Endoplasmic reticulum stress and the development of endothelial dysfunction

Potential preservative mechanisms of cardiac rehabilitation pathways on endothelial function in coronary heart disease

Cardiac rehabilitation, a comprehensive exercise-based lifestyle and medical management, is effective in decreasing morbidity and improving life quality in patients with coronary heart disease. Endothelial function, an irreplaceable indicator in coronary heart disease progression, is measured by various methods in traditional cardiac rehabilitation pathways, including medicinal treatment, aerobic training, and smoking cessation. Nevertheless, studies on the effect of some emerging cardiac rehabilitation programs on endothelial function are limited. This article briefly reviewed the endothelium-beneficial effects of different cardiac rehabilitation pathways, including exercise training, lifestyle modification and psychological intervention in patients with coronary heart disease, and related experimental models, and summarized both uncovered and potential cellular and molecular mechanisms of the beneficial roles of various cardiac rehabilitation pathways on endothelial function. In exercise training and some lifestyle interventions, the enhanced bioavailability of nitric oxide, increased circulating endothelial progenitor cells (EPCs), and decreased oxidative stress are major contributors to preventing endothelial dysfunction in coronary heart disease. Moreover, the preservation of endothelial-dependent hyperpolarizing factors and inflammatory suppression play roles. On the one hand, to develop more endothelium-protective rehabilitation methods in coronary heart disease, adequately designed and sized randomized multicenter clinical trials should be advanced using standardized cardiac rehabilitation programs and existing assessment methods. On the other hand, additional studies using suitable experimental models are warranted to elucidate the relationship between some new interventions and endothelial protection in both macro- and microvasculature.

Toll-like receptor 3 involvement in vascular function

Maintaining endothelial cell (EC) and vascular smooth muscle cell (VSMC) integrity is an important component of human health and disease because both EC and VSMC regulate various functions, including vascular tone control, cellular adhesion, homeostasis and thrombosis regulation, proliferation, and vascular inflammation. Diverse stressors affect functions in both ECs and VSMCs and abnormalities of functions in these cells play a crucial role in cardiovascular disease initiation and progression. Toll-like receptors (TLRs) are important detectors of pathogen-associated molecular patterns derived from various microbes and viruses as well as damage-associated molecular patterns derived from damaged cells and perform innate immune responses. Among TLRs, several studies reveal that TLR3 plays a key role in initiation, development and/or protection of diseases, and an emerging body of evidence indicates that TLR3 presents components of the vasculature, including ECs and VSMCs, and plays a functional role. An agonist of TLR3, polyinosinic-polycytidylic acid [poly (I:C)], affects ECs, including cell death, inflammation, chemoattractant, adhesion, permeability, and hemostasis. Poly (I:C) also affects VSMCs including inflammation, proliferation, and modulation of vascular tone. Moreover, alterations of vascular function induced by certain molecules and/or interventions are exerted through TLR3 signaling. Hence, we present the association between TLR3 and vascular function according to the latest studies.

The role of taurine through endoplasmic reticulum in physiology and pathology

Taurine is a sulfur-containing amino acid found in many cell organelles that plays a wide range of biological roles, including bile salt production, osmoregulation, oxidative stress reduction, and neuromodulation. Taurine treatments have also been shown to ameliorate the onset and development of many diseases, including hypertension, fatty liver, neurodegenerative diseases and ischemia-reperfusion injury, by exerting antioxidant, anti-inflammatory, and antiapoptotic effects. The endoplasmic reticulum (ER) is a dynamic organelle involved in a wide range of cellular functions, including lipid metabolism, calcium storage and protein stabilization. Under stress, the disruption of the ER environment leads to the accumulation of misfolded proteins and a characteristic stress response called the unfolded protein response (UPR). The UPR protects cells from stress and helps to restore cellular homeostasis, but its activation promotes cell death under prolonged ER stress. Recent studies have shown that ER stress is closely related to the onset and development of many diseases. This article reviews the beneficial effects and related mechanisms of taurine by regulating the ER in different physiological and pathological states, with the aim of providing a reference for further research and clinical applications.

Recent progress of endoplasmic reticulum stress in the mechanism of atherosclerosis

The research progress of endoplasmic reticulum (ER) stress in atherosclerosis (AS) is of great concern. The ER, a critical cellular organelle, plays a role in important biological processes including protein synthesis, folding, and modification. Various pathological factors may cause ER stress, and sustained or excessive ER stress triggers the unfolded protein response, ultimately resulting in apoptosis and disease. Recently, researchers have discovered the importance of ER stress in the onset and advancement of AS. ER stress contributes to the occurrence of AS through different pathways such as apoptosis, inflammatory response, oxidative stress, and autophagy. Therefore, this review focuses on the mechanisms of ER stress in the development of AS and related therapeutic targets, which will contribute to a deeper understanding of the disease's pathogenesis and provide novel strategies for preventing and treating AS.

A bibliometric analysis of endoplasmic reticulum stress and atherosclerosis

The mechanisms underlying the occurrence and development of atherosclerosis (AS) are diverse, among which endoplasmic reticulum stress (ERS) is an important mechanism that should not be overlooked. However, up to now, there has been no bibliometric study on the relationship between ERS and AS. To understand the research progress in ERS and AS, this paper conducted a statistical analysis of publications in this field using bibliometrics. A total of 1,035 records were retrieved from the Web of Science Core Collection. CiteSpace, VOSviewer, and the R package "bibliometric" were used to analyze the spatiotemporal distribution, countries, authors, institutions, journals, references, and keywords of the literature, and to present the basic information of this field through visualized maps, as well as determine the collaboration relationships among researchers in this field. This field has gradually developed and stabilized over the past 20 years. The current research hotspots in this field mainly include the relationship between ERS and AS-related cells, the mechanisms by which ERS promotes AS, related diseases, and associated cytokines, etc. Vascular calcification, endothelial dysfunction, NLRP3 inflammasome, and heart failure represent the frontier research in this field and are becoming new research hotspots. It is hoped that this study will provide new insights for research and clinical work in the field of ERS and AS.

A perspective on exogenous redox regulation mediated by transfused RBCs subject to the storage lesion

Granted with a potent ability to interact with and tolerate oxidative stressors, RBCs scavenge most reactive oxygen and nitrogen species (RONS) generated in circulation. This essential non-canonical function, however, renders RBCs susceptible to damage when vascular RONS are generated in excess, making vascular redox imbalance a common etiology of anemia, and thus a common indication for transfusion. This accentuates the relevance of impairments in redox metabolism during hypothermic storage, as the exposure to chronic oxidative stressors upon transfusion could be exceedingly deleterious to stored RBCs. Herein, we review the prominent mechanisms of the hypothermic storage lesion that alter the ability of RBCs to scavenge exogenous RONS as well as the associated clinical relevance.

Lipid droplets, autophagy, and ER stress as key (survival) pathways during ischemia-reperfusion of transplanted grafts

Ischemia-reperfusion injury is an event concerning any organ under a procedure of transplantation. The early result of ischemia is hypoxia, which causes malfunction of mitochondria and decrease in cellular ATP. This leads to disruption of cellular metabolism. Reperfusion also results in cell damage due to reoxygenation and increased production of reactive oxygen species, and later by induced inflammation. In damaged and hypoxic cells, the endoplasmic reticulum (ER) stress pathway is activated by increased amount of damaged or misfolded proteins, accumulation of free fatty acids and other lipids due to inability of their oxidation (lipotoxicity). ER stress is an adaptive response and a survival pathway, however, its prolonged activity eventually lead to induction of apoptosis. Sustaining cell functionality in stress conditions is a great challenge for transplant surgeons as it is crucial for maintaining a desired level of graft vitality. Pathways counteracting negative consequences of ischemia-reperfusion are autophagy and lipid droplets (LD) metabolism. Autophagy remove damaged organelles and molecules driving them to lysosomes, digested simpler compounds are energy source for the cell. Mitophagy and ER-phagy results in improvement of cell energetic balance and alleviation of ER stress. This is important in sustaining metabolic homeostasis and thus cell survival. LD metabolism is connected with autophagy as LD are degraded by lipophagy, a source of free fatty acids and glycerol-thus autophagy and LD can readily remove lipotoxic compounds in the cell. In conclusion, monitoring and pharmaceutic regulation of those pathways during transplantation procedure might result in increased/improved vitality of transplanted organ.

