Tumor Necrosis Factor-α Induces Intrinsic Apoptotic Signaling During Renal Obstruction Through Truncated Bid Activation

Abstract

Tumor necrosis factor-alpha has a significant role in renal tubular cell apoptosis during obstruction induced renal injury. While we have previously reported the role of tumor necrosis factor-alpha in extrinsic pathway apoptotic signaling during renal obstruction, to our knowledge its effect on intrinsic pathway signaling and mitochondrial release of cytochrome C has not previously been evaluated. Male Sprague-Dawley rats were anesthetized and underwent unilateral ureteral obstruction vs sham operation. At 24 hours before surgery and every 84 hours thereafter the animals received vehicle or a pegylated form of soluble tumor necrosis factor receptor type 1. The kidneys were harvested 1 week postoperatively. The renal cortex was analyzed for tumor necrosis factor-alpha production (enzyme-linked immunosorbent assay), apoptosis (TUNEL and enzyme-linked immunosorbent assay), Bcl-2, Bcl-x(L), Bax, caspase 8 and truncated Bid expression (Western blot), and mitochondrial cytochrome C release (immunohistochemistry). Renal obstruction induced increased tumor necrosis factor-alpha production, apoptotic renal tubular death, the expression of Bax, caspase 8 and truncated BID, and mitochondrial release of cytochrome C, while simultaneously stimulating decreased Bcl-2 and Bcl-x(L) expression. Treatment with the pegylated form of soluble tumor necrosis factor receptor type 1 significantly decreased obstruction induced tumor necrosis factor-alpha production, apoptosis, Bax, caspase 8, truncated Bid expression and mitochondrial cytochrome C release, and increased Bcl-2 and Bcl-x(L) expression. These results demonstrate that tumor necrosis factor-alpha stimulates Bid and subsequent intrinsic apoptotic signaling pathway activation during unilateral ureteral obstruction, resulting in mitochondrial cytochrome C release and apoptotic cell death. We identified tumor necrosis factor-alpha neutralization as a potential therapeutic option for ameliorating obstruction induced renal injury.