Toll-like receptor 4-induced endoplasmic reticulum stress contributes to impairment of vasodilator action of insulin

Endoplasmic Reticulum Stress in Hypertension and Salt Sensitivity of Blood Pressure

PURPOSE OF REVIEW

Hypertension is a principal risk factor for cardiovascular morbidity and mortality, with its severity exacerbated by high sodium intake, particularly in individuals with salt-sensitive blood pressure. However, the mechanisms underlying hypertension and salt sensitivity are only partly understood. Herein, we review potential interactions in hypertension pathophysiology involving the immune system, endoplasmic reticulum (ER) stress, the unfolded protein response (UPR), and proteostasis pathways; identify knowledge gaps; and discuss future directions.

RECENT FINDINGS

Recent advancements by our research group and others reveal interactions within and between adaptive and innate immune responses in hypertension pathophysiology. The salt-immune-hypertension axis is further supported by the discovery of the role of dendritic cells in hypertension, marked by isolevuglandin (IsoLG) formation. Alongside these broadened understandings of immune-mediated salt sensitivity, the contributions of T cells to hypertension have been recently challenged by groups whose findings did not support increased resistance of Rag-1-deficient mice to Ang II infusion. Hypertension has also been linked to ER stress and the UPR. Notably, a holistic approach is needed because the UPR engages in crosstalk with autophagy, the ubiquitin proteasome, and other proteostasis pathways, that may all involve hypertension. There is a critical need for studies to establish cause and effect relationships between ER stress and the UPR in hypertension pathophysiology in humans and to determine whether the immune system and ER stress function mainly to exacerbate or initiate hypertension and target organ injury. This review of recent studies proposes new avenues for future research for targeted therapeutic interventions.

Reappraisal of Adipose Tissue Inflammation in Obesity

Chronic low-grade inflammation is a central component in the pathogenesis of obesity-related expansion of adipose tissue and complications in other metabolic tissues. Five different signaling pathways are defined as dominant determinants of adipose tissue inflammation: These are increased circulating endotoxin due to dysregulation in the microbiota-gut-brain axis, systemic oxidative stress, macrophage accumulation, and adipocyte death. Finally, the nucleotide-binding and oligomerization domain (NOD) leucine-rich repeat family pyrin domain-containing 3 (NLRP3) inflammasome pathway is noted to be a key regulator of metabolic inflammation. The NLRP3 inflammasome and associated metabolic inflammation play an important role in the relationships among fatty acids and obesity. Several highly active molecules, including primarily leptin, resistin, adiponectin, visfatin, and classical cytokines, are abundantly released from adipocytes. The most important cytokines that are released by inflammatory cells infiltrating obese adipose tissue are tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), monocyte chemoattractant protein 1 (MCP-1) (CCL-2), and IL-1. All these molecules mentioned above act on immune cells, causing local and then general inflammation. Three metabolic pathways are noteworthy in the development of adipose tissue inflammation: toll-like receptor 4 (TLR4)/phosphatidylinositol-3'-kinase (PI3K)/Protein kinase B (Akt) signaling pathway, endoplasmic reticulum (ER) stress-derived unfolded protein response (UPR), and inhibitor of nuclear factor kappa-B kinase beta (IKKβ)-nuclear factor kappa B (NF-κB) pathway. In fact, adipose tissue inflammation is an adaptive response that contributes to a visceral depot barrier that effectively filters gut-derived endotoxin. Excessive fatty acid release worsens adipose tissue inflammation and contributes to insulin resistance. However, suppression of adipose inflammation in obesity with anti-inflammatory drugs is not a rational solution and paradoxically promotes insulin resistance, despite beneficial effects on weight gain. Inflammatory pathways in adipocytes are indeed indispensable for maintaining systemic insulin sensitivity. Cannabinoid type 1 receptor (CB1R) is important in obesity-induced pro-inflammatory response; however, blockade of CB1R, contrary to anti-inflammatory drugs, breaks the links between insulin resistance and adipose tissue inflammation. Obesity, however, could be decreased by improving leptin signaling, white adipose tissue browning, gut microbiota interactions, and alleviating inflammation. Furthermore, capsaicin synthesized by chilies is thought to be a new and promising therapeutic option in obesity, as it prevents metabolic endotoxemia and systemic chronic low-grade inflammation caused by high-fat diet.

Microbiome Dysbiosis: A Pathological Mechanism at the Intersection of Obesity and Glaucoma

The rate at which obesity is becoming an epidemic in many countries is alarming. Obese individuals have a high risk of developing elevated intraocular pressure and glaucoma. Additionally, glaucoma is a disease of epidemic proportions. It is characterized by neurodegeneration and neuroinflammation with optic neuropathy and the death of retinal ganglion cells (RGC). On the other hand, there is growing interest in microbiome dysbiosis, particularly in the gut, which has been widely acknowledged to play a prominent role in the etiology of metabolic illnesses such as obesity. Recently, studies have begun to highlight the fact that microbiome dysbiosis could play a critical role in the onset and progression of several neurodegenerative diseases, as well as in the development and progression of several ocular disorders. In obese individuals, gut microbiome dysbiosis can induce endotoxemia and systemic inflammation by causing intestinal barrier malfunction. As a result, bacteria and their metabolites could be delivered via the bloodstream or mesenteric lymphatic vessels to ocular regions at the level of the retina and optic nerve, causing tissue degeneration and neuroinflammation. Nowadays, there is preliminary evidence for the existence of brain and intraocular microbiomes. The altered microbiome of the gut could perturb the resident brain-ocular microbiome ecosystem which, in turn, could exacerbate the local inflammation. All these processes, finally, could lead to the death of RGC and neurodegeneration. The purpose of this literature review is to explore the recent evidence on the role of gut microbiome dysbiosis and related inflammation as common mechanisms underlying obesity and glaucoma.

