Melvin J. Glimcher

Receptor-Ligand Interaction Between CD44 and Osteopontin (Eta-1)

The CD44 family of surface receptors regulates adhesion, movement, and activation of normal and neoplastic cells. The cytokine osteopontin (Eta-1), which regulates similar cellular functions, was found to be a protein ligand of CD44. Osteopontin induces cellular chemotaxis but not homotypic aggregation, whereas the inverse is true for the interaction between CD44 and a carbohydrate ligand, hyaluronate. The different responses of cells after CD44 ligation by either osteopontin or hyaluronate may account for the independent effects of CD44 on cell migration and growth. This mechanism may also be exploited by tumor cells to promote metastasis formation.

Biochemical studies on repair cartilage resurfacing experimental defects in the rabbit knee.

UNLABELLED Wounds penetrating articular cartilage to bone heal with cartilage described variably as either fibrous or hyaline. In the present study, such repair cartilage was induced in the rabbit for biochemical comparison with normal articular cartilage. The main collagen in the repair tissue after three weeks was type I. By six to eight weeks, type II had become predominant and continued to be enriched up to one year; but type I still persisted as a significant constituent of the repair tissue even after a year, so the repair cartilage never fully resembled normal articular cartilage. From radiochemical analysis, type II was determined to be the major collagen synthesized by the repair tissue after three to four weeks. After six months, the repair cartilage contained more collagen and less hexosamine than control cartilage, suggesting that the fibrous texture that often developed was due to a loss of proteoglycans rather than to a change in the type of collagen. CLINICAL RELEVANCE Procedures capable of inducing the differentiation of authentic articular cartilage to resurface degenerated human joints would be invaluable. Surgical methods, such as drilling through to subchondral bone, are often attempted. It is not known, however, whether the cartilage that forms is true articular cartilage or, for example, fibrocartilage. The present experimental study in rabbits compared the properties of such repair cartilage with those of normal articular cartilage.

Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age: 2. Investigations in the nu3PO4 domain.

SummaryIn order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO42− groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO42−-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and β tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in thev4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520–530 and 540–550 cm−1 are assigned to HPO42−. Reference to known calcium phosphates shows that bands in this domain also exist in HPO42−-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO42− environments. The third absorption band (610–615 cm−1) is not related to HPO42− or OH− ions. It appears to be due to a labile PO43− environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610–615 cm−1 band is related to an absorption band at 560 cm−1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO43− environment exhibited a heterogeneous distribution in the insoluble precipitate.

A heritable disorder of connective tissue. Hydroxylysine-deficient collagen disease.

Abstract Two sisters nine and 12 years of age presented with a similar clinical picture consisting of severe scoliosis, recurrent joint dislocation and hyperextensible skin and joints. Amino acid a...

Bone mineral: update on chemical composition and structure

The structure of the Ca–P solid phase in bone was first identified by deJong in 1926 as a crystalline calcium phosphate similar to geological apatite by chemical analyses and, most importantly, by X-ray diffraction [1]. The X-ray diffraction data was confirmed a few years later [2]. These findings initiated a flurry of research on a more detailed chemical composition and crystal structure of both geological and synthetic apatites and of bone mineral, initially carried out principally by geologists, crystallographers, and chemists, but later by biochemists and physiologists because of the clear potential of this new information to shed light on the biological and physiological functions of bonemineral and as indicators of disorders of the skeletal system. It soon became clear that there were significant structural and chemical compositional differences between the many different geological hydroxyapatites, synthetic hydroxyapatites, and the apatite crystals found in bone and related skeletal tissues in addition to the very large size of the geological and many of the synthetic apatite crystals, compared with the extremely small particle size of bone mineral. Further studies were directed in roughly three avenues: continued more careful and complete analytical compositional data of bone mineral, from which it was clearly established that the chemical composition of bone crystals in many ways did not correspond to the chemical compositions of stoichiometric hydroxyapatite. Indeed, the bone crystals were found to contain significant and varying amounts of carbonate and HPO4 ions. Much later, it was discovered by a variety of techniques, including solid-state NMR [3], Raman spectroscopy [4], and inelastic neutron scattering [5], that the biological bone apatites contain only a very small percentage of the total number of hydroxyl groups present in highly purified synthetic calcium hydroxyapatites. Other studies clearly pointed out that a substantial fraction of the phosphate ions are situated on the surfaces of the bone mineral crystals which are mainly protonated and in a disordered environment [6], in contrast to the phosphate ions in lattice positions, which are unprotonated. Also, other uniquely protonated phosphate ions were identified in bone mineral by phosphorus 31 NMR spectroscopy, which are not present in synthetic calcium phosphate apatites [7]. Structural studies were first carried out to determine crystal size by measuring the extent of X-ray diffraction peak broadening [8], which yielded crystal sizes varying from 31 to 290Å. More detailed structural data were obtained by the then recently introduced field of electron microscopy and electron diffraction [9–11], which revealed that the bone crystals were thin plates, approximately 500Å long, 250Å wide, and 100Å thick. However, calculations from low-angle X-ray diffraction scattering studies [12–14] were more consistent with the conclusions that the bone crystals were very much smaller than those observed by Osteoporos Int (2009) 20:1013–1021 DOI 10.1007/s00198-009-0860-y

