Bo Wikström

Kinetic Studies on Epiphyseal Growth Cartilage in the Normal Mouse

The synthesis of DNA was studied in the proximal tibial growth plate of 25-day-old healthy NMRI mice by using the thymidine analog bromodeoxyuridine (BrdUrd), which is incorporated into cells in the S-phase. Such cells were found only in the upper three fifths of the morphologically defined proliferating zone. This zone was therefore subdivided into a functional proliferating zone (the S-phase zone) where most, if not all, chondrocytes proliferate, and a remaining maturation zone. The BrdUrd containing immunoreactive cells could then be followed at different intervals and they were found at the chondro-osseous junction after only 36 h. By using double-labeling with BrdUrd and iododeoxyuridine (IdUrd) the duration of cell cycle components could be estimated; that is, the time for DNA synthesis (S-phase), second gap and mitosis (G2 + M-phase), and remaining first gap (G1). We determined an S-phase time of 7.1 h and an average cell-cycle duration of 36 h. The G2 + M-phase was estimated as 3.5-4 h, leaving an average G1-phase time of 25 h, which probably varies considerably between chondrocytes. By combining these data with morphometrical data regarding distances between cells, we calculated a total growth rate of 9.0 microm/h. Of this rate, 80% was entirely related to the process of hypertrophy--that is, longitudinal expansion without any corresponding increase in cell number--and 75 % was the result of processes outside the S-phase zone. Five percent of the growth was due to the expansion of cell distances within the S-phase zone. In this way longitudinal expansion can be studied at different levels in the growth plate and the data permit calculation of changes in volumes of the extracellular matrix. The largest increases in matrix volume occurred in the hypertrophic zone. These data may serve as a basis for further studies on matrix turnover in relation to growth.

Determination of N-acetyl- and N-glycolylneuraminic acids in glycoconjugates by reversed-phase high-performance liquid chromatography with ultraviolet detection

Abstract A rapid and sensitive method for the determination of sialic acids is described. The measurement is based on isocratic high-performance liquid chromatography, whereby N-acetylneuraminic and N-glycolylneuraminic acids are separated. The total amounts of these acids can be determined after hydrolysis and per-O-benzoylation. The conditions for hydrolysis and derivatization were optimized for measurement of these sialic acids in glycoconjugates. The benzoyl derivatives were chromatographed on a reversed-phase column with 67% (v/v) aqueous acetonitrile and the eluted peaks were monitored by UV detection. The method allows the determination of picomole amounts. the reaction was shown to give linear calibration graphs over the entire range tested. i.e. , up to 160 nmol (50 μg) of each of the sialic acids.

Analysis of dentine glycosaminoglycans using high-performance liquid chromatography

SummaryPuppy dentine was prepared using ultracentrifugation of tooth powder in organic density gradients. The glycosaminoglycans of the obtained tissue fraction were prepared after papain digestion andβ-elimination, using preparative chromatography on DEAE-cellulose and CPC-cellulose. These polysaccharide fractions were analyzed using highly sensitive HPLC procedures. One such HPLC procedure allowed hyaluronic acid to be determined in less than microgram amounts.The glycosaminoglycans thus prepared consisted only of chondroitin-4-sulfate, chondroitin-6-sulfate, and small amounts of highly hybridized dermatan sulfate, while the experiments failed to demonstrate even trace amounts of keratan sulfate, hyaluronic acid or heparan sulfate.

Dyggve-Melchior-Clausen dysplasia. Morphological and biochemical findings in cartilage growth zones.

ABSTRACT. The results of light and electron microscopic examination and of biochemical proteoglycan studies of costochondral and iliac crest biopsies from a recently diagnosed case of Dyggve‐Melchior‐Clausen dysplasia are reported. At light microscopy of resting cartilage large lacunae containing clusters of five or more chondrocytes were seen in some areas. In the hyaline cartilage there were scattered fibrous foci but no mineralized areas. Electron microscopy revealed chondrocytes containing widened cisternae of rough endoplasmic reticulum and vesicles coated with a smooth single‐layered membrane. The content of the cisternae and of the vesicles was amorphous. Throughout the cartilage a considerable proportion of the chondrocytes displayed more or less pronounced necrobiotic changes. The biochemical analysis showed an increased amount of glucosaminoglycans in the cartilage and indicated that the ability of proteoglycan monomers to reaggregate to hyaluronic acid chains was decreased. Our findings support the suggestion that Dyggve‐Melchior‐Clausen dysplasia is due to a disturbance in proteoglycan metabolism.

Morphological studies of the epiphyseal growth zone in the brachymorphic (bm/bm) mouse

SummaryLight microscopy, including immunohistochemical techniques, and electron microscopy were performed on epiphyseal growth cartilage from brachymorphic (bm/bm) mice and age-matched phenotypically normal siblings aged 5, 16 and 25 days. In the bm/bm mice light microscopy showed a disturbed columnar arrangement and numerous chondrocytes with pronounced regressive changes. The normal development of proliferative cells into hypertrophic cells was halted and thus only a rather small and ill-defined hypertrophic zone was seen. The calcifying zone was irregular and the normal lacunae were replaced by a densely staining matrix. Using immunofluorescence techniques, the presence of considerable amounts of both type II and type V collagen was demonstrated in the bm/bm mice, while the cartilage from controls contained only type II. Ultrastructurally the lacunar matrix contained bundles of fine fibrils without the typical collagen periodicity which might indicate synthesis of a defective procollagen. Our observations together with the previously demonstrated deficiency of 3′-phosphoadenosine 5′-phosphosulphate, illustrate the complexity of the growth cartilage disturbance in the bm/bm mouse. Most of our findings are at variance with those described in the literature and possible pathogenetic mechanisms for the observed alterations in the growth cartilage are discussed.

