A Novel Mediator of Arsenic-Induced Pancreatic Beta-Cell Dysfunction

With up to 140 million people living above arsenic (AS)-contaminated groundwater, AS exposure presents a major health risk worldwide. Studies have revealed a positive correlation between AS exposure and diabetes, where those suffering from symptoms of chronic AS toxicity have 5-6 times the local rates of diabetes. Recent mouse models of AS exposure suggested that this form of diabetes may be mediated by pancreatic β-cell dysfunction. To evaluate this possibility, the MIN6-K8 mouse β-cell line was utilized as a model. Three days of physiologically-relevant AS exposure decreased glucose-induced insulin secretion (GIIS) without effects on basal secretion. Three days of exposure to 1 µM AS decreased GIIS more than 60% without effects on cell count, total protein, total DNA, mitochondrial mass, or O₂ consumption. RNAseq analysis of AS-exposed MIN6-K8 cells revealed 3 significantly regulated genes previously unassociated with β-cell function.

Each gene was individually knocked down by siRNA in the presence of AS. Knockdown of one of these genes, UDP-glucuronosyltransferase 1a6a (Ugt1a6a), partially recovered GIIS in AS-exposed cells. Ugt1a6a is a phase 2 detoxification enzyme for the conjugation of small aromatic compounds. The precursor and rate-limiting factor for serotonin production, 5-hydroxytryptophan (5-HTP), a known target of Ugt1a6a and modulator of GIIS, was decreased following AS exposure. Therefore, the AS-mediated increase in Ugt1a6a expression may deplete serotonin, and secondarily 5-HTP, decreasing GIIS. This work introduces a gene with a novel role in β-cell physiology and arsenic-mediated pathology.