Endoplasmic reticulum stress sensor protein kinase R-like endoplasmic reticulum kinase (PERK) protects against pressure overload-induced heart failure and lung remodeling

PERK's novel agonist protects against myocardial ischemia-reperfusion injury by modulating ER-mitochondria contacts and phosphatidic acid transport

The role of PERK in maintaining the homeostasis of mitochondria-associated membrane (MAM) is believed to exert a significant impact on mitochondrial energy metabolism and structural morphology. However, there exists controversy regarding the therapeutic effect of PERK activation on ischemia-reperfusion injury. We have discovered a novel agonist for PERK named ZY341. ZY341 interacts with the active pocket of PERK through π-π stacking interaction, and surface plasmon resonance experiments have confirmed its exceptional affinity as an agonist with a Kd value of 17.5 μM. This study provides initial evidence that ZY341 exhibits potent activity as a PERK agonist, effectively activating the PERK/eIF2α pathway in a mouse model of ischemia-reperfusion and demonstrating significant anti-apoptotic effects on cardiomyocytes. Ischemia-reperfusion not only induces cardiomyocyte apoptosis but also leads to substantial increases in MAM-mediated mitochondrial calcium overload, resulting in severe damage to mitochondrial structure and function. ZY341 significantly protects cardiac myocytes' respiratory capacity and improves heart function. Mechanistically, through PERK activation, ZY341 inhibits abnormal binding between VAPB-PTPIP51 complex in OGD/R models, regulates MAM-mediated calcium ion and phosphatidic acid transport homeostasis, suppresses mitochondrial fragmentation thereby significantly enhancing cardiac function. In conclusion, this study unveils new avenues for targeting PERK as a therapeutic strategy for myocardial ischemia-reperfusion treatment.

Homeostasis control in health and disease by the unfolded protein response

Cells rely on the endoplasmic reticulum (ER) to fold and assemble newly synthesized transmembrane and secretory proteins - essential for cellular structure-function and for both intracellular and intercellular communication. To ensure the operative fidelity of the ER, eukaryotic cells leverage the unfolded protein response (UPR) - a stress-sensing and signalling network that maintains homeostasis by rebalancing the biosynthetic capacity of the ER according to need. The metazoan UPR can also redirect signalling from cytoprotective adaptation to programmed cell death if homeostasis restoration fails. As such, the UPR benefits multicellular organisms by preserving optimally functioning cells while removing damaged ones. Nevertheless, dysregulation of the UPR can be harmful. In this Review, we discuss the UPR and its regulatory processes as a paradigm in health and disease. We highlight important recent advances in molecular and mechanistic understanding of the UPR that enable greater precision in designing and developing innovative strategies to harness its potential for therapeutic gain. We underscore the rheostatic character of the UPR, its contextual nature and critical open questions for its further elucidation.

Molecular Mechanisms Underlying Heart Failure and Their Therapeutic Potential

Heart failure (HF) is a prominent fatal cardiovascular disorder afflicting 3.4% of the adult population despite the advancement of treatment options. Therefore, a better understanding of the pathogenesis of HF is essential for exploring novel therapeutic strategies. Hypertrophy and fibrosis are significant characteristics of pathological cardiac remodeling, contributing to HF. The mechanisms involved in the development of cardiac remodeling and consequent HF are multifactorial, and in this review, the key underlying mechanisms are discussed. These have been divided into the following categories thusly: (i) mitochondrial dysfunction, including defective dynamics, energy production, and oxidative stress; (ii) cardiac lipotoxicity; (iii) maladaptive endoplasmic reticulum (ER) stress; (iv) impaired autophagy; (v) cardiac inflammatory responses; (vi) programmed cell death, including apoptosis, pyroptosis, and ferroptosis; (vii) endothelial dysfunction; and (viii) defective cardiac contractility. Preclinical data suggest that there is merit in targeting the identified pathways; however, their clinical implications and outcomes regarding treating HF need further investigation in the future. Herein, we introduce the molecular mechanisms pivotal in the onset and progression of HF, as well as compounds targeting the related mechanisms and their therapeutic potential in preventing or rescuing HF. This, therefore, offers an avenue for the design and discovery of novel therapies for the treatment of HF.

Irisin Mitigates Doxorubicin-Induced Cardiotoxicity by Reducing Oxidative Stress and Inflammation via Modulation of the PERK-eIF2α-ATF4 Pathway

Purpose

Doxorubicin (DOX), an anthracycline antibiotic, has limited clinical use due to its pronounced cardiotoxicity. Irisin, a myokine known for its metabolic regulation, has shown therapeutic effects on cardiovascular disease. This study investigates the potential cardioprotective function of irisin in reducing the cardiac injury induced by DOX.

Methods

In vitro, H9c2 cells were pretreated with irisin (20 nM) for 24 hours before exposure to DOX (1 μM). In vivo, C57BL/6 mice were administered DOX (5 mg/kg/week, i.p.) for 4 weeks, reaching a cumulative dose of 20 mg/kg. Irisin (1 mg/kg/ 3 days, i.p.) was administered to the mice both 7 days prior to and during DOX injection.Cardiac function was evaluated by echocardiography, and cardiac histology was assessed using HE, WGA, and Masson staining. Myocardial injury markers were quantified using ELISA, and apoptosis was analyzed via TUNEL staining. Oxidative stress was determined by measuring antioxidase activity, MDA and GSH levels, and DHE staining, while mitochondrial superoxide production was assessed using MitoSOX Red. Mitochondrial morphology and function evaluated using transmission electron microscopy and Seahorse analysis, respectively Inflammatory cytokines were quantified in serum and cell supernatants. The role of the PERK-eIF2α-ATF4 pathway mediated by irisin was investigated by Western blot. Using adeno-associated virus serotype-9 carrying mouse FNDC5 shRNA (AAV9-shFNDC5) further validated the protective role of irisin in DOX-induced myocardial injury.

Results

Irisin reduced DOX-induced cardiac dysfunction and fibrosis. Moreover, irisin mitigated oxidative stress and inflammation through inhibiting the PERK-eIF2α-ATF4 pathway activated by DOX, thus preserving mitochondrial function. While cardiac FNDC5 knockdown exacerbated DOX-induced heart injury and PERK-eIF2α-ATF4 activation, which was partially reversed by irisin.

Conclusion

Irisin mitigates oxidative stress and inflammation by modulating the PERK-eIF2α-ATF4 pathway, highlighting its potential as a prospective approach for combating DOX-induced cardiotoxicity.

Altered mitochondrial unfolded protein response and FGF21 secretion in MASLD progression and the effect of exercise intervention

A high-calorie diet and lack of exercise are the most important risk factors contributing to metabolic dysfunction-associated steatotic liver disease (MASLD) initiation and progression. The precise molecular mechanisms of mitochondrial function alteration during MASLD development remain to be fully elucidated. In this study, a total of 60 male C57BL/6J mice were maintained on a normal or amylin liver NASH (AMLN) diet for 6 or 10 weeks. Some of the mice were then subjected to voluntary wheel running, while the other mice were fed a normal or AMLN diet until 14 and 18 weeks. The results showed that hepatic lipid deposition and the PERK-eIF2α-ATF4 pathway were significantly increased with prolonged duration of AMLN diet. However, expression of mitochondrial unfolded protein response (UPRmt) genes and mitokine FGF21 secretion were significantly enhanced in the 14-week AMLN diet mice, but were markedly reduced with the excessive lipid deposition induced by longer AMLN diet. Additionally, the exercise intervention acts as a regulator to optimize UPRmt signal transduction and to enhance mitochondrial homeostasis by improving mitochondrial function, reversing the UPRmt activation pattern, and increasing FGF21 secretion, which plays a pivotal role in delaying the occurrence and development of MASLD.

