A human COL2A1 gene with an Arg519Cys mutation causes osteochondrodysplasia in transgenic mice

Alterations in ECM signature underscore multiple sub-phenotypes of intervertebral disc degeneration

The intervertebral disc is a specialized connective tissue critical for absorption of mechanical loads and providing flexibility to the spinal column. The disc ECM is complex and plays a vital role in imparting tissue its biomechanical function. The central NP is primarily composed of large aggregating proteoglycans (PGs) while surrounding AF is composed of fibrillar collagens, I and II. Aggrecan and versican in particular, due to their high concentration of sulfated GAG chains form large aggregates with hyaluronic acid (HA) and provide water binding capacity to the disc. Degradation of aggrecan core protein due to aggrecanase and MMP activity, SNPs that affect number of chondroitin sulfate (CS) substitutions and alteration in enzymes critical in synthesis of CS chains can impair the aggrecan functionality. Similarly, levels of many matrix and matrix-related molecules e.g. Col2, Col9, HAS2, ccn2 are dysregulated during disc degeneration and genetic animal models have helped establish causative link between their expression and disc health. In the degenerating and herniated discs, increased levels of inflammatory cytokines such as TNF-α, IL-1β and IL-6 are shown to promote matrix degradation through regulating expression and activity of critical proteases and stimulate immune cell activation. Recent studies of different mouse strains have better elucidated the broader impact of spontaneous degeneration on disc matrix homeostasis. SM/J mice showed an increased cell apoptosis, loss of cell phenotype, and cleavage of aggrecan during early stages followed by tissue fibrosis evident by enrichment of several collagens, SLRPs and fibronectin. In summary, while disc degeneration encompasses wide spectrum of degenerative phenotypes extensive matrix degradation and remodeling underscores all of them.

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The intervertebral disc absorbs loads and provides flexibility to the spine.

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The ECM is complex and vital for imparting tissue its biomechanical function.

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Numerous types of proteoglycans and collagens designate the quality of the disc.

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Many matrix and matrix-related molecules are dysregulated during disc degeneration.

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Matrix degradation and remodeling underscores wide spectrum of phenotype.

Skeletal deterioration in COL2A1-related spondyloepiphyseal dysplasia occurs prior to osteoarthritis

OBJECTIVE

Spondyloepiphyseal dysplasia, a combination of progressive arthropathy with variable signs of skeletal dysplasia, can be a result of mutations in the collagen, type II, alpha 1 (COL2A1) gene. However, the bone involvement (e.g., density, microstructure) in this disorder has hitherto not been studied.

DESIGN

A 50-year-old female patient and her 8-year-old son with flattening of vertebral bodies and early-onset osteoarthritis were genetically tested using a custom designed gene bone panel including 386 genes. Bone microstructure and turnover were assessed using high-resolution peripheral quantitative computed tomography (HR-pQCT) and serum bone turnover markers, respectively. Furthermore, the bone and cartilage phenotype of male mice heterozygous for the loss-of-function mutation of Col2a1 (Col2a1^+/d) was analyzed compared to wildtype littermates using μ-CT and histomorphometry.

RESULTS

We identified a dominant COL2A1 mutation (c.620G > A p.(Gly207Glu)) indicating spondyloepiphyseal dysplasia in the female patient and her son, both being severely affected by skeletal deterioration. Although there was no osteoarthritis detectable at first visit, the son was affected by trabecular osteopenia, which progressed over time. In an iliac crest biopsy obtained from the mother, osteoclast indices were remarkably increased. Col2a1^+/d mice developed a moderate skeletal phenotype expressed by reduced cortical and trabecular parameters at 4 weeks. Importantly, no articular defects could be observed in the knee joints at 4 weeks, while osteoarthritis was only detectable in 12-week-old mice.

CONCLUSIONS

Our results indicate that collagen type II deficiency in spondyloepiphyseal dysplasia leads to skeletal deterioration with early-onset in humans and mice that occurs prior to the development of osteoarthritis.

A novel de novo mutation in COL2A1 leading to spondyloepiphyseal dysplasia congenita in a Chinese family

Spondyloepiphyseal dysplasia congenita (SEDC) is an extremely rare autosomal dominant chondrodysplasia that is usually caused by substitution of glycine with another amino acid in the triple helical region of COL2A1. Herein, we describe a case of SEDC in a Chinese family with a novel de novo mutation in the COL2A1 gene, c.1150G>A (p.Gly384Ser), which may impair protein stability and lead to dysfunction of type II collagen.

