Collagen production of osteoblasts revealed by ultra-high voltage electron microscopy

Abstract

In the bone, collagen fibrils form a lamellar structure called the "twisted plywood-like model." Because of this unique structure, bone can withstand various mechanical stresses. However, the formation of this structure has not been elucidated because of the difficulty of observing the collagen fibril production of the osteoblasts via currently available methods. This is because the formation occurs in the very limited space between the osteoblast layer and bone matrix. In this study, we used ultra-high-voltage electron microscopy (UHVEM) to observe collagen fibril production three-dimensionally. UHVEM has 3-MV acceleration voltage and enables us to use thicker sections. We observed collagen fibrils that were beneath the cell membrane of osteoblasts elongated to the outside of the cell. We also observed that osteoblasts produced collagen fibrils with polarity. By using AVIZO software, we observed collagen fibrils produced by osteoblasts along the contour of the osteoblasts toward the bone matrix area. Immediately after being released from the cell, the fibrils run randomly and sparsely. But as they recede from the osteoblast, the fibrils began to run parallel to the definite direction and became thick, and we observed a periodical stripe at that area. Furthermore, we also observed membrane structures wrapped around filamentous structures inside the osteoblasts. The filamentous structures had densities similar to the collagen fibrils and a columnar form and diameter. Our results suggested that collagen fibrils run parallel and thickly, which may be related to the lateral movement of the osteoblasts. UHVEM is a powerful tool for observing collagen fibril production.

COL4A1 promotes the growth and metastasis of hepatocellular carcinoma cells by activating FAK-Src signaling

“…They are essential in extra cellular matrix (ECM) which is the major component in tumor microenvironment and can regulate tumor cell behaviors [5,6]. Collagen proteins are produced and secreted by fibroblasts [7], osteoblasts [8], hematopoietic cells [9], and also can be biosynthesized and regulated by endothelial cells [10,11] and cancer cells [12]. Over the last few years, accumulated evidences have indicated that some collagens are differentially expressed in cancer.…”

Proximate mechanisms involved in the formation of Secondary Osteon Morphotypes

“…One observation that also makes it unlikely that type 1 processes control predominant CFO is that the processes are perpendicular within the lamellae of alternating SOMs regardless of the lamella being dark or bright (27,69). We also suggest that pre-collagen molecules that are in a liquid crystalline phase (70) begin to orient within the osteoblast (41,71) in accordance with patterns of ciliary motion (▶ Fig. 9) prior to their evagination by fibropositors.…”

“…To us it seems unlikely that this cell migration occurs during osteon formation because the osteoblasts are spatially constrained in circular/cylindrical groups when they form osteon lamellae. In a study of trabecular bone formation in embryonic chick calvaria, Hosaki-Takamiya et al (41) stated that "in order to form the lamellar structure, the [31]). (a and b) Two osteons with orthogonal plywood designs that have alternating fibril directions (but are not considered "alternating osteons") that give rise to either bright (a) or dark (b) type osteons, which are the result of their marked oblique-to-transverse orientation (bright, also see lower right image in ▶ Fig.…”

Biomimetic mineralization using matrix vesicle nanofragments

“…In this study, we identified the initial steps of mineral formation in mouse calvaria, and found that osteoblasts first release collagen fibers, which is in accordance with previous studies showing the three dimensional morphometry of collagen fibrils during initial stages of mineralization. 14,15 Subsequently, osteoblasts secrete MVs in large amounts and can build a large bone area of 1200 μm in length in the initial 24 h.…”