Endoplasmic reticulum stress and diabetic cardiomyopathy

Cardioprotective effects of liposomal resveratrol in diabetic rats: unveiling antioxidant and anti-inflammatory benefits

As a consequence of chronic hyperglycemia, diabetes complications and tissue damage are exacerbated. There is evidence that natural phytochemicals, including resveratrol, a bioactive polyphenol, may be able to reduce oxidative stress and improve insulin sensitivity. However, resveratrol's limited bioavailability hampers its therapeutic effectiveness. By using liposomes, resveratrol may be better delivered into the body and be more bioavailable. The objective of this study was to assess the cardioprotective potential of liposome-encapsulated resveratrol (LR) in a streptozotocin-induced (STZ) diabetic rat model. Adult male Wistar rats were categorized into five groups: control, diabetic, resveratrol-treated (40 mg/kg), liposomal resveratrol (LR)-treated (20 mg/kg) and liposomal resveratrol (LR)-treated (40 mg/kg) for a five-week study period. We compared the effects of LR to those of resveratrol (40 mg/kg) on various parameters, including serum levels of cardiac markers, tissue levels of pro-inflammatory cytokines, nuclear transcription factor, oxidative stress markers, and apoptotic markers. LR treatment in STZ-diabetic rats resulted in notable physiological improvements, including blood glucose regulation, inflammation reduction, oxidative stress mitigation, and apoptosis inhibition. LR effectively lowered oxidative stress and enhanced cardiovascular function. It also demonstrated a remarkable ability to suppress NF-kB-mediated inflammation by inhibiting the pro-inflammatory cytokines TNF-α and IL-6. Additionally, LR restored the antioxidant enzymes, catalase and glutathione peroxidase, thereby effectively counteracting oxidative stress. Notably, LR modulated apoptotic regulators, including caspase, Bcl2, and Bax, suggesting a role in regulating programmed cell death. These biochemical alterations were consistent with improved structural integrity of cardiac tissue as revealed by histological examination. In comparison, resveratrol exhibited lower efficacy at an equivalent dosage. Liposomal resveratrol shows promise in alleviating hyperglycemia-induced cardiac damage in diabetes. Further research is warranted to explore its potential as a therapeutic agent for diabetic cardiovascular complications and possible cardioprotective effects.

PDZD8 Augments Endoplasmic Reticulum-Mitochondria Contact and Regulates Ca2+ Dynamics and Cypd Expression to Induce Pancreatic β-Cell Death during Diabetes

BACKGRUOUND

Diabetes mellitus (DM) is a chronic metabolic disease that poses serious threats to human physical and mental health worldwide. The PDZ domain-containing 8 (PDZD8) protein mediates mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) formation in mammals. We explored the role of PDZD8 in DM and investigated its potential mechanism of action.

METHODS

High-fat diet (HFD)- and streptozotocin-induced mouse DM and palmitic acid (PA)-induced insulin 1 (INS-1) cell models were constructed. PDZD8 expression was detected using immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. MAM formation, interactions between voltage-dependent anion-selective channel 1 (VDAC1) and inositol 1,4,5-triphosphate receptor type 1 (IP3R1), pancreatic β-cell apoptosis and proliferation were detected using transmission electron microscopy (TEM), proximity ligation assay (PLA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, immunofluorescence staining, and Western blotting. The mitochondrial membrane potential, cell apoptosis, cytotoxicity, and subcellular Ca2+ localization in INS-1 cells were detected using a JC-1 probe, flow cytometry, and an lactate dehydrogenase kit.

RESULTS

PDZD8 expression was up-regulated in the islets of HFD mice and PA-treated pancreatic β-cells. PDZD8 knockdown markedly shortened MAM perimeter, suppressed the expression of MAM-related proteins IP3R1, glucose-regulated protein 75 (GRP75), and VDAC1, inhibited the interaction between VDAC1 and IP3R1, alleviated mitochondrial dysfunction and ER stress, reduced the expression of ER stress-related proteins, and decreased apoptosis while increased proliferation of pancreatic β-cells. Additionally, PDZD8 knockdown alleviated Ca2+ flow into the mitochondria and decreased cyclophilin D (Cypd) expression. Cypd overexpression alleviated the promoting effect of PDZD8 knockdown on the apoptosis of β-cells.

CONCLUSION

PDZD8 knockdown inhibited pancreatic β-cell death in DM by alleviated ER-mitochondria contact and the flow of Ca2+ into the mitochondria.

Cardioprotective effects of GPER agonist in ovariectomized diabetic rats: reversing ER stress and structural changes

The incidence of diabetic cardiomyopathy (DCM) significantly increases in postmenopausal women, suggesting protective roles of estrogen. Excessive endoplasmic reticulum (ER) stress alters myocardial structure, which plays a crucial role in DCM. The G protein-coupled estrogen receptor (GPER) has been demonstrated to have cardioprotective effects, but it remains unclear whether these effects involve the amelioration of structural changes induced by ER stress. The objective of this study was to determine whether GPER can prevent cardiac structural changes by attenuating ER stress. Female ovariectomized (OVX) rats were divided into three groups: OVX, OVX + T2D, and OVX + T2D + G1. T2D was induced by a high-fat diet, and streptozotocin and G1, a GPER agonist, were administered for 6 weeks. Finally, histological changes of the myocardium were examined and the expression of sarcoplasmic reticulum calcium ATPase (SERCA2α), GRP78 as an ER stress marker, and apoptotic signalings were determined by Western blot. We observed that the induction of T2D resulted in an increased cardiac weight index, left ventricular wall thickness, and myocyte diameter. However, GPER activation reversed these changes. T2D increased cardiac protein levels of GRP78, caspase-12, and Bax, while decreasing levels of SERCA2α and Bcl-2. Nevertheless, GPER activation reduced the expression of GRP78 in OVX + T2D rats. Furthermore, GPER activation significantly reduced cardiac caspase-12 and Bax levels and increased SERCA2α and Bcl-2 expression. In conclusion, our data suggest that GPER activation ameliorates DCM by inhibiting ER stress-induced cardiac structural changes. These findings provide a new potential target for therapeutic intervention and drug discovery specifically tailored for postmenopausal diabetic women.

The detrimental role of galectin-3 and endoplasmic reticulum stress in the cardiac consequences of myocardial ischemia in the context of obesity

The association between cardiac fibrosis and galectin-3 was evaluated in patients with acute myocardial infarction (MI). The role of galectin-3 and its association with endoplasmic reticulum (ER) stress activation in the progression of cardiovascular fibrosis was also evaluated in obese-infarcted rats. The inhibitor of galectin-3 activity, modified citrus pectin (MCP; 100 mg/kg/day), and the inhibitor of the ER stress activation, 4-phenylbutyric acid (4-PBA; 500 mg/kg/day), were administered for 4 weeks after MI in obese rats. Overweight-obese patients who suffered a first MI showed higher circulating galectin-3 levels, higher extracellular volume, and LV infarcted size, as well as lower E/e'ratio and LVEF compared with normal-weight patients. A correlation was observed between galectin-3 levels and extracellular volume. Obese-infarcted animals presented cardiac hypertrophy and reduction in LVEF, and E/A ratio as compared with control animals. They also showed an increase in galectin-3 gene expression, as well as cardiac fibrosis and reduced autophagic flux. These alterations were associated with ER stress activation characterized by enhanced cardiac levels of binding immunoglobulin protein, which were correlated with those of galectin-3. Both MCP and 4-PBA not only reduced cardiac fibrosis, oxidative stress, galectin-3 levels, and ER stress activation, but also prevented cardiac functional alterations and ameliorated autophagic flux. These results show the relevant role of galectin-3 in the development of diffuse fibrosis associated with MI in the context of obesity in both the animal model and patients. Galectin-3 in tandem with ER stress activation could modulate different downstream mechanisms, including inflammation, oxidative stress, and autophagy.

Alcohol Intake Provoked Cardiomyocyte Apoptosis Via Activating Calcium-Sensing Receptor and Increasing Endoplasmic Reticulum Stress and Cytosolic [Ca2+]i

BACKGROUND

Cardiomyocyte apoptosis plays an important role in alcoholic cardiac injury. However, the association between calcium-sensing receptor (CaSR) and alcohol-induced cardiomyocyte apoptosis remain unclear. Therefore, we investigated the role and its moleculer mechanism of CaSR in rat cardiomyocyte apoptosis induced by alcohol.

