Regulation of heat shock protein 60 and 72 expression in the failing heart

Emerging role of heat shock proteins in cardiovascular diseases

Heat Shock Proteins (HSPs) are evolutionarily conserved proteins from prokaryotes to eukaryotes. They are ubiquitous proteins involved in key physiological and cellular pathways (viz. inflammation, immunity and apoptosis). Indeed, the survivability of the cells under various stressful conditions depends on appropriate levels of HSP expression. There is a growing line of evidence for the role of HSPs in regulating cardiovascular diseases (CVDs) (viz. hypertension, atherosclerosis, atrial fibrillation, cardiomyopathy and heart failure). Furthermore, studies indicate that a higher concentration of circulatory HSP antibodies correlate to CVDs; some are even potential markers for CVDs. The multifaceted roles of HSPs in regulating cellular signaling necessitate unraveling their links to pathophysiology of CVDs. This review aims to consolidate our understanding of transcriptional (via multiple transcription factors including HSF-1, NF-κB, CREB and STAT3) and post-transcriptional (via microRNAs including miR-1, miR-21 and miR-24) regulation of HSPs. The cytoprotective nature of HSPs catapults them to the limelight as modulators of cell survival. Yet another attractive prospect is the development of new therapeutic strategies against cardiovascular diseases (from hypertension to heart failure) by targeting the regulation of HSPs. Moreover, this review provides insights into how genetic variation of HSPs can contribute to the manifestation of CVDs. It would also offer a bird's eye view of the evolving role of different HSPs in the modulation and manifestation of cardiovascular disease.

Traditional Chinese Medicine Targeting Heat Shock Proteins as Therapeutic Strategy for Heart Failure

Heart failure (HF) is the terminal stage of multifarious heart diseases and is responsible for high hospitalization rates and mortality. Pathophysiological mechanisms of HF include cardiac hypertrophy, remodeling and fibrosis resulting from cell death, inflammation and oxidative stress. Heat shock proteins (HSPs) can ameliorate folding of proteins, maintain protein structure and stability upon stress, protect the heart from cardiac dysfunction and ameliorate apoptosis. Traditional Chinese medicine (TCM) regulates expression of HSPs and has beneficial therapeutic effect in HF. In this review, we summarized the function of HSPs in HF and the role of TCM in regulating expression of HSPs. Studying the regulation of HSPs by TCM will provide novel ideas for the study of the mechanism and treatment of HF.

Association of Aberrant DNA Methylation Level in the CD4 and JAK-STAT-Pathway-Related Genes with Mastitis Indicator Traits in Chinese Holstein Dairy Cattle

The present study was designed to evaluate the gene expression and DNA methylation level in the promoter region of the CD4 and the JAK-STAT-pathway-related genes. A total of 24 samples were deployed in the gene expression and 118 samples were used in the DNA methylation study. Student's t-tests were used to analyze the gene expression and DNA methylation. The evaluation of DNA methylation in promoter regions of JAK2 and STAT5A revealed hypo-methylation levels of CpG sites and higher gene expression in cows diagnosed with mastitis as compared to the healthy control, and vice versa in those with CD4. DNA methylation was negatively correlated with gene expression in JAK2, STAT5A, and CD4 genes. Six, two, and four active transcription factors were identified on the CpG sites in the promoter regions of JAK2, STAT5A, and CD4 genes, respectively. Regarding correlation analysis, the DNA methylation levels of CD4 showed significantly higher positive correlations with somatic cell counts (p < 0.05). Findings of the current study inferred that aberrant DNA methylation in the CpG sites at the 1 kb promoter region in JAK2, STAT5A, and CD4 genes due to mastitis in cows can be used as potential epigenetic markers to estimate bovine mastitis susceptibility in dairy cattle.

Role of mitochondrial quality surveillance in myocardial infarction: From bench to bedside

Myocardial infarction (MI) is the irreversible death of cardiomyocyte secondary to prolonged lack of oxygen or fresh blood supply. Historically considered as merely cardiomyocyte powerhouse that manufactures ATP and other metabolites, mitochondrion is recently being identified as a signal regulator that is implicated in the crosstalk and signal integration of cardiomyocyte contraction, metabolism, inflammation, and death. Mitochondria quality surveillance is an integrated network system modifying mitochondrial structure and function through the coordination of various processes including mitochondrial fission, fusion, biogenesis, bioenergetics, proteostasis, and degradation via mitophagy. Mitochondrial fission favors the elimination of depolarized mitochondria through mitophagy, whereas mitochondrial fusion preserves the mitochondrial network upon stress through integration of two or more small mitochondria into an interconnected phenotype. Mitochondrial biogenesis represents a regenerative program to replace old and damaged mitochondria with new and healthy ones. Mitochondrial bioenergetics is regulated by a metabolic switch between glucose and fatty acid usage, depending on oxygen availability. To maintain the diversity and function of mitochondrial proteins, a specialized protein quality control machinery regulates protein dynamics and function through the activity of chaperones and proteases, and induction of the mitochondrial unfolded protein response. In this review, we provide an overview of the molecular mechanisms governing mitochondrial quality surveillance and highlight the most recent preclinical and clinical therapeutic approaches to restore mitochondrial fitness during both MI and post-MI heart failure.

HSP60 participates in the anti-glioma effects of curcumin

The chaperone protein heat shock protein 60 (HSP60) is considered a tumor promoter in several types of primary human tumors, where it orchestrates a broad range of survival programs. Curcumin (CCM) is well-established to exhibit several anticancer properties with an excellent safety profile. Our previous study showed that CCM suppresses extracellular HSP60 expression, which is typically released by activated microglia, and acts as an inflammatory factor by binding to Toll-like receptor 4 (TLR-4) on the cell membrane. The present study assessed whether CCM exerted its anti-neuroglioma effects on U87 cells via inhibition of HSP60/TLR-4 signaling, similar to that in microglia. The results demonstrated that CCM significantly inhibited the viability and invasive capacity of neuroglioma U87 cells as evidenced by a Cell Counting Kit-8 assay. Western blotting and ELISA results showed that CCM decreased the expression of HSP60 and its transcriptional factor, heat shock factor 1, and reduced HSP60 release. Accordingly, TLR-4, as the target of HSP60, and its downstream signaling proteins myeloid differentiation primary response 88 (MYD88), NF-κB, inducible nitric oxide synthase and cytokines IL-1β and IL-6 were downregulated by CCM. The expression levels of apoptotic factors associated with NF-κB activation, including TNF-α and caspase-3 were increased in U87 cells by CCM treatment, while p53 expression, a tumor suppressor, was shown to be decreased. Based on the results of the present study, CCM may exert its anti-tumor effects in U87 cells by inhibiting the HSP60/TLR-4/MYD88/NF-κB pathway and inducing tumor cell apoptosis. Thus, CCM may be used as a potential therapy for the clinical treatment of neuroglioma.

