Autophagy modulation: a potential therapeutic approach in cardiac hypertrophy

Fenofibrate reduces cardiac remodeling by mitochondrial dynamics preservation in a renovascular model of cardiac hypertrophy

Fenofibrate, a PPAR-α agonist clinically used to lower serum lipid levels, reduces cardiac remodeling and improves cardiac function. However, its mechanism of action is not completely elucidated. In this study we examined the effect of fenofibrate on mitochondria in a rat model of renovascular hypertension, focusing on mediators controlling mitochondrial dynamics and autophagy. Rats with two-kidney one-clip (2K1C) hypertension were treated with fenofibrate 150 mg/kg/day (2K1C-FFB) or vehicle (2K1C-VEH) for 8 weeks. Systolic blood pressure and cardiac functional were in-vivo assessed, while cardiomyocyte size and protein expression of mediators of cardiac hypertrophy and mitochondrial dynamics were ex-vivo examined by histological and Western blot analyses. Fenofibrate treatment counteracted the development of hypertension and the increase of left ventricular mass, relative wall thickness and cross-sectional area of cardiomyocytes. Furthermore, fenofibrate re-balanced the expression Mfn2, Drp1 and Parkin, regulators of fusion, fission, mitophagy respectively. Regarding autophagy, the LC3-II/LC3-I ratio was increased in 2K1C-VEH and 2K1C-FFB, whereas the autophagy was increased only in 2K1C-FFB. In cultured H9C2 cardiomyoblasts, fenofibrate reversed the Ang II-induced mRNA up-regulation of hypertrophy markers Nppa and Myh7, accumulation of reactive oxygen species and depolarization of the mitochondrial membrane exerting protection mediated by up-regulation of the Uncoupling protein 2. Our results indicate that fenofibrate acts directly on cardiomyocytes and counteracts the pressure overload-induced cardiac maladaptive remodeling. This study reveals a so far hidden mechanism involving mitochondrial dynamics in the beneficial effects of fenofibrate, support its repurposing for the treatment of cardiac hypertrophy and provide new potential targets for its pharmacological function.

Meteorin-like (METRNL) attenuates hypertensive induced cardiac hypertrophy by inhibiting autophagy via activating BRCA2

Hypertension, a prevalent cardiovascular ailment globally, can precipitate numerous complications, notably hypertensive cardiomyopathy. Meteorin-like (METRNL) is demonstrated to possess potential protective properties on cardiovascular diseases. However, its specific role and underlying mechanism in hypertensive myocardial hypertrophy remain elusive. Spontaneously hypertensive rats (SHRs) served as hypertensive models to explore the effects of METRNL on hypertension and its induced myocardial hypertrophy. The research results indicate that, in contrast to Wistar-Kyoto (WKY) rats, SHRs exhibit significant symptoms of hypertension and myocardial hypertrophy, but cardiac-specific overexpression (OE) of METRNL can partially ameliorate these symptoms. In H9c2 cardiomyocytes, METRNL suppresses Ang II-induced autophagy by controlling the BRCA2/Akt/mTOR signaling pathway. But when BRCA2 expression is knocked down, this effect will be suppressed. Collectively, METRNL emerges as a potential therapeutic target for hypertensive cardiomyopathy.

ATGL deficiency aggravates pressure overload-triggered myocardial hypertrophic remodeling associated with the proteasome-PTEN-mTOR-autophagy pathway

Persistent myocardial hypertrophy frequently leads to heart failure (HF). Intramyocardial triacylglycerol (TAG) accumulation is closely related with cardiac remodeling and abnormal contractile function. Adipose triglyceride lipase (ATGL), a key enzyme in TAG metabolism, regulates cardiac function. However, its associated molecular pathways have not been fully defined. Here, cardiac hypertrophy and HF were induced in wild-type (WT) or ATGL knockout (KO) mice through transverse aortic constriction (TAC) for up to 4 weeks. TAC in WT mice significantly reduced cardiac function and autophagy while enhancing left ventricular hypertrophy, interstitial fibrosis, inflammatory response, superoxide generation, and cardiomyocyte apoptosis, accompanied with upregulation of the proteasome activity, reduction of PTEN level and activation of AKT-mTOR signaling, and these effects were further aggravated in ATGL KO mice. Interestingly, ATGL KO-mediated cardiac dysfunction and remodeling were markedly reversed by proteasome inhibitor (epoxomicin) or autophagic activator (rapamycin), but accelerated by PTEN inhibitor (VO-OHpic) or autophagy inhibitor 3-MA. Mechanistically, ATGL KO upregulated proteasome expression and activity, which in turn mediates PTEN degradation leading to activation of AKT-mTOR signaling and inhibition of autophagy, thereby enhancing hypertrophic remodeling and HF. In conclusion, ATGL KO contributes to TAC-induced cardiac dysfunction and adverse remodeling probably associated with the proteasome-PTEN-mTOR-autophagy pathway. Therefore, modulation of this pathway may have a therapeutic effect potential for hypertrophic heart disease. TAC-induced downregulation of ATGL results in increased proteasome (β1i/β2i/β5i) activity, which in turn promotes degradation of PTEN and activation of AKT-mTOR signaling and then inhibits autophagy and ATP production, thereby leading to cardiac hypertrophic remodeling and dysfunction. Conversely, blocking proteasome activity or activating autophagy attenuates these effects.

