Excessive fluoride impairs autophagy flux in ameloblasts which is prevented by the autophagy activator rapamycin

Fluoride induces osteoblast autophagy by inhibiting the PI3K/AKT/mTOR signaling pathway in vivo and in vitro

Fluorosis primarily manifests as bone damage in the form of dental fluorosis and skeletal fluorosis and represents a critical global public health challenge. However, few studies have examined autophagy-related signaling pathways in skeletal fluorosis. This study aimed to investigate the effect of fluoride on autophagy in osteoblasts using comprehensive methods and to explore the role of the PI3K/AKT/mTOR signaling pathway in regulating fluoride-induced autophagy in osteoblasts. Sprague-Dawley (SD) rats were exposed to different concentrations of fluoride (NaF: 5, 50, and 100 mg/L) for six months. Primary osteoblasts were treated with 0.5, 1.0, or 3.0 mM NaF. Hematoxylin and eosin (H&E) staining, transmission electron microscopy (TEM), immunohistochemistry (IHC), immunofluorescence staining, and western blotting were performed to evaluate morphological changes in bone tissues and autophagosomes and to detect the protein expression of autophagy-related markers and PI3K/AKT/mTOR signaling pathway-related molecules both in vivo and in vitro. The bone tissues of fluoride-exposed rats showed osteosclerosis, autophagosomes and autolysosomes. LC3B immunofluorescence staining revealed an increase in autophagosomes in the primary osteoblasts treated with fluoride. The LC3Ⅱ/Ⅰ ratio and levels of autophagy-related markers (Beclin 1 and Atg7) were increased, whereas P62 levels were decreased in bone tissues and primary osteoblasts in the fluoride groups. Simultaneously, p-AKT and p-mTOR levels were reduced in bone tissues and primary osteoblasts in the fluoride groups. Moreover, a PI3K inhibitor (LY294002) further downregulated p-AKT and p-mTOR protein expression but slightly increased the LC3Ⅱ/Ⅰ ratio in primary osteoblasts. These results demonstrate that fluoride induces autophagy in osteoblasts by inhibiting the PI3K/AKT/mTOR signaling pathway, which deepens our understanding of the molecular mechanisms underlying fluoride-induced bone damage and provides a theoretical basis for the prevention and treatment of skeletal fluorosis.

Advances in epidemiological status and pathogenesis of dental fluorosis

Fluoride is commonly consider as a "double-edged sword" because low consumption of fluoride can effectively prevent dental caries, but excessive consumption of fluoride can cause fluorosis. Dental fluorosis (DF) is a characteristic feature of fluorosis in the oral cavity that is manifested as tooth color changes and evident enamel defect. Presently, the pathogenesis of DF remains unclear. Herein, we have summarized the research progress in the pathogenesis and mechanism of DF in the past 5 years.

Co-exposure to molybdenum and cadmium triggers pyroptosis and autophagy by PI3K/AKT axis in duck spleens

Excessive amounts of molybdenum (Mo) and cadmium (Cd) are toxicant, but their combined immunotoxicity are not clearly understood. To estimate united impacts of Mo and Cd on pyroptosis and autophagy by PI3K/AKT axis in duck spleens, Mo or/and Cd subchronic toxicity models of ducks were established by feeding diets with different dosages of Mo or/and Cd. Data show that Mo or/and Cd cause oxidative stress by increasing MDA concentration, and decreasing T-AOC, CAT, GSH-Px and T-SOD activities, restrain PI3K/AKT axis by decreasing PI3K, AKT, p-AKT expression levels, which evokes pyroptosis and autophagy by elevating IL-1β, IL-18 concentrations and NLRP3, Caspase-1, ASC, GSDME, GSDMA, NEK7, IL-1β, IL-18 expression levels, promoting autophagosomes, LC3 puncta, Atg5, LC3A, LC3B, LC3II/LC3I and Beclin-1 expression levels, and reducing expression levels of P62 and Dynein. Furthermore, the variations of abovementioned indexes are most pronounced in co-treated group. Overall, results reveal that Mo or/and Cd may evoke pyroptosis and autophagy by PI3K/AKT axis in duck spleens. The association of Mo and Cd exacerbates the changes.