Endothelial Kruppel-like factor 4 regulates angiogenesis and the Notch signaling pathway

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.

Origin and stepwise evolution of vertebrate lungs

Lungs are essential respiratory organs in terrestrial vertebrates, present in most bony fishes but absent in cartilaginous fishes, making them an ideal model for studying organ evolution. Here we analysed single-cell RNA sequencing data from adult and developing lungs across vertebrate species, revealing significant similarities in cell composition, developmental trajectories and gene expression patterns. Surprisingly, a large proportion of lung-related genes, coexpression patterns and many lung enhancers are present in cartilaginous fishes despite their lack of lungs, suggesting that a substantial genetic foundation for lung development existed in the last common ancestor of jawed vertebrates. In addition, the 1,040 enhancers that emerged since the last common ancestor of bony fishes probably contain lung-specific elements that led to the development of lungs. We further identified alveolar type 1 cells as a mammal-specific alveolar cell type, along with several mammal-specific genes, including ager and sfta2, that are highly expressed in lungs. Functional validation showed that deletion of sfta2 in mice leads to severe respiratory defects, highlighting its critical role in mammalian lung features. Our study provides comprehensive insights into the evolution of vertebrate lungs, demonstrating how both regulatory network modifications and the emergence of new genes have shaped lung development and specialization across species.

Unraveling the Molecular Mechanisms of SIRT7 in Angiogenesis: Insights from Substrate Clues

Angiogenesis, a vital physiological or pathological process regulated by complex molecular networks, is widely implicated in organismal development and the pathogenesis of various diseases. SIRT7, a member of the Sirtuin family of nicotinamide adenine dinucleotide + (NAD+) dependent deacetylases, plays crucial roles in cellular processes such as transcriptional regulation, cell metabolism, cell proliferation, and genome stability maintenance. Characterized by its enzymatic activities, SIRT7 targets an array of substrates, several of which exert regulatory effects on angiogenesis. Experimental evidence from in vitro and in vivo studies consistently demonstrates the effects of SIRT7 in modulating angiogenesis, mediated through various molecular mechanisms. Consequently, understanding the regulatory role of SIRT7 in angiogenesis holds significant promise, offering novel avenues for therapeutic interventions targeting either SIRT7 or angiogenesis. This review delineates the putative molecular mechanisms by which SIRT7 regulates angiogenesis, taking its substrates as a clue, endeavoring to elucidate experimental observations by integrating knowledge of SIRT7 substrates and established angiogenenic mechanisms.

The kruppel-like factor (KLF) family, diseases, and physiological events

The Kruppel-Like Factor family of regulatory proteins, which has 18 members, is transcription factors. This family contains zinc finger proteins, regulates the activation and suppression of transcription, and binds to DNA, RNA, and proteins. Klfs related to the immune system are Klf1, Klf2, Klf3, Klf4, Klf6, and Klf14. Klfs related to adipose tissue development and/or glucose metabolism are Klf3, Klf7, Klf9, Klf10, Klf11, Klf14, Klf15, and Klf16. Klfs related to cancer are Klf3, Klf4, Klf5, Klf6, Klf7, Klf8, Klf9, Klf10, Klf11, Klf12, Klf13, Klf14, Klf16, and Klf17. Klfs related to the cardiovascular system are Klf4, Klf5, Klf10, Klf13, Klf14, and Klf15. Klfs related to the nervous system are Klf4, Klf7, Klf8, and Klf9. Klfs are associated with diseases such as carcinogenesis, oxidative stress, diabetes, liver fibrosis, thalassemia, and the metabolic syndrome. The aim of this review is to provide information about the relationship of Klfs with some diseases and physiological events and to guide future studies.

KLF4 down-regulation underlies placental angiogenesis impairment induced by maternal glucose intolerance in late pregnancy

Maternal glucose intolerance in late pregnancy can easily impair pregnancy outcomes and placental development. The impairment of placental angiogenesis is closely related to the occurrence of glucose intolerance during pregnancy, but the mechanism remains largely unknown. In this study, the pregnant mouse model of maternal high-fat diet and endothelial injury model of porcine vascular endothelial cells (PVECs) was used to investigate the effect of glucose intolerance on pregnancy outcomes and placental development. Feeding pregnant mice, a high-fat diet was shown to induce glucose intolerance in late pregnancy, and significantly increase the incidence of resorbed fetuses. Moreover, a decrease was observed in the proportion of blood sinusoids area and the expression level of CD31 in placenta, indicating that placental vascular development was impaired by high-fat diet. Considering that hyperglycemia is an important symptom of glucose intolerance, we exposed PVECs to high glucose (50 mM), which verified the negative effects of high glucose on endothelial function. Bioinformatics analysis further emphasized that high glucose exposure could significantly affect the angiogenesis-related functions of PVECs and predicted that Krüppel-like factor 4 (KLF4) may be a key mediator of these functional changes. The subsequent regulation of KLF4 expression confirmed that the inhibition of KLF4 expression was an important reason why high glucose impaired the endothelial function and angiogenesis of PVECs. These results indicate that high-fat diet can aggravate maternal glucose intolerance and damage pregnancy outcome and placental angiogenesis, and that regulating the expression of KLF4 may be a potential therapeutic strategy for maintaining normal placental angiogenesis.

Discovery of Transcription Factors Involved in the Maintenance of Resident Vascular Endothelial Stem Cell Properties

A resident vascular endothelial stem cell (VESC) population expressing CD157 has been identified recently in mice. Herein, we identified transcription factors (TFs) regulating CD157 expression in endothelial cells (ECs) that were associated with drug resistance, angiogenesis, and EC proliferation. In the first screening, we detected 20 candidate TFs through the CD157 promoter and gene expression analyses. We found that 10 of the 20 TFs induced CD157 expression in ECs. We previously reported that 70% of CD157 VESCs were side population (SP) ECs that abundantly expressed ATP-binding cassette (ABC) transporters. Here, we found that the 10 TFs increased the expression of several ABC transporters in ECs and increased the proportion of SP ECs. Of these 10 TFs, we found that six (Atf3, Bhlhe40, Egr1, Egr2, Elf3, and Klf4) were involved in the manifestation of the SP phenotype. Furthermore, the six TFs enhanced tube formation and proliferation in ECs. Single-cell RNA sequence data in liver ECs suggested that Atf3 and Klf4 contributed to the production of CD157+ VESCs in the postnatal period. We concluded that Klf4 might be important for the development and maintenance of liver VESCs. Our work suggests that a TF network is involved in the differentiation hierarchy of VESCs.

Cooperative Response to Endocardial Notch Reveals Interaction With Hippo Pathway

BACKGROUND

The endocardium is a crucial signaling center for cardiac valve development and maturation. Genetic analysis has identified several human endocardial genes whose inactivation leads to bicuspid aortic valve formation and calcific aortic valve disease, but knowledge is very limited about the role played in valve development and disease by noncoding endocardial regulatory regions and upstream factors.

METHODS

We manipulated Notch signaling in mouse embryonic endocardial cells by short-term and long-term coculture with OP9 stromal cells expressing Notch ligands and inhibition of Notch activity. We examined the transcriptional profile and chromatin accessibility landscape for each condition, integrated transcriptomic, transcription factor occupancy, chromatin accessibility, and proteomic datasets. We generated in vitro and in vivo models with CRISPR-Cas9-edited deletions of various noncoding regulatory elements and validated their regulatory potential.

