The role of the proteasome in heart disease

Small molecules as modulators of the proteostasis machinery: Implication in cardiovascular diseases

With the escalating prevalence of cardiovascular diseases, the substantial socioeconomic burden on healthcare systems is intensifying. Accumulating empirical evidence underscores the pivotal role of the proteostasis network in regulating cardiac homeostasis and function. Disruptions in proteostasis may contribute to the loss of protein function or the acquisition of toxic functions, which are intricately linked to the development of cardiovascular ailments such as atrial fibrillation, heart failure, atherosclerosis, and cardiac aging. It is widely acknowledged that the proteostasis network encompasses molecular chaperones, autophagy, and the ubiquitin proteasome system (UPS). Consequently, the proteostasis network emerges as an appealing target for therapeutic interventions in cardiovascular diseases. Numerous small molecules, acting as modulators of the proteostasis machinery, have exhibited therapeutic efficacy in managing cardiovascular diseases. This review centers on elucidating the role of the proteostasis network in various cardiovascular diseases and explores the potential of small molecules as therapeutic agents.

Myocardial Protection and Current Cancer Therapy: Two Opposite Targets with Inevitable Cost

Myocardial protection against ischemia/reperfusion injury (IRI) is mediated by various ligands, activating different cellular signaling cascades. These include classical cytosolic mediators such as cyclic-GMP (c-GMP), various kinases such as Phosphatydilinositol-3- (PI3K), Protein Kinase B (Akt), Mitogen-Activated-Protein- (MAPK) and AMP-activated (AMPK) kinases, transcription factors such as signal transducer and activator of transcription 3 (STAT3) and bioactive molecules such as vascular endothelial growth factor (VEGF). Most of the aforementioned signaling molecules constitute targets of anticancer therapy; as they are also involved in carcinogenesis, most of the current anti-neoplastic drugs lead to concomitant weakening or even complete abrogation of myocardial cell tolerance to ischemic or oxidative stress. Furthermore, many anti-neoplastic drugs may directly induce cardiotoxicity via their pharmacological effects, or indirectly via their cardiovascular side effects. The combination of direct drug cardiotoxicity, indirect cardiovascular side effects and neutralization of the cardioprotective defense mechanisms of the heart by prolonged cancer treatment may induce long-term ventricular dysfunction, or even clinically manifested heart failure. We present a narrative review of three therapeutic interventions, namely VEGF, proteasome and Immune Checkpoint inhibitors, having opposing effects on the same intracellular signal cascades thereby affecting the heart. Moreover, we herein comment on the current guidelines for managing cardiotoxicity in the clinical setting and on the role of cardiovascular confounders in cardiotoxicity.

Genome-wide transcript and protein analysis highlights the role of protein homeostasis in the aging mouse heart

Investigation of the molecular mechanisms of aging in the human heart is challenging because of confounding factors, such as diet and medications, as well as limited access to tissues from healthy aging individuals. The laboratory mouse provides an ideal model to study aging in healthy individuals in a controlled environment. However, previous mouse studies have examined only a narrow range of the genetic variation that shapes individual differences during aging. Here, we analyze transcriptome and proteome data from 185 genetically diverse male and female mice at ages 6, 12, and 18 mo to characterize molecular changes that occur in the aging heart. Transcripts and proteins reveal activation of pathways related to exocytosis and cellular transport with age, whereas processes involved in protein folding decrease with age. Additional changes are apparent only in the protein data including reduced fatty acid oxidation and increased autophagy. For proteins that form complexes, we see a decline in correlation between their component subunits with age, suggesting age-related loss of stoichiometry. The most affected complexes are themselves involved in protein homeostasis, which potentially contributes to a cycle of progressive breakdown in protein quality control with age. Our findings highlight the important role of post-transcriptional regulation in aging. In addition, we identify genetic loci that modulate age-related changes in protein homeostasis, suggesting that genetic variation can alter the molecular aging process.

Proteome dynasmics and bioinformatics reveal major alterations in the turnover rate of functionally related cardiac and plasma proteins in a dog model of congestive heart failure

Protein pool turnover is a critically important cellular homeostatic component, yet it has been little explored in the context of heart failure (HF) pathophysiology. We employed in vivo ²H labeling/ proteome dynamics for non-biased discovery of turnover alterations involving functionally linked cardiac and plasma proteins in canine tachypacing-induced HF, an established preclinical model of dilated cardiomyopathy. Compared to control, dogs with congestive HF displayed bidirectional turnover changes of 28 cardiac proteins, i.e. reduced half-life of several key enzymes involved in glycolysis, homocysteine metabolism and glycogenesis, and increased half-life of proteins involved in proteolysis. Changes in plasma proteins were more modest: only 5 proteins, involved in various functions including proteolysis inhibition, hemoglobin, calcium and ferric-iron binding, displayed increased or decreased turnover rates. In other dogs undergoing cardiac tachypacing, we infused for 2 weeks the myokine Follistatin-like protein 1 (FSTL1), known for its ameliorative effects on HF-induced alterations. Proteome dynamics proved very sensitive in detecting the partial or complete prevention, by FSTL1, of cardiac and plasma protein turnover alterations. In conclusion, our study unveiled, for the first time in a large mammal, numerous HF-related alterations that may serve as the basis for future mechanistic research and/or as conceptually new molecular markers.

E3-ligase knock down revealed differential titin degradation by autopagy and the ubiquitin proteasome system

The sarcomere protein titin is a major determinant of cardiomyocyte stiffness and ventricular distensibility. The constant mechanical stress on titin requires well-controlled protein quality control, the exact mechanisms of which have not yet been fully elucidated. Here, we analyzed E3-ligases potentially responsible for cardiac titin ubiquitination and specifically studied the involvement of the autophagosomal system in titin degradation. Pharmacological inhibition of autophagy and the proteasome in cultured primary rat cardiomyocytes significantly elevated titin ubiquitination and increased titin degradation. Using in-vitro pull down assays we identified binding of E3-ligases MuRF1-3, CHIP and Fbx32 to several titin domains. Immunofluorescence analysis showed sarcomeric localization of the E3-ligases. siRNA-mediated knock-down of the E3-ligases MuRF-1, -3 and a combination of CHIP/Fbx32 significantly reduced autophagy-related titin ubiquitination, whereas knock-down of MuRF-2 and -3 reduced proteasome-related titin ubiquitination. We demonstrated that the proteasomal and the autophagosomal-lysosomal system participate in degradation of the titin filament. We found that ubiquitination and degradation of titin are partially regulated by E3-ligases of the MuRF family. We further identified CHIP and Fbx32 as E3-ligases involved in titin ubiquitination.

