CalR: A Web-Based Analysis Tool for Indirect Calorimetry Experiments

Post-translational control of beige fat biogenesis by PRDM16 stabilization

Compelling evidence shows that brown and beige adipose tissue are protective against metabolic diseases1,2. PR domain-containing 16 (PRDM16) is a dominant activator of the biogenesis of beige adipocytes by forming a complex with transcriptional and epigenetic factors and is therefore an attractive target for improving metabolic health3-8. However, a lack of knowledge surrounding the regulation of PRDM16 protein expression hampered us from selectively targeting this transcriptional pathway. Here we identify CUL2-APPBP2 as the ubiquitin E3 ligase that determines PRDM16 protein stability by catalysing its polyubiquitination. Inhibition of CUL2-APPBP2 sufficiently extended the half-life of PRDM16 protein and promoted beige adipocyte biogenesis. By contrast, elevated CUL2-APPBP2 expression was found in aged adipose tissues and repressed adipocyte thermogenesis by degrading PRDM16 protein. Importantly, extended PRDM16 protein stability by adipocyte-specific deletion of CUL2-APPBP2 counteracted diet-induced obesity, glucose intolerance, insulin resistance and dyslipidaemia in mice. These results offer a cell-autonomous route to selectively activate the PRDM16 pathway in adipose tissues.

Overexpressing the hydroxycarboxylic acid receptor 1 in mouse brown adipose tissue restores glucose tolerance and insulin sensitivity in diet-induced obese mice

Interscapular brown adipose tissue (BAT) plays an important role in controlling glucose homeostasis. Increased glucose entry and glycolysis in BAT result in lactate production and release. The adipose tissue expresses the lactate receptor hydrocarboxylic acid receptor 1 (HCAR1), markedly downregulated in male diet-induced obese (DIO) and ob/ob mice. In this study, we examined the role of HCAR1 in BAT in controlling glucose homeostasis in male DIO mice. We overexpressed HCAR1 in BAT by injecting adeno-associated viruses (AAVs) expressing HCAR1 into the BAT pads of male DIO C57BL/6J mice. Overexpressing HCAR1 in BAT resulted in augmented glucose uptake by BAT in response to treatment with the HCAR1 agonist. HCAR1 overexpression elevated BAT temperature associated with increased thermogenic gene expression in BAT. HCAR1 overexpression prevented body weight gain in male DIO mice. Importantly, mice overexpressing HCAR1 in BAT exhibited improved glucose tolerance and insulin sensitivity. HCAR1 overexpression upregulated the Slc2a4 gene expression and promoted GLUT4 trafficking to the plasma membrane. In addition, mice overexpressing HCAR1 displayed a decrease in hormone-sensitive lipase (HSL) phosphorylation and increased lipogenic enzyme gene expression in BAT. Unlike DIO mice, overexpressing HCAR1 in BAT of mice fed a low-fat diet did not change body weight gain and glucose homeostasis. Taken together, our results support the interpretation that HCAR1 expressed in BAT promotes glucose entry and reduces lipolysis in BAT of male DIO mice. As activation of HCAR1 in BAT restores body weight, glucose tolerance, and insulin sensitivity in male DIO mice, our study suggests that interoceptive lactate detection via HCAR1 in BAT can regulate glucose and lipid substrate utilization and/or availability to promote healthy metabolism.NEW & NOTEWORTHY HCAR1 expressed in BAT can promote glucose entry and reduce lipolysis, resulting in body weight loss and increased insulin sensitivity. Hence, targeting HCAR1 in BAT would provide an alternative way to control body weight and euglycemia in individuals with obesity.

Exercise modulates central and peripheral inflammatory responses and ameliorates methamphetamine-induced anxiety-like symptoms in mice

Anxiety-like symptoms are common symptoms of methamphetamine (METH) users, especially in the acute withdrawal period, which is an important factor for the high relapse rate during METH acute withdrawal. Exercise has been demonstrated to relieve anxiety-like symptoms during METH withdrawal, but the underlying mechanisms of this anti-anxiety effect are still unclear. Activated microglia and abnormal neuroinflammation play an important role in the pathogenesis of anxiety-like symptoms after METH withdrawal. Moreover, peripheral immune factors were also significantly associated with anxiety symptoms. However, the effects of treadmill exercise on microglial function and neuroinflammation in the striatum and hippocampus during acute METH withdrawal have not been reported. In the current study, we found severe peripheral immune dysfunction in METH users during acute withdrawal, which may in part contribute to anxiety symptoms during METH acute withdrawal. We also showed that 2 weeks of METH exposure induced anxiety-like symptoms in the acute withdrawal period. Additionally, METH exposure resulted in increased microglial activation and proinflammatory cytokines released in the mouse striatum and hippocampus during acute withdrawal. We next evaluated the effects of treadmill exercise in countering anxiety-like symptoms induced by METH acute withdrawal. The results showed that anxiety-like symptoms induced by acute METH withdrawal were attenuated by coadministration of treadmill exercise. In addition, treadmill exercise counteracted METH-induced microglial activation in the mouse striatum and various subregions of the hippocampus. Furthermore, treadmill exercise also reversed the increase in proinflammatory cytokines induced by acute METH withdrawal in the mouse striatum, hippocampus and serum. Our findings suggest that the anti-anxiety effect of treadmill exercise may be mediated by reducing microglial activation and regulating central and peripheral inflammatory responses.

Central FGF21 production regulates memory but not peripheral metabolism

Fibroblast growth factor 21 (FGF21) is a liver-derived endocrine hormone that functions to regulate energy homeostasis and macronutrient intake. Recently, FGF21 was reported to be produced and secreted from hypothalamic tanycytes, to regulate peripheral lipid metabolism; however, rigorous investigation of FGF21 expression in the brain has yet to be accomplished. Using a mouse model that drives CRE recombinase in FGF21-expressing cells, we demonstrate that FGF21 is not expressed in the hypothalamus, but instead is produced from the retrosplenial cortex (RSC), an essential brain region for spatial learning and memory. Furthermore, we find that central FGF21 produced in the RSC enhances spatial memory but does not regulate energy homeostasis or sugar intake. Finally, our data demonstrate that administration of FGF21 prolongs the duration of long-term potentiation in the hippocampus and enhances activation of hippocampal neurons. Thus, endogenous and pharmacological FGF21 appear to function in the hippocampus to enhance spatial memory.

Zhou et al. reveal that the endocrine hormone FGF21 is expressed in the brain. Central FGF21 expression occurs in distinct areas, including the retrosplenial cortex, but not the hypothalamus. Interestingly, brain-derived FGF21 regulates spatial memory formation, but not metabolism, and the converse is true for liver-derived FGF21.

Human CIDEC transgene improves lipid metabolism and protects against high-fat diet-induced glucose intolerance in mice

Cell death–inducing DNA fragmentation factor-like effector C (CIDEC) expression in adipose tissue positively correlates with insulin sensitivity in obese humans. Further, E186X, a single-nucleotide CIDEC variant is associated with lipodystrophy, hypertriglyceridemia, and insulin resistance. To establish the unknown mechanistic link between CIDEC and maintenance of systemic glucose homeostasis, we generated transgenic mouse models expressing CIDEC (Ad-CIDECtg) and CIDEC E186X variant (Ad-CIDECmut) transgene specifically in the adipose tissue. We found that Ad-CIDECtg but not Ad-CIDECmut mice were protected against high-fat diet-induced glucose intolerance. Furthermore, we revealed the role of CIDEC in lipid metabolism using transcriptomics and lipidomics. Serum triglycerides, cholesterol, and low-density lipoproteins were lower in high-fat diet-fed Ad-CIDECtg mice compared to their littermate controls. Mechanistically, we demonstrated that CIDEC regulates the enzymatic activity of adipose triglyceride lipase via interacting with its activator, CGI-58, to reduce free fatty acid release and lipotoxicity. In addition, we confirmed that CIDEC is indeed a vital regulator of lipolysis in adipose tissue of obese humans, and treatment with recombinant CIDEC decreased triglyceride breakdown in visceral human adipose tissue. Our study unravels a central pathway whereby adipocyte-specific CIDEC plays a pivotal role in regulating adipose lipid metabolism and whole-body glucose homeostasis. In summary, our findings identify human CIDEC as a potential ‘drug’ or a ‘druggable’ target to reverse obesity-induced lipotoxicity and glucose intolerance.

Calcium/calmodulin-dependent protein kinase kinase 2 regulates hepatic fuel metabolism

OBJECTIVE

The liver is the primary internal metabolic organ that coordinates whole body energy homeostasis in response to feeding and fasting. Genetic ablation or pharmacological inhibition of calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) has been shown to significantly improve hepatic health and peripheral insulin sensitivity upon overnutrition with high fat diet. However, the precise molecular underpinnings that explain this metabolic protection have remained largely undefined.

