The Endothelium: An Active Regulator of Lipid and Glucose Homeostasis

Glucose metabolite methylglyoxal induces vascular endothelial cell pyroptosis via NLRP3 inflammasome activation and oxidative stress in vitro and in vivo

Methylglyoxal (MGO), a reactive dicarbonyl metabolite of glucose, plays a prominent role in the pathogenesis of diabetes and vascular complications. Our previous studies have shown that MGO is associated with increased oxidative stress, inflammatory responses and apoptotic cell death in endothelial cells (ECs). Pyroptosis is a novel form of inflammatory caspase-1-dependent programmed cell death that is closely associated with the activation of the NOD-like receptor 3 (NLRP3) inflammasome. Recent studies have shown that sulforaphane (SFN) can inhibit pyroptosis, but the effects and underlying mechanisms by which SFN affects MGO-induced pyroptosis in endothelial cells have not been determined. Here, we found that SFN prevented MGO-induced pyroptosis by suppressing oxidative stress and inflammation in vitro and in vivo. Our results revealed that SFN dose-dependently prevented MGO-induced HUVEC pyroptosis, inhibited pyroptosis-associated biochemical changes, and attenuated MGO-induced morphological alterations in mitochondria. SFN pretreatment significantly suppressed MGO-induced ROS production and the inflammatory response by inhibiting the NLRP3 inflammasome (NLRP3, ASC, and caspase-1) signaling pathway by activating Nrf2/HO-1 signaling. Similar results were obtained in vivo, and we demonstrated that SFN prevented MGO-induced oxidative damage, inflammation and pyroptosis by reversing the MGO-induced downregulation of the NLRP3 signaling pathway through the upregulation of Nrf2. Additionally, an Nrf2 inhibitor (ML385) noticeably attenuated the protective effects of SFN on MGO-induced pyroptosis and ROS generation by inhibiting the Nrf2/HO-1 signaling pathway, and a ROS scavenger (NAC) and a permeability transition pore inhibitor (CsA) completely reversed these effects. Moreover, NLRP3 inhibitor (MCC950) and caspase-1 inhibitor (VX765) further reduced pyroptosis in endothelial cells that were pretreated with SFN. Collectively, these findings broaden our understanding of the mechanism by which SFN inhibits pyroptosis induced by MGO and suggests important implications for the potential use of SFN in the treatment of vascular diseases.

A systems view of the vascular endothelium in health and disease

The dysfunction of blood-vessel-lining endothelial cells is a major cause of mortality. Although endothelial cells, being present in all organs as a single-cell layer, are often conceived as a rather inert cell population, the vascular endothelium as a whole should be considered a highly dynamic and interactive systemically disseminated organ. We present here a holistic view of the field of vascular research and review the diverse functions of blood-vessel-lining endothelial cells during the life cycle of the vasculature, namely responsive and relaying functions of the vascular endothelium and the responsive roles as instructive gatekeepers of organ function. Emerging translational perspectives in regenerative medicine, preventive medicine, and aging research are developed. Collectively, this review is aimed at promoting disciplinary coherence in the field of angioscience for a broader appreciation of the importance of the vasculature for organ function, systemic health, and healthy aging.

Activated Clec4nhi Neutrophils Aggravate Lung Injury in an Endothelial IGFBP7-Dependent Manner

The role of endothelial cells in acute lung injury (ALI) has been widely elaborated, but little is known about the role of different subtypes of endothelial cells in ALI. ALI models were established by lipopolysaccharide. Single-cell RNA sequencing was used to identify differential molecules in endothelial subtypes and the heterogeneity of lung immune cells. Specific antibodies were used to block insulin-like growth factor binding protein 7 (IGFBP7), and AAVshIGP7 was used to specifically knock down IGFBP7. Here, we found that IGFBP7 was the most differentially expressed molecule in diverse subsets of endothelial cells and that IGFBP7 was strongly associated with inflammatory responses. Elevated IGFBP7 significantly exacerbated barrier dysfunction in ALI, whereas blockade of IGFBP7 partially reversed barrier damage. General capillary cells are the primary source of elevated serum IGFBP7 after ALI. Using single-cell RNA sequencing, we identified significantly increased Clec4nhi neutrophils in mice with ALI, whereas IGFBP7 knockdown significantly reduced infiltration of Clec4nhi cells and mitigated barrier dysfunction in ALI. In addition, we found that IGFBP7 activated the NF-κB signaling axis by promoting phosphorylation and ubiquitination degradation of F-box/WD repeat-containing protein 2 (FBXW2), thereby exacerbating barrier dysfunction in ALI. Taken together, our data indicate that blockade of serum IGFBP7 or IGFBP7 depletion in general capillary cells reversed barrier damage in ALI. Therefore, targeting IGFBP7 depletion could be a novel strategy for treating ALI.