Clarifying the pharmacological mechanisms of action of Shenfu Decoction on cardiovascular diseases using a network pharmacology approach

Since the molecular mechanisms underlying in the pathogenesis of cardiovascular diseases (CVD) are extremely complex and have not yet been elucidated in detail, CVD remain the leading cause of death worldwide. Traditional Chinese medicine involves the treatment of disease from an overall perspective, and its therapeutic effects on CVD have been demonstrated. However, the mechanisms contributing to the multiscale treatment of cardiovascular diseases at the systematic level remain unclear. Network pharmacology methods and a gene chip data analysis were integrated and applied in the present study, which was conducted to investigate the potential target genes and related pathways of Shenfu Decoction (SFD) for the treatment of myocardial injury. The gene chip analysis was initially performed, followed by network pharmacology to identify differentially expressed genes (DEG) and a functional enrichment analysis. Protein-protein networks were constructed and a module analysis was conducted. A network analysis was used to identify the target genes of SFD. Regarding the results obtained, 1134 DEG were identified using the STRING website. The module analysis revealed that nine hub genes exhibited ubiquitin-protein ligase activity. Therefore, SFD significantly alters the expression of ubiquitination-related genes and, thus, plays an important therapeutic role in the treatment of heart failure. In conclusion, hub genes may provide a more detailed understanding of the molecular mechanisms of action of as well as candidate targets for SFD therapy.

Structure, Dynamics and Function of the 26S Proteasome

The 26S proteasome is the most complex ATP-dependent protease machinery, of ~2.5 MDa mass, ubiquitously found in all eukaryotes. It selectively degrades ubiquitin-conjugated proteins and plays fundamentally indispensable roles in regulating almost all major aspects of cellular activities. To serve as the sole terminal "processor" for myriad ubiquitylation pathways, the proteasome evolved exceptional adaptability in dynamically organizing a large network of proteins, including ubiquitin receptors, shuttle factors, deubiquitinases, AAA-ATPase unfoldases, and ubiquitin ligases, to enable substrate selectivity and processing efficiency and to achieve regulation precision of a vast diversity of substrates. The inner working of the 26S proteasome is among the most sophisticated, enigmatic mechanisms of enzyme machinery in eukaryotic cells. Recent breakthroughs in three-dimensional atomic-level visualization of the 26S proteasome dynamics during polyubiquitylated substrate degradation elucidated an extensively detailed picture of its functional mechanisms, owing to progressive methodological advances associated with cryogenic electron microscopy (cryo-EM). Multiple sites of ubiquitin binding in the proteasome revealed a canonical mode of ubiquitin-dependent substrate engagement. The proteasome conformation in the act of substrate deubiquitylation provided insights into how the deubiquitylating activity of RPN11 is enhanced in the holoenzyme and is coupled to substrate translocation. Intriguingly, three principal modes of coordinated ATP hydrolysis in the heterohexameric AAA-ATPase motor  were discovered to regulate intermediate functional steps of the proteasome, including ubiquitin-substrate engagement, deubiquitylation, initiation of substrate translocation and processive substrate degradation. The atomic dissection of the innermost working of the 26S proteasome opens up a new era in our understanding of the ubiquitin-proteasome system and has far-reaching implications in health and disease.

NSAIDs-dependent adaption of the mitochondria-proteasome system in immortalized human cardiomyocytes

The progressive consumption growth of non-steroidal anti-inflammatory drugs (NSAIDs) has progressively raised the attention toward the gastrointestinal, renal, and cardiovascular toxicity. Increased risk of cardiovascular diseases was strictly associated with the usage of COX-2 selective NSAIDs. Other studies allowed to clarify that the cardiovascular risk is not limited to COX-2 selective but also extended to non-selective NSAIDs, such as Diclofenac and Ketoprofen. To date, although a less favorable cardiovascular risk profile for Diclofenac as compared to Ketoprofen is reported, the mechanisms through which NSAIDs cause adverse cardiovascular events are not entirely understood. The present study aimed to evaluate the effects of Ketoprofen in comparison with Diclofenac in immortalized human cardiomyocytes. The results obtained highlight the dose-dependent cardiotoxicity of Diclofenac compared to Ketoprofen. Despite both drugs induce the increase in ROS production, decrease of mitochondrial membrane potential, and proteasome activity modulation, only Diclofenac exposure shows a marked alteration of these intracellular parameters, leading to cell death. Noteworthy, Diclofenac decreases the proteasome 26S DC and this scenario may be dependent on the intracellular overload of oxidized proteins. The data support the hypothesis that immortalized human cardiomyocytes exposed to Ketoprofen are subjected to tolerable stress events, conversely Diclofenac exposition triggers cell death.

Non-Hematologic Toxicity of Bortezomib in Multiple Myeloma: The Neuromuscular and Cardiovascular Adverse Effects

Simple Summary

Multiple myeloma (MM) is a still uncurable tumor of mainly elderly patients originating from the terminally differentiated B cells. Introduction to the treatment of MM patients of a new class of drugs called proteasome inhibitors (bortezomib followed by carfilzomib and ixazomib) significantly improved disease control. Proteasome inhibitors interfere with the major mechanism of protein degradation in a cell leading to the severe imbalance in the protein turnover that is deadly to MM cells. Currently, these drugs are the mainstream of MM therapy but are also associated with an increased rate of the injuries to multiple organs and tissues. In this review, we summarize the current knowledge on the molecular mechanisms of the first-in-class proteasome inhibitor bortezomib-induced disturbances in the function of peripheral nerves and cardiac and skeletal muscle.

Abstract

The overall approach to the treatment of multiple myeloma (MM) has undergone several changes during the past decade. and proteasome inhibitors (PIs) including bortezomib, carfilzomib, and ixazomib have considerably improved the outcomes in affected patients. The first-in-class selective PI bortezomib has been initially approved for the refractory forms of the disease but has now become, in combination with other drugs, the backbone of the frontline therapy for newly diagnosed MM patients, as well as in the maintenance therapy and relapsed/refractory setting. Despite being among the most widely used and highly effective agents for MM, bortezomib can induce adverse events that potentially lead to early discontinuation of the therapy with negative effects on the quality of life and outcome of the patients. Although peripheral neuropathy and myelosuppression have been recognized as the most relevant bortezomib-related adverse effects, cardiac and skeletal muscle toxicities are relatively common in MM treated patients, but they have received much less attention. Here we review the neuromuscular and cardiovascular side effects of bortezomib. focusing on the molecular mechanisms underlying its toxicity. We also discuss our preliminary data on the effects of bortezomib on skeletal muscle tissue in mice receiving the drug.

Targeting Protein Kinase G to Treat Cardiac Proteotoxicity

Impaired or insufficient protein kinase G (PKG) signaling and protein quality control (PQC) are hallmarks of most forms of cardiac disease, including heart failure. Their dysregulation has been shown to contribute to and exacerbate cardiac hypertrophy and remodeling, reduced cell survival and disease pathogenesis. Enhancement of PKG signaling and PQC are associated with improved cardiac function and survival in many pre-clinical models of heart disease. While many clinically used pharmacological approaches exist to stimulate PKG, there are no FDA-approved therapies to safely enhance cardiomyocyte PQC. The latter is predominantly due to our lack of knowledge and identification of proteins regulating cardiomyocyte PQC. Recently, multiple studies have demonstrated that PKG regulates PQC in the heart, both during physiological and pathological states. These studies tested already FDA-approved pharmacological therapies to activate PKG, which enhanced cardiomyocyte PQC and alleviated cardiac disease. This review examines the roles of PKG and PQC during disease pathogenesis and summarizes the experimental and clinical data supporting the utility of stimulating PKG to target cardiac proteotoxicity.

