Beyond endothelial cells:Neurovascular dysfunction and cellular heterogeneity in cerebral cavernous malformations

Maintaining blood vessel integrity is an active process, necessary for their proper functioning and adaptation to changing conditions. Aberrations in any of these vascular processes results in consequences exemplified in cerebral cavernous malformation (CCM). Patients with this neurovascular disease can experience neurological symptoms and hemorrhages; with surgical resection as the main treatment. The exact mechanisms through which lesions form and progress are not fully understood. This thesis aimed to elucidate novel mechanisms in the initiation and progression of CCM. In paper I, the molecular mechanisms underlying hemostasis in CCM were studied. We showed that hemostasis is dysregulated in murine and human CCM, leading to clot formation and hypoxia. Additionally, we observed that CCM lesions simultaneously express pro and anticoagulant proteins. However, we observed heterogeneity in the vascular expression of these pro and anticoagulant proteins which may potentially affect response to therapies. Paper II focused on inflammation in CCM, where we demonstrated that a chronic inflammatory microenvironment exists in CCM. We also showed that neutrophils produced neutrophil extracellular traps (NETs) in human and murine CCM, and contribute negatively to CCM pathogenesis. Paper III focused on the therapeutic inhibition of NETs in murine CCM using Cl-amidine. We found that NETs contribute to coagulation, endothelial dysfunction and neuroinflammation in CCM. Additionally, we observed activation of fibroblasts and microglia cells which promoted CCM pathogenesis. In Paper IV, we presented a novel proteomic approach for human CCMs, which allowed high-throughput protein screening. Our studies showed a dysregulation of the neurovascular unit’s components in CCM. Additionally, we report CCM-relevant brain proteins, which can serve as disease biomarkers. In Paper V, we present a proof-of-concept approach using CCM paraffin-embedded biopsy samples for transcriptomic analysis. Using spatial transcriptomics, we elucidated thrombomodulin heterogeneity in CCM lesions. Collectively, our studies demonstrate that immunothrombosis and neuroinflammation occur in CCM and that CCM pathogenesis goes beyond endothelial dysfunction, affecting other cells of the neurovascular unit. Furthermore, we highlight vascular heterogeneity in CCM and its implications for CCM therapy development. Our studies have increased the understanding of CCM pathogenesis and offer potential pathways that can be targeted for treatment in CCM patients.