Stimulation of vasculogenesis and leukopoiesis of embryonic stem cells by extracellular transfer RNA and ribosomal RNA

Effect of Extracellular Ribonucleic Acids on Neurovascularization in Osteoarthritis

Osteoarthritis is a degenerative disease characterized by abnormal neurovascularization at the osteochondral junctions, the regulatory mechanisms of which remain poorly understood. In the present study, a murine osteoarthritic model with augmented neurovascularization at the osteochondral junction is used to examine this under-evaluated facet of degenerative joint dysfunction. Increased extracellular RNA (exRNA) content is identified in neurovascularized osteoarthritic joints. It is found that the amount of exRNA is positively correlated with the extent of neurovascularization and the expression of vascular endothelial growth factor (VEGF). In vitro binding assay and molecular docking demonstrate that synthetic RNAs bind to VEGF via electrostatic interactions. The RNA-VEGF complex promotes the migration and function of endothelial progenitor cells and trigeminal ganglion cells. The use of VEGF and VEGFR2 inhibitors significantly inhibits the amplification of the RNA-VEGF complex. Disruption of the RNA-VEGF complex by RNase and polyethyleneimine reduces its in vitro activities, as well as prevents excessive neurovascularization and osteochondral deterioration in vivo. The results of the present study suggest that exRNAs may be potential targets for regulating nerve and blood vessel ingrowth under physiological and pathological joint conditions.

Novel insight into miRNA biology and its role in the pathogenesis of systemic lupus erythematosus

MicroRNAs(miRNAs) have emerged as key regulators that control and influence gene expression as well as multiple biological processes depending on their potential binding sites in human-protein coding genes and other unconventional patterns, including coding for peptides, activating Toll-like receptors as a ligand, and other manners. Accumulating evidence has demonstrated that microRNA expression is tightly regulated during phases of development, differentiation, and effector functions of immune cells, immunological disorders of systemic lupus erythematosus (SLE). This review outlines the biogenesis of miRNAs and their unconventional functions as well as underlying cellular and molecular mechanisms. It then summarizes our current knowledge about how the biogenesis of miRNAs is regulated. Moreover, an overview was provided concerning the role of abnormal expression of miRNAs in lupus immune cells. In particular, we will shed some light on the recent advances in the role of miRNAs and exosome-derived miRNAs in immunological and epigenetic pathways in the pathogenesis of SLE.

Downregulation of NAGLU in VEC Increases Abnormal Accumulation of Lysosomes and Represents a Predictive Biomarker in Early Atherosclerosis

Cardiovascular diseases (CVDs), predominantly caused by atherosclerosis (AS), are the leading cause of mortality worldwide. Although a great number of previous studies have attempted to reveal the molecular mechanism of AS, the underlying mechanism has not been fully elucidated. The aberrant expression profiling of vascular endothelial cells (VECs) gene in early atherosclerosis (EAS) was analyzed according to the dataset (GSE132651) downloaded from the Gene Expression Omnibus (GEO) database. We primarily performed functional annotation analysis on the downregulated genes (DRGs). We further identified that α-N-acetylglucosaminidase (NAGLU), one of the DRGs, played a critical role in the progression of EAS. NAGLU is a key enzyme for the degradation of heparan sulfate (HS), and its deficiency could cause lysosomal accumulation and lead to dysfunctions of VECs. We found that siRNA knockdown of NAGLU in human umbilical vein endothelial cell (HUVEC) aggravated the abnormal accumulation of lysosomes and HS. In addition, the expression of NAGLU was reduced in the EAS model constructed by ApoE−/- mice. Furthermore, we also showed that heparin-binding EGF-like growth factor (HB-EGF) protein was upregulated while NAGLU knockdown in HUVEC could specifically bind to vascular endothelial growth factor receptor 2 (VEGFR2) and promote its phosphorylation, ultimately activating the phosphorylation levels of extracellular signal-regulated kinases (ERKs). However, the application of selective VEGFR2 and ERKs inhibitors, SU5614 and PD98059, respectively, could reverse the abnormal lysosomal storage caused by NAGLU knockdown. These results indicated that downregulation of NAGLU in HUVEC increases the abnormal accumulation of lysosomes and may be a potential biomarker for the diagnosis of EAS.