Heat shock protein 60 and cardiovascular diseases: An intricate love-hate story

Cardiovascular diseases (CVDs) are the result of complex pathophysiological processes in the tissues comprising the heart and blood vessels. Inflammation is the main culprit for the development of cardiovascular dysfunction, and it may be traced to cellular stress events including apoptosis, oxidative and shear stress, and cellular and humoral immune responses, all of which impair the system's structure and function. An intracellular chaperone, heat shock protein 60 (HSP60) is an intriguing example of a protein that may both be an ally and a foe for cardiovascular homeostasis; on one hand providing protection against cellular injury, and on the other triggering damaging responses through innate and adaptive immunity. In this review we will discuss the functions of HSP60 and its effects on cells and the immune system regulation, only to later address its implications in the development and progression of CVD. Lastly, we summarize the outcome of various studies targeting HSP60 as a potential therapeutic strategy for cardiovascular and other diseases.

Mechanistic implications of altered protein expression in rheumatic heart disease

Rheumatic heart disease (RHD) is a major cause of cardiovascular morbidity and mortality in low- and middle-income countries, where living conditions promote spread of group A β-haemolytic streptococcus. Autoimmune reactions due to molecular mimicry of bacterial epitopes by host proteins cause acute rheumatic fever (ARF) and subsequent disease progression to RHD. Despite knowledge of the factors that predispose to ARF and RHD, determinants of the progression to valvular damage and the molecular events involved remain incompletely characterised. This review focuses on altered protein expression in heart valves, myocardial tissue and plasma of patients with RHD and pathogenic consequences on RHD. Proteins mainly involved in structural organization of the valve matrix, blood homeostasis and immune response were altered due to RHD pathogenesis. Study of secreted forms of these proteins may aid the development of non-invasive biomarkers for early diagnosis and monitoring outcomes in RHD. Valve replacement surgery, the single evidence-based strategy to improve outcomes in severe RHD, is costly, largely unavailable in low- and middle-income countries (LMIC) and requires specialised facilities. When diagnosed early, penicillin prophylaxis may be used to delay progression to severe valvular damage. Echocardiography and cardiovascular magnetic resonance and the standard imaging tools recommended to confirm early diagnosis remain largely unavailable and inaccessible in most LMIC and both require expensive equipment and highly skilled persons for manipulation as well as interpretation of results. Changes in protein expression in heart valves and myocardium are associated with progressive valvular deformation in RHD. Understanding these protein changes should shed more light on the mechanisms of pathogenicity, while secreted forms of these proteins may provide leads towards a biomarker for non-invasive early detection of RHD.

Heat Shock Protein 60 in Cardiovascular Physiology and Diseases

Heat shock protein 60 (HSP60) is a highly conserved protein abundantly expressed in both prokaryotic and eukaryotic cells. In mammals, HSP60 has been primarily considered to reside in the mitochondria, where HSP60 and HSP10 form a complex and facilitate mitochondrial protein folding. However, HSP60 is also observed in the cytoplasm, the plasma membrane, and the extracellular space. HSP60 regulates a broad spectrum of cellular events including protein trafficking, peptide hormone signaling, cell survival, cell proliferation, inflammation, and immunization. In the cardiovascular system, growing evidence indicates that HSP60 could not only play an important role under physiological conditions, but also regulate the initiation and progression of heart failure and atherosclerosis. In this review, we focus on recent progress in understanding the function of HSP60 in cardiomyocytes, endothelial cells, and vascular smooth muscle cells (VSMCs), respectively, and discuss the related signaling pathways that have been found in these cells, so as to illustrate the role of HSP60 in the development of cardiovascular disease.

Left ventricular hypertrophy is associated with overexpression of HSP60, TLR2, and TLR4 in the myocardium

Left ventricular hypertrophy is a common adaptive response to increased cardiac workload. Cardiomyocytes growth and increase in contractile force are conditioned by sufficient energy production, which implies appropriate mitochondrial function. The 60 kDa heat shock protein (HSP60) is a chaperone essential for mitochondrial proteostasis, but when translocates from mitochondria, it can also act as a potent inflammatory mediator binding to toll-like receptors (TLRs). In this study, we aimed to compare the expression pattern of HSP60, TLR2, and TLR4 in hypertrophic vs non-hypertrophic, normal human myocardium. We further examined whether HSP60 in situ binds to TLRs in hypertrophic myocardial tissue. In addition, expression of activated downstream targets of TLR 2/4 pathways was also evaluated.For this purpose, immunohistochemical expression analyses were performed on myocardial tissue samples obtained during the autopsy of human subjects in which left ventricular hypertrophy was the only cardiopathological finding and had died from sudden cardiac death, as well as from the subjects without any cardiac pathology, that died by unnatural death (accident or suicide). Double immunofluorescence was used to examine HSP60 translocation, while proximity ligation assay (PLA) was performed to assess HSP60 and TLRs interactions.Hypertrophic myocardium showed significantly higher expression of HSP60, TLR2, and TLR4 compared to normal myocardium. Furthermore, in hypertrophic cardiomyocytes, we found membrane translocation of HSP60 and signs of HSP60/TLR interactions.Conclusion: The obtained data point to an important supportive role of HSP60 in adaptive cardiomyocytes growth, while concomitant induction of TLR2 and TLR4 candidates HSP60-TLRs interactions as an early events during pathogenesis of secondary complications consequently to the left ventricular hypertrophy.

