Exploring the Secretome’s Biomarker and Analgesic Potential

Abstract

Diagnostic and prognostic biomarkers of nerve injury and/or pain as well as improved pain therapeutics are needed, both on the battlefield to treat injured Service Members and in the civilian sector. Our previous research indicates that there are several differentially expressed (DE) extracellular vesicle-derived microRNAs (EV-miRNAs) isolated from rat plasma following spinal nerve ligation (SNL). As such, EV-miRNAs hold promise as biomarkers and therapeutic targets. The secretome contains biological mediators, including EVs, which are released into the extracellular space. In this study we focus on evaluating EV-non-coding RNAs (ncRNAs), examine effects of SNL on key protein expression in the prefrontal cortex (PFC), and test the secretome’s analgesic properties. To accomplish these goals, anesthetized male Sprague Dawley rats underwent SNL and nociceptive behavior measurements, plasma collection followed by EV RNA isolation, small RNA sequencing, and analysis. Expression of several key proteins in the PFC was determined by Wes/Jess analysis. The secretome bath was applied directly to the ligated nerve and the paw withdrawal threshold (PWT) was measured. We identified differences in several classes of ncRNAs such as piRNAs, snoRNAs, and snRNAs post-SNL. Levels of phosphorylated forms of P70S6K and ERK1 were increased in the dorsal PFC at 15 days post-SNL. Bath application of the secretome directly to the ligated nerve resulted in recovery of the reduced PWT (increased mechanical sensitivity) that is induced by SNL. Here, we have identified specific EV-ncRNAs that could contribute to the formation of pain. Furthermore, we have evaluated a novel product for analgesic efficacy that could function to exploit the underlying mechanisms that contribute to pain development, thus reducing acute pain. This is key in treating Service Members on the battlefield in order to prevent pain chronification.