetes.

TIGAR exacerbates obesity by triggering LRRK2-mediated defects in macroautophagy and chaperone-mediated autophagy in adipocytes

ABSTRACT Obesity is one of the most common metabolic diseases around the world, which is distinguished by the abnormal buildup of triglycerides within adipose cells. Recent research has revealed that autophagy regulates lipid mobilization to maintain energy balance. TIGAR (Trp53 induced glycolysis regulatory phosphatase) has been identified as a glycolysis inhibitor, whether it plays a role in the metabolism of lipids is unknown. Here, we found that TIGAR transgenic (TIGAR+/+) mice exhibited increased fat mass and trended to obesity phenotype. Non-target metabolomics showed that TIGAR caused the dysregulation of the metabolism profile. The quantitative transcriptome sequencing identified an increased levels of LRRK2 and RAB7B in the adipose tissue of TIGAR+/+ mice. It was confirmed in vitro that TIGAR overexpression increased the levels of LRRK2 by inhibiting polyubiquitination degradation, thereby suppressing macroautophagy and chaperone-mediated autophagy (CMA) while increasing lipid accumulation which were reversed by the LRRK2 inhibitor DNL201. Furthermore, TIGAR drove LRRK2 to interact with RAB7B for suppressing lysosomal degradation of lipid droplets, while the increased lipid droplets in adipocytes were blocked by the RAB7B inhibitor ML282. Additionally, fat-specific TIGAR knockdown of TIGAR+/+ mice alleviated the symptoms of obesity, and adipose tissues-targeting superiority DNL201 nano-emulsion counteracted the obesity phenotype in TIGAR+/+ mice. In summary, the current results indicated that TIGAR performed a vital function in the lipid metabolism through LRRK2-mediated negative regulation of macroautophagy and CMA in adipocyte. The findings suggest that TIGAR has the potential to serve as a viable therapeutic target for treating obesity and its associated metabolic dysfunction.

Enhancing Fat Graft Survival via Upregulating Autophagy of Adipocytes.

Autophagy is a cellular self-protection mechanism. The upregulation of adipose-derived stem cells' (ADSCs) autophagy can promote fat graft survival. However, the effect of interfering with adipocyte autophagy on graft survival is still unknown. In addition, autophagy is involved in adipocyte dedifferentiation. We investigated the effect of autophagy on adipocyte dedifferentiation and fat graft survival. The classic autophagy regulatory drugs rapamycin (100nM) and 3-methyladenine (3-MA; 10mM) were used to treat adipocytes, adipocyte dedifferentiation was observed, and their effects on ADSCs were detected. In our experiments, 100nM rapamycin, 10mM 3-MA and saline were mixed with human adipose tissue and transplanted into nude mice. At 2, 4, 8 and 12 weeks postoperatively, the grafts were harvested for histological and immunohistochemical analysis. Rapamycin and 3-MA can promote and inhibit adipocyte dedifferentiation by regulating autophagy. Both drugs can inhibit ADSC proliferation, and 10mM 3-MA can inhibit ADSC adipogenesis. At weeks 8 and 12, the volume retention rate of the rapamycin group (8 weeks, 64.77% ± 6.36%; 12 weeks, 56.13% ± 4.73%) was higher than the control group (8 weeks, 52.62% ± 4.04%; P < 0.05; 12 weeks, 43.17% ± 6.02%; P < 0.05) and the rapamycin group had more viable adipocytes and better vascularization. Compared with the control group, the volume retention rate, viable adipocytes and vascularization of the 3-MA group decreased. Rapamycin can promote adipocyte dedifferentiation by upregulating autophagy to promote fat graft survival. 3-MA can inhibit graft survival, but its mechanism includes the inhibition of adipocyte dedifferentiation and ADSC proliferation and adipogenesis. This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Extracellular Vimentin Alters Energy Metabolism And Induces Adipocyte Hypertrophy.