Empagliflozin reduces endoplasmic reticulum stress associated TXNIP/NLRP3 activation in tunicamycin-stimulated aortic endothelial cells

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have proven to be of therapeutic significance for cardiovascular diseases beyond the treatment of type 2 diabetes. Recent studies have demonstrated the beneficial effects of SGLT2i on endothelial cell (EC) dysfunction, but the underlying cellular mechanisms remain to be clarified. In this study, we sought to understand the effect of empagliflozin (EMPA; Jardiance®) on cell homeostasis and endoplasmic reticulum (ER) stress signaling. ER stress was induced by tunicamycin (Tm) in human abdominal aortic ECs treated with EMPA over 24 h. Tm-induced ER stress caused increases in the protein expression of thioredoxin interacting protein (TXNIP), NLR-family pyrin domain-containing protein 3 (NLRP3), C/EBP homologous protein (CHOP), and in the ratio of phospho-eIF2α/eIF2α. EMPA (50-100 µM) resulted in a dampened downstream activation of ER stress as seen by the reduced expression of CHOP and TXNIP/NLRP3 in a dose-dependent manner. Nuclear factor erythroid 2-related factor 2 (nrf2) translocation was also attenuated in EMPA-treated ECs. These results suggest that EMPA improves redox signaling under ER stress which in turn attenuates the activation of TXNIP/NLRP3.

Inhibition of endoplasmic reticulum stress restores the balance of renal RAS components and lowers blood pressure in the spontaneously hypertensive rats

BACKGROUND

Endoplasmic reticulum (ER) stress has been shown to play a critical role in the pathogenesis of hypertension. However, the underlying mechanisms for lowering blood pressure (BP) by suppressing ER stress remain unclear. Here, we hypothesized that inhibition of ER stress could restore the balance between RAS components and lower BP in spontaneously hypertensive rats (SHRs).

METHODS

Wistar-Kyoto (WKY) rats and SHRs received vehicle or 4-PBA, an ER stress inhibitor, in the drinking water for 4 weeks. BP was measured by tail-cuff plethysmography, and the expression of RAS components was examined by Western blot.

RESULTS

Compared with vehicle-treated WKY rats, vehicle-treated SHRs exhibited higher blood pressure and increased renal ER stress and oxidative stress, accompanied by impaired diuresis and natriuresis. Moreover, SHRs had higher ACE and AT₁R and lower AT₂R, ACE2, and MasR expressions in the kidney. Interestingly, 4-PBA treatment improved impaired diuresis and natriuresis and lowered blood pressure in SHRs, accompanied by reducing ACE and AT₁R protein expression and increasing AT₂R, ACE2, and MasR expression in the kidneys of SHRs. In addition, these changes were associated with the reduction of ER stress and oxidative stress.

CONCLUSIONS

These results suggest that the imbalance of renal RAS components was associated with increased ER stress in SHRs. Inhibition of ER stress with 4-PBA reversed the imbalance of renal RAS components and restored the impaired diuresis and natriuresis, which, at least in part, explains the blood pressure-lowering effects of 4-PBA in hypertension.

Calciprotein Particles Induce Cellular Compartment-Specific Proteome Alterations in Human Arterial Endothelial Cells

Calciprotein particles (CPPs) are indispensable scavengers of excessive Ca2+ and PO43- ions in blood, being internalised and recycled by liver and spleen macrophages, monocytes, and endothelial cells (ECs). Here, we performed a pathway enrichment analysis of cellular compartment-specific proteomes in primary human coronary artery ECs (HCAEC) and human internal thoracic artery ECs (HITAEC) treated with primary (amorphous) or secondary (crystalline) CPPs (CPP-P and CPPs, respectively). Exposure to CPP-P and CPP-S induced notable upregulation of: (1) cytokine- and chemokine-mediated signaling, Ca2+-dependent events, and apoptosis in cytosolic and nuclear proteomes; (2) H+ and Ca2+ transmembrane transport, generation of reactive oxygen species, mitochondrial outer membrane permeabilisation, and intrinsic apoptosis in the mitochondrial proteome; (3) oxidative, calcium, and endoplasmic reticulum (ER) stress, unfolded protein binding, and apoptosis in the ER proteome. In contrast, transcription, post-transcriptional regulation, translation, cell cycle, and cell-cell adhesion pathways were underrepresented in cytosol and nuclear compartments, whilst biosynthesis of amino acids, mitochondrial translation, fatty acid oxidation, pyruvate dehydrogenase activity, and energy generation were downregulated in the mitochondrial proteome of CPP-treated ECs. Differentially expressed organelle-specific pathways were coherent in HCAEC and HITAEC and between ECs treated with CPP-P or CPP-S. Proteomic analysis of mitochondrial and nuclear lysates from CPP-treated ECs confirmed bioinformatic filtration findings.

Portulaca Oleracea L. (Purslane) Extract Protects Endothelial Function by Reducing Endoplasmic Reticulum Stress and Oxidative Stress through AMPK Activation in Diabetic Obese Mice

Portulaca oleracea L. (purslane) is a food and a traditional drug worldwide. It exhibits anti-inflammatory, anti-oxidative, anti-tumor, and anti-diabetic bioactivities; but its activity on diabetic-associated endothelial dysfunction is unknown. This study aimed to investigate the effect of purslane on endothelial function and the underlying mechanisms. Male C57BL/6 mice had 14-week ad libitum access to a high-fat rodent diet containing 60% kcal% fat to induce obesity and diabetes whereas purslane extract (200 mg/kg/day) was administered during the last 4 weeks via intragastric gavage. Primary rat aortic endothelial cells and isolated mouse aortas were cultured with a risk factor, high glucose or tunicamycin, together with purslane extract. By ESI-QTOF-MS/MS, flavonoids and their glycoside products were identified in the purslane extract. Exposure to high glucose or tunicamycin impaired acetylcholine-induced endothelium-dependent relaxations in aortas and induced endoplasmic reticulum (ER) stress and oxidative stress with the downregulation of 5' AMP-activated protein kinase (AMPK)/ endothelial nitric oxide synthase (eNOS) signaling. Co-incubation with purslane significantly ameliorated these impairments. The effects of purslane were abolished by Compound C (AMPK inhibitor). Four-week purslane treatment ameliorated aortic relaxations, ER stress, and oxidative stress in diabetic obese mice. This study supported that purslane protected endothelial function, and inhibited ER stress and oxidative stress in vasculature through AMPK/eNOS activation, revealing its therapeutic potential against vascular complications in diabetes.

The role and mechanisms of microvascular damage in the ischemic myocardium

Following myocardial ischemic injury, the most effective clinical intervention is timely restoration of blood perfusion to ischemic but viable myocardium to reduce irreversible myocardial necrosis, limit infarct size, and prevent cardiac insufficiency. However, reperfusion itself may exacerbate cell death and myocardial injury, a process commonly referred to as ischemia/reperfusion (I/R) injury, which primarily involves cardiomyocytes and cardiac microvascular endothelial cells (CMECs) and is characterized by myocardial stunning, microvascular damage (MVD), reperfusion arrhythmia, and lethal reperfusion injury. MVD caused by I/R has been a neglected problem compared to myocardial injury. Clinically, the incidence of microvascular angina and/or no-reflow due to ineffective coronary perfusion accounts for 5-50% in patients after acute revascularization. MVD limiting drug diffusion into injured myocardium, is strongly associated with the development of heart failure. CMECs account for > 60% of the cardiac cellular components, and their role in myocardial I/R injury cannot be ignored. There are many studies on microvascular obstruction, but few studies on microvascular leakage, which may be mainly due to the lack of corresponding detection methods. In this review, we summarize the clinical manifestations, related mechanisms of MVD during myocardial I/R, laboratory and clinical examination means, as well as the research progress on potential therapies for MVD in recent years. Better understanding the characteristics and risk factors of MVD in patients after hemodynamic reconstruction is of great significance for managing MVD, preventing heart failure and improving patient prognosis.

Beyond UPR: cell-specific roles of ER stress sensor IRE1α in kidney ischemic injury and transplant rejection

Kidney damage due to ischemia or rejection results in the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER) lumen, a condition known as "ER stress." Inositol-requiring enzyme 1α (IRE1α), the first ER stress sensor found, is a type I transmembrane protein with kinase and endoribonuclease activity. On activation, IRE1α nonconventionally splices an intron from unspliced X-box-binding protein 1 (XBP1) mRNA to produce XBP1s mRNA that encodes the transcription factor, XBP1s, for the expression of genes encoding proteins that mediate the unfolded protein response. The unfolded protein response promotes the functional fidelity of ER and is required for secretory cells to sustain protein folding and secretory capability. Prolonged ER stress can lead to apoptosis, which may result in detrimental repercussions to organ health and has been implicated in the pathogenesis and progression of kidney diseases. The IRE1α-XBP1 signaling acts as a major arm of unfolded protein response and is involved in regulating autophagy, cell differentiation, and cell death. IRE1α also interacts with activator protein-1 and nuclear factor-κB pathways to regulate inflammatory responses. Studies using transgenic mouse models highlight that the roles of IRE1α differ depending on cell type and disease setting. This review covers these cell-specific roles of IRE1α signaling and the potential for therapeutic targeting of this pathway in the context of ischemia and rejection affecting the kidneys.

