Arbour, D. | bioRxiv Science

bioRxiv2024

Cannabinoid type-1 (CB1) receptors in glial cells promote neuromuscular junction repair following nerve injury.

Cannabinoids are frequently used in the treatment of neuropathic pain related to nerve injury. However, despite evidence for their roles in the regulation of axonal guidance and synapse formation during development of the central nervous system (CNS), their possible involvement in response to peripheral nerve injury remains poorly defined and the knowledge of its role is mostly related to the peripheral sensory system. Following nerve injury, contemporary to axonal repair, massive morphological and functional changes reshape synaptic elements at neuromuscular junctions (NMJs) aiming to promote their reinnervation. This process is mediated in part by Perisynaptic Schwann cells (PSCs), glial cells at the NMJ essential for its maintenance and repair. Here we investigated the novel role of Cannabinoid type-1 receptor (CB1R) at NMJ, in particular on PSCs, during motor nerve recovery following nerve injury. Using morphological analysis, we studied the consequences of CB1R pharmacological and genetic blockade following denervation and reinnervation in adult NMJs. CB1R blockade caused an acceleration of the denervation process followed by a great delay in reinnervation as indicated by a significant percentage of denervated NMJs, accompanied by a decrease of mono- and poly-innervated NMJs. Remarkably, a similar phenomenon was observed when CB1R is selectively knocked-out in glia, indicating that the protective actions of these receptors are largely glia-dependent. These data highlight a novel role of the endocannabinoid system at NMJs, where the CB1Rs on PSCs can control NMJ denervation and reinnervation following nerve injury. A better understanding of the functional mechanisms underlying CB1R role in NMJ repair may contribute to finding a new pharmacological treatment having a dual role in improvements of motor recovery and in pain-related relief.

neuroscience↗

bioRxiv2020

Properties of Glial Cell at the Neuromuscular Junction are Incompatible with synaptic repair in the SOD1G37R ALS mouse model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motoneurons in a motor-unit (MU) dependent manner. Glial dysfunction contributes to numerous aspects of the disease. At the neuromuscular junction (NMJ), early alterations in perisynaptic Schwann cell (PSC), glial cells at this synapse, may impact their ability to regulate NMJ stability and repair. Indeed, muscarinic receptors (mAChR) regulate the repair phenotype of PSCs and are overactivated at disease-resistant NMJs (Soleus muscle) in SOD1G37R mice. However, it remains unknown whether this is the case at disease-vulnerable NMJs and whether it translates into an impairment of PSC-dependent repair mechanisms. We used Soleus and Sternomastoid muscles from SOD1G37R mice and performed Ca2+-imaging to monitor PSC activity and used immunohistochemistry to analyze their repair and phagocytic properties. We show that PSC mAChR-dependent activity was transiently increased at disease-vulnerable NMJs (Sternomastoid muscle). Furthermore, PSCs from both muscles extended disorganized processes from denervated NMJs and failed to initiate or guide nerve terminal sprouts at disease-vulnerable NMJs, a phenomenon essential for compensatory reinnervation. This was accompanied by a failure of numerous PSCs to upregulate Galectin-3 (MAC-2), a marker of glial axonal debris phagocytosis, upon NMJ denervation in SOD1 mice. Finally, differences in these PSC-dependent NMJ repair mechanisms were MU-type dependent, thus reflecting MU vulnerability in ALS. Together, these results reveal that neuron-glia communication is ubiquitously altered at the NMJ in ALS. This appears to prevent PSCs from adopting a repair phenotype, resulting in a maladapted response to denervation at the NMJ in ALS. SIGNIFICANCE STATEMENTUnderstanding how the complex interplay between neurons and glial cells ultimately lead to the degeneration of motor neurons and loss of motor function is a fundamental question to comprehend amyotrophic lateral sclerosis. An early and persistent alteration of glial cell activity takes place at the neuromuscular junction (NMJ), the output of motor neurons, but its impact on NMJ repair remains unknown. Here, we reveal that glial cells at disease-vulnerable NMJs often fail to guide compensatory nerve terminal sprouts and to adopt a phagocytic phenotype on denervated NMJs in SOD1G37R mice. These results show that glial cells at the NMJ elaborate an inappropriate response to NMJ degeneration in a manner that reflects motor-unit vulnerability and potentially impairs compensatory reinnervation.

neuroscience↗