Autophagy in transition from hypertrophic cardiomyopathy to heart failure

Exercise training decreases the load and changes the content of circulating SDS-resistant protein aggregates in patients with heart failure with reduced ejection fraction

BACKGROUND

Heart failure (HF) often disrupts the protein quality control (PQC) system leading to protein aggregate accumulation. Evidence from tissue biopsies showed that exercise restores PQC system in HF; however, little is known about its effects on plasma proteostasis.

AIM

To determine the effects of exercise training on the load and composition of plasma SDS-resistant protein aggregates (SRA) in patients with HF with reduced ejection fraction (HFrEF).

METHODS

Eighteen patients with HFrEF (age: 63.4 ± 6.5 years; LVEF: 33.4 ± 11.6%) participated in a 12-week combined (aerobic plus resistance) exercise program (60 min/session, twice per week). The load and content of circulating SRA were assessed using D2D SDS-PAGE and mass spectrometry. Cardiorespiratory fitness, quality of life, and circulating levels of high-sensitive C-reactive protein, N-terminal pro-B-type natriuretic peptide (NT-proBNP), haptoglobin and ficolin-3, were also evaluated at baseline and after the exercise program.

RESULTS

The exercise program decreased the plasma SRA load (% SRA/total protein: 38.0 ± 8.9 to 36.1 ± 9.7%, p = 0.018; % SRA/soluble fraction: 64.3 ± 27.1 to 59.8 ± 27.7%, p = 0.003). Plasma SRA of HFrEF patients comprised 31 proteins, with α-2-macroglobulin and haptoglobin as the most abundant ones. The exercise training significantly increased haptoglobin plasma levels (1.03 ± 0.40 to 1.11 ± 0.46, p = 0.031), while decreasing its abundance in SRA (1.83 ± 0.54 × 1011 to 1.51 ± 0.59 × 1011, p = 0.049). Cardiorespiratory fitness [16.4(5.9) to 19.0(5.2) ml/kg/min, p = 0.002], quality of life, and circulating NT-proBNP [720.0(850.0) to 587.0(847.3) pg/mL, p = 0.048] levels, also improved after the exercise program.

CONCLUSION

Exercise training reduced the plasma SRA load and enhanced PQC, potentially via haptoglobin-mediated action, while improving cardiorespiratory fitness and quality of life of patients with HFrEF.

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.

Ubiquitin, p62, and Microtubule-Associated Protein 1 Light Chain 3 in Cardiomyopathy

Background: The accumulation of ubiquitinated proteins has been detected in diseased hearts and has been associated with the expression of p62 and microtubule-associated protein 1 light chain 3 (LC3), which are related to autophagy. We evaluated differences in ubiquitin accumulation and p62 and LC3 expression in cardiomyopathy using endomyocardial biopsies. Methods and Results: We studied 24 patients (aged 24-70 years; mean age 55 years) diagnosed with dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), or non-cardiomyopathy (NCM) who underwent endomyocardial biopsy. Biopsied samples were evaluated by microscopy for ubiquitin accumulation and expression of p62 and LC3. Ubiquitin accumulation and p62 and LC3 expression were observed in all patients. Ubiquitin accumulation was higher in DCM than in HCM or NCM; p62 expression was higher in DCM than in HCM. There were no significant differences in LC3 expression among the groups. Ubiquitin accumulation was significantly related to serum N-terminal pro B-type natriuretic peptide concentration and the expression of p62, but not LC3. Conclusions: Ubiquitin accumulation was more prominent in DCM than in HCM and NCM, which may be due to a relative shortage of clearance, including autophagy, compared with production.

Treatment of myocardial interstitial fibrosis in pathological myocardial hypertrophy

Pathological myocardial hypertrophy can be caused by a variety of diseases, mainly accompanied by myocardial interstitial fibrosis (MIF), which is a diffuse and patchy process, appearing as a combination of interstitial micro-scars and perivascular collagen fiber deposition. Different stimuli may trigger MIF without cell death by activating a variety of fibrotic signaling pathways in mesenchymal cells. This manuscript summarizes the current knowledge about the mechanism and harmful outcomes of MIF in pathological myocardial hypertrophy, discusses the circulating and imaging biomarkers that can be used to identify this lesion, and reviews the currently available and potential future treatments that allow the individualized management of patients with pathological myocardial hypertrophy.