Multigenic Delineation of Lower Jaw Deformity in Triploid Atlantic Salmon (Salmo salar L.)

Lower jaw deformity (LJD) is a skeletal anomaly affecting farmed triploid Atlantic salmon (Salmo salar L.) which leads to considerable economic losses for industry and has animal welfare implications. The present study employed transcriptome analysis in parallel with real-time qPCR techniques to characterise for the first time the LJD condition in triploid Atlantic salmon juveniles using two independent sample sets: experimentally-sourced salmon (60 g) and commercially produced salmon (100 g). A total of eleven genes, some detected/identified through the transcriptome analysis (fbn2, gal and gphb5) and others previously determined to be related to skeletal physiology (alp, bmp4, col1a1, col2a1, fgf23, igf1, mmp13, ocn), were tested in the two independent sample sets. Gphb5, a recently discovered hormone, was significantly (P < 0.05) down-regulated in LJD affected fish in both sample sets, suggesting a possible hormonal involvement. In-situ hybridization detected gphb5 expression in oral epithelium, teeth and skin of the lower jaw. Col2a1 showed the same consistent significant (P < 0.05) down-regulation in LJD suggesting a possible cartilaginous impairment as a distinctive feature of the condition. Significant (P < 0.05) differential expression of other genes found in either one or the other sample set highlighted the possible effect of stage of development or condition progression on transcription and showed that anomalous bone development, likely driven by cartilage impairment, is more evident at larger fish sizes. The present study improved our understanding of LJD suggesting that a cartilage impairment likely underlies the condition and col2a1 may be a marker. In addition, the involvement of gphb5 urges further investigation of a hormonal role in LJD and skeletal physiology in general.

Molecular genetics of the COL2A1-related disorders

Type II collagen, comprised of three identical alpha-1(II) chains, is the major collagen synthesized by chondrocytes, and is found in articular cartilage, vitreous humour, inner ear and nucleus pulposus. Mutations in the collagen type II alpha-1 gene (COL2A1) have been reported to be responsible for a series of abnormalities, known as type II collagenopathies. To date, 16 definite disorders, inherited in an autosomal dominant or recessive pattern, have been described to be associated with the COL2A1 mutations, and at least 405 mutations ranging from point mutations to complex rearrangements have been reported, though the underlying pathogenesis remains unclear. Significant clinical heterogeneity has been reported in COL2A1-associated type II collagenopathies. In this review, we highlight current knowledge of known mutations in the COL2A1 gene for these disorders, as well as genetic animal models related to the COL2A1 gene, which may help us understand the nature of complex phenotypes and underlying pathogenesis of these conditions.

Extracellular matrix and developing growth plate

Growth plate is a specialized cartilaginous structure that mediates the longitudinal growth of skeletal bones. It consists of ordered zones of chondrocytes that secrete an extracellular matrix (ECM) composed of specific types of collagens and proteoglycans. Several heritable human skeletal dysplasias are caused by mutations in these ECM components and this review focuses on the roles of type II, IX, X, and XI collagens, aggrecan, matrilins, perlecan, and cartilage oligomeric matrix protein in the growth plate as deduced from human disease phenotypes and mouse models. Substantial advances have been achieved in deciphering the interaction networks and individual roles of these components in the construction of the growth plate ECM. Furthermore, ER stress and other cellular responses have been identified as key downstream effects of the ECM mutations contributing to abnormal growth plate development. The next challenge is to utilize the molecular level knowledge for the development of potential therapeutics.

Endoplasmic reticulum stress-unfolding protein response-apoptosis cascade causes chondrodysplasia in a col2a1 p.Gly1170Ser mutated mouse model

The collagen type II alpha 1 (COL2A1) mutation causes severe skeletal malformations, but the pathogenic mechanisms of how this occurs are unclear. To understand how this may happen, a col2a1 p.Gly1170Ser mutated mouse model was constructed and in homozygotes, the chondrodysplasia phenotype was observed. Misfolded procollagen was largely synthesized and retained in dilated endoplasmic reticulum and the endoplasmic reticulum stress (ERS)-unfolded protein response (UPR)-apoptosis cascade was activated. Apoptosis occurred prior to hypertrophy, prevented the formation of a hypertrophic zone, disrupted normal chondrogenic signaling pathways, and eventually caused chondrodysplasia. Heterozygotes had normal phenotypes and endoplasmic reticulum stress intensity was limited with no abnormal apoptosis detected. Our results suggest that earlier chondrocyte death was related to the ERS-UPR-apoptosis cascade and that this was the chief cause of chondrodysplaia. The col2a1 p.Gly1170Ser mutated mouse model offered a novel connection between misfolded collagen and skeletal malformation. Further investigation of this mouse mutant model can help us understand mechanisms of type II collagenopathies.

