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Non-canonical thyroid hormone signaling mediates cardiometabolic effects in vivo

ABSTRACT: Thyroid hormone (TH) and TH receptors (TRs) α and β act by binding to TH response elements (TREs) in regulatory regions of target genes. This nuclear signaling is established as the canonical pathway for TH action. In addition, however, TRs can activate intra-cellular second messenger signaling pathways. Whether such non-canonical TR signaling is physiologically relevant in vivo is unknown. Here we generated knock-in mice with a mutation in the TR DNA-binding domain that abrogates binding to DNA and TREs and leads to a complete loss of canonical TH action. We show that several important physiological TH effects are preserved despite disrupted DNA-binding, most notably heart rate, body temperature, blood glucose and triglyceride concentration, all of which were regulated by non-canonical TR signaling. Additionally, we confirm that TRE-binding defective TRβ leads to disruption of the hypothalamic-pituitary-thyroid axis with resistance to TH, while mutation of TRα causes a severe delay in skeletal development, showing TRE-mediated and tissue-specific canonical signaling. Our findings provide first in vivo evidence that non-canonical TR signaling exerts important cardiometabolic effects, which are clearly separated from canonical actions. Consequently, these data challenge the current paradigm that TH action is exclusively mediated through regulation of gene transcription at the nuclear level.

ORGANISM(S): Mus musculus

PROVIDER: GSE104877 | GEO | 2017/11/01

SECONDARY ACCESSION(S): PRJNA414077

REPOSITORIES: GEO

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Project description:Thyroid hormones (THs) play a critical role in development and throughout adulthood. THs act through the thyroid receptor (TR), which binds to the TH response element (TRE) to regulate the expression of target genes. Although TH action has been studied for decades, surprisingly few TREs have been well validated and characterized. In this study we used chromatin immunoprecipitation followed by microarray analysis (ChIP-chip) to identify TR-binding sites in juvenile (postnatal day 15) mice liver. Microarray analysis revealed twelve TR-binding sites consistent between all analyzed samples. In silico analysis was carried out to search for moderately conserved classic TRE sequences within these novel binding regions, which led to the identification of six candidate TREs within three binding regions. Luciferase reporter assays confirmed the presence of a TRE in the promoter region of DEAD (Asp-Glu-Ala-Asp) box polypeptide 54 (Ddx54) and thyroid hormone responsive SPOT14 (Thrsp). The TR/retinoid X receptor (RXR) heterodimer and RXR homodiner were shown to bind the promoter region of Ddx54 and drive gene expression in the presence of 9-cis-retinoic acid (9cRA). The promoter region of Thrsp was shown to allow binding of the TR/RXR heterodimer, and both T3 and 9cRA were able to significantly increase luciferase activity. The RXR homodimer was also able to bind the response element in the promoter region of Thrsp and increase luciferase activity. Overall, ChIP-chip analysis revealed a relatively limited number of TR-binding sites in juvenile mouse liver despite previous studies showing that numerous genes can be affected by TH disruption at that developmental stage, suggesting that TH action may also be mediated through other intermediates. Collectively the results provide an important step towards characterizing TR-binding sites and identifying the underlying drivers of TR-gene regulation. Three samples were analyzed (total input and immunoprecipitated for each samples).

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Non-canonical thyroid hormone signaling mediates cardiometabolic effects in vivo

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