RESULTS

We identified primary and secondary transcriptional responses to Notch ligands in the mouse embryonic endocardium, and a NOTCH-dependent transcriptional signature in valve development and disease. By defining the changes in the chromatin accessibility landscape and integrating with the landscape in developing mouse endocardium and adult human valves, we identify potential noncoding regulatory elements, validated selected candidates, propose interacting cofactors, and define the timeframe of their regulatory activity. Additionally, we found cooperative transcriptional repression with Hippo pathway by inhibiting nuclear Yap (Yes-associated protein) activity in the endocardium during cardiac valve development.

CONCLUSIONS

Sequential Notch-dependent transcriptional regulation in the embryonic endocardium involves multiple factors. Notch activates certain noncoding elements through these factors and simultaneously suppresses elements that could hinder cardiac valve development and homeostasis. Biorxviv: https://www.biorxiv.org/content/10.1101/2023.03.23.533882v1.full.

Micro-Executor of Natural Products in Metabolic Diseases

Obesity, diabetes, and cardiovascular diseases are the major chronic metabolic diseases that threaten human health. In order to combat these epidemics, there remains a desperate need for effective, safe, and easily available therapeutic strategies. Recently, the development of natural product research has provided new methods and options for these diseases. Numerous studies have demonstrated that microRNAs (miRNAs) are key regulators of metabolic diseases, and natural products can improve lipid and glucose metabolism disorders and cardiovascular diseases by regulating the expression of miRNAs. In this review, we present the recent advances involving the associations between miRNAs and natural products and the current evidence showing the positive effects of miRNAs for natural product treatment in metabolic diseases. We also encourage further research to address the relationship between miRNAs and natural products under physiological and pathological conditions, thus leading to stronger support for drug development from natural products in the future.

MicroRNAs in Tumor Endothelial Cells: Regulation, Function and Therapeutic Applications

Tumor endothelial cells (TECs) are key stromal components of the tumor microenvironment, and are essential for tumor angiogenesis, growth and metastasis. Accumulating evidence has shown that small single-stranded non-coding microRNAs (miRNAs) act as powerful endogenous regulators of TEC function and blood vessel formation. This systematic review provides an up-to-date overview of these endothelial miRNAs. Their expression is mainly regulated by hypoxia, pro-angiogenic factors, gap junctions and extracellular vesicles, as well as long non-coding RNAs and circular RNAs. In preclinical studies, they have been shown to modulate diverse fundamental angiogenesis-related signaling pathways and proteins, including the vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway; the rat sarcoma virus (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway; the phosphoinositide 3-kinase (PI3K)/AKT pathway; and the transforming growth factor (TGF)-β/TGF-β receptor (TGFBR) pathway, as well as krüppel-like factors (KLFs), suppressor of cytokine signaling (SOCS) and metalloproteinases (MMPs). Accordingly, endothelial miRNAs represent promising targets for future anti-angiogenic cancer therapy. To achieve this, it will be necessary to further unravel the regulatory and functional networks of endothelial miRNAs and to develop safe and efficient TEC-specific miRNA delivery technologies.

Krüppel-like factor 10 modulates stem cell phenotypes of pancreatic adenocarcinoma by transcriptionally regulating notch receptors

BACKGROUND

Pancreatic adenocarcinoma (PDAC) is well known for its rapid distant metastasis and local destructive behavior. Loss of Krüppel-like factor 10 (KLF10) contributes to distant migration of PDAC. The role of KLF10 in modulating tumorigenesis and stem cell phenotypes of PDAC is unclear.

METHODS

Additional depletion of KLF10 in KC (LSL: Kras^G12D; Pdx1-Cre) mice, a spontaneous murine PDAC model, was established to evaluate tumorigenesis. Tumor specimens of PDAC patients were immune-stained of KLF10 to correlate with local recurrence after curative resection. Conditional overexpressing KLF10 in MiaPaCa and stably depleting KLF10 in Panc-1 (Panc-1-pLKO-shKLF10) cells were established for evaluating sphere formation, stem cell markers expression and tumor growth. The signal pathways modulated by KLF10 for PDAC stem cell phenotypes were disclosed by microarray analysis and validated by western blot, qRT-PCR, luciferase reporter assay. Candidate targets to reverse PDAC tumor growth were demonstrated in murine model.

RESULTS

KLF10, deficient in two-thirds of 105 patients with resected pancreatic PDAC, was associated with rapid local recurrence and large tumor size. Additional KLF10 depletion in KC mice accelerated progression from pancreatic intraepithelial neoplasia to PDAC. Increased sphere formation, expression of stem cell markers, and tumor growth were observed in Panc-1-pLKO-shKLF10 compared with vector control. Genetically or pharmacologically overexpression of KLF10 reversed the stem cell phenotypes induced by KLF10 depletion. Ingenuity pathway analysis and gene set enrichment analysis showed that Notch signaling molecules, including Notch receptors 3 and 4, were over-expressed in Panc-1-pLKO-shKLF10. KLF10 transcriptionally suppressed Notch-3 and -4 by competing with E74-like ETS transcription factor 3, a positive regulator, for promoter binding. Downregulation of Notch signaling, either genetically or pharmacologically, ameliorated the stem cell phenotypes of Panc-1-pLKO-shKLF10. The combination of metformin, which upregulated KLF10 expression via phosphorylating AMPK, and evodiamine, a non-toxic Notch-3 methylation stimulator, delayed tumor growth of PDAC with KLF10 deficiency in mice without prominent toxicity.

CONCLUSIONS

These results demonstrated a novel signaling pathway by which KLF10 modulates stem cell phenotypes in PDAC through transcriptionally regulating Notch signaling pathway. The elevation of KLF10 and suppression of Notch signaling may jointly reduce PDAC tumorigenesis and malignant progression.

KLF4 transcription factor in tumorigenesis

Krüppel-like transcriptional factor is important in maintaining cellular functions. Deletion of Krüppel-like transcriptional factor usually causes abnormal embryonic development and even embryonic death. KLF4 is a prominent member of this family, and embryonic deletion of KLF4 leads to alterations in skin permeability and postnatal death. In addition to its important role in embryo development, it also plays a critical role in inflammation and malignancy. It has been investigated that KLF4 has a regulatory role in a variety of cancers, including lung, breast, prostate, colorectal, pancreatic, hepatocellular, ovarian, esophageal, bladder and brain cancer. However, the role of KLF4 in tumorigenesis is complex, which may link to its unique structure with both transcriptional activation and transcriptional repression domains, and to the regulation of its upstream and downstream signaling molecules. In this review, we will summarize the structural and functional aspects of KLF4, with a focus on KLF4 as a clinical biomarker and therapeutic target in different types of tumors.

Multi-species meta-analysis identifies transcriptional signatures associated with cardiac endothelial responses in the ischaemic heart

AIM

Myocardial infarction remains the leading cause of heart failure. The adult human heart lacks the capacity to undergo endogenous regeneration. New blood vessel growth is integral to regenerative medicine necessitating a comprehensive understanding of the pathways that regulate vascular regeneration. We sought to define the transcriptomic dynamics of coronary endothelial cells following ischaemic injuries in the developing and adult mouse and human heart and to identify new mechanistic insights and targets for cardiovascular regeneration.

METHODS AND RESULTS

We carried out a comprehensive meta-analysis of integrated single-cell RNA-sequencing data of coronary vascular endothelial cells from the developing and adult mouse and human heart spanning healthy and acute and chronic ischaemic cardiac disease. We identified species-conserved gene regulatory pathways aligned to endogenous neovascularization. We annotated injury-associated temporal shifts of the endothelial transcriptome and validated four genes: VEGF-C, KLF4, EGR1, and ZFP36. Moreover, we showed that ZFP36 regulates human coronary endothelial cell proliferation and defined that VEGF-C administration in vivo enhances clonal expansion of the cardiac vasculature post-myocardial infarction. Finally, we constructed a coronary endothelial cell meta-atlas, CrescENDO, to empower future in-depth research to target pathways associated with coronary neovascularization.

