PPARδ Is Required for Exercise to Attenuate Endoplasmic Reticulum Stress and Endothelial Dysfunction in Diabetic Mice

Pharmacological basis and new insights of resveratrol action in the cardiovascular system

Resveratrol (trans-3,4',5-trihydroxystilbene) belongs to the family of natural phytoalexins. Resveratrol first came to our attention in 1992, following reports of the cardioprotective effects of red wine. Thereafter, resveratrol was shown to exert antioxidant, anti-inflammatory, anti-proliferative, and angio-regulatory effects against atherosclerosis, ischaemia, and cardiomyopathy. This article critically reviews the current findings on the molecular basis of resveratrol-mediated cardiovascular benefits, summarizing the broad effects of resveratrol on longevity regulation, energy metabolism, stress resistance, exercise mimetics, circadian clock, and microbiota composition. In addition, this article also provides an update, both preclinically and clinically, on resveratrol-induced cardiovascular protection and discusses the adverse and inconsistent effects of resveratrol reported in both preclinical and clinical studies. Although resveratrol has been claimed as a master anti-aging agent against several age-associated diseases, further detailed mechanistic investigation is still required to thoroughly unravel the therapeutic value of resveratrol against cardiovascular diseases at different stages of disease development. LINKED ARTICLES: This article is part of a themed section on The Pharmacology of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.6/issuetoc.

Omentin-1 protects against high glucose-induced endothelial dysfunction via the AMPK/PPARδ signaling pathway

High glucose-induced endothelial dysfunction is a critical initiating factor in the development of diabetic vascular complications. Omentin-1 has been regarded as a novel biomarker of endothelial function in subjects with type-2 diabetes (T2D); however, it is unclear whether omentin-1 has any direct effect in ameliorating high glucose-induced endothelial dysfunction. In the present study, we analyzed the effect of omentin-1 on high glucose-induced endothelial dysfunction in isolated mouse aortas and mouse aortic endothelial cells (MAECs). Vascular reactivity in aortas was measured using wire myography. The expression levels of AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor δ (PPARδ), Akt, endothelial nitric-oxide synthase (eNOS), and endoplasmic reticulum (ER)-stress markers in MAECs were determined by Western blotting. The production of reactive oxygen species (ROS) and nitric oxide (NO) was assessed by diluted fluoroprobe, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) and 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM DA), respectively. We found that ex vivo treatment with omentin-1 reversed impaired endothelial-dependent relaxations (EDR) in mouse aortas after high-glucose insult. Elevated ER-stress markers, oxidative stress, and reduction of NO production induced by high glucose in MAECs were reversed by omentin-1 treatment. Omentin-1 also effectively reversed tunicamycin-induced ER stress responses in MAECs, as well as ameliorated impairment of endothelial-dependent relaxation in mouse aortas. Moreover, omentin-1 increased AMPK phosphorylation with a subsequent increase in PPARδ expression, while also restoring the decreased phosphorylation of Akt and eNOS. The effects of omentin-1 were abolished by cotreatment of compound C (AMPK inhibitor) and GSK0660 (PPARδ antagonist). These data indicate that omentin-1 protects against high glucose-induced vascular-endothelial dysfunction through inhibiting ER stress and oxidative stress and increasing NO production via activation of AMPK/PPARδ pathway.

