Hyaluronan and proximal tubular cell migration

Background. The ubiquitous polysaccharide hyaluronan has been associated with both acute renal injury and progressive renal disease. The aim of this study was to examine the effect of hyaluronan on proximal tubular cell migration. Methods. The proximal tubular cell line, HK-2 cells, were grown in monolayer culture, and cell migration following addition of hyaluronan characterized in an in vitro model of injury that we have previously developed and characterized. Results. Addition of well-defined preparations of exogenous hyaluronan increased cell migration; however, optimum enhancement of migration was seen with hyaluronan of high molecular weight. Activation of the mitogen-activated protein kinase (MAPK) signaling cascade, as assessed by increased expression of the dually phosphorylated active form of MAPK, could be demonstrated following addition of hyaluronan. This was blocked by the addition of a specific antibody to the hyaluronan receptor, CD44. Hyaluronan-dependent enhanced migration was also abrogated by addition the CD44 blocking antibody, and by inhibition of MAPK kinase (MEK) activity. Generation of a denuded area also led to increased synthesis of endogenous hyaluronan and activation of MAPK, and blockage of either CD44 or MAPK activation inhibited proximal tubule cell (PTC) migration and re-epithelialization under nonstimulated conditions. Conclusion. We have demonstrated that hyaluronan activation of the MAPK pathway through binding to its receptor CD44, enhances proximal tubule cell (PTC) migration. In addition, the results suggest that mechanical injury of PTC stimulated hyaluronan generation. These observations may have implications for both recovery from acute tubular injury and progressive renal fibrosis.