The long-term goals of this project are to gain insights into mechanisms by which extracellular matrix components contribute to assembly, maintenance and function of vascular and epithelial tissues. The work is focused on a component of basement membranes, the specialized structures that separate epithelial and endothelial cells from underlying connective tissues. This component, collagen XVIII, interacts with other basement membrane constituents and receptors on adjacent cells via one of its domains, endostatin. In humans, recessive mutations resulting in loss of collagen XVIII/endostatin cause Knobloch syndrome. Knobloch patients have abnormalities that include high myopia, vitreoretinal degeneration, retinal detachment and midline defects in bones of the skull;some patients have imaging abnormalities in the brain suggesting defects in neuronal migration. We have generated a mouse model of Knobloch syndrome and identified developmental and age dependent defects in eyes leading to dysfunction of retinal pigment epithelial cells and progressive loss of vision. Laser-induced choroidal neovascularization in mutant eyes is significantly enhanced compared to control eyes. Systemic administration of endostatin, normally released from collagen XVIII and circulating in blood, reduces the neovascularization response in mutant animals to that of controls;increasing endostatin levels in control animals also suppresses the response. A combination of cell biological, biochemical and genetic approaches are proposed to further study the mechanisms by which collagen XVIII supports the functions of epithelial and vascular endothelial cells. Molecular and functional changes in retinal pigment epithelial cells caused by loss of collagen XVIII will be characterized. Studies of mouse lines generated to restrict excision of the Col18a1 gene to retinal pigment epithelial or vascular endothelial cells will address the question of whether abnormalities in Knobloch patients and mice lacking collagen XVIII are caused by loss of collagen XVIII in eye tissues or are consequences of systemic effects. Experimental cell biological and genetic strategies will be used to determine by what process loss of collagen XVIII leads to accumulation of protein deposits behind the retina similar to what is seen in age- dependent macular degeneration. Genetic strategies will test hypotheses of how interactions between cell surface receptors and endostatin affect angiogenesis. The work is likely to generate not only new insights into mechanisms by which collagen XVIII/endostatin maintains retinal pigment epithelial function and a basis for therapeutic strategies for patients with Knobloch syndrome, it also will add significantly to broader efforts aimed at developing/refining anti-angiogenic therapies in diseases such as age dependent macular degeneration and cancer.
This research project examines the mechanisms by which collagen XVIII/endostatin supports the differentiated functions of epithelial cells and inhibits angiogenesis. The investigators have generated a mouse model of Knobloch syndrome, a genetic disorder of retinal degeneration and vision loss in childhood caused by mutations in collagen XVIII/endostatin. The results of the studies are likely to provide a basis for strategies to treat Knobloch syndrome, improve clinical management of age-dependent macular degeneration, and suppress angiogenesis-dependent disease processes such as cancer.
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