Endoplasmic Reticulum Stress and Mitochondrial Function in Airway Smooth Muscle

Inflammatory airway diseases such as asthma affect more than 300 million people world-wide. Inflammation triggers pathophysiology via such as tumor necrosis factor α (TNFα) and interleukins (e.g., IL-13). Hypercontraction of airway smooth muscle (ASM) and ASM cell proliferation are major contributors to the exaggerated airway narrowing that occurs during agonist stimulation. An emergent theme in this context is the role of inflammation-induced endoplasmic reticulum (ER) stress and altered mitochondrial function including an increase in the formation of reactive oxygen species (ROS). This may establish a vicious cycle as excess ROS generation leads to further ER stress. Yet, it is unclear whether inflammation-induced ROS is the major mechanism leading to ER stress or the consequence of ER stress. In various diseases, inflammation leads to an increase in mitochondrial fission (fragmentation), associated with reduced levels of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2). Mitochondrial fragmentation may be a homeostatic response since it is generally coupled with mitochondrial biogenesis and mitochondrial volume density thereby reducing demand on individual mitochondrion. ER stress is triggered by the accumulation of unfolded proteins, which induces a homeostatic response to alter protein balance via effects on protein synthesis and degradation. In addition, the ER stress response promotes protein folding via increased expression of molecular chaperone proteins. Reduced Mfn2 and altered mitochondrial dynamics may not only be downstream to ER stress but also upstream such that a reduction in Mfn2 triggers further ER stress. In this review, we summarize the current understanding of the link between inflammation-induced ER stress and mitochondrial function and the role played in the pathophysiology of inflammatory airway diseases.

Imbalance of ER and Mitochondria Interactions: Prelude to Cardiac Ageing and Disease?

Cardiac disease is still the leading cause of morbidity and mortality worldwide, despite some exciting and innovative improvements in clinical management. In particular, atrial fibrillation (AF) and heart failure show a steep increase in incidence and healthcare costs due to the ageing population. Although research revealed novel insights in pathways driving cardiac disease, the exact underlying mechanisms have not been uncovered so far. Emerging evidence indicates that derailed proteostasis (i.e., the homeostasis of protein expression, function and clearance) is a central component driving cardiac disease. Within proteostasis derailment, key roles for endoplasmic reticulum (ER) and mitochondrial stress have been uncovered. Here, we describe the concept of ER and mitochondrial stress and the role of interactions between the ER and mitochondria, discuss how imbalance in the interactions fuels cardiac ageing and cardiac disease (including AF), and finally assess the potential of drugs directed at conserving the interaction as an innovative therapeutic target to improve cardiac function.

Free fatty acid-induced H2O2 activates TRPM2 to aggravate endothelial insulin resistance via Ca2+-dependent PERK/ATF4/TRB3 cascade in obese mice

Transient Receptor Potential Melastatin-2 (TRPM2) is a nonselective cation channel mediating Ca²⁺ influx in response to oxidative stress. Given that insulin resistance-related endothelial dysfunction in obesity attributes to fatty-acid-induced reactive oxygen species (ROS) overproduction, in this study, we addressed the possible role of TRPM2 in obesity-related endothelial insulin resistance and the underlying mechanisms. Whole-cell patch clamp technique, intracellular Ca²⁺ concentration measurement, western blot, vasorelaxation assay, and high-fat diet (HFD)-induced obese model were employed to assess the relationship between TRPM2 and endothelial insulin response. We found that both the expression and activity of TRPM2 were higher in endothelial cells of obese mice. Palmitate rose a cationic current in endothelial cells which was inhibited or enlarged by TRPM2 knockdown or overexpression. Silencing of TRPM2 remarkably improved insulin-induced endothelial Akt activation, nitric oxide synthase (eNOS) phosphorylation and nitric oxide (NO) production, while TRPM2 overexpression resulted in the opposite effects. Furthermore, TRPM2-mediated Ca²⁺ entry, CaMKII activation and the following activation of PERK/ATF4/TRB3 cascade were involved in the mechanism of obesity or palmitate-induced endothelial insulin resistance. Notably, in vivo study, knockdown of TRPM2 with adeno-associated virus harboring short-hairpin RNA (shRNA) against TRPM2 alleviated endothelial insulin resistance and ameliorated endothelium-dependent vasodilatation in obese mice. Thus, these results suggest that TRPM2-activated Ca²⁺ signaling is necessary to induce insulin resistance-related endothelial dysfunction in obesity. Downregulation or pharmacological inhibition of TRPM2 channels may lead to the development of effective drugs for treatment of endothelial dysfunction associated with oxidative stress state.