Mitochondrial Dysfunction in Cardiac Disease: The Fort Fell

Myocardial cells and the extracellular matrix achieve their functions through the availability of energy. In fact, the mechanical and electrical properties of the heart are heavily dependent on the balance between energy production and consumption. The energy produced is utilized in various forms, including kinetic, dynamic, and thermal energy. Although total energy remains nearly constant, the contribution of each form changes over time. Thermal energy increases, while dynamic and kinetic energy decrease, ultimately becoming insufficient to adequately support cardiac function. As a result, toxic byproducts, unfolded or misfolded proteins, free radicals, and other harmful substances accumulate within the myocardium. This leads to the failure of crucial processes such as myocardial contraction-relaxation coupling, ion exchange, cell growth, and regulation of apoptosis and necrosis. Consequently, both the micro- and macro-architecture of the heart are altered. Energy production and consumption depend on the heart's metabolic resources and the functional state of the cardiac structure, including cardiomyocytes, non-cardiomyocyte cells, and their metabolic and energetic behavior. Mitochondria, which are intracellular organelles that produce more than 95% of ATP, play a critical role in fulfilling all these requirements. Therefore, it is essential to gain a deeper understanding of their anatomy, function, and homeostatic properties.

The impact of cannabinoid receptor 1 absence on mouse liver mitochondria homeostasis: insight into mitochondrial unfolded protein response

Introduction

The contribution of Cannabinoid type 1 receptor (CB1) in mitochondrial energy transduction mechanisms and mitochondrial activities awaits deeper investigations. Our study aims to assess the impact of CB1 absence on the mitochondrial compartment in the liver, focusing on both functional aspects and remodeling processes.

Methods

We used CB1-/- and CB1+/+ male mice. Cytochrome C Oxidase activity was determined polarographically. The expression and the activities of separated mitochondrial complexes and supercomplexes were performed by using Blue-Native Page, Western blotting and histochemical staining for in-gel activity. Key players of Mitochondrial Quality Control processes were measured using RT-qPCR and Western blotting. Liver fine sub-cellular ultrastructural features were analyzed by TEM analysis.

Results and discussion

In the absence of CB1, several changes in the liver occur, including increased oxidative capacity, reduced complex I activity, enhanced complex IV activity, general upregulation of respiratory supercomplexes, as well as higher levels of oxidative stress. The mitochondria and cellular metabolism may be affected by these changes, increasing the risk of ROS-related damage. CB1-/- mice show upregulation of mitochondrial fusion, fission and biogenesis processes which suggests a dynamic response to the absence of CB1. Furthermore, oxidative stress disturbs mitochondrial proteostasis, initiating the mitochondrial unfolded protein response (UPRmt). We noted heightened levels of pivotal enzymes responsible for maintaining mitochondrial integrity, along with heightened expression of molecular chaperones and transcription factors associated with cellular stress reactions. Additionally, our discoveries demonstrate a synchronized reaction to cellular stress, involving both UPRmt and UPRER pathways.

CD8 T cells promote heart failure progression in mice with preexisting left ventricular dysfunction

Introduction

Even under the standard medical care, patients with left ventricular (LV) failure or heart failure (HF) often progress to pulmonary hypertension and right ventricular (RV) hypertrophy. We previously showed that inflammation and regulatory T cells (Tregs) modulate HF progression in mice with preexisting LV failure. The main objective of this study is to determine the role of CD8+ T cells in modulating LV failure and the consequent pulmonary inflammation and RV hypertrophy in mice with preexisting LV failure.

Methods

Mice with LV failure produced by transverse aortic constriction (TAC) were randomized to depletion of cytotoxic CD8+ T cells, Tregs, or both using specific blocking antibodies. Cardiac function, lung inflammation, fibrosis, vascular remodeling, and right ventricular remodeling were determined.

Results

LV failure caused pulmonary inflammation, fibrosis, vascular remodeling, and RV hypertrophy. Depletion of CD8+ T cells significantly attenuated above changes in mice with preexisting LV failure. LV failure was associated with increased CD4+ and CD8+ T cell activation, and increased ratios of activated T cells to Tregs. Treg depletion exacerbated lung inflammation and HF progression, as well as lung CD4+ and CD8+ T cell infiltration and activation in HF mice. However, CD8+ T cells depletion rescue these mice from exacerbated lung inflammation and RV hypertrophy after Treg depletion.

Discussion

Our findings demonstrate an important role of CD8+ T cells in promoting pulmonary inflammation and RV hypertrophy in mice with preexisting LV failure. Depletion of CD8+ T cells also rescued HF mice from the exacerbated HF progression by Treg depletion.

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

Cardiovascular protection of YiyiFuzi powder and the potential mechanisms through modulating mitochondria-endoplasmic reticulum interactions

Cardiovascular diseases (CVD) remain the leading cause of death worldwide and represent a major public health challenge. YiyiFuzi Powder (YYFZ), composed of Coicis semen and Fuzi, is a classical traditional Chinese medicine prescription from the Synopsis of Golden Chamber dating back to the Han Dynasty. Historically, YYFZ has been used to treat various CVD, rooted in Chinese therapeutic principles. Network pharmacology analysis indicated that YYFZ may exhibit direct or indirect effects on mitochondria-endoplasmic reticulum (ER) interactions. This review, focusing on the cardiovascular protective effects of Coicis semen and Fuzi, summarizes the potential mechanisms by which YYFZ acts on mitochondria and the ER. The underlying mechanisms are associated with regulating cardiovascular risk factors (such as blood lipids and glucose), impacting mitochondrial structure and function, modulating ER stress, inhibiting oxidative stress, suppressing inflammatory responses, regulating cellular apoptosis, and maintaining calcium ion balance. The involved pathways include, but were not limited to, upregulating the IGF-1/PI3K/AKT, cAMP/PKA, eNOS/NO/cGMP/SIRT1, SIRT1/PGC-1α, Klotho/SIRT1, OXPHOS/ATP, PPARα/PGC-1α/SIRT3, AMPK/JNK, PTEN/PI3K/AKT, β2-AR/PI3K/AKT, and modified Q cycle signaling pathways. Meanwhile, the MCU, NF-κB, and JAK/STAT signaling pathways were downregulated. The PERK/eIF2α/ATF4/CHOP, PERK/SREBP-1c/FAS, IRE1, PINK1-dependent mitophagy, and AMPK/mTOR signaling pathways were bidirectionally regulated. High-quality experimental studies are needed to further elucidate the underlying mechanisms of YYFZ in CVD treatment.

FICD deficiency protects mice from hypertrophy-induced heart failure via BiP-mediated activation of the UPR ER and ER-phagy

Cardiomyocytes require the HSP70 chaperone BiP to maintain proteostasis in the endoplasmic reticulum (ER) following cardiac stress. The adenylyl transferase (AMPylase) FICD is increasingly recognized to regulate BiP activity through the post-translational addition of an adenosine monophosphate moiety to BiP surface residues. However, the physiological impact of FICD-mediated BiP regulation in the context of cardiovascular health is unknown. Here, we find that FICD deficiency prevents pressure overload-associated heart failure, hypertrophy, and fibrosis, and that FICD knockout mice maintain normal cardiac function after cardiac pressure overload. At a cellular level, we observe that FICD-mediated BiP AMPylation blunts the induction of the unfolded protein response (UPR ER ) and impairs BiP interaction with FAM134B, an ER-phagy receptor, thus limiting ER-phagy induction under stress. In contrast, FICD loss significantly increases BiP-dependent UPR ER induction and ER-phagy in stressed cardiomyocytes. We also uncover cell type-specific consequences of FICD activity in response to ER stress, positioning FICD as a critical proteostasis regulator in cardiac tissue. Our results highlight a novel regulatory paradigm controlling stress resilience in cardiomyocytes and offer a rationale to consider FICD as a therapeutic target to treat cardiac hypertrophy.

