Progressive degeneration of articular cartilage and intervertebral discs. An experimental study in transgenic mice bearing a type IX collagen mutation

Tissue engineered nucleus pulposus tissue formed on a porous calcium polyphosphate substrate

STUDY DESIGN

This study describes the formation of nucleus pulposus tissue using a novel tissue engineering approach.

OBJECTIVES

To determine if a construct composed of nucleus pulposus tissue on the surface of a calcium polyphosphate substrate could be formed in vitro with properties similar to native nucleus pulposus tissue.

SUMMARY OF BACKGROUND DATA

There is no optimal treatment for the persistent pain associated with intervertebral disc degeneration. Disc replacement using artificial intervertebral discs has met with some success, and biologic transplantation is limited by the availability of donor tissues.

METHODS

Nucleus pulposus cells were isolated from bovine caudal intervertebral discs. Cells were seeded at high density on the upper surface of a porous bone substitute material (calcium polyphosphate) and maintained up to 6 weeks in culture. In vitro formed tissue was compared to native nucleus pulposus for histologic appearance, biochemical composition (tissue cellularity, proteoglycan and collagen accumulation), and compressive mechanical properties.

RESULTS

When maintained on the surface of a three-dimensional substrate, nucleus pulposus cells formed a continuous layer of tissue with a proteoglycan content equivalent to the native tissue. Although collagen accumulation attained only 26% than that of the native tissue, there was no difference in tissue stiffness, viscosity, or weight-bearing capacity of the in vitro formed tissue when compared with the native tissue.

CONCLUSION

Nucleus pulposus-like tissue formed in vitro on the surface of a calcium polyphosphate substrate resembles the native tissue in terms of proteoglycan content and compressive mechanical properties. These studies are the first step toward developing a functional spinal unit in vitro.

The role of collagen IX tryptophan polymorphisms in symptomatic intervertebral disc disease in Southern European patients

STUDY DESIGN

We conducted a cross-sectional, genotyping study of intervertebral disc disease patients and controls.

OBJECTIVES

To determine the contribution of COL9A2 and COL9A3 Tryptophan polymorphisms to intervertebral disc disease development in a genetically heterogeneous, Southern European population compared to previous Finnish studies.

SUMMARY OF BACKGROUND DATA

The COL9A2 and COL9A3 genes encode the alpha2 and alpha3 chains of Collagen IX. Recent Finnish studies suggest that a tryptophan polymorphism in the COL9A2 gene (Trp2) results in hereditary intervertebral disc disease, whereas a similar tryptophan mutation in COL9A3 (Trp3) conveys a 3-fold risk of intervertebral disc disease.

METHODS

We studied 105 symptomatic patients with radiographically and/or surgically proven lumbar (98%, n = 103) or cervical (2%, n = 2) intervertebral disc disease and 102 age-matched controls without spinal complaints from hospitals in Athens, Greece. Intervertebral disc disease was defined as significant disc herniation resulting in persistent back or leg pain. We genotyped all patients for COL9A2 and COL9A3 allele variations using a polymerase chain reaction-based technique.

RESULTS

None of our patients had the Trp2 allele. Consistent with previous Finnish findings, more Greek intervertebral disc disease cases (8.6%) than controls (4.9%) had at least 1 Trp3 allele, but this difference did not reach statistical significance (P = 0.293). The allele frequency of the Trp3 mutation was significantly higher among previously studied Finnish patients with intervertebral disc disease (12.3%) than among the Southern European patients with intervertebral disc disease in our study (4.3%), P = 0.001.

CONCLUSIONS

The differences in Trp allele frequency we found between Greek and Finnish patients with intervertebral disc disease most likely represent true differences in polymorphism prevalence between the respective populations. The 2 previously described Trp alleles in COL9A2 and COL9A3 are likely to be less significant susceptibility factors for intervertebral disc disease development in Southern European populations.

