Regulation of type 1 iodothyronine deiodinase by LXRα

A regulatory element associated to NAFLD in the promoter of DIO1 controls LDL-C, HDL-C and triglycerides in hepatic cells

BACKGROUND

Genome-wide association studies (GWAS) have identified genetic variants linked to fat metabolism and related traits, but rarely pinpoint causative variants. This limitation arises from GWAS not considering functional implications of noncoding variants that can affect transcription factor binding and potentially regulate gene expression. The aim of this study is to investigate a candidate noncoding functional variant within a genetic locus flagged by a GWAS SNP associated with non-alcoholic fatty liver disease (NAFLD), a condition characterized by liver fat accumulation in non-alcohol consumers.

METHODS

CRISPR-Cas9 gene editing in HepG2 cells was used to modify the regulatory element containing the candidate functional variant linked to NAFLD. Global gene expression in mutant cells was assessed through RT-qPCR and targeted transcriptomics. A phenotypic assay measured lipid droplet accumulation in the CRISPR-Cas9 mutants.

RESULTS

The candidate functional variant, rs2294510, closely linked to the NAFLD-associated GWAS SNP rs11206226, resided in a regulatory element within the DIO1 gene's promoter region. Altering this element resulted in changes in transcription factor binding sites and differential expression of candidate target genes like DIO1, TMEM59, DHCR24, and LDLRAD1, potentially influencing the NAFLD phenotype. Mutant HepG2 cells exhibited increased lipid accumulation, a hallmark of NAFLD, along with reduced LDL-C, HDL-C and elevated triglycerides.

CONCLUSIONS

This comprehensive approach, that combines genome editing, transcriptomics, and phenotypic assays identified the DIO1 promoter region as a potential enhancer. Its activity could regulate multiple genes involved in the NAFLD phenotype or contribute to defining a polygenic risk score for enhanced risk assessment in NAFLD patients.

Bezafibrate induces hypothyroidism in a patient with resistance to thyroid hormone β due to a G347R variant

OBJECTIVE

A unique clinical course was observed in a patient with resistance to thyroid hormone β (RTHβ) caused by a variant of the THRB gene leading to the replacement of glycine with arginine in codon 347 (p.G347R). He presented with the syndrome of inappropriate secretion of thyrotropin (TSH) (free T4 [fT4]: 32.43 pmol/L, TSH: 4.67 mIU/L), but slowly developed progressive hypothyroidism (fT4: 8.37 pmol/L, TSH: 100.90 mIU/L) that resolved after suspending bezafibrate (BZ) treatment (fT4: 32.18 pmol/L, TSH: 7.14 mIU/L). This study clinically and experimentally evaluated this interesting phenomenon.

METHODS

A retrospective cohort analysis of non-RTHβ patients was performed at Kyoto University Hospital. Data before BZ treatment were compared to the first data after treatment. Using reporter assays of iodothyronine deiodinases (DIO1, DIO2, DIO3) in HEK293T cells, we performed functional analyses of mutant thyroid hormone receptor β with p.G347R (G347R TRβ). Mice with G347R TRβ were generated by hydrodynamic gene delivery.

RESULTS

In non-RTHβ patients (n = 7), BZ treatment did not change serum free T3 and TSH but significantly increased fT4 (p = .008). BZ administration increased DIO3 reporter activity in the context of G347R TRβ, whereas did not change DIO1 and DIO2 reporter activity. In the livers of mice with G347R TRβ, BZ administration increased reverse T3 content, which corresponded to an increase in Dio3 messenger RNA.

CONCLUSIONS

While hypothyroidism associated with BZ treatment did not occur in non-RTHβ patients, it was observed in a patient with RTHβ due to the p.G347R variant. Liver DIO3 upregulation might involve this hypothyroidism.

8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a Cause of Autoimmune Thyroid Diseases (AITD) During Pregnancy?

The thyroid is not necessary to sustain life. However, thyroid hormones (TH) strongly affect the human body. Functioning of the thyroid gland affects the reproductive capabilities of women and men, as well as fertilization and maintaining a pregnancy. For the synthesis of TH, hydrogen peroxide (H2O2) is necessary. From the chemical point of view, TH is a reactive oxygen species (ROS) and serves as an oxidative stress (OS) promoter. H2O2 concentration in the thyroid gland is much higher than in other tissues. Therefore, the thyroid is highly exposed to OS. 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) are DNA lesions resulting from ROS action onto guanine moiety. Due to their abundance, they are recognized as biomarkers of OS. As thyroid function is correlated with the level of OS, 8-oxodG and 8-OHdG has been taken under consideration. Studies correlate the oxidative DNA damage with various thyroid diseases (TD) such as Hashimoto's thyroiditis (HT), Graves' disease (GD), and thyroid cancer. Human sexual function and fertility are also affected by OS and TD. Hypothyroidism and hyperthyroidism diagnosed in pregnant women have a negative effect on pregnancy as it may increase the risk of miscarriage or fetus mortality. In the case of TD in the mother, fetal health is also at risk - neurodevelopment and cognitive function of the child may be impaired in its future life. This review presents thyroid function in the context of TD during pregnancy. The authors introduce OS and describe oxidative DNA lesions as a crucial marker of thyroid pathologies.