Extracellular RNA as a Versatile DAMP and Alarm Signal That Influences Leukocyte Recruitment in Inflammation and Infection

Upon vascular injury, tissue damage, ischemia, or microbial infection, intracellular material such as nucleic acids and histones is liberated and comes into contact with the vessel wall and circulating blood cells. Such "Danger-associated molecular patterns" (DAMPs) may thus have an enduring influence on the inflammatory defense process that involves leukocyte recruitment and wound healing reactions. While different species of extracellular RNA (exRNA), including microRNAs and long non-coding RNAs, have been implicated to influence inflammatory processes at different levels, recent in vitro and in vivo work has demonstrated a major impact of ribosomal exRNA as a prominent DAMP on various steps of leukocyte recruitment within the innate immune response. This includes the induction of vascular hyper-permeability and vasogenic edema by exRNA via the activation of the "vascular endothelial growth factor" (VEGF) receptor-2 system, as well as the recruitment of leukocytes to the inflamed endothelium, the M1-type polarization of inflammatory macrophages, or the role of exRNA as a pro-thrombotic cofactor to promote thrombosis. Beyond sterile inflammation, exRNA also augments the docking of bacteria to host cells and the subsequent microbial invasion. Moreover, upon vessel occlusion and ischemia, the shear stress-induced release of exRNA initiates arteriogenesis (i.e., formation of natural vessel bypasses) in a multistep process that resembles leukocyte recruitment. Although exRNA can be counteracted for by natural circulating RNase1, under the conditions mentioned, only the administration of exogenous, thermostable, non-toxic RNase1 provides an effective and safe therapeutic regimen for treating the damaging activities of exRNA. It remains to be investigated whether exRNA may also influence viral infections (including COVID-19), e.g., by supporting the interaction of host cells with viral particles and their subsequent invasion. In fact, as a consequence of the viral infection cycle, massive amounts of exRNA are liberated, which can provoke further tissue damage and enhance virus dissemination. Whether the application of RNase1 in this scenario may help to limit the extent of viral infections like COVID-19 and impact on leukocyte recruitment and emigration steps in immune defense in order to limit the extent of associated cardiovascular diseases remains to be studied.

Omega-3 and Omega-6 polyunsaturated fatty acids stimulate vascular differentiation of mouse embryonic stem cells

Polyunsaturated fatty acids (PUFAs) and their metabolites may influence cell fate regulation. Herein, we investigated the effects of linoleic acid (LA) as ω-6 PUFA, eicosapentaenoic acid (EPA) as ω-3 PUFA and palmitic acid (PA) on vasculogenesis of embryonic stem (ES) cells. LA and EPA increased vascular structure formation and protein expression of the endothelial-specific markers fetal liver kinase-1, CD31 as well as VE-cadherin, whereas PA was without effect. LA and EPA increased reactive oxygen species (ROS) and nitric oxide (NO), activated endothelial NO synthase (eNOS) and raised intracellular calcium. The calcium response was inhibited by the intracellular calcium chelator BAPTA, sulfo-N-succinimidyl oleate which is an antagonist of CD36, the scavenger receptor for fatty acid uptake as well as by a CD36 blocking antibody. Prevention of ROS generation by radical scavengers or the NADPH oxidase inhibitor VAS2870 and inhibition of eNOS by L-NAME blunted vasculogenesis. PUFAs stimulated AMP activated protein kinase-α (AMPK-α) as well as peroxisome proliferator-activated receptor-α (PPAR-α). AMPK activation was abolished by calcium chelation as well as inhibition of ROS and NO generation. Moreover, PUFA-induced vasculogenesis was blunted by the PPAR-α inhibitor GW6471. In conclusion, ω-3 and ω-6 PUFAs stimulate vascular differentiation of ES cells via mechanisms involving calcium, ROS and NO, which regulate function of the energy sensors AMPK and PPAR-α and determine the metabolic signature of vascular cell differentiation.

The Extraordinary Role of Extracellular RNA in Arteriogenesis, the Growth of Collateral Arteries

Arteriogenesis is an intricate process in which increased shear stress in pre-existing arteriolar collaterals induces blood vessel expansion, mediated via endothelial cell activation, leukocyte recruitment and subsequent endothelial and smooth muscle cell proliferation. Extracellular RNA (eRNA), released from stressed cells or damaged tissue under pathological conditions, has recently been discovered to be liberated from endothelial cells in response to increased shear stress and to promote collateral growth. Until now, eRNA has been shown to enhance coagulation and inflammation by inducing cytokine release, leukocyte recruitment, and endothelial permeability, the latter being mediated by vascular endothelial growth factor (VEGF) signaling. In the context of arteriogenesis, however, eRNA has emerged as a transmitter of shear stress into endothelial activation, mediating the sterile inflammatory process essential for collateral remodeling, whereby the stimulatory effects of eRNA on the VEGF signaling axis seem to be pivotal. In addition, eRNA might influence subsequent steps of the arteriogenesis cascade as well. This article provides a comprehensive overview of the beneficial effects of eRNA during arteriogenesis, laying the foundation for further exploration of the connection between the damaging and non-damaging effects of eRNA in the context of cardiovascular occlusive diseases and of sterile inflammation.