Pathobiological Mechanisms of Endothelial Dysfunction Induced by tert-Butyl Hydroperoxide via Apoptosis, Necrosis and Senescence in a Rat Model

Background: Endothelial dysfunction is one of the underlying causes for vascular diseases. tert-Butyl hydroperoxide (t-BHP), a short-chain lipid hydroperoxide analog, has been reported to cause adverse effects in different systems. However, the adverse actions of t-BHP on inducing endothelial dysfunction are unclear and remain under investigation. Aim of the present study was to identify the pathobiological mechanisms of t-BHP in rat aortic endothelial cells and thoracic aorta. Methods: Primary cultured cells were treated with vehicle or t-BHP (50, 100, 250, 500, and 1,000 μM). Cells were harvested and specific analyses regarding cellular apoptosis, necrosis, and senescence were conducted. Additionally, t-BHP (0.1, 0.2, and 0.4 mmol/kg body weight) or vehicle were administered to male rats (the young group at 6 weeks of age and the mature adult group at 24 weeks of age) daily through intraperitoneal injections. At 10 days after the first drug treatment apoptotic endothelial toxicity was evaluated by biochemical, histological, and immunofluorescent staining analyses. Results: Dose-dependent effects of t-BHP were observed for the reduction of cell viability, deterioration of cell toxicity, initiation of cell cycle arrest, and triggering of apoptosis and necrosis. Moreover, increase of cells stained positive for senescence-associated beta-galactosidase (SA-β-Gal), amelioration of telomerase activity, and precipitations of necrotic, cell cycle, and apoptotic signaling regulatory proteins were also found in the in vitro model. In the in vivo study, results indicated that t-BHP at higher doses enlarged the intima-medial thickness of descending aorta in the mature adult group, but led to aortic narrowing in the young group. Increased injuries were observed by upregulating endothelial apoptosis- and senescence-positive staining, along with caspase-3 activity and down-regulating telomerase activity. Conclusion: These results confirmed that t-BHP impaired aortic endothelial cell survival at least partially by the activation of p53-mediated signaling pathways, inhibition of cell cycle regulatory proteins, and initiation of cellular senescence-related signaling pathways. In conclusion, t-BHP was found to be a major trigger for impairing aortic endothelial cell survival and deteriorating vascular dysfunction in experimental practice.

Impact of thermal stress on expression dynamics of HSP60 in cardiac fibroblast cells of goat

The present study was aimed to determine the impact of thermal stress on expression dynamics of heat shock protein 60 (HSP60) mRNA in cultured cardiac fibroblast cells of the goat. The heart tissues (n = 6) from different goats were used for the culture study. The cardiac fibroblast cells were cultured and subjected to thermal stress at 42 °C for 0, 20, 60 and 100 min. The relative abundance of HSP60 mRNA was assessed by quantitative real-time PCR (qRT-PCR). The cardiac cells exposed to thermal stress at 42 °C for 0 min was taken as control. The relative abundance of HSP60 mRNA did not change at 20 min of thermal stress as compared to control. Thereafter, the relative abundance of HSP60 mRNA was significantly up-regulated (p < 0.05) at 60 min and 100 min of thermal stress. However, the highest mRNA expression of HSP60 was noticed at 100 min of thermal stress. The present study indicates that, thermal stress modulates the mRNA expression HSP60 in cultured caprine cardiac fibroblast cells.

Recovery of the Xenopus laevis heart from ROS-induced stress utilizes conserved pathways of cardiac regeneration

Urodele amphibians and some fish are capable of regenerating up to a quarter of their heart tissue after cardiac injury. While many anuran amphibians like Xenopus laevis are not capable of such feats, they are able to repair lesser levels of cardiac damage, such as that caused by oxidative stress, to a far greater degree than mammals. Using an optogenetic stress induction model that utilizes the protein KillerRed, we have investigated the extent to which mechanisms of cardiac regeneration are conserved during the restoration of normal heart morphology post oxidative stress in X. laevis tadpoles. We focused particularly on the processes of cardiomyocyte proliferation and dedifferentiation, as well as the pathways that facilitate the regulation of these processes. The cardiac response to KillerRed-induced injury in X. laevis tadpole hearts consists of a phase dominated by indicators of cardiac stress, followed by a repair-like phase with characteristics similar to mechanisms of cardiac regeneration in urodeles and fish. In the latter phase, we found markers associated with partial dedifferentiation and cardiomyocyte proliferation in the injured tadpole heart, which, unlike in regenerating hearts, are not dependent on Notch or retinoic acid signaling. Ultimately, the X. laevis cardiac response to KillerRed-induced oxidative stress shares characteristics with both mammalian and urodele/fish repair mechanisms, but is nonetheless a unique form of recovery, occupying an intermediate place on the spectrum of cardiac regenerative ability. An understanding of how Xenopus repairs cardiac damage can help bridge the gap between mammals and urodeles and contribute to new methods of treating heart disease.

Heat Shock Proteins: Protection and Potential Biomarkers for Ischemic Injury of Cardiomyocytes After Surgery

The heat shock proteins are endogenous proteins with the ability to act as molecular chaperones. Methods that provide cell protection by way of some damage can positively influence the results of surgery. The present review summarizes current knowledge concerning the cardioprotective role of the heat shock proteins as occurs in heart damage, including relevant information about the stresses that regulate the expression of these proteins and their potential role as biomarkers of heart disease.

Identification of Proteins Differentially Expressed in the Striatum by Melatonin in a Middle Cerebral Artery Occlusion Rat Model-a Proteomic and in silico Approach

Ischemic stroke is characterized by permanent or transient obstruction of blood flow, which initiates a cascading pathological process, starting from acute ATP loss to subsequent membrane depolarization, glutamate excitotoxicity, and calcium overload. Melatonin is a potent antioxidant that exerts protective effects in different experimental stroke models. In this study, melatonin effects were demonstrated by a proteomic and in silico approach. The proteomic study identified differentially expressed proteins by 2D gel electrophoresis in the striatum 24 h after middle cerebral artery occlusion. Proteomic analysis revealed several proteins with aberrant expression and was validated by western blot and immunofluorescence analysis. Homology modeling was performed to build 3D structures for γ-enolase, thioredoxin (TRX), and heat shock 60 (HSP60) by the template crystal structures using a protein data bank as a sequence database. The structure refinement of each model was achieved by energy minimization via molecular dynamic simulation, and the generated models were further assessed for stability by Procheck and ProSA. The models were processed for docking analysis using AutoDock Vina, and post-docking analysis was determined by discovery studio. The proteomic study showed decreased expression of γ-enolase, TRX, and protein phosphatase 2A subunit B and increased expression of collapsin response mediator protein 2 and HSP60 in the striatum after ischemic injury. Treatment with melatonin modulated the expression profiles of these proteins. This study demonstrated the neuroprotective role of melatonin in the ischemic striatum using a proteomic and in silico approach. Collectively, melatonin may act in a multimechanistic way by modulating the expression of several proteins in the ischemic striatum.

