Sterol regulatory element binding protein 2 activation of NLRP3 inflammasome in endothelium mediates hemodynamic-induced atherosclerosis susceptibility

BACKGROUND

The molecular basis for the focal nature of atherosclerotic lesions is poorly understood. Here, we explored whether disturbed flow patterns activate an innate immune response to form the NLRP3 inflammasome scaffold in vascular endothelial cells via sterol regulatory element binding protein 2 (SREBP2).

METHODS AND RESULTS

Oscillatory flow activates SREBP2 and induces NLRP3 inflammasome in endothelial cells. The underlying mechanisms involve SREBP2 transactivating NADPH oxidase 2 and NLRP3. Consistently, SREBP2, NADPH oxidase 2, and NLRP3 levels were elevated in atheroprone areas of mouse aortas, suggesting that the SREBP2-activated NLRP3 inflammasome causes functionally disturbed endothelium with increased inflammation. Mimicking the effect of atheroprone flow, endothelial cell-specific overexpression of the activated form of SREBP2 synergized with hyperlipidemia to increase atherosclerosis in the atheroresistant areas of mouse aortas.

CONCLUSIONS

Atheroprone flow induces NLRP3 inflammasome in endothelium through SREBP2 activation. This increased innate immunity in endothelium synergizes with hyperlipidemia to cause topographical distribution of atherosclerotic lesions.

LINC00341 exerts an anti-inflammatory effect on endothelial cells by repressing VCAM1

The long noncoding RNAs (lncRNAs), which constitute a large portion of the transcriptome, have gained intense research interest because of their roles in regulating physiological and pathophysiological functions in the cell. We identified from RNA-Seq profiling a set of lncRNAs in cultured human umbilical vein endothelial cells (HUVECs) that are differentially regulated by atheroprotective vs. atheroprone shear flows. Among the comprehensively annotated lncRNAs, including both known and novel transcripts, LINC00341 is one of the most abundant lncRNAs in endothelial cells. Moreover, its expression level is enhanced by atheroprotective pulsatile shear flow and atorvastatin. Overexpression of LINC00341 suppresses the expression of vascular cell adhesion molecule 1 (VCAM1) and the adhesion of monocytes induced by atheroprone flow and tumor necrosis factor-alpha. Underlying this anti-inflammatory role, LINC00341 guides enhancer of zest homolog 2, a core histone methyltransferase of polycomb repressive complex 2, to the promoter region of the VCAM1 gene to suppress VCAM1. Network analysis reveals that the key signaling pathways (e.g., Rho and PI3K/AKT) are co-regulated with LINC00341 in endothelial cells in response to pulsatile shear. Together, these findings suggest that LINC00341, as an example of lncRNAs, plays important roles in modulating endothelial function in health and disease.

JAGGED-NOTCH3 signaling in vascular remodeling in pulmonary arterial hypertension

Within the pulmonary arterial tree, the NOTCH3 pathway is crucial in controlling vascular smooth muscle cell proliferation and maintaining smooth muscle cells in an undifferentiated state. Pulmonary arterial hypertension (PAH) is a fatal disease without cure, characterized by elevated pulmonary vascular resistance due to vascular smooth muscle cell proliferation in precapillary arteries, perivascular inflammation, and asymmetric neointimal hyperplasia. Here, we show that human PAH is characterized by overexpression of the NOTCH ligand JAGGED-1 (JAG-1) in small pulmonary artery smooth muscle cells and that JAG-1 selectively controls NOTCH3 signaling and cellular proliferation in an autocrine fashion. In contrast, the NOTCH ligand DELTA-LIKE 4 is minimally expressed in small pulmonary artery smooth muscle cells from individuals with PAH, inhibits NOTCH3 cleavage and signaling, and retards vascular smooth muscle cell proliferation. A new monoclonal antibody for the treatment of PAH, which blocks JAG-1 cis- and trans-induced cleavage of the NOTCH3 receptor in the pulmonary vasculature, was developed. Inhibition of JAG-1-induced NOTCH3 signaling in the lung reverses clinical and pathologic pulmonary hypertension in two rodent models of disease, without toxic side effects associated with nonspecific NOTCH inhibitors. Our data suggest opposing roles of NOTCH ligands in the pulmonary vasculature in pulmonary hypertension. We propose that selectively targeting JAG-1 activation of NOTCH3 may be an effective, safe strategy to treat PAH.

