Fourier transform infrared microspectroscopic analysis identifies alterations in mineral properties in bones from mice transgenic for type X collagen

Type X collagen has been implicated in the morphogenetic events of endochondral ossification (EO), including the calcification of hypertrophic cartilage and trabeculae prior to their replacement by bone and marrow. Recently, transgenic mice, which expressed a truncated collagen X protein, were reported to exhibit morphologic alterations in all tissues arising through EO. Specifically, the growth plates were compressed within the zone of cartilage hypertrophy, and the number and size of calcified trabeculae were reduced. The condition in the mouse is comparable to Schmid metaphyseal chondrodysplasia in humans for which, to date, 20 defined type X collagen mutations have been reported. The transgenic mouse showed no alterations in mineralization by conventional histology, however, it did show a decrease in newly formed bony trabeculae, and a thinning of periosteal bones. Fourier transform infrared (FTIR) spectroscopy has previously been shown to provide quantitative and qualitative information about the relative amount of mineral and carbonate present, mineral composition, and crystal perfection. To determine whether the expression of abnormal collagen X molecules had an effect on mineral properties, the “quality” of mineral crystals was analyzed in thin sections of tibia from day 17 and day 25 genotypically negative (normal) and positive (mutant) mice from several independent transgenic mouse lines showing varying degrees of the mutant phenotype, by means of Fourier transform infrared microscopic analysis (FTIRM). The results indicate definite differences between normal and transgenic mice calcified cartilage mineral, both in the amount present and the “quality” of the crystals. Calcified cartilage mineral from transgenic mice exhibited less crystallinity and higher acidic phosphate content than the corresponding mineral from normal specimens.