The milk thistle (Silybum marianum) compound Silibinin stimulates leukopoiesis from mouse embryonic stem cells

The milk thistle compound Silibinin (i.e., a 1:1 mixture of Silybin A and Silybin B) stimulates vasculogenesis of mouse embryonic stem (ES) cells. Because vasculogenesis and leukopoiesis are interrelated, the effect of Silibinin on leukopoiesis of ES cells was investigated. Treatment of differentiating ES cells with hydrosoluble Silibinin-C-2',3-dihydrogen succinate dose-dependent increased the number of CD18+ , CD45+ , and CD68+ cells, indicating leukocyte/macrophage differentiation. Silibinin treatment activated phosphoinositide 3-kinase (PI3K), AKT (protein kinase B), signal transducer and activator of transcription 3 (STAT3), stimulated hypoxia-induced factor-1α (HIF-1α), and vascular endothelial growth factor receptor 2 (VEGFR2) expression and raised intracellular nitric oxide (NO). Western blot experiments showed that upon coincubation with either the PI3K inhibitor LY294002, the STAT3 inhibitor Stattic, the AKT antagonist AKT inhibitor VIII, or the NO inhibitor L-NAME, the Silibinin-induced expression of CD18, CD45, and CD68 was abolished. Moreover, the stimulation of HIF-1α and VEGFR2 expression was blunted upon STAT3 and PI3K/AKT inhibition. Treatment of differentiating ES cells with L-NAME abolished the stimulation of VEGFR2 and VE-cadherin expression achieved with Silibinin, indicating that NO is involved in vasculogenesis and leukocyte differentiation pathways. In summary, the data of the present study demonstrate that Silibinin stimulates leukocyte differentiation of ES cells, which is associated to vasculogenesis and regulated by PI3K/AKT-, STAT3-, and NO-mediated signaling.

The Importance of NADPH Oxidases and Redox Signaling in Angiogenesis

Eukaryotic cells have to cope with the constant generation of reactive oxygen species (ROS). Although the excessive production of ROS might be deleterious for cell biology, there is a plethora of evidence showing that moderate levels of ROS are important for the control of cell signaling and gene expression. The family of the nicotinamide adenine dinucleotide phosphate oxidases (NADPH oxidases or Nox) has evolved to produce ROS in response to different signals; therefore, they fulfil a central role in the control of redox signaling. The role of NADPH oxidases in vascular physiology has been a field of intense study over the last two decades. In this review we will briefly analyze how ROS can regulate signaling and gene expression. We will address the implication of NADPH oxidases and redox signaling in angiogenesis, and finally, the therapeutic possibilities derived from this knowledge will be discussed.

NADPH oxidase (NOX) 1 mediates cigarette smoke-induced superoxide generation in rat vascular smooth muscle cells

Smoking is a well-established risk factor for cardiovascular diseases. Oxidative stress is one of the common etiological factors, and NADPH oxidase (NOX) has been suggested as a potential mediator of oxidative stress. In this study, cigarette smoke (CS)-induced superoxide production was characterized in vascular smooth muscle cells (VSMC). CS was prepared in forms of cigarette smoke extract (CSE) and total particulate matter (TPM). Several molecular probes for reactive oxygen species were trialed, and dihydroethidium (DHE) and WST-1 were chosen for superoxide detection considering the autofluorescence, light absorbance, and peroxidase inhibitory activity of CS. Both CSE and TPM generated superoxide in a VSMC culture system by stimulating cells to produce superoxide and by directly producing superoxide in the aqueous solution. NOX, specifically NOX1 was found to be an important cellular source of superoxide through experiments with the NOX inhibitors diphenyleneiodonium (DPI) and VAS2870 as well as isoform-specific NOX knockdown. NOX inhibitors and the superoxide dismutase mimetic TEMPOL reduced the cytotoxicity of CSE, thus suggesting the contribution of NOX1-derived superoxide to cytotoxicity. Since NOX1 is known to mediate diverse pathological processes in the vascular system, NOX1 may be a critical effector of cardiovascular toxicity caused by smoking.

