Expression of cartilage oligomeric matrix protein (COMP) by embryonic and adult osteoblasts.

Cartilage oligomeric matrix protein has been implicated as an important component of endochondral ossification because of its direct effects on chondrocytes. The importance of this protein for skeletal development and growth has been recently illustrated by the identification of mutations in cartilage oligomeric protein genes in two types of inherited chondrodysplasias and osteoarthritic phenotypes: multiple epiphyseal dysplasia and pseudoachondroplasia. In the present study, we report the presence of cartilage oligomeric protein in embryonic and adult osteoblasts. A foot from a 21-week-old human fetus, subchondral bone obtained from knee replacement surgery in an adult patient, and a limb from a 19-day-postcoital mouse embryo were analyzed with immunostaining and in situ hybridization. In the human fetal foot, cartilage oligomeric protein was localized to osteoblasts of the bone collar and at the newly formed bone at the growth plate and bone diaphyses. Immunostaining was performed on the adult subchondral bone and showed positive intracellular staining for cartilage oligomeric protein of the osteoblasts lining the trabecular bone. There was no staining of the osteocytes. Immunostaining of the mouse limb showed the most intense staining for cartilage oligomeric protein in the hypertrophic chondrocytes and in the surrounding osteoblast cells of the developing bone. Cartilage oligomeric protein mRNA and protein were detected in an osteoblast cell line (MG-63), and cartilage oligomeric protein mRNA was detected from human cancellous bone RNA. These results suggest that the altered structure of cartilage oligomeric protein by the mutations seen in pseudoachondroplasia and multiple epiphyseal dysplasia may have direct effects on osteoblasts, contributing to the pathogenesis of these genetic disorders.

Molecular cloning, sequencing, and tissue and developmental expression of mouse cartilage oligomeric matrix protein (COMP).

Mouse cartilage oligomeric matrix protein cDNA was cloned and sequenced by a reverse transcription-polymerase chain reaction. The open reading frame encoded a product of 755 amino acids that shares a high degree of identity to and possesses all the characteristic molecular features of both rat and human cartilage oligomeric matrix protein. This suggests that cartilage oligomeric matrix protein is highly conserved during evolution. The clone was 83, 84, and 95% identical to human, bovine, and rat cartilage oligomeric matrix protein cDNA, respectively. In tissues from the adult mouse, cartilage oligomeric matrix protein was expressed not only in cartilage and tendon but in trachea, bone, skeletal muscle, eye, heart, and placenta as well, and no expression was found in other tissues. Immunohistology revealed that cartilage oligomeric matrix was deposited as early as 10 days post coitus in predifferentiated mouse embryo mesenchyme. It was detected in all cartilaginous tissues and in the skeletal muscles of the embryo at day 13. As development progressed, accumulation of cartilage oligomeric matrix protein was marked in the growth plate. At 19 days post coitus, it was prominently deposited in the hypertrophic zone of the growth plate, perichondrium, and periosteum and in the superficial layer of the articular cartilage surface but was absent in the more central areas of the epiphyseal cartilage. The restricted tissue distribution and expression of cartilage oligomeric matrix protein in developing as well as adult mouse tissues suggest the regulation of this protein at the transcriptional level. The findings reported herein are the first detailed characterization of the distribution of cartilage oligomeric matrix protein during early skeletal development of the mouse.

Localization and expression of cartilage oligomeric matrix protein by human rheumatoid and osteoarthritic synovium and cartilage.