Activation of sterol regulatory element-binding proteins (SREBPs) is critical in IL-8-induced angiogenesis

Angiogenesis is essential in many physiological and pathological processes and can be stimulated by many different factors. To better understand and to manipulate this process more effectively, it would be beneficial to identify molecules common to the signaling pathways stimulated by different classes of angiogenic factors. Sterol regulatory element-binding proteins (SREBPs) are involved in the metabolism of cholesterol and fatty acids, molecules that are critical in membrane biology, and hence, many of the processes involved in angiogenesis. Here, we show that angiogenic factors of different families, such as basic fibroblast growth factor, thrombin, and interleukin (IL)-8, stimulate SREBP activation, whereas nonangiogenic factors, such as transforming growth factor-beta1, do not. We focused our detailed studies on IL-8 in vitro and in vivo, as this chemokine is also involved in inflammation and hence, has the potential to be critical in inflammation-induced angiogenesis, a process common to many diseases. Using human microvascular endothelial cells, a rabbit skin wound-healing model, and the chorioallantoic membrane assay, we show that IL-8 stimulates the activation of SREBP-1 and -2, and this activation is specific and receptor-mediated. SREBP activation leads to activation of RhoA through 3-hydroxy-3-methylglutaryl CoA reductase. RhoA is a small guanosinetriphosphatase, important in cytoskeletal functions, which in turn, are critical in many of the cellular processes needed for angiogenesis. Given that diverse, angiogenic factors use different cell-surface receptors, identification of this common step in the signal-transduction pathway provides the opportunity for novel approaches for prevention and treatment of diseases involving abnormal angiogenesis.

Endocytic Adaptors in Cardiovascular Disease

Endocytosis is the process of actively transporting materials into a cell by membrane engulfment. Traditionally, endocytosis was divided into three forms: phagocytosis (cell eating), pinocytosis (cell drinking), and the more selective receptor-mediated endocytosis (clathrin-mediated endocytosis); however, other important endocytic pathways (e.g., caveolin-dependent endocytosis) contribute to the uptake of extracellular substances. In each, the plasma membrane changes shape to allow the ingestion and internalization of materials, resulting in the formation of an intracellular vesicle. While receptor-mediated endocytosis remains the best understood pathway, mammalian cells utilize each form of endocytosis to respond to their environment. Receptor-mediated endocytosis permits the internalization of cell surface receptors and their ligands through a complex membrane invagination process that is facilitated by clathrin and adaptor proteins. Internalized vesicles containing these receptor-ligand cargoes fuse with early endosomes, which can then be recycled back to the plasma membrane, delivered to other cellular compartments, or destined for degradation by fusing with lysosomes. These intracellular fates are largely determined by the interaction of specific cargoes with adaptor proteins, such as the epsins, disabled-homolog 2 (Dab2), the stonin proteins, epidermal growth factor receptor substrate 15, and adaptor protein 2 (AP-2). In this review, we focus on the role of epsins and Dab2 in controlling these sorting processes in the context of cardiovascular disease. In particular, we will focus on the function of epsins and Dab2 in inflammation, cholesterol metabolism, and their fundamental contribution to atherogenicity.

Inpatient use of metformin and acarbose is associated with reduced mortality of COVID-19 patients with type 2 diabetes mellitus

Aims

Type 2 diabetes mellitus (T2DM) is a strong risk factor for complications of coronavirus disease 2019 (COVID‐19). The effect of T2DM medications on COVID‐19 outcomes remains unclear. In a retrospective analysis of a cohort of 131 patients with T2DM hospitalized for COVID‐19 in Wuhan, we have previously found that metformin use prior to hospitalization is associated with reduced mortality. The current study aims to investigate the effects of inpatient use of T2DM medications, including metformin, acarbose, insulin and sulfonylureas, on the mortality of COVID‐19 patients with T2DM during hospitalization.