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.

Thalidomide Alleviates Pulmonary Fibrosis Induced by Silica in Mice by Inhibiting ER Stress and the TLR4-NF-κB Pathway

Silicosis is the most prevalent occupational disease in China. It is a form of pulmonary fibrosis caused by the inhalation of silicon particles. As there is no cure for the potentially lethal and progressive condition, the treatment of silicotic fibrosis is an important and difficult problem to address. Thalidomide, a drug with anti-inflammatory and immunoregulatory properties, has been reported to have lung-protective effects. The purpose of this study was to observe the therapeutic effect of thalidomide on silicotic mice and to determine the protective mechanism. By using silicotic mice models and MH-S cells, we found the expression of endoplasmic reticulum stress (ER stress) and Toll-like receptor 4 (TLR4)-nuclear factor kappa-B (NF-κB) pathway as well as inflammation-related factors were upregulated in the macrophages of silicotic mice. The same indexes were detected in silica-stimulated MH-S cells, and the results were consistent with those in vivo. That is, silica activated ER stress and the TLR4-NF-κB pathway as well as the inflammatory response in vitro. Treating both silicotic mice and silica-stimulated MH-S cells with thalidomide inhibited ER stress and the TLR4-NF-κB pathway as well as the inflammatory response. The present study demonstrates thalidomide as a potential therapeutic agent against silicosis.

Long-term high-fructose high-fat diet feeding elicits insulin resistance, exacerbates dyslipidemia and induces gut microbiota dysbiosis in WHHL rabbits

The metabolic syndrome (MetS) has become a global public health burden due to its link to cardiovascular disease and diabetes mellitus. The present study was designed to characterize the metabolic and cardiovascular disturbances, as well as changes in gut microbiota associated with high-fructose high-fat diet (HFFD)-induced MetS in Watanabe heritable hyperlipidemic (WHHL) rabbits. Twenty-one Watanabe rabbits were assigned to a control (n = 9) and HFFD (n = 12) groups, receiving a chow diet and a HFFD, respectively. During a 12-weeks protocol, morphological parameters were monitored; plasma fasting levels of lipids, glucose and insulin were measured and a glucose tolerance test (GTT) was performed. HOMA-IR was calculated. Cardiac function and vascular reactivity were evaluated using the Langendorff isolated heart and isolated carotid arteries methods, respectively. 16S rRNA sequencing of stool samples was used to determine gut microbial composition and abundance. HFFD-fed Watanabe rabbits exhibited increased fasting insulin (p < 0.03, 12^th week vs. Baseline), HOMA-IR (p < 0.03 vs. Control), area under the curve of the GTT (p < 0.02 vs. Control), triglycerides (p < 0.05, 12^th week vs. Baseline), TC (p < 0.01 vs. Control), LDL-C (p < 0.001 vs. Control). The HFFD group also displayed a significant decrease in intestinal microbial richness, evenness and diversity (FDR < 0.001, FDR < 0.0001, FDR < 0.01, respectively vs. Control group) and an increase in its Firmicutes/Bacteroidetes ratio (R = 3.39 in control vs. R = 28.24 in the HFFD group) indicating a shift in intestinal microbial composition and diversity. Our results suggest that HFFD induces insulin resistance and gut microbiota dysbiosis and accentuates dyslipidemia; and that, when subjected to HFFD, Watanabe rabbits might become a potential diet-induced MetS animal models with two main features, dyslipidemia and insulin resistance.

Molecular Mechanism of Lipotoxicity as an Interesting Aspect in the Development of Pathological States-Current View of Knowledge

Free fatty acids (FFAs) play numerous vital roles in the organism, such as contribution to energy generation and reserve, serving as an essential component of the cell membrane, or as ligands for nuclear receptors. However, the disturbance in fatty acid homeostasis, such as inefficient metabolism or intensified release from the site of storage, may result in increased serum FFA levels and eventually result in ectopic fat deposition, which is unfavorable for the organism. The cells are adjusted for the accumulation of FFA to a limited extent and so prolonged exposure to elevated FFA levels results in deleterious effects referred to as lipotoxicity. Lipotoxicity contributes to the development of diseases such as insulin resistance, diabetes, cardiovascular diseases, metabolic syndrome, and inflammation. The nonobvious organs recognized as the main lipotoxic goal of action are the pancreas, liver, skeletal muscles, cardiac muscle, and kidneys. However, lipotoxic effects to a significant extent are not organ-specific but affect fundamental cellular processes occurring in most cells. Therefore, the wider perception of cellular lipotoxic mechanisms and their interrelation may be beneficial for a better understanding of various diseases’ pathogenesis and seeking new pharmacological treatment approaches.

Predicting Diagnostic Gene Biomarkers Associated With Immune Checkpoints, N6-Methyladenosine, and Ferroptosis in Patients With Acute Myocardial Infarction

This study aimed to determine early diagnosis genes of acute myocardial infarction (AMI) and then validate their association with ferroptosis, immune checkpoints, and N6-methyladenosine (m6A), which may provide a potential method for the early diagnosis of AMI. Firstly, we downloaded microarray data from NCBI (GSE61144, GSE60993, and GSE42148) and identified differentially expressed genes (DEGs) in samples from healthy subjects and patients with AMI. Also, we performed systematic gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses and used STRING to predict protein interactions. Moreover, MCC and MCODE algorithms in the cytoHubba plug-in were used to screen nine key genes in the network. We then determined the diagnostic significance of the nine obtained DEGs by plotting receiver operating characteristic curves using a multiscale curvature classification algorithm. Meanwhile, we investigated the relationship between AMI and immune checkpoints, ferroptosis, and m6A. In addition, we further validated the key genes through the GSE66360 dataset and consequently obtained nine specific genes that can be used as early diagnosis biomarkers for AMI. Through screening, we identified 210 DEGs, including 53 downregulated and 157 upregulated genes. According to GO, KEGG, and key gene screening results, FPR1, CXCR1, ELANE, TLR2, S100A12, TLR4, CXCL8, FPR2 and CAMP could be used for early prediction of AMI. Finally, we found that AMI was associated with ferroptosis, immune checkpoints, and m6A and FPR1, CXCR1, ELANE, TLR2, S100A12, TLR4, CXCL8, FPR2 and CAMP are effective markers for the diagnosis of AMI, which can provide new prospects for future studies on the pathogenesis of AMI.

