Biology subjects

Flamant, F.

Publications and source records attributed to Flamant, F..

8 recordsLinked to original sources

bioRxiv2025

Extrahepatic effects of thyroid hormone and resmetirom override their beneficial hepatic effects in alcohol-associated liver disease in mice

BackgroundAlcohol-associated liver disease (ALD) is a common type of liver disease worldwide. Excessive consumption of ethanol (EtOH) causes fat accumulation leading to hepatic steatosis. Hepatic thyroid hormone (TH) action or liver-specific thyromimetics, e.g. resmetirom, can reduce hepatic triglycerides. We therefore hypothesized that TH treatment could ameliorate ALD. MethodsTo induce ALD, mice were treated with either EtOH or liquid control diet for 10 days followed by a single EtOH or maltose control gavage on day 11. The liquid diets were supplemented with solvent, T3 or Resmetirom. We studied WT and hepatocyte-specific TR{beta} KO mice (hepTR{beta}KO). Effects were measured by clinical chemistry, liver staining, hepatic triglyceride content, and RNA-sequencing. ResultsSurprisingly, resmetirom had no beneficial effect and T3 treatment even aggravated EtOH-induced steatosis (increased liver weight and hepatic triglycerides). The liver phenotype was worsened in hepTR{beta}KO mice, which still suggested beneficial effects of hepatic TR{beta} signaling in WT mice. These seemingly paradoxical results could be explained by extrahepatic effects in WAT: WAT weight and adipocyte size were reduced by EtOH, T3 and resmetirom. These data indicate lipolysis and subsequent fatty acid accumulation in the liver, explaining the more severe ALD phenotype with T3 and attenuated effect of resmetirom. As WAT loss was reduced in hepTR{beta}KO mice, the hepatic TR{beta} mediated the extrahepatic effects of T3 and resmetirom on WAT. ConclusionWe conclude that extrahepatic TH effects in WAT were detrimental in ALD and counteracted beneficial local hepatic TH/TR{beta} action. As WAT loss appeared to originate from the hepatic TR{beta}, this also applied to resmetirom.

pathology↗

bioRxiv2024

Thyroid hormones act as a timer for the postnatal maturation of parvalbumin neurons in mouse neocortex

Thyroid hormones (THs) are required for proper maturation of parvalbumin-expressing GABAergic interneurons in the mouse neocortex, which function is essential to maintain a proper balance between neuronal excitation and inhibition. However, the timeline of this TH action has yet to be elucidated. Here, we used several mouse models expressing dominant negative mutations of the TH nuclear receptor 1 (TR1), to better define the time window during which THs promote the maturation of parvalbumin neurons. The action of THs during the first three postnatal weeks appears to be necessary to initiate the elaboration of a specialized extracellular matrix called the perineuronal net. Transcriptome analysis identified a small set of putative target genes for TR1, which are at the origin of the postnatal remodeling of the repertoire of ions channels and the elaboration of perineuronal nets. These data suggest that THs act as a timer to define the temporal boundaries of the critical period of heightened cortical plasticity, which plays a fundamental role in the development of neuronal circuits. Significance statementThyroid hormones exert a major influence on late neurodevelopment, acting directly on gene expression by binding to nuclear receptors present in all cell types. This study reports the discovery of a direct link between the transcriptional regulation exerted by the thyroid hormones in GABAergic neurons and the timing of the critical period of heightened plasticity. This provides a general framework to understand the pathology associated with altered thyroid hormone signaling.

developmental biology↗

bioRxiv2024

Thyroid hormones maintain parvalbumin neuron functions in mouse neocortex

Parvalbumin-expressing GABAergic interneurons play a key role in maintaining the excitation-inhibition balance in the mammalian neocortex. While postnatal maturation of parvalbumin neurons is highly sensitive to thyroid hormone deficiency, the role of these hormones in mature parvalbumin neurons remains poorly understood. Here, we addressed the possibility that thyroid hormones are also required to maintain the function of mature parvalbumin neurons in the mouse neocortex. To this end, Cre/loxP recombination system was used to express a dominant-negative mutated receptor of thyroid hormones to selectively eliminate thyroid hormone signaling in parvalbumin neurons after the onset of parvalbumin expression. We analyzed the neocortical phenotype of these mice by combining genomics, histology, electrophysiology, sleep recordings and behavioral analysis. In the mutant mice, gene expression analysis revealed a decreased expression of key perineuronal net components. parvalbumin neuron excitability was decreased and mice displayed behavioral hyperactivity and increased susceptibility to epileptic seizures. Additionally, sleep analysis revealed that mutant mice spent more time awake, and had a delayed transition to sleep. Electrophysiological recordings further demonstrated altered gamma oscillations in the somatosensory cortex. The findings of this study underscore that thyroid hormones are essential not only for the differentiation of parvalbumin interneurons, but also for the maintenance of their inhibitory function after the onset of parvalbumin expression. As a consequence, alterations in thyroid hormone signaling, during development or in adulthood, may contribute to the occurrence of neurological and psychiatric disorders involving altered cortical oscillations.