Sequence variations in the collagen IX and XI genes are associated with degenerative lumbar spinal stenosis

BACKGROUND

Degenerative lumbar spinal stenosis (LSS) is usually caused by disc herniation or degeneration. Several genetic factors have been implicated in disc disease. Tryptophan alleles in COL9A2 and COL9A3 have been shown to be associated with lumbar disc disease in the Finnish population, and polymorphisms in the vitamin D receptor gene (VDR) (FokI and TaqI), the matrix metalloproteinase-3 gene (MMP-3) and an aggrecan gene (AGC1) VNTR have been reported to be associated with disc degeneration. In addition, an IVS6-4 a>t polymorphism in COL11A2 has been found in connection with stenosis caused by ossification of the posterior longitudinal ligament in the Japanese population.

OBJECTIVE

To study the role of genetic factors in LSS.

METHODS

29 Finnish probands were analysed for mutations in the genes coding for intervertebral disc matrix proteins, COL1A1, COL1A2, COL2A1, COL9A1, COL9A2, COL9A3, COL11A1, COL11A2, and AGC1. VDR and MMP-3 polymorphisms were also analysed. Sequence variations were tested in 56 Finnish controls.

RESULTS

Several disease associated alleles were identified. A splice site mutation in COL9A2 leading to a premature translation termination codon and the generation of a truncated protein was identified in one proband, another had the Trp2 allele, and four others the Trp3 allele. The frequency of the COL11A2 IVS6(-4) t allele was 93.1% in the probands and 72.3% in controls (p = 0.0016). The differences in genotype frequencies for this site were less significant (p = 0.0043).

CONCLUSIONS

Genetic factors have an important role in the pathogenesis of LSS.

Matrix deposition of tryptophan-containing allelic variants of type IX collagen in developing human cartilage

Genetic polymorphisms that encode a tryptophan (Trp) residue in the triple-helical domain of the alpha2 (Trp2) or alpha3 chain (Trp3) of human type IX collagen have been linked to risk of degenerative intervertebral disc disease. To determine whether these two allelic variants express protein that may affect the extracellular matrix of cartilage in vivo, we examined the properties of resident type IX collagen in an anonymous collection of embryonic and fetal human cartilage samples screened for Trp genotypes. No difference was found in the yield and electrophoretic properties of pepsin-solubilized type IX collagen between Trp2, Trp3 and non-Trp cartilage samples. On Western blot analysis, a polyclonal antiserum raised against a synthetic peptide matching the immediate Trp-containing sequence of the Trp3 allele reacted specifically with the alpha3(IX) chain prepared from Trp3 cartilage samples. Two-dimensional peptide mapping of type IX collagen in CNBr-digests of whole tissue gave indistinguishable fingerprints for Trp2, Trp3 and control tissues, including the yield of cross-linked peptides. Analysis of one cartilage sample that was homozygous for the Trp2 allele also gave a normal yield of collagen IX, including its alpha2 chain and a normal profile of cross-linked peptides. Together, the findings indicate that both Trp2 and Trp3 allelic products are incorporated into the cross-linked fibrillar network of developing human cartilage apparently normally. Any pathological consequences are likely, therefore, to be long-term and indirect rather than from overt misassembly of matrix.

Clinical phenotype and molecular diagnosis of multiple epiphyseal dysplasia with relative hip sparing during childhood (EDM2)

We report on a family of 19 individuals over four generations in which 12 members are affected with a variant of multiple epiphyseal dysplasia. Beginning in childhood, the disease leads to pain and stiffness of knees, ankles, elbows and finger joints. Some adult patients repeatedly suffer from free articular bodies resulting in locking of the joint. Finally, affected individuals are prone to the development of early degenerative joint disease. Mutation screening of candidate regions revealed a novel point mutation at position -1 in the COL9A2 exon 3/intron 3 splicing region. This G --> C substitution most probably induces an alteration of the splicing process. Family screening was carried out by both automated sequencing and by digestion of amplicons with BsaWI. We confirmed the nucleotide substitution in eight clinically affected family members as well as in three presymptomatic young children. Electron microscopy showed that the diameter of collagen fibrils from arthroscopically removed free articular bodies of two patients was not obviously different from that of normal articular cartilage. Together with previous reports our results indicate that mutations leading to skipping of exon 3 within the COL3 domain of the alpha2-chain of collagen type IX may be relatively common in patients with a special subtype of multiple epiphyseal dysplasia (MED) in which the hips are not markedly affected at early age (EDM2). In these patients and their families, mutation screening of the candidate regions may help to confirm the diagnosis, lead to appropriate advice for lifestyle and well based genetic counseling.

