Exp Clin Endocrinol Diabetes 2014; 122 - LB12
DOI: 10.1055/s-0034-1372318

The mouse Leydig cell line MLTC-1 prefers L-thyroxine over 3,3',5-triiodo-L-thyronine in transport across plasma membrane and shows steroidogenesis response to thyroid hormone treatment

E Rijntjes 1, A Dresler 1, E Wirth 1, D Rathmann 1, J Köhrle 1
  • 1Institut für Experimentelle Endokrinologie, Charité Universitätsmedizin-Berlin, CVK, Berlin, Germany

Alterations in thyroid hormone (TH) levels influence growth and development of the testis. We hypothesise that transmembrane TH transport proteins and local deiodination of T4 play a pivotal role in Leydig cell specific compensatory mechanisms counteracting systemic hypothyroidism. In order to test the impact of local TH availability for Leydig cell function, we exposed MLTC1 (murine Leydig cell line) under various culture conditions to TH and/or hCG and analyzed gene and protein expression and functional activity of steroidogenesis by tandem mass spectrometry (LC-MS/MS) of cellular extracts and conditioned media.

We were able to identify expression of several TH transporters (Lat1, Lat2 and Mct8) in the MLTC1. Transcript levels of selenoenzymes involved in TH metabolism, Dio2 and Dio3, were low. MTLC1 cells exposed to various TH (1µM; 15' or 60') to determine TH uptake. In order of preference, T4, 3,5T2, 3,3'-T2, T1AM and T3 were transported into the MLTC1 cells. A combination of TH transporter inhibitors decreased uptake of TH by approximately 50%, with notable exception of non-inhibited T1AM uptake.

Next, serum-starved MLTC1 cells were treated with hCG (100mU/ml) and/or T3 and/or T4 (100nM) for 1h. hCG stimulated gene expression of the steroidogenic enzymes 3βHsd1 and Star, whereas treatment with TH alone did not. A combination of hCG and T4, but not hCG and T3, synergistically enhanced transcript levels compared to hCG alone. hCG also stimulated functional steroidogenesis and secretion of steroid hormones. The combination of hCG and TH did not change the steroid production.

These findings suggest that several TH and their metabolites can be taken up by this Leydig cell line, with a surprising preference for T4 over T3, at least partially mediated by known transmembrane TH transporter proteins. Whether altered levels of free TH impact on transporter activity and local TH availability remains to be studied.

Supported by DFG grants RI 2457/1 and KO 922/17 – 1.