Cholesterol metabolites modulate ionotropic P2X4 and P2X7 receptor current in microglia cells

The central nervous system is a well-known steroidogenic tissue producing, among others, cholesterol metabolites such as neuroactive steroids, oxysterols and steroid hormones. It is well known that these endogenous molecules affect several receptor classes, including ionotropic GABAergic and NMDA glutamatergic receptors in neurons. It has been shown that also ionotropic purinergic (P2X) receptors are cholesterol metabolites' targets. Among P2X receptors, purinergic P2X4 and P2X7 receptors are expressed in microglia, the innate immune cells involved in the brain inflammatory response. In this study, we explore the ionotropic purinergic receptors modulation by cholesterol metabolites in microglia. Patch-clamp experiments were performed in BV2 cells, a murine microglia cell line, to evaluate effects of cholesterol metabolites using micro- and nanomolar concentrations. About P2X4 receptor, we found that testosterone butyrate (20 μM and 200 nM) and allopregnanolone (10 μM and 100 nM) both potentiated its current, while neither 25-hydroxycholesterol (10 μM and 100 nM) nor 17β-estradiol (1 μM) showed any effects. On the other hand, P2X7 receptor current was potentiated by allopregnanolone (10 μM) and 25-hydroxycholesterol (10 μM and 100 nM). Taken together, our data show that modulation of either P2X4 and P2X7 current is affected differently by cholesterol metabolites, suggesting a structure-activity relationship among these players. Identifying the possible link between purinergic transmission, microglia and cholesterol metabolites will allow to define new targets for drug development to treat neuroinflammation.