2,3,7,8-Tetrachlorodibenzo- p -dioxin Mediated Cleft palate by Mouse Embryonic Palate Mesenchymal Cells

TCDD induces cleft palate through exosomes derived from mesenchymal cells

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a ubiquitous environmental toxicant and a notable teratogenic agent for cleft palate (CP), a common congenital structural malformation that can result from abnormalities during palatal shelf connection and/or fusion. The development of the palate requires precise coordination between mesenchymal and epithelial cells. Exosomes are vesicles secreted by cells and participate in organ development by transferring various bioactive molecules between cells and regulating cell proliferation, migration, apoptosis, and epithelial-mesenchymal transition (EMT); these vesicles represent a new method of intercellular communication. To explore how TCDD could influence palatal cell behaviors and communication, we treated mesenchymal cells with TCDD, collected the exosomes secreted by the cells, assessed the 2 types of palatal cells, and then observed the effects of TCDD-induced exosomes. We found that the effects of TCDD-induced exosomes were equal to those of TCDD. Thus, TCDD might change the genetic materials of palatal cells and exosomes to cause dysregulated gene expression from parental cells, affect cellular information communicators, and induce abnormal cellular behaviors that could lead to CP.

Chloroquine regulates the proliferation and apoptosis of palate development on mice embryo by activating P53 through blocking autophagy in vitro

Cleft lip and palate is one of the most frequent congenital developmental defects. Autophagy is a highly conserved process of cell self-degradation in eukaryotes, involving multiple biological processes in which chloroquine (CQ) is the most common inhibitor. However, whether CQ affects and how it affects palate development is unknown. Mouse embryonic palatal cells (MEPCs) were treated with CQ to observe cell viability, apoptosis, migration, osteogenic differentiation by cell proliferation assay, flow cytometric analysis, scratch assay, and alizarin red staining. PI staining was used to measure cell cycle distribution. Immunofluorescence (IF) assay and transmission electron microscopy were used to detect autophagosomes. The autophagy-related factors (LC3 and P62), apoptosis-related markers (P53, caspase-3 cleaved caspase-3, BAX, and BCL-2), and cell cycle-related proteins (P21, CDK2, CDK4, cyclin D1, and cyclin E) were all measured by western blot. CQ inhibited the proliferation of MEPCs by arresting the G0/G1 phase of the cell cycle in a concentration- and time-dependent manner with cell cycle-related proteins P21 upregulated and CDK2, CDK4, cyclin D1, and cyclin E downregulated. Then we detected CQ also induced cell apoptosis in a dose-dependent manner by decreasing the BCL-2/BAX ratio and increasing cleaved caspase-3. Next, it was investigated that migration and osteogenesis of MEPCs decreased with CQ treatment in a dose-dependent manner. Meanwhile, CQ blocked the autophagy pathway by upregulating LC3II and P62 expressions which activated the P53 pathway. CQ activates P53 which affects MEPC biological characteristics by changing the proliferation and apoptosis of MEPCs through inhibiting autophagy.

The role of MEG3 in the proliferation of palatal mesenchymal cells is related to the TGFβ/Smad pathway in TCDD inducing cleft palate

Cleft palate (CP) is a common birth defect with a high incidence of occurrence in humans. The 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) is a highly toxic halogenated aromatic hydrocarbon, with a strong CP effect on mice. Increasing recent evidences have shown that long-noncoding RNAs (lncRNAs) play an important role in several diseases, including CP. However, there is a paucity of studies on the role of lncRNA MEG3 in the occurrence and development of TCDD-induced CP. In this study, the relationship between MEG3 and the proliferation of palatal mesenchymal cells and the underlying molecular mechanism were studied by establishing fetal CP with TCDD (64 μg/kg) in C57BL/6N mice. The results revealed that MEG3 was highly expressed during the critical period of CP formation and that the fetal mesenchymal proliferation was significantly inhibited at certain critical periods in the mice receiving TCDD. In addition, we noted a possibility of a crosstalk between MEG3 and the TGF-β/Smad pathway, such that the inhibition of the TGF-β/Smad pathway was induced by TCDD. Cumulatively, our study suggests that TCDD-induced CP may be caused by MEG3 inhibition of the proliferation of palatal mesenchymal cells involving the TGFβ/Smad pathway, which may provide a novel perspective to understand the pathogenesis of CP.

Susceptibility to DNA damage caused by abrogation of Rad54 homolog B: A putative mechanism for chemically induced cleft palate

Exposure to environmental toxicants such as all-trans retinoic acid (atRA) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) may cause cleft palate (CP), which process is related to DNA damage. Rad54B, an important DNA damage repaired protein, has been proved to be associated with non-syndromic cleft lip with palate (NSCLP). In the present study, we sought to clarify the role of Rad54B in palatal development and environment-induced CP. atRA (100 mg/kg) and TCDD (40 μg/kg) were used to induce CP in mice (C57BL/6 J mice). In this study, mouse embryonic heads were collected on embryonic day (E) 13.5∼16.5. The expression level of DNA repair protein Rad54 homolog B (Rad54B) was significantly decreased while those of the DNA double-strand breaks (DSBs) marker γ-H2A.X, apoptosis marker caspase-3 and p53 were significantly increased in the palatal shelves upon exposure to atRA and TCDD relative to the control. Primary mouse embryonic palatal mesenchymal cells (MEPMs) were cultured and transfected with siRNA or adenovirus in vitro to knock down or increase the level of Rad54B. Rad54B knockdown resulted in increased cellular S-phase arrest and apoptosis as well as decreased cell proliferation. Rad54B overexpression also increased apoptosis and reduced cell proliferation. Western blotting was used to detect the level of γ-H2A.X in transfected cells stimulated with etoposide (ETO, a DSBs inducer), and after 5 μM ETO stimulation of transfected MEPMs, the expression of γ-H2A.X was increased in Rad54B-knockdown cells. The expression of Mdm2, Mdmx and p53 with changes in Rad54B was also detected and coimmunoprecipitation was performed to analyze the combination of Mdm2 and p53 when Rad54B was changed in MEPMs. Knockdown of Rad54B inhibited the expression of Mdm2 and Mdmx, while the level of p53 increased. The coimmunoprecipitation results showed a decreased combination of Mdm2 and p53 when Rad54B was knocked down. Therefore, Rad54B can regulate the cell cycle, proliferation, and apoptosis of MEPMs. The loss of Rad54B increased the sensitivity of MEPMs to DSBs inducers, promoted apoptosis, and suppressed the proliferation of MEPMs by inhibiting the degradation of p53. Taken together, these findings suggest that Rad54B may play a key regulatory role in environment-induced CP.

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.