Assessment of Autophagy Markers Suggests Increased Activity Following LVAD Therapy

Left ventricular reverse remodeling in heart failure is associated with improved clinical outcomes. However, the molecular features that drive this process are poorly defined. Left ventricular assist devices (LVADs) are the therapy associated with the greatest reverse remodeling and lead to partial myocardial recovery in most patients. In this study, we examined whether autophagy may be implicated in post-LVAD reverse remodeling. We found expression of key autophagy factors increased post-LVAD, while autophagic substrates decreased. Autolysosome numbers increased post-LVAD, further indicating increased autophagy. These findings support the conclusion that mechanical unloading activates autophagy, which may underly the reverse remodeling observed.

Cardiomyocyte ZKSCAN3 regulates remodeling following pressure-overload

Autophagy is important for protein and organelle quality control. Growing evidence demonstrates that autophagy is tightly controlled by transcriptional mechanisms, including repression by zinc finger containing KRAB and SCAN domains 3 (ZKSCAN3). We hypothesize that cardiomyocyte-specific ZKSCAN3 knockout (Z3K) disrupts autophagy activation and repression balance and exacerbates cardiac pressure-overload-induced remodeling following transverse aortic constriction (TAC). Indeed, Z3K mice had an enhanced mortality compared to control (Con) mice following TAC. Z3K-TAC mice that survived exhibited a lower body weight compared to Z3K-Sham. Although both Con and Z3K mice exhibited cardiac hypertrophy after TAC, Z3K mice exhibited TAC-induced increase of left ventricular posterior wall thickness at end diastole (LVPWd). Conversely, Con-TAC mice exhibited decreases in PWT%, fractional shortening (FS%), and ejection fraction (EF%). Autophagy genes (Tfeb, Lc3b, and Ctsd) were decreased by the loss of ZKSCAN3. TAC suppressed Zkscan3, Tfeb, Lc3b, and Ctsd in Con mice, but not in Z3K. The Myh6/Myh7 ratio, which is related to cardiac remodeling, was decreased by the loss of ZKSCAN3. Although Ppargc1a mRNA and citrate synthase activities were decreased by TAC in both genotypes, mitochondrial electron transport chain activity did not change. Bi-variant analyses show that while in Con-Sham, the levels of autophagy and cardiac remodeling mRNAs form a strong correlation network, such was disrupted in Con-TAC, Z3K-Sham, and Z3K-TAC. Ppargc1a also forms different links in Con-sham, Con-TAC, Z3K-Sham, and Z3K-TAC. We conclude that ZKSCAN3 in cardiomyocytes reprograms autophagy and cardiac remodeling gene transcription, and their relationships with mitochondrial activities in response to TAC-induced pressure overload.

Nrf2 signaling in diabetic nephropathy, cardiomyopathy and neuropathy: Therapeutic targeting, challenges and future prospective

Western lifestyle contributes to an overt increase in the prevalence of metabolic anomalies including diabetes mellitus (DM) and obesity. Prevalence of DM is rapidly growing worldwide, affecting many individuals in both developing and developed countries. DM is correlated with the onset and development of complications with diabetic nephropathy (DN), diabetic cardiomyopathy (DC) and diabetic neuropathy being the most devastating pathological events. On the other hand, Nrf2 is a regulator for redox balance in cells and accounts for activation of antioxidant enzymes. Dysregulation of Nrf2 signaling has been shown in various human diseases such as DM. This review focuses on the role Nrf2 signaling in major diabetic complications and targeting Nrf2 for treatment of this disease. These three complications share similarities including the presence of oxidative stress, inflammation and fibrosis. Onset and development of fibrosis impairs organ function, while oxidative stress and inflammation can evoke damage to cells. Activation of Nrf2 signaling significantly dampens inflammation and oxidative damage, and is beneficial in retarding interstitial fibrosis in diabetic complications. SIRT1 and AMPK are among the predominant pathways to upregulate Nrf2 expression in the amelioration of DN, DC and diabetic neuropathy. Moreover, certain therapeutic agents such as resveratrol and curcumin, among others, have been employed in promoting Nrf2 expression to upregulate HO-1 and other antioxidant enzymes in the combat of oxidative stress in the face of DM.