Proteasome biology and therapeutics in cardiac diseases

The ubiquitin proteasome system (UPS) is the major pathway for intracellular protein degradation in most organs, including the heart. UPS controls many fundamental biological processes such as cell cycle, cell division, immune responses, antigen presentation, apoptosis, and cell signaling. The UPS not only degrades substrates but also regulates activity of gene transcription at the post-transcription level. Emerging evidence suggests that impairment of UPS function is sufficient to cause a number of cardiac diseases, including heart failure, cardiomyopathies, hypertrophy, atrophy, ischemia-reperfusion, and atherosclerosis. Alterations in the expression of UPS components, changes in proteasomal peptidase activities and increased ubiquitinated and oxidized proteins have also been detected in diabetic cardiomyopathy (DCM). However, the pathophysiological role of the UPS in DCM has not been examined. Recently, in vitro and in vivo studies have proven highly valuable in assessing effects of various stressors on the UPS and, in some cases, suggesting a causal link between defective protein clearance and disease phenotypes in different cardiac diseases, including DCM. Translation of these findings to human disease can be greatly strengthened by corroboration of discoveries from experimental model systems using human heart tissue from well-defined patient populations. This review will summarize the general role of the UPS in different cardiac diseases, with major focus on DCM, and on recent advances in therapeutic development.

Detecting potential pleiotropy across cardiovascular and neurological diseases using univariate, bivariate, and multivariate methods on 43,870 individuals from the eMERGE network

The link between cardiovascular diseases and neurological disorders has been widely observed in the aging population. Disease prevention and treatment rely on understanding the potential genetic nexus of multiple diseases in these categories. In this study, we were interested in detecting pleiotropy, or the phenomenon in which a genetic variant influences more than one phenotype. Marker-phenotype association approaches can be grouped into univariate, bivariate, and multivariate categories based on the number of phenotypes considered at one time. Here we applied one statistical method per category followed by an eQTL colocalization analysis to identify potential pleiotropic variants that contribute to the link between cardiovascular and neurological diseases. We performed our analyses on ~530,000 common SNPs coupled with 65 electronic health record (EHR)-based phenotypes in 43,870 unrelated European adults from the Electronic Medical Records and Genomics (eMERGE) network. There were 31 variants identified by all three methods that showed significant associations across late onset cardiac- and neurologic- diseases. We further investigated functional implications of gene expression on the detected "lead SNPs" via colocalization analysis, providing a deeper understanding of the discovered associations. In summary, we present the framework and landscape for detecting potential pleiotropy using univariate, bivariate, multivariate, and colocalization methods. Further exploration of these potentially pleiotropic genetic variants will work toward understanding disease causing mechanisms across cardiovascular and neurological diseases and may assist in considering disease prevention as well as drug repositioning in future research.

Treatment with crocin improves cardiac dysfunction by normalizing autophagy and inhibiting apoptosis in STZ-induced diabetic cardiomyopathy

BACKGROUND AND AIM

The association of diabetes mellitus (DM) and poor metabolic control with high incidence of cardiovascular diseases is well established. The aim of this study was to investigate the potential cardioprotective effect of crocin (Crocus sativus L. extract) on diabetic heart dysfunction and to elucidate the mediating molecular mechanisms.

METHODS AND RESULTS

Streptozotocin (STZ)-induced diabetic rats were treated with two different concentrations of crocin (10 or 20 mg/kg), while isolated cardiac myocytes exposed to 25 mM glucose, were treated with 1 or 10 μM of crocin. Treatment of STZ-diabetic rats with crocin resulted in normalization of plasma glucose levels, inhibition of cardiac hypertrophy and fibrosis, and improvement of cardiac contractile function. Heat Shock Response was enhanced. Myocardial AMPK phosphorylation was increased after treatment with crocin, resulting in normalization of autophagy marker proteins (LC3BII/LC3BI ratio, SQSTM1/p62 and Beclin-1), while the diabetes-induced myocardial apoptosis was decreased. Similar results regarding the effect of crocin on autophagy and apoptosis pathways were obtained in isolated cardiac myocytes exposed to high concentration of glucose.

CONCLUSION

The results suggest that crocin improves the deteriorated cardiac function in diabetic animals by enhancing the heat shock response, inhibiting apoptosis and normalizing autophagy in cardiac myocytes. Thus, treatment with crocin may represent a novel approach for treating diabetic cardiomyopathy.

Emergence of Members of TRAF and DUB of Ubiquitin Proteasome System in the Regulation of Hypertrophic Cardiomyopathy

The ubiquitin proteasome system (UPS) plays an imperative role in many critical cellular processes, frequently by mediating the selective degradation of misfolded and damaged proteins and also by playing a non-degradative role especially important as in many signaling pathways. Over the last three decades, accumulated evidence indicated that UPS proteins are primal modulators of cell cycle progression, DNA replication, and repair, transcription, immune responses, and apoptosis. Comparatively, latest studies have demonstrated a substantial complexity by the UPS regulation in the heart. In addition, various UPS proteins especially ubiquitin ligases and proteasome have been identified to play a significant role in the cardiac development and dynamic physiology of cardiac pathologies such as ischemia/reperfusion injury, hypertrophy, and heart failure. However, our understanding of the contribution of UPS dysfunction in the plausible development of cardiac pathophysiology and the complete list of UPS proteins regulating these afflictions is still in infancy. The recent emergence of the roles of TNF receptor-associated factor (TRAFs) and deubiquitinating enzymes (DUBs) superfamily in hypertrophic cardiomyopathy has enhanced our knowledge. In this review, we have mainly compiled the TRAF superfamily of E3 ligases and few DUBs proteins with other well-documented E3 ligases such as MDM2, MuRF-1, Atrogin-I, and TRIM 32 that are specific to myocardial hypertrophy. In this review, we also aim to highlight their expression profile following physiological and pathological stimulation leading to the onset of hypertrophic phenotype in the heart that can serve as biomarkers and the opportunity for the development of novel therapies.