METHODS

To characterize the role of CaMKK2 in hepatic metabolism, we developed and challenged liver-specific CaMKK2 knockout (CaMKK2LKO) mice with high fat diet and performed glucose and insulin tolerance tests to evaluate peripheral insulin sensitivity. We used a combination of RNA-Sequencing, glucose and fatty acid istotopic tracer studies, a newly developed Seahorse assay for measuring the oxidative capacity of purified peroxisomes, and a degenerate peptide libarary to identify putative CaMKK2 substrates that mechanistically explain the protective effects of hepatic CaMKK2 ablation.

RESULTS

Consistent with previous findings, we show that hepatic CaMKK2 ablation significantly improves indices of peripheral insulin sensitivity. Mechanistically, we found that CaMKK2 phosphorylates and regulates GAPDH to promote glucose metabolism and PEX3 to blunt peroxisomal fatty acid catabolism in the liver.

CONCLUSION

CaMKK2 is a central metabolic fuel sensor in the liver that significantly contributes to whole body systems metabolism.

Effects of Coix Seed Extract, Bifidobacterium BPL1, and Their Combination on the Glycolipid Metabolism in Obese Mice

Coix seed extract (CSE) and probiotics have been reported to regulate glycolipid metabolism via different modes of action. We tested the effects of CSE, Bifidobacterium BPL1, and their combination to determine their effects on glycolipid metabolism in obese mice. Male C57BL/6J mice were fed a high-fat diet for 8 weeks to establish an obesity model. Obese mice were selected and divided into four groups: the model control group and three intervention groups. After 10 weeks of continuous gavage intervention, the mice in the intervention groups exhibited lower body weight (lower about 2.31 g, vs. HFD mice 42.23 g) and epididymal (lower about 0.37 g, vs. HFD mice 2.5 g) and perirenal fat content (lower about 0.47 g, vs. HFD mice 0.884 g); decreased fasting blood glucose, total cholesterol, triglycerides, and VLDL; and increased HLDL, respiratory exchange ratio, energy expenditure, and amount of exercise performed. CSE, BPL1 and their combination can effectively control the weight gain in obese mice, reduce fat content, and regulate blood lipids and abnormal blood sugar. These results may be related to reduce the chronic inflammatory states, improve energy metabolism, exercise, relieve insulin sensitivity, and reduce lipid synthesis via the intervention of CSE, BPL1 and their combination. Compared with the single use of CSE alone, the combination of CSE + BPL1 can better exert the regulation function of intestinal flora, and change in the abundance of bacteria that could improve the level of inflammatory factors, such as increasing Bifidobacterium, reducing Lactococcus. Compared with the use of BPL1 alone, the combination of CSE and BPL1 can better regulate pancreatic islet and improve blood sugar. CSE may act directly on body tissues to exert anti-inflammatory effects. BPL1 and CSE + BPL1 may improve the structure and function of the intestinal flora, and reduce tissue inflammation.

An isoproteic cocoa butter-based ketogenic diet fails to improve glucose homeostasis and promote weight loss in obese mice

High-fat and very low-carbohydrate based ketogenic diets have gained considerable popularity as a nonpharmacological strategy for obesity, due to their potential to enhance weight loss and improve glucose homeostasis. However, the effectiveness of a ketogenic diet toward metabolic health is equivocal. To better understand the impact of ketogenic diets in obesity, male and female mice were fed a 60% cocoa butter-based high-fat diet for 16-wk to induce obesity, following which mice were transitioned to either an 85% cocoa butter fat-based ketogenic diet, a 10% cocoa butter fat-based low-fat diet, or maintained on a high-fat diet for an additional 8-wk. All experimental diets were matched for sucrose and protein content and contained an identical micronutrient profile, with complex carbohydrates being the primary carbohydrate source in the low-fat diet. The transition to a ketogenic diet was ineffective at promoting significant body fat loss and improving glucose homeostasis in obese male and female mice. Alternatively, obese male and female mice transitioned to a low-fat and high-complex carbohydrate diet exhibited beneficial body composition changes and improved glucose tolerance that may, in part, be attributed to a mild decrease in food intake and a mild increase in energy expenditure. Our findings support the consumption of a diet low in saturated fat and rich in complex carbohydrates as a potential dietary intervention for the treatment of obesity and obesity-induced impairments in glycemia. Furthermore, our results suggest that careful consideration should be taken when considering a ketogenic diet as a nonpharmacological strategy for obesity.NEW & NOTEWORTHY It has been demonstrated that ketogenic diets may be a nutritional strategy for alleviating hyperglycemia and promoting weight loss in obesity. However, there are a number of inconsistencies with many of these studies, especially with regard to the macronutrient and micronutrient compositions of the diets being compared. Our work demonstrates that a ketogenic diet that is both micronutrient-matched and isoproteic with its comparator diets fails to improve glycemia or promote weight loss in obese mice.

Deletion of LDLRAP1 Induces Atherosclerotic Plaque Formation, Insulin Resistance, and Dysregulated Insulin Response in Adipose Tissue

Dyslipidemia, vascular inflammation, obesity, and insulin resistance often overlap and exacerbate each other. Mutations in low density lipoprotein receptor adaptor protein-1 (LDLRAP1) lead to LDLR malfunction and are associated with the autosomal recessive hypercholesterolemia disorder in humans. However, direct causality on atherogenesis in a defined preclinical model has not been reported. The objective of this study was to test the hypothesis that deletion of LDLRAP1 will lead to hypercholesteremia and atherosclerosis. LDLRAP1^-/- mice fed a high-fat Western diet had significantly increased plasma cholesterol and triglyceride concentrations accompanied with significantly increased plaque burden compared with wild-type controls. Unexpectedly, LDLRAP1^-/- mice gained significantly more weight compared with controls. Even on a chow diet, LDLRAP1^-/- mice were insulin-resistant, and calorimetric studies suggested an altered metabolic profile. The study showed that LDLRAP1 is highly expressed in visceral adipose tissue, and LDLRAP1^-/- adipocytes are significantly larger, have reduced glucose uptake and AKT phosphorylation, but have increased CD36 expression. Visceral adipose tissue from LDLRAP1^-/- mice was hypoxic and had gene expression signatures of dysregulated lipid storage and energy homeostasis. These data are the first to indicate that lack of LDLRAP1 directly leads to atherosclerosis in mice and also plays an unanticipated metabolic regulatory role in adipose tissue. LDLRAP1 may link atherosclerosis and hypercholesterolemia with common comorbidities of obesity and insulin resistance.

Age-dependent impact of two exercise training regimens on genomic and metabolic remodeling in skeletal muscle and liver of male mice

Skeletal muscle adapts to different exercise training modalities with age; however, the impact of both variables at the systemic and tissue levels is not fully understood. Here, adult and old C57BL/6 male mice were assigned to one of three groups: sedentary, daily high-intensity intermittent training (HIIT), or moderate intensity continuous training (MICT) for 4 weeks, compatible with the older group's exercise capacity. Improvements in body composition, fasting blood glucose, and muscle strength were mostly observed in the MICT old group, while effects of HIIT training in adult and old animals was less clear. Skeletal muscle exhibited structural and functional adaptations to exercise training, as revealed by electron microscopy, OXPHOS assays, respirometry, and muscle protein biomarkers. Transcriptomics analysis of gastrocnemius muscle combined with liver and serum metabolomics unveiled an age-dependent metabolic remodeling in response to exercise training. These results support a tailored exercise prescription approach aimed at improving health and ameliorating age-associated loss of muscle strength and function in the elderly.