Leptin Induced TLR4 Expression via the JAK2-STAT3 Pathway in Obesity-Related Osteoarthritis

Obesity is considered as a risk factor of osteoarthritis (OA), but the precise relationship is still poorly understood. Leptin, one of the most relevant factors secreted by adipose tissues, plays an important role in the pathogenesis of OA. Our aim was to investigate the regulation and molecular mechanism of the leptin signaling pathway in obesity-related OA. SD rats were fed with a high-fat diet (HFD) for 5, 15, and 27 weeks. The levels of leptin in serum increased from W5, while in the synovial fluid increased from W15. The histological evaluation showed that the pathological changes of OA occurred at 27 weeks rather than 5 or 15 weeks. We also found that leptin induced CD14/TLR4 activation by the JAK2-STAT3 signaling pathway to promote OA. Moreover, silencing SOCS3 enhanced leptin-induced JAK2-STAT3-CD14/TLR4 activation in rat primary chondrocytes. Our findings indicated that leptin may be one of the initiating factors of obesity-related OA. TLR4 is at least partially regulated by leptin through the JAK2-STAT3-CD14 pathway. Meanwhile, SOCS3 acting as a negative feedback inhibitor of leptin signaling presented a potential therapeutic prospect for obesity-related OA. Our study provided new evidence suggesting the key role of leptin in mediating obesity-related OA process and its underlying mechanisms.

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.

TLR4/TRAF6/NOX2 signaling pathway is involved in ventilation-induced lung injury via endoplasmic reticulum stress in murine model

In ventilation-induced lung injury (VILI), prolonged nonpathogen-mediated inflammation is triggered as a result of alveolar hyperinflation. In our previous study, we suggested that endoplasmic reticulum (ER) stress-mediated inflammation was involved in VILI, but how ER stress is triggered remains unknown. Toll-like receptor 4 (TLR4) activation plays an important role in mechanical ventilation (MV)-induced lung inflammation, however, it is unknown whether ER stress is activated by TLR4 to participate in VILI. In this study, C57BL/6 mice were exposed to MV with high tidal volumes (HTV 20 ml/kg). Mice were pretreated with TAK-242 the TLR4 inhibitor, C25-140, the TRAF6 inhibitor, or GSK2795039, the NOX2 inhibitor. Lung tissue and bronchoalveolar lavage fluid (BALF) were collected to measure lung injury, inflammatory responses and mRNA/protein expression associated with ER stress and the TLR4/TRAF6/NOX2 signaling pathway. Our results indicate that MV with HTV caused the TLR4/TRAF6/NOX2 signaling pathway activation and production of large amounts of ROS, which led to ER stress and NF-κB mediated inflammation in VILI. Furthermore, TLR4/TRAF6/NOX2 signaling pathway inhibition attenuated ER stress response and alleviate lung injury in mice.

Network pharmacology combined with metabolomics to study the mechanism of Shenyan Kangfu Tablets in the treatment of diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Shenyan Kangfu Tablets (SYKFT) is a traditional prescription evolved from Shenqi Pills. It has been included in the Synopsis of the Golden Chamber for more than 2000 years. SYKFT was listed as a national Chinese medicine protected class by the China Food and Drug Administration. Diabetic nephropathy (DN) is one of the serious microvascular diseases caused by diabetes and is also one of the important factors leading to the death of patients. The pathogenesis of DN is diverse and complex, and there is no particularly effective drug treatment. There is clinical evidence that SYKFT has a good therapeutic effect on DN with no obvious adverse effects, but the mechanism of treatment is not clear.

AIM OF THE STUDY

In this study, network pharmacology was combined with metabolomics technology to explore the mechanism of SYKFT in the treatment of DN.

MATERIALS AND METHODS

First, the research team conducted a qualitative study of the chemical components contained in SYKFT, and carried out network pharmacology to search for potential targets based on the characterized chemical components. Second, we analysed the metabolic profile of db/db mouse urine based on UHPLC-QTOF-MS technology, and biomarkers were identified by multivariate statistical analysis. Then, we performed further pathway enrichment analysis. Finally, the results of metabolomics and network pharmacology were conjointly analysed.

RESULTS

Seventy-five chemical components of SYKFT were identified. According to the TCMSP database, the corresponding targets of the qualitatively identified components were searched, and a total of 36 potentially active components and 160 targets related to DN were obtained. A total of 38 biomarkers were found in metabolomics based on UHPLC-QTOF-MS technology. Biosynthesis of unsaturated fatty acids and starch and sucrose metabolism are the most related pathways, the former of which has been rarely reported concerning DN. Finally, the results of the joint analysis show that two targets, hexokinase 2 (HK2) and maltase glucoamylase (MGAM), are the overlapping targets. It means they are not only the related targets of pathways involved in potential biomarkers in metabolomics but also the intersection targets of diseases and drugs identified by network pharmacology.

CONCLUSIONS

The study reveals that the potential mechanism of SYKFT is most related to insulin resistance (IR) in the treatment of DN. It also proves that network pharmacology combined with metabolomics to find the mechanisms by which herbs treat complex diseases is a feasible tool.