Sacubitril/valsartan (LCZ696) ameliorates hyperthyroid-induced cardiac hypertrophy in male rats through modulation of miR-377, let-7 b, autophagy, and fibrotic signaling pathways

Hyperthyroidism is associated with cardiac hypertrophy, fibrosis, and increased risk of cardiovascular mortality. Sacubitril/valsartan (LCZ696) is a new combined drug that has shown promise for the treatment of hyperthyroidism-associated heart failure; however, the underlying molecular mechanisms, including the contributions of epigenetic regulation, remain unclear. The present study was designed to investigate the therapeutic efficacy of LCZ696 and the potential contributions of microRNA regulation in a rat model of hyperthyroidism-induced cardiac hypertrophy. Cardiac hypertrophy was induced by intraperitoneal administration of levothyroxine. Sixty adult male Wistar rats were randomly allocated to four equal groups (15 rats each): control, cardiac hypertrophy (CH), CH + valsartan, and CH + LCZ696. Treatment with LCZ696 or valsartan significantly improved hemodynamic abnormalities, normalized serum concentrations of natriuretic peptide, fibroblast growth factor-23, and cardiac inflammatory markers compared to CH group rats. Treatment with LCZ696 or valsartan also normalized myocardial expression levels of autophagy markers, fibrotic markers, PPAR-ϒ, mir-377, and let-7b. In addition, both valsartan and LCZ696 ameliorated collagen deposition, ventricular degeneration, and various ultrastructural abnormalities induced by levothyroxine. The beneficial effects of LCZ696 were superior to those of valsartan alone. The superior efficacy of LCZ696 may be explained by the stronger modulation of miR-377 and let-7b.

The Pathophysiology of Left Ventricular Hypertrophy, beyond Hypertension, in Autosomal Dominant Polycystic Kidney Disease

Heart disease is one of the leading causes of death in autosomal dominant polycystic kidney disease (ADPKD) patients. Left ventricular hypertrophy (LVH) is an early and severe complication in ADPKD patients. Two decades ago, the prevalence of LVH on echocardiography in hypertensive ADPKD patients was shown to be as high as 46%. Recent studies using cardiac magnetic resonance imaging have shown that the prevalence of LVH in ADPKD patients may be lower. The true prevalence of LVH in ADPKD patients is controversial. There is evidence that factors other than hypertension contribute to LVH in ADPKD patients. Studies have shown that young normotensive ADPKD adults and children have a higher left ventricular mass index compared to controls and that the prevalence of LVH is high in patients with ADPKD whose blood pressure is well controlled. Polycystin-1 (PC-1) and polycystin-2 (PC-2) control intracellular signaling pathways that can influence cardiac function. Perturbations of PC-1 or PC-2 in the heart can lead to profound changes in cardiac structure and function independently of kidney function or blood pressure. PC-1 can influence mammalian target of rapamycin and mitophagy and PC-2 can influence autophagy, processes that play a role in LVH. Polymorphisms in the angiotensin-converting enzyme gene may play a role in LVH in ADPKD. This review will detail the pathophysiology of LVH, beyond hypertension, in ADPKD.

Calpains as Potential Therapeutic Targets for Myocardial Hypertrophy

Despite advances in its treatment, heart failure remains a major cause of morbidity and mortality, evidencing an urgent need for novel mechanism-based targets and strategies. Myocardial hypertrophy, caused by a wide variety of chronic stress stimuli, represents an independent risk factor for the development of heart failure, and its prevention constitutes a clinical objective. Recent studies performed in preclinical animal models support the contribution of the Ca²⁺-dependent cysteine proteases calpains in regulating the hypertrophic process and highlight the feasibility of their long-term inhibition as a pharmacological strategy. In this review, we discuss the existing evidence implicating calpains in the development of cardiac hypertrophy, as well as the latest advances in unraveling the underlying mechanisms. Finally, we provide an updated overview of calpain inhibitors that have been explored in preclinical models of cardiac hypertrophy and the progress made in developing new compounds that may serve for testing the efficacy of calpain inhibition in the treatment of pathological cardiac hypertrophy.