Carfilzomib

Carfilzomib (CFZ) is a potent, second-generation proteasome inhibitor (PI), with significant activity as a single agent and in combination with other antimyeloma agents in patients with relapsed or refractory multiple myeloma (RRMM). CFZ binds selectively and irreversibly to its target and leads to antiproliferative and proapoptotic effects on cancer cells. This irreversible inhibition is dose- and time-dependent in vitro and in vivo. CFZ as monotherapy and in combination with other antimyeloma agents (e.g., as CFZ and dexamethasone [Kd]) achieved very good responses, progression-free survival (PFS) and overall survival (OS). In several ongoing studies, CFZ is being investigated in triplet and quadruplet schedules of CFZ, lenalidomide and dexamethasone (KRd), CFZ, cyclophosphamide, dexamethasone (KCd) and with antibodies, like elotuzumab or daratumumab. The multitude of completed and ongoing studies confirmed a tolerable safety profile of CFZ, a significantly lower incidence of neuropathy compared to bortezomib (BTZ) and a slightly higher incidence of cardiotoxicity, which is closely observed and precautions taken to avoid them as best as possible. In July 2012, the US Food and Drug Administration (FDA) approved CFZ as a single agent for RRMM patients with disease progression after two prior therapies, including BTZ and immunomodulatory drugs (IMiDs). The combination of KRd and Kd followed, being approved by both FDA and European Medicines Agency (EMA) in 2015 and 2016, respectively. Moreover, CFZ is being evaluated in patients with newly diagnosed MM (NDMM), in high-risk smoldering MM and for maintenance approaches.

A retrospective analysis of 3954 patients in phase 2/3 trials of bortezomib for the treatment of multiple myeloma: towards providing a benchmark for the cardiac safety profile of proteasome inhibition in multiple myeloma

This retrospective analysis aimed to establish the overall cardiac safety profile of bortezomib using patient-level data from one phase 2 and seven phase 3 studies in previously untreated and relapsed/refractory multiple myeloma (MM). Seven clinically relevant primary [congestive heart failure (CHF), arrhythmias, ischaemic heart disease (IHD), cardiac death] and secondary (hypertension, dyspnoea, oedema) cardiac endpoints were defined based on MedDRA v16.0 preferred terms. 2509 bortezomib-treated patients and 1445 patients in non-bortezomib-based control arms were included. The incidence of grade ≥3 CHF was 1·3-4·0% in studies in relapsed/refractory MM and 1·2-4·7% in previously untreated MM (2·0-7·6% all grades), with no significant differences between bortezomib- and non-bortezomib-based arms in comparative studies. Incidences of arrhythmias (1·3-5·9% grade ≥2; 0·6-4·1% grade ≥3), IHD (1·2-2·9% all grades; 0·4-2·7% grade ≥3) and cardiac death (0-1·4%) were low, with no differences between bortezomib-based and non-bortezomib-based arms. Higher rates of oedema (mostly grade 1/2) were seen in bortezomib-based versus non-bortezomib-based arms in one study and a pooled transplant study analysis. Logistic regression analyses of comparative studies showed no impact on cardiac risk with bortezomib-based versus non-bortezomib-based treatment. Bortezomib-based treatment was associated with low incidences of cardiac events.

Safety issues and management of toxicities associated with new treatments for multiple myeloma

INTRODUCTION

In the last decade, the availability of new drugs for the treatment of Multiple Myeloma (MM) significantly improved patients' outcomes, but also raised attention towards a new spectrum of adverse events. Recently, four novel agents with different mechanisms of action (carfilzomib, elotuzumab, daratumumab and panobinostat) have been approved for the treatment of MM. This review aims at providing physicians with the tools to recognize and handle toxicity issues related with these new treatments. Areas covered: This review focuses on the management of drug related adverse events of the latest approved drug combinations. New drug combinations under development and still in the phase of approval will be briefly discussed. PubMed was searched using the terms 'toxicity', 'carfilzomib', 'elotuzumab' 'daratumumab' and 'panobinostat'. Phase II and III clinical trials and previously published analyses on toxicities were reviewed. For new drug combination abstracts presented at the latest ASH, ASCO and EHA meetings as well as clinicaltrial.gov website was searched and reviewed. Expert commentary: With the development of newer drugs and the availability of different treatment options for MM patients, an accurate evaluation of treatment side effects, their prompt recognition and management is mandatory for all clinical hematologists.

Sodium 4-Phenylbutyrate Attenuates Myocardial Reperfusion Injury by Reducing the Unfolded Protein Response

BACKGROUND

The unfolded protein response (UPR) plays a pivotal role in ischemia-reperfusion (I/R) injury in various organs such as heart, brain, and liver. Sodium 4-phenylbutyrate (PBA) reportedly acts as a chemical chaperone that reduces UPR. In the present study, we evaluated the effect of PBA on reducing the UPR and protecting against myocardial I/R injury in mice.

METHODS

Male C57BL/6 mice were subjected to 30-minute myocardial I/R, and were treated with phosphate-buffered saline (as a vehicle) or PBA.

RESULTS

At 4 hours after reperfusion, mice treated with PBA had reduced serum cardiac troponin I levels and numbers of apoptotic cells in left ventricles (LVs) in myocardial I/R. Infarct size had also reduced in mice treated with PBA at 48 hours after reperfusion. At 2 hours after reperfusion, UPR markers, including eukaryotic initiation of the factor 2α-subunit, activating transcription factor-6, inositol-requiring enzyme-1, glucose-regulated protein 78, CCAAT/enhancer-binding protein (C/EBP) homologous protein, and caspase-12, were significantly increased in mice treated with vehicle compared to sham-operated mice. Administration of PBA significantly reduced the I/R-induced increases of these markers. Cardiac function and dimensions were assessed at 21 days after I/R. Sodium 4-phenylbutyrate dedicated to the improvement of cardiac parameters deterioration including LV end-diastolic diameter and LV fractional shortening. Consistently, PBA reduced messenger RNA expression levels of cardiac remodeling markers such as collagen type 1α1, brain natriuretic peptide, and α skeletal muscle actin in LV at 21 days after I/R.

CONCLUSION

Unfolded protein response mediates myocardial I/R injury. Administration of PBA reduces the UPR, apoptosis, infarct size, and preserved cardiac function. Hence, PBA may be a therapeutic option to attenuate myocardial I/R injury in clinical practice.

Proteostasis and SUMO in the heart

Heart proteostasis relies on a complex and integrated network of molecular processes surveilling organ performance under physiological and pathological conditions. For this purpose, cardiac cells depend on the correct function of their proteolytic systems, such as the ubiquitin-proteasome system (UPS), autophagy and the calpain system. Recently, the role of protein SUMOylation (an ubiquitin-like modification), has emerged as important modulator of cardiac proteostasis, which will be the focus of this review.

Diclofenac induces proteasome and mitochondrial dysfunction in murine cardiomyocytes and hearts

BACKGROUND

One of the most common nonsteroidal anti-inflammatory drugs (NSAIDs) used worldwide, diclofenac (DIC), has been linked to increased risk of cardiovascular disease (CVD). The molecular mechanism(s) by which DIC causes CVD is unknown.

METHODS

Proteasome activities were studied in hearts, livers, and kidneys from male Swiss Webster mice treated with either 100mg/kg DIC for 18h (acute treatment) or 10mg/kg DIC for 28days (chronic treatment). Cultured H9c2 cells and neonatal cardiomyocytes were also treated with different concentrations of DIC and proteasome function, cell death and ROS generation studied. Isolated mouse heart mitochondria were utilized to determine the effect of DIC on various electron transport chain complex activities.