A mutation of the Col2a1 gene (G1170S) alters the transgenic murine phenotype and cartilage matrix homeostasis

BACKGROUND/PURPOSE

Genomic studies have revealed that there is a significant association between a point mutation of the human Col2A1 gene (G1170S) and several hip disorders. The purpose of the study was to explore the phenotype and altered cartilage matrix homeostasis of transgenic mice carrying this mutated Col2a1 gene.

METHODS

Wild-type and transgenic mice were used as the control and study groups, respectively. Body weight measurement, radiographic analysis, and histological analysis of the mice were carried out to describe differences between the wild-type and transgenic mice at different ages. Cartilage metabolism studies were also carried out, including an MTT assay of cellular proliferation and nitric oxide and glycosaminoglycan assays. Allelic expression levels of the mutant A allele and the normal G allele were established by TaqMan assay. Cytokine and protease gene expression were measured.

RESULTS

Transgenic mice had a lower mean body weight, a deformed skeletal structure, and abnormal cartilage histomorphology. Chondrocyte proliferation was significantly compromised and this was linked to significantly higher NO secretion and less soluble glycosaminoglycan formation. TNF-α and IL-1β gene expression was significantly upregulated, while MMP-13 gene expression was significantly downregulated.

CONCLUSION

The mutant G1170S Col2a1 gene in mice clearly alters the transgenic murine phenotype and cartilage matrix homeostasis.

Engineering of cartilage in recombinant human type II collagen gel in nude mouse model in vivo

OBJECTIVE

Our goal was to test the recombinant human type II collagen (rhCII) material as a gel-like scaffold for chondrocytes in a nude mouse model in vivo.

DESIGN

Isolated bovine chondrocytes (6x10(6)) were seeded into rhCII gels (rhCII-cell) and injected subcutaneously into the backs of nude mice. For comparison, chondrocytes (6x10(6)) in culture medium (Med-cell) and cell-free rhCII gels (rhCII-gel) were similarly injected (n=24 animals, total of three injections/animal). After 6 weeks, the tissue constructs were harvested and analyzed.

RESULTS

Chondrocytes with or without rhCII-gel produced white resilient tissue, which in histological sections had chondrocytes in lacunae-like structures. Extracellular matrix stained heavily with toluidine blue stain and had strongly positive collagen type II immunostaining. The tissue did not show any evidence of vascular invasion or mineralization. The cell-free rhCII-gel constructs showed no signs of cartilage tissue formation. Cartilage tissue produced by Med-cell was thin and macroscopically uneven, while the rhCII-cell construct was smooth and rounded piece of neotissue. RhCII-cell constructs were statistically thicker than Med-cell ones. However, no statistical differences were found between the groups in terms of glycosaminoglycan (GAG) content or biomechanical properties.

CONCLUSIONS

These results show that rhCII-gel provides good expansion and mechanical support for the formation of cartilage neotissue. RhCII material may allow favorable conditions in the repair of chondral lesions.

Injury-induced sequential transformation of notochordal nucleus pulposus to chondrogenic and fibrocartilaginous phenotype in the mouse

