Matrix vesicles

ACP reveals discoidal and spherical forms87, but it is questionable whether these two forms actually exist in living bone. It has been assumed to be more likely that they are produced by drying or aging of the sample materials. Amorphous mineral material occurs in matrix vesicles of newly synthesizing bone. This less dense amorphous mineral material appears to occupy the position of the vesicle membrane and it may be the precursor of bone material88. ... 

The consistent finding of sizeable amounts of partially degraded PL in the matrix vesicle fraction131-133, plus the demonstrated barrier to 45 Ca exchange... 

Extracellular vesicles or matrix vesicles have not been identified in any invertebrates445. In bone formation, it has been suggested that they provide a basis for... 

In these tissues the distribution of vesicles correspond closely to the patterns of matrix mineralization. Furthermore, it has been suggested that crystals of HA are deposited within the vesicles. Subsequently apatite is deposited within the vesicles and upon their surfaces to produce typical modular clusters of mineral. Such morphological observations strongly implicate the matrix vesicles in the formation of apatite crystals (Fig. 9). Once the first crystals are formed, they mineralize further by epitactic crystal growth458. ... 

The one structural feature common to cell matrix vesicles is the enveloping membrane which appears trilaminar under the electron microscope. The term vesicle ... 

Fig. 10. Schematic presentation of the theories of mineralization in matrix vesicles, a) Theory of Anderson458 b) Theory of Thyberg642). (After Hohling et al.641 )...

The first evidence that matrix vesicles contained enzymes came from cytochemical studies on epiphyseal cartilage in which alkaline phosphatase and ATPase were discovered on the surface of the vesicle461 462). 

The lysosomal acid phosphatase was cytochemically shown to be present in dense bodies of chondrocytes but not in the nearly matrix vesicles461,462). Subsequent studies have confirmed that the amount of acid phosphatase in isolated vesicles is low and also that the activities of -glucuronidase and cathepsin D in the isolated vesicles were negligible463). The evidence indicates that matrix vesicles are not lysosomal. Isolated vesicles contain comparatively little mitochondrial succinic dehydrogenase, suggesting that the matrix vesicles and mitochondria were not identical458). 

Matrix vesicles are markedly rich in Ca compared to epiphyseal chondrocytes, even in the proliferation zone. The Ca and inorganic phosphate concentrations are greater than can occur together in solution. X-ray diffraction of the freezedried vesicles failed to detect any apatite phase467), while membrane-enclosed vesicle-like structures were found to be filled with amorphous electron-dense material468). However, it has been suggested that HA is formed within matrix vesicles459). 

However, increasing evidence points to the key role of extracellular matrix vesicles in the initiation of biological calcification455,456,458,469,487-49°). 

Calcification can be visualized in two phases. In the first phase, phosphate accumulates within the matrix vesicles through the enzyme hydrolysis of inorganic pyrophosphate (and perhaps other phosphate esters)458. ... 

Schraer, H., Gay, C. V. Matrix vesicles in newly synthesizing bone observed after ultra-cryotomy and ultramicroincineration. Calc. Tiss. Res. 23, 185 (1977)... 

Peress, N., Anderson, H. C., Sajdera, S. W, The lipids of matrix vesicles from bovine fetal epiphyseal cartilage, Calc. Tiss. Res. 14, 275 (1974)... 

Wuthier, R. E, Lipid composition of isolated epiphyseal cartilage cells, membranes and matrix vesicles. Biochim. Biophys. Acta 409, 128 (1975)... 

Majeska, R. J., Wuthier, R. E. Localization of matrix vesicle phospholipids by labeling with trinitrobenzenesulfonate (TNBS). Intern. Assn. Dent. Res., Preprinted Abstracts. 54th General Session, Abstr. No. 205 (1976)... 

Wuthier, R. E., Gore, S. T. Partition of inorganic ions and phospholipids in isolated cell, membrane and matrix vesicle fractions Evidence for Ca-Pj-acidic phospholipid complexes. Calc. Tiss. Res. 24, 163 (1977)... 

Thybeig, J., Friberg, U. Ultrastructure and phosphatase activity of matrix vesicles and cytoplasmic dense bodies in the epiphyseal plate. J. Ultrastruct. Res. 33, 554 (1970)... 

Ah, S. Y. Analysis of matrix vesicles and their role in calcification of epiphyseal cartilage. Fed. Proc. 35, 135 (1976)... 

Felix, R., Fleisch, H. Pyrophosphatase and ATPase of isolated cartilage matrix vesicles. 

It was stated that hydrated calcium monohydrogen phosphate in amorphous or cryptocrystalline form is a potential precursor in the formation of hydroxyapatite because the structural position of Ca2+ on (010) and (110) crystal planes of both minerals essentially correspond to one another492. These planes of calcium ions could easily serve as transition boundaries with little distortion of crystal structure the same holds true for octacalcium phosphate or defect apatites. Thus apatite may form from amorphous or microcrystalline calcium monohydrogen phosphate possible via octacalcium phosphate or defect apatites. This process may already start inside the matrix vesicles and continue during extravesicular activities. 

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