CONCLUSION

We present a high-resolution single-cell meta-atlas of healthy and injured coronary endothelial cells in the mouse and human heart, revealing a suite of novel targets with great potential to promote vascular regeneration, and providing a rich resource for therapeutic development.

Krüppel-like factors in tumors: Key regulators and therapeutic avenues

Krüppel-like factors (KLFs) are a group of DNA-binding transcriptional regulators with multiple essential functions in various cellular processes, including proliferation, migration, inflammation, and angiogenesis. The aberrant expression of KLFs is often found in tumor tissues and is essential for tumor development. At the molecular level, KLFs regulate multiple signaling pathways and mediate crosstalk among them. Some KLFs may also be molecular switches for specific biological signals, driving their transition from tumor suppressors to promoters. At the histological level, the abnormal expression of KLFs is closely associated with tumor cell stemness, proliferation, apoptosis, and alterations in the tumor microenvironment. Notably, the role of each KLF in tumors varies according to tumor type and different stages of tumor development rather than being invariant. In this review, we focus on the advances in the molecular biology of KLFs, particularly the regulations of several classical signaling pathways by these factors, and the critical role of KLFs in tumor development. We also highlight their strong potential as molecular targets in tumor therapy and suggest potential directions for clinical translational research.

Remarkable sex-specific differences at single-cell resolution in neonatal hyperoxic lung injury

Exposure to supraphysiological concentrations of oxygen (hyperoxia) predisposes to bronchopulmonary dysplasia (BPD), which is characterized by abnormal alveolarization and pulmonary vascular development, in preterm neonates. Neonatal hyperoxia exposure is used to recapitulate the phenotype of human BPD in murine models. Male sex is considered an independent predictor for the development of BPD, but the main mechanisms underlying sexually dimorphic outcomes are unknown. Our objective was to investigate sex-specific and cell-type specific transcriptional changes that drive injury in the neonatal lung exposed to hyperoxia at single-cell resolution and delineate the changes in cell-cell communication networks in the developing lung. We used single-cell RNA sequencing (scRNAseq) to generate transcriptional profiles of >35,000 cells isolated from the lungs of neonatal male and female C57BL/6 mice exposed to 95% [Formula: see text] between PND1-5 (saccular stage of lung development) or normoxia and euthanized at PND7 (alveolar stage of lung development). ScRNAseq identified 22 cell clusters with distinct populations of endothelial, epithelial, mesenchymal, and immune cells. Our data identified that the distal lung vascular endothelium (composed of aerocytes and general capillary endothelial cells) is exquisitely sensitive to hyperoxia exposure with the emergence of an intermediate capillary endothelial population with both general capillaries (gCap) and aerocytes or alveolar capillaries (aCap) markers. We also identified a myeloid-derived suppressor cell population from the lung neutrophils. Sex-specific differences were evident in all lung cell subpopulations but were striking among the lung immune cells. Finally, we identified that the specific intercellular communication networks and the ligand-receptor pairs that are impacted by neonatal hyperoxia exposure.

MED1 Regulates BMP/TGF-β in Endothelium: Implication for Pulmonary Hypertension

BACKGROUND

Dysregulated BMP (bone morphogenetic protein) or TGF-β (transforming growth factor beta) signaling pathways are imperative in idiopathic and familial pulmonary arterial hypertension (PAH) as well as experimental pulmonary hypertension (PH) in rodent models. MED1 (mediator complex subunit 1) is a key transcriptional co-activator and KLF4 (Krüppel-like factor 4) is a master transcription factor in endothelium. However, MED1 and KLF4 epigenetic and transcriptional regulations of the BMP/TGF-β axes in pulmonary endothelium and their dysregulations leading to PAH remain elusive. We investigate the MED1/KLF4 co-regulation of the BMP/TGF-β axes in endothelium by studying the epigenetic regulation of BMPR2 (BMP receptor type II), ETS-related gene (ERG), and TGFBR2 (TGF-β receptor 2) and their involvement in the PH.

METHODS

High-throughput screening involving data from RNA-seq, MED1 ChIP-seq, H3K27ac ChIP-seq, ATAC-seq, and high-throughput chromosome conformation capture together with in silico computations were used to explore the epigenetic and transcriptional regulation of BMPR2, ERG, and TGFBR2 by MED1 and KLF4. In vitro experiments with cultured pulmonary arterial endothelial cells (ECs) and bulk assays were used to validate results from these in silico analyses. Lung tissue from patients with idiopathic PAH, animals with experimental PH, and mice with endothelial ablation of MED1 (EC-MED1-/-) were used to study the PH-protective effect of MED1.

RESULTS

Levels of MED1 were decreased in lung tissue or pulmonary arterial endothelial cells from idiopathic PAH patients and rodent PH models. Mechanistically, MED1 acted synergistically with KLF4 to transactivate BMPR2, ERG, and TGFBR2 via chromatin remodeling and enhancer-promoter interactions. EC-MED1-/- mice showed PH susceptibility. In contrast, MED1 overexpression mitigated the PH phenotype in rodents.

CONCLUSIONS

A homeostatic regulation of BMPR2, ERG, and TGFBR2 in ECs by MED1 synergistic with KLF4 is essential for the normal function of the pulmonary endothelium. Dysregulation of MED1 and the resulting impairment of the BMP/TGF-β signaling is implicated in the disease progression of PAH in humans and PH in rodent models.

Inhibitory Effect of Essential Oil From Fructus of Alpinia zerumbet on Endothelial-to-Mesenchymal Transformation Induced by TGF-β1 and Downregulation of KLF4

Essential oil from fructus of Alpinia zerumbet (EOFAZ) protects vascular endothelial cell (VEC) injury. Stimulation and injury factors can induce phenotypic changes in VECs and the occurrence of endothelial-mesenchymal transformation (EndMT), accelerating the occurrence and development of cardiovascular diseases. We investigated the role of EOFAZ in EndMT induced by transforming growth factor-β1 (TGF-β1). All experiments were performed using human umbilical vein endothelial cells (HUVECs). HUVECs were preincubated with EOFAZ for 2 hours and then coincubated with TGF-β1 for 72 hours. Krüpple-like factor 4 (KLF4) was inhibited by small interfering RNA or overexpressed by adenovirus infection. Wound healing, transwell, and angiogenesis assays were used to evaluate the migration ability of HUVECs. Quantitative RT-PCR and Western blotting were used for mRNA and protein expression analyses, respectively. Immunofluorescence staining was used to detect expression of related markers. A coimmunoprecipitation assay verified the interaction between KLF4 and acetylated histone H3. TGF-β1 contributed to EndMT in HUVECs in a time-dependent manner, mainly manifested as an increase in cell migration ability and changes in the expression of EndMT-related mRNAs and proteins. EOFAZ could inhibit EndMT induced by TGF-β1. The results after transfection with siKLF4 were similar to those of EOFAZ treatment. After EOFAZ treatment, the expression of KLF4 and acetylated histone H3 decreased, and protein interactions between them decreased, while expression of the Notch/Snail signal axis decreased. EOFAZ can attenuate endothelial injuries and suppress EndMT in HUVECs under TGF-β1 stimulation conditions because it may downregulate KLF4, decrease histone H3 acetylation, and inhibit the transduction of the Notch/Snail signaling axis.