METHODS

Alcohol-induced cardiomyocyte apoptosis in vivo and in vitro model of rats were applied in this study. The expression of CaSR, endoplasmic reticulum stress markers and apoptosis were tested by immunohistological staining, western blot, TUNEL and flow cytometry, respectively. [Ca2+]i were detected by confocal laser scanning microscopy.

RESULTS

Compared with the control group, alcohol intake (AI) led to abnormal arrangements of cardiomyocytes and obvious increase of myocardial apoptosis. Moreover, AI also significantly upregulated protein expression of CaSR, GRP94, caspase-12 and CHOP. Alcohol induced apoptosis of cultured cardiomyocytes of rats in a dose-dependent way. Activation of CaSR markedly enhanced cardiomyocyte apoptosis and ERS induced by alcohol, ERS inducer also significantly increased cardiomyocyte apoptosis without activating CaSR. Furthermore, GdCl3 augmented alcohol-induced increase of [Ca2+]i in cardiomyocytes, which was attenuated by NPS2390 but not 4-PBA pre-treatment.

CONCLUSIONS

Alcohol could induce cardiomyocyte apoptosis in rats in vivo and in vitro, which was mediated probably via activating CaSR, and then ERS and the increase of the cytosolic [Ca2+]i. This provides a potential target for preventing cardiomyocyte apoptosis and cardiomyopathy induced by alochol.

Chinese herbal medicine and active ingredients for diabetic cardiomyopathy: molecular mechanisms regulating endoplasmic reticulum stress

Background: Diabetic cardiomyopathy (DCM) is one of the serious microvascular complications of diabetes mellitus. It is often associated with clinical manifestations such as arrhythmias and heart failure, and significantly reduces the quality of life and years of survival of patients. Endoplasmic reticulum stress (ERS) is the removal of unfolded and misfolded proteins and is an important mechanism for the maintenance of cellular homeostasis. ERS plays an important role in the pathogenesis of DCM by causing cardiomyocyte apoptosis, insulin resistance, calcium imbalance, myocardial hypertrophy and fibrosis. Targeting ERS is a new direction in the treatment of DCM. A large number of studies have shown that Chinese herbal medicine and active ingredients can significantly improve the clinical outcome of DCM patients through intervention in ERS and effects on myocardial structure and function, which has become one of the hot research directions. Purpose: The aim of this review is to elucidate and summarize the roles and mechanisms of Chinese herbal medicine and active ingredients that have the potential to modulate endoplasmic reticulum stress, thereby contributing to better management of DCM. Methods: Databases such as PubMed, Web of Science, China National Knowledge Internet, and Wanfang Data Knowledge Service Platform were used to search, analyze, and collect literature, in order to review the mechanisms by which phytochemicals inhibit the progression of DCM by targeting the ERS and its key signaling pathways. Keywords used included "diabetic cardiomyopathy" and "endoplasmic reticulum stress." Results: This review found that Chinese herbs and their active ingredients can regulate ERS through IRE1, ATF6, and PERK pathways to reduce cardiomyocyte apoptosis, ameliorate myocardial fibrosis, and attenuate myocardial hypertrophy for the treatment of DCM. Conclusion: A comprehensive source of information on potential ERS inhibitors is provided in this review. The analysis of the literature suggests that Chinese herbal medicine and its active ingredients can be used as potential drug candidates for the treatment of DCM. In short, we cannot ignore the role of traditional Chinese medicine in regulating ERS and treating DCM, and look forward to more research and new drugs to come.

Transcription factor EB: A potential integrated network regulator in metabolic-associated cardiac injury

With the worldwide pandemic of metabolic diseases, such as obesity, diabetes, and non-alcoholic fatty liver disease (NAFLD), cardiometabolic disease (CMD) has become a significant cause of death in humans. However, the pathophysiology of metabolic-associated cardiac injury is complex and not completely clear, and it is important to explore new strategies and targets for the treatment of CMD. A series of pathophysiological disturbances caused by metabolic disorders, such as insulin resistance (IR), hyperglycemia, hyperlipidemia, mitochondrial dysfunction, oxidative stress, inflammation, endoplasmic reticulum stress (ERS), autophagy dysfunction, calcium homeostasis imbalance, and endothelial dysfunction, may be related to the incidence and development of CMD. Transcription Factor EB (TFEB), as a transcription factor, has been extensively studied for its role in regulating lysosomal biogenesis and autophagy. Recently, the regulatory role of TFEB in other biological processes, including the regulation of glucose homeostasis, lipid metabolism, etc. has been gradually revealed. In this review, we will focus on the relationship between TFEB and IR, lipid metabolism, endothelial dysfunction, oxidative stress, inflammation, ERS, calcium homeostasis, autophagy, and mitochondrial quality control (MQC) and the potential regulatory mechanisms among them, to provide a comprehensive summary for TFEB as a potential new therapeutic target for CMD.

Multi-omics analysis reveals attenuation of cellular stress by empagliflozin in high glucose-treated human cardiomyocytes

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors constitute the gold standard treatment for type 2 diabetes mellitus (T2DM). Among them, empagliflozin (EMPA) has shown beneficial effects against heart failure. Because cardiovascular diseases (mainly diabetic cardiomyopathy) are the leading cause of death in diabetic patients, the use of EMPA could be, simultaneously, cardioprotective and antidiabetic, reducing the risk of death from cardiovascular causes and decreasing the risk of hospitalization for heart failure in T2DM patients. Interestingly, recent studies have shown that EMPA has positive benefits for people with and without diabetes. This finding broadens the scope of EMPA function beyond glucose regulation alone to include a more intricate metabolic process that is, in part, still unknown. Similarly, this significantly increases the number of people with heart diseases who may be eligible for EMPA treatment.

METHODS

This study aimed to clarify the metabolic effect of EMPA on the human myocardial cell model by using orthogonal metabolomics, lipidomics, and proteomics approaches. The untargeted and multivariate analysis mimicked the fasting blood sugar level of T2DM patients (hyperglycemia: HG) and in the average blood sugar range (normal glucose: NG), with and without the addition of EMPA.

RESULTS

Results highlighted that EMPA was able to modulate and partially restore the levels of multiple metabolites associated with cellular stress, which were dysregulated in the HG conditions, such as nicotinamide mononucleotide, glucose-6-phosphate, lactic acid, FA 22:6 as well as nucleotide sugars and purine/pyrimidines. Additionally, EMPA regulated the levels of several lipid sub-classes, in particular dihydroceramide and triacylglycerols, which tend to accumulate in HG conditions resulting in lipotoxicity. Finally, EMPA counteracted the dysregulation of endoplasmic reticulum-derived proteins involved in cellular stress management.

CONCLUSIONS

These results could suggest an effect of EMPA on different metabolic routes, tending to rescue cardiomyocyte metabolic status towards a healthy phenotype.

The role of circadian clock-controlled mitochondrial dynamics in diabetic cardiomyopathy

Diabetes mellitus is a metabolic disease with a high prevalence worldwide, and cardiovascular complications are the leading cause of mortality in patients with diabetes. Diabetic cardiomyopathy (DCM), which is prone to heart failure with preserved ejection fraction, is defined as a cardiac dysfunction without conventional cardiac risk factors such as coronary heart disease and hypertension. Mitochondria are the centers of energy metabolism that are very important for maintaining the function of the heart. They are highly dynamic in response to environmental changes through mitochondrial dynamics. The disruption of mitochondrial dynamics is closely related to the occurrence and development of DCM. Mitochondrial dynamics are controlled by circadian clock and show oscillation rhythm. This rhythm enables mitochondria to respond to changing energy demands in different environments, but it is disordered in diabetes. In this review, we summarize the significant role of circadian clock-controlled mitochondrial dynamics in the etiology of DCM and hope to play a certain enlightening role in the treatment of DCM.

Metal-Binding Proteins Cross-Linking with Endoplasmic Reticulum Stress in Cardiovascular Diseases

The endoplasmic reticulum (ER), an essential organelle in eukaryotic cells, is widely distributed in myocardial cells. The ER is where secreted protein synthesis, folding, post-translational modification, and transport are all carried out. It is also where calcium homeostasis, lipid synthesis, and other processes that are crucial for normal biological cell functioning are regulated. We are concerned that ER stress (ERS) is widespread in various damaged cells. To protect cells' function, ERS reduces the accumulation of misfolded proteins by activating the unfolded protein response (UPR) pathway in response to numerous stimulating factors, such as ischemia or hypoxia, metabolic disorders, and inflammation. If these stimulatory factors are not eliminated for a long time, resulting in the persistence of the UPR, it will aggravate cell damage through a series of mechanisms. In the cardiovascular system, it will cause related cardiovascular diseases and seriously endanger human health. Furthermore, there has been a growing number of studies on the antioxidative stress role of metal-binding proteins. We observed that a variety of metal-binding proteins can inhibit ERS and, hence, mitigate myocardial damage.

