Identifying Plasma Derived Extracellular Vesicle (EV) Contained Biomarkers in the Development of Chronic Neuropathic Pain.

Research into potentially novel biomarkers for chronic pain development is lacking. microRNAs (miRNAs) are attractive candidates as biomarkers due to their conservation across species, stability in liquid biopsies, and variation that corresponds to a pathologic state. miRNAs can be sorted into extracellular vesicles (EVs) within the cell and released from the site of injury. EVs transfer cargo molecules between cells thus affecting key intercellular signaling pathways. The focus of this study was to determine the plasma derived EV miRNA content in a chronic neuropathic pain rat model. This was accomplished by performing either spinal nerve ligation (SNL; n = 6) or sham (n = 6) surgery on anesthetized male Sprague-Dawley rats. Mechanosensitivity was assessed and plasma derived EV RNA was isolated at baseline (BL), day 3, and 15 postnerve injury. EV extracted small RNA was sequenced followed by differentially expressed (DE) miRNAs and gene target enrichment/signaling pathway analysis performed using R packages and TargetScan/Ingenuity pathway analysis (IPA), respectively. Seven of the DE miRNAs were validated by Reverse Transcription-quantitative Polymerase Chain Reaction (RT-qPCR). The data indicated that SNL rats displayed a time-dependent threshold reduction in response to evoked stimuli from day 3 to day 15 postnerve injury. The data also revealed that 22 and 74 miRNAs at day 3 and 15, respectively, and 33 miRNAs at both day 3 and 15 were uniquely DE between the SNL and sham groups. The key findings from this proposal include (1) the majority of the DE EV miRNAs, which normally function to suppress inflammation, were downregulated, and (2) several of the plasma derived DE EV miRNAs reflect previously observed changes in the injured L5 nerve. The plasma derived DE EV miRNAs regulate processes important in the development and maintenance of neuropathic pain states and potentially serve as key regulators, biomarkers, and targets in the progression and treatment of chronic neuropathic pain. PERSPECTIVE: This article describes the DE miRNA content of plasma derived EVs, comparing neuropathic pain to normal conditions. This data indicates that EV miRNAs may be important in nociception and may also serve as biomarkers for chronic pain. These results encourage further research on EV miRNAs in chronic neuropathic pain sufferers.