Oxidative stress induced by palmitic acid modulates KCa2.3 channels in vascular endothelium

Elevated plasma free fatty acids level has been implicated in the development of insulin resistance, inflammation, and endothelial dysfunction in diabetic and nondiabetic individuals. However, the underlying mechanisms still remain to be defined. Herein, we investigated the effect of palmitic acid (PA), the most abundant saturated fatty acid in the human body, on small-conductance Ca²⁺-activated potassium channels (K_Ca2.3)-mediated relaxation in rodent resistance arteries and the underlying molecular mechanism. The effect of PA on K_Ca2.3 in endothelium was evaluated using real-time PCR, Western blotting, whole-cell patch voltage-clamp, wire and pressure myograph system, and reactive oxygen species (ROS) were measured by using dihydroethidium and 2', 7'-dichlorofluorescein diacetate. K_Ca2.3-mediated vasodilatation responses to acetylcholine and NS309 (agonist of K_Ca2.3 and K_Ca3.1) were impaired by incubation of normal mesenteric arteries with 100 μM PA for 24 h. In cultured human umbilical vein endothelial cells (HUVECs), PA decreased K_Ca2.3 current and expression at mRNA and protein levels. Incubation with the NADPH oxidase (Nox) inhibitor dibenziodolium (DPI) partly inhibited the PA-induced ROS production and restored K_Ca2.3 expression. Inhibition of either p38-MAPK or NF-κB using specific inhibitors (SB203580, SB202190 or Bay11-7082, pyrrolidinedithiocarbamate) attenuated PA-induced downregulation of K_Ca2.3 and inhibition of p38-MAPK also attenuated PA-induced phosphorylation of NF-κB p65. Furthermore, DPI reversed the increment of phospho-p38-MAPK by PA. These results demonstrated that PA downregulated K_Ca2.3 expressions via Nox/ROS/p38-MAPK/NF-κB signaling leading to endothelial vasodilatory dysfunction.

Exercise for Prevention and Relief of Cardiovascular Disease: Prognoses, Mechanisms, and Approaches

This review is aimed at summarizing the new findings about the multiple benefits of exercise on cardiovascular disease (CVD). We pay attention to the prevalence and risk factors of CVD and mechanisms and recommendations of physical activity. Physical activity can improve insulin sensitivity, alleviate plasma dyslipidemia, normalize elevated blood pressure, decrease blood viscosity, promote endothelial nitric oxide production, and improve leptin sensitivity to protect the heart and vessels. Besides, the protective role of exercise on the body involves not only animal models in the laboratory but also clinical studies which is demonstrated by WHO recommendations. The general exercise intensity for humans recommended by the American Heart Association to prevent CVD is moderate exercise of 30 minutes, 5 times a week. However, even the easiest activity is better than nothing. What is more, owing to the different physical fitness of individuals, a standard exercise training cannot provide the exact treatment for everyone. So personalization of exercise will be an irresistible trend and bring more beneficial effects with less inefficient physical activities. This paper reviews the benefits of exercise contributing to the body especially in CVD through the recent mechanism studies.

Endothelial TFEB (Transcription Factor EB) Restrains IKK (IκB Kinase)-p65 Pathway to Attenuate Vascular Inflammation in Diabetic db/db Mice

Objective—

TFEB (transcription factor EB) was recently reported to be induced by atheroprotective laminar flow and play an anti-atherosclerotic role by inhibiting inflammation in endothelial cells (ECs). This study aims to investigate whether TFEB regulates endothelial inflammation in diabetic db/db mice and the molecular mechanisms involved.