Ubiquitin Carboxyl-Terminal Hydrolase L1 of Cardiomyocytes Promotes Macroautophagy and Proteostasis and Protects Against Post-myocardial Infarction Cardiac Remodeling and Heart Failure

Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinase known to play essential roles in the nervous tissue. Myocardial upregulation of UCHL1 was observed in human dilated cardiomyopathy and several animal models of heart disease, but the (patho)physiological significance of UCHL1 in cardiomyocytes remains undefined. Hence, we conducted this study to fill this critical gap. We produced cardiomyocyte-restricted Uchl1 knockout (CKO) by coupling the Uchl1-floxed allele with transgenic Myh6-Cre in C57B/6J inbred mice. Mice transgenic for Myh6-Cre were used as controls (CTL). Myocardial Uchl1 proteins were markedly reduced in CKO mice but they did not display discernible abnormal phenotype. Ten-week old CTL or CKO mice were subjected to left anterior descending artery ligation (myocardial infarction, MI) or sham surgery (Sham) and characterized at 7- and 28-day after surgery. Compared with Sham mice, significant increases in myocardial UCHL1 proteins were detected in CTL MI but not in CKO MI mice. MI-induced left ventricular (LV) chamber dilation, reduction of ejection fraction (EF) and fractional shortening (FS), and LV anterior wall thinning detected by echocardiography were comparable between the CTL MI and CKO MI groups 7-day post-MI. However, by 28-day post-MI, MI-induced LV chamber dilatation, EF and FS reduction, increases of myocardial ubiquitin conjugates, and increases in the heart weight to body weight ratio and the ventricular weight to body weight ratio were significantly more pronounced in CKO MI than CTL MI mice. As further revealed by LV pressure-volume relationship analyses, CKO MI mice but not CTL MI mice displayed significant decreases in stroke volume, cardiac output, and the maximum rates of LV pressure rising or declining and of LV volume declining, as well as significant increases in LV end-diastolic pressure and Tau, compared with their respective Sham controls. LC3-II flux assays reveal that autophagic flux is decreased in CKO mouse myocardium as well as in cultured Uchl1-deficient cardiomyocytes. In conclusion, UCHL1 of cardiomyocytes is dispensable for development but promotes macroautophagy in cardiomyocytes. Upregulation of UCHL1 in post-MI hearts occurs primarily in the cardiomyocytes and protects against post-MI cardiac remodeling and malfunction likely through supporting autophagic flux and proteostasis during a stress condition.

The Interplay between Autophagy and Redox Signaling in Cardiovascular Diseases

Reactive oxygen and nitrogen species produced at low levels under normal cellular metabolism act as important signal molecules. However, at increased production, they cause damage associated with oxidative stress, which can lead to the development of many diseases, such as cardiovascular, metabolic, neurodegenerative, diabetes, and cancer. The defense systems used to maintain normal redox homeostasis plays an important role in cellular responses to oxidative stress. The key players here are Nrf2-regulated redox signaling and autophagy. A tight interface has been described between these two processes under stress conditions and their role in oxidative stress-induced diseases progression. In this review, we focus on the role of Nrf2 as a key player in redox regulation in cell response to oxidative stress. We also summarize the current knowledge about the autophagy regulation and the role of redox signaling in this process. In line with the focus of our review, we describe in more detail information about the interplay between Nrf2 and autophagy pathways in myocardium and the role of these processes in cardiovascular disease development.

YQFM alleviated cardiac hypertrophy by apoptosis inhibition and autophagy regulation via PI3K/AKT/mTOR pathway

ETHNOPHARMACOLOGICAL RELEVANCE

As a traditional compound preparation of Chinese medicine, Yiqi Fumai lyophilized injection (YQFM) has protective effects on various cardiac diseases including cardiac hypertrophy, which is the primary cause of arrhythmia. However, the involved mechanism remains unclear.

AIM OF THE STUDY

This study was projected to investigate whether YQFM could prevent cardiac hypertrophy and arrhythmia concurrence.