Obstructive sleep apnea hypopnea syndrome and vascular lesions: An update on what we currently know

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is the most prevalent sleep and respiratory disorder. This syndrome can induce severe cardiovascular and cerebrovascular complications, and intermittent hypoxia is a pivotal contributor to this damage. Vascular pathology is closely associated with the impairment of target organs, marking a focal point in current research. Vascular lesions are the fundamental pathophysiological basis of multiorgan ailments and indicate a shared pathogenic mechanism among common cardiovascular and cerebrovascular conditions, suggesting their importance as a public health concern. Increasing evidence shows a strong correlation between OSAHS and vascular lesions. Previous studies predominantly focused on the pathophysiological alterations in OSAHS itself, such as intermittent hypoxia and fragmented sleep, leading to vascular disruptions. This review aims to delve deeper into the vascular lesions affected by OSAHS by examining the microscopic pathophysiological mechanisms involved. Emphasis has been placed on examining how OSAHS induces vascular lesions through disruptions in the endothelial barrier, metabolic dysregulation, cellular phenotype alterations, neuroendocrine irregularities, programmed cell death, vascular inflammation, oxidative stress and epigenetic modifications. This review examines the epidemiology and associated risk factors for OSAHS and vascular diseases and subsequently describes the existing evidence on vascular lesions induced by OSAHS in the cardiovascular, cerebrovascular, retinal, renal and reproductive systems. A detailed account of the current research on the pathophysiological mechanisms mediating vascular lesions caused by OSAHS is provided, culminating in a discussion of research advancements in therapeutic modalities to mitigate OSAHS-related vascular lesions and the implications of these treatment strategies.

The Role of Vascular Endothelial Dysfunction in Hypertension With Hearing Loss

Hypertension can cause hearing loss, but there is no clear definition of the mechanism(s) involved. The study aimed to explore the role of vascular endothelial dysfunction in hypertension with hearing loss. Patients with hypertension were divided into two groups based on hearing loss. Pure tone audiometry (PTA) and endothelial function testing were performed. A total of 216 (432 ears) hypertensive patients were divided into hypertension with hearing loss group (n = 104) and hypertension without hearing loss group (n = 112). The vascular endothelial biomarkers, ET-1 (endothelin-1) and vWF (von Willebrand factor) were significantly higher (P < .05) in the hypertension with hearing loss group. RHI (reactive hyperemia index), ET-1, and vWF were the factors related to hearing loss. The area under the receiver operating characteristic (ROC) curve (AUC) of RHI in the diagnosis of hypertension with hearing loss was .652 (95% CI .552-.751, P = .005), and the Youden index was 26.2%. The AUC of ET-1 was .706 (95% CI .612-.799, P = .001), and the Youden index was 38.9%. The AUC of vWF was .617 (95% CI .512-.721, P = .003), and the Youden index was 28.1%. Vascular endothelial dysfunction may play a role in the pathogenesis of hypertension with hearing loss.

Disturbed endothelial cell signaling in tumor progression and therapy resistance

Growth of new blood vessels is considered requisite to cancer progression. Recent findings revealed that in addition to inducing angiogenesis, tumor-derived factors alter endothelial cell gene transcription within the tumor mass but also systemically throughout the body. This subsequently contributes to immunosuppression, altered metabolism, therapy resistance and metastasis. Clinical studies demonstrated that targeting the endothelium can increase the success rate of immunotherapy. Single-cell technologies revealed remarkable organ-specific endothelial heterogeneity that becomes altered by the presence of a tumor. In metastases, endothelial transcription differs remarkably between newly formed and co-opted vessels which may provide a basis for developing new therapies to target endothelial cells and overcome therapy resistance more effectively. This review addresses how cancers impact the endothelium to facilitate tumor progression.

Suppression of angiopoietin-like 4 reprograms endothelial cell metabolism and inhibits angiogenesis

Angiopoietin-like 4 (ANGPTL4) is known to regulate various cellular and systemic functions. However, its cell-specific role in endothelial cells (ECs) function and metabolic homeostasis remains to be elucidated. Here, using endothelial-specific Angptl4 knock-out mice (Angptl4iΔEC), and transcriptomics and metabolic flux analysis, we demonstrate that ANGPTL4 is required for maintaining EC metabolic function vital for vascular permeability and angiogenesis. Knockdown of ANGPTL4 in ECs promotes lipase-mediated lipoprotein lipolysis, which results in increased fatty acid (FA) uptake and oxidation. This is also paralleled by a decrease in proper glucose utilization for angiogenic activation of ECs. Mice with endothelial-specific deletion of Angptl4 showed decreased pathological neovascularization with stable vessel structures characterized by increased pericyte coverage and reduced permeability. Together, our study denotes the role of endothelial-ANGPTL4 in regulating cellular metabolism and angiogenic functions of EC.

Missing links in preeclampsia cell model systems of endothelial dysfunction

Preeclampsia, one of the main hypertensive disorders of pregnancy, is associated with circulating factors released by the ischemic placenta accompanied by systemic endothelial dysfunction. The etiology of preeclampsia remains poorly understood although it is associated with high maternal and fetal mortality and increased cardiovascular disease risk. Most cell model systems used for studying endothelial dysfunction have not taken into account hemodynamic physical factors such as shear-stress forces which may prevent extrapolation of cell data to in vivo settings. We overview the role of hemodynamic forces in modulating endothelial cell function and discuss strategies to reproduce this biological characteristic in vitro to improve our understanding of endothelial dysfunction associated with preeclampsia.

