Glutamate Regulates Caveolin Expression in Rat Hippocampal Neurons

Caveolae are cholesterol-rich, membrane microdomains that appear critical to signaling between extracellular and intracellular macromolecules as well as cholesterol homeostasis. Caveolae formation is modulated by caveolin, a protein family that is the proteinaceous hallmark of caveolae. Very little is known regarding the events that modulate caveolin expression and regulation in neurons. To detect caveolin expression in neurons, primary rat hippocampal neurons were harvested at embryonic day 18, maintained for 7 days in vitro, and then analyzed for caveolin immunofluorescence. Caveolin-1 immunoreactivity was detected in cells that were identified as neurons by morphology and concurrent microtubule-associated protein (MAP2) staining. Changes in caveolin-1 expression were evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR) analyses of RNA isolated from hippocampal neurons treated with glutamate receptor agonists. Glutamate induced a concentration-dependent increase in caveolin-1 mRNA. The largest increases in caveolin-1 mRNA were detected after 6 hours of treatment. Kainate and AMPA both mimicked glutamate effects on caveolin-1 mRNA expression. Western blot analyses revealed that caveolin was induced at the protein level as well. Taken together, these data suggest that glutamate can regulate caveolin expression through kainate and AMPA ionotropic glutamate receptors.