Coordinate Changes in Histone Modifications, mRNA Levels, and Metabolite Profiles in Clonal INS-1 832/13 β-Cells Accompany Functional Adaptations to Lipotoxicity

Abstract

Background: Epigenetic regulation may mediate lipotoxic effects on ␤-cells in type 2 diabetes. Results: Lipotoxicity impairs insulin secretion, and alters metabolism, gene expression, and histone marks in INS-1 832/13 ␤-cells. Conclusion: Perturbed insulin secretion results from epigenetic, genetic, and metabolic adaptations to increased fatty acid metabolism in ␤-cells. Significance: Elucidation of the link between lipotoxicity and insulin secretion is crucial for understanding the pathogenesis of type 2 diabetes.

The Pancreatic β-Cell: A Bioenergetic Perspective

“…In low glucose, INS-1 832/13 cells oxidized labeled palmitate to CO 2 at rates of 0.2-0.4 nmol·min Ϫ1 ·mg protein Ϫ1 (279,332,407). These rates are comparable to those for the utilization of 2.8 mM glucose by these cells (332).…”

“…While the authors found a fivefold increase in glutamate within 30 min in INS-1E cells and human islets, other workers (49,314) found no correlation between islet glutamate levels and insulin secretion with a variety of secretagogues, while metabolite profiling of INS-1 832/13 cells showed no significant change in whole cell glutamate levels between low and high glucose (332). The reason for these discrepancies is unclear.…”

“…Although lipolysis correlates with insulin secretion, ␤-oxidation shows an inverse correlation. As in other cell types, ␤-oxidation is inhibited in high glucose, via activation of Ac-CoA carboxylase, generation of malonyl-CoA and consequent inhibition of carnitine-palmitoyl transferase-1 (CPT-1) (85,332,407,456).…”

“…The free, unbound, fatty acid concentration under these conditions is only ϳ10 -20 nM (105,442). While the need for albumin binding is generally appreciated in the literature, molar ratios of 6:1 or even higher have been employed in vitro (144,285,332,472), producing unbound fatty acid concentrations close to 1 M, or 100 times higher than the normal physiological range (FIGURE 8A). One concern in such studies is the possibility that excessive fatty acid exposure in vitro may produce artifactual changes in metabolism, for example, due to nonspecific mitochondrial uncoupling (269,277), that might mask a physiologically relevant positive signaling or bioenergetic effect.…”

“…In low glucose, INS-1 832/13 cells oxidized labeled palmitate to CO 2 at rates of 0.2-0.4 nmol·min Ϫ1 ·mg protein Ϫ1 (279,332,407). These rates are comparable to those for the utilization of 2.8 mM glucose by these cells (332). It should be noted that INS-1 832/13 cells can produce acetoacetylCoA and utilize ␤-hydroxybutyrate and acetoacetate (318,320), raising the possibility that ketone bodies could be produced by ␤-oxidation, in which case label from 14 Clabeled palmitate would not be liberated stoichiometrically as 14 CO 2 .…”