Micro-RNA 92a as a Therapeutic Target for Cardiac Microvascular Dysfunction in Diabetes

Microvascular dysfunction is a pathological hallmark of diabetes, and is central to the ethology of diabetes-associated cardiac events. Herein, previous studies have highlighted the role of the vasoactive micro-RNA 92a (miR-92a) in small, as well as large, animal models. In this study, we explore the effects of miR-92a on mouse and human cardiac microvascular endothelial cells (MCMEC, HCMEC), and its underlying molecular mechanisms. Diabetic HCMEC displayed impaired angiogenesis and a pronounced inflammatory phenotype. Quantitative PCR (qPCR) showed an upregulation of miR-92a in primary diabetic HCMEC. Downregulation of miR-92a by antagomir transfection in diabetic HCMEC rescued angiogenesis and ameliorated diabetic endothelial bed inflammation. Furthermore, additional analysis of potential in silico-identified miR-92a targets in diabetic HCMEC revealed the miR-92a dependent downregulation of an essential metalloprotease, ADAM10. Accordingly, downregulation of ADAM10 impaired angiogenesis and wound healing in MCMEC. In myocardial tissue slices from diabetic pigs, ADAM10 dysregulation in micro- and macro-vasculature could be shown. Altogether, our data demonstrate the role of miR-92a in cardiac microvascular dysfunction and inflammation in diabetes. Moreover, we describe for the first time the metalloprotease ADAM10 as a novel miR-92a target, mediating its anti-angiogenic effect.

Role of Krüppel-like factors in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare but deadly disease with a complex pathogenesis. Recent evidence demonstrates that Krüppel-like factors, a diverse family of transcription factors, are involved in several key disease processes such as the phenotypic transition of endothelial cells and smooth muscle cells. Importantly, manipulation of certain Krüppel-like factors enables protection or attenuation against pulmonary arterial hypertension in both animal models and preliminary human studies. In this review, we discuss how Krüppel-like factors, in particular Krüppel-like factors 2, 4 and 5 contribute to the pathological phenomena seen in pulmonary arterial hypertension and how associated signaling and microRNA pathways may be suitable targets for new therapies.

Markers of Endothelial Cells in Normal and Pathological Conditions

Endothelial cells (ECs) line the blood vessels and lymphatic vessels, as well as heart chambers, forming the border between the tissues, on the one hand, and blood or lymph, on the other. Such a strategic position of the endothelium determines its most important functional role in the regulation of vascular tone, hemostasis, and inflammatory processes. The damaged endothelium can be both a cause and a consequence of many diseases. The state of the endothelium is indicated by the phenotype of these cells, represented mainly by (trans)membrane markers (surface antigens). This review defines endothelial markers, provides a list of them, and considers the mechanisms of their expression and the role of the endothelium in certain pathological conditions.

The association between KLF4 as a tumor suppressor and the prognosis of hepatocellular carcinoma after curative resection

Krüppel-like factor 4 (KLF4), a zinc-finger transcription factor in klfs family, is known for its crucial role in regulating cell growth, proliferation, and differentiation. This research aimed to explore the prognostic significance of KLF4 in hepatocellular carcinoma's (HCC) patients after curative resection and the role of KLF4 in HCC progression. There were 185 HCC patients who had hepatectomy from July 2010 to July 2011 included in this study. KLF4 expression was detected by microarray immunohistochemical technique, western blot, and qRT-PCR. Then, the correlation between the prognosis of patients and KLF4 expression was evaluated based on patients' follow-up data. The research found KLF4 expression was significantly downregulated in HCC tissues compared to para-tumorous tissues. More importantly, the overall survival rate (OS) and recurrence-free survival rate (RFS) of HCC patients with low KLF4 expression were both significantly decreased compared to those with a high level of KLF4. Further function and mechanism analysis showed that KLF4 could inhibit the proliferation, migration, invasion and epithelial-mesenchymal transition of HCC cells. The study revealed that KLF4 was not only a tumor suppressor in HCC but also can be regarded as a valuable prognostic factor and potential biological target for diagnosis and treatment in HCC patients.

CASIN and AMD3100 enhance endothelial cell proliferation, tube formation and sprouting

Endothelial dysfunction is prominent in atherosclerosis, hypertension, diabetes, peripheral and cardiovascular diseases, and stroke. Novel therapeutic approaches to these conditions often involve development of tissue-engineered veins with ex vivo expanded endothelial cells. However, high cell number requirements limit these approaches to become applicable to clinical applications and highlight the requirement of technologies that accelerate expansion of vascular-forming cells. We have previously shown that novel small molecules could induce hematopoietic stem cell expansion ex vivo. We hypothesized that various small molecules targeting hematopoietic stem cell quiescence and mobilization could be used to induce endothelial cell expansion and angiogenesis due to common origin and shared characteristics of endothelial and hematopoietic cells. Here, we have screened thirty-five small molecules and found that CASIN and AMD3100 increase endothelial cell expansion up to two-fold and induce tube formation and ex vivo sprouting. In addition, we have studied how CASIN and AMD3100 affect cell migration, apoptosis and cell cycle of endothelial cells. CASIN and AMD3100 upregulate key endothelial marker genes and downregulate a number of cyclin dependent kinase inhibitors. These findings suggest that CASIN and AMD3100 could be further tested in the development of artificial vascular systems and vascular gene editing technologies. Furthermore, these findings may have potential to contribute to the development of alternative treatment methods for diseases that cause endothelial damage.

The dual role of mir-146a in metastasis and disease progression

OBJECTIVE

MicroRNAs are ribonucleic acids that are single-stranded and endogenous non-coding acids that regulate gene expression in later stages of the translation process by binding to genomic regulatory sites. miR146a is mostly involved in the regulation of inflammatory systems and another process that role in the innate immune system. In the present review, we have focused on the recent acquisitions about the main role played by mir146a in the control of the immune system and tumorigenesis. The main purpose of this review article is to systematically investigate the mir146a and its role in regulating signaling pathways involved in cancer and the immune system as well as its involved therapeutic methods.

METHODS

Systematic search of MEDLINE, Web of Science and Cochrane Library was conducted for all comparative studies from 2000 to 2019 with the limitations of the English language.

RESULTS

For a notable period of time, researchers have mainly focused on the therapeutic mechanisms of mir146a involved in the modulation of inflammatory and anti-inflammatory genes. We found that levels of mir146a expression were associated with cancer cell metastasis as a dual role (Inhibitory and stimulatory roles). The results of various studies also showed that this microRNA has a therapeutic role through its effects on other gene expressions such as NF-kB, SIRT1, TNF- α and IL-1β and leads to disease control.

CONCLUSION

Knowledge about alterations in mir146a regulation will give a better understanding of the molecular basis for various chronic inflammatory diseases and cancers.

Regulation of cancer stem cell properties, angiogenesis, and vasculogenic mimicry by miR-450a-5p/SOX2 axis in colorectal cancer

Growing evidence indicates that a small number of cancer cells express stem cell markers and possess stem cell-like properties that promote malignant progression. Sex-determining region Y-box2 (SOX2) is a stem cell transcription factor essential for maintaining the properties of cancer stem cell (CSC). As CSC properties have been associated with angiogenesis and vasculogenic mimicry (VM), we aimed to comprehensively investigate whether SOX2 regulates CSC properties, angiogenesis, and VM in colorectal carcinoma (CRC) and its potential mechanism in this study. For this study, sphere formation assay, flow cytometry, cell survival analysis, tube formation, 3D culture, immunoblot, mouse model, and luciferase reporter assay were performed in vivo and in vitro. Expressions of SOX2 and miR-450a-5p in CRC tissue samples were examined through immunohistochemistry. First, the expression of SOX2 was not only associated with poor differentiation and prognosis but also promoted angiogenesis and VM. Knockdown of SOX2 ceased stemness properties, angiogenesis, and VM, along with decreased expression of CD133, CD31, and VE-cadherin as observed in functional experiments. Downregulation of SOX2 was found to inhibit tumorigenesis in vivo. Second, miR-450a-5p suppressed the expression of SOX2 by targeting its 3’UTR region directly and hence restrained SOX2-induced CSC properties, angiogenesis, and VM. Moreover, SOX2 overexpression preserved the miR-450a-5p-induced inhibition of CRC properties, angiogenesis, and VM. Finally, clinical samples exhibited a negative correlation between miR-450a-5p and SOX2. Patients with higher SOX2 and lower miR-450a-5p expressions had a poorer prognosis than patients with inverse expressions. Conclusively, we elucidated a unique mechanism of miR-450a-5p-SOX2 axis in the regulation of stemness, angiogenesis, and VM, which may act as a potential therapeutic practice in CRC.