Previous studies have reported that oxidative stress contributes to obesity characterized by adipocyte hypertrophy. However, mechanism has not been studied extensively. In the current study, we evaluated role of extracellular vimentin secreted by oxidized low-density lipoprotein (oxLDL) in energy metabolism in adipocytes. We treated 3T3-L1-derived adipocytes with oxLDL and measured vimentin which was secreted in the media. We evaluated changes in uptake of glucose and free fatty acid, expression of molecules functioning in energy metabolism, synthesis of adenosine triphosphate (ATP) and lactate, markers for endoplasmic reticulum (ER) stress and autophagy in adipocytes treated with recombinant vimentin. Adipocytes secreted vimentin in response to oxLDL. Microscopic evaluation revealed that vimentin treatment induced increase in adipocyte size and increase in sizes of intracellular lipid droplets with increased intracellular triglyceride. Adipocytes treated with vimentin showed increased uptake of glucose and free fatty acid with increased expression of plasma membrane glucose transporter type 1 (GLUT1), GLUT4, and CD36. Vimentin treatment increased transcription of GLUT1 and hypoxia-inducible factor 1α (Hif-1α) but decreased GLUT4 transcription. Adipose triglyceride lipase (ATGL), peroxisome proliferator-activated receptor γ (PPARγ), sterol regulatory element-binding protein 1 (SREBP1), diacylglycerol O-acyltransferase 1 (DGAT1) and 2 were decreased by vimentin treatment. Markers for ER stress were increased and autophagy was impaired in vimentin-treated adipocytes. No change was observed in synthesis of ATP and lactate in the adipocytes treated with vimentin. We concluded that extracellular vimentin regulates expression of molecules in energy metabolism and promotes adipocyte hypertrophy. Our results show that vimentin functions in the interplay between oxidative stress and metabolism, suggesting a mechanism by which adipocyte hypertrophy is induced in oxidative stress.

Chloroquine attenuates diet-induced obesity and glucose intolerance through a mechanism that might involve FGF-21, but not UCP-1-mediated thermogenesis and inhibition of adipocyte autophagy

Chloroquine diphosphate (CQ), a weak base used to inhibit autophagic flux and treat malaria and rheumatoid diseases, has been shown, through unknown mechanisms, to improve glucose and lipid homeostasis in patients and rodents. We investigate herein the molecular mechanisms underlying these CQ beneficial metabolic actions in diet-induced obese mice. For this, C57BL6/J mice fed with either a chow or a high-fat diet (HFD) and uncoupling protein 1 (UCP-1) KO and adipocyte Atg7-deficient mice fed with a HFD were treated or not with CQ (60 mg/kg of body weight/day) during 8 weeks and evaluated for body weight, adiposity, glucose homeostasis and brown and white adipose tissues (BAT and WAT) UCP-1 content. CQ reduced body weight gain and adipose tissue and liver masses in mice fed with a HFD, without altering food intake, oxygen consumption, respiratory exchange ratio, spontaneous motor activity and feces caloric content. CQ attenuated the insulin intolerance, hyperglycemia, hyperinsulinemia, hypertriglyceridemia and hypercholesterolemia induced by HFD intake, such effects that were associated with increases in serum and liver fibroblast growth factor 21 (FGF-21) and BAT and WAT UCP-1 content. Interestingly, CQ beneficial metabolic actions of reducing body weight and adiposity and improving glucose homeostasis were preserved in HFD-fed UCP-1 KO and adipocyte Atg7 deficient mice. CQ reduces body weight gain and adiposity and improves glucose homeostasis in diet-induced obese mice through mechanisms that might involve FGF-21, but not UCP1-mediated nonshivering thermogenesis or inhibition of adipocyte autophagy.

Lipid kinase PIK3C3 maintains healthy brown and white adipose tissues to prevent metabolic diseases

Adequate mass and function of adipose tissues (ATs) play essential roles in preventing metabolic perturbations. The pathological reduction of ATs in lipodystrophy leads to an array of metabolic diseases. Understanding the underlying mechanisms may benefit the development of effective therapies. Several cellular processes, including autophagy and vesicle trafficking, function collectively to maintain AT homeostasis. Here, we investigated the impact of adipocyte-specific deletion of the lipid kinase phosphatidylinositol 3-kinase catalytic subunit type 3 (PIK3C3) on AT homeostasis and systemic metabolism in mice. We report that PIK3C3 functions in all ATs and that its absence disturbs adipocyte autophagy and hinders adipocyte differentiation, survival, and function with differential effects on brown and white ATs. These abnormalities cause loss of white ATs, whitening followed by loss of brown ATs, and impaired "browning" of white ATs. Consequently, mice exhibit compromised thermogenic capacity and develop dyslipidemia, hepatic steatosis, insulin resistance, and type 2 diabetes. While these effects of PIK3C3 largely contrast previous findings with the autophagy-related (ATG) protein ATG7 in adipocytes, mice with a combined deficiency in both factors reveal a dominant role of the PIK3C3-deficient phenotype. We have also found that dietary lipid excess exacerbates AT pathologies caused by PIK3C3 deficiency. Surprisingly, glucose tolerance is spared in adipocyte-specific PIK3C3-deficient mice, a phenotype that is more evident during dietary lipid excess. These findings reveal a crucial yet complex role for PIK3C3 in ATs, with potential therapeutic implications.