Apurinic/apyrimidinic endonuclease 1 regulates palmitic acid-mediated apoptosis in cardiomyocytes via endoplasmic reticulum stress

Cardiomyocyte apoptosis caused by fat metabolism disorder plays an essential role in the pathogenesis of diabetic cardiomyopathy (DCM). Apurinic/apyrimidinic endonuclease 1 (APE1) has multiple functions, including regulating redox and DNA repair. However, the role of APE1 in the pathogenesis of DCM remains unclear. To investigate the mechanism of APE1 on high-fat induced apoptosis in H9C2 cells, we treated H9C2 cells with palmitic acid (PA) as an apoptosis model caused by hyperlipidemia. We found that PA reduced the viability and increased apoptosis of H9C2 cells by inducing up-regulation of APE1 protein and endoplasmic reticulum (ER) stress. APE1 knockdown enhanced PA-induced apoptosis, and ER stress and overexpression of APE1 demonstrated the opposite effect. Furthermore, APE1 regulated PA-induced apoptosis via ER stress. The APE1 mutant (C65A, lack of redox regulation) loses its protective effect against ER stress and apoptosis. These findings indicate that APE1 protects PA-induced H9C2 cardiomyocyte apoptosis through ER stress via its redox-regulated function. This study provided new insights into the therapy for DCM.

Protein persulfidation: Rewiring the hydrogen sulfide signaling in cell stress response

The past few decades have witnessed significant progress in the discovery of hydrogen sulfide (H₂S) as a ubiquitous gaseous signaling molecule in mammalian physiology, akin to nitric oxide and carbon monoxide. As the third gasotransmitter, H₂S is now known to exert a wide range of physiological and cytoprotective functions in the biological systems. However, endogenous H₂S concentrations are usually low, and its potential biologic mechanisms responsible have not yet been fully clarified. Recently, a growing body of evidence has demonstrated that protein persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH) elicited by H₂S, is a fundamental mechanism of H₂S-mediated signaling pathways. Persulfidation, as a biological switch for protein function, plays an important role in the maintenance of cell homeostasis in response to various internal and external stress stimuli and is also implicated in numerous diseases, such as cardiovascular and neurodegenerative diseases and cancer. In this review, the biological significance of protein persulfidation by H₂S in cell stress response is reviewed providing a framework for understanding the multifaceted roles of H₂S. A mechanism-guided perspective can help open novel avenues for the exploitation of therapeutics based on H₂S-induced persulfidation in the context of diseases.

Lipoxin and glycation in SREBP signaling: Insight into diabetic cardiomyopathy and associated lipotoxicity

Diabetes and cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Diabetes increases cardiovascular risk through hyperglycemia and atherosclerosis. Chronic hyperglycemia accelerates glycation reaction, which forms advanced glycation end products (AGEs). Additionally, hyperglycemia with enhanced levels of cholesterol, native and oxidized low-density lipoproteins, free fatty acids, and oxidative stress induces lipotoxicity. Accelerated glycation and disturbed lipid metabolism are characteristic features of diabetic heart failure. SREBP signaling plays a significant role in lipid and glucose homeostasis. AGEs increase lipotoxicity in diabetic cardiomyopathy by inhibiting SREBP signaling. While anti-inflammatory lipid mediators, lipoxins resolve inflammation caused by lipotoxicity by upregulating the PPARγ expression and regulating CD36. PPARγ connects the bridge between glycation and lipoxin in SREBP signaling. A summary of treatment modalities against diabetic cardiomyopathy is given in brief. This review indicates the novel therapeutic approach in the crosstalk between glycation and lipoxin in SREBP signaling.

A comprehensive review of the novel therapeutic targets for the treatment of diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is characterized by structural and functional abnormalities in the myocardium affecting people with diabetes. Treatment of DCM focuses on glucose control, blood pressure management, lipid-lowering, and lifestyle changes. Due to limited therapeutic options, DCM remains a significant cause of morbidity and mortality in patients with diabetes, thus emphasizing the need to develop new therapeutic strategies. Ongoing research is aimed at understanding the underlying molecular mechanism(s) involved in the development and progression of DCM, including oxidative stress, inflammation, and metabolic dysregulation. The goal is to develope innovative pharmaceutical therapeutics, offering significant improvements in the clinical management of DCM. Some of these approaches include the effective targeting of impaired insulin signaling, cardiac stiffness, glucotoxicity, lipotoxicity, inflammation, oxidative stress, cardiac hypertrophy, and fibrosis. This review focuses on the latest developments in understanding the underlying causes of DCM and the therapeutic landscape of DCM treatment.

ER stress and calcium-dependent arrhythmias

The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca²⁺ that activates cardiomyocyte contractile machinery. Disturbances in finely-tuned SR Ca²⁺ release by SR Ca²⁺ channel ryanodine receptor (RyR2) and SR Ca²⁺ reuptake by SR Ca²⁺-ATPase (SERCa2a) not only impair contraction, but also contribute to cardiac arrhythmia trigger and reentry. Besides being the main Ca²⁺ storage organelle, SR in cardiomyocytes performs all the functions of endoplasmic reticulum (ER) in other cell types including protein synthesis, folding and degradation. In recent years ER stress has become recognized as an important contributing factor in many cardiac pathologies, including deadly ventricular arrhythmias. This brief review will therefore focus on ER stress mechanisms in the heart and how these changes can lead to pro-arrhythmic defects in SR Ca²⁺ handling machinery.

Multi-organ FGF21-FGFR1 signaling in metabolic health and disease

Metabolic syndrome is a chronic systemic disease that is particularly manifested by obesity, diabetes, and hypertension, affecting multiple organs. The increasing prevalence of metabolic syndrome poses a threat to public health due to its complications, such as liver dysfunction and cardiovascular disease. Impaired adipose tissue plasticity is another factor contributing to metabolic syndrome. Emerging evidence demonstrates that fibroblast growth factors (FGFs) are critical players in organ crosstalk via binding to specific FGF receptors (FGFRs) and their co-receptors. FGFRs activation modulates intracellular responses in various cell types under metabolic stress. FGF21, in particular is considered as the key regulator for mediating systemic metabolic effects by binding to receptors FGFR1, FGFR3, and FGFR4. The complex of FGFR1 and beta Klotho (β-KL) facilitates endocrine and paracrine communication networks that physiologically regulate global metabolism. This review will discuss FGF21-mediated FGFR1/β-KL signaling pathways in the liver, adipose, and cardiovascular systems, as well as how this signaling is involved in the interplay of these organs during the metabolic syndrome. Furthermore, the clinical implications and therapeutic strategies for preventing metabolic syndrome and its complications by targeting FGFR1/β-KL are also discussed.

Irisin alleviates high glucose-induced hypertrophy in H9c2 cardiomyoblasts by inhibiting endoplasmic reticulum stress

BACKGROUND

Endoplasmic reticulum stress (ERS) plays an important role in the process of myocardial hypertrophy in diabetic cardiomyopathy (DCM). Irisin, a novel cytokine, has been found to protect against cardiac diastolic dysfunction in DCM. We aimed to investigate the role of irisin in cardiac hypertrophy and to elucidate the underlying mechanisms.

METHODS

H9c2 cells were induced with 33 mM glucose to construct a cardiac hypertrophy cell model, which was then treated with irisin in the presence or absence of the ERS inducer tunicamycin (TM). The cell surface area was measured by FITC-phalloidin staining. The atrial natriuretic peptide levels were detected by an enzyme-linked immunosorbent assay. Furthermore, the expression of the ERS-related proteins, P-PERK, PERK, IRE1α and GRP78, was detected by western blotting.

RESULTS

Irisin significantly reduced myocardial hypertrophy and suppressed high glucose (HG)-induced oxidative stress. Meanwhile, the protective effect of irisin on cardiomyoblasts was reversed by the ERS inducer, TM. Additionally, we detected ERS-associated signaling pathway proteins and found that irisin significantly reduced the protein expression levels of GRP78 and p-PERK/PERK.

CONCLUSION

These results suggest that irisin ameliorates HG-induced cardiac hypertrophy by inhibiting ERS.

