Project description:The counterregulatory response to hypoglycemia, which restores normal blood glucose levels to ensure sufficient provision of glucose to the brain, is critical for survival. To discover underlying brain regulatory systems, we performed a genetic screen in recombinant inbred mice for quantitative trait loci (QTL) controlling glucagon secretion in response to neuroglucopenia. We identified a QTL on the distal part of chromosome 7 and combined this genetic information with transcriptomic analysis of hypothalami. This revealed Fgf15 as the strongest candidate to control the glucagon response. Fgf15 was found to be expressed by neurons of the dorsomedial hypothalamus and the perifornical area. Intracerebroventricular injection of FGF19, the human ortholog of Fgf15, reduced activation by neuroglucopenia of dorsal vagal complex neurons and of the parasympathetic nerve, leading to a lower glucagon secretion. These data show that Fgf15 in hypothalamic neurons is a regulator of vagal nerve activity in response to neuroglucopenia.
Project description:Mouse FGF15 and human FGF19 are orthologous proteins that regulate bile acid metabolism. However, other hepatic functions of FGF15/19 are not well characterized.
Project description:Lysosome-mediated macroautophagy, including lipophagy, is activated under nutrient deprivation but is repressed after feeding. We show that feeding unexpectedly activates intestinal lipophagy in a manner dependent on both the orphan nuclear receptor, small heterodimer partner (SHP/NR0B2), and the late fed-state gut hormone, fibroblast growth factor-15/19 (FGF15/19). Postprandial intestinal triglycerides (TGs) and apolipoprotein-B48 (ApoB48), the TG-rich chylomicron marker, were elevated in SHP-knockout and FGF15-knockout mice. Genomic analyses in mouse intestine revealed that SHP partners with the key lysosomal activator, transcription factor-EB (TFEB), upregulating autophagy/lipolysis network genes after feeding. In HT29 intestinal cells, FGF19 treatment activated lipophagy in a manner dependent on both SHP and TFEB, reducing TG and ApoB48 levels. Mechanistically, feeding-induced FGF15/19 signaling increases nuclear localization of TFEB and SHP via PKCβ/ζ-mediated phosphorylation, leading to transcriptional induction of Ulk1 and Atgl. Collectively, these results demonstrate that after feeding, FGF15/19-activated SHP and TFEB paradoxically activate gut lipophagy, limiting postprandial TG levels. As excess lipids cause dyslipidemia and obesity, the FGF15/19-SHP-TFEB axis that reduces intestinal TGs via lipophagic activation provides promising therapeutic targets for obesity-associated metabolic disease.
Project description:Hepatic lipogenesis is normally tightly regulated but is aberrantly elevated in obesity. Fibroblast Growth Factor-19 (FGF19, mouse FGF15) is a late fed-state gut hormone that decreases hepatic lipid levels by unclear mechanisms. We examined whether FGF15/19 and FGF15/19-activated Small Heterodimer Partner (SHP/NR0B2) have a role in transcriptional repression of lipogenesis. Comparative genomic analyses reveal that most of the SHP cistrome, including lipogenic genes repressed by FGF19, have overlapping CpG islands. FGF19 treatment or SHP overexpression in mice inhibits lipogenesis in a DNA methyltransferase-3a (DNMT3A)-dependent manner. FGF19-mediated activation of SHP via phosphorylation recruits DNMT3A to lipogenic genes, leading to DNA methylation and gene repression. In non-alcoholic fatty liver disease (NAFLD) patients and obese mice, occupancy of SHP and DNMT3A and DNA methylation at lipogenic genes are low, with elevated gene expression. These results demonstrate that FGF15/19 represses hepatic lipogenesis by activating SHP and DNMT3A physiologically, which is likely dysregulated in NAFLD.
Project description:Mouse FGF15 and human FGF19 are orthologous proteins that regulate bile acid metabolism. However, other hepatic functions of FGF15/19 are not well characterized. We used microarrays to analyze global hepatic gene expression in mice administered FGF15 or FGF19. Total liver RNA was isolated from wild-type mice administered vehicle, purified FGF15 or recombinant FGF19 for 6 hr via a jugular vein injection as described (Inagaki et al., 2005). Mice did not have access to food throughout the 6 hr treatment, and livers were harvested and immediately frozen in liquid nitrogen. Microarray analyses were performed using the Mouse Genome 430A 2.0 array.
Project description:Inappropriate glucagon secretion deteriorates glycemic control in type 1 and type 2 diabetes. While insulin is known to regulate glucagon secretion via its receptor in alpha cells, the role of downstream proteins and signaling pathways underlying the actions of insulin are not fully defined. Using in vivo (knockout) and in vitro (knockdown) studies targeting insulin receptor substrate (IRS) proteins, we compared the relative roles of IRS1 versus IRS2 in regulating alpha cell function. Alpha cell-specific IRS1 knock out (alpha IRS1KO) mice exhibit glucose intolerance and inappropriate glucagon suppression during glucose-tolerance tests. In contrast, alpha cell-specific IRS2 knock outs (alpha IRS2KO) manifest normal glucose tolerance and suppression of glucagon secretion after glucose administration. Alpha cell lines with stable knockdown of IRS1 (alpha IRS1KD) are unable to repress glucagon mRNA expression and exhibit reduction in phosphorylation of AKT. However, glucagon mRNA expression was suppressed in response to insulin stimulation in a stable IRS2 knock down alpha cell line (alpha IRS2KD). Alpha IRS1KD cells also display suppressed global protein translation including glucagon, impaired cytoplasmic Ca2+ response and mitochondrial function. These data argue for IRS1 as a dominant regulator of pancreatic alpha cell function.
Project description:This SuperSeries is composed of the following subset Series: GSE11240: An RNAi Screen of Chromatin Proteins Identifies Tip60-p400 as a Regulator of Embryonic Stem Cell Identity, Experiment A GSE11241: An RNAi Screen of Chromatin Proteins Identifies Tip60-p400 as a Regulator of Embryonic Stem Cell Identity, Experiment B Keywords: SuperSeries Refer to individual Series