MiR-126-3p-Enriched Extracellular Vesicles from Hypoxia-Preconditioned VSC 4.1 Neurons Attenuate Ischaemia-Reperfusion-Induced Pain Hypersensitivity by Regulating the PIK3R2-Mediated Pathway.

Recent evidence suggests that hypoxia preconditioning can alter the microRNA (miRNA) profile of extracellular vesicles (EVs) and has better neuroprotective effects when enriched miRs are delivered to recipients. However, the roles of exosomal miRNAs in regulating ischaemia-reperfusion (IR)-induced pain hypersensitivity are largely unknown. Thus, we isolated EVs from normoxia-conditioned neurons (Nor-VSC EVs) and Hypo-VSC EVs by ultracentrifugation. After the initial screening by a microarray analysis and quantitative RT-PCR (qRT-PCR), miR-126-3p, which was detected as the most altered miR in the Hypo-VSC EVs, was further confirmed by applying GW4869 to inhibit exosomal secretion. Moreover, transfection with a miR-126 mimic obviously increased miR-126-3p expression in Nor-VSC EVs, whereas a miR-126 inhibitor prevented the increase in miR-126-3p in Hypo-VSC EVs. A rat model of pain was established by performing 8-min occlusion of the aorta. Following IR, compared with the Nor-VSC EVs- or antagomir-126-injected rats, the Hypo-VSC EVs-injected rats displayed improved pain hypersensitivity demonstrated as higher PWT and PWL values. Mechanistically, PIK3R2 is a target of miR-126-3p and might be a modulator of the phosphoinositide 3-kinase (PI3K)/Akt pathway as the PIK3R2 and PI3K immunoreactivities in each group were changed in opposite directions. Compared with the controls, higher protein levels of PI3K and phosphorylated Akt but lower levels of phosphorylated nuclear factor-κ B (NF-κB), tumour necrosis factor (TNF)-α and interleukin (IL)-1β were detected in the spinal cords of the Hypo-VSC EVs-injected rats, and these effects were impaired by an injection of Hypo-VSC EVs combined with antagomir-126. Collectively, the miR-126-3p-enriched Hypo-VSC EVs attenuated IR-induced pain hypersensitivity by restoring miR-126-3p expression in the injured spinal cord and subsequently modulating PIK3R2-mediated PI3K/Akt and NF-κB signalling pathways.