ZFP36L2 Role in Thyroid Functionality.

Francesco Albano,Valeria Tucci,Massimo Mallardo,Filomena Russo,Concetta Ambrosino,Perry J Blackshear,Marco Colella,Immacolata Porreca,Pina Marotta,Luca Roberto,Mario De Felice,Carla Reale

doi:10.3390/ijms22179379

Abstract

Thyroid hormone levels are usually genetically determined. Thyrocytes produce a unique set of enzymes that are dedicated to thyroid hormone synthesis. While thyroid transcriptional regulation is well-characterized, post-transcriptional mechanisms have been less investigated. Here, we describe the involvement of ZFP36L2, a protein that stimulates degradation of target mRNAs, in thyroid development and function, by in vivo and in vitro gene targeting in thyrocytes. Thyroid-specific Zfp36l2-/- females were hypothyroid, with reduced levels of circulating free Thyroxine (cfT4) and Triiodothyronine (cfT3). Their hypothyroidism was due to dyshormonogenesis, already evident one week after weaning, while thyroid development appeared normal. We observed decreases in several thyroid-specific transcripts and proteins, such as Nis and its transcriptional regulators (Pax8 and Nkx2.1), and increased apoptosis in Zfp36l2-/- thyroids. Nis, Pax8, and Nkx2.1 mRNAs were also reduced in Zfp36l2 knock-out thyrocytes in vitro (L2KO), in which we confirmed the increased apoptosis. Finally, in L2KO cells, we showed an altered response to TSH stimulation regarding both thyroid-specific gene expression and cell proliferation and survival. This result was supported by increases in P21/WAF1 and p-P38MAPK levels. Mechanistically, we confirmed Notch1 as a target of ZFP36L2 in the thyroid since its levels were increased in both in vitro and in vivo models. In both models, the levels of Id4 mRNA, a potential inhibitor of Pax8 activity, were increased. Overall, the data indicate that the regulation of mRNA stability by ZFP36L2 is a mechanism that controls the function and survival of thyrocytes.

Highlights

Congenital hypothyroidism (CH) is a state of inadequate thyroid hormone production at birth
ELISA measurement of circulating thyroid hormones in serum samples did not show any major differences in circulating free T4 levels between Zfp36l2-/- and control mice at postnatal day seven (PND 7, data not shown). cfT4 levels were reduced in Zfp36l2-/mice at PND 21 (Figure 1a), possibly because the THs supplied by the mother, through lactation, were no longer sufficient
It is noteworthy that several recent papers have described the role of splicing modulation in thyroid development in vivo [49], suggesting this mode of post-transcriptional regulation as a mechanism involved in thyroid development, function, carcinogenesis, and thyroid

Summary

Introduction

Congenital hypothyroidism (CH) is a state of inadequate thyroid hormone production at birth. It may involve both thyroid dysgenesis or dyshormonogenesis and defects of thyroid development/position of thyroid hormone (TH) biosynthesis [1]. Thyroid dysgenesis has been primarily associated with mutations in genes such as those encoding the TSH receptor (Tshr) [2], Forkhead box protein E1 (Foxe1) [3], and the Paired box protein Pax-8 (Pax8) [4,5]. Pax8-/-, Nkx2.1-/-, and Foxe1-/- mice reveal the importance of these genes in thyroid development [7], few germline mutations have been detected in the corresponding genes in human patients [8,9,10,11,12,13]. Papers published in the past ten years on this issue suggest that mechanisms leading to congenital thyroid dysfunction are heterogeneous [14] and involve several signaling pathways, including Notch1 [15]

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Conclusion