Erianin alleviated liver steatosis by enhancing Nrf2-mediated VE-cadherin expression in vascular endothelium

Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common chronic liver disease and is closely associated with metabolic syndrome. Endothelial dysfunction was involved in many metabolic diseases, but the concrete participation of hepatic vascular endothelial dysfunction in liver steatosis that is an early stage of NAFLD is still unclear. In this study, the formation of liver steatosis and the elevation of serum insulin content were observed accompanying with the decreased vascular endothelial cadherin (VE-cadherin) expression in hepatic vessels from db/db mice, Goto-Kakizaki (GK) and high-fat diet (HFD)-fed rats. Liver steatosis was obviously enhanced in mice after the application of VE-cadherin neutralizing antibody. In vitro results showed that insulin decreased VE-cadherin expression and caused endothelial barrier breakdown. Furthermore, the alteration of VE-cadherin expression was found to be positively related with the transcriptional activation of nuclear erythroid 2-related factor 2 (Nrf2), and chromatin immunoprecipitation (ChIP) assay displayed that Nrf2 could directly regulate VE-cadherin expression. Insulin reduced Nrf2 activation by decreasing sequestosome-1 (p62/SQSTM1) expression downstream of insulin receptor. Moreover, the p300-mediated Nrf2 acetylation was weakened by enhancing the competitive binding of transcription factor GATA-binding protein 4 (GATA4) to p300. Finally, we found that erianin, a natural compound, could promote VE-cadherin expression by inducing Nrf2 activation, thereby alleviating liver steatosis in GK rats. Our results suggest that hepatic vascular endothelial dysfunction owing to the VE-cadherin deficiency dependent on the reduced Nrf2 activation promoted liver steatosis, and erianin alleviated liver steatosis through enhancing Nrf2-mediated VE-cadherin expression.

Overview of mechanism and consequences of endothelial leakiness caused by metal and polymeric nanoparticles

Nanoparticles (NPs) exhibit unique physicochemical properties that enable them to overcome biological barriers and to be considered one of the best materials with anticancer properties. Most of the administered NPs that end up in the bloodstream interact with the endothelial layer. The interaction of the NPs with the endothelium widens the existing gaps or induces new ones in the monolayer of vascular endothelial cells, thus increasing the access to the target sites in the organism. This type of interaction can lead to NP-modulated endothelial leakiness (NanoEL). The most important factors determining NanoEL are the physicochemical properties of the NPs. NP-modulated endothelial leakiness can lead to the discovery of new therapeutic targets and strategies to improve drug delivery through controlling and regulating NanoEL. Nevertheless, the NanoEL mechanism also carries some limitations that result from an incomplete understanding of NP metabolism and toxicity, and the possibility of their participation in the unintended bidirectional vascular permeability, which may contribute to the formation of cancer metastases. In this review we are focusing on the effect of metal and polymeric NPs on mechanism and degree of induction of NanoEL, as well as on the benefits and risks of using NPs that induce endothelial leakiness.

lncRNA NEAT1/miR-495-3p regulates angiogenesis in burn sepsis through the TGF-β1 and SMAD signaling pathways

INTRODUCTION

To investigate the role of the long-chain noncoding RNA (lncRNA) nuclear enriched abundant transcript 1 (NEAT1) in the process of angiogenesis in human umbilical vein endothelial cells (HUVECs) and illustrate its potential role in burn sepsis (BS) pathogenesis.

METHODS

HUVECs were treated with BS patient serum or healthy control serum. NEAT1 shRNA, miR-495-3p mimics, and miR-495-3p inhibitor were transfected into HUVECs. NEAT1 and miR-495-3 levels in serum or HUVECs were detected using quantitative reverse transcription-polymerase chain reaction. Cell counting kit-8 and flow cytometry assays were used to explore the proliferation and apoptosis of HUVECs. The expression of vascular endothelial growth factor (VEGF) in the supernatant was detected using enzyme-linked immunosorbent assay. Tube formation of HUVECs was also analyzed. Western blot analysis was used to analyze signaling pathway proteins.

RESULTS

In HUVECs stimulated with BS patient serum, NEAT1 expression was increased, while miR-495-3p expression was decreased. In addition, NEAT1 silencing by specific shRNA inhibited cell proliferation, VEGF production, and tube formation under burn patient serum treatment, which decreased the TGFβ1/SMAD signaling pathway activation. Moreover, miR-495-3p minics inhibited angiogenesis and the activation of signaling pathways induced by NEAT1 shRNA. Furthermore, miR-495-3p inhobitor promoted angiogenesis in HUVECs and activated the TGFβ1/SMAD signaling pathway. In patients with BS, NEAT1 expression was significantly increased and miR-495-3p expression was decreased compared to healthy controls, and NEAT1 and miR-495-3p expression was associated with the clinical features of patients.

CONCLUSIONS

Our results indicate that lncRNA NEAT1 regulates angiogenesis and activates the TGFβ1/SMAD signaling pathway during the occurrence of BS.

