Role of calcium in lipopolysaccharide-induced calcitonin gene expression in human adipocytes

Abstract

Severe systemic infections induce ubiquitous calcitonin (CALC) gene expression with release of calcitonin peptides, namely procalcitonin, calcitonin gene-related peptide and adrenomedullin. Using an in vitro model for bacterial infection, we tested the hypothesis that intracellular calcium concentration ([Ca2+]i) is elevated after lipopolysaccharide (LPS) stimulation and is responsible for the LPS-mediated increase in CALC gene expression and protein secretion. In our human adipocyte model, LPS did not show any cytotoxic effects and induced increased CALC-I gene mRNA expression. Additionally, LPS provoked an elevation in [Ca2+]i. The LPS-induced increase in CALC-I gene mRNA was partially blocked with verapamil, an L-type calcium channel blocker and blocked almost completely with 2-aminoethoxydiphenyl borate, a blocker of store-operated calcium entry and inositol triphosphate-mediated calcium release. Treatment of cells with substances elevating [Ca2+] i led to an increased CALC-I mRNA expression level. The combination of LPS with substances raising [Ca2+]i even potentiated this increase. At the same time, elevated [Ca2+]i attenuated the expression level of the CALC-V gene. These findings indicate that, in human adipocytes, changes in [Ca2+]i are involved in LPSregulated expression of CALC genes, thereby strengthening previous findings postulating a crucial role of intracellular calcium homeostasis in the state of bacterial infection and sepsis.