gms | German Medical Science

Objective: Cerebral cavernous malformations can be detected in about 1 in 200 persons. The treatment of these low-flow neurovascular malformations is challenging when facing multiple lesions or localization in the brainstem. Studies revealed a disturbed morphology of the blood-brain-barrier in such lesions. In hereditary cases three responsible genes are known (CCM1, CCM2, CCM3). The aim of this study is to identify and functionally characterize signaling pathways between endothelial cells and pericytes, which are responsible for the disruption of the blood-brain-barrier and subsequent formation of cavernomas.

Method: CCM1-deficient human umbilical vein endothelial cells (HUVEC) were injected into immunodeficient mice together with Matrigel^® and VEGF. After four weeks plugs were removed and pericyte coverage of the newly formed blood vessels determined. 2.) Knock-down and overexpression of CCM1 in HUVEC was achieved by lentiviral transduction and RNA interference. After RNA isolation and cDNA synthesis relevant genes for endothelial cell-pericyte interactions were analyzed by qRT-PCR. 3.) Notch3, a pericyte-bound receptor for a ligand regulated by CCM1 in endothelial cells was manipulated in the same manner. Notch3-manipulated pericytes were functionally characterized in endothelial cell - pericyte coculture adhesion and migration assays.

Results: We could show that 1.) silencing of CCM1 in endothelial cells leads to decreased coverage with pericytes in vivo. 2.) At least one gene relevant for endothelial cell- pericyte interactions downstream of CCM1 in endothelial cells was identified. 3.) Notch3 expression in pericytes plays a relevant role for the interaction with endothelial cells.

Conclusions: CCM1 regulates the interaction between endothelial cells and pericytes. These cells, lying between endothelial cells and astrocytes, are essential for blood-brain-barrier homeostasis. Silencing CCM1 leads to decreased pericyte coverage. Genes regulated by CCM1 activate Notch3 in pericytes. Notch3-deficient pericytes show impaired adhesion and chemotaxis to endothelial cells in vitro. These experimental findings are in accordance with the pathological picture of cavernoma lesions and give novel molecular insights into their pathogenesis.