Effect of TCDD on the fate of epithelial cells isolated from human fetal palatal shelves (hFPECs)

Upregulated LncRNA-Meg3 modulates the proliferation and survival of MEPM cells via interacting with Smad signaling in TCDD-induced cleft palate

Exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in utero can result in high rates of cleft palate (CP) formation, yet the underlying mechanisms remain to be characterized. In vivo, the lncRNA Meg3 was upregulated following TCDD treatment in CP-associated murine embryonic palatal tissue, with concomitant changes in proliferative and apoptotic activity in these murine embryonic palatal mesenchymal (MEPM) cells. Meg3 can modulate the TGF-β/Smad to control the proliferation, survival, and differentiation of cells. Accordingly, TCCD and TGF-β1 were herein used to treat MEPM cells in vitro, revealing that while TCDD exposure altered the proliferative activity and apoptotic death of these cells, exogenous TGF-β1 exposure antagonized these effects via TGF-β/Smad signaling. TCDD promoted Meg3 upregulation, whereas TGF-β1 suppressed TCDD-driven upregulation of this lncRNA. Meg3 was additionally determined to directly interact with Smad2, with significant Meg3 enrichment in Smad2-immunoprecipitates following TCDD treatment. When Meg3 was silenced, the impact of TCDD on Smad signaling, proliferative activity, and apoptosis were ablated, while the effects of exogenous TGF-β1 were unchanged. This supports a model wherein Meg3 is upregulated in TCDD-exposed palatal tissue whereupon it can interact with Smad2 to suppress Smad-dependent signaling, thus controlling MEPM cell proliferation and apoptosis, contributing to TCDD-induced CP, which provides a theoretical support for the precautions of cleft palate induced by TCDD.

Toxicology knowledge graph for structural birth defects

BACKGROUND

Birth defects are functional and structural abnormalities that impact about 1 in 33 births in the United States. They have been attributed to genetic and other factors such as drugs, cosmetics, food, and environmental pollutants during pregnancy, but for most birth defects there are no known causes.

METHODS

To further characterize associations between small molecule compounds and their potential to induce specific birth abnormalities, we gathered knowledge from multiple sources to construct a reproductive toxicity Knowledge Graph (ReproTox-KG) with a focus on associations between birth defects, drugs, and genes. Specifically, we gathered data from drug/birth-defect associations from co-mentions in published abstracts, gene/birth-defect associations from genetic studies, drug- and preclinical-compound-induced gene expression changes in cell lines, known drug targets, genetic burden scores for human genes, and placental crossing scores for small molecules.

RESULTS

Using ReproTox-KG and semi-supervised learning (SSL), we scored >30,000 preclinical small molecules for their potential to cross the placenta and induce birth defects, and identified >500 birth-defect/gene/drug cliques that can be used to explain molecular mechanisms for drug-induced birth defects. The ReproTox-KG can be accessed via a web-based user interface available at https://maayanlab.cloud/reprotox-kg . This site enables users to explore the associations between birth defects, approved and preclinical drugs, and all human genes.

CONCLUSIONS

ReproTox-KG provides a resource for exploring knowledge about the molecular mechanisms of birth defects with the potential of predicting the likelihood of genes and preclinical small molecules to induce birth defects.

Proper modulation of AHR signaling is necessary for establishing neural connectivity and oligodendrocyte precursor cell development in the embryonic zebrafish brain

2,3,7,8-tetrachlorodibenzo-[p]-dioxin (TCDD) is a persistent global pollutant that exhibits a high affinity for the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. Epidemiological studies have associated AHR agonist exposure with multiple human neuropathologies. Consistent with the human data, research studies using laboratory models have linked pollutant-induced AHR activation to disruptions in learning and memory as well as motor impairments. Our understanding of endogenous AHR functions in brain development is limited and, correspondingly, scientists are still determining which cell types and brain regions are sensitive to AHR modulation. To identify novel phenotypes resulting from pollutant-induced AHR activation and ahr2 loss of function, we utilized the optically transparent zebrafish model. Early embryonic TCDD exposure impaired embryonic brain morphogenesis, resulted in ventriculomegaly, and disrupted neural connectivity in the optic tectum, habenula, cerebellum, and olfactory bulb. Altered neural network formation was accompanied by reduced expression of synaptic vesicle 2. Loss of ahr2 function also impaired nascent network development, but did not affect gross brain or ventricular morphology. To determine whether neural AHR activation was sufficient to disrupt connectivity, we used the Gal4/UAS system to express a constitutively active AHR specifically in differentiated neurons and observed disruptions only in the cerebellum; thus, suggesting that the phenotypes resulting from global AHR activation likely involve multiple cell types. Consistent with this hypothesis, we found that TCDD exposure reduced the number of oligodendrocyte precursor cells and their derivatives. Together, our findings indicate that proper modulation of AHR signaling is necessary for the growth and maturation of the embryonic zebrafish brain.

