Endothelial Krüppel-like factor 2/4: Regulation and function in cardiovascular diseases

This review presents an overview of the regulation, function, disease-relevance and pharmacological regulation of the critical endothelial transcription factors KLF2/4 in vasculature. The regulatory mechanisms of KLF2/4 expression and activity in vascular endothelium in response to hemodynamic forces and biochemical stimuli are depicted. The functional effects mediated by direct or indirect target genes of KLF2/4 in endothelial cells are systematically summarized. The contributory roles that dysregulated KLF2/4 play in relevant cardiovascular pathologies, such as atherosclerotic vascular lesions, pulmonary arterial hypertension and vascular complications of diabetes were reviewed. Moreover, this review also discusses the pharmacological regulation of KLF2/4 by drugs used in clinics and therapeutic possibility by directly targeting these two transcription factors for treating atherosclerotic cardiovascular diseases. Finally, prospective opinions on the gaps in disclosing novel vascular function mediated by KLF2/4 and future research needs are expressed.

The role of the JunD-RhoH axis in the pathogenesis of hairy cell leukemia and its ability to identify existing therapeutics that could be repurposed to treat relapsed or refractory disease

Hairy cell leukemia (HCL) is an indolent malignancy of mature B-lymphocytes. While existing front-line therapies achieve excellent initial results, a significant number of patients relapse and become increasingly treatment resistant. A major molecular driver of HCL is aberrant interlocking expression of the transcription factor JunD and the intracellular signaling molecule RhoH. Here we discuss the molecular basis of how the JunD-RhoH axis contributes to HCL pathogenesis. We also discuss how leveraging the JunD-RhoH axis identifies CD23, CD38, CD66a, CD115, CD269, integrin β7, and MET as new potential therapeutic targets. Critically, preclinical studies have already demonstrated that targeting CD38 with isatuximab effectively treats preexisiting HCL. Isatuximab and therapeutics directed against each of the other six new HCL targets are currently in clinical use to treat other disorders. Consequently, leveraging the JunD-RhoH axis has identified a battery of therapies that could be repurposed as new means of treating relapsed or refractory HCL.

Reconceptualizing Endothelial-to-mesenchymal transition in atherosclerosis: Signaling pathways and prospective targeting strategies

BACKGROUND

The modification of endothelial cells (ECs) biological function under pathogenic conditions leads to the expression of mesenchymal stromal cells (MSCs) markers, defined as endothelial-to-mesenchymal transition (EndMT). Invisible in onset and slow in progression, atherosclerosis (AS) is a potential contributor to various atherosclerotic cardiovascular diseases (ASCVD). By triggering AS, EndMT, the "initiator" of AS, induces the progression of ASCVD such as coronary atherosclerotic heart disease (CHD) and ischemic cerebrovascular disease (ICD), with serious clinical complications such as myocardial infarction (MI) and stroke. In-depth research of the pathomechanisms of EndMT and identification of potential targeted therapeutic strategies hold considerable research value for the prevention and treatment of ASCVD-associated with delayed EndMT. Although previous studies have progressively unraveled the complexity of EndMT and its pathogenicity triggered by alterations in vascular microenvironmental factors, systematic descriptions of the most recent pathogenic roles of EndMT in the progression of AS, targeted therapeutic strategies, and their future research directions are scarce.

AIM OF REVIEW

We aim to provide new researchers with comprehensive knowledge of EndMT in AS. We exhaustively review the latest research advancements in the field and provide a theoretical basis for investigating EndMT, a biological process with sophisticated mechanisms.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review summarized that altered hemodynamics with microenvironmental crosstalk consisting of inflammatory responses or glycolysis, oxidative stress, lactate or acetyl-CoA (Ac-CoA), fatty acid oxidation (FAO), intracellular iron overload, and transcription factors, including ELK1 and STAT3, modulate the EndMT and affect AS progression. In addition, we provide new paradigms for the development of promising therapeutic agents against these disease-causing processes and indicate promising directions and challenges that need to be addressed to elucidate the EndMT process.

LncRNA MALAT1 facilitates BM-MSCs differentiation into endothelial cells and ameliorates erectile dysfunction via the miR-206/CDC42/PAK1/paxillin signalling axis

BACKGROUND

Erectile dysfunction (ED) is a common male sexual dysfunction, with an increasing incidence, and the current treatment is often ineffective.

METHODS

Vascular endothelial growth factor (VEGFA) was used to treat bone marrow-derived mesenchymal stem cells (BM-MSCs), and their cell migration rates were determined by Transwell assays. The expression of the von Willebrand Factor (vWF)VE-cadherin, and endothelial nitric oxide synthase(eNOS) endothelial markers was determined by qRT‒PCR and Western blot analyses. The MALAT1-induced differentiation of BM-MCs to ECs via the CDC42/PAK1/paxillin pathway was explored by transfecting VEGFA-induced BM-MSC with si-MALAT1 and overexpressing CDC42 and PAK1. The binding capacity between CDC42, PAK1, and paxillin in VEGFA-treated and non-VEGFA-treated BM-MSCs was examined by protein immunoprecipitation. MiR-206 was overexpressed in VEGFA-induced BM-MSC, and the binding sites of MALAT1, miR-206, and CDC42 were identified using a luciferase assay. Sixty male Sprague‒Dawley rats were divided into six groups (n = 10/group). DMED modelling was demonstrated by APO experiments and was assessed by measuring blood glucose levels. Erectile function was assessed by measuring the intracavernosa pressure (ICP) and mean arterial pressure (MAP). Penile erectile tissue was analysed by qRT‒PCR, Western blot analysis, and immunohistochemical staining.

RESULTS

MALAT1 under VEGFA treatment conditions regulates the differentiation of BM-MSCs into ECs by modulating the CDC42/PAK1/paxillin axis. In vitro experiments demonstrated that interference with CDC42 and MALAT1 expression inhibited the differentiation of BM-MSCs to ECs. CDC42 binds to PAK1, and PAK1 binds to paxillin. In addition, CDC42 in the VEGFA group had a greater ability to bind to PAK1, whereas PAK1 in the VEGFA group had a greater ability to bind to paxillin. Overexpression of miR-206 in VEGFA-induced BM-MSCs demonstrated that MALAT1 competes with the CDC42 3'-UTR for binding to miR-206, which in turn is involved in the differentiation of BM-MSCs to ECs. Compared to the DMED model group, the ICP/MAP ratio was significantly greater in the three BM-MSCs treatment groups.

CONCLUSIONS

MALAT1 facilitates BM-MSC differentiation into ECs by regulating the miR-206/CDC42/PAK1/paxillin axis to improve ED. The present findings revealed the vital role of MALAT1 in the repair of BM-MSCs for erectile function and provided new mechanistic insights into the BM-MSC-mediated repair of DMED.

Endothelial activation and fibrotic changes are impeded by laminar flow-induced CHK1-SENP2 activity through mechanisms distinct from endothelial-to-mesenchymal cell transition

Background

The deSUMOylase sentrin-specific isopeptidase 2 (SENP2) plays a crucial role in atheroprotection. However, the phosphorylation of SENP2 at T368 under disturbed flow (D-flow) conditions hinders its nuclear function and promotes endothelial cell (EC) activation. SUMOylation has been implicated in D-flow-induced endothelial-to-mesenchymal transition (endoMT), but the precise role of SENP2 in counteracting this process remains unclear.

