Fibrillar collagens are the most abundant components of the extracellular matrix and provide stability to connective tissues, such as bone, cartilage and skin. An imbalance in collagen turnover ...inevitably affects the function of these tissues. Therefore, the molecular and cellular mechanisms involved in the synthesis and degradation of collagen have received increasing attention. This short review attempts to summarize our present understanding of how different pathways of collagen degradation are used by different cell types.
•Extracellular degradation of collagen is in use under pathological conditions.•Intracellular degradation of fibrillar collagen is crucial for maintaining collagen homeostasis in physiology.•Both extracellular and intracellular pathways of collagen degradation enable cells to degrade different types of collagen.•Different pathways for extracellular and intracellular degradation by a wide range of specialized cell types have been identified.
Periodontal ligament (PDL) cells are mechanosensitive and have the potential to differentiate into osteoblast‐like cells under the influence of cyclic tensile force (CTF). CTF modulates the ...expression of regulatory proteins including bone morphogenetic proteins (BMPs), which are essential for the homeostasis of the periodontium. Among the BMPs, BMP9 is one of the most potent osteogenic BMPs. It is yet unknown whether CTF affects the expression of BMP9 and mineralization. Here, we demonstrated that continuously applied CTF for only the first 6 hr stimulated the synthesis of BMP9 and induced mineral deposition within 14 days by human PDL cells. Stimulation of
BMP9 expression depended on ATP and P2Y
1 receptors. Apyrase, an ecto‐ATPase, inhibited CTF‐mediated ATP‐induced
BMP9 expression. The addition of ATP increased the expression of
BMP9. Loss of function experiments using suramin (a broad‐spectrum P2Y antagonist), MRS2179 (a specific P2Y
1 receptor antagonist), MRS 2365 (a specific P2Y
1 agonist), U‐73122 (a phospholipase C PLC inhibitor), and thapsigargin (enhancer of intracytosolic calcium) revealed the participation of P2Y
1 in regulating the expression of
BMP9. This was mediated by an increased level of intracellular Ca
2+ through the PLC pathway. A neutralizing anti‐BMP9 antibody decreased mineral deposition, which was stimulated by CTF for almost 45% indicating a role of BMP9 in an in vitro mineralization. Collectively, our findings suggest an essential modulatory role of CTF in the homeostasis and regeneration of the periodontium.
CTF induces mineral deposition by human PDL cells and the concomitant stimulated expression of BMP9, which proved to be crucial for the mineral deposition. CTF increases the expression of BMP9 depending on ATP and P2Y1 receptors through the activation of phospholipase C and calcium signaling.
Chitosan/dicarboxylic acid (CS/DA) scaffold has been developed as a bone tissue engineering material. This study evaluated a CS/DA scaffold with and without seeded primary human periodontal ligament ...cells (hPDLCs) in its capacity to regenerate bone in calvarial defects of mice. The osteogenic differentiation of hPDLCs was analyzed by bone nodule formation and gene expression. In vivo bone regeneration was analyzed in mice calvarial defects. Eighteen mice were divided into 3 groups: one group with empty defects, one group with defects with CS/DA scaffold, and a group with defects with CS/DA scaffold and with hPDLCs. After 6 and 12 weeks, new bone formation was assessed using microcomputed tomography (Micro-CT) and histology. CS/DA scaffold significantly promoted in vitro osteoblast-related gene expression (RUNX2, OSX, COL1, ALP, and OPN) by hPDLCs. Micro-CT revealed that CS/DA scaffolds significantly promoted in vivo bone regeneration both after 6 and 12 weeks (
< 0.05). Histological examination confirmed these findings. New bone formation was observed in defects with CS/DA scaffold; being similar with and without hPDLCs. CS/DA scaffolds can be used as a bone regenerative material with good osteoinductive/osteoconductive properties.
Blood monocytes are precursors of dendritic cells, macrophages, and osteoclasts. They are a heterogeneous cell population with differences in size, phenotype, and function. Although monocytes ...maintain several tissue-specific populations of immune cells in homeostasis, their contribution to populations of dendritic cells, macrophages, and osteoclasts is significantly increased in inflammation. Identification of a growing number of functionally different subsets of cells within populations of monocyte-derived immune cells has recently put monocyte heterogeneity into sharp focus. Here, we summarize recent findings in monocyte heterogeneity and their differentiation into dendritic cells, macrophages, and osteoclasts. We also discuss these advances in the context of the formation of functionally different monocyte-derived subsets of dendritic cells, macrophages, and osteoclasts.
