title: 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.
authors.affiliation: Department of Nephrology, Chinese PLA General Hospital (301 Hospital), Kidney Institute of Chinese PLA, State Key Laboratory of Kidney Diseases (2011DAV00088), National Clinical Research Center for Kidney Diseases (2013BAI09B05), Nanchang, PR China.
authors.forename: Xiu-Juan
authors.initials: XJ
authors.lastname: Liu
authors.forename: Yan
authors.initials: Y
authors.lastname: Tan
authors.forename: Yan-Qiu
authors.initials: YQ
authors.lastname: Geng
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Jun-Hong
authors.initials: JH
authors.lastname: Ye
authors.forename: Xiu-Ying
authors.initials: XY
authors.lastname: Yin
authors.forename: Bo
authors.initials: B
authors.lastname: Fu
mesh_terms: D058186:Acute Kidney Injury / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000502:physiology; D000860:Hypoxia / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009393:Nephritis / Q000378:metabolism*; D017208:Rats, Wistar; D053218:Receptors, Death Domain / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
chemical_list: D053218:Receptors, Death Domain; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4