Blockage of the peri-synaptic Schwann cell nicotinic α7 receptor inhibitory drive increases the neuromuscular performance in rats with experimental autoimmune Myasthenia gravis: repurposing dipyridamole usage in myasthenics

Acetylcholine spillover from the neuromuscular synapse triggers an inhibitory drive via the activation of nicotinic α7 receptors (α7nAChRs) on perisynaptic Schwann cells (PSCs). This mechanism involves the outflow of adenosine from PSCs via ENT1 transporters and subsequent activation of presynaptic inhibitory A₁ receptors. Reinforcement of this sensing inhibitory pathway by cholinesterase (AChE) inhibitors may partially attenuate their efficacy for Myasthenia gravis treatment. Here, we investigated whether this neuromuscular break is still operative in an experimental autoimmune Myasthenia gravis (EAMG) rat model and if it is prone to pharmacological manipulation. Phrenic nerve-hemidiaphragm preparations were isolated from control and EAMG male Wistar rats. We used fluorescence video-microscopy with FM4-64 to assess nerve-evoked (50 Hz-bursts) transmitter exocytosis. Myographic recordings were used to evaluate muscle fatigue. Transmitter exocytosis was depressed in diaphragms of EAMG rats compared to controls. Direct activation of PSCs α7nAChRs with PNU282987 or pretreatment with AChE inhibitors, like neostigmine and ambenonium, exaggerated the neuromuscular transmission deficits in EAMG animals. The α7nAChR antagonist, methyllycaconitine, reversed the neuromuscular transmission deficits caused by PNU282987, neostigmine and ambenonium. Inhibition of ENT1-mediated adenosine outflow from PSCs with dipyridamole attenuated the paradoxical inhibitory effect of neostigmine on nerve-evoked transmitter exocytosis and, thus, the neuromuscular tetanic fade in EAMG rats. In conclusion, breaking the PSC-mediated α7nAChRs inhibitory drive with methyllycaconitine and dipyridamole may synergistically improve the neuromuscular performance and prevent fatigue in EAMG rats treated with AChE inhibitors. Therefore, we suggest repurposing the old antiplatelet vasodilator, dipyridamole, as a relatively safe add-on therapy for drug-resistant Myasthenia gravis.