Metabolic Impact of MKP-2 Upregulation in Obesity Promotes Insulin Resistance and Fatty Liver Disease

The mechanisms connecting obesity with type 2 diabetes, insulin resistance, nonalcoholic fatty liver disease, and cardiovascular diseases remain incompletely understood. The function of MAPK phosphatase-2 (MKP-2), a type 1 dual-specific phosphatase (DUSP) in whole-body metabolism, and how this contributes to the development of diet-induced obesity, type 2 diabetes (T2D), and insulin resistance is largely unknown. We investigated the physiological contribution of MKP-2 in whole-body metabolism and whether MKP-2 is altered in obesity and human fatty liver disease using MKP-2 knockout mice models and human liver tissue derived from fatty liver disease patients. We demonstrate that, for the first time, MKP-2 expression was upregulated in liver tissue in humans with obesity and fatty liver disease and in insulin-responsive tissues in mice with obesity. MKP-2-deficient mice have enhanced p38 MAPK, JNK, and ERK activities in insulin-responsive tissues compared with wild-type mice. MKP-2 deficiency in mice protects against diet-induced obesity and hepatic steatosis and was accompanied by improved glucose homeostasis and insulin sensitivity. Mkp-2^−/− mice are resistant to diet-induced obesity owing to reduced food intake and associated lower respiratory exchange ratio. This was associated with enhanced circulating insulin-like growth factor-1 (IGF-1) and stromal cell-derived factor 1 (SDF-1) levels in Mkp-2^−/− mice. PTEN, a negative regulator of Akt, was downregulated in livers of Mkp-2^−/− mice, resulting in enhanced Akt activity consistent with increased insulin sensitivity. These studies identify a novel role for MKP-2 in the regulation of systemic metabolism and pathophysiology of obesity-induced insulin resistance and fatty liver disease.

OMA1 mediates local and global stress responses against protein misfolding in CHCHD10 mitochondrial myopathy

Mitochondrial stress triggers a response in the cell’s mitochondria and nucleus, but how these stress responses are coordinated in vivo is poorly understood. Here, we characterize a family with myopathy caused by a dominant p.G58R mutation in the mitochondrial protein CHCHD10. To understand the disease etiology, we developed a knockin (KI) mouse model and found that mutant CHCHD10 aggregated in affected tissues, applying a toxic protein stress to the inner mitochondrial membrane. Unexpectedly, the survival of CHCHD10-KI mice depended on a protective stress response mediated by the mitochondrial metalloendopeptidase OMA1. The OMA1 stress response acted both locally within mitochondria, causing mitochondrial fragmentation, and signaled outside the mitochondria, activating the integrated stress response through cleavage of DAP3-binding cell death enhancer 1 (DELE1). We additionally identified an isoform switch in the terminal complex of the electron transport chain as a component of this response. Our results demonstrate that OMA1 was critical for neonatal survival conditionally in the setting of inner mitochondrial membrane stress, coordinating local and global stress responses to reshape the mitochondrial network and proteome.

Targeting parvalbumin promotes M2 macrophage polarization and energy expenditure in mice

Exercise benefits M2 macrophage polarization, energy homeostasis and protects against obesity partially through exercise-induced circulating factors. Here, by unbiased quantitative proteomics on serum samples from sedentary and exercised mice, we identify parvalbumin as a circulating factor suppressed by exercise. Parvalbumin functions as a non-competitive CSF1R antagonist to inhibit M2 macrophage activation and energy expenditure in adipose tissue. More importantly, serum concentrations of parvalbumin positively correlate with obesity in mouse and human, while treating mice with a recombinant parvalbumin blocker prevents its interaction with CSF1R and promotes M2 macrophage polarization and ameliorates diet-induced obesity. Thus, although further studies are required to assess the significance of parvalbumin in mediating the effects of exercise, our results implicate parvalbumin as a potential therapeutic strategy against obesity in mice.

A novel role for GalNAc-T2 dependent glycosylation in energy homeostasis

OBJECTIVE

GALNT2, encoding polypeptide N-acetylgalactosaminyltransferase 2 (GalNAc-T2), was initially discovered as a regulator of high-density lipoprotein metabolism. GalNAc-T2 is known to exert these effects through post-translational modification, i.e., O-linked glycosylation of secreted proteins with established roles in plasma lipid metabolism. It has recently become clear that loss of GALNT2 in rodents, cattle, nonhuman primates, and humans should be regarded as a novel congenital disorder of glycosylation that affects development and body weight. The role of GALNT2 in metabolic abnormalities other than plasma lipids, including insulin sensitivity and energy homeostasis, is poorly understood.

METHODS

GWAS data from the UK Biobank was used to study variation in the GALNT2 locus beyond changes in high-density lipoprotein metabolism. Experimental data were obtained through studies in Galnt2-/- mice and wild-type littermates on both control and high-fat diet.

RESULTS

First, we uncovered associations between GALNT2 gene variation, adiposity, and body mass index in humans. In mice, we identify the insulin receptor as a novel substrate of GalNAc-T2 and demonstrate that Galnt2-/- mice exhibit decreased adiposity, alterations in insulin signaling and a shift in energy substrate utilization in the inactive phase.

CONCLUSIONS

This study identifies a novel role for GALNT2 in energy homeostasis, and our findings suggest that the local effects of GalNAc-T2 are mediated through posttranslational modification of the insulin receptor.

Mitochondrial uncoupling attenuates sarcopenic obesity by enhancing skeletal muscle mitophagy and quality control

BACKGROUND

Sarcopenic obesity is a highly prevalent disease with poor survival and ineffective medical interventions. Mitochondrial dysfunction is purported to be central in the pathogenesis of sarcopenic obesity by impairing both organelle biogenesis and quality control. We have previously identified that a mitochondrial-targeted furazano[3,4-b]pyrazine named BAM15 is orally available and selectively lowers respiratory coupling efficiency and protects against diet-induced obesity in mice. Here, we tested the hypothesis that mitochondrial uncoupling simultaneously attenuates loss of muscle function and weight gain in a mouse model of sarcopenic obesity.

METHODS

Eighty-week-old male C57BL/6J mice with obesity were randomized to 10 weeks of high fat diet (CTRL) or BAM15 (BAM15; 0.1% w/w in high fat diet) treatment. Body weight and food intake were measured weekly. Body composition, muscle function, energy expenditure, locomotor activity, and glucose tolerance were determined after treatment. Skeletal muscle was harvested and evaluated for histology, gene expression, protein signalling, and mitochondrial structure and function.

RESULTS

BAM15 decreased body weight (54.0 ± 2.0 vs. 42.3 ± 1.3 g, P < 0.001) which was attributable to increased energy expenditure (10.1 ± 0.1 vs. 11.3 ± 0.4 kcal/day, P < 0.001). BAM15 increased muscle mass (52.7 ± 0.4 vs. 59.4 ± 1.0%, P < 0.001), strength (91.1 ± 1.3 vs. 124.9 ± 1.2 g, P < 0.0001), and locomotor activity (347.0 ± 14.4 vs. 432.7 ± 32.0 m, P < 0.001). Improvements in physical function were mediated in part by reductions in skeletal muscle inflammation (interleukin 6 and gp130, both P < 0.05), enhanced mitochondrial function, and improved endoplasmic reticulum homeostasis. Specifically, BAM15 activated mitochondrial quality control (PINK1-ubiquitin binding and LC3II, P < 0.01), increased mitochondrial activity (citrate synthase and complex II activity, all P < 0.05), restricted endoplasmic reticulum (ER) misfolding (decreased oligomer A11 insoluble/soluble ratio, P < 0.0001) while limiting ER stress (decreased PERK signalling, P < 0.0001), apoptotic signalling (decreased cytochrome C release and Caspase-3/9 activation, all P < 0.001), and muscle protein degradation (decreased 14-kDa actin fragment insoluble/soluble ratio, P < 0.001).

CONCLUSIONS

Mitochondrial uncoupling by agents such as BAM15 may mitigate age-related decline in muscle mass and function by molecular and cellular bioenergetic adaptations that confer protection against sarcopenic obesity.

Constitutive loss of DNMT3A causes morbid obesity through misregulation of adipogenesis

DNA Methyltransferase 3 A (DNMT3A) is an important facilitator of differentiation of both embryonic and hematopoietic stem cells. Heterozygous germline mutations in DNMT3A lead to Tatton-Brown-Rahman Syndrome (TBRS), characterized by obesity and excessive height. While DNMT3A is known to impact feeding behavior via the hypothalamus, here we investigated a role in adipocyte progenitors utilizing heterozygous knockout mice that recapitulate cardinal TBRS phenotypes. These mice become morbidly obese due to adipocyte enlargement and tissue expansion. Adipose tissue in these mice exhibited defects in preadipocyte maturation and precocious activation of inflammatory gene networks, including interleukin-6 signaling. Adipocyte progenitor cell lines lacking DNMT3A exhibited aberrant differentiation. Furthermore, mice in which Dnmt3a was specifically ablated in adipocyte progenitors showed enlarged fat depots and increased progenitor numbers, partly recapitulating the TBRS obesity phenotypes. Loss of DNMT3A led to constitutive DNA hypomethylation, such that the DNA methylation landscape of young adipocyte progenitors resemble that of older wild-type mice. Together, our results demonstrate that DNMT3A coordinates both the central and local control of energy storage required to maintain normal weight and prevent inflammatory obesity.

