Role of p53-Dependent Activation of Caspases in Chronic Obstructive Uropathy: Evidence from p53 Null Mutant Mice YEONG-JIN CHOI,* LEONARDO MENDOZA, † SUK-JOO RHA,* DAVID SHEIKH-HAMAD, ‡ ELZBIETA BARANOWSKA-DACA,* VINH NGUYEN,* C. WAYNE SMITH, † GEORGE NASSAR, ‡ WADI N. SUKI, ‡ and LUAN D. TRUONG* ‡ Renal Pathology Laboratory, *Department of Pathology and † Department of Medicine, The Methodist Hospital; and ‡ Department of Pediatrics, Texas Children’s Hospital and Baylor College of Medicine, Houston, Texas. Abstract. Chronic obstructive uropathy (COU) created by uni- lateral ureteric ligation is associated with increased renal cell apoptosis and p53 expression. Genetically engineered mice were used to examine the role of p53 in renal cell apoptosis in COU and the involved molecular pathways. Obstructed kid- neys in p53+/+, p53+/-, and p53-/- mice were examined at days 4, 7, 15, 20, and 30 for apoptosis, and mRNA were examined for p53, members of the bcl-2 family, the death receptor family, and the common effectors of apoptosis. Ob- structed kidneys in p53+/- and p53-/- mice exhibited equal attenuation of tubular and interstitial cell apoptosis (70 and 50%, respectively), compared with p53+/+ mice. However, p53 gene deficiency did not confer complete protection from apoptosis. Obstructed kidneys from p53-/- mice did not express p53 mRNA, whereas those from p53+/- and p53+/+ mice displayed mild and marked increase in their expression, respectively. Obstructed kidneys in p53+/+, p53+/-, and p53-/- mice displayed upregulation of mRNA for members of the bcl-2 family and most of the death receptor family, except for a lower level of tumor necrosis factor receptor-1, TRAIL, and FAP in p53+/+ mice. Obstructed kidneys in p53-/- and p53+/- mice showed virtual absence of caspase 11 and marked attenuation of caspases 1 and 12, contrasted with their strong expression in p53+/+ kidneys. These data suggest that apoptosis in obstructed kidneys involves p53- dependent as well as p53-independent pathways. The p53- dependent pathway may involve activation of caspases 1, 11, and 12, whereas the p53-independent pathway may involve activation of members of the bcl-2 and death receptor families. Kidneys with chronic obstructive uropathy (COU) develop progressive tubulointerstitial damage (1–3). Although several tubular changes, such as dilation, atrophy, and immature phe- notype, are widely recognized, tubular cell apoptosis has emerged recently as a crucial lesion in COU (1,3,4). We demonstrated a marked increase in tubular and interstitial cell apoptosis in kidneys with COU (3), and this increase is asso- ciated with a parallel increase in p53 mRNA. Increased p53 expression during apoptosis has been reported in cells of di- verse origins, including hepatocytes (5) and neurons (6), and in cultured cells treated with DNA-damaging agents (7,8). These observations suggest that p53 activation may have a role in the development of apoptosis after ureteric obstruction. The molecular control of apoptosis is only partially under- stood. It likely involves two distinct pathways that share a common downstream arm. The first pathway involves the activation of death receptors (Fas, tumor necrosis factor-1 [TNFR-1], TRAIL) by their respective ligands (9 –13). The generated signal activates cytosolic adapter molecules (e.g., TRADD, RIP, FADD, FAF) and results in the conversion of pro-caspase 8 to caspase 8. Caspase 8 converts pro-caspases 3, 6, and 7 into their respective active caspases, which are re- sponsible for the cellular changes that are characteristic of apoptosis (10,11,14). The second pathway involves the bcl-2 family and is initiated by a large variety of environmental stresses, such as radiation, heat, or growth factor deficiency (15–18). These signals are transmitted to the mitochondria by an unknown mechanism and influence the balance between apoptosis promoters (bax, bcl-xS, bad, and bak) and inhibitors (bcl-2, bcl-xL, bcl-w, and bfl-1) among the bcl-2 family. These proteins reside in the mitochondrial membrane and share struc- tural homology (15,16). Apoptotic signals that originate from this pathway result in the activation of pro-caspase 9 by cyto- chrome c and apoptosis protease activating factor-1 (15,19). Caspase 9, in turn, activates pro-caspases 3, 6, and 7, a step that represents the onset of the common arm of both death receptor and bcl-2 apoptotic pathways (15). Other caspases, including caspases 1, 11, and 12, have been recognized recently (20) and reported to have a regulatory role in apoptosis and inflamma- tory response (20 –22). However, their location in the apoptotic pathways has not been firmly established. Although it is well established that p53 promotes apoptosis Received March 6, 2000. Accepted October 19, 2000. Correspondence to Dr. Luan D. Truong, Department of Pathology, M.S. 205, The Methodist Hospital, Houston, TX 77030. Phone: 713-394-6481; Fax: 713-793-1473; E-mail: ltruong@bcm.tmc.edu 1046-6673/1205-0983 Journal of the American Society of Nephrology Copyright © 2001 by the American Society of Nephrology J Am Soc Nephrol 12: 983–992, 2001