RESULTS

DIC significantly inhibited the chymotrypsin-like proteasome activity in rat cardiac H9c2 cells, murine neonatal cardiomyocytes, and mouse hearts, but did not affect proteasome subunit expression levels. Proteasome activity was also affected in liver and kidney tissues from DIC treated animals. The levels of polyubiquitinated proteins increased in hearts from DIC treated mice. Importantly, the levels of oxidized proteins increased while the β5i immunoproteasome activity decreased in hearts from DIC treated mice. DIC increased ROS production and cell death in H9c2 cells and neonatal cardiomyocytes while the cardioprotective NSAID, aspirin, had no effect on ROS levels or cell viability. DIC inhibited mitochondrial Complex III, a major source of ROS, and impaired mitochondrial membrane potential suggesting that mitochondria are the major sites of ROS generation.

CONCLUSION

These results suggest that DIC induces cardiotoxicity by a ROS dependent mechanism involving mitochondrial and proteasome dysfunction.

Sodium Sulfide Attenuates Ischemic-Induced Heart Failure by Enhancing Proteasomal Function in an Nrf2-Dependent Manner

BACKGROUND

Therapeutic strategies aimed at increasing hydrogen sulfide (H2S) levels exert cytoprotective effects in various models of cardiovascular injury. However, the underlying mechanism(s) responsible for this protection remain to be fully elucidated. Nuclear factor E2-related factor 2 (Nrf2) is a cellular target of H2S and facilitator of H2S-mediated cardioprotection after acute myocardial infarction. Here, we tested the hypothesis that Nrf2 mediates the cardioprotective effects of H2S therapy in the setting of heart failure.

METHODS AND RESULTS

Mice (12 weeks of age) deficient in Nrf2 (Nrf2 KO; C57BL/6J background) and wild-type littermates were subjected to ischemic-induced heart failure. Wild-type mice treated with H2S in the form of sodium sulfide (Na2S) displayed enhanced Nrf2 signaling, improved left ventricular function, and less cardiac hypertrophy after the induction of heart failure. In contrast, Na2S therapy failed to provide protection against heart failure in Nrf2 KO mice. Studies aimed at evaluating the underlying cardioprotective mechanisms found that Na2S increased the expression of proteasome subunits, resulting in an increased proteasome activity and a reduction in the accumulation of damaged proteins. In contrast, Na2S therapy failed to enhance the proteasome and failed to attenuate the accumulation of damaged proteins in Nrf2 KO mice. Additionally, Na2S failed to improve cardiac function when the proteasome was inhibited.

CONCLUSIONS

These findings indicate that Na2S therapy enhances proteasomal activity and function during the development of heart failure in an Nrf2-dependent manner and that this enhancement leads to attenuation in cardiac dysfunction.

Substrate Ubiquitination Controls the Unfolding Ability of the Proteasome

In eukaryotic cells, proteins are targeted to the proteasome for degradation by polyubiquitination. These proteins bind to ubiquitin receptors, are engaged and unfolded by proteasomal ATPases, and are processively degraded. The factors determining to what extent the proteasome can successfully unfold and degrade a substrate are still poorly understood. We find that the architecture of polyubiquitin chains attached to a substrate affects the ability of the proteasome to unfold and degrade the substrate, with K48- or mixed-linkage chains leading to greater processivity than K63-linked chains. Ubiquitin-independent targeting of substrates to the proteasome gave substantially lower processivity of degradation than ubiquitin-dependent targeting. Thus, even though ubiquitin chains are removed early in degradation, during substrate engagement, remarkably they dramatically affect the later unfolding of a protein domain. Our work supports a model in which a polyubiquitin chain associated with a substrate switches the proteasome into an activated state that persists throughout the degradation process.

Case series discussion of cardiac and vascular events following carfilzomib treatment: possible mechanism, screening, and monitoring

BACKGROUND

Carfilzomib is a selective proteasome inhibitor approved in the United States in 2012 for the treatment of relapsed and refractory multiple myeloma. Although cardiopulmonary and vascular events have been reported infrequently, they can be potentially serious complications, and their incidence and pathophysiology following carfilzomib treatment remain poorly characterized in a real-world patient population.

METHODS

We retrospectively reviewed the records of 67 patients with relapsed and/or refractory multiple myeloma treated at our institution.

RESULTS

We describe 12 patients who experienced cardiac or vascular-related adverse events subsequent to carfilzomib-based treatment (median age, 59 years [range, 49-77]). Nine patients had prior autologous stem cell transplant, and three had prior anthracycline exposure. Detailed case reports are provided for five representative patients: (1) systemic hypertension in a 65-year-old Caucasian female with a history of hypertension, hypothyroidism, and stage III chronic kidney disease; (2) pulmonary hypertension in a 72-year-old Caucasian male with a history of recurrent respiratory infections and chronic right lower extremity deep venous thrombosis; (3) acute renal insufficiency with increased blood pressure in a 50-year-old Caucasian male with a history of hypertension and stage IV chronic kidney disease; (4) heart failure in a 64-year-old African American female with a history of hypertension; and (5) dyspnea and lung disease in a 58-year-old Asian American male with a history significant for hepatitis B virus infection.

CONCLUSIONS

While cardiac and vascular-related adverse events were reported in patients with relapsed and/or refractory multiple myeloma who were treated with carfilzomib, most patients had a history of the specific cardiac or vascular adverse event they exhibited and demonstrated an improvement or resolution in symptoms after the discontinuation of therapy. Appropriate screening and monitoring could potentially allow at-risk patients to benefit fully from treatment with carfilzomib.

Molecular remodeling of left and right ventricular myocardium in chronic anthracycline cardiotoxicity and post-treatment follow up

Chronic anthracycline cardiotoxicity is a serious clinical issue with well characterized functional and histopathological hallmarks. However, molecular determinants of the toxic damage and associated myocardial remodeling remain to be established. Furthermore, details on the different propensity of the left and right ventricle (LV and RV, respectively) to the cardiotoxicity development are unknown. Hence, the aim of the investigation was to study molecular changes associated with remodeling of the LV and RV in chronic anthracycline cardiotoxicity and post-treatment follow up. The cardiotoxicity was induced in rabbits with daunorubicin (3 mg/kg/week for 10 weeks) and animals were sacrificed either at the end of the treatment or after an additional 10 weeks. Daunorubicin induced severe and irreversible cardiotoxicity associated with LV dysfunction and typical morphological alterations, whereas the myocardium of the RV showed only mild changes. Both ventricles also showed different expression of ANP after daunorubicin treatment. Daunorubicin impaired the expression of several sarcomeric proteins in the LV, which was not the case of the RV. In particular, a significant drop was found in titin and thick filament proteins at both mRNA and protein level and this might be connected with persistent LV down-regulation of GATA-4. In addition, the LV was more affected by treatment-induced perturbations in calcium handling proteins. LV cardiomyocytes showed marked up-regulation of desmin after the treatment and vimentin was mainly induced in LV fibroblasts, whereas only weaker changes were observed in the RV. Remodeling of extracellular matrix was almost exclusively found in the LV with particular induction of collagen I and IV. Hence, the present study describes profound molecular remodeling of myocytes, non-myocyte cells and extracellular matrix in response to chronic anthracycline treatment with marked asymmetry between LV and RV.

