Dexmedetomidine is known to alleviate cerebral ischemia-reperfusion injury (CIRI). We established a rat model of CIRI, which exhibited higher neurological deficit scores and a greater number of apoptotic cells in the cerebral ischemic penumbra than controls. Dexmedetomidine reversed the neuronal apoptosis and improved neurological function in this model. We then examined Sigma-1 receptor (Sig-1R) expression on the endoplasmic reticulum (ER) in brain tissues at different reperfusion time points. Sig-1R expression increased with CIRI and decreased with increasing reperfusion times. After 24 hours of reperfusion, dexmedetomidine upregulated Sig-1R expression, and ER stress proteins (GRP78, CHOP, JNK and Caspase-3) were detected in brain tissues with Western blotting. Moreover, GRP78 expression followed a pattern similar to Sig-1R. Dexmedetomidine induced GRP78 expression but inhibited CHOP, Caspase-3 and phosphorylated-JNK expression in brain tissues. A Sig-1R-specific inhibitor reduced GRP78 expression and partially inhibited the upregulation of GRP78 by dexmedetomidine. The inhibitor also increased CHOP and Caspase-3 expression and partially reversed the inhibitory effects of dexmedetomidine on these pro-apoptotic ER stress proteins. These results suggest that dexmedetomidine at least partially inhibits ER stress-induced apoptosis by activating Sig-1R, thereby attenuating brain damage after 24 hours of ischemia-reperfusion.
Background/Aims: Lipopolysaccharide (LPS) pretreatment has a strong neuroprotective effect on cerebral ischaemia/reperfusion injury (IRI), but the mechanism has not been fully elucidated to date. This study investigated the effect of LPS pretreatment on the pathway mediated by endoplasmic reticulum (ER) stress–CCAAT/enhancer-binding protein- homologous protein (CHOP) and the role of this pathway on cerebral ischaemia/reperfusion (I/R)-induced inflammation and apoptosis. Methods: Healthy male BALB/c mice were randomised into four groups as follows: sham operation group (sham group, n=30); LPS group (BALB/c mice treated with LPS, n=30); ischaemia/reperfusion group (I/R group, n=30) and I/R+LPS group (BALB/c mice treated with LPS before ischaemia, n=30). The mice were pre-treated with LPS (0.2 mg/kg) intra-peritoneally for three days prior to cerebral ischaemia. After 24 hours, the neurological deficit score, TTC staining and TUNEL assay were used to assess the neuroprotective effect of the LPS pretreatment against cerebral IRI. To assess whether the ER stress-CHOP pathway participated in the LPS-pretreatment neuroprotective mechanism, the expression levels of related proteins (GRP78, CHOP, caspase-12 and caspase-3) from the ischaemic cortical penumbra were detected via a western blot analysis. An immunohistochemical study was used to detect the expression and location of CHOP in the cortical penumbra. To further assess the protective effect of the LPS pretreatment, the concentrations of inflammatory factors (TNF-α, IL-6, IL-1β and IL-10) in the cortical penumbra were measured by ELISA, and ER stress-CHOP pathway inflammation-related caspase-11 was analysed through western blot analysis. Results: As demonstrated by the experiments, the pretreatment with LPS significantly reduced the neurological deficit score and the infarct size of cerebral IRI. The expression levels of ER stress-CHOP pathway related proteins (GRP78, CHOP, caspase-12 and caspase-3) from the cortical penumbra were significantly decreased by LPS, as well as the level of apoptosis in the cells in the brain. Immunohistochemistry showed that the expression of CHOP significantly decreased after the LPS pretreatment. Furthermore, the concentrations of inflammatory factors (TNF-α, IL-1β, IL-6) were reduced after the LPS pretreatment, whereas the anti-inflammatory cytokine IL-10 was upregulated. In addition, ER stress-CHOP pathway inflammation-related caspase-11 expression was significantly suppressed after the pretreatment with LPS. Conclusions: LPS pretreatment significantly ameliorates the effects of cerebral IRI by inhibiting inflammation and apoptosis, and the potential mechanism of the neuroprotective effect may be associated with the ER stress-CHOP mediated signalling pathway.
Berberine (BBR) has a neuroprotective effect against ischemic stroke, but its specific protective mechanism has not been clearly elaborated. This study explored the effect of BBR on the canopy FGF signaling regulator 2 (CNPY2) signaling pathway in the ischemic penumbra of rats. The model of cerebral ischemia-reperfusion injury (CIRI) was established by the thread embolization method, and BBR was gastrically perfused for 48 h or 24 h before operation and 6 h after operation. The rats were randomly divided into four groups: the Sham group, BBR group, CIRI group, and CIRI + BBR group. After 2 h of ischemia, followed by 24 h of reperfusion, we confirmed the neurologic dysfunction and apoptosis induced by CIRI in rats (p < 0.05). In the ischemic penumbra, the expression levels of CNPY2-regulated endoplasmic reticulum stress-induced apoptosis proteins (CNPY2, glucose-regulated protein 78 (GRP78), double-stranded RNA-activated protein kinase-like ER kinase (PERK), C/EBP homologous protein (CHOP), and Caspase-3) were significantly increased, but these levels were decreased after BBR treatment (p < 0.05). To further verify the inhibitory effect of BBR on CIRI-induced neuronal apoptosis, we added an endoplasmic reticulum-specific agonist and a PERK inhibitor to the treatment. BBR was shown to significantly inhibit the expression of apoptotic proteins induced by endoplasmic reticulum stress agonist, while the PERK inhibitor partially reversed the ability of BBR to inhibit apoptotic protein (p < 0.05). These results confirm that berberine may inhibit CIRI-induced neuronal apoptosis by downregulating the CNPY2 signaling pathway, thereby exerting a neuroprotective effect.
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