Soluble and insoluble protein aggregates, endoplasmic reticulum stress, and vascular dysfunction in Alzheimer's disease and cardiovascular diseases

Dementia refers to a particular group of symptoms characterized by difficulties with memory, language, problem-solving, and other thinking skills that affect a person's ability to perform everyday activities. Alzheimer's disease (AD) is the most common form of dementia, affecting about 6.2 million Americans aged 65 years and older. Likewise, cardiovascular diseases (CVDs) are a major cause of disability and premature death, impacting 126.9 million adults in the USA, a number that increases with age. Consequently, CVDs and cardiovascular risk factors are associated with an increased risk of AD and cognitive impairment. They share important age-related cardiometabolic and lifestyle risk factors, that make them among the leading causes of death. Additionally, there are several premises and hypotheses about the mechanisms underlying the association between AD and CVD. Although AD and CVD may be considered deleterious to health, the study of their combination constitutes a clinical challenge, and investigations to understand the mechanistic pathways for the cause-effect and/or shared pathology between these two disease constellations remains an active area of research. AD pathology is propagated by the amyloid β (Aβ) peptides. These peptides give rise to small, toxic, and soluble Aβ oligomers (SPOs) that are nonfibrillar, and it is their levels that show a robust correlation with the extent of cognitive impairment. This review will elucidate the interplay between the effects of accumulating SPOs in AD and CVDs, the resulting ER stress response, and their role in vascular dysfunction. We will also address the potential underlying mechanisms, including the possibility that SPOs are among the causes of vascular injury in CVD associated with cognitive decline. By revealing common mechanistic underpinnings of AD and CVD, we hope that novel experimental therapeutics can be designed to reduce the burden of these devastating diseases. Graphical abstract Alzheimer's disease (AD) pathology leads to the release of Aβ peptides, and their accumulation in the peripheral organs has varying effects on various components of the cardiovascular system including endoplasmic reticulum (ER) stress and vascular damage. Image created with BioRender.com.

Protective effects of paeoniflorin on cardiovascular diseases: A pharmacological and mechanistic overview

Background and ethnopharmacological relevance: The morbidity and mortality of cardiovascular diseases (CVDs) are among the highest of all diseases, necessitating the search for effective drugs and the improvement of prognosis for CVD patients. Paeoniflorin (5beta-[(Benzoyloxy)methyl] tetrahydro-5-hydroxy-2-methyl-2,5-methano-1H-3,4-dioxacyclobuta [cd] pentalen-1alpha (2H)-yl-beta-D-glucopyranoside, C₂₃H₂₈O₁₁) is mostly derived from the plants of the family Paeoniaceae (a single genus family) and is known to possess multiple pharmacological properties in the treatment of CVDs, making it a promising agent for the protection of the cardiovascular system. Aim of the study: This review evaluates the pharmacological effects and potential mechanisms of paeoniflorin in the treatment of CVDs, with the aim of advancing its further development and application. Methods: Various relevant literatures were searched in PubMed, ScienceDirect, Google Scholar and Web of Science. All eligible studies were analyzed and summarized in this review. Results: Paeoniflorin is a natural drug with great potential for development, which can protect the cardiovascular system by regulating glucose and lipid metabolism, exerting anti-inflammatory, anti-oxidative stress, and anti-arteriosclerotic activities, improving cardiac function, and inhibiting cardiac remodeling. However, paeoniflorin was found to have low bioavailability, and its toxicology and safety must be further studied and analyzed, and clinical studies related to it must be carried out. Conclusion: Before paeoniflorin can be used as an effective therapeutic drug for CVDs, further in-depth experimental research, clinical trials, and structural modifications or development of new preparations are required.

Ginsentide TP1 Protects Hypoxia-Induced Dysfunction and ER Stress-Linked Apoptosis

Hypoxia-induced vascular endothelial dysfunction (VED) is a significant contributor to several severe human diseases, including heart disease, stroke, dementia, and cancer. However, current treatment options for VED are limited due to the lack of understanding of the underlying disease mechanisms and therapeutic leads. We recently discovered a heat-stable microprotein in ginseng, called ginsentide TP1, that has been shown to reduce vascular dysfunction in cardiovascular disease models. In this study, we use a combination of functional assays and quantitative pulsed SILAC proteomics to identify new proteins synthesized in hypoxia and to show that ginsentide TP1 provides protection for human endothelial cells against hypoxia and ER stress. Consistent with the reported findings, we also found that hypoxia activates various pathways related to endothelium activation and monocyte adhesion, which in turn, impairs nitric oxide (NO) synthase activity, reduces the bioavailability of NO, and increases the production of reactive oxygen species that contribute to VED. Additionally, hypoxia triggers endoplasmic reticulum stress and initiates apoptotic signaling pathways associated with cardiovascular pathology. Treatment with ginsentide TP1 reduced surface adhesion molecule expression, prevented activation of the endothelium and leukocyte adhesion, restored protein hemostasis, and reduced ER stress to protect against hypoxia-induced cell death. Ginsentide TP1 also restored NO signaling and bioavailability, reduced oxidative stress, and protected endothelial cells from endothelium dysfunction. In conclusion, this study shows that the molecular pathogenesis of VED induced by hypoxia can be mitigated by treatment with ginsentide TP1, which could be one of the key bioactive compounds responsible for the "cure-all" effect of ginseng. This research may lead to the development of new therapies for cardiovascular disorders.

Endoplasmic Reticulum Stress: A Key Regulator of Cardiovascular Disease

The problems associated with economic development and social progress have led to an increase in the occurrence of cardiovascular diseases (CVDs), which affect the health of an increasing number of people and are a leading cause of disease and population mortality worldwide. Endoplasmic reticulum stress (ERS), a hot topic of interest for scholars in recent years, has been confirmed in numerous studies to be an important pathogenetic basis for many metabolic diseases and play an important role in maintaining physiological processes. The endoplasmic reticulum (ER) is a major organelle that is involved in protein folding and modification synthesis, and ERS occurs when several physiological and pathological factors allow excessive amounts of unfolded/misfolded proteins to accumulate. ERS often leads to initiation of the unfolded protein response (UPR) in a bid to re-establish tissue homeostasis; however, UPR has been documented to induce vascular remodeling and cardiomyocyte damage under various pathological conditions, leading to or accelerating the development of CVDs such as hypertension, atherosclerosis, and heart failure. In this review, we summarize the latest knowledge gained concerning ERS in terms of cardiovascular system pathophysiology, and discuss the feasibility of targeting ERS as a novel therapeutic target for the treatment of CVDs. Investigation of ERS has immense potential as a new direction for future research involving lifestyle intervention, the use of existing drugs, and the development of novel drugs that target and inhibit ERS.

Endoplasmic Reticulum Stress and Renin-Angiotensin System Crosstalk in Endothelial Dysfunction

BACKGROUND

Vascular endothelial dysfunction (VED) significantly results in catastrophic cardiovascular diseases with multiple aetiologies. Variations in vasoactive peptides, including angiotensin II and endothelin 1, and metabolic perturbations like hyperglycaemia, altered insulin signalling, and homocysteine levels result in pathogenic signalling cascades, which ultimately lead to VED. Endoplasmic reticulum (ER) stress reduces nitric oxide availability, causes aberrant angiogenesis, and enhances oxidative stress pathways, consequently promoting endothelial dysfunction. Moreover, the renin-angiotensin system (RAS) has widely been acknowledged to impact angiogenesis, endothelial repair and inflammation. Interestingly, experimental studies at the preclinical level indicate a possible pathological link between the two pathways in the development of VED. Furthermore, pharmacological modulation of ER stress ameliorates angiotensin-II mediated VED as well as RAS intervention either through inhibition of the pressor arm or enhancement of the depressor arm of RAS, mitigating ER stress-induced endothelial dysfunction and thus emphasizing a vital crosstalk.

CONCLUSION

Deciphering the pathway overlap between RAS and ER stress may open potential therapeutic avenues to combat endothelial dysfunction and associated diseases. Several studies suggest that alteration in a component of RAS may induce ER stress or induction of ER stress may modulate the RAS components. In this review, we intend to elaborate on the crosstalk of ER stress and RAS in the pathophysiology of VED.

Chitooligosaccharide prevents vascular endothelial cell apoptosis by attenuation of endoplasmic reticulum stress via suppression of oxidative stress through Nrf2-SOD1 up-regulation

CONTEXT

Endoplasmic reticulum (ER) stress contributes to endothelium pathological conditions. Chitooligosaccharides (COS) have health benefits, but their effect on endothelial cells is unknown. We demonstrate for the first time a protective effect of COS against ER-induced endothelial cell damage.

