Interstitial alpha-smooth muscle actin: a prognostic marker in membranous nephropathy

Membranous nephropathy in adults causes 20% of nephrotic syndromes. Spontaneous outcome of this glomerulopathy is difficult to evaluate from clinical and histological data. Some patients can achieve complete remission, while others develop progressive renal failure. In this study we assessed alpha-smooth muscle actin (alpha-SMA) expression in renal interstitial myofibroblasts as a marker to predict the outcome of membranous nephropathy.

Renal function tests in tandem with alpha-SMA immunolabelling were performed on 25 patients with a mean follow-up of 7.2+/-5.6 years. The intensity of interstitial alpha-SMA (ialpha-SMA) immunostaining was compared to changes in glomerular filtration rate (GFR) evaluated by inulin clearance, between the time of diagnosis (GFR1) and the end of follow-up (GFR2).

A significant correlation (r = 0.62, p<0.001) was found, between the intensity of interstitial myofibroblasts, immunolabeling and GFR at the end of follow-up. Moreover, the annual GFR variation and the annual percentage of GFR variation were correlated to interstitial myofibroblast labeling (respectively r = 0.62, p<0.001; r = 0.67, p<0.001). In addition, the importance of proteinuria, initial GFR impairment and fibrosis were confirmed as prognostic criteria.

This study strongly shows that ialpha-SMA expression is a useful and early prognostic marker in the evolution of membranous nephropathy.