Transcription factor Krüppel-like factor 2 plays a vital role in endothelial colony forming cells differentiation

KLF2 Orchestrates Pathological Progression of Infantile Hemangioma through Hemangioma Stem Cell Fate Decisions

Infantile hemangioma (IH) is the most prevalent vascular tumor during infancy, characterized by a rapid proliferation phase of disorganized blood vessels and spontaneous involution. IH possibily arises from a special type of multipotent stem cells called hemangioma stem cells (HemSCs), which could differentiate into endothelial cells, pericytes, and adipocytes. However, the underlying mechanisms that regulate the cell fate determination of HemSCs remain elusive. Here, we unveil KLF2 as a candidate transcription factor involved in the control of HemSCs differentiation. KLF2 exhibits high expression in endothelial cells in proliferating IH but diminishes in adipocytes in involuting IH. Using a combination of in vitro culture of patient-derived HemSCs and HemSCs implantation mouse models, we show that KLF2 governs the proliferation, apoptosis and cell cycle progression of HemSCs. Importantly, KLF2 acts as a crucial determinant of HemSCs' fate, directing their differentiation toward endothelial cells while inhibiting adipogenesis. Knockdown of KLF2 induces a pro-adipogenic transcriptome in HemSCs, leading to impaired blood vessel formation and accelerated adipocyte differentiation. Collectively, our findings highlight KLF2 as a critical regulator controlling the progression and involution of IH by modulating HemSCs' cell fate decisions.

Yeast beta-glucan mediates histone deacetylase 5-induced angiogenesis in vascular endothelial cells

The role of yeast-derived β-glucan in angiogenesis has not been elucidated because there have been few specific studies on its clinical and physiological significance. Therefore, this study investigated the correlation between β-glucan and histone deacetylase 5 (HDAC5) in human umbilical vein endothelial cells (HUVECs), revealing the role of β-glucan in angiogenesis. We confirmed that HDAC5 was phosphorylated by β-glucan stimulation and released from the nucleus to the cytoplasm. Furthermore, we found that β-glucan-stimulated HDAC5 translocation mediates the transcriptional activation of MEF2. As a result, the expression of KLF2, EGR2, and NR4A2, whose expression is MEF2-dependent and involved in angiogenesis, increased. Thus, we showed the activity of β-glucan in angiogenesis through in vitro and ex vivo assays including cell migration, tube formation, and aortic ring analyses. Specifically, application of an HDAC5 inhibitor repressed MEF2 transcriptional activation in both in vitro and ex vivo angiogenesis. HDAC5 inhibitor LMK235 inhibited the proangiogenic activity of beta-glucan, suggesting that β-glucan induces angiogenesis through HDAC5. These findings suggest that HDAC5 is essential for angiogenesis, and that β-glucan induces angiogenesis. In conclusion, this study demonstrates that β-glucan induces angiogenesis through HDAC5. It also suggests that β-glucan has potential value as a novel therapeutic agent for modulating angiogenesis.

Salvianolic Acid B Suppresses ER Stress-Induced NLRP3 Inflammasome and Pyroptosis via the AMPK/FoxO4 and Syndecan-4/Rac1 Signaling Pathways in Human Endothelial Progenitor Cells

Mounting evidence demonstrates uncontrolled endoplasmic reticulum (ER) stress responses can activate the inflammasome, which generally results in endothelial dysfunction, a major pathogenetic factor of chronic inflammatory diseases such as atherosclerosis. Salvianolic acid B (SalB), produced by Radix Salviae, exerts antioxidative and anti-inflammatory activities in multiple cell types. However, SalB's effects on ER stress-related inflammasome and endothelial dysfunction remain unknown. Here, we showed SalB substantially abrogated ER stress-induced cell death and reduction in capillary tube formation, with declined intracellular reactive oxygen species (ROS) amounts and restored mitochondrial membrane potential (MMP), as well as increased expression of HO-1 and SOD2 in bone marrow-derived endothelial progenitor cells (BM-EPCs). ER stress suppression by CHOP or caspase-4 siRNA transfection attenuated the protective effect of SalB. Additionally, SalB alleviated ER stress-mediated pyroptotic cell death via the suppression of TXNIP/NLRP3 inflammasome, as evidenced by reduced cleavage of caspase-1 and interleukin- (IL-) 1β and IL-18 secretion levels. Furthermore, this study provided a mechanistic basis that AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 signaling pathway modulation by SalB substantially prevented BM-EPCs damage associated with ER stress by decreasing intracellular ROS amounts and inducing NLRP3-dependent pyroptosis. In summary, our findings identify that ER stress triggered mitochondrial ROS release and NLRP3 generation in BM-EPCs, while SalB inhibits NLRP3 inflammasome-mediated pyroptotic cell death by regulating the AMPK/FoxO4/KLF2 and Syndecan-4/Rac1/ATF2 pathways. The current findings reveal SalB as a potential new candidate for the treatment of atherosclerotic heart disease.