Method

We developed a phospho-specific SENP2 S344 antibody and generated knock-in (KI) mice with a phospho-site mutation of SENP2 S344A using CRISPR/Cas9 technology. We then investigated the effects of SENP2 S344 phosphorylation under two distinct flow patterns and during hypercholesteremia (HC)-mediated EC activation.

Result

Our findings demonstrate that laminar flow (L-flow) induces phosphorylation of SENP2 at S344 through the activation of checkpoint kinase 1 (CHK1), leading to the inhibition of ERK5 and p53 SUMOylation and subsequent suppression of EC activation. We observed a significant increase in lipid-laden lesions in both the aortic arch (under D-flow) and descending aorta (under L-flow) of female hypercholesterolemic SENP2 S344A KI mice. In male hypercholesterolemic SENP2 S344A KI mice, larger lipid-laden lesions were only observed in the aortic arch area, suggesting a weaker HC-mediated atherogenesis in male mice compared to females. Ionizing radiation (IR) reduced CHK1 expression and SENP2 S344 phosphorylation, attenuating the pro-atherosclerotic effects observed in female SENP2 S344A KI mice after bone marrow transplantation (BMT), particularly in L-flow areas. The phospho-site mutation SENP2 S344A upregulates processes associated with EC activation, including inflammation, migration, and proliferation. Additionally, fibrotic changes and up-regulated expression of EC marker genes were observed. Apoptosis was augmented in ECs derived from the lungs of SENP2 S344A KI mice, primarily through the inhibition of ERK5-mediated expression of DNA damage-induced apoptosis suppressor (DDIAS).

Summary

In this study, we have revealed a novel mechanism underlying the suppressive effects of L-flow on EC inflammation, migration, proliferation, apoptosis, and fibrotic changes through promoting CHK1-induced SENP2 S344 phosphorylation. The phospho-site mutation SENP2 S344A responds to L-flow through a distinct mechanism, which involves the upregulation of both mesenchymal and EC marker genes.

SUMOylation targeting mitophagy in cardiovascular diseases

Small ubiquitin-like modifier (SUMO) plays a key regulatory role in cardiovascular diseases, such as cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. As a multifunctional posttranslational modification molecule in eukaryotic cells, SUMOylation is essentially associated with the regulation of mitochondrial dynamics, especially mitophagy, which is involved in the progression and development of cardiovascular diseases. SUMOylation targeting mitochondrial-associated proteins is admittedly considered to regulate mitophagy activation and mitochondrial functions and dynamics, including mitochondrial fusion and fission. SUMOylation triggers mitochondrial fusion to promote mitochondrial dysfunction by modifying Fis1, OPA1, MFN1/2, and DRP1. The interaction between SUMO and DRP1 induces SUMOylation and inhibits lysosomal degradation of DRP1, which is further involved in the regulation of mitochondrial fission. Both SUMOylation and deSUMOylation contribute to the initiation and activation of mitophagy by regulating the conjugation of MFN1/2 SERCA2a, HIF1α, and PINK1. SUMOylation mediated by the SUMO molecule has attracted much attention due to its dual roles in the development of cardiovascular diseases. In this review, we systemically summarize the current understanding underlying the expression, regulation, and structure of SUMO molecules; explore the biochemical functions of SUMOylation in the initiation and activation of mitophagy; discuss the biological roles and mechanisms of SUMOylation in cardiovascular diseases; and further provide a wider explanation of SUMOylation and deSUMOylation research to provide a possible therapeutic strategy for cardiovascular diseases. Considering the precise functions and exact mechanisms of SUMOylation in mitochondrial dysfunction and mitophagy will provide evidence for future experimental research and may serve as an effective approach in the development of novel therapeutic strategies for cardiovascular diseases. Regulation and effect of SUMOylation in cardiovascular diseases via mitophagy. SUMOylation is involved in multiple cardiovascular diseases, including cardiac hypertrophy, hypertension, atherosclerosis, and cardiac ischemia-reperfusion injury. Since it is expressed in multiple cells associated with cardiovascular disease, SUMOylation can be regulated by numerous ligases, including the SENP family proteins PIAS1, PIASy/4, UBC9, and MAPL. SUMOylation regulates the activation and degradation of PINK1, SERCA2a, PPARγ, ERK5, and DRP1 to mediate mitochondrial dynamics, especially mitophagy activation. Mitophagy activation regulated by SUMOylation further promotes or inhibits ventricular diastolic dysfunction, perfusion injury, ventricular remodelling and ventricular noncompaction, which contribute to the development of cardiovascular diseases.

miR-185-5p Regulates Inflammation and Phagocytosis through CDC42/JNK Pathway in Macrophages

Macrophage activation is an essential component of systemic chronic inflammation and chronic inflammatory diseases. Emerging evidence implicates miR-185-5p in chronic inflammation diseases. However, the regulatory role of miR-185-5p in macrophage pro-inflammatory activation has not been studied previously. Here, we identified that miR-185-5p was one of the top genes and effectively downregulated in two macrophage miRNA expression datasets from GEO. Under LPS stress, miR-185-5p overexpression reduced pro-inflammatory cytokine expression, suppressed phagocytosis in RAW264.7 macrophage. miR-185-5p inhibitors augmented pro-inflammatory effects of LPS in macrophage. Mechanically, miR-185-5p sponged and negatively regulated the protein expression of CDC42. Ablation of CDC42 with selective CDC42 inhibitor CASIN reversed the pro-inflammatory effect of miR-185-5p inhibitors through inhibiting MAPK/JNK pathways. Collectively, these data demonstrate that miR-185-5p exhibited anti-inflammatory functions in LPS-induced RAW264.7 macrophages at least partially through CDC42/JNK pathways. Our findings yield insights into the understanding of miR-185-5p-regulated network in macrophages inflammation, which is beneficial for exploring miRNA-protein interaction in atherosclerotic inflammation.

Pinitol Protects Against Ox-Low-Density Lipoprotein-Induced Endothelial Inflammation and Monocytes Attachment

ABSTRACT

Atherosclerosis is a cardiovascular disease that affects a majority of people around the world at old age. Atherosclerosis is slow to develop and challenging to treat. Endothelial dysfunction caused by oxidative stress, inflammation, and other pathological factors drives the process of atherogenesis. LOX-1 is one of the main scavenging receptors for oxidized low-density lipoprotein (ox-LDL) and contributes to atherogenesis by inducing overproduction of reactive oxygen species, increased expression of proinflammatory cytokines, and secretion of cellular adhesion molecules. In addition, activation of LOX-1 inhibits the expression of KLF2, a key protective factor against atherosclerosis. In this study, we investigated the effects of pinitol, and naturally occurring cyclic polyol, on endothelial dysfunction induced by ox-LDL. Our findings show that pinitol revealed a good safety profile, as evidenced by reducing lactate dehydrogenase release in human aortic endothelial cells. In our experiments, pinitol reduced the production of reactive oxygen species and expression of IL-6 and monocyte chemoattractant protein-1 induced by ox-LDL. Pinitol also significantly reduced the attachment of THP-1 monocytes to endothelial cells via downregulation of vascular cellular adhesion molecule-1 and E-selectin. Importantly, we found that pinitol reduced the expression of LOX-1 induced by ox-LDL and rescued the expression of KLF2, which is dependent on ERK5 expression. Together, our findings provide notable evidence that pinitol may have potential implication in the prevention and treatment of atherosclerosis.

