Project description:Atherosclerosis, which develops in the inner layer of arteries, is the major cause of myocardial infarction and stroke. Atherosclerotic plaques develop preferentially in arterial regions exposed to disturbed blood flow, such as vessel curvatures, bifurcations and branching points, where endothelial cells develop an inflammatory phenotype. How disturbed flow induces endothelial cell inflammation is incompletely understood. We show here that histone H3.3 phosphorylation at serine 31 (H3.3S31) plays a critical role in disturbed flow-induced endothelial inflammation, as it allows the rapid induction of FOS and FOSB, which are required for disturbed flow-induced inflammatory gene expression. We identified protein kinase N1 (PKN1) as the kinase responsible for disturbed flow-induced H3.3S31 phosphorylation. PKN1 becomes activated by disturbed flow in an integrin a5b1-dependent manner and then translocates to the cell nucleus. We found that PKN1 is also involved in the phosphorylation of the AP-1 transcription factor JUN. Mice with endothelium-specific loss of PKN1 or endothelial expression of S31 phosphorylation-deficient mutants of H.3.3 show reduced endothelial inflammation and disturbed flow-induced vascular remodeling in vitro and in vivo. Our data identify a novel mechanism of H3.3S31 phosphorylation which may serve as a target for preventive and therapeutic anti-atherosclerotic strategies.
Project description:Atherosclerosis, which develops in the inner layer of arteries, is the major cause of myocardial infarction and stroke. Atherosclerotic plaques develop preferentially in arterial regions exposed to disturbed blood flow, such as vessel curvatures, bifurcations and branching points, where endothelial cells develop an inflammatory phenotype. How disturbed flow induces endothelial cell inflammation is incompletely understood. We show here that histone H3.3 phosphorylation at serine 31 (H3.3S31) plays a critical role in disturbed flow-induced endothelial inflammation, as it allows the rapid induction of FOS and FOSB, which are required for disturbed flow-induced inflammatory gene expression. We identified protein kinase N1 (PKN1) as the kinase responsible for disturbed flow-induced H3.3S31 phosphorylation. PKN1 becomes activated by disturbed flow in an integrin a5b1-dependent manner and then translocates to the cell nucleus. We found that PKN1 is also involved in the phosphorylation of the AP-1 transcription factor JUN. Mice with endothelium-specific loss of PKN1 or endothelial expression of S31 phosphorylation-deficient mutants of H.3.3 show reduced endothelial inflammation and disturbed flow-induced vascular remodeling in vitro and in vivo. Our data identify a novel mechanism of H3.3S31 phosphorylation which may serve as a target for preventive and therapeutic anti-atherosclerotic strategies.
Project description:Atherosclerosis, which develops in the inner layer of arteries, is the major cause of myocardial infarction and stroke. Atherosclerotic plaques develop preferentially in arterial regions exposed to disturbed blood flow, such as vessel curvatures, bifurcations and branching points, where endothelial cells develop an inflammatory phenotype. How disturbed flow induces endothelial cell inflammation is incompletely understood. We show here that histone H3.3 phosphorylation at serine 31 (H3.3S31) plays a critical role in disturbed flow-induced endothelial inflammation, as it allows the rapid induction of FOS and FOSB, which are required for disturbed flow-induced inflammatory gene expression. We identified protein kinase N1 (PKN1) as the kinase responsible for disturbed flow-induced H3.3S31 phosphorylation. PKN1 becomes activated by disturbed flow in an integrin a5b1-dependent manner and then translocates to the cell nucleus. We found that PKN1 is also involved in the phosphorylation of the AP-1 transcription factor JUN. Mice with endothelium-specific loss of PKN1 or endothelial expression of S31 phosphorylation-deficient mutants of H.3.3 show reduced endothelial inflammation and disturbed flow-induced vascular remodeling in vitro and in vivo. Our data identify a novel mechanism of H3.3S31 phosphorylation which may serve as a target for preventive and therapeutic anti-atherosclerotic strategies.
Project description:Exposure of the arterial endothelium to low and disturbed flow is a risk factor for the erosion and rupture of atherosclerotic plaques and aneurysms. Circulating and locally produced proteins are known to contribute to an altered matrix composition at the site of lesions, and to contribute to inflammatory processes within the lesions by altering the sub-endothelial matrix. We have previously shown that immune-cell regulated alternative splicing of Fibronectin (FN) protects against flow-induced hemorrhage. Here, we perform quantitative proteomic analysis of enriched extracellular matrix preparations from murine carotid arteries exposed to low and disturbed flow in vivo and examine serum derived and endothelial cell contributions to the sub-endothelial matrix in vitro. Our results reveal the extent of the dynamic alterations in extracellular matrix composition in the acute response to low and disturbed flow, and show how changes in the splicing of FN, a common response in vascular inflammation and remodeling, affects matrix composition.