MORPHOLOGICAL AND BIOCHEMICAL ANALYSIS OF BIOPSY SPECIMENS IN DISORDERS OF SKELETAL DEVELOPMENT

ABSTRACT. A programme for combined morphological and biochemical analysis of cartilage‐bone biopsy material is described. The structural analysis includes light and electron microscopy, and the biochemistry is focused on polysaccharides. A procedure for isolation and characterization of proteoglycans and glycosaminoglycans from dry cartilage in amounts down to 1 mg is described. The procedure is exemplified by analyses of material from patients with osteogenesis imperfecta, mucopolysaccharidosis IV‐Morquio and metaphyseal chondrodysplasia type McKusick. In osteogenesis imperfecta characteristic morphological alterations were demonstrated. Apart from increased chondroitin sulphate molecular weights, the biochemical analyses showed values within the assumedly normal range. In Morquios disease extensive intracellular deposits in single membrane vacuoles were observed in both chondrocytes and osteocytes. There were indications that these deposits contained keratan sulphate, which also occurred in increased amounts in the total tissue preparation. Furthermore, the tendency to formation of proteoglycan aggregates was decreased. In the tissue from the patients with the McKusick syndrome insignificant ultrastructural changes, mainly affecting the mitochondria, were found. The biochemical results were within the assumedly normal range. The significance of these findings and the possibilities of further methodological development are discussed.

Stereological analysis of the epiphyseal growth cartilage in the brachymorphic (bm/bm) mouse, with special reference to the distribution of matrix vesicles

SummaryThe brachymorphic (bm/bm) mutation in the mouse leads to disproportional dwarfism due to a disturbance of endochondral bone formation. The morphological characteristics of bm/bm epiphyseal growth cartilage are signs of cellular degeneration and disintegration and alteration of the composition of the extracellular matrix, with an abnormal mineralization pattern. The present stereological study of the bm/bm growth plate revealed a clearly altered distribution of matrix vesicles as compared with the controls. It was also demonstrated that the bm/bm matrix vesicles have an abnormal size distribution, with an increased mean caliper diameter. The biological significance of these findings is discussed in relation to the different hypotheses on the origin of matrix vesicles and their possible role in the mineralization process. The results support the opinion that extracellular matrix vesicles, at least partly, constitute cellular debris.

Growth Parameters in the Epiphyseal Cartilage of Brachymorphic (bm/bm) Mice

Abstract. We studied kinetics in the epiphyseal cartilage of the brachymorphic (bm/bm) mouse, combining morphometry and labeling with halogenated nucleotides. The defective synthesis of the sulfate donor PAPS in these homozygous mutants is evident in tissues with a large production of glycosaminoglycans; these compounds become undersulfated. Compared with their heterozygous siblings, the longitudinal growth of the mutant mice was reduced by two-thirds. This was mainly associated with (1) reduced height of the proliferating zone, (2) a substantial number of G0 cells in this zone, and (3) reduced hypertrophy which, in turn, may be related to premature mineralization and prevention of normal expansion of cells. No significant effects on cell-cycle parameters were detected, such as S-phase time or cell-cycle time, and the rate at which each cell increased the matrix volume seemed normal. An effect on matrix mineralization may be related to known changes in the structure of matrix PGs, whereas the effect on proliferation may be related to other factors. Candidates for such other effects of undersulfation are the cell surface PGs, which are important for binding of growth factors.

Proteoglycans and Glycosaminoglycans in Cartilage from the Brachymorphic (bm/bm) mouse

The brachymorphic (bm/bm) mouse is a disproportionate dwarf with a disturbance of the endochondral growth of the skeleton. Rib cartilage from 25-day-old affected animals and their normal siblings was analyzed for its contents and composition of proteoglycans. In addition to the previously reported undersulfation of chondroitin sulfate, it was demonstrated that one of the two types of aggregating proteoglycan and possibly the small ones are decreased in bm/bm costal cartilage, both in the growth region and in the remaining part. The molecular defect of the bm/bm condition is known to affect the synthesis of 3-phosphoadenosine 5-phosphosulfate (Sugahara and Schwartz, Proc. Natl. Acad. Sci. USA 76: 6615-6618, 1979). The above finding therefore suggests the existence of feedback mechanisms for the regulation of proteoglycan synthesis, whereby the undersulfation of glycosaminoglycans would result in decreased synthesis or increased turnover of certain proteoglycan subpopulations. Analysis of the glycosaminoglycan side chains indicated that mouse rib cartilage contains small amounts of keratan sulfate of extremely small size. The affected and control tissues, however, seemed to contain equal amounts of both glucosamine and galactosamine.