Osteoblasts are differentiated from mesenchymal progenitor cells in the inner and outer periosteum and the bone marrow, and can specifically secrete a variety of biologically active substances, regulating and affecting the process of bone formation and reconstruction.
At different maturity stages, osteoblasts show 4 different morphologies in vivo, namely preosteoblast, osteoblast, osteocyte and bonelining cell. Pre-osteoblasts are precursors of osteoblasts, differentiated by stromal stem cells, developed along the osteoblast lineage, and are located outside the osteoblasts that cover the bone-forming surface. Mature osteoblasts are monolayer cells located on the surface of bone, and they play an important role in synthesizing bone matrix. Osteoblasts are the main functional cells of bone formation and are responsible for the synthesis, secretion and mineralization of bone matrix. Human and animal bone tissues are constantly being reconstructed. The process of bone reconstruction includes the breakdown and absorption of bones and the formation of new bones. Osteoclasts are responsible for bone breakdown and absorption, while osteoclasts are responsible for new bone formation. Osteoclasts are attached to the old bone area, secreting acidic substances to dissolve minerals, secreting proteases to digest the bone matrix, and forming bone resorption pits; thereafter, osteoblasts migrate to the site of absorption, secrete bone matrix, and mineralize form new bone. The balance between osteogenesis and osteogenesis is the key to maintaining normal bone mass.
Osteoclast (OC) is the main functional cell for bone resorption, and plays an important role in bone development, growth, repair, and reconstruction. Osteoclasts originate from the blood mononuclear-macrophage system, which is a special terminally differentiated cell. It can be fused by its mononuclear precursor cells in many ways to form huge multinucleated cells.
Osteoclasts are known for their bone resorption function. Furthermore, as a component of bone tissue, it functions as a bone resorption. Osteoclasts and osteoblasts (also known as bone-forming cells) correspond functionally. The two work together to play an important role in the development and formation of bones. Highly expressed tartrate resistant acid phosphatase and cathepsin K are the main markers of osteoclasts. But beyond that, osteoclasts have other biological effects. By July 18, the effects of hematopoiesis, bone formation, bone angiogenesis, and osteocalcin were found. Osteoclasts have a special absorption function. Macrophages also participate in the process of bone resorption in the absorption of certain local inflammatory lesions.
Osteoblast and Osteoclast Markers Proteins
Bone homeostasis depends on the balance of osteoblast deposition and osteoclast absorption. This dynamic process is responsible for the continuous remodeling of skeletal tissue and is essential to maintaining the size, shape and integrity of the bone. The disruption of bone homeostasis is accompanied by diseases including osteoporosis, arthritis and many hereditary bone diseases. Osteoblasts are mainly labeled proteins, namely osteocalcin, DMP-1, osteoostin. Osteoclast marker proteins are RANK, OSCAR, and calcitonin.
Osteocalcin is a non-collagen hormone found in bones and dentin. Since osteocalcin has a gla domain, its synthesis depends on vitamin K. Osteocalcin acts as a hormone in the body in its uncarboxylated form, sending signals in the pancreas, fat, muscle, testes and brain. In the pancreas, osteocalcin acts on beta cells, causing beta cells in the pancreas to release more insulin. In adipocytes, osteocalcin triggers the release of adiponectin, which increases insulin sensitivity. In muscle, osteocalcin acts on muscle cells to promote energy use and utilization, and in this way enhances exercise capacity. In the brain, osteocalcin plays an important role in development and function.
Dentin matrix acid phosphoprotein 1 (DMP-1)
Dentin matrix acid phosphoprotein 1 is a protein encoded by the DMP1 gene in humans. DeThis protein is essential for the correct mineralization of bones and dentin and is found in various cells in bone and tooth tissue. The protein contains a large number of acidic domains, multiple phosphorylation sites, functional arg-gly-asp cell attachment sequences, and a DNA-binding domain. In undifferentiated osteoblasts, it is mainly a nuclear protein that regulates osteoblast-specific gene expression. During osteoblast maturation, proteins are phosphorylated and exported to the extracellular matrix where they coordinate the formation of mineralized matrix. Mutations in this gene are known to cause autosomal recessive hypophosphatemia, which is manifested as disease and osteomalacia. The genetic structure is conserved in mammals. Two transcript variants encoding different isoforms have been described for this gene.
Calcitonin is a 32 amino acid peptide hormone secreted by parathyroid glandular follicular cells (also known as C cells) in the pharyngeal throat of many people. It reduces blood calcium (Ca2+), as opposed to the effect of parathyroid hormone (PTH). Calcitonin has been found in fish, reptiles, birds and mammals. It is not as important in humans as it is in other animals, because its function is usually not important in the regulation of normal calcium homeostasis. It belongs to the calcitonin-like protein family.