Redox Aspects of Chaperones in Cardiac Function

Molecular chaperones are stress proteins that allow the correct folding or unfolding as well as the assembly or disassembly of macromolecular cellular components. Changes in expression and post-translational modifications of chaperones have been linked to a number of age- and stress-related diseases including cancer, neurodegeneration, and cardiovascular diseases. Redox sensible post-translational modifications, such as S-nitrosylation, glutathionylation and phosphorylation of chaperone proteins have been reported. Redox-dependent regulation of chaperones is likely to be a phenomenon involved in metabolic processes and may represent an adaptive response to several stress conditions, especially within mitochondria, where it impacts cellular bioenergetics. These post-translational modifications might underlie the mechanisms leading to cardioprotection by conditioning maneuvers as well as to ischemia/reperfusion injury. In this review, we discuss this topic and focus on two important aspects of redox-regulated chaperones, namely redox regulation of mitochondrial chaperone function and cardiac protection against ischemia/reperfusion injury.

Neuroprotective effect of heat shock protein 60 on matrine-suppressed microglial activation

Matrine (MT) is the primary active alkaloid separated from members of the Sophora genus. Previous studies have reported that MT has anti-inflammatory effects in the central nervous system (CNS). However, the underlying molecular mechanism of the neuroprotective effect of MT remains unclear, particularly the role of heat shock protein 60 (HSP60). Microglia are macrophages in the CNS that serve an essential role in the innate immune system by producing various proinflammatory and neurotoxic factors. In addition, HSP60 is released by activated microglia causing an autoimmune response. The present study aimed to investigate whether MT could inhibit the activation of microglia via suppressing the HSP60 signaling pathway. The results demonstrated that the expression and release of HSP60 in LPS-activated BV2 microglial cells was significantly decreased by MT treatment. Extracellular HSP60 is a ligand of toll like receptor 4 (TLR-4); thus, it was hypothesized that secreted HSP60 could bind to TLR-4 on microglia and activate the TLR-4 signaling pathway. As expected, western blotting and ELISA results revealed that MT significantly inhibited the LPS-induced increase in TLR-4, myeloid differentiation primary response protein MyD88, caspase-3 and tumor necrosis factor-α. In conclusion, the results of the present study provide a novel direction for the prevention and treatment of neurodegenerative diseases characterized by microglial activation.

Microglia activation triggers oligodendrocyte precursor cells apoptosis via HSP60

Reactive microglia are present in lesions of myelin-associated white matter disorders resulting in injuries to oligodendrocyte precursor cells (OPCs). Therefore, protection of OPCs from injury due to excessive activation of microglia is important in treating these diseases. Heat shock protein 60 (HSP60) has been demonstrated to be released extracellularly in the failing heart upon stress or injury. However, the role of HSP60 in the central nervous system and whether it participates in the toxic effects of microglia on OPCs remains unclear. The present study used the co-culture, cell death assays, binding assays, immunochemistry, western blot and ELISA. HSP60 was demonstrated to be released extracellularly by LPS-activated microglia and to bind to OPCs, triggering OPC apoptosis. When pretreated with toll-like receptor (TLR) 4 blocking antibody, the viability of OPCs increased, while the expression of nuclear factor κB (NFκB), caspase 3 and the release of proinflammatory cytokines triggered by HSP60 decreased. These results suggest that HSP60 released by microglia may mediate OPC apoptosis through binding to TLR4 on the surface of OPCs and subsequently activating the TLR4-NFκB signaling pathway. HSP60 may, therefore, serve as a potential target for treatment of myelin-associated neurodegenerative diseases that are accompanied by microglia activation.

Paying for the Tolls: The High Cost of the Innate Immune System for the Cardiac Myocyte

The cardiac myocyte differs strikingly from the specialized cells of the immune system, which has two different responses to invading organisms and tissue damage. Adaptive or acquired immunity generates highly specific antibodies in response to threats and is an essential component of immunity; however, adaptive immunity can take 4-7 days to mobilize, and a more primitive response, innate immunity, fills the gap. Innate immunity is expressed in complex and in primitive life forms. Specialized receptors, Toll-like receptors (TLRs), which are widely distributed throughout different tissues recognize danger signals and rapidly respond with the release of noxious substances, such as TNFα. The problem is that many endogenous molecules have been found to act as ligands for specific TLRs, and when these molecules are released into the extracellular environment, they can cause problems by activating innate immunity and an inflammatory response. In cardiac myocytes heat shock protein (HSP)60 can activate TLR4, as can HMGB1, and this type of response can amplify the response to ischemia/reperfusion leading to increased cell and tissue injury. Activation of TLRs can potentially amplify chronic, inflammatory diseases, such as ischemic heart failure. Thus, it is important to understand the regulation of the TLRs and their downstream effects. This chapter will focus on the TLRs and cardiac myocytes.

Oxymatrine inhibits microglia activation via HSP60-TLR4 signaling

Oxymatrine (OMT) is an alkaloid extracted from Sophora flavescens, which has broad anti-inflammatory, antitumor and immunosuppressant actions. However, the underlying molecular mechanisms have remained elusive. Heat shock protein 60 (HSP60) has recently been shown to have an important role in autoimmune reactions. The present study aimed to investigate whether OMT exerts its anti-inflammatory effects by inhibiting microglial activation and examined the role of HSP60 in this process. Western blot analysis and ELISA showed that OMT decreased the expression and release of HSP60 by LPS-activated BV2 cells. The expression of heat shock factor 1, the transcription factor of HSP60, was also suppressed by OMT. Extracellular HSP60 has been previously indicated to induce microglial apoptosis through the Toll-like receptor (TLR)-4 pathway. Flow cytometric analysis demonstrated that LPS treatment induced apoptosis of BV2 cells, which was inhibited by OMT in parallel with inhibition of LPS-induced expression of TLR-4. Furthermore, OMT was shown to suppress the levels of myeloid differentiation factor (MYD)88, nuclear factor (NF)-κB, caspase-3, inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β and IL-6. In light of these results, it was concluded that OMT may exert its neuroprotective effects via HSP60/TLR-4/MYD88/NF-κB signaling pathways to inhibit microglial activation. OMT may therefore offer substantial therapeutic potential for treating neurodegenerative diseases associated with microglial activation.