Histological and Immunohistochemical Studies to Determine the Mechanism of Cleft Palate Induction after Palatal Fusion in Mice Exposed to TCDD

Rupture of the basement membrane in fused palate tissue can cause the palate to separate after fusion in mice, leading to the development of cleft palate. Here, we further elucidate the mechanism of palatal separation after palatal fusion in 8–10-week-old ICR female mice. On day 12 of gestation, 40 μg/kg of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), sufficient to cause cleft palate in 100% of mice, was dissolved in 0.4 mL of olive oil containing toluene and administered as a single dose via a gastric tube. Fetal palatine frontal sections were observed by H&E staining, and epithelial cell adhesion factors, apoptosis, and cell proliferation were observed from the anterior to posterior palate. TUNEL-positive cells and Ki67-positive cells were observed around the posterior palatal dissection area of the TCDD-treated group. Moreover, in fetal mice exposed to TCDD, some fetuses exhibited cleft palate dehiscence during fusion. The results suggest that palatal dehiscence may be caused by abnormal cell proliferation in epithelial tissues, decreased intercellular adhesion, and inhibition of mesenchymal cell proliferation. By elucidating the mechanism of cleavage after palatal fusion, this research can contribute to establishing methods for the prevention of cleft palate development.

Environmental mechanisms of orofacial clefts

Orofacial clefts (OFCs) are among the most common birth defects and impart a significant burden on afflicted individuals and their families. It is increasingly understood that many nonsyndromic OFCs are a consequence of extrinsic factors, genetic susceptibilities, and interactions of the two. Therefore, understanding the environmental mechanisms of OFCs is important in the prevention of future cases. This review examines the molecular mechanisms associated with environmental factors that either protect against or increase the risk of OFCs. We focus on essential metabolic pathways, environmental signaling mechanisms, detoxification pathways, behavioral risk factors, and biological hazards that may disrupt orofacial development.

The cleft palate candidate gene BAG6 supports FoxO1 acetylation to promote FasL-mediated apoptosis during palate fusion

BACKGROUND

Cleft palate is a common craniofacial defect, which occurs when the palate fails to fuse during development. During fusion, the palatal shelves migrate towards the embryonic midline to form a seam. Apoptotic elimination of medial edge epithelium (MEE) cells along this seam is required for the completion of palate fusion.

METHODS

Whole exome sequencing (WES) of six Chinese cleft palate families was applied to identify novel cleft palate-associated gene variants. Palatal fusion and immunofluorescence studies were performed in a murine palatal shelf organ culture model. Gene and protein expression were analyzed by qPCR and immunoblotting in murine MEE cells during seam formation in vivo. Mechanistic immunoprecipitation studies were performed in murine MEE cells in vitro.

RESULTS

WES identified Bcl-2 associated anthanogene 6 (BAG6) as a novel cleft palate-associated gene. In murine MEE cells, we discovered upregulation of Bag6 and the transcription factor forkhead box protein O1 (FoxO1) during seam formation in vivo. Using a palatal shelf organ culture model, we demonstrate that nuclear-localized Bag6 enhances MEE cell apoptosis by promoting p300's acetylation of FoxO1, thereby promoting transcription of the pro-apoptotic Fas ligand (FasL). Subsequent gain- and loss-of-function studies in the organ culture model demonstrated that FasL is required for Bag6/acFoxO1-mediated activation of pro-apoptotic Bax/caspase-3 signaling, MEE apoptosis, and palate fusion. Palatal shelf contact was shown to enhance Bag6 nuclear localization and upregulate nuclear acFoxO1 in MEE cells.

CONCLUSIONS

These findings demonstrate that nuclear-localized Bag6 and p300 co-operatively enhance FoxO1 acetylation to promote FasL-mediated MEE apoptosis during palate fusion.