Intermittent prednisone treatment in mice promotes exercise tolerance in obesity through adiponectin

The fat-muscle communication regulates metabolism and involves circulating signals like adiponectin. Modulation of this cross-talk could benefit muscle bioenergetics and exercise tolerance in conditions like obesity. Chronic daily intake of exogenous glucocorticoids produces or exacerbates metabolic stress, often leading to obesity. In stark contrast to the daily intake, we discovered that intermittent pulses of glucocorticoids improve dystrophic muscle metabolism. However, the underlying mechanisms, particularly in the context of obesity, are still largely unknown. Here we report that in mice with diet-induced obesity, intermittent once-weekly prednisone increased total and high-molecular weight adiponectin levels and improved exercise tolerance and energy expenditure. These effects were dependent upon adiponectin, as shown by genetic ablation of the adipokine. Upregulation of Adipoq occurred through the glucocorticoid receptor (GR), as this effect was blocked by inducible GR ablation in adipocytes. The treatment increased the muscle metabolic response of adiponectin through the CAMKK2-AMPK cascade. Our study demonstrates that intermittent glucocorticoids produce healthful metabolic remodeling in diet-induced obesity.

The immune checkpoint B7-H3 (CD276) regulates adipocyte progenitor metabolism and obesity development

The immune checkpoint B7-H3 (CD276) is a member of the B7 family that has been studied in the tumor microenvironment and immunotherapy, but its potential role in metabolism remains largely unknown. Here, we show that B7-H3 is highly expressed in mouse and human adipose tissue at steady state, with the highest levels in adipocyte progenitor cells. B7-H3 is rapidly down-regulated upon the initiation of adipocyte differentiation. Combined RNA sequencing and metabolic studies reveal that B7-H3 stimulates glycolytic and mitochondrial activity of adipocyte progenitors. Loss of B7-H3 in progenitors results in impaired oxidative metabolism program and increased lipid accumulation in derived adipocytes. Consistent with these observations, mice knocked out for B7-H3 develop spontaneous obesity, metabolic dysfunction, and adipose tissue inflammation. Our results reveal an unexpected metabolic role for B7-H3 in adipose tissue and open potential new avenues for the treatment of metabolic diseases by targeting the B7-H3 pathway.

Insulin action and resistance are dependent on a GSK3β-FBXW7-ERRα transcriptional axis

Insulin resistance, a harbinger of the metabolic syndrome, is a state of compromised hormonal response resulting from the dysregulation of a wide range of insulin-controlled cellular processes. However, how insulin affects cellular energy metabolism via long-term transcriptional regulation and whether boosting mitochondrial function alleviates insulin resistance remains to be elucidated. Herein we reveal that insulin directly enhances the activity of the nuclear receptor ERRα via a GSK3β/FBXW7 signaling axis. Liver-specific deletion of GSK3β or FBXW7 and mice harboring mutations of ERRα phosphosites (ERRα3SA) co-targeted by GSK3β/FBXW7 result in accumulated ERRα proteins that no longer respond to fluctuating insulin levels. ERRα3SA mice display reprogrammed liver and muscle transcriptomes, resulting in compromised energy homeostasis and reduced insulin sensitivity despite improved mitochondrial function. This crossroad of insulin signaling and transcriptional control by a nuclear receptor offers a framework to better understand the complex cellular processes contributing to the development of insulin resistance.

Inhibition of nonalcoholic fatty liver disease in mice by selective inhibition of mTORC1

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) remain without effective therapies. The mechanistic target of rapamycin complex 1 (mTORC1) pathway is a potential therapeutic target, but conflicting interpretations have been proposed for how mTORC1 controls lipid homeostasis. We show that selective inhibition of mTORC1 signaling in mice, through deletion of the RagC/D guanosine triphosphatase-activating protein folliculin (FLCN), promotes activation of transcription factor E3 (TFE3) in the liver without affecting other mTORC1 targets and protects against NAFLD and NASH. Disease protection is mediated by TFE3, which both induces lipid consumption and suppresses anabolic lipogenesis. TFE3 inhibits lipogenesis by suppressing proteolytic processing and activation of sterol regulatory element-binding protein-1c (SREBP-1c) and by interacting with SREBP-1c on chromatin. Our data reconcile previously conflicting studies and identify selective inhibition of mTORC1 as a potential approach to treat NASH and NAFLD.

Protein tyrosine phosphatase receptor δ serves as the orexigenic asprosin receptor

Asprosin is a fasting-induced glucogenic and centrally acting orexigenic hormone. The olfactory receptor Olfr734 is known to be the hepatic receptor for asprosin that mediates its effects on glucose production, but the receptor for asprosin's orexigenic function has been unclear. Here, we have identified protein tyrosine phosphatase receptor δ (Ptprd) as the orexigenic receptor for asprosin. Asprosin functions as a high-affinity Ptprd ligand in hypothalamic AgRP neurons, regulating the activity of this circuit in a cell-autonomous manner. Genetic ablation of Ptprd results in a strong loss of appetite, leanness, and an inability to respond to the orexigenic effects of asprosin. Ablation of Ptprd specifically in AgRP neurons causes resistance to diet-induced obesity. Introduction of the soluble Ptprd ligand-binding domain in the circulation of mice suppresses appetite and blood glucose levels by sequestering plasma asprosin. Identification of Ptprd as the orexigenic asprosin receptor creates a new avenue for the development of anti-obesity therapeutics.

Lactate Is a Key Mediator That Links Obesity to Insulin Resistance via Modulating Cytokine Production From Adipose Tissue

Numerous evidence indicates that inflammation in adipose tissue is the primary cause of systemic insulin resistance induced by obesity. Obesity-associated changes in circulating LPS level and hypoxia/HIF-1α activation have been proposed to be involved in boosting obesity-induced inflammation. However, there is poor understanding of what triggers obesity-induced inflammation. In this study, we pinpoint lactate as a key trigger to mediate obesity-induced inflammation and systemic insulin resistance. Specific deletion of Slc16a1 that encodes MCT1, the primary lactate transporter in adipose tissues, robustly elevates blood levels of proinflammatory cytokines and aggravates systemic insulin resistance without alteration of adiposity in mice fed high-fat diet. Slc16a1 deletion in adipocytes elevates intracellular lactate level while reducing circulating lactate concentration. Mechanistically, lactate retention due to Slc16a1 deletion initiates adipocyte apoptosis and cytokine release. The locally recruited macrophages amplify the inflammation by release of proinflammatory cytokines to the circulation, leading to insulin resistance in peripheral tissues. This study, therefore, indicates that lactate within adipocytes has a key biological function linking obesity to insulin resistance, and harnessing lactate in adipocytes can be a promising strategy to break this link.

Gabrb3 endothelial cell-specific knockout mice display abnormal blood flow, hypertension, and behavioral dysfunction

Our recent studies uncovered a novel GABA signaling pathway in embryonic forebrain endothelial cells that works independently from neuronal GABA signaling and revealed that disruptions in endothelial GABA_A receptor-GABA signaling from early embryonic stages can directly contribute to the origin of psychiatric disorders. In the GABA_A receptor β3 subunit endothelial cell conditional knockout (Gabrb3^ECKO) mice, the β3 subunit is deleted selectively from endothelial cells, therefore endothelial GABA_A receptors become inactivated and dysfunctional. There is a reduction in vessel densities and increased vessel morphology in the Gabrb3^ECKO telencephalon that persists in the adult neocortex. Gabrb3^ECKO mice show behavioral deficits such as impaired reciprocal social interactions, communication deficits, heightened anxiety, and depression. Here, we characterize the functional changes in Gabrb3^ECKO mice by evaluating cortical blood flow, examine the consequences of loss of endothelial Gabrb3 on cardiac tissue, and define more in-depth altered behaviors. Red blood cell velocity and blood flow were increased in the cortical microcirculation of the Gabrb3^ECKO mice. The Gabrb3^ECKO mice had a reduction in vessel densities in the heart, similar to the brain; exhibited wavy, myocardial fibers, with elongated 'worm-like' nuclei in their cardiac histology, and developed hypertension. Additional alterations in behavioral function were observed in the Gabrb3^ECKO mice such as increased spontaneous exploratory activity and rearing in an open field, reduced short term memory, decreased ambulatory activity in CLAMS testing, and altered prepulse inhibition to startle, an important biomarker of psychiatric diseases such as schizophrenia. Our results imply that vascular Gabrb3 is a key player in the brain as well as the heart, and its loss in both organs can lead to concurrent development of psychiatric and cardiac dysfunction.

