Heat shock protein gp96 and NAD(P)H oxidase 4 play key roles in Toll-like receptor 4-activated apoptosis during renal ischemia-reperfusion injury
Résumé
Ischemia/reperfusion injury (IRI) causes inflammation and cell injury as a result of activating innate immune signaling. Toll-like receptor 4 (TLR4) plays a key role in mediating kidney damages during IRI, but the downstream signaling pathway(s) stimulating apoptosis remains debated. Here we show that TLR4 mediates MyD88-dependent activation of TNF receptor-associated factor 2 (TRAF2), apoptosis signal-regulatory kinase 1 (ASK1), and JNK and p38 MAP kinases in ischemic-reperfused kidneys and post-hypoxic renal tubule epithelial cells (RTECs). Hypoxia stimulated the expression of the endoplasmic-resident gp96, which co-immunoprecipitated TLR4, while silencing gp96 mRNA expression impaired hypoxia-induced apoptosis in TLR4-expressing RTECs. NAD(P)H oxidase 4 (NOX4) was shown to interact with TLR4 and to be required in lipopolysaccharide-induced production of reactive oxygen species (ROS). IRI stimulated the expression of a 28-kDa NOX4 spliced isoform abundantly expressed in wild-type RTECs, which co-immunoprecipitated with TLR4, but not with gp96 in TLR4-deficient RTECs. Silencing NOX4 mRNA expression impaired hypoxia-induced activation of ASK1 and both JNK and p38, leading to the inhibition of ROS production and apoptosis in post-hypoxic TLR4-expressing RTECs. These findings demonstrate that, concomitantly to the activation of p38, the gp96/TLR4 interaction is required for activation of ASK1/JNK signaling in post-hypoxic mouse RTECs, and that the 28-kDa NOX4 plays a key role in TLR4-mediated apoptosis during renal IRI.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...