Effect of preproTRH antisense on thyrotropin-releasing hormone synthesis and viability of cultured rat diencephalic neurons.

To investigate a possible neurotropic role for thyrotropin-releasing hormone (TRH) in the central nervous system, we used recombinant antisense TRH adenovirus (TRHav) to "knock out" TRH in cultured 17-d fetal rat diencephalon. The morphology along with beta-galactosidase (beta-gal) enzyme histochemistry (X-gal staining) and TRH content (femtomoles/well) were used to measure the effect of antisense TRH virus. Control adenovirus mediated beta-gal transfection efficiency was nearly 85%, as shown by positive X-gal staining, and was without effect on cell morphology, TRH content, or the normal response to glucocorticoid (dexamethasone) exposure with enhanced TRH expression. A significant 90% decline in TRH content as well as changes in neuronal morphology (shrunken cell bodies and short dendrites) were observed after 14 but not 7 d following TRHav treatment. The addition of synthetic TRH peptide at 2.5 microM along with TRHav, but not dexamethasone, partly prevented the morphologic changes. No morphologic changes were seen in wild-type AtT20 cells, a pituitary cell line that does not produce TRH. To investigate whether neuronal death from loss of proTRH was owing to apoptosis, neuronal DNA change by means of fluorescent dye H-33342 staining, TUNEL staining, and DNA laddering analysis was examined. Eighty to 90% positive H-33342 and TUNEL staining as well as a 180- to 200-bp DNA fragment on DNA laddering analysis were found as compared to control. These results indicate that proTRH gene expression prevents neuronal apoptosis and may play a role in neuronal development and function.