Fenofibrate suppresses corneal neovascularization by regulating lipid metabolism through PPARα signaling pathway

Purpose: The purpose of this study was to explore the potential underlying mechanism of anti-vascular effects of peroxisome proliferator-activated receptor α (PPARα) agonist fenofibrate against corneal neovascularization (CNV) through the changes of lipid metabolism during CNV. Methods: A suture-induced CNV model was established and the clinical indications were evaluated from day 1 to day 7. Treatments of vehicle and fenofibrate were performed for 5 days after suture and the CNV areas were compared among the groups. The eyeballs were collected for histological analysis, malondialdehyde (MDA) measurement, terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL) staining, western blot, quantitative real-time PCR (qRT-PCR) assays and immunohistochemical (IHC) staining to elucidate pathological changes and the underlying mechanism. Results: Lipi-Green staining and MDA measurement showed that lipid deposition and peroxidation were increased in the CNV cornea while the expression of long-chain acyl-coenzyme A synthetase 1 (ACSL1), carnitine palmitoyltransterase 1A(CPT1A) and medium-chain acyl-coenzyme A dehydrogenase (ACADM), which are key enzymes of fatty acid β-oxidation (FAO) and targeted genes of peroxisome proliferator-activated receptor alpha (PPARα) pathway, were decreased in CNV cornea. Fenofibrate suppressed lipid accumulation and peroxidation damage in the CNV cornea. Fenofibrate upregulated the expression levels of PPARα, ACSL1, CPT1A, and ACADM compared with vehicle group. IHC staining indicated that fenofibrate also decreased the expression of VEGFa, VEGFc, TNFα, IL1β and CD68. Conclusion: Disorder of lipid metabolism may be involved in the formation of suture-induced CNV and fenofibrate played anti-neovascularization and anti-inflammatory roles on cornea by regulating the key enzymes of lipid metabolism and ameliorating lipid peroxidation damage of cornea through PPARα signaling pathway.

Adipose endothelial cells mastering adipose tissues metabolic fate

Dynamic communication within adipose tissue depends on highly vascularized structural characteristics to maintain systemic metabolic homoeostasis. Recently, it has been noted that adipose endothelial cells (AdECs) act as essential bridges for biological information transmission between adipose-resident cells. Hence, paracrine regulators that mediate crosstalk between AdECs and adipose stromal cells were summarized. We also highlight the importance of AdECs to maintain adipocytes metabolic homoeostasis by regulating insulin sensitivity, lipid turnover and plasticity. The differential regulation of AdECs in adipose plasticity often depends on vascular density and metabolic states. Although choosing pro-angiogenic or anti-angiogenic therapies for obesity is still a matter of debate in clinical settings, the growing numbers of drugs have been confirmed to play an anti-obesity effect by affecting vascularization. Pharmacologic angiogenesis intervention has great potential as therapeutic strategies for obesity.

Lipedema: Insights into Morphology, Pathophysiology, and Challenges

Lipedema is an adipofascial disorder that almost exclusively affects women. Lipedema leads to chronic pain, swelling, and other discomforts due to the bilateral and asymmetrical expansion of subcutaneous adipose tissue. Although various distinctive morphological characteristics, such as the hyperproliferation of fat cells, fibrosis, and inflammation, have been characterized in the progression of lipedema, the mechanisms underlying these changes have not yet been fully investigated. In addition, it is challenging to reduce the excessive fat in lipedema patients using conventional weight-loss techniques, such as lifestyle (diet and exercise) changes, bariatric surgery, and pharmacological interventions. Therefore, lipedema patients also go through additional psychosocial distress in the absence of permanent treatment. Research to understand the pathology of lipedema is still in its infancy, but promising markers derived from exosome, cytokine, lipidomic, and metabolomic profiling studies suggest a condition distinct from obesity and lymphedema. Although genetics seems to be a substantial cause of lipedema, due to the small number of patients involved in such studies, the extrapolation of data at a broader scale is challenging. With the current lack of etiology-guided treatments for lipedema, the discovery of new promising biomarkers could provide potential solutions to combat this complex disease. This review aims to address the morphological phenotype of lipedema fat, as well as its unclear pathophysiology, with a primary emphasis on excessive interstitial fluid, extracellular matrix remodeling, and lymphatic and vasculature dysfunction. The potential mechanisms, genetic implications, and proposed biomarkers for lipedema are further discussed in detail. Finally, we mention the challenges related to lipedema and emphasize the prospects of technological interventions to benefit the lipedema community in the future.

Therapeutic Applications of Nanomedicine in Metabolic Diseases by Targeting the Endothelium

The endothelial cells not only constitute the barrier between the blood and interstitial space, but also actively regulate vascular tone, blood flow, and the function of adjacent parenchymal cells. The close anatomical relationship between endothelial cells and highly vascularized metabolic organs suggests that the crosstalk between these units is vital for systemic metabolic homeostasis. Here, we review recent studies about the pivotal role of endothelial cells in metabolic diseases. Specifically, we discuss how the dysfunction of endothelial cells directly contributes to the development of insulin resistance (IR), type 2 diabetes mellitus (T2DM), atherosclerosis, and non-alcoholic fatty liver disease (NAFLD) via communication with parenchymal cells. Furthermore, although many biological macromolecules have been shown to ameliorate the progression of metabolic diseases by improving endothelial function, the low solubility, poor bioavailability, or lack of specificity of these molecules limit their clinical application. Given the advantages in drug delivery of nanomedicine, we focus on summarizing the reports that improving endothelial dysfunction through nanomedicine-based therapies provides an opportunity for preventing metabolic diseases.

