Neuronal injury is the primary cause of poor outcome after subarachnoid hemorrhage (SAH). The apolipoprotein E (APOE) gene has been suggested to be involved in the prognosis of SAH patients. However, the role of APOE in neuronal injury after SAH has not been well studied. In this study, SAH was induced in APOE-knockout (APOE^-/-) and wild-type (WT) mice to investigate the impact of APOE deficiency on neuronal injury in the early phase of SAH. The experiments of this study were performed in murine SAH models in vivo and primary cultured microglia and neurons in vitro. The SAH model was induced by endovascular perforation in APOE^-/- and APOE WT mice. The mortality rate, weight loss, and neurological deficits were recorded within 72 h after SAH. The neuronal injury was assessed by detecting the neuronal apoptosis and axonal injury. The activation of microglia was assessed by immunofluorescent staining of Iba-1, and clodronate liposomes were used for inhibiting microglial activation. The expression of JNK/c-Jun was evaluated by immunofluorescent staining or western blotting. The expression of TNF-α, IL-1β, and IL-6 was evaluated by ELISA. Primary cultured microglia were treated with hemoglobin (Hb) in vitro for simulating the pathological process of SAH. SP600125, a JNK inhibitor, was used for evaluating the role of JNK in neuroinflammation. Nitrite production was detected for microglial activation, and flow cytometry was performed to detect apoptosis in vitro. The results suggested that SAH induced early neuronal injury and neurological deficits in mice. APOE deficiency resulted in more severe neurological deficits after SAH in mice. The neurological deficits were associated with exacerbation of neuronal injury, including neuronal apoptosis and axonal injury. Moreover, APOE deficiency enhanced microglial activation and related inflammatory injury on neurons. Inhibition of microglia attenuated neuronal injury in mice, whereas inhibition of JNK inhibited microglia-mediated inflammatory response in vitro. Taken together, JNK/c-Jun was involved in the enhancement of microglia-mediated inflammatory injury in APOE^-/- mice. APOE deficiency aggravates neuronal injury which may account for the poor neurological outcomes of APOE^-/- mice. The possible protective role of APOE against EBI via the modulation of inflammatory response indicates its potential treatment for SAH.

Background and Purpose—: Early brain injury is proposed to be the primary cause of the poor outcome after subarachnoid hemorrhage (SAH), which is closely related to the neural apoptosis. To date, the relationship between peroxisome proliferator–activated receptor β/δ (PPARβ/δ) and nuclear factor-κB/matrix metalloproteinase-9 (NF-κB/MMP-9) pathway, both of which are closely related to apoptotic effects, has been poorly studied in SAH. The present study was undertaken to evaluate the effects of PPARβ/δ on early brain injury and NF-κB/MMP-9 pathway after SAH in rats. Methods—: SAH model was established by injecting nonheparinized autologous arterial blood into the prechiasmatic cistern in male Sprague–Dawley rats. Adenoviruses or small interfering RNAs were injected into the right lateral cerebral ventricle to, respectively, up- or downregulate PPARβ/δ expression before SAH. All animals were assessed with a neurological score and then killed at 24 hours after SAH surgery. The indexes of brain water content, blood–brain barrier permeability, and apoptosis were used to detect brain injury. The expression of PPARβ/δ, NF-κB, and MMP-9 were measured by immunohistochemistry, gelatin zymography, and Western Blot methods, respectively. In addition, GW0742, a specific agonist of PPARβ/δ, was used to treat SAH in rats, the effects of which were evaluated by neurological scoring and Evans blue extravasation. Results—: Overexpression of PPARβ/δ by adenoviruses treatment significantly ameliorated brain injury with improvement in neurological deficits, brain edema, blood–brain barrier impairment, and neural cell apoptosis at 24 hours after SAH in rats, whereas downregulation of PPARβ/δ by small interfering RNAs administration resulted in the reverse effects of the above. The expression levels of NF-κB and MMP-9 were markedly downregulated when PPARβ/δ increased after PPARβ/δ adenovirus transfection and upregulated when PPARβ/δ decreased by PPARβ/δ small interfering RNAs treatment. Moreover, GW0742 improved neurological deficits and reduced Evans blue extravasation at 24 hours after SAH. Conclusions—: PPARβ/δ’s overexpression may attenuate early brain injury after rats’ SAH administration, which reduces neural apoptosis possibly through blocking NF-κB/MMP-9 pathway.

We previously discovered that traumatic brain injury (TBI) induces significant perturbations in long noncoding RNA (lncRNA) levels in the mouse cerebral cortex, and lncRNA‐AK046375 is one of the most significantly changed lncRNAs after TBI. lncRNA‐AK046375 overexpression and knockdown models were successfully constructed both in vitro and in vivo. In cultured primary cortical neurons and astrocytes, lncRNA‐AK046375 sequestered miR‐491‐5p, thereby enhancing the expression of metallothionein‐2 (MT2), which ameliorated oxidative‐induced cell injury. In addition, upregulated lncRNA‐AK046375 promoted the recovery of motor, learning, and memory functions after TBI in C57BL/6 mice, and the underlying mechanism may be related to ameliorated apoptosis, inhibited oxidative stress, reduced brain edema, and relieved loss of tight junction proteins at the blood‐brain barrier in the mouse brain. Therefore, we conclude that lncRNA‐AK046375 enhances MT2 expression by sequestering miR‐491‐5p, ultimately strengthening antioxidant activity, which ameliorates neurological deficits post‐TBI.

Some studies have confirmed the neuroprotective effect of remote ischemic conditioning against stroke. Although numerous animal researches have shown that the neuroprotective effect of remote ischemic conditioning may be related to neuroinflammation, cellular immunity, apoptosis, and autophagy, the exact underlying molecular mechanisms are unclear. This review summarizes the current status of different types of remote ischemic conditioning methods in animal and clinical studies and analyzes their commonalities and differences in neuroprotective mechanisms and signaling pathways. Remote ischemic conditioning has emerged as a potential therapeutic approach for improving stroke-induced brain injury owing to its simplicity, non-invasiveness, safety, and patient tolerability. Different forms of remote ischemic conditioning exhibit distinct intervention patterns, timing, and application range. Mechanistically, remote ischemic conditioning can exert neuroprotective effects by activating the Notch1/phosphatidylinositol 3-kinase/Akt signaling pathway, improving cerebral perfusion, suppressing neuroinflammation, inhibiting cell apoptosis, activating autophagy, and promoting neural regeneration. While remote ischemic conditioning has shown potential in improving stroke outcomes, its full clinical translation has not yet been achieved.