Construction of PIK3C3 Transgenic Pig and Its Pathogenesis of Liver Damage

As a member of the PIKs family, PIK3C3 participates in autophagy and plays a central role in liver function. Several studies demonstrated that the complete suppression of PIK3C3 in mammals can cause hepatomegaly and hepatosteatosis. However, the function of PIK3C3 overexpression on the liver and other organs is still unknown. In this study, we successfully generated PIK3C3 transgenic pigs through somatic cell nuclear transfer (SCNT) by designing a specific vector for the overexpression of PIK3C3. Plasmid identification was performed through enzyme digestion and transfected into the fetal fibroblasts derived from Diannan miniature pigs. After 2 weeks of culturing, six positive colonies obtained from a total of 14 cell colonies were identified through PCR. One positive cell line was selected as the donor cell line for SCNT for the construction of PIK3C3transgenic pigs. Thirty single blastocysts were collected and identified as PIK3C3 transgenic-positive blastocysts. Two surrogates became pregnant after transferring the reconstructed embryos into four surrogates. Fetal fibroblasts of PIK3C3-positive fetuses identified through PCR were used as donor cells for SCNT to generate PIK3C3 transgenic pigs. To further explore the function of PIK3C3 overexpression, genotyping and phenotyping of the fetuses and piglets obtained were performed by PCR, immunohistochemical, HE, and apoptosis staining. The results showed that inflammatory infiltration and vacuolar formation in hepatocytes and apoptotic cells, and the mRNA expression of NF-κB, TGF-β1, TLR4, TNF-α, and IL-6 significantly increased in the livers of PIK3C3 transgenic pigs when compared with wild-type (WT) pigs. Immunofluorescence staining showed that LC3B and LAMP-1-positive cells increased in the livers of PIK3C3 transgenic pigs. In the EBSS-induced autophagy of the porcine fibroblast cells (PFCs), the accumulated LC3II protein was cleared faster in PIK3C3 transgenic (PFCs) thanWT (PFCs). In conclusion, PIK3C3 overexpression promoted autophagy in the liver and associated molecular mechanisms related to the activation of ULK1, AMBR1, DRAM1, and MTOR, causing liver damage in pigs. Therefore, the construction of PIK3C3 transgenic pigs may provide a new experimental animal resource for liver diseases.

Accelerated Growth, Differentiation, and Ploidy with Reduced Proliferation of Right Ventricular Cardiomyocytes in Children with Congenital Heart Defect Tetralogy of Fallot

The myocardium of children with tetralogy of Fallot (TF) undergoes hemodynamic overload and hypoxemia immediately after birth. Comparative analysis of changes in the ploidy and morphology of the right ventricular cardiomyocytes in children with TF in the first years of life demonstrated their significant increase compared with the control group. In children with TF, there was a predominantly diffuse distribution of Connexin43-containing gap junctions over the cardiomyocytes sarcolemma, which redistributed into the intercalated discs as cardiomyocytes differentiation increased. The number of Ki67-positive cardiomyocytes varied greatly and amounted to 7.0–1025.5/10⁶ cardiomyocytes and also were decreased with increased myocytes differentiation. Ultrastructural signs of immaturity and proliferative activity of cardiomyocytes in children with TF were demonstrated. The proportion of interstitial tissue did not differ significantly from the control group. The myocardium of children with TF under six months of age was most sensitive to hypoxemia, it was manifested by a delay in the intercalated discs and myofibril assembly and the appearance of ultrastructural signs of dystrophic changes in the cardiomyocytes. Thus, the acceleration of ontogenetic growth and differentiation of the cardiomyocytes, but not the reactivation of their proliferation, was an adaptation of the immature myocardium of children with TF to hemodynamic overload and hypoxemia.

CircHIPK3 regulates the autophagy and apoptosis of hypoxia/reoxygenation-stimulated cardiomyocytes via the miR-20b-5p/ATG7 axis

Autophagy and apoptosis are involved in myocardial ischemia/reperfusion (I/R) injury. Research indicates that circular RNA HIPK3 (circHIPK3) is crucial to cell autophagy and apoptosis in various cancer types. However, the role of circHIPK3 in the regulation of cardiomyocyte autophagy and apoptosis during I/R remains unknown. Our study aimed to examine the regulatory effect of circHIPK3 during myocardial I/R and investigate its mechanism in cardiomyocyte autophagy and apoptosis. Methods and results. The expression of circHIPK3 was upregulated during myocardial I/R injury and hypoxia/reoxygenation (H/R) injury of cardiomyocytes. To study the potential role of circHIPK3 in myocardial H/R injury, we performed gain-of-function and loss-of-function analyses of circHIPK3 in cardiomyocytes. Overexpression of circHIPK3 significantly promoted H/R-induced cardiomyocyte autophagy and cell injury (increased intracellular reactive oxygen species (ROS) and apoptosis) compared to those in the control group, while silencing of circHIPK3 showed the opposite effect. Further research found that circHIPK3 acted as an endogenous miR-20b-5p sponge to sequester and inhibit miR-20b-5p activity, resulting in increased ATG7 expression. In addition, miR-20b-5p inhibitors reversed the decrease in ATG7 induced by silencing circHIPK3. Conclusions. CircHIPK3 can accelerate cardiomyocyte autophagy and apoptosis during myocardial I/R injury through the miR-20b-5p/ATG7 axis. These data suggest that circHIPK3 may serve as a potential therapeutic target for I/R.