Transcription factor KLF2 enhances the sensitivity of breast cancer cells to cisplatin by suppressing kinase WEE1

Cisplatin is an effective chemotherapeutic agent in facilitating the inhibition of proliferation, migration, and invasion in cancerous cells. However, the detailed mechanism of the regulation by cisplatin of human breast cancer cells is still unclear. This study aimed to investigate the mechanism of kruppel-like factor 2 (KLF2) transcription factor in cisplatin therapy for breast cancer. RT-qPCR was performed to quantify the expression of KLF2 and WEE1 in clinical tissue samples from breast cancer patients and in MDA-MB-231 cells. ChIP assay and dual-luciferase reporter assay were used to analyze the potential-binding sites of KLF2 and WEE1 promoter. Gain- or loss-of-function approaches were used to manipulate KLF2 and WEE1 in cisplatin-treated MDA-MB-231 cells, and the mechanism of KLF2 in breast cancer was evaluated both via CCK-8 assay, flow cytometry, Transwell assay, and Western blot. Further validation of the KLF2 was performed on nude mouse models. Breast cancer tissues and cells showed a relative decline of KLF2 expression and abundant WEE1 expression. Cisplatin inhibited the proliferation, migration, and invasion of MDA-MB-231 cells. Overexpression of KLF2 enhanced the inhibitory effect of cisplatin on the malignant characteristics of MDA-MB-231 cells in vitro. KLF2 targeted WEE1 and negatively regulated its expression, thus enhancing the sensitivity to cisplatin of breast cancer cells as well as tumor-bearing mice. Overall, these results suggest that KLF2 can potentially inhibit WEE1 expression and sensitize breast cancer cells to cisplatin, thus presenting a promising adjunct treatment.

Gene therapy for critical limb ischemia: Per aspera ad astra

Peripheral artery diseases remain a serious public health problem. Although there are many traditional methods for their treatment using conservative therapeutic techniques and surgery, gene therapy is an alternative and potentially more effective treatment option especially for "no option" patients. This review treats the results of many years of research and application of gene therapy as an example of treatment of patients with critical limb ischemia. Data on successful and unsuccessful attempts to use this technology for treating this disease are presented. Trends in changing the paradigm of approaches to therapeutic angiogenesis are noted: from viral vectors to non-viral vectors, from gene transfer to the whole organism to targeted transfer to cells and tissues, from single gene use to combination of genes; from DNA therapy to RNA therapy, from in vivo therapy to ex vivo therapy.

Down-regulated microRNA-199a-3p enhances osteogenic differentiation of bone marrow mesenchymal stem cells by targeting Kdm3a in ovariectomized rats

Osteoporosis is a prevalent systemic skeletal disorder entailing bone fragility and increased fracture risk, often emerging in post-menopausal life. Emerging evidence implicates the dysregulation of microRNAs (miRNAs or miRs) in the progression of osteoporosis. This study investigated the effect of miR-199a-3p on osteoporosis and its underlying mechanism. We first examplished an ovariectomized (OVX)-induced rat osteoporosis model, and then isolated mesenchymal stem cells (MSCs) from bone marrow of the model rats. The overexpression and knock down of miR-199a-3p were conducted in OVX rats and MSCs to verify the role of miR-199a-3p on MSC differentiation. Calcium nodules were measured using alizarin red S (ARS) staining. RT-qPCR and Western blot assay were performed to measure the expression of miR-199a-3p, Kdm3a and osteogenic differentiation-related markers in rat tissues and cells. The correlation between miR-199a-3p and Kdm3a was confirmed using dual-luciferase reporter assay. The enrichment of Kdm3a at the Erk2 and Klf2 promoter was assessed using chromatin immunoprecipitation (ChIP) assay. Isolated MSCs were positive for CD29, CD44, CD90, and CD45, suggesting successful isolation of MSCs. There was increased expression of miR-199a-3p and inhibited osteogenic differentiation in OVX rats. Kdm3a was negatively targeted by miR-199a-3p. Our results also demonstrated that Kdm3a elevated the expression of Erk2 and Erk2 by promoting Erk2 and Klf2 demethylation, which further contributed to osteogenic differentiation. Overall, our results revealed a regulatory network of miR-199a-3p in osteogenic differentiation, highlighting miR-199a-3p as a potential target for therapeutic interventions in osteoporosis.

