Importance of lactate dehydrogenase for the regulation of glycolytic flux and insulin secretion in insulin-producing cells

• Published in: Biochemical journal Vol. 352 Pt 2; no. 2; pp. 373 - 380
• Main Authors: Alcazar, O, Tiedge, M, Lenzen, S
• Format: Journal Article
• Language: English
• Published: England 01.12.2000
• Subjects: Base Sequence; DNA Primers; Glucose - metabolism; Glycolysis; Insulin - metabolism; Insulin Secretion; Islets of Langerhans - drug effects; Islets of Langerhans - enzymology; Islets of Langerhans - metabolism; L-Lactate Dehydrogenase - metabolism; Lactic Acid - biosynthesis; Lactic Acid - pharmacology; Pyruvic Acid - pharmacology
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3520373

The role of lactate dehydrogenase (LDH) in the generation of the metabolic signal for insulin secretion was studied after stable overexpression in INS-1 and RINm5F insulin-producing cells. INS-1 cells with a 25-fold overexpression of LDH-A, the highest level achieved, showed a 20-30% decrease in the glucose oxidation rate at glucose concentrations above 5 mM when compared with control cells, whereas values were unchanged at lower glucose concentrations. Lactate release increased in parallel with a decrease in the glucose oxidation rate. However, the INS-1 cell glucose-induced insulin secretory response, together with the rate of glucose utilization, were not significantly affected by LDH-A overexpression. Despite 3-fold overexpression of LDH-A in glucose-unresponsive RINm5F cells, there was no change in insulin secretion, glucose metabolism or lactate production in these cells. Exogenously added pyruvate and lactate potentiated glucose-stimulated insulin secretion in INS-1 cells, an effect that was abolished after LDH-A overexpression. Both compounds significantly decreased glucose oxidation rates in control cells. After overexpression of LDH-A in INS-1 cells, the effects of pyruvate and lactate on glucose oxidation were diminished. On the other hand, after LDH-A overexpression, both glycolytic metabolites decreased the glucose utilization rate at 5 mM glucose. The present data suggest that the level of LDH expression in insulin-secreting cells is critical for correct channelling of pyruvate towards mitochondrial metabolism. Interestingly, glucokinase-mediated glycolytic flux was decreased after LDH-A overexpression. Thus preferential channelling of glucose towards aerobic metabolism by glucokinase may be determined, at least in part, by the low level of constitutive expression of LDH-A in pancreatic beta-cells. In conclusion, the level of LDH expression in insulin-secreting cells is an important determinant of the physiological insulin-secretory capacity, and also determines how pyruvate and lactate affect insulin secretion.