Expression of apoptosis regulatory proteins in tubular epithelium stressedin culture or following acute renal failure

Background. While tubular cell death is a characteristic of acute renal fai lure (ARF), the molecular mechanisms that modulate this cell death are uncl ear. Cell fate in acute renal failure hinges on a balance of survival and m ortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal fail ure. Method. The expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic a cid or in renal tubular epithelial cells (MCT) stressed in culture. Results. Renal mRNA levels encoding for c-myc and BclxL were elevated in AR F while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. E xpression of tumor necrosis factor (TNF-alpha), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increa sed in some tubuli and absent in others, while Bcl2 expression decreased di ffusely. Bar staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is pr esent in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) a nd sensitization to TNF-alpha-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-alpha increas ed the mRNA levels encoding for c-myc and decreased BclxL expression. Neith er MCT cells nor the kidney expressed BclxS. Conclusions. A relative deficit of survival factors likely contributes to c hanges in levels of BclxL and Bar in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-alpha that is incre ased in ARF and a potential source of increased c-myc, a downstream facilit ator of cell death. These findings implicate members of the Bcl2 Family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.