Epigenetic regulation in the etiopathology of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are vascular anomalies that occur almost exclusively in the central nervous system. They form mulberry-like vascular structures found in venous or capillary vessels where blood flow perfusion is low. CCMs are caused by biallelic loss of the CCM proteins CCM1/KRIT1, CCM2, or CCM3/PDCD10, which triggers a pathological signaling cascade involving mitogen-activated protein kinase (MAPK) kinase kinase 3 (MEKK3) and downstream Krüppel-like factor 2 (KLF2). However, our understanding of the downstream target genes activated by KLF2 remains limited, given that KLF2 is a mechanosensitive transcription factor activated by blood flow under normal physiological conditions. In this study, I identified Chromobox Protein Homolog 7 (CBX7), a component of the Polycomb Repressive Complex 1 involved in pathological CCM-KLF2 signaling in a zebrafish Ccm model. CBX7/cbx7a mRNA is highly upregulated in zebrafish Ccm-depleted tissues, which is later confirmed in lesions of CCM patients. Using CRISPR/Cas9-mediated mutagenesis, I demonstrated that cbx7a depletion (or knockout) suppresses Ccm phenotypes in zebrafish, notably in cardiac tissue and other major vessel beds. Subsequently, I examined the interaction between Cbx7a and Klf2 by combining various genetic tools that manipulate their expression levels, along with blood flow as a physiological factor. I found that Klf2 triggers Cbx7a expression, with further increases observed when blood flow is absent. Next, I performed transcriptomic analysis to identify pathways regulated by Cbx7a in CCM, revealing that angiogenesis and Wnt signaling pathways are among those upregulated in CCM and modulated by Cbx7a. Functional experiments later validated the roles of angiogenesis involving Angpt1-Tie1/2 signaling and Wnt signaling involving Wnt9b in CCM pathology. Additionally, I demonstrated that Cbx7a can be targeted pharmacologically via inhibitor treatments. Overall, my work discovers a novel factor that, together with KLF2, modulates pathogenic targets in CCM pathology and offers a promising therapeutic target to tackle the disease.