Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS). Pathological studies of CNS tissue have shown that endothelial cell (ECs) inflammation, associated with focal breakdown of the blood-brain barrier (BBB) and neo-angiogenesis, is prevalent in demyelinating plaques in both human MS and the experimental autoimmune encephalitis (EAE) animal model. Neo-angiogenesis and BBB damage contribute to leakage of serum components, infiltration of immune cells into the CNS, neuroinflammation, axonal demyelination, neuronal dysfunction, and disease progression.
While the increase in vessel density has been documented for both MS and EAE lesions, the origin and pathways that drive neo-angiogenesis in EAE are poorly understood.
To address these questions, we performed single-cell RNA-sequencing of ECs isolated from spinal cords of acute and chronic MOG35-55 EAE in mice. Based on expression of blood vessel subtype-specific markers, we identified 13 distinct EC clusters with arterial, capillary, venous and venule identity for disease and control states. We performed differential gene expression, gene ontology and gene set enrichment analyses between control and disease EC clusters of the same subtype identity to identify which clusters have gene expression profiles consistent with neo-angiogenesis in EAE.
Finally, we examined the signaling pathways that may trigger pathogenic angiogenesis in EAE.
We found that molecular signatures of neo-angiogenesis are upregulated specifically in the venous ECs during the acute, and to a lesser extent chronic, EAE. RNA fluorescent in situ hybridization confirmed increased expression of two angiogenic tip cell markers, Egfl7 and Mcam, in the demyelinating white matter lesions acute and chronic EAE spinal cords relative to controls.
Finally, we examined the signaling pathways that may trigger pathogenic angiogenesis in EAE. Preliminary results demonstrate that, in contrast to developmental angiogenesis, TGF-β signaling may be the primary driver of neo-angiogenesis in EAE and may be a potential novel disease target.
While most current disease-modifying MS therapies aim to reduce both inflammation and infiltration of immune cells into the CNS, our findings may lead to development of novel therapeutics that reduce pathogenic neo-angiogenesis and improve long-term neurological deficits in MS.