SAT-162 Hepatocyte Nuclear Factor-4α (HNF44α) as a Target to Treat DM

Abstract

Diabetes Mellitus (DM) is a metabolic disorder with multiple etiology and characterized by chronic hyperglycemia. It results from total (Type 1) or partial (Type 2) depletion of β cells, associated or not with insulin resistance (IR). Any Processes that promote the functional β-cell mass regeneration may be a target for DM treatment. HNF4α is an important transcription factor for pancreatic β cells because, beyond the control of the insulin gene, it regulates the expression of genes related to glucose metabolism, it is crucial in increasing beta cell mass in response to stress, such as in pregnancy and it is important to β-cell fate. However, little is known of its involvement in pancreatic β-cell apoptosis and regeneration. Based on the fact that HNF4α (1) participates in cell death processes, (2) controls processes of compensatory increase of β-cell mass, and (3) acts directly in regenerative processes, we aimed to unravel possible mechanisms, dependent of HNF4α, which can be used to treat Diabetes Mellitus. First we analyzed, in vitro , the consequence of HNF4α knockdown in human β-cell line EndoC-βH1 in the gene expression of several markers to islet-cell fate and in the cytokine-induced apoptosis. We observed that the siRNA for HNF4α reduced the expression of genes important to β-cell fate (PDX-1, NKX2.2, MAF-A, UCN-3 and KIR) and increased the expression of genes not-related with β-cell (NGN3, SOX9 and GLUCAGON). In additional, HNF4α knockdown prevented the cytokine-induced Caspase-3 cleavage in human EndoC-βH1 and rat INS-1E cell line. Then, we addressed our focus to the HNF4α ability to promote β-cell expansion in response to a metabolic demand. Here we investigated the HNF4α role in the IR-induced β-cell proliferation. We used WildType (C) and Knockout (K) animals for HNF4-alpha (HNF4α loxP/loxP;Ins.Cre ). After CRE-recombinase activation the induction of Knockout was confirmed by ipGTT. To induce an IR, animals C and K were treated (D) or not-treated (S) with 100 mg/kg of dexamethasone for 5 consecutive days. Then, we analyzed GSIS, pancreatic morphometry (IHC) and expression of genes involved in pancreatic islet cell proliferation/transdifferentiation. We observed that indeed Dexa induced an IR and a β-cell mass expansion in CD mice, which were not observed in KD mice. Moreover, Dexa induced, in CD mice, an increase in genes involved in islet-cell expansion (Glucagon, Somatostatin, PDX1, PAX4, HHEX, NGN3) and this increased were abolished in KD mice. So, we observed that HNF4α seems to be important in the β-cell fate since its knockdown induces a non-β-cell gene expression in a β-cell line. Moreover, HNF4α acts in the β-cell death process and is involved in the Dexa-induced β-cell mass expansion. Taking together, HNF4α may be a target to prevent β-cell apoptosis and to induce β-cell regeneration. Financial Support: FAPESC/CNPq/CAPES/FAPESP.