Microvillar injury in renal tubular epithelial cells induced by calcium oxalate crystal and the protective role of epigallocatechin-3-gallate

Pathogenic mechanisms of kidney stone disease remained unclear. This study investigated its initial cellular/molecular mechanisms when calcium oxalate monohydrate (COM) crystal adhered to renal tubular cells. Transmission electron microscopy revealed decreased length and density of microvilli, whereas Western blot analysis showed that whole-cell ezrin (a microvillus-stabilizing protein), not beta-actin, was decreased in COM-treated cells. Immunofluorescence staining, followed by laser-scanning confocal microscopy and subcellular fractionations, revealed decreases in both ezrin and F-/beta-actin at apical membrane. Cytoskeletal extraction by Triton X-100 showed reduced cytoskeleton-associated ezrin, consistent with colocalization data of ezrin/F-actin. Thr(567)-phosphorylated ezrin and RhoA increased in COM-treated cells. A protein oxidation blot assay showed an increase in oxidized proteins in COM-treated cells that could be prevented by epigallocatechin-3-gallate (EGCG), which also preserved the whole-cell ezrin level, stabilized apical membrane ezrin/F-actin colocalization, and maintained microvillar structure in COM-treated and H2O2-treated cells. Our data clearly demonstrated the reduction of ezrin and actin expression at the apical membrane of COM-treated cells, most likely because of oxidative stress, which could be prevented by EGCG. These findings provide a novel approach to better understanding of the pathogenesis of kidney stone disease in its initial phase and offer potential preventive strategy against microvillar injury induced by COM crystals in patients with kidney stones.-Fong-ngern, K., Vinaiphat, A., Thongboonkerd, V. Microvillar injury in renal tubular epithelial cells induced by calcium oxalate crystal and the protective role of epigallocatechin-3-gallate.