Background: Down Syndrome (DS) patients have a higher incidence of primary hypothyroidism. We previously demonstrated that transgenic mice overexpressing Dyrk1A had developmental (larger primary thyroids at E15.5 stage of development), morphological (disorganized follicles) and functional (significant lower plasma T4) impairments similar to DS thyroidal impairments (Endocrinology 2015). DYRK1A, localized in the DS critical region on chromosome 21, is therefore the candidate gene for thyroid dysgenesis in DS.
Objective and hypotheses: We investigated the molecular mechanism involved. Our hypothesis is that Dyrk1A directly interacts with the molecules involved in thyroid development.
Method: We performed western blots from embryonic wild type and transgenic Dyrk1a+/++ thyroids at E13.5, E15.5 and E17.5 with anti-Pax8 and anti-Foxe1 antibodies. The thyroidal human immortalized cells NThy.Ori were transfected with pGFP, pGFP-Dyrk1a, pFlag, pFlagFoxe1 and pFlag-Foxe1+pGFP-Dyrk1a. Immunoprecipitation from transfected cells were performed with anti-Flag antibody and immunoblots with anti-Dyrk1A antibody. Expression of NKX2-1, FOXE1, PAX8, THYROGLOBULIN (TG) and SODIUM IODIDE SYMPORTER (NIS) was studied by q-RTPCR in NThy.Ori and primary human thyrocytes transfected the same way.
Results: We found an increased signal of FOXE1 blot in Dyrk1a+/++ embryonic thyroids at E15.5, suggesting a direct effect of Dyrk1a on Foxe1. Immunoprecipitation revealed an interaction between GFP-DYRK1A and Flag-FOXE1 proteins. We found a significant overexpression of FOXE1 (1.4 fold expression, P=0.002), TG (3.2 fold expression, P=0.002) and NIS (10 fold expression, P=0.02) in cells transfected with pGFP-Dyrk1a, but no significant differences in NKX2−1 and PAX8 expression. Similar results were confirmed in primary human thyrocytes.
Conclusion: Overexpression of DYRK1A in embryonic thyroids leads to FOXE1 overexpression. We found a direct interaction between DYRK1A and FOXE1 by immunoprecipitationin a human thyroidal cell line, which can explain an overexpression of FOXE1 and secondarily to THYROGLOBULIN and NIS overexpression. Therefore, we can conclude that primary hypothyroidism in Down syndrome could be explained by this interaction.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology