Immunolocalization of the cleavage of the aggrecan core protein at the Asn341-Phe342 bond, as an indicator of the location of the metalloproteinases active in the lysis of the rat growth plate

In view of the extensive lysis of hyaline cartilage known to take place during endochondral bone formation, the current study was designed to test the hypothesis that metalloproteinases are the agents that mediate this lysis. Since these enzymes have been shown in vitro to cleave the core protein of the major proteoglycan of cartilage, aggrecan, at the Asn341-Phe342 bond, an immunohistochemical method has been developed to find out whether or not there are sites in the growth plate of the rat tibia where cleavage of this bond takes place. The cleavage of aggrecan by metalloproteinases is followed by the retention of the fragment known as G1, for it includes the G1 domain. Since the G1 fragment terminates in the amino acid residues ...FVDIPEN, we prepared an antiserum against FVDIPEN, confirmed its specificity, then applied it to the growth plate of 21-day-old rat tibia in the hope of localizing the G1 fragments. The antiserum specificity was shown by its recognition of the ...FVDIPEN sequence at the C-terminus of peptides and of G1 fragments produced by aggrecan cleavage. When the antiserum was applied to Western blots of guanidinium chloride extracts prepared from epiphyseal growth plate, it recognized two species (56 and 52 kDa), which differed only in the degree of glycosylation. These fragments were comparable in size to the G1 fragments generated by the action of recombinant metalloproteinase in vitro, thus confirming antiserum specificity for these fragments. Applying the antiserum to cryosections of 21-day-old rat tibiae revealed immunostaining at two intensities within the growth plate matrix: a strong staining was observed in a 1-5 microm-wide layer designated "peripheral" matrix, which borders the epiphyseal and metaphyseal marrow spaces as well as the perichondrium, while a weak staining was found in the rest of the plate, designated "central" matrix. The abundance of G1 fragments terminating in ...FVDIPEN in the peripheral matrix indicates that this is where the growth plate is lysed to achieve longitudinal and latitudinal bone growth. The site where metalloproteinases exert their main lytic activity is a thin layer of matrix separating central from peripheral matrix.

Acellular calcified columns in the normal growth plate of mouse vertebrae

The present study aims to demonstrate the calcified columnar structures of the growth plate of mouse vertebrae and to show their age related changes. For light microscopy, paraffin sections of decalcified lumbar spines were stained with hematoxylin-eosin or toluidine blue; methacrylate sections of undecalcified specimens were stained to detect calcium precipitate. For scanning electron microscopy, lumbar spines treated with 5% NaClO solution were dehydrated by acetone and metal-coated. Light microscopy of hematoxylin-eosin stained sections revealed that the acellular columnar structures appeared between the chondrocyte stacks in the growth plate. These structures were stained more densely by toluidine blue. The methacrylate-embedded sections for calcium staining showed calcium deposition in the columns. Scanning electron microscopy of NaClO-treated specimens enabled the direct observation of the columns on both the epiphyseal and diaphyseal bone surfaces facing the cartilaginous growth plate. Numerous projections on each surface were distributed in mirror images ; the corresponding projections were similar in size and shape, indicating that the projections bonded with each other and formed calcified columns in the cartilaginous growth plate. Longitudinal sections of the spine confirmed these findings. The calcified columns first appeared about 2 or 3 weeks of age and increased in number with time. While increasing in number, they also grew in size fusing with the neighboring ones. The proportional area of the columns occupying the surface facing the growth plate also increased with age. These findings indicate that the calcified column ultimately concerns the cessation of the bone growth.

