IMPAIRMENT BY INTERLEUKIN 1-BETA AND TUMOUR NECROSIS FACTOR A OF THE GLUCAGON-INDUCED INCREASE IN PHOSPHOENOLPYRUVATE CARBOXYKINASE GENE EXPRESSION AND GLUCONEOGENESIS IN CULTURED RAT HEPATOCYTES

摘要

The influence of the inflammatory mediators interleukin 1 beta (IL1 beta) and tumour necrosis factor alpha (TNF alpha) on the glucagon-induced expression of phosphoenolpyruvate carboxykinase (PCK) and on glucose formation via gluconeogenesis was investigated in cultured rat hepatocytes. Gene expression was monitored by determination of mRNA levels and of enzyme activity. Glucose formation was estimated with newly synthesized radioactive glucose derived from a radiolabelled lactate precursor. Glucagon (0.1 or 1 nM) induced PCK mRNA transiently to a maximum 2 h after its application. In the presence of recombinant human (rh) IL1 beta or rhTNF alpha the increase in PCK mRNA levels was totally inhibited at 0.1 nM glucagon, whereas at 1 nM glucagon the maximal increase was inhibited by only 25%. Glucagon (0.1 or 1 nM) induced PCK activity to a maximum after 4 h (4-fold and 6-fold over prestimulatory activity respectively). In the presence of rhIL1 beta or rhTNF alpha the maximal increase was inhibited by approx. 50%. Addition of rhIL1 beta or rhTNF alpha 2 h after glucagon at the maximal glucagon-induced PCK mRNA levels, accelerated the decay of PCK mRNA. Glucagon (0.1 or 1 nM) increased glucose formation from lactate by 1.3-fold and 1.7-fold respectively over unstimulated rates. In the presence of rhIL1 beta or rhTNF alpha, this increase in glucose formation was inhibited by 60-90%. At 0.1 nM, glucagon doubled the intracellular cAMP concentration. This increase was prevented by rhIL1 beta or rhTNF alpha. At 1 nM, glucagon increased cAMP concentrations by in-fold. In the presence of rhIL1 beta or rhTNF alpha this increase was inhibited by 70 %. From the results it is suggested that rhIL1 beta and rhTNF alpha prevented glucagon-stimulated PCK gene expression and gluconeogenesis at least in part by inhibition of the glucagon-stimulated increase in cAMP concentrations.