Degeneration of the intervertebral disc

The intervertebral disc is a cartilaginous structure that resembles articular cartilage in its biochemistry, but morphologically it is clearly different. It shows degenerative and ageing changes earlier than does any other connective tissue in the body. It is believed to be important clinically because there is an association of disc degeneration with back pain. Current treatments are predominantly conservative or, less commonly, surgical; in many cases there is no clear diagnosis and therapy is considered inadequate. New developments, such as genetic and biological approaches, may allow better diagnosis and treatments in the future.

Recent advances in disc cell biology

STUDY DESIGN

There have been many advances over the past decade in understanding and experimentally modulating biologic aspects of intervertebral disc cell function. An overview of the current state of this biologic research is presented.

OBJECTIVES

To provide clinicians with a review of important recent advances in biologic studies of the disc and their implications for potential disc therapies.

SUMMARY OF BACKGROUND DATA

Historically, anatomic, biochemical, radiologic, and biomechanical studies of the intervertebral disc formed the foundation on which our understanding of disc function was built. Magnetic resonance imaging techniques that allowed viewing of soft tissue components of the disc further advanced imaging capabilities.

METHODS

Recent publications are reviewed.

RESULTS

Experimental approaches over the past decade have enabled researchers to look more critically at disc cell function. This is important because disc cell function produces the extracellular matrix components of the disc, which, in turn, shape the disc's subsequent physiologic and biomechanical functions. New approaches to the study of disc cell function, methods to manipulate disc cells, studies of intact discs and disc nutrition, vertebral endplate structure and function, tissue engineering, gene therapy, and the potential of stem cells in disc therapy are reviewed and discussed.

CONCLUSIONS

Many believe that disc degeneration has a cellular basis. New research is helping us better understand healthy, aging, and degenerating discs. Modern methods to manipulate and modulate disc cell function open exciting and challenging new therapeutic possibilities for future biologic treatments of disc degeneration.

Lifelong voluntary joint loading increases osteoarthritis in mice housing a deletion mutation in type II procollagen gene, and slightly also in non-transgenic mice

OBJECTIVES

To investigate the effects of voluntary running on the incidence and severity of osteoarthritis (OA) and associated changes in cartilage matrix and subchondral bone in a transgenic Del1 mouse model for OA.

METHODS

Del1 mice and their non-transgenic littermate controls were housed from the age of 5-6 weeks to 15 months in individual cages with running wheels. The running activity of each mouse was monitored for the entire 12 month period. Additional Del1 and control mice were housed in individual cages without running wheels. At the end of the experiment the severity of OA was evaluated by light microscopy, and the articular cartilage matrix changes by digital densitometry and quantitative polarised light microscopy.

RESULTS

Lifelong voluntary running increased the incidence and severity of OA significantly in Del1 mice (transgenic runners), and slightly also in non-transgenic runners. Severe OA changes increased from 39% in transgenic non-runners to 90% in transgenic runners (p=0.006) in lateral tibial condyles, and from 24% to 80% (p=0.013) in lateral femoral condyles, respectively. The proteoglycan content of articular cartilage was reduced in transgenic runners in comparison with transgenic non-runners (p=0.0167), but a similar effect was not seen in non-transgenic runners compared with non-transgenic non-runners. No attributable differences were seen in the collagen network of articular cartilage or in the subchondral bone between any of the groups.

CONCLUSION

The Del1 mutation has earlier been shown to disturb the assembly of the cartilage collagen network and thereby increase the incidence and severity of OA with age. In this study, voluntary running was shown to increase further cartilage damage in the lateral compartments of the knee. This suggests that articular cartilage in Del1 mice is less resistant to physical loading than in control mice. Despite severe OA lesions in the knee joint at the age of 15 months, Del1 mice continued to run voluntarily 2-3 km every night.