Local hyperthermia therapy induces browning of white fat and treats obesity

Beige fat plays key roles in the regulation of systemic energy homeostasis; however, detailed mechanisms and safe strategy for its activation remain elusive. In this study, we discovered that local hyperthermia therapy (LHT) targeting beige fat promoted its activation in humans and mice. LHT achieved using a hydrogel-based photothermal therapy activated beige fat, preventing and treating obesity in mice without adverse effects. HSF1 is required for the effects since HSF1 deficiency blunted the metabolic benefits of LHT. HSF1 regulates Hnrnpa2b1 (A2b1) transcription, leading to increased mRNA stability of key metabolic genes. Importantly, analysis of human association studies followed by functional analysis revealed that the HSF1 gain-of-function variant p.P365T is associated with improved metabolic performance in humans and increased A2b1 transcription in mice and cells. Overall, we demonstrate that LHT offers a promising strategy against obesity by inducing beige fat activation via HSF1-A2B1 transcriptional axis.

Adipocyte-Specific CDK7 Ablation Leads to Progressive Loss of Adipose Tissue and Metabolic Dysfunction

Adipose tissue regulates whole-body energy homeostasis. Both lipodystrophy and obesity, the extreme and opposite aspects of adipose tissue dysfunction, result in metabolic disorders: insulin resistance and hepatic steatosis. Cyclin-dependent kinases (CDKs) have been reported to be involved in adipose tissue development and functions. Using adipose tissue-specific knockout mice, here we demonstrate that the deletion of CDK7 in adipose tissue results in progressive lipodystrophy, insulin resistance, impaired adipokine secretion and down-regulation of fat-specific genes, which are aggravated on high-fat diet and during aging. Our studies suggest that CDK7 is a key regulatory component of adipose tissue maintenance and systemic energy homeostasis.

Defining the mammalian coactivation of hepatic 12-h clock and lipid metabolism

The 12-h clock coordinates lipid homeostasis, energy metabolism, and stress rhythms via the transcriptional regulator XBP1. However, the biochemical and physiological bases for integrated control of the 12-h clock and diverse metabolic pathways remain unclear. Here, we show that steroid receptor coactivator SRC-3 coactivates XBP1 transcription and regulates hepatic 12-h cistrome and gene rhythmicity. Mice lacking SRC-3 show abnormal 12-h rhythms in hepatic transcription, metabolic functions, systemic energetics, and rate-limiting lipid metabolic processes, including triglyceride, phospholipid, and cardiolipin pathways. Notably, 12-h clock coactivation is not only preserved, with its cistromic activation priming ahead of the zeitgeber cue of light, but concomitant with rhythmic remodeling in the absence of food. These findings reveal that SRC-3 integrates the mammalian 12-h clock, energy metabolism, and membrane and lipid homeostasis and demonstrates a role for the 12-h clock machinery as an active transcriptional mechanism in anticipating physiological and metabolic energy needs and stresses.

Disruption of STIM1-mediated Ca2+ sensing and energy metabolism in adult skeletal muscle compromises exercise tolerance, proteostasis, and lean mass

OBJECTIVE

Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane endoplasmic/sarcoplasmic reticulum (E/SR) protein recognized for its role in a store operated Ca2+ entry (SOCE), an ancient and ubiquitous signaling pathway. Whereas STIM1 is known to be indispensable during development, its biological and metabolic functions in mature muscles remain unclear.

METHODS

Conditional and tamoxifen inducible muscle STIM1 knock-out mouse models were coupled with multi-omics tools and comprehensive physiology to understand the role of STIM1 in regulating SOCE, mitochondrial quality and bioenergetics, and whole-body energy homeostasis.

RESULTS

This study shows that STIM1 is abundant in adult skeletal muscle, upregulated by exercise, and is present at SR-mitochondria interfaces. Inducible tissue-specific deletion of STIM1 (iSTIM1 KO) in adult muscle led to diminished lean mass, reduced exercise capacity, and perturbed fuel selection in the settings of energetic stress, without affecting whole-body glucose tolerance. Proteomics and phospho-proteomics analyses of iSTIM1 KO muscles revealed molecular signatures of low-grade E/SR stress and broad activation of processes and signaling networks involved in proteostasis.

CONCLUSION

These results show that STIM1 regulates cellular and mitochondrial Ca2+ dynamics, energy metabolism and proteostasis in adult skeletal muscles. Furthermore, these findings provide insight into the pathophysiology of muscle diseases linked to disturbances in STIM1-dependent Ca2+ handling.

Endothelial Piezo1 sustains muscle capillary density and contributes to physical activity

Piezo1 forms mechanically activated nonselective cation channels that contribute to endothelial response to fluid flow. Here we reveal an important role in the control of capillary density. Conditional endothelial cell-specific deletion of Piezo1 in adult mice depressed physical performance. Muscle microvascular endothelial cell apoptosis and capillary rarefaction were evident and sufficient to account for the effect on performance. There was selective upregulation of thrombospondin-2 (TSP2), an inducer of endothelial cell apoptosis, with no effect on TSP1, a related important player in muscle physiology. TSP2 was poorly expressed in muscle endothelial cells but robustly expressed in muscle pericytes, in which nitric oxide (NO) repressed the Tsp2 gene without an effect on Tsp1. In endothelial cells, Piezo1 was required for normal expression of endothelial NO synthase. The data suggest an endothelial cell-pericyte partnership of muscle in which endothelial Piezo1 senses blood flow to sustain capillary density and thereby maintain physical capability.

Methods for the Comprehensive in vivo Analysis of Energy Flux, Fluid Homeostasis, Blood Pressure, and Ventilatory Function in Rodents

Cardiovascular disease represents the leading cause of death in the United States, and metabolic diseases such as obesity represent the primary impediment to improving cardiovascular health. Rodent (mouse and rat) models are widely used to model cardiometabolic disease, and as a result, there is increasing interest in the development of accurate and precise methodologies with sufficiently high resolution to dissect mechanisms controlling cardiometabolic physiology in these small organisms. Further, there is great utility in the development of centralized core facilities furnished with high-throughput equipment configurations and staffed with professional content experts to guide investigators and ensure the rigor and reproducibility of experimental endeavors. Here, we outline the array of specialized equipment and approaches that are employed within the Comprehensive Rodent Metabolic Phenotyping Core (CRMPC) and our collaborating laboratories within the Departments of Physiology, Pediatrics, Microbiology & Immunology, and Biomedical Engineering at the Medical College of Wisconsin (MCW), for the detailed mechanistic dissection of cardiometabolic function in mice and rats. We highlight selected methods for the analysis of body composition and fluid compartmentalization, electrolyte accumulation and flux, energy accumulation and flux, physical activity, ingestive behaviors, ventilatory function, blood pressure, heart rate, autonomic function, and assessment and manipulation of the gut microbiota. Further, we include discussion of the advantages and disadvantages of these approaches for their use with rodent models, and considerations for experimental designs using these methods.

Nicotinamide riboside supplementation confers marginal metabolic benefits in obese mice without remodeling the muscle acetyl-proteome

Nicotinamide riboside supplements (NRS) have been touted as a nutraceutical that promotes cardiometabolic and musculoskeletal health by enhancing nicotinamide adenine dinucleotide (NAD+) biosynthesis, mitochondrial function, and/or the activities of NAD-dependent sirtuin deacetylase enzymes. This investigation examined the impact of NRS on whole body energy homeostasis, skeletal muscle mitochondrial function, and corresponding shifts in the acetyl-lysine proteome, in the context of diet-induced obesity using C57BL/6NJ mice. The study also included a genetically modified mouse model that imposes greater demand on sirtuin flux and associated NAD+ consumption, specifically within muscle tissues. In general, whole body glucose control was marginally improved by NRS when administered at the midpoint of a chronic high-fat diet, but not when given as a preventative therapy upon initiation of the diet. Contrary to anticipated outcomes, the study produced little evidence that NRS increases tissue NAD+ levels, augments mitochondrial function, and/or mitigates diet-induced hyperacetylation of the skeletal muscle proteome.