neuroscience↗

bioRxiv2022

An atlas of thyroid hormone receptors target genes in mouse tissues

We gathered in a single database available RNA-seq and ChIP-seq data to better characterize the target genes of the thyroid hormone receptors in several cell types. This database can serve as a resource to analyze the mode of action of the hormone. Also, it is an easy-handling convenient tool to obtain information on specific genes in regards to T3 regulation, or extract larger list of genes of interest based on the users criteria. Overall, this atlas is a unique compilation of recent sequencing data focusing on thyroid hormones, their receptors, mode of action, targets and roles which may profit researchers within the field. A preliminary analysis indicates extensive variations in the repertoire of target genes which transcription is upregulated by chromatin-bound nuclear receptor. Although it has a major influence, chromatin accessibility is not the only parameter that determines the cellular selectivity of hormonal response.

genomics↗

bioRxiv2022

Brown adipocytes local response to thyroid hormone is required for adaptive thermogenesis in adult male mice

Thyroid hormone (T3) and its nuclear receptors (TR) are important regulators of energy expenditure and adaptive thermogenesis, notably through their action in the brown adipose tissue (BAT). However, T3 acts in many other peripheral and central tissues which are also involved in energy expenditure. The general picture of how T3 regulates BAT thermogenesis is currently not fully established, notably due to the absence of extensive omics analyses and the lack of specific mice model. Here, we first used transcriptome and cistrome analyses to establish the list of T3/TR direct target genes in brown adipocytes. We then developed a novel model of transgenic mice, in which T3-signaling is specifically suppressed in brown adipocytes at adult stage. We addressed the capacity of these mice to mount a thermogenic response when challenged by either a cold exposure or a high-fat diet, and analyzed the associated changes in BAT transcriptome. We conclude that T3 plays a crucial role in the thermogenic response of the BAT, controlling the expression of genes involved in lipid and glucose metabolism and regulating BAT proliferation. The resulting picture provides an unprecedented view on the pathways by which T3 activates energy expenditure through an efficient adaptive thermogenesis in the BAT. Significance StatementThyroid hormones (TH) increase energy expenditure by regulating the expression of target genes in many metabolic tissues. Among them, brown adipose tissue (BAT) dissipates biochemical energy into heat production to notably prevent hypothermia during cold exposure. Hypothyroid mice display inefficient BAT thermogenesis suggesting that TH are crucial for this process. Here, we eliminated TH signaling specifically in brown adipocytes and expose the mice to different physiological stressors. We showed that TH signaling is crucial for BAT thermogenesis as it controls the expression of genes involved in proliferation and in the metabolism of lipids and glucose, the main energy resources for BAT thermogenesis. This study provides an unprecedented view on the pathways by which T3 activates energy expenditure the BAT.

genomics↗

bioRxiv2022

Functional definition of thyroid hormone response elements based on a synthetic STARR-seq screen

When bound to thyroid hormone, the nuclear receptor TR1 activates the transcription of a number of genes in many cell types. It mainly acts by binding DNA as an heterodimer with RXRs at specific response elements related to the DR4 consensus sequence. However, the number of DR4-like elements in the genome exceed by far the number of occupied sites, indicating that minor variations in nucleotides composition deeply influence the DNA-binding capacity and transactivation activity of TR1. An improved protocol of synthetic STARR-seq was used to quantitatively assess the transcriptional activity of thousands of synthetic sites in parallel. This functional screen highlights a strong correlation between the affinity of the heterodimers for DNA and their capacity to mediate the thyroid hormone response.

molecular biology↗

bioRxiv2020

In vitro assessment of the capacity of pesticides to act as agonists/antagonists of the thyroid hormone nuclear receptors.

Several in vitro tests, including transcriptome analysis of neural cells, were performed to assess the capacity of 33 pesticides to act as thyroid hormone disruptors (THD). Although some pesticides elicit a cellular response, which interferes with thyroid hormone signaling, we found no evidence that they can act as receptor agonists or antagonists. We conclude that the nuclear receptors of thyroid hormone are not common targets of THD, and that pesticide neurodevelopmental toxicity is not explained by a general alteration of neural cell response to thyroid hormone.

pharmacology and toxicology↗

bioRxiv2019

A pivotal genetic program controlled by thyroid hormone during the maturation of GABAergic neurons in mice

In mammals, brain development is critically dependent on proper thyroid hormone signaling, via the TR1 nuclear receptor. However, the downstream mechanisms by which TR1 impacts brain development are currently unknown, notably because this receptor is expressed ubiquitously from early stages of development. In order to better define the function of TR1 in the developing brain, we used mouse genetics to induce the expression of a dominant-negative mutation of the receptor specifically in GABAergic neurons, the main inhibitory neurons in the brain, which were previously identified as sensitive to hypothyroidism. This triggered post-natal epileptic seizures, reflecting a profound impairment of GABAergic neuron maturation in different brain areas. Analysis of transcriptome and TR1 cistrome also allowed us to identify a small set of genes, the transcription of which is upregulated by TR1 in GABAergic neurons during post-natal maturation of the striatum and which probably play an important role during neurodevelopment. Thus, our results point to GABAergic neurons as direct targets of thyroid hormone during brain development and suggest that many defects seen in hypothyroid brains may be secondary to GABAergic neuron malfunction.

developmental biology↗