Ultrastructure of the human intervertebral disc during aging and degeneration: comparison of surgical and control specimens

STUDY DESIGN

Human intervertebral disc tissue from the annulus was obtained in a prospective study investigating the ultrastructural features of disc cells and extracellular matrix. Experimental studies were approved by the authors' Human Subjects Institutional Review Board. Discs were obtained from surgical specimens and control donors.

OBJECTIVE

To compare the cellular and extracellular matrix characteristics of the annulus from control and surgical disc specimens using electron microscopy and specialized fixation that visualizes proteoglycans.

SUMMARY OF THE BACKGROUND DATA

The ultrastructural features of disc cells and the disc matrix have received little attention, as compared with the literature on age- and disease-related changes in bone and cartilage.

METHODS

Ultrastructural studies investigated disc tissue obtained from control and surgical disc specimens using transmission electron microscopy. Specialized fixation with ruthenium red was used to highlight matrix proteoglycans.

RESULTS

Cellular and extracellular matrix fine structure was assessed in disc specimens from 29 control donors (newborns to 79-year-olds) and surgical disc specimens from 49 patients (16- to 77-year-olds). Control and surgical tissue showed similar ultrastructural features. Unusual matrix surrounding and encircling single cells or clusters of cells was common (48% of control and 63% of surgical specimens) and often contained fibrous long-spacing collagen (41.3% of control and 36.7% of surgical specimens). Ruthenium red greatly aided visualization of proteoglycans pooled in lacunar spaces. Variable cross-sectional diameters of collagen fibrils was present in 34% of control and 59% of surgical specimens. Regions with sparse interterritorial matrix were common. Cell morphology showed both cells with apoptotic nuclei and synthetically active cells that appeared healthy.

CONCLUSIONS

Control and surgical specimens of the annulus showed similar ultrastructural features. Heterogeneity of collagen fibril diameter is an important observation because it is believed that fibril size relates to biomechanical disc function. Fibrous long-spacing collagen may reflect extracellular matrix remodeling or the presence of previous fibril depolymerization followed by repolymerization and reassociation with proteoglycans. Synthetic activity of disc cells is reflected in active rough endoplasmic reticulum, Golgi, and pools of proteoglycans in lacunar spaces and unusual extracellular matrix components that encircle cells and cell clusters. Such components may influence biomechanical quality. Departures from normal extracellular matrix organization of the aging or degenerating disc undoubtedly contribute to decreased biomechanical function of the annulus because they disrupt the normal annulus architecture. This study underscores the need for a fuller understanding of the dynamic relation between disc cells and the surrounding extracellular matrix, which they continually produce and remodel.

Biochemical and morphological changes in herniated human intervertebral disc

The molecular and morphologic features of herniated human intervertebral disc tissues are of particular importance to clarify the pathogenesis. The present study analyzed the biochemical and morphological features of herniated intervertebral disc tissues to determine the constituent factors responsible for intervertebral disc herniation. A total of 32 herniated disc specimens and 4 control disc samples were analyzed. Collagen subunit composition, collagenase activity, lipid peroxidation level, caspase-3 activity, metal levels, morphologic studies, and genetic analysis were performed on herniated disc tissues of chronic (group A) and acute (group B) group and compared with findings of control group. Nick translation analysis in situ revealed apoptotic-positive stained DNA fragments as black-brown spots in herniated disc tissues. The presence of type II collagen in control disc samples and its absence in herniated samples were confirmed immunohistochemically. The increased caspase-3 activity, the apoptotic-positive stained DNA fragments, and the electron microscopic findings suggest enhanced programmed cell death in herniated discs. The significant increase in lipid peroxidation levels and collagenase activity, and the low metal levels suggest the enhancement of cell death signals in herniated discs, caused by oxygen stress. Linkage analysis of herniated disc tissues in Japanese individuals may suggest ethnic variation. These findings may be helpful in understanding the pathogenesis of herniated disc disease.

Magnetic resonance imaging findings in relation to the COL9A2 tryptophan allele among patients with sciatica

STUDY DESIGN

The phenotype of patients with sciatica who have the Trp2 allele is characterized cross-sectionally.

OBJECTIVE

To determine whether it is possible to differentiate patients with the Trp2 allele clinically or by magnetic resonance imaging.

