3-Iodothyronamine (3-T(1)AM) is an endogenous thyroid hormone metabolite. The profound pharmacological effects of 3-T(1)AM on energy metabolism and thermal homeostasis have raised interest to elucidate its signaling properties in tissues that pertain to metabolic regulation and thermogenesis. Previous studies identified G protein-coupled receptors (GPCRs) and transient receptor potential channels (TRPs) as targets of 3-T(1)AM in different cell types. These two superfamilies of membrane proteins are largely expressed in tissue which influences energy balance and metabolism. As the first indication that 3-T(1)AM virtually modulates the function of the neurons in hypothalamus, we observed that intraperitoneal administration of 50 mg/kg bodyweight of 3-T(1)AM significantly increased the c-FOS activation in the paraventricular nucleus (PVN) of C57BL/6 mice. To elucidate the underlying mechanism behind this 3-T(1)AM-induced signalosome, we used three different murine hypothalamic cell lines, which are all known to express PVN markers, GT1-7, mHypoE-N39 (N39) and mHypoE-N41 (N41). Various aminergic GPCRs, which are the known targets of 3-T(1)AM, as well as numerous members of TRP channel superfamily, are expressed in these cell lines. Effects of 3-T(1)AM on activation of GPCRs were tested for the two major signaling pathways, the action of G alpha(s)/adenylyl cyclase and G(i/o). Here, we demonstrated that this thyroid hormone metabolite has no significant effect on G(i/o) signaling and only a minor effect on the G alpha(s)/adenylyl cyclase pathway, despite the expression of known GPCR targets of 3-T(1)AM. Next, to test for other potential mechanisms involved in 3-T(1)AM-induced c-FOS activation in PVN, we evaluated the effect of 3-T(1)AM on the intracellular Ca2+ concentration and whole-cell currents. The fluorescence-optic measurements showed a significant increase of intracellular Ca2+ concentration in the three cell lines in the presence of 10 mu M 3-T(1)AM. Furthermore, this thyroid hormone metabolite led to an increase of whole-cell currents in N41 cells. Interestingly, the TRPM8 selective inhibitor (10 mu M AMTB) reduced the 3-T(1)AM stimulatory effects on cytosolic Ca2+ and whole-cell currents. Our results suggest that the profound pharmacological effects of 3-T(1)AM on selected brain nuclei of murine hypothalamus, which are known to be involved in energy metabolism and thermoregulation, might be partially attributable to TRP channel activation in hypothalamic cells.
600 Technik, Medizin, angewandte Wissenschaften::610 Medizin und Gesundheit::610 Medizin und Gesundheit
3-Iodothyronamine activates a set of membrane proteins in murine hypothalamic cell lines
Frontiers in Endocrinology
Frontiers Media S.A.
Charité - Universitätsmedizin Berlin