Therapeutic Potential of Endothelial Colony-Forming Cells in Ischemic Disease: Strategies to Improve their Regenerative Efficacy

Cardiovascular disease (CVD) comprises a range of major clinical cardiac and circulatory diseases, which produce immense health and economic burdens worldwide. Currently, vascular regenerative surgery represents the most employed therapeutic option to treat ischemic disorders, even though not all the patients are amenable to surgical revascularization. Therefore, more efficient therapeutic approaches are urgently required to promote neovascularization. Therapeutic angiogenesis represents an emerging strategy that aims at reconstructing the damaged vascular network by stimulating local angiogenesis and/or promoting de novo blood vessel formation according to a process known as vasculogenesis. In turn, circulating endothelial colony-forming cells (ECFCs) represent truly endothelial precursors, which display high clonogenic potential and have the documented ability to originate de novo blood vessels in vivo. Therefore, ECFCs are regarded as the most promising cellular candidate to promote therapeutic angiogenesis in patients suffering from CVD. The current briefly summarizes the available information about the origin and characterization of ECFCs and then widely illustrates the preclinical studies that assessed their regenerative efficacy in a variety of ischemic disorders, including acute myocardial infarction, peripheral artery disease, ischemic brain disease, and retinopathy. Then, we describe the most common pharmacological, genetic, and epigenetic strategies employed to enhance the vasoreparative potential of autologous ECFCs by manipulating crucial pro-angiogenic signaling pathways, e.g., extracellular-signal regulated kinase/Akt, phosphoinositide 3-kinase, and Ca²⁺ signaling. We conclude by discussing the possibility of targeting circulating ECFCs to rescue their dysfunctional phenotype and promote neovascularization in the presence of CVD.

EPO could be regulated by HIF-1 and promote osteogenesis and accelerate bone repair

Bone defects caused by many factors prompt further study of pathological process and restoration methods. This study was aimed to clarify the effect of erythropoietin on the repair of bone defect. We added the designated concentration of rhEPO to endothelial progenitor cells and marrow stromal cells, then detected its osteogenic and angiogenesis effects. The results showed that rhEPO promoted the proliferation of EPC and ST2 by promoting the mitosis without affecting cell apoptosis. The protein and mRNA levels of angiogenesis and osteogenic related factors exhibited higher expressions. Additionally, rhEPO encapsulated in PLGA scaffolds accelerated the new bone formation in rat calvaria bone defect model. Since the centre of bone defect was hypoxia environment, we cultured EPC and ST2 under hypoxia. SiRNA and an inhibitor of HIF-1 were used to interfere HIF-1, then the following changes of VEGF and EPO were detected. The results showed that all the factors were upregulated under the hypoxia environment. The expression of VEGF at protein and mRNA level decreased as HIF-1 was inhibited or interfered from 6 h, while the mRNA expression of EPO from 6 h and changed significantly at protein level from 12 h. Therefore, EPO is a promising factor for further studies.