ACE2 pathway regulates thermogenesis and energy metabolism

Identification of key regulators of energy homeostasis holds important therapeutic promise for metabolic disorders, such as obesity and diabetes. ACE2 cleaves angiotensin II (Ang II) to generate Ang-(1-7) which acts mainly through the Mas1 receptor. Here, we identify ACE2 pathway as a critical regulator in the maintenance of thermogenesis and energy expenditure. We found that ACE2 is highly expressed in brown adipose tissue (BAT) and that cold stimulation increases ACE2 and Ang-(1-7) levels in BAT and serum. Ace2 knockout mice (Ace2^-/y) and Mas1 knockout mice (Mas1^-/-) displayed impaired thermogenesis. Mice transplanted with brown adipose tissue from Mas1^-/- display metabolic abnormalities consistent with those seen in the Ace2 and Mas1 knockout mice. In contrast, impaired thermogenesis of Lepr^db/db obese diabetic mice and high-fat diet-induced obese mice were ameliorated by overexpression of Ace2 or continuous infusion of Ang-(1-7). Activation of ACE2 pathway was associated with improvement of metabolic parameters, including blood glucose, lipids, and energy expenditure in multiple animal models. Consistently, ACE2 pathway remarkably enhanced the browning of white adipose tissue. Mechanistically, we showed that ACE2 pathway activated Akt/FoxO1 and PKA pathway, leading to induction of UCP1 and activation of mitochondrial function. Our data propose that adaptive thermogenesis requires regulation of ACE2 pathway and highlight novel potential therapeutic targets for the treatment of metabolic disorders.

Metabolic Phenotyping in Mice with NASH Using Indirect Calorimetry

Obesity caused by caloric overload has assumed epidemic proportions. Obesity is frequently associated with metabolic dysfunctions, such as type 2 diabetes, non-alcoholic steatohepatitis (NASH), cardiovascular diseases, and cancer. Metabolic phenotyping is a set of techniques for studying metabolic dysfunction and behavior information including energy expenditure, body weight gain, glucose homeostasis, and lipid profile. Among different metabolic phenotyping methods, indirect calorimetry is an indispensable tool for quantifying the energy balance/imbalance in various mouse models, which enables researchers to probe the development of disease and to evaluate the therapeutic benefit from different interventions. In this chapter, we will describe the procedures of metabolic phenotyping using indirect calorimetry in db/db mouse, a metabolic disorder mouse model which develops NASH.

Human loss-of-function variants in the serotonin 2C receptor associated with obesity and maladaptive behavior

Serotonin reuptake inhibitors and receptor agonists are used to treat obesity, anxiety and depression. Here we studied the role of the serotonin 2C receptor (5-HT_2CR) in weight regulation and behavior. Using exome sequencing of 2,548 people with severe obesity and 1,117 control individuals without obesity, we identified 13 rare variants in the gene encoding 5-HT_2CR (HTR2C) in 19 unrelated people (3 males and 16 females). Eleven variants caused a loss of function in HEK293 cells. All people who carried variants had hyperphagia and some degree of maladaptive behavior. Knock-in male mice harboring a human loss-of-function HTR2C variant developed obesity and reduced social exploratory behavior; female mice heterozygous for the same variant showed similar deficits with reduced severity. Using the 5-HT_2CR agonist lorcaserin, we found that depolarization of appetite-suppressing proopiomelanocortin neurons was impaired in knock-in mice. In conclusion, we demonstrate that 5-HT_2CR is involved in the regulation of human appetite, weight and behavior. Our findings suggest that melanocortin receptor agonists might be effective in treating severe obesity in individuals carrying HTR2C variants. We suggest that HTR2C should be included in diagnostic gene panels for severe childhood-onset obesity.

BCAA-BCKA axis regulates WAT browning through acetylation of PRDM16

The link between branched-chain amino acids (BCAAs) and obesity has been known for decades but the functional role of BCAA metabolism in white adipose tissue (WAT) of obese individuals remains vague. Here, we show that mice with adipose tissue knockout of Bcat2, which converts BCAAs to branched-chain keto acids (BCKAs), are resistant to high-fat diet-induced obesity due to increased inguinal WAT browning and thermogenesis. Mechanistically, acetyl-CoA derived from BCKA suppresses WAT browning by acetylation of PR domain-containing protein 16 (PRDM16) at K915, disrupting the interaction between PRDM16 and peroxisome proliferator-activated receptor-γ (PPARγ) to maintain WAT characteristics. Depletion of BCKA-derived acetyl-CoA robustly prompts WAT browning and energy expenditure. In contrast, BCKA supplementation re-establishes high-fat diet-induced obesity in Bcat2 knockout mice. Moreover, telmisartan, an anti-hypertension drug, significantly represses Bcat2 activity via direct binding, resulting in enhanced WAT browning and reduced adiposity. Strikingly, BCKA supplementation reverses the lean phenotype conferred by telmisartan. Thus, we uncover the critical role of the BCAA-BCKA axis in WAT browning.

The impact of intermittent exercise on mouse ethanol drinking and abstinence-associated affective behavior and physiology

BACKGROUND

Negative emotional states are associated with the initiation and maintenance of alcohol use and drive relapse to drinking during withdrawal and protracted abstinence. Physical exercise is correlated with decreased negative affective symptoms, although a direct relationship between drinking patterns and exercise level has not been fully elucidated.

METHODS

We incorporated intermittent running wheel access into a chronic continuous access, two-bottle choice alcohol drinking model in female C57BL/6J mice. Wheel access was granted intermittently once mice established a preference for alcohol over water. After 6 weeks, alcohol was removed (forced abstinence) and mice were given continuous access to unlocked or locked wheels. Negative affect-like behavior, home cage behavior, and metabolic activity were measured during protracted abstinence.

RESULTS

Wheel access shifted drinking patterns in the mice, increasing drinking when the wheel was locked, and decreasing drinking when unlocked. Moreover, alcohol preference and consumption were strongly negatively correlated with the amount of running. An assessment of negative affect-like behavior in abstinence via the novelty suppressed feeding and saccharin preference tests (SPT) showed that unlimited wheel access mitigated abstinence-induced latency increases. Mice in abstinence also spent more time sleeping during the active dark cycle than control mice, providing additional evidence for abstinence-induced anhedonia- and depression-like behavior. Furthermore, running wheel access in abstinence decreased dark cycle sleep to comparable alcohol- and wheel-naïve mice. Given the positive impact of exercise and the negative impact of alcohol on metabolic health, we compared metabolic phenotypes of alcohol-abstinent mice with and without wheel access. Wheel access increased energy expenditure, carbon dioxide production, and oxygen consumption, providing a potential metabolic mechanism through which wheel access improves affective state.

CONCLUSIONS

This study suggests that including exercise in AUD treatment regimens has the potential to reduce drinking, improve affective state during abstinence and could serve as a non-pharmacological approach to prevent the development of an AUD in high-risk individuals.

Crocetin Alleviates Ovariectomy-Induced Metabolic Dysfunction through Regulating Estrogen Receptor β

Metabolic dysfunction (MD) is a major health problem threatening the life quality of menopausal women. Saffron has been widely used in herb prescriptions for treating menopausal syndrome. However, the pharmacological effects and mechanisms of saffron are poorly understood. Here, we investigated the effect of crocin, the major ingredient of saffron and its active metabolite in blood, crocetin, on MD and lipid metabolism in ovariectomized (OVX) mice and 3T3-L1 adipocytes. The present study showed that intragastric treatment of crocin prevented weight gain, fat accumulation, and insulin resistance in OVX mice by increasing energy expenditure and fat oxidation. Mechanistically, crocin influenced adipose tissue homeostasis by regulating adipogenic and lipolytic factors, which was strongly associated with the restoration of the downregulated ERβ function in white adipose tissue (WAT). In vitro, crocetin facilitated lipid metabolism in an ERβ-dependent manner. Our results demonstrated the beneficial effects of crocetin/crocin-mediated intervention against metabolic dysfunction, revealing a prospective therapeutic application in menopausal women.

Endothelial Cell CD36 Reduces Atherosclerosis and Controls Systemic Metabolism

High-fat Western diets contribute to tissue dysregulation of fatty acid and glucose intake, resulting in obesity and insulin resistance and their sequelae, including atherosclerosis. New therapies are desperately needed to interrupt this epidemic. The significant idea driving this research is that the understudied regulation of fatty acid entry into tissues at the endothelial cell (EC) interface can provide novel therapeutic targets that will greatly modify health outcomes and advance health-related knowledge. Dysfunctional endothelium, defined as activated, pro-inflammatory, and pro-thrombotic, is critical in atherosclerosis initiation, in modulating thrombotic events that could result in myocardial infarction and stroke, and is a hallmark of insulin resistance. Dyslipidemia from high-fat diets overwhelmingly contributes to the development of dysfunctional endothelium. CD36 acts as a receptor for pathological ligands generated by high-fat diets and in fatty acid uptake, and therefore, it may additionally contribute to EC dysfunction. We created EC CD36 knockout (CD36°) mice using cre-lox technology and a cre-promoter that does not eliminate CD36 in hematopoietic cells (Tie2e cre). These mice were studied on different diets, and crossed to the low density lipoprotein receptor (LDLR) knockout for atherosclerosis assessment. Our data show that EC CD36° and EC CD36°/LDLR° mice have metabolic changes suggestive of an uncompensated role for EC CD36 in fatty acid uptake. The mice lacking expression of EC CD36 had increased glucose clearance compared with controls when fed with multiple diets. EC CD36° male mice showed increased carbohydrate utilization and decreased energy expenditure by indirect calorimetry. Female EC CD36°/LDLR° mice have reduced atherosclerosis. Taken together, these data support a significant role for EC CD36 in systemic metabolism and reveal sex-specific impact on atherosclerosis and energy substrate use.