Potential targets for the treatment of MI: GRP75-mediated Ca2+ transfer in MAM

After myocardial infarction (MI), there is a notable disruption in cellular calcium ion homeostasis and mitochondrial function, which is believed to be intricately linked to endoplasmic reticulum (ER) stress. This research endeavors to elucidate the involvement of glucose regulated protein 75 (GRP75) in post-MI calcium ion homeostasis and mitochondrial function. In MI rats, symptoms of myocardial injury were accompanied by an increase in the activation of ER stress. Moreover, in oxygen-glucose deprivation (OGD)-induced cardiomyocytes, it was confirmed that inhibiting ER stress exacerbated intracellular Ca2+ disruption and cell apoptosis. Concurrently, the co-localization of GRP75 with IP3R and VDAC1 increased under ER stress in cardiomyocytes. In OGD-induced cardiomyocytes, knockdown of GRP75 not only reduced the Ca2+ levels in both the ER and mitochondria and improved the ultrastructure of cardiomyocytes, but it also increased the number of contact points between the ER and mitochondria, reducing mitochondria associated endoplasmic reticulum membrane (MAM) formation, and decreased cell apoptosis. Significantly, knockdown of GRP75 did not affect the protein expression of PERK and hypoxia-inducible factor 1α (HIF-1α). Transcriptome analysis of cardiomyocytes revealed that knockdown of GRP75 mainly influenced the molecular functions of sialyltransferase and IP3R, as well as the biosynthesis of glycosphingolipids and lactate metabolism. The complex interaction between the ER and mitochondria, driven by the GRP75 and its associated IP3R1-GRP75-VDAC1 complex, is crucial for calcium homeostasis and cardiomyocyte's adaptive response to ER stress. Modulating GRP75 could offer a strategy to regulate calcium dynamics, diminish glycolysis, and thereby mitigate cardiomyocyte apoptosis.

Milestone Papers on Signal Transduction Mechanisms of Hypertension and Its Complications

To celebrate 100 years of American Heart Association-supported cardiovascular disease research, this review article highlights milestone papers that have significantly contributed to the current understanding of the signaling mechanisms driving hypertension and associated cardiovascular disorders. This article also includes a few of the future research directions arising from these critical findings. To accomplish this important mission, 4 principal investigators gathered their efforts to cover distinct yet intricately related areas of signaling mechanisms pertaining to the pathogenesis of hypertension. The renin-angiotensin system, canonical and novel contractile and vasodilatory pathways in the resistance vasculature, vascular smooth muscle regulation by membrane channels, and noncanonical regulation of blood pressure and vascular function will be described and discussed as major subjects.

Loss of TRIM29 mitigates viral myocarditis by attenuating PERK-driven ER stress response in male mice

Viral myocarditis, an inflammatory disease of the myocardium, is a significant cause of sudden death in children and young adults. The current coronavirus disease 19 pandemic emphasizes the need to understand the pathogenesis mechanisms and potential treatment strategies for viral myocarditis. Here, we found that TRIM29 was highly induced by cardiotropic viruses and promoted protein kinase RNA-like endoplasmic reticulum kinase (PERK)-mediated endoplasmic reticulum (ER) stress, apoptosis, and reactive oxygen species (ROS) responses that promote viral replication in cardiomyocytes in vitro. TRIM29 deficiency protected mice from viral myocarditis by promoting cardiac antiviral functions and reducing PERK-mediated inflammation and immunosuppressive monocytic myeloid-derived suppressor cells (mMDSC) in vivo. Mechanistically, TRIM29 interacted with PERK to promote SUMOylation of PERK to maintain its stability, thereby promoting PERK-mediated signaling pathways. Finally, we demonstrated that the PERK inhibitor GSK2656157 mitigated viral myocarditis by disrupting the TRIM29-PERK connection, thereby bolstering cardiac function, enhancing cardiac antiviral responses, and curbing inflammation and immunosuppressive mMDSC in vivo. Our findings offer insight into how cardiotropic viruses exploit TRIM29-regulated PERK signaling pathways to instigate viral myocarditis, suggesting that targeting the TRIM29-PERK axis could mitigate disease severity.

Unfolded protein response suppression potentiates LPS-induced barrier dysfunction and inflammation in bovine pulmonary artery endothelial cells

The development of novel strategies to counteract diseases related to barrier dysfunction is a priority, since sepsis and acute respiratory distress syndrome are still associated with high mortality rates. In the present study, we focus on the effects of the unfolded protein response suppressor (UPR) 4-Phenylbutyrate (4-PBA) in Lipopolysaccharides (LPS)-induced endothelial injury, to investigate the effects of that compound in the corresponding damage. 4-PBA suppressed binding immunoglobulin protein (BiP) - a UPR activation marker - and potentiated LPS - induced signal transducer and activator of transcription 3 (STAT3) and extracellular signal‑regulated protein kinase (ERK) 1/2 activation. In addition to those effects, 4-PBA enhanced paracellular hyperpermeability in inflamed bovine pulmonary endothelial cells, and did not affect cell viability in moderate concentrations. Our observations suggest that UPR suppression due to 4-PBA augments LPS-induced endothelial injury, as well as the corresponding barrier disruption.

ATF6 protects against protein misfolding during cardiac hypertrophy

Cardiomyocytes activate the unfolded protein response (UPR) transcription factor ATF6 during pressure overload-induced hypertrophic growth. The UPR is thought to increase ER protein folding capacity and maintain proteostasis. ATF6 deficiency during pressure overload leads to heart failure, suggesting that ATF6 protects against myocardial dysfunction by preventing protein misfolding. However, conclusive evidence that ATF6 prevents toxic protein misfolding during cardiac hypertrophy is still pending. Here, we found that activation of the UPR, including ATF6, is a common response to pathological cardiac hypertrophy in mice. ATF6 KO mice failed to induce sufficient levels of UPR target genes in response to chronic isoproterenol infusion or transverse aortic constriction (TAC), resulting in impaired cardiac growth. To investigate the effects of ATF6 on protein folding, the accumulation of poly-ubiquitinated proteins as well as soluble amyloid oligomers were directly quantified in hypertrophied hearts of WT and ATF6 KO mice. Whereas only low levels of protein misfolding was observed in WT hearts after TAC, ATF6 KO mice accumulated increased quantities of misfolded protein, which was associated with impaired myocardial function. Collectively, the data suggest that ATF6 plays a critical adaptive role during cardiac hypertrophy by protecting against protein misfolding.

Effect of CB1 Receptor Deficiency on Mitochondrial Quality Control Pathways in Gastrocnemius Muscle

This study aims to explore the complex role of cannabinoid type 1 receptor (CB1) signaling in the gastrocnemius muscle, assessing physiological processes in both CB1+/+ and CB1-/- mice. The primary focus is to enhance our understanding of how CB1 contributes to mitochondrial homeostasis. At the tissue level, CB1-/- mice exhibit a substantial miRNA-related alteration in muscle fiber composition, characterized by an enrichment of oxidative fibers. CB1 absence induces a significant increase in the oxidative capacity of muscle, supported by elevated in-gel activity of Complex I and Complex IV of the mitochondrial respiratory chain. The increased oxidative capacity is associated with elevated oxidative stress and impaired antioxidant defense systems. Analysis of mitochondrial biogenesis markers indicates an enhanced capacity for new mitochondria production in CB1-/- mice, possibly adapting to altered muscle fiber composition. Changes in mitochondrial dynamics, mitophagy response, and unfolded protein response (UPR) pathways reveal a dynamic interplay in response to CB1 absence. The interconnected mitochondrial network, influenced by increased fusion and mitochondrial UPR components, underlines the dual role of CB1 in regulating both protein quality control and the generation of new mitochondria. These findings deepen our comprehension of the CB1 impact on muscle physiology, oxidative stress, and MQC processes, highlighting cellular adaptability to CB1-/-. This study paves the way for further exploration of intricate signaling cascades and cross-talk between cellular compartments in the context of CB1 and mitochondrial homeostasis.

Endoplasmic reticulum stress-mediated cell death in cardiovascular disease

The endoplasmic reticulum (ER) plays a vital function in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) can trigger various modes of cell death by activating the unfolded protein response (UPR) signaling pathway. Cell death plays a crucial role in the occurrence and development of diseases such as cancer, liver diseases, neurological diseases, and cardiovascular diseases. Several cardiovascular diseases including hypertension, atherosclerosis, and heart failure are associated with ER stress. ER stress-mediated cell death is of interest in cardiovascular disease. Moreover, an increasing body of evidence supports the potential of modulating ERS for treating cardiovascular disease. This paper provides a comprehensive review of the UPR signaling pathway, the mechanisms that induce cell death, and the modes of cell death in cardiovascular diseases. Additionally, we discuss the mechanisms of ERS and UPR in common cardiovascular diseases, along with potential therapeutic strategies.

