Glucokinase activation is beneficial or toxic to cultured rat pancreatic islets depending on the prevailing glucose concentration

Abstract

Roma LP, Duprez J, Jonas JC. Glucokinase activation is beneficial or toxic to cultured rat pancreatic islets depending on the prevailing glucose concentration. Am J Physiol Endocrinol Metab 309: E632-E639, 2015. First published August 11, 2015; doi:10.1152/ajpendo.00154.2015.-In rat pancreatic islets, ␤-cell gene expression, survival, and subsequent acute glucose stimulation of insulin secretion (GSIS) are optimally preserved by prolonged culture at 10 mM glucose (G10) and markedly altered by culture at G5 or G30. Here, we tested whether pharmacological glucokinase (GK) activation prevents these alterations during culture or improves GSIS after culture. Rat pancreatic islets were cultured 1-7 days at G5, G10, or G30 with or without 3 M of the GK activator Ro 28-0450 (Ro). After culture, ␤-cell apoptosis and islet gene mRNA levels were measured, and the acute glucose-induced increase in NAD(P)H autofluorescence, intracellular calcium concentration, and insulin secretion were tested in the absence or presence of Ro. Prolonged culture of rat islets at G5 or G30 instead of G10 triggered ␤-cell apoptosis and reduced their glucose responsiveness. Addition of Ro during culture differently affected ␤-cell survival and glucose responsiveness depending on the glucose concentration during culture: it was beneficial to ␤-cell survival and function at G5, detrimental at G10, and ineffective at G30. In contrast, acute GK activation with Ro increased the glucose sensitivity of islets cultured at G10 but failed at restoring ␤-cell glucose responsiveness after culture at G5 or G30. We conclude that pharmacological GK activation prevents the alteration of ␤-cell survival and function by long-term culture at G5 but mimics glucotoxicity when added to G10. The complex effects of glucose on the ␤-cell phenotype result from changes in glucose metabolism and not from an effect of glucose per se. apoptosis; glucotoxicity; insulin secretion; pancreatic ␤-cell GLUCOSE STIMULATION OF INSULIN SECRETION (GSIS) by endocrine pancreatic ␤-cells depends on the acceleration of glucose metabolism through glycolysis and the TCA cycle, with enhanced production of metabolic coupling factors (25,39,41). Besides these rapid effects, glucose exerts complex long-term effects on the ␤-cell phenotype (2,10,16,18,27,45). During long-term culture of rodent islets, ␤-cell gene expression, survival, and glucose responsiveness are optimally preserved in the presence of 10 mM glucose (G10), whereas they are markedly altered by culture at either nonstimulating (G5) or very high (G30) glucose concentrations. In other words, culture at G10 vs. G5 is beneficial, whereas culture at G30 vs. G10 is detrimental to ␤-cell gene expression, survival, and glucose responsiveness. The beneficial effect of culture at G10 vs. G5 is usually attributed to the stimulation of energetic metabolism. In contrast, the deleterious effects of culture at G30 vs. G10, which we later refer to as glucotoxicity, could result from the further increase in metabolism with increased production o...

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