DT-13 induced apoptosis and promoted differentiation of acute myeloid leukemia cells by activating AMPK-KLF2 pathway

Acute myeloid leukemia (AML) is a malignant disease originating from hematopoietic stem cells (HSC). Chemotherapy and/or HSC transplantation is unsatisfactory due to serious side effects, multidrug resistance, and high relapse rate. Thus, alternative strategies are urgently needed to develop more effective therapies. Liriope muscari baily saponins C (DT-13) is a novel compound isolated from Liriope muscari (Decne.) Baily, and exhibited a potent cytotoxicity against several solid tumors. However, the anti-AML activity of DT-13 and the potential mechanisms are still unknown. This study is the first to demonstrate that DT-13 had preferential cytotoxicity against AML cells, and remarkably inhibited proliferation and colony forming ability. Moreover, DT-13 induced the death receptor pathway-dependent apoptosis of HL-60 and Kasumi-1 cells by up-regulating Fas, FasL, DR5 and TRAIL as well as promoted the cleavage of caspase 8, caspase 3 and PARP. Meanwhile, DT-13 induced the differentiation with morphological change related to myeloid differentiation, elevated NBT and α-NAE positive cell rates, differentiation markers CD11b and CD14 as well as level of transcription factors C/EBPα and C/EBPβ. RNA-sequencing analysis revealed that KLF2 may be one of the potential targets regulated by DT-13. Further studies indicated that KLF2 played a critical role in DT-13-induced apoptosis and differentiation. Moreover, activation of AMPK-FOXO was proved to be the upstream of KLF2 pathway that contributed to the induction of apoptosis and differentiation by DT-13. Additionally, restoration of KLF2 by DT-13 was highly correlated with the AMPK-related histone acetylation mechanisms. Finally, DT-13 exhibited an obvious anti-AML effect in NOD/SCID mice with the engraftment of HL-60 cells. Our study suggests that DT-13 may serve as a novel agent for AML by AMPL-KLF2-mediated apoptosis and differentiation.

High Expression of RING Finger Protein 126 Predicts Unfavorable Prognosis of Epithelial Ovarian Cancer

Background

Ovarian cancer (OC) is one of the leading causes of cancer-related mortality worldwide. The clinical outcome of EOC remains unsatisfactory with current therapeutic approaches such as surgery and platinum/taxane-based chemotherapy. Therefore, novel prognostic markers and personalized therapies targeting specific molecules are urgently needed. Here, we explored whether RNF126, an E3 ubiquitin ligase, is a potential biomarker for epithelial ovarian cancer (EOC).

Material/Methods

This was a retrospective cohort study of 122 EOC patients. The chi-square test was used to assess correlations between RNF126 level and clinical characteristics of enrolled patients. Univariate and multivariate analyses were performed to monitor the prognosis of enrolled patients. In addition, proliferation and invasion assays were conducted to assess the cellular effects of RNF126 on SKOV3 cell progression.

Results

Immunohistochemistry analysis (IHC) revealed that RNF126 was upregulated in EOC tissues compared to adjacent ovarian tissues. In addition, RNF126 expression was remarkably associated with LN metastasis, pathological differentiation, and FIGO stage. RNF126 protein level was found to be an independent biomarker for predication of prognosis in ovarian cancer patients. Cellular results showed that RNF126 enhanced the proliferation and invasion abilities of SKOV3 cells.

Conclusions

Upregulated protein level of RNF126 in EOC tissues is a biomarker predicting poor outcomes of EOC patients.

Pulmonary hypertension secondary to congenital diaphragmatic hernia: factors and pathways involved in pulmonary vascular remodeling

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is characterized by pulmonary hypoplasia and pulmonary hypertension (PHTN). PHTN secondary to CDH is a result of vascular remodeling, a structural alteration in the pulmonary vessel wall that occurs in the fetus. Factors involved in vascular remodeling have been reported in several studies, but their interactions remain unclear. To help understand PHTN pathophysiology and design novel preventative and treatment strategies, we have conducted a systematic review of the literature and comprehensively analyzed all factors and pathways involved in the pathogenesis of pulmonary vascular remodeling secondary to CDH in the nitrofen model. Moreover, we have linked the dysregulated factors with pathways involved in human CDH. Of the 358 full-text articles screened, 75 studies reported factors that play a critical role in vascular remodeling secondary to CDH. Overall, the impairment of epithelial homeostasis present in pulmonary hypoplasia results in altered signaling to endothelial cells, leading to endothelial dysfunction. This causes an impairment of the crosstalk between endothelial cells and pulmonary artery smooth muscle cells, resulting in increased smooth muscle cell proliferation, resistance to apoptosis, and vasoconstriction, which clinically translate into PHTN.

