Collagen Structure-Function Mapping Informs Applications for Regenerative Medicine.

Type I collagen, the predominant protein of vertebrates, assembles into fibrils that orchestrate the form and function of bone, tendon, skin, and other tissues. Collagen plays roles in hemostasis, wound healing, angiogenesis, and biomineralization, and its dysfunction contributes to fibrosis, atherosclerosis, cancer metastasis, and brittle bone disease. To elucidate the type I collagen structure-function relationship, we constructed a type I collagen fibril interactome, including its functional sites and disease-associated mutations.

Epiphyseal abnormalities, trabecular bone loss and articular chondrocyte hypertrophy develop in the long bones of postnatal Ext1-deficient mice.

Long bones are integral components of the limb skeleton. Recent studies have indicated that embryonic long bone development is altered by mutations in Ext genes and consequent heparan sulfate (HS) deficiency, possibly due to changes in activity and distribution of HS-binding/growth plate-associated signaling proteins. Here we asked whether Ext function is continuously required after birth to sustain growth plate function and long bone growth and organization.

Defective endochondral ossification-derived matrix and bone cells alter the lymphopoietic niche in collagen X mouse models.

Despite the appreciated interdependence of skeletal and hematopoietic development, the cell and matrix components of the hematopoietic niche remain to be fully defined. Utilizing mice with disrupted function of collagen X (ColX), a major hypertrophic cartilage matrix protein associated with endochondral ossification, our data identified a cytokine defect in trabecular bone cells at the chondro-osseous hematopoietic niche as a cause for aberrant B lymphopoiesis in these mice. Specifically, analysis of ColX transgenic and null mouse chondro-osseous regions via micro-computed tomography revealed an altered trabecular bone environment.

Altered matrix at the chondro-osseous junction leads to defects in lymphopoiesis.

The collagen X transgenic and null (ColX-Tg/KO) mice have revealed a link between endochondral ossification (EO) and hematopoiesis, and thus serve as model systems to study hematopoietic niches. The altered collagen X function in ColX-Tg/KO mice resulted not only in skeletal defects, which included changes in growth plate ultrastructure, altered localization of heparan sulfate proteoglycans (HSPG), and reduced trabecular bone, but also in hematopoietic defects, which included reduced B lymphocyte numbers throughout life without associated increases in B cell apoptosis. Consequently, the ColX-Tg/KO mice exhibited diminished in vitro and in vivo immune responses.

Congenic mice confirm that collagen X is required for proper hematopoietic development.

The link between endochondral skeletal development and hematopoiesis in the marrow was established in the collagen X transgenic (Tg) and null (KO) mice. Disrupted function of collagen X, a major hypertrophic cartilage matrix protein, resulted in skeletal and hematopoietic defects in endochondrally derived tissues. Manifestation of the disease phenotype was variable, ranging from perinatal lethality in a subset of mice, to altered lymphopoiesis and impaired immunity in the surviving mice.

Heparan sulfate proteoglycans: a GAGgle of skeletal-hematopoietic regulators.

This review summarizes our current understanding of the presence and function of heparan sulfate proteoglycans (HSPGs) in skeletal development and hematopoiesis. Although proteoglycans (PGs) comprise a large and diverse group of cell surface and matrix molecules, we chose to focus on HSPGs owing to their many proposed functions in skeletogenesis and hematopoiesis. Specifically, we discuss how HSPGs play predominant roles in establishing and regulating niches during skeleto-hematopoietic development by participating in distinct developmental processes such as patterning, compartmentalization, growth, differentiation, and maintenance of tissues.

Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.

Perlecan knock-in mice were developed to model Schwartz-Jampel syndrome (SJS), a skeletal disease resulting from decreased perlecan. Two mouse strains were generated: those carrying a C-to-Y mutation at residue 1532 and the neomycin cassette (C1532Yneo) and those harboring the mutation alone (C1532Y). Immunostaining, biochemistry, size measurements, skeletal studies and histology revealed Hspg2 transcriptional changes in C1532Yneo mice, leading to reduced perlecan secretion and a skeletal disease phenotype characteristic of SJS patients.

Chicken collagen X regulatory sequences restrict transgene expression to hypertrophic cartilage in mice.

Collagen X is produced by hypertrophic cartilage undergoing endochondral ossification. Transgenic mice expressing defective collagen X under the control of 4.7- or 1.

Linking hematopoiesis to endochondral skeletogenesis through analysis of mice transgenic for collagen X.

Each skeletal element where marrow develops is first defined by a hypertrophic cartilage blueprint. Through programmed tissue substitution, the cartilaginous skeletal model is replaced by trabecular bone and marrow, with accompanying longitudinal tissue growth. During this process of endochondral ossification, hypertrophic cartilage expresses a unique matrix molecule, collagen X.