Synovium and cartilage from patients with osteoarthritis or rheumatoid arthritis were analyzed for expression of cartilage oligomeric matrix protein. Immunostaining of synovium with antiserum to cartilage oligomeric matrix protein demonstrated positive staining in both diseases. In osteoarthritis, there was positive staining within the synovial cells and immediately subjacent connective tissue, with less intense staining in the deeper connective tissue. In rheumatoid arthritis, there was less intense staining within the synovial cells and marked intense staining in the deeper connective tissue. In situ hybridization performed with an antisense digoxigenin-labeled riboprobe to human cartilage oligomeric matrix protein confirmed the presence of cartilage oligomeric matrix protein mRNA in the cells of the synovial lining in both types of synovium. Quantitative polymerase chain reaction with a cartilage oligomeric matrix protein MIMIC demonstrated increased cartilage oligomeric matrix protein mRNA in rheumatoid cartilage and synovium as compared with osteoarthritic cartilage and synovium, respectively; mRNA levels in rheumatoid synovium were similar to those from osteoarthritic chondrocytes. As a result of the high expression of cartilage oligomeric matrix protein from rheumatoid synovium, inflammatory synovium should be considered as a potential tissue source of cartilage oligomeric matrix protein in any investigation of biological markers of cartilage metabolism. The upregulated expression of cartilage oligomeric matrix protein in inflammatory tissues suggests its in vivo regulation by cytokines.

Experimental infection of cynomolgus monkeys with simian parvovirus.

Simian parvovirus is a recently discovered parvovirus that was first isolated from cynomolgus monkeys. It is similar to human B19 parvovirus in terms of virus genome, tropism for erythroid cells, and characteristic pathology in natural infections. Cynomolgus monkeys were infected with simian parvovirus to investigate their potential usefulness as an animal model of human B19 parvovirus. Six adult female cynomolgus monkeys were inoculated with purified simian parvovirus by the intravenous or intranasal route and monitored for evidence of clinical abnormalities; this included the preparation of complete hematological profiles. Viremia and simian parvovirus-specific antibody were determined in infected monkeys by dot blot and Western blot assays, respectively. Bone marrow was examined at necropsy 6, 10, or 15 days postinfection. All of the monkeys developed a smoldering, low-grade viremia that peaked approximately 10 to 12 days after inoculation. Peak viremia coincided with the appearance of specific antibody and was followed by sudden clearance of the virus and complete, but transient, absence of reticulocytes from the peripheral blood. Clinical signs were mild and involved mainly anorexia and slight weight loss. Infection was associated with a mild decrease in hemoglobin, hematocrit, and erythrocyte numbers. Bone marrow showed marked destruction of erythroid cells coincident with peak viremia. Our findings indicate that infection of healthy monkeys by simian parvovirus is self-limited and mild, with transient cessation of erythropoiesis. Our study has reproduced Koch's postulates and further shown that simian parvovirus infection of monkeys is almost identical to human B19 parvovirus infection of humans. Accordingly, this animal model may prove valuable in the study of the pathogenesis of B19 virus infection.

Increased degradation and altered tissue distribution of cartilage oligomeric matrix protein in human rheumatoid and osteoarthritic cartilage.

We investigated the degradation and tissue distribution of cartilage oligomeric matrix protein in normal, osteoarthritic, and rheumatoid arthritic articular cartilage of the human knee. Cartilage was subjected to sequential extractions with buffers containing neutral salt, with EDTA, and finally with guanidine/HCl and then was analyzed by Western blotting with a polyclonal antiserum to human cartilage oligomeric matrix protein. Western blots of the nine neutral salt extracts from normal cartilage revealed mostly intact pentameric molecules of cartilage oligomeric matrix protein, in contrast to the 13 osteoarthritic and five rheumatoid arthritic cartilage samples that demonstrated marked degradation of cartilage oligomeric matrix protein as noted by a predominance of reduction-sensitive bands at approximately 150 kDa and nonreduction-sensitive bands in the 67-94 kDa range. The EDTA and guanidine/HCl extracts from all groups were similar and showed mostly intact molecules of cartilage oligomeric matrix protein, with smaller amounts of degraded cartilage oligomeric matrix protein identical to those resolved by the Western blots of the neutral salt extracts. Western blots of matched pairs of synovial fluid and cartilage extracts demonstrated cartilage oligomeric matrix protein fragments of the same molecular mass. Competitive enzyme-linked immunosorbent assay revealed significantly less cartilage oligomeric matrix protein in rheumatoid articular cartilage than in either normal or osteoarthritic cartilage. In contrast to normal cartilage, where cartilage oligomeric matrix protein was predominantly localized to the interterritorial matrix throughout all zones of the matrix, with increased staining in the deeper cartilaginous zones, the most intense staining in osteoarthritic cartilage was in the superficial zones of fibrillated cartilage, with little to no immunostaining in the midzones and relatively poor staining in the deeper cartilaginous zones. This distribution was the inverse of that for proteoglycans, as demonstrated by toluidine blue staining, where proteoglycans were depleted primarily from the superficial fibrillated cartilage. In mild to moderately affected rheumatoid cartilage, the tissue distribution of cartilage oligomeric matrix protein was similar to the distribution of proteoglycans, with relatively uniform staining of the interterritorial and territorial matrics. In more severely affected rheumatoid cartilage, the superficial zones demonstrated punctate immunostaining for cartilage oligomeric matrix protein in the interterritorial and territorial matrics, and staining was restricted to the territorial matrix in the deep cartilaginous zones. It is evident from this study that (a) noncollagenous proteins such as cartilage oligomeric matrix protein are greatly affected in arthritis, (b) degradation fragments released from the matrix into the synovial fluid reflect the processes occurring within the matrix, and (c) different zones of the articular cartilage are susceptible to degradation of cartilage oligomeric matrix protein in the different disease processes.

