Genetic aspects of familial osteoarthritis

Exposure to acrylamide induces skeletal developmental toxicity in zebrafish and rat embryos

Acrylamide is a well-known carcinogen and neurotoxic substance that has been discovered in frying or baking carbohydrate-rich foods and is widely found in soils and groundwater. The purpose of this study was to investigate the adverse effects of exposure to acrylamide on skeletal development. After treatment with acrylamide in zebrafish embryos, the survival and hatching rates decreased, and the body length shortened, with cartilage malformation and a decrease in skeletal area. Exposure to acrylamide in maternal rats during the lactation period disturbed bone mineral density, serum levels of parathyroid hormone, and the expression of skeletal development-related genes in neonates. Exposure to acrylamide in pregnant rats during the pregnancy period decreased the trabecular density and inhibited cartilage formation by delaying the differentiation of osteoblasts and promoting the maturation of osteoclasts in rat embryos. Furthermore, acrylamide intervention downregulated the expression of chondrocyte and osteoblast differentiation-related genes (sox9a, bmp2, col2a1, and runx2), and upregulated the expression of osteoclast marker genes (rankl and mcsf) in zebrafish and rat embryos at different gestational stages. Our results indicated that exposure to acrylamide dysregulated signature gene and protein expression profiles of skeletal development by suppressing the differentiation and maturation of osteoblasts and cartilage matrix and promoting the formation of osteoclasts, and ultimately induced skeletal abnormality in morphology, which brings increasing attention to the intergenerational toxicity of acrylamide via mother-to-child transmission.

Primary osteoarthritis no longer primary: three subsets with distinct etiological, clinical, and therapeutic characteristics

BACKGROUND

Osteoarthritis (OA) has been historically divided into primary and secondary. Primary OA has been defined as an idiopathic condition developing in previously undamaged joints in the absence of an obvious causative mechanism. During the last few years a large amount of evidence has provided new insights into the biochemistry and molecular biology of cartilage, subchondral bone, and other articular tissues, which suggest distinct etiopathogenetic mechanisms in some forms of primary OA.

OBJECTIVE

To propose an etiopathogenic classification of primary OA in the light of the significant progress in the understanding of the disease.

METHODS

A review of the literature was performed by searching the Medline and PubMed databases from 1952 to November 2008 using the following keywords: genetic alteration, heritability, estrogen, menopause, and aging either alone or in various combinations with joint, cartilage, subchondral bone, synovium, ligaments, muscle, tendons, OA, and osteoporosis.

RESULTS

Numerous studies have shown that genetic alterations, menopause-related estrogen deficiency, and aging play crucial roles in the molecular pathophysiological events involved in the process of cartilage and joint damage and thus in development of OA. We propose classifying primary OA into 3 distinct although interrelated subsets: type I OA, genetically determined; type II OA, estrogen hormone dependent; and type III OA, aging related.

CONCLUSIONS

The 3 proposed subsets of OA display distinct etiological, clinical, and therapeutic characteristics and should therefore no longer be considered to be "Primary OA."

Variability in tendon and knee joint biomechanics among inbred mouse strains

Hereditary factors are thought to be responsible for impaired tendon function and joint laxity. The present study investigated the genotypic variability of knee laxity and stiffness and tendon mechanical and geometric properties among 16-week-old female A/J, C57BL/6J (B6), and C3H/HeJ (C3H) inbred mice. In one group of mice, knee mechanics were quantified using a custom loading apparatus enabling translation of the tibia against a stationary femur. In a second group, flexor digitorum longus and Achilles tendons from the left hind limb underwent biomechanical testing, while those of the contralateral limb were analyzed histologically for determination of cross-sectional area. Our results demonstrate that tendon and joint mechanics varied significantly among the inbred mouse strains, indicating that biomechanical properties are genetically determined. A/J mouse knees exhibited greater laxity (p < 0.001) and lower stiffness (p < 0.001) compared to those of the B6 and C3H mice. The genotypic differences in whole joint properties were similar to those of the tendons' structural biomechanical traits. Although body mass did not differ (p > 0.2) among the three strains, significant genotypic differences were found at the whole tendon, material quality, and morphological levels of the tissue hierarchy. Furthermore, genetic regulation of tendon mechanical properties varied with anatomic site. Patterns of genotypic differences in tendon size were not consistent with those of biomechanical properties, suggesting that unique combinations of structural and compositional factors contribute to tendon growth, adaptation, and development. Therefore, the three inbred strains constitute a useful experimental model to elucidate genetic control of structure-function relationships in normal and healing tendons and ligaments.