OBJECTIVE

To evaluate the protective effect of COS on ER stress-induced apoptosis in endothelial cells.

MATERIAL AND METHODS

Endothelial (EA.hy926) cells were pre-treated with COS (250 or 500 μg/mL) for 24 h, and then treated with 0.16 μg/mL of Tg for 24 h and compared to the untreated control. Apoptosis and necrosis were detected by Annexin V-FITC/propidium iodide co-staining. Reactive oxygen species (ROS) were measured with the DCFH₂-DA and DHE probes. The protective pathway and ER stress markers were evaluated by reverse transcription-polymerase chain reaction, western blot, and immunofluorescence analyses.

RESULTS

COS attenuated ER stress-induced cell death. The viability of EA.hy926 cells treated with Tg alone was 44.97 ± 1% but the COS pre-treatment increased cells viability to 74.74 ± 3.95% in the 250 μg/mL COS and 75.34 ± 2.4% in the 500 μg/mL COS treatments. Tg induced ER stress and ROS, which were associated with ER stress-mediated death. Interestingly, COS reduced ROS by upregulating nuclear factor-E2-related factor 2 (Nrf2), and the oxidative enzymes, superoxide dismutase1 (SOD1) and catalase. COS also suppressed up-regulation of the ER-related apoptosis protein, CHOP induced by Tg.

CONCLUSIONS

COS protected against ER stress-induced apoptosis in endothelial cells by suppressing ROS and up-regulation Nrf2 and SOD1. These findings support the use of COS to protect endothelial cells.

Angiotensin-(1–9) prevents angiotensin II-induced endothelial apoptosis through CNPY2/PERK pathway

Endothelial apoptosis caused by activation of renin-angiotensin system (RAS) plays a vital part in the occurrence and progress of hypertension. Angiotensin-(1-9) (Ang-(1-9)) is a peptide of the counter-regulatory non-classical RAS with anti-hypertensive effects in vascular endothelial cells (ECs). However, the mechanism of action remains unclear. Considering that the endothelial apoptosis was closely related to endoplasmic reticulum stress (ERS) and mitochondrial function. Herein, we aimed to elucidate the effects of Ang-(1-9) on endothelial apoptosis and the underlying molecular mechanism in angiotensin II (Ang II) induced hypertension. In human umbilical vascular endothelial cells (HUVECs), we observed Ang-(1-9) inhibited Ang II-induced ERS associated endothelial apoptosis. Mechanically, Ang-(1-9) inhibited endothelial apoptosis by blocking CNPY2/PERK mediated CaMKII/Drp1-dependent mitochondrial fission and eIF2α/CHOP signal. Consistent with above effects in HUVECs, in Ang II-induced hypertensive mice, we found administration of exogenous Ang-(1-9) attenuated endothelial apoptosis and arterial blood pressure, which were mediated by CNPY2/PERK signaling pathway. Our study indicated Ang-(1-9) inhibited Ang II-induced hypertension through CNPY2/PERK pathway. These findings may provide new insights for prevention and treatment of hypertension in future.

High Glycemia and Soluble Epoxide Hydrolase in Females: Differential Multiomics in Murine Brain Microvasculature

The effect of a high glycemic diet (HGD) on brain microvasculature is a crucial, yet understudied research topic, especially in females. This study aimed to determine the transcriptomic changes in female brain hippocampal microvasculature induced by a HGD and characterize the response to a soluble epoxide hydrolase inhibitor (sEHI) as a mechanism for increased epoxyeicosatrienoic acids (EETs) levels shown to be protective in prior models of brain injury. We fed mice a HGD or a low glycemic diet (LGD), with/without the sEHI (t-AUCB), for 12 weeks. Using microarray, we assessed differentially expressed protein-coding and noncoding genes, functional pathways, and transcription factors from laser-captured hippocampal microvessels. We demonstrated for the first time in females that the HGD had an opposite gene expression profile compared to the LGD and differentially expressed 506 genes, primarily downregulated, with functions related to cell signaling, cell adhesion, cellular metabolism, and neurodegenerative diseases. The sEHI modified the transcriptome of female mice consuming the LGD more than the HGD by modulating genes involved in metabolic pathways that synthesize neuroprotective EETs and associated with a higher EETs/dihydroxyeicosatrienoic acids (DHETs) ratio. Our findings have implications for sEHIs as promising therapeutic targets for the microvascular dysfunction that accompanies vascular dementia.

NF-κB and its crosstalk with endoplasmic reticulum stress in atherosclerosis

Atherosclerosis (AS) is a common cardiovascular disease with complex pathogenesis, in which multiple pathways and their interweaving regulatory mechanism remain unclear. The primary transcription factor NF-κB plays a critical role in AS via modulating the expression of a series of inflammatory mediators under various stimuli such as cytokines, microbial antigens, and intracellular stresses. Endoplasmic reticulum (ER) stress, caused by the disrupted synthesis and secretion of protein, links inflammation, metabolic signals, and other cellular processes via the unfolded protein response (UPR). Both NF-κB and ER stress share the intersection regarding their molecular regulation and function and are regarded as critical individual contributors to AS. In this review, we summarize the multiple interactions between NF-κB and ER stress activation, including the UPR, NLRP3 inflammasome, and reactive oxygen species (ROS) generation, which have been ignored in the pathogenesis of AS. Given the multiple links between NF-κB and ER stress, we speculate that the integrated network contributes to the understanding of molecular mechanisms of AS. This review aims to provide an insight into these interactions and their underlying roles in the progression of AS, highlighting potential pharmacological targets against the atherosclerotic inflammatory process.

Induction of the ER stress response in NRVMs is linked to cardiotoxicity caused by celastrol

Celastrol is a quinone methide triterpenoid extracted from the root bark of Tripterygium wilfordii Hook F, and it exhibits extensive biological activities such as anti-cancer effects. However, narrow therapeutic window together with undesired side effects limit its clinical application. In this study, we explore celastrol's cardiotoxicity using the methods of histology and cell biology. The results show that celastrol administration dose-dependently induces cardiac dysfunction in mice as manifested by left ventricular dilation, myocardial interstitial fibrosis, and cardiomyocyte hypertrophy. Exposure to celastrol greatly decreases neonatal rat ventricular myocyte (NRVM) viability and promotes its apoptosis. More importantly, we demonstrate that celastrol exerts its pro-apoptotic effects through endoplasmic reticulum (ER) stress and unfolded protein response. Furthermore, siRNA targeting C/EBP homologous protein, a pivotal component of ER stress-mediated apoptosis, effectively prevents the pro-apoptotic effect of celastrol. Taken together, our results demonstrate the potential cardiotoxicity of celastrol and a direct involvement of ER stress in the celastrol-induced apoptosis of NRVMs. Thus, we recommend careful evaluation of celastrol's cardiovascular effects when using it in the clinic.

Inhibition of Endoplasmic Reticulum Stress Improves Acetylcholine-Mediated Relaxation in the Aorta of Type-2 Diabetic Rats

Endoplasmic reticulum (ER) stress contributes to insulin resistance and macro- and microvascular complications associated with diabetes. This study aimed to evaluate the effect of ER stress inhibition on endothelial function in the aorta of type-2 diabetic rats. Type-2 diabetes was developed in male Sprague-Dawley rats using a high-fat diet and low-dose streptozotocin. Rat aortic tissues were harvested to study endothelial-dependent relaxation. The mechanisms for acetylcholine-mediated relaxation were investigated using pharmacological blockers, Western blotting, oxidative stress, and inflammatory markers. Acetylcholine-mediated relaxation was diminished in the aorta of diabetic rats compared to control rats; supplementation with TUDCA improved relaxation. In the aortas of control and diabetic rats receiving TUDCA, the relaxation was mediated via eNOS/PI3K/Akt, NAD(P)H, and the KATP channel. In diabetic rats, acetylcholine-mediated relaxation involved eNOS/PI3K/Akt and NAD(P)H, but not the KATP channel. The expression of ER stress markers was upregulated in the aorta of diabetic rats and reduced with TUDCA supplementation. The expression of eNOS and Akt were lower in diabetic rats but were upregulated after supplementation with TUDCA. The levels of MDA, IL-6, and SOD activity were higher in the aorta of the diabetic rats compared to control rats. This study demonstrated that endothelial function was impaired in diabetes, however, supplementation with TUDCA improved the function via eNOS/Akt/PI3K, NAD(P)H, and the KATP channel. The improvement of endothelial function was associated with increased expressions of eNOS and Akt. Thus, ER stress plays a crucial role in the impairment of endothelial-dependent relaxation. Mitigating ER stress could be a potential strategy for improving endothelial dysfunction in type-2 diabetes.