Osteoarthritis in cynomolgus macaques. II. Detection of modulated proteoglycan epitopes in cartilage and synovial fluid.

The purpose of the present study was to determine the usefulness of the monoclonal antibodies 7-D-4 and 3-B-3 as biomarkers of severity of naturally occurring osteoarthritis in the knee joints of adult cynomolgus macaques. The antibodies were used to immunolocate chondroitin sulfate proteoglycan epitopes in articular cartilage or synovial fluid from knee joints with a range in severity of osteoarthritis. The joints were examined radiographically, grossly, microradiographically, and histologically to characterize the severity of disease, and the results of three different methods of proteoglycan analysis (immunohistochemistry, enzyme-linked immunosorbent assay, and Western blot analysis) were compared. Subjectively, the degree of positive immunostaining for 7-D-4 was minimal in normal sites and increased as damage to articular cartilage increased. The scores for 7-D-4 immunostaining in the medial tibial plateau (the site most severely involved in this model) were correlated significantly with severity of damage to articular cartilage (p < 0.05, r2 = 0.50), thus supporting the subjective observations. The ratio of 7-D-4 to sulfated glycosaminoglycans in synovial fluid also was correlated with the score for 7-D-4 immunostaining in the medial tibial plateau (p < 0.05, r2 = 0.54) and with the score for 3-B-3 immunostaining in the medial femoral condyle (p < 0.05, r2 = 0.65). There were no significant correlations among scores for 3-B-3 immunostaining, severity scores, and the ratios of 3-B-3 to sulfated glycosaminoglycans in the synovial fluid. By Western blot analysis, both epitopes were sensitive markers of early cartilage damage in young adult monkeys but were less sensitive in older monkeys. This work provides evidence that measurement of the epitope recognized by 7-D-4 in synovial fluid or, by immunohistochemical or Western blot methods, in articular cartilage has potential use as a marker of severity of naturally occurring osteoarthritis.

Immunolocalization of noncollagenous bone matrix proteins in lumbar vertebrae from intact and surgically menopausal cynomolgus monkeys.

The noncollagenous matrix proteins, composing about 10% of the organic matrix of bone, are considered important for cell matrix organization and regulation of mineralization in bone. In the present study, seven of the major noncollagenous bone matrix proteins were localized immunohistochemically in serial sections of lumbar vertebrae from 24 (12 intact and 12 ovariectomized) adult female cynomolgus monkeys (Macaca fascicularis). Osteocalcin was the only protein restricted to bone cells and mineralized bone matrix. Bone sialoprotein was present in both bone and calcified cartilage, and all the other proteins were distributed in soft tissues as well as bone. Staining for both osteocalcin and bone sialoprotein was present diffusely throughout the bone matrix, but osteonectin, osteopontin, matrix gla protein, decorin, and biglycan staining was concentrated along bone surfaces. Osteoid was negative for osteocalcin and bone sialoprotein, but all other proteins had areas of positive immunostaining within osteoid. All proteins except biglycan exhibited strong immunostaining of a subset of active osteoblasts, suggesting that they may be markers of osteoblast maturity or state of activation. The pattern of immunostaining in intact and surgically menopausal monkeys was similar, except that staining for matrix proteins concentrated along bone surfaces appeared to be more widely distributed in the surgically menopausal monkeys, probably due to the higher rate of bone formation in these animals.