SIRT1 regulates endoplasmic reticulum stress-related organ damage

Endoplasmic reticulum (ER) stress plays a key role in the pathogenesis of several organ damages. Studies show that excessive ER stress (ERS) can destroy cellular homeostasis, causing cell damage and physiological dysfunction in various organs. In recent years, Sirtuin1 (SIRT1) has become a research hotspot on ERS. Increasing evidence suggests that SIRT1 plays a positive role in various ERS-induced organ damage via multiple mechanisms, including inhibiting cellular apoptosis and promoting autophagy. SIRT1 can also alleviate liver, heart, lung, kidney, and intestinal damage by inhibiting ERS. We discuss the possible mechanism of SIRT1, explore potential therapeutic targets of diseases, and provide a theoretical basis for treating ERS-related diseases.

The PERK Branch of the Unfolded Protein Response Safeguards Protein Homeostasis and Mesendoderm Specification of Human Pluripotent Stem Cells

Cardiac development involves large-scale rearrangements of the proteome. How the developing cardiac cells maintain the integrity of the proteome during the rapid lineage transition remains unclear. Here it is shown that proteotoxic stress visualized by the misfolded and/or aggregated proteins appears during early cardiac differentiation of human pluripotent stem cells and is resolved by activation of the PERK branch of unfolded protein response (UPR). PERK depletion increases misfolded and/or aggregated protein accumulation, leading to pluripotency exit defect and impaired mesendoderm specification of human pluripotent stem cells. Mechanistically, it is found that PERK safeguards mesendoderm specification through its conserved downstream effector ATF4, which subsequently activates a novel transcriptional target WARS1, to cope with the differentiation-induced proteotoxic stress. The results indicate that protein quality control represents a previously unrecognized core component of the cardiogenic regulatory network. Broadly, these findings provide a framework for understanding how UPR is integrated into the developmental program by activating the PERK-ATF4-WARS1 axis.

Andrographolide contributes to the attenuation of cardiac hypertrophy by suppressing endoplasmic reticulum stress

CONTEXT

Andrographolide (Andr) is a bioactive Andr diterpenoid extracted from herbaceous Andrographis paniculata (Burm. F.) Wall. ex Nees (Acanthaceae). Andr can relieve cardiac dysfunction in mice by inhibiting the mitogen-activated protein kinases (MAPK) pathway.

OBJECTIVE

This study investigates the efficacy and underlying mechanism of Andr on cardiac hypertrophy in mice.

MATERIALS AND METHODS

Male C57 mice (20-25 g, 6-8 weeks) were divided into four groups (n = 10 mice/group) as sham group (sham operation), transverse aortic constriction (TAC) model group, TAC + Andr 100 mg/kg group and TAC + Andr 200 mg/kg group. Andr groups were given intragastric administration of Andr (100 and 200 mg/kg) once a day for 14 consecutive days. An in vitro hypertrophy model was established by adding 1 μM of Ang II to H9c2 cells for 48 h induction.

RESULTS

In TAC-mice, Andr improved echocardiographic indices [reduced LVESD (30.4% or 37.1%) and LVEDD (24.8% or 26.4%), increased EF (22.9% or 42.6%) and FS (25.4% or 52.2%)], reduced BNP (11.5% or 23.6%) and Ang II levels (10.3% or 32.8%), attenuates cardiac fibrosis and reduces cardiac cell apoptosis in TAC mice. In vitro, Andr attenuated cardiomyocyte hypertrophy and decreased the protein expression of GRP78 (67.8%), GRP94 (47.6%), p-PERK (44.9%) and CHOP (66.8%) in Ang-II-induced H9c2 cells and reversed after endoplasmic reticulum (ER) stress agonist Tunicamycin (TN) treatment.

DISCUSSION AND CONCLUSIONS

Andr was found to be an anti-hypertrophic regulator, which could attenuate cardiac hypertrophy by suppressing ER stress. It may be a new therapeutic drug for cardiac hypertrophy.

IL-6/gp130/STAT3 signaling contributed to the activation of the PERK arm of the unfolded protein response in response to chronic β-adrenergic stimulation

Prolonged activation of the PERK branch of the unfolded protein response (UPR) promotes cardiomyocytes apoptosis in response to chronic β-adrenergic stimulation. STAT3 plays a critical role in β-adrenergic functions in the heart. However, whether STAT3 contributed to β-adrenoceptor-mediated PERK activation and how β-adrenergic signaling activates STAT3 remains unclear. This study aimed to investigate whether STAT3-Y705 phosphorylation contributed to the PERK arm activation in cardiomyocytes and if IL-6/gp130 signaling was involved in the chronic β-AR-stimulation-induced STAT3 and PERK arm activation. We found that the PERK phosphorylation was positively associated with STAT3 activation. Wild-type STAT3 plasmids transfection activated the PERK/eIF2α/ATF4/CHOP pathway in cardiomyocytes while dominant negative Y705F STAT3 plasmids caused no obvious effect on PERK signaling. Stimulation with isoproterenol produced a significant increase in the level of IL-6 in the cardiomyocyte's supernatants, while IL-6 silence inhibited PERK phosphorylation but failed to attenuate STAT3 activation in response to isoproterenol stimulation. Gp130 silence attenuated isoproterenol-induced STAT3 activation and PERK phosphorylation. Inhibiting IL-6/gp130 pathway by bazedoxifene and inhibiting STAT3 by stattic both reversed isoproterenol-induced STAT3-Y705 phosphorylation, ROS production, PERK activation, IRE1α activation, and cardiomyocytes apoptosis in vitro. Bazedoxifene (5 mg/kg/day by oral gavage once a day) exhibited similar effect as carvedilol (10 mg/kg/day by oral gavage once a day) on attenuating chronic isoproterenol (30 mg/kg by abdominal injection once a day, 7 days) induced cardiac systolic dysfunction, cardiac hypertrophy and fibrosis in C57BL/6 mice. Meanwhile, bazedoxifene attenuates isoproterenol-induced STAT3-Y705 phosphorylation, PERK/eIF2α/ATF4/CHOP activation, IRE1α activation, and cardiomyocytes apoptosis to a similar extend as carvedilol in the cardiac tissue of mice. Our results showed that chronic β-adrenoceptor-mediated stimulation activated the STAT3 and PERK arm of the UPR at least partially via IL-6/gp130 pathway. Bazedoxifene has great potential to be used as an alternative to conventional β-blockers to attenuate β-adrenoceptor-mediated maladaptive UPR.

Selenium nanoparticles alleviate deoxynivalenol-induced intestinal epithelial barrier dysfunction by regulating endoplasmic reticulum stress in IPEC-J2 cells

The intestinal epithelial barrier plays a crucial role in maintaining human and animal health. Deoxynivalenol (DON) is a mycotoxin that contaminates cereal-based foods worldwide, which is a serious threat to human and animal health. This study was aimed to investigate the protective effect of selenium nanoparticles (SeNPs) synthesized by Lactobacillus casei ATCC 393 against DON-induced intestinal epithelial barrier dysfunction and its relationship with PERK-mediated signaling pathway. IPEC-J2 cells were randomly assigned to four groups: Con (vehicle), DON (0.6 μg DON/mL, 48 h), SeNPs+DON (8 μg Se/mL, 24 h; 0.6 μg DON/mL, 48 h) and SeNPs (8 μg Se/mL, 24 h). Compared with Con group, the transepithelial electrical resistance (TEER) and the tight junction proteins expression of IPEC-J2 cells exposed to DON was increased and decreased, respectively. In addition, DON exposure led to increased ROS content, decreased antioxidant capacity, structural damage of endoplasmic reticulum (ER), and activation of endoplasmic reticulum stress (ERS)-related protein kinase R-like endoplasmic reticulum kinase (PERK) pathway in IPEC-J2. Compared with SeNPs+DON group, SeNPs alleviated oxidative stress, ER structure damage and PERK pathway activation and the increase of intestinal epithelial permeability of IPEC-J2 cells exposed to DON. PERK agonist (CCT020312) and inhibitor (GSK2656157) treatments were performed to identify the role of PERK signaling pathway in the regulatory effects of SeNPs on DON-induced intestinal epithelial barrier dysfunction. Compared with SeNPs+DON group, PERK agonist increased the expression levels of p-PERK. PERK inhibitor exerted a similar inhibitory effect to SeNPs on the p-PERK expression. In conclusion, SeNPs effectively alleviate DON-induced intestinal epithelial barrier dysfunction in IPEC-J2 cells, which are closely associated with ERS-related PERK signaling pathway. This will provide a potential solution for prevention and control of DON in the aquaculture industry.

