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Laminar shear stress induces gene expression via Ca2+ independent pathways in renal IMCD tubular epithelia

Abundant evidence exists demonstrating that laminar shear stress (LSS) raises intracellular calcium ([Ca2+]i) in renal epithelial cells. We hypothesized, as has been shown in endothelial cells (ECs) for monocyte chemoattractant protein‐1 (MCP‐1) and cyclooxygenase‐2 (ptgs‐2), that LSS also induces gene expression via Ca independent pathways in renal tubular epithelia. Immortalized murine inner medullary collecting duct (IMCD) cells were grown to confluence, placed in a laminar flow chamber, exposed to a LSS of 0.4 dynes/cm2, and collected for RNA or cellular protein lysate for RT‐PCR and Western blotting, respectively. We found abundant MCP‐1 and ptgs‐2 mRNA in IMCD cells subjected to LSS and it exceeded that detected in static controls. Treatment of IMCD cells with BAPTA‐AM, a [Ca2+]i chelator, or colchicine, an inhibitor of tubulin polymerization, inhibited ptgs‐2 mRNA induction but did not effect LSS induced MCP‐1 mRNA. This suggested that ptgs‐2, but not MCP‐1, is induced by a Ca2+‐dependent process. Western blotting of sheared and static IMCD cells for phosphorylated extracellular regulated kinase (pERK) showed that sheared cells expressed more pERK than static cells. Inhibition of pERK by PD98059 prevented LSS induced MCP‐1 mRNA. Thus, LSS induces MCP‐1 mRNA via a Ca2+–independent pERK‐dependent pathway in IMCD cells.