Exercise-mediated regulation of autophagy in the cardiovascular system

Cardiovascular disease is the leading cause of human death worldwide. Autophagy is an evolutionarily conserved degradation pathway, which is a highly conserved cellular degradation process in which lysosomes decompose their own organelles and recycle the resulting macromolecules. Autophagy is critical in maintaining cardiovascular homeostasis and function, and excessive or insufficient autophagy or autophagic flux can lead to cardiovascular disease. Enormous evidence indicates that exercise training plays a beneficial role in the prevention and treatment of cardiovascular diseases. The regulation of autophagy during exercise is a bidirectional process. For cardiovascular disease caused by either insufficient or excessive autophagy, exercise training restores normal autophagy function and delays the progression of cardiovascular disease. An in-depth exploration and discussion of exercise-mediated regulation of autophagy in the cardiovascular system can broaden our view about the prevention of various autophagy-related diseases through exercise training. In this article, we review autophagy and its related signaling pathways, as well as autophagy-dependent beneficial effects of exercise in cardiovascular system.

[Hypertrophic cardiomyopathy. Cardiomyocyte ultrastructure, the specific or stereotypic signs]

Hypertrophic cardiomyopathy (HCM) is a congenital disease caused by mutations in a number of sarcomere proteins. According to the type of mutation, clinical observations record similar clinical manifestations, myocardial pathological changes, and the timing of manifestation of the disease in HCM patients.

OBJECTIVE

To study cardiomyocyte (CMC) ultrastructural changes in the interventricular septum (IVS) of patients with HCM and evaluate their specificity for this pathology.

MATERIAL AND METHODS

IVS myocardial samples taken from 44 HCM patients aged 18-59 years at IVS myoectomy underwent an electron microscopic study. The diameter of CMCs and their nuclei was measured in semithin sections.

RESULTS

A morphometric examination of the IVS myocardium in HCM patients revealed moderate hypertrophy of CMCs and their nuclei, the diameters of which averaged 23.7±4.4 and 5.2±0.9 μm, respectively. The IVS CMCs were characterized by the ultrastructural signs of hypertrophy: the larger size and number of structures ensuring contractile and synthetic functions; the myocytes contained higher amounts of myofibrils, intermyofibrillar mitochondria, granular endoplasmic reticulum cisterns, and free ribosomes. On the contrary, some CMCs had fewer myofibrils in the perinuclear region, which is an adaptive change under hemodynamic overload conditions. In addition, a number of myocytes displayed signs of dystrophic changes: the appearance of lipofuscin granules, myelin figures, phagosomes, lipid droplets, and vacuoles, which can fill all free sarcoplasmic zones.

CONCLUSION

Ultrastructural changes characteristic of hypertrophy were found in IVS CMCs in HCM patients. In addition, there was partial myofibrillar loss and dystrophic changes in a number of myocytes, which are stereotypic compensatory-adaptive changes under hemodynamic overload conditions. All the above-mentioned changes in the CMC ultrastructure are characteristic of myocardial hypertrophy, but not specific for hypertrophic cardiomyopathy.

PKD deletion promotes autophagy and inhibits hypertrophy in cardiomyocyte

Protein kinase D (PKD) plays an important role in the development of cardiac hypertrophy induced by pressure overload. However, the mechanism involved is unclear. This study, using primary cardiomyocyte culture, PKD knockdown and overexpression, and other molecular techniques, tested our hypothesis that PKD pathway mediates cardiac hypertrophy by negatively regulating autophagy in cardiomyocyte. Neonatal cardiomyocytes were isolated from Wistar rats and cell hypertrophy was induced by norepinephrine treatment (PE, 10^-4 mol/L), and divided into the following groups: (1) Vehicle; (2) PE; (3) PE + control siRNA; (4) PE + Rapamycin (100 nM); (5) PE + PKD-siRNA (2 × 10⁸ U/0.1 ml); (6) PE + PKD siRNA + 3 MA (10 mM). The results showed that PE treatment induced cardiomyocyte hypertrophy, which were confirmed by cell size and biomarkers of cardiomyocyte hypertrophy including increased ANP and BNP mRNA. PKD knockdown or Rapamycin significantly inhibited PE-induced cardiomyocyte hypertrophy. In addition, PKD siRNA increased autophagy activity determined by electron microscopy, increased biomarkers of autophagy by Western blot, accompanied by down-regulated AKT/mTOR/S6K pathway. All the effects of PKD knockout were inhibited by co-treatment with 3-MA, an autophagy inhibitor. Oppositely, the autophagy in cardiomyocytes was inhibited by PKD overexpression. These results suggest that PKD participates in the development of cardiac hypertrophy by regulating autophagy via AKT/mTOR/S6K pathway.

Modulation of autophagy in human diseases strategies to foster strengths and circumvent weaknesses

Autophagy is central to the maintenance of intracellular homeostasis across species. Accordingly, autophagy disorders are linked to a variety of diseases from the embryonic stage until death, and the role of autophagy as a therapeutic target has been widely recognized. However, autophagy-associated therapy for human diseases is still in its infancy and is supported by limited evidence. In this review, we summarize the landscape of autophagy-associated diseases and current autophagy modulators. Furthermore, we investigate the existing autophagy-associated clinical trials, analyze the obstacles that limit their progress, offer tactics that may allow barriers to be overcome along the way and then discuss the therapeutic potential of autophagy modulators in clinical applications.