Extracellular vesicle glucose transporter-1 and glycan features in monocyte-endothelial inflammatory interactions

Monocyte-induced endothelial cell inflammation is associated with multiple pathological conditions, and extracellular vesicles (EVs) are essential nanosized components of intercellular communication. EVs derived from endotoxin-stimulated monocytes were previously shown to carry pro-inflammatory proteins and RNAs. The role of glucose transporter-1 (GLUT-1) and glycan features in monocyte-derived EV-induced endothelial cell inflammation remains largely unexplored. This study demonstrates that EVs derived from endotoxin-stimulated monocytes activate inflammatory pathways in endothelial cells, which are partially attributed to GLUT-1. Alterations in glycan features and increased levels of GLUT-1 were observed in EVs derived from endotoxin-stimulated monocytes. Notably, inhibition of EV-associated GLUT-1, through the use of fasentin, suppressed EV-induced inflammatory cytokines in recipient endothelial cells.

Autologous Human Immunocompetent White Adipose Tissue-on-Chip

Obesity and associated diseases, such as diabetes, have reached epidemic proportions globally. In this era of "diabesity", white adipose tissue (WAT) has become a target of high interest for therapeutic strategies. To gain insights into mechanisms of adipose (patho-)physiology, researchers traditionally relied on animal models. Leveraging Organ-on-Chip technology, a microphysiological in vitro model of human WAT is introduced: a tailored microfluidic platform featuring vasculature-like perfusion that integrates 3D tissues comprising all major WAT-associated cellular components (mature adipocytes, organotypic endothelial barriers, stromovascular cells including adipose tissue macrophages) in an autologous manner and recapitulates pivotal WAT functions, such as energy storage and mobilization as well as endocrine and immunomodulatory activities. A precisely controllable bottom-up approach enables the generation of a multitude of replicates per donor circumventing inter-donor variability issues and paving the way for personalized medicine. Moreover, it allows to adjust the model's degree of complexity via a flexible mix-and-match approach. This WAT-on-Chip system constitutes the first human-based, autologous, and immunocompetent in vitro adipose tissue model that recapitulates almost full tissue heterogeneity and can become a powerful tool for human-relevant research in the field of metabolism and its associated diseases as well as for compound testing and personalized- and precision medicine applications.

The Inflamm-Aging Model Identifies Key Risk Factors in Atherosclerosis

Background: Atherosclerosis, one of the main threats to human life and health, is driven by abnormal inflammation (i.e., chronic inflammation or oxidative stress) during accelerated aging. Many studies have shown that inflamm-aging exerts a significant impact on the occurrence of atherosclerosis, particularly by inducing an immune homeostasis imbalance. However, the potential mechanism by which inflamm-aging induces atherosclerosis needs to be studied more thoroughly, and there is currently a lack of powerful prediction models.

Methods: First, an improved inflamm-aging prediction model was constructed by integrating aging, inflammation, and disease markers with the help of machine learning methods; then, inflamm-aging scores were calculated. In addition, the causal relationship between aging and disease was identified using Mendelian randomization. A series of risk factors were also identified by causal analysis, sensitivity analysis, and network analysis.

Results: Our results revealed an accelerated inflamm-aging pattern in atherosclerosis and suggested a causal relationship between inflamm-aging and atherosclerosis. Mechanisms involving inflammation, nutritional balance, vascular homeostasis, and oxidative stress were found to be driving factors of atherosclerosis in the context of inflamm-aging.

Conclusion: In summary, we developed a model integrating crucial risk factors in inflamm-aging and atherosclerosis. Our computation pipeline could be used to explore potential mechanisms of related diseases.

Impact of Sodium-Glucose Cotransporter 2 (SGLT2) Inhibitors on Arterial Stiffness and Vascular Aging-What Do We Know So Far? (A Narrative Review)

Vascular aging, early vascular aging or supernormal vascular aging are concepts used for estimating the cardiovascular risk at a certain age. From the famous line of Thomas Sydenham that "a man is as old as his arteries" to the present day, clinical studies in the field of molecular biology of the vasculature have demonstrated the active role of vascular endothelium in the onset of cardiovascular diseases. Arterial stiffness is an important cardiovascular risk factor associated with the occurrence of cardiovascular events and a high risk of morbidity and mortality, especially in the presence of diabetes. Sodium-glucose cotransporter 2 inhibitors decrease arterial stiffness and vascular resistance by decreasing endothelial cell activation, stimulating direct vasorelaxation and ameliorating endothelial dysfunction or expression of pro-atherogenic cells and molecules.

Preclinical atherosclerosis and cardiovascular events: Do we have a consensus about the role of preclinical atherosclerosis in the prediction of cardiovascular events?

Atherosclerosis has a long preclinical phase, and the risk of cardiovascular (CV) events may be high in asymptomatic subjects. Conventional risk factors provide information for the statistical probability of developing CV events, but they lack precision in asymptomatic subjects. This review aims to summarize the role of some widely publicized indicators of early atherosclerosis in predicting CV events. The earliest measurable indicator of the atherosclerotic process is endothelial dysfunction, measured by flow-mediated dilation (FMD) of the brachial artery. However, reduced FMD is a stronger predictor of future CV events in patients with existing CV disease than in apparently healthy persons. Alternatively, measurement of carotid artery intima-media thickness does not improve the predictive value of risk factor scores, while detection of asymptomatic atherosclerotic plaques in carotid or common femoral arteries by ultrasound indicates high CV risk. Coronary calcium is a robust and validated help in the estimation of vascular changes and risk, which may improve risk stratification beyond traditional risk factors with relatively low radiation exposure. Arterial stiffness of the aorta, measured as the carotid-femoral pulse wave velocity is an independent marker of CV risk at the population level, but it is not recommended as a routine procedure because of measurement difficulties. Low ankle-brachial index (ABI) indicates flow-limiting atherosclerosis in the lower limbs and indicates high CV risk, while normal ABI does not rule out advanced asymptomatic atherosclerosis. Novel circulating biomarkers are associated with the atherosclerotic process. However, because of limited specificity, their ability to improve risk classification at present remains low.