Approach and Results—

Endothelial denudation shows that TFEB is mainly expressed in ECs in mouse aortas. Western blotting shows TFEB total protein level decreases whereas the p-TFEB S142 (phosphorylated form of TFEB) increases in db/db mouse aortas, suggesting a decreased TFEB activity. Adenoviral TFEB overexpression reduces endothelial inflammation as evidenced by decreased expression of vascular inflammatory markers in db/db mouse aortas, and reduced expression of a wide range of adhesion molecules and chemokines in human umbilical vein ECs. Monocyte attachment assay shows TFEB suppresses monocyte adhesion to human umbilical vein ECs. RNA sequencing of TFEB-overexpressed human umbilical vein ECs suggested TFEB inhibits NF-κB (nuclear factor-kappa B) signaling. Indeed, luciferase assay shows TFEB suppresses NF-κB transcriptional activity. Mechanistically, TFEB suppresses IKK (IκB kinase) activity to protect IκB-α from degradation, leading to reduced p65 nuclear translocation. Inhibition of IKK by PS-1145 abolished TFEB silencing-induced inflammation in human umbilical vein ECs. Lastly, we identified KLF2 (Krüppel-like factor 2) upregulates TFEB expression and promoter activity. Laminar flow experiment showed that KLF2 is required for TFEB induction by laminar flow and TFEB is an anti-inflammatory effector downstream of laminar flow-KLF2 signaling in ECs.

Conclusions—

These findings suggest that TFEB exerts anti-inflammatory effects in diabetic mice and such function in ECs is achieved by inhibiting IKK activity and increasing IκBα level to suppress NF-κB activity. KLF2 mediates TFEB upregulation in response to laminar flow.

Gymnemic acid alleviates inflammation and insulin resistance via PPARδ- and NFκB-mediated pathways in db/db mice

GA ameliorates obesity-induced inflammation and IR via PPARδ- and NFκB-mediated signaling in the liver, skeletal muscle and adipose tissue of db/db mice.

The Role of PPAR-δ in Metabolism, Inflammation, and Cancer: Many Characters of a Critical Transcription Factor

Peroxisome proliferator-activated receptor-delta (PPAR-δ), one of three members of the PPAR group in the nuclear receptor superfamily, is a ligand-activated transcription factor. PPAR-δ regulates important cellular metabolic functions that contribute to maintaining energy balance. PPAR-δ is especially important in regulating fatty acid uptake, transport, and β-oxidation as well as insulin secretion and sensitivity. These salutary PPAR-δ functions in normal cells are thought to protect against metabolic-syndrome-related diseases, such as obesity, dyslipidemia, insulin resistance/type 2 diabetes, hepatosteatosis, and atherosclerosis. Given the high clinical burden these diseases pose, highly selective synthetic activating ligands of PPAR-δ were developed as potential preventive/therapeutic agents. Some of these compounds showed some efficacy in clinical trials focused on metabolic-syndrome-related conditions. However, the clinical development of PPAR-δ agonists was halted because various lines of evidence demonstrated that cancer cells upregulated PPAR-δ expression/activity as a defense mechanism against nutritional deprivation and energy stresses, improving their survival and promoting cancer progression. This review discusses the complex relationship between PPAR-δ in health and disease and highlights our current knowledge regarding the different roles that PPAR-δ plays in metabolism, inflammation, and cancer.

Long Noncoding RNA LINC01619 Regulates MicroRNA-27a/Forkhead Box Protein O1 and Endoplasmic Reticulum Stress-Mediated Podocyte Injury in Diabetic Nephropathy

AIMS

Altered activities of long noncoding RNAs (lncRNAs) have been implicated in the regulation of microRNAs. microRNA-27a (miR-27a) upregulation has been shown to induce endoplasmic reticulum (ER) stress podocyte injury in diabetic nephropathy (DN). Herein, we aim to interrogate the mutually regulated network of miR-27a with long intergenic noncoding RNA 1619 (LINC01619) and the target gene.

