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Cerebrovascular Smooth Muscle Cells as the Drivers of Intramural Periarterial Drainage of the Brain.

ABSTRACT: The human brain is the organ with the highest metabolic activity but it lacks a traditional lymphatic system responsible for clearing waste products. We have demonstrated that the basement membranes of cerebral capillaries and arteries represent the lymphatic pathways of the brain along which intramural periarterial drainage (IPAD) of soluble metabolites occurs. Failure of IPAD could explain the vascular deposition of the amyloid-beta protein as cerebral amyloid angiopathy (CAA), which is a key pathological feature of Alzheimer's disease. The underlying mechanisms of IPAD, including its motive force, have not been clarified, delaying successful therapies for CAA. Although arterial pulsations from the heart were initially considered to be the motive force for IPAD, they are not strong enough for efficient IPAD. This study aims to unravel the driving force for IPAD, by shifting the perspective of a heart-driven clearance of soluble metabolites from the brain to an intrinsic mechanism of cerebral arteries (e.g., vasomotion-driven IPAD). We test the hypothesis that the cerebrovascular smooth muscle cells, whose cycles of contraction and relaxation generate vasomotion, are the drivers of IPAD. A novel multiscale model of arteries, in which we treat the basement membrane as a fluid-filled poroelastic medium deformed by the contractile cerebrovascular smooth muscle cells, is used to test the hypothesis. The vasomotion-induced intramural flow rates suggest that vasomotion-driven IPAD is the only mechanism postulated to date capable of explaining the available experimental observations. The cerebrovascular smooth muscle cells could represent valuable drug targets for prevention and early interventions in CAA.

SUBMITTER: Aldea R

PROVIDER: S-EPMC6357927 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The senescence of vascular smooth muscle cells (VSMCs) has been implicated as a causal pro-inflammatory mechanism for cardiovascular disease development and progression of atherosclerosis, the instigator of ischemic heart disease. Contemporary limitations related to studying this cellular population and senescence-related therapeutics are caused by a lack of specific markers enabling their detection. Therefore, we aimed to profile a phenotypical and molecular signature of senescent VSMCs to allow reliable identification. To achieve this goal, we have compared non-senescent and senescent VSMCs from two in vitro models of senescence, replicative senescence (RS) and DNA-damage induced senescence (DS), by analyzing the expressions of established senescence markers: cell cycle inhibitors- p16 INK4a, p14 ARF, p21 and p53; pro-inflammatory factors-Interleukin 1β (IL-1β), IL-6 and high mobility group box-1 (HMGB-1); contractile proteins-smooth muscle heavy chain- (MYH11), smoothelin and transgelin (TAGLN), as well as structural features (nuclear morphology and LMNB1 (Lamin B1) expression). The different senescence-inducing modalities resulted in a lack of the proliferative activity. Nucleomegaly was seen in senescent VSMC as compared to freshly isolated VSMC Phenotypically, senescent VSMC appeared with a significantly larger cell size and polygonal, non-spindle-shaped cell morphology. In line with the supposed switch to a pro-inflammatory phenotype known as the senescence associated secretory phenotype (SASP), we found that both RS and DS upregulated IL-1β and released HMGB-1 from the nucleus, while RS also showed IL-6 upregulation. In regard to cell cycle-regulating molecules, we detected modestly increased p16 levels in both RS and DS, but largely inconsistent p21, p14ARF, and p53 expressions in senescent VSMCs. Since these classical markers of senescence showed insufficient deregulation to warrant senescent VSMC detection, we have conducted a non-biased proteomics and in silico analysis of RS VSMC demonstrating altered RNA biology as the central molecular feature of senescence in this cell type. Therefore, key proteins involved with RNA functionality, HMGB-1 release, LMNB-1 downregulation, in junction with nuclear enlargement, can be used as markers of VSMC senescence, enabling the detection of these pathogenic pro-inflammatory cells in future therapeutic studies in ischemic heart disease and atherosclerosis.

Project description:Background and Aims: Atherosclerosis, a major contributor to cardiovascular and cerebrovascular diseases, remains a leading cause of global mortality and morbidity. This study focuses on the role of chemokine-like receptor 1 (CMKLR1) in VSMCs and its potential impact on atherosclerotic plaque formation and remodelling. Methods: Cmklr1-/-Apoe-/- mice, generated using CRISPR/Cas9 technology, were fed a high-fat western diet for 16 weeks to model atherosclerosis. Primary VSMCs were isolated from Cmklr1-/- and Cmklr1+/+ mice for in vitro experiments. Cell viability, senescence-associated β-galactosidase staining, and RNA interference were performed to assess the effect of CMKLR1 deficiency on VSMCs. Various assays, including flow cytometry, immunocytochemistry, and RNA-seq analysis, were employed to investigate the molecular mechanisms and downstream signals associated with CMKLR1 deficiency. Results: CMKLR1 deficiency was found to disrupt the cell cycle, leading to VSMC senescence both in vitro and in vivo. Cmklr1-/-Apoe-/- mice exhibited increased atherosclerotic plaque burden, emphasizing the role of CMKLR1 in plaque stability. Transcriptome analysis revealed significant changes in cellular components and biological processes, with a particular impact on the extracellular matrix and cellular response to stimulus. The TGFβ signalling pathway emerged as a potential downstream target of CMKLR1, affecting VSMC differentiation, vessel development, and extracellular matrix synthesis. The deficiency of CMKLR1 led to a reduction in TGFβ1 expression and downstream molecule SM22α, influencing plaque composition and stability. Conclusion: This study demonstrates that CMKLR1 deficiency promotes VSMC senescence and exacerbates atherosclerosis. The disrupted TGFβ signalling pathway, identified as a potential molecular mechanism, provides insights into the complex regulatory network associated with CMKLR1 in atherosclerotic plaque formation and remodelling. These findings highlight the importance of CMKLR1 in atherosclerosis and its potential as a therapeutic target for plaque stability.

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Cerebrovascular Smooth Muscle Cells as the Drivers of Intramural Periarterial Drainage of the Brain.

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