Abstract
Neuronal α7 and α4β2 are the predominant nicotinic acetylcholine receptor (nAChR) subtypes found in the brain, particularly in the hippocampus. The effects of lovastatin, an inhibitor of cholesterol biosynthesis, on these two nAChRs endogenously expressed in rat hippocampal neuronal cells were evaluated in the 0.01-1 µM range. Chronic (14 days) lovastatin treatment augmented cell-surface levels of α7 and α4 nAChRs, as measured by fluorescence microscopy and radioactive ligand binding assays. This was accompanied in both cases by an increase in total protein receptor levels as determined by Western blots. At low lovastatin concentrations (10-100 nM), the increase in α4 nAChR in neurites was higher than in neuronal cell somata; the opposite occurred at higher (0.5-1 µM) lovastatin concentrations. In contrast, neurite α7 nAChRs raised more than somatic α7 nAChRs at all lovastatin concentrations tested. These results indicate that cholesterol levels homeostatically regulate α7 and α4 nAChR levels in a differential manner through mechanisms that depend on statin concentration and receptor localization. The neuroprotective pleomorphic effects of statins may act by reestablishing the homeostatic equilibrium.