HSP60 mediates the neuroprotective effects of curcumin by suppressing microglial activation

Curcumin has anti-inflammatory and antioxidant properties and has been widely used to treat or prevent neurodegenerative diseases. However, the mechanisms underlying the neuroprotective effects of curcumin are not well known. In the present study, the effect of curcumin on lipopolysaccharide (LPS)-stimulated BV2 mouse microglia cells was investigated using enzyme-linked immunosorbent assays of the culture medium and western blotting of cell lysates. The results showed that curcumin significantly inhibited the LPS-induced expression and release of heat shock protein 60 (HSP60) in the BV2 cells. The level of heat shock factor (HSF)-1 was upregulated in LPS-activated BV2 microglia, indicating that the increased expression of HSP60 was driven by HSF-1 activation. However, the increased HSF-1 level was downregulated by curcumin. Extracellular HSP60 is a ligand of Toll-like receptor 4 (TLR-4), and the level of the latter was increased in the LPS-activated BV2 microglia and inhibited by curcumin. The activation of TLR-4 is known to be associated with the activation of myeloid differentiation primary response 88 (MyD88) and nuclear factor (NF)-κB, with the subsequent production of proinflammatory and neurotoxic factors. In the present study, curcumin demonstrated marked suppression of the LPS-induced expression of MyD88, NF-κB, caspase-3, inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β and IL-6 in the microglia. These results indicate that curcumin may exert its neuroprotective and anti-inflammatory effects by inhibiting microglial activation through the HSP60/TLR-4/MyD88/NF-κB signaling wpathway. Therefore, curcumin may be useful for the treatment of neurodegenerative diseases that are associated with microglial activation.

Cardiosphere-derived cells from pediatric end-stage heart failure patients have enhanced functional activity due to the heat shock response regulating the secretome

We have demonstrated that human neonatal cardiosphere-derived cells (CDCs) derived from the young are more regenerative due to their robust secretome. However, it is unclear how the decompensated pediatric heart impacts the functional activity of their CDCs. Our aim was to characterize the potency of pediatric CDCs derived from normal functioning myocardium of control heart disease (CHD) patients to those generated from age-matched end stage heart failure (ESHF) patients and to determine the mechanisms involved. ESHF-derived CDCs contained a higher number of c-kit(+) , Islet-1(+) , and Sca-1(+) cells. When transplanted into an infarcted rodent model, ESHF-derived CDCs significantly demonstrated higher restoration of ventricular function, prevented adverse remodeling, and enhanced angiogenesis when compared with CHD patients. The superior functional recovery of the ESHF-derived CDCs was mediated in part by increased SDF-1α and VEGF-A secretion resulting in augmented recruitment of endogenous stem cells and proliferation of cardiomyocytes. We determined the mechanism is due to the secretome directed by the heat shock response (HSR), which is supported by three lines of evidence. First, gain of function studies demonstrated that increased HSR induced the lower functioning CHD-derived CDCs to significantly restore myocardial function. Second, loss-of function studies targeting the HSR impaired the ability of the ESHF-derived CDCs to functionally recover the injured myocardium. Finally, the native ESHF myocardium had an increased number of c-kit(+) cardiac stem cells. These findings suggest that the HSR enhances the functional activity of ESHF-derived CDCs by increasing their secretome activity, notably SDF-1α and VEGF-A.

Selenoproteins and heat shock proteins play important roles in immunosuppression in the bursa of Fabricius of chickens with selenium deficiency

Selenium (Se) is necessary for the immune system in chicken and mediates its physiological functions through selenoproteins. Heat shock proteins (Hsps) are indispensable for maintaining normal cell function and for directing the immune response. The aim of the present study was to investigate the effects of Se deficiency on the messenger ribonucleic acid (mRNA) expression levels of selenoproteins and Hsps as well as immune functions in the chicken bursa of Fabricius. Two groups of chickens, namely the control and Se-deficient (L group) groups, were reared for 55 days. The chickens were offered a basal diet, which contained 0.15 mg Se/kg in the diet fed to the control group and 0.033 mg Se/kg in the diet fed to the L group. We performed real-time quantitative polymerase chain reaction to detect the mRNA expression levels of selenoproteins and Hsps on days 15, 25, 35, 45 and 55. Western blotting was used to determine the protein expression levels of Hsps on days 35, 45 and 55, and immune functions were assessed through an enzyme-linked immunosorbent assay on days 15, 35, and 55. The data showed that the mRNA expression levels of selenoproteins, such as Txnrd1, Txnrd2, Txnrd3, Dio1, Dio2, Dio3, GPx1, GPx2, GPx3 GPx4, Sepp1, Selo, Sel-15, Sepx1, Sels, Seli, Selu, Selh, and SPS2, were significantly lower (P < 0.05) in the L group compared with the control group. Additionally, the mRNA and protein expression levels of Hsps (Hsp27, Hsp40, Hsp60, Hsp70, and Hsp90) were also significantly higher (P < 0.05) in the L group. The expression levels of IL-2, IL-6, IL-8, IL-10, IL-17, IL-1β, IFN-α, IFN-β, and IFN-γ were significantly lower (P < 0.05) and TNF-α was significantly higher (P < 0.05) in the L group compared with the control group. Our results show that immunosuppression was accompanied by a downregulation of mRNA expression levels of selenoproteins and an upregulation of the Hsp mRNA expression levels. Thus, Se deficiency causes defects in the chicken bursa of Fabricius, and selenoproteins and Hsps play important roles in immunosuppression in the bursa of Fabricius of chickens with Se deficiency.