Methods

We continue to carry out a retrospective analysis of a cohort of 131 patients with T2DM hospitalized for COVID‐19 and treated with different combinations of diabetes medications.

Results

We found that patients using metformin (p = .02) and acarbose (p = .04), alone or both together (p = .03), after admission were significantly more likely to survive than those who did not use either metformin or acarbose. 37 patients continued to take metformin after admission and 35 (94.6%) survived. Among the 57 patients who used acarbose after admission, 52 survived (91.2%). A total of 20 patients used both metformin and acarbose, while 57 used neither. Of the 20 dual‐use patients, 19 (95.0%) survived.

Conclusion

Our analyses suggest that inpatient use of metformin and acarbose together or alone during hospitalization should be studied in randomized trials.

AMPK upregulates KCa2.3 channels and ameliorates endothelial dysfunction in diet-induced obese mice

The opening of endothelial small-conductance calcium-activated potassium channels (K_Ca2.3) is essential for endothelium-dependent hyperpolarization (EDH), which predominantly occurs in small resistance arteries. Adenosine monophosphate-activated protein kinase (AMPK), an important metabolic regulator, has been implicated in regulating endothelial nitric oxide synthase activity. However, it was unclear whether AMPK regulated endothelial K_Ca2.3-mediated EDH-type vasodilation. Using bioinformatics analysis and myograph system, we investigated the regulation by AMPK of K_Ca2.3 in human umbilical vein endothelial cells (HUVECs) or mouse second-order mesenteric resistance arteries. In HUVECs, AMPK activation either by activators (AICAR, A769662 and MK-8722) or expression of the constitutively active form of AMPK significantly upregulated K_Ca2.3 expression. Such effects were abolished by AMPK inhibitor (compound C) or AMPK α1-/α2-siRNA, extracellular-signal-regulated-kinase 5 (ERK5) inhibitor (ERK5-IN-1), and specific siRNA to myocyte-enhancer factor 2 (MEF2) or krüppel-like factor 2/4 (KLF2/4). K_Ca2.3 expression was significantly reduced in mesenteric resistance arteries in AMPKα2 knockout mice when compared with littermate control mice. Furthermore, in high-fat diet fed mice, 2-week treatment with AICAR restored endothelial K_Ca2.3 expression in mesenteric resistance arteries with improved endothelial dysfunction. Our results demonstrate that activation of AMPK upregulates K_Ca2.3 channel expression through the ERK5-MEF2-KLF2/4 signaling pathway in vascular endothelium, which contributes to benefits through K_Ca2.3-mediated EDH-type vasodilation in mesenteric resistance arteries.

Inpatient Use of Metformin and Acarbose Is Associated with Reduced Mortality of COVID-19 Patients with Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a strong risk factor for complications of coronavirus disease 2019 (COVID-19). The effect of T2DM medications on COVID-19 outcomes remains unclear. In a retrospective analysis of a cohort of 131 patients with T2DM hospitalized for COVID-19 in Wuhan, we have previously found that metformin use prior to hospitalization is associated with reduced mortality. Here we continue to investigate the effects of inpatient use of T2DM medications, including metformin, acarbose, insulin, and sulfonylureas, on the mortality of COVID-19 patients with T2DM during hospitalization. We found that patients using metformin and acarbose, alone or both together, after admission were significantly more likely to survive than those who did not use either metformin or acarbose. Thus, our analyses suggest that inpatient use of metformin and acarbose together or alone during hospitalization should be studied in randomized trials.