MATERIALS AND METHODS

The cardiac hypertrophy rats were established by transverse aortic ligation and the H9c2 hypertrophy cardiomyocyte was induced by angiotensin II (AngII). The electrocardiogram (ECG) was conducted to estimate the arrhythmia occurrence of cardiac hypertrophy rats under isoprenaline (iso) treatment. The cardiac related indicators and histopathology were also detected. The protective effects of YQFM on H9c2 hypertrophy cardiomyocyte were determined by the cell size measurement, apoptosis detection and mitochondrial membrane potential measurement. The cardiac hypertrophy relative proteins (ANP and BNP), autophagy related factors (LC3II, p62 and Beclin-1), apoptosis related markers (p53, caspase 3, Bax and Bcl-2) and the PI₃K/AKT/mTOR pathway expressions were all measured by Western blot.

RESULTS

YQFM decreased the arrhythmia occurrence and improved cardiac function in cardiac hypertrophy rats. YQFM also reduced the H9c2 cardiomyocyte size and alleviated the cardiomyocyte apoptosis induced by AngII. In addition, YQFM inhibited cell apoptosis by increasing Bcl-2/Bax ratio and decreasing caspase 3 and p53 expressions in vitro and vivo. Meanwhile, YQFM regulated the autophagy pathway by down-regulating of LC3II and Beclin-1 expressions, as well as up-regulating of p62 expression. Finally, the results showed that YQFM could activate the PI₃K/AKT/mTOR pathway by enhancing the p-AKT, p-PI₃K and p-mTOR expressions.

CONCLUSION

Our results displayed that YQFM attenuated the cardiac hypertrophy by apoptosis inhibition and autophagy regulation via PI₃K/AKT/mTOR pathway.

Alarin moderated myocardial hypertrophy via inhibiting cyclic adenosine monophosphate/protein kinase A signaling pathway to attenuate autophagy

Alarin could alleviate myocardial infarction-induced heart failure. The present study was to explore whether alarin could alleviate myocardial hypertrophy via inhibiting cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signaling pathway to attenuate autophagy. Myocardial hypertrophy was induced by angiotensin (Ang) II infusion in vivo in mice and by Ang II treatment of neonatal rat cardiomyocytes (NRCMs) in vitro. The Ang II-induced hypertrophy and fibrosis of the heart were alleviated after alarin administration in mice. The increased atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and beta-myosin heavy chain (β-MHC), and the decreased alpha-myosin heavy chain (α-MHC) induced by Ang II were reversed by alarin treatment in NRCMs. Alarin inhibited the increases of cAMP and PKA in NRCMs. Treatment with cAMP or overexpression of PKA blocked the attenuating effects of alarin on Ang II-induced hypertrophy in NRCMs. Alarin reduced the Ang II-induced increases of LC3, Beclin 1, autophagy-related gene (Atg)3 and Atg5 in NRCMs. The overexpression of cAMP and PKA reversed the alleviating effects of alarin on the increased autophagy induced by Ang II in NRCMs. These results indicated that alarin could moderate cardiac remodeling. Alarin improved myocardial hypertrophy via inhibiting the cAMP/PKA signaling pathway to attenuate autophagy.

TFEB insufficiency promotes cardiac hypertrophy by blocking autophagic degradation of GATA4

Autophagosome-lysosome pathway (ALP) insufficiency has been suggested to play a critical role in the pathogenesis of cardiac hypertrophy. However, the mechanisms underlying ALP insufficiency remain largely unknown, and strategies to specifically manipulate ALP insufficiency for treating cardiac hypertrophy are lacking. Transcription factor EB (TFEB), as a master regulator of ALP, regulates the generation and function of autophagosomes and lysosomes. We found that TFEB was significantly decreased, whereas autophagosome markers were increased in phenylephrine (PE)-induced and transverse aortic constriction-induced cardiomyocyte hypertrophy and failing hearts from patients with dilated cardiomyopathy. Knocking down TFEB induced ALP insufficiency, as indicated by increased autophagosome markers, decreased light chain 3II flux, and cardiomyocyte hypertrophy manifested through increased levels of atrial natriuretic peptide and β-myosin heavy chain and enlarged cell size. The effects of TFEB knockdown were abolished by promoting autophagy. TFEB overexpression improved autophagic flux and attenuated PE-stimulated cardiomyocyte hypertrophy and transverse aortic constriction-induced hypertrophic remodeling, fibrosis, and cardiac dysfunction. Curcumin analog compound C1, a specific TFEB activator, similarly attenuated PE-induced ALP insufficiency and cardiomyocyte hypertrophy. TFEB knockdown increased the accumulation of GATA4, a transcription factor for several genes causing cardiac hypertrophy by blocking autophagic degradation of GATA4, whereas knocking down GATA4 attenuated TFEB downregulation-induced cardiomyocyte hypertrophy. Both TFEB overexpression and C1 promoted GATA4 autophagic degradation and alleviated PE-induced cardiomyocyte hypertrophy. In conclusion, TFEB downregulation plays a vital role in the development of pressure overload-induced cardiac hypertrophy by causing ALP insufficiency and blocking autophagic degradation. Activation of TFEB represents a potential therapeutic strategy for treating cardiac hypertrophy.