Activation of Gαq in Cardiomyocytes Increases Vps34 Activity and Stimulates Autophagy

Receptors that activate the heterotrimeric G protein Gαq are thought to play a role in the development of heart failure. Dysregulation of autophagy occurs in some pathological cardiac conditions including heart failure, but whether Gαq is involved in this process is unknown. We used a cardiomyocyte-specific transgenic mouse model of inducible Gαq activation (termed GαqQ209L) to address this question. After 7 days of Gαq activation, GαqQ209L hearts contained more autophagic vacuoles than wild type hearts. Increased levels of proteins involved in autophagy, especially p62 and LC3-II, were also seen. LysoTracker staining and western blotting showed that the number and size of lysosomes and lysosomal protein levels were increased in GαqQ209L hearts, indicating enhanced lysosomal degradation activity. Importantly, an autophagic flux assay measuring LC3-II turnover in isolated adult cardiomyocytes indicated that autophagic activity is enhanced in GαqQ209L hearts. GαqQ209L hearts exhibited elevated levels of the autophagy initiation complex, which contains the Class III phosphoinositide 3-kinase Vps34. As a consequence, Vps34 activity and phosphatidylinositol 3-phosphate levels were higher in GαqQ209L hearts than wild type hearts, thus accounting for the higher abundance of autophagic vacuoles. These results indicate that an increase in autophagy is an early response to Gαq activation in the heart.

Proteostasis in cardiac health and disease

The incidence and prevalence of cardiac diseases, which are the main cause of death worldwide, are likely to increase because of population ageing. Prevailing theories about the mechanisms of ageing feature the gradual derailment of cellular protein homeostasis (proteostasis) and loss of protein quality control as central factors. In the heart, loss of protein patency, owing to flaws in genetically-determined design or because of environmentally-induced 'wear and tear', can overwhelm protein quality control, thereby triggering derailment of proteostasis and contributing to cardiac ageing. Failure of protein quality control involves impairment of chaperones, ubiquitin-proteosomal systems, autophagy, and loss of sarcomeric and cytoskeletal proteins, all of which relate to induction of cardiomyocyte senescence. Targeting protein quality control to maintain cardiac proteostasis offers a novel therapeutic strategy to promote cardiac health and combat cardiac disease. Currently marketed drugs are available to explore this concept in the clinical setting.

Autophagy modulation: a potential therapeutic approach in cardiac hypertrophy

Autophagy is an evolutionarily conserved process used by the cell to degrade cytoplasmic contents for quality control, survival for temporal energy crisis, and catabolism and recycling. Rapidly increasing evidence has revealed an important pathogenic role of altered activity of the autophagosome-lysosome pathway (ALP) in cardiac hypertrophy and heart failure. Although an early study suggested that cardiac autophagy is increased and that this increase is maladaptive to the heart subject to pressure overload, more recent reports have overwhelmingly supported that myocardial ALP insufficiency results from chronic pressure overload and contributes to maladaptive cardiac remodeling and heart failure. This review examines multiple lines of preclinical evidence derived from recent studies regarding the role of autophagic dysfunction in pressure-overloaded hearts, attempts to reconcile the discrepancies, and proposes that resuming or improving ALP flux through coordinated enhancement of both the formation and the removal of autophagosomes would benefit the treatment of cardiac hypertrophy and heart failure resulting from chronic pressure overload.

Autophagic vacuoles in cardiomyocytes of dilated cardiomyopathy with initially decompensated heart failure predict improved prognosis

Autophagy is a process of bulk protein degradation and organelle turnover, and is a current therapeutic target in several diseases. The present study aimed to clarify the significance of myocardial autophagy of patients with dilated cardiomyopathy (DCM). Left ventricular endomyocardial biopsy was performed in 250 consecutive patients with DCM (54.9±13.9 years; male, 79%), initially presenting with decompensated heart failure (HF). The association of these findings with HF mortality or recurrence was examined. Myofilament changes, which are apparent in the degenerated cardiomyocytes of DCM, were recognized in 164 patients (66%), and autophagic vacuoles in cardiomyocytes were identified in or near the area of myofilament changes in 86 patients (34%). Morphometrically, fibrosis (odds ratio [OR], 0.96; 95% confidence interval [CI], 0.93 to 0.99) and mitochondrial abnormality (OR, 2.24; 95% CI, 1.23 to 4.08) were independently related with autophagic vacuoles. During the follow-up period of 4.9±3.9 y, 24 patients (10%) died, including 10 (4%) who died of HF, and 67 (27%) were readmitted for HF recurrence. Multivariate analysis identified a family history of DCM (hazard ratio [HR], 2.117; 95% CI, 1.199 to 3.738), hemoglobin level (HR, 0.845; 95% CI, 0.749 to 0.953), myofilament changes (HR, 13.525; 95% CI, 5.340 to 34.255), and autophagic vacuoles (HR, 0.214; 95% CI, 0.114 to 0.400) as independent predictors of death or readmission due to HF recurrence. In conclusion, autophagic vacuoles in cardiomyocytes are associated with a better HF prognosis in patients with DCM, suggesting autophagy may play a role in the prevention of myocardial degeneration.

