Inhibition of TLR4 prevents hippocampal hypoxic-ischemic injury by regulating ferroptosis in neonatal rats

Abstract

Inflammation and cell death play important roles in the pathogenesis of hypoxic-ischemic brain damage (HIBD). Toll-like receptor 4 (TLR4) triggers the activation of the inflammatory pathway. Ferroptosis, a newly identified type of regulated cell death, is implicated in various diseases involving neuronal injury. However, the role of ferroptosis in HIBD has not been elucidated. The objectives of this study were to explore the function and mechanism of TLR4 in neuronal ferroptosis in the context of HIBD. A neonatal rat model of hypoxia-ischemia (HI) and a cell model of oxygen-glucose deprivation (OGD) were employed. TAK-242, a TLR4-specific antagonist, was used to evaluate the effect of TLR4 on neuronal ferroptosis in vivo. A TAK-242 inhibitor and a p38 inhibitor (SB203580) were administered to HT22 hippocampal neurons to explore the association between TLR4 in inflammation and ferroptosis in vitro. The effects of TLR4 on ferroptosis were assessed by the Western blot, real-time PCR, immunofluorescence staining, cell viability and transmission electron microscopy (TEM) assays. HI insult significantly upregulated the TLR4, increased the p53 level, reduced the SLC7A11 and GPX4 levels, and caused mitochondrial damage, thereby inducing neuronal ferroptosis in the hippocampus. Inhibition of TLR4 inhibited the expression of ferroptosis-related proteins, decreased the expression of ferroptosis-related genes and the proinflammatory milieu, attenuated oxidative stress and mitochondrial injury and, finally, ameliorated the activation of hippocampal neuronal ferroptosis following HIBD. Consistent with the results of these in vivo experiments, TLR4 inhibition also attenuated OGD-induced ferroptosis by suppressing oxidative stress and p38MAPK signaling, ultimately increasing neuronal cell viability. Finally, the in vitro and in vivo results demonstrated that TAK-242 exerted neuroprotective and antiferroptotic effects by suppressing TLR4-p38 MAPK signaling. TLR4 activation induced neuronal ferroptosis following both HIBD and OGD. Inhibition of TLR4 attenuated oxidative stress-induced damage, decreased the activation of ferroptosis, and attenuated neuroinflammation following HIBD. In this study, we demonstrated that the inhibition of TLR4-p38 MAPK signaling modulates HIBD- or OGD-induced ferroptosis in neuronal cells and may play a novel role in brain homeostasis.

Keywords: Ferroptosis; Hypoxic-ischemic brain damage; Neuroinflammation; Oxidative stress; TLR4.