Tadahiro Takayama

Advanced glycation end products (AGEs) are compounds that accumulate in hyperglycemic states, contributing significantly to the development of diabetes and its complications, including the exacerbation of periodontal disease. We hypothesized that AGEs affect the expression of inflammatory mediators in gingival cells, thus contributing to the increased severity of periodontitis observed in diabetic patients. Thus, we stimulated the gingival epithelial carcinoma-derived cell line, Ca9-22, with AGEs and examined their effect on the expression of prostaglandin E₂ (PGE₂) and its primary synthesizing enzyme, cyclooxygenase 2 (COX2), key inflammatory mediators in periodontitis. AGEs significantly increased the expression levels of COX2 (n = 6, p < 0.001) and the production of PGE₂ (n = 5, p < 0.05) compared to untreated control and bovine serum albumin (BSA) groups. The receptor for AGEs (RAGE) inhibitor FPS-ZM1 blocked the AGEs-stimulatory effects on COX2 (n = 7, p < 0.01), PGE₂ (n = 6, p < 0.001), and Toll-like receptor 4 (TLR4) expression (n = 7, p < 0.001). Furthermore, AGEs induced the phosphorylation of protein kinase C (p-PKC) via the TLR4 pathway (n = 7, p < 0.01). Crucially, AGEs enhanced NF-κB nuclear accumulation, which was inhibited by blocking either RAGE (n = 5, p < 0.0001) or TLR4 (n = 5, p < 0.0001). In conclusion, these findings demonstrate that AGEs increase PGE₂ production in Ca9-22 cells primarily through a signaling cascade involving RAGE and the TLR4-PKC-NF-κB pathway. Our results suggest TLR4 as a critical mediator that contributes to AGEs-induced inflammation.

Developmental endothelial locus-1 (DEL-1) has traditionally been characterized within the scientific community as having anti-inflammatory properties with potential inhibitory effects on osteoclast formation. Our investigation challenges this paradigm by examining Del-1 expression in RAW264.7 cells and bone marrow-derived macrophages (BMMs) during osteoclastogenesis, as well as its functional impact on osteoclast development and activity. Our experimental findings revealed that Del-1 mRNA levels were markedly elevated in cells stimulated by the receptor activator of the nuclear factor κB ligand compared to unstimulated precursors. When cultured with varying concentrations of recombinant DEL-1, osteoclast differentiation increased in a dose-dependent manner. Furthermore, BMMs isolated from ovariectomized mice exhibited significantly higher Del-1 mRNA expression than those from control animals. To confirm DEL-1’s role, we employed RNA interference techniques, demonstrating that DEL-1 silencing in RAW264.7 cells substantially reduced osteoclast formation. These results suggest that DEL-1 plays a previously unrecognized role in promoting osteoclastogenesis and may contribute to bone metabolism imbalances in conditions like osteoporosis, highlighting its complex role in skeletal homeostasis and its potential as a therapeutic target.

Advanced glycation end-products (AGEs) are increased under hyperglycemia in vivo and are associated with the onset of diabetes. According to previous studies, AGEs exacerbate inflammatory diseases. However, the mechanism by which AGEs aggravate osteoblast inflammation remains unknown. Therefore, the aim of this study was to determine the effects of AGEs on the production of inflammatory mediators in MC3T3-E1 cells and the underlying molecular mechanisms. Co-stimulation with AGEs and lipopolysaccharide (LPS) was found to increase the mRNA and protein levels of cyclooxygenase 2 (COX2), interleukin-1α (IL-1α), S100 calcium-binding protein A9 (S100A9), and the production of prostaglandin E₂ (PGE₂) compared to no stimulation (untreated control) or individual stimulation with LPS or AGEs. In contrast, the phospholipase C (PLC) inhibitor, U73122, inhibited these stimulatory effects. Co-stimulation with AGEs and LPS also increased the nuclear translocation of nuclear factor-kappa B (NF-κB) compared to no stimulation (untreated control) or individual stimulation with LPS or AGE. However, this increase was inhibited by U73122. Co-stimulation with AGEs and LPS-induced phosphorylated phospholipase Cγ1 (p-PLCγ1) and phosphorylated c-Jun N-terminal kinase (p-JNK) expression compared to no stimulation or individual stimulation with LPS or AGEs. U73122 inhibited the effects induced by co-stimulation. siPLCγ1 did not increase the expression of p-JNK and the translocation of NF-κB. Overall, co-stimulation with AGEs and LPS may promote inflammation mediators in MC3T3-E1 cells by activating the nuclear translocation of NF-κB via PLCγ1-JNK activation.

The use of biomaterials and bioactive agents has shown promise in bone defect repair, leading to the development of strategies for bone regeneration. Various artificial membranes, especially collagen membranes (CMs) that are widely used for periodontal therapy and provide an extracellular matrix-simulating environment, play a significant role in promoting bone regeneration. In addition, numerous growth factors (GFs) have been used as clinical applications in regenerative therapy. However, it has been established that the unregulated administration of these factors may not work to their full regenerative potential and could also trigger unfavorable side effects. The utilization of these factors in clinical settings is still restricted due to the lack of effective delivery systems and biomaterial carriers. Hence, considering the efficiency of bone regeneration, both spaces maintained using CMs and GFs can synergistically create successful outcomes in bone tissue engineering. Therefore, recent studies have demonstrated a significant interest in the potential of combining CMs and GFs to effectively promote bone repair. This approach holds great promise and has become a focal point in our research. The purpose of this review is to highlight the role of CMs containing GFs in the regeneration of bone tissue, and to discuss their use in preclinical animal models of regeneration. Additionally, the review addresses potential concerns and suggests future research directions for growth factor therapy in the field of regenerative science.

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