Type IX collagen is crucial for normal hearing.

cDNA microarray analysis indicated that COL9A1 and COL9A3 are highly expressed in the human inner ear, suggesting that type IX collagen has a crucial functional role in the inner ear. This study further confirmed, by means of real-time PCR, the presence of collagen type IX genes in the mouse inner ear. Immunocytochemical analysis also revealed that type IX collagen is distributed in the tectorial membrane, where it co-localizes with type II collagen, indicating that type IX collagen may contribute to the three-dimensional integrated structure of type II collagen molecules. Mice with targeted disruption of the col9a1 gene were shown through assessment by auditory brain stem response to have hearing loss, suggesting an important role of type IX collagen in maintaining normal hearing. At the light microscopic level, the tectorial membrane of knock-out mice was found to be abnormal in shape, and electron microscopy confirmed disturbance of organization of the collagen fibrils. An antibody against type II collagen failed to detect type II collagen in the tectorial membrane of type IX collagen knock-out mice, suggesting that a lack of type IX collagen may affect the three-dimensional structure of type II collagen molecules. These findings indicate that genes encoding each chain of type IX collagen may fulfill an important function associated with the tectorial membrane in the auditory system.

Transfer of proalpha2(I) cDNA into cells of a murine model of human Osteogenesis Imperfecta restores synthesis of type I collagen comprised of alpha1(I) and alpha2(I) heterotrimers in vitro and in vivo.

The oim mouse is a model of human Osteogenesis Imperfecta (OI) that has deficient synthesis of proalpha2(I) chains. Cells isolated from oim mice synthesize alpha1(I) collagen homotrimers that accumulate in tissues. To explore the feasibility of gene therapy for OI, a murine proalpha2(I) cDNA was inserted into an adenovirus vector and transferred into bone marrow stromal cells isolated from oim mice femurs. The murine cDNA under the control of the cytomegalovirus early promoter was expressed by the transduced cells. Analysis of the collagens synthesized by the transduced cells demonstrated that the cells synthesized stable type I collagen comprised of alpha1(I) and alpha2(I) heterotrimers in the correct ratio of 2:1. The collagen was efficiently secreted and also the cells retained the osteogenic potential as indicated by the expression of alkaline phosphatase activity when the transduced cells were treated with recombinant human bone morphogenetic protein 2. Injection of the virus carrying the murine proalpha2(I) cDNA into oim skin demonstrated synthesis of type I collagen comprised of alpha1 and alpha2 chains at the injection site. These preliminary data demonstrate that collagen genes can be transferred into bone marrow stromal cells as well as fibroblasts in vivo and that the genes are efficiently expressed. These data encourage further studies in gene replacement for some forms of OI and use of bone marrow stromal cells as vehicles to deliver therapeutic genes to bone.

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.

High levels of expression of full length human pro-alpha 2(V) collagen cDNA in pro-alpha 2(V)-deficient hamster cells.

A full length cDNA encoding human pro-alpha 2(V) collagen was constructed. Partial sequencing of the cDNA and primer extension analysis of mRNA from fibroblasts found that pro-alpha 2(V) mRNA differs from the mRNAs of other fibrillar collagens in the increased length of its 5'-untranslated region. The pro-alpha 2(V) cDNA was placed downstream of the human cytomegalovirus immediate early promoter/regulatory sequences for expression studies in cultured Chinese hamster lung cells. These cells have been shown previously to synthesize large quantities of pro-alpha 1(V) homotrimers as their only collagenous product. Transfection resulted in a number of clonal cell lines that express human alpha 2(V) RNA at levels comparable to, and in some cases greater than, levels found in normal human skin fibroblasts. Pro-alpha 2(V) chains produced in the majority of clonal lines were of sufficient quantity to complex all available endogenous pro-alpha 1(V) chains. Chimeric heterotrimers, composed of hamster alpha 1(V) and human alpha 2(V) chains in a 2:1 ratio, were stable to pepsin digestion and were found predominantly associated with the cell layer. Surprisingly, pro-alpha 2(V) chains, in excess to pro-alpha 1(V) chains, were found in the extracellular matrix and, in much greater abundance, in media. These chains were pepsin sensitive, indicating that pro-alpha 2(V) chains can be secreted as nonstable homotrimers or as free chains.

Ehlers-Danlos syndrome. A variant characterized by the deficiency of pro alpha 2 chain of type I procollagen.

The clinical findings and biochemical studies are described for a 30-year-old man with Ehlers-Danlos syndrome. Type analysis of collagen produced by cultured fibroblasts revealed the lack of a detectable pro alpha 2 chain of type I procollagen. The intracellular degradation rate of newly synthesized collagen was higher than that of normal cells, resulting in the reduction of net collagen production. Clinical manifestations characterized by cardiovascular abnormalities due to decreased collagen deposition in the aortic valve and the wall of aorta, hypermobility of the joints, and hyperextensibility of the skin in this patient may be closely related to the observations described above.

Spontaneous coronary artery dissection: case report and evidence for a defect in collagen metabolism.

Spontaneous coronary artery dissection is a rare disease with a higher prevalence in women, especially in the post-partum state. In one case, we attempted to relate this pathology to a disorder in collagen metabolism. A 32-year-old woman presented two episodes of myocardial infarction, 2 and 4 months after delivery which were shown to be due to two consecutive coronary artery dissections on coronary angiogram. Collagen metabolism was investigated in skin fibroblast cultures derived from the patient, and in control fibroblast cultures. After protein labelling in culture, total protein and collagen synthesis were determined. Quantification of procollagen synthesized in cell cultures and their rate of conversion into collagen were determined both in the culture media and a cell layer extract by DEAE cellulose chromatography. The results showed a reduced total collagen synthesis in the cultures of the patient in comparison with control cultures. The ratio between type I and III procollagen was not altered. The rate of conversion of procollagen into collagen was higher in the pathological cultures than in control cultures. Impaired collagen synthesis due perhaps to a change in hormonal equilibrium in the post-partum state might therefore have been responsible for coronary artery dissection.

The clinical features of homozygous alpha 2(I) collagen deficient osteogenesis imperfecta.

The detailed clinical features and progress of a child with homozygous alpha 2(I) collagen deficiency are described. Clinically, the disease presents as severe progressive Sillence type III osteogenesis imperfecta. The main biochemical defect is the synthesis of an abnormal pro alpha 2(I) chain which does not associate with pro alpha 1(I) chains and therefore is not incorporated into triple helical trimers of type I procollagen which can be used to assemble collagen fibres.