Project description:Objective The vessel wall is continuously exposed to hemodynamic forces generated by blood flow. Endothelial mechanosensors perceive and translate mechanical signals via cellular signaling pathways into biological processes that control endothelial development, phenotype and function. Here, we aim to unravel the molecular mechanisms underlying endothelial mechanosensing. Approach and results We applied a quantitative mass spectrometry approach combined with cell surface chemical footprinting to assess the hemodynamic effects on the endothelium on a system-wide level. These studies revealed that of the >5000 quantified proteins 104 were altered, which were highly enriched for extracellular matrix proteins and proteins involved in cell-matrix adhesion. Cell surface proteomics furthermore indicated that LAMA4 was proteolytically processed upon flow-exposure, which corresponded to the decreased LAMA4 mass observed on immunoblot. Immunofluorescence microscopy studies highlighted that the endothelial basement membrane was drastically remodeled upon flow exposure. We observed a network-like pattern of LAMA4 and LAMA5, which corresponded to the localization of laminin-adhesion molecules ITGA6 and ITGB4. Furthermore, the adaptation to flow-exposure did not affect the inflammatory response to tumor necrosis factor α, indicating that inflammation and flow trigger fundamentally distinct endothelial signaling pathways with limited reciprocity and synergy. Conclusions Taken together, this study uncovers the blood flow-induced remodeling of the basement membrane and stresses the importance of the subendothelial basement membrane in vascular homeostasis.
Project description:While much progress has been made in identifying the mechanisms that trigger endothelial activation and inflammatory cell recruitment during atherosclerosis, less is known about the intrinsic pathways that counteract these events. Here we identified NOTCH1 as an antagonist of endothelial cell activation. NOTCH1 was constitutively expressed by adult arterial endothelium, but levels were significantly reduced by high fat diet. Furthermore, treatment of human aortic endothelial cells (HAEC) with inflammatory lipids (Ox-PAPC) and pro-inflammatory cytokines (TNFalpha and IL1beta) decreased Notch1 expression and signaling in vitro through a mechanism that requires STAT3 activation. Reduction of NOTCH1 in HAEC by siRNA, in the absence of inflammatory lipids or cytokines, increased inflammatory molecules and binding of monocytes. Conversely, some of the effects mediated by Ox-PAPC were reversed by increased NOTCH1 signaling; suggesting a link between lipid-mediated inflammation and Notch1. Interestingly, reduction of NOTCH1 by Ox-PAPC in HAEC was associated with a genetic variant previously correlated to HDL in a human GWAS. Finally endothelial Notch1 heterozygous mice showed higher diet-induced atherosclerosis. Based on these findings, we propose that reduction of endothelial NOTCH1 is a predisposing factor in the onset of vascular inflammation and initiation of atherosclerosis. Transcript profile from Human Aortic Endothelial Cells (HAEC) transfected with siRNA targeting NOTCH1 (n=3) or treated with Ox-PAPC (Oxidized 1-Palmitoyl-2-Arachidonoyl-sn-glycero-3-PhosphoCholine) for 6 hours (n=3) were compared to control HAEC (transfected with control siRNA and control media; n=3).
Project description:Atherosclerosis preferentially occurs in arterial regions of disturbed blood flow (d-flow), which alters gene expression, endothelial function, and atherosclerosis. Here, we show that d-flow regulates genome-wide DNA methylation patterns in a DNA methyltransferase (DNMT)-dependent manner. D-flow induced expression of DNMT1 in mouse arterial endothelium in vivo and in cultured endothelial cells by oscillatory shear (OS) in vitro. The DNMT inhibitor 5-Aza-2’deoxycytidine (5Aza) or DNMT1 siRNA significantly reduced OS-induced endothelial inflammation. Moreover, 5Aza reduced lesion formation in two ApoE-/- mouse atherosclerosis models. To identify the 5Aza mechanisms, we conducted two genome-wide studies: reduced representation bisulfite sequencing (RRBS) and microarray using endothelial-enriched gDNA and RNA, respectively, from the partially-ligated left carotid artery (LCA exposed to d-flow) and the right contralateral control (RCA) of mice treated with 5Aza or vehicle. Systems biological analyses using RRBS and transcriptome data revealed 11 mechanosensitive genes whose promoters were hypermethylated under d-flow conditions, but rescued by 5Aza treatment. Of those, the two transcription factors HoxA5 and Klf3 contain cAMP- response-elements, and their methylation status could serve as a mechanosensitive master switch in gene expression. Our results demonstrate that d-flow controls epigenomic DNA methylation patterns in a DNMT-dependent manner, which in turn alters endothelial gene expression and induces atherosclerosis.
