Sex-dependent additive effects of dorzagliatin and incretin on insulin secretion in a novel mouse model of GCK-MODY

Abstract

Glucokinase (GK) catalyses the key regulatory step in glucose-stimulated insulin secretion. Correspondingly, hetero- and homozygous mutations in human GCK cause maturity-onset diabetes of the young (GCK-MODY) and permanent neonatal diabetes (PNDM), respectively. To explore the possible utility of glucokinase activators (GKA) and of glucagon-like receptor-1 (GLP-1) agonists in these diseases, we have developed a novel hypomorphic Gck allele in mice encoding an aberrantly spliced mRNA deleted for exons 2 and 3. In islets from homozygous knock-in (GckKI/KI) mice, GK immunoreactivity was reduced by >85%, and glucose-stimulated insulin secretion eliminated. Homozygous GckKI/KI mice were smaller than wildtype littermates and displayed frank diabetes (fasting blood glucose >18 mmol/L; HbA1c [~]12%), ketosis and nephropathy. Heterozygous GckKI/+ mice were glucose intolerant (HbA1c [~]5.5%). Abnormal glucose-stimulated Ca2+ dynamics and beta cell-beta cell connectivity in GckKI/+ islets were completely reversed by the recently-developed GKA, dorzagliatin, which was largely inactive in homozygous GckKI/KI mouse islets. The GLP-1 receptor agonist exendin-4 improved glucose tolerance in male GckKI/+ mice, an action potentiated by dorzagliatin, in male but not female mice. Sex-dependent additive effects of these agents were also observed on insulin secretion in vitro. Combined treatment with GKA and incretin may thus be useful in GCK-MODY or GCK-PNDM. Article Highlightsa. Glucokinase deficiency can drive maturity-onset diabetes of the young (GCK-MODY; heterozygotes) and permanent neonatal diabetes (GCK-PNDM; homozygotes) b. We describe a hypomorphic Gck allele where aberrant splicing in islets lowers GK activity to by [~]85%. We use these mice to explore the effects of the glucokinase activator, dorzagliatin, and incretin on insulin secretion c. Whereas heterozygous mutant mice are mildly hyperglycemic, homozygotes have frank diabetes but survive to adulthood. Dorzagliatin potentiates the effects of GLP-1 receptor activation sex-dependently in heterozygotes d. Combined use of these drugs may be useful in some forms of GCK diabetes