Abstract
Bone structural integrity and shape are maintained by removal of old matrix by osteoclasts and in-situ synthesis of new bone by osteoblasts. These cells comprise the basic multicellular unit (BMU). Bone mass maintenance is determined by the net anabolic activity of the BMU, when the matrix elaboration of the osteoblasts equals or exceeds the bone resorption by the osteoclasts. The normal function of the BMU causes a continuous remodeling process of the bone, with deposition of bony matrix (osteoid) along the vectors of the generated force by gravity and attached muscle activity. The osteoblasts are derived from mesenchymal stem cells (MSCs). Circulating hormones and locally produced cytokines and growth factors modulate the replication and differentiation of osteoclast and osteoblast progenitors. The appropriate number of the osteoblasts in the BMU is determined by the differentiation of the precursor bone-marrow stem cells into mature osteoblasts, their proliferation with subsequent maturation into metabolically active osteocytes, and osteoblast degradation by apoptosis. Thus, the two crucial points to target when planning to control the osteoblast population are the processes of cell proliferation and apoptosis, which are regulated by cellular hedgehog and Wnt pathways that involve humoral and mechanical stimulations. Osteoblasts regulate both bone matrix synthesis and mineralization directly by their own synthetic activities, and bone resorption indirectly by its paracrinic effects on osteoclasts. The overall synthetic and regulatory activities of osteoblasts govern bone tissue integrity and shape.
Highlights
INTRODUCTIONBone functions as an anchorage for muscles enabling movement, and as a protective boundary for vital organs such as brain and spinal cord
We describe how the osteoblasts regulate mineralization of bone matrix
The osteoblasts are derived from mesenchymal stem cells (MSCs)
Summary
Bone functions as an anchorage for muscles enabling movement, and as a protective boundary for vital organs such as brain and spinal cord. The macrophage colony-stimulating factor (MCSF), receptor activator of nuclear factor (NF)kappaB ligand (RANKL), and osteoprotegerin (OPG) are local factors that are secreted by the mesenchymal progenitors of the osteoblasts The former two agents positively regulate the osteoclasts’ transformation from their progenitors. Osteoclast apoptosis is negatively controlled by the RANKL and induced by the OPG.[10] The estrogens and PTH have a protective anti-apoptotic role on the osteoblasts and their precursors.[11] From these complex interactions it is clear that, the components of the BMU originate from the two distinct groups of the progenitor cells, the cells from the mesenchymal origin (MSCs) govern the whole BMU function by their positive and negative feedback signals.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