A novel peroxisome proliferator-activated receptor gamma ligand improves insulin sensitivity and promotes browning of white adipose tissue in obese mice

OBJECTIVE

Nuclear receptor Peroxisome Proliferator-Activated Receptor γ (PPARγ) is a promising target for the treatment of type 2 diabetes. The antidiabetic drug thiazolidinediones (TZDs) are potent insulin sensitizers as full agonists of PPARγ, but cause unwanted side effects. Recent discoveries have shown that TZDs improve insulin sensitivity by blocking PPARγ phosphorylation at S273, which decouples the full agonism-associated side effects. PPARγ ligands that act through the blockage of PPARγ phosphorylation but lack the full agonist activity would be expected to improve insulin sensitivity without TZD-associated side effects, however, chemicals that carry such traits and bind to PPARγ with high-affinity are lacking. Moreover, TZDs are known to promote white-to-brown adipocyte conversion and energy expenditure and appear to require their full agonism on PPARγ for this activity. It is unknown whether a partial or non-TZD agonist of PPARγ is capable of promoting browning effect. In this study, we developed a novel non-TZD partial agonist of PPARγ and investigated its function on insulin sensitivity and white-to-brown conversion and energy expenditure in diet-induced obese mice.

METHODS

A novel indole-based chemical WO95E was designed via medicinal chemistry and tested for PPARγ binding and activity and for the effect on PPARγ phosphorylation. Diet-induced obese mice were administered with WO95E for 4 weeks. Insulin sensitivity, glucose tolerance, body weight, fat tissue weight, adipocyte size, morphology, energy expenditure, and expression levels of genes involved in PPARγ activity, thermogenesis/browning, and TZD-related side effects were evaluated.

RESULTS

WO95E binds to PPARγ with high affinity and acts as a PPARγ partial agonist. WO95E inhibits PPARγ phosphorylation and regulates PPARγ phosphorylation-dependent genes. WO95E ameliorates insulin resistance and glucose tolerance in mice of diet-induced obesity, with minimal TZD use-associated side effects. We found that WO95E promotes white-to-brown adipocyte conversion and energy expenditure and hence protects against diet-induced obesity. WO95E decreases the size of adipocytes and suppresses adipose tissue inflammation. WO95E also suppresses obesity-associated liver steatosis.

CONCLUSIONS

WO95E improves insulin sensitivity and glucose homeostasis and promotes browning and energy expenditure by acting as a novel PPARγ phosphorylation inhibitor/partial agonist. Our findings suggest the potential of this compound or its derivative for the therapeutic treatment of insulin resistance and obesity.

Brown Fat Dnmt3b Deficiency Ameliorates Obesity in Female Mice

Obesity results from a chronic energy imbalance due to energy intake exceeding energy expenditure. Activation of brown fat thermogenesis has been shown to combat obesity. Epigenetic regulation, including DNA methylation, has emerged as a key regulator of brown fat thermogenic function. Here we aimed to study the role of Dnmt3b, a DNA methyltransferase involved in de novo DNA methylation, in the regulation of brown fat thermogenesis and obesity. We found that the specific deletion of Dnmt3b in brown fat promotes the thermogenic and mitochondrial program in brown fat, enhances energy expenditure, and decreases adiposity in female mice fed a regular chow diet. With a lean phenotype, the female knockout mice also exhibit increased insulin sensitivity. In addition, Dnmt3b deficiency in brown fat also prevents diet-induced obesity and insulin resistance in female mice. Interestingly, our RNA-seq analysis revealed an upregulation of the PI3K-Akt pathway in the brown fat of female Dnmt3b knockout mice. However, male Dnmt3b knockout mice have no change in their body weight, suggesting the existence of sexual dimorphism in the brown fat Dnmt3b knockout model. Our data demonstrate that Dnmt3b plays an important role in the regulation of brown fat function, energy metabolism and obesity in female mice.

Peptide-YY3-36/glucagon-like peptide-1 combination treatment of obese diabetic mice improves insulin sensitivity associated with recovered pancreatic β-cell function and synergistic activation of discrete hypothalamic and brainstem neuronal circuitries

OBJECTIVE

Obesity-linked type 2 diabetes (T2D) is a worldwide health concern and many novel approaches are being considered for its treatment and subsequent prevention of serious comorbidities. Co-administration of glucagon like peptide 1 (Fc-GLP-1) and peptide YY_3-36 (Fc-PYY_3-36) renders a synergistic decrease in energy intake in obese men. However, mechanistic details of the synergy between these peptide agonists and their effects on metabolic homeostasis remain relatively scarce.

METHODS

In this study, we utilized long-acting analogues of GLP-1 and PYY_3-36 (via Fc-peptide conjugation) to better characterize the synergistic pharmacological benefits of their co-administration on body weight and glycaemic regulation in obese and diabetic mouse models. Hyperinsulinemic-euglycemic clamps were used to measure weight-independent effects of Fc-PYY_3-36 + Fc-GLP-1 on insulin action. Fluorescent light sheet microscopy analysis of whole brain was performed to assess activation of brain regions.

RESULTS

Co-administration of long-acting Fc-IgG/peptide conjugates of Fc-GLP-1 and Fc-PYY_3-36 (specific for PYY receptor-2 (Y2R)) resulted in profound weight loss, restored glucose homeostasis, and recovered endogenous β-cell function in two mouse models of obese T2D. Hyperinsulinemic-euglycemic clamps in C57BLKS/J db/db and diet-induced obese Y2R-deficient (Y2RKO) mice indicated Y2R is required for a weight-independent improvement in peripheral insulin sensitivity and enhanced hepatic glycogenesis. Brain cFos staining demonstrated distinct temporal activation of regions of the hypothalamus and hindbrain following Fc-PYY_3-36 + Fc-GLP-1R agonist administration.

CONCLUSIONS

These results reveal a therapeutic approach for obesity/T2D that improved insulin sensitivity and restored endogenous β-cell function. These data also highlight the potential association between the gut-brain axis in control of metabolic homeostasis.

Enteric pathogens induce tissue tolerance and prevent neuronal loss from subsequent infections

The enteric nervous system (ENS) controls several intestinal functions including motility and nutrient handling, which can be disrupted by infection-induced neuropathies or neuronal cell death. We investigated possible tolerance mechanisms preventing neuronal loss and disruption in gut motility after pathogen exposure. We found that following enteric infections, muscularis macrophages (MMs) acquire a tissue-protective phenotype that prevents neuronal loss, dysmotility, and maintains energy balance during subsequent challenge with unrelated pathogens. Bacteria-induced neuroprotection relied on activation of gut-projecting sympathetic neurons and signaling via β2-adrenergic receptors (β2AR) on MMs. In contrast, helminth-mediated neuroprotection was dependent on T cells and systemic production of interleukin (IL)-4 and IL-13 by eosinophils, which induced arginase-expressing MMs that prevented neuronal loss from an unrelated infection located in a different intestinal region. Collectively, these data suggest that distinct enteric pathogens trigger a state of disease or tissue tolerance that preserves ENS number and functionality.

Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity

Endurance exercise promotes skeletal muscle vascularization, oxidative metabolism, fiber-type switching, and neuromuscular junction integrity. Importantly, the metabolic and contractile properties of the muscle fiber must be coupled to the identity of the innervating motor neuron (MN). Here, we show that muscle-derived neurturin (NRTN) acts on muscle fibers and MNs to couple their characteristics. Using a muscle-specific NRTN transgenic mouse (HSA-NRTN) and RNA sequencing of MN somas, we observed that retrograde NRTN signaling promotes a shift toward a slow MN identity. In muscle, NRTN increased capillary density and oxidative capacity and induced a transcriptional reprograming favoring fatty acid metabolism over glycolysis. This combination of effects on muscle and MNs makes HSA-NRTN mice lean with remarkable exercise performance and motor coordination. Interestingly, HSA-NRTN mice largely recapitulate the phenotype of mice with muscle-specific expression of its upstream regulator PGC-1ɑ1. This work identifies NRTN as a myokine that couples muscle oxidative capacity to slow MN identity.

