Expression of a brain/embryo-type myosin heavy chain isoform (MIIB2) in chronic glomerulonephritis, especially IgA glomerulonephritis

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Proliferation of mesangial cells is frequently found in glomerulonephritis such as IgA glomerulonephritis. Recent reports suggest that a brain/embryo-type myosin isoform (MIIB2) is involved in cell proliferation. We have studied the expression of MIIB2 in renal biopsy samples from patients with various renal diseases and in the renal tissues from the rat model of mesangial proliferative glomerulonephritis induced with anti-Thy 1.1 antibody. Immunohistochemical analysis of the biopsy samples using an anti-brain-type myosin heavy chain-specific monoclonal antibody (HBM1) indicated that 92% of the samples from patients with IgA glomerulonephritis contained a significant population of mesangial cells that reacted with the antibody. Most of sample from patients with other types of proliferative glomerular diseases also contained HBM1-reactive mesangial cells, while none of the samples from patients with non-proliferative glomerular diseases contained a significant population of HBM1-reactive mesangial cells. The anti-Thy 1.1-injected rats began to express an increased level of a brain/embryo-type myosin heavy chain isoform (MIIB2) in the mesangial cells at 5 days after injection of the antibody and continued to express the isoform up to the 10th day. On the other hand, the expression of the proliferating cell unclear antigen in the mesangial cells was induced at 3 days after injection of anti-Thy 1.1 antibody and was maximal at the 4th day. The expression of type I collagen, a major extracellular matrix component of the glomeruli, was induced about 5 days after injection of the anti-Thy 1.1 antibody. These results indicate that the expression of the MIIB2 isoform by mesangial cells is accelerated in proliferative glomerulonephritis and suggest that the myosin isoform is involved in the phenotypic transformations of the glomerular tissues rather than in the cell proliferation.