MiR-26a-5p alleviates cardiac hypertrophy and dysfunction via targeting ADAM17

Cardiac hypertrophy has been a high prevalence rate throughout the world. It has posed a big threat to public health due to limited therapeutic approaches. Previous studies showed that pathological cardiac hypertrophy was associated with autophagy, microRNAs (miRNA), and other signaling pathways, while the molecular mechanisms remain incompletely characterized. In this study, we used thoracic aortic constriction (TAC)-induced mice and angiotensin-II (Ang-II)-induced H9C2 cell line as cardiac hypertrophy model to investigate the role of miR-26a-5p in cardiac hypertrophy. We found that miR-26a-5p was downregulated in cardiac hypertrophy mice. Overexpression of miR-26a-5p by type 9 recombinant adeno-associated virus (rAAV9) reversed the heart hypertrophic manifestations. The phenotypes were also promoted by miR-26a-5p inhibitor in Ang-II-induced H9C2 cells. Through miRNA profile analysis and dual-luciferase reporter assay, ADAM17 was identified as a direct target of miR-26a-5p. Restored expression of ADAM17 disrupted the effect of miR-26a-5p on cardiac hypertrophy. To sum up, these results indicated that miR-26a-5p played an inhibitory role in cardiac hypertrophy and dysfunction via targeting ADAM17. The miR-26a-5p-ADAM17-cardiac hypertrophy axis provided special insight and a new molecular mechanism for a better understanding of cardiac hypertrophy disease, as well as the diagnostic and therapeutic practice.

Ginkgolide B Protects Cardiomyocytes from Angiotensin II-Induced Hypertrophy via Regulation of Autophagy through SIRT1-FoxO1

Ginkgolide B (GB) is an active ingredient extracted from Ginkgo biloba leaves. However, the effects of GB on cardiac hypertrophy remain unclear. The study is aimed at determining whether GB could alleviate cardiac hypertrophy and exploring its underlying molecular mechanism. Rat cardiomyocyte cell line H9c2 cells were pretreated with GB and incubated with angiotensin II (Ang II) to simulate an in vitro cardiac hypertrophy model. Cell viability, cell size, hypertrophy markers, and autophagy were determined in H9c2 cells after Ang II treatment. Proteins involved in autophagy and the SIRT1 pathway were determined by western blot. Our data demonstrated that GB attenuated Ang II-induced cardiac hypertrophy and reduced the mRNA expressions of hypertrophy marker, atrial natriuretic peptide (ANP), and β-myosin heavy chain (β-MHC). GB further increased Ang II-induced autophagy in H9c2 cells and modulated expressions of autophagy-related proteins Beclin1 and P62. Modulation of autophagy using autophagy inhibitor 3-methyladenine (3-MA) could abrogate GB-downregulated transcription of NPPA. We then showed that GB attenuated Ang II-induced oxidative stress and reduction in SIRT1 and FoxO1 protein expression. Finally, the effect of GB on autophagy and cardiac hypertrophy could be reversed by SIRT1 inhibitor EX-527. GB inhibits Ang II-induced cardiac hypertrophy by enhancing autophagy via the SIRT1-FoxO1 signaling pathway and might be a potential agent in treating pathological cardiac hypertrophy.

Effects of omega-3 fatty acids and metformin combination on diabetic cardiomyopathy in rats through autophagic pathway