Effect of nicotinamide N-methyltransferase on lipid accumulation in 3T3-L1 adipocytes

ABSTRACT Nicotinamide N-methyltransferase (NNMT) is a methylase, and its expression is positively correlated with obesity and insulin resistance. This study aims to detect the effects of NNMT on lipid accumulation, triglyceride content, adipocyte differentiation-related transcription factors, genes related to lipid metabolism, adipokine expression, and autophagy in adipocytes. Lentivirus vectors and eukaryotic expression plasmids were used to interfere with NNMT expression. The Oil Red O method was used to detect lipid accumulation, and colorimetry was used to detect triglyceride levels. The transcription of adipocyte differentiation-related transcription factors (PPARγ, C/EBPα, and SREBP1), lipid metabolism-related genes (FABP4, FAS, FATP1 [SLC27A1], and LPL), adipokines (ADIPOQ and LEP) and autophagy-related genes (Beclin1, ATG7, ATG12, and ATG14) was detected by quantitative real-time polymerase chain reaction (RT-qPCR), and the protein expressions of PPARγ, ADIPOQ, LC3I, LC3II, Beclin1, and P62 were detected by western blot analysis. Compared with the control group, the knockdown of NNMT expression reduced lipid accumulation and triglyceride content in 3T3-L1 cells. The transcription of PPARγ, C/EBPα, SREBP1, FABP4, FASN, FATP1, LPL, Beclin1, ATG7, ATG12, and ATG14 decreased, while ADIPOQ and LEP transcription increased. The expression of PPARγ, LC3I/II, and Beclin1 proteins also decreased, while ADIPOQ and P62 protein expression increased. The over-expression NNMT group showed experimental results opposite to those described above. Interference with the expression of NNMT affects lipid accumulation, triglyceride content after cell differentiation, adipocyte differentiation-related transcription factors, genes related to lipid metabolism, the expression of adipokines, and autophagy in adipocytes.

Loss of RUBCN/rubicon in adipocytes mediates the upregulation of autophagy to promote the fasting response

ABSTRACT Upon fasting, adipocytes release their lipids that accumulate in the liver, thus promoting hepatic steatosis and ketone body production. However, the mechanisms underlying this process are not fully understood. In this study, we found that fasting caused a substantial decrease in the adipose levels of RUBCN/rubicon, a negative regulator of macroautophagy/autophagy, along with an increase in autophagy. Adipose-specific rubcn-knockout mice exhibited systemic fat loss that was not accelerated by fasting. Genetic inhibition of autophagy in adipocytes in fasted mice led to a reduction in fat loss, hepatic steatosis, and ketonemia. In terms of mechanism, autophagy decreased the levels of its substrates NCOA1/SRC-1 and NCOA2/TIF2, which are also coactivators of PPARG/PPARγ, leading to a fasting-induced reduction in the mRNA levels of adipogenic genes in adipocytes. Furthermore, RUBCN in adipocytes was degraded through the autophagy pathway, suggesting that autophagic degradation of RUBCN serves as a feedforward system for autophagy induction during fasting. Collectively, we propose that loss of adipose RUBCN promotes a metabolic response to fasting via increasing autophagic activity.

Mutation of Beclin1 acetylation site at K414 alleviates high glucose-induced podocyte impairment in the early stage of diabetic nephropathy by inhibiting hyperactivated autophagy.

