Dual signal transduction pathways activated by TSH receptors in rat primary tanycyte cultures

Abstract

Tanycytes play multiple roles in hypothalamic functions, including sensing peripheral nutrients and metabolic hormones, regulating neurosecretion and mediating seasonal cycles of reproduction and metabolic physiology. This last function reflects the expression of TSH receptors in tanycytes, which detect photoperiod-regulated changes in TSH secretion from the neighbouring pars tuberalis. The present overall aim was to determine the signal transduction pathway by which TSH signals in tanycytes. Expression of the TSH receptor in tanycytes of 10-day-old Sprague Dawley rats was observed by in situ hybridisation. Primary ependymal cell cultures prepared from 10-day-old rats were found by immunohistochemistry to express vimentin but not GFAP and by PCR to express mRNA for Dio2, Gpr50, Darpp-32 and Tsh receptors that are characteristic of tanycytes. Treatment of primary tanycyte/ependymal cultures with TSH (100 IU/l) increased cAMP as assessed by ELISA and induced a cAMP-independent increase in the phosphorylation of ERK1/2 as assessed by western blot analysis. Furthermore, TSH (100 IU/l) stimulated a 2.17-fold increase in Dio2 mRNA expression. We conclude that TSH signal transduction in cultured tanycytes signals via Ga s to increase cAMP and via an alternative G protein to increase phosphorylation of ERK1/2.

Thyroid hormone activation of retinoic acid synthesis in hypothalamic tanycytes

“…Primary tanycyte cultures were prepared from 10‐day‐old male Sprague Dawley rat pups as previously described (Bolborea et al, 2015; De Seranno et al, 2004; Prevot et al, 2003). Brains were removed under sterile conditions, placed in ice‐cold DMEM/F‐12 medium containing penicillin/streptomycin and 25 mM HEPES and the median eminence dissected.…”

Glial cells and energy balance

“…These glial cells capture T 4 from the peripheral circulation and then liberate T 3 into the hypothalamus (Barrett et al 2007) where it regulates, for example, the response of the orexigenic NPY/AgRP neurons (Coppola et al 2007). The expression of Dio2 is increased in these glial cells in conditions of starvation or inflammation and follows a photoperiodic pattern in seasonal mammals (Bolborea et al 2015). In rats, the intracerebroventricular administration of TSH for 2 weeks increases Dio2 levels in the ependymal layer (Helfer et al 2013) and TSH also stimulates Dio2 synthesis in vitro in primary tanycyte cultures (Bolborea et al 2015), indicating a direct effect on these cells.…”

“…The expression of Dio2 is increased in these glial cells in conditions of starvation or inflammation and follows a photoperiodic pattern in seasonal mammals (Bolborea et al 2015). In rats, the intracerebroventricular administration of TSH for 2 weeks increases Dio2 levels in the ependymal layer (Helfer et al 2013) and TSH also stimulates Dio2 synthesis in vitro in primary tanycyte cultures (Bolborea et al 2015), indicating a direct effect on these cells. Indeed, they express the TSH receptor (TSHR), with TSHR expression being very high in the ventral region of the ependyma lining the third ventricle (Bolborea et al 2015), an area with a high density of tanycytes.…”

“…In rats, the intracerebroventricular administration of TSH for 2 weeks increases Dio2 levels in the ependymal layer (Helfer et al 2013) and TSH also stimulates Dio2 synthesis in vitro in primary tanycyte cultures (Bolborea et al 2015), indicating a direct effect on these cells. Indeed, they express the TSH receptor (TSHR), with TSHR expression being very high in the ventral region of the ependyma lining the third ventricle (Bolborea et al 2015), an area with a high density of tanycytes. The response of R65 Review p argente-arizón and others Glial cells and energy balance tanycytes to TSH elicits both an increase in cAMP levels and ERK1/2 activation (Bolborea et al 2015), but it is still unclear if this signaling is common to all tanycytes or if it is region specific (Bolborea et al 2015).…”

“…Indeed, they express the TSH receptor (TSHR), with TSHR expression being very high in the ventral region of the ependyma lining the third ventricle (Bolborea et al 2015), an area with a high density of tanycytes. The response of R65 Review p argente-arizón and others Glial cells and energy balance tanycytes to TSH elicits both an increase in cAMP levels and ERK1/2 activation (Bolborea et al 2015), but it is still unclear if this signaling is common to all tanycytes or if it is region specific (Bolborea et al 2015). In summary, tanycytes determine the T 3 levels in the hypothalamus through Dio2 activity, which is modulated by TSH levels in the third ventricle.…”