Signal transduction involved in lipoxin A4‑induced protection of tubular epithelial cells against hypoxia/reoxygenation injury.

Previous studies have reported that lipoxin A4 (LXA4) may exert a renoprotective effect on ischemia/reperfusion injury in various animal models. The underlying mechanism of LXA4‑induced renoprotection during ischemia/reperfusion injury remains to be elucidated. The present study investigated LXA4‑induced protection on renal tubular cells subjected to hypoxia/reoxygenation (H/R) injury, and determined the effects of peroxisome proliferator‑activated receptor‑γ (PPARγ) and heme oxygenase‑1 (HO‑1) on LXA4 treatment. HK‑2 human tubular epithelial cells exposed to H/R injury were pretreated with LXA4, signal molecule inhibitors or the HO‑1 inhibitor zinc protoporphyrin‑IX, or were transfected with PPARγ small interfering RNA (siRNA) or nuclear factor E2‑related factor 2 (Nrf2) siRNA. The protein and mRNA expression levels of PPARγ and HO‑1 were analyzed using western blotting and reverse transcription‑quantitative polymerase chain reaction. Binding activity of Nrf2 to the HO‑1 E1 enhancer was determined using chromatin immunoprecipitation. Nrf2 binding to the HO‑1 antioxidant responsive element (ARE) was assessed using electrophoretic mobility shift assay. Preincubation of cells with LXA4 exposed to H/R injury led to a decreased production of inducible nitrogen oxide synthase, malondialdehyde, γ‑glutamyl transpeptidase, leucine aminopeptidase and N‑acetyl‑β‑glucosaminidase. In addition, LXA4 pretreatment increased cell viability, protein and mRNA expression levels of PPARγ and HO‑1 and PPARγ and HO‑1 promoter activity. SB20358 is a p38 mitogen‑activated protein kinase (p38 MAPK) pathway inhibitor, which reduced LXA4‑induced PPARγ expression levels. LXA4 treatment upregulated p38 MAPK activation, Nrf2 nuclear translocation and increased binding activity of Nrf2 to HO‑1 ARE and E1 enhancer in cells exposed to H/R injury. Transfection of the cells with PPARγ siRNA reduced the LXA4‑induced Nrf2 translocation. Transfection of the cells with PPARγ siRNA or Nrf2 siRNA also reduced the LXA4‑induced increase in HO‑1 expression. In conclusion, LXA4‑induced protection of renal tubular cells against H/R injury was associated with the induction of PPARγ and HO‑1, via activation of the p38 MAPK pathway, as well as Nrf2 nuclear translocation and binding to HO‑1 ARE and E1 enhancer. Therefore, LXA4‑induced renoprotection is associated with activation of the p38 MAPK/PPARγ/Nrf2‑ARE/HO‑1 pathway.