Comparison of the biological behaviors of palatal mesenchymal and epithelial cells induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in vitro

2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD) effectively induces cleft palate at increased doses, but its mechanism of involvement is unclear, and arguments have examined palatal shelf contact and/or fusion failure. The role of different types of cells constituting palatal skulls remains elusive regarding TCDD dosage. No reports have simultaneously compared the biological behaviors of TCDD- induced mesenchymal and epithelial cells in vitro. This study employed primary epithelial and mesenchymal cells as models in vitro to explore proliferation, migration, apoptosis and epithelial-to-mesenchymal transition with two different doses of TCDD (10 nmol/L, 100 nmol/L), contrasted with a control group without TCDD. Interestingly, we found the EMT process of primary palatal epithelial cells occurred automatically in vitro without helping bilateral palatal contact. The results showed that, with the low dose of TCDD, transformation of epithelial cells to mesenchymal cells was inhibited, and mesenchymal cell proliferation and migration were promoted. At high doses, mesenchymal cells decreased, preventing palate development, uprising and contact, while the EMT of epithelial cells decreased. Regardless of dose of TCDD, no impact on migration and apoptosis of epithelial cells was noted, but there was increased apoptosis of mesenchymal cell in a dose-dependent manner.

A comprehensive analysis of AHRR gene as a candidate for cleft lip with or without cleft palate

Cleft lip and palate (CL/P) is among the most common congenital malformations and affects 1 in 700 newborns. CL/P is caused by genetic and environmental factors (maternal smoking, alcohol or drug use and others). Many genes and loci were associated with cleft lip/palate but the amount of heterogeneity justifies identifying new causal genes and variants. AHRR (Aryl-Hydrocarbon Receptor Repressor) gene has recently been related to CL/P however, few functional studies analyze the genotypephenotype interaction of AHRR with CL/P. Several studies associate the molecular pathway of AHRR to CL/P which indicates this gene as a functional candidate in CL/P etiology.

METHODS

Systematic Literature Review was performed using PUBMED database with the keywords cleft lip, cleft palate, orofacial cleft, AHRR and synonyms. SLR resulted in 37 included articles.

RESULTS

AHRR is a positional and functional candidate gene for CL/P. In silico analysis detected interactions with other genes previously associated to CL/P like ARNT and CYP1A1. AHRR protein regulates cellular toxicity through TCDD mediated AHR pathway. Exposure to TCDD in animal embryos is AHR mediated and lead to cleft palate due to palate fusion failure and post fusion rupture. AHRR regulates cellular growth and differentiation, fundamental to lip and palatogenesis. AHRR decreases carcinogenesis and recently a higher tumor risk has been described in CL/P patients and families. AHRR is also a smoking biomarker due to changed methylation sites found in smokers DNA although folate intake may partially revert these methylation alterations. This corroborates the role of maternal smoking and lack of folate supplementation as risk factors for CL/P.

CONCLUSION

This research identified the importance of AHRR in dioxin response and demonstrated an example of genetic and environmental interaction, indispensable in the development of many complex diseases.

Sperm Quality in Mouse After Exposure to Low Doses of TCDD

Background:

In the last decade, the harmful use of dioxin has been demonstrated in human health and in the whole environment. It is well known among scientists that 2, 3, 7, 8-tetrachloro dibenzo-p-dioxin (TCDD) is an environmental pollutant that causes endocrine disruption, which causes male reproductive toxicity.

Objective:

The objective of the present study was to evaluate the toxicity effect of low doses of TCDD in male CD1 mice.

Materials and Methods:

Three concentrations of TCDD (0.375, 0.75, 1.5 mg / kg) were analyzed and the effects on spermatozoa were evaluated 10 days after oral administration of the product. As bioindicators of TCDD toxicity, an exhaustive analysis of several spermatic parameters including motility, vitality, count, morphology and viability, flow cytometry was used to determine the affected sperm population by cytotoxicity and apoptosis. In addition, a morphometric analysis of testicles was performed.

Results:

The results show that the body weight of the treated animals was reduced in medium and high doses (0.75, 1.5 mg / kg) with respect to the control groups. In the groups treated with TCDD, the abnormal head of the sperm increased by 52.5% more than the control group. Significant differences in apoptosis were observed between the negative control and vehicle control, including the median dose (0.75 mg / kg).

Conclusion:

It is concluded that at these low doses there was an impact on the quality of the mouse sperm, adding an effect on apoptosis and cytotoxicity of sperm exposed to these doses of TCDD.