Ultrastructural modifications of the extracellular matrix upon calcification of growth plate cartilage as revealed by quick-freeze deep etching technique

The ultrastructural changes in cartilage matrix that occur during calcification have been examined in chick epiphyseal growth plate cartilage prepared by quick-frozen, deep-etched, and rotary shadowed replicas. The extracellular cartilage matrix contains a reticular network closely associated with an extensive network of collagen. The components of the reticular network, including thick and thin filaments, are attached directly to the cell membrane, matrix vesicle membrane, and collagen fibrils. This network, which interconnects the matrix vesicles and collagen, fills the extracellular matrix. The dimensions of the reticular network seem to remain almost constant in size from the reserve and proliferative zones to the calcifying zone. The collagen fibrils seem to consist of subfibrillar structures that branch and anastomose. In optimally quick-frozen, deep-etched, prepared collagen, a cross-banding pattern was exposed. Globular structures stud the collagen fibrils, which gradually diminish in number from the reserve zone down to the calcifying zone. The matrix vesicles, when fractured, showed a granular appearance. In most cases, the fracture plane passed through the bilayer of the matrix vesicle membrane. The true surface of the matrix vesicle membrane, therefore, was exposed after deep etching. At the calcifying zone, crystal deposition had occurred in needle-like and/or plate-like form within the membrane-bound matrix vesicles. The reticular network was still intact in the vicinity of the calcified matrix, but in the intercrystalline space, neither the reticular structure nor the globular structure was detectable. Within the calcified matrix, both reticular and granular structures had disappeared from the interfibrillar space of the collagen fibrils.

Low energy loss electron microscopy of chromophores

A novel prism-mirror-prism imaging electron spectrometer with 1 eV energy resolution for a transmission electron microscope permits imaging with spectral energies corresponding to light-optical colour absorptions. The instrument selects the molecular orbital excitations of natural chromophores or of specific dyes normally used in biological light microscopy for delineation and chemical identification, but images them with electron microscopic detail. Heavy atom contrast agents customarily used in electron microscopy are not required. The first results exploit the intrinsic red colour of hematin molecules to demonstrate the potential of the technique and address its spatial resolution. Glycosaminoglycans in cartilage stained with Alcian blue are selectively depicted in situ by means of the electron-induced molecular absorption of this chromophore. Thus, with the use of specific colours the direct or indirect analysis of local chemistry by electron microscopy is possible, and can be carried out with a depiction of spatial detail as small as 16 A, or at least 100-fold finer than observed by light microscopy.

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.

Prepubertal oophorectomy limits the accumulation of cancellous bone in the femur of growing rats with long-term effects on metaphyseal bone architecture

Bone loss after oophorectomy of adult rats is more rapid and complete in the metaphysis than in the epiphysis of the femur, particularly in the proximal region of the metaphysis distant from the growth plate. This study was undertaken to determine the effects of prepubertal oophorectomy, on femoral cancellous bone acquisition during growth. Rats were oophorectomized (OVX) or sham operated at 3 weeks of age and killed at intervals up to 78 weeks for scanning electron microscopy and histomorphometry of the distal femur. Differences in cancellous bone architecture between the two groups was evident after 6 weeks of age. Relatively minor differences were found in the part of the metaphysis near the growth plate and in the epiphysis, with less trabeculae in the primary spongiosa and 1 to 2 less trabeculae/mm in the secondary spongiosa. However, as metaphyseal growth proceeded, trabeculae were present for a greater distance up the femoral shaft in controls than in OVX rats, with mean BV/TV in the proximal part of the metaphysis increasing from 1.4% at 6 weeks to 13.4% at 20 weeks in controls, with no increase in the OVX rats. We find that the lack of ovarian hormones increases the rate of destruction of trabeculae near the metaphyseal-diaphyseal junction.

Structural changes in blood vessels entering the growth plate during growth in rats

We observed the structural changes in blood vessels entering the growth plates of the femur and tibia of rats during growth using scanning electron microscopy. The penetrating vessels had blind endings which were bulbous at a time when rats showed rapid skeletal development. With subsequent slowing of development, the density of the vessels decreased and the blind endings became short stumps. These changes were more prominent in the proximal femur than in the distal femur and proximal tibia. The present study indicates an intimate relation between endochondral ossification in the growth plate and the structure of the penetrating vessels.