Hepatokine Pregnancy Zone Protein Governs the Diet-Induced Thermogenesis Through Activating Brown Adipose Tissue

Intermittent fasting (IF), as a dietary intervention for weight loss, takes effects primarily through increasing energy expenditure. However, whether inter-organ systems play a key role in IF remains unclear. Here, a novel hepatokine, pregnancy zone protein (PZP) is identified, which has significant induction during the refeeding stage of IF. Further, loss of function studies and protein therapeutic experiment in mice revealed that PZP promotes diet-induced thermogenesis through activating brown adipose tissue (BAT). Mechanistically, circulating PZP can bind to cell surface glucose-regulated protein of 78 kDa (GRP78) to promote uncoupling protein 1 (UCP1) expression via a p38 MAPK-ATF2 signaling pathway in BAT. These studies illuminate a systemic regulation in which the IF promotes BAT thermogenesis through the endocrinal system and provide a novel potential target for treating obesity and related disorders.

Melanocortin 4 receptor stimulation prevents anti-depressant-associated weight gain in mice caused by long-term fluoxetine exposure

Contrasting with the predicted anorexigenic effect of increasing brain serotonin signaling, long-term use of selective serotonin reuptake inhibitors (SSRIs) antidepressants correlates with body weight gain. This adverse outcome increases the risk of transitioning to obesity and interferes with treatment compliance. Here we show that orally administered fluoxetine (Flx), a widely prescribed SSRI, increased body weight by enhancing food intake in healthy mice at two different time points and through two distinct mechanisms. Within hours, Flx decreased the activity of a subset of brainstem serotonergic neurons by triggering autoinhibitory signaling through the Htr1a receptor. Upon longer treatment Flx blunted Htr2c expression/signaling, decreased the phosphorylation of Creb and Stat3 and dampened the production of POMC/α-MSH in hypothalamic neurons, thereby increasing food intake. Accordingly, exogenous stimulation of the melanocortin 4 receptor (MC4R) by co-treating mice with Flx and lipocalin-2, an anorexigenic hormone signaling through this receptor, normalized feeding and body weight. Flx and other SSRIs also inhibit CREB/STAT3 phosphorylation in a human neuronal cell line suggesting that these non-canonical effects could also occur in long-term users of SSRIs. By defining the molecular basis of the long-term SSRIs-associated weight gain this study proposes a therapeutic strategy to counter it.

Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Objective

Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of body temperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms.

Methods

Distinct thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis.

Results

In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice.

Conclusion

This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

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Thyroid hormones are essential for the regulation of body temperature.

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Thyroid hormone-deficient (hypothyroid) mice show distinct leptin serum concentrations in response to changes in ambient housing temperature.

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High leptin serum levels confer a stimulatory effect on the hypothalamic-pituitary-thyroid axis.

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High leptin serum level prevents fall in body temperature in hypothyroid mice at room temperature through its pyrexic effects.

Nicotinamide riboside has minimal impact on energy metabolism in mouse models of mild obesity

Supplementation with precursors of NAD has been shown to prevent and reverse insulin resistance, mitochondrial dysfunction, and liver damage in mouse models of diet-induced obesity. We asked whether the beneficial effects of supplementation with the NAD precursor nicotinamide riboside (NR) are dependent on mouse strain. We compared the effects of NR supplementation on whole-body energy metabolism and mitochondrial function in mildly obese C57BL/6N and C57BL/6J mice, two commonly used strains to investigate metabolism. Male C57BL/6N and C57BL/6J mice were fed a high-fat diet (HFD) or standard chow with or without NR supplementation for 8 weeks. Body and organ weights, glucose tolerance, and metabolic parameters as well as mitochondrial O2 flux in liver and muscle fibers were assessed. We found that NR supplementation had no influence on body or organ weight, glucose metabolism or hepatic lipid accumulation, energy expenditure, or metabolic flexibility but increased mitochondrial respiration in soleus muscle in both mouse strains. Strain-dependent differences were detected for body and fat depot weight, fasting blood glucose, hepatic lipid accumulation, and energy expenditure. We conclude that, in mild obesity, NR supplementation does not alter metabolic phenotype in two commonly used laboratory mouse strains.

HIV-1 Viral Protein R Couples Metabolic Inflexibility With White Adipose Tissue Thermogenesis

Persons living with HIV (PLWH) manifest chronic disorders of brown and white adipose tissues that lead to diabetes and metabolic syndrome. The mechanisms that link viral factors to defective adipose tissue function and abnormal energy balance in PLWH remain incompletely understood. Here, we explored how the HIV accessory protein viral protein R (Vpr) contributes to adaptive thermogenesis in two mouse models and human adipose tissues. Uncoupling protein 1 (UCP1) gene expression was strongly increased in subcutaneous white adipose tissue (WAT) biopsy specimens from PLWH and in subcutaneous WAT of the Vpr mice, with nearly equivalent mRNA copy number. Histology and functional studies confirmed beige transformation in subcutaneous but not visceral WAT in the Vpr mice. Measurements of energy balance indicated Vpr mice displayed metabolic inflexibility and could not shift efficiently from carbohydrate to fat metabolism during day-night cycles. Furthermore, Vpr mice showed a marked inability to defend body temperature when exposed to 4°C. Importantly, Vpr couples higher tissue catecholamine levels with UCP1 expression independent of β-adrenergic receptors. Our data reveal surprising deficits of adaptive thermogenesis that drive metabolic inefficiency in HIV-1 Vpr mouse models, providing an expanded role for viral factors in the pathogenesis of metabolic disorders in PLWH.

Cyp2c-deficiency depletes muricholic acids and protects against high-fat diet-induced obesity in male mice but promotes liver damage

Objective

Murine-specific muricholic acids (MCAs) are reported to protect against obesity and associated metabolic disorders. However, the response of mice with genetic depletion of MCA to an obesogenic diet has not been evaluated. We used Cyp2c-deficient (Cyp2c^−/−) mice, which lack MCAs and thus have a human-like bile acid (BA) profile, to directly investigate the potential role of MCAs in diet-induced obesity.

Methods

Male and female Cyp2c^−/− mice and wild-type (WT) littermate controls were fed a standard chow diet or a high-fat diet (HFD) for 18 weeks. We measured BA composition from a pool of liver, gallbladder, and intestine, as well as weekly body weight, food intake, lean and fat mass, systemic glucose homeostasis, energy expenditure, intestinal lipid absorption, fecal lipid, and energy content.

Results

Cyp2c-deficiency depleted MCAs and caused other changes in BA composition, namely a decrease in the ratio of 12α-hydroxylated (12α-OH) BAs to non-12α-OH BAs, without altering the total BA levels. While WT male mice became obese after HFD feeding, Cyp2c^−/− male mice were protected from obesity and associated metabolic dysfunctions. Cyp2c^−/− male mice also showed reduced intestinal lipid absorption and increased lipid excretion, which was reversed by oral gavage with the 12α-OH BA and taurocholic acid (TCA). Cyp2c^−/− mice also showed increased liver damage, which appeared stronger in females.

Conclusions

MCA does not protect against diet-induced obesity but may protect against liver injury. Reduced lipid absorption in Cyp2c-deficient male mice is potentially due to a reduced ratio of 12α-OH/non-12α-OH BAs.

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Presence of MCA does not necessarily protect against diet-induced obesity.

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Cyp2c deficiency promotes resistance to diet-induced obesity in males.

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Cyp2c-knockout mice have decreased the ratio of 12α-OH/non-12α-OH BAs that promotes decreased intestinal lipid absorption.

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Cyp2c-knockout mice have improved glucose homeostasis.

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Cyp2c-deficiency promotes mild and severe liver injury in male and female mice, respectively.

Vascepa protects against high-fat diet-induced glucose intolerance, insulin resistance, and impaired β-cell function

Omega-3 fatty acid prescription drugs, Vascepa (≥96% eicosapentaenoic acid [EPA] ethyl ester) and Lovaza (46.5% EPA and 37.5% docosahexaenoic acid ethyl ester) are known therapeutic regimens to treat hypertriglyceridemia. However, their impact on glucose homeostasis, progression to type 2 diabetes, and pancreatic beta cell function are not well understood. In the present study, mice were treated with Vascepa or Lovaza for one week prior to six weeks of high-fat diet feeding. Vascepa but not Lovaza led to reduced insulin resistance, reduced fasting insulin and glucose, and improved glucose intolerance. Vascepa improved beta cell function, reduced liver triglycerides with enhanced expression of hepatic fatty acid oxidation genes, and altered microbiota composition. Vascepa has protective effects on diet-induced insulin resistance and glucose intolerance in mice.