MEKK3-TGFβ crosstalk regulates inward arterial remodeling

Arterial remodeling is an important adaptive mechanism that maintains normal fluid shear stress in a variety of physiologic and pathologic conditions. Inward remodeling, a process that leads to reduction in arterial diameter, plays a critical role in progression of such common diseases as hypertension and atherosclerosis. Yet, despite its pathogenic importance, molecular mechanisms controlling inward remodeling remain undefined. Mitogen-activated protein kinases (MAPKs) perform a number of functions ranging from control of proliferation to migration and cell-fate transitions. While the MAPK ERK1/2 signaling pathway has been extensively examined in the endothelium, less is known about the role of the MEKK3/ERK5 pathway in vascular remodeling. To better define the role played by this signaling cascade, we studied the effect of endothelial-specific deletion of its key upstream MAP3K, MEKK3, in adult mice. The gene's deletion resulted in a gradual inward remodeling of both pulmonary and systematic arteries, leading to spontaneous hypertension in both vascular circuits and accelerated progression of atherosclerosis in hyperlipidemic mice. Molecular analysis revealed activation of TGFβ-signaling both in vitro and in vivo. Endothelial-specific TGFβR1 knockout prevented inward arterial remodeling in MEKK3 endothelial knockout mice. These data point to the unexpected participation of endothelial MEKK3 in regulation of TGFβR1-Smad2/3 signaling and inward arterial remodeling in artery diseases.

Reciprocal regulation of endothelial-mesenchymal transition by MAPK7 and EZH2 in intimal hyperplasia and coronary artery disease

Endothelial-mesenchymal transition (EndMT) is a form of endothelial dysfunction wherein endothelial cells acquire a mesenchymal phenotype and lose endothelial functions, which contributes to the pathogenesis of intimal hyperplasia and atherosclerosis. The mitogen activated protein kinase 7 (MAPK7) inhibits EndMT and decreases the expression of the histone methyltransferase Enhancer-of-Zeste homologue 2 (EZH2), thereby maintaining endothelial quiescence. EZH2 is the catalytic subunit of the Polycomb Repressive Complex 2 that methylates lysine 27 on histone 3 (H3K27me3). It is elusive how the crosstalk between MAPK7 and EZH2 is regulated in the endothelium and if the balance between MAPK7 and EZH2 is disturbed in vascular disease. In human coronary artery disease, we assessed the expression levels of MAPK7 and EZH2 and found that with increasing intima/media thickness ratio, MAPK7 expression decreased, whereas EZH2 expression increased. In vitro, MAPK7 activation decreased EZH2 expression, whereas endothelial cells deficient of EZH2 had increased MAPK7 activity. MAPK7 activation results in increased expression of microRNA (miR)-101, a repressor of EZH2. This loss of EZH2 in turn results in the increased expression of the miR-200 family, culminating in decreased expression of the dual-specificity phosphatases 1 and 6 who may repress MAPK7 activity. Transfection of endothelial cells with miR-200 family members decreased the endothelial sensitivity to TGFβ1-induced EndMT. In endothelial cells there is reciprocity between MAPK7 signaling and EZH2 expression and disturbances in this reciprocal signaling associate with the induction of EndMT and severity of human coronary artery disease.

The MEK5/ERK5 Pathway in Health and Disease

The MEK5/ERK5 mitogen-activated protein kinases (MAPK) cascade is a unique signaling module activated by both mitogens and stress stimuli, including cytokines, fluid shear stress, high osmolarity, and oxidative stress. Physiologically, it is mainly known as a mechanoreceptive pathway in the endothelium, where it transduces the various vasoprotective effects of laminar blood flow. However, it also maintains integrity in other tissues exposed to mechanical stress, including bone, cartilage, and muscle, where it exerts a key function as a survival and differentiation pathway. Beyond its diverse physiological roles, the MEK5/ERK5 pathway has also been implicated in various diseases, including cancer, where it has recently emerged as a major escape route, sustaining tumor cell survival and proliferation under drug stress. In addition, MEK5/ERK5 dysfunction may foster cardiovascular diseases such as atherosclerosis. Here, we highlight the importance of the MEK5/ERK5 pathway in health and disease, focusing on its role as a protective cascade in mechanical stress-exposed healthy tissues and its function as a therapy resistance pathway in cancers. We discuss the perspective of targeting this cascade for cancer treatment and weigh its chances and potential risks when considering its emerging role as a protective stress response pathway.

Effects of Shear Stress on Production of FVIII and vWF in a Cell-Based Therapeutic for Hemophilia A

Microfluidic technology enables recapitulation of organ-level physiology to answer pertinent questions regarding biological systems that otherwise would remain unanswered. We have previously reported on the development of a novel product consisting of human placental cells (PLC) engineered to overexpress a therapeutic factor VIII (FVIII) transgene, mcoET3 (PLC-mcoET3), to treat Hemophilia A (HA). Here, microfluidic devices were manufactured to model the physiological shear stress in liver sinusoids, where infused PLC-mcoET3 are thought to lodge after administration, to help us predict the therapeutic outcome of this novel biological strategy. In addition to the therapeutic transgene, PLC-mcoET3 also constitutively produce endogenous FVIII and von Willebrand factor (vWF), which plays a critical role in FVIII function, immunogenicity, stability, and clearance. While vWF is known to respond to flow by changing conformation, whether and how shear stress affects the production and secretion of vWF and FVIII has not been explored. We demonstrated that exposure of PLC-mcoET3 to physiological levels of shear stress present within the liver sinusoids significantly reduced mRNA levels and secreted FVIII and vWF when compared to static conditions. In contrast, mRNA for the vector-encoded mcoET3 was unaltered by flow. To determine the mechanism responsible for the observed decrease in FVIII and vWF mRNA, PCR arrays were performed to evaluate expression of genes involved in shear mechanosensing pathways. We found that flow conditions led to a significant increase in KLF2, which induces miRNAs that negatively regulate expression of FVIII and vWF, providing a mechanistic explanation for the reduced expression of these proteins in PLC under conditions of flow. In conclusion, microfluidic technology allowed us to unmask novel pathways by which endogenous FVIII and vWF are affected by shear stress, while demonstrating that expression of the therapeutic mcoET3 gene will be maintained in the gene-modified PLCs upon transplantation, irrespective of whether they engraft within sites that expose them to conditions of shear stress.

Chemokine mediated signalling within arteries promotes vascular smooth muscle cell recruitment

The preferential accumulation of vascular smooth muscle cells (vSMCs) on arteries versus veins during early development is a well-described phenomenon, but the molecular pathways underlying this polarization are not well understood. In zebrafish, the cxcr4a receptor (mammalian CXCR4) and its ligand cxcl12b (mammalian CXCL12) are both preferentially expressed on arteries at time points consistent with the arrival and differentiation of the first vSMCs during vascular development. We show that autocrine cxcl12b/cxcr4 activity leads to increased production of the vSMC chemoattractant ligand pdgfb by endothelial cells in vitro and increased expression of pdgfb by arteries of zebrafish and mice in vivo. Additionally, we demonstrate that expression of the blood flow-regulated transcription factor klf2a in primitive veins negatively regulates cxcr4/cxcl12 and pdgfb expression, restricting vSMC recruitment to the arterial vasculature. Together, this signalling axis leads to the differential acquisition of vSMCs at sites where klf2a expression is low and both cxcr4a and pdgfb are co-expressed, i.e. arteries during early development.

Stratman et al. provide evidence linking the cxcl12b/cxcr4a signaling axis in endothelial cells to an increased release of platelet-derived growth factor b, leading to the recruitment of smooth muscle cells to developing arteries. This signalling axis is suppressed in the venous endothelium during early development by the high expression of blood flow-regulated transcription factor klf2a.

Increased expression of EGR1 and KLF4 by polysulfide via activation of the ERK1/2 and ERK5 pathways in cultured intestinal epithelial cells

Sodium trisulfide (Na₂S₃) releases hydrogen polysulfide (H₂S_n) and is useful for the investigation of the effects of H₂S_n on the cell functions. In the present study, we first examined the effects of Na₂S₃ on the gene expression of IEC-6 cells, a rat intestinal epithelial cell line. Microarray analysis and reverse transcription-polymerase chain reaction analysis revealed that Na₂S₃ increased the gene expression of early growth response 1 (EGR1) and Kruppel-like transcription factor 4 (KLF4). It was interesting that U0126, an inhibitor of the activation of extracellular signal-regulated kinase 1 (ERK1), ERK2, and ERK5, inhibited the Na₂S₃-induced gene expression of EGR1 and KLF4. Na₂S₃ activated ERK1 and ERK2 (ERK1/2) within 15 min. In addition to ERK1/2, Na₂S₃ activated ERK5. We noticed that the electrophoretic mobility of ERK5 was decreased after Na₂S₃ treatment. Phos-tag analysis and in vitro dephosphorylation of the cell extracts indicated that the gel-shift of ERK5 was due to its phosphorylation. The gel-shift of ERK5 was inhibited completely by both U0126 and ERK5-IN-1, a specific inhibitor of ERK5. From these results, we concluded that the gel-shift of ERK5 was induced through autophosphorylation by activated ERK5 after Na₂S₃ treatment. The present study suggested that H₂S_n affected various functions of intestinal epithelial cells through the activation of the ERK1/2 and ERK5 pathways.

Fractionated radiation suppresses Kruppel-like factor 2 pathway to a greater extent than by single exposure to the same total dose

Kruppel-like factor 2 (KLF2) is a positive transcriptional regulator of several endothelial protective molecules, including thrombomodulin (TM), a surface receptor, and endothelial nitric oxide synthase (eNOS), an enzyme that generates nitric oxide (NO). Loss of TM and eNOS causes endothelial dysfunction, which results in suppressed generation of activated protein C (APC) by TM-thrombin complex and in upregulation of intercellular adhesion molecule 1 (ICAM-1). Mechanistic studies revealed that activation of extracellular signal-regulated kinase 5 (ERK5) via upregulation of myocyte enhancer factor 2 (MEF2) induces KLF2 expression. Radiation causes endothelial dysfunction, but no study has investigated radiation's effects on the KLF2 pathway. Because fractionated radiation is routinely used during cancer radiotherapy, we decided to delineate the effects of radiation dose fractionation on the KLF2 signaling cascade at early time points (up to 24 h). We exposed human primary endothelial cells to radiation as a series of fractionated or as a single exposure, with the same total dose delivered to each group. We measured the expression and activity of critical members of the KLF2 pathway at subsequent time points, and determined whether pharmacological upregulation of KLF2 can reverse the radiation effects. Compared to single exposure, fractionated radiation profoundly suppressed KLF2, TM, and eNOS levels, subdued APC generation, declined KLF2 binding ability to TM and eNOS promoters, enhanced ICAM-1 expression, and decreased expression of upstream regulators of KLF2 (ERK5 and MEF2). Pharmacological inhibitors of the mevalonate pathway prevented fractionated-radiation-induced suppression of KLF2, TM, and eNOS expression. Finally, fractionated irradiation to thoracic region more profoundly suppressed KLF2 and enhanced ICAM-1 expression than single exposure in the lung at 24 h. These data clearly indicate that radiation dose fractionation plays a critical role in modulating levels of KLF2, its upstream regulators, and its downstream target molecules in endothelial cells. Our findings will provide important insights for selecting fractionated regimens during radiotherapy and for developing strategies to alleviate radiotherapy-induced toxicity to healthy tissues.

Laquinimod Protects Against TNF-α-Induced Attachment of Monocytes to Human Aortic Endothelial Cells (HAECs) by Increasing the Expression of KLF2

Introduction

As a worldwide health issue, the treatment and prevention of atherosclerosis present an important goal. Increased levels of proinflammatory cytokines such as TNF-α-associated chronic inflammatory response cause endothelial cells to lose their ability to regulate vascular function. Lipid-laden immune cells are recruited to the endothelium where they adhere to the endothelial wall and invade the intimal space, thereby leading to the development of atherosclerotic lesions, fatty plaques, and thickening of the arterial wall. In the present study, for the first time, we investigated the effects of laquinimod, an immunomodulatory agent used for the treatment of multiple sclerosis, on human aortic endothelial in a TNF-α-induced atherosclerotic microenvironment. At present, the mechanism of action of laquinimod is not well defined.

Methods

The effects of laquinimod on the gene expression of IL-6, MCP-1, VCAM-1, E-selectin, and KLF2 were measured by real-time PCR. ELISA assay was used to determine protein secretion and expression. Phosphorylation of ERK5 and the protein level of KLF2 were measured by Western blot analysis. The attachment of monocytes to endothelial cells was assayed by calcein-AM staining and fluorescent microscopy.

Results

Our findings demonstrate that laquinimod reduced the expression of key inflammatory cytokines and chemokines, including IL-6, MCP-1, and HMGB1. We further demonstrate that laquinimod significantly reduced the attachment of monocytes to endothelial cells, which is mediated through reduced expression of the cellular adhesion molecules VCAM-1 and E-selectin. Here, we found that laquinimod could significantly increase the expression of KLF2 through activation of ERK5 signaling. The results of our KLF2 knockdown experiment confirm that the effects of laquinimod observed in vitro are dependent on KLF2 expression.

Conclusion

Together, these findings suggest a potential antiatherosclerotic capacity of laquinimod. Further research will elucidate the underlying mechanisms.

CDC42 Deletion Elicits Cerebral Vascular Malformations via Increased MEKK3-Dependent KLF4 Expression

RATIONALE

Aberrant formation of blood vessels precedes a broad spectrum of vascular complications; however, the cellular and molecular events governing vascular malformations are not yet fully understood.

OBJECTIVE

Here, we investigated the role of CDC42 (cell division cycle 42) during vascular morphogenesis and its relative importance for the development of cerebrovascular malformations.

METHODS AND RESULTS

To avoid secondary systemic effects often associated with embryonic gene deletion, we generated an endothelial-specific and inducible knockout approach to study postnatal vascularization of the mouse brain. Postnatal endothelial-specific deletion of Cdc42 elicits cerebrovascular malformations reminiscent of cerebral cavernous malformations (CCMs). At the cellular level, loss of CDC42 function in brain endothelial cells (ECs) impairs their sprouting, branching morphogenesis, axial polarity, and normal dispersion within the brain tissue. Disruption of CDC42 does not alter EC proliferation, but malformations occur where EC proliferation is the most pronounced during brain development-the postnatal cerebellum-indicating that a high, naturally occurring EC proliferation provides a permissive state for the appearance of these malformations. Mechanistically, CDC42 depletion in ECs elicited increased MEKK3 (mitogen-activated protein kinase kinase kinase 3)-MEK5 (mitogen-activated protein kinase kinase 5)-ERK5 (extracellular signal-regulated kinase 5) signaling and consequent detrimental overexpression of KLF (Kruppel-like factor) 2 and KLF4, recapitulating the hallmark mechanism for CCM pathogenesis. Through genetic approaches, we demonstrate that the coinactivation of Klf4 reduces the severity of vascular malformations in Cdc42 mutant mice. Moreover, we show that CDC42 interacts with CCMs and that CCM3 promotes CDC42 activity in ECs.

