Ribozyme-mediated reduction of wild-type and mutant cartilage oligomeric matrix protein (COMP) mRNA and protein

Matrix in Medicine: Health Consequences of Mutant Cartilage Oligomeric Matrix Protein and its relationship to abnormal growth and to joint degeneration

Cartilage oligomeric matrix protein (COMP), an extracellular matrix protein, has been shown to enhance proliferation and mechanical integrity in the matrix, supporting functions of the growth plate and articular cartilage. Mutations in COMP cause pseudoachondroplasia (PSACH), a severe dwarfing condition associated with premature joint degeneration and significant lifelong joint pain. The MT (mutant)-COMP mouse mimics PSACH with decreased limb growth, early joint degeneration and pain. Ablation of endoplasmic reticulum stress CHOP signaling eliminated pain and prevented joint degeneration. The health effects of mutant COMP are discussed in relation to cellular/chondrocyte stress in the growth plate, articular cartilage and nearby tissues, and the implications for therapeutic approaches. There are many similarities between osteoarthritis and mutant-COMP protein-induced joint degeneration, suggesting that the relevance of findings in the joints may extend beyond PSACH to idiopathic primary OA.

Gene therapy for chondral and osteochondral regeneration: is the future now?

Gene therapy might represent a promising strategy for chondral and osteochondral defects repair by balancing the management of temporary joint mechanical incompetence with altered metabolic and inflammatory homeostasis. This review analysed preclinical and clinical studies on gene therapy for the repair of articular cartilage defects performed over the last 10 years, focussing on expression vectors (non-viral and viral), type of genes delivered and gene therapy procedures (direct or indirect). Plasmids (non-viral expression vectors) and adenovirus (viral vectors) were the most employed vectors in preclinical studies. Genes delivered encoded mainly for growth factors, followed by transcription factors, anti-inflammatory cytokines and, less frequently, by cell signalling proteins, matrix proteins and receptors. Direct injection of the expression vector was used less than indirect injection of cells, with or without scaffolds, transduced with genes of interest and then implanted into the lesion site. Clinical trials (phases I, II or III) on safety, biological activity, efficacy, toxicity or bio-distribution employed adenovirus viral vectors to deliver growth factors or anti-inflammatory cytokines, for the treatment of osteoarthritis or degenerative arthritis, and tumour necrosis factor receptor or interferon for the treatment of inflammatory arthritis.

Antisense Reduction of Mutant COMP Reduces Growth Plate Chondrocyte Pathology

Mutations in cartilage oligomeric matrix protein cause pseudoachondroplasia, a severe disproportionate short stature disorder. Mutant cartilage oligomeric matrix protein produces massive intracellular retention of cartilage oligomeric matrix protein, stimulating ER and oxidative stresses and inflammation, culminating in post-natal loss of growth plate chondrocytes, which compromises linear bone growth. Treatments for pseudoachondroplasia are limited because cartilage is relatively avascular and considered inaccessible. Here we report successful delivery and treatment using antisense oligonucleotide technology in our transgenic pseudoachondroplasia mouse model. We demonstrate delivery of human cartilage oligomeric matrix protein-specific antisense oligonucleotides to cartilage and reduction of cartilage oligomeric matrix protein expression, which largely alleviates pseudoachondroplasia growth plate chondrocyte pathology. One antisense oligonucleotide reduced steady-state levels of cartilage oligomeric matrix protein mRNA and dampened intracellular retention of mutant cartilage oligomeric matrix protein, leading to a reduction of inflammatory markers and cell death and partial restoration of proliferation. This novel and exciting work demonstrates that antisense-based therapy is a viable approach for treating pseudoachondroplasia and other human cartilage disorders.

The thrombospondins

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate cell-dependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.

Disorders of the growth plate

PURPOSE OF REVIEW

To summarize the recent advances in our understanding of the majors genes involved in chondrogenesis and their molecular mechanisms.

RECENT FINDINGS

Disorders of the growth plate and the resulting skeletal dysplasias are a consequence of defects in genes involved in various stages of the chondrocyte proliferation and differentiation process. Recent identification of disease genes has provided insights into the pathophysiology of many skeletal dysplasias.

SUMMARY

This knowledge enhances our understanding of the physiology and pathophysiology of the growth plate. Many skeletal dysplasias can now be characterized at the molecular level, allowing clinicians to provide accurate molecular diagnoses and counseling. Further research in this area will likely provide insights into possible therapeutic options for disorders of the growth plate.