JNK Signaling Pathway Mediates Fluoride-Induced Upregulation of CK1α during Enamel Formation

TGF-β1/Smad3 Signaling Is Required to Alleviate Fluoride-Induced Enamel Hypomineralization

Excessive fluoride intake during enamel development can affect enamel mineralization, leading to dental fluorosis. However, its potential mechanisms remain largely unexplored. In the present study, we aimed to investigate the impact of fluoride on the expressions of RUNX2 and ALPL during mineralization and the effect of TGF-β1 administration on fluoride treatment. A dental fluorosis model of newborn mice and an ameloblast cell line ALC were both used in the present study. The mice of the NaF group, including the mothers and newborns, were fed with water containing 150 ppm NaF after delivery to induce dental fluorosis. The mandibular incisors and molars showed significant abrasion in the NaF group. Immunostaining, qRT-PCR, and Western blotting analysis indicated that exposure to fluoride markedly down-regulated RUNX2 and ALPL in mouse ameloblasts and ALCs. Besides, fluoride treatment significantly decreased the mineralization level detected by ALP staining. Furthermore, exogenous TGF-β1 up-regulated RUNX2 and ALPL and promoted mineralization, while the addition of SIS3 could block such TGF-β1-induced up-regulation. In TGF-β1 conditional knockout mice, the immunostaining of RUNX2 and ALPL was weaker compared with wild-type mice. Exposure to fluoride inhibited the expressions of TGF-β1 and Smad3. Co-treatment of TGF-β1 and fluoride up-regulated RUNX2 and ALPL compared with the fluoride alone treatment, promoting mineralization. Collectively, our data indicated that TGF-β1/Smad3 signaling pathway was necessary for the regulatory effects of fluoride on RUNX2 and ALPL, and the fluoride-induced suppression of ameloblast mineralization was mitigated by activating TGF-β1/Smad3 signaling pathway.

TNF-α-induced down-regulation of type I interferon receptor contributes to acquired resistance of cervical squamous cancer to Cisplatin

We aimed to investigate the effects of tumor necrosis factor (TNF)-α on the expression of interferon α/β receptor subunit 1 (IFNAR1) and cervical squamous cancer (CSCC) resistance to Cisplatin, as well as the underlying mechanisms. Kaplan-Meier analysis was used to plot the overall survival curves. SiHa cells were treated with 20 ng/ml TNF-α to determine cell proliferation in human CSCC cells and the expression of IFNAR1. The effects of TNF-α on the downstream signaling pathway, including casein kinase 1α (CK1α), were investigated using the caspase protease inhibitor FK009, the c-Jun kinase inhibitor SP600125, and the nuclear factor kappa-B inhibitor ammonium pyrrolidinedithiocarbamate (PDTC). TNF-α induced down-regulation of IFNAR1 in human CSCC cells and promoted proliferation of SiHa cells. SiHa cells were transfected with the catalytic inactive mutant CK1α K49A, and the ability of TNF-α to induce down-regulation of IFNAR1 expression was found to be significantly diminished in this context. FK009 and PDTC had no obvious effect on the expression of CK1α, however, SP600125 significantly reduced the expression of CK1α in the presence of TNF-α. SiHa cells treated with TNF-α showed reduced sensitivity to Cisplatin and exhibited higher cell viability, while the sensitivity of SiHa cells to Cisplatin was restored after treatment with CK1α inhibitor D4476. Additionally, we constructed a TNF-α overexpressing SiHa cell line and a transplanted tumor model. The results were similar to those of in vitro efficacy. We demonstrate that TNF-α-induced down-regulation of type I interferon receptor contributes to acquired resistance of cervical squamous cancer to Cisplatin.

Effect of Long Non-coding RNA and DNA Methylation on Gene Expression in Dental Fluorosis

In the process of tooth development, the interaction between genetic information, epigenetic inheritance, and environment jointly affects the teeth formation. At present, the mechanism of dental fluorosis is rarely studied from transcriptomics, and there is no report on epigenetic perspective. In the study, SD rats were randomly divided into dental fluorosis group and control group fed with NaF (150 mg/L) or distilled water for 8 weeks. After 3.5 days of birth, the RNAs or DNA of rat mandibular molars were detected by RNA-seq or MethylTarget, respectively. The results demonstrated that a total of 1723 differentially expressed genes (DEGs) and 2511 differential expression lncRNAs (DE-lncRNAs) were mainly involved in the ion channels, calcium ion transport, and immunomodulatory signaling pathways. ATP2C1 and Nr1d1, which were related to Ca2+ transport, cellular calcium homeostasis, endoplasmic reticulum stress and immunity, may be the key genes in the formation of dental fluorosis. Notably, we also found that the immune response plays an important role in the formation of dental fluorosis, and a large amount of DEGs was enriched in immune regulation and NF-κB signaling pathways. Furthermore, the methylation levels of 13 sites were increased in Ago4, Atf3, Atp2c1, Dusp1, Habp4, and Mycl, while methylation levels of 5 CpG sites decreased in Ago4, Atp2c1, Habp4, and Traf6, and conformably, the expression of these genes have been significantly changed. This study comprehensively analyzed the occurrence mechanism of dental fluorosis from transcriptomics and epigenetics, so as to provide theoretical reference for further research.

Role of oxidative stress-mediated cell death and signaling pathways in experimental fluorosis

Free radicals and other oxidants have enticed the interest of researchers in the fields of biology and medicine, owing to their role in several pathophysiological conditions, including fluorosis (Fluoride toxicity). Radical species affect cellular biomolecules such as nucleic acids, proteins, and lipids, resulting in oxidative stress. Reactive oxygen species-mediated oxidative stress is a common denominator in fluoride toxicity. Fluorosis is a global health concern caused by excessive fluoride consumption over time. Fluoride alters the cellular redox homeostasis, and its toxicity leads to the activation of cell death mechanisms like apoptosis, autophagy, and necroptosis. Even though a surfeit of signaling pathways is involved in fluorosis, their toxicity mechanisms are not fully understood. Thus, this review aims to understand the role of reactive species in fluoride toxicity with an outlook on the effects of fluoride in vitro and in vivo models. Also, we emphasized the signal transduction pathways and the mechanism of cell death implicated in fluoride-induced oxidative stress.