SCOPE:High-fat diet (HFD) induces overeating and obesity. Green tea (-)-epigallocatechin-3-gallate (EGCG) reduces HFD-induced body weight and body fat gain mainly through increased lipid metabolism and fat oxidation. However, little is known about its effect on HFD-induced alterations in feeding behavior.METHODS AND RESULTS:Three diet groups of wildtype C57B/6j male mice at 5 months old were fed on normal chow diet, 1 week of HFD (60% of energy) and 3 months of HFD (diet-induced obesity (DIO)) prior to EGCG supplement in respective diet. EGCG had no effect on feeding behavior in normal chow diet group. Increased daytime feeding induced by HFD was selectively corrected by EGCG treatment in HFD groups, including reversed food intake, feeding frequency and meal size in HFD + EGCG group, and reduced food intake and feeding frequency in DIO + EGCG group. Moreover, EGCG treatment altered diurnally oscillating expression pattern of key appetite-regulating genes, including AGRP, POMC, and CART, and key circadian genes Clock and Bmal1 in hypothalamus of DIO mice, indicating its central effect on feeding regulation.CONCLUSION:Our study demonstrates that EGCG supplement specifically counteracts daytime overeating induced by HFD in mice, suggesting its central role in regulating feeding behavior and energy homeostasis.

Nuclear ubiquitous casein and cyclin-dependent kinase substrate (NUCKS) is highly expressed in the brain and peripheral metabolic organs, and regulates transcription of a number of genes involved in insulin signalling. Whole-body depletion of NUCKS (NKO) in mice leads to obesity, glucose intolerance and insulin resistance. However, a tissue-specific contribution of NUCKS to the observed phenotypes remains unknown. Considering the pivotal roles of insulin signalling in the brain, especially in the hypothalamus, we examined the functions of hypothalamic NUCKS in the regulation of peripheral glucose metabolism. Insulin signalling in the hypothalamus was impaired in the NKO mice when insulin was delivered through intracerebroventricular injection. To validate the hypothalamic specificity, we crossed transgenic mice expressing Cre-recombinase under the Nkx2.1 promoter with floxed NUCKS mice to generate mice with hypothalamus-specific deletion of NUCKS (HNKO). We fed the HNKO and littermate control mice with a normal chow diet (NCD) and a high-fat diet (HFD), and assessed glucose tolerance, insulin tolerance and metabolic parameters. HNKO mice showed mild glucose intolerance under an NCD, but exacerbated obesity and insulin resistance phenotypes under an HFD. In addition, NUCKS regulated levels of insulin receptor in the brain. Unlike HNKO mice, mice with immune-cell-specific deletion of NUCKS (VNKO) did not develop obesity or insulin-resistant phenotypes under an HFD. These studies indicate that hypothalamic NUCKS plays an essential role in regulating glucose homoeostasis and insulin signalling in vivo.

OBJECTIVE:Although both insulin and glucagon are intimately involved in the regulation of glucose homeostasis, the intrinsic control of glucagon secretion, including the biogenesis and exocytosis of glucagon-containing granules, is far less understood compared with that of insulin. As Brefeldin A-inhibited guanine nucleotide exchange protein 3 (BIG3) is a negative regulator of insulin-granule biogenesis and insulin secretion, we investigated whether BIG3 plays any role in alpha-cells and glucagon secretion.METHODS:We examined the expression of BIG3 in islet cells by immuno-fluorescence and confocal microscopy, and measured glucagon production and secretion in BIG3-depleted and wild-type mice, islets and cells.RESULTS:BIG3 is highly expressed in pancreatic alpha-cells in addition to beta-cells, but is absent in delta-cells. Depletion of BIG3 in alpha-cells leads to elevated glucagon production and secretion. Consistently, BIG3-knockout (BKO) mice display increased glucagon release under hypoglycemic conditions.CONCLUSIONS:Together with our previous studies, the current data reveal a conserved role for BIG3 in regulating alpha- and beta-cell functions. We propose that BIG3 negatively regulates hormone production at the secretory granule biogenesis stage and that such regulatory mechanism may be used in secretory pathways of other endocrine cells.

Although much is known about the molecular players in insulin signaling, there is scant information about transcriptional regulation of its key components. We now find that NUCKS is a transcriptional regulator of the insulin signaling components, including the insulin receptor (IR). Knockdown of NUCKS leads to impaired insulin signaling in endocrine cells. NUCKS knockout mice exhibit decreased insulin signaling and increased body weight/fat mass along with impaired glucose tolerance and reduced insulin sensitivity, all of which are further exacerbated by a high-fat diet (HFD). Genome-wide ChIP-seq identifies metabolism and insulin signaling as NUCKS targets. Importantly, NUCKS is downregulated in individuals with a high body mass index and in HFD-fed mice, and conversely, its levels increase upon starvation. Altogether, NUCKS is a physiological regulator of energy homeostasis and glucose metabolism that works by regulating chromatin accessibility and RNA polymerase II recruitment to the promoters of IR and other insulin pathway modulators.