Our group recently reported that a mutation of the novel Beclin1 K414R acetylation site impacts the stability of Beclin1 protein, which decreases autophagy in adipocytes and further impedes adipocyte differentiation and lipolysis. This study was to explore whether Beclin1 acetylation plays a role in the early renal injury induced by high glucose and to further investigate the K414R mutation site in podocytes. Male Sprague-Dawley rats were randomized to con (control) and diabetic nephropathy (DN) groups. The DN group was induced by a single 55mg/kg intraperitoneal injection of streptozotocin and fed a high-fat and high-sugar diet (the con group received an equal volume of the vehicle and fed a plain diet), after 3days of induction, blood glucose levels were measured to confirm the onset of diabetes. Then, at weeks 0 and 4, the biochemical index was assayed and renal cortex tissues were harvested. MPC5 podocytes were cultured in vitro. Beclin1 (K414R)-pLVX-ZsGreen1-N1(wild-type or mutant) lentiviral plasmids were transfected into podocytes. Western blot or immunoprecipitation was used to test proteins or the acetylation levels respectively, and immunohistochemistry was used to analyze morphological changes of podocytes. Immunofluorescence was used to detect the aggregation of LC3 puncta. The acetylation level of Beclin1 was upregulated with podocyte injury exacerbated in high glucose at 24h and that a mutation at K414R could inhibit hyperactivated autophagy, which ameliorated podocyte impairment. These findings suggest that the acetylation site at K414 is a critical molecule and drug target and that further research into this area is warranted.

ACSS3 in brown fat drives propionate catabolism and its deficiency leads to autophagy and systemic metabolic dysfunction.

Propionate is a gut microbial metabolite that has been reported to have controversial effects on metabolic health. Here we show that propionate is activated by acyl‐CoA synthetase short‐chain family member 3 (ACSS3), located on the mitochondrial inner membrane in brown adipocytes. Knockout of Acss3 gene (Acss3–/–) in mice reduces brown adipose tissue (BAT) mass but increases white adipose tissue (WAT) mass, leading to glucose intolerance and insulin resistance that are exacerbated by high‐fat diet (HFD). Intriguingly, Acss3–/– or HFD feeding significantly elevates propionate levels in BAT and serum, and propionate supplementation induces autophagy in cultured brown and white adipocytes. The elevated levels of propionate in Acss3–/– mice similarly drive adipocyte autophagy, and pharmacological inhibition of autophagy using hydroxychloroquine ameliorates obesity, hepatic steatosis and insulin resistance of the Acss3–/– mice. These results establish ACSS3 as the key enzyme for propionate metabolism and demonstrate that accumulation of propionate promotes obesity and Type 2 diabetes through triggering adipocyte autophagy.

Sirt1 coordinates with ERα to regulate autophagy and adiposity

Sex difference in adiposity has long been recognized but the mechanism remains incompletely understood. Previous studies suggested that adiposity was regulated by autophagy in response to energy status change. Here, we show that the energy sensor Sirt1 mediates sex difference in adiposity by regulating autophagy and adipogenesis in partnership with estrogen receptor α (ERα). Autophagy and adipogenesis were suppressed by Sirt1 activation or overexpression, which was associated with reduced sex difference in adiposity. Mechanistically, Sirt1 deacetylated and activated AKT and STAT3, resulting in suppression of autophagy and adipogenesis via mTOR-ULK1 and p55 cascades. ERα induced Sirt1 expression and inhibited autophagy in adipocytes, while silencing Sirt1 reversed the effects of ERα on autophagy and promoted adipogenesis. Moreover, Sirt1 deacetylated ERα, which constituted a positive feedback loop in the regulation of autophagy and adiposity. Our results revealed a new mechanism of Sirt1 regulating autophagy in adipocytes and shed light on sex difference in adiposity.

Trehalose induces SQSTM1/p62 expression and enhances lysosomal activity and antioxidative capacity in adipocytes.

Adipocytes, which comprise the majority of white adipose tissue (WAT), are involved in obesity-related pathology via various mechanisms, including disturbed lysosomal enzymatic activity and accumulation of oxidative stress. Sequestosome 1 (SQSTM1/p62) is an autophagy marker that participates in antioxidative responses via the activation of nuclear factor erythroid-derived 2-like 2 (NRF2). Trehalose is a non-reducing disaccharide reported to suppress adipocyte hypertrophy in obese mice and improve glucose tolerance in humans. We recently revealed that trehalose increases SQSTM1 levels and enhances antioxidative capacity in hepatocytes. Here, to further evaluate the mechanism behind the beneficial effects of trehalose on metabolism, we examined SQSTM1 levels, autophagy, and oxidative stress in trehalose-treated adipocytes. We initially confirmed that trehalose increases SQSTM1 transcription and protein levels without affecting autophagy in adipocytes. Trehalose also elevated transcription of several lysosomal genes and the activity of cathepsin L, a lysosomal enzyme, independently of the transcription factor EB. In agreement with our data from hepatocytes, trehalose induced the nuclear translocation of NRF2 and the transcription of its downstream antioxidative genes, resulting in reduced cellular reactive oxygen species levels. Moreover, some cellular trehalose was detected in trehalose-treated adipocytes, implying that extracellular trehalose is taken into cells. These observations reveal the mechanism behind the beneficial effects of trehalose on metabolism and suggest its potential for preventing or treating obesity-related pathology.

