Chymase increases glomerular albumin permeability via protease-activated receptor-2

Increased infiltration of the kidney by mast cells is associated with proteinuria, and interstitial fibrosis in various renal diseases. Mast cells produce serine proteases including tryptase and chymase (MCC) that act via protease-activated receptors (PARs) to induce synthesis of fibrogenic cytokines by renal cells. In the present study, we investigated direct effect of MCC and role of PARs on glomerular albumin permeability (P-alb). Isolated rat glomeruli were incubated with MCC (0.1, 1, 10, and 100 ng/ml) for 5-30 min in presence or absence of PAR-1 and PAR-2 blocking antibodies. P-alb was determined from the change in glomerular volume in response to an albumin oncotic gradient. The effect of direct activation of PARs on P-alb was verified by incubating glomeruli with synthetic hexapeptide known to activate PAR-1 and PAR-2. MCC increased P-alb of isolated rat glomeruli in a dose- and time-dependent manner. Blocking PAR-2 prevented MCC-mediated increase in P-alb. RT-PCR analysis of glomerular RNA demonstrated the presence of constitutively expressed PAR-1, -2, and -3 and low levels of PAR-4. In addition, direct activation of PAR-2 by hexapeptide SLIGKV increased P-alb comparable to MCC, whereas PAR-1 activation by TFLLRN had no effect on P-alb. Our results document that MCC induces increase in P-alb and that this effect is mediated through PAR-2. MCC may also play a role in renal scarring. We propose that inhibiting MCC activity or blocking the activation of PAR-2 may provide new targets for therapy in renal diseases.