Diabetic cardiomyopathy is a primary cause of increased morbidity and mortality in diabetics. Evidence has suggested a pivotal role for interrupted mitochondrial dynamics and quality control machinery in the onset and development of diabetic cardiomyopathy. Sequestosome 1 (SQSTM1) is a major reporter of selective autophagic activity. Other than controlling the expression of genes involved in mitochondrial biogenesis, recently peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) was reported to directly affect SQSTM1 gene expression. Calcineurin, a pivotal mediator of cardiac hypertrophy, has been also linked to enhanced expression of SQSTM1. This study aimed to test the cardioprotective effects of adding ω-3 polyunsaturated fatty acids (PUFAs) to metformin in a rat model of type 2 diabetes mellitus and to evaluate the molecular mechanisms underlying their effects on mitochondrial quality. Diabetes was induced in male Sprague Dawley rats by a high-fat diet for 6 weeks, followed by a low-dose streptozotocin (35 mg/kg). Diabetic rats were either treated with metformin (150 mg/kg/d), ω-3 PUFAs (300 mg/kg/d), or their combination in the same doses for further 8 weeks. Along with metabolic and pathological derangements, we report that correlating with electron microscopic evidence of mitochondrial degeneration, gene expression of the autophagic indicators SQSTM1, PGC-1α, and calcineurin were decreased in the hearts of diabetic rats. Independent of its anti-hyperglycemic effects, metformin successfully preserved mitochondrial integrity and upregulated myocardial PGC-1α, calcineurin, and SQSTM1 gene expression. ω-3 PUFAs possess synergistic cardioprotection when added to metformin, suggested by improvements in myocardial ultrastructure, autophagic activity, and SQSTM1 gene expression.

Schisandra chinensis polysaccharides prevent cardiac hypertrophy by dissociating thioredoxin-interacting protein/thioredoxin-1 complex and inhibiting oxidative stress

Cardiac hypertrophy is a current, major, global health challenge. Oxidative stress is an important mechanism that contributes to the pathogenesis of cardiac hypertrophy. Schisandra chinensis polysaccharides (SCP), the primary active constituent in Schisandra chinensis, have antioxidative properties. Here, we investigated the role played by SCP in a cardiac hypertrophy model mouse induced by transverse aortic constriction (TAC). We found that SCP treatment improved cardiac function by inhibiting myocardial hypertrophy and oxidative stress. Angiotensin II was used to induce cardiomyocyte hypertrophy and oxidative stress in vitro. We discovered that the antioxidant effects of SCP were mediated through the regulation of the thioredoxin-interacting protein (TXNIP)/Thioredoxin-1 (Trx-1) pathway. Using molecular docking, we found that SCP binds to Arg207, Ser169, Lys166, Lys286 and Ser285 in TXNIP through hydrogen bonds. TXNIP is an endogenous inhibitor of Trx-1, and the binding SCP with TXNIP may restrict or interfere with the binding between TXNIP and Trx-1, resulting in Trx-1 activation. In conclusion, our findings demonstrated that the potential use of SCP as a TXNIP inhibitor to attenuate oxidative stress, suggesting that TXNIP might represent a potential therapeutic target for the treatment of cardiac hypertrophy.

Autophagy Controls Nrf2-Mediated Dichotomy in Pressure Overloaded Hearts

Burgeoning evidence has indicated that normal autophagy is required for nuclear factor erythroid 2-related factor (Nrf2)-mediated cardiac protection whereas autophagy inhibition turns on Nrf2-mediated myocardial damage and dysfunction in a setting of pressure overload (PO). However, such a concept remains to be fully established by a careful genetic interrogation in vivo. This study was designed to validate the hypothesis using a mouse model of PO-induced cardiomyopathy and heart failure, in which cardiac autophagy and/or Nrf2 activity are genetically inhibited. Myocardial autophagy inhibition was induced by cardiomyocyte-restricted (CR) knockout (KO) of autophagy related (Atg) 5 (CR-Atg5KO) in adult mice. CR-Atg5KO impaired cardiac adaptations while exacerbating cardiac maladaptive responses in the setting of PO. Notably, it also turned off Nrf2-mediated defense while switching on Nrf2-operated tissue damage in PO hearts. In addition, cardiac autophagy inhibition selectively inactivated extracellular signal regulated kinase (ERK), which coincided with increased nuclear accumulation of Nrf2 and decreased nuclear translocation of activated ERK in cardiomyocytes in PO hearts. Mechanistic investigation revealed that autophagy is required for the activation of ERK, which suppresses Nrf2-driven expression of angiotensinogen in cardiomyocytes. Taken together, these results provide direct evidence consolidating the notion that normal autophagy enables Nrf2-operated adaptation while switching off Nrf2-mediated maladaptive responses in PO hearts partly through suppressing Nrf2-driven angiotensinogen expression in cardiomyocytes.

Sophoricoside ameliorates cardiac hypertrophy by activating AMPK/mTORC1-mediated autophagy

Aim: The study aims to evaluate protective effects of sophoricoside (Sop) on cardiac hypertrophy. Meanwhile, the potential and significance of Sop should be broadened and it should be considered as an attractive drug for the treatment of pathological cardiac hypertrophy and heart failure.

