TAZ/WWTR1 Mediates the Pulmonary Effects of NKX2-1 Mutations in Brain-Lung-Thyroid Syndrome

Systematic review of thyroid function in NKX2-1-related disorders: Screening and diagnosis

BACKGROUND

NKX2-1-related disorders (NKX2-1-RD) are rare conditions affecting lung, thyroid, and brain development, primarily caused by pathogenic variants or deletions in the NKX2-1 gene. Congenital hypothyroidism (CH) is a common endocrine manifestation, leading to irreversible intellectual disability if left untreated.

OBJECTIVES

The aim was to evaluate the current evidence for the use of screening and diagnostic techniques for endocrine alterations in patients with NKX2-1-RD.

METHODS

This systematic review was reported following the PRISMA guidelines. Two separate research questions in PICO format were addressed to cover initial screening and diagnosis procedures for endocrine diseases in patients with NKX2-1-RD. Eligibility criteria focused on patients with genetic confirmation of the disease and hypothyroidism. Various databases were searched, and data were extracted and assessed independently by two reviewers.

RESULTS

Out of 1012 potentially relevant studies, 46 were included, for a total of 113 patients. CH was the most frequent endocrine alteration (45% of patients). Neonatal screening was reported in only 21% of patients based on blood TSH measurements. TSH thresholds varied widely across studies, making hypothyroidism detection ranges difficult to establish. Diagnostic tests using serum TSH were used to diagnose hypothyroidism or confirm its presence. 35% of patients were diagnosed at neonatal age, and 42% at adult age. Other hormonal dysfunctions identified due to clinical signs, such as anterior pituitary deficiencies, were detected later in life. Thyroid scintigraphy and ultrasonography allowed for the description of the thyroid gland in 30% of cases of hypothyroidism. Phenotypic variability was observed in individuals with the same variants, making genotype-phenotype correlations challenging.

CONCLUSION

This review highlights the need for standardized protocols in endocrine screening for NKX2-1-RD, emphasizing the importance of consistent methodology and hormone threshold levels. Variability in NKX2-1 gene variants further complicates diagnostic efforts. Future research should concentrate on optimizing early screening protocols and diagnostic strategies.

A Novel Missense Variant in the NKX2-1 Homeodomain Prevents Transcriptional Rescue by TAZ

Background: Brain-lung-thyroid syndrome (BLTS) is caused by NKX2-1 haploinsufficiency, resulting in chorea/choreoathetosis, respiratory problems, and hypothyroidism. Genes interacting with NKX2-1 mutants influence its phenotypic variability. We report a novel NKX2-1 missense variant and the modifier function of TAZ/WWTR1 in BLTS. Methods: A child with BLTS underwent next-generation sequencing panel testing for thyroid disorders. His family was genotyped for NKX2-1 variants and screened for germline mosaicism. Mutant NKX2-1 was generated, and transactivation assays were performed on three NKX2-1 target gene promoters. DNA binding capacity and protein-protein interaction were analyzed. Results: The patient had severe BLTS and carried a novel missense variant c.632A>G (p.N211S) in NKX2-1, which failed to bind to specific DNA promoters, reducing their transactivation. TAZ cotransfection did not significantly increase transcription of these genes, although the variant retained its ability to bind to TAZ. Conclusions: We identify a novel pathogenic NKX2-1 variant that causes severe BLTS and is inherited through germline mosaicism. The mutant lacks DNA-binding capacity, impairing transactivation and suggesting that NKX2-1 binding to DNA is essential for TAZ-mediated transcriptional rescue.

Functional characterization of two novel NKX2-1 frameshift variants that cause pulmonary surfactant dysfunction

BACKGROUND

We aim to report two unrelated patients with pulmonary surfactant dysfunction (PSD) that carried two novel NKX2-1 frameshift variants, and evaluated the impact of these variants in vitro.

METHODS

We enrolled children with PSD and NKX2-1 variants, and collected their clinical information and follow-up data. We constructed wild-type (WT) and variant NKX2-1 plasmids and transfected them into A549 and HEK293T cells. The functional characterization of variants was then evaluated by qRT-PCR, western blot, immunofluorescence, electrophoretic mobility shift assay, and dual-luciferase reporter assay.

