Activation of ERK accelerates repair of renal tubular epithelial cells, whereas it inhibits progression of fibrosis following ischemia/reperfusion injury

Extracellular signal-regulated kinase (ERK) signals play important roles in cell death and survival. However, the role of ERK in the repair process after injury remains to be defined in the kidney. Here, we investigated the role of ERK in proliferation and differentiation of tubular epithelial cells, and proliferation of interstitial cells following ischemia/reperfusion (I/R) injury in the mouse kidney. Mice were subjected to 30 min of renal ischemia. Some mice were administered with U0126, a specific upstream inhibitor of ERK, daily during the recovery phase, beginning at 1 day after ischemia until sacrifice. I/R caused severe tubular cell damage and functional loss in the kidney. Nine days after ischemia, the kidney was restored functionally with a partial restoration of damaged tubules and expansion of fibrotic lesions. ERK was activated by I/R and the activated ERK was sustained for 9 days. U0126 inhibited the proliferation, basolateral relocalization of Na,K-ATPase and lengthening of primary cilia in tubular epithelial cells, whereas it enhanced the proliferation of interstitial cells and accumulation of extracellular matrix. Furthermore, U0126 elevated the expression of cell cycle arrest-related proteins, p21 and phospholylated-chk2 in the post-ischemic kidney. U0126 mitigated the post-I/R increase of Sec10 which is a crucial component of exocyst complex and an important factor in ciliogenesis and tubulogenesis. U0126 also enhanced the expression of fibrosis-related proteins, TGF-β1 and phosphorylated NF-κB after ischemia. Our findings demonstrate that activation of ERK is required for both the restoration of damaged tubular epithelial cells and the inhibition of fibrosis progression following injury.