Matrix vesicles in osteomalacic hypophosphatasia bone contain apatite-like mineral crystals

Hypophosphatasia, a heritable disease characterized by deficient activity of the tissue nonspecific isoenzyme of alkaline phosphatase (TNSALP), results in rickets and osteomalacia. Although identification of TNSALP gene defects in hypophosphatasia establishes a role of ALP in skeletal mineralization, the precise function remains unclear. The initial site of mineralization (primary mineralization) normally occurs within the lumen of TNSALP-rich matrix vesicles (MVs) of growth cartilage, bone, and dentin. We investigated whether defective calcification in hypophosphatasia is due to a paucity and/or a functional failure of MVs secondary to TNSALP deficiency. Nondecalcified autopsy bone and growth plate cartilage from five patients with perinatal (lethal) hypophosphatasia were studied by nondecalcified light and electron microscopy to assess MV numbers, size, shape, and ultrastructure and whether hypophosphatasia MVs contain apatite-like mineral, as would be the case if these MVs retained their ability to concentrate calcium and phosphate internally despite a paucity of TNSALP in their investing membranes. We found that hypophosphatasia MVs are present in approximately normal numbers and distribution and that they are capable of initiating internal mineralization. There is retarded extravesicular crystal propagation. Thus, in hypophosphatasia the failure of bones to calcify appears to involve a block of the vectorial spread of mineral from initial nuclei within MVs, outwards, into the matrix. We conclude that hypophosphatasia MVs can concentrate calcium and phosphate internally despite a deficiency of TNSALP activity.

MC22-33F monoclonal antibody shows unmasked polar head groups of choline-containing phospholipids in cartilage and bone

The importance of the role lipids may have in biological calcification, and the paucity and poor specificity of the methods available for studying their ultrastructural localization, call for further investigations involving new techniques. The monoclonal antibody MC22-33F displays a specific reaction with phosphatidylcholine, sphingomyelin and dimethylphosphatidylethanolamine, as confirmed by its reaction with synthetic lyposomes of pure phosphatidylcholine. For this reason, it was used to demonstrate the presence and ultrastructural localization of choline-containing phospholipids in calcifying cartilage and bone. The MC22-33F MAb immunoreaction was found in the cytoplasm of maturing and hypertrophic and, to a lesser extent, proliferating and degenerating chondrocytes; it was strongly positive in matrix vesicles, at the periphery of calcification nodules, and at the periphery of calcified matrix. In bone, the immunoreaction was especially strong along the peripheral membrane of the osteoblasts, in the interfibrillary spaces of the osteoid border, in matrix vesicles and in the peripheral zone of the calcification nodules. The central zone of the nodules, the fully calcified matrix and most of the intracellular membranes were negative in both cartilage and bone. These results confirm the presence of choline-containing phospholipids in early areas of calcification, including matrix vesicles. They also show that the intracellular membrane phospholipids are not accessible to the antibody, possibly because they are masked by other substances. These are not proteoglycans, because their enzymatic digestion does not increase or modify the reactivity of MC22-33F MAb. In spite of this limitation, MC22-33F MAb offers considerable advantages in the study of the calcification process, because the positive immunoreaction of the calcifying bone matrix, and the negativity of calcified matrix, confirm without doubt that phospholipids have an active role in biological calcification.

Growth hormone, IGF-I, and exercise effects on non-weight-bearing fast muscles of hypophysectomized rats

The effects of growth hormone (GH) or insulin-like growth factor I (IGF-I) with or without exercise (ladder climbing) in countering the effects of unweighting on fast muscles of hypophysectomized rats during 10 days of hindlimb suspension were determined. Compared with untreated suspended rats, muscle weights were 16-29% larger in GH-treated and 5-15% larger in IGF-I-treated suspended rats. Exercise alone had no effect on muscle weights. Compared with ambulatory control, the medial gastrocnemius weight in suspended, exercised rats was larger after GH treatment and maintained with IGF-I treatment. The combination of GH or IGF-I plus exercise in suspended rats resulted in an increase in size of each predominant fiber type, i.e., types I, I + IIa and IIa + IIx, in the medial gastrocnemius compared with untreated suspended rats. Normal ambulation or exercise during suspension increased the proportion of fibers expressing embryonic myosin heavy chain in hypophysectomized rats. The phenotype of the medial gastrocnemius was minimally affected by GH, IGF-I, and/or exercise. These results show that there is an IGF-I, as well as a GH, and exercise interactive effect in maintaining medial gastrocnemius fiber size in suspended hypophysectomized rats.