SUMMARY OF BACKGROUND DATA

Several studies have indicated a positive family history for intervertebral disc disease. Previously, a dominantly inherited defect was identified in the COL9A2 gene that changed a codon for glutamine to that for tryptophan in the alpha2 chain of collagen IX (Trp2 allele). This change may render intervertebral discs more fragile.

METHODS

Clinical findings, clinical symptoms, and magnetic resonance imaging (1.5-T) findings from 159 patients with sciatica were evaluated according to the presence of the Trp2 allele. Additionally, the magnetic resonance imaging scans of 22 family members from three families were evaluated. These scans were analyzed intervertebral disc and endplate degeneration, Schmorl's nodes, transverse tears (hyperintensity in the region of Sharpey's fibers), high-intensity zone lesions (bright spots in the dorsal anulus), and radial tears (hyperintense linear area from the nucleus to the outer part of the anulus on T2 sequences).

RESULTS

Six patients with sciatica and 11 family members had the Trp2 allele. No homozygotes were found. Clinical symptoms of patients with and those without the Trp2 allele were similar. Patients with sciatica who had the Trp2 allele were significantly more flexible (P < 0.05), according to the modified Schober measure. The disc and endplate degeneration in 6 patients with the Trp2 allele and their 18 controls (matched for age, occupation, gender) without the allele did not differ significantly, whereas family members with the Trp2 allele had a greater degree of disc and endplate degeneration at L5-S1. The overall prevalence of endplate degeneration was high in this study. The prevalences of dorsal transverse tears, high-intensity zone lesions, and Schmorl's nodes did not differ among patients with sciatica or family members according to the presence of the Trp2 allele. There was, however, a trend for increased prevalence of radial tears in nonherniated discs among the Trp2 allele-positive subjects (3 of 6 patients with sciatica and 3 of 11 family members), as compared with the Trp2-negatives subjects (none of 18 "matched" patients or 11 family members).

CONCLUSION

The patients with the Trp2 allele were more flexible, and more often tended to have a radial tear in a nonherniated disc than their control counterparts.

Clinical and demographic prognostic indicators for human disc cell proliferation in vitro: pilot study

STUDY DESIGN

Human anulus cells were cultured under control and experimental conditions to study associations between proliferation and clinical-demographic features of subjects from which cells were obtained. Statistical multiple regression analyses were applied to develop mathematic models relating proliferation to age, gender, Thompson score (denoting stage of disc degeneration), and status (control donor [postmortem]; surgical patient).

OBJECTIVES

To identify the effect of donor characteristics on proliferative capacities of human disc cells.

SUMMARY OF BACKGROUND DATA

As therapeutic options for disc degeneration increase, novel biologic options are important future considerations. Little is known about the influence of clinical-demographic features on cell proliferation.

METHODS

Anulus cells were studied in two designs: 1) Cells from 12 individuals were grown in monolayer with 50 ng/mL interleukin growth factor-1 (IGF-I), 100 ng/mL insulin, or control conditions. 2) Cells from nine individuals were grown in three-dimensional culture with 10 ng/mL IGF-I or control conditions. Cell proliferation data and data on age, gender, Thompson score, and status were collected. Standard statistical analyses were used to develop correlation models.

RESULTS

Data from monolayer experiments produced significant models fitting proliferation in the presence of low serum, 50 ng/mL IGF-I, or insulin, with age, gender, Thompson score, and status (respective R2: 0.827, 0.680, 0.850). Three-dimensional cultures exposed to 10 ng/mL IGF-I resulted in proliferation that correlated in a significant negative manner with Thompson score (r = -0.798).

CONCLUSIONS

Clinical-demographic prognostic indicators may help predict levels of proliferation. Greater age, greater disc degeneration, female gender, and surgical derivation had deleterious effects on proliferation potential in this model.

More knee joint osteoarthritis (OA) in mice after inactivation of one allele of type II procollagen gene but less OA after lifelong voluntary wheel running exercise

OBJECTIVE

To investigate the incidence and severity of osteoarthritis (OA) and the effects of voluntary wheel running in normal mice and mice carrying either a targeted inactivation of one allele, heterozygous 'knockout', of Col2a1 gene or both alleles, homozygous 'knockout', of Col11a2 gene.

