Transforming growth factor-beta and astrocytic conditioned medium influence luteinizing hormone-releasing hormone gene expression in the hypothalamic cell line GT1

On the basis of our previous observations indicating that a principle [possibly transforming growth factor-beta 1 (TGF beta 1)] secreted by type 1 astrocytes may increase the release of LHRH in the GT1 cell line, it was deemed of interest to analyze whether TGF beta 1 might influence LHRH gene expression in addition to LHRH release in GT1-1 neurons. The effects of TGF beta 1 on the levels of LHRH messenger RNA (mRNA) present in GT1-1 cells have been compared to those found after either coculture of these cells with type 1 astrocytes or exposure of GT1-1 cells to the conditioned medium in which type 1 astrocytes were grown for 24 h. The data obtained indicate that 1) TGF beta 1 increases LHRH mRNA levels 1 and 6 h after the beginning of treatment; longer exposures (24 h) bring about a decrease in LHRH gene expression; 2) a significant stimulatory effect of TGF beta 1 (1 and 6 h of exposure) is also evident on LHRH release; 3) the exposure to the conditioned medium of type 1 astrocytes is able to increase LHRH gene expression in GT1-1 cells at 1 h; LHRH mRNA levels show a small decrease after 6 h of exposure, which becomes more evident at 24 h; and 4) the coculture of GT1-1 cells with type 1 astrocytes is not able to modify LHRH mRNA levels at any time considered. The present data support the concept that glial cells are able to control, possibly through the release of TGF beta, the gene expression of LHRH in hypothalamic neurons.