Empagliflozin mitigates endothelial inflammation and attenuates endoplasmic reticulum stress signaling caused by sustained glycocalyx disruption

The disruption of the endothelial cell (EC) glycocalyx (GCX) leads to cellular dysfunction promoting inflammation and cardiovascular disease progression. Recent studies have shown that empagliflozin (EMPA; Jardiance), a sodium-glucose cotransporter 2 inhibitor used in the treatment of type 2 diabetes, can improve EC functions impacted by GCX disruption although the exact cellular mechanisms remain to be elucidated. In this study, the effect of EMPA on EC inflammatory response induced by sustained GCX disruption was investigated. Human aortic ECs were cultured under shear (10 dyne/cm²) for 24 h with or without sustained degradation of heparan sulfate (HS). HS degradation increased inflammatory cell adhesion to ECs. EMPA (50 μM) normalized adhesion levels under sustained HS degradation. Protein expressions of eNOS, phospho-eNOS Ser1177 and ICAM-1 remained unchanged between conditions. Transcriptome analysis revealed the induction of the unfolded protein response (UPR) through the increased expression of ATF3, ATF4, DDIT3 (CHOP), EIF2AK3 (PERK), HSPA5 (Grp78), PPP1R15A (GADD34) and TRIB3 which was in part downregulated by EMPA. mRNA and protein expression of thioredoxin interacting protein (TXNIP) was also downregulated by EMPA. Mitigation of oxidative stress with N-Acetyl-L-cysteine resulted in similar reduction in inflammatory cell adhesion compared to EMPA which could indicate a potential mechanism by which EMPA normalized the inflammatory response. In conclusion, this study demonstrated the potential of EMPA to resolve the inflammatory response of ECs caused by sustained GCX disruption while altering UPR signaling under endoplasmic reticulum stress.

The Effect of Tauroursodeoxycholic Acid (TUDCA) Treatment on Pregnancy Outcomes and Vascular Function in a Rat Model of Advanced Maternal Age

Advanced maternal age (≥35 years) increases the risk of vascular complications in pregnancy that can result in fetal growth restriction and preeclampsia. Endoplasmic reticulum (ER) stress has been linked to adverse pregnancy outcomes in these complicated pregnancies. However, the role of ER stress in advanced maternal age is not known. We hypothesize that increased ER stress contributes to altered vascular function and poor pregnancy outcomes, and that treatment with the ER-stress inhibitor TUDCA will improve pregnancy outcomes. First, young and aged non-pregnant/pregnant rats were used to assess ER stress markers in mesenteric arteries; mesenteric artery phospho-eIF2α and CHOP expression were increased in aged dams compared to young dams. In a second study, young and aged control and TUDCA-treated dams were studied on gestational day (GD) 20 (term = 22 days). TUDCA treatment was provided via the drinking water throughout pregnancy (GD0-GD20; calculated dose of 150 mg/kg/day TUDCA). ER stress markers were quantified in mesenteric arteries, blood pressure was measured, pregnancy outcomes were recorded, mesenteric and main uterine arteries were isolated and vascular function was assessed by wire myography. Aged dams had increased phospho-eIF2α and CHOP expression, reduced fetal weight, reduced litter size, and impaired uterine artery relaxation. In the aged dams, TUDCA treatment reduced phospho-eIF2α and CHOP expression, reduced blood pressure, improved fetal body weight, and tended to improve uterine artery function compared to control-treated aged dams. In conclusion, our data illustrate the role of ER stress, as well as TUDCA as a potential therapeutic that may benefit pregnancy outcomes in advanced maternal age.

Protection by metformin against severe Covid-19: an in-depth mechanistic analysis

Since the outbreak of Covid-19, several observational studies on diabetes and Covid-19 have reported a favourable association between metformin and Covid-19-related outcomes in patients with type 2 diabetes mellitus (T2DM). This is not surprising since metformin affects many of the pathophysiological mechanisms implicated in SARS-CoV-2 immune response, systemic spread and sequelae. A comparison of the multifactorial pathophysiological mechanisms of Covid-19 progression with metformin's well-known pleiotropic properties suggests that the treatment of patients with this drug might be particularly beneficial. Indeed, metformin could alleviate the cytokine storm, diminish virus entry into cells, protect against microvascular damage as well as prevent secondary fibrosis. Although our in-depth analysis covers many potential metformin mechanisms of action, we want to highlight more particularly its unique microcirculatory protective effects since worsening of Covid-19 disease clearly appears as largely due to severe defects in the structure and functioning of microvessels. Overall, these observations confirm that metformin is a unique, pleiotropic drug that targets many of Covid-19′s pathophysiology processes in a diabetes-independent manner.

The Regulation of Endoplasmic Reticulum Stress in Cancer: Special Focuses on Luteolin Patents

Cancer is a major health problem across the globe, and is expeditiously growing at a faster rate worldwide. The endoplasmic reticulum (ER) is a membranous cell organelle having inextricable links in cellular homeostasis. Altering ER homeostasis initiates various signaling events known as the unfolded protein response (UPR). The basic purpose of the UPR is to reinstate the homeostasis; however, a continuous UPR can stimulate pathways of cell death, such as apoptosis. As a result, there is great perturbation to target particular signaling pathways of ER stress. Flavonoids have gained significant interest as a potential anticancer agent because of their considerable role in causing cytotoxicity of the cancerous cells. Luteolin, a flavonoid isolated from natural products, is a promising phytochemical used in the treatment of cancer. The current study is designed to review the different endoplasmic reticulum stress pathways involved in the cancer, mechanistic insights of luteolin as an anticancer agent in modulating ER stress, and the available luteolin patent formulations were also highlighted. The patents were selected on the basis of pre-clinical and/or clinical trials, and established antitumor effects using patent databases of FPO IP and Espacenet. The patented formulation of luteolin studied so far has shown promising anticancer potential against different cancer cell lines. However, further research is still required to determine the molecular targets of such bioactive molecules so that they can be used as anticancer drugs.

p62/sequestosome 1 attenuates methylmercury-induced endoplasmic reticulum stress in mouse embryonic fibroblasts

Methylmercury (MeHg) is a hazardous environmental pollutant that causes serious toxicity in humans and animals, as well as proteotoxic stress. In our previous study, we found that MeHg induces the expression of p62/sequestosome 1 (p62) that selectively targets ubiquitinated proteins for degradation via autophagy, and that p62 might protect cells against MeHg toxicity. To further investigate the role of p62 in MeHg-induced stress responses, we evaluated the role of p62 in MeHg-induced endoplasmic reticulum (ER) stress in p62 knockout (p62KO) mouse embryonic fibroblasts (MEFs). Treatment of wild-type (WT) MEFs were treated with MeHg (1 μM) increased mRNA levels of Chop encoding C/EBP homologous protein, Trib3 encoding Tribbles homolog 3, and Dnajb9 encoding DnaJ heat-shock protein family (Hsp40) member B9 increased, suggesting that ER stress is elicited by MeHg stress. Additionally, p62KO MEFs treated with MeHg showed a higher mRNA expression of Chop and Trib3 relative to that in WT MEFs. Furthermore, knock-in of GFP-p62 to p62KO cells diminished the Chop and Trib3 induction responses to MeHg stress and resulted in a higher cell viability than that of p62KO MEFs. These results suggest that the protective role of p62 against MeHg toxicity is partly mediated by suppressing the ER stress response.

The cardioprotective effects of hydrogen sulfide by targeting endoplasmic reticulum stress and the Nrf2 signaling pathway: A review

Cardiac diseases are emerging due to lifestyle, urbanization, and the accelerated aging process. Oxidative stress has been associated with cardiac injury progression through interference with antioxidant strategies and endoplasmic reticulum (ER) function. Hydrogen sulfide (H₂ S) is generated endogenously from l-cysteine in various tissues including heart tissue. Pharmacological evaluation of H₂ S has suggested a potential role for H₂ S against diabetic cardiomyopathy, ischemia/reperfusion injury, myocardial infarction, and cardiotoxicity. Nuclear factor E2-related factor 2 (Nrf2) activity is crucial for cell survival in response to oxidative stress. H₂ S up-regulates Nrf2 expression and its related signaling pathway in myocytes. H₂ S also suppresses the expression and activity of ER stress-related proteins. H₂ S has been reported to improve various cardiac conditions through antioxidant and anti-ER stress-related activities.