CONCLUSIONS

We show that endothelial-specific deletion of Cdc42 elicits CCM-like cerebrovascular malformations and that CDC42 is engaged in the CCM signaling network to restrain the MEKK3-MEK5-ERK5-KLF2/4 pathway.

Activation of GPR81 by lactate inhibits oscillatory shear stress-induced endothelial inflammation by activating the expression of KLF2

Atherosclerosis is a common and deadly cardiovascular disease with extremely high prevalence. Areas of the vasculature exposed to oscillatory shear stress (OSS) or disturbed blood flow are particularly prone to the development of atherosclerotic lesions. In part, various mechanosensitive receptors on the surface of endothelial cells play a role in regulating the ability of the vasculature to cope with variations in blood flow patterns. However, the exact mechanisms behind flow-mediated endothelial responses remain poorly understood. Along with the development of highly specific receptor agonists, the class of G coupled-protein receptors has been receiving increasing attention as potential therapeutic targets. G coupled-protein receptor 81 (GPR81), also known as hydroxycarboxylic acid receptor 1 (HCA₁ ), is activated by lactate, its endogenous ligand. In the present study, we show for the first time that expression of GPR81 is significantly downregulated in response to OSS in endothelial cells and that activation of GPR81 using physiologically relevant doses of lactate can rescue OSS-induced reduced GPR81 expression. Importantly, our findings demonstrate that activation of GPR81 can exert valuable atheroprotective effects in endothelial cells exposed to OSS by reducing oxidative stress and significantly downregulating the expression of inflammatory cytokines including interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1, and high mobility group box 1 (HMGB1). We also show that activation of GPR81 can potentially prevent the attachment of monocytes to the endothelium by suppressing OSS-induced secretion of vascular cellular adhesion molecule (VCAM)-1 and endothelial-selectin (E-selectin). Finally, we show that activation of GPR81 can rescue OSS-induced reduced expression of the key atheroprotective transcription factor Kruppel-like factor 2 (KLF2), which is mediated through the extracellular-regulated kinase 5 (ERK5) pathway. These findings demonstrate a potential protective role of GPR81 against atherogenesis and that targeted activation of GPR81 may inhibit endothelial inflammation and dysfunction induced by OSS.

Sulforaphane inhibits epithelial-mesenchymal transition by activating extracellular signal-regulated kinase 5 in lung cancer cells

Epithelial-mesenchymal transition (EMT) contributes to the initiation, invasion, metastasis and drug resistance of cancer. The function of extracellular signal-regulated kinase 5 (ERK5) in lung cancer progression remains elusive. In this study, we investigated the effect of sulforaphane (SFN) on lung cancer EMT and the role of ERK5 in its effect. Wound healing and Transwell assays were applied to examine the migratory and invasive capacity in vitro. Quantitative real-time polymerase chain reaction and immunoblotting analysis were performed to investigate the expression of mRNA and protein levels. Small-interfering RNA was used to silence ERK5. Xenograft model was used to confirm the effect of SFN in vivo. Enhanced EMT and decreased ERK5 activation were observed in lung cancer cells in comparison with normal human bronchial epithelial cells. SFN diminished the migratory and invasive capacity of lung cancer cells. Additionally, significantly increased expression of epithelial markers (E-cadherin and ZO-1), decreased expression of mesenchymal markers (N-cadherin and Snail1) and activation of ERK5 were observed after SFN treatment. The inhibitory effect of SFN on lung cancer cell EMT was attenuated by ERK5 silencing. SFN-induced EMT suppression and ERK5 activation were further confirmed in lung cancer xenograft mouse model. The present study illustrated for the first time that ERK5 activation mediates SFN suppression of lung cancer cell EMT. These findings could provide new insights into the function of ERK5 in EMT regulation and the potential therapeutic application of SFN in cancer intervention.

Krüppel-like factor 2 inhibits hepatocarcinogenesis through negative regulation of the Hedgehog pathway

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. The most important reason for the occurrence of HCC is hepatitis C or B infection. Moreover, genetic factors play an important role in the tumorigenesis of HCC. Here, we demonstrated that Krüppel-like factor 2 (KLF2) expression was downregulated in HCC samples compared with adjacent tissues. Additionally, KLF2 was shown to inhibit the growth, migration and colony-formation ability of liver cancer cells. Further mechanistic studies revealed that KLF2 can compete with Gli1 for interaction with HDAC1 and restrains Hedgehog signal activation. Together, our results suggest that KLF2 has potential as a diagnostic biomarker and therapeutic target for the treatment of HCC.

Recent advances in cerebral cavernous malformation research

Cerebral cavernous malformations (CCM) are manifested by microvascular lesions characterized by leaky endothelial cells with minimal intervening parenchyma predominantly in the central nervous system predisposed to hemorrhagic stroke, resulting in focal neurological defects. Till date, three proteins are implicated in this condition: CCM1 (KRIT1), CCM2 (MGC4607), and CCM3 (PDCD10). These multi-domain proteins form a protein complex via CCM2 that function as a docking site for the CCM signaling complex, which modulates many signaling pathways. Defects in the formation of this signaling complex have been shown to affect a wide range of cellular processes including cell-cell contact stability, vascular angiogenesis, oxidative damage protection and multiple biogenic events. In this review we provide an update on recent advances in structure and function of these CCM proteins, especially focusing on the signaling cascades involved in CCM pathogenesis and the resultant CCM cellular phenotypes in the past decade.

ERK5/KLF2 activation is involved in the reducing effects of puerarin on monocyte adhesion to endothelial cells and atherosclerotic lesion in apolipoprotein E-deficient mice

Puerarin has properties of anti-oxidation and anti-inflammation, which has been demonstrated protective effects in atherosclerosis and other cardiovascular diseases. However, the detail molecular mechanism still remains unclear. Here, we determined whether the atheroprotective effect of puerarin was by reducing monocyte adhesion and explored the underlying mechanism. The results showed that puerarin dose- and time-dependently reduced oxLDL-induced monocyte THP-1 adhesion to HUVECs and the expression of adhesion-related genes such as VCAM-1, ICAM-1, MCP-1 and IL-8 in HUVECs. Puerarin activated ERK5 phosphorylation and up-regulated expressions of downstream KLF2 and its targeted genes endothelial nitric oxide synthase and thrombomodulin. However, the protective effects were reversed by ERK5/KLF2 pathway inhibitor XDM8-92, BIX02189 or KLF2 siRNA suggesting the pathway involved in the function. The ex vivo assay, in which THP-1 adhesion to endothelium isolated from apoE-/- mice received various treatments further confirmed the results from HUVECs. Finally, we found that the atherosclerotic lesions in both cross sections at aortic root and whole aorta were significantly reduced in high fat-diet (HFD) mice with puerarin treatment compared with the HFD-only mice, but were increased respectively by 76% and 71% in XMD8-92 group, and 82% and 73% in BIX02189 group. Altogether, the data revealed that puerarin inhibited the monocyte adhesion in vitro and in vivo and thus reduced atherosclerotic lesions in apoE-/- mice; the protective effects were mediated by activation of ERK5/KLF2 signaling pathway. Our findings advance the understanding of puerarin function in atherosclerosis and point out a way to prevent the disease.

