The role of Collagen COL22A1 in intracranial aneurysms and vascular stability

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Project Summary Intracranial aneurysms (IA) are berry- or balloon-like defects in the wall of a major intracranial artery and are present in 1-2% of the population. They commonly result in subarachnoid hemorrhage, which leads to death in 30-40% of the patients. There is currently no effective therapy to treat SAH and only limited treatment options to prevent IA rupture. Both environmental and genetic factors have been attributed to the aneurysm formation; however, the genetic factors and their underlying mechanisms are still largely unknown. We have identified mutations in collagen COL22A1 as potential contributors to the development of IAs in human patients. In the Familial Intracranial Aneurysm study, led by our collaborators, whole exome sequencing resulted in identification of a single nucleotide polymorphism (SNP) in a highly conserved region of COL22A1 present in only affected family members. However, biological function of COL22A1 is currently not known, and it is not clear if the identified mutation is causative of aneurysms in humans. We propose to use a zebrafish model to determine the function of COL22A1 in maintaining vascular integrity and to identify potential therapeutic strategies that would lead to the prevention of aneurysm formation and rupture. The protein sequence of COL22A1 is highly conserved between humans and zebrafish, and the zebrafish have emerged as a highly advantageous model system for in vivo analysis of vascular function and disease mechanisms. Our preliminary data indicate that COL22A1 zebrafish mutants display increased susceptibility to hemorrhages and show abnormal vascular dilations comparable to aneurysms in human patients, while inducible expression of the human mutant SNP results in increased frequency of hemorrhages in zebrafish embryos. We hypothesize that COL22A1 is involved in regulating vascular integrity and permeability and that mutations in COL22A1 cause intracranial aneurysms. The following specific aims are proposed: 1) Determine the functional role of COL22A1 in the maintenance of vascular stability; 2) Determine if mutations in COL22A1 cause intracranial aneurysms; 3) Perform a chemical screen to discover drug candidates that suppress hemorrhages in COL22A1 mutant embryos. Zebrafish COL22A1 mutant embryos and adults will be analyzed for morphological and functional defects. The human mutation will be modeled in zebrafish by creating a knock-in allele using a CRISPR / Cas9 mediated homology-directed repair and analyzing it for IA related phenotypes. A chemical library screen will be performed using zebrafish COL22A1 mutants to identify candidate drugs that may compensate for the deficiency in COL22A1 function. The proposed project will identify the biological function of COL22A1 homolog in vivo. It will further determine if mutations in COL22A1 cause IAs, and identify drug candidates that can be used for IA treatments. Understanding genetic causes of aneurysms will enable screening to identify patients at risk and will promote development of new treatments that can prevent devastating consequences of intracranial hemorrhages.