Role of Mechanistic Target of Rapamycin and Autophagy in Alcohol-Induced Adipose Atrophy and Liver Injury

Chronic alcohol consumption induces adipose tissue atrophy. However, the mechanisms for how alcohol induces lipodystrophy and its impact on liver steatosis and injury are not fully elucidated. Autophagy is a highly conserved lysosomal degradation pathway, which regulates cellular homeostasis. Mice with autophagy deficiency in adipose tissue have impaired adipogenesis. However, whether autophagy plays a role in alcohol-induced adipose atrophy and how altered adipocyte autophagy contributes to alcohol-induced liver injury remain unclear. To determine the role of adipose autophagy and mechanistic target of rapamycin (mTOR) in alcohol-induced adipose and liver pathogenesis, we generated adipocyte-specific Atg5 knockout (KO), adipocyte-specific mTOR KO, adipocyte-specific Raptor KO, and adipocyte-specific tuberous sclerosis complex 1 KO mice by crossing floxed mice with Adipoq-Cre. The KO mice and their matched wild-type mice were challenged with chronic-plus-binge alcohol mouse model. Chronic-plus-binge alcohol induced adipose atrophy with increased autophagy and decreased Akt/mTOR signaling in epididymal adipose tissue in wild-type mice. Adipocyte-specific Raptor KO mice experienced exacerbated alcohol-induced steatosis, but neither adipocyte-specific mTOR nor adipocyte-specific tuberous sclerosis complex 1 KO mice exhibited similar detrimental effects. Adipocyte-specific Atg5 KO mice had increased circulating levels of fibroblast growth factor 21 and adiponectin and were resistant to alcohol-induced adipose atrophy and liver injury. In conclusion, autophagy deficiency in adipose tissue leads to reduced sensitivity to alcohol-induced adipose atrophy, which ameliorates alcohol-induced liver injury in mice.

FAM134B improves preadipocytes differentiation by enhancing mitophagy

Family with Sequence Similarity 134, Member B (FAM134B) is a protein that known to be necessary for the long-term survival of nociceptive and autonomic ganglion neurons. Recent work has exhibited that FAM134B plays a pivotal role in autophagy-mediated turnover of endoplasmic reticulum (ER) membranes, tumor inhibition and lipid homeostasis. In this study, we provide mechanistic links between FAM134B and adipocyte differentiation. Here, we found that adipocyte-specific FAM134B overexpression mice are obese and have increased white adipose tissue (WAT) mass. Serum tests showed that they developed high glucose level and severe insulin resistance. In addition, they also exhibited enhanced autophagy and reduced mitochondria amount, suggesting the function of FAM134B to promote autophagy in adipocytes. Overexpression of FAM134B in 3 T3-L1 preadipocytes promoted autophagy and differentiation, while the effect could be inhibited after treatment with autophagyinhibitors, 3-methyladenine (3-MA). Overexpressioncells also showed an early reduction of mitochondria number, while its autophagy flux level increased fast from differentiation day 2. These findings indicate that FAM134B improves adipocytes differentiation through enhancing mitophagy.

Suppression of Brown Adipocyte Autophagy Improves Energy Metabolism by Regulating Mitochondrial Turnover.

