Reverse T interacts with αvβ3 integrin receptor and restores enzyme activities in the hippocampus of hypothyroid developing rats: Insight on signaling mechanisms.

In the present study we provide evidence that 3,3',5'-triiodothyronine (reverse T, rT) restores neurochemical parameters induced by congenital hypothyroidism in rat hippocampus. Congenital hypothyroidism was induced by adding 0.05% propylthiouracil in the drinking water from gestation day 8 and continually up to lactation day 15. In the in vivo rT exposure, hypothyroid 12-day old pups were daily injected with rT (50 ng/kg body weight) or saline until day 14. In the ex vivo rT treatment, hippocampal slices from 15-day-old hypothyroid pups were incubated for 30 min with or without rT (1 nM). We found that ex vivo and/or in vivo exposure to rT failed in restoring the decreased C-glutamate uptake; however, restored the phosphorylation of glial fibrillary acidic protein (GFAP), Ca influx, aspartate transaminase (AST), glutamine synthetase (GS) and gamma-glutamate transferase (GGT) activities, as well as glutathione (GSH) levels in hypothyroid hippocampus. In addition, rT improved C-2-deoxy-D-glucose uptake and lactate dehydrogenase (LDH) activity. Receptor agonists/antagonists (RGD peptide and AP-5), kinase inhibitors of p38MAPK, ERK1/2, CaMKII, PKA (SB239063, PD98059, KN93 and H89, respectively), L-type voltage-dependent calcium channel blocker (nifedipine) and intracellular calcium chelator (BAPTA-AM) were used to determine the mechanisms of the nongenomic rT action on GGT activity. Using molecular docking analysis, we found rT interaction with αvβ3 integrin receptors, nongenomically activating signaling pathways (PKA, CaMKII, p38MAPK) that restored GGT activity. We provide evidence that rT is an active TH metabolite and our results represent an important contribution to elucidate the nonclassical mechanism of action of this metabolite in hypothyroidism.