Essential amino acid starvation induces cell cycle arrest, autophagy, and inhibits osteogenic differentiation in murine osteoblast.

This study investigates the effects of essential amino acid (EAA) starvation on murine osteoblasts cells and the underlying mechanisms. We performed and observed the cell proliferation, autophagy, and osteogenic differentiation under deprivation of EAA in vitro. The results showed that EAA starvation resulted in cell cycle arrest via phosphorylation of the MAPK signaling pathway, leading to inhibition of cell proliferation and osteogenic differentiation. Additionally, the LKB1-AMPK signaling pathway was also found to be phosphorylated, inducing autophagy. These findings highlight the significant role of EAA in regulating cellular processes. Furthermore, this study contributes to our understanding of the effects of nutrient deprivation on cellular physiology and may aid in the development of novel therapeutic strategies for diseases associated with amino acid metabolism.

Intracellular glucose starvation inhibits osteogenic differentiation in human periodontal ligament cells.

BACKGROUND: Periodontal ligament cells (PDLCs), as mesenchymal cells in the oral cavity, are closely linked to periodontal tissue regeneration. However, the effect of local glucose deficiency on periodontal tissue regeneration, such as immediately post-surgery, remains unknown. OBJECTIVE: In the present study, we investigated the effect of a low-glucose environment on the proliferation and osteogenic differentiation of PDLCs. MATERIALS AND METHODS: We used media with five glucose concentrations (100, 75, 50, 25, and 0 mg/dL) and focused on the effects of a low-glucose environment on the proliferation, osteogenic differentiation, and autophagy of PDLCs. Additionally, we focused on changes in lactate production in a low-glucose environment and investigated the involvement of lactate with AZD3965, a monocarboxylate transporter-1 (MCT-1) inhibitor. RESULTS: The low-glucose environment inhibited PDLCs proliferation, migration, and osteogenic differentiation, and induced the expression of the autophagy-related factors LC3 and p62. Lactate and ATP production were decreased under low-glucose conditions. The addition of AZD3965 (MCT-1 inhibitor) in normal glucose conditions caused a similar trend as in low-glucose conditions on PDLCs. CONCLUSION: Our results suggest lactate production through glucose metabolism in the osteogenic differentiation of PDLCs. A low-glucose environment decreased lactate production, inhibiting cell proliferation, migration, and osteogenic differentiation and inducing autophagy in PDLCs.

Glucose Starvation-Caused Oxidative Stress Induces Inflammation and Autophagy in Human Gingival Fibroblasts.

Gingival tissue experiences an environment of nutrient shortage, such as low glucose conditions, after periodontal surgery. Our previous studies found that this low glucose condition inhibits normal gingival cell functions. However, the mechanism by which this glucose-deficient environment causes cellular damage to human gingival fibroblasts (HGnFs) remains unclear. This study aimed to investigate the biological effects of ROS induction on HGnFs under low glucose conditions. ROS levels and cellular anti-ROS ability of HGnFs under different glucose concentrations were evaluated by measuring ROS formation and the expression of superoxide dismutase and heme oxygenase 1. Changes in cellular viability were investigated using 5-bromo-2'-deoxyuridine assay and cell survival detection, and the cellular damage was evaluated by the expression of inflammatory cytokines and changes in the expression of autophagy-related protein. ROS formation was then blocked using N-acetyl-L-cysteine (NAC), and the effects of ROS on HGnFs under low glucose conditions were investigated. Low glucose conditions induced ROS accumulation, reduced cellular activity, and induced inflammation and autophagy. After NAC application, the anti-ROS capacity increased, cellular activity improved, and inflammation and autophagy were controlled. This can be effectively controlled by the application of antioxidants such as NAC.

The expression of 11ß-hydroxysteroid dehydrogenase type 1 is increased in experimental periodontitis in rats.

BACKGROUND: The involvement of 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1), which converts inactive glucocorticoids into active glucocorticoids intracellularly, in metabolic diseases and chronic inflammatory diseases has been elucidated. We recently reported that an increase in 11ß-HSD1 expression was associated with chronic periodontitis in humans irrespective of obesity. To further clarify the role of 11ß-HSD1 in chronic periodontitis, the expression of 11ß-HSD1 was investigated in experimental periodontitis model in rats. METHODS: Experimental periodontitis was induced by silk ligature of left maxillary second molars of 7-week-old male Wistar rats, and periodontal tissues were collected at day 3. The expression of 11ß-HSD1, 11ß-HSD2, and TNFα mRNA was examined using real time reverse transcription-polymerase chain reaction. The expression of TNFα was used as an indicator of inflammation. Thus, the rats in which the levels of TNFα mRNA were increased in the ligature-induced periodontitis compared with the control were analysed. RESULTS: The findings demonstrated that the expression of 11ß-HSD1 mRNA was significantly increased in experimental periodontitis compared with the control. The increase in the levels of 11ß-HSD1 mRNA in the ligature-induced periodontitis compared with the control was positively correlated with that of TNFα mRNA. On the other hand, the expression of 11ß-HSD2 mRNA, which inactivates glucocorticoids, was slightly decreased in experimental periodontitis. Therefore, the ratio of 11ß-HSD1 versus 11ß-HSD2 mRNA was significantly higher in experimental periodontitis than in the control. CONCLUSIONS: These results suggest that the increased expression of 11ß-HSD1, which would result in the increased levels of intracellular glucocorticoids, may play a role in the pathophysiology of experimental periodontitis.

The increased ratio of 11ß-hydroxysteroid dehydrogenase type 1 versus 11ß-hydroxysteroid dehydrogenase type 2 in chronic periodontitis irrespective of obesity.

11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1), which converts inactive cortisone to active cortisol, has been reported to play an important role in metabolic diseases as well as chronic inflammatory diseases. The involvement of 11ß-HSD1 in chronic periodontitis was investigated in the present study. The relationship between the levels of 11ß-HSD1, chronic periodontitis, and body mass index (BMI) was analyzed. The expression of 11ß-HSD1 mRNA was significantly higher in the chronic periodontitis group than in the control group. Since the expression of 11ß-HSD2, which converts active cortisol to inactive cortisone, was slightly lower in the chronic periodontitis group than in the controls, the ratio of 11ß-HSD1 versus 11ß-HSD2 was significantly higher in the chronic periodontitis group than in the controls. A correlation was not observed between BMI and the level of 11ß-HSD1 or between BMI and the ratio of 11ß-HSD1 versus 11ß-HSD2. These results suggested that an increase in the ratio of 11ß-HSD1 versus 11ß-HSD2 was associated with chronic periodontitis irrespective of obesity.