TLR4-mediated pyroptosis in human hepatoma-derived HuH-7 cells induced by a branched-chain polyunsaturated fatty acid, geranylgeranoic acid

A branched-chain polyunsaturated fatty acid, geranylgeranoic acid (GGA; C_20:4), which is an endogenous metabolite derived from the mevalonate pathway in mammals, has been reported to induce cell death in human hepatoma cells. We have previously shown that the lipid-induced unfolded protein response (UPR) is an upstream cellular process for an incomplete autophagic response that might be involved in GGA-induced cell death. Here, we found that Toll-like receptor 4 (TLR4)-mediated pyroptosis in HuH-7 cells occurred by GGA treatment. The TLR4-specific inhibitor VIPER prevented both GGA-induced cell death and UPR. Knockdown of the TLR4 gene attenuated GGA-induced cell death significantly. Upon GGA-induced UPR, caspase (CASP) 4 (CASP4) was activated immediately and gasdermin D (GSDMD) was translocated concomitantly to the plasma membrane after production of the N-terminal fragment of GSDMD. Then, cellular CASP1 activation occurred following a second gradual up-regulation of the intracellular Ca²⁺ concentration, suggesting that GGA activated the inflammasome. Indeed, the mRNA levels of NOD-like receptor family pyrin domain containing 3 (NLRP3) and interleukin-1 β (IL1B) genes were up-regulated dramatically with translocation of cytoplasmic nuclear factor-κB (NF-κB) to nuclei after GGA treatment, indicating that GGA induced priming of the NLRP3 inflammasome through NF-κB activation. GGA-induced up-regulation of CASP1 activity was blocked by either oleic acid, VIPER, MCC950 (a selective inhibitor of the NLRP3 inflammasome), or CASP4-specific inhibitor peptide cotreatment. Pyroptotic cell death was also confirmed morphologically by bleb formation in time-series live cell imaging of GGA-treated cells. Taken together, the present results strongly indicate that GGA causes pyroptotic cell death in human hepatoma-derived HuH-7 via TLR4 signalling.

Heme Causes Pain in Sickle Mice via Toll-Like Receptor 4-Mediated Reactive Oxygen Species- and Endoplasmic Reticulum Stress-Induced Glial Activation

Aims: Lifelong pain is a hallmark feature of sickle cell disease (SCD). How sickle pathobiology evokes pain remains unknown. We hypothesize that increased cell-free heme due to ongoing hemolysis activates toll-like receptor 4 (TLR4), leading to the formation of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. Together, these processes lead to spinal microglial activation and neuroinflammation, culminating in acute and chronic pain. Results: Spinal heme levels, TLR4 transcripts, oxidative stress, and ER stress were significantly higher in sickle mice than controls. In vitro, TLR4 inhibition in spinal cord microglial cells attenuated heme-induced ROS and ER stress. Heme treatment led to a time-dependent increase in the characteristic features of sickle pain (mechanical and thermal hyperalgesia) in both sickle and control mice; this effect was absent in TLR4-knockout sickle and control mice. TLR4 deletion in sickle mice attenuated chronic and hypoxia/reoxygenation (H/R)-evoked acute hyperalgesia. Sickle mice treated with the TLR4 inhibitor resatorvid; selective small-molecule inhibitor of TLR4 (TAK242) had significantly reduced chronic hyperalgesia and had less severe H/R-evoked acute pain with quicker recovery. Notably, reducing ER stress with salubrinal ameliorated chronic hyperalgesia in sickle mice. Innovation: Our findings demonstrate the causal role of free heme in the genesis of acute and chronic sickle pain and suggest that TLR4 and/or ER stress are novel therapeutic targets for treating pain in SCD. Conclusion: Heme-induced microglial activation via TLR4 in the central nervous system contributes to the initiation and maintenance of sickle pain via ER stress in SCD. Antioxid. Redox Signal. 34, 279-293.

Long-chain acyl-CoA synthetase-1 mediates the palmitic acid-induced inflammatory response in human aortic endothelial cells

Saturated fatty acid (SFA) induces proinflammatory response through a Toll-like receptor (TLR)-mediated mechanism, which is associated with cardiometabolic diseases such as obesity, insulin resistance, and endothelial dysfunction. Consistent with this notion, TLR2 or TLR4 knockout mice are protected from obesity-induced proinflammatory response and endothelial dysfunction. Although SFA causes endothelial dysfunction through TLR-mediated signaling pathways, the mechanisms underlying SFA-stimulated inflammatory response are not completely understood. To understand the proinflammatory response in vascular endothelial cells in high-lipid conditions, we compared the proinflammatory responses stimulated by palmitic acid (PA) and other canonical TLR agonists [lipopolysaccharide (LPS), Pam3-Cys-Ser-Lys4 (Pam₃CSK₄), or macrophage-activating lipopeptide-2)] in human aortic endothelial cells. The expression profiles of E-selectin and the signal transduction pathways stimulated by PA were distinct from those stimulated by canonical TLR agonists. Inhibition of long-chain acyl-CoA synthetases (ACSL) by a pharmacological inhibitor or knockdown of ACSL1 blunted the PA-stimulated, but not the LPS- or Pam₃CSK₄-stimulated proinflammatory responses. Furthermore, triacsin C restored the insulin-stimulated vasodilation, which was impaired by PA. From the results, we concluded that PA stimulates the proinflammatory response in the vascular endothelium through an ACSL1-mediated mechanism, which is distinct from LPS- or Pam₃CSK₄-stimulated responses. The results suggest that endothelial dysfunction caused by PA may require to undergo intracellular metabolism. This expands the understanding of the mechanisms by which TLRs mediate inflammatory responses in endothelial dysfunction and cardiovascular disease.