RESULTS

LINC01619 downregulation was found in human DN renal biopsy tissues and contributed to proteinuria and diminished renal function. LINC01619 was expressed in podocyte cytoplasm and involved in ER stress signaling pathway. LINC01619 exerted biological function by serving as a "sponge" for miR-27a, which negatively targeted forkhead box protein O1 (FOXO1) and activated ER stress. In diabetic rats and high-glucose cultured podocytes, LINC01619 triggered oxidative stress and podocyte injuries as demonstrated by increased apoptosis, diffuse podocyte foot process effacement, and decreased renal function. Innovation and Conclusion: This study demonstrates that LINC01619 functions as a competing endogenous RNA and regulates miR-27a/FOXO1-mediated ER stress and podocyte injury in DN. Antioxid. Redox Signal. 29, 355-376.

Exercise ameliorates endoplasmic reticulum stress-mediated vascular dysfunction in mesenteric arteries in atherosclerosis

Endoplasmic reticulum (ER) stress is closely associated with atherosclerosis, but the effects of exercise on ER stress-mediated endothelial dysfunction in atherosclerosis is not yet fully understood. We assessed endothelium-dependent vasodilation in isolated mesenteric arteries from wild type (WT), WT with exercise (WT-EX), ApoE knockout (ApoE KO), and ApoE KO mice with exercise (ApoE KO-EX). Vasodilation to acetylcholine (ACh) was elicited in the presence of inhibitors of ER stress, eNOS, caspase-1, and UCP-2 (Tudca, L-NAME, AC-YVARD-cmk, and Genipin, respectively) and the ER stress inducer (Tunicamycin). Immunofluorescence was used to visualize the expression of CHOP, as an indicator of ER stress, in superior mesenteric arteries (SMA). Dilation to ACh was attenuated in ApoE KO but was improved in ApoE KO-EX. Incubation of Tudca and AC-YVARD-cmk improved ACh-induced vasodilation in ApoE KO. L-NAME, tunicamycin, and Genipin attenuated vasodilation in WT, WT-EX and ApoE KO-EX, but not in ApoE KO. Exercise training reversed the increase in CHOP expression in the endothelium of SMA of ApoE KO mice. We conclude that ER stress plays a significant role in endothelial dysfunction of resistance arteries in atherosclerosis and that exercise attenuates ER stress and regulates its critical downstream signaling pathways including eNOS, UCP-2 and caspase-1.

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.

Retracted Article: Ligustrazine attenuates renal damage by inhibiting endoplasmic reticulum stress in diabetic nephropathy by inactivating MAPK pathways

Diabetic nephropathy (DN) is a major cause of chronic kidney disease around the world.

Protein aggregation, cardiovascular diseases, and exercise training: Where do we stand?

Cells ensure their protein quality control through the proteostasis network. Aging and age-related diseases, such as neurodegenerative and cardiovascular diseases, have been associated to the reduction of proteostasis network efficiency and, consequently, to the accumulation of protein misfolded aggregates. The decline in protein homeostasis has been associated with the development and progression of atherosclerotic cardiovascular disease, cardiac hypertrophy, cardiomyopathies, and heart failure. Exercise training is a key component of the management of patients with cardiovascular disease, consistently improving quality of life and prognosis. In this review, we give an overview on age-related protein aggregation, the role of the increase of misfolded protein aggregates on cardiovascular pathophysiology, and describe the beneficial or deleterious effects of the proteostasis network on the development of cardiovascular disease. We subsequently discuss how exercise training, a key lifestyle intervention in those with cardiovascular disease, could restore proteostasis and improve disease status.