Abstract 92: Oxidative Stress Induces Endothelial Dysfunction: Role of Sterol Regulatory Element Binding Protein 2 and MicroRNA-92a

Oxidative stress, elevated in pathophysiological conditions such as hypertension, hyperlipidemia, and aging affects endothelial homeostasis by impairing endothelial nitric oxide synthase (eNOS)-derived NO bioavailability and promoting inflammatory response. We recently demonstrated that atheroprone flow activates sterol regulatory element binding protein (SREBP) 2 and induces endothelial innate immunity, evidenced by NLRP3 inflammasome activation. Transgenic mice overexpressing endothelium-specific SREBP2 (EC-SREBP2) manifest accelerated atherosclerosis synergized by hyperlipidemia. In the current study, we investigated whether oxidative stress activates SREBP2 in endothelial cells (ECs), contributing to endothelial dysfunction. Several oxidative stress-inducing stimuli, i.e. hydrogen peroxide, Angiotensin II, and oxidized-LDL, all activates SREBP2 in ECs. Furthermore, SREBP2 transactivates microRNA-92a (miR-92a), previously shown to be dysregulated in ischemia and atherosclerosis. Chromatin immunoprecipitation, together with gain- and loss-of-function assays revealed that oxidative stress-activated SREBP2 induces miR-92a, which in turn targets several key molecules including Kruppel-like factor (KLF) 2, KLF4, and Sirtuin 1. As a result, NLRP3 inflammasome is activated and eNOS inhibited. In EC-SREBP2 mice, locked nucleic acid (LNA) inhibition of miR-92a improves vasodilatory function. In an Angiotensin II-challenged model, LNA-92a ameliorates atherogenesis in EC-SREBP2 with an ApoE-/- background. Collectively, these findings suggest a novel link between oxidative stress and the endothelial inflammation involving SREBP2-miR-92a-inflammasome. This newly defined pathway could be a therapeutic target to intervene endothelial dysfunction during the onset of atherosclerosis.

Pulsatile flow induces chromatin interaction with lamin-associated proteins to enrich H3K9 methylation in endothelial cells

Endothelial cells (ECs) are constantly exposed to hemodynamic forces, which play a crucial role in regulating EC functions. Pulsatile laminar shear stress (PS), representing atheroprotective flow, maintains the anti-inflammation and homeostatic phenotype of ECs, but the comprehensive mechanism underlying the PS-repression of inflammatory genes remains to be determined. In this study, we investigated the role of chromatin organization in mediating the effects of PS on inflammatory gene expression in ECs. We demonstrated that PS induced the expression of histone methyltransferase SUV39H1 to promote heterochromatin formation via H3K9 trimethylation (H3K9me3) enrichment, a hallmark gene repression mechanism. SUV39H1 interacts with lamin-associated proteins and facilitates the perinuclear localization of the H3K9me3-enrichment. Silencing the lamin-associated protein emerin (EMD) not only led to the reductions of cytoskeletal F-actin formation and perinuclear H3K9me3 enrichment; but also the impairment of PS-induced SUV39H1 expression, H3K9me3 enrichment at E-selectin and vascular cell adhesion molecule 1 loci to revert their PS-repressed expression. Hence, EMD acts as a hub to transmit mechanical cues from the cytoskeleton to the nucleus and recruits SUV39H1, which regulate nuclear organization, chromatin state, and gene expression. These results accentuate the critical role of nuclear architecture in mechanotransduction and EC responses to mechanical stimuli.

Endothelium-specific SIRT7 targeting ameliorates pulmonary hypertension through Krüpple-like factor 4 deacetylation

AIMS

Pulmonary hypertension (PH) is a pulmonary vascular disease characterized by a high mortality rate. Pulmonary arterial endothelium cells (PAECs) serve as a primary sensor of various environmental cues, such as shear stress and hypoxia, but PAEC dysfunction may trigger vascular remodelling during the onset of PH. This study aimed to illustrate the role of Sirtuin 7 (SIRT7) in endothelial dysfunction during PH and explore the potential therapeutic strategy for PH.