Metformin reduces saturated fatty acid-induced lipid accumulation and inflammatory response by restoration of autophagic flux in endothelial cells

Autophagy, an integral part of the waste recycling process, plays an important role in cellular physiology and pathophysiology. Impaired autophagic flux causes ectopic lipid deposition, which is defined as the accumulation of lipids in non-adipose tissue. Ectopic lipid accumulation is observed in patients with cardiometabolic syndrome, including obesity, diabetes, insulin resistance, and cardiovascular complications. Metformin is the first line of treatment for type 2 diabetes, and one of the underlying mechanisms for the anti-diabetic effect of metformin is mediated by the stimulation of AMP-activated protein kinase (AMPK). Because the activation of AMPK is crucial for the initiation of autophagy, we hypothesize that metformin reduces the accumulation of lipid droplets by increasing autophagic flux in vascular endothelial cells. Incubation of vascular endothelial cells with saturated fatty acid (SFA) increased the accumulation of lipid droplets and impaired autophagic flux. We observed that the accumulation of lipid droplets was reduced, and the autophagic flux was enhanced by treatment with metformin. The knock-down of AMPKα by using siRNA blunted the effect of metformin. Furthermore, treatment with SFA or inhibition of autophagy increased leukocyte adhesion, whereas treatment with metformin decreased the SFA-induced leukocyte adhesion. The results suggest a novel mechanism by which metformin protects vascular endothelium from SFA-induced ectopic lipid accumulation and pro-inflammatory responses. In conclusion, improving autophagic flux may be a therapeutic strategy to protect endothelial function from dyslipidemia and diabetic complications.

Sildenafil citrate long-term treatment effects on cardiovascular reactivity in a SHR experimental model of metabolic syndrome

Much evidence indicates that metabolic syndrome is strongly correlated with a decrease in nitric oxide and an increase in oxidative stress leading to cardiovascular alterations. In recent years, gut microbiota has emerged as a new contributor to the metabolic syndrome establishment and associated cardiovascular diseases, but the underlying mechanisms remain unclear. We hypothesized that a positive modulation of cyclic guanosine monophosphate (cGMP) pathway, through phosphodiesterase type 5 (PDE5) inhibition could prevent cardiovascular alterations and gut dysbiosis that may be associated to metabolic syndrome. Spontaneously hypertensive rats (SHR) were randomly divided into 4 groups: control, cafeteria diet (CD) and sildenafil citrate treated groups (5mg/kg per os) were given either a CD or a standard chow diet for 10 weeks. Body weight, arterial blood pressure and glucose tolerance test were monitored. At the 10^th week, cardiac inotropy and coronary perfusion pressure were evaluated on isolated heart according to Langendorff method. Cumulative concentration response curves to phenylephrine and acetylcholine were determined on thoracic aorta rings for vascular reactivity evaluation. Faecal samples were collected for the gut microbiota analysis. Compared to the control group, CD-fed rats showed a significant increase in body weight gain, arterial blood pressure and were glucose intolerant. This group showed also a decrease in β-adrenoceptor-induced cardiac inotropy and coronary vasodilation. Gut microbiota analysis revealed a significant reduction in the abundance of Lactobocillus spp in cafeteria diet-fed rats when compared to the control ones. Sildenafil citrate long-term treatment decreased weight gain and arterial blood pressure, improved coronary vasodilation and reduced α_1-adrenoceptor-induced vasoconstriction in CD group. However, it did not reverse gut dysbiosis induced by chronic CD feeding. These results suggest that cGMP pathway targeting may be a potential therapeutic strategy for the management of the metabolic syndrome and associated cardiovascular disorders.

Commensal Escherichia coli Aggravates Acute Necrotizing Pancreatitis through Targeting of Intestinal Epithelial Cells

An increase of Escherichia-Shigella was previously reported in acute necrotizing pancreatitis (ANP). We investigated whether Escherichia coli MG1655, an Escherichia commensal organism, increased intestinal injury and aggravated ANP in rats. ANP was induced by retrograde injection of 3.5% sodium taurocholate into the biliopancreatic duct. Using gut microbiota-depleted rats, we demonstrated that gut microbiota was involved in the pancreatic injury and intestinal barrier dysfunction in ANP. Using 16S rRNA gene sequencing and quantitative PCR, we found intestinal dysbiosis and a significant increase of E. coli MG1655 in ANP. Afterward, administration of E. coli MG1655 by gavage to gut microbiota-depleted rats with ANP was performed. We observed that after ANP induction, E. coli MG1655-monocolonized rats presented more severe injury in the pancreas and intestinal barrier function than gut microbiota-depleted rats. Furthermore, Toll-like receptor 4 (TLR4)/MyD88/p38 mitogen-activated protein (MAPK) and endoplasmic reticulum stress (ERS) activation in intestinal epithelial cells were also increased more significantly in the MG1655-monocolonized ANP rats. In vitro, the rat ileal epithelial cell line IEC-18 displayed aggravated tumor necrosis factor alpha-induced inflammation and loss of tight-junction proteins in coculture with E. coli MG1655, as well as TLR4, MyD88, and Bip upregulation. In conclusion, our study shows that commensal E. coli MG1655 increases TLR4/MyD88/p38 MAPK and ERS signaling-induced intestinal epithelial injury and aggravates ANP in rats. Our study also describes the harmful potential of commensal E. coli in ANP.IMPORTANCE This study describes the harmful potential of commensal E. coli in ANP, which has not been demonstrated in previous studies. Our work provides new insights into gut bacterium-ANP cross talk, suggesting that nonpathogenic commensals could also exhibit adverse effects in the context of diseases.