Association of circulating growth differentiation factor-15, Krüppel-like factor 4 and growth arrest-specific 6 with coronary artery disease

BACKGROUND

Current assessment tools for patients with acute chest pain are either traumatic (coronary angiography) or unreliable (measurement of cardiac troponin concentrations). We investigated whether the novel cardiovascular stress markers, serum growth differentiation factor-15 (GDF-15), Krüppel-like factor 4 (KLF4) and growth arrest-specific 6 (gas6) may be useful biomarkers of coronary artery disease (CAD).

METHODS

A total of 350 male patients were enrolled, 198 with CAD and 152 controls, based on coronary angiography. GDF-15, KLF4 and gas6 concentrations were measured using commercial enzyme-linked immunosorbent assay kits. Multivariate logistic regression and multivariate linear regression were performed to evaluate potential associations of GDF-15, KLF4 and gas6 with risk of CAD or CAD severity.

RESULTS

Serum GDF-15, KLF4 and gas6 concentrations were significantly higher in male patients with CAD than in control subjects (P < .05), and they correlated significantly with involvement of coronary vessels (P < .05). After adjusting for confounding factors, we found that circulating GDF-15 concentrations remained positively associated with the presence of CAD (odds ratio [OR] per 1-standard deviation [SD] increase, 3.182; 95% confidence interval [CI] 1.586 to 6.382; P = .001), as did KLF4 concentrations (OR per 1-SD increase, 13.05; 95% CI 2.940 to 57.921, P = .001). Moreover, circulating GDF-15 concentrations were positively associated with the Gensini score (estimated SD change per 1-SD increase, 22.091; 95% CI 9.147 to 35.035, P = .001), as were KLF4 concentrations (estimated SD change per 1-SD increase, 27.996; 95% CI 10.082 to 45.910, P = .002). Gas6, in contrast, showed no relationship to presence of CAD or Gensini score.

, CONCLUSIONS

In this case-control study, increased concentrations of circulating GDF-15 and KLF4 were significantly associated with the presence and severity of CAD.

Angiogenic Endothelial Cell Signaling in Cardiac Hypertrophy and Heart Failure

Endothelial cells are, by number, one of the most abundant cell types in the heart and active players in cardiac physiology and pathology. Coronary angiogenesis plays a vital role in maintaining cardiac vascularization and perfusion during physiological and pathological hypertrophy. On the other hand, a reduction in cardiac capillary density with subsequent tissue hypoxia, cell death and interstitial fibrosis contributes to the development of contractile dysfunction and heart failure, as suggested by clinical as well as experimental evidence. Although the molecular causes underlying the inadequate (with respect to the increased oxygen and energy demands of the hypertrophied cardiomyocyte) cardiac vascularization developing during pathological hypertrophy are incompletely understood. Research efforts over the past years have discovered interesting mediators and potential candidates involved in this process. In this review article, we will focus on the vascular changes occurring during cardiac hypertrophy and the transition toward heart failure both in human disease and preclinical models. We will summarize recent findings in transgenic mice and experimental models of cardiac hypertrophy on factors expressed and released from cardiomyocytes, pericytes and inflammatory cells involved in the paracrine (dys)regulation of cardiac angiogenesis. Moreover, we will discuss major signaling events of critical angiogenic ligands in endothelial cells and their possible disturbance by hypoxia or oxidative stress. In this regard, we will particularly highlight findings on negative regulators of angiogenesis, including protein tyrosine phosphatase-1B and tumor suppressor p53, and how they link signaling involved in cell growth and metabolic control to cardiac angiogenesis. Besides endothelial cell death, phenotypic conversion and acquisition of myofibroblast-like characteristics may also contribute to the development of cardiac fibrosis, the structural correlate of cardiac dysfunction. Factors secreted by (dysfunctional) endothelial cells and their effects on cardiomyocytes including hypertrophy, contractility and fibrosis, close the vicious circle of reciprocal cell-cell interactions within the heart during pathological hypertrophy remodeling.

Kruppel-like factor 4 regulates developmental angiogenesis through disruption of the RBP-J-NICD-MAML complex in intron 3 of Dll4

Angiogenesis is a multistep process that requires highly regulated endothelial cell (EC) behavior. The transcription factor Krüppel-like factor 4 (KLF4) is a critical regulator of several basic EC functions; we have recently shown that KLF4 disturbs pathological (tumor) angiogenesis by mediating the expression of members of VEGF and Notch signaling pathways. Notch signaling is central to orchestration of sprouting angiogenesis but little is known about the upstream regulation of Notch itself. To determine the role of KLF4 in normal (developmental) angiogenesis, we used a mouse retinal angiogenesis model. We found that endothelial-specific overexpression of KLF4 in transgenic mice (EC-K4 Tg) leads to increased vessel density, branching and number of tip cell filopodia as assessed on postnatal day 6 (P6). The hypertrophic vasculature seen with sustained KLF4 overexpression is not stable and undergoes prominent remodeling during P7-P12 resulting in a normal appearing retinal vasculature in adult EC-K4 Tg mice. We find that KLF4 inhibits Delta-like 4 (DLL4) expression in the angiogenic front during retinal vascular development. Furthermore, in an oxygen-induced retinopathy model, overexpression of KLF4 results in decreased vaso-obliteration and neovascular tuft formation that is similar to genetic or pharmacologic DLL4 inhibition. Mechanistically, we show that KLF4 disables the activity of the essential Notch transcriptional activator RBP-J by interfering with binding of co-activators NICD and MAML at intron 3 of the Notch ligand DLL4. In summary, our experimental results demonstrate a regulatory role of KLF4 in developmental angiogenesis through regulation of DLL4 transcription.

Krüppel-like factors and vascular wall homeostasis

Cardiovascular diseases (CVDs) are major causes of death worldwide. Identification of promising targets for prevention and treatment of CVDs is paramount in the cardiovascular field. Numerous transcription factors regulate cellular function through modulation of specific genes and thereby are involved in the physiological and pathophysiological processes of CVDs. Although Krüppel-like factors (KLFs) have a similar protein structure with a conserved zinc finger domain, they possess distinct tissue and cell distribution patterns as well as biological functions. In the vascular system, KLF activities are regulated at both transcriptional and posttranscriptional levels. Growing in vitro, in vivo, and genetic epidemiology studies suggest that specific KLFs play important roles in vascular wall biology, which further affect vascular diseases. KLFs regulate various functional aspects such as cell growth, differentiation, activation, and development through controlling a whole cluster of functionally related genes and modulating various signaling pathways in response to pathological conditions. Therapeutic targeting of selective KLF family members may be desirable to achieve distinct treatment effects in the context of various vascular diseases. Further elucidation of the association of KLFs with human CVDs, their underlying molecular mechanisms, and precise protein structure studies will be essential to define KLFs as promising targets for therapeutic interventions in CVDs.

MiR-212 Attenuates MPP⁺-Induced Neuronal Damage by Targeting KLF4 in SH-SY5Y Cells

PURPOSE

Parkinson's disease (PD) is a common age-dependent neurodegenerative disease. MiR-212 has been demonstrated to exert protective effects in several neurological disorders. The present study aimed to investigate the role and underlying molecular mechanism of miR-212 in PD.

