Differential expression of Selective Alzheimer Disease Indicator (Seladin-1)/DHCR24 gene in immortalized GnRH neurons

Membrane cholesterol-enriched lipid domains (lipid-rafts) are essential for the structural and functional integrity of neuronal membranes; they have been involved in a variety of different functions (e.g., signal transduction, lipid transport and metabolism, cell growth and migration) and can be modified by aging and certain neurodegenerative diseases. Recently, a new gene termed "selective Alzheimer’s disease indicator 1" (Sel-1) was shown to confer resistance to Alzheimer’s disease-associated neurodegeneration acting as a antiapoptotic agent; Sel-1 was found to be identical to the human gene which encodes for a cholesterol-biosynthetic enzyme 3beta-hydroxysterol delta24-reductase (DHCR24), found to be mutated in the patients affected by desmosterolosis. In the present study we used immortalized neurons derived from mature (GT1-7 cell line) and from immature (GN11 cell line) GnRH neurons to investigate the role of Sel-1/DHCR24 on neuronal functions. By real time-PCR technique, we found that GT1-7 cells present 10-100 times higher levels of Sel-1 mRNA compared to GN11 cells. The immunoreactivity of endogenous Sel-1 appears mainly distributed around the nucleus associated by endoplasmic reticulum; transfection of a fluorescent construct of Sel-1 (Sel-1GFP) showed a similar distribution of the protein. The staining of the two cell lines with filipin, a fluorescent polyene antibiotic that detects unesterified cholesterol, revealed a significant accumulation of free cholesterol in vesicular structures. Finally, we report the differential modification of the expression of Sel-1 under several toxic insults (oxidative stress, cholesterol depletion, beta-amyloid). In conclusion, these data indicate that mature and immature GnRH neurons differentially express Sel-1, providing a good cell model to investigate the role of this protein and of cholesterol in neuronal physiopathology. (Grants: MIUR COFIN2003-2005, 2003060512 and Fondazione CARIPLO)