Steps toward the Elucidation of the Axonal Transcriptome of Human Peripheral Nerves

Recent studies conducted in rodents demonstrate the presence of translational machinery and mRNAs in peripheral axons. These studies also show that local translation of mRNAs in distal axons is important for axon growth, maintenance and regeneration and facilitates communication with the cell body. However, the question remains of which mRNAs are localized to axons of human peripheral neurons. In addition, an important component of axonal transport resides within the UnTranslated Region (UTR) of an mRNA. The 3’ UTR regulates mRNA subcellular localization, and these sequences can be highly divergent across species. The 3’ UTR contains cis-elements (or motifs) that are recognized by RNA-binding proteins (RBPs) for axonal transport. To address this in humans, we used human peripheral nerves collected from amputation surgeries combined with bulk-RNA and single-nuclei sequencing, in situ hybridization and Visium spatial transcriptomics. In our human sural nerve datasets, we detect sensory genes with known function in pain such as NTRK1 that are not expressed in non-neuronal cells present in sural nerves. This suggests that certain mRNAs may be transported to the peripheral sensory axon. We have conducted analysis of motifs-RBPs interactions for the putative axonal mRNAs. We identified RBPs, such as the fragile X mental retardation protein (FMRP), in the sural nerve. We are also using Visium spatial transcriptomics and publicly available datasets to characterize potential interactions between non-neuronal cells and nerve fibers. Our results demonstrate that immune cells present in the skin express several ligands that can interact with human sensory neurons. We detected several macrophage ligands that can interact with TRPV1, which is expressed in nociceptive fibers. Among those ligands are KNG1, FAAH and CALM1 which have known roles in peripheral pain. Maintaining the integrity of long axons is crucial and this work will provide new, fundamental insight into mechanisms that cause peripheral neuropathies. Recent studies conducted in rodents demonstrate the presence of translational machinery and mRNAs in peripheral axons. These studies also show that local translation of mRNAs in distal axons is important for axon growth, maintenance and regeneration and facilitates communication with the cell body. However, the question remains of which mRNAs are localized to axons of human peripheral neurons. In addition, an important component of axonal transport resides within the UnTranslated Region (UTR) of an mRNA. The 3’ UTR regulates mRNA subcellular localization, and these sequences can be highly divergent across species. The 3’ UTR contains cis-elements (or motifs) that are recognized by RNA-binding proteins (RBPs) for axonal transport. To address this in humans, we used human peripheral nerves collected from amputation surgeries combined with bulk-RNA and single-nuclei sequencing, in situ hybridization and Visium spatial transcriptomics. In our human sural nerve datasets, we detect sensory genes with known function in pain such as NTRK1 that are not expressed in non-neuronal cells present in sural nerves. This suggests that certain mRNAs may be transported to the peripheral sensory axon. We have conducted analysis of motifs-RBPs interactions for the putative axonal mRNAs. We identified RBPs, such as the fragile X mental retardation protein (FMRP), in the sural nerve. We are also using Visium spatial transcriptomics and publicly available datasets to characterize potential interactions between non-neuronal cells and nerve fibers. Our results demonstrate that immune cells present in the skin express several ligands that can interact with human sensory neurons. We detected several macrophage ligands that can interact with TRPV1, which is expressed in nociceptive fibers. Among those ligands are KNG1, FAAH and CALM1 which have known roles in peripheral pain. Maintaining the integrity of long axons is crucial and this work will provide new, fundamental insight into mechanisms that cause peripheral neuropathies.