Distinct changes of myocyte autophagy during myocardial hypertrophy and heart failure: association with oxidative stress

NEW FINDINGS

What is the central question of this study? We investigated the changes of myocyte autophagy during the stages of myocardial hypertrophy and failure and the relationship between autophagy and oxidative stress. What is the main findings and its importance? Myocyte autophagy is reduced during myocardial hypertrophy and increased during heart failure. Reduced autophagy is correlated with myocyte hypertrophy, and increased autophagy is correlated with myocyte apoptosis. The distinct alterations are associated with oxidative stress. Hydrogen peroxide causes distinct, concentration-dependent changes in autophagy in cultured cardiomyocytes. Oxidative stress may mediate the distinct alterations of myocyte autophagy during cardiac hypertrophy and failure. Myocyte autophagy occurs at basal levels in the heart in normal conditions and increases in heart failure. However, the changes of myocyte autophagy during the stages of myocardial hypertrophy and failure are not fully understood. Little is known about the relationship among myocyte autophagy, hypertrophy, apoptosis and oxidative stress. In the present study, we first examined the changes of myocyte autophagy in mice with chronic pressure overload and the relationships between myocyte autophagy and hypertrophy, apoptosis and oxidative stress. Second, we determined the direct role of hydrogen peroxide on autophagy in cultured cardiomyocytes. Eight-week-old male C57BL/6J mice underwent transverse aortic constriction (TAC) or sham operation. In TAC mice, left ventricular wall thickness was increased at 1 week and increased further at 9 weeks. Left ventricular end-diastolic dimension showed no change at 1 week, but increased at 9 weeks in association with systolic dysfunction. Myocyte autophagy was decreased at 1 week after TAC, and the decrease was correlated with increased myocyte size. Myocyte autophagy was increased at 9 weeks after TAC, and the increase was correlated with increased myocyte apoptosis. The alterations in autophagy after TAC were associated with myocardial oxidative stress. Hydrogen peroxide caused distinct, concentration-dependent changes in autophagy in cultured cardiomyocytes. In conclusion, myocyte autophagy was decreased during myocardial hypertrophy and increased during heart failure. The distinct changes were associated with myocyte hypertrophy, apoptosis and oxidative stress. These findings suggest that oxidative stress may mediate the distinct alterations of myocyte autophagy during myocardial hypertrophy and heart failure.

Scanning Electron Microscopy of Macerated Tissue to Visualize the Extracellular Matrix

Fibrosis is a component of all forms of heart disease regardless of etiology, and while much progress has been made in the field of cardiac matrix biology, there are still major gaps related to how the matrix is formed, how physiological and pathological remodeling differ, and most importantly how matrix dynamics might be manipulated to promote healing and inhibit fibrosis. There is currently no treatment option for controlling, preventing, or reversing cardiac fibrosis. Part of the reason is likely the sheer complexity of cardiac scar formation, such as occurs after myocardial infarction to immediately replace dead or dying cardiomyocytes. The extracellular matrix itself participates in remodeling by activating resident cells and also by helping to guide infiltrating cells to the defunct lesion. The matrix is also a storage locker of sorts for matricellular proteins that are crucial to normal matrix turnover, as well as fibrotic signaling. The matrix has additionally been demonstrated to play an electromechanical role in cardiac tissue. Most techniques for assessing fibrosis are not qualitative in nature, but rather provide quantitative results that are useful for comparing two groups but that do not provide information related to the underlying matrix structure. Highlighted here is a technique for visualizing cardiac matrix ultrastructure. Scanning electron microscopy of decellularized heart tissue reveals striking differences in structure that might otherwise be missed using traditional quantitative research methods.

The role of autophagy in cardiac hypertrophy

Autophagy is conserved in nature from lower eukaryotes to mammals and is an important self-cannibalizing, degradative process that contributes to the elimination of superfluous materials. Cardiac hypertrophy is primarily characterized by excess protein synthesis, increased cardiomyocyte size, and thickened ventricular walls and is a major risk factor that promotes arrhythmia and heart failure. In recent years, cardiomyocyte autophagy has been considered to play a role in controlling the hypertrophic response. However, the beneficial or aggravating role of cardiomyocyte autophagy in cardiac hypertrophy remains controversial. The exact mechanism of cardiomyocyte autophagy in cardiac hypertrophy requires further study. In this review, we summarize the controversies associated with autophagy in cardiac hypertrophy and provide insights into the role of autophagy in the development of cardiac hypertrophy. We conclude that future studies should emphasize the relationship between autophagy and the different stages of cardiac hypertrophy, as well as the autophagic flux and selective autophagy. Autophagy will be a potential therapeutic target for cardiac hypertrophy.