Further observations on programmed cell death in the epiphyseal growth plate: comparison of normal and dyschondroplastic epiphyses

The objective of the investigation was to provide information on apoptosis in the normal epiphysis and to assess apoptosis in the plate of the dyschondroplastic chick. Apoptosis was evaluated using two terminal deoxynucleotide transferase end-labeling procedures, DNA fragmentation and nuclear morphology. We found that there was a minimal level of apoptosis in the dyschondroplastic cartilage. In the tibial dyschondroplastic (TD) lesion itself, only about 3% of cells are positive in the articular and proliferative regions; 11% of prehypertrophic chondrocytes are stained by the end-labeling procedure, and most of the cells are localized around vascular channels at the calcifying front. This finding suggests that dyschondroplasia is linked to impairment of apoptosis, and as a result the tissue contains immature cells that have outlived their normal life span. In contrast, in the normal plate, we noted that when the proliferative period was complete, the cells became terminal transferase positive; in addition, chondrocytes in the normal plate exhibited DNA fragmentation. Semiquantitative analysis of stained chondrocytes in the growth plate indicate that in the proliferative zone 15.5% of cells are terminal deoxynucleotidyl transferase (TUNEL) positive; in contrast, 44% of postmitotic chondrocytes are stained by the TUNEL procedure. The presence of a sharp border between the pre- and postmitotic zones suggests that the stimulus for apoptosis is maturation dependent and reflects local metabolic control. We also examined apoptosis in metaphyseal osteoblasts. We found that adjacent to the epiphysis, many osteoblasts were undergoing apoptosis. In more mature sites in the metaphysis, there was less cell death, indicating that osteoblast apoptosis was delayed and cells were completing their normal life cycle. Although terminal transferase end-labeled cells were not seen in articular cartilage, we noted that fibroblasts, in the perichondrial ligament surrounding the articular as well as the epiphyseal regions of the plate, were undergoing apoptosis. Apoptosis at this site may be related to lateral expansion of the cartilages, reflect a high cell turnover rate at the junction between the tissues, and result from paracrine signals received from the underlying cartilage.

Fine needle tissue aspiration for accurate localization of histological specimens from complex structures

A procedure is presented for exact, detailed comparison of light and electron microscopic analyses of tissues with complex architecture. Earlier techniques require one to make drawings of tissue pieces to be analyzed by electron microscopy to permit rough localization of the origin of the tissue pieces. Specifically, exact analysis of fetal cartilage and bone is hampered by the complicated arrangement of both tissue components, severely limiting the assessment of electron microscopic analyses. The advantage of the technique described here is that it allows precise localization of the tissue sample in the original tissue area. Punches 1 min in diameter were obtained from femora and coxae with a syringe and embedded for light and electron microscopy. The remaining tissue with its exactly defined punctures is prepared for standard histology. Human fetal cartilage and bone tissue were used to demonstrate this technique, but this procedure may be used for other kinds of tissues.

Ultrastructural immunolocalization of cartilage oligomeric matrix protein (COMP) in porcine growth cartilage

Cartilage oligomeric matrix protein (COMP) is a macromolecule of yet unknown function with restricted distribution among tissues. In the present study, the ultrastructural localization of COMP in porcine immature joint cartilage and growth plate cartilage was semiquantitatively delineated. Tissues were fixed in a mixture of low concentration glutar- and paraformaldehyde, embedded at low temperature, and subjected to immunocytochemistry using polyclonal antibodies raised against bovine COMP. Protein A-coated colloidal gold was used for detection. The most intense immunolabeling for COMP was noted in the proliferative zones of the growth cartilages. Here the concentration of immunomarker was higher in the territorial compartment than in the pericellular and interterritorial areas. A low concentration of COMP was observed in the resting and hypertrophic zones. The immunolabeling for COMP did not differ between the three matrix compartments of these zones. Supported by previous data obtained by in situ hybridization, the concentration of immunolabeling in the proliferative zone indicates a high rate of COMP synthesis in proliferative chondrocytes. Hence, COMP may be considered as a marker for normal differentiation into proliferative chondrocytes.

