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Habenular Tcf7l2 links nicotine addiction to diabetes

ABSTRACT: Nicotine contained in tobacco smoke increases blood glucose levels in humans, and the risk of developing diabetes is dramatically increased in habitual smokers. Little is currently known about how nicotine increases blood glucose levels or the relevance of this action to either the persistence of the smoking habit or the pathophysiology of diabetes in smokers. Here, we show that the diabetes-associated gene Tcf7l2 is highly expressed in the medial habenula (mHb), where it regulates the function of local nicotinic acetylcholine receptors. We find that Tcf7l2 mutant (Tcf7l2mut) rats consume far greater quantities of nicotine than wild-type rats. Similarly, CRISPR-mediated cleavage of wild-type Tcf7l2 in the mHb increases nicotine intake in mice. Polysynaptic tracing identified a connection from the mHb to the pancreas, and nicotine-induced activation of the mHb elevates blood glucose. This effect is mimicked by chemogenetic stimulation of the mHb and blocked by Tcf7l2 knockdown in mHb. A history of nicotine consumption elevates circulating levels of the pancreas-derived hormones glucagon and insulin and precipitates diabetes-like dysregulation of blood glucose homeostasis in wild-type rats, whereas Tcf7l2mut rats are resistant to these actions of nicotine. Our findings suggest that Tcf7l2 regulates the stimulatory actions of nicotine on the habenula-pancreas axis, linkings the addictive properties of nicotine to its diabetes-promoting actions.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE137118 | GEO | 2019/09/10

REPOSITORIES: GEO

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Project description:TCF7L2 is one of the strongest type 2 diabetes (T2DM) candidate genes to emerge from GWAS studies, but the mechanisms by which it regulates the pathways which are important in the pathogenesis of type 2 diabetes are unknown. Previous in vitro and in vivo studies have focused on the link between TCF7L2 and insulin secretion as an explanation for the association between TCF7L2 and T2DM. However, TCF7L2 and the Wnt/β-catenin pathway are important for metabolic zonation in the liver. This raises the interesting possibility that TCF7L2 may influence glucose homeostasis by regulating hepatic glucose production (HGP). To examine this question, we utilized the H4IIE cell as a model of HGP. Inhibition of HGP in H4IIE cells from lactate and pyruvate was highly sensitive to physiological concentrations of insulin and metformin. Silencing of TCF7L2 protein expression induced a 5-fold increase in basal HGP (P<0.0001), and this was accompanied by marked increase in the expression of several key gluconeogenic genes. FBPase, PEPCK and G6Pase mRNA were up-regulated 2.5-fold (P<0.0001), 1.4-fold (P<0.01) and 2.3-fold (P<0.0001), respectively, compared to scramble siRNA. Compared to their respective baseline values, insulin and metformin suppressed HGP equally in the scramble and TCF7L2 siRNA cells, but HGP remained elevated in TCF7L2 silenced cells due to the increased baseline HGP. Using chromatin immunoprecipitation sequencing (ChIP-Seq), we investigated the direct transcriptional targets of TCF7L2 in hepatocytes. A total of 2119 ChIP peaks were detected, of which 36% were located inside gene boundaries and, overall, a total of 65% of all binding events were within 50 Kb of a gene. De novo motif analysis revealed remarkable conservation of the long and short TCF7L2 consensus binding sites in the rat hepatocytes. Pathway analysis showed that the top two disease categories over-represented in our dataset were “non-insulin dependent diabetes” (155 genes; P = 1.63 x 10-10) and “diabetes mellitus” (245 genes; P = 7.4 x 10-12). Inspection of genes in these categories revealed that TCF7L2 directly binds to multiple genes important in the regulation of glucose metabolism in the liver, including PEPCK, FBP1, IRS1, IRS2, AKT2 ADIPOR1, PDK4 and CPT1A. Our findings suggest a novel mechanism for the regulation of HGP by TCF7L2, and provide a possible explanation for the association of TCF7L2 polymorphisms with the incidence of T2DM. two samples: TCF7L2 ChIP-Seq and Input DNA

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Habenular Tcf7l2 links nicotine addiction to diabetes

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