Project description:Atherosclerosis preferentially occurs in arterial regions of disturbed blood flow (d-flow), which alters gene expression, endothelial function, and atherosclerosis. Here, we show that d-flow regulates genome-wide DNA methylation patterns in a DNA methyltransferase (DNMT)-dependent manner. D-flow induced expression of DNMT1 in mouse arterial endothelium in vivo and in cultured endothelial cells by oscillatory shear (OS) in vitro. The DNMT inhibitor 5-Aza-2’deoxycytidine (5Aza) or DNMT1 siRNA significantly reduced OS-induced endothelial inflammation. Moreover, 5Aza reduced lesion formation in two ApoE-/- mouse atherosclerosis models. To identify the 5Aza mechanisms, we conducted two genome-wide studies: reduced representation bisulfite sequencing (RRBS) and microarray using endothelial-enriched gDNA and RNA, respectively, from the partially-ligated left carotid artery (LCA exposed to d-flow) and the right contralateral control (RCA) of mice treated with 5Aza or vehicle. Systems biological analyses using RRBS and transcriptome data revealed 11 mechanosensitive genes whose promoters were hypermethylated under d-flow conditions, but rescued by 5Aza treatment. Of those, the two transcription factors HoxA5 and Klf3 contain cAMP- response-elements, and their methylation status could serve as a mechanosensitive master switch in gene expression. Our results demonstrate that d-flow controls epigenomic DNA methylation patterns in a DNMT-dependent manner, which in turn alters endothelial gene expression and induces atherosclerosis. We used 6- to 8-week-old male C57Bl/6 mice (The Jackson Laboratory) according to the approved Institutional Animal Care and Use Committee protocol by Emory University. Mice were subjected to partial carotid ligation surgery under anesthesia. Briefly, 3 of 4 caudal branches of LCA (left external carotid, internal carotid, and occipital artery) were ligated with 6-0 silk suture, although the superior thyroid artery was left intact. Development of low and oscillatory blood flow in the Left Carotid Artery of each mouse was determined by ultrasound measurements. Each sample contained total RNA from 3 pooled RCAs or LCAs. We ran 3 samples of LCA, RCA, AzaLCA, and AzaRCA on 2 microarrays.
Project description:Low and disturbed blood flow drives the progression of arterial diseases including atherosclerosis and aneurysms. The endothelial response to flow and its interactions with recruited platelets and leukocytes determine disease progression. Here, we report widespread changes in alternative splicing of pre-mRNA in the flow-activated murine arterial endothelium in vivo. Alternative splicing was suppressed by depletion of platelets and macrophages recruited to the arterial endothelium under low and disturbed flow. Binding motifs for the Rbfox-family are enriched adjacent to many of the regulated exons. Endothelial deletion of Rbfox2, the only family member expressed in arterial endothelium, suppresses a subset of the changes in transcription and RNA splicing induced by low flow. Our data reveal an alternative splicing program activated by Rbfox2 in the endothelium on recruitment of platelets and macrophages and demonstrate its relevance in transcriptional responses during flow-driven vascular inflammation.
Project description:While much progress has been made in identifying the mechanisms that trigger endothelial activation and inflammatory cell recruitment during atherosclerosis, less is known about the intrinsic pathways that counteract these events. Here we identified NOTCH1 as an antagonist of endothelial cell activation. NOTCH1 was constitutively expressed by adult arterial endothelium, but levels were significantly reduced by high fat diet. Furthermore, treatment of human aortic endothelial cells (HAEC) with inflammatory lipids (Ox-PAPC) and pro-inflammatory cytokines (TNFalpha and IL1beta) decreased Notch1 expression and signaling in vitro through a mechanism that requires STAT3 activation. Reduction of NOTCH1 in HAEC by siRNA, in the absence of inflammatory lipids or cytokines, increased inflammatory molecules and binding of monocytes. Conversely, some of the effects mediated by Ox-PAPC were reversed by increased NOTCH1 signaling; suggesting a link between lipid-mediated inflammation and Notch1. Interestingly, reduction of NOTCH1 by Ox-PAPC in HAEC was associated with a genetic variant previously correlated to HDL in a human GWAS. Finally endothelial Notch1 heterozygous mice showed higher diet-induced atherosclerosis. Based on these findings, we propose that reduction of endothelial NOTCH1 is a predisposing factor in the onset of vascular inflammation and initiation of atherosclerosis.