The multifaceted roles of the adipose tissue vasculature

The prevalence of obesity and its associated pathologies continue to increase, which has led to a renewed interest in our major weight-regulating organ, the white adipose tissue. It has become clear that its development, expansion, and physiological function depend on proper crosstalk between each of its cellular constituents, with a central role for the vascular endothelium lining the blood vessels. Although first considered a mere barrier, the endothelium has emerged as a dynamic unit modulating many critical adipose tissue functions. It not only oversees the uptake of all nutrients to be stored in the adipocytes but also provides an important growth niche for adipocyte progenitors and regulates the expandability of the tissue during overfeeding and obesity. In this review, we describe the reciprocal relationship between endothelial cells, adipocytes, and obesity. We present recent studies that support an important role for endothelial cells as central mediators of many of the physiological and pathological functions of the adipose tissue and highlight several unknown aspects of adipose tissue vascular biology. This new perspective could present exciting opportunities to develop new therapeutic approaches against obesity-related pathologies and is thus of great interest in our increasingly obese society.

Angiocrine polyamine production regulates adiposity

Reciprocal interactions between endothelial cells (ECs) and adipocytes are fundamental to maintain white adipose tissue (WAT) homeostasis, as illustrated by the activation of angiogenesis upon WAT expansion, a process that is impaired in obesity. However, the molecular mechanisms underlying the crosstalk between ECs and adipocytes remain poorly understood. Here, we show that local production of polyamines in ECs stimulates adipocyte lipolysis and regulates WAT homeostasis in mice. We promote enhanced cell-autonomous angiogenesis by deleting Pten in the murine endothelium. Endothelial Pten loss leads to a WAT-selective phenotype, characterized by reduced body weight and adiposity in pathophysiological conditions. This phenotype stems from enhanced fatty acid β-oxidation in ECs concomitant with a paracrine lipolytic action on adipocytes, accounting for reduced adiposity. Combined analysis of murine models, isolated ECs and human specimens reveals that WAT lipolysis is mediated by mTORC1-dependent production of polyamines by ECs. Our results indicate that angiocrine metabolic signals are important for WAT homeostasis and organismal metabolism.

Metformin prevents methylglyoxal-induced apoptosis by suppressing oxidative stress in vitro and in vivo

Methylglyoxal (MGO) is an active metabolite of glucose and plays a prominent role in the pathogenesis of diabetic vascular complications, including endothelial cell apoptosis induced by oxidative stress. Metformin (MET), a widely prescribed antidiabetic agent, appears to reduce excessive reactive oxygen species (ROS) generation and limit cell apoptosis. However, the molecular mechanisms underlying this process are still not fully elucidated. We reported here that MET prevents MGO-induced apoptosis by suppressing oxidative stress in vitro and in vivo. Protein expression and protein phosphorylation were investigated using western blotting, ELISA, and immunohistochemical staining, respectively. Cell viability and apoptosis were assessed by the MTT assay, TUNEL staining, and Annexin V-FITC and propidium iodide double staining. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Our results revealed that MET prevented MGO-induced HUVEC apoptosis, inhibited apoptosis-associated biochemical changes such as loss of MMP, the elevation of the Bax/Bcl-2 ratio, and activation of cleaved caspase-3, and attenuated MGO-induced mitochondrial morphological alterations in a dose-dependent manner. MET pretreatment also significantly suppressed MGO-stimulated ROS production, increased signaling through the ROS-mediated PI3K/Akt and Nrf2/HO-1 pathways, and markedly elevated the levels of its downstream antioxidants. Finally, similar results were obtained in vivo, and we demonstrated that MET prevented MGO-induced oxidative damage, apoptosis, and inflammation. As expected, MET reversed MGO-induced downregulation of Nrf2 and p-Akt. In addition, a PI3K inhibitor (LY-294002) and a Nrf2 inhibitor (ML385) observably attenuated the protective effects of MET on MGO-induced apoptosis and ROS generation by inhibiting the Nrf2/HO-1 pathways, while a ROS scavenger (NAC) and a permeability transition pores inhibitor (CsA) completely reversed these effects. Collectively, these findings broaden our understanding of the mechanism by which MET regulates apoptosis induced by MGO under oxidative stress conditions, with important implications regarding the potential application of MET for the treatment of diabetic vascular complications.

