Metabolic activation-driven mitochondrial hyperpolarization predicts insulin secretion in human pancreatic beta-cells

Abstract

Mitochondrial metabolism plays a central role in insulin secretion in pancreatic beta-cells. Generation of protonmotive force and ATP synthesis from glucose-originated pyruvate are critical steps in the canonical pathway of glucose-stimulated insulin secretion. Mitochondrial metabolism is intertwined with pathways that are thought to amplify insulin secretion with mechanisms distinct from the canonical pathway, and the relative importance of these two pathways is controversial. Here I show that glucose-induced mitochondrial membrane potential (MMP) hyperpolarization is necessary for, and predicts, the rate of insulin secretion in primary cultured human beta-cells. When glucose concentration is elevated, increased metabolism results in a substantial MMP hyperpolarization, as well as in increased rates of ATP synthesis and turnover marked by faster cell respiration. Using modular kinetic analysis I explored what properties of cellular energy metabolism enable a large glucose-induced change in MMP in human beta-cells. I found that an ATP-dependent pathway activates glucose or substrate oxidation, acting as a positive feedback in energy metabolism. This activation mechanism is essential for concomitant fast respiration and high MMP, and for a high magnitude glucose-induced MMP hyperpolarization and therefore for insulin secretion.

Mitochondrial Superoxide Production Decreases on Glucose-Stimulated Insulin Secretion in Pancreatic β Cells Due to Decreasing Mitochondrial Matrix NADH/NAD+Ratio

“…Glucose-induced decrease in J m rates was also observed in the presence of etomoxir (Fig. 4A) (24), AOA (of a lower extent) ( Supplementary Fig. S2Cc), and when the malate/ aspartate shuttle (Fig.…”

Functional changes in beta cells during ageing and senescence

“…Other studies have provided supporting evidence for ageassociated changes in important components of the stimulussecretion coupling mechanism, such as a decline in the coordination of calcium dynamics, gap junction coupling and insulin secretion with age in humans [11]. Another key player of insulin secretion is mitochondrial activity, which is impaired in aged human islets as measured by NADPH fluorescence lifetime imaging [10,23]. A study performed in single human beta cells suggested that the mechanistic deficit underlying changes in mitochondrial activity is located upstream of the citric acid cycle (CAC), thus altering the control of mitochondrial membrane potential [24].…”

Glucose-Induced Expression of DAPIT in Pancreatic β-Cells

“…As we demonstrated in INS-1E cells, expression of the DAPIT and other F O subunits determined the intensity of ATP synthesis. The latter is indicated by the V 3 / V 4 ratio, increases with the increasing glucose from insulin non-stimulating (3 mM) to insulin stimulating concentration (>8 mM) [ 11 , 12 , 14 , 15 , 16 ]. However, as we now show, this does not proceed in DAPIT-deficient cells.…”

“…Another peculiar aspect of the pancreatic β-cell glucose sensor is the steepness of the related dose–response, i.e., insulin release dependence vs. glucose concentration [ 11 , 12 , 14 , 15 , 16 ]. The revealed narrowing of mitochondrial cristae may hypothetically contribute to this steepness, such as observed in INS-1E cells during GSIS [ 17 ] or upon the increased load of cell-permeant Krebs cycle substrate [ 18 , 19 ].…”