Crosstalk between endoplasmic reticulum stress and non-coding RNAs in cardiovascular diseases

Cells are exposed to various pathological stimulus within the cardiovascular system that challenge cells to adapt and survive. Several of these pathological stimulus alter the normal function of the endoplasmic reticulum (ER), leading to the accumulation of unfolded and misfolded proteins, thus triggering the unfolded protein response (UPR) to cope with the stress or trigger apoptosis of damaged cells. Downstream components of the UPR regulate transcription and translation reprogramming to ensure selective gene expression in response to pathological stimulus, including the expression of non-coding RNAs (ncRNAs). The ncRNAs play crucial roles in regulating transcription and translation, and their aberrant expression is associated with the development of cardiovascular disease (CVD). Notably, ncRNAs and ER stress can modulate each other and synergistically affect the development of CVD. Therefore, studying the interaction between ER stress and ncRNAs is necessary for effective prevention and treatment of CVD. In this review, we discuss the UPR signaling pathway and ncRNAs followed by the interplay regulation of ER stress and ncRNAs in CVD, which provides further insights into the understanding of the pathogenesis of CVD and therapeutic strategies. This article is categorized under: RNA in Disease and Development > RNA in Disease.

LncRNAs and CircRNAs in Endoplasmic Reticulum Stress: A Promising Target for Cardiovascular Disease?

The endoplasmic reticulum (ER) is a principal subcellular organelle responsible for protein quality control in the secretory pathway, preventing protein misfolding and aggregation. Failure of protein quality control in the ER triggers several molecular mechanisms such as ER-associated degradation (ERAD), the unfolded protein response (UPR) or reticulophagy, which are activated upon ER stress (ERS) to re-establish protein homeostasis by transcriptionally and translationally regulated complex signalling pathways. However, maintenance over time of ERS leads to apoptosis if such stress cannot be alleviated. The presence of abnormal protein aggregates results in loss of cardiomyocyte protein homeostasis, which in turn results in several cardiovascular diseases such as dilated cardiomyopathy (DCM) or myocardial infarction (MI). The influence of a non-coding genome in the maintenance of proper cardiomyocyte homeostasis has been widely proven. To date, the impact of microRNAs in molecular mechanisms orchestrating ER stress response has been widely described. However, the role of long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) is just beginning to be addressed given the potential role of these RNA classes as therapeutic molecules. Here, we provide a current state-of-the-art review of the roles of distinct lncRNAs and circRNAs in the modulation of ERS and UPR and their impact in cardiovascular diseases.

Three tyrosine kinase inhibitors cause cardiotoxicity by inducing endoplasmic reticulum stress and inflammation in cardiomyocytes

BACKGROUND

Tyrosine kinase inhibitors (TKIs) are anti-cancer therapeutics often prescribed for long-term treatment. Many of these treatments cause cardiotoxicity with limited cure. We aim to clarify molecular mechanisms of TKI-induced cardiotoxicity so as to find potential targets for treating the adverse cardiac complications.

METHODS

Eight TKIs with different levels of cardiotoxicity reported are selected. Phenotypic and transcriptomic responses of human cardiomyocytes to TKIs at varying doses and times are profiled and analyzed. Stress responses and signaling pathways that modulate cardiotoxicity induced by three TKIs are validated in cardiomyocytes and rat hearts.

RESULTS

Toxicity rank of the eight TKIs determined by measuring their effects on cell viability, contractility, and respiration is largely consistent with that derived from database or literature, indicating that human cardiomyocytes are a good cellular model for studying cardiotoxicity. When transcriptomes are measured for selected TKI treatments with different levels of toxicity in human cardiomyocytes, the data are classified into 7 clusters with mainly single-drug clusters. Drug-specific effects on the transcriptome dominate over dose-, time- or toxicity-dependent effects. Two clusters with three TKIs (afatinib, ponatinib, and sorafenib) have the top enriched pathway as the endoplasmic reticulum stress (ERS). All three TKIs induce ERS in rat primary cardiomyocytes and ponatinib activates the IRE1α-XBP1s axis downstream of ERS in the hearts of rats underwent a 7-day course of drug treatment. To look for potential triggers of ERS, we find that the three TKIs induce transient reactive oxygen species followed by lipid peroxidation. Inhibiting either PERK or IRE1α downstream of ERS blocks TKI-induced cardiac damages, represented by the induction of cardiac fetal and pro-inflammatory genes without causing more cell death.

CONCLUSIONS

Our data contain rich information about phenotypic and transcriptional responses of human cardiomyocytes to eight TKIs, uncovering potential molecular mechanisms in modulating cardiotoxicity. ER stress is activated by multiple TKIs and leads to cardiotoxicity through promoting expression of pro-inflammatory factors and cardiac fetal genes. ER stress-induced inflammation is a promising therapeutic target to mitigate ponatinib- and sorafenib-induced cardiotoxicity.

ER stress induces upregulation of transcription factor Tbx20 and downstream Bmp2 signaling to promote cardiomyocyte survival

In the mammalian heart, fetal cardiomyocytes proliferate prior to birth; however, they exit the cell cycle shortly after birth. Recent studies show that adult cardiomyocytes re-enters the cell cycle postinjury to promote cardiac regeneration. The endoplasmic reticulum (ER) orchestrates the production and assembly of different types of proteins, and a disruption in this machinery leads to the generation of ER stress, which activates the unfolded protein response. There is a very fine balance between ER stress-mediated protective and proapoptotic responses. T-box transcription factor 20 (Tbx20) promotes embryonic and adult cardiomyocyte proliferation postinjury to restore cardiac homeostasis. However, the function and regulatory interactions of Tbx20 in ER stress-induced cardiomyopathy have not yet been reported. We show here that ER stress upregulates Tbx20, which activates downstream bone morphogenetic protein 2 (Bmp2)-pSmad1/5/8 signaling to induce cardiomyocyte proliferation and limit apoptosis. However, augmenting ER stress reverses this protective response. We also show that increased expression of tbx20 during ER stress is mediated by the activating transcription factor 6 arm of the unfolded protein response. Cardiomyocyte-specific loss of Tbx20 results in decreased cardiomyocyte proliferation and increased apoptosis. Administration of recombinant Bmp2 protein during ER stress upregulates Tbx20 leading to augmented proliferation, indicating a feed-forward loop mechanism. In in vivo ER stress, as well as in diabetic cardiomyopathy, the activity of Tbx20 is increased with concomitant increased cardiomyocyte proliferation and decreased apoptosis. These data support a critical role of Tbx20-Bmp2 signaling in promoting cardiomyocyte survival during ER stress-induced cardiomyopathies.