Endoplasmic Reticulum Stress: A Critical Molecular Driver of Endothelial Dysfunction and Cardiovascular Disturbances Associated with Diabetes

Physical inactivity and sedentary lifestyle contribute to the widespread epidemic of obesity among both adults and children leading to rising cases of diabetes. Cardiovascular disease complications associated with obesity and diabetes are closely linked to insulin resistance and its complex implications on vascular cells particularly endothelial cells. Endoplasmic reticulum (ER) stress is activated following disruption in post-translational protein folding and maturation within the ER in metabolic conditions characterized by heavy demand on protein synthesis, such as obesity and diabetes. ER stress has gained much interest as a key bridging and converging molecular link between insulin resistance, oxidative stress, and endothelial cell dysfunction and, hence, represents an interesting drug target for diabetes and its cardiovascular complications. We reviewed here the role of ER stress in endothelial cell dysfunction, the primary step in the onset of atherosclerosis and cardiovascular disease. We specifically focused on the contribution of oxidative stress, insulin resistance, endothelial cell death, and cellular inflammation caused by ER stress in endothelial cell dysfunction and the process of atherogenesis.

TAK-875 Mitigates β-Cell Lipotoxicity-Induced Metaflammation Damage through Inhibiting the TLR4-NF-κB Pathway

Metabolic inflammatory damage, characterized by Toll-like receptor 4 (TLR4) signaling activation, is a major mechanism underlying lipotoxicity-induced β-cell damage. The present study is aimed at determining whether G protein-coupled receptor 4 (GPR40) agonist can improve β-cell lipotoxicity-induced damage by inhibiting the TLR4-NF-κB pathway. Lipotoxicity, inflammation-damaged β-cells, obese SD, and TLR4^KO rat models were used in the study. In vitro, TAK-875 inhibited the lipotoxicity- and LPS-induced β-cell apoptosis in a concentration-dependent manner, improved the insulin secretion, and inhibited the expression of TLR4 and NF-κB subunit P65. Besides, silencing of TLR4 expression enhanced the protective effects of TAK-875, while TLR4 overexpression attenuated this protective effect. Activation of TLR4 or NF-κB attenuated the antagonism of TAK-875 on PA-induced damage. Moreover, the above process of TAK-875 was partially independent of GPR40 expression. TAK-875 reduced the body weight and inflammatory factors, rebalanced the number and distribution of α or β-cells, inhibited the apoptosis of islet cells, and inhibited the expression of TLR4 and NF-κB subunit P65 in obese rats. Further knockout of the rat TLR4 gene delayed the damage induced by the high-fat diet and synergy with the action of TAK-875. These data suggest that GPR40 agonists antagonized the lipotoxicity β-cell damage by inhibiting the TLR4-NF-κB pathway.

MD1 Deficiency Promotes Inflammatory Atrial Remodelling Induced by High-Fat Diets

BACKGROUND

Myeloid differentiation protein 1 (MD1) is expressed in various tissues, including the heart. However, the role of MD1 in obesity-related atrial remodelling remains incompletely understood. Here, this study intends to determine the regulatory role and underlying mechanisms of MD1 in obesity-related atrial remodelling.

METHODS

A high-fat diet (HFD) feeding was performed in 6-week-old MD1-knockout (MD1-KO) mice and wild-type (WT) littermates for 20 weeks. Morphological, biochemical, functional, histological, and electrophysiological studies were conducted at the age of 26 weeks.

RESULTS

Our results revealed that the MD1 expression levels were downregulated in the atrium of the HFD-fed induced obesity mice. An increase in body weight, glucose intolerance, hyperlipidemia, and adverse atrial remodelling, such as atrial inflammation and fibrosis, were induced by HFD feeding in WT mice. Vulnerability to atrial fibrillation (AF) was also significantly increased by HFD feeding in WT mice. In addition, these adverse effects caused by HFD-fed induced obesity were further exaggerated in MD1-KO mice compared with WT mice. Mechanistically, MD1-KO activated TLR4/NF-κB signaling pathways, which led to atrial remodelling in mice fed by HFD by increasing the phosphorylation of p65 and IκBα.

CONCLUSIONS

Our data suggested that MD1 deficiency played an important role in accelerating the development of inflammatory atrial fibrosis and increasing vulnerability to AF in mice with HFD-fed induced obesity, providing an essential target for improving HFD-induced atrial remodelling.

Resistin-Induced Endoplasmic Reticulum Stress Contributes to the Impairment of Insulin Signaling in Endothelium

Background: Endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of obesity, insulin resistance and cardiovascular diseases (CVDs). Impairment of insulin vascular action may represent a mechanism linking insulin resistance and CVDs. The present study tested the hypothesis that adipocyte-derived resistin inhibits insulin-stimulated endothelial NO production through the induction of ER stress.

Methods and Results: Human umbilical vein endothelial cells (HUVC) were incubated with tunicamycin (an inducer of ER stress, 1–20 μg/mL) or resistin (10–100 ng/mL) for 1 h. Either tunicamycin or resistin increased GRP78 (an ER stress marker) expression associated with the impairment of insulin-stimulated Akt/eNOS phosphorylation, which were prevented by TUDCA (an ER stress suppressor). Resistin increased reactive oxygen species (ROS) production, antioxidant treatment inhibited resistin-induced GRP78 expression and impairment of insulin Akt/eNOS signaling, suggesting that ROS may involve resistin-induced ER stress. Resistin also increased JNK phosphorylation, which was prevented by TUDCA. JNK inhibitor SP600125 relieved the resistin inhibitory effects on endothelial insulin Akt/eNOS signaling. In ex vivo experiments, the incubation of aortic rings with resistin impaired insulin- but not acetylcholine-induced vasodilation, which was restored by TUDCA. LNAME (a NOS inhibitor) abolished insulin-induced vasorelaxation in the control or the resistin-treated aortic rings. In addition, resistin increased the mRNA expressions of proinflammatory cytokines tumor nuclear factor (TNF)α and interleukin (IL)-1β, which were also prevented by TUDCA.