RESULTS

Two novel heterozygous frameshift variants of NKX2-1, i.e., c.705delC (Gly236Alafs*29) and c.313_316 dup (Asn106Lysfs*304), were identified in children from two unrelated families. We discerned attenuated mRNA and protein expression in the Asn106Lysfs*304 variant, and reduced DNA -binding as well as transcriptional activation capabilities in both variants. While the Asn106Lysfs*304 variant lost its synergistic interactions with PAX8 and TAZ, the Gly236Alafs*29 variant partially retained its residual transcriptional activation capabilities and synergistic interactions with PAX8 and TAZ.

CONCLUSIONS

We reported on two children with two novel NKX2-1 frameshift variants. In vitro experiments revealed that the two frameshift variants have common and different mechanisms based on the loss or conservation of domains, which partially explained the phenotypical heterogeneity.

IMPACT

Pulmonary surfactant dysfunction is a rare heterogeneous disease that exhibits a great burden on children's quality of life. We reported two novel NKX2-1 frameshift variants carried by two children with different clinical phenotypes, thus broadening our knowledge base of gene variations and phenotypes in NKX2-1. We performed an in vitro study and uncovered different pathogenic mechanisms underlying the actions of two novel variants, and thereby partially explained the mechanisms of phenotypical heterogeneity caused by NKX2-1 variants.

Chorea: An unusual manifestation of endocrine diseases

Chorea is a movement disorder involving involuntary movements of muscles of the face, neck, and limbs, usually caused by basal ganglia lesions. As an important part of the presentation of many neurological diseases, chorea is also an unusual manifestation of endocrine diseases and can be challenging to diagnose. Although the most common etiology of chorea is genetic, it is vital to identify acquired or symptomatic chorea, as these are potentially treatable conditions. This review summarizes the latest developments in various endocrine disease-related chorea, which will help clinicians to correctly identify and accurately treat it.

A Critical Balance Between PAX8 and the Hippo Mediator TAZ Determines Sodium/Iodide Symporter Expression and Function

Background: The Hippo pathway has a fundamental role in tissue homeostasis, but little is known about how this signaling cascade is controlled in the thyroid. PAX8 is an essential driver of thyroid differentiation and is involved in the control of genes crucial for thyroid hormone biosynthesis, including the sodium/iodide symporter (NIS; SLC5A5). A role for the Hippo mediator transcriptional coactivator with PDZ-binding motif (TAZ) as a coactivator of PAX8 to promote thyroglobulin expression has been previously described. Here, we studied the role of TAZ on thyroid differentiation focusing on PAX8-mediated Slc5a5 transcription. Methods: Gene silencing and overexpression assays were performed in rat PCCl3 thyroid follicular cells (TFCs) to determine the role of TAZ in the regulation of Slc5a5. Transcriptional activity of the Hippo mediators was investigated by chromatin immunoprecipitation and promoter-reporter gene activity. Hippo component levels and location were analyzed in PCCl3 cells and in mouse thyroid under different treatment conditions. Results: By suppressing the expression of PAX8 and its binding to the Slc5a5 upstream enhancer, TAZ inhibits Slc5a5 expression, impairing NIS membrane location and activity. Other Hippo effectors such as YAP1 and TEAD1 were not required for the repressor effect of TAZ. We also found an interplay between the Hippo, thyrotropin (TSH), and transforming growth factor β1 (TGFβ) pathways in TFCs. TSH via cyclic adenosine monophosphate activated Hippo signaling pathway and, consequently, TAZ was excluded from the nucleus. We confirmed this in hypothyroid mice, characterized by elevated TSH serum levels, which showed downregulated activation of Hippo signaling in thyroid. Conversely, TAZ nuclear retention was promoted by TGFβ, a potent NIS repressor, and TAZ silencing markedly relieved the TGFβ-induced inhibition of the symporter. Conclusions: We demonstrate that the effects of TAZ are promoter specific, as it functions as a corepressor of PAX8 to modulate Slc5a5 expression in TFCs. Overall, our data place TAZ as an integrator of the different signaling pathways that control NIS expression, pointing to a role for TAZ in thyroid differentiation and identifying the Hippo pathway as a relevant target to recover NIS levels in thyroid cancer cells.

Deciphering an isolated lung phenotype of NKX2-1 frameshift pathogenic variant

BACKGROUND

to perform a functional analysis of a new NK2 homeobox 1 (NKX2-1) variant (c.85_86del denominated NKX2-1^DEL) identified in a family presenting with isolated respiratory disease, in comparison to another frameshift variant (c.254dup denominated NKX2-1^DUP) identified in a subject with classical brain-lung-thyroid syndrome.

