HNF1A deficiency causes reduced calcium levels, accumulation of abnormal insulin granules and uncoupled insulin to C-peptide secretion in a stem cell model of MODY3

Abstract Mutations in HNF1A cause Maturity Onset Diabetes of the Young type 3 (MODY3), the most prevalent form of monogenic diabetes. Using stem cell-derived pancreatic endocrine cells from human embryonic stem cells (hESCs) with induced hypomorphic mutations in HNF1A, we show that HNF1A orchestrates a transcriptional program required for calcium-dependent insulin secretion. HNF1A-deficient β-cells display a reduction in CACNA1A and intracellular calcium levels, as well as impaired insulin granule exocytosis in association with SYT13 down-regulation. Knockout of CACNA1A and SYT13 reproduce the relevant phenotypes. Retention of insulin is associated with accumulation of enlarged secretory granules, and altered stoichiometry of secreted insulin to C-peptide. Glibenclamide, a sulfonylurea drug used in the treatment of MODY3 patients, increases intracellular calcium, and thereby restores C-peptide and insulin secretion to a normal ratio. While insulin secretion defects are constitutive in cells with complete HNF1A loss of function, β-cells from patients with heterozygous hypomorphic HNF1A mutations are initially normal, but lose the ability to secrete insulin and acquire abnormal stoichiometric secretion ratios, while gene corrected cells remain normal. Our studies provide the molecular basis for the treatment of MODY3 with sulfonylureas, and demonstrate promise for the use of cell therapies for MODY3.