MATERIALS AND METHODS

1-methyl-4-phenylpyridinium (MPP+)-induced SH-SY5Y cells were applied as a PD model in vitro. RT-qPCR was used to measure the expression of miR-212 and Kruppel-like factor 4 (KLF4) mRNA. Western blot analysis was performed to detect the protein levels of KLF4, Notch1 and Jagged1. Cell viability and apoptosis were determined by the Cell Counting Kit-8 and flow cytometry, respectively. Quantitative analysis of caspase-3 activity, lactate dehydrogenase (LDH), reactive oxygen species (ROS), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), and interleukin-1 beta (IL-1β) was conducted with corresponding ELISA kits. Dual-luciferase reporter assay was employed to evaluate the relationship between miR-212 and KLF4.

RESULTS

MiR-212 was downregulated in MPP⁺-induced SH-SY5Y cells. Also, miR-212 alleviated MPP⁺-induced SH-SY5Y cell damage, embodied by increased cell viability, decreased caspase-3 activity, LDH release, ROS production, TNF-α, and IL-1β expression, as well as elevated SOD levels. KLF4 was a direct target of miR-212, and miR-212 repressed KLF4 expression in a post-transcriptional manner. Moreover, miR-212-mediated protection effects were abated following KLF4 expression restoration in MPP⁺-induced SH-SY5Y cells, represented as lowered cell viability and enhanced apoptotic rate. Furthermore, Notch signaling was involved in the regulation of miR-212/KLF4 axis in MPP⁺-induced SH-SY5Y cells.

CONCLUSION

miR-212 might attenuate MPP⁺-induced neuronal damage by regulating KLF4/Notch signaling pathway in SH-SY5Y cells, a promising target for PD therapy.

Increasing aggressiveness of patient-derived xenograft models of cervix carcinoma during serial transplantation

Four patient-derived xenograft (PDX) models (BK-12, ED-15, HL-16, LA-19) of carcinoma of the uterine cervix have been developed in our laboratory, and their stability during serial transplantation in vivo was investigated in this study. Two frozen cell stocks were established, one from xenografted tumors in passage 2 (early generation) and the other from xenografted tumors transplanted serially in mice for approximately two years (late generation), and the biology of late generation tumors was compared with that of early generation tumors. Late generation tumors showed higher incidence of lymph node metastases than early generation tumors in three models (ED-15, HL-16, LA-19), and the increased metastatic propensity was associated with increased tumor growth rate, increased microvascular density, and increased expression of angiogenesis-related and cancer stem cell-related genes. Furthermore, late generation tumors showed decreased fraction of pimonidazole-positive tissue (i.e., decreased fraction of hypoxic tissue) in two models (HL-16, LA-19) and decreased fraction of collagen-I-positive tissue (i.e., less extensive extracellular matrix) in two models (ED-15, HL-16). This study showed that serially transplanted PDXs may not necessarily mirror the donor patients’ diseases, and consequently, proper use of serially transplanted PDX models in translational cancer research requires careful molecular monitoring of the models.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Markers and Biomarkers of Endothelium: When Something Is Rotten in the State

Endothelium is a community of endothelial cells (ECs), which line the blood and lymphatic vessels, thus forming an interface between the tissues and the blood or lympha. This strategic position of endothelium infers its indispensable functional role in controlling vasoregulation, haemostasis, and inflammation. The state of endothelium is simultaneously the cause and effect of many diseases, and this is coupled with modifications of endothelial phenotype represented by markers and with biochemical profile of blood represented by biomarkers. In this paper, we briefly review data on the functional role of endothelium, give definitions of endothelial markers and biomarkers, touch on the methodological approaches for revealing biomarkers, present an implicit role of endothelium in some toxicological mechanistic studies, and survey the role of reactive oxygen species (ROS) in modulation of endothelial status.

Inhibition of the H3K9 methyltransferase G9A attenuates oncogenicity and activates the hypoxia signaling pathway

Epigenetic mechanisms play important roles in the regulation of tumorigenesis, and hypoxia-induced epigenetic changes may be critical for the adaptation of cancer cells to the hypoxic microenvironment of solid tumors. Previously, we showed that loss-of-function of the hypoxia-regulated H3K9 methyltransferase G9A attenuates tumor growth. However, the mechanisms by which blockade of G9A leads to a tumor suppressive effect remain poorly understood. We show that G9A is highly expressed in breast cancer and is associated with poor patient prognosis, where it may function as a potent oncogenic driver. In agreement with this, G9A inhibition by the small molecule inhibitor, BIX-01294, leads to increased cell death and impaired cell migration, cell cycle and anchorage-independent growth. Interestingly, whole transcriptome analysis revealed that genes involved in diverse cancer cell functions become hypoxia-responsive upon G9A inhibition. This was accompanied by the upregulation of the hypoxia inducible factors HIF1α and HIF2α during BIX-01294 treatment even in normoxia that may facilitate the tumor suppressive effects of BIX-01294. HIF inhibition was able to reverse some of the transcriptional changes induced by BIX-01294 in hypoxia, indicating that the HIFs may be important drivers of these derepressed target genes. Therefore, we show that G9A is a key mediator of oncogenic processes in breast cancer cells and G9A inhibition by BIX-01294 can successfully attenuate oncogenicity even in hypoxia.

Differential microRNA expression in human placentas of term intra-uterine growth restriction that regulates target genes mediating angiogenesis and amino acid transport

Placental insufficiency leading to intrauterine growth restriction (IUGR) demonstrates perturbed gene expression affecting placental angiogenesis and nutrient transfer from mother to fetus. To understand the post-transcriptional mechanisms underlying such placental gene expression changes, our objective was to identify key non-coding microRNAs that express biological function. To this end, we initially undertook microarrays targeting microRNAs in a small sub-set of placentas of appropriate (AGA) versus small for gestational age (SGA) weight infants, and observed up-regulation of 97 miRs and down-regulation of 44 miRs in SGA versus AGA. In a larger cohort of samples (AGA, n = 21; SGA, n = 11; IUGR subset, n = 5), we validated by qRT-PCR differential expression of three specific microRNAs (miR-10b, -363 and -149) that target genes mediating angiogenesis and nutrient transfer. Validation yielded an increase in miR-10b and -363 expression of ~2.5-fold (p<0.02 each) in SGA versus AGA, and of ~3-fold (p<0.005) in IUGR versus AGA, with no significant change despite a trending increase in miR-149. To further establish a cause-and-effect paradigm, employing human HTR8 trophoblast cells, we assessed the effect of nutrient deprivation on miR expression and inhibition of endogenous miRs on target gene expression. In-vitro nutrient deprivation (~50%) increased the expression of miR-10b and miR-149 by 1.5-fold (p<0.02) while decreasing miR-363 (p<0.0001). Inhibition of endogenous miRs employing antisense sequences against miR-10b, -363 and -149 revealed an increase respectively in the expression of the target genes KLF-4 (transcription factor which regulates angiogenesis), SNAT1 and 2 (sodium coupled neutral amino acid transporters) and LAT2 (leucine amino acid transporter), which translated into a similar change in the corresponding proteins. Finally to establish functional significance we performed dual-luciferase reporter assays with 3'-insertion of miR-10b alone and observed a ~10% reduction in the 5'-luciferase activity versus the control. Lastly, we further validated by microarray and employing MirWalk software that the pathways and target genes identified by differentially expressed miRs in SGA/IUGR compared to AGA are consistent in a larger cohort. We have established the biological significance of various miRs that target common transcripts mediating pathways of importance, which are perturbed in the human IUGR placenta.