Absence of ERK5/MAPK7 delays tumorigenesis in Atm-/- mice

Ataxia-telangiectasia mutated (ATM) is a cell cycle checkpoint kinase that upon activation by DNA damage leads to cell cycle arrest and DNA repair or apoptosis. The absence of Atm or the occurrence of loss-of-function mutations in Atm predisposes to tumorigenesis. MAPK7 has been implicated in numerous types of cancer with pro-survival and pro-growth roles in tumor cells, but its functional relation with tumor suppressors is not clear. In this study, we show that absence of MAPK7 delays death due to spontaneous tumor development in Atm^−/− mice. Compared with Atm^−/− thymocytes, Mapk7^−/−Atm^−/− thymocytes exhibited an improved response to DNA damage (increased phosphorylation of H2AX) and a restored apoptotic response after treatment of mice with ionizing radiation. These findings define an antagonistic function of ATM and MAPK7 in the thymocyte response to DNA damage, and suggest that the lack of MAPK7 inhibits thymic lymphoma growth in Atm^−/− mice by partially restoring the DNA damage response in thymocytes.

Elevated Expression of miR302-367 in Endothelial Cells Inhibits Developmental Angiogenesis via CDC42/CCND1 Mediated Signaling Pathways

Rationale: Angiogenesis is critical for embryonic development and microRNAs fine-tune this process, but the underlying mechanisms remain incompletely understood.

Methods: Endothelial cell (EC) specific miR302-367 line was used as gain-of-function and anti-miRs as loss-of-function models to investigate the effects of miR302-367 on developmental angiogenesis with embryonic hindbrain vasculature as an in vivo model and fibrin gel beads and tube formation assay as in vitro models. Cell migration was evaluated by Boyden chamber and scratch wound healing assay and cell proliferation by cell count, MTT assay, Ki67 immunostaining and PI cell cycle analysis. RNA high-throughput sequencing identified miR-target genes confirmed by chromatin immunoprecipitation and 3'-UTR luciferase reporter assay, and finally target site blocker determined the pathway contributing significantly to the phenotype observed upon microRNA expression.

Results: Elevated EC miR302-367 expression reduced developmental angiogenesis, whereas it was enhanced by inhibition of miR302-367, possibly due to the intrinsic inhibitory effects on EC migration and proliferation. We identified Cdc42 as a direct target gene and elevated EC miR302-367 decreased total and active Cdc42, and further inhibited F-actin formation via the WASP and Klf2/Grb2/Pak1/LIM-kinase/Cofilin pathways. MiR302-367-mediated-Klf2 regulation of Grb2 for fine-tuning Pak1 activation contributing to the inhibited F-actin formation, and then the attenuation of EC migration. Moreover, miR302-367 directly down-regulated EC Ccnd1 and impaired cell proliferation via the Rb/E2F pathway.

Conclusion: miR302-367 regulation of endothelial Cdc42 and Ccnd1 signal pathways for EC migration and proliferation advances our understanding of developmental angiogenesis, and meanwhile provides a rationale for future interventions of pathological angiogenesis that shares many common features of physiological angiogenesis.

Fluid shear stress regulates the expression of Lectin-like oxidized low density lipoprotein receptor-1 via KLF2-AP-1 pathway depending on its intensity and pattern in endothelial cells

BACKGROUND AND AIMS

Vascular endothelial cells (ECs) are exposed to fluid shear stress (FSS), which modulates vascular pathophysiology. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is crucial in endothelial dysfunction and atherosclerosis. We elucidated the mechanism regulating LOX-1 expression in ECs by FSS.

METHODS

Human umbilical vein endothelial cells were exposed to laminar shear stress (LSS) of indicated intensities using a unidirectional steady flow, or to oscillatory shear stress (OSS) using a bidirectional disturbed flow. In vivo studies were performed in a mouse model of partial carotid ligation and human pulmonary artery sections.

RESULTS

Within ECs, OSS upregulated LOX-1 expression, while LSS (20 dyne/cm²) downregulated it. We confirmed that OSS-induced LOX-1 expression was suppressed when the mechanotransduction was inhibited by knockdown of the mechanosensory complex. In addition, we demonstrated that Kruppel-like factor 2 (KLF2) has an inhibitory role on OSS-induced LOX-1 expression. Next, we determined that activator protein-1 (AP-1) was the key transcription factor inducing LOX-1 expression by OSS, which was inhibited by KLF2 overexpression. To explore whether the intensity of LSS affects LOX-1 expression, we tested three different intensities (20, 60, and 120 dyne/cm²) of LSS. We observed higher LOX-1 expression with high shear stresses of 120 dyne/cm² compared to 20 and 60 dyne/cm², with OSS-like KLF2-AP-1 signaling patterns. Furthermore, ECs within disturbed flow regions showed upregulated LOX-1 expression in vivo.

CONCLUSIONS

We concluded that LOX-1 expression on ECs is regulated via FSS depending on its intensity as well as pattern. Furthermore, this is mediated through the KLF2-AP1 pathway of mechanotransduction.

Suberanilohydroxamic Acid as a Pharmacological Kruppel-Like Factor 2 Activator That Represses Vascular Inflammation and Atherosclerosis

BACKGROUND

Kruppel-like factor 2 (KLF2) is an important zinc-finger transcription factor that maintains endothelial homeostasis by its anti-inflammatory, -thrombotic, -oxidative, and -proliferative effects in endothelial cells. In light of the potent vasoprotective effects of KLF2, modulating KLF2 expression or function could give rise to new therapeutic strategies to treat cardiovascular diseases.

METHODS AND RESULTS

High-throughput drug screening based on KLF2 promoter luciferase reporter assay was performed to screen KLF2 activators. Real-time PCR and western blot were used to detect gene and protein expression. Identified KLF2 activator was orally administered to ApoE^-/- mice to evaluate anti-atherosclerotic efficacy. By screening 2400 compounds in the Spectrum library, we identified suberanilohydroxamic (SAHA) acid, also known as vorinostat as a pharmacological KLF2 activator through myocyte enhancer factor 2. We found that SAHA exhibited anti-inflammatory effects and attenuated monocyte adhesion to endothelial cells inflamed with tumor necrosis factor alpha. We further showed that the inhibitory effect of SAHA on endothelial inflammation and ensuing monocyte adhesion was KLF2 dependent using KLF2-deficient mouse lung endothelial cells or KLF2 small interfering RNA- depleted human endothelial cells. Importantly, we observed that oral administration of SAHA reduced diet-induced atherosclerotic lesion development in ApoE^-/- mice without significant effect on serum lipid levels.

CONCLUSIONS

These results demonstrate that SAHA has KLF2-dependent anti-inflammatory effects in endothelial cells and provide the proof of concept that KLF2 activation could be a promising therapeutic strategy for treating atherosclerosis.