Paracrine Role of the Endothelium in Metabolic Homeostasis in Health and Nutrient Excess

The vascular endothelium traditionally viewed as a simple physical barrier between the circulation and tissue is now well-established as a key organ mediating whole organism homeostasis by release of a portfolio of anti-inflammatory and pro-inflammatory vasoactive molecules. Healthy endothelium releases anti-inflammatory signaling molecules such as nitric oxide and prostacyclin; in contrast, diseased endothelium secretes pro-inflammatory signals such as reactive oxygen species, endothelin-1 and tumor necrosis factor-alpha (TNFα). Endothelial dysfunction, which has now been identified as a hallmark of different components of the cardiometabolic syndrome including obesity, type 2 diabetes and hypertension, initiates and drives the progression of tissue damage in these disorders. Recently it has become apparent that, in addition to vasoactive molecules, the vascular endothelium has the potential to secrete a diverse range of small molecules and proteins mediating metabolic processes in adipose tissue (AT), liver, skeletal muscle and the pancreas. AT plays a pivotal role in orchestrating whole-body energy homeostasis and AT dysfunction, characterized by local and systemic inflammation, is central to the metabolic complications of obesity. Thus, understanding and targeting the crosstalk between the endothelium and AT may generate novel therapeutic opportunities for the cardiometabolic syndrome. Here, we provide an overview of the role of the endothelial secretome in controlling the function of AT. The endothelial-derived metabolic regulatory factors are grouped and discussed based on their physical properties and their downstream signaling effects. In addition, we focus on the therapeutic potential of these regulatory factors in treating cardiometabolic syndrome, and discuss areas of future study of potential translatable and clinical significance. The vascular endothelium is emerging as an important paracrine/endocrine organ that secretes regulatory factors in response to nutritional and environmental cues. Endothelial dysfunction may result in imbalanced secretion of these regulatory factors and contribute to the progression of AT and whole body metabolic dysfunction. As the vascular endothelium is the first responder to local nutritional changes and adipocyte-derived signals, future work elucidating the changes in the endothelial secretome is crucial to improve our understanding of the pathophysiology of cardiometabolic disease, and in aiding our development of new therapeutic strategies to treat and prevent cardiometabolic syndrome.

Cardiac Metabolism and Contractile Function in Mice with Reduced Trans-Endothelial Fatty Acid Transport

The heart is a metabolic omnivore that combusts a considerable amount of energy substrates, mainly long-chain fatty acids (FAs) and others such as glucose, lactate, ketone bodies, and amino acids. There is emerging evidence that muscle-type continuous capillaries comprise the rate-limiting barrier that regulates FA uptake into cardiomyocytes. The transport of FAs across the capillary endothelium is composed of three major steps-the lipolysis of triglyceride on the luminal side of the endothelium, FA uptake by the plasma membrane, and intracellular FA transport by cytosolic proteins. In the heart, impaired trans-endothelial FA (TEFA) transport causes reduced FA uptake, with a compensatory increase in glucose use. In most cases, mice with reduced FA uptake exhibit preserved cardiac function under unstressed conditions. When the workload is increased, however, the total energy supply relative to its demand (estimated with pool size in the tricarboxylic acid (TCA) cycle) is significantly diminished, resulting in contractile dysfunction. The supplementation of alternative fuels, such as medium-chain FAs and ketone bodies, at least partially restores contractile dysfunction, indicating that energy insufficiency due to reduced FA supply is the predominant cause of cardiac dysfunction. Based on recent in vivo findings, this review provides the following information related to TEFA transport: (1) the mechanisms of FA uptake by the heart, including TEFA transport; (2) the molecular mechanisms underlying the induction of genes associated with TEFA transport; (3) in vivo cardiac metabolism and contractile function in mice with reduced TEFA transport under unstressed conditions; and (4) in vivo contractile dysfunction in mice with reduced TEFA transport under diseased conditions, including an increased afterload and streptozotocin-induced diabetes.

MRI-based in vivo detection of coronary microvascular dysfunction before alterations in cardiac function induced by short-term high-fat diet in mice

Endothelial dysfunction is one of the hallmarks of vascular abnormalities in metabolic diseases and has been repeatedly demonstrated in coronary and peripheral circulation in mice fed high-fat diet (HFD), particularly after long-term HFD. However, the temporal relationship between development of coronary microvascular endothelial dysfunction and deterioration in diastolic and systolic cardiac function after short-term feeding with HFD has not yet been studied. This study aimed to correlate the changes in coronary microvascular endothelial function and global cardiac performance indices in vivo after short-term feeding with HFD in mice. Short-term feeding with a HFD (60% fat + 1% cholesterol) resulted in severely impaired coronary microvascular function, as evidenced by the diminished effect of nitric oxide synthase inhibition (by L-NAME) assessed using T1 mapping via in vivo MRI. Deterioration of coronary microvascular function was detected as early as after 7 days of HFD and further declined after 8 weeks on a HFD. HFD-induced coronary microvascular dysfunction was not associated with impaired myocardial capillary density and was present before systemic insulin resistance assessed by a glucose tolerance test. Basal coronary flow and coronary reserve, as assessed using the A2A adenosine receptor agonist regadenoson, were also not altered in HFD-fed mice. Histological analysis did not reveal cardiomyocyte hypertrophy or fibrosis. Increased lipid accumulation in cardiomyocytes was detected as early as after 7 days of HFD and remained at a similar level at 8 weeks on a HFD. Multiparametric cardiac MRI revealed a reduction in systolic heart function, including decreased ejection rate, increased end-systolic volume and decreased myocardial strain in diastole with impaired ejection fraction, but not until 4 weeks of HFD. Short-term feeding with HFD resulted in early endothelial dysfunction in coronary microcirculation that preceded alteration in cardiac function and systemic insulin resistance.

