Differential effects of triiodothyronine and the thyroid hormone receptor ß-Specific agonist GC-1 on thyroid hormone target genes in the brain

8 pages, 5 figures, 1 table.The availability of synthetic thyroid hormone receptor agonists provides a valuable tool to analyze whether specific receptor isoforms mediate specific physiological responses to thyroid hormone. GC-1 is a thyroid hormone analog displaying selectivity for thyroid hormone receptor ß. We have analyzed the effect of GC-1 on expression of thyroid hormone target genes in the cerebrum and cerebellum. Congenitally hypothyroid rats were treated with single daily doses of either T3 or GC-1. Both compounds similarly induced Purkinje cell protein-2 (PCP-2) in the cerebellum. Expression of RC3 and Rhes in the caudate, and hairless, neurotrophin-3, Reelin, and Rev-ErbA{alpha} in the cerebellum, was analyzed by in situ hybridization on postnatal d 16. Hypothyroidism strongly decreased expression of RC3 and Rhes in the caudate, and hairless, Rev-ErbA{alpha}, and neurotrophin-3 in the cerebellum, and increased Reelin. T3 treatment normalized the expression of all genes. However, GC-1 effectively normalized expression of Rhes and Reelin only. The lack of a GC-1 effect on most cerebellar genes can be explained by the known distribution of thyroid hormone receptor {alpha} and ß isoforms. However, in the caudate, RC3 and Rhes are expressed in the same cells, and therefore, they may represent specific gene responses linked to specific thyroid hormone receptor isoforms.This work was supported by grants from the Ministry of Science and Technology (BFI2002-00489), FIS, Instituto de Salud Carlos III, Red de Centros RCMN (C03/08), and the National Institutes of Health (DK 52798). B.M. is a postdoctoral fellow from the Community of Madrid, and J.M. is a predoctoral fellow from the Ministry of Science and Technology.Peer reviewe