Perivascular fibroblasts, vascular fibrosis, and their contributions to cerebral amyloid angiopathy

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Project summary Cerebral amyloid angiopathy (CAA) is a disease that occurs when amyloid beta (Aβ) forms deposits on brain blood vessels. CAA frequently co-occurs with Alzheimer’s disease (AD) and is a significant risk factor for intracranial hemorrhage and dementia. There are no approved treatments for CAA, and the molecular etiology of the disease remains unclear, which has prevented the development of effective therapeutic interventions. Here, we propose to study cerebral perivascular fibroblasts and vascular fibrosis signaling pathways as potential contributors to CAA pathology. More than 20 years ago, pioneering work showed that astrocyte-specific upregulation of transforming growth factor beta 1 (TGFβ1), a master regulator of tissue fibrosis, could specifically induce Aβ pathology in the cerebrovasculature that was reminiscent of CAA. However, the mechanistic actions of TGFβ1 that could drive such a response were never elucidated. In studying postmortem human brain tissue from CAA patients, we have found that cerebral perivascular fibroblasts acquire myofibroblast markers around vessels with Aβ deposition and fibrotic signatures—this phenotype is observed specifically in CAA but not AD or age-matched controls. Further, this phenotype is replicated in 5xFAD mice after intracerebroventricular injections of human vascular-derived human Aβ seeds, which yields CAA-like pathology. Hence, we hypothesize that activation of perivascular fibroblasts and fibrotic signaling pathways in the perivascular niche leads to Aβ deposition, vascular fibrosis, and acquisition of the CAA phenotype. In Aim 1, we will explore this hypothesis within two complementary mouse models using three-dimensional tissue imaging techniques, single-cell RNA sequencing, and blood flow measurements. In Aim 2, we will leverage a novel bioengineered model of human cerebral arterioles to understand how TGFβ1 shapes the fibrotic microenvironment through multicellular crosstalk. In Aim 3, again in mouse models, we will target cerebral perivascular fibroblasts and fibrotic signaling pathways using gene silencing techniques and small molecule treatments and determine if CAA pathology is lessened. Collectively, these studies will unveil and characterize how perivascular fibroblasts and vascular fibrosis contribute to CAA pathology. Moreover, these investigations will identify potential preclinical drug development strategies focused on targeting fibroblast activation and signaling pathways that contribute to a pro- fibrotic microenvironment in CAA.