Tannic acid as a plant-derived polyphenol exerts vasoprotection via enhancing KLF2 expression in endothelial cells

The transcription factor Kruppel-like factor 2 (KLF2) is a critical anti-inflammatory and anti-atherogenic molecule in vascular endothelium. Enhancing KLF2 expression and activity improves endothelial function and prevents atherosclerosis. However, the pharmacological and molecular regulators for KLF2 are scarce. Using high-throughput luciferase reporter assay to screen for KLF2 activators, we have identified tannic acid (TA), a polyphenolic compound, as a potent KLF2 activator that attenuates endothelial inflammation. Mechanistic studies suggested that TA induced KLF2 expression in part through the ERK5/MEF2 pathway. Functionally, TA markedly decreased monocyte adhesion to ECs by reducing expression of adhesion molecule VCAM1. Using lung ECs isolated from Klf2^+/+ and Klf2^+/− mice, we showed that the anti-inflammatory effect of TA is dependent on KLF2. Collectively, our results demonstrate that TA is a potent KLF2 activator and TA attenuated endothelial inflammation through upregulation of KLF2. Our findings provide a novel mechanism for the well-established beneficial cardiovascular effects of TA and suggest that KLF2 could be a novel therapeutic target for atherosclerotic vascular disease.

Extracellular Signal-Regulated Kinase 5 is Required for Low-Concentration H2O2-Induced Angiogenesis of Human Umbilical Vein Endothelial Cells

Background. The aim of this study was to assess the effects of low concentrations of H₂O₂ on angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro and explore the underlying mechanisms. Methods. HUVECs were cultured and stimulated with different concentrations of H₂O₂. Flow cytometric analysis was used to select an optimal concentration of H₂O₂ for the following experiments. Cell proliferation, migration, and tubule formation were evaluated by Cell Counting Kit-8 (CCK-8) assays, scratch wound assays, and Matrigel tubule formation assays, respectively. For gain and loss of function studies, constitutively active MEK5 (CA-MEK5) and ERK5 shRNA lentiviruses were used to activate or knock down extracellular signal-regulated kinase 5 (ERK5). Results. We found that low concentrations of H₂O₂ promoted HUVECs proliferation, migration, and tubule formation. ERK5 in HUVECs was significantly activated by H₂O₂. Enhanced ERK5 activity significantly amplified the proangiogenic effects of H₂O₂; in contrast, ERK5 knock-down abrogated the effects of H₂O₂. Conclusions. Our results confirmed that low concentrations of H₂O₂ promoted HUVECs angiogenesis in vitro, and ERK5 is an essential mediator of this process. Therefore, ERK5 may be a potential therapeutic target for promoting angiogenesis and improving graft survival.

Shear Stress Induces Change in Extracellular Signal-Regulated Kinase 5 Levels with Sustained Activation under Disturbed and Continuous Laminar Flow

Extracellular signal-regulated kinase 5 (ERK5) has been reported to regulate endothelial integrity and protect from vascular dysfunction under laminar flow. Previously reported research indicates that under laminar flow ERK5 is activated with production of atheroprotective molecules. However, the characterization of ERK5 activation and levels under different flow patterns has not been investigated. Confluent HUVECs were serum-starved then seeded on glass slides. HUVECs incubated in 1% FBS were exposed to continuous laminar flow (CLF), to-and-fro flow (TFF), or pulsatile forward flow (PFF) in a parallel plate flow chamber. At the end of experimentation, cell lysates were immunoblotted with antibodies to phospho-ERK5 and total ERK5. ERK5 activation was assessed by the levels of phosphorylated ERK5. The densitometric mean ± SEM is calculated and analyzed by ANOVA. p < 0.05 is considered significant. Levels of ERK5 decreased with all flow conditions with the largest decrease in TFF flow condition. TFF and CLF exhibited sustained ERK5 phosphorylation in HUVECs stimulated for up to 4 hours. PFF had transient phosphorylation of ERK5 at 2 hours, which then became undetectable at 4 hours of exposure to flow. Also, TFF and CLF both showed decreased levels at 4 hours, suggesting a decrease in activation for these flow conditions. Exposure of HUVEC to different types of shear stress results in varying patterns of activation of ERK5. Activation of ERK5 with TFF suggests a role in the pathogenesis of atherosclerosis and vascular remodeling under disturbed flow conditions.

Scutellarin attenuates vasospasm through the Erk5-KLF2-eNOS pathway after subarachnoid hemorrhage in rats

Angiographic vasospasm, especially in the early phases (<72h) of subarachnoid hemorrhage (SAH), is one of the major complications after an aneurysm rupture and is often the cause of delayed neurological deterioration. Scutellarin (SCU), a flavonoid extracted from the traditional Chinese herb Erigeron breviscapus, has been widely accepted as an antioxidant, but the effect of SCU on vasospasm after SAH remains elusive. Endovascular perforation was conducted to induce SAH in Sprague-Dawley rats. Then, the underlying mechanism of the anti-vasospasm effect of SCU was investigated using a modified Garcia scale, India ink angiography, cross-sectional area analysis, immunohistochemistry staining and western blot. SCU (50μM, 100mg/kg) alleviated angiographic vasospasm and improved neurological function 48h after SAH and enhanced the expression of endothelial nitric oxide synthase (eNOS) at the intima of cerebral arteries. In addition, SCU upregulated the expression of phosphorylated extracellular-regulated kinase 5 (p-Erk5) and Kruppel-like factor 2 (KLF2) at 48h after SAH. However, the effects of SCU were reversed by the Erk5 inhibitor XMD8-92. Our results indicate that SCU could attenuate vasospasm and neurological deficits via modulating the Erk5-KLF2-eNOS pathway after SAH, which may provide an experimental basis for the clinical use of SCU treatment in SAH patients.

KLF4 is a key determinant in the development and progression of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are vascular malformations located within the central nervous system often resulting in cerebral hemorrhage. Pharmacological treatment is needed, since current therapy is limited to neurosurgery. Familial CCM is caused by loss‐of‐function mutations in any of Ccm1, Ccm2, and Ccm3 genes. CCM cavernomas are lined by endothelial cells (ECs) undergoing endothelial‐to‐mesenchymal transition (EndMT). This switch in phenotype is due to the activation of the transforming growth factor beta/bone morphogenetic protein (TGFβ/BMP) signaling. However, the mechanism linking Ccm gene inactivation and TGFβ/BMP‐dependent EndMT remains undefined. Here, we report that Ccm1 ablation leads to the activation of a MEKK3‐MEK5‐ERK5‐MEF2 signaling axis that induces a strong increase in Kruppel‐like factor 4 (KLF4) in ECs in vivo. KLF4 transcriptional activity is responsible for the EndMT occurring in CCM1‐null ECs. KLF4 promotes TGFβ/BMP signaling through the production of BMP6. Importantly, in endothelial‐specific Ccm1 and Klf4 double knockout mice, we observe a strong reduction in the development of CCM and mouse mortality. Our data unveil KLF4 as a therapeutic target for CCM.

Blood Brothers: Hemodynamics and Cell-Matrix Interactions in Endothelial Function

SIGNIFICANCE

Alterations in endothelial function contribute to a variety of vascular diseases. In pathological conditions, the endothelium shows a reduced ability to regulate vasodilation (endothelial dysfunction) and a conversion toward a proinflammatory and leaky phenotype (endothelial activation). At the interface between the vessel wall and blood, the endothelium exists in a complex microenvironment and must translate changes in these environmental signals to alterations in vessel function. Mechanical stimulation and endothelial cell interactions with the vascular matrix, as well as a host of soluble factors, coordinately contribute to this dynamic regulation.

RECENT ADVANCES

Blood hemodynamics play an established role in the regulation of endothelial function. However, a growing body of work suggests that subendothelial matrix composition similarly and coordinately regulates endothelial cell phenotype such that blood flow affects matrix remodeling, which affects the endothelial response to flow.

