Injured kidney cells express SM22α (transgelin): Unique features distinct from α-smooth muscle actin (αSMA)

Aim: SM22 alpha (transgelin) has been focused upon as a player in the process of phenotypic changes of types of cells. The SM22 alpha expression in the rat anti-glomerular basement membrane (GBM) nephritis model and differences from an established phenotypic marker for the myofibroblast, alpha-smooth muscle actin (alpha SMA), were investigated. Methods: The rat kidney tissues were processed for histological studies, immunohistochemical and immunoelectronmicroscopy analyses on days 0, 7, 28, 42 and 56 after injection of rabbit anti-GBM serum for the disease induction. Results: Immunohistochemistry with anti-SM22 alpha antibodies (Ab) revealed that kidneys of the nephritic rats on day 7 expressed SM22 alpha in podocytes, crescentic cells and epithelial cells of Bowman's capsule. After 28 days, SM22 alpha was also expressed in peritubular interstitial cells. Double immunofluorescence with anti-SM22 alpha Ab and anti-alpha SMA Ab showed that SM22 alpha was preferentially expressed in podocytes, whereas alpha SMA was positive in mesangial cells on day 7. After day 28, both molecules became positive in peritubular interstitial cells. Conclusion: SM22 alpha was expressed in epithelial cells of inflamed glomeruli in the early phase, and then also in peritubular interstitial cells in the later phase of anti-GBM nephritis model. SM22 alpha presented unique kinetics of expression distinct from alpha SMA.