Osteoblastic lysosome plays a central role in mineralization

phys.org | 2/18/2019 | Staff
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Mineralization is mediated by osteoblasts, which secrete mineral precursors through matrix vesicles (MVs) as a fundamental process in vertebrates. The vesicles are calcium and phosphate rich, containing organic materials such as acidic proteins. In a new study now published in Science Advances, Tomoaki Iwayama and colleagues at the departments of periodontology, biomedical research, oral science, biomaterials and oral anatomy development used scanning electron-assisted dielectric microscopy (SE-ADM) and super-resolution microscopy (SRM) to assess live osteoblasts during conditions of mineralization at nano-level resolution. They found the calcium-containing vesicles to be multi-vesicular bodies containing mineralizing nanovesicles or matrix vesicles (MVs). According to the observations, the MVs could be transported together with lysosomes and secreted by exocytosis. Iwayama et al. presented proof that the lysosomes could transport amorphous calcium phosphate in mineralizing osteoblast cells.

During the physiological process of bone mineralization, the deposition of calcium phosphate crystals occurs in the extracellular matrix as a fundamental process in all vertebrates. In 1967, biologists Clarke Anderson and Ermanno Bonucci, individually visualized mineral-related particles in the extracellular space using electron microscopy (EM). Scientists later recognized these particles as mineralizing nano-vesicles or matrix vesicles (MVs). During the past 50 years of EM studies on MVs, biologists have grappled to understand the mechanism of MV formation and secretion, which remains largely unknown.

Process - Cells - EM - Preparation - EM

Clarifying the mineralizing process of live cells with EM is challenging since sample preparation for EM requires steps on both chemical fixation and alcoholic dehydration. The steps can induce artefacts and even dissolve or remove unstable mineral precursors leaving an organic scaffold known as a "crystal ghost". While scientists had successfully used the process of EM using fixed and dehydrated tissue to view the structure of mineralized collagen fibrils in bone, to study mineral precursors, they must employ cryo-EM processes to avoid dehydration and facilitate costly, extremely fast cooling...
(Excerpt) Read more at: phys.org
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