It is increasingly apparent that Schwann cells (SCs) in the peripheral nervous system (PNS) function as a unit with neurons to regulate sensory function. When the PNS is injured or stressed, SCs become activated for repair. This involves dramatic SC phenotypic transformation. If this process is abnormal or inhibited, peripheral nerve injury may result in chronic debilitating pain, a problem observed in the general population, including numerous Veterans. Treatment options for chronic neuropathic pain are very limited, and alternatives without addiction are badly needed. We hypothesize that in response to injury, SC activation is variable from cell to cell so that a continuum of SC activation states co-exist. We also hypothesize that the SC Repair Program may be augmented therapeutically to improve outcomes. The major goal of this research project is to determine whether we can target SC LDL Receptor-related Protein-1 (LRP1), a receptor that we have identified as playing a central role in the SC Repair Program, to improve pain outcomes following peripheral nerve injury. To accomplish our goals, three Specific Aims are proposed. In Specific Aim 1, we build on our LC-MS/MS proteomics data obtained from our previously funded VA Merit Award. We identified an endogenous axon-derived protein, PACSIN 1 as a lead LRP1 ligand candidate that robustly activated cell signaling pathways associated with the SC Repair Program. We now seek to identify the SC LRP1 binding domain in PACSIN 1 through site-directed mutagenesis, with the long-term goal of producing a more druggable pain therapeutic. We then design synthetic PACSIN 1 peptides that are tested and validated in cell signaling, survival and migration assays associated with the SC Repair Program. Next, we compare gene expression in SCs after PACSIN 1 transactivation of TrkC, activation by other LRP1 agonists (EI-tPA, SP16) or direct TrkC activation by neurotrophin-3 (NT-3), with the goal of identifying an optimized SC LRP1 agonist. In Specific Aim 2, our goal is to test LRP1 agonists in a mouse model of chemotherapy-induced painful peripheral neuropathy (CIPPN). We build upon our published data showing that LRP1 agonists reduce acute, inflammatory, and neuropathic pain after traumatic injury, and apply it to paclitaxel induced painful neuropathy, a commonly used chemotherapeutic agent in the Veteran population. We will measure several pain modalities in our studies to better understand the experiential pain associated with CIPPN. We utilize mice with genetic deletion of LRP1 in SCs (scLRP1-/-) generated in my laboratory, to test our hypothesis that SC LRP1 regulates neuroinflammation and whether LRP1 agonists specifically target SC LRP1. Finally, in Specific Aim 3, we will test whether LRP1 agonists regulate neuroinflammation induced by CIPPN in lumbar DRGs. We then utilize single-cell RNASeq to define the cellular landscape of CIPPN nerves and identify differences in subpopulations of glia and immune cells when PIPN nerves are treated with LRP1 agonists or when SC LRP1 is absent. We consider this project innovative because we target a known anti-inflammatory receptor, LRP1 in SCs, instead of neurons to treat chronic pain. This work provides a translational opportunity to improve chronic pain management in our VA patients.

The major objective of this research project is to determine whether molecular mediators, generated by injured peripheral nerves or genetically engineered to bind the low-density lipoprotein receptor related protein (LRP1), regulate Schwann cell physiology, and prevent the development of painful peripheral neuropathy. We hypothesize that activation of Schwann cell LRP1 will limit neuroinflammation in DRGs and change the cellular landscape of peripheral nerves induced by toxic chemotherapy drugs. Identifying novel activators of the SC Repair Program will provide innovative strategies for treating painful peripheral neuropathies which is highly prevalent in veterans.