Intracranial Aneurysm-Associated COL22A1 Variants Impair Cerebrovascular Structure and Barrier Integrity in Zebrafish.

Intracranial aneurysms (IAs) represent a major clinical concern due to their risk of rupture and the resulting morbidity and mortality. Both environmental and genetic factors contribute to IA susceptibility, yet the genetic causes of IA remain poorly understood. We previously identified several single nucleotide variants (SNVs) in collagen XXII (COL22A1) in affected individuals with IA. However, the functional impact of these variants has not been determined, and it remains unclear whether and how they increase IA susceptibility. Here, we tested the functional effect of these variants in a zebrafish embryo model. Inducible overexpression of six human COL22A1 SNVs increased the incidence of cranial hemorrhage in zebrafish embryos, while overexpression of wild-type COL22A1 had no significant effect. Overexpression of DNA construct encoding COL22A1 P989L variant disrupted intracranial vascular architecture, leading to reduced vessel length, altered vascular surface parameters, and abnormal arterial patterning. Overexpression of the P989L SNV also caused pronounced vascular leakage, reduced pericyte number, and decreased expression of the tight junction proteins Claudin-5 and ZO-1. P989L SNV overexpression was also associated with increased expression of the endoplasmic reticulum stress marker hspa5. In silico modeling suggested that the P989L variant likely perturbs triple-helix formation in COL22A1, thereby causing protein misfolding and compromising its function. Together, these findings demonstrate the deleterious effects of IA-associated COL22A1 variants on vascular function and stability and suggest that these variants may increase the incidence of IA in humans.