Articular-cartilage matrix gamma-carboxyglutamic acid-containing protein. Characterization and immunolocalization.

Matrix gamma-carboxyglutamic acid (Gla)-containing protein (MGP) was found to be present in articular cartilage by Western-blot analysis of guanidinium chloride extracts of human and bovine cartilage and was further localized by immunohistochemical studies on human and monkey specimens. In newborn articular cartilage MGP was present diffusely throughout the matrix, whereas in growth-plate cartilage it was seen mainly in late hypertrophic and calcifying-zone chondrocytes. In adult articular cartilage MGP was present primarily in chondrocytes and the pericellular matrix. Immunoelectron microscopy studies revealed an association between MGP and vesicular structures with an appearance consistent with matrix vesicles. MGP may be an important regulator of cartilage calcification because of its localization in cartilage and the known affinity of Gla-containing proteins for Ca2+ and hydroxyapatite.

Autoimmune vasculitis in MRL/Mp-lpr/lpr mice: orthochromatic basophils participate in the development of delayed-type hypersensitivity angiitis.

The pathogenesis of autoimmune vasculitis is poorly understood. Understanding the immunologic mechanisms governing this disease requires precise identification of the cells which comprise the lesion. In this report, we have evaluated tissue sections from MRL/lpr mice from 16 to 45 weeks of age, representing all stages of clinical vasculitis. We demonstrate that basophil myelocytes participate in the evolution of the delayed-type hypersensitivity (DTH) response which initiates and perpetuates autoimmune vasculitis in these mice. These findings raise questions regarding the immunologic mechanisms by which basophils develop in this lesion and the interaction of basophils. VSMCs and lymphocytes in vasculitic angiodestruction.

Synthesis of IL-1 alpha and IL-1 beta by arterial cells in atherosclerosis.

Interleukin-1 (IL-1) has been implicated as a regulatory protein in the development and clinical sequelae of atherosclerosis. To determine which cells in the atherosclerotic plaque synthesize IL-1 in situ, the authors evaluated histologic sections of iliac arteries from cynomolgus monkeys using probes for IL-1 alpha and beta. A polyclonal antibody to IL-1 alpha and beta was used to determine if proteins were concomitantly produced. The predominant cells expressing IL-1 alpha and beta mRNA were foam cells in the intima. Adherent leukocytes and vascular smooth muscle cells (VSMCs) expressed mRNA for IL-1 alpha. Microvascular endothelium expressed mRNA for both IL-1 alpha and beta. IL-1 proteins were located frequently in cells expressing IL-1 mRNA. These results indicate that endothelium and VSMCs, in conjunction with macrophages, serve as localized sources of IL-1 protein synthesis. These findings suggest that vascular cells may contribute directly to the pathogenesis of atherosclerotic vascular disease by actively secreting potent biologic mediators that modify vascular and immune cell function.

T-cell lymphosarcoma in a female African green monkey (Cercopithecus aethiops).

A female African green monkey developed a generalized lymphosarcoma spontaneously that clinically and pathologically resembled malignant lymphoma in human beings infected with human T-lymphotropic virus type I. The monkey was serologically positive for simian T-lymphotropic virus. Immunocytochemical analysis of routinely fixed and paraffin embedded tumor tissue demonstrated neoplastic cells that stained positive with antihuman monoclonal UCHL1 which recognized a T-cell-restricted isotype of leukocyte common antigen.