SUMMARY While fatty acids (FAs) released by white adipose tissue (WAT) provide energy for other organs, lipolysis is also critical in brown adipose tissue (BAT), generating FAs for oxidation and UCP-1 activation for thermogenesis. Here, we show that adipose-specific ablation of desnutrin/ATGL in mice converts BAT to a WAT-like tissue. These mice exhibit severely impaired thermogenesis with increased expression of WAT-enriched genes but decreased BAT genes including UCP-1 with lower PPARα binding to its promoter, revealing the requirement of desnutrin-catalyzed lipolysis for maintaining BAT phenotype. We also show that desnutrin is phosphorylated by AMPK at S406, increasing TAG hydrolase activity, and provide evidence for increased lipolysis by AMPK phosphorylation of desnutrin in adipocytes and in vivo. Despite adiposity and impaired BAT function, desnutrin-ASKO mice have improved hepatic insulin sensitivity with lower DAG levels. Overall, desnutrin is phosphorylated/activated by AMPK to increase lipolysis and brings FA oxidation and UCP-1 induction for thermogenesis.

Lipogenesis is exquisitely regulated by nutritional/hormonal states. Transcription of fatty acid synthase (FAS), a central enzyme in lipogenesis, is low in fasting but increases drastically with feeding. In transcriptional activation of FAS by feeding/insulin, USF constitutively bound to the −65 E-box is required. Here, we show that USF functions as a molecular switch by recruiting various interacting proteins during the fasting/feeding transition. During feeding/insulin, USF-1 recruits and is phosphorylated by DNA-PK, which is dephosphorylated/activated by PP1. Phosphorylation of USF-1 allows recruitment of and acetylation by P/CAF, resulting in the FAS promoter activation. In fasting, USF-1 is deacetylated by HDAC9 causing the promoter inactivation. DNA break/repair components associated with USF also bring about transient DNA breaks during feeding-induced FAS activation. In DNA-PK deficient SCID mice, feeding induced USF-1 phosphorylation/acetylation, DNA-breaks, and FAS activation leading to lipogenesis are impaired, resulting in decreased liver and circulating triglyceride levels. Our study demonstrates that DNA-PK mediates the feeding/insulin-dependent lipogenic gene activation.

Summary Uncoupling protein 1 (UCP1) mediates non-shivering thermogenesis and, upon cold exposure, is induced in BAT and subcutaneous white adipose tissue (iWAT). Here, by high-throughput screening using the UCP1 promoter, we identify Zfp516 as a novel transcriptional activator of UCP1 as well as PGC1α thereby promoting a BAT program. Zfp516 itself is induced by cold and sympathetic stimulation through the cAMP-CREB/ATF2 pathway. Zfp516 directly binds to the proximal region of the UCP1 promoter, not to the enhancer region where other transcription factors bind, and interacts with PRDM16 to activate the UCP1 promoter. Although ablation of Zfp516 causes embryonic lethality, knockout embryos still show drastically reduced BAT mass. Overexpression of Zfp516 in adipose tissue promotes browning of iWAT even at room temperature, increasing body temperature, energy expenditure, and preventing diet-induced obesity. Zfp516 may represent a future target for obesity therapeutics.

The rising incidence of obesity and related disorders such as diabetes and heart disease has focused considerable attention on the discovery of novel therapeutics. One promising approach has been to increase the number or activity of brown-like adipocytes in white adipose depots, as this has been shown to prevent diet-induced obesity and reduce the incidence and severity of type 2 diabetes. Thus, the conversion of fat-storing cells into metabolically active thermogenic cells has become an appealing therapeutic strategy to combat obesity. Here, we report a screening platform for the identification of small molecules capable of promoting a white-to-brown metabolic conversion in human adipocytes. We identified two inhibitors of Janus Kinase (JAK) activity with no precedent in adipose tissue biology that stably confer brown-like metabolic activity to white adipocytes. Importantly, these metabolically converted adipocytes exhibit elevated UCP1 expression and increased mitochondrial activity. We further found that repression of interferon signalling and activation of hedgehog signalling in JAK-inactivated adipocytes contributes to the metabolic conversion observed in these cells. Our findings highlight a novel role for the JAK/STAT pathway in the control of adipocyte function and establish a platform to identify compounds for the treatment of obesity.

Preadipocyte factor 1 (Pref-1, also called Dlk1/FA1) is a molecular gatekeeper of adipogenesis which acts by maintaining the preadipocyte state and preventing adipocyte differentiation. Pref-1 is made as an epidermal growth factor-like repeat containing transmembrane protein, and is cleaved by TNFα-converting enzyme (TACE) to generate a soluble form, which acts as an autocrine/paracrine factor. Pref-1 upregulates Sox9 expression by activating the ERK/MAPK pathway and the Pref-1 interaction with fibronectin is required for inhibition of adipogenesis. Pref-1 also prevents brown adipocyte differentiation and its thermogenic function. Here, we highlight the recent evidence for the role of Pref-1 in adipogenesis.