Importance of Autophagy in Mediating Cellular Responses to Iron Overload in Cardiomyocytes

Both iron overload and deficiency can promote development of cardiomyopathy. Advances in our knowledge from recent research have indicated numerous potential cellular mechanisms. Regulation of myocardial autophagy by iron is of particular interest and will be reviewed here. Autophagy is already well established to play a significant role in regulating the development of heart failure. This review will focus on regulation of autophagy by iron, crosstalk between autophagy and other cellular process which have also already been implicated in heart failure (oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, ferroptosis) and the therapeutic potential of targeting these interactions.

Glucose fluctuation promotes cardiomyocyte apoptosis by triggering endoplasmic reticulum (ER) stress signaling pathway in vivo and in vitro

Glucose fluctuation is more harmful than sustained hyperglycemia, but the effect on cardiomyocyte apoptosis have not yet been clarified. In this study, we aim to identify the effect of glucose fluctuation on cardiomyocyte apoptosis and explore the underlying mechanism. Sprague-Dawley rats were intraperitoneally injected with streptozotocin (STZ) and divided into three groups: controlled diabetic group (C-STZ); uncontrolled diabetic group (U-STZ) and glucose fluctuated diabetic group (GF-STZ). After twelve weeks, echocardiography, Hematoxylin-eosin (HE) staining, and Masson staining were adopted to assess the cardiac function and pathological changes. TUNEL staining was used to detect apoptotic cells. Expressions of apoptosis-related proteins and key molecules in the endoplasmic reticulum (ER) stress pathway were determined via western blots. Further, primary cardiomyocytes incubated in different glucose conditions were treated with the inhibitor of ER stress to explore the causative role of ER stress in glucose fluctuation-induced cardiomyocyte apoptosis. In vivo, we demonstrated that glucose fluctuation promoted cardiomyocyte apoptosis, and were more harmful to cardiomyocytes than sustained hyperglycemia. Moreover, glucose fluctuation significantly triggered ER stress signaling pathway. In vitro, primary cardiomyocyte apoptosis induced by glucose fluctuation and the activation of ER stress were significantly attenuated by 4-PBA, which is an ER stress inhibitor. Above all, glucose fluctuation can promote cardiomyocyte apoptosis through triggering the ER stress signaling pathway in diabetic rats and in primary cardiomyocytes.

Mitochondrial ROS in Slc4a11 KO Corneal Endothelial Cells Lead to ER Stress

Recent studies from Slc4a11 -/- mice have identified glutamine-induced mitochondrial dysfunction as a significant contributor toward oxidative stress, impaired lysosomal function, aberrant autophagy, and cell death in this Congenital Hereditary Endothelial Dystrophy (CHED) model. Because lysosomes are derived from endoplasmic reticulum (ER)-Golgi, we asked whether ER function is affected by mitochondrial ROS in Slc4a11 KO corneal endothelial cells. In mouse Slc4a11 -/- corneal endothelial tissue, we observed the presence of dilated ER and elevated expression of ER stress markers BIP and CHOP. Slc4a11 KO mouse corneal endothelial cells incubated with glutamine showed increased aggresome formation, BIP and GADD153, as well as reduced ER Ca2+ release as compared to WT. Induction of mitoROS by ETC inhibition also led to ER stress in WT cells. Treatment with the mitochondrial ROS quencher MitoQ, restored ER Ca2+ release and relieved ER stress markers in Slc4a11 KO cells in vitro. Systemic MitoQ also reduced BIP expression in Slc4a11 KO endothelium. We conclude that mitochondrial ROS can induce ER stress in corneal endothelial cells.

LCZ696 Protects against Diabetic Cardiomyopathy-Induced Myocardial Inflammation, ER Stress, and Apoptosis through Inhibiting AGEs/NF-κB and PERK/CHOP Signaling Pathways

The present study is designed to determine the effect of LCZ696 on DCM in rats and investigate the underlying mechanism involved. Diabetes was induced by feeding rats with a high-fat diet for six weeks following a single injection of STZ (30 mg/kg). Diabetic rats were divided into three groups (n = 10). LCZ696 and valsartan treatment was started two weeks after diabetic induction and continued for eight weeks. At the end of the treatment, serum and cardiac tissues were analyzed by RT-PCR, Western blot, and ELISA kits. LCZ696 and valsartan ameliorated DCM progression by inhibiting AGEs formation at activity levels; pro-apoptotic markers (BAX/Bcl2 ratio and caspase-3) in mRNA and protein expressions, the NF-κB at mRNA; and protein levels associated with the restoration of elevated proinflammatory cytokines such as the TNF-α, IL-6, and IL-1β at the activity level. Furthermore, LCZ696 and valsartan contribute to restoring the induction of ER stress parameters (GRP78, PERK, eIF2a, ATF4, and CHOP) at mRNA and protein levels. LCZ696 and valsartan attenuated DCM by inhibiting the myocardial inflammation, ER stress, and apoptosis through AGEs/NF-κB and PERK/CHOP signaling cascades. Collectively, the present results reveal that LCZ696 had a more protective solid effect against DCM than valsartan.

Preliminary evidence for the presence of multiple forms of cell death in diabetes cardiomyopathy

Diabetic mellitus (DM) is a common degenerative chronic metabolic disease often accompanied by severe cardiovascular complications (DCCs) as major causes of death in diabetic patients with diabetic cardiomyopathy (DCM) as the most common DCC. The metabolic disturbance in DCM generates the conditions/substrates and inducers/triggers and activates the signaling molecules and death executioners leading to cardiomyocyte death which accelerates the development of DCM and the degeneration of DCM to heart failure. Various forms of programmed active cell death including apoptosis, pyroptosis, autophagic cell death, autosis, necroptosis, ferroptosis and entosis have been identified and characterized in many types of cardiac disease. Evidence has also been obtained for the presence of multiple forms of cell death in DCM. Most importantly, published animal experiments have demonstrated that suppression of cardiomyocyte death of any forms yields tremendous protective effects on DCM. Herein, we provide the most updated data on the subject of cell death in DCM, critical analysis of published results focusing on the pathophysiological roles of cell death, and pertinent perspectives of future studies.

Granulocyte colony-stimulating factor reduces the endoplasmic reticulum stress in a rat model of diabetic cardiomyopathy

Prolonged endoplasmic reticulum (ER) stress contributes to the apoptosis of cardiomyocytes, which leads to the development of diabetic cardiomyopathy. Previously, we reported that the granulocyte colony-stimulating factor (G-CSF) reduces the cardiomyocyte apoptosis in diabetic cardiomyopathy; however, the precise mechanisms associated with this process are not yet fully understood. Therefore, in this study, we investigated whether the mechanism of the anti-apoptotic effect of G-CSF was associated with ER stress in a rat model of diabetic cardiomyopathy. Diabetic cardiomyopathy was induced in rats using a high-fat diet combined with the administration of a low-dose of streptozotocin. Diabetic rats were treated with G-CSF or saline for 5 days. Cardiac function was evaluated using serial echocardiography before and 4 weeks after treatment. The rate of cardiomyocyte apoptosis and the expression levels of proteins related to ER stress, including glucose-regulated protein 78 (GRP78), caspase-9, and caspase-12 were analyzed in the cardiac tissue. G-CSF treatment significantly reduced cardiomyocyte apoptosis in the diabetic myocardium and downregulated the expression levels of these proteins in diabetic rats treated with low-dose streptozotocin when compared to that in rats treated with saline. In addition, G-CSF treatment significantly downregulated the expression levels of proteins related to ER stress, such as GRP78, inositol-requiring enzyme-1α (IRE-1α), and C/EBP homologous protein (CHOP) in H9c2 cells under high glucose (HG) conditions. Moreover, G-CSF treatment significantly improved the diastolic dysfunction in serial echocardiography assessments. In conclusion, the anti-apoptotic effect of G-CSF may be associated with the downregulation of ER stress.

An Updated Insight Into Molecular Mechanism of Hydrogen Sulfide in Cardiomyopathy and Myocardial Ischemia/Reperfusion Injury Under Diabetes

Cardiovascular diseases are the most common complications of diabetes, and diabetic cardiomyopathy is a major cause of people death in diabetes. Molecular, transcriptional, animal, and clinical studies have discovered numerous therapeutic targets or drugs for diabetic cardiomyopathy. Within this, hydrogen sulfide (H₂S), an endogenous gasotransmitter alongside with nitric oxide (NO) and carbon monoxide (CO), is found to play a critical role in diabetic cardiomyopathy. Recently, the protective roles of H₂S in diabetic cardiomyopathy have attracted enormous attention. In addition, H₂S donors confer favorable effects in myocardial infarction, ischaemia-reperfusion injury, and heart failure under diabetic conditions. Further studies have disclosed that multiplex molecular mechanisms are responsible for the protective effects of H₂S against diabetes-elicited cardiac injury, such as anti-oxidative, anti-apoptotic, anti-inflammatory, and anti-necrotic properties. In this review, we will summarize the current findings on H₂S biology and pharmacology, especially focusing on the novel mechanisms of H₂S-based protection against diabetic cardiomyopathy. Also, the potential roles of H₂S in diabetes-aggravated ischaemia-reperfusion injury are discussed.