METHODS

Mice lived until 15 months of age in individual cages. Running activity was recorded around the clock. OA changes were evaluated from serial knee joint sections by light microscopy.

RESULTS

Heterozygous inactivation of Col2a1 gene coding for type II procollagen made the cartilage more susceptible to OA. At 15 months of age, OA prevalence was 60-90% in knockouts and 20-45% in normal controls (P < 0.01-0.001). Unexpectedly, a reduction of OA due to wheel running was observed in both knockout strains (P< 0.05-0.01). This effect was most evident in the femoral condyles. Incidence of OA in runners was approximately 50-85% of that in sedentary littermates. OA prevalence was higher in normal control and runner mice with high body weight. Running did not affect OA development in normal mice.

CONCLUSION

Heterozygous knockout of Col2a1 gene increased the OA prevalence in mice. Lifelong voluntary wheel running had a protective effect against OA in both knockout mice lines. The reason for this remains unknown. Reduction of OA may result from the reorganization and strengthening of the articular cartilage collagen network and/or adjacent muscles due to running, or lower body weight. Increased compliance of the articular cartilage and bones of the knockout mice may also contribute to the reduction of OA in exercised animals.

COL9A2 allelotypes in intervertebral disc disease

An allelic variation of the COL9A2 gene encoding the alpha(2)-chain of collagen IX has recently been identified as a genetic risk factor for intervertebral disc prolapse, resulting in a tryptophane (Trp) substitution at position 326 of the protein. To enable quick screening of a large population we established a single enzyme (BsmFI) restriction assay which was validated by screening disc tissue samples of 250 patients (age, 47.1 +/- 13.7 years). Positive results were confirmed by nucleotide sequencing. The Trp allele was found in three patients (1.2%) who suffered from their first prolapse and were significantly older (70.7 +/- 8.5 years) than the other 247 patients. Since the substitution affects a domain covalently linked to collagen II fibrils, we conclude that this allelotype may contribute to reduced collagen crosslinking, disc instability and eventually prolapse in the elderly.

Mammalian skeletogenesis and extracellular matrix: what can we learn from knockout mice?

Formation of the vertebrate skeleton and the proper functions of bony and cartilaginous elements are determined by extracellular, cell surface and intracellular molecules. Genetic and biochemical analyses of human heritable skeletal disorders as well as the generation of knockout mice provide useful tools to identify the key players of mammalian skeletogenesis. This review summarises our recent work with transgenic animals carrying ablated genes for cartilage extracellular matrix proteins. Some of these mice exhibit a lethal phenotype associated with severe skeletal defects (type II collagen-null, perlecan-null), whereas others show mild (type IX collagen-null) or no skeletal abnormalities (matrilin-1-null, fibromodulin-null, tenascin-C-null). The appropriate human genetic disorders are discussed and contrasted with the knockout mice phenotypes.

Familial incidence of intervertebral disc herniation: an hypothesis suggesting that laminectomy and discectomy may be counterproductive

OBJECTIVE

To determine (1) if familial and genetic factors play a role in the genesis of disc herniation, (2) the incidence of multiple disc herniations, (3) the incidence of disc reherniation in patients treated with standard laminectomy and discectomy, and (4) to construct a hypothesis that best explains all three.

SUMMARY BACKGROUND DATA

It is known that there is a substantial incidence of disc herniation in first order relatives of patients with herniated nucleus pulposa (HNP), that multiple disc herniations are not uncommon, and that disc reherniations and repeat operations after laminectomy and discectomy range from 5 to 37%. Also, there is a recent report of a genetic defect leading to defective cross-linkage of collagen strands in patients with HNP.

METHODS

Using the questionnaire method, a group of the author's patients with documented HNP treated with percutaneous laser disc decompression (PLDD) was surveyed as to the existence of known disc herniations among first order relatives. Analysis of the author's series of 621 patients with HNP disclosed the incidence of multiple disc herniations. A comprehensive literature search provided data on reherniations and reoperations following laminectomy and discectomy.

