Link extracellular function of tRNA synthetase with pathological mechanism of disease

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Abstract Aminoacyl-tRNA synthetases (aaRSs) are a family of essential enzymes that catalyze the first reaction in protein biosynthesis, namely, the charging of transfer RNAs (tRNAs) with their cognate amino acids. Due to the importance of protein synthesis in most cells, it is not surprising that almost all aaRSs family members have been linked through bi-allelic mutations to human diseases that often affect multiple organ systems. Interestingly, human aaRSs also have wide- ranging non-enzymatic functions regulating many important biological processes. Therefore, in principle, regulatory functions of aaRSs could also be involved in the disease mechanism. However, the challenge lies in the difficulties to dissect the impact of regulatory functions from that of the enzymatic roles. In addition to being in the cytosol where protein synthesis occurs, aaRSs are frequently detected in the extracellular space, such as in cell culture media and in the systemic circulations of humans and mice. Yet, the physiological significance of extracellular tRNA synthetases remains unknown. This project aims to investigate pathophysiological function of extracellular tRNA synthetases. We focus on a selective group of aaRSs linked to a specific neurodegenerative disease – Charcot-Marie-Tooth disease (CMT) – through dominant mono- allelic mutations. Under the support of GM for the last 10 years, we established that the extracellular presence of glycyl-tRNA synthetase (GlyRS or GARS; the first and the most prominent CMT-linked aaRS) is relevant to the disease and we identified specific cell signaling pathways dysregulated by CMT-causing GlyRS mutants. Our future research will investigate the involvement of a particular signaling pathway in all aaRS-linked CMT subtypes and uncover extracellular roles of aaRS in the normal cell signaling process.