IL-12α deficiency attenuates pressure overload-induced cardiac inflammation, hypertrophy, dysfunction, and heart failure progression

IL-12α plays an important role in modulating inflammatory response, fibroblast proliferation and angiogenesis through modulating macrophage polarization or T cell function, but its effect on cardiorespiratory fitness is not clear. Here, we studied the effect of IL-12α on cardiac inflammation, hypertrophy, dysfunction, and lung remodeling in IL-12α gene knockout (KO) mice in response to chronic systolic pressure overload produced by transverse aortic constriction (TAC). Our results showed that IL-12α KO significantly ameliorated TAC-induced left ventricular (LV) failure, as evidenced by a smaller decrease of LV ejection fraction. IL-12α KO also exhibited significantly attenuated TAC-induced increase of LV weight, left atrial weight, lung weight, right ventricular weight, and the ratios of them in comparison to body weight or tibial length. In addition, IL-12α KO showed significantly attenuated TAC-induced LV leukocyte infiltration, fibrosis, cardiomyocyte hypertrophy, and lung inflammation and remodeling (such as lung fibrosis and vessel muscularization). Moreover, IL-12α KO displayed significantly attenuated TAC-induced activation of CD4+ T cells and CD8+ T cells in the lung. Furthermore, IL-12α KO showed significantly suppressed accumulation and activation of pulmonary macrophages and dendritic cells. Taken together, these findings indicate that inhibition of IL-12α is effective in attenuating systolic overload-induced cardiac inflammation, heart failure development, promoting transition from LV failure to lung remodeling and right ventricular hypertrophy.

Growth Hormone-Releasing Hormone in Endothelial Inflammation

The discovery of hypothalamic hormones propelled exciting advances in pharmacotherapy and improved life quality worldwide. Growth hormone-releasing hormone (GHRH) is a crucial element in homeostasis maintenance, and regulates the release of growth hormone from the anterior pituitary gland. Accumulating evidence suggests that this neuropeptide can also promote malignancies, as well as inflammation. Our review is focused on the role of that 44 - amino acid peptide (GHRH) and its antagonists in inflammation and vascular function, summarizing recent findings in the corresponding field. Preclinical studies demonstrate the protective role of GHRH antagonists against endothelial barrier dysfunction, suggesting that the development of those peptides may lead to new therapies against pathologies related to vascular remodeling (eg, sepsis, acute respiratory distress syndrome). Targeted therapies for those diseases do not exist.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

UPRmt and coordinated UPRER in type 2 diabetes

The mitochondrial unfolded protein response (UPR^mt) is a molecular mechanism that maintains mitochondrial proteostasis under stress and is closely related to various metabolic diseases, such as type 2 diabetes (T2D). Similarly, the unfolded protein response of the endoplasmic reticulum (UPR^ER) is responsible for maintaining proteomic stability in the endoplasmic reticulum (ER). Since the mitochondria and endoplasmic reticulum are the primary centers of energy metabolism and protein synthesis in cells, respectively, a synergistic mechanism must exist between UPR^mt and UPR^ER to cooperatively resist stresses such as hyperglycemia in T2D. Increasing evidence suggests that the protein kinase RNA (PKR)-like endoplasmic reticulum kinase (PERK) signaling pathway is likely an important node for coordinating UPR^mt and UPR^ER. The PERK pathway is activated in both UPR^mt and UPR^ER, and its downstream molecules perform important functions. In this review, we discuss the mechanisms of UPR^mt, UPR^ER and their crosstalk in T2D.

Inhibitory effect of (pro)renin receptor decoy inhibitor PRO20 on endoplasmic reticulum stress during cardiac remodeling

Background: Ectopic activation of renin-angiotensin-system contributes to cardiovascular and renal diseases. (Pro)renin receptor (PRR) binds to renin and prorenin, participating in the progression of nephrology. However, whether PRR could be considered as a therapeutic target for cardiac remodeling and heart failure remains unknown.

Materials and methods: Transverse aortic constriction (TAC) surgery was performed to establish a mouse model of chronic pressure overload-induced cardiac remodeling. Neonatal rat cardiomyocytes (CMs) and cardiac fibroblasts (CFs) were isolated and stimulated by Angiotensin II (Ang II). PRR decoy inhibitor PRO20 was synthesized and used to evaluate its effect on cardiac remodeling.

Results: Soluble PRR and PRR were significantly upregulated in TAC-induced cardiac remodeling and Ang II-treated CMs and CFs. Results of In vivo experiments showed that suppression of PRR by PRO20 significantly retarded cardiac remodeling and heart failure indicated by morphological and echocardiographic analyses. In vitro experiments, PRO20 inhibited CM hypertrophy, and also alleviated CF activation, proliferation and extracellular matrix synthesis. Mechanically, PRO20 enhanced intracellular cAMP levels, but not affected cGMP levels in CMs and CFs. Moreover, treatment of PRO20 in CFs markedly attenuated the production of reactive oxygen species and phosphorylation of IRE1 and PERK, two well-identified markers of endoplasmic reticulum (ER) stress. Accordingly, administration of PRO20 reversed ER stressor thapsigargin-induced CM hypertrophy and CF activation/migration.

Conclusion: Taken together, these findings suggest that inhibition of PRR by PRO20 attenuates cardiac remodeling through increasing cAMP levels and reducing ER stress in both CMs and CFs.

Resveratrol and regular exercise may attenuate hypertension-induced cardiac dysfunction through modulation of cellular stress responses

AIMS

Hypertension is one of the major causes of cardiac damage. In this study, the effects of resveratrol supplementation and regular exercise on hypertension-induced cellular stress responses of myocardium were compared.

MAIN METHODS

Hypertension was induced in male Wistar rats by deoxycorticosterone-acetate + salt administration for 12 weeks. Resveratrol and regular exercise were applied for the last six weeks. In addition to biochemical and molecular examinations, isoprenaline, phenylephrine and, acetylcholine-mediated contractions and sinus rate were recorded in the isolated cardiac tissues.

KEY FINDINGS

Resveratrol and regular exercise reduced systolic blood pressure in hypertensive rats. The altered adrenergic and cholinergic responses of the right atrium and left papillary muscles in hypertension were separately improved by resveratrol and regular exercise. Resveratrol and regular exercise decreased plasma and cardiac total antioxidant capacity and, augmented the expression of antioxidant genes in hypertensive rats. While regular exercise restored the increase in p-PERK expression associated with endoplasmic reticulum stress and decrease in mitophagic marker PINK1 expression, resveratrol only ameliorated PINK1 expression in hypertensive rats. Resveratrol and exercise training suppressed hypertension-induced NLRP3 inflammasome activation by reversing the increase in NLRP3, p-NF-κB expression and the mature-IL-1β/pro-IL-1β and cleaved-caspase-1/pro-caspase-1 ratio. Resveratrol and exercise enhanced mRNA expression of caspase-3, bax, and bcl-2 involved in the apoptotic pathway, but attenuated phosphorylation of stress-related mitogenic proteins p38 and JNK induced by hypertension.

SIGNIFICANCE

Our study demonstrated the protective effect of resveratrol and exercise on hypertension-induced cardiac dysfunction by modulating cellular stress responses including oxidative stress, ER stress, mitophagy, NLRP3 inflammasome-mediated inflammation, and mitogenic activation.

Intermedin1-53 Inhibits NLRP3 Inflammasome Activation by Targeting IRE1α in Cardiac Fibrosis

Intermedin (IMD), a paracrine/autocrine peptide, protects against cardiac fibrosis. However, the underlying mechanism remains poorly understood. Previous study reports that activation of nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome contributes to cardiac fibrosis. In this study, we aimed to investigate whether IMD mitigated cardiac fibrosis by inhibiting NLRP3. Cardiac fibrosis was induced by angiotensin II (Ang II) infusion for 2 weeks in rats. Western blot, real-time PCR, histological staining, immunofluorescence assay, RNA sequencing, echocardiography, and hemodynamics were used to detect the role and the mechanism of IMD in cardiac fibrosis. Ang II infusion resulted in rat cardiac fibrosis, shown as over-deposition of myocardial interstitial collagen and cardiac dysfunction. Importantly, NLRP3 activation and endoplasmic reticulum stress (ERS) were found in Ang II-treated rat myocardium. Ang II infusion decreased the expression of IMD and increased the expression of the receptor system of IMD in the fibrotic rat myocardium. IMD treatment attenuated the cardiac fibrosis and improved cardiac function. In addition, IMD inhibited the upregulation of NLRP3 markers and ERS markers induced by Ang II. In vitro, IMD knockdown by small interfering RNA significantly promoted the Ang II-induced cardiac fibroblast and NLRP3 activation. Moreover, silencing of inositol requiring enzyme 1 α (IRE1α) blocked the effects of IMD inhibiting fibroblast and NLRP3 activation. Pre-incubation with PKA pathway inhibitor H89 blocked the effects of IMD on the anti-ERS, anti-NLRP3, and anti-fibrotic response. In conclusion, IMD alleviated cardiac fibrosis by inhibiting NLRP3 inflammasome activation through suppressing IRE1α via the cAMP/PKA pathway.