Bortezomib, a proteasome inhibitor, attenuates angiotensin II-induced hypertension and aortic remodeling in rats

Background

Hypertension is a highly prevalent disorder and a major risk factor for cardiovascular diseases. Hypertensive vascular remodeling is the pathological mal-adaption of blood vessels to the hypertensive condition that contributes to further development of high blood pressure and end-organ damage. Hypertensive remodeling involves, at least in part, changes in protein turnover. The ubiquitin proteasome system (UPS) is a major protein quality and quantity control system. This study tested the hypothesis that the proteasome inhibitor, bortezomib, would attenuate AngII-induced hypertension and its sequelae such as aortic remodeling in rats.

Methodology/Principal Findings

Male Sprague Dawley rats were subjected to AngII infusion for two weeks in the absence or presence of bortezomib. Mean arterial pressure was measured in conscious rats. Aortic tissue was collected for estimation of wall area, collagen deposition and expression of tissue inhibitors of matrix metalloproteases (TIMP), Ki67 (a marker of proliferation), reactive oxygen species (ROS) and VCAM-1 (a marker of inflammation). AngII infusion increased arterial pressure significantly (160±4 mmHg vs. vehicle treatment 133±2 mmHg). This hypertensive response was attenuated by bortezomib (138±5 mmHg). AngII hypertension was associated with significant increases in aortic wall to lumen ratio (∼29%), collagen deposition (∼14%) and expression of TIMP1 and TIMP2. AngII also increased MMP2 activity, proteasomal chymotrypsin-like activity, Ki67 staining, ROS generation and VCAM-1 immunoreactivity. Co-treatment of AngII-infused rats with bortezomib attenuated these AngII-induced responses.

Conclusions

Collectively, these data support the idea that proteasome activity contributes to AngII-induced hypertension and hypertensive aortic vascular remodeling at least in part by modulating TIMP1/2 and MMP2 function. Preliminary observations are consistent with a role for ROS, inflammatory and proliferative mechanisms in this effect. Further understanding of the mechanisms by which the proteasome is involved in hypertension and vascular structural remodeling may reveal novel targets for pharmacological treatment of hypertension, hypertensive remodeling or both.

Altered ubiquitin-proteasome signaling in right ventricular hypertrophy and failure

Alterations in the ubiquitin-proteasome system (UPS) have been described in left ventricular hypertrophy and failure, although results have been inconsistent. The role of the UPS in right ventricular (RV) hypertrophy (RVH) and RV failure (RVF) is unknown. Given the greater percent increase in RV mass associated with RV afterload stress, as present in many congenital heart lesions, we hypothesized that alterations in the UPS could play an important role in RVH/RVF. UPS expression and activity were measured in the RV from mice with RVH/RVF secondary to pulmonary artery constriction (PAC). Epoxomicin and MG132 were used to inhibit the proteasome, and overexpression of the 11S PA28α subunit was used to activate the proteasome. PAC mice developed RVH (109.3% increase in RV weight to body weight), RV dilation with septal shift, RV dysfunction, and clinical RVF. Proteasomal function (26S β₅ chymotrypsin-like activity) was decreased 26% (P < 0.05). Protein expression of 19S subunit Rpt5 (P < 0.05), UCHL1 deubiquitinase (P < 0.0001), and Smurf1 E3 ubiquitin ligase (P < 0.01) were increased, as were polyubiquitinated proteins (P < 0.05) and free-ubiquitins (P = 0.05). Pro-apoptotic Bax was increased (P < 0.0001), whereas anti-apoptotic Bcl-2 decreased (P < 0.05), resulting in a sixfold increase in the Bax/Bcl-2 ratio. Proteasomal inhibition did not accelerate RVF. However, proteasome enhancement by cardiac-specific proteasome overexpression partially improved survival. Proteasome activity is decreased in RVH/RVF, associated with upregulation of key UPS regulators and pro-apoptotic signaling. Enhancement of proteasome function partially attenuates RVF, suggesting that UPS dysfunction contributes to RVF.

Regulation of the proteasome by ATP: implications for ischemic myocardial injury and donor heart preservation

Several lines of evidence suggest that proteasomes are involved in multiple aspects of myocardial physiology and pathology, including myocardial ischemia-reperfusion injury. It is well established that the 26S proteasome is an ATP-dependent enzyme and that ischemic heart disease is associated with changes in the ATP content of the cardiomyocyte. A functional link between the 26S proteasome, myocardial ATP concentrations, and ischemic cardiac injury, however, has been suggested only recently. This review discusses the currently available data on the pathophysiological role of the cardiac proteasome during ischemia and reperfusion in the context of the cellular ATP content. Depletion of the myocardial ATP content during ischemia appears to activate the 26S proteasome via direct regulatory effects of ATP on 26S proteasome stability and activity. This implies pathological degradation of target proteins by the proteasome and could provide a pathophysiological basis for beneficial effects of proteasome inhibitors in various models of myocardial ischemia. In contrast to that in the ischemic heart, reduced and impaired proteasome activity is detectable in the postischemic heart. The paradoxical findings that proteasome inhibitors showed beneficial effects when administered during reperfusion in some studies could be explained by their anti-inflammatory and immune suppressive actions, leading to reduction of leukocyte-mediated myocardial reperfusion injury. The direct regulatory effects of ATP on the 26S proteasome have implications for the understanding of the contribution of the 26S proteasome to the pathophysiology of the ischemic heart and its possible role as a therapeutic target.

Proteasome inhibition decreases inflammation in human endothelial cells exposed to lipopolysaccharide

BACKGROUND

The proteasome degrades ubiquitinated proteins and is the major pathway for intracellular protein degradation. The role of the proteasome in endothelial dysfunction observed in septic shock remains unknown. We stimulated primary cultures of human umbilical vein endothelial cells with lipopolysaccharide (LPS) and investigated effects on the proteasome. We hypothesized that proteasome inhibition would decrease endothelial cell activation, oxidative stress, and alter the proteome.

METHODS

Endothelial cells were exposed to LPS (100 ng/mL) for 6 hours with or without lactacystin (5 mM), a proteasome inhibitor. Proteasome content and ubiquitinated proteins were measured by enzyme-linked immunosorbent assay and immunoblot, respectively. Markers of cellular activation, vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, were measured by immunoblot and immunoassay. Superoxide anion production was determined by dihydroethidium assay, and nitrotyrosine (a marker of peroxynitrite) was visualized by immunofluoresence. The endothelial cell proteome was analyzed by 2D gel electrophoresis.