The GLP-1 receptor agonist liraglutide protects against oxidized LDL-induced endothelial inflammation and dysfunction via KLF2

Cardiovascular complications are the major causes of the mortality and morbidities in diabetic patients. The diabetic patients have an increased risk of developing atherosclerosis, which could lead to heart attack and stroke. Glucagon-like peptide 1 (GLP-1) receptor agonists are a class of potent anti-glycemic agents to treat diabetes. Recently, several GLP-1 receptor agonists have been found to have cardiovascular benefit independent of their glucose lowing ability. Liraglutide is one of clinically approved effective GLP-1 receptor agonists. In this study, we explored the molecular mechanism of Liraglutide against oxidized low-density lipoprotein (ox-LDL) in cultured endothelial cells. Our data show that Liraglutide treatment ameliorates ox-LDL caused reduction of the transcriptional factor KLF2. In the same experiment, Liraglutide also rescues ox-LDL induced reduction of mitogen-activated protein kinase (MAPK) kinase extracellular signal regulated kinase 5 (ERK5) phosphorylation, and blockage of ERK5 activity by its inhibitor XMD8-92 abolishes the protection of Liraglutide on KLF2 expression. These facts suggest that the action of Liraglutide on endothelial KLF2 is dependent on ERK5. Liraglutide also recovers ox-LDL caused reduction of endothelial tight junctions protein Occludin and ameliorates ox-LDL induced endothelial monolayer permeability increase. On the other hand, Liraglutide inhibits ox-LDL induced expression of vascular adhesion molecules (E-selectin and vascular cell adhesion molecule 1), and prevents ox-LDL induced attachment of monocytes adhesion to endothelial cells. Moreover, Liraglutide mitigates ox-LDL triggered reduction of endothelial nitric oxide synthase (eNOS) expression and NO release. Collectively, our study provides multiple facets of the mechanisms that Liraglutide is a protective agent in endothelial cells and has the potential implication in therapeutic usage of vascular complication in diabetes patients. © 2019 IUBMB Life, 71(9):1347-1354, 2019.

The role of endothelial colony forming cells in kidney cancer's pathogenesis, and in resistance to anti-VEGFR agents and mTOR inhibitors: A speculative review

Renal cell carcinoma (RCC) is highly dependent on angiogenesis, due to the overactivation of the VHL/HIF/VEGF/VEGFRs axis; this justifies the marked sensitivity of this neoplasm to antiangiogenic agents which, however, ultimately fail to control tumor growth. RCC also frequently shows alterations in the mTOR signaling pathway, and mTOR inhibitors have shown a similar pattern of initial activity/late failure as pure antiangiogenic agents. Understanding mechanisms of resistance to these agents would be key to improve the outcome of our patients. Circulating endothelial cells are a family of mainly bone marrow-derived progenitors, which have been postulated to be responsible of the reactivation of angiogenesis in different tumors. In this review, we shall discuss the complex nature and function of these cells, the evidence pro and contra their contribution to tumor vascularization, especially as far as RCC is concerned, and their possible role in determining resistance to presently available treatments.

Ghrelin Stimulates Endothelial Cells Angiogenesis through Extracellular Regulated Protein Kinases (ERK) Signaling Pathway

Adipose tissue is hyper-vascularized. Vessels in adipose tissue not only supply nutrients and oxygen to nourish adipocytes, but also provide cytokines that regulate mass and function of adipose tissue. Understanding the fundamental mechanisms how vessels modulate adipocyte functions would provide new therapeutic options for treatment of metabolic disease and obesity. In recent years, researches about ghrelin are focused on glucose and lipid metabolism, but its effect on vascular function remains uncharacterized. In the present study, ghrelin receptor gene deletion mice (Ghsr^-/- mice) were used to study ghrelin-regulated vascular metabolism in white adipose tissue. Ghsr^-/- mice demonstrated lower food intake, lower body weight, and resistance to high-fat diet-induced obesity. The number of vessels in white adipose tissue was decreased in Ghsr^-/- mice when compared with wild type mice fed with high-fat diet. To further define ghrelin effects in vitro, we used endothelial progenitor cells from wild type and Ghsr^-/- mice as well as human umbilical vein endothelial cells in our experiments. We found that ghrelin stimulated endothelial cells angiogenesis and migration through the MEK-ERK signaling pathway. [d-Lys3]-GHRP-6 and PD98059 could reverse the effects of ghrelin on endothelial cells. Our study indicates that ghrelin activates its receptor on endothelial cells to promote angiogenesis and migration via a mechanism involving the extracellular regulated protein kinases (ERK) signaling pathway.

