Distribution Of Matrix Vesicles Research Articles

Differential involvement of matrix vesicles during the initial and appositional mineralization processes in bone, dentin, and cementum

The distribution of matrix vesicles and its role in biological mineralization were examined in bone and dental hard tissues of the rat after daily administrations of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), a potent inhibitor of mineralization, for 7 or 14 days. Newly formed, nonmineralized matrices of the HEBP-affected bone and mesodermal dental hard tissues other than circumpulpal dentin contained numerous mineral-filled matrix vesicles (MV), randomly distributed throughout the collagenous matrix. The distribution density of the mineral-filled MV in the HEBP-affected matrices of calvaria, metaphyseal trabecular bone, alveolar bone, and cellular cementum ranged from 60 to 70 per 100 μm 2, and no statistically significant differences were noted among the values. In the HEBP-affected dentin, however, MV were located only in the nonmineralized matrix of mantle dentin and totally absent in the circumpulpal dentin layers. Instead, the HEBP-affected circumpulpal dentin contained a dense meshwork of noncollagenous matrix enriched with calcium and phosphorus. Comparable meshwork structures were undetectable in nonmineralized matrices of the other hard tissues affected by HEBP. These observations suggest that a certain population of MV (60–70 per 100 μm 2) is involved in the process of appositional mineralization in most of the mesodermal hard tissues, in addition to their well-known role in initial mineral induction in these tissues. Circumpulpal dentin appears to be an exception, where MV are not required for the appositional mineralization process. Exclusive localization of dentin phosphoproteins in circumpulpal dentin layers must take place to facilitate appositional mineralization at the calcification front, in the absence of MV.

Changes in the fetal tibial growth plate secondary to maternal zinc deficiency in the rat: A histological and histochemical study

Zinc deficiency (ZD) is teratogenic in rats, and fetal skeletal defects are prominent. To elucidate further the effects of maternal ZD in the fetal skeleton, we performed a morphological and histochemical study of tibial growth plate (GP) in ZD rat fetuses. The histochemical study included the identification of calcium, of hydrolytic enzymes associated with the process of calcification, and of oxidative enzymes related to energy production and to the synthesis of proteoglycans. Pregnant Sprague-Dawley rats were fed (1) a control diet (76.4 micrograms Zn/g diet) ad libitum (group C), (2) a zinc-deficient diet (0 micrograms/g) ad libitum (group ZD), or (3) the control diet pair-fed to the ZD rats (group PF). On day 21 of gestation, laparotomies were performed, the fetuses were removed, and fetal tibiae obtained. Specimens were stained with hematoxylin-eosin (H&E) and Masson Trichrome and were processed for identification of alkaline phosphatase, adenosine triphosphatase, succinic dehydrogenase, NADH dehydrogenase, and calcium. The morphologic patterns found in ZD fetal tibiae indicated defects in various cell types implicated in bone metabolism. Staining for hydrolytic enzymes revealed alterations in the size and distribution of matrix vesicles and a weaker staining for ATPase in ZD fetuses. Staining for oxidative enzymes was overall more intense in ZD fetal tibiae. ZD fetuses also presented irregular and defective calcification. These findings indicate that severe maternal ZD in the rat results in structural and functional alterations in the GP of fetal bone, leading to a defective endochondral ossification.

Matrix Vesicles in Bone Tumors

Bone tumors were categorized into alkaline phosphatase (ALPase)-positive (2 ossifying fibromas, 1 benign osteoblastoma and 16 osteosarcomas) and negative (2 chondromas, 2 chondrosarcomas, 3 non-ossifying fibromas, 2 malignant fibrous histiocytomas and 6 giant cell tumors of bone) groups. Production and distribution of matrix vesicles (MVs) in the tumor tissues were examined to clarify their role in neoplastic bone formation. Four distinct types of MV were isolated primarily in ALPase positive bone tumors: empty, amorphous, crystalline and ruptured MVs. They were formed by budding off from the cytoplasmic projections of the osteoblastic tumor cells. The significance of differences in the production rate of MVs between ALPase-positive and negative bone tumors was investigated in view of the predominantly high production of MVs in ALPase-positive bone tumors. Many more mature MVs (crystalline and ruptured) were observed in the osteoblastic lesions of osteosarcoma than in the fibroblastic and MFH-like lesions, suggesting an intimate relationship with maturation and differentiation of the osteoblastic tumor cells. The above findings indicate that production of MVs is one of the diagnostic parameters for osteoblast-derived bone tumors, as well as ALPase activity, and that vesicle-induced mineralization is a major mineralization mechanism in neoplastic bone formation.

Structure and distribution of matrix vesicles in dentin matrix of red sea bream, Pagrus major.

Structure and distribution of matrix vesicles in dentin matrix of red sea bream, Pagrus major.