Endocrine Abstracts

The vulnerability of early central nervous system (CNS) development to thyroid hormone (TH) deprivation has been highlighted by studies showing an association between maternal hypothyroxinemia during the first trimester and long-term neurodevelopmental delay in the offspring. The molecular mechanisms underlying this observation are, however, poorly understood. It is known that the actions of triiodothyronine (T3), the active TH metabolite, are primarily mediated by TRs, which act as nuclear transcription factors. We investigated the use of NT2 cells (an embryonal cell line from a human teratocarcinoma which displays characteristics of CNS precursor cells) as an in vitro human model of TH action in the CNS. NT2 cells can differentiate into functional neurons, astrocytes and oligodendrocytes. We have previously demonstrated that they are T3 responsive, and express TR-alpha1, -alpha2 and -beta1. When NT2 cells cultured in media supplemented with stripped FBS were treated with 50 or 100nM T3, there was significantly increased cell proliferation compared to 0nM T3 controls (21%, p<0.001 and 18%, p<0.01 respectively) at 120 hours post-T3-treatment as assessed by thiazolyl blue (MTT) proliferation assays. Transient transfection of the non-ligand binding TR-beta1 mutant delta337, previously described in the syndrome of TH resistance, increased NT2 proliferation both in the presence and absence of T3 compared to cells transfected with vector only from 24 hours (4.4%, p<0.001) to 96 hours (12%, p<0.001) post-T3-treatment. Interestingly, this pro-proliferative effect of delta337 was lost when NT2 cells were co-transfected with wild type TR-beta1. Conclusion: Endogenous TR-beta1 may have a role in suppressing NT2 cell proliferation. The pro-proliferative effects of T3 in NT2 cells are not mediated by TR-beta1.