Lipopolysaccharide Downregulates Kruppel-Like Factor 2 (KLF2) via Inducing DNMT1-Mediated Hypermethylation in Endothelial Cells

KLF2 plays a protective role in antiinflammation and endothelial function, and can be regulated by promoter methylation alteration. Lipopolysaccharide (LPS) is a mediator of inflammatory responses, which causes epigenetic change of certain genes in host cells. We thus aimed to determine whether LPS could control the KLF2 expression by inducing methylation in promoter region. DNA methylation of 16 CpG sites within KLF2 promoter region was detected by bisulfite sequencing PCR. Results showed that methylation at 12 CpG sites were significantly increased in HUVECs after exposure to LPS among the total 16 sites, and the average level was increased by 57%. The KLF2 expressions assessed by reverse transcription quantitative real-time PCR and Western blot were significantly downregulated compared that without LPS simulation. Moreover, both messenger RNA and protein levels of KLF2 in HUVEC co-treated with LPS and DNA methyltransferase (DNMT) 1 small interfering RNA were dramatically higher than that treated with LPS only. Similar result was obtained when the cells were incubated in combination with LPS and 5-aza-2'-deoxycytidine (AZA), suggesting that the reduction of KLF2 expression induced by LPS can be reversed by DNMT1 inhibition. Finally, the presence of AZA changed the expression of genes that depends on KLF2 in LPS-stimulated HUVECs, which downregulated the E-selectin and VCAM and increased the eNOS and thrombomodulin expression. Our data demonstrated that LPS exposure resulted in hypermethylation in KLF2 promoter in HUVECs, which subsequently led to downregulation of the KLF2 expression. The study suggested that epigenetic alteration is involved in LPS-induced inflammatory response and provided a new insight into atherogenesis.

AMPK-KLF2 signaling pathway mediates the proangiogenic effect of erythropoietin in endothelial colony-forming cells

Endothelial colony-forming cells (ECFCs) were proved to take part in postnatal vasculogenesis and injury repair. The angiogenic properties of ECFCs could be influenced by various cytokines, chemokines, and growth factors. Erythropoietin (EPO) is a promising cytokine participating in angiogenesis. However, the mechanisms for EPO's proangiogenic effect still remain largely elusive. Here, we investigated the role of the AMP-activated protein kinase (AMPK)-Krüppel-like factor 2 (KLF2) signaling pathway in the proangiogenic effect of EPO in ECFCs. Human ECFCs were isolated from cord blood and cultured. EPO significantly enhanced the migration and tube formation capacities of ECFCs and markedly increased the expression of endothelial markers and vascular endothelial growth factor (VEGF). Further, EPO caused the phosphorylation of AMPK and endothelial nitric oxide synthase, a process in which KLF2 was also upregulated on both mRNA and protein levels. The upregulation of KLF2 was blocked by inhibiting AMPK with Compound C or Ad-AMPK-DN, a recombinant adenovirus that encoded a dominant-negative mutant of AMPK. Furthermore, knockdown of KLF2 showed no effect on AMPK but abolished the EPO-enhanced migration and tube formation capacities of ECFCs. Of note, knockdown of KLF2 also diminished the EPO-induced expression of endothelial markers and VEGF; overexpression of KLF2 promoted the expression of endothelial markers and VEGF and enhanced the migration and tube formation capacities of ECFCs. These data suggest that upregulation of KLF2 by AMPK plays an essential role in EPO-induced angiogenesis.