Effects of intermittent ladder-climbing exercise training on mitochondrial biogenesis and endoplasmic reticulum stress of the cardiac muscle in obese middle-aged rats

The aim of this study is to investigate the effects of intermittent ladder-climbing exercise training on mitochondrial biogenesis and ER stress of the cardiac muscle in high fat diet-induced obese middle-aged rats. We induced obesity over 6 weeks of period in 40 male Sprague-Dawley rats around 50 weeks old, and were randomly divided into four experimental groups: chow, HFD, exercise+HFD, and exercise+chow. The exercising groups underwent high-intensity intermittent training using a ladder-climbing and weight exercise 3 days/week for a total of 8 weeks. High-fat diet and concurrent exercise resulted in no significant reduction in body weight but caused a significant reduction in visceral fat weight (p<0.05). Expression of PPARδ increased in the exercise groups and was significantly increased in the high-fat diet+exercise group (p<0.05). Among the ER stress-related proteins, the expression levels of p-PERK and CHOP, related to cardiac muscle damage, were significantly higher in the cardiac muscle of the high-fat diet group (p<0.05), and were significantly reduced by intermittent ladder-climbing exercise training (p<0.05). Specifically, this reduction was greater when the rats underwent exercise after switching back to the chow diet with a reduced caloric intake. Collectively, these results suggest that the combination of intermittent ladder-climbing exercise training and a reduced caloric intake can decrease the levels of ER stress-related proteins that contribute to cardiac muscle damage in obesity and aging. However, additional validation is required to understand the effects of these changes on mitochondrial biogenesis during exercise.

The Role of Endoplasmic Reticulum Stress in Cardiovascular Disease and Exercise

Endoplasmic reticulum (ER) stress, which is highly associated with cardiovascular disease, is triggered by a disturbance in ER function because of protein misfolding or an increase in protein secretion. Prolonged disruption of ER causes ER stress and activation of the unfolded protein response (UPR) and leads to various diseases. Eukaryotic cells respond to ER stress via three major sensors that are bound to the ER membrane: activating transcription factor 6 (ATF6), inositol-requiring protein 1α (IRE1α), and protein kinase RNA-like ER kinase (PERK). Chronic activation of ER stress causes damage in endothelial cells (EC) via apoptosis, inflammation, and oxidative stress signaling pathways. The alleviation of ER stress has recently been accepted as a potential therapeutic target to treat cardiovascular diseases such as heart failure, hypertension, and atherosclerosis. Exercise training is an effective nonpharmacological approach for preventing and alleviating cardiovascular disease. We here review the recent viewing of ER stress-mediated apoptosis and inflammation signaling pathways in cardiovascular disease and the role of exercise in ER stress-associated diseases.

NGF Attenuates High Glucose-Induced ER Stress, Preventing Schwann Cell Apoptosis by Activating the PI3K/Akt/GSK3β and ERK1/2 Pathways

Diabetic peripheral neuropathy (DPN) is one of the most common and troublesome complications of diabetes mellitus. It has been demonstrated that nerve growth factor (NGF) exerts a pivotal role in the regulation of neuronal growth and the promotion of DPN recovery. However, the exact molecular mechanisms are not well understood. Recent studies have indicated that as a novel therapeutic target, endoplasmic reticulum (ER) stress participates in the onset and progression of DPN. In the present study, it has been demonstrated that NGF prevents the sciatic nerve from degeneration and demyelination in DPN rats. Thus, RSC 96 cells, which retain the characteristic features of Schwann cells (SCs), were cultured in medium containing 30 mM glucose (high glucose, HG) to mimic SCs in DPN mice. The 50-ng/ml dose of NGF was identified to be the optimal concentration for treating an excessive ER stress level under HG conditions for 24 h. We found that NGF treatment significantly inhibits HG-induced ER stress and subsequently suppresses ER-related apoptosis. Further, NGF administration also activates the upstream signaling pathway of ER stress, PI3K/Akt/GSK3β signaling and ERK1/2 signaling. Co-treatment with the PI3K inhibitor LY294002 or ERK1/2 inhibitor U0126 significantly reverses the protective role of NGF on HG-induced excessive ER stress and subsequent apoptosis. These observations suggest that the neuroprotective role of NGF in DPN is mediated by the inhibition of excessive ER stress via the activation of the PI3K/Akt/GSK3β and ERK1/2 signaling pathways.