Immune-related oxysterol modulates neuromuscular transmission via non-genomic liver X receptor-dependent mechanism

Inflammatory reactions induce changes in the neuromuscular system. The mechanisms underlying this link are unclear. Besides cytokines and reactive oxygen species (ROS), production of an antiviral oxysterol 25-hydroxycholesterol (25HC) by immune cells is quickly increased in response to inflammation. Hypothetically, 25HC could contribute to regulation of neuromuscular activity as well as redox status. We found that 25HC (0.01-10 mu M) can bidirectionally modulate neurotransmission in mice diaphragm, the main respiratory muscle. Low concentrations (<= 0.1 mu M) of 25HC reduced involvement of synaptic vesicles (SVs) into exocytosis during 20-Hz activity, whereas higher inflammatory-related concentrations (>= 1 mu M) had a profound potentiating effect on SV mobilization. The latter stimulatory action of 25HC was accompanied by increase in Ca2+ release from intracellular stores via IP3 receptors. Both increase in SV mobilization and [Ca2(+)]in were suppressed by a specific antagonist of liver X receptors (LXRs). These receptors formed clusters within the synaptic membranes in a lipid raft-dependent manner. Either raft disruption or intracellular Ca2+ chelation prevented (HC)-H-25-mediated acceleration of the exocytotic rate. The same action had inhibition of estrogen receptor alpha, Gi-protein, G beta gamma, phospholipase C and protein kinase C. Additionally, 1 mu M 25HC upregulated ROS production in a Ca2+-dependent way and an antioxidant partially decreased the exocytosis-promoting effect of 25HC. Thus, 25HC has prooxidant properties and it is a potent regulator of SV mobilization via activation of lipid raft-associated LXRs which can trigger signaling via estrogen receptor alpha - Gi-protein - G beta gamma - phospholipase C - Ca2+ - protein kinase C pathway. 25HC-mediated increase in ROS may modulate this signaling.

Automated summary

Inflammatory reactions can induce changes in the neuromuscular system. The oxysterol 25-hydroxycholesterol (25HC) may regulate neurotransmission and contribute to neuromuscular activity via activation of lipid raft-associated LXRs. 25HC-mediated increase in ROS production may modulate signaling pathways involving estrogen receptor alpha - Gi-protein - G beta gamma - phospholipase C - Ca2+ - protein kinase C.