ORAI1 Activates Proliferation of Lymphatic Endothelial Cells in Response to Laminar Flow Through Krüppel-Like Factors 2 and 4

RATIONALE

Lymphatic vessels function to drain interstitial fluid from a variety of tissues. Although shear stress generated by fluid flow is known to trigger lymphatic expansion and remodeling, the molecular basis underlying flow-induced lymphatic growth is unknown.

OBJECTIVE

We aimed to gain a better understanding of the mechanism by which laminar shear stress activates lymphatic proliferation.

METHODS AND RESULTS

Primary endothelial cells from dermal blood and lymphatic vessels (blood vascular endothelial cells and lymphatic endothelial cells [LECs]) were exposed to low-rate steady laminar flow. Shear stress-induced molecular and cellular responses were defined and verified using various mutant mouse models. Steady laminar flow induced the classic shear stress responses commonly in blood vascular endothelial cells and LECs. Surprisingly, however, only LECs showed enhanced cell proliferation by regulating the vascular endothelial growth factor (VEGF)-A, VEGF-C, FGFR3, and p57/CDKN1C genes. As an early signal mediator, ORAI1, a pore subunit of the calcium release-activated calcium channel, was identified to induce the shear stress phenotypes and cell proliferation in LECs responding to the fluid flow. Mechanistically, ORAI1 induced upregulation of Krüppel-like factor (KLF)-2 and KLF4 in the flow-activated LECs, and the 2 KLF proteins cooperate to regulate VEGF-A, VEGF-C, FGFR3, and p57 by binding to the regulatory regions of the genes. Consistently, freshly isolated LECs from Orai1 knockout embryos displayed reduced expression of KLF2, KLF4, VEGF-A, VEGF-C, and FGFR3 and elevated expression of p57. Accordingly, mouse embryos deficient in Orai1, Klf2, or Klf4 showed a significantly reduced lymphatic density and impaired lymphatic development.

CONCLUSIONS

Our study identified a molecular mechanism for laminar flow-activated LEC proliferation.

Krüppel-like factor 4 (KLF4): What we currently know

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor that regulates diverse cellular processes such as cell growth, proliferation, and differentiation. Since its discovery in 1996, KLF4 has been gaining a lot of attention, particularly after it was shown in 2006 as one of four factors involved in the induction of pluripotent stem cells (iPSCs). Here we review the current knowledge about the different functions and roles of KLF4 in various tissue and organ systems.

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.

Inhibition of miR-7 promotes angiogenesis in human umbilical vein endothelial cells by upregulating VEGF via KLF4

Recent lentiviral-based microRNA (miRNA) library screening has identified miRNA-7 (miR-7) as an anti‑angiogenic miRNA in human umbilical vein endothelial cells (HUVECs). However, the underlying mechanism of miR-7 in the suppression of angiogenesis remains largely unknown. In the present study, we report that miR-7 inhibition promoted angiogenesis by upregulating vascular endothelial growth factor (VEGF) and directly targeting Krüppel-like factor 4 (KLF4). Downregulation of miR-7 promoted tube formation of HUVECs, accompanied by upregulation of mRNA and protein levels of both VEGF and KLF4. miR-7 directly targeted KLF4 as demonstrated by luciferase reporter assay and miR-7 mimics decreased KLF4. Furthermore, bioinformatic analysis revealed the presence of multiple DNA-binding elements of KLF4 in the VEGF promoter. Chromatin immunoprecipitation (ChIP) demonstrated that the KLF4 antibody specifically pulled down the VEGF promoter in the HUVECs. Furthermore, ectopic overexpression of KLF4 induced VEGF mRNA and protein levels. In addition, KLF4 silencing inhibited the angiogenesis induced by the miR-7 inhibitor in the HUVECs. Our results demonstrated that KLF4 is a direct target of miR-7 and a transcription activator of VEGF. These findings indicate that the miR-7-KLF4-VEGF signaling axis plays an important role in the regulation of angiogenesis in HUVECs, suggesting that miR-7 is a potential agent for the development of anti-angiogenic therapeutics in vascular diseases and solid tumors.

Tongxinluo (TXL), a Traditional Chinese Medicinal Compound, Improves Endothelial Function After Chronic Hypoxia Both In Vivo and In Vitro

Vascular injury after chronic hypoxia leads to endothelial injury and structural damage to tight junctions (TJs), thereby resulting in a variety of cardiovascular diseases. Thus, attenuating hypoxia-induced damage has great significance for the prevention and treatment of cardiovascular disease. The aim of this study was to investigate whether the endothelial protection conferred by tongxinluo (TXL), a traditional Chinese medicinal compound, is related to its regulation of TJ protein expression. In vivo, we found that TXL could promote hypoxia-induced angiogenesis in lung and liver tissue. In vitro, we found that CoCl₂ treatment significantly reduced the expression of the TJ proteins occludin, claudin-1, VE-cadherin, and beta-catenin in cultured human cardiac microvascular endothelial cells. TXL pretreatment abrogated the CoCl₂-induced downregulation of these TJ proteins. Conversely, overexpression of Krüppel-like factor 4 (KLF4) inhibited the expression of TJ proteins in human cardiac microvascular endothelial cells, an effect that was reversed by TXL pretreatment. Further experiments showed that TXL could promote endothelial cell proliferation by increasing KLF4 phosphorylation, thereby reversing the effect of KLF4 on the expression of TJ proteins. These findings provide a new molecular mechanism for the TXL-induced increase in TJ protein expression.

MicroRNA-10b regulates epithelial-mesenchymal transition by modulating KLF4/Notch1/E-cadherin in cisplatin-resistant nasopharyngeal carcinoma cells

Epithelial-mesenchymal transition (EMT) is an initiating event in tumor cell invasion and metastasis that contributes to therapeutic resistance to compounds including cisplatin. MicroRNAs (miRNAs) have been associated with EMT as well as resistance to standard therapies. However, the underlying mechanisms by which miRNAs control the development of resistance to cisplatin (DDP), and the accompanying EMT-like properties are required to elucidate. Here we show that microRNA-10b (miR-10b) is up-regulated in HNE1/DDP cells, and inhibition of miR-10b expression reversed the EMT phenotype. However, over-expression of miR-10b was able to promote the acquisition of an EMT phenotype in HNE1 cells. Additionally, we identified that miR-10b expression inversely correlates with KLF4, which then controls expression of Notch1. Knock-down of Notch1 inhibited cell migration, invasion, and reversed EMT in HNE1/DDP cells, which was dependent on miR-10b. In summary, our results reveal that miR-10b regulates EMT by modulating KLF4/Notch1/E-cadherin expression, which promotes invasion and migration of nasal pharyngeal carcinoma cells.

Endothelial Transdifferentiation of Tumor Cells Triggered by the Twist1-Jagged1-KLF4 Axis: Relationship between Cancer Stemness and Angiogenesis

Tumor hypoxia is associated with malignant biological phenotype including enhanced angiogenesis and metastasis. Hypoxia increases the expression of vascular endothelial cell growth factor (VEGF), which directly participates in angiogenesis by recruiting endothelial cells into hypoxic area and stimulating their proliferation, for increasing vascular density. Recent research in tumor biology has focused on the model in which tumor-derived endothelial cells arise from tumor stem-like cells, but the detailed mechanism is not clear. Twist1, an important regulator of epithelial-mesenchymal transition (EMT), has been shown to mediate tumor metastasis and induce tumor angiogenesis. Notch signaling has been demonstrated to be an important player in vascular development and tumor angiogenesis. KLF4 (Krüppel-like factor 4) is a factor commonly used for the generation of induced pluripotent stem (iPS) cells. KLF4 also plays an important role in the differentiation of endothelial cells. Although Twist1 is known as a master regulator of mesoderm development, it is unknown whether Twist1 could be involved in endothelial transdifferentiation of tumor-derived cells. This review focuses on the role of Twist1-Jagged1/Notch-KLF4 axis on tumor-derived endothelial transdifferentiation, tumorigenesis, metastasis, and cancer stemness.

