Which of the following is not a step in the formation of endochondral bone?
Shotgun histology endochondral ossification
a summary Tissue engineered cartilage replacements that cause endochondral ossification are a regenerative technique for bone defect healing. Multipotent mesenchymal stromal cells (MSCs) normally shape a cartilage template in vitro, which can then be inserted to promote bone formation in vivo. The addition of allogeneic MSCs to tissue engineered cartilage constructs could increase their clinical utility in three ways. For starters, having a ready-to-use build will help speed up the treatment process. Second, MSCs extracted and extended from a single donor could be used to treat several patients at the same time, lowering the cost of medical procedures. Finally, more control over the efficiency of MSC chondrogenic differentiation will be necessary. Given the advantages of using allogeneic cell sources for bone regeneration in the field, their immunogenicity is a major barrier to their clinical use. The goal of this review is to raise awareness of immune cells’ function in endochondral ossification, especially during regenerative strategies in which the immune response is influenced by implanted biomaterials and/or cells. We are especially interested in how the implantation of an allogeneic cartilaginous tissue engineered construct affects the balance between immune response and bone regeneration.
Anatomy and physiology – development of bone
IntroductionChondrocyte differentiation is essential for the long-term growth of the skeleton, which culminates in endochondral ossification. Endochondral ossification starts with the formation of a cartilage template and finishes with the replacement of the cartilage template with bone. Transcription factors, extracellular matrix proteins, and many signaling pathways, including Wnt signaling, all play a role in chondrocyte differentiation . In skeletal growth, Wnt signaling controls whether mesenchymal stem cells differentiate into chondrocytes or osteoblasts . Low levels of -catenin-dependent canonical wnt signaling, which promotes Sox9 expression and activity, induce differentiation against the chondrogenic lineage . The phenotype of adult articular chondrocytes is preserved by a well-balanced -catenin level . Chondrogenic hypertrophy, on the other hand, is caused by high levels of wnt/-catenin signaling [2–4].
Sclerostin, which is produced by the SOST gene in osteocytes, is a known negative regulator of bone formation. SOST is a potent inhibitor of the canonical Wnt signaling pathway and a ligand for LRP5/LRP6 [5, 6]. Recent research has discovered that the SOST gene is also expressed by chondrocytes , and that altering its function can affect articular cartilage and subchondral bone . Extensive research into the role of sclerostin may lead to a better understanding of the physiology and pathology of bone and cartilage. However, the role of sclerostin in the progression of chondrogenic differentiation is still unknown, as is the possible utility of sclerostin in the regulation of endochondral ossification.
Bone + cartilage 5- endochondral ossification
Endochondral bone formation is a significant phase in the growth of bones and the healing of fractures (Gerstenfeld et al., 2003; Shapiro, 2008). The growth plate and the fracture callus, in particular, are distinguished by a highly structured cartilaginous system in which chondrocytes develop a hypertrophic phenotype over time (Gerstenfeld et al., 2003). When chondrocytes become hypertrophic, they change their expression profile, upregulate osteogenesis-related genes, and secrete proangiogenic factors and metalloproteinases (Gawlitta et al., 2010). Blood vessel invasion, osteoprogenitor cell and osteoclast penetration, and the final remodeling of the cartilaginous prototype into new bone are both aided by this (Gawlitta et al., 2010).
Human MSCs were isolated from a 20-year-old female patient’s bone marrow aspirate. According to a procedure approved by the local Medical Ethics Committee, the aspirate was obtained after informed consent (University Medical Center Utrecht). As previously mentioned, the mononuclear fraction was separated using Ficoll-paque (Sigma-Aldrich, Zwijndrecht, Netherlands) and seeded on plastic to pick for adherence (Gawlitta et al., 2012). The adherent cells were cultured in MSC expansion medium, which consisted of -MEM (22561, Invitrogen), supplemented with 10% heat-inactivated fetal bovine serum (S14068S1810, Biowest), 0.2 mM L-ascorbic acid 2-phosphate (A8960, Sigma), 100 U/mL penicillin with 100 mg/mL streptomycin (15140, Invitrogen), and 1 ng/ml basic (233-FB; R&D Systems).
Bone formation growth
or mesoderm elsewhere in the body (e.g., middle ear bones and temporal bones) (Fig. 1A). The formation of a mesenchymal condensation is required for chondrogenic differentiation to occur (Thorogood and Hinchliffe 1975). Condensation occurs in the limb bud primarily as a result of aggressive cell gathering rather than changes in cell proliferation.
Prehypertrophy (brown), hypertrophy (green), and terminal hypertrophy are all stages of maturation (orange). (D) Bone collar development and vascularization of cartilage. Blood vessels (red with neutralizing antibodies, N-CAM and N-cadherin, which mediate Ca2+-dependent and -independent cell–cell adhesion, respectively) are implicated in mediating cell–cell adhesion during condensation following terminal hypertrophy of chondrocytes (DeLise et al. 2000). N-CAM-deficient mice, on the other hand, matured to adulthood with no established chondrogenesis defect (Cremer et al. 1994), and N-cadherin-deficient embryos died prematurely (at embryonic day 10 [E10]), preventing mesenchymal condensation studies.