MON-450 - Dopamine Secretion Is Regulated by TSH

Extra-thyroidal expression of TSH receptor (TSHR) has been reported in different regions of the brain. Systematic review and meta-analysis studies have implicated a strong correlation between thyroid dysfunction and Parkinson’s disease (PD). We recently reported that TSH enhances neurite outgrowth in human SH-SY5Y neuroblastoma cells. To examine the role of TSHR and its activation on dopamine regulation, we differentiated SH-SY5Y cells into dopaminergic neurons using an 18-day differentiation protocol. The presence of the TSHR in these cells was confirmed by digital PCR and immunostaining. Furthermore, to examine the effects of TSHR activation on dopamine release, we developed a red fluorescent dopamine biosensor stably expressed in HEK cells for quantitative assessments. Optimization of our stable biosensor showed a high efficacy and dynamic range in detecting dopamine in the culture medium when standardized with dopamine hydrochloride, thus providing an effective tool to study dopamine secretion. The expression of tyrosine hydroxylase (TH), an upstream key enzyme for dopamine synthesis, was quantitated by digital PCR after TSH treatment. Our study showed that TSHRs, expressed 12-fold higher in differentiated dopaminergic neurons compared with undifferentiated SH-SY5Y cells, were functional in cAMP signaling. Through estimating the dopamine levels in the culture medium using the biosensor, stimulation of the dopaminergic neurons with bovine TSH (bTSH) for 2 hrs at 37 C resulted in a dose-dependent suppression of dopamine secretion (904 ± 7.32 µM, 749 ± 27.7 µM, 608 ± 21.8 µM and 0 µM dopamine with 0, 10, 100 and 1000 µU/ml bTSH, respectively). A similar trend in dopamine suppression was noted with recombinant TSH, suggesting specific action of TSH on this pathway. This suppression was reversed using a potent TSHR blocking antibody, further confirming that TSH inhibits dopamine secretion. We also found a dose-dependent decrease in TH mRNA transcripts, suggesting that TSHR activation is a negative regulator of dopamine synthesis in dopaminergic neurons. Finally, suppression of dopamine secretion was recapitulated when differentiated SH-SY5Y neurons were stimulated with our TSHR-specific allosteric agonists MS437 and MS438, suggesting an important role of TSHR activation in these cells. These data demonstrate that TSHR activation inhibits dopamine synthesis, which could help explain the effects seen in TSH excess or deficiency in vivo.

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