Honokiol regulates endoplasmic reticulum stress by promoting the activation of the sirtuin 1-mediated protein kinase B pathway and ameliorates high glucose/high fat-induced dysfunction in human umbilical vein endothelial cells

Honokiol plays an important role in anti-oxidation, but its role in diabetic vascular complications is unclear. In this study, the effects of honokiol in high glucose/high fat (HG/HF)-induced human umbilical vein endothelial cells (HUVECs) were explored. After pre-treatment with honokiol, the cells were transferred to an HG/HF medium, and cell viability and apoptosis were respectively measured by methyl tetrazolium and flow cytometry. Moreover, the contents of reactive oxygen species (ROS), malondialdehyde (MDA), and superoxide dismutase (SOD) were measured. The expressions of C/EBP homologous protein (CHOP), glucose-regulated protein 78 (GRP78), phosphorylated-protein kinase RNA-like endoplasmic reticulum kinase (p-PERK), phosphorylated-inositol requiring enzyme-1α (p-IRE1α), cleaved caspase-3 and SIRT1 were determined by Western blot or quantitative reverse transcription PCR, respectively. Finally, the viability, apoptosis, and the contents of ROS, MDA, and SOD, as well as the expressions of CHOP, GRP78, p-PERK, p-IRE1α, cleaved caspase-3, Akt, p-Akt, and SIRT1 in the cells transfected with small interfering RNA SIRT1 (siSIRT1) were detected by the previously mentioned methods. Honokiol reversed the effect of HG/HF on promoting cell apoptosis, ROS and MDA contents, and the expressions of CHOP, GRP78, p-PERK, p-IRE1α and cleaved caspase-3, and also reversed the inhibitory effect of HG/HF on cell viability, SOD content and SIRT1 expression. However, siSIRT1 reversed the above effects caused by honokiol. Honokiol activated SIRT1 promoter. SIRT1 interacted with Akt, consequently promoting the activity of Akt. Therefore, honokiol activates the Akt pathway by regulating SIRT1 expression to regulate endoplasmic reticulum stress, promotes cell viability and inhibits the apoptosis of HG/HF-induced HUVECs.

Protein tyrosine phosphatase 1B inhibition improves endoplasmic reticulum stress‑impaired endothelial cell angiogenic response: A critical role for cell survival

Endoplasmic reticulum (ER) stress contributes to endothelial dysfunction, which is the initial step in atherogenesis. Blockade of protein tyrosine phosphatase (PTP)1B, a negative regulator of insulin receptors that is critically located on the surface of ER membrane, has been found to improve endothelial dysfunction. However, the role of ER stress and its related apoptotic sub‑pathways in PTP1B‑mediated endothelial dysfunction, particularly its angiogenic capacity, have not yet been fully elucidated. Thus, the present study aimed to investigate the impact of PTP1B suppression on ER stress‑mediated impaired angiogenesis and examined the contribution of apoptotic signals in this process. Endothelial cells were exposed to pharmacological ER stressors, including thapsigargin (TG) or 1,4‑dithiothreitol (DTT), in the presence or absence of a PTP1B inhibitor or small interfering (si)RNA duplexes. Then, ER stress, angiogenic capacity, cell cycle, apoptosis and the activation of key apoptotic signals were assessed. It was identified that the inhibition of PTP1B prevented ER stress caused by DTT and TG. Moreover, ER stress induction impaired the activation of endothelial nitric oxide synthase (eNOS) and the angiogenic capacity of endothelial cells, while PTP1B inhibition exerted a protective effect. The results demonstrated that blockade or knockdown of PTP1B prevented ER stress‑induced apoptosis and cell cycle arrest. This effect was associated with reduced expression levels of caspase‑12 and poly (ADP‑Ribose) polymerase 1. PTP1B blockade also suppressed autophagy activated by TG. The current data support the critical role of PTP1B in ER stress‑mediated endothelial dysfunction, characterized by reduced angiogenic capacity, with an underlying mechanism involving reduced eNOS activation and cell survival. These findings provide evidence of the therapeutic potential of targeting PTP1B in cardiovascular ischemic conditions.

The Oncogene Transcription Factor EB Regulates Vascular Functions

Transcription factor EB (TFEB) represents an emerging player in vascular biology. It belongs to the bHLH-leucine zipper transcription factor microphthalmia family, which includes microphthalmia-associated transcription factor, transcription factor E3 and transcription factor EC, and is known to be deregulated in cancer. The canonical transcriptional pathway orchestrated by TFEB adapts cells to stress in all kinds of tissues by supporting lysosomal and autophagosome biogenesis. However, emerging findings highlight that TFEB activates other genetic programs involved in cell proliferation, metabolism, inflammation and immunity. Here, we first summarize the general principles and mechanisms by which TFEB activates its transcriptional program. Then, we analyze the current knowledge of TFEB in the vascular system, placing particular emphasis on its regulatory role in angiogenesis and on the involvement of the vascular unit in inflammation and atherosclerosis.

Toward Raman Subcellular Imaging of Endothelial Dysfunction

Multiple diseases are at some point associated with altered endothelial function, and endothelial dysfunction (ED) contributes to their pathophysiology. Biochemical changes of the dysfunctional endothelium are linked to various cellular organelles, including the mitochondria, endoplasmic reticulum, and nucleus, so organelle-specific insight is needed for better understanding of endothelial pathobiology. Raman imaging, which combines chemical specificity with microscopic resolution, has proved to be useful in detecting biochemical changes in ED at the cellular level. However, the detection of spectroscopic markers associated with specific cell organelles, while desirable, cannot easily be achieved by Raman imaging without labeling. This critical review summarizes the current advances in Raman-based analysis of ED, with a focus on a new approach involving molecular Raman reporters that could facilitate the study of biochemical changes in cellular organelles. Finally, imaging techniques based on both conventional spontaneous Raman scattering and the emerging technique of stimulated Raman scattering are discussed.

Novel Insight into the Role of Endoplasmic Reticulum Stress in the Pathogenesis of Myocardial Ischemia-Reperfusion Injury

Impaired function of the endoplasmic reticulum (ER) is followed by evolutionarily conserved cell stress responses, which are employed by cells, including cardiomyocytes, to maintain and/or restore ER homeostasis. ER stress activates the unfolded protein response (UPR) to degrade and remove abnormal proteins from the ER lumen. Although the UPR is an intracellular defense mechanism to sustain cardiomyocyte viability and heart function, excessive activation initiates ER-dependent cardiomyocyte apoptosis. Myocardial ischemia/reperfusion (I/R) injury is a pathological process occurring during or after revascularization of ischemic myocardium. Several molecular mechanisms contribute to the pathogenesis of cardiac I/R injury. Due to the dual protective/degradative effects of ER stress on cardiomyocyte viability and function, it is of interest to understand the basic concepts, regulatory signals, and molecular processes involved in ER stress following myocardial I/R injury. In this review, therefore, we present recent findings related to the novel components of ER stress activation. The complex effects of ER stress and whether they mitigate or exacerbate myocardial I/R injury are summarized to serve as the basis for research into potential therapies for cardioprotection through control of ER homeostasis.

Oxidative Stress and Vascular Damage in the Context of Obesity: The Hidden Guest

The vascular system plays a central role in the transport of cells, oxygen and nutrients between different regions of the body, depending on the needs, as well as of metabolic waste products for their elimination. While the structure of different components of the vascular system varies, these structures, especially those of main arteries and arterioles, can be affected by the presence of different cardiovascular risk factors, including obesity. This vascular remodeling is mainly characterized by a thickening of the media layer as a consequence of changes in smooth muscle cells or excessive fibrosis accumulation. These vascular changes associated with obesity can trigger functional alterations, with endothelial dysfunction and vascular stiffness being especially common features of obese vessels. These changes can also lead to impaired tissue perfusion that may affect multiple tissues and organs. In this review, we focus on the role played by perivascular adipose tissue, the activation of the renin-angiotensin-aldosterone system and endoplasmic reticulum stress in the vascular dysfunction associated with obesity. In addition, the participation of oxidative stress in this vascular damage, which can be produced in the perivascular adipose tissue as well as in other components of the vascular wall, is updated.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

Cardiovascular diseases (CVDs), such as ischaemic heart disease, cardiomyopathy, atherosclerosis, hypertension, stroke and heart failure, are among the leading causes of morbidity and mortality worldwide. Although specific CVDs and the associated cardiometabolic abnormalities have distinct pathophysiological and clinical manifestations, they often share common traits, including disruption of proteostasis resulting in accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER proteostasis is governed by the unfolded protein response (UPR), a signalling pathway that adjusts the protein-folding capacity of the cell to sustain the cell's secretory function. When the adaptive UPR fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis. ER stress functions as a double-edged sword, with long-term ER stress resulting in cellular defects causing disturbed cardiovascular function. In this Review, we discuss the distinct roles of the UPR and ER stress response as both causes and consequences of CVD. We also summarize the latest advances in our understanding of the importance of the UPR and ER stress in the pathogenesis of CVD and discuss potential therapeutic strategies aimed at restoring ER proteostasis in CVDs.

