From Matrix Vesicles to Miniature Rocks: Evolution of Calcium Deposits in Calf Costochondral Junctions

Abstract

Objective Initial stages of cartilage matrix calcification depend on the activity of matrix vesicles. The purpose of the study was to describe how calcified matrix vesicles join into larger structures, to present their up-to-date undescribed 3-dimensional image, and to observe how calcified matrix relates to chondrocyte lacunae. Design Calcified cartilage was obtained from the zone of provisional calcification of calf costochondral junctions, then enzymatically isolated and studied by microtomography, scanning electron microscopy, atomic force microscopy and X-ray diffraction, and Fourier transform infrared spectroscopy. Results Hyaluronidase digestion released packets of granules surrounded by the cartilage matrix. Further digestion, with collagenase and trypsin, removed matrix and exposed granules with dimensions within 50 to 150 nm range, which we consider as equivalent of calcified matrix vesicles. Granules joined into larger groups with dimensions of 0.5 to 2 μm, which we call globular units. Certain matrix vesicles appeared well connected but contained globular units that had spaces filled with electron lucent material, presumably matrix or chondrocyte remnants. Globular units were organized into massive structures taking the shape of oval plates. Comparison of these plates with lacunae containing isogenous groups of chondrocytes from proliferative zone of costochondral junction suggests that the cells from a single lacuna were responsible for the formation of one plate. The plates were connected with each other and extended over provisional calcification zone. Conclusions The outcome showed how particular calcified matrix vesicles associate into globular units, which organize into massive structures assuming the shape of oval plates and eventually cover large areas of cartilage matrix.

Investigating the interfaces of the epiphyseal plate: An integrated approach of histochemistry, microtomography and SEM

“…In places where the mineralization in still underway they are more easily identifiable, but they are present everywhere. They have been reported in other cartilages as well (Anderson, 1969 ; Claassen et al, 2017 ; Jaroszewicz et al, 2021 ) and represent a different mineralization pattern than the collagen‐driven mineralization of bone (Christoffersen & Landis, 1991 ). Briefly, in bone and in calcifying tendons the process begins simultaneously in a huge number of independent collagen fibrils: tiny, needle‐shaped mineral particles appear in the gap zone of type I‐based collagen fibrils and subsequently grow into plate‐like particles, invade the overlap zone and eventually swell and loosen the collagen fibril which merge with neighbouring ones (Landis et al, 1996 ; Reznikov et al, 2018 ; Xu et al, 2020 ).…”

“…In places where the mineralization in still underway they are more easily identifiable, but they are present everywhere. They have been reported in other cartilages as well (Anderson, 1969;Claassen et al, 2017;Jaroszewicz et al, 2021) and represent a different mineralization pattern than the collagen-driven mineralization of bone (Christoffersen & Landis, 1991). Briefly, in bone and in calcifying F I G U R E 8 A higher magnification detail from an incompletely calcified zone of a native, untreated specimen.…”

Could BMPs Therapy Be Improved if BMPs Were Used in Composition Acting during Bone Formation in Endochondral Ossification?

“…Calcification of longitudinal septa begins in the middle part of the proliferative zone due to the activity of matrix vesicles; detached from chondrocytes and carrying alkaline phosphatase, components necessary for calcium phosphate deposition and also BMPs 1–7 and VEGF [ 69 ]. In the provisional calcification zone, about 70% of the matrix is calcified, with the remaining matrix either adhering to or enclosed within calcium deposits [ 70 , 71 ].…”

Growth factors in the initial stage of bone formation, analysis of their expression in chondrocytes from epiphyseal cartilage of rat costochondral junction

“…They serve as initiation sites of mineral deposition in the cartilage [9][10][11]. Calcified matrix vesicles join into larger structures, called globular units and finally into massive calcium phosphate deposits occupying most of the calcification zone territory [12].…”