METHODS

pathogenic variants were introduced into the pcDNA3-1(+)-wt-TTF1 plasmid. The proteins obtained were analyzed by western blot assay. Subcellular localization was assessed by confocal microscopy in A549 and Nthy cells. Transactivation of SFTPA, SFTPB, SFTPC, and ABCA3 promoters was assessed in A549 cells. Thyroglobulin promoter activity was measured with the paired box gene 8 (PAX8) cofactor in Nthy cells.

RESULTS

The two sequence variants were predicted to produce aberrant proteins identical from the 86th amino acid, with deletion of their functional homeodomain, including the nuclear localization signal. However, 3D conformation prediction of the conformation prediction of the mutant protein assumed the presence of a nuclear localization signal, a bipartite sequence, confirmed by confocal microscopy showing both mutant proteins localized in the nucleus and cytoplasm. Transcriptional activity with SFTPA, SFTPB, SFTPC, ABCA3 and thyroglobulin promoters was significantly decreased with both variants. However, with NKX2-1^DEL, thyroglobulin transcriptional activity was maintained with the addition of PAX8.

CONCLUSION

These results provide novel insights into understanding the molecular mechanism of phenotypes associated with NKX2-1 pathogenic variants.

Differential chromatin binding of the lung lineage transcription factor NKX2-1 resolves opposing murine alveolar cell fates in vivo

Differential transcription of identical DNA sequences leads to distinct tissue lineages and then multiple cell types within a lineage, an epigenetic process central to progenitor and stem cell biology. The associated genome-wide changes, especially in native tissues, remain insufficiently understood, and are hereby addressed in the mouse lung, where the same lineage transcription factor NKX2-1 promotes the diametrically opposed alveolar type 1 (AT1) and AT2 cell fates. Here, we report that the cell-type-specific function of NKX2-1 is attributed to its differential chromatin binding that is acquired or retained during development in coordination with partner transcriptional factors. Loss of YAP/TAZ redirects NKX2-1 from its AT1-specific to AT2-specific binding sites, leading to transcriptionally exaggerated AT2 cells when deleted in progenitors or AT1-to-AT2 conversion when deleted after fate commitment. Nkx2-1 mutant AT1 and AT2 cells gain distinct chromatin accessible sites, including those specific to the opposite fate while adopting a gastrointestinal fate, suggesting an epigenetic plasticity unexpected from transcriptional changes. Our genomic analysis of single or purified cells, coupled with precision genetics, provides an epigenetic basis for alveolar cell fate and potential, and introduces an experimental benchmark for deciphering the in vivo function of lineage transcription factors.

Transient PAX8 Expression in Islets During Pregnancy Correlates With β-Cell Survival, Revealing a Novel Candidate Gene in Gestational Diabetes Mellitus

Transient Pax8 expression was reported in mouse islets during gestation, whereas a genome-wide linkage and admixture mapping study highlighted PAX8 as a candidate gene for diabetes mellitus (DM). We sought the significance of PAX8 expression in mouse and human islet biology. PAX8 was induced in gestating mouse islets and in human islets treated with recombinant prolactin. Global gene expression profiling of human and mouse islets overexpressing the corresponding species-specific PAX8 revealed the modulation of distinct genetic pathways that converge on cell survival. Accordingly, apoptosis was reduced in PAX8-overexpressing islets. These findings support that PAX8 could be a candidate gene for the study of gestational DM (GDM). PAX8 was genotyped in patients with GDM and gestational thyroid dysfunction (GTD), a pathology commonly found in patients with mutations on PAX8 A novel missense PAX8 mutation (p.T356M, c.1067C>T) was identified in a female diagnosed with GDM and GTD as well as in her father with type 2 DM but was absent in control patients. The p.T356M variant did not alter protein stability or cellular localization, whereas its transactivation activity was hindered. In parallel, a retrospective clinical analysis uncovered that a pregnant female harboring a second PAX8 mutation (p.P25R, c.74C>G) previously reported to cause congenital hypothyroidism also developed GDM. These data indicate that increased expression of PAX8 affects islet viability and that PAX8 could be considered as a candidate gene for the study of GDM.