Living with the enemy: from protein-misfolding pathologies we know, to those we want to know

Conformational diseases are caused by the aggregation of misfolded proteins. The risk for such pathologies develops years before clinical symptoms appear, and is higher in people with alpha-1 antitrypsin (AAT) polymorphisms. Thousands of people with alpha-1 antitrypsin deficiency (AATD) are underdiagnosed. Enemy-aggregating proteins may reside in these underdiagnosed AATD patients for many years before a pathology for AATD fully develops. In this perspective review, we hypothesize that the AAT protein could exert a new and previously unconsidered biological effect as an endogenous metal ion chelator that plays a significant role in essential metal ion homeostasis. In this respect, AAT polymorphism may cause an imbalance of metal ions, which could be correlated with the aggregation of amylin, tau, amyloid beta, and alpha synuclein proteins in type 2 diabetes mellitus (T2DM), Alzheimer's and Parkinson's diseases, respectively.

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.

The Role of Epidermal Growth Factor Receptor Family of Receptor Tyrosine Kinases in Mediating Diabetes-Induced Cardiovascular Complications

Diabetes mellitus is a major debilitating disease whose global incidence is progressively increasing with currently over 463 million adult sufferers and this figure will likely reach over 700 million by the year 2045. It is the complications of diabetes such as cardiovascular, renal, neuronal and ocular dysfunction that lead to increased patient morbidity and mortality. Of these, cardiovascular complications that can result in stroke and cardiomyopathies are 2- to 5-fold more likely in diabetes but the underlying mechanisms involved in their development are not fully understood. Emerging research suggests that members of the Epidermal Growth Factor Receptor (EGFR/ErbB/HER) family of tyrosine kinases can have a dual role in that they are beneficially required for normal development and physiological functioning of the cardiovascular system (CVS) as well as in salvage pathways following acute cardiac ischemia/reperfusion injury but their chronic dysregulation may also be intricately involved in mediating diabetes-induced cardiovascular pathologies. Here we review the evidence for EGFR/ErbB/HER receptors in mediating these dual roles in the CVS and also discuss their potential interplay with the Renin-Angiotensin-Aldosterone System heptapeptide, Angiotensin-(1-7), as well the arachidonic acid metabolite, 20-HETE (20-hydroxy-5, 8, 11, 14-eicosatetraenoic acid). A greater understanding of the multi-faceted roles of EGFR/ErbB/HER family of tyrosine kinases and their interplay with other key modulators of cardiovascular function could facilitate the development of novel therapeutic strategies for treating diabetes-induced cardiovascular complications.

Maternal Obesity: A Focus on Maternal Interventions to Improve Health of Offspring

Maternal obesity has many implications for offspring health that persist throughout their lifespan that include obesity and cardiovascular complications. Several different factors contribute to obesity and they encompass interplay between genetics and environment. In the prenatal period, untreated obesity establishes a foundation for a myriad of symptoms and negative delivery experiences, including gestational hypertensive disorders, gestational diabetes, macrosomia, and labor complications. However, data across human and animal studies show promise that nutritional interventions and physical activity may rescue much of the adverse effects of obesity on offspring metabolic health. Further, these maternal interventions improve the health of the offspring by reducing weight gain, cardiovascular disorders, and improving glucose tolerance. Mechanisms from animal studies have also been proposed to elucidate the signaling pathways that regulate inflammation, lipid metabolism, and oxidative capacity of the tissue, ultimately providing potential specific courses of treatment. This review aims to pinpoint the risks of maternal obesity and provide plausible intervention strategies. We delve into recent research involving both animal and human studies with maternal interventions. With the increasing concerning of obesity rates witnessed in the United States, it is imperative to acknowledge the long-term effects posed on future generations and specifically modify maternal nutrition and care to mitigate these adverse outcomes.

Effects of Bergamot Polyphenols on Mitochondrial Dysfunction and Sarcoplasmic Reticulum Stress in Diabetic Cardiomyopathy

Cardiovascular disease is the leading cause of death and disability in the Western world. In order to safeguard the structure and the functionality of the myocardium, it is extremely important to adequately support the cardiomyocytes. Two cellular organelles of cardiomyocytes are essential for cell survival and to ensure proper functioning of the myocardium: mitochondria and the sarcoplasmic reticulum. Mitochondria are responsible for the energy metabolism of the myocardium, and regulate the processes that can lead to cell death. The sarcoplasmic reticulum preserves the physiological concentration of the calcium ion, and triggers processes to protect the structural and functional integrity of the proteins. The alterations of these organelles can damage myocardial functioning. A proper nutritional balance regarding the intake of macronutrients and micronutrients leads to a significant improvement in the symptoms and consequences of heart disease. In particular, the Mediterranean diet, characterized by a high consumption of plant-based foods, small quantities of red meat, and high quantities of olive oil, reduces and improves the pathological condition of patients with heart failure. In addition, nutritional support and nutraceutical supplementation in patients who develop heart failure can contribute to the protection of the failing myocardium. Since polyphenols have numerous beneficial properties, including anti-inflammatory and antioxidant properties, this review gathers what is known about the beneficial effects of polyphenol-rich bergamot fruit on the cardiovascular system. In particular, the role of bergamot polyphenols in mitochondrial and sarcoplasmic dysfunctions in diabetic cardiomyopathy is reported.

The Cross-Links of Endoplasmic Reticulum Stress, Autophagy, and Neurodegeneration in Parkinson's Disease

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder, and it is characterized by the selective loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc), as well as the presence of intracellular inclusions with α-synuclein as the main component in surviving DA neurons. Emerging evidence suggests that the imbalance of proteostasis is a key pathogenic factor for PD. Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) and autophagy, two major pathways for maintaining proteostasis, play important roles in PD pathology and are considered as attractive therapeutic targets for PD treatment. However, although ER stress/UPR and autophagy appear to be independent cellular processes, they are closely related to each other. In this review, we focused on the roles and molecular cross-links between ER stress/UPR and autophagy in PD pathology. We systematically reviewed and summarized the most recent advances in regulation of ER stress/UPR and autophagy, and their cross-linking mechanisms. We also reviewed and discussed the mechanisms of the coexisting ER stress/UPR activation and dysregulated autophagy in the lesion regions of PD patients, and the underlying roles and molecular crosslinks between ER stress/UPR activation and the dysregulated autophagy in DA neurodegeneration induced by PD-associated genetic factors and PD-related neurotoxins. Finally, we indicate that the combined regulation of ER stress/UPR and autophagy would be a more effective treatment for PD rather than regulating one of these conditions alone.

Protective effects of BiP inducer X (BIX) against diabetic cardiomyopathy in rats

Diabetic cardiomyopathy (DC) is associated with impaired endoplasmic reticulum (ER) function, development of ER stress, and induction of cardiac cell apoptosis. Preventive effects of BiP inducer X (BIX) were investigated against DC characteristic changes in a type 2 diabetes rat model. To establish diabetes, a high-fat diet and a single dose of streptozotocin were administered. Then, animals were assigned into the following groups: control, BIX, diabetic animals monitored for one, two, and three weeks. Diabetic rats were treated with BIX for one, two, and three weeks. Expressions of various ER stress and apoptotic markers were assessed by immunoblotting method. CHOP gene expression was assessed by Real-time PCR. Tissue expression of BiP was evaluated by immunohistochemistry method. Hematoxylin and eosin and Masson's trichrome staining were performed to assess histological changes in the left ventricle. Cardiac cell apoptosis was examined using TUNEL assay. BIX administration suppressed the activation of the ER stress markers and cleavage of procaspase-3 in the diabetic rats. Likewise, tissue expression of BiP protein was increased, while CHOP mRNA levels were decreased. These results were accompanied by reducing cardiac fibrosis and myocardial cell apoptosis suggesting protective effects of BIX against the development of DC by decreasing cardiomyocyte apoptosis and fibrosis.