CRITICAL ISSUES

Hemodynamics and soluble factors likely affect endothelial matrix remodeling through multiple mechanisms, including transforming growth factor β signaling and alterations in cell-matrix receptors, such as the integrins. Likewise, differential integrin signaling following matrix remodeling appears to regulate several key flow-induced responses, including nitric oxide production, regulation of oxidant stress, and activation of proinflammatory signaling and gene expression. Microvascular remodeling responses, such as angiogenesis and arteriogenesis, may also show coordinated regulation by flow and matrix.

FUTURE DIRECTIONS

Identifying the mechanisms regulating the dynamic interplay between hemodynamics and matrix remodeling and their contribution to the pathogenesis of cardiovascular disease remains an important research area with therapeutic implications across a variety of conditions. Antioxid. Redox Signal. 25, 415-434.

Expression of p21-activated kinases 1 and 3 is altered in the brain of subjects with depression

The p21-activated kinases (PAKs) of group I are the main effectors for the small Rho GTPases, critically involved in neurodevelopment, plasticity and maturation of the nervous system. Moreover, the neuronal complexity controlled by PAK1/PAK3 signaling determines the postnatal brain size and synaptic properties. Stress induces alterations at the level of structural and functional synaptic plasticity accompanied by reductions in size and activity of the hippocampus and the prefrontal cortex (PFC). These abnormalities are likely to contribute to the pathology of depression and, in part, reflect impaired cytoskeleton remodeling pointing to the role of Rho GTPase signaling. Thus, the present study assessed the expression of the group I PAKs and their activators in the brain of depressed subjects. Using quantitative polymerase chain reaction (qPCR), mRNA levels and coexpression of the group I PAKs: PAK1, PAK2, and PAK3 as well as of their activators: RAC1, CDC42 and ARHGEF7 were examined in postmortem samples from the PFC (n=25) and the hippocampus (n=23) of subjects with depression and compared to control subjects (PFC n=24; hippocampus n=21). Results demonstrated that mRNA levels of PAK1 and PAK3, are significantly reduced in the brain of depressed subjects, with PAK1 being reduced in the PFC and PAK3 in the hippocampus. No differences were observed for the ubiquitously expressed PAK2. Following analysis of gene coexpression demonstrated disruption of coordinated gene expression in the brain of subjects with depression. Abnormalities in mRNA expression of PAK1 and PAK3 as well as their altered coexpression patterns were detected in the brain of subjects with depression.

BET Bromodomain Suppression Inhibits VEGF-induced Angiogenesis and Vascular Permeability by Blocking VEGFR2-mediated Activation of PAK1 and eNOS

The tyrosine kinase receptor vascular endothelial growth factor receptor 2 (VEGFR2) is a critical modulator of angiogenesis. Increasing evidence indicate the important role of bromodomain and extra-terminal domain (BET) of chromatin adaptors in regulating tumor growth and inflammatory response. However, whether BET proteins have a role in angiogenesis and endothelial permeability is unclear. In this study, we observed that treatment with JQ1, a specific BET inhibitor, suppressed in vitro tube formation of human umbilical vein endothelial cells (HUVECs) and in vivo angiogenesis in a Matrigel plug and oxygen-induced retinopathy neovascularization. JQ1 attenuated the VEGF-induced decrease in TEER in HUVECs and prevented Evans blue dye leakage in the VEGF-induced Miles assay in athymic Balb/c nude mice. BET inhibition with JQ1 or shRNA for Brd2 or Brd4 suppressed VEGF-induced migration, proliferation, and stress fiber formation of HUVECs. Furthermore, BET inhibition suppressed phosphorylation of VEGFR2 and PAK1, as well as eNOS activation in VEGF-stimulated HUVECs. Inhibition with VEGFR2 and PAK1 also reduced migration and proliferation, and attenuated the VEGF-induced decrease in TEER. Thus, our observations suggest the important role of BET bromodomain in regulating VEGF-induced angiogenesis. Strategies that target the BET bromodomain may provide a new therapeutic approach for angiogenesis-related diseases.

p21-Activated Kinase 2 Regulates Endothelial Development and Function through the Bmk1/Erk5 Pathway

p21-activated kinases (Paks) have been shown to regulate cytoskeleton rearrangements, cell proliferation, attachment, and migration in a variety of cellular contexts, including endothelial cells. However, the role of endothelial Pak in embryo development has not been reported, and currently, there is no consensus on the endothelial function of individual Pak isoforms, in particular p21-activated kinase 2 (Pak2), the main Pak isoform expressed in endothelial cells. In this work, we employ genetic and molecular studies that show that Pak2, but not Pak1, is a critical mediator of development and maintenance of endothelial cell function. Endothelial depletion of Pak2 leads to early embryo lethality due to flawed blood vessel formation in the embryo body and yolk sac. In adult endothelial cells, Pak2 depletion leads to severe apoptosis and acute angiogenesis defects, and in adult mice, endothelial Pak2 deletion leads to increased vascular permeability. Furthermore, ubiquitous Pak2 deletion is lethal in adult mice. We show that many of these defects are mediated through a newly unveiled Pak2/Bmk1 pathway. Our results demonstrate that endothelial Pak2 is essential during embryogenesis and also for adult blood vessel maintenance, and they also pinpoint the Bmk1/Erk5 pathway as a critical mediator of endothelial Pak2 signaling.

The Ins and Outs of Small GTPase Rac1 in the Vasculature

The Rho family of small GTPases forms a 20-member family within the Ras superfamily of GTP-dependent enzymes that are activated by a variety of extracellular signals. The most well known Rho family members are RhoA (Ras homolog gene family, member A), Cdc42 (cell division control protein 42), and Rac1 (Ras-related C3 botulinum toxin substrate 1), which affect intracellular signaling pathways that regulate a plethora of critical cellular functions, such as oxidative stress, cellular contacts, migration, and proliferation. In this review, we describe the current knowledge on the role of GTPase Rac1 in the vasculature. Whereas most recent reviews focus on the role of vascular Rac1 in endothelial cells, in the present review we also highlight the functional involvement of Rac1 in other vascular cells types, namely, smooth muscle cells present in the media and fibroblasts located in the adventitia of the vessel wall. Collectively, this overview shows that Rac1 activity is involved in various functions within one cell type at distinct locations within the cell, and that there are overlapping but also cell type-specific functions in the vasculature. Chronically enhanced Rac1 activity seems to contribute to vascular pathology; however, Rac1 is essential to vascular homeostasis, which makes Rac1 inhibition as a therapeutic option a delicate balancing act.

The influence of dysfunctional signaling and lipid homeostasis in mediating the inflammatory responses during atherosclerosis

Atherosclerosis, the underlying cause of myocardial infarction and thrombotic cerebrovascular events, is responsible for the majority of deaths in westernized societies. Mortality from this disease is also increasing at a marked rate in developing countries due to the acquisition of a westernized lifestyle accompanied with elevated rates of obesity and diabetes. Atherosclerosis is recognized as a chronic inflammatory disorder associated with lipid accumulation and the development of fibrotic plaques within the walls of medium and large arteries. A range of immune cells, such as macrophages and T-lymphocytes, through the action of various cytokines, such as interleukins-1 and -33, transforming growth factor-β and interferon-γ, orchestrates the inflammatory response in this disease. The disease is also characterized by marked dysfunction in lipid homeostasis and signaling pathways that control the inflammatory response. This review will discuss the molecular basis of atherosclerosis with particular emphasis on the roles of the immune cells and cytokines along with the dysfunctional lipid homeostasis and cell signaling associated with this disease.