Class III PI3K-mediated prolonged activation of autophagy plays a critical role in the transition of cardiac hypertrophy to heart failure

Pathological cardiac hypertrophy often leads to heart failure. Activation of autophagy has been shown in pathological hypertrophic hearts. Autophagy is regulated positively by Class III phosphoinositide 3-kinase (PI3K). However, it is unknown whether Class III PI3K plays a role in the transition of cardiac hypertrophy to heart failure. To address this question, we employed a previously established cardiac hypertrophy model in heat shock protein 27 transgenic mice which shares common features with several types of human cardiomyopathy. Age-matched wild-type mice served as control. Firstly, a prolonged activation of autophagy, as reflected by autophagosome accumulation, increased LC3 conversion and decreased p62 protein levels, was detected in hypertrophic hearts from adaptive stage to maladaptive stage. Moreover, morphological abnormalities in myofilaments and mitochondria were presented in the areas accumulated with autophagosomes. Secondly, activation of Class III PI3K Vacuolar protein sorting 34 (Vps34), as demonstrated by upregulation of Vps34 expression, increased interaction of Vps34 with Beclin-1, and deceased Bcl-2 expression, was demonstrated in hypertrophic hearts from adaptive stage to maladaptive stage. Finally, administration with Wortmaninn, a widely used autophagy inhibitor by suppressing Class III PI3K activity, significantly decreased autophagy activity, improved morphologies of intracellular apartments, and most importantly, prevented progressive cardiac dysfunction in hypertrophic hearts. Collectively, we demonstrated that Class III PI3K plays a central role in the transition of cardiac hypertrophy to heart failure via a prolonged activation of autophagy in current study. Class III PI3K may serve as a potential target for the treatment and management of maladaptive cardiac hypertrophy.

MiR-451 is decreased in hypertrophic cardiomyopathy and regulates autophagy by targeting TSC1

The molecular mechanisms that drive the development of cardiac hypertrophy in hypertrophic cardiomyopathy (HCM) remain elusive. Accumulated evidence suggests that microRNAs are essential regulators of cardiac remodelling. We have been suggested that microRNAs could play a role in the process of HCM. To uncover which microRNAs were changed in their expression, microRNA microarrays were performed on heart tissue from HCM patients (n = 7) and from healthy donors (n = 5). Among the 13 microRNAs that were differentially expressed in HCM, miR-451 was the most down-regulated. Ectopic overexpression of miR-451 in neonatal rat cardiomyocytes (NRCM) decreased the cell size, whereas knockdown of endogenous miR-451 increased the cell surface area. Luciferase reporter assay analyses demonstrated that tuberous sclerosis complex 1 (TSC1) was a direct target of miR-451. Overexpression of miR-451 in both HeLa cells and NRCM suppressed the expression of TSC1. Furthermore, TSC1 was significantly up-regulated in HCM myocardia, which correlated with the decreased levels of miR-451. As TSC1 is a known positive regulator of autophagy, we examined the role of miR-451 in the regulation of autophagy. Overexpression of miR-451 in vitro inhibited the formation of the autophagosome. Conversely, miR-451 knockdown accelerated autophagosome formation. Consistently, an increased number of autophagosomes was observed in HCM myocardia, accompanied by up-regulated autophagy markers, and the lipidated form of LC3 and Beclin-1. Taken together, our findings indicate that miR-451 regulates cardiac hypertrophy and cardiac autophagy by targeting TSC1. The down-regulation of miR-451 may contribute to the development of HCM and may be a potential therapeutic target for this disease.

Modulating autophagy: a strategy for cancer therapy

Autophagy is a process in which long-lived proteins, damaged cell organelles, and other cellular particles are sequestered and degraded. This process is important for maintaining the cellular microenvironment when the cell is under stress. Many studies have shown that autophagy plays a complex role in human diseases, especially in cancer, where it is known to have paradoxical effects. Namely, autophagy provides the energy for metabolism and tumor growth and leads to cell death that promotes tumor suppression. The link between autophagy and cancer is also evident in that some of the genes that regulate Carcinogenesis, oncogenes and tumor suppressor genes, participate in or impact the autophagy process. Therefore, modulating autophagy will be a valuable topic for cancer therapy. Many studies have shown that autophagy can inhibit the tumor growth when autophagy modulators are combined with radiotherapy and/or chemotherapy. These findings suggest that autophagy may be a potent target for cancer therapy.

Myofibroblast-mediated mechanisms of pathological remodelling of the heart

The syncytium of cardiomyocytes in the heart is tethered within a matrix composed principally of type I fibrillar collagen. The matrix has diverse mechanical functions that ensure the optimal contractile efficiency of this muscular pump. In the diseased heart, cardiomyocytes are lost to necrotic cell death, and phenotypically transformed fibroblast-like cells-termed 'myofibroblasts'-are activated to initiate a 'reparative' fibrosis. The structural integrity of the myocardium is preserved by this scar tissue, although at the expense of its remodelled architecture, which has increased tissue stiffness and propensity to arrhythmias. A persisting population of activated myofibroblasts turns this fibrous tissue into a living 'secretome' that generates angiotensin II and its type 1 receptor, and fibrogenic growth factors (such as transforming growth factor-β), all of which collectively act as a signal-transducer-effector signalling pathway to type I collagen synthesis and, therefore, fibrosis. Persistent myofibroblasts, and the resultant fibrous tissue they produce, cause progressive adverse myocardial remodelling, a pathological hallmark of the failing heart irrespective of its etiologic origin. Herein, we review relevant cellular, subcellular, and molecular mechanisms integral to cardiac fibrosis and consequent remodelling of atria and ventricles with a heterogeneity in cardiomyocyte size. Signalling pathways that antagonize collagen fibrillogenesis provide novel strategies for cardioprotection.