The high abundance of mitochondria and the expression of mitochondrial uncoupling protein 1 (UCP1) confer upon brown adipose tissue (BAT) the unique capacity to convert chemical energy into heat at the expense of ATP synthesis. It was long believed that BAT is present only in infants, and so, it was not considered as a potential therapeutic target for metabolic syndrome; however, the discovery of metabolically active BAT in adult humans has re-stimulated interest in the contributions of BAT metabolic regulation and dysfunction to health and disease. Here we demonstrate that brown adipocyte autophagy plays a critical role in the regulation BAT activity and systemic energy metabolism. Mice deficient in brown adipocyte autophagy due to BAT-specific deletion of Atg7—a gene essential for autophagosome generation—maintained higher mitochondrial content due to suppression of mitochondrial clearance and exhibited improved insulin sensitivity and energy metabolism. Autophagy was upregulated in BAT of older mice compared to younger mice, suggesting its involvement in the age-dependent decline of BAT activity and metabolic rate. These findings suggest that brown adipocyte autophagy plays a crucial role in metabolism and that targeting this pathway may be a potential therapeutic strategy for metabolic syndrome.

Identification of miRNAs Mediating Effects of the Renin Angiotensin System in Adipose Tissue (P21-076-19)

ObjectivesRenin angiotensin system (RAS) classically known to regulate blood pressure, is also involved in several metabolic disorders including obesity. Interestingly, RAS components are highly expressed in adipose tissue; however, mechanisms underlying RAS-obesity interactions are still ambiguous and limited information is available about RAS regulation in adipose tissue. We identified previously that RAS overactivation induces ER stress and inflammation, and our goal is to characterize additional mechanisms linking RAS to obesity. Hence, we hypothesized that overactivation of angiotensinogen (Agt, precursor protein in RAS), modulates processes linked to metabolic diseases such as oxidative stress, apoptosis and autophagy in adipocytes. MethodsmRNA and small RNA profiling were performed in adipose tissues of male wild type B6 mice (Wt) and transgenic mice (Agt-Tg) overexpressing Agt which were either fed a low fat (LF) or a high fat (HF) diet with or without RAS inhibitor captopril, an angiotensin converting enzyme inhibitor. ResultsWe identified 18 miRNAs and 5 miRNAs, which were significantly either up or downregulated respectively in Tg compared to Wt mice. Of these, we validated expression of mir195 and 690 which were significantly higher in Tg compared to Wt mice. Furthermore, these miRNAs were significantly reduced in high fat-fed Tg mice treated with captopril compared to non-treated high fat fed mice, indicating the role of angiotensin II in regulation of these miRNAs. Additionally, we identified and validated several genes involved in physiological processes such as oxidative stress and autophagy, some of which were direct targets of the above miRNAs. Mitogen-activated protein kinases including Mapk4, Map3k4, and Map3k7; Caspase 3, 8 and 9; autophagic genes such as autophagy 5 (Atg5), Atg14 and beclin1 were all significantly higher in Tg compared to Wt mice. Additional mechanistic studies are ongoing in cultured adipocytes to further dissect molecular mechanisms linking RAS to obesity. ConclusionsOverexpression of RAS in adipose tissue alters various physiological processes such as oxidative stress, apoptosis and autophagy, which could be mediated, in part through regulatory miRNAs. These pathways and miRNAs could be potential therapeutic targets to reduce RAS-associated metabolic diseases. Funding SourcesAmerican Heart Association.

Polyphenol Compounds Attenuate High‐Dose PUFA‐Induced Oxidative Damage in Adipocytes

Although polyunsaturated fatty acids (PUFAs) are beneficial fatty acids, their excessive deposition can easily lead to lipid‐induced oxidation damage. It has recently been shown that diets rich in particular polyphenols may improve the oxidative status of tissues with high PUFA content. However, the underlying mechanism for this remains elusive. Therefore, a model is created of high‐dose PUFA injury in adipocytes, which investigates the effects of rosmarinic acid (RA) and caffeic acid (CA) on the alleviation of oxidative damage induced by high doses of PUFAs. It is observed that high‐dose linolenic acids (ALA) enhance lipid oxidation, inflammation, and autophagy in adipocytes. However, RA and CA attenuate the high‐dose ALA‐enhanced expression of inflammatory cytokines and microtubule‐associated protein 1, light chain 3, beta (MAP1LC3B). In addition, they reduce the intracellular levels of malondialdehyde (MDA) that are elevated by high doses of ALA, and modulate the activities of superoxide dismutase (SOD), catalase antioxidant (CAT), and glutathione peroxidase (GSH‐Px) enzymes. The protective effects of RA and CA on adipocyte oxidative stress are in part associated with their capacity to improve the activities of antioxidant enzymes and exert free radical‐scavenging activity. Collectively, these results suggest that RA and CA may have potential benefits in protecting adipose cells from high‐dose PUFA‐induced oxidative damage.Practical Applications: It is known that a diet rich in PUFAs has beneficial effects on cardiovascular disease. However, an accumulation of unsaturated fatty acids in tissues is more susceptible to lipid oxidation. In this study, it is found that polyphenols have the potential to protect adipose cells from high‐dose PUFAs‐induced damage. It has also been suggested that the consumption of a diet enriched in polyphenols could be beneficial for the prevention of lipid peroxidation and maintaining the balance between oxidative and anti‐oxidative processes.Polyphenols suppress the formation of lipid peroxy radical species. The process of lipid peroxidation consists of initiation, propagation, and termination. In the termination reaction, polyphenols may donate a hydrogen atom to the lipid radical, resulting in the termination of lipid peroxy radical species formation. In addition, polyphenols may improve the activity of antioxidant enzymes, thereby suppressing the formation of lipid peroxy radical species.

