Cholesterol-Lowering Treatment Suppresses Neuromuscular Transmission Via Presynaptic Mechanism at the Mouse Diaphragm Muscle

Statins are widely prescribed and effective cholesterol-lowering drugs for the therapy of cerebrovascular and cardiovascular disorders. The main side effects limiting statin use are muscle-related adverse events, including weakness and myopathy. The precise mechanisms of statin-induced muscle damage remain to be elucidated. Possible alterations in neuromuscular transmission might contribute to the statin side effects. Here, we studied the action of one-month treatment with atorvastatin, the most prescribed statin, on the functioning of neuromuscular junctions and related processes in the mouse diaphragm. We found that atorvastatin treatment decreases evoked acetylcholine (ACh) release and involvement of synaptic vesicles in exocytosis during intense nerve activation, as well as recovery of ACh release after tetanic stimulation. This was accompanied by increased immunolabeling of synapsin 1, a protein retaining synaptic vesicles in a non-active pool, and decreased non-quantal ACh release under resting conditions. Additionally, atorvastatin administration decreased perimeters of postsynaptic ACh receptor clusters without signs of muscle denervation. Diaphragm contractile responses to phrenic nerve stimulation at moderate-to-high frequencies and peak inspiratory flow, an indicator of diaphragm function in vivo, were decreased in atorvastatin-treated mice, whereas diaphragm contractions elicited by direct stimulation of muscle fibers were unchanged. Thus, atorvastatin treatment caused a decline in evoked ACh release and synaptic vesicle recruitment into neurotransmission that could lead to a reduction of diaphragm contractile responses to phrenic nerve activity and peak inspiratory flow. These alterations, in combination with decreased non-quantal ACh release and neuromuscular junction size, may contribute to statin-associated muscle symptoms.