Circulating levels of matrix metalloproteinases MMP-3 and MMP-2 in renal transplant recipients with chronic transplant nephropathy.

BACKGROUND: Chronic transplant nephropathy remains the major cause of graft loss after the first year post transplant, with the exception of death with functioning graft. The histological hallmark of chronic kidney rejection is progressive fibrosis in which extracellular matrix turnover plays an important role. This turnover is regulated by several systems of connective tissue proteases, the matrix metalloproteinases family being one of them. Every metalloproteinase exerts a different function over extracellular matrix proteins and can contribute to the pathogenesis of several diseases, such as rheumatoid arthritis and glomerulonephritis. The role of metalloproteinases in the pathogenesis of chronic transplant nephropathy and in kidney transplantation has not yet been addressed. METHODS: We measured the serum levels of proMMP-1, proMMP-2 and proMMP-3 by ELISA in 40 patients with chronic transplant nephropathy, 30 with acute rejection, 30 with stable graft function for a time equivalent to chronic transplant nephropathy, 30 with stable graft function for a time equivalent to acute rejection, and 30 healthy age-paired blood donors. RESULTS: Serum proMMP-2 and proMMP-3 were significantly higher in patients with chronic transplant nephropathy than in patients with acute rejection, stable graft function and healthy donors. The most striking finding was the significant positive correlation observed between serum levels of proMMP-3 and serum creatinine, and between circulating levels of proMMP-2 and proteinuria. Serum concentration of proMMP-1 was increased in patients with acute rejection compared with those with stable graft function and healthy donors. CONCLUSIONS: Serum proMMP-2 and proMMP-3 reflect the changes of glomerular and interstitial extracellular matrix in chronic transplant nephropathy, suggesting that they could play a role in the pathogenesis of this condition. Acute rejection is associated with increased levels of proMMP-1, which could be a reflection of the stimulation induced by a number of inflammatory cytokines produced in such a process.