Plasma proteins and activated immune cells are known contributors of vascular brain disorders. However, the mechanisms and routes involved are still unclear. In order to understand the cross-talk between plasma proteins and the brain, we knocked down circulating C1 inhibitor (C1INH) in wild-type (WT) mice using antisense-oligonucleotide (ASO) technique and examined the brain. C1INH is a plasma protein inhibitor of vascular inflammation induced by activation of the kallikrein-kinin system (KKS) and the complement system. This knockdown induced the activation of the KKS but spared the activation of the classical complement system. Activation of the KKS induced an upregulation of the bradykinin pathway in the periphery and the brain, resulting in hypotension. Blood-brain barrier (BBB) permeability, plasma protein extravasations, activated glial cells and elevated levels of IL-1beta, IL-6, TNF-alpha, and iNOS were detected in brains of C1INH ASO treated mice. Infiltrating innate immune cells were evident, entering the brain through the lateral ventricle walls and the neurovascular units. The mice showed normal motor functions, however, cognition was impaired. Altogether, our results highlight the important role of regulated plasma-C1INH as a gatekeeper of the neurovascular system. Thus, manipulation of C1INH in neurovascular disorders might be therapeutically beneficial.

Knockdown of endogenous circulating C1 inhibitor induces neurovascular impairment, neuroinflammation and cognitive decline