Foreign body multinucleated giant cells (FBGCs) and osteoclasts share several characteristics, like a common myeloid precursor cell, multinuclearity, expression of tartrate-resistant acid phosphatase ...(TRAcP) and dendritic cell-specific transmembrane protein (DC-STAMP). However, there is an important difference: osteoclasts form and reside in the vicinity of bone, while FBGCs form only under pathological conditions or at the surface of foreign materials, like medical implants. Despite similarities, an important distinction between these cell types is that osteoclasts can resorb bone, but it is unknown whether FBGCs are capable of such an activity. To investigate this, we differentiated FBGCs and osteoclasts in vitro from their common CD14+ monocyte precursor cells, using different sets of cytokines. Both cell types were cultured on bovine bone slices and analyzed for typical osteoclast features, such as bone resorption, presence of actin rings, formation of a ruffled border, and characteristic gene expression over time. Additionally, both cell types were cultured on a biomimetic hydroxyapatite coating to discriminate between bone resorption and mineral dissolution independent of organic matrix proteolysis. Both cell types differentiated into multinucleated cells on bone, but FBGCs were larger and had a higher number of nuclei compared to osteoclasts. FBGCs were not able to resorb bone, yet they were able to dissolve the mineral fraction of bone at the surface. Remarkably, FBGCs also expressed actin rings, podosome belts and sealing zones--cytoskeletal organization that is considered to be osteoclast-specific. However, they did not form a ruffled border. At the gene expression level, FBGCs and osteoclasts expressed similar levels of mRNAs that are associated with the dissolution of mineral (e.g., anion exchange protein 2 (AE2), carbonic anhydrase 2 (CAII), chloride channel 7 (CIC7), and vacuolar-type H+-ATPase (v-ATPase)), in contrast the matrix degrading enzyme cathepsin K, which was hardly expressed by FBGCs. Functionally, the latter cells were able to dissolve a biomimetic hydroxyapatite coating in vitro, which was blocked by inhibiting v-ATPase enzyme activity. These results show that FBGCs have the capacity to dissolve the mineral phase of bone, similar to osteoclasts. However, they are not able to digest the matrix fraction of bone, likely due to the lack of a ruffled border and cathepsin K.
Abstract A resorbable bone graft substitute should mimic native bone in its capacity to support bone formation and be remodeled by osteoclasts (OCl) or other multinucleated cells such as foreign body ...giant cells (FBGC). We hypothesize that by changing the scale of surface architecture of beta-tricalcium phosphate (TCP), cellular resorption can be influenced. CD14+ monocyte precursors were isolated from human peripheral blood ( n = 4 independent donors) and differentiated into OCl or FBGC on the surface of TCP discs comprising either submicron- or micron-scale surface topographical features (TCPs and TCPb, respectively). On submicrostructured TCPs, OCl survived, fused, differentiated, and extensively resorbed the substrate; however, on microstructured TCPb, OCl survival, TRAP activation, and fusion were attenuated. Importantly, no resorption was observed on microstructured TCPb. By confocal microscopy, OCl formed on TCPs contained numerous actin rings allowing for resorption, but not on TCPb. In comparison, FBGC could not resorb either TCP material, suggesting that osteoclast-specific machinery is necessary to resorb TCP. By tuning surface architecture, it appears possible to control osteoclast resorption of calcium phosphate. This approach presents a useful strategy in the design of resorbable bone graft substitutes.
Wounds in adults are frequently accompanied by scar formation. This scar can become fibrotic due to an imbalance between extracellular matrix (ECM) synthesis and ECM degradation. Oral mucosal wounds, ...however, heal in an accelerated fashion, displaying minimal scar formation. The exact mechanisms of scarless oral healing are yet to be revealed. This review highlights possible mechanisms involved in the difference between scar‐forming dermal vs. scarless oral mucosal wound healing. Differences were found in expression of ECM components, such as procollagen I and tenascin‐C. Oral wounds contained fewer immune mediators, blood vessels, and profibrotic mediators but had more bone marrow–derived cells, a higher reepithelialization rate, and faster proliferation of fibroblasts compared with dermal wounds. These results form a basis for further research that should be focused on the relations among ECM, immune cells, growth factors, and fibroblast phenotypes, as understanding scarless oral mucosal healing may ultimately lead to novel therapeutic strategies to prevent fibrotic scars.
Background: Increased level of proinflammatory cytokine interleukin (IL)‐12 correlates with the severity of periodontitis. Yet, a possible role of IL‐12 in periodontal disease has not been clarified. ...The aim of this study is to investigate whether IL‐12 affects expression of receptor activator of nuclear factor‐kappa B (NF‐κB) ligand (RANKL), a potent osteoclast‐stimulating factor, by human periodontal ligament (hPDL) cells.
Methods: To determine the effect of IL‐12, hPDL cells were incubated with recombinant human IL‐12 (p70) in a dose‐ (0 to 10 ng/mL) and time‐dependent manner. Expression of RANKL was evaluated at mRNA and protein levels. Underlying signaling pathways of IL‐12 were determined by using specific inhibitors.
Results: Under the influence of IL‐12, hPDL cells expressed significantly higher levels of RANKL. Expression was mediated by signal transducer and activator of transcription 4 and NF‐κB signaling pathways. Conditioned medium of IL‐12–incubated cells proved to contain molecule(s) that induced RANKL expression. Addition of suramin (G protein–coupled receptor inhibitor) and ethylene glycol tetraacetic acid (calcium chelator) suggested existence of intermediate molecule(s) that could activate heterotrimeric G protein signaling in a calcium‐dependent pathway.
Conclusions: Expression of RANKL by hPDL cells significantly increased after IL‐12 treatment. Therefore, this study supports a close interrelationship between immune and skeletal systems and suggests an osteolytic role of IL‐12 in pathogenesis of periodontal disease.
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