Tropomyosin dephosphorylation results in compensated cardiac hypertrophy

Phosphorylation of tropomyosin (Tm) has been shown to vary in mouse models of cardiac hypertrophy. Little is known about the in vivo role of Tm phosphorylation. This study examines the consequences of Tm dephosphorylation in the murine heart. Transgenic (TG) mice were generated with cardiac specific expression of α-Tm with serine 283, the phosphorylation site of Tm, mutated to alanine. Echocardiographic analysis and cardiomyocyte cross-sectional area measurements show that α-Tm S283A TG mice exhibit a hypertrophic phenotype at basal levels. Interestingly, there are no alterations in cardiac function, myofilament calcium (Ca(2+)) sensitivity, cooperativity, or response to β-adrenergic stimulus. Studies of Ca(2+) handling proteins show significant increases in sarcoplasmic reticulum ATPase (SERCA2a) protein expression and an increase in phospholamban phosphorylation at serine 16, similar to hearts under exercise training. Compared with controls, the decrease in phosphorylation of α-Tm results in greater functional defects in TG animals stressed by transaortic constriction to induce pressure overload-hypertrophy. This is the first study to investigate the in vivo role of Tm dephosphorylation under both normal and cardiac stress conditions, documenting a role for Tm dephosphorylation in the maintenance of a compensated or physiological phenotype. Collectively, these results suggest that modification of the Tm phosphorylation status in the heart, depending upon the cardiac state/condition, may modulate the development of cardiac hypertrophy.

Cardiac-specific catalase overexpression rescues anthrax lethal toxin-induced cardiac contractile dysfunction: role of oxidative stress and autophagy

BACKGROUND

Lethal and edema toxins secreted by Bacillus anthracis during anthrax infection were found to incite serious cardiovascular complications. However, the underlying mechanisms in anthrax lethal toxin-induced cardiac anomalies remain unknown. This study was designed to evaluate the impact of antioxidant enzyme catalase in anthrax lethal toxin-induced cardiomyocyte contractile dysfunction.

METHODS

Wild type (WT) and cardiac-specific catalase overexpression mice were challenged with lethal toxin (2 μg/g, intraperotineally (i.p.)). Cardiomyocyte contractile and intracellular Ca(2+) properties were assessed 18 h later using an IonOptix edge-detection system. Proteasome function was assessed using chymotrypsin-like and caspase-like activities. GFP-LC3 puncta and Western blot analysis were used to evaluate autophagy and protein ubiquitination.

RESULTS

Lethal toxin exposure suppressed cardiomyocyte contractile function (suppressed peak shortening, maximal velocity of shortening/re-lengthening, prolonged duration of shortening/re-lengthening, and impaired intracellular Ca(2+) handling), the effects of which were alleviated by catalase. In addition, lethal toxin triggered autophagy, mitochondrial and ubiquitin-proteasome defects, the effects of which were mitigated by catalase. Pretreatment of cardiomyocytes from catalase mice with the autophagy inducer rapamycin significantly attenuated or ablated catalase-offered protection against lethal toxin-induced cardiomyocyte dysfunction. On the other hand, the autophagy inhibitor 3-MA ablated or significantly attenuated lethal toxin-induced cardiomyocyte contractile anomalies.

CONCLUSIONS

Our results suggest that catalase is protective against anthrax lethal toxin-induced cardiomyocyte contractile and intracellular Ca(2+) anomalies, possibly through regulation of autophagy and mitochondrial function.

Modulation of the cardiovascular system by leptin

It is well established that individuals with the metabolic syndrome have a significantly increased risk of cardiovascular disease and much effort has been expended to elicit the underlying mechanisms. Various studies have proposed that excessive or deficient physiological effects mediated by leptin make an important contribution, yet many paradoxical observations often preclude a clear definition of the role of leptin. This review article will briefly discuss principal and most recent evidence on direct and indirect regulation of the cardiovascular system by leptin, focusing on cardiac structural and functional as well as vascular effects.

Facilitated ethanol metabolism promotes cardiomyocyte contractile dysfunction through autophagy in murine hearts

Chronic drinking leads to myocardial contractile dysfunction where ethanol metabolism plays an essential role. Acetaldehyde, the main ethanol metabolite, mediates alcohol-induced cell injury although the underlying mechanism is still elusive. This study was designed to examine the mechanism involved in accelerated ethanol metabolism-induced cardiac defect with a focus on autophagy. Wild-type FVB and cardiac-specific overexpression of alcohol dehydrogenase mice were placed on a 4% nutrition-balanced alcohol diet for 8 weeks. Myocardial histology, immunohistochemistry, autophagy markers and signal molecules were examined. Expression of micro RNA miR-30a, a potential target of Beclin 1, was evaluated by real-time PCR. Chronic alcohol intake led to cardiac acetaldehyde accumulation, hypertrophy and overt autophagosome accumulation (LC3-II and Atg7), the effect of which was accentuated by ADH. Signaling molecules governing autophagy initiation including class III PtdIns3K, phosphorylation of mTOR and p70S6K were enhanced and dampened, respectively, following alcohol intake. These alcohol-induced signaling responses were augmented by ADH. ADH accentuated or unmasked alcohol-induced downregulation of Bcl-2, Bcl-xL and MiR-30a. Interestingly, ADH aggravated alcohol-induced p62 accumulation. Autophagy inhibition using 3-MA abolished alcohol-induced cardiomyocyte contractile anomalies. Moreover, acetaldehyde led to cardiomyocyte contractile dysfunction and autophagy induction, which was ablated by 3-MA. Ethanol or acetaldehyde increased GFP-LC3 puncta in H9c2 cells, the effect of which was ablated by 3-MA but unaffected by lysosomal inhibition using bafilomycin A(1), E64D and pepstatin A. In summary, these data suggested that facilitated acetaldehyde production via ADH following alcohol intake triggered cardiac autophagosome formation along with impaired lysosomal degradation, en route to myocardial defect.