Determining the neuroprotective effects of dextromethorphan in lipopolysaccharide‑stimulated BV2 microglia

Microglial activation has been recognized as being vital in the pathogenesis of several neurodegenerative disorders. Therefore, the identification of therapeutic drugs to prevent microglial activation and thus protect against inflammation‑mediated neuronal injury, is required. In the present study, dextromethorphan (DM), a compound widely used in antitussive remedies that has been demonstrated to possess neuroprotective effects, was shown to reduce proinflammatory mediator production in lipopolysaccharide (LPS)‑stimulated BV2 mouse microglial cells. Western blot analysis revealed that DM markedly suppressed the activation of nuclear factor‑κB (NFκB), caspase‑3 signaling and the expression of another inflammation‑inducing factor, heat shock protein 60 (HSP60) and heat shock factor‑1, induced by LPS in BV2 cells. Results from ELISA assay demonstrated that DM reduced the release of HSP60, nitric oxide (NO), inducible NO synthase, tumor necrosis factor‑α, interleukin (IL)‑1β and IL‑6 induced by LPS in BV2 microglia. These results were confirmed by immunofluorescence, suggesting that DM may exert a neuroprotective and anti‑inflammatory effect by inhibiting microglial activation through the HSP60‑NFκB signaling pathway. Therefore, DM may offer substantial therapeutic benefits in the treatment of neurodegenerative diseases that are accompanied by microglial activation.

Heat shock proteins and cardiovascular disease

Atherosclerosis is the leading global cause of mortality, morbidity, and disability. Heat shock proteins (HSPs) are a highly conserved family of proteins with diverse functions expressed by all cells exposed to environmental stress. Studies have reported that several HSPs may be potential risk markers of atherosclerosis and related cardiovascular diseases, or may be directly involved in the atherogenic process itself. HSPs are expressed by cells in atherosclerotic plaque and anti-HSP has been reported to be increased in patients with vascular disease. Autoimmune responses may be generated against antigens present within the atherosclerotic plaque, including HSP and may lead to a cycle of ongoing vascular injury. It has been suggested that by inducing a state of tolerance to these antigens, the atherogenic process may be limited and thus provide a potential therapeutic approach. It has been suggested that anti-HSPs are independent predictors of risk of vascular disease. In this review, we summarize the current understanding of HSP in cardiovascular disease and highlight their potential role as diagnostic agents and therapeutic targets.

Comparison of the ventricle muscle proteome between patients with rheumatic heart disease and controls with mitral valve prolapse: HSP 60 may be a specific protein in RHD

Objective. Rheumatic heart disease (RHD) is a serious autoimmune heart disease. The present study was aimed at identifying the differentially expressed proteins between patients with RHD and controls with mitral valve prolapse. Methods. Nine patients with RHD and nine controls with mitral valve prolapsed were enrolled for this study. Two-dimensional difference in-gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) were performed. Results. A total of 39 protein spots with differential expressions were identified between the two groups (P < 0.05, Average Ratio > 1.2 or Average Ratio < −1.2) and four upregulated proteins (including heat shock protein 60 (HSP 60), desmin, PDZ and LIM domain protein 1, and proteasome subunit alpha type-1) and three downregulated proteins (including tropomyosin alpha-1 chain, malate dehydrogenase, and chaperone activity of bc1 complex homolog) were determined. Conclusion. These seven proteins, especially HSP 60, may serve as potential biomarkers for the diagnosis of RHD and provide evidence to explain the mechanisms of this complex disease in the future.

Innate immunity and cardiomyocytes in ischemic heart disease

Myocardial ischemia/reperfusion (I/R) is the most common cause of myocardial inflammation, which is primarily a manifestation of the innate immune responses. Innate immunity is activated when pattern recognition receptors (PRRs) respond to molecular patterns common to microbes and to danger signals expressed by injured or infected cells, so called pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). The expression of various PRRs in cardiomyocytes and the release of DAMPs from cardiomyocytes subjected to I/R injury, through active mechanisms as well as passive processes, enable cardiomyocytes to generate innate immune responses. Studies in isolated heart and cardiomyocytes have confirmed the inflammatory and functional effects of cardiac PRRs especially Toll-like receptors in response to I/R-derived DAMPs, such as heat shock proteins. This review addresses the active role of cardiomyocytes in mediating innate inflammatory responses to myocardial I/R. We propose that cardiomyocytes act as innate immune cells in myocardial I/R injury.

Inflammatory stress and sarcomagenesis: a vicious interplay

Chronic inflammation represents one of the hallmarks of cancer, but its role in sarcomagenesis has long been overlooked. Sarcomas are a rare and heterogeneous group of tumors of mesenchymal origin accounting for less than 1 % of cancers in adults but 21 % of cancers in the pediatric population. Sarcomas are associated with bad prognosis, and their management requires a multidisciplinary team approach. Several lines of evidence indicate that inflammation has been implicated in sarcomagenesis leading to the activation of the key transcription factors HIF-1, NF- κB, and STAT-3 involved in a complex inflammatory network. In the past years, an increasing number of new targets have been identified in the treatment of sarcomas leading to the development of new drugs that aim to interrupt the vicious connection between inflammation and sarcomagenesis. This article makes a brief overview of preclinical and clinical evidence of the molecular pathways involved in the inflammatory stress response in sarcomagenesis and the most targeted therapies.

The role of heat shock proteins in inflammatory injury induced by cold stress in chicken hearts

The aim of this study was to investigate the effects of cold stress on the expression levels of heat shock proteins (Hsps90, 70, 60, 40, and 27) and inflammatory factors (iNOS, COX-2, NF-κB, TNF-α, and PTGEs) and oxidative indexes in hearts of chickens. Two hundred forty 15-day-old male chickens were randomly divided into 12 groups and kept at the temperature of 12 ± 1 °C for acute and chronic cold stress. There were one control group and five treatment groups for acute cold stress, three control groups, and three treatment groups for chronic cold stress. After cold stress, malondialdehyde level increased in chicken heart; the activity of superoxide dismutase and glutathione peroxidase in the heart first increased and then decreased. The inflammatory factors mRNA levels were increased in cold stress groups relative to control groups. The histopathological analysis showed that heart tissues were seriously injured in the cold stress group. Additionally, the mRNA levels of Hsps (70, 60, 40, and 27) increased significantly (P < 0.05) in the cold stress groups relative to the corresponding control group. Meanwhile, the mRNA level and protein expression of Hsp90 decreased significantly (P < 0.05) in the stress group, and showed a gradually decreasing tendency. These results suggested that the levels of inflammatory factors and Hsps expression levels in heart tissues can be influenced by cold stress. Hsps commonly played an important role in the protection of the heart after cold stress.

CD4+ CD28(null) cells are an independent predictor of mortality in patients with heart failure

AIMS

Immune activation and subsequent release of proinflammatory cytokines plays a central role in the pathophysiology of chronic heart failure (CHF). Cytotoxic CD4(+)CD28(null) cells are generated under inflammatory conditions and implicated in a variety of pathological processes like atherosclerosis and autoimmune diseases. The study aim was to assess the impact of CD4(+)CD28(null) cells on survival in CHF patients.