Overexpression of miR-18a negatively regulates myocyte enhancer factor 2D to increase the permeability of the blood-tumor barrier via Krüppel-like factor 4-mediated downregulation of zonula occluden-1, claudin-5, and occludin

miR-18a represses angiogenesis and tumor evasion by weakening vascular endothelial growth factor and transforming growth factor-β signaling to prolong the survival of glioma patients, although it is thought to be an oncogene. This study investigates the potential effects of miR-18a on the permeability of the blood-tumor barrier (BTB) and its possible molecular mechanisms. An in vitro BTB model was successfully established. The endogenous expression of miR-18a in glioma vascular endothelial cells (GECs) was significantly lower than that in normal vascular ECs, and the overexpression of miR-18a significantly increased the permeability of the BTB as well as downregulating the mRNA and protein expressions of tight junction-related proteins zonula occluden-1 (ZO-1), claudin-5, and occludin in GECs. Dual luciferase reporter assays revealed that miR-18a bound to the 3'-untranslated region (3'UTR) of myocyte enhancer factor 2D (MEF2D). The overexpression of both miR-18a and MEF2D with the 3'UTR significantly weakened the effect caused by miR-18a of decreasing the mRNA and protein expressions of ZO-1, claudin-5 and occludin and of increasing the permeability of the BTB. Chromatin immunoprecipitation showed that MEF2D could directly bind to KLF4 promoter. This study shows that miR-18a targets and negatively regulates MEF2D, which further regulates tight junction-related proteins ZO-1, claudin-5, and occludin through transactivation of KLF4 and, finally, changes the permeability of the BTB. MiR-18a should garner growing attention because it might serve as a potential target in opening the BTB and providing a new strategy for the treatment of gliomas.

HIV vasculopathy: role of mononuclear cell-associated Krüppel-like factors 2 and 4

OBJECTIVE

To determine the relationships between Krüppel-like factors (KLF) 2 and 4, immune-activation, and subclinical vascular disease in HIV-infected patients on antiretroviral therapy (ART).

DESIGN

Double-blind, randomized, placebo-controlled trial.

METHODS

We studied 74 HIV-infected adults on ART enrolled in a randomized clinical trial of statin therapy. KLF2 and KLF4 gene expression was measured by quantitative PCR from peripheral blood mononuclear cells (PBMCs) at baseline and after 24 weeks of 10 mg daily rosuvastatin or placebo. At the same time points, T-cell and monocyte activation were assessed by flow cytometry and vascular health was assessed by cardiac computed tomography and carotid ultrasound.

RESULTS

KLF4 expression was negatively correlated with duration of ART (r = -0.351, P = 0.004) and positively correlated with measures of immune activation: proinflammatory monocytes [CD14CD16 (r = 0.343, P = 0.003)], patrolling monocytes [CD14CD16 (r = 0.276, P = 0.017)], and activated CD8 T-lymphocytes [CD8DRCD38 (r = 0.264, P = 0.023)]. KLF2 expression was negatively correlated with subclinical atherosclerosis: mean-mean common carotid artery intima-media thickness (r = -0.231, P = 0.048), mean-max carotid artery intima-media thickness (r = -0.271, P = 0.020), and coronary artery calcium score (r = -0.254, P = 0.029). There were no statistically significant changes in KLF2/4 expression in PBMCs after 24 weeks of rosuvastatin.

CONCLUSION

Expression of KLF4 in PBMCs positively correlates with cellular markers of immune activation, whereas KLF2 expression negatively correlates with markers of subclinical atherosclerosis in this HIV-infected population on ART. Additional studies are needed to determine if targeted interventions might alter KLF2/4 expression to reduce inflammation and vascular risk in humans.

Kruppel-like factor 4 is critical for transcriptional control of cardiac mitochondrial homeostasis

Mitochondrial homeostasis is critical for tissue health, and mitochondrial dysfunction contributes to numerous diseases, including heart failure. Here, we have shown that the transcription factor Kruppel-like factor 4 (KLF4) governs mitochondrial biogenesis, metabolic function, dynamics, and autophagic clearance. Adult mice with cardiac-specific Klf4 deficiency developed cardiac dysfunction with aging or in response to pressure overload that was characterized by reduced myocardial ATP levels, elevated ROS, and marked alterations in mitochondrial shape, size, ultrastructure, and alignment. Evaluation of mitochondria isolated from KLF4-deficient hearts revealed a reduced respiration rate that is likely due to defects in electron transport chain complex I. Further, cardiac-specific, embryonic Klf4 deletion resulted in postnatal premature mortality, impaired mitochondrial biogenesis, and altered mitochondrial maturation. We determined that KLF4 binds to, cooperates with, and is requisite for optimal function of the estrogen-related receptor/PPARγ coactivator 1 (ERR/PGC-1) transcriptional regulatory module on metabolic and mitochondrial targets. Finally, we found that KLF4 regulates autophagy flux through transcriptional regulation of a broad array of autophagy genes in cardiomyocytes. Collectively, these findings identify KLF4 as a nodal transcriptional regulator of mitochondrial homeostasis.

KLF4 Promotes Angiogenesis by Activating VEGF Signaling in Human Retinal Microvascular Endothelial Cells

The transcription factor Krüppel-like factor 4 (KLF4) has been implicated in regulating cell proliferation, migration and differentiation in a variety of human cells and is one of four factors required for the induction of pluripotent stem cell reprogramming. However, its role has not been addressed in ocular neovascular diseases. This study investigated the role of KLF4 in angiogenesis and underlying molecular mechanisms in human retinal microvascular endothelial cells (HRMECs). The functional role of KLF4 in HRMECs was determined following lentiviral vector mediated inducible expression and shRNA knockdown of KLF4. Inducible expression of KLF4 promotes cell proliferation, migration and tube formation. In contrast, silencing KLF4 inhibits cell proliferation, migration, tube formation and induces apoptosis in HRMECs. KLF4 promotes angiogenesis by transcriptionally activating VEGF expression, thus activating the VEGF signaling pathway in HRMECs.

Induction of GADD34 Regulates the Neurotoxicity of Amyloid β

The possible roles played by growth arrest and DNA damage-inducible gene 34 (GADD34) in Alzheimer's disease (AD) are so far less understood. In this study, we found that GADD34 was increased in the brains of AD transgenic J20 mice. The deposition of β-amyloid (Aβ) peptide is the main component of neurotic plaques in AD brain. Thus, we examined the effect of Aβ in the expression of GADD34 in human SH-SY5Y cells in vitro. Amyloid β (Aβ1-42) treatment led to increased expression of GADD34. Pretreatment with 50 nmol/L of c-Jun N-terminal kinases (JNK) inhibitor SP600125 abolished the upregulation of GADD34. c-Jun silencing by transfection with c-Jun small-interfering RNA abolished the effects of Aβ1-42 on the expression of GADD34. Importantly, chromatin immunoprecipitation studies verified the ability of c-Jun to bind to the GADD34 promoter, and this ability was increased more than 3-fold by Aβ1-42. These data suggest that the induction of GADD34 by Aβ is mediated by JNK/c-Jun pathway. Finally, depletion of GADD34 significantly rescued Aβ-induced cell apoptosis as evidenced by a marked decrease in the number of terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells. Consistently, knockdown of GADD34 attenuated caspase 3 activation induced by Aβ1-42.