RESULTS

In 174 respondents, the number with first order relatives who had HNP was 74 (or 43%). This compares with the national incidence of HNP of 1.7%. The statistical significance yields a P = 0.0001. In the 621 patients with known HNP, the number who had more than one herniated disc was 236 (or 38%). In multiple reports in the literature, the incidence of reherniation after laminectomy and discectomy ranged from 5 to 37%.

CONCLUSIONS

The simplest hypothesis explaining all of the above is that intervertebral disc herniation is due to an acute or subacute increase of intradiscal pressure acting against a congenitally weak anulus fibrosus and posterior longitudinal ligament, and therefore laminectomy and discectomy, by further weakening these structures, may be counterproductive.

A short isoform of Col9a1 supports alveolar bone repair

Bone wound created in intramembranous alveolar bone heals without the formation of cartilage precursor tissue. However, the expression of cartilage collagen mRNAs has been suggested. In this report, we examined the expression and the potential role of type IX collagen in bone restoration and remodeling. The sequence specific polymerase chain reaction demonstrated the exclusive expression of short transcriptional isoform of alpha1(IX) collagen (Col9a1) in alveolar bone wound healing, while the long isoform of Col9a1 transcript was absent. Type IX collagen was immunolocalized in the preliminary matrix organized in granulation tissue before trabecular bone formation in tooth extraction socket. In Col9a1-null mutant mice, there were considerable variations in alveolar bone wound healing with the absence of or abnormally organized trabecular bone. Occasionally, unusual apposition of cortical-bone-like layers in bone marrow space was observed. The Col9a1-null mice indicated no growth retardation, and their facial and long bones maintained the normal size and shape. However, the primary spongiosa region of adult Col9a1 mutant mice showed an abnormal trabecular bone structure associated with abnormal immunostaining with the hypertrophic cartilage specific type X collagen antibody. These data suggest that type IX collagen short transcriptional variant is involved in the restoration and remodeling processes of trabecular bone.

Association between an aggrecan gene polymorphism and lumbar disc degeneration

STUDY DESIGN

A case-control study using magnetic resonance imaging findings and a polymerase chain reaction assay to investigate the association between aggrecan gene polymorphism and lumbar disc degeneration.

OBJECTIVE

To analyze whether the aggrecan gene polymorphism is related to lumbar disc disease in young women.

SUMMARY OF BACKGROUND DATA

It has been suggested that a genetic factor or familial predisposition contributes to the development of lumbar disc herniation. However, the precise genetic component related to disc disease remains unclear. Recently, a polymorphism has been identified in the region of the human aggrecan gene. The expressed variable numbers of tandem repeat polymorphism occur in the highly conserved repeat region.

METHODS

The participants were 64 young women with or without low back problems. Magnetic resonance imaging was used to evaluate the degeneration and herniation of the intervertebral disc. Genomic deoxyribonucleic acid was extracted from all participants. A polymerase chain reaction assay was carried out to detect the alleles of the aggrecan gene. The association of intervertebral disc degeneration and herniation with the distribution of the aggrecan gene alleles was analyzed.

RESULTS

Findings showed an overrepresentation of alleles with small numbers of repeats in subjects with multilevel disc degeneration, thus indicating a significant distribution difference. There also was a significant difference between the distribution of alleles and the severity of disc degeneration. No significant association was found between any of the alleles either in number or type of disc herniation.

CONCLUSIONS

The current study showed that multilevel and severe disc degeneration was present in the participants with shorter variable numbers of tandem repeat length of the aggrecan gene. This suggests that subjects with shorter variable numbers of tandem repeat length of the aggrecan gene have a risk of having multilevel disc degeneration develop at an early age.

Heritabilities of radiologic osteoarthritis in peripheral joints and of disc degeneration of the spine

OBJECTIVE

To estimate the genetic influence on the occurrence of radiologic osteoarthritis (ROA) in the knees, hips, and hands and disc degeneration of the spine in the general population.