METHODS AND RESULTS

SIRT7 levels were measured in human and murine experimental PH samples. Bioinformatic analysis, immunoprecipitation, and deacetylation assay were used to identify the association between SIRT7 and Krüpple-like factor 4 (KLF4), a key transcription factor essential for endothelial cell (EC) homeostasis. Sugen5416 + hypoxia (SuHx)-induced PH mouse models and cell cultures were used for the study of the therapeutic effect of SIRT7 for PH. SIRT7 level was significantly reduced in lung tissues and PAECs from PH patients and the SuHx-induced PH mouse model as compared with healthy controls. Pulmonary endothelium-specific depletion of Sirt7 increased right ventricular systolic pressure and exacerbated right ventricular hypertrophy in the SuHx-induced PH model. At the molecular level, we identified KLF4 as a downstream target of SIRT7, which deacetylated KLF4 at K228 and inhibited the ubiquitination-proteasome degradation. Thus, the SIRT7/KLF4 axis maintained PAEC homeostasis by regulating proliferation, migration, and tube formation. PAEC dysfunction was reversed by adeno-associated virus type 1 vector-mediated endothelial overexpression of Sirt7 or supplementation with nicotinamide adenine dinucleotide (NAD)+ intermediate nicotinamide riboside which activated Sirt7; both approaches successfully reversed PH phenotypes.

CONCLUSION

The SIRT7/KLF4 axis ensures PAEC homeostasis, and pulmonary endothelium-specific SIRT7 targeting might constitute a PH therapeutic strategy.

Abstract 007: Athero-protective Flow Regulation of ITPR3: an Epigenetic Approach

Background: The topographic distribution of atherosclerosis in human vasculature underscores the role of shear stress in regulating gene expression and function in the endothelium. Recent advances in understanding of mechanotransduction reveal that epigenetic regulation is integral to shear stress-mediated gene expression. With the use of ChIP-seq and ATAC-seq, the current study aims to demonstrate the link between histone modifications and transcriptional regulation in endothelial cells (ECs) in response to shear stress.

Methods and Results: We found that pulsatile shear (PS)- and oscillatory shear (OS)-induced differential H3K27ac enrichments were associated with adjacent gene expression in ECs, approximately 30% of which showed significant positive correlation (Pearson’s correlation coefficient >0.7). In silico prediction revealed that Krüppel-like factor 4 (KLF4) binding motifs were enriched in the PS-enhanced H3K27ac regions. By integrating genes that are induced by PS, have the KLF4 binding loci, and contain PS-associated H3K27ac in their promoter regions, we identified 18 novel PS-upregulated genes. Validating these results in mouse ECs isolated from intima of the thoracic aorta vs aortic arch, lung ECs from EC-KLF4-TG vs EC-KLF4-KO mice, and atorvastatin-treated vs control ECs, we found that Inositol 1,4,5-trisphosphate receptor type 3 (ITPR3) had the most robust expression in multiple systems. Consistent with these findings, ATAC-seq and ChIP-qPCR demonstrated a specific locus in the promoter region of the ITPR3 gene that was essential for KLF4 binding, H3K27ac enrichment, chromatin accessibility, and ITPR3 transcription. Deletion of this KLF4 binding locus in ECs by using CRISPR-Cas9 resulted in blunted calcium influx, reduced eNOS expression, and diminished NO bioavailability. Furthermore, ITPR-KO mice fed an atherogenic diet resulted in exacerbated atherosclerosis compared to wildtype littermates.

Conclusions: Using a multi-layer systems approach, we have demonstrated that KLF4 is crucial for the histone modifications that allow the transcriptional activation of ITPR3 in ECs. This novel mechanism contributes to Ca2 + -dependent eNOS activation and EC homeostasis by maintaining an athero-protective phenotype.

Early-Onset Hypertension and Sex-Specific Residual Risk for Cardiovascular Disease in Type 2 Diabetes

OBJECTIVE

To investigate whether the sex disparities in type 2 diabetes-associated cardiovascular disease (CVD) risks may be related to early-onset hypertension that could benefit from intensive blood pressure (BP) control.