ERGIC3 Silencing Additively Enhances the Growth Inhibition of BFA on Lung Adenocarcinoma Cells

BACKGROUND

Brefeldin A (BFA) has been known to induce endoplasmic reticulum stress (ERS) and Golgi body stress in cancer cells. ERGIC3 (endoplasmic reticulum-Golgi intermediate compartment 3) is a type II transmembrane protein located in the endoplasmic reticulum and Golgi body. ERGIC3 over-expression is frequently observed in cancer cells.

OBJECTIVE

In this study, we aim to explore whether BFA administered concurrently with ERGIC3 silencing would work additively or synergistically inhibit cancer cell growth.

METHODS

ERGIC3-siRNA was used to knock-down the expression of ERGIC3 and BFA was used to induce ERS in lung cancer cell lines GLC-82 and A549. Q-RT-PCR and Western Blot analysis were used to detect the expression of ERGIC3 and downstream molecules. GraphPad Prism 6 was used to quantify the data.

RESULTS

We demonstrated that silencing of ERGIC3 via siRNA effectively led to down-regulation of ERGIC3 at both mRNA and protein levels in GLC-82 and A549 cells. While BFA or ERGIC3- silencing alone could induce ERS and inhibit cell growth, the combination treatment of lung cancer cells with ERGIC3-silencing and BFA was able to additively enhance the inhibition effects of cell growth through up-regulation of GRP78 resulting in cell cycle arrest.

CONCLUSION

ERGIC3 silencing in combination with BFA treatment could additively inhibit lung cancer cell growth. This finding might shed a light on new adjuvant therapy for lung adenocarcinoma.

Zonisamide, an antiepileptic drug, alleviates diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress

Endoplasmic reticulum stress (ER stress) plays a key role in the development of cardiac hypertrophy and diabetic cardiomyopathy (DCM). Zonisamide (ZNS) was originally developed as an antiepileptic drug. Studies have shown that ZNS suppresses ER stress-induced neuronal cell damage in the experimental models of Parkinson's disease. Herein, we investigated whether ZNS improved DCM by attenuating ER stress-induced apoptosis. C57BL/6J mice were fed with high-fat diet (HFD) and intraperitoneally injected with low-dose streptozotocin (STZ) to induce type 2 diabetes mellitus (T2DM), and then treated with ZNS (40 mg·kg-1·d-1, i.g.) for 16 weeks. We showed that ZNS administration slightly ameliorated the blood glucose levels, but significantly alleviated diabetes-induced cardiac dysfunction and hypertrophy. Furthermore, ZNS administration significantly inhibited the Bax and caspase-3 activity, upregulated Bcl-2 activity, and decreased the proportion of TUNEL-positive cells in heart tissues. We analyzed the hallmarks of ER stress in heart tissues, and revealed that ZNS administration significantly decreased the protein levels of GRP78, XBP-1s, ATF6, PERK, ATF4, and CHOP, and elevated Hrd1 protein. In high glucose (HG)-treated primary cardiomyocytes, application of ZNS (3 μM) significantly alleviated HG-induced cardiomyocyte hypertrophy and apoptosis. ZNS application also suppressed activated ER stress in HG-treated cardiomyocytes. Moreover, preapplication of the specific ER stress inducer tunicamycin (10 ng/mL) eliminated the protective effects of ZNS against HG-induced cardiac hypertrophy and ER stress-mediated apoptosis. Our findings suggest that ZNS improves the cardiac diastolic function in diabetic mice and prevents T2DM-induced cardiac hypertrophy by attenuating ER stress-mediated apoptosis.

The aftermath of the interplay between the endoplasmic reticulum stress response and redox signaling

The endoplasmic reticulum (ER) is an essential organelle of eukaryotic cells. Its main functions include protein synthesis, proper protein folding, protein modification, and the transportation of synthesized proteins. Any perturbations in ER function, such as increased demand for protein folding or the accumulation of unfolded or misfolded proteins in the ER lumen, lead to a stress response called the unfolded protein response (UPR). The primary aim of the UPR is to restore cellular homeostasis; however, it triggers apoptotic signaling during prolonged stress. The core mechanisms of the ER stress response, the failure to respond to cellular stress, and the final fate of the cell are not yet clear. Here, we discuss cellular fate during ER stress, cross talk between the ER and mitochondria and its significance, and conditions that can trigger ER stress response failure. We also describe how the redox environment affects the ER stress response, and vice versa, and the aftermath of the ER stress response, integrating a discussion on redox imbalance-induced ER stress response failure progressing to cell death and dynamic pathophysiological changes.

The endoplasmic reticulum (ER), a cellular organelle responsible for protein folding, is sensitive to chemical imbalances that can induce stress, leading to cell death and disease. Researchers in South Korea, led by Han-Jung Chae from Jeonbuk National University in Jeonju and Hyung-Ryong Kim from Dankook University in Cheonan, review how the ER counters changes in its environment that spur protein folding defects by activating a series of signaling pathways, known collectively as the unfolded protein response. Redox imbalance, may fail adaptive ER stress response that can damage the ER and surrounding mitochondria by modifying cysteine residues. The interaction between the two stress systems, ER stress and oxidative stress, has profound negative impacts on normal physiology. Targeting one or both of these stress mechanisms may therefore be an effective means of treating disease.

Dapagliflozin Suppresses ER Stress and Improves Subclinical Myocardial Function in Diabetes: From Bedside to Bench

Dapagliflozin (DAPA), a sodium-glucose cotransporter 2 inhibitor, is approved for treatments of patients with diabetes. The DAPA-HF (Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure) trial disclosed DAPA's benefits in symptomatic heart failure, but the underlying mechanism remains largely unknown. In this longitudinal and prospective study, we investigated changes of left ventricular functions including speckle tracking in patients with diabetes who were free from symptomatic heart failure post-DAPA treatment. Using a rat model with streptozotocin-induced diabetes, we measured the effects of DAPA on myocardial function. In patients with diabetes, following 6 months of DAPA treatment, despite no significant changes in left ventricular ejection fraction, the diastolic function and longitudinal strain improved. Likewise, compared with control, the diabetic rat heart developed pronounced fibrosis and a decline in strain and overall hemodynamics, all of which were mitigated by DAPA treatment. In contrast, despite insulin exerting a glucose-lowering effect, it failed to improve myocardial function and fibrosis. In our in vitro study, under high glucose cardiomyocytes showed significant activations of apoptosis, reactive oxygen species, and endoplasmic reticulum (ER) stress-associated proteins, which were attenuated by the coincubation of DAPA. Mechanistically, DAPA suppressed ER stress, reduced myocardial fibrosis, and improved overall function. The results can lead to further improvement in management of left ventricular function in patients with diabetes.

Exogenous hydrogen sulfide inhibits apoptosis by regulating endoplasmic reticulum stress-autophagy axis and improves myocardial reconstruction after acute myocardial infarction

During acute myocardial infarction, endoplasmic reticulum (ER) stress-induced autophagy and apoptosis have been shown as important pathogeneses of myocardial reconstruction. Importantly, hydrogen sulfide (H2S), as a third endogenous gas signaling molecule, exerts strong cytoprotective effect on anti-ER stress, autophagy regulation and antiapoptosis. Here, we showed that H2S treatment inhibits apoptosis by regulating ER stress-autophagy axis and improves myocardial reconstruction after acute myocardial infarction. We found that H2S intervention improved left ventricle function, reduced glycogen deposition in myocardial tissue mesenchyme, and inhibited apoptosis. Moreover, the expressions of fibrosis indicators (Col3a1 and Col1a2), ER stress-related proteins (CHOP and BIP/ERP78), autophagy-related proteins (Beclin and ATG5), apoptosis protein (Bax), as well as fibrosis protein Col4a3bp were all decreased after treatment with H2S. H2S administration also maintained MMP/TIMP balance. Mechanistically, H2S activated the PI3K/AKT signaling pathway. In addition, H2S treatment also reduced the expressions of ER stress-related proteins, autophagy-related proteins, and apoptins in in vitro experiments. Interestingly, activation of ER stress-autophagy axis could reverse the inhibitory effect of H2S on myocardial apoptosis. Altogether, these results suggested that exogenous H2S suppresses myocardial apoptosis by blocking ER stress-autophagy axis, which in turn reverses cardiac remodeling after myocardial infarction.