Aryl Hydrocarbon Receptor Promotes Liver Polyploidization and Inhibits PI3K, ERK, and Wnt/β-Catenin Signaling

Aryl hydrocarbon receptor (AhR) deficiency alters tissue homeostasis. However, how AhR regulates organ maturation and differentiation remains mostly unknown. Liver differentiation entails a polyploidization process fundamental for cell growth, metabolism, and stress responses. Here, we report that AhR regulates polyploidization during the preweaning-to-adult mouse liver maturation. Preweaning AhR-null (AhR−/−) livers had smaller hepatocytes, hypercellularity, altered cell cycle regulation, and enhanced proliferation. Those phenotypes persisted in adult AhR−/− mice and correlated with compromised polyploidy, predominance of diploid hepatocytes, and enlarged centrosomes. Phosphatidylinositol-3-phosphate kinase (PI3K), extracellular signal-regulated kinase (ERK), and Wnt/β-catenin signaling remained upregulated from preweaning to adult AhR-null liver, likely increasing mammalian target of rapamycin (mTOR) activation. Metabolomics revealed the deregulation of mitochondrial oxidative phosphorylation intermediates succinate and fumarate in AhR−/− liver. Consistently, PI3K, ERK, and Wnt/β-catenin inhibition partially rescued polyploidy in AhR−/− mice. Thus, AhR may integrate survival, proliferation, and metabolism for liver polyploidization. Since tumor cells tend to be polyploid, AhR modulation could have therapeutic value in the liver.

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AhR is required for liver polyploidization during preweaning-to-adult transition

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INS-R/PI3K/AKT, ERK, Wnt/β-Cat and mTOR are downregulated during liver polyploidization

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Reduced polyploidy relates with enhanced mitochondrial metabolism in AhR-null liver

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Understanding how AhR modulates polyploidy may provide strategies against cancer

The aryl hydrocarbon receptor in the crossroad of signalling networks with therapeutic value

The aryl hydrocarbon receptor (AhR) is well-known for its major contributions to the cellular responses against environmental toxins and carcinogens. Notably, AhR has also emerged as a key transcription factor controlling many physiological processes including cell proliferation and apoptosis, differentiation, adhesion and migration, pluripotency and stemness. These novel functions have broadened our understanding of the signalling pathways and molecular intermediates interacting with AhR under both homeostatic and pathological conditions. Recent discoveries link AhR with the function of essential organs such as liver, skin and gonads, and with complex organismal structures including the immune and cardiovascular systems. The identification of potential endogenous ligands able to regulate AhR activity, opens the possibility of designing ad hoc molecules with pharmacological and/or therapeutic value to treat human diseases in which AhR may have a causal role. Integration of experimental data from in vitro and in vivo studies with "omic" analyses of human patients affected with cancer, immune diseases, inflammation or neurological disorders will likely contribute to validate the clinical relevance of AhR and the possible benefits of modulating its activity by pharmacologically-driven strategies. In this review, we will highlight signalling pathways involved in human diseases that could be targetable by AhR modulators and discuss the feasibility of using such molecules in therapy. The pros and cons of AhR-aimed approaches will be also mentioned.

Aryl hydrocarbon receptor suppresses the osteogenesis of mesenchymal stem cells in collagen-induced arthritic mice through the inhibition of β-catenin

The contributions of aryl hydrocarbon receptor (Ahr) to the pathogenesis of rheumatoid arthritis (RA), particularly bone loss, have not been clearly explored. The imbalance between osteoblasts and osteoclasts is a major reason for bone loss. The dysfunction of osteoblasts, which are derived from mesenchymal stem cells (MSCs), induced bone erosion occurs earlier and is characterized as more insidious. Here, we showed that the nuclear expression and translocation of Ahr were both significantly increased in MSCs from collagen-induced arthritis (CIA) mice. The enhanced Ahr suppressed the mRNA levels of osteoblastic markers including Alkaline phosphatase (Alp) and Runt-related transcription factor 2 (Runx2) in the differentiation of MSCs to osteoblasts in CIA. The 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated activation of Ahr dose-dependently suppressed the expression of osteoblastic markers. In addition, the expression of β-catenin was reduced in CIA MSCs compared with control, and the TCDD-mediated activation of the Ahr significantly inhibited β-catenin expression. The Wnt3a-induced the activation of Wnt/β-catenin pathway partly rescued the osteogenesis decline induced by TCDD. Taken together, these results indicate that activated Ahr plays a negative role in CIA MSCs osteogenesis, possibly by suppressing the expression of β-catenin.