The Presence of Cholesteryl Ester Transfer Protein (CETP) in Endothelial Cells Generates Vascular Oxidative Stress and Endothelial Dysfunction

Endothelial dysfunction precedes atherosclerosis and is an independent predictor of cardiovascular events. Cholesterol levels and oxidative stress are key contributors to endothelial damage, whereas high levels of plasma high-density lipoproteins (HDL) could prevent it. Cholesteryl ester transfer protein (CETP) is one of the most potent endogenous negative regulators of HDL-cholesterol. However, whether and to what degree CETP expression impacts endothelial function, and the molecular mechanisms underlying the vascular effects of CETP on endothelial cells, have not been addressed. Acetylcholine-induced endothelium-dependent relaxation of aortic rings was impaired in human CETP-expressing transgenic mice, compared to their non-transgenic littermates. However, endothelial nitric oxide synthase (eNOS) activation was enhanced. The generation of superoxide and hydrogen peroxide was increased in aortas from CETP transgenic mice, while silencing CETP in cultured human aortic endothelial cells effectively decreased oxidative stress promoted by all major sources of ROS: mitochondria and NOX2. The endoplasmic reticulum stress markers, known as GADD153, PERK, and ARF6, and unfolded protein response effectors, were also diminished. Silencing CETP reduced endothelial tumor necrosis factor (TNF) α levels, intercellular cell adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) expression, diminishing monocyte adhesion. These results support the notion that CETP expression negatively impacts endothelial cell function, revealing a new mechanism that might contribute to atherosclerosis.

Endoplasmic Reticulum (ER) Stress-Generated Extracellular Vesicles (Microparticles) Self-Perpetuate ER Stress and Mediate Endothelial Cell Dysfunction Independently of Cell Survival

Circulating extracellular vesicles (EVs) are recognized as biomarkers and effectors of endothelial dysfunction, the initiating step of cardiovascular abnormalities. Among these EVs, microparticles (MPs) are vesicles directly released from the cytoplasmic membrane of activated cells. MPs were shown to induce endothelial dysfunction through the activation of endoplasmic reticulum (ER) stress. However, it is not known whether ER stress can lead to MPs release from endothelial cells and what biological messages are carried by these MPs. Therefore, we aimed to assess the impact of ER stress on MPs shedding from endothelial cells, and to investigate their effects on endothelial cell function. EA.hy926 endothelial cells or human umbilical vein endothelial cells (HUVECs) were treated for 24 h with ER stress inducers, thapsigargin or dithiothreitol (DTT), in the presence or absence of 4-Phenylbutyric acid (PBA), a chemical chaperone to inhibit ER stress. Then, MPs were isolated and used to treat cells (10–20 μg/mL) for 24–48 h before assessing ER stress response, angiogenic capacity, nitric oxide (NO) release, autophagy and apoptosis. ER stress (thapsigargin or DDT)-generated MPs did not differ quantitatively from controls; however, they carried deleterious messages for endothelial function. Exposure of endothelial cells to ER stress-generated MPs increased mRNA and protein expression of key ER stress markers, indicating a vicious circle activation of ER stress. ER stress (thapsigargin)-generated MPs impaired the angiogenic capacity of HUVECs and reduced NO release, indicating an impaired endothelial function. While ER stress (thapsigargin)-generated MPs altered the release of inflammatory cytokines, they did not, however, affect autophagy or apoptosis in HUVECs. This work enhances the general understanding of the deleterious effects carried out by MPs in medical conditions where ER stress is sustainably activated such as diabetes and metabolic syndrome.

Effect of endoplasmic reticulum stress on endothelial ischemia-reperfusion injury in humans

Endoplasmic reticulum stress contributes to ischemia-reperfusion (I/R) injury in rodent and cell models. However, the contribution of endoplasmic reticulum stress in the pathogenesis of endothelial I/R injury in humans is unknown. We tested the hypothesis that compared with placebo, inhibition of endoplasmic reticulum stress via ingestion of tauroursodeoxycholic acid would prevent the attenuation of endothelium-dependent vasodilation following I/R injury. Twelve young adults (6 women) were studied following ingestion of a placebo or 1,500 mg tauroursodeoxycholic acid (TUDCA). Endothelium-dependent vasodilation was assessed via brachial artery flow-mediated dilation (duplex ultrasonography) before and after I/R injury, which was induced by 20 min of arm ischemia followed by 20 min of reperfusion. Endothelium-independent vasodilation (glyceryl trinitrate-mediated vasodilation) was also assessed after I/R injury. Compared with placebo, TUDCA ingestion increased circulating plasma concentrations by 145 ± 90 ng/ml and increased concentrations of the taurine unconjugated form, ursodeoxycholic acid, by 560 ± 156 ng/ml (both P < 0.01). Ischemia-reperfusion injury attenuated endothelium-dependent vasodilation, an effect that did not differ between placebo (pre-I/R, 5.0 ± 2.1% vs. post-I/R, 3.5 ± 2.2%) and TUDCA (pre-I/R, 5.6 ± 2.1% vs. post-I/R, 3.9 ± 2.1%; P = 0.8) conditions. Similarly, endothelium-independent vasodilation did not differ between conditions (placebo, 19.6 ± 4.8% vs. TUDCA, 19.7 ± 6.1%; P = 0.9). Taken together, endoplasmic reticulum stress does not appear to contribute to endothelial I/R injury in healthy young adults.

Interplay between Endoplasmic Reticulum Stress and Large Extracellular Vesicles (Microparticles) in Endothelial Cell Dysfunction

Upon increased demand for protein synthesis, accumulation of misfolded and/or unfolded proteins within the endoplasmic reticulum (ER), a pro-survival response is activated termed unfolded protein response (UPR), aiming at restoring the proper function of the ER. Prolonged activation of the UPR leads, however, to ER stress, a cellular state that contributes to the pathogenesis of various chronic diseases including obesity and diabetes. ER stress response by itself can result in endothelial dysfunction, a hallmark of cardiovascular disease, through various cellular mechanisms including apoptosis, insulin resistance, inflammation and oxidative stress. Extracellular vesicles (EVs), particularly large EVs (lEVs) commonly referred to as microparticles (MPs), are membrane vesicles. They are considered as a fingerprint of their originating cells, carrying a variety of molecular components of their parent cells. lEVs are emerging as major contributors to endothelial cell dysfunction in various metabolic disease conditions. However, the mechanisms underpinning the role of lEVs in endothelial dysfunction are not fully elucidated. Recently, ER stress emerged as a bridging molecular link between lEVs and endothelial cell dysfunction. Therefore, in the current review, we summarized the roles of lEVs and ER stress in endothelial dysfunction and discussed the molecular crosstalk and relationship between ER stress and lEVs in endothelial dysfunction.

Procyanidin B2 mitigates endothelial endoplasmic reticulum stress through a PPARδ-Dependent mechanism

Hyperglycemia-induced endothelial endoplasmic reticulum (ER) stress is implicated in the pathophysiology of diabetes and its vascular complications. Procyanidins are enriched in many plant foods and have been demonstrated to exert several beneficial effects on diabetes, cardiovascular and other metabolic diseases. In the present study, we investigated the effect of procyanidin B2 (PCB2), the most widely distributed natural procyanidin, on ER stress evoked by high glucose in endothelial cells (ECs) and the underlying mechanisms. We showed that PCB2 mitigated the high glucose-activated ER stress pathways (PERK, IRE1α and ATF6) in human vascular ECs. In addition, we found that PCB2 attenuated endothelial ER stress via the activation of peroxisome proliferator-activated receptor δ (PPARδ). We demonstrated that PCB2 directly bound to and activated PPARδ. Conversely, GSK0660, a selective PPARδ antagonist, attenuated the suppressive effect of PCB2 on the ER stress signal pathway. Functionally, PCB2 ameliorated the high glucose-impaired endothelium-dependent relaxation in mouse aortas. The protective effect of PCB2 on vasodilation was abolished in the aortas pretreated with GSK0660 or those from the EC-specific PPARδ knockout mice. Moreover, the protective effects of PCB2 on ER stress and endothelial dysfunction required the inter-dependent actions of PPARδ and AMPK. Collectively, we demonstrated that PCB2 mitigated ER stress and ameliorated vasodilation via a PPARδ-mediated mechanism beyond its classic action as a scavenger of free radicals. These findings further highlighted the novel roles of procyanidins in intervening the ER stress and metabolic disorders related to endothelial dysfunction.