Intervertebral disc degeneration has been widely studied in different animal models. To test the hypothesis that needle puncture could induce progressive biochemical and molecular changes in murine discs, we established a mouse tail model to investigate the pathogenesis and molecular mechanism of puncture-induced disc degeneration. Caudal discs in mouse tails were punctured using a 31G gauge needle at controlled depth under microscopic guidance. The progress of the disc degeneration was evaluated by radiographic analysis of disc height, histological grading and glycosaminoglycan (GAG) quantification pre-operation and 1, 2, 6 and 12 weeks post-puncture. Gene and protein expression of the extracellular matrix (ECM) was analysed by RT-PCR, in situ hybridization and immunohistochemistry. Histological study and disc height analysis revealed progressive degenerative changes in the punctured discs. Compared with the pre-operation control group, total GAG content decreased 40% (p < 0.05) and aggrecan (Acan), decorin (Dcn) and versican (Vcan; Cspg2) expression was down-regulated at 12 weeks post-puncture. A transient increase of Col2a1-expressing cells and elevation of collagen II protein in the nucleus pulposus (NP) was detected. Fibronectin (Fn1) expression was up-regulated 50% and deposition of collagen I in NP was observed at 12 weeks post-puncture. This study is the first to use an injury-induced model to study disc degeneration in mouse. The disc degeneration involves a transient transformation of NP from notochordal to chondrogenic and eventually into fibrocartilaginous phenotype. The degenerative changes have some similarity to human disc degeneration, suggesting that this model may potentially be used in future to study the molecular mechanism and dissect the pathways of disc degeneration.

The retinoic acid binding protein CRABP2 is increased in murine models of degenerative joint disease

Introduction

Osteoarthritis (OA) is a debilitating disease with poorly defined aetiology. Multiple signals are involved in directing the formation of cartilage during development and the vitamin A derivatives, the retinoids, figure prominently in embryonic cartilage formation. In the present study, we examined the expression of a retinoid-regulated gene in murine models of OA.

Methods

Mild and moderate forms of an OA-like degenerative disease were created in the mouse stifle joint by meniscotibial transection (MTX) and partial meniscectomy (PMX), respectively. Joint histopathology was scored using an Osteoarthritis Research Society International (OARSI) system and gene expression (Col1a1, Col10a1, Sox9 and Crabp2) in individual joints was determined using TaqMan quantitative PCR on RNA from microdissected articular knee cartilage.

Results

For MTX, there was a significant increase in the joint score at 10 weeks (n = 4, p < 0.001) in comparison to sham surgeries. PMX surgery was slightly more severe and produced significant changes in joint score at six (n = 4, p < 0.01), eight (n = 4, p < 0.001) and 10 (n = 4, p < 0.001) weeks. The expression of Col1a1 was increased in both surgical models at two, four and six weeks post-surgery. In contrast, Col10a1 and Sox9 for the most part showed no significant difference in expression from two to six weeks post-surgery. Crabp2 expression is induced upon activation of the retinoid signalling pathway. At two weeks after surgery in the MTX and PMX animals, Crabp2 expression was increased about 18-fold and about 10-fold over the sham control, respectively. By 10 weeks, Crabp2 expression was increased about three-fold (n = 7, not significant) in the MTX animals and about five-fold (n = 7, p < 0.05) in the PMX animals in comparison to the contralateral control joint.

Conclusions

Together, these findings suggest that the retinoid signalling pathway is activated early in the osteoarthritic process and is sustained during the course of the disease.

Disturbed synthesis of type II collagen interferes with rate of bone formation and growth and increases bone resorption in transgenic mice

Transgenic mice carrying an internally deleted human type II collagen gene (COL2A1) were used to study bone growth and development. This mutation has previously been shown to disturb the development of collagen fibrils in articular cartilage, causing chondrodysplasia and osteoarthritis. Type II collagen expression in bones was investigated with immunohistochemistry. The development and mineralization of the skeleton and anthropometric measurements on bones were evaluated using X-rays and dynamic histomorphometry. Type II collagen was expressed in the cartilage of developing bones. The bones of transgenic mice were smaller compared with the controls. The bone mass remained almost unchanged in transgenic mice after 1 month of age, leading to differences of 47% in trabecular bone volume (P = 0.012) and 40% in trabecular thickness (P < 0.01) at the age of 3 months compared with controls. At the age of 3 months the eroded surface per bone volume was 31% greater in transgenic mice compared with controls (P < 0.05). Trabecular thickness correlated positively with body weight (R = 0.71, P < 0.001). Interestingly, body weight correlated with bone volume in control mice (R = 0.27, P < 0.01), but no correlation was observed in transgenic mice. The disturbed synthesis of cartilage-specific type II collagen in growing transgenic mice retarded bone development, increased bone resorption, and altered tissue properties. This led to a negative net bone balance and small bone size. The results support the idea that an altered synthesis of cartilage-specific molecule(s) can disturb postnatal bone development and growth.