RESULTS

LPS stimulation of endothelial cells significantly increased proteasome content, whereas the total levels of ubquitinated proteins decreased. This suggests that LPS activates the proteasome system in endothelial cells. LPS increased total content and cell surface expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, whereas proteasome inhibition ameliorated these increases. LPS increased both superoxide anion production and nitrotyrosine staining. Proteasome inhibition decreased both markers of cellular oxidative stress. Proteomic analysis identified two novel proteins upregulated by LPS and normalized with proteasome inhibition as follows: guanine nucleotide binding protein-1 and heterogeneous ribonucleoprotein K transcript variant.

CONCLUSIONS

These results suggest that inhibition of the proteasome diminishes a number of markers of cellular stress induced by LPS. The proteasome may be a promising therapeutic target in clinical situations of severe pro-inflammatory stress.

Pregnancy is associated with decreased cardiac proteasome activity and oxidative stress in mice

During pregnancy, the heart develops physiological hypertrophy. Proteasomal degradation has been shown to be altered in various models of pathological cardiac hypertrophy. Since the molecular signature of pregnancy-induced heart hypertrophy differs significantly from that of pathological heart hypertrophy, we investigated whether the cardiac proteasomal proteolytic pathway is affected by pregnancy in mice. We measured the proteasome activity, expression of proteasome subunits, ubiquitination levels and reactive oxygen production in the hearts of four groups of female mice: i) non pregnant (NP) at diestrus stage, ii) late pregnant (LP), iii) one day post-partum (PP1) and iv) 7 days post-partum (PP7). The activities of the 26 S proteasome subunits β1 (caspase-like), and β2 (trypsin-like) were significantly decreased in LP (β1∶83.26±1.96%; β2∶74.74±1.7%, normalized to NP) whereas β5 (chymotrypsin-like) activity was not altered by pregnancy but significantly decreased 1 day post-partum. Interestingly, all three proteolytic activities of the proteasome were restored to normal levels 7 days post-partum. The decrease in proteasome activity in LP was not due to the surge of estrogen as estrogen treatment of ovariectomized mice did not alter the 26 S proteasome activity. The transcript and protein levels of RPN2 and RPT4 (subunits of 19 S), β2 and α7 (subunits of 20 S) as well as PA28α and β5i (protein only) were not significantly different among the four groups. High resolution confocal microscopy revealed that nuclear localization of both core (20S) and RPT4 in LP is increased ∼2-fold and is fully reversed in PP7. Pregnancy was also associated with decreased production of reactive oxygen species and ubiquitinated protein levels, while the de-ubiquitination activity was not altered by pregnancy or parturition. These results indicate that late pregnancy is associated with decreased ubiquitin-proteasome proteolytic activity and oxidative stress.

Ubiquitin receptors and protein quality control

Protein quality control (PQC) is essential to intracellular proteostasis and is carried out by sophisticated collaboration between molecular chaperones and targeted protein degradation. The latter is performed by proteasome-mediated degradation, chaperone-mediated autophagy (CMA), and selective macroautophagy, and collectively serves as the final line of defense of PQC. Ubiquitination and subsequently ubiquitin (Ub) receptor proteins (e.g., p62 and ubiquilins) are important common factors for targeting misfolded proteins to multiple quality control destinies, including the proteasome, lysosomes, and perhaps aggresomes, as well as for triggering mitophagy to remove defective mitochondria. PQC inadequacy, particularly proteasome functional insufficiency, has been shown to participate in cardiac pathogenesis. Tremendous advances have been made in unveiling the changes of PQC in cardiac diseases. However, the investigation into the molecular pathways regulating PQC in cardiac (patho)physiology, including the function of most ubiquitin receptor proteins in the heart, has only recently been initiated. A better understanding of molecular mechanisms governing PQC in cardiac physiology and pathology will undoubtedly provide new insights into cardiac pathogenesis and promote the search for novel therapeutic strategies to more effectively battle heart disease.This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Cardiac systolic dysfunction in doxorubicin-challenged rats is associated with upregulation of MuRF2 and MuRF3 E3 ligases

Doxorubicin (DOXO) is an efficient and low-cost chemotherapeutic agent. The use of DOXO is limited by its side effects, including cardiotoxicity, that may progress to cardiac failure as a result of multifactorial events that have not yet been fully elucidated. In the present study, the effects of DOXO at two different doses were analyzed to identify early functional and molecular markers of cardiac distress. One group of rats received 7.5 mg/kg of DOXO (low-dose group) and was followed for 20 weeks. A subset of these animals was then subjected to an additional cycle of DOXO treatment, generating a cumulative dose of 20 mg/kg (high-dose group). Physiological and biochemical parameters were assessed in both treatment groups and in a control group that received saline. Systolic dysfunction was observed only in the high-dose group. Mitochondrial function analysis showed a clear reduction in oxidative cellular respiration for animals in both DOXO treatment groups, with evidence of complex I damage being observed. Transcriptional analysis by quantitative polymerase chain reaction revealed an increase in atrial natriuretic peptide transcript in the high-dose group, which is consistent with cardiac failure. Analysis of transcription levels of key components of the cardiac ubiquitin-proteasome system found that the ubiquitin E3 ligase muscle ring finger 1 (MuRF1) was upregulated in both the low- and high-dose DOXO groups. MuRF2 and MuRF3 were also upregulated in the high-dose group but not in the low-dose group. This molecular profile may be useful as an early physiological and energetic cardiac failure indicator for testing therapeutic interventions in animal models.

The endoplasmic reticulum in cardiovascular health and disease

The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory and integral membrane protein synthesis demands of the cell, as well as adaptive responses set up for the endoplasmic reticulum to rely on when stressed. These pathways are both essential and complex, and because of these 2 factors, several situations can lead to a dysfunctional endoplasmic reticulum and result in a dysfunctional cell with the potential to contribute to the progression of disease. The endoplasmic reticulum has been implicated in several metabolic, neurodegenerative, inflammatory, autoimmune, and renal diseases and disorders, and in particular, cardiovascular diseases. The role of the endoplasmic reticulum in cardiovascular disease shows how the change in function of a particular microscopic organelle can lead to macroscopic changes in the form of disease.

Exercise training prevents oxidative stress and ubiquitin-proteasome system overactivity and reverse skeletal muscle atrophy in heart failure

Background

Heart failure (HF) is known to lead to skeletal muscle atrophy and dysfunction. However, intracellular mechanisms underlying HF-induced myopathy are not fully understood. We hypothesized that HF would increase oxidative stress and ubiquitin-proteasome system (UPS) activation in skeletal muscle of sympathetic hyperactivity mouse model. We also tested the hypothesis that aerobic exercise training (AET) would reestablish UPS activation in mice and human HF.

Methods/Principal Findings

Time-course evaluation of plantaris muscle cross-sectional area, lipid hydroperoxidation, protein carbonylation and chymotrypsin-like proteasome activity was performed in a mouse model of sympathetic hyperactivity-induced HF. At the 7^th month of age, HF mice displayed skeletal muscle atrophy, increased oxidative stress and UPS overactivation. Moderate-intensity AET restored lipid hydroperoxides and carbonylated protein levels paralleled by reduced E3 ligases mRNA levels, and reestablished chymotrypsin-like proteasome activity and plantaris trophicity. In human HF (patients randomized to sedentary or moderate-intensity AET protocol), skeletal muscle chymotrypsin-like proteasome activity was also increased and AET restored it to healthy control subjects’ levels.