METHODS AND RESULTS

Circulating lymphocytes from 107 CHF patients were analyzed for the distribution of CD4 subsets by flow cytometry. During a median follow-up of 23 months, 22 (20%) persons died. CD4(+)CD28(null) cells independently predicted all-cause mortality with an adjusted hazard ratio (HR) of 1.88 per 1-standard deviation increase (95% confidence interval (CI): 1.26-2.79, P = 0.002) and with a HR of 1.83 for cardiovascular mortality (95% CI: 1.18-2.86, P = 0.008), respectively. Further, we found a significant association with NT-proBNP (r = 0.23).

CONCLUSION

Circulating CD4(+)CD28(null) cells are associated with CHF severity and are a strong and independent predictor of mortality in CHF fostering the implication of the immune system in CHF pathophysiology.

Gut microbiota imbalance and chaperoning system malfunction are central to ulcerative colitis pathogenesis and can be counteracted with specifically designed probiotics: a working hypothesis

In this work, we propose that for further studies of the physiopathology and treatment for inflammatory bowel diseases, an integral view of the conditions, including the triad of microbiota-heat shock proteins (HSPs)-probiotics, ought to be considered. Microbiota is the complex microbial flora that resides in the gut, affecting not only gut functions but also the health status of the whole body. Alteration in the microbiota's composition has been implicated in a variety of pathological conditions (e.g., ulcerative colitis, UC), involving both gut and extra-intestinal tissues and organs. Some of these pathologies are also associated with an altered expression of HSPs (chaperones) and this is the reason why they may be considered chaperonopathies. Probiotics, which are live microorganisms able to restore the correct, healthy equilibrium of microbiota composition, can ameliorate symptoms in patients suffering from UC and modulate expression levels of HSPs. However, currently probiotic therapy follows ex-adiuvantibus criteria, i.e., treatments with beneficial effects but whose mechanism of action is unknown, which should be changed so the probiotics needed in each case are predetermined on the basis of the patient's microbiota. Consequently, efforts are necessary to develop diagnostic tools for elucidating levels and distribution of HSPs and the microbiota composition (microbiota fingerprint) of each subject and, thus, guide specific probiotic therapy, tailored to meet the needs of the patient. Microbiota fingerprinting ought to include molecular biology techniques for sequencing highly conserved DNA, e.g., genes encoding 16S RNA, for species identification and, in addition, quantification of each relevant microbe.

Neuroprotective effects of Lycium barbarum polysaccharides in lipopolysaccharide-induced BV2 microglial cells

Polysaccharides extracted from Lycium barbarum (LBPs) possess a wide variety of biological activities. However, their neuroprotective effects have not yet been fully elucidated. The aim of the present study was to investigate the inhibitory effects of LBPs on the production of lipopolysaccharide (LPS)‑induced proinflammatory mediators in BV2 microglia. BV2 mouse microglial cells were cultured and an MTT assay was performed to determine whether LBPs had an effect on the apoptosis of LPS-stimulated BV2 cells. Our data showed that LPS induced the activation of nuclear factor‑κB (NF‑κB) and its upstream protein caspase 3, upregulated the expression of an additional apoptosis‑inducing factor, heat shock protein 60 (HSP60), in BV2 microglial cells and increased the release of TNF-α and HSP60 in the culture media. Following treatment with LBPs, the activated NF‑κB and caspase 3 were significantly suppressed. Furthermore, the enhanced expression of HSP60 was reduced and the LPS-induced release of TNF-α and HSP60 were inhibited. These results suggest that LBPs may have therapeutic potential for the treatment of neurodegenerative diseases that are accompanied by microglial activation.

Improved Metabolic Control in Diabetes, HSP60, and Proinflammatory Mediators

The diabetes-atherosclerosis relationship remains to be fully defined. Repeated prolonged hyperglycemia, increased ROS production and endothelial dysfunction are important factors. One theory is that increased blood levels of heat shock protein (HSP)60 are proinflammatory, through activation of innate immunity, and contribute to the progression of vascular disease. It was hypothesized that improvement of diabetes control in patients presenting with metabolic syndrome would lower HSP60, and anti-HSP60 antibody levels and decrease inflammatory markers. Paired sera of 17 Italian patients, before and after intensive treatment, were assayed for cytokines, HSP60 and anti-HSP60 antibodies. As expected, intensive treatment was associated with a decrease in HgbA1C (P < 0.001) and BMI (P < 0.001). After treatment, there was a significant decrease in IL-6 (P < 0.05). HSP60 levels were before treatment −6.9 + 1.9, after treatment −7.1 + 2.0 ng/mL (P = ns). Overall HSP60 concentrations were lower than published reports. Anti-HSP60 antibody titers were high and did not decrease with treatment. In conclusion, improvement of diabetic control did not alter HSP60 concentrations or antiHSP60 antibody titers, but led to a reduction of IL-6 levels.

Convergent sets of data from in vivo and in vitro methods point to an active role of Hsp60 in chronic obstructive pulmonary disease pathogenesis

Background

It is increasingly clear that some heat shock proteins (Hsps) play a role in inflammation. Here, we report results showing participation of Hsp60 in the pathogenesis of chronic obstructive pulmonary diseases (COPD), as indicated by data from both in vivo and in vitro analyses.

Methods and Results

Bronchial biopsies from patients with stable COPD, smoker controls with normal lung function, and non-smoker controls were studied. We quantified by immunohistochemistry levels of Hsp10, Hsp27, Hsp40, Hsp60, Hsp70, Hsp90, and HSF-1, along with levels of inflammatory markers. Hsp10, Hsp40, and Hsp60 were increased during progression of disease. We found also a positive correlation between the number of neutrophils and Hsp60 levels. Double-immunostaining showed that Hsp60-positive neutrophils were significantly increased in COPD patients. We then investigated in vitro the effect on Hsp60 expression in bronchial epithelial cells (16HBE) caused by oxidative stress, a hallmark of COPD mucosa, which we induced with H₂O₂. This stressor determined increased levels of Hsp60 through a gene up-regulation mechanism involving NFkB-p65. Release of Hsp60 in the extracellular medium by the bronchial epithelial cells was also increased after H₂O₂ treatment in the absence of cell death.