Activation of the discoidin domain receptor 2 induces expression of matrix metalloproteinase 13 associated with osteoarthritis in mice

Human genetic studies indicate that mutations in type IX and XI collagens result in early-onset osteoarthritis (OA) with a wide spectrum of osteochondrodysplasia. However, a convincing causal chain of events underlying the role of these collagen mutations in the pathogenesis of OA has not been elucidated. Here we show that the expression of a cell surface collagen receptor, discoidin domain receptor 2 (DDR2), is increased in chondrocytes of the articular cartilage of knee joints in mice that develop OA as a result of a heterozygous mutation in type XI collagen. At the same time point, 6 months, we also found increased expression and activity of matrix metalloproteinase 13 (MMP-13) in the mutant mouse knee cartilage. The expression of both DDR2 and MMP-13 was increased in chondrocytes cultured on plates coated with native type II collagen but not on gelatin, and overexpression of DDR2, but not of a truncated form, was found to induce the expression of MMP-13 when chondrocytes were cultured on type II collagen but not on plastic. The DDR2-induced expression of MMP-13 appears to be specific, since we did not observe induction of MMP-1, MMP-3, MMP-8, ADAMTS-4, ADAMTS-5, and IL-1 transcripts in human chondrocytes or Mmp-3, Mmp-8, Adamts-4, Adamts-5, and Il-1 in mouse chondrocytes. Our data suggest that the defect in the cartilage matrix of mice that are heterozygous for a type XI collagen mutation (cho/+) permits activation and up-regulation of DDR2 in chondrocytes. This could be due to increased exposure of chondrocytes to type II collagen as a result of the decreased amount of type XI collagen in the mutant cartilage. The specific induction of MMP-13 by DDR2 in response to its cartilage-specific ligand, type II collagen, may contribute to cartilage damage in hereditary OA.

Genome scan for quantity of hand osteoarthritis: the Framingham Study

OBJECTIVE

To search for markers linked to quantity of radiographic hand osteoarthritis (OA) in the Framingham Heart Study.

METHODS

The sample included 684 original cohort members and 793 offspring in 296 pedigrees. Radiographic OA features evaluated included the Kellgren/Lawrence (K/L) score, osteophytes, and joint space narrowing (0-3 scale). Four quantitative phenotypes were computed from these measurements: sum of K/L scores across hand joints, sum of osteophyte scores, sum of joint space narrowing scores, and proportion of affected joints. Prior to linkage analysis, these phenotypes were adjusted for age using a linear regression analysis from which standardized residuals were computed. The regression analysis was performed separately for each sex and each generation. The variance component model (SOLAR) was then applied to the normalized scores of the residuals.

RESULTS

The average age was 62 years for the original cohort and 54 years for the offspring. Fifty percent of the original cohort and 30% of their offspring had at least 1 affected joint (K/L score >or=2). Heritability ranged from 28% (proportion of joints affected with OA) to 34% (sum of K/L scores). Eight chromosomal regions indicated suggestive linkage (multipoint logarithm of odds [LOD] score >1.5) for at least 1 phenotype; LOD scores were highest for joint space narrowing, with a multipoint LOD score = 2.96 on chromosome 1p at D1S1665. Chromosomes 7, 9, 13, and 19 indicated consistent LOD score elevation for multiple OA phenotypes.

CONCLUSION

There are several chromosomes that may harbor OA susceptibility genes. Further investigation of these regions using larger studies and finer maps will be important to confirm linkage.

Effects of lateral-wedged insoles on kinetics at the knee

Lateral-wedged insoles have been shown to help clinically alleviate pain associated with medial compartment osteoarthritis. This study analyzed the effects of lateral-wedged insoles on the gait and medial knee compartment load of 17 healthy subjects. Three-dimensional gait analysis was performed for each subject with and without wearing a 5 degrees lateral-wedged insole. Subjects walked at a constant velocity for both conditions. A motion analysis system and force plate were used to calculate temporal and spatial parameters, joint angles, moments, and powers. An analytical model was developed to estimate medial compartment loads at the knee for each subject during both conditions. Results were compared with a Student's paired t test. There were no significant differences in temporal and spatial parameters, joint angles at the hip, knee, and ankle, or kinetics at the hip and ankle. However, the external varus moment and estimated medial compartment load at the knee were reduced significantly with the addition of the lateral-wedged insole. These results suggest that the pain relief and improvement in function reported by patients with osteoarthritis while using lateral-wedged insoles may be achieved by a reduction in external varus moment and medial compartment load.

Type II collagen degradation in spontaneous osteoarthritis in C57Bl/6 and BALB/c mice

OBJECTIVE

Degradation of type II collagen during osteoarthritis (OA) is thought to be the key process leading to cartilage destruction. In this study, we investigated whether OA is characterized by either a generalized breakdown of the collagenous network or a localized process. Furthermore, we determined if collagen degradation was linked to cell death.

METHODS

Two mouse strains that develop spontaneous OA, C57Bl/6 and BALB/c mice, were examined. Type II collagen degradation in type II collagen-induced arthritis was also examined for comparison. Immunolocalization with the COL2-3/4m and COL2-3/4C antibodies was used to demonstrate denatured type II collagen and the collagenase cleavage site in type II collagen, respectively.

RESULTS

Both the C57Bl/6 and the BALB/c mice developed OA changes, although clear compartmental differences existed between the two strains. In both strains, type II collagen degradation was clearly present at sites of degeneration, but was absent from intact articular cartilage. Collagen degradation was absent from areas with cell death.