Electron microscopic observations of bone tissue prepared anhydrously in organic solvents

Methods have been developed which permit electron optical examination of sections of undecalcified bone tissue which have been exposed only to organic solvents, thus minimizing artifacts induced in the mineral phase by aqueous solvents. Dense mineral granules are observed in the mitochondria of bone cells in unstained sections treated anhydrously, strongly suggesting that a solid phase of calcium phosphate exists in the mitochondria of these cells in vivo . Mineralization of the extracellular tissue spaces is first observed in the form of clusters or aggregates of small mineral particles. The very rapid increase in the size of the clusters and in the mass of mineral in the extracellular tissue space results principally from an increase in the number of additional particles formed rather than from the growth of the mineral particles first deposited. The physical chemical and biological significance of these findings is discussed.

Electron diffraction and electron probe microanalysis of the mineral phase of bone tissue prepared by anhydrous techniques.

Selected area electron diffraction and high spatial resolution, nondispersive electron probe Xray microanalysis have been used to examine the nature of the solid phase mineral deposits of specific ultrastructural components in freshly dissected, undecalcified bone tissue from embryonic chicks, prepared anhydrously with either 100% ethylene glycol or dry ultracryomicrotomy. No electron diffraction patterns of a specific calcium phosphate solid phase are generated from the dense mitochondrial granules of osteoblasts, shown to contain calcium and phosphorus by electron probe microanalysis, and from the early mineral deposits from certain regions of newly synthesized bone. Similar results are obtained from a synthetic preparation of an amorphous calcium phosphate. Absence of an electron diffraction pattern is not caused by an insufficient mass of the calcium phosphate solid phase. The electron diffraction patterns of the more heavily mineralized older regions of the bone show the reflections and characteristics of poorly crystalline hydroxyapatite. There is a progressive change in the electron diffraction pattern approaching that of crystalline hydroxyapatite with increasing distance from the periosteal surface. Electron probe microanalysis of the same tissue components and regions shows that the changes in the electron diffraction characteristics are accompanied by an increase in the Ca/P ratios of the solid mineral phase.

Shape and size of isolated bone mineralites measured using atomic force microscopy

The inorganic phase of bone is comprised primarily of very small mineralites. The size and shape of these mineralites play fundamental roles in maintaining ionic homeostasis and in the biomechanical function of bone. Using atomic force microscopy, we have obtained direct three‐dimensional visual evidence of the size and shape of native protein‐free mineralites isolated from mature bovine bone. Approximately 98% of the mineralites are less than 2 nm thick displaying a plate‐like habit. Distributions of both thickness and width show single peaks. The distribution of lengths may be multimodal with distinct peaks separated by ∼6 nm. Application of our results is expected to be of use in the design of novel orthopaedic biomaterials. In addition, they provide more accurate inputs to molecular‐scale models aimed at predicting the physiological and mechanical behavior of bone.

Recent studies of bone mineral: Is the amorphous calcium phosphate theory valid?

Abstract Recent studies on bone mineral are reviewed, with particular emphasis on the nature of the initial mineral deposited and the changes occuring during further mineralization and maturation. It is shown that amorphous calcium phosphate, which has been proposed as the precursor of hydroxyapatite in bone mineral, cannot be detected in significant quantity in the earliest bone mineral formed, and furthermore that there is evidence that no progressive decrease in amount of any amorphous phase occurs with bone maturation. We conclude in general that the X-ray difraction pattern and non-stoichiometric composition of bone mineral, and the changes in these characteristic observed with age and maturation cannot be explained by the presence of a second phase in progressively decreasing proportion whether it be amorphous calcium phosphate, octacalcium phosphate, brushite or some other distinct phase. The structural and compositional changes observed with age and maturation in bone mineral are consistent with a general increase in the degree of crystal perfection of a calcium phosphate phase best described as a poorly crystalline hydroxyapatite, although the exact details of the stuctural and compositional modification taking place with maturation must await further research. The role of brushite, which has been proposed as the earliest solid calcium phosphate phase deposited in at least one species, is reviewed.

X-ray diffraction studies of the crystallinity of bone mineral in newly synthesized and density fractionated bone

SummaryThe crystallinity of bone mineral at different stages of maturation has been measured by quantitative X-ray diffraction methods. Crystallinity measurements were made on tibial middiaphyses from 17-day embryonic chicks, newlyformed periosteal bone from embryonic chicks, and density-fractionated bone from post-hatch chickens from 5 weeks to 2 years of age. For a given animal age and degree of mineralization, crystallinity increases with animal age, indicating that changes in bone mineral occur even after mineralization is complete or nearly complete.