Nox2 contributes to the arterial endothelial specification of mouse induced pluripotent stem cells by upregulating Notch signaling

Reactive oxygen species (ROS) have a crucial role in stem-cell differentiation; however, the mechanisms by which ROS regulate the differentiation of stem cells into endothelial cells (ECs) are unknown. Here, we determine the role of ROS produced by NADPH oxidase 2 (Nox2) in the endothelial-lineage specification of mouse induced-pluripotent stem cells (miPSCs). When wild-type (WT) and Nox2-knockout (Nox2^−/−) miPSCs were differentiated into ECs (miPSC-ECs), the expression of endothelial markers, arterial endothelial markers, pro-angiogenic cytokines, and Notch pathway components was suppressed in the Nox2^−/− cells but increased in both WT and Nox2^−/− miPSCs when Nox2 expression was upregulated. Higher levels of Nox2 expression increased Notch signaling and arterial EC differentiation, and this increase was abolished by the inhibition of ROS generation or by the silencing of Notch1 expression. Nox2 deficiency was associated with declines in the survival and angiogenic potency of miPSC-ECs, and capillary and arterial density were lower in the ischemic limbs of mice after treatment with Nox2^−/− miPSC-ECs than WT miPSC-EC treatment. Taken together, these observations indicate that Nox2-mediated ROS production promotes arterial EC specification in differentiating miPSCs by activating the Notch signaling pathway and contributes to the angiogenic potency of transplanted miPSC-derived ECs.

Sources and Functions of Extracellular Small RNAs in Human Circulation

Various biotypes of endogenous small RNAs (sRNAs) have been detected in human circulation, including microRNAs, transfer RNAs, ribosomal RNA, and yRNA fragments. These extracellular sRNAs (ex-sRNAs) are packaged and secreted by many different cell types. Ex-sRNAs exhibit differences in abundance in several disease states and have, therefore, been proposed for use as effective biomarkers. Furthermore, exosome-borne ex-sRNAs have been reported to elicit physiological responses in acceptor cells. Exogenous ex-sRNAs derived from diet (most prominently from plants) and microorganisms have also been reported in human blood. Essential issues that remain to be conclusively addressed concern the (a) presence and sources of exogenous ex-sRNAs in human bodily fluids, (b) detection and measurement of ex-sRNAs in human circulation, (c) selectivity of ex-sRNA export and import, (d) sensitivity and specificity of ex-sRNA delivery to cellular targets, and (e) cell-, tissue-, organ-, and organism-wide impacts of ex-sRNA-mediated cell-to-cell communication. We survey the present state of knowledge of most of these issues in this review.

Extracellular Ribonucleic Acids (RNA) Enter the Stage in Cardiovascular Disease

Inflammatory and ischemic cardiovascular diseases, especially atherosclerosis and myocardial infarction, remain the number one cause of death in the Western world, whereas the therapeutic options currently available are still limited. Several recent findings have indicated that nucleic acids, particularly extracellular ribosomal RNA and micro-RNAs, significantly contribute to the adverse outcome of atherosclerosis, myocardial infarction, and other cardiovascular diseases. Extracellular RNAs act as novel danger-associated molecular pattern signals and potent cofactors in cardiovascular inflammation and thrombosis, particularly when accumulating in the extracellular space under tissue-damaging or pathological conditions. In this concise review article, the different entities of extracellular RNAs, their cellular sources, and their putative functional contribution to the pathogenesis of cardiovascular diseases will be discussed. In fact, it remains a tightrope walk for these polyanionic molecules outside cells to promote defense reactions on the one side but to provoke cardiovascular disease development on the other side, dependent on their concentration, the environmental conditions, and the cellular stimuli engaged. Thus, we will discuss the mechanisms and cellular responses by which extracellular RNAs operate between defense and disease. Finally, natural counteracting molecules, such as RNase1, will be focused on to elaborate their protective functions in the context of inflammatory and ischemic cardiovascular diseases with the possibility to apply them as novel interventional strategies.

Stem Cell Spheroid-Based Sprout Assay in Three-Dimensional Fibrin Scaffold: A Novel In Vitro Model for the Study of Angiogenesis

Angiogenesis is a complex process of critical importance during development and in physiological and pathophysiological conditions. There is considerable research interest in studying the angiogenesis cascade and consequently a need for a physiologically valid, quantitative, and cost-effective assay. In this chapter, we describe the stem cell spheroid-based sprout assay in three-dimensional fibrin scaffold which allows fast and easy screening of pro- and anti-angiogenic effects of substances with a high degree of reproducibility.