RESEARCH DESIGN AND METHODS

We analyzed intensive versus standard BP control in relation to incident CVD events in women and men with type 2 diabetes, based on their age of hypertension diagnosis.

RESULTS

Among 3,792 adults with type 2 diabetes (49% women), multivariable-adjusted CVD risk was increased per decade earlier age at hypertension diagnosis (hazard ratio 1.11 [1.03-1.21], P = 0.006). Excess risk associated with early-diagnosed hypertension was attenuated in the presence of intensive versus standard antihypertensive therapy in women (P = 0.036) but not men (P = 0.76).

CONCLUSIONS

Women with type 2 diabetes and early-onset hypertension may represent a higher-risk subpopulation that not only contributes to the excess in diabetes-related CVD risk for women but may benefit from intensive BP control.

Downregulation of Signaling-active IGF-1 by Dipeptidyl Peptidase IV (DPP-IV)

Functioning as an extracellular protease, dipeptidyl peptidase IV (DPP-IV) preferentially cleaves the peptide bond after the penultimate proline residue. We report here that DPP-IV cleaves the first two amino acids from insulin-like growth factor 1 (IGF-1), revealed by mass spectrometry. The kinetic parameters of the proteolytic cleavage indicate that this reaction is physiologically relevant. Interestingly, truncated IGF-1 is less potent than the full-length protein in activating the IGF-1R, but binds more readily to IGF-binding protein 3 (IGFBP3). Quantitative RT-PCR showed that the level of DPP-IV mRNA is dramatically lower in lung squamous cell carcinoma tissues than in adjacent nonneoplastic lung tissues. However, this reduction was not observed in lung adenocarcinoma tissues. Our study suggests a possible link between IGF-1 and DPP-IV in cancer development in a specific tumor niche. A DPP-IV-related pathway may be important in mitigating IGF-1 signaling. Consequently, a robust IGF signaling pathway may accelerate early carcinogenesis in environments lacking DPP-IV.

Multi-Organ System Metabolic Stress and Sex-Divergent Vascular Associations

Introduction

Women experience excess cardiovascular risk compared to men in the setting of similar metabolic disease burden. This consistent finding could be related to sex differences in the vascular response to various forms of metabolic stress. In this study we examine the association of both systemic and organ-specific metabolic stress with vascular health in women and men.

Methods

We conducted an observational study of 4,299 adult participants (52% women, aged 59±13 years) of the National Health and Nutrition Examination Survey (NHANES) 2017-2018 cohort and 110,225 adult outpatients (55% women, aged 64±16 years) of the Cedars-Sinai Medical Center (CSMC) 2019 cohort. We used natural splines to examine the association of systemic and organ-specific measures of metabolic stress including body mass index (BMI), hemoglobin A1c (HbA1c), hepatic FIB-4 score, and CKD-EPI estimated glomerular filtration rate (eGFR) on systolic blood pressure (SBP). Piecewise linear models were generated using normal value thresholds (BMI <25 kg/m 2 , HbA1c <5.7%, FIB-4 <1.3, and eGFR ≥90 ml/min), which approximated observed spline breakpoints. The primary outcome was increase in SBP (relative to a sex-specific physiologic baseline SBP) in association with increase in level of each metabolic measure.

Results

Women compared to men demonstrated larger magnitudes and an earlier onset of increase in SBP per increment increase across all metabolic stress measures. The slope of SBP increase per increment of each metabolic measure was greater for women than men particularly for metabolic measures within the normal range, with slope differences of 1.71 mmHg per kg/m2 of BMI, 9.61 mmHg per %HbA1c, 6.45 mmHg per FIB-4 unit, and 0.37 mmHg per ml/min decrement of eGFR in the NHANES cohort (P difference <0.05 for all). Overall results were consistent in the CSMC cohort.

Conclusions

Women exhibited greater vascular sensitivity in the setting of multiple types of metabolic stress, particularly in periods representing the transition from metabolic health to disease. These findings underscore the importance of involving early metabolic health interventions as part of efforts to mitigate vascular risks in both women and men.