LRRC19-A Bridge between Selenium Adjuvant Therapy and Renal Clear Cell Carcinoma: A Study Based on Datamining

Kidney renal clear cell carcinoma (KIRC) is the most common and fatal subtype of renal cancer. Antagonistic associations between selenium and cancer have been reported in previous studies. Selenium compounds, as anti-cancer agents, have been reported and approved for clinical trials. The main active form of selenium in selenoproteins is selenocysteine (Sec). The process of Sec biosynthesis and incorporation into selenoproteins plays a significant role in biological processes, including anti-carcinogenesis. However, a comprehensive selenoprotein mRNA analysis in KIRC remains absent. In the present study, we examined all 25 selenoproteins and identified key selenoproteins, glutathione peroxidase 3 (GPX3) and type 1 iodothyronine deiodinase (DIO1), with the associated prognostic biomarker leucine-rich repeat containing 19 (LRRC19) in clear cell renal cell carcinoma cases from The Cancer Genome Atlas (TCGA) database. We performed validations for the key gene expression levels by two individual clear cell renal cell carcinoma cohorts, GSE781 and GSE6344, datasets from the Gene Expression Omnibus (GEO) database. Multivariate survival analysis demonstrated that low expression of LRRC19 was an independent risk factor for OS. Gene set enrichment analysis (GSEA) identified tyrosine metabolism, metabolic pathways, peroxisome, and fatty acid degradation as differentially enriched with the high LRRC19 expression in KIRC cases, which are involved in selenium therapy of clear cell renal cell carcinoma. In conclusion, low expression of LRRC19 was identified as an independent risk factor, which will advance our understanding concerning the selenium adjuvant therapy of clear cell renal cell carcinoma.

Restoration of type 1 iodothyronine deiodinase expression in renal cancer cells downregulates oncoproteins and affects key metabolic pathways as well as anti-oxidative system

Type 1 iodothyronine deiodinase (DIO1) contributes to deiodination of 3,5,3’,5’-tetraiodo-L-thyronine (thyroxine, T4) yielding of 3,5,3’-triiodothyronine (T3), a powerful regulator of cell differentiation, proliferation, and metabolism. Our previous work showed that loss of DIO1 enhances proliferation and migration of renal cancer cells. However, the global effects of DIO1 expression in various tissues affected by cancer remain unknown. Here, the effects of stable DIO1 re-expression were analyzed on the proteome of renal cancer cells, followed by quantitative real-time PCR validation in two renal cancer-derived cell lines. DIO1-induced changes in intracellular concentrations of thyroid hormones were quantified by L-MS/MS and correlations between expression of DIO1 and potential target genes were determined in tissue samples from renal cancer patients. Stable re-expression of DIO1, resulted in 26 downregulated proteins while 59 proteins were overexpressed in renal cancer cells. The ‘downregulated’ group consisted mainly of oncoproteins (e.g. STAT3, ANPEP, TGFBI, TGM2) that promote proliferation, migration and invasion. Furthermore, DIO1 re-expression enhanced concentrations of two subunits of thyroid hormone transporter (SLC7A5, SLC3A2), enzymes of key pathways of cellular energy metabolism (e.g. TKT, NAMPT, IDH2), sex steroid metabolism and anti-oxidative response (AKR1C2, AKR1B10). DIO1 expression resulted in elevated intracellular concentration of T4. Expression of DIO1-affected genes strongly correlated with DIO1 transcript levels in tissue samples from renal cancer patients as well as with their poor survival. This first study addressing effects of deiodinase re-expression on proteome of cancer cells demonstrates that induced DIO1 re-expression in renal cancer robustly downregulates oncoproteins, affects key metabolic pathways, and triggers proteins involved in anti-oxidative protection. This data supports the notion that suppressed DIO1 expression and changes in local availability of thyroid hormones might favor a shift from a differentiated to a more proliferation-prone state of cancer tissues and cell lines.