Development of an Oral GCPII Inhibitor for Peripheral Nerve Injury in Aging - PROJECT SUMMARY Peripheral nerves possess a remarkable ability to regenerate after injury; however, this regenerative capacity declines significantly with age, leading to prolonged or permanent functional impairments in older adults. This age-related deficit has been linked to dysfunction in Schwann cells and macrophages, two cell types critical for nerve repair. Glutamate carboxypeptidase II (GCPII) is a membrane-bound enzyme that hydrolyzes the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG), releasing glutamate. GCPII is expressed in both Schwann cells and macrophages, and its expression is markedly upregulated following peripheral nerve injury (PNI) across species—including mice, rats, swine, and humans—with even greater increases observed in aging. Given that GCPII directly regulates glutamatergic signaling in peripheral nerves and that excessive glutamate is implicated in nerve injury, we investigated GCPII inhibition as a potential therapeutic strategy. Our preliminary data shows that treatment with the prototype GCPII inhibitor 2-PMPA significantly enhances remyelination and functional recovery in aged mice following PNI. However, critical barriers must be overcome to advance this strategy toward clinical translation. Specifically: (1) 2-PMPA is highly charged, with poor oral bioavailability and limited tissue penetration, necessitating pharmacological optimization; (2) the underlying mechanisms by which GCPII inhibition improves regeneration remain undefined; and (3) while elevated GCPII expression has been observed in multiple human PNI samples, additional data are needed to characterize its temporal dynamics and the influence of age and sex, which are critical for translation. To address these important gaps, we assembled an interdisciplinary team of preclinical and clinical investigators with expertise in preclinical PNI models, clinical treatment of PNI patients, and drug discovery and development. The team will complete the following 3 aims. AIM 1: Evaluate the efficacy of the new orally bioavailable GCPII inhibitor, tetra(ODOL)-2-PMPA, in aged mice following PNI using electron microscopy, electrophysiology, and behavioral assays to assess morphological and functional recovery. AIM 2: Elucidate the molecular mechanisms underlying GCPII inhibition–mediated recovery using glutamate receptor antagonists, GCPII knockout mice, and spatial transcriptomics in Schwann cells and macrophages. AIM 3: Using human tissues from PNI patients and iPSC Schwann-neuron co-cultures, examine GCPII expression and activity by age, sex, and time post-injury. Myelination outcomes in the co-culture model will also be utilized to assess the functional impact of inhibition. Successful execution of these aims will result in an orally available GCPII inhibitor ready for IND-enabling studies to support future clinical studies aimed at improving recovery from PNI, particularly in the aging population.
