Sox9 is involved in the thyroid differentiation program and is regulated by crosstalk between TSH, TGF\u03b2 and thyroid transcription factors

Arístides López-Márquez,Christophe E Pierreux,Andrea Martínez-Cano,Carlos Carrasco-López,Pilar Santisteban,Pascale Lemoine

doi:10.1038/s41598-022-06004-1

Abstract

While the signaling pathways and transcription factors involved in the differentiation of thyroid follicular cells, both in embryonic and adult life, are increasingly well understood, the underlying mechanisms and potential crosstalk between the thyroid transcription factors Nkx2.1, Foxe1 and Pax8 and inductive signals remain unclear. Here, we focused on the transcription factor Sox9, which is expressed in Nkx2.1-positive embryonic thyroid precursor cells and is maintained from embryonic development to adulthood, but its function and control are unknown. We show that two of the main signals regulating thyroid differentiation, TSH and TGFβ, modulate Sox9 expression. Specifically, TSH stimulates the cAMP/PKA pathway to transcriptionally upregulate Sox9 mRNA and protein expression, a mechanism that is mediated by the binding of CREB to a CRE site within the Sox9 promoter. Contrastingly, TGFβ signals through Smad proteins to inhibit TSH-induced Sox9 transcription. Our data also reveal that Sox9 transcription is regulated by the thyroid transcription factors, particularly Pax8. Interestingly, Sox9 significantly increased the transcriptional activation of Pax8 and Foxe1 promoters and, consequently, their expression, but had no effect on Nkx2.1. Our study establishes the involvement of Sox9 in thyroid follicular cell differentiation and broadens our understanding of transcription factor regulation of thyroid function.

Highlights

While the signaling pathways and transcription factors involved in the differentiation of thyroid follicular cells, both in embryonic and adult life, are increasingly well understood, the underlying mechanisms and potential crosstalk between the thyroid transcription factors Nkx2.1, Foxe[1] and Pax[8] and inductive signals remain unclear
Given the expression of Sox[9] in the embryonic thyroid and its potential to regulate the differentiation of thyroid follicular cells, we studied the role of Sox[9] in thyroid follicular cell development, its control by the main regulators of thyroid function, TSH and TGFβ, and its involvement in the transcriptional network that controls thyroid differentiation and homeostasis
Likewise, silencing CREB expression blunted TSH- and forskolin-induced Sox[9] expression (Fig. 2F). These results indicate that TSH/cAMP-dependent stimulation of Sox[9] expression is mediated, at least in part, by the CREB transcription factor

Summary

Introduction

While the signaling pathways and transcription factors involved in the differentiation of thyroid follicular cells, both in embryonic and adult life, are increasingly well understood, the underlying mechanisms and potential crosstalk between the thyroid transcription factors Nkx2.1, Foxe[1] and Pax[8] and inductive signals remain unclear. We focused on the transcription factor Sox[9], which is expressed in Nkx2.1-positive embryonic thyroid precursor cells and is maintained from embryonic development to adulthood, but its function and control are unknown. During embryogenesis in the mouse, a small group of cells from the primitive pharyngeal endoderm simultaneously begin to express the so-called thyroid transcription factors Nkx2.1, Pax[8] and Foxe[1] at embryonic day (E) 8.5, a process known as specification. Thyrotropin (TSH)[22] and transforming gowth factor (TGFβ)[23,24] appear to play critical roles Acting through their respective main signaling pathways, cAMP/CREB and Smad, both ligands regulate the expression of thyroid differentiation markers such as Pax825,26, Foxe[127], thyroglobulin (Tg)[28,29], thyroperoxidase (TPO)[24,30] and the sodium iodide symporter (NIS)[31]

Methods

Results

Conclusion