SUMMARY Pref-1 is an EGF-repeat containing protein that inhibits adipocyte differentiation. To better understand the origin and development of white adipose tissue (WAT), we generated transgenic mouse models for transient or permanent fluorescent labeling of cells using the Pref-1 promoter, facilitating inducible ablation. We show that Pref-1 marked cells retain proliferative capacity and are very early adipose precursors, prior to expression of Zfp423 or PPAR g. In addition, Pref-1 marked cells establish adipose precursors as mesenchymal, but not endothelial or pericyte in origin. During embryogenesis, Pref-1 marked cells first appear in the dorsal mesenteric region as early as E10.5. These cells become lipid-laden adipocytes at E17.5 in the subcutaneous region, whereas visceral WAT develops after birth. Finally, ablation of Pref-1 marked cells prevents not only embryonic WAT development but also later adult adipose expansion upon high fat feeding, demonstrating the requirement of Pref-1 cells for adipogenesis.

SUMMARY Fatty acid and triglyceride synthesis is induced in response to feeding and insulin. This lipogenic induction involves coordinate transcriptional activation of lipogenic enzymes, including fatty acid synthase and glycerol-3-phosphate acyltransferase. We recently reported the importance of USF-1 phosphorylation and subsequent acetylation in insulin-induced lipogenic gene activation. Here, we show that Brg1/Brm-associated factor (BAF) 60c is a specific chromatin remodeling component for lipogenic gene transcription in liver. In response to insulin, BAF60c is phosphorylated at S247 by atypical PKCζ/λ, which causes translocation of BAF60c to the nucleus and allows a direct interaction of BAF60c with USF-1 that is phosphorylated by DNA-PK and acetylated by P/CAF. Thus, BAF60c is recruited to form the lipoBAF complex to remodel chromatin structure and to activate lipogenic genes. Consequently, BAF60c promotes lipogenesis in vivo and increases triglyceride levels, demonstrating its role in metabolic adaption to activate the lipogenic program in response to feeding and insulin.

The endocannabinoid (EC) system regulates food intake and energy metabolism. Cannabinoid receptor type 1 (CB1) antagonists show promise in the treatment of obesity and its metabolic consequences. Although the reduction in adiposity resulting from therapy with CB1 antagonists may not account fully for the concomitant improvements in dyslipidemia, direct effects of overactive EC signaling on plasma lipoprotein metabolism have not been documented. The present study used a chemical approach to evaluate the direct effects of increased EC signaling in mice by inducing acute elevations of endogenously produced cannabinoids through pharmacological inhibition of their enzymatic hydrolysis by isopropyl dodecylfluorophosphonate (IDFP). Acute IDFP treatment increased plasma levels of triglyceride (TG) (2.0-to 3.1-fold) and cholesterol (1.3-to 1.4-fold) in conjunction with an accumulation in plasma of apolipoprotein (apo)E-depleted TG-rich lipoproteins. These changes did not occur in either CB1-null or apoE-null mice, were prevented by pretreatment with CB1 antagonists, and were not associated with reduced hepatic apoE gene expression. Although IDFP treatment increased hepatic mRNA levels of lipogenic genes (Srebp1 and Fas), there was no effect on TG secretion into plasma. Instead, IDFP treatment impaired clearance of an intravenously administered TG emulsion, despite increased postheparin lipoprotein lipase activity. Therefore, overactive EC signaling elicits an increase in plasma triglyceride levels associated with reduced plasma TG clearance and an accumulation in plasma of apoE-depleted TG-rich lipoproteins. These findings suggest a role of CB1 activation in the pathogenesis of obesity-related hypertriglyceridemia and underscore the potential efficacy of CB1 antagonists in treating metabolic disease.2-arachidonoylglycerol ͉ hypertriglyceridemia ͉ monoaylglycerol lipase ͉ organophosphorus ͉ cannabinoid receptor O besity elicits a cluster of interrelated disorders, termed the ''metabolic syndrome,'' that increases the risk of cardiovascular disease (1). Epidemiological and genetic data indicate that dysregulation of the endocannabinoid (EC) system increases adiposity in humans (2-4). Pharmacological or genetic ablation of the cannabinoid type 1 receptor (CB1) in normal mice and in diet-induced and genetic mouse models of obesity results in a transient hypophagic response mediated through the hypothalamus, but there also are prolonged effects on weight loss, adiposity, and normalization of metabolic parameters, including plasma lipids (5-11). These effects suggest that the improvement in adiposity-related measures with CB1 inactivation is not limited to reduced food intake, a major known effect of CB1 inactivation (5, 11). CB1 activation in liver increases de novo lipogenesis and decreases fatty acid oxidation (12, 13). High-fat diet or chronic ethanol treatment increases cannabinoid signaling tone via increased hepatic CB1 receptor density and EC levels leading to CB1-mediated hepatic steatosis (12, 13). These observations...