Endoplasmic Reticulum-Mitochondria Contacts: A Potential Therapy Target for Cardiovascular Remodeling-Associated Diseases

Cardiovascular remodeling occurs in cardiomyocytes, collagen meshes, and vascular beds in the progress of cardiac insufficiency caused by a variety of cardiac diseases such as chronic ischemic heart disease, chronic overload heart disease, myocarditis, and myocardial infarction. The morphological changes that occur as a result of remodeling are the critical pathological basis for the occurrence and development of serious diseases and also determine morbidity and mortality. Therefore, the inhibition of remodeling is an important approach to prevent and treat heart failure and other related diseases. The endoplasmic reticulum (ER) and mitochondria are tightly linked by ER-mitochondria contacts (ERMCs). ERMCs play a vital role in different signaling pathways and provide a satisfactory structural platform for the ER and mitochondria to interact and maintain the normal function of cells, mainly by involving various cellular life processes such as lipid metabolism, calcium homeostasis, mitochondrial function, ER stress, and autophagy. Studies have shown that abnormal ERMCs may promote the occurrence and development of remodeling and participate in the formation of a variety of cardiovascular remodeling-associated diseases. This review focuses on the structure and function of the ERMCs, and the potential mechanism of ERMCs involved in cardiovascular remodeling, indicating that ERMCs may be a potential target for new therapeutic strategies against cardiovascular remodeling-induced diseases.

Integrated Stress Response Couples Mitochondrial Protein Translation With Oxidative Stress Control

BACKGROUND

The integrated stress response (ISR) is an evolutionarily conserved process to cope with intracellular and extracellular disturbances. Myocardial infarction is a leading cause of death worldwide. Coronary artery reperfusion, the most effective means to mitigate cardiac damage of myocardial infarction, causes additional reperfusion injury. This study aimed to investigate the role of the ISR in myocardial ischemia/reperfusion (I/R).

METHODS

Cardiac-specific gain- and loss-of-function approaches for the ISR were used in vivo. Myocardial I/R was achieved by ligation of the cardiac left anterior descending artery for 45 minutes followed by reperfusion for different times. Cardiac function was assessed by echocardiography. Cultured H9c2 cells, primary rat cardiomyocytes, and mouse embryonic fibroblasts were used to dissect underlying molecular mechanisms. Tandem mass tag labeling and mass spectrometry was conducted to identify protein targets of the ISR. Pharmacologic means were tested to manipulate the ISR for therapeutic exploration.

RESULTS

We show that the PERK (PKR-like endoplasmic reticulum resident kinase)/eIF2α (α subunit of eukaryotic initiation factor 2) axis of the ISR is strongly induced by I/R in cardiomyocytes in vitro and in vivo. We further reveal a physiologic role of PERK/eIF2α signaling by showing that acute activation of PERK in the heart confers robust cardioprotection against reperfusion injury. In contrast, cardiac-specific deletion of PERK aggravates cardiac responses to reperfusion. Mechanistically, the ISR directly targets mitochondrial complexes through translational suppression. We identify NDUFAF2 (NADH:ubiquinone oxidoreductase complex assembly factor 2), an assembly factor of mitochondrial complex I, as a selective target of PERK. Overexpression of PERK suppresses the protein expression of NDUFAF2 and PERK inhibition causes an increase of NDUFAF2. Silencing of NDUFAF2 significantly rescues cardiac cell survival from PERK knockdown under I/R. We show that activation of PERK/eIF2α signaling reduces mitochondrial complex-derived reactive oxygen species and improves cardiac cell survival in response to I/R. Moreover, pharmacologic stimulation of the ISR protects the heart against reperfusion damage, even after the restoration of occluded coronary artery, highlighting clinical relevance for myocardial infarction treatment.

CONCLUSIONS

These results suggest that the ISR improves cell survival and mitigates reperfusion damage by selectively suppressing mitochondrial protein synthesis and reducing oxidative stress in the heart.

Cardiac hypertrophy caused by hyperthyroidism in rats: the role of ATF-6 and TRPC1 channels

Hyperthyroidism influences the development of cardiac hypertrophy. Transient receptor potential canonical channels (TRPCs) and endoplasmic reticulum (ER) stress are regarded as critical pathways in cardiac hypertrophy. Hence, we aimed to identify the TRPCs associated with ER stress in hyperthyroidism-induced cardiac hypertrophy. Twenty adult Wistar albino male rats were used in the study. The control group was fed with standard food and tap water. The group with hyperthyroidism was also fed with standard rat food, along with tap water that contained 12 mg/L of thyroxine (T4) for 4 weeks. At the end of the fourth week, the serum-free triiodothyronine (T3), T4, and thyroid-stimulating hormone (TSH) levels of the groups were measured. The left ventricle of each rat was used for histochemistry, immunohistochemistry, Western blot, total antioxidant capacity (TAC), and total oxidant status (TOS) analysis. As per our results, activating transcription factor 6 (ATF-6), inositol-requiring kinase 1 (IRE-1), and TRPC1, which play a significant role in cardiac hypertrophy caused by hyperthyroidism, showed increased activation. Moreover, TOS and serum-free T3 levels increased, while TAC and TSH levels decreased. With the help of the literature review in our study, we could, for the first time, indicate that the increased activation of ATF-6, IRE-1, and TRPC1-induced deterioration of the Ca2+ ion balance leads to hypertrophy in hyperthyroidism due to heart failure.

Perk heterozygosity ameliorates chronic hypoxia-induced pulmonary hypertension and right ventricular hypertrophy in male rats

BACKGROUND

Pulmonary hypertension (PH) is a rare and deadly disease characterized by remodeling of the pulmonary vasculature and increased pulmonary artery pressure. hypobaric pulmonary hypertension (HPH) is clinically classified as group 4 of pulmonary hypertension and has a poor prognosis . Previous reports showed that HPH was associated with increased endoplasmic reticulum (ER) stress. The protein kinase R-like endoplasmic reticulum kinase (PERK) is an ER-associated stress protein. However, to date, its physiological effects on HPH and RVF development remains unknown. This study aimed to assess PERK's role in HPH and RV function using in vivo experimental model.

METHODS

Perk-knockout male Sprague-Dawley rats were generated and were housed in either a hypobaric chamber or in a normoxic environment. After stimulation for 4 weeks, the hemodynamic parameters of the rats were measured. The heart and lungs were harvested for pathological observation. Blood was collected for the detection of inflammatory indexes. The right ventricle tissue was collected to assess phosphorylated-AKT, ROCK1, ET1, and MMP2 protein expression.

RESULTS: WE FIRSTLY GENERATED PERK+/− RATS,

Under normal conditions, Perk^+/- rats showed no changes in mPAP(mean pulmonary artery pressure), RVHI(Right ventricular hypertrophy index), cardiomyocyte size and interstitial fibrosis, and pulmonary vascular remodeling. However, in response to chronic hypoxia, Perk^+/- rats exhibited decreased in mPAP, RVHI, ventricular fibrosis, and lung remodeling compared to wild-type rats. Perk^+/- rats also showed lower expression of phosphor-AKT, ROCK1, ET1, and MMP2 protein in response to chronic hypoxia.

CONCLUSIONS

These findings suggest that Perk heterozygosity protects against HPH and Perk may be a suitable target for treating HPH.

