Short-chain 3-hydroxyacyl-CoA dehydrogenase is a negative regulator of insulin secretion in response to fuel and non-fuel stimuli in INS832/13 β-cells

Background: Hyperinsulinemia associated with non-ketotic hypoglycemia is observed in patients with mutated beta-oxidation enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase (HADHSC). In the present study, we investigated the mechanism underlying HADHSC-mediated regulation of insulin secretion. Methods: Knockdown of HADHSC expression by RNA interference in INS832/13 beta-cells was achieved using short hairpin RNA and short interference RNA. Results: Knockdown of HADHSC increased both fuel-(glucose or leucine plus glutamine) and non-fuel (high KCl)-induced insulin secretion. Enhanced glucose-stimulated insulin secretion (GSIS) induced by HADHSC knockdown was independent of changes in cytosolic Ca2+ and also occurred in the presence of fatty acids. L-Carnitine, used in the formation of acyl-carnitine compounds, increased GSIS in control cells, but was unable to further increase the augmented GSIS in HADHSC-knockdown cells. The pan transaminase inhibitor amino-oxyacetate reversed HADHSC knockdown-mediated increases in GSIS. Oxidation of [1-C-14]-palmitate and -octanoate was not reduced in HADHSC-knockdown cells. L-3-Hydroxybutyryl-carnitine (tested using its precursor L-3-hydroxybutyrate) and L-3-hydroxyglutarate, which accumulate in blood and urine, respectively, of HADHSC-deficient patients, did not change insulin secretion. Conclusions: Insulin secretion promoted by both fuel and non-fuel stimuli is negatively regulated by HADHSC. Enhanced secretion after HADHSC knockdown is not due to inhibition of fatty acid oxidation causing an accumulation of long-chain fatty acids or their CoA derivatives. L-3-Hydroxybutyrate and L-3-ydroxyglutarate do not mediate enhanced secretion caused by reduced HADHSC activity. Transamination reaction(s) and the formation of short-chain acylcarnitines and CoAs may be implicated in the mechanism whereby HADHSC deficiency results in enhanced insulin secretion and hyperinsulinemia.