Conclusion: Our results support the ideal that ER stress may play an important role for resistin impairment of vascular insulin signaling and insulin action. The mitigation of ER stress may represent a new strategy for prevention and treatment of CVDs in obesity and insulin resistant-related diseases.

Western diet triggers Toll-like receptor 4 signaling-induced endothelial dysfunction in female Wistar rats

Overconsumption of a diet rich in fat and carbohydrates, called the Western diet, is a major contributor to the global epidemic of cardiovascular disease. Despite previously documented cardiovascular protection exhibited in female rats, this safeguard may be lost under certain metabolic stressors. We hypothesized that female Wistar rats challenged by a Western diet composed of 21% fat and 50% carbohydrate (34.1% sucrose) for 17 wk would develop endothelial dysfunction via endothelial Toll-like receptor 4 (TLR4) signaling. Western diet-fed female rats exhibited dysregulation of metabolism, revealing increased body weight and abdominal fat, decreased expression of adiponectin in white adipose tissue, glucose intolerance, and impaired insulin sensitivity. Western diet exposure increased hepatic triglycerides and cholesterol alongside hepatic steatosis, categorizing nonalcoholic fatty liver disease. Moreover, a Western diet negatively affected vascular function, revealing hypertension, impaired endothelium-dependent vasorelaxation, aortic remodeling, and increased reactive oxygen species (ROS) production. Aortic protein expression of TLR4 and its downstream proteins were markedly increased in the Western diet-fed group in association with elevated serum levels of free fatty acids. In vitro experiments were conducted to test whether free fatty acids contribute to vascular ROS overproduction via the TLR4 signaling pathway. Cultured endothelial cells were stimulated with palmitate in the presence of TAK-242, a TLR4 signaling inhibitor. Palmitate-induced overgeneration of ROS in endothelial cells was abolished in the presence of TAK-242. Our data show that a Western diet induced endothelial dysfunction in female rats and suggest that endothelial TLR4 signaling may play a key role in abolishing female cardiovascular protection. NEW & NOTEWORTHY A Western diet induced elevated levels of free fatty acids, produced nonalcoholic fatty liver disease, and provoked endothelial dysfunction in female rats in association with Toll-like receptor 4 signaling-mediated vascular reactive oxygen species production. Limited consumption of a Western diet in premenopausal women may decrease their risk of cardiovascular complications.

Endoplasmic Reticulum Stress, a Driver or an Innocent Bystander in Endothelial Dysfunction Associated with Hypertension?

PURPOSE OF REVIEW

Hypertension (htn) is a polygenic disorder that effects up to one third of the US population. The endoplasmic reticulum (ER) stress response is a homeostatic pathway that regulates membrane structure, protein folding, and secretory function. Emerging evidence suggests that ER stress may induce endothelial dysfunction; however, it is unclear whether ER stress-associated endothelial dysfunction modulates htn.

RECENT FINDINGS

Exogenous and endogenous molecules activate ER stress in the endothelium, and ER stress mediates some forms of neurogenic htn, such as angiotensin II-dependent htn. Human studies suggest that ER stress induces endothelial dysfunction, though direct evidence that ER stress augments blood pressure in humans is lacking. However, animal and cellular models demonstrate direct evidence that ER stress influences htn. ER stress is likely one of many players in a complex interplay among molecular pathways that influence the expression of htn. Targeted activation of specific ER stress pathways may provide novel therapeutic opportunities.

Stearic acid at physiologic concentrations induces in vitro lipotoxicity in circulating angiogenic cells

BACKGROUND AND AIMS

Saturated free fatty acids (SFAs) can induce lipotoxicity in different cells. No studies have investigated the effects of SFA in circulating angiogenic cells (CACs), which play a key role in endothelial repair processes. The aim of the study was to assess the effects of SFAs, specifically stearic acid (SA), on viability and function of CACs and to investigate potential underlying molecular mechanisms.

METHODS

CACs were isolated from healthy subjects by established methods. CACs were incubated with BSA-complexed stearate (100 μM) to assess the time course (from 8 to 24 h exposure) of the effects on viability and apoptosis (activation of caspases 3/7), angiogenic function (tube formation assay), pro-inflammatory cytokine (IL-1β, IL-6, IL-8, MCP-1 and TNFα) gene expression (qPCR) and secretion (ELISA), activation of MAPK (JNK, p38 and Erk1/2) by Western blot and endoplasmic reticulum (ER) stress marker (CHOP, BIP, ATF4, XBP-1 and sXBP-1) gene expression by qPCR.

RESULTS

Stearic acid activates effector caspases in CACs in a dose- and time-dependent manner. SA also impairs CAC function and increases pro-inflammatory molecule (IL-1β, IL-6, IL-8, MCP-1 and TNFα) gene expression and secretion in CACs starting from 3 h of incubation. The activation of JNK by SA mediates pro-inflammatory response, but it may be not necessary for apoptosis. Moreover, SA induces the expression of ER stress markers across the three branches of the ER stress response.

CONCLUSIONS

In humans, both function and viability of CACs are exquisitely vulnerable to physiologic concentrations of stearate; lipotoxic impairment of endothelial repair processes may be implicated in vascular damage caused by SFAs.

TLR4 regulates insulin-resistant proteins to increase apoptosis in the mouse retina

OBJECTIVE AND DESIGN

Work in multiple organs has suggested that toll-like receptor 4 (TLR4) may play a role in insulin resistance. Additional studies have shown a negative role for TLR4 on retinal health. We have previously reported that β-adrenergic receptors can regulate both TLR4 signal transduction, as well as insulin signaling in the retina and in retinal endothelial cells. Thus, we hypothesized that TLR4 would regulate retinal insulin signaling.

MATERIALS AND METHODS

We used endothelial cell-specific TLR4 knockout mice, as well as TLR4-overexpressing mice for these studies.