Physicochemical characterization of the nucleational core of matrix vesicles

While previous studies revealed that matrix vesicles (MV) contain a nucleational core (NC) that converts to apatite when incubated with synthetic cartilage lymph, the initial mineral phase present in MV is not well characterized. This study explored the physicochemical nature of this Ca2+ and Pi-rich NC. MV, isolated from growth plate cartilage, were analyzed directly by solid-state 31P NMR, or incubated with hydrazine or NaOCl to remove organic constituents. Other samples of MV were subjected to sequential treatments with enzymes, salt solutions, and detergents to expose the NC. We examined the NC using transmission electron microscopy, energy-dispersive analysis with x-rays, and electron and x-ray diffraction, Fourier transform-infrared spectroscopy, high performance thin-layer chromatographic analysis, and SDS-polyacrylamide gel electrophoresis. We found that most of the MV proteins and lipids could be removed without destroying the NC; however, NaOCl treatment annihilated its activity. SDS-polyacrylamide gel electrophoresis showed that annexin V, a phosphatidylserine (PS)-dependent Ca2+-binding protein, was the major protein in the NC; high performance thin-layer chromatographic analysis revealed that the detergents removed the majority of the polar lipids, but left significant free cholesterol and fatty acids, and small but critical amounts of PS. Transmission electron microscopy showed that the NC was composed of clusters of approximately 1.0 nm subunits, which energy-dispersive analysis with x-rays revealed contained Ca and Pi with a Ca/P ratio of 1.06 +/- 0. 01. Electron diffraction, x-ray diffraction, and Fourier transform-infrared analysis all indicated that the NC was noncrystalline. 1H-Cross-polarization 31P NMR indicated that the solid phase of MV was an HPO42--rich mixture of amorphous calcium phosphate and a complex of PS, Ca2+, and Pi. Taken together, our findings indicate that the NC of MV is composed of an acid-phosphate-rich amorphous calcium phosphate intermixed with PS-Ca2+-Pi, annexin V, and other proteins and lipids.

The influence of trace elements on calcium phosphate formation by matrix vesicles

The effects of two inhibitors, fluoride (F-) and zinc (Zn2+), were studied on the formation of mineral by matrix vesicles (MV) in an in vitro system. Kinetically, mineral formation by MV incubated in a synthetic cartilage lymph (SCL) is characterized by three phases: a lag period, a period of rapid uptake, and finally a period of slow uptake. Zn2+ at > or = 5 microM completely inhibited MV mineralization; at < or = 1 microM, it had little effect on rate of ion uptake, but delayed conversion of an OCP-like intermediate into hydroxyapatite (OHAp). F- at > or = 10 microM reduced the rate of rapid uptake by MV and caused the OCP-like precursor to convert to OHAp. When synthetic OCP was seeded into SCL, mineralization ensued and OHAp became the dominant phase. With Zn2+ present, OCP-like features persisted longer; with F-, the OCP-like features were lost more rapidly. When ACP was seeded into SCL, OHAp formed; Zn2+ at < or = 1 microM caused OCP-like mineral to form. Our findings indicate that Zn2+ stabilizes a noncrystalline precursor in MV regulating the length of the lag period; Zn2+ also favors the formation of an OCP-like intermediate whose growth accounts for the rapid uptake phase. This OCP-like phase appears to nucleate formation of OHAp by MV.

Morphological and biochemical evidence for apoptosis in the terminal hypertrophic chondrocytes of the growth plate

The purpose of this study was to investigate the mechanism of cell death in chondrocytes of the growth plate. In the degenerative chondrocyte zone of the growth plate, apoptotic chondrocytes were defeated by the in situ nick end labelling method, by DNA analysis in agarose gel, and by electron microscopy. The results of the in situ nick end labelling method and the occurrence of a ladder pattern of DNA in agarose gel analysis indicated the activation of endogenous endonucleases, resulting in DNA fragmentation. Electron micrographs showed the early morphological changes associated with apoptosis. This report presents both morphological and biochemical evidence for apoptosis in the terminal hypertrophic chondrocytes of the growth plate. These data suggest that apoptosis of degenerative chondrocytes may play an important role in the control of normal and pathological endochondral ossification.

