The regulation of leptin gene expression in the C6 glioblastoma cell line

The hormone leptin is implicated in the regulation of appetite and body wei ght in rodents, primates and humans. We reported that the leptin gene (ob) is expressed in the brain, but the factors which control ob expression in t he central nervous system are not known. We previously showed that brain-de rived rat C6 glioblastoma cells express ob mRNA and protein. In the present study we examined the regulation of ob expression in C6 cells. Leptin and leptin receptor immunoreactivity was detected in C6 cells, suggesting a pos sible autocrine role for leptin. The identity of the leptin immunoreactivit y (OB-ir) in C6 cells was confirmed by immunoprecipitation and Western blot ting using two leptin specific polyclonal antibodies. Using RT-PCR analysis a product of the expected size for the short, but not the long, leptin rec eptor isoform was detected in C6 cells. Cells were maintained in serum-free (SF) media for 0-24 h in the presence of various regulators of leptin expr ession. Leptin mRNA levels were significantly higher in cells treated with dbcAMP (1 mM), IGF 1 (100 ng/ml) or insulin (5 mu g/ml) compared to SF cont rols. In contrast, corticosterone (10(-7)M) reduced leptin mRNA. In the pre sence of dbcAMP, C6 cells undergo a dramatic alteration in morphology which is coincident with an apparent increase in the number of leptin-ir nuclei and an increase in leptin immunoreactivity. In contrast to C6 cells, glucoc orticoids are reported to increase leptin levels in adipocytes/adipose tiss ue, while increases in intracellular cAMP levels are reported to reduce lep tin levels. Overall, our in vitro data suggest that the regulation of lepti n gene expression in C6 glioblastoma cells is different from that in adipoc ytes. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.