METHODS

A random sample of 1,583 individuals was drawn to estimate the prevalence of ROA and disc degeneration in the general population. Of 118 probands with multiple affected joint sites who were derived from this sample, we were able to recruit 257 siblings. The variance of ROA and disc degeneration within sibling pairs was compared with the variance between sibling pairs. Heritability estimates for ROA in the knees, hips, and hands and for disc degeneration of the spine were calculated. OA was defined according to radiologic criteria, using the Kellgren/Lawrence grading system.

RESULTS

We observed that hand ROA and disc degeneration of the spine were statistically significantly more frequent in siblings than in the random sample, whereas the prevalence of knee and of hip ROA was similar and lower, respectively. Heritability estimates for hand ROA and disc degeneration were statistically significant, P = 0.56 (95% confidence interval [95% CI] 0.34-0.76) and P = 0.75 (95% CI 0.30-1.00), respectively. For knee and hip ROA, no evidence of a genetic effect in the general population was found. Finally, the heritability estimate for a score that summed the number of joints affected in the knees, hips, hands, and spine was 0.78 (95% CI 0.52-0.98). All heritability estimates were adjusted for age, sex, body mass index, and bone mineral density.

CONCLUSION

The present study shows that in the general population, there is a strong genetic effect for hand ROA and disc degeneration of the spine. The findings on the total number of joints affected at multiple sites suggest genetic susceptibility to generalized OA.

An allele of COL9A2 associated with intervertebral disc disease

Intervertebral disc disease is one of the most common musculoskeletal disorders. A number of environmental and anthropometric risk factors may contribute to it, and recent reports have suggested the importance of genetic factors as well. The COL9A2 gene, which codes for one of the polypeptide chains of collagen IX that is expressed in the intervertebral disc, was screened for sequence variations in individuals with intervertebral disc disease. The analysis identified a putative disease-causing sequence variation that converted a codon for glutamine to one for tryptophan in six out of the 157 individuals but in none of 174 controls. The tryptophan allele cosegregated with the disease phenotype in the four families studied, giving a lod score (logarithm of odds ratio) for linkage of 4.5, and subsequent linkage disequilibrium analysis conditional on linkage gave an additional lod score of 7.1.

Differences between the thermal stabilities of the three triple-helical domains of type IX collagen

Fibre-forming collagens in dilute solution show highly co-operative helix-coil transitions at temperatures that are remarkably close to the body temperature of the animal from which the collagen was extracted. This close correlation holds across animal Phyla and the transition temperatures, which range from 5 degrees C to 40 degrees C, are adjusted to suit by changing the primary structure, especially the concentration of the water-bridge-enhancing hydroxyproline residue. Fibril-forming collagens are thermally stabilised by fibrillogenesis, which causes a loss of random coil configurational entropy by intermolecular and intramolecular cross-linking and by spacial confinement of the molecule within the lattice of the fibre. But this mechanism cannot apply to the full length of the type IX collagen molecule, since its COL3 arm, according to current models, projects out from the stabilising influence of the type II fibre. In this paper we examine the thermal stability of the type IX collagen molecule and its three triple-helical domains, thereby demonstrating that the COL3 arm is much more stable than the rest of the molecule. At a scanning rate of 60 deg. C/h COL3 exhibited an unfolding endotherm with a tmax at 49.0 degrees C, well above body temperature. Corresponding peak maxima for COL1 and COL2 were seen at 40.6 degrees C and 39.6 degrees C, respectively. The sizes of the thermally labile units of COL1, COL2 and COL3, calculated from the measured activation enthalpies, were 24, 28 and 28 residues, respectively, much smaller than type I (65 residues) because of the relatively short lengths of triple helix to be unfolded. However, unlike type I collagen, no regions of the required size were found completely devoid of hydroxyproline. Consequently, the intrinsic stabilities of these thermally labile units were higher than that of type I with DeltaH updownarrow DeltaS updownarrow for COL1, COL2 and COL3 being, respectively, 385 K, 371 K and 384 K, contrasting with the much lower 349 K of type I collagen. We therefore speculate that the increased thermal stability of the thermally labile units was caused by the presence of the water-bridge-enhancing residue, hydroxyproline. Finally the stabilisation of type IX collagen tissue is considered and an alternative structural organisation of the type IX molecule on the type II fibre is proposed.