Ultrastructural and biochemical aspects of matrix vesicle-mediated mineralization

Abstract

SummaryMatrix vesicle-mediated mineralization is an orchestrated sequence of ultrastructural and biochemical events that lead to crystal nucleation and growth. The influx of phosphate ions into the matrix vesicle is mediated by several proteins such as TNAP, ENPP1, Pit1, annexin and so forth. The catalytic activity of ENPP1 generates pyrophosphate (PPi) using extracellular ATPs as a substrate, and the resultant PPi prevents crystal overgrowth. However, TNAP hydrolyzes PPi into phosphate ion monomers, which are then transported into the matrix vesicle through Pit1. Accumulation of Ca2+ and PO43− inside matrix vesicles then induces crystalline nucleation, with calcium phosphate crystals budding off radially, puncturing the matrix vesicle’s membrane and finally growing out of it to form mineralized nodules.

Matrix vesicles from chondrocytes and osteoblasts: Their biogenesis, properties, functions and biomimetic models

“…5). Saos-2 cells [149] and osteoblasts [150] produced vesicles containing electron-dense material as probed by TEM. Ca 2+ and P i were mostly co-localized inside vesicles as monitored by X-ray analysis (Fig.…”

Biological application of focus ion beam-scanning electron microscopy (FIB-SEM) to the imaging of cartilaginous fibrils and osteoblastic cytoplasmic processes

“…Bone and cartilage are abundant with collagen fibrils (8,20,21), which facilitate the deposition of uranyl acetate and lead aspartate. Therefore, it was necessary to extend block staining for a longer period, as well as to repeat the washing procedures to obtain FIB-SEM images of enough resolution so that proper comparison with TEM images was possible.…”

“…3 and 4). These extracellular vesicles may be "matrix vesicles" secreted by proliferative chondrocytes, but it is well-known that mineralization takes place from the upper layer of the hypertrophic zone of the growth plate cartilage (8,13,21). To identify the matrix vesicle, it is necessary to verify the presence of a variety of enzymes and membrane transporters involved in mineralization.…”

How To Build a Bone: PHOSPHO1, Biomineralization, and Beyond

“…The structure and function of MVs in skeletal and vascular mineralization has recently been reviewed by several authors . The biogenesis of these vesicles may occur through multiple proposed mechanisms; however, the most prevalent theories include polarized budding from the parental cell membrane, or from microvilli on the cell surface, as demonstrated in hypertrophic chondrocytes and SaOS‐2 osteoblast‐like cells .…”

“…(55,(57)(58)(59)(60)(61)(62)(63) The structure and function of MVs in skeletal and vascular mineralization has recently been reviewed by several authors. (53,(64)(65)(66)(67) The biogenesis of these vesicles may occur through multiple proposed mechanisms; however, the most prevalent theories include polarized budding from the parental cell membrane, or from microvilli on the cell surface, as demonstrated in hypertrophic chondrocytes and SaOS-2 osteoblast-like cells. (68)(69)(70)(71) The theorized function of MVs in biomineralization is to facilitate a localized concentration of Ca 2+ and P i , protected from the ECM, from which hydroxyapatite or its precursors may form.…”