PUROMYCIN AMINONUCLEOSIDE INHIBITS MESANGIAL CELL-INDUCED CONTRACTION OF COLLAGEN GELS BY STIMULATING PRODUCTION OF REACTIVE OXYGEN SPECIES

Glomerular epithelial cell injury is thought to be the primary reason for the development of proteinuria in puromycin aminonucleoside nephrosis (PAN), the rat model of nephrotic syndrome. By comparison mesangial cells are considered resistant to the effects of puromycin. The purpose of the present study was to investigate whether puromycin in non cytotoxic concentrations caused mesangial cell dysfunction, with particular reference to cell-extracellular matrix interactions. Mesangial cells, when embedded in collagen gels, contract after exposure to minimal essential medium (MEM) containing fetal bovine serum (FBS). This contractility, measured by determining changes in area of the collagen gel, is inhibited by puromycin in a dose dependant manner from 2.5 mu g/ml to 160 mu g/ml. At these concentrations there is no alteration of cell viability as measured by the tetrazolium salt (MTT) method and trypan blue exclusion. Immunocytochemistry with rhodamine phalloidin reveals that actin filaments are not disrupted. The antioxidants, superoxide dismutase (SOD) and catalase as well as diphenylene iodonium (DPI), a flavoprotein inhibitor, not only counteracted the effect of puromycin on gel contraction, but also enhanced gel contraction when added to mesangial cells on their own. Aminotriazole, an inhibitor of endogenous catalase, inhibited mesangial cell-induced gel contraction in a dose dependent manner (5 mM to 40 mM), and this effect was completely reversed by addition of catalase. Mesangial cells preloaded with dihydrorhodamine and exposed to puromycin (5 mu g/ml to 160 mu g/ml) exhibited a dose dependent increase in rhodamine 123 fluorescence, indicating production of reactive oxygen species (ROS). This effect was blocked by the addition of DPI. We conclude that: (i) puromycin, in concentrations similar to those that cause glomerular epithelial cell changes in vitro, also inhibits mesangial cell-induced contractility in collagen gels; (ii) endogenous ROS production by mesangial cells inhibits their ability to contract collagen gels; and (iii) mesangial cells stimulated by puromycin produce increased amounts of ROS which causes inhibition of mesangial cell-collagen gel contraction. Thus mesangial cells may play a previously unrecognized role in the pathogenesis of PAN, either directly through ROS-induced mesangial cell dysfunction or indirectly through increased production of ROS and secondary damage to adjacent glomerular epithelial cells.