Glucagon-like peptide-1 influences proliferation within the spinal cord; an effect via cerebrospinal fluid contacting neurons?

The influence of glucagon-like peptide-1 (GLP-1) on CNS functions, such as neurogenesis, neuroprotection, and anti-neuroinflammation, prompted investigation into its role in spinal neurogenesis. Ependymal cells (ECs) in the vicinity of the central canal, possess neural stem cell-like characteristics and rapidly proliferate after injury. While GLP-1R mRNA is distributed across spinal cord neurons and glia, its specific expression within the ependymal layer is yet to be resolved. Of particular interest are the cerebrospinal fluid contacting neurons (CSFcNs), which express GLP-1R mRNA, making them the focus of our study. Immunohistochemistry revealed that approximately 80% of CSFcNs express GLP-1Rs, uniformly distributed throughout the spinal cord. Moreover, a significant number of CSFcNs in the thoracic region receive direct contacts from GLP-1 producing neurons, indicating their integration into the broader spinal GLP-1 network. Calcium imaging in spinal cord slices demonstrated that liraglutide, a GLP-1R agonist, elicited concentration-dependent increases in calcium spiking event frequency and decreases in amplitude. Prolonged liraglutide exposure resulted in a complete reduction of spiking activity in some CSFcNs, which recovered following extended washing with aCSF. The effects of GLP-1R agonists on spinal cord cell proliferation were examined in ex vivo acute slices, organotypic spinal cord slice cultures (OSCSCs), and in vivo healthy mouse models. GLP-1R agonist application elicited higher levels of proliferation compared to control within the ependymal cell layer, in both acute slices and OSCSCs. This effect was enhanced when OSCSCs were cultured on liraglutide-infused hydrogels. Intriguingly, intraperitoneal injections of liraglutide in vivo revealed fewer labelled proliferating cells than control, particularly within the ependymal cell layer and the white matter. In summary, this study uncovers functional GLP-1Rs in CSFcNs, influencing calcium dynamics and potentially shaping neurogenesis within the spinal cord's ependymal cell layer. These findings illuminate an intricate interplay between GLP-1 and the spinal cord network, offering promising avenues for therapeutic interventions in spinal cord injuries and degenerative conditions.