SM22α: The Novel Phenotype Marker of Injured Glomerular Epithelial Cells in Anti-Glomerular Basement Membrane Nephritis

Abstract

Background/Aims: Our previous comprehensive analysis of the genes expressed in kidneys with anti-glomerular basement membrane (GBM) nephritis using DNA microarrays showed that SM22α was one of the highly expressed genes. SM22α is a 22-kDa cytoskeletal protein that is exclusively expressed in smooth muscle cells. We investigated the localization of SM22α at mRNA and protein levels, and its pathological significance in anti-GBM nephritis kidneys. Methods: Northern blot analysis, in situ hybridization, immunohistochemistry and double immunofluorescence studies were performed. The specific antibody (Ab) against SM22α was obtained by immunization of rabbits with recombinant rat SM22α protein. Results: SM22α mRNA expression was upregulated in kidneys and inducibly expressed in the parietal and visceral glomerular epithelial cells in anti-GBM nephritis kidneys. Immunohistochemistry with anti-SM22α Ab showed that SM22α protein was localized in the same series of cells. Double immunofluorescence with anti-SM22α and anti-glomerular cell markers demonstrated that SM22α might be expressed in epithelial cells of injured glomeruli. In visceral epithelial cells, SM22α might be expressed in cells in which podocyte specific markers, podocalyxin and nephrin were lost. Conclusion: The injured glomerular epithelial cells in anti-GBM nephritis might undergo structural and functional alterations, including the expression of a smooth muscle marker, SM22α.