Cellular and extracellular matrix of bone, with principles of synthesis and dependency of mineral deposition on cell membrane transport

Bone differs from other connective tissues; it is isolated by a layer of osteoblasts that are connected by tight and gap junctions. This allows bone to create dense lamellar type I collagen, control pH, mineral deposition, and regulate water content forming a compact and strong structure. New woven...

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Bibliographic Details
Published in:American Journal of Physiology: Cell Physiology 2020-01, Vol.318 (1), p.C111-C124
Main Authors: Schlesinger, Paul H, Blair, Harry C, Beer Stolz, Donna, Riazanski, Vladimir, Ray, Evan C, Tourkova, Irina L, Nelson, Deborah J
Format: Article
Language:English
Subjects:
Animals
Bone Density
Bone Matrix - metabolism
Bone Morphogenetic Protein Receptors - metabolism
Bone Morphogenetic Proteins - metabolism
Cell Differentiation
Humans
Membrane Transport Proteins - metabolism
Models, Biological
Osteoblasts - metabolism
Osteogenesis
Receptors, Transforming Growth Factor beta - metabolism
Signal Transduction
Theme
Transforming Growth Factor beta - metabolism
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Summary:Bone differs from other connective tissues; it is isolated by a layer of osteoblasts that are connected by tight and gap junctions. This allows bone to create dense lamellar type I collagen, control pH, mineral deposition, and regulate water content forming a compact and strong structure. New woven bone formed after degradation of mineralized cartilage is rapidly degraded and resynthesized to impart structural order for local bone strength. Ossification is regulated by thickness of bone units and by patterning via bone morphogenetic receptors including activin, other bone morphogenetic protein receptors, transforming growth factor-β receptors, all part of a receptor superfamily. This superfamily interacts with receptors for additional signals in bone differentiation. Important features of the osteoblast environment were established using recent tools including osteoblast differentiation in vitro. Osteoblasts deposit matrix protein, over 90% type I collagen, in lamellae with orientation alternating parallel or orthogonal to the main stress axis of the bone. Into this organic matrix, mineral is deposited as hydroxyapatite. Mineral matrix matures from amorphous to crystalline hydroxyapatite. This process includes at least two-phase changes of the calcium-phosphate mineral as well as intermediates involving tropocollagen fibrils to form the bone composite. Beginning with initiation of mineral deposition, there is uncertainty regarding cardinal processes, but the driving force is not merely exceeding the calcium-phosphate solubility product. It occurs behind a epithelial-like layer of osteoblasts, which generate phosphate and remove protons liberated during calcium-phosphate salt deposition. The forming bone matrix is discontinuous from the general extracellular fluid. Required adjustment of ionic concentrations and water removal from bone matrix are important details remaining to be addressed.
ISSN:0363-6143
1522-1563
DOI:10.1152/ajpcell.00120.2019