CONCLUSION

These results indicate that type II collagen degradation in spontaneous murine OA is associated with degeneration and is a localized, instead of a generalized, process.

Towards a molecular understanding of arthritis

Several different agents including free radicals, oxidizing compounds and proteases are believed to play a role in the onset of arthritis. The evidence and underlying chemistry presently available for each destructive agent are presented.

A human-specific polymorphism in the coding region of the aggrecan gene. Variable number of tandem repeats produce a range of core protein sizes in the general population

Aggrecan, one of the major structural genes of cartilage, encodes a proteoglycan core protein composed of an extended central glycosaminoglycan-bearing domain, flanked by globular domains at each end. The central region consists of long stretches of repeating amino acids that serve as attachment sites for glycosaminoglycans such as chondroitin and keratan sulfate; the terminal globular domains interact with other cartilage components. The glycosaminoglycan attachment region is encoded in several species by a single large exon, within which are several different types of repeating sequences. Several species show within this exon a similar block of conserved repeats for attachment of chondroitin sulfate, but in humans this group of repeats is particularly well conserved. Examination of genomic DNA from a population of unrelated individuals by polymerase chain reaction or Southern blot assays shows this block of repeat sequences exists in multiple allelic forms, which differ by the number of repeats at this site in each allele. Thirteen different alleles have been identified, with repeat numbers ranging from 13 to 33. This is an unusual example of an expressed variable number of tandem repeat polymorphism. This polymorphism is apparently restricted to humans, of several species examined. This polymorphism results in individuals with differing length aggrecan core proteins, bearing different numbers of potential attachment sites for chondroitin sulfate. The possibility exists for a molecular understanding of biological variation in cartilage functional properties.

Testing the eukaryotic promoters for efficient expression of exogenous genes in chondrocytes and synoviocytes

To identify suitable promoters for expressing exogenous genes in arthritic joints, the constitutive, simian virus 40 (SV 40) and IL-1 or metal inducible, human stromelysin and metallothionein (MT) gene promoters were tested for their activity in chondrocytes and synovial fibroblasts. Transient transfection with plasmids containing the reporter chloramphenicol acetyltransferase (CAT) gene attached to these promoters showed that SV40, stromelysin and MT promoters drove CAT expression with different strengths in primary bovine chondrocytes. The MTI-F and MT-IG gene promoters were also functional in human chondrocytes. The SV40, IL-1 inducible stromelysin-1 and MT-IG driven CAT activity was also detectable in human synoviocytes. Therefore, chondrocytes and synoviocytes have the trans-acting factors necessary for transcription from the respective promoters which may be conserved in bovine and human cells. These promoters could be useful for expressing potentially therapeutic anti-inflammatory and anti-erosive genes in arthritic joints.

New perspectives on osteoarthritis

Osteoarthritis (OA) is the most common rheumatologic disease, afflicting tens of millions of U.S. citizens. It is not an inevitable consequence of aging; rather, it is a degenerative process acquired because of metabolic, mechanical, genetic, and other influences. It is characterized by progressive loss of cartilage and bony overgrowth. Because cartilage is not innervated, the pain of OA arises from secondary effects, such as joint capsule distention, stretching of periosteal nerve endings, and, possibly, synovial inflammation. Psychologic factors, including stress and depression, may influence the perception of pain by OA patients. The risk of OA apparently is not increased by normal joint use, but persons who participate in competitive sports or who play with abnormal or injured joints are at increased risk. Obesity increases OA risk, and weight loss has been found to decrease it. Some forms of premature OA appear to be inherited. The objective diagnosis of OA is made on the basis of radiography. However, many individuals with radiographic evidence of OA are asymptomatic in the affected joint. It is essential to ensure that pain in the affected joint is attributable to OA and not another cause. The management of OA should include physical medicine measures such as heat or cold therapy and often neglected environmental measures, such as reducing chair height and using shoe orthotics. Therapeutic exercise is beneficial for many patients and includes an initial warm-up with range of motion, muscle strengthening, and aerobic activity (such as swimming). A major question in the pharmacologic management of OA is whether nonsteroidal anti-inflammatory drugs (NSAIDs) are superior to analgesics in terms of symptomatic relief; studies indicate that they are not. The question is relevant because of the adverse effects of NSAID use, particularly in the elderly population.

Mechanisms of joint destruction, pain and disability in osteoarthritis

Osteoarthritis is characterised by progressive erosion of articular cartilage, and bony overgrowth at the joint margins. Cartilage integrity requires a balance between synthesis and degradation of matrix components, and the latter is augmented in osteoarthritis through the action of chondrocyte-derived metalloproteinases. Synthesis rates also increase but fail to keep pace with the losses. Synovial inflammation, a mild and inconstant feature of osteoarthritis, is more likely to be a consequence of cartilage breakdown than a cause, and its contribution to pain is uncertain. The origins of pain and disability are complex; pathological changes in the joint capsule and periarticular ligaments are a likely source, but nocturnal pain may be related to raised pressure in subchondral bone. In addition to structural damage in the joint, psychosocial factors, muscle weakness, and comorbidities may contribute.