Differential effects of simvastatin on mesangial cells

Background. Statins are increasingly recognized as mediators of direct cellular effects independent of their lipid lowering capacity. Therefore, the time and concentration dependence of various statin-mediated cellular alterations was compared in renal mesangial cells. Methods. The effects of statins on cell proliferation, gene expression, cytoskeletal alterations, apoptosis, and cytotoxicity were analyzed in cultured mesangial cells using standard techniques. Results. Simvastatin and lovastatin decreased proliferation and cell number of rat mesangial cells concentration-dependently. Concurrently, the expression of the fibrogenic protein connective tissue growth factor (CTGF) was impaired and actin stress fibers, which are typical of mesangial cells in culture, became disassembled by simvastatin. A decrease of the posttranslational modification of RhoA by geranylgeranyl moieties was detected, supporting a role for RhoA as mediator of statin effects. Induction of apoptosis, determined by activation of caspase-3 and DNA fragmentation, and necrosis only occurred at later time points, when the morphology of the cells was strongly altered and the cells detached from the surface due to changes in the actin cytoskeleton. Basically, the same results were obtained with a human mesangial cell line. Furthermore, statin effects were mimicked by inhibition of the geranylgeranyltransferase. Conclusion. Most of the cellular effects of the lipophilic statins occurred within the same time and concentration range, suggesting a common molecular mechanism. Only apoptosis and necrosis were observed at later time points or with higher concentrations of simvastatin and thus seem to be secondary to the changes in gene expression and alterations of the actin cytoskeleton.