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

Up-regulation of Thioredoxin 1 by aerobic exercise training attenuates endoplasmic reticulum stress and cardiomyocyte apoptosis following myocardial infarction

Exercise training (ET) has been reported to reduce oxidative stress and endoplasmic reticulum (ER) stress in the heart following myocardial infarction (MI). Thioredoxin 1 (Trx1) plays a protective role in the infarcted heart. However, whether Trx1 regulates ER stress of the infarcted heart and participates in ET-induced cardiac protective effects are still not well known. In this work, H9c2 cells were treated with hydrogen peroxide (H₂O₂) and recombinant human Trx1 protein (TXN), meanwhile, adult male C57B6L mice were used to establish the MI model, and subjected to a six-week aerobic exercise training (AET) with or without the injection of Trx1 inhibitor, PX-12. Results showed that H₂O₂ significantly increased reactive oxygen species (ROS) level and the expression of TXNIP, CHOP and cleaved caspase12, induced cell apoptosis; TXN intervention reduced ROS level and the expression of CHOP and cleaved caspase12, and inhibited cell apoptosis in H₂O₂-treated H9c2 cells. Furthermore, AET up-regulated endogenous Trx1 protein expression and down-regulated TXNIP expression, restored ROS level and the expression of ER stress-related proteins, inhibited cell apoptosis as well as improved cardiac fibrosis and heart function in mice after MI. PX-12 partly inhibited the AET-induced beneficial effects in the infarcted heart. This study demonstrates that Trx1 attenuates ER stress-induced cell apoptosis, and AET reduces MI-induced ROS overproduction, ER stress and cell apoptosis partly through up-regulating of Trx1 expression in mice with MI.

Apelin-13 Inhibits Methylglyoxal-Induced Unfolded Protein Responses and Endothelial Dysfunction via Regulating AMPK Pathway

It has been suggested that methylglyoxal (MGO), a glycolytic metabolite, has more detrimental effects on endothelial dysfunction than glucose itself. Recent reports showed that high glucose and MGO induced endoplasmic reticulum (ER) stress and myocyte apoptosis in ischemic heart disease was inhibited by apelin. The goal of the study is to investigate the molecular mechanism by which MGO induces endothelial dysfunction via the regulation of ER stress in endothelial cells, and to examine whether apelin-13, a cytoprotective polypeptide ligand, protects MGO-induced aortic endothelial dysfunction. MGO-induced ER stress and apoptosis were determined by immunoblotting and MTT assay in HUVECs. Aortic endothelial dysfunction was addressed by en face immunostaining and acetylcholine-induced vasodilation analysis with aortic rings from mice treated with MGO in the presence or absence of apelin ex vivo. TUDCA, an inhibitor of ER stress, inhibited MGO-induced apoptosis and reduction of cell viability, suggesting that MGO signaling to endothelial apoptosis is mediated via ER stress, which leads to activation of unfolded protein responses (UPR). In addition, MGO-induced UPR and aortic endothelial dysfunction were significantly diminished by apelin-13. Finally, this study showed that apelin-13 protects MGO-induced UPR and endothelial apoptosis through the AMPK pathway. Apelin-13 reduces MGO-induced UPR and endothelial dysfunction via regulating the AMPK activating pathway, suggesting the therapeutic potential of apelin-13 in diabetic cardiovascular complications.

Sepsis causes heart injury through endoplasmic reticulum stress-mediated apoptosis signaling pathway

Endoplasmic reticulum stress (ERS), arising from the loss of dynamic balance in endoplasmic reticulum function under stress and inflammation, has been implicated in the progression of sepsis. Multiple organ failure caused by sepsis still has a high mortality rate, of which the heart is one of the more damaged organs. In this research, a rat model of sepsis was set up by cecal ligation and puncture (CLP); serum myocardial enzyme levels were measured using an automated biochemical analyzer, inflammatory cytokine levels were measured by ELISA kit, and cardiac histology and cardiomyocyte apoptosis were measured by hematoxylin and eosin (H&E) staining and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to assess the extent of myocardial damage. Western blot was used to detect expression of related proteins. The results showed that serum myocardial enzymes and pro-inflammatory factors were elevated in septic rats, and the increase was most significant in the CLP 24 h group. At the same time, the myocardium of septic rats had a histopathologic abnormality. After CLP, levels of endoplasmic reticulum stress related protein were upregulated. After 12 and 24 hours, the density of apoptotic cells in the myocardium of CLP-treated rats increased significantly, and the expression of apoptosis-related proteins changed significantly. This suggests that the unfolded protein response occurs during sepsis and causes damage to the heart muscle. Endoplasmic reticulum stress-mediated apoptotic signaling pathway is one of the causes of cardiac injury caused by sepsis, and may be a key to clinical prevention of cardiac dysfunction caused by sepsis.

VLDL and HDL attenuate endoplasmic reticulum and metabolic stress in HL-1 cardiomyocytes

Lipoproteins have a vital role in the development of metabolic and cardiovascular diseases ranging from protective to deleterious effects on target tissues. VLDL has been shown to induce lipotoxic lipid accumulation and exert a variety of negative effects on cardiomyocytes. Lipotoxicity and endoplasmic reticulum (ER) stress are proposed to be the mediators of damaging effects of metabolic diseases on cardiovascular system. We treated cardiomyocytes with lipoproteins to evaluate the adaptability of these cells to metabolic stress induced by starvation and excess of lipoproteins, and to evaluate the effect of lipoproteins and lipid accumulation on ER stress. VLDL reversed metabolic stress induced by starvation, while HDL did not. VLDL induced dose-dependent lipid accumulation in cardiomyocytes, which however did not result in reduced cell viability or induction of ER stress. Moreover, VLDL or HDL pre-treatment reduced ER stress in cardiomyocytes induced by tunicamycin and palmitic acid as measured by the expression of ER stress markers, even in conditions of increased lipid accumulation. VLDL and HDL induced activation of pro-survival ERK1/2 in cardiomyocytes; however, this activation was not involved in the protection against ER stress. Additionally, we observed that LDLR and VLDLR are regulated differently by lipoproteins and cellular stress, as lipoproteins induced VLDLR protein independently of the level of lipid accumulation. We conclude that VLDL is not a priori detrimental for cardiomyocytes and can even have beneficial effects, enabling cell survival under starvation and attenuating ER stress.

Gene therapy targeting cardiac phosphoinositide 3-kinase (p110α) attenuates cardiac remodeling in type 2 diabetes

Diabetic cardiomyopathy is a distinct form of heart disease that represents a major cause of death and disability in diabetic patients, particularly, the more prevalent type 2 diabetes patient population. In the current study, we investigated whether administration of recombinant adeno-associated viral vectors carrying a constitutively active phosphoinositide 3-kinase (PI3K)(p110α) construct (rAAV6-caPI3K) at a clinically relevant time point attenuates diabetic cardiomyopathy in a preclinical type 2 diabetes (T2D) model. T2D was induced by a combination of a high-fat diet (42% energy intake from lipid) and low-dose streptozotocin (three consecutive intraperitoneal injections of 55 mg/kg body wt), and confirmed by increased body weight, mild hyperglycemia, and impaired glucose tolerance (all P < 0.05 vs. nondiabetic mice). After 18 wk of untreated diabetes, impaired left ventricular (LV) systolic dysfunction was evident, as confirmed by reduced fractional shortening and velocity of circumferential fiber shortening (Vcf_c, all P < 0.01 vs. baseline measurement). A single tail vein injection of rAAV6-caPI3K gene therapy (2×10¹¹vector genomes) was then administered. Mice were followed for an additional 8 wk before end point. A single injection of cardiac targeted rAAV6-caPI3K attenuated diabetes-induced cardiac remodeling by limiting cardiac fibrosis (reduced interstitial and perivascular collagen deposition, P < 0.01 vs. T2D mice) and cardiomyocyte hypertrophy (reduced cardiomyocyte size and Nppa gene expression, P < 0.001 and P < 0.05 vs. T2D mice, respectively). The diabetes-induced LV systolic dysfunction was reversed with rAAV6-caPI3K, as demonstrated by improved fractional shortening and velocity of circumferential fiber shortening (all P < 0.05 vs pre-AAV measurement). This cardioprotection occurred in combination with reduced LV reactive oxygen species (P < 0.05 vs. T2D mice) and an associated decrease in markers of endoplasmic reticulum stress (reduced Grp94 and Chop, all P < 0.05 vs. T2D mice). Together, our findings demonstrate that a cardiac-selective increase in PI3K(p110α), via rAAV6-caPI3K, attenuates T2D-induced diabetic cardiomyopathy, providing proof of concept for potential translation to the clinic.NEW & NOTEWORTHY Diabetes remains a major cause of death and disability worldwide (and its resultant heart failure burden), despite current care. The lack of existing management of heart failure in the context of the poorer prognosis of concomitant diabetes represents an unmet clinical need. In the present study, we now demonstrate that delayed intervention with PI3K gene therapy (rAAV6-caPI3K), administered as a single dose in mice with preexisting type 2 diabetes, attenuates several characteristics of diabetic cardiomyopathy, including diabetes-induced impairments in cardiac remodeling, oxidative stress, and function. Our discovery here contributes to the previous body of work, suggesting the cardioprotective effects of PI3K(p110α) could be a novel therapeutic approach to reduce the progression to heart failure and death in diabetes-affected patients.