Conclusions

This is the first report clearly pointing to participation of Hsps, particularly Hsp60, in COPD pathogenesis. Hsp60 induction by NFkB-p65 and its release by epithelial cells after oxidative stress can have a role in maintaining inflammation, e.g., by stimulating neutrophils activity. The data open new scenarios that might help in designing efficacious anti-inflammatory therapies centered on Hsp60 and applicable to COPD.

The heat shock paradox and cardiac myocytes: role of heat shock factor

The induction of the heat shock (HS) response is accepted to be a protective response, reducing injury and improving cell survival. However, when inflammation precedes HS, there is an unexpected increase in injury, known as the HS paradox, which is hypothesized to be a mechanism underlying multiorgan dysfunction. We hypothesized that the HS paradox would occur in adult cardiac myocytes and that HS factor (HSF) 1 would contribute to injury. Heat shock at 42°C and TNF (10 ng/mL) were used as the HS and the inflammatory insult, respectively. The combination of TNF followed by HS (TNF/HS) caused the greatest amount of apoptosis in adult rat cardiac myocytes. TNF/HS resulted in an increase in HS protein (HSP) 60, compared with untreated cells, those receiving HS/TNF, or TNF alone. There was no increase in heme oxygenase 1 in any of the groups. Heat shock protein 72 increased in all the groups, with the greatest levels with TNF/HS. Nuclear factor κB activation was greatest with TNF/HS. Pretreatment with a DNA-binding decoy for HSF-1 prevented the increase in HSPs and decreased apoptosis in all groups. However, the increase in iNOS, seen in all treatment groups, was unaffected by the HSF-1-binding decoy. We conclude that the HS paradox occurs in adult cardiac myocytes, that HSP60 is increased as part of the HS paradox, and that HSF-1 activation contributes to injury.

Heat shock proteins in stabilization of spontaneously restored sinus rhythm in permanent atrial fibrillation patients after mitral valve surgery

A spontaneously restored sinus rhythm in permanent atrial fibrillation patients has been often observed after mitral valve (MV) surgery, but persisting duration in sinus rhythm varies from patient to patient. Heat shock proteins (Hsps) may be involved in pathogenesis of atrial fibrillation. We hypothesized that stabilization of restored sinus rhythm is associated with expression of Hsps in the atria. To test this hypothesis, clinical data, biopsies of right atrial appendage, and blood samples were collected from 135 atrial fibrillation patients who spontaneously restored sinus rhythm after conventional isolated MV replacement. Comparison was made between patients who had recurrence of atrial fibrillation within 7 days (AF) vs. patients with persisted sinus rhythm for more than 7 days (SR). Results showed that SR patients had higher activity of heat shock transcription factor 1 (HSF1) as well as upregulated expressions of heat shock cognate 70, Hsp70, and Hsp27 in the tissues. The activation of HSF1-Hsps pathway was associated with less-aggressive pathogenesis as reflected by lower rates of myolysis, apoptosis, interstitial fibrosis, and inflammation in SR patients. However, Hsp60 was lower in both tissue and plasma in SR patients, and was positively correlated with apoptosis, interstitial fibrosis, and inflammation. These findings suggest that the Hsps play important roles in stabilization of restored sinus rhythm after MV surgery by inhibiting AF-related atrial remodeling and arrhythmogenic substrates in atrial fibrillation patients. Low circulating Hsp60 levels preoperatively might predict a stable spontaneously restored sinus rhythm postoperatively.

Myocardial ischemia activates an injurious innate immune signaling via cardiac heat shock protein 60 and Toll-like receptor 4

Innate immune response after transient ischemia is the most common cause of myocardial inflammation and may contribute to injury, yet the detailed signaling mechanisms leading to such a response are not well understood. Herein we tested the hypothesis that myocardial ischemia activates interleukin receptor-associated kinase-1 (IRAK-1), a kinase critical for the innate immune signaling such as that of Toll-like receptors (TLRs), via a mechanism that involves heat shock proteins (HSPs) and TLRs. Coronary artery occlusion induced a rapid myocardial IRAK-1 activation within 30 min in wild-type (WT), TLR2(-/-), or Trif(-/-) mice, but not in TLR4(def) or MyD88(-/-) mice. HSP60 protein was markedly increased in serum or in perfusate of isolated heart following ischemia/reperfusion (I/R). In vitro, recombinant HSP60 induced IRAK-1 activation in cells derived from WT, TLR2(-/-), or Trif(-/-) mice, but not from TLR4(def) or MyD88(-/-) mice. Both myocardial ischemia- and HSP60-induced IRAK-1 activation was abolished by anti-HSP60 antibody. Moreover, HSP60 treatment of cardiomyocytes (CMs) led to marked activation of caspase-8 and -3, but not -9. Expression of dominant-negative mutant of Fas-associated death domain protein or a caspase-8 inhibitor completely blocked HSP60-induced caspase-8 activation, suggesting that HSP60 likely activates an apoptotic program via the death-receptor pathway. In vivo, I/R-induced myocardial apoptosis and cytokine expression were significantly attenuated in TLR4(def) mice or in WT mice treated with anti-HSP60 antibody compared with WT controls. Taken together, the current study demonstrates that myocardial ischemia activates an innate immune signaling via HSP60 and TLR4, which plays an important role in mediating apoptosis and inflammation during I/R.

Mitochondria and heart failure: new insights into an energetic problem

Cardiac mitochondria are powerful organelles supplying energy to support the high adenosine triphosphate (ATP) consumption of the beating heart. The progression of HF (HF) is characterized by diminished energy metabolism, calcium mishandling, reactive oxygen species (ROS) generation and apoptotic cell death. Although the etiologies of HF are multifactoral, many of the changes of HF are associated with cardiac mitochondrial dysfunction either directly or indirectly. A number of studies have established the role of calcium mishandling and reduced ATP production in mitochondrial dysfunction in HF. More recent work has contributed to our understanding of the role of ROS and proapoptotic protein release by the mitochondria in HF. New interest has been generated in mitochondria by the relatively recent identification of the processes of fusion and fission, which are critical to the maintenance of healthy mitochondria. Fission and fusion also have significant roles in apoptosis. Other studies have shown that estrogen has important functions in the mitochondria, including regulation of mitochondrial gene expression. Aging alone contributes to the development of HF through multiple mechanisms. These new insights into HF have implications for our understanding of this important disease, and will be reviewed here.