NLRP3 inflammasome in endothelial dysfunction

Inflammasomes are a class of cytosolic protein complexes. They act as cytosolic innate immune signal receptors to sense pathogens and initiate inflammatory responses under physiological and pathological conditions. The NLR-family pyrin domain-containing protein 3 (NLRP3) inflammasome is the most characteristic multimeric protein complex. Its activation triggers the cleavage of pro-interleukin (IL)-1β and pro-IL-18, which are mediated by caspase-1, and secretes mature forms of these mediators from cells to promote the further inflammatory process and oxidative stress. Simultaneously, cells undergo pro-inflammatory programmed cell death, termed pyroptosis. The danger signals for activating NLRP3 inflammasome are very extensive, especially reactive oxygen species (ROS), which act as an intermediate trigger to activate NLRP3 inflammasome, exacerbating subsequent inflammatory cascades and cell damage. Vascular endothelium at the site of inflammation is actively involved in the regulation of inflammation progression with important implications for cardiovascular homeostasis as a dynamically adaptable interface. Endothelial dysfunction is a hallmark and predictor for cardiovascular ailments or adverse cardiovascular events, such as coronary artery disease, diabetes mellitus, hypertension, and hypercholesterolemia. The loss of proper endothelial function may lead to tissue swelling, chronic inflammation, and the formation of thrombi. As such, elimination of endothelial cell inflammation or activation is of clinical relevance. In this review, we provided a comprehensive perspective on the pivotal role of NLRP3 inflammasome activation in aggravating oxidative stress and endothelial dysfunction and the possible underlying mechanisms. Furthermore, we highlighted the contribution of noncoding RNAs to NLRP3 inflammasome activation-associated endothelial dysfunction, and outlined potential clinical drugs targeting NLRP3 inflammasome involved in endothelial dysfunction. Collectively, this summary provides recent developments and perspectives on how NLRP3 inflammasome interferes with endothelial dysfunction and the potential research value of NLRP3 inflammasome as a potential mediator of endothelial dysfunction.

Role of Endoplasmic Reticulum Stress in Atherosclerosis and Its Potential as a Therapeutic Target

Endoplasmic reticulum (ER) stress is closely associated with atherosclerosis and related cardiovascular diseases (CVDs). It occurs due to various pathological factors that interfere with ER homeostasis, resulting in the accumulation of unfolded or misfolded proteins in the ER lumen, thereby causing ER dysfunction. Here, we discuss the role of ER stress in different types of cells in atherosclerotic lesions. This discussion includes the activation of apoptotic and inflammatory pathways induced by prolonged ER stress, especially in advanced lesional macrophages and endothelial cells (ECs), as well as common atherosclerosis-related ER stressors in different lesional cells, which all contribute to the clinical progression of atherosclerosis. In view of the important role of ER stress and the unfolded protein response (UPR) signaling pathways in atherosclerosis and CVDs, targeting these processes to reduce ER stress may be a novel therapeutic strategy.

The microscopic anatomy of endothelial cells in human atherosclerosis: Focus on ER and mitochondria

Once regarded merely as a bland lipid storage disease consequence of aging, atherosclerosis is currently considered a slow and continuous inflammatory process (partially controllable by treatment) with complex etiology involving a multitude of genetic and environmental risk factors which ultimately result in the formation of the plaque. The vascular endothelium, a monolayer of endothelial cells (ECs), is an important regulatory "organ" critical for cardiovascular homeostasis in health which also contributes significantly to the pathomechanisms of several disease states, including atherosclerosis. Over the years, there has been evidence highlighting the central role of endoplasmic reticulum (ER) in the maintenance of endothelial function and perturbations in ER biology have been proposed to adversely affect a diverse range of endothelial functions. Of particular interest is the evidence that under certain pathophysiological circumstances, abnormal ER ultrastructure correlates with altered ER function and signaling and can contribute to cell injury and apoptosis. Therefore, the ultrastructural traits of ER membranes can have important implications not only for their functional bearings but also for the etiology and pathophysiology of diverse human disorders. With regard to atherosclerosis, the focus of ER research has been centered on the molecular signals originated from the ER to manage conditions of stress, leaving the fine structure of this organelle an almost unexplored (but promising) area of studies. There is, also, increasing evidence that mitochondrial dysfunction plays a critical role in promoting cell apoptosis, inflammation, and oxidative stress, thereby contributing to atheroma growth. It is within this context that the present study has been undertaken to investigate the microscopic architecture of ECs in human atherosclerosis and to determine whether the potential structural abnormalities of ER and mitochondria may play a central pathogenic role in atherogenesis or may merely reflect the condition of a tissue whose integrity has already been disturbed or destroyed. For this purpose, transmission electron microscopy (TEM) remains a powerful technique that can not only provide information about the ultrastructural state of cell organelles but also allow the correlation between different subcellular alterations indicative of a certain pathophysiological condition and cellular response. The present study expands the spectrum of ultrastructural defects known to exist in human atherosclerosis and suggests that ER alterations may be of great importance in the pathogenesis of the disease. The architectural changes of ER may be considered early pathological events that precede any overt histologic abnormalities in the vascular endothelium and its subcellular organelles, primarily the mitochondrial pool.

Hyperosmotic stress promotes endoplasmic reticulum stress-dependent apoptosis in adult rat cardiac myocytes

In different pathological situations, cardiac cells undergo hyperosmotic stress and cell shrinkage. This change in cellular volume has been associated with contractile dysfunction and cell death. However, the intracellular mechanisms involved in hyperosmotic stress-induced cell death have not been investigated in depth in adult cardiac myocytes. Given that osmotic stress has been shown to promote endoplasmic reticulum stress (ERS), a recognized trigger for apoptosis, we examined whether hyperosmotic stress triggers ERS in adult cardiac myocytes and if so whether this mechanism mediates hyperosmotic stress-induced cell death. Adult rat cardiomyocytes cultured overnight in a hypertonic solution (HS) containing mannitol as the osmolite, showed increased expression of ERS markers, GRP78, CHOP and cleaved-Caspase-12, compared with myocytes in isotonic solution (IS), suggesting that hyperosmotic stress induces ERS. In addition, HS significantly reduced cell viability and increased TUNEL staining and the expression of active Caspase-3, indicative of apoptosis. These effects were prevented with the addition of the ERS inhibitor, 4-PBA, indicating that hyperosmotic stress-induced apoptosis is mediated by ERS. Hyperosmotic stress-induced apoptosis was also prevented when cells were cultured in the presence of a Ca²⁺-chelating agent (EGTA) or the CaMKII inhibitor (KN93), suggesting that hyperosmotic stress-induced ERS is mediated by a Ca²⁺ and CaMKII-dependent mechanism. Similar results were observed when hyperosmotic stress was induced using glucose as the osmolite. We conclude that hyperosmotic stress promotes ERS by a CaMKII-dependent mechanism leading to apoptosis of adult cardiomyocytes. More importantly, we demonstrate that hyperosmotic stress-triggered ERS contributes to hyperglycemia-induced cell death.

Exercise training ameliorates cerebrovascular dysfunction in a murine model of Alzheimer's disease: role of the P2Y2 receptor and endoplasmic reticulum stress

Cerebrovascular dysfunction is a critical risk factor for the pathogenesis of Alzheimer's disease (AD). The purinergic P2Y2 receptor and endoplasmic reticulum (ER) stress are tightly associated with vascular dysfunction and the pathogenesis of AD. However, the protective effects of exercise training on P2Y2 receptor- and ER stress-associated cerebrovascular dysfunction in AD are mostly unknown. Control (C57BL/6, CON) and AD (APP/PS1dE9, AD) mice underwent treadmill exercise training (EX). 2-MeS-ATP-induced dose-dependent vasoreactivity was determined by using a pressurized posterior cerebral artery (PCA) from 10-12-mo-old mice. Human brain microvascular endothelial cells (HBMECs) were exposed to laminar shear stress (LSS) at 20 dyn/cm² for 30 min, 2 h, and 24 h. The expression of P2Y2 receptors, endothelial nitric oxide synthase (eNOS), and ER stress signaling were quantified by Western blot analysis. Notably, exercise converted ATP-induced vasoconstriction in the PCA from AD mice to vasodilation in AD+EX mice to a degree commensurate to the vascular reactivity observed in CON mice. Exercise reduced the expression of amyloid peptide precursor (APP) and increased the P2Y2 receptor and Akt/eNOS expression in AD mice brain. Mechanistically, LSS increased the expression of both P2Y2 receptor and eNOS protein in HBMECs, but these increases were blunted by a P2Y2 receptor antagonist in HBMECs. Exercise also reduced the expression of aberrant ER stress markers p-IRE1, p/t-eIF2α, and CHOP, as well as Bax/Bcl-2, in AD mice brain. Collectively, our results demonstrate for the first time that exercise mitigates cerebrovascular dysfunction in AD through modulating P2Y2 receptor- and ER stress-dependent endothelial dysfunction.NEW & NOTEWORTHY A limited study has investigated whether exercise training can improve cerebrovascular function in Alzheimer's disease. The novel findings of the study are that exercise training improves cerebrovascular dysfunction through enhancing P2Y2 receptor-mediated eNOS signaling and reducing ER stress-associated pathways in AD. These data suggest that exercise training, which regulates P2Y2 receptor and ER stress in AD brain, is a potential therapeutic strategy for Alzheimer's disease.