METHODS

Western blotting and ELISA analyses were done for investigations of insulin receptor, insulin receptor substrate 1 (IRS-1) serine 307, and Akt phosphorylation, as well as cleaved caspase 3 levels in the mouse retina.

RESULTS

We found that loss of TLR4 led to increased insulin receptor and Akt phosphorylation, as well as decreased IRS-1^Ser307 levels. In support of these results, TLR4 overexpression decreased insulin signaling and the cleavage of caspase 3.

CONCLUSIONS

Therefore, these results suggest that TLR4 plays a key role in insulin signaling in the retina. Reduction of TLR4 levels may be protective to the retina.

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Endothelial cells control vascular tone by releasing nitric oxide (NO) produced by endothelial NO synthase. The activity of endothelial NO synthase is modulated by the calcium concentration and by post-translational modifications (eg, phosphorylation). When NO reaches vascular smooth muscle, soluble guanylyl cyclase is its primary target producing cGMP. NO production is stimulated by circulating substances (eg, catecholamines), platelet products (eg, serotonin), autacoids formed in (eg, bradykinin) or near (eg, adiponectin) the vascular wall and physical factors (eg, shear stress). NO dysfunction can be caused, alone or in combination, by abnormal coupling of endothelial cell membrane receptors, insufficient supply of substrate (l-arginine) or cofactors (tetrahydrobiopterin), endogenous inhibitors (asymmetrical dimethyl arginine), reduced expression/presence/dimerization of endothelial NO synthase, inhibition of its enzymatic activity, accelerated disposition of NO by reactive oxygen species and abnormal responses (eg, biased soluble guanylyl cyclase activity producing cyclic inosine monophosphate) of the vascular smooth muscle. Major culprits causing endothelial dysfunction, irrespective of the underlying pathological process (aging, obesity, diabetes mellitus, and hypertension), include stimulation of mineralocorticoid receptors, activation of endothelial Rho-kinase, augmented presence of asymmetrical dimethyl arginine, and exaggerated oxidative stress. Genetic and pharmacological interventions improve dysfunctional NO-mediated vasodilatations if protecting the supply of substrate and cofactors for endothelial NO synthase, preserving the presence and activity of the enzyme and reducing reactive oxygen species generation. Common achievers of such improvement include maintained levels of estrogens and increased production of adiponectin and induction of silent mating-type information regulation 2 homologue 1. Obviously, endothelium-dependent relaxations are not the only beneficial action of NO in the vascular wall. Thus, reduced NO-mediated responses precede and initiate the atherosclerotic process.

Endoplasmic reticulum stress and the development of endothelial dysfunction

The vascular endothelium plays a critical role in cardiovascular homeostasis, and thus identifying the underlying causes of endothelial dysfunction has important clinical implications. In this regard, the endoplasmic reticulum (ER) has recently emerged as an important regulator of metabolic processes. Dysfunction within the ER, broadly termed ER stress, evokes the unfolded protein response (UPR), an adaptive pathway that aims to restore ER homeostasis. Although the UPR is the first line of defense against ER stress, chronic activation of the UPR leads to cell dysfunction and death and has recently been implicated in the pathogenesis of endothelial dysfunction. Numerous risk factors for endothelial dysfunction can induce ER stress, which may in turn disrupt endothelial function via direct effects on endothelium-derived vasoactive substances or by activating other pathogenic cellular networks such as inflammation and oxidative stress. This review summarizes the available data linking ER stress to endothelial dysfunction.

Role of endoplasmic reticulum stress in endothelial dysfunction

AIM

Endoplasmic reticulum (ER) stress is implicated in the pathogenesis of several human disorders, including cardiovascular disease (CVD). CVD recognizes endothelial dysfunction (ED) as its pathogenetic primum movens; interestingly a large body of evidence has identified the unchecked ER stress response as a main actor in vascular damage elicited by various cardio-metabolic risk factors. In the present Review, we summarize findings from experimental studies on the ER stress-related ED, focusing on the mechanisms underlying this association.

DATA SYNTHESIS

Different noxious agents, such as hyperhomocysteinemia, hyperlipidemia, hyperglycemia and chronic inflammation, induce ED promoting an amplified ER stress response as demonstrated by several studies in animal models, as well as in human primary and immortalized endothelial cells. ER stress represents therefore a key mediator of vascular damage, operating in a setting of increased inflammatory burden and oxidative stress, thus contributing to foster a vicious pathogenic cycle.

CONCLUSIONS

Experimental studies summarized in this Review strongly suggest that an unchecked ER stress response plays a central role in the pathogenesis of ED and, consequently, CVD. Counteracting ER stress may thus represent a promising, even if largely unexplored as-yet, therapeutic approach aimed to prevent vascular damage, slowing the progression from ED to cardiovascular events.

Insulin resistance: vascular function and exercise

Insulin resistance associated with metabolic syndrome and Type 2 diabetes mellitus is an epidemic metabolic disorder, which increases the risk of cardiovascular complications. Impaired vascular endothelial function is an early marker for atherosclerosis, which causes cardiovascular complications. Both experimental and clinical studies indicate that endothelial dysfunction in vasculatures occurs with insulin resistance. The associated physiological mechanisms are not fully appreciated yet, however, it seems that augmented oxidative stress, a physiological imbalance between oxidants and antioxidants, in vascular cells is a possible mechanism involved in various vascular beds with insulin resistance and hyperglycemia. Regardless of the inclusion of resistance exercise, aerobic exercise seems to be beneficial for vascular endothelial function in both large conduit and small resistance vessels in both clinical and experimental studies with insulin resistance. In clinical cases, aerobic exercise over 8 weeks with higher intensity seems more beneficial than the cases with shorter duration and lower intensity. However, more studies are needed in the future to elucidate the physiological mechanisms by which vascular endothelial function is impaired in insulin resistance and improved with aerobic exercise.