Background:

Increase of collagen I (COL I)/COL III ratio enhances vessel wall stiffness and renders vessels less resistant to blood flow and pressure changes. We hypothesized that COL I/COL III ratio is increased in the brain arteriovenous malformations (bAVMs), which is associated with bAVM hemorrhage.

Method:

Surgically resected human bAVM samples and mouse bAVMs induced in three transgenic mouse lines with activin receptor-like kinase 1 or endoglin deletion in the endothelial cells or in the brain focally. Colony-stimulating factor receptor inhibitor was used to transiently deplete microglia. COL I and COL III levels, hemorrhage, and gene expression in bAVMs were analyzed.

Results:

The COL I and COL III levels and the COL I/COL III ratio were higher on human and mouse bAVMs than controls, which was associated with bAVM hemorrhage. Col I and Col III mRNAs were also increased in mouse bAVMs. The degree of microhemorrhage in mouse bAVMs was positively correlated with Col I/Col III ratios. Transient depletion of microglia reduced Col I/Col III ratio and microhemorrhage in mouse bAVMs.

Conclusion:

COL I/COL III ratio are increased in bAVM vessels, which is associated with bAVM hemorrhage. Depletion of microglia reduces Col I/Col III ratio and hemorrhage in mice bAVMs.