The mechanism(s) of cerebral ischemia-reperfusion injury are complex, involving excitatory amino acid toxicity, oxidative stress, and inflammatory responses . These factors are interconnected and ultimately lead to the induction of apoptotic signaling and programmed neuronal cell death . Apoptosis after cerebral ischemia-reperfusion injury is a major form of neuronal death . The inhibition of apoptosis can be used as a potential therapeutic intervention to protect cerebral ischemia-reperfusion injury. In this study, an OGD / R cell model of PC12 cells was established to simulate cerebral ischemia-reperfusion injury in vitro to explore the neuroprotective effects of Dexmedetomidine.
Dex is a highly selective and specific α2 adrenoceptor agonist that exhibits a broad spectrum of effects, including sedation, hypnosis, anesthesia and analgesia . Dex is 1600-fold more selective for α2 over α1, and inhibits apoptosis, exerting neuroprotective effects in the developing brain . The mechanism(s) mediating these effects are however poorly understood.
MiRNAs participate in a range of essential biological processes including neuronal apoptosis during ischemic stroke and nervous system dysfunction . Here, we explored the underlying biological mechanisms of DEX in OGD/R-induced neurotoxicity and assessed the involvement of miR-17-5p and potential molecular factors.
TLR4 belongs to the Toll-like receptor family. These represent innate pattern recognition receptors that mediate the host response to pathogen infection . TLR4 activation promotes the production of inflammatory cytokines, such as IL-1β, TNF-α, and IL-6 . Aberrant IL-1β and IL-6 responses induced by TLR4 were observed in patient.
We found that miR-17-5p was downregulated in the OGD/R group and mediated OGD/R-induced inflammation and apoptosis. Dex treatment increased miR-17-5p expression in a dose-dependent manner in PC12 cells, the overexpression of which led to the dampening of inflammatory responses due to NF-κB inhibition. The downregulation of miR-17-5p produced the opposite phenotype. To explore the detailed mechanisms underlying these effects, the StarBase v2.0 database was employed with miR-17-5p identified as a potential miRNA. Further results showed that miR-17-5p negatively correlated with TLR4, with luciferase gene reporter assays showing that miR-17-5p binds to TLR4. However, the functions of miR-17-5p were not defined. To further investigate the role of miR-17-5p in OGD/R-induced inflammation and apoptosis in PC12 cells, miR-17-5p mimics and inhibitors were respectively transfected into each group. We found that miR-17-5p inhibits OGD/R-induced inflammation and apoptosis. We identified NF-κB signaling as a potential mediator of miR-17-5p and found that miR-17-5p inhibits TLR4/NF-κB signaling. Taken together, we postulate that Dex upregulates miR-17-5p which inhibits NF-κB, thereby reducing OGD/R-induced inflammation and apoptosis. Moreover, we found that the inhibition of OGD/R-induced inflammation and apoptosis were suppressed following TLR4 overexpression and miR-17-5p silencing.
Previous studies have shown that Dexmedetomidine attenuates oxygen-glucose deprivation/reperfusion-induced inflammation and apoptosis in PC12 cells through its effects on the miR-17-5p/TLR4/NF-κB axis. These data suggest that Dex represents a novel intervention strategy for cerebral ischemia-reperfusion injury. These findings now require verification in human stroke patients.
Some limitations should be noted. Firstly, the optimal concentration of Dex in vivo was not investigated. As such, multiple doses of Dex require investigation in further in vivo experiments. Secondly, we found that Dex up-regulates the expression of miR-17-5p in PC12 cells. Further studies are now required to confirm these effects in vivo.