Type X collagen is colocalized with a proteoglycan epitope to form distinct morphological structures in bovine growth cartilage

Using antibodies raised against type X collagen, isolated from deer antler, we have immunolocalized type X collagen in growth plate and epiphyseal cartilage from fetal and ambulatory calves. In ambulatory calf growth plate, type X collagen was demonstrated to be present in longitudinal septa that extend from the resting zone into the underlying trabecular bone. The much more restricted distribution of type X collagen seen in fetal growth plate, both here and previously, suggested that prominent localization of type X collagen to the longitudinal septa was stimulated by weight bearing. The location of type X collagen has been compared with that of an epitope (7D4), composed of specific sulfation patterns in chondroitin sulfate of some aggrecan molecules. Colocalization of type X collagen with the 7D4 epitope in longitudinal septa of growth plates from ambulatory calves suggested these molecules contribute to the formation and function of longitudinal septa. Immunolocalization of type X collagen and 7D4 in calf epiphyseal cartilage demonstrated colocalization at an interface that appears to represent the junction of articular cartilage and cartilage associated with formation of the secondary ossification center. Immunolocalization of type X collagen and the 7D4 proteoglycan epitope in these structures suggested that type X collagen and the 7D4 epitope form structures with important mechanical roles and capacity to influence the morphology of associated bony structures.

Cartilage-bone replacement in endochondral ossification of mandibular condylar heads in young beagle dogs

The cellular mechanisms of cartilage-bone replacement in endochondral bone formation, in mandibular condylar heads, are poorly understood. In particular, there is no definitive evidence indicating whether cartilage is resorbed by so-called chondroclasts. Using 3-week-old male beagle dogs, we examined the cartilage-bone replacement processes in mandibular condylar heads by means of light and electron microscopy. Calcification of the cartilage matrix occurred in the central area of the longitudinal septa but not in thin transverse septa. Chondrocytic lacunae were opened by the removal of transverse septa by perivascular rough-surfaced endoplasmic reticulum (RER)-rich mononuclear cells. These cells also phagocytosed calcified cartilage fragments in the surface layer of longitudinal septa. Shortly thereafter, a thin bone layer was deposited on the remaining longitudinal septa by invading osteoblasts. Preosteoclastic multinucleated cells in lacunar canals developed neither ruffled borders nor clear zones in the cartilage matrix, but once the bone layer had been deposited on the remaining cartilage, these structures formed. Our results suggest that the cartilage-bone replacement in mandibular condylar heads involves four sequential processes: 1) degradation of the transverse septal cartilage by RER-rich mononuclear cells, 2) phagocytosis of calcified cartilage fragments in the longitudinal septa by these cells, 3) bone deposition of the remaining longitudinal septa, and 4) degradation of both bone and calcified cartilage by differentiated osteoclasts.

A specific collagen type II gene (COL2A1) mutation presenting as spondyloperipheral dysplasia

We report on a patient with a skeletal dysplasia characterized by short stature, spondylo-epiphyseal involvement, and brachydactyly E-like changes. This condition has been described as spondyloperipheral dysplasia and the few published cases suggest autosomal dominant inheritance with considerable clinical variability. We found our sporadic case to be due to a collagen type II defect resulting from a specific COL2A1 mutation. This mutation is the first to be located at the C-terminal outside the helical domain of COL2A1. A frameshift as consequence of a 5 bp duplication in exon 51 leads to a stop codon. The resulting truncated C-propeptide region seems to affect helix formation and produces changes of chondrocyte morphology, collagen type II fibril structure and cartilage matrix composition. Our case with its distinct phenotype adds another chondrodysplasia to the clinical spectrum of type II collagenopathies.