Obesity as a Risk Factor for Severe COVID-19 and Complications: A Review

Emerging data suggest that obesity is a major risk factor for the progression of major complications such as acute respiratory distress syndrome (ARDS), cytokine storm and coagulopathy in COVID-19. Understanding the mechanisms underlying the link between obesity and disease severity as a result of SARS-CoV-2 infection is crucial for the development of new therapeutic interventions and preventive measures in this high-risk group. We propose that multiple features of obesity contribute to the prevalence of severe COVID-19 and complications. First, viral entry can be facilitated by the upregulation of viral entry receptors, like angiotensin-converting enzyme 2 (ACE2), among others. Second, obesity-induced chronic inflammation and disruptions of insulin and leptin signaling can result in impaired viral clearance and a disproportionate or hyper-inflammatory response, which together with elevated ferritin levels can be a direct cause for ARDS and cytokine storm. Third, the negative consequences of obesity on blood coagulation can contribute to the progression of thrombus formation and hemorrhage. In this review we first summarize clinical findings on the relationship between obesity and COVID-19 disease severity and then further discuss potential mechanisms that could explain the risk for major complications in patients suffering from obesity.

Contrasting strategies of hypoxic cardiac performance and metabolism in cichlids and armoured catfish

The heart of tropical fishes is a particularly useful model system in which to investigate mechanisms of hypoxic tolerance. Here we focus on insights gained from two groups of fishes, cichlids and armoured catfishes. Cichlids respond to hypoxia by entering a sustained hypometabolism with decreased heart performance to match whole animal circulatory needs. Heart rate is decreased along with protein turnover to reduce adenosine triphosphate demand. This occurs despite the inherent capacity for high levels of cardiac power development. Although highly hypoxic tolerant at the whole animal level, the heart of cichlids does not have high constitutive activities of glycolytic enzymes compared to other species. Information is conflicting with respect to changes in glycolytic gene expression and enzyme activity following hypoxic exposure with some studies showing increases and others decreases. In contrast to cichlids, species of armoured catfish, that are routinely exposed to water of low oxygen content, do not display hypoxic bradycardia. Under hypoxia there are early changes in glucose trafficking suggestive of activation of glycolysis before lactate accumulation. Thereafter, heart glycogen is mobilized and lactate accumulates in both heart and blood, in some species to very high levels. Heart performance under hypoxia is enhanced by defense of intracellular pH. A functional sarcoplasmic reticulum and binding of hexokinase to the outer mitochondrial membrane may also play a role in cardioprotection. Maintenance of heart performance under hypoxia may relate to a tradeoff between air breathing via a modified stomach and circulatory demands for digestion.

Endothelial Nox5 Expression Modulates Glucose Uptake and Lipid Accumulation in Mice Fed a High-Fat Diet and 3T3-L1 Adipocytes Treated with Glucose and Palmitic Acid

Obesity is a global health issue associated with insulin resistance and altered lipid homeostasis. It has been described that reactive oxygen species (ROS) derived from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) activity are involved in the development of these pathologies. The present study describes the role of endothelial NOX5 expression over adipose tissue by using two experimental systems: NOX5 conditional knock-in mice fed with a high-fat diet and 3T3-L1 adipocytes cultured with conditioned media of NOX5-expressing endothelial cells previously treated with glucose and palmitic acid. Animals expressing NOX5 presented lower body weight gain and less mesenteric and epididymal adipose mass compared to control mice fed with the same diet. NOX5-expressing mice also showed significantly lower glycaemia and improved insulin-induced glucose uptake. In addition, Glut4 and Caveolin 1 (Cav1) expression were significantly increased in the adipose tissue of these animals. Likewise, 3T3-L1 adipocytes treated with conditioned media from NOX5-expressing endothelial cells, incubated with high glucose and palmitic acid, presented a reduction in lipid accumulation and an increase in glucose uptake. Moreover, a significant increase in the expression of Glut4 and Cav1 was also detected in these cells. Taken together, all these data support that, in response to a highly caloric diet, NOX5 endothelial activity may regulate glucose sensitivity and lipid homeostasis in the adipose tissue.

Trans-endothelial trafficking of metabolic substrates and its importance in cardio-metabolic disease

The endothelium acts as a gatekeeper, controlling the movement of biomolecules between the circulation and underlying tissues. Although conditions of metabolic stress are traditionally considered as causes of endothelial dysfunction, a principal driver of cardiovascular disease, accumulating evidence suggests that endothelial cells are also active players in maintaining local metabolic homeostasis, in part, through regulating the supply of metabolic substrates, including lipids and glucose, to energy-demanding organs. Therefore, endothelial dysfunction, in terms of altered trans-endothelial trafficking of these substrates, may in fact be an early contributor towards the establishment of metabolic dysfunction and subsequent cardiovascular disease. Understanding the molecular mechanisms that underpin substrate trafficking through the endothelium represents an important area within the vascular and metabolism fields that may offer an opportunity for identifying novel therapeutic targets. This mini-review summarises the emerging mechanisms regulating the trafficking of lipids and glucose through the endothelial barrier and how this may impact on the development of cardio-metabolic disease.