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

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

The Heart of the Alzheimer's: A Mindful View of Heart Disease

Purpose of Review: This review summarizes the current evidence for the involvement of proteotoxicity and protein quality control systems defects in diseases of the central nervous and cardiovascular systems. Specifically, it presents the commonalities between the pathophysiology of protein misfolding diseases in the heart and the brain. Recent Findings: The involvement of protein homeostasis dysfunction has been for long time investigated and accepted as one of the leading pathophysiological causes of neurodegenerative diseases. In cardiovascular diseases instead the mechanistic focus had been on the primary role of Ca2+ dishomeostasis, myofilament dysfunction as well as extracellular fibrosis, whereas no attention was given to misfolding of proteins as a pathogenetic mechanism. Instead, in the recent years, several contributions have shown protein aggregates in failing hearts similar to the ones found in the brain and increasing evidence have highlighted the crucial importance that proteotoxicity exerts via pre-amyloidogenic species in cardiovascular diseases as well as the prominent role of the cellular response to misfolded protein accumulation. As a result, proteotoxicity, unfolding protein response (UPR), and ubiquitin-proteasome system (UPS) have recently been investigated as potential key pathogenic pathways and therapeutic targets for heart disease. Summary: Overall, the current knowledge summarized in this review describes how the misfolding process in the brain parallels in the heart. Understanding the folding and unfolding mechanisms involved early through studies in the heart will provide new knowledge for neurodegenerative proteinopathies and may prepare the stage for targeted and personalized interventions.

Mitochondrial Membrane Intracellular Communication in Healthy and Diseased Myocardium

Research efforts in the twenty-first century have been paramount to the discovery and development of novel pharmacological treatments in a variety of diseases resulting in improved life expectancy. Yet, cardiac disease remains a leading cause of morbidity and mortality worldwide. Over time, there has been an expansion in conditions such as atrial fibrillation (AF) and heart failure (HF). Although past research has elucidated specific pathways that participate in the development of distinct cardiac pathologies, the exact mechanisms of action leading to disease remain to be fully characterized. Protein turnover and cellular bioenergetics are integral components of cardiac diseases, highlighting the importance of mitochondria and endoplasmic reticulum (ER) in driving cellular homeostasis. More specifically, the interactions between mitochondria and ER are crucial to calcium signaling, apoptosis induction, autophagy, and lipid biosynthesis. Here, we summarize mitochondrial and ER functions and physical interactions in healthy physiological states. We then transition to perturbations that occur in response to pathophysiological challenges and how this alters mitochondrial–ER and other intracellular organelle interactions. Finally, we discuss lifestyle interventions and innovative therapeutic targets that may be used to restore beneficial mitochondrial and ER interactions, thereby improving cardiac function.

High GRP78 levels in Covid-19 infection: A case-control study

Introduction

Covid-19 infection was declared a global pandemic by WHO on March 11, 2020. GRP78 protein is known to be involved in the intrusion of numerous viruses. Our current study tries to provide some insight into the variation of GRP78 protein levels in patients with Covid-19 (−) pneumonia, Covid-19 (+) pneumonia, and CT negative Covid-19 infection in comparison to the normal population through a larger number of cases.

Materials and methods

42 patients who have Covid-19 (−) pneumonia; 72 patients who have Covid-19 infection (30 pneumonia,42 CT negative patients) and 30 patient who have no known diseases (control group) have included in the study after the clinical and radiological evaluation. Serum GRP78 levels of the subjects were measured through a commercially available enzyme-linked immunosorbent assay (ELISA) kit.

Results

The GRP78 level was found to be significantly higher in the Covid-19 infection group than both Covid-19 (−) pneumonia and control group (p = 0.031 and p = 0.0001, respectively).No significant difference was evident between Covid-19 (−) pneumonia, Covid-19 (+) pneumonia and CT negative Covid 19 infection groups with respect to GRP78 levels (p = 0.09). In addition, the GRP78 levels were significantly higher in the Covid-19 (−) pneumonia group than the control group (p = 0.0001).

Conclusion

This prospective case-control study reveals that the serum GRP78 levels significantly increased during Covid-19 infection in comparison to both the Covid-19 (−) pneumonia and the control group. As the association between SARS-CoV-2 virus and GRP78 protein is revealed more clearly, this association may come to the fore as a therapeutic target.

Involvement of the unfolded protein response in the protective effects of growth hormone releasing hormone antagonists in the lungs

Growth hormone releasing hormone (GHRH) antagonists enhance endothelial barrier function and counteract the LPS-induced lung endothelial hyperpermeability, the cardinal feature of the acute respiratory distress syndrome (ARDS). The unfolded protein response (UPR) is a multifaceted molecular mechanism, strongly involved in tissue defense against injury. The current study introduces the induction of UPR by GHRH antagonists, since those peptides induced several UPR activation markers, including the inositol-requiring enzyme-1α (IRE1α), the protein kinase RNA-like ER kinase (PERK), and the activating transcription factor 6 (ATF6). On the other hand, the GHRH agonist MR-409 exerted the opposite effects. Furthermore, GHRH antagonists counteracted the kifunensine (UPR suppressor)-induced lung endothelial barrier dysfunction. Our observations suggest that UPR mediates, at least in part, the protective effects of GHRH antagonists in the lung microvasculature. To the best of our knowledge; this is the first study to provide experimental evidence in support of the hypothesis that UPR induction is a novel mechanism by which GHRH antagonists oppose severe human disease, including ARDS.

Clinical and Proteomic Correlates of Plasma ACE2 (Angiotensin-Converting Enzyme 2) in Human Heart Failure

ACE2 (angiotensin-converting enzyme 2) is a key component of the renin-angiotensin-aldosterone system. Yet, little is known about the clinical and biologic correlates of circulating ACE2 levels in humans. We assessed the clinical and proteomic correlates of plasma (soluble) ACE2 protein levels in human heart failure. We measured plasma ACE2 using a modified aptamer assay among PHFS (Penn Heart Failure Study) participants (n=2248). We performed an association study of ACE2 against ≈5000 other plasma proteins measured with the SomaScan platform. Plasma ACE2 was not associated with ACE inhibitor and angiotensin-receptor blocker use. Plasma ACE2 was associated with older age, male sex, diabetes mellitus, a lower estimated glomerular filtration rate, worse New York Heart Association class, a history of coronary artery bypass surgery, and higher pro-BNP (pro-B-type natriuretic peptide) levels. Plasma ACE2 exhibited associations with 1011 other plasma proteins. In pathway overrepresentation analyses, top canonical pathways associated with plasma ACE2 included clathrin-mediated endocytosis signaling, actin cytoskeleton signaling, mechanisms of viral exit from host cells, EIF2 (eukaryotic initiation factor 2) signaling, and the protein ubiquitination pathway. In conclusion, in humans with heart failure, plasma ACE2 is associated with various clinical factors known to be associated with severe coronavirus disease 2019 (COVID-19), including older age, male sex, and diabetes mellitus, but is not associated with ACE inhibitor and angiotensin-receptor blocker use. Plasma ACE2 protein levels are prominently associated with multiple cellular pathways involved in cellular endocytosis, exocytosis, and intracellular protein trafficking. Whether these have a causal relationship with ACE2 or are relevant to novel coronavirus-2 infection remains to be assessed in future studies.

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.

PERK-Mediated Suppression of microRNAs by Sildenafil Improves Mitochondrial Dysfunction in Heart Failure

Oxidative/nitrosative stress is a major trigger of cardiac dysfunction, involving the unfolded protein response and mitochondrial dysfunction. Activation of nitric oxide-cyclic guanosine monophosphate-protein kinase G signaling by sildenafil improves cardiac mal-remodeling during pressure-overload-induced heart failure. Transcriptome analysis was conducted in failing hearts with or without sildenafil treatment. Protein kinase R-like endoplasmic reticulum (ER) kinase (PERK) downstream signaling pathways, EIF2 and NRF2, were significantly altered. Although EIF2 signaling was suppressed, NRF2 signaling was upregulated, inhibiting the maturation of miR 24-3p through EGFR-mediated Ago2 phosphorylation. To study the effect of sildenafil on these pathways, we generated cardiac-specific PERK knockout mice. In these mice, sildenafil could not inhibit the maturations, the nuclear translocation of NRF2 was suppressed, and mitochondrial dysfunction advanced. Altogether, these results show that PERK-mediated suppression of miRNAs by sildenafil is vital for maintaining mitochondrial homeostasis through NRF2-mediated oxidative stress response.