An unknown spondylo-meta-epiphyseal dysplasia in sibs with extreme short stature

In three sibs of Jordanian descent a unique type of severe spondylo-meta-epiphyseal dysplasia results in extreme disproportionate dwarfism. They have a distinct facial appearance with hypotelorism, prognathia, and hypodontia. The limbs are short and the hands and feet stubby. Radiologically, the irregular end plates of the vertebral bodies, the very small and late appearing epiphyseal ossification centres, and the hypoplastic acetabular roofs are most impressive. Histopathologic studies of the growth plate demonstrate characteristic findings with fingerprint-like inclusion bodies in the hypertrophic chondrocytes. This seems to be a distinct, autosomal recessive skeletal dysplasia.

Ultrastructural localization of the C-propeptide released from type II procollagen in fetal bovine growth plate cartilage

We used immunochemical and immunoelectron gold techniques to determine whether the C-propeptide previously identified in the matrix of endochondral cartilage (CPII) was still a part of the Type 11 procollagen molecule or had been released from it. Guanidinium hydrochloride extraction, followed by SDS-PAGE and Western blotting techniques and immunoelectron localization, revealed that predominantly only the released form (hereafter referred to as released CPII) was detected. The ultrastructural distribution of this CPII was examined with affinity-purified antibodies and with immunogold or immunoperoxidase localization techniques in the presence or absence of embedding resins. These methods yielded similar results. Although no significant amount of this CPII was retained in the matrix after guanidinium hydrochloride extraction, it was present in two recognizable sites under normal conditions, i.e., locally concentrated in a random association with collagen fibrils in the nonmineralized matrix and mainly concentrated in interfibrillar mineralizing sites in the mineralized matrix. These results suggest that the C-propeptide that has been released from Type II procollagen associates with collagen fibrils and then preferentially associates with mineralizing sites when these form in the endochondral cartilage. The significance of this preference for mineral is not known but may have something to do with its high affinity for hydroxyapatite.

Changes in bone metabolism and epiphysial growth plate in bovine Hyena disease induced by administration of vitamin AD3E premix or Vitamin A

The changes in bone metabolism and morphology of chondrocytes in bovine Hyena disease caused by administration of vitamin AD3E premix (V-AD3E) or vitamin A (V-A) were examined. At the each age, 5 calves were used. Among them, Hyena disease was recognized in 3 calves; a calf administered a high dose of V-AD3E premix (V-A 3,000,000, V-D3 300,000, and V-E 1,200 I.U./day), a calf administered a half dose of the V-AD3E premix, and a calf administered only V-A 3,000,000 I.U./day. The remaining calves without Hyena disease were a calf administered only V-D3 300,000 I.U./day and a control calf. Each agent was administered orally for 10 days from 1 week after birth. In the 3 calves with Hyena disease, the bone metabolism in bone histomorphometry of ilium was in the state of low turnover at the age of 50 days. The bone volume was small at the age of 12 months. The epiphysial growth plates of the distal femurs and the proximal tibias partially disappeared and the chondrocyte lacunas in them were flattened. The matrix fibers of epiphysial growth plates were thinner in diameter and higher in density than those of the control calf. In the calf administered only V-D3, the values of bone volume decreased with aging. In conclusion, Hyena disease may be caused by excessive administration of V-A, because hypervitaminosis A suppressed the activity of differentiation and proliferation in chondrocytes and osteoblasts, and excessive administration of V-D3 may promote these actions.

Matrix vesicles and focal proteoglycan aggregates are the nucleation sites revealed by the lanthanum incubation method: a correlated study on the hypertrophic zone of the rat epiphyseal cartilage