Impaired cardiac autophagy in patients developing postoperative atrial fibrillation

OBJECTIVES

Postoperative atrial fibrillation (POAF) is a common complication after on-pump heart surgery. Several histologic abnormalities, such as interstitial fibrosis and vacuolization, have been described in atrial samples from patients developing POAF. This ultrastructural remodeling has been associated with the establishment of a proarrhythmic substrate. We studied whether atrial autophagy is activated in patients who develop POAF.

METHODS

A total of 170 patients in sinus rhythm who had undergone elective coronary artery bypass grafting were included. Systemic inflammatory markers were measured at baseline and 72 hours after surgery. During the procedure, samples of the right atrial appendages were obtained for evaluation of remodeling by light and electron microscopy. Protein ubiquitination and autophagy-related LC3B processing were assessed by Western blot.

RESULTS

Of these patients, 22% developed POAF. The level of high-sensitivity C-reactive protein, fibrosis, inflammation, myxoid degeneration, and ubiquitin-aggregates in the atria did not differ between patients with and without POAF. Electron microphotographs of those with POAF showed a significant accumulation of autophagic vesicles and lipofuscin deposits. Total protein ubiquitination was similar in the patients with and without POAF, but LC3B processing was markedly reduced in those with POAF, suggesting a selective impairment in autophagic flow.

CONCLUSIONS

This study provides novel evidence that ultrastructural atrial remodeling characterized by an impaired cardiac autophagy is present in patients developing POAF after coronary artery bypass surgery.

Role of autophagy in heart failure associated with aging

Heart failure is a progressive disease, leading to reduced quality of life and premature death. Adverse ventricular remodeling involves changes in the balance between cardiomyocyte protein synthesis and degradation, forcing these myocytes in equilibrium between life and death. In this context, autophagy has been recognized to play a role in the pathophysiology of heart failure. At basal levels, autophagy performs housekeeping functions, maintaining cardiomyocyte function and ventricular mass. Autophagy also occurs in the failing human heart, and upregulation has been reported in animal models of pressure overload-induced heart failure. Although the factors that determine whether autophagy will be protective or detrimental are not well known, the level and duration of autophagy seem important. Autophagy may antagonize ventricular hypertrophy by increasing protein degradation, which decreases tissue mass. However, the rate of protective autophagy declines with age. The inability to remove damaged structures results in the progressive accumulation of 'garbage', including abnormal intracellular proteins aggregates and undigested materials such as lipofuscin. Eventually, the progress of these changes results in enhanced oxidative stress, decreased ATP production, collapse of the cellular catabolic machinery, and cell death. By contrast, in load-induced heart failure, the extent of autophagic flux can rise to maladaptive levels. Excessive autophagy induction leads to autophagic cell death and loss of cardiomyocytes and may contribute to the worsening of heart failure. Accordingly, the development of therapies that up-regulate the repair qualities of the autophagic process and down-regulate the cell death aspects would be of great value in the treatment of heart failure.

Nitric oxide/reactive oxygen species generation and nitroso/redox imbalance in heart failure: from molecular mechanisms to therapeutic implications

Adaptation of the heart to intrinsic and external stress involves complex modifications at the molecular and cellular levels that lead to tissue remodeling, functional and metabolic alterations, and finally to failure depending upon the nature, intensity, and chronicity of the stress. Reactive oxygen species (ROS) have long been considered as merely harmful entities, but their role as second messengers has gradually emerged. At the same time, our comprehension of the multifaceted role of nitric oxide (NO) and the related reactive nitrogen species (RNS) has been upgraded. The tight interlay between ROS and RNS suggests that their imbalance may implicate the impairment in physiological NO/redox-based signaling that contributes to the failing of the cardiovascular system. This review initially provides basic concepts on the role of nitroso/oxidative stress in the pathophysiology of heart failure with a particular focus on sources of ROS/RNS, their downstream targets, and endogenous modulators. Then, the role of NO/redox regulation of cardiomyocyte function, including calcium homeostasis, electrogenesis, and insulin signaling pathways, is described. Finally, an overview of old and emerging therapeutic opportunities in heart failure is presented, focusing on modulation of NO/redox mechanisms and discussing benefits and limitations.