Pathological pericyte expansion and impaired endothelial cell-pericyte communication in endothelial Rbpj deficient brain arteriovenous malformation

Abstract

Pericytes, like vascular smooth muscle cells, are perivascular cells closely associated with blood vessels throughout the body. Pericytes are necessary for vascular development and homeostasis, with particularly critical roles in the brain, where they are involved in regulating cerebral blood flow and establishing the blood-brain barrier. A role for pericytes during neurovascular disease pathogenesis is less clear—while some studies associate decreased pericyte coverage with select neurovascular diseases, others suggest increased pericyte infiltration in response to hypoxia or traumatic brain injury. Here, we used an endothelial loss-of-function Recombination signal binding protein for immunoglobulin kappa J region (Rbpj)/Notch mediated mouse model of brain arteriovenous malformation (AVM) to investigate effects on pericytes during neurovascular disease pathogenesis. We tested the hypothesis that pericyte expansion, via morphological changes, and Platelet-derived growth factor B/Platelet-derived growth factor receptor β (Pdgf-B/Pdgfrβ)-dependent endothelial cell-pericyte communication are affected, during the pathogenesis of Rbpj mediated brain AVM in mice. Our data show that pericyte coverage of vascular endothelium expanded pathologically, to maintain coverage of vascular abnormalities in brain and retina, following endothelial deletion of Rbpj. In Rbpj-mutant brain, pericyte expansion was likely attributed to cytoplasmic process extension and not to increased pericyte proliferation. Despite expanding overall area of vessel coverage, pericytes from Rbpj-mutant brains showed decreased expression of Pdgfrβ, Neural (N)-cadherin, and cluster of differentiation (CD)146, as compared to controls, which likely affected Pdgf-B/Pdgfrβ-dependent communication and appositional associations between endothelial cells and pericytes in Rbpj-mutant brain microvessels. By contrast, and perhaps by compensatory mechanism, endothelial cells showed increased expression of N-cadherin. Our data identify cellular and molecular effects on brain pericytes, following endothelial deletion of Rbpj, and suggest pericytes as potential therapeutic targets for Rbpj/Notch related brain AVM.

Rbpj Deficiency Disrupts Vascular Remodeling via Abnormal Apelin and Cdc42 (Cell Division Cycle 42) Activity in Brain Arteriovenous Malformation

“…We first defined the timing of early postnatal bAVM initiation and progression. While Rbpj deletion was verified in brain tissues at P14, 6,16 and from isolated brain ECs at P7, 17 we wanted to identify a timepoint at which Rbpj was absent from ECs, but at which features of bAVM had not developed, to circumvent confounding effects of established pathologies. We bred Cdh5(PAC)-CreER T2 ; Rbpj flox/ WT (control) and Cdh5(PAC)-CreER T2 ; Rbpj flox/flox (Rbpj iΔEC mutant) mice and induced endothelial Rbpj deletion at P1 and P2.…”

Pericytes and vascular smooth muscle cells in central nervous system arteriovenous malformations

“…Because of the strong requirement for Notch signaling in endothelial cells to prevent the development of brain AVMs, changes in the mural cell compartment were frequently overseen or not documented in the different mutants described above. In another study of Rbpj deletion from endothelial cells, numerous Frontiers in Physiology frontiersin.org pericyte abnormalities were seen in brain and retina AVMs, including abnormal morphology and increased pericyte area with unchanged pericyte coverage of vessels (Selhorst et al, 2022). In this AVM model, pericytes expressed reduced levels of Pdgfrb, Cdh2, and Cd146 (Selhorst et al, 2022), suggesting that, in addition to preventing AVMs, endothelial Rbpj controls the expression of factors promoting pericyte recruitment and association with endothelial cells.…”

“…Research shows that brain AVMs affect vessel permeability and thus disrupt blood brain barrier (BBB) function (Hirunpattarasilp et al, 2019;Lendahl et al, 2019;Adhicary et al, 2023). Because brain capillaries (also known as microvessels) participate with other cell types as part of the neurovascular unit (NVU), it follows that brain AVMs lead to perturbed communication with other vascular cells (e.g., mural cells) and brain cells (e.g., astrocytes, neurons) (Winkler et al, 2022;Winkler et al, 2018;Chapman et al, 2022;Selhorst et al, 2022). Because NVU function is critical for brain homeostasis, including BBB integrity and neurovascular coupling, it is important to understand how NVU cells are affected during brain AVMs.…”

“…Pericytes have also been reported to have stem-like cell properties that allow them to retain their potency and differentiate into other cell types, depending on the physiological situation (Özen et al, 2014;Nakagomi et al, 2015;Brown et al, 2019;Farahani et al, 2019). Though the mechanisms that trigger pericyte transdifferentiation are not clear, a few CNS AVM models suggest that pathological changes in pericytes-molecular and morphological changes-trigger pericytes to acquire SMC characteristics, such as contractile properties (Diéguez-Hurtado et al, 2019;Selhorst et al, 2022) (Table 1).…”

“…However, these early studies did not document whether AVMs were arising in the brain. Additional work using mouse models to activate (Murphy et al, 2008;Murphy et al, 2012;Murphy et al, 2014;Nielsen et al, 2023) or suppress Notch signaling (Nielsen et al, 2014;Selhorst et al, 2022;Adhicary et al, 2023) in endothelial cells was essential to pinpoint the role of Notch in brain AVMs.…”