TRPC3-mediated Ca2+ signals as a promising strategy to boost therapeutic angiogenesis in failing hearts: The role of autologous endothelial colony forming cells

Endothelial progenitor cells (EPCs) are a sub-population of bone marrow-derived mononuclear cells that are released in circulation to restore damaged endothelium during its physiological turnover or rescue blood perfusion after an ischemic insult. Additionally, they may be mobilized from perivascular niches located within larger arteries' wall in response to hypoxic conditions. For this reason, EPCs have been regarded as an effective tool to promote revascularization and functional recovery of ischemic hearts, but clinical application failed to exploit the full potential of patients-derived cells. Indeed, the frequency and biological activity of EPCs are compromised in aging individuals or in subjects suffering from severe cardiovascular risk factors. Rejuvenating the reparative phenotype of autologous EPCs through a gene transfer approach has, therefore, been put forward as an alternative approach to enhance their therapeutic potential in cardiovascular patients. An increase in intracellular Ca²⁺ concentration constitutes a pivotal signal for the activation of the so-called endothelial colony forming cells (ECFCs), the only known truly endothelial EPC subset. Studies from our group showed that the Ca²⁺ toolkit differs between peripheral blood- and umbilical cord blood (UCB)-derived ECFCs. In the present article, we first discuss how VEGF uses repetitive Ca²⁺ spikes to regulate angiogenesis in ECFCs and outline how VEGF-induced intracellular Ca²⁺ oscillations differ between the two ECFC subtypes. We then hypothesize about the possibility to rejuvenate the biological activity of autologous ECFCs by transfecting the cell with the Ca²⁺ -permeable channel Transient Receptor Potential Canonical 3, which selectively drives the Ca²⁺ response to VEGF in UCB-derived ECFCs.

Natural compound bavachalcone promotes the differentiation of endothelial progenitor cells and neovascularization through the RORα-erythropoietin-AMPK axis

In cardiovascular diseases, endothelial function is impaired and the level of circulating endothelial progenitor cells (EPCs) is low. This study investigated whether the natural bioactive component bavachalcone (BavaC) induces the differentiation of EPCs and neovascularization in vivo; the underlying mechanisms were also examined. We observed that the treatment of rat bone marrow–derived cells with a very low dose of BavaC significantly promoted EPC differentiation. In our hindlimb ischemia models, low–dose BavaC administered orally for 14 days stimulated the recovery of ischemic hindlimb blood flow, increased circulating EPCs, and promoted capillary angiogenesis. The BavaC treatment of rat bone marrow cells for 24 h initiated the AMP–activated protein kinase (AMPK) activity required for the differentiation of EPCs. Further testing revealed that BavaC and CGP52608, a retinoic acid receptor–related orphan receptor α (RORα) activator, enhanced the activity of RORα1 and EPO luciferase reporter gene. BavaC treatment also elevated EPO mRNA and protein expression in vitro and in vivo and the circulating EPO levels in rats. By contrast, the RORα antagonist VPR66 inhibited BavaC–induced EPO reporter activity, and differentiation of bone marrow cells into endothelial progenitor cells. Overall, this study revealed that BavaC promotes EPC differentiation and neovascularization through a RORα–EPO–AMPK axis. BavaC can be used as a promising angiogenesis agent for enhancing angiogenesis and tissue repair.

Aging and the Krüppel-like factors

The mammalian Krüppel-like factors (KLFs) are a family of zinc-finger containing transcription factors with diverse patterns of expression and a wide array of cellular functions. While their roles in mammalian physiology are well known, there is a growing appreciation for their roles in modulating the fundamental progression of aging. Here we review the current knowledge of Krüppel-like factors with a focus on their roles in processes regulating aging and age-associated diseases.

Histone deacetylases and cardiovascular cell lineage commitment

Cardiovascular diseases (CVDs), which include all diseases of the heart and circulation system, are the leading cause of deaths on the globally. During the development of CVDs, choric inflammatory, lipid metabolism disorder and endothelial dysfunction are widely recognized risk factors. Recently, the new treatment for CVDs that designed to regenerate the damaged myocardium and injured vascular endothelium and improve recovery by the use of stem cells, attracts more and more public attention. Histone deacetylases (HDACs) are a family of enzymes that remove acetyl groups from lysine residues of histone proteins allowing the histones to wrap the DNA more tightly and commonly known as epigenetic regulators of gene transcription. HDACs play indispensable roles in nearly all biological processes, such as transcriptional regulation, cell cycle progression and developmental events, and have originally shown to be involved in cancer and neurological diseases. HDACs are also found to play crucial roles in cardiovascular diseases by modulating vascular cell homeostasis (e.g., proliferation, migration, and apoptosis of both ECs and SMCs). This review focuses on the roles of different members of HDACs and HDAC inhibitor on stem cell/ progenitor cell differentiation toward vascular cell lineages (endothelial cells, smooth muscle cells and Cardiomyocytes) and its potential therapeutics.

