Mesangial expression of a nonmuscle myosin heavy chain, SMemb, is associated with glomerular sclerosis and renal prognosis in IgA nephropathy.

To characterize the phenotypic alteration in mesangial cells in human glomerulonephritis, we investigated the expression of nonmuscle-type myosin heavy chain, SMemb, and alpha-smooth muscle actin (alpha-SM actin) in IgA nephropathy. The expression of SMemb and alpha-SM actin was examined by immunohistochemistry in biopsy specimens from 45 patients with IgA nephropathy. We examined a total of 489 glomeruli representing all patients enrolled, and found that mesangial expression of SMemb and alpha-SM actin was associated with mesangial proliferation. Only mesangial expression of SMemb showed a significant relationship with mesangial matrix accumulation. Semiquantitative evaluation using composite expression scores showed that the expression of SMemb was elevated in the patients with poor renal prognosis. The expression of alpha-SM actin showed no significant relationship with renal prognosis. These results suggest that mesangial expression of SMemb is an important factor in the progression of IgA nephropathy, and that SMemb and alpha-SM actin are associated with the activation of mesangial cells by different mechanisms.