Skeletal calcification patterns of batoid, teleost, and mammalian models: Calcified cartilage versus bone matrix

Abstract

This study compares the skeletal calcification pattern of batoid Raja asterias with the endochondral ossification model of mammalians Homo sapiens and teleost Xiphias gladius. Skeletal mineralization serves to stiffen the mobile elements for locomotion. Histology, histochemistry, heat deproteination, scanning electron microscopy (SEM)/EDAX analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectrometry (FTIR) have been applied in the study. H. sapiens and X. gladius bone specimens showed similar profiles, R. asterias calcified cartilage diverges for higher water release and more amorphous bioapatite. In endochondral ossification, fetal calcified cartilage is progressively replaced by bone matrix, while R. asterias calcified cartilage remains un-remodeled throughout the life span. Ca²⁺ and PO₄ ^3- concentration in extracellular matrix is suggested to reach the critical salts precipitation point through H₂ O recall from extracellular matrix into both chondroblasts or osteoblasts. Cartilage organic phase layout and incomplete mineralization allow interstitial fluids diffusion, chondrocytes survival, and growth in a calcified tissue lacking of a vascular and canalicular system. HIGHLIGHTS: Comparative physico-chemical characterization (TGA, DTG and DSC) testifies the mass loss due to water release, collagen and carbonate decomposition of the three tested matrices. R. asterias calcified cartilage water content is higher than that of H. sapiens and X. gladius, as shown by the respectively highest dehydration enthalpy values. Lower crystallinity degree of R. asterias calcified cartilage can be related to the higher amount of collagen in amorphous form than in bone matrix. These data can be discussed in terms of the mechanostat theory (Frost, 1966) or by organic/inorganic phase transformation in the course evolution from fin to limbs. Mineral analysis documented different charactersof R. asterias vs H. sapiens and X. gladius calcified matrix.

Keywords: calcified cartilage; comparative histology; growth pattern; mineralization; morphology.