Epigenetic regulation of endothelial-cell-mediated vascular repair

Maintenance of vascular integrity is essential for the prevention of vascular disease and for recovery following cardiovascular, cerebrovascular and peripheral vascular events including limb ischemia, heart attack and stroke. Endothelial stem/progenitor cells have recently gained considerable interest due to their potential use in stem cell therapies to mediate revascularization after ischemic injury. Therefore, there is an urgent need to understand fundamental mechanisms regulating vascular repair in specific cell types to develop new beneficial therapeutic interventions. In this review, we highlight recent studies demonstrating that epigenetic mechanisms (including post-translational modifications of DNA and histones as well as non-coding RNA-mediated processes) play essential roles in the regulation of endothelial stem/progenitor cell functions through modifying chromatin structure. Furthermore, we discuss the potential of using small molecules that modulate the activities of epigenetic enzymes to enhance the vascular repair function of endothelial cells and offer insight on potential strategies that may accelerate clinical applications.

May the remodeling of the Ca²⁺ toolkit in endothelial progenitor cells derived from cancer patients suggest alternative targets for anti-angiogenic treatment?

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain the metastatic switch in a number of solid cancers, including breast cancer (BC) and renal cellular carcinoma (RCC). Preventing EPC mobilization causes tumor shrinkage. Novel anti-angiogenic treatments have been introduced in therapy to inhibit VEGFR-2 signaling; unfortunately, these drugs blocked tumor angiogenesis in pre-clinical murine models, but resulted far less effective in human patients. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis in cancer patients could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca²⁺ entry (SOCE) regulates the growth of human EPCs, and it is mediated by the interaction between the endoplasmic reticulum Ca²⁺-sensor, Stim1, and the plasmalemmal Ca²⁺ channels, Orai1 and TRPC1. EPCs do not belong to the neoplastic clone: thus, unlike tumor endothelium and neoplastic cells, they should not remodel their Ca²⁺ toolkit in response to tumor microenvironment. However, our recent work demonstrated that EPCs isolated from naïve RCC patients (RCC-EPCs) undergo a dramatic remodeling of their Ca²⁺ toolkit by displaying a remarkable drop in the endoplasmic reticulum Ca²⁺ content, by down-regulating the expression of inositol-1,4,5-receptors (InsP3Rs), and by up-regulating Stim1, Orai1 and TRPC1. Moreover, EPCs are dramatically less sensitive to VEGF stimulation both in terms of Ca²⁺ signaling and of gene expression when isolated from tumor patients. Conversely, the pharmacological abolition of SOCE suppresses proliferation in these cells. These results question the suitability of VEGFR-2 as a therapeutically relevant target for anti-angiogenic treatments and hint at Orai1 and TRPC1 as more promising alternatives. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Regulation of EPCs: The Gateway to Blood Vessel Formation

Endothelial progenitor cells (EPCs) are primitive endothelial precursors which are known to functionally contribute to the pathogenesis of disease. To date a number of distinct subtypes of these cells have been described, with differing maturation status, cellular phenotype, and function. Although there is much debate on which subtype constitutes the true EPC population, all subtypes have endothelial characteristics and contribute to neovascularisation. Vasculogenesis, the process by which EPCs contribute to blood vessel formation, can be dysregulated in disease with overabundant vasculogenesis in the context of solid tumours, leading to tumour growth and metastasis, and conversely insufficient vasculogenesis can be present in an ischemic environment. Importantly, it is widely known that transcription factors tightly regulate cellular phenotype and function by controlling the expression of particular target genes and in turn regulating specific signalling pathways. This suggests that transcriptional regulators may be potential therapeutic targets to control EPC function. Herein, we discuss the observed EPC subtypes described in the literature and review recent studies describing the role of a number of transcriptional families in the regulation of EPC phenotype and function in normal and pathological conditions.