Cluster and Factor Analysis of Elements in Serum and Urine of Diabetic Patients with Peripheral Neuropathy and Healthy People

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus, presented as a major teratogenic cause worldwide. This study discussed alternation and correlation of magnesium (Mg), calcium (Ca), copper (Cu), zinc (Zn), iron (Fe), chromium (Cr), and selenium (Se) among DPN patients and healthy people using multivariate statistical analysis. Fifty patients with DPN were recruited from endocrinology department, First Hospital of Jilin University between January 2010 and October 2011 and also 50 healthy subjects were enrolled at the same time. Inductively coupled plasma mass spectrometry (ICP-MS) was used to assay elements in serum and urine. Cluster analysis was used to clarify alternation of elements' homogeneity. Factor analysis was performed to evaluate the most informative kinds of elements. Mg, Ca, Zn, and Cr in DPN patients were significantly lower in serum whereas significantly higher in urine. Elements were clustered into 4 or 5 clusters based on internal association using between-groups linkage algorithm. Serum Cr, Se, and Fe were grouped, and Mg related to Ca more closely in both serum and urine in DPN. Factor analysis revealed discrepancies of elements' contribution. Cr, Se, and Fe appeared to be the most crucial factors contributing to DPN. Mg, Ca, Zn, and Cu were more influential, whereas Cr became less potent to disease. Contributed value of elements could be determined and specified using loadings in scree plot. Future studies and delicate statistical models should be applied.

Endoplasmic reticulum stress and focused drug discovery in cardiovascular disease

Endoplasmic reticulum (ER) is an intracellular membranous organelle involved in the synthesis, folding, maturation and post-translation modification of secretory and transmembrane proteins. Therefore, ER is closely related to the maintenance of intracellular homeostasis and the good balance between health and diseases. Endoplasmic reticulum stress (ERS) occurs when unfolded/misfolded proteins accumulate after disturbance of ER environment. In response to ERS, cells trigger an adaptive response called the Unfolded protein response (UPR), which helps cells cope with the stress. In recent years, a large number of studies show that ERS can aggravate cardiovascular diseases. ERS-related proteins expression in cardiovascular diseases is on the rise. Therefore, down-regulation of ERS is critical for alleviating symptoms of cardiovascular diseases, which may be used in the near future to treat cardiovascular diseases. This article reviews the relationship between ERS and cardiovascular diseases and drugs that inhibit ERS. Furthermore, we detail the role of ERS inhibitors in the treatment of cardiovascular disease. Drugs that inhibit ERS are considered as promising strategies for the treatment of cardiovascular diseases.

Inhibition of the SIRT1 signaling pathway exacerbates endoplasmic reticulum stress induced by renal ischemia/reperfusion injury in type 1 diabetic rats

The aim of the present study was to investigate whether the diabetic kidney is more susceptible to ischemia/reperfusion (I/R) injury, and identify the potential mechanisms involved. An animal model of type 1 diabetes was created by treating rats with streptozotocin (STZ). This model was then used, along with healthy controls, to investigate the effect of diabetes mellitus (DM) on renal I/R injury. After 45 min of ischemia and 24 h of reperfusion, kidney and serum samples were acquired and used to evaluate function and histopathological injury in the kidneys. Western blotting was also used to determine the expression levels of key proteins. Rats experiencing renal I/R exhibited significant characteristics of renal dysfunction, reduced levels of Sirtuin 1 (SIRT1) protein (a key signaling protein in the kidneys), increased endoplasmic reticulum stress (ERS) and pyroptosis. Furthermore, diabetic rats exhibited further reductions in the levels of SIRT1 in response to renal I/R injury and an increase in the levels of ERS. These effects were all alleviated by the administration of a SIRT1 agonist. The present analysis revealed that the SIRT1-mediated activation of ER stress and pyroptosis played a pivotal role in diabetic rats subjected to renal I/R injury. Downregulation of the SIRT1 signaling pathway were exacerbated in response to renal I/R injury-induced acute kidney injury (AKI). The present data indicated that DM enhanced ER stress and increased pyroptosis by downregulating the SIRT1 signaling pathway.

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.

Huoxue Qianyang decoction ameliorates cardiac remodeling in obese spontaneously hypertensive rats in association with ATF6-CHOP endoplasmic reticulum stress signaling pathway regulation

OBJECTIVE

Endoplasmic reticulum (ER) stress is involved in hypertension related cardiac remodeling. We aimed to evaluate the effects of Huoxue Qianyang (HXQY) decoction on cardiac remodeling in obese spontaneously hypertensive rats (SHRs), and explore its impacts on the activating transcription factor 6 (ATF6)-C/EBP homologous protein (CHOP) ER stress signaling pathway.

METHODS

Twenty-seven obese SHRs were randomly divided into Obese SHR, Obese SHR + HXQY and Obese SHR + Valsartan groups, and treated with the indicated drugs for 8 weeks. Nine age-matched male SHRs were used as controls. Systolic blood pressure (SBP), body weight (BW), and the left ventricular mass index (LVMI) were measured weekly or at end point. Then, angiotensin II (Ang II), fasting glucose (FPG) and fasting insulin (FIN), total cholesterol (TC), LDL-cholesterol (LDL-C), HDL-cholesterol (HDL-C) and triglyceride (TG) levels were evaluated with commercial kits. Apoptotic cardiomyocytes were detected by the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method. The expression levels of GRP78, ATF6, PERK/pPERK and CHOP were assessed by quantitative PCR and Western blot.

RESULTS

Treatment with HXQY decoction resulted in significantly reduced SBP, BW, LVMI, Ang II, TC and LDL-C levels, as well as the homeostasis model assessment of insulin resistance (HOMA-IR) score in obese SHRs. Apoptosis in heart tissues of obese SHRs was significantly attenuated after HXQY decoction administration, paralleling reduced expression of GRP78, ATF6, PERK/pPERK and CHOP at both mRNA and protein levels.

CONCLUSION

Cardiac remodeling in obese SHRs is ameliorated by intervention with HXQY decoction in association with inhibited ATF6-CHOP ER stress signaling pathway.

Effect of 4-Phenylbutyric Acid and Tauroursodeoxycholic Acid on Magnesium and Calcium Metabolism in Streptozocin-Induced Type 1 Diabetic Mice

Recent evidence has identified a role of micronutrients, such as magnesium (Mg²⁺) and calcium (Ca²⁺), in glycemic control. 4-Phenylbutyric acid (PBA) and tauroursodeoxycholic acid (TUDCA) are molecular chaperones that can improve protein folding and alleviate endoplasmic reticulum (ER) stress. Increasingly, research is focusing on the association between molecular chaperones and micronutrients. This study established and characterized a mouse model of type 1 diabetes (T1D) and investigated the effect of PBA and TUDCA on Mg²⁺ and Ca²⁺ metabolism in these mice. T1D was established in Friend virus B-type mice using multiple low doses of streptozotocin. Mice were administered chaperones. Mg²⁺and Ca²⁺ levels in tissues and serum were detected using acid digestion and ICP-MS. At 2 weeks and 2 months after chaperone administration was initiated, Mg²⁺ levels in the heart, liver, kidney, and serum and Ca²⁺ levels in spleen and serum of T1D mice were significantly decreased compared with controls; Ca²⁺ levels in the kidney and muscle of T1D mice were significantly increased; Mg²⁺ and Ca²⁺ levels in the heart, liver, kidney, muscle, spleen, and serum were positively correlated in control and T1D mice; and PBA restored renal Mg²⁺ levels to normal values and TUDCA restored hepatic, renal, and serum Mg²⁺ levels and renal and serum Ca²⁺ levels to normal values in T1D mice. PBA restored muscular Ca²⁺ levels to normal values in T1D mice at 2 months after chaperone or vehicle administration was initiated. Further research is required to investigate the underlying mechanisms by which chaperones regulate micronutrients in diabetes.