Correlated studies were performed with light and electron microscopy, and backscattered electron image in conjunction with X-ray microanalysis, of lanthanum-incubated epiphyseal cartilage of the young rat. The hall-mark of this procedure is the appearance of LaP electron-dense deposits (not present in control sections) in precise sites of the hypertrophic zone. The ultrastructural study revealed a dual nature of these sites: "dense matrix vesicles" and "focal filament aggregates". The dense matrix vesicles are a specific type of matrix vesicle with the intrinsic capacity of precipitating LaP mineral, as soon as they originate from the hypertrophic chondrocytes. Furthermore, the matrix vesicles were found to be heterogeneous because lanthanum-devoid, "light matrix vesicles" were also present. The focal filament aggregates, which were not recognized in unstained sections and in controls, are apparently focal concentrations of proteoglycans with high lanthanum binding capacity, although the presence in them of other components (e.g., type X collagen, C-propeptide of type II collagen) cannot be excluded. The were in close connection with the light matrix vesicles in the upper hypertrophic zone, and were loaded with a variable quantity of LaP irregular electron-dense deposits in the lower hypertrophic zone. These irregular deposits are similar to, but distinct from, calcification nodules. The lanthanum incubation method indirectly detects the matrix Ca-binding components (which bind La ions), and the calcification initiation sites (which precipitate a LaP-mineral phase). A sequence is proposed of successive steps of LaP nucleation within the focal filament aggregates, which possibly mimics calcium phosphate deposition. Such a sequence seems to require the participation not only of dense matrix vesicles, but also of the filamentous components of the focal aggregates, possibly together with the activity of alkaline phosphatase.

Immunohistochemical and ultrastructural localization of CGRP-positive nerve fibers at the epiphyseal trabecules facing the growth plate of rat femurs

We performed immunohistochemical and ultrastructural studies to disclose a possible relationship between nerve fibers and bone metabolism. Immunohistochemical distribution of calcitonin gene-related peptide (CGRP)-positive nerve fibers during bone development was assessed in the femurs of rats. CGRP-positive nerve fibers were denser in the epiphysis than in the metaphysis. These nerve fibers particularly ran along the epiphyseal trabecules facing the growth plate and came in contact with osteoclasts. Many osteoclasts at the epiphyseal trabecules facing the growth plate contained abundant toluidine blue and periodic acid-Schiff-positive granules. Electron microscopy revealed that these osteoclasts have many membrane-bound, electron-dense granular structures and dilated cisterns of rough endoplasmic reticulum containing electron-dense material. They were often surrounded by clear cells displaying features of nerve fiber and had no ruffled border. Furthermore, ultrastructural observations revealed electron-dense structures coating the cytoplasmic side of plasma membranes of the nerve fibers. We also observed coated pits in the cytoplasm of the osteoclasts facing the nerve fibers. To further clarify the role of innervation, we compared trabecules of rats undergoing denervation of the sciatic nerve with those from unoperated rats. Denervation resulted in a significant increase in the number of cement lines on the epiphyseal trabecules facing the growth plate. These results suggest that the osteoclasts at the epiphyseal trabecules facing the growth plate are in part regulated by CGRP-positive nerve fibers. Thus, CGRP-positive nerve fibers could be a crucial element in bone metabolism during bone growth and development.

Ultrastructural immunolocalization of fibronectin in epiphyseal and metaphyseal bone of young rats

Fibronectin is a well known glycoprotein of extracellular connective tissue matrices due to a specific amino acid-sequence (RGD) suggested to act as an attachment factor in cell-cell or cell-matrix interactions. Although also present in bone, little is known about the role of fibronectin in this tissue. To obtain data for discussions on function we used ultrastructural immunolocalization techniques to quantitatively examine the distribution of fibronectin in various bone matrix compartments. The study was focused on three different stages of endochondral ossification in growing long bones of young rats. The results show large amounts of fibronectin in mature bone tissue. At a higher magnification, an obvious fibronectin association to individual fibrils of collagen type I was demonstrated. Intracellular labeling was observed in Golgi-related vesicles in some active osteoblasts of metaphyseal bone, indicating local synthesis of fibronectin. In contrast to previous suggestions based on light microscopic observations, the labeling of bone or cartilage matrices facing the surface of all cell types were low. The pattern is clearly different from that of osteopontin and bone sialoprotein, two other bone matrix proteins with the same cell-binding sequence. Our results indicate that fibronectin at these stages of development participates in matrix organization rather than being an important link between cartilage or bone matrix and adjacent cells.