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

Abstract

Ischemia/reperfusion injury (IRI) causes inflammation and cell injury as a result of activating innate immune signaling. Toll-like receptor 4 (TLR4) has a key role in mediating kidney damages during IRI, but the downstream signaling pathway(s) stimulating apoptosis remains debated. In this study we show that TLR4 mediates MyD88-dependent activation of TNF receptor-associated factor 2, apoptosis signal-regulating kinase 1 (ASK1), and Jun N-terminal kinase (JNK) and p38 MAP kinases in ischemicreperfused kidneys and posthypoxic renal tubule epithelial cells (RTECs). Hypoxia stimulated the expression of the endoplasmic-resident gp96, which co-immunoprecipitated TLR4, whereas silencing gp96 mRNA expression impaired hypoxiainduced 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 posthypoxic TLR4-expressing RTECs. These findings show that, concomitantly to the activation of p38, the gp96/TLR4 interaction is required for activation of ASK1/JNK signaling in posthypoxic mouse RTECs, and that the 28-kDa NOX4 has a key role in TLR4-mediated apoptosis during renal IRI.

Tanshinone IIA pretreatment attenuates ischemia/reperfusion-induced renal injury

“…Caspase-3 plays a role in apoptosis process started by various procedures (19). It can be activated by splitting of DNA cyclin-dependent kinases to change its structure and promote cell apoptosis (29). The present data suggest that supplementation with tanshinone IIA significantly inhibited the increase cleaved caspase-3 protein expression in I/RIRI rats.…”

“…Necrocytosis is located at central area of ischemia, while cell apoptosis is mainly observed at ischemic penumbra (28). Previous studies have indicated that I/RIRI apoptosis is regulated by a variety of genes (29). Caspase-3 is the most critical apoptotic protease in caspases cascade reaction (30).…”

Impact of endogenous hydrogen sulfide on toll-like receptor pathway in renal ischemia/reperfusion injury in rats

“…20 The family members, TLR-2 and TLR-4, are constitutively expressed in renal tubular epithelial cells. 21 They are activated in renal IRI and induce kidney inflammation and apoptosis, which may cause AKI. [21][22] Therefore, the aim of this study was to investigate the impact of endogenous H 2 S on TLR pathways in renal IRI in rats.…”

Identification of NCF2/p67phox as a novel p53 target gene

“…[11][12][13] Recently, Nox2 and other Nox isoforms have been shown to be involved in tumor cell proliferation. [14][15][16][17][18] The upregulation of Nox is critical to support the elevated glycolysis by providing additional NAD+, and it has been consistently observed in cancer cells and in primary pancreatic cancer tissues with compromised mitochondria. 9,19 In addition, in acute leukemic cell lines, Nox2-and/or Nox4-derived ROS are crucially involved in the modulation of glucose transport (mediated by Glut1), which is frequently upregulated controlled, a task which is performed by two interconnected systems: thioredoxin and glutathione system.…”