The novel adipokine CTRP5 is a negative regulator of white adipose tissue browning

The browning of white adipose tissue predominantly emerges as an adaptation to environmental cues, such as cold exposure. The enhanced browning of adipose tissue results in improved energy and glucose homeostasis and reduced fat mass and body weight, which is greatly beneficial for the treatment of obesity and other metabolic diseases. C1q/TNF-related protein 5 (CTRP5) is a novel adipokine associated with a variety of endocrine and metabolic diseases; however, whether it can regulate the metabolism of adipose tissue itself remains unknown.In this study, we demonstrated that the expression of CTRP5 in murine subcutaneous white adipose tissue (scWAT) was significantly decreased when the mice were exposed to cold temperatures. The lentivirus-mediated overexpression of CTRP5 in mice repressed the adipose tissue browning, leading to reduced heat production, decreased expression of the browning marker uncoupling protein 1 (UCP1) and decreased browning-related gene expression. Mechanistically, we found that autophagy was inhibited after cold exposure, but this inhibition was alleviated after CTRP5 overexpression. In primary cultured adipocytes, CTRP5 suppressed UCP1 expression, whereas 3-MA (an autophagy inhibitor) rescued the suppression.All of these results demonstrated that CTRP5 is a negative regulator of adipose browning. CTRP5 exerts its effect, at least in part, by suppressing adipocyte autophagy. Our findings indicated that CTRP5 is a novel promising therapeutic target for obesity and other metabolic diseases.

Salt-inducible kinase 2 regulates TFEB and is required for autophagic flux in adipocytes

Dysregulation of autophagy has been observed in obesity and type 2 diabetes. Salt-inducible kinase 2 (SIK2), a member of the AMPK-related kinase family, is downregulated in adipocytes from obese or insulin resistant individuals and was previously demonstrated to regulate autophagy in cancer and normal cell lines. The aim of this study was thus to investigate a potential role of SIK2 in the regulation of adipocyte autophagy. To do so, SIK2 siRNA silencing or SIKs pharmacological inhibition of SIK2 was employed in murine differentiated 3T3-L1 adipocytes and autophagic flux was monitored. Our data indicate that SIK2 is required for both autophagic flux and expression of TFEB, the transcription factor that regulates autophagy, in adipocytes. The effect of SIK2 on autophagic flux occurs before the regulation of TFEB protein levels, suggesting different mechanisms whereby SIK2 stimulates autophagy. This study broadens the current knowledge on autophagy regulation and SIK2 function in adipocytes.

Autophagy Ablation in Adipocytes Induces Insulin Resistance and Reveals Roles for Lipid Peroxide and Nrf2 Signaling in Adipose-Liver Crosstalk

Autophagy is a homeostatic cellular process involved in the degradation of long-lived or damaged cellular components. The role of autophagy in adipogenesis is well recognized, but its role in mature adipocyte function is largely unknown. We show that the autophagyproteins Atg3 and Atg16L1 are required for proper mitochondrial function in mature adipocytes. In contrast to previous studies, we found that post-developmental ablation of autophagy causes peripheral insulin resistance independently of diet or adiposity. Finally, lack of adipocyte autophagy reveals cross talk between fat and liver, mediated by lipid peroxide-induced Nrf2 signaling. Our data reveal a role for autophagy in preventing lipid peroxide formation and its transfer in insulin-sensitive peripheral tissues.