Knockdown of interleukin‐6 plays a neuroprotective role against hypoxia‐ischemia in neonatal rats via inhibition of caspase 3 and Bcl‐2‐associated X protein signaling pathway

Abstract

This study aimed to investigate the role of interleukin-6 (IL-6) in the pathogenesis of neonatal hypoxic-ischemic encephalopathy (NHIE). Sprague-Dawley (SD) rats were used for the establishment of hypoxic-ischemic (HI) model. The Zea-Longa scoring was used to evaluate the extent of the neurological deficits. Triphenyl tetrazolium chloride (TTC) staining was used to measure the volume of infarction in the brain following HI protocol. The expression of IL-6 in the cortex and/or hippocampus at multiple time points after HI was examined by immunohistochemistry, western blotting and immunofluorescence. Moreover, small interfering RNAs (siRNA) were used to inhibit the expression of IL-6 in-vitro and in-vivo, and the concomitant expression of the Bcl-2 associated X protein (BAX) and caspase 3 was also measured. HI induced a significant brain damage, and these pathological changes were accompanied by IL-6 upregulation which was found localized in cortical neurons. The inhibition of IL-6 expression fostered neuronal and axonal growth, and a reduction in cellular apoptosis in cortical neuronal cultures, and cortex and hippocampus of neonatal rats. The expression of apoptotic markers such as BAX and caspase 3 was closely associated with IL-6. Downregulation of IL-6 could ameliorate HI-induced deficiencies by mediating the expression of caspase 3 and BAX.

Effects of Neonatal Hypoxic-Ischemic Injury on Brain Sterol Synthesis and Metabolism

“…Although not measured in this study, IL-6 may also be a surrogate for apoptotic injury, as silencing of IL-6 attenuates apoptosis through suppression of caspase 3. 28 In the severely affected mice in our study, there was a significant increase in desmosterol, 7-DHC, 8-DHC, and cholesterol 24 hours after injury as compared with control, although numbers were smaller for this subgroup, so the study was not fully powered for this analysis. 7-DHC and 8-DHC are highly reactive and oxidizable; thus, accumulation of 7-DHC and 8-DHC could be an adaptive response to protect membrane lipids from oxidative stress.…”

“…Given the variability in injury severity in the mouse model used in this study, we chose to further analyze the sterols stratified by injury severity using IL-6. IL-6 has previously been shown to be increased in the cortex and hippocampus after HIBI 28 representing the overall increased inflammatory cytokine release that occurs after HIBI. Although not measured in this study, IL-6 may also be a surrogate for apoptotic injury, as silencing of IL-6 attenuates apoptosis through suppression of caspase 3.…”