Proximal Tubule Toll-Like Receptor 4 Expression Linked to Inflammation and Apoptosis following Hypoxia/Reoxygenation Injury

Abstract

Background: Toll-like receptor 4 (TLR4) plays a key role in mediating kidney damage during ischemia/reperfusion (I/R) injury, and its expression is enhanced following renal I/R injury. Our study focused on TLR4 silencing-mediated downstream antiapoptotic pathways during hypoxia/reoxygenation (H/R) and investigated whether TLR4 overexpression exacerbates the renal damage induced by I/R injury. Methods: Proximal tubule epithelial cells (PTECs) were isolated and H/R injury mediated by ATP depletion, and replenishment was performed to mimic in vivo I/R injury. PTECs were transfected with either TLR4 siRNA or TLR4-overexpressing vectors to determine the contribution of TLR4 to H/R injury-induced apoptosis and inflammatory response. Results: H/R injury significantly enhanced PTEC apoptosis (p < 0.01) and the production of tumor necrosis factor (TNF)-α and interleukin (IL)-8; however, TLR4 silencing significantly reversed these effects (p < 0.05). Moreover, compared to PTECs or PTECs-siCon exposed to H/R injury, overexpression of TLR4 further upregulated TNF-α and IL-8 (p < 0.05), but did not enhance apoptosis. The expression of cytochrome C and caspases 3, 8, and 9 was decreased in the siTLR4 group compared to controls after H/R injury, whereas TLR4 silencing did not alter CHOP expression. TLR4 overexpression failed to promote the expression of cytochrome C and caspases 3, 8, and 9, and reduced the expression of CHOP and GPR78. Conclusions: Knockdown of TLR4 could protect PTECs from H/R injury via inhibiting mitochondrial and death receptor pathways. TLR4 overexpression did not increase PTEC apoptosis induced by H/R injury due in part to the downregulation of CHOP.