Conclusions

Collectively, our data provide evidence that AET effectively counteracts redox imbalance and UPS overactivation, preventing skeletal myopathy and exercise intolerance in sympathetic hyperactivity-induced HF in mice. Of particular interest, AET attenuates skeletal muscle proteasome activity paralleled by improved aerobic capacity in HF patients, which is not achieved by drug treatment itself. Altogether these findings strengthen the clinical relevance of AET in the treatment of HF.

Posttranslational modifications in connexins and pannexins

Posttranslational modification is a common cellular process that is used by cells to ensure a particular protein function. This can happen in a variety of ways, e.g., from the addition of phosphates or sugar residues to a particular amino acid, ensuring proper protein life cycle and function. In this review, we assess the evidence for ubiquitination, glycosylation, phosphorylation, S-nitrosylation as well as other modifications in connexins and pannexin proteins. Based on the literature, we find that posttranslational modifications are an important component of connexin and pannexin regulation.

Phosphoprotein abundance changes in hypertensive cardiac remodeling

There is over-whelming evidence that protein phosphorylations regulate cardiac function and remodeling. A wide variety of protein kinases, e.g., phosphoinositide 3-kinase (PI3K), Akt, GSK-3, TGFβ, and PKA, MAPKs, PKC, Erks, and Jaks, as well as phosphatases, e.g., phosphatase I (PP1) and calcineurin, control cardiomyocyte growth and contractility. In the present work, we used global phosphoprotein profiling to identify phosphorylated proteins associated with pressure overload (PO) cardiac hypertrophy and heart failure. Phosphoproteins from hypertrophic and systolic failing hearts from male hypertensive Dahl salt-sensitive rats, trans-aortic banded (TAC), and spontaneously hypertensive heart failure (SHHF) rats were analyzed. Profiling was performed by 2-dimensional difference in gel electrophoresis (2D-DIGE) on phospho-enriched proteins. A total of 25 common phosphoproteins with differences in abundance in (1) the 3 hypertrophic and/or (2) the 2 systolic failure heart models were identified (CI>99%) by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) and Mascot analysis. Among these were (1) myofilament proteins, including alpha-tropomyosin and myosin regulatory light chain 2, cap Z interacting protein (cap ZIP), and tubulin β5; (2) mitochondrial proteins, including pyruvate dehydrogenase α, branch chain ketoacid dehydrogenase E1, and mitochondrial creatine kinase; (3) phosphatases, including protein phosphatase 2A and protein phosphatase 1 regulatory subunit; and (4) other proteins including proteosome subunits α type 3 and β type 7, and eukaryotic translation initiation factor 1A (eIF1A). The results include previously described and novel phosphoproteins in cardiac hypertrophy and systolic failure.

Proteasome functional insufficiency in cardiac pathogenesis

The ubiquitin-proteasome system (UPS) is responsible for the degradation of most cellular proteins. Alterations in cardiac UPS, including changes in the degradation of regulatory proteins and proteasome functional insufficiency, are observed in many forms of heart disease and have been shown to play an important role in cardiac pathogenesis. In the past several years, remarkable progress in understanding the mechanisms that regulate UPS-mediated protein degradation has been achieved. A transgenic mouse model of benign enhancement of cardiac proteasome proteolytic function has been created. This has led to the first demonstration of the necessity of proteasome functional insufficiency in the genesis of important pathological processes. Cardiomyocyte-restricted enhancement of proteasome proteolytic function by overexpression of proteasome activator 28α protects against cardiac proteinopathy and myocardial ischemia-reperfusion injury. Additionally, exciting advances have recently been achieved in the search for a pharmacological agent to activate the proteasome. These breakthroughs are expected to serve as an impetus to further investigation into the involvement of UPS dysfunction in molecular pathogenesis and to the development of new therapeutic strategies for combating heart disease. An interplay between the UPS and macroautophagy is increasingly suggested in noncardiac systems but is not well understood in the cardiac system. Further investigations into the interplay are expected to provide a more comprehensive picture of cardiac protein quality control and degradation.

Proteasome malfunction activates macroautophagy in the heart

Protein quality control (PQC) senses and repairs misfolded/unfolded proteins and, if the repair fails, degrades the terminally misfolded polypeptides through an intricate collaboration between molecular chaperones and targeted proteolysis. Proteolysis of damaged proteins is performed primarily by the ubiquitin-proteasome system (UPS). Macroautophagy (commonly known as autophagy) may also play a role in PQC-associated proteolysis, especially when UPS function becomes inadequate. The development of a range of heart diseases, including bona fide cardiac proteinopathies and various forms of cardiac dysfunction has been linked to proteasome functional insufficiency (PFI). Both PFI and activation of autophagy have been observed in the heart of well-established mouse models of cardiac proteinopathy. A causal relationship between PFI and autophagic activation was suggested by a study using cultured cardiomyocytes but has not been established in the heart of intact animals. Taking advantage of an autophagy reporter, we demonstrated here that pharmacologically induced proteasome inhibition is sufficient to activate autophagy in cardiomyocytes in both intact animals and cell cultures, unveiling a potential cross-talk between the two major degradation pathways in cardiac PQC.

Inhibition of Ras-GTPase farnesylation and the ubiquitin-proteasome system or treatment with angiotensin-(1-7) attenuates spinal cord injury-induced cardiac dysfunction

Cardiovascular diseases are one of the principal causes of death and disability in people with spinal cord injury (SCI). The present study was designed to investigate if acute treatment with FPTIII (an inhibitor of Ras-GTPase farnesylation) or MG132 (an inhibitor of ubiquitin-proteasome pathway [UPS]) or administration of angiotensin-(1-7), also known as Ang-(1-7), (a known inhibitor of cardiac NF-kB) would be cardioprotective. The weight drop technique produced a consistent contusive injury of the spinal cord at the T13 segment. Hearts were isolated from rats either 6 months (SCI-6) or 12 months (SCI-12) after SCI. Hearts were perfused for 30 min and then subjected to 30 min ischemia followed by 30 min reperfusion (I/R). Recovery of cardiac function after I/R was measured as left ventricular developed pressure (P(max)) and coronary flow (CF). Drugs were given during perfusion before hearts were exposed to ischemia and reperfusion. Percent recovery (%R) in P(max) and CF in hearts from control animals were 48±6 and 50±5, respectively, whereas none of the hearts from animals with SCI recovered after 30 min of ischemia. Treatment with FPTIII, MG 132, or Ang-(1-7) before ischemia for 30 min led to significant recovery of heart function following ischemia in SCI-6 but not in SCI-12 animals. Thus we have shown that acute treatments with FPTIII, MG132, or Ang-(1-7) improve cardiac recovery following ischemic insult in animals with SCI and may represent novel therapeutic agents for preventing ischemia-induced cardiac dysfunction in patients with SCI.