Inhibition of histone deacetylase activates side population cells in kidney and partially reverses chronic renal injury

Bone morphogenic protein (BMP)-7 is expressed in the adult kidney and reverses chronic renal injury when given exogenously. Here, we report that a histone deacetylase inhibitor, trichostatin A (TSA), attenuates chronic renal injury, in part, by augmenting the expression of BMP-7 in kidney side population (SP) cells. We induced accelerated nephrotoxic serum nephritis (NTN) in C57BL/6 mice and treated them with TSA for 3 weeks. Compared with vehicle-treated NTN mice, treatment with TSA prevented the progression of proteinuria, glomerulosclerosis, interstitial fibrosis, and loss of kidney SP cells. Basal gene expression of renoprotective factors such as BMP-7, vascular endothelial growth factor, and hepatocyte growth factor was significantly higher in kidney SP cells as compared with non-SP cells. Treatment with TSA significantly upregulated the expression of BMP-7 in SP cells but not in non-SP cells. Moreover, initiation of treatment with TSA after 3 weeks of NTN (for 3 weeks, until 6 weeks) partially but significantly reversed renal dysfunction. Our results indicate an important role of SP cells in the kidney as one of the possible generator cells of BMP-7 and TSA as a stimulator of the cells in reversing chronic renal disease.