Enhanced Expression of the Cytoskeletal-Associated Protein, Paxillin, in Experimental Nephrotic Syndrome

Background In the model of aminonucleoside of Puromycin (PAN)-induced nephrotic syndrome we assessed changes in glomerular expression of three proteins that regulate cell adhesion to extracellular matrix: paxillin, focal adhesion kinase (FAK), and Rho. Methods Following a single intravenous injection of PAN in Sprague-Dawley rats, proteinuria ensued and glomeruli were isolated at three stages: prior to onset of proteinuria (days 1 and 2), and when proteinuria peaked (day 9), subsided (day 29) or resolved (day 35). Glomerular protein lysates were analyzed by Western blot for expression of paxillin, FAK, and Rho. Results There was a progressive increase in glomerular paxillin level that peaked concomitantly with heavy proteinuria (day 9). Paxillin remained increased during the recovery phase of PAN-induced injury and when proteinuria resolved. Expression of FAK and Rho remained unchanged at all time points. To explore whether the increase in paxillin expression following administration of PAN was due to a direct effect on glomerular epithelial cells (GEC), cultured rat GECs were incubated with PAN for 3, 6, and 24 hours, and expression of paxillin was assessed in GEC lysates by Western blot analysis. No change in paxillin levels was observed. Conclusions In PAN-induced nephrotic syndrome there is a preferential increase in paxillin expression that cannot be accouted for by an effect of PAN on GEC paxillin synthesis. We propose that the enhanced paxillin synthesis in the course of PAN-induced GEC injury reflects perturbations in contact between GEC and the GBM and may play a role in regulating adherence of GEC to the GBM. (Journal Investig Med 1998;46:284-289)