Induction of p27KIP1 after unilateral ureteral obstruction is independent of angiotensin II

Abstract

Background: Unilateral ureteral obstruction (UUO) is characterized by proliferation of tubular and interstitial cells, and infiltration of the renal parenchyma with macrophages/monocytes. These alterations lead ultimately to tubulointerstitial fibrosis and tubular atrophy. Some of these changes are caused by an activated renin-angiotensin system (RAS). We have previously demonstrated that angiotensin II induces the expression of the cell cycle inhibitor p27KIP1 in cultured tubular cells. The current study tested the hypothesis that interference with the RAS may modulate renal expression of p27KIP1 after UUO.

Methods: The ureter of the left kidney of Sprague-Dawley rats was ligated. Sham-operated animals served as controls. Rats were randomized in four groups and received one of the following: no therapy, enalapril, losartan, or triple therapy (hydralazine, reserpine, hydrochlorothiazide). Kidneys were removed and cortical protein lysates were prepared for the detection of p27KIP1 by Western blotting. Immunohistochemistry was performed for p27KIP1, PCNA, ED-1, and alpha-smooth muscle actin. Apoptosis was quantified by TUNEL-staining.

Results: p27KIP1 expression as detected by Western blotting reached a maximum 10 days after UUO. Tubular and interstitial cells contributed to this increase in p27KIP1 expression whereas the number of glomerular p27KIP1 positive cell did not change. p27KIP1-positive cells were macrophages/monocytes (positive ED-1 staining) or had the characteristics of myofibroblasts (positive alpha-smooth muscle actin staining). Tubular and interstitial proliferation [proliferating cell nuclear antigen (PCNA)-positive staining] and apoptosis [terminal deoxy transferase uridine triphosphate nick end labeling (TUNEL) staining] also was increased after UUO. However, individual cells stained either positive for p27KIP1 or PCNA, but not both. Although enalapril and losartan reduced the number of macrophages/monocytes and attenuated the degree of tubular and interstitial apoptosis, these drugs did not influence p27KIP1 expression. There was no change in the number of p27KIP1-positive cells in the contralateral kidney undergoing hypertrophy.

Conclusion: Induction of p27KIP1 in this model represents an endogenous response to likely limit proliferation that is independent of angiotensin II. Since there was no close correlation between apoptosis and p27KIP1 expression, it may be that the overall number of p27KIP1 expressing cells sets a general restriction point for apoptosis rather than defines an individual level of cell fate.