Methods: Using the phenylephrine (PE)-induced neonatal rat cardiomyocytes (NRCMs) enlargement model, the potent protection of Sop against cardiomyocytes enlargement was evaluated. The function of Sop was validated in mice received transverse aortic coarctation (TAC) or sham surgery. At 1 week after TAC surgery, mice were treated with Sop for the following 4 weeks, the hearts were harvested after echocardiography examination.

Results: Our study revealed that Sop significantly mitigated TAC-induced heart dysfunction, cardiomyocyte hypertrophy and cardiac fibrosis. Mechanistically, Sop treatment induced a remarkable activation of AMPK/mTORC1-autophagy cascade following sustained hypertrophic stimulation. Importantly, the protective effect of Sop was largely abolished by the AMPKα inhibitor Compound C, suggesting an AMPK activation-dependent manner of Sop function on suppressing pathological cardiac hypertrophy.

Conclusion: Sop ameliorates cardiac hypertrophy by activating AMPK/mTORC1-mediated autophagy. Hence, Sop might be an attractive candidate for the treatment of pathological cardiac hypertrophy and heart failure.

Role of PI3-Kinase in Angiotensin II-Induced Cardiac Hypertrophy: Class I Versus Class III

Cardiac hypertrophy is an adaptive response to cardiac overload initially but turns into a decompensated condition chronically, leading to heart failure and sudden cardiac death. The molecular mechanisms involved in cardiac hypertrophy and the signaling pathways that contribute to the switch from compensation to decompensation are not fully clear. The aim of the current study was to examine the role of PI3-kinases Class I (PI3KC1) and Class III (PI3KC3) in angiotensin (Ang) II-induced cardiac hypertrophy. The results demonstrate that treatment of cardiomyocytes with Ang II caused dose-dependent increases in autophagy, with an increasing phase followed by a decreasing phase. Ang II-induced autophagic increases were potentiated by inhibition of PI3KC1 with LY294002, but were impaired by inhibition of PI3KC3 with 3-methyladenine (3-MA). In addition, blockade of PI3KC1 significantly attenuated Ang II-induced ROS production and cardiomyocyte hypertrophy. In contrast, blockade of PI3KC3 potentiated Ang II-induced ROS production and cardiac hypertrophy. Moreover, blockade of PI3KC1 by overexpression of dominant negative p85 subunit of PI3KC1 significantly attenuated Ang II-induced cardiac hypertrophy in normotensive rats. Taken together, these results demonstrate that both PI3KC1 and PI3KC3 are involved in Ang II-induced cardiac hypertrophy by different mechanisms. Activation of PI3KC1 impairs autophagy activity, leading to accumulation of mitochondrial ROS, and, hence, cardiac hypertrophy. In contrast, activation of PI3KC3 improves autophagy activity, thereby reducing mitochondrial ROS and leads to a protective effect on Ang II-induced cardiac hypertrophy.

Ghrelin inhibited pressure overload-induced cardiac hypertrophy by promoting autophagy via CaMKK/AMPK signaling pathway

Ghrelin, a novel gut hormone, has been shown to exert protective effects on cardiac dysfunction and remodeling. However, the underlying mechanisms of its protective effects remain unclear. Here, we investigated the effects of ghrelin on cardiac hypertrophy and explored the mechanisms involved. Ghrelin (30 μg.kg^-1. day^-1) was systemically administered to rats with cardiac hypertrophy induced by abdominal aortic constriction (AAC) by a mini-osmotic pump the next day after surgery continuously for 4 weeks. The AAC treated rats without ghrelin infusion showed decreased ghrelin content and expression of its receptors in the hearts. Exogenous ghrelin greatly attenuated cardiac hypertrophy as shown by heart weight to tibial length (HW/TL), hemodynamics, echocardiography, histological analyses, and expression of hypertrophic markers induced by AAC. This corresponded with decreased cardiac fibrosis and inflammation in the hearts of AAC rats treated with ghrelin. Moreover, ghrelin significantly increased the myocardial expression of autophagy markers, which was further confirmed in cultured cardiomyocytes. Concurrently, cardiomyocyte apoptosis in vivo and in vitro was ameliorated by ghrelin, which was reversed by inhibition of autophagy. The enhancement of autophagy and inhibition of apoptosis by ghrelin were eliminated on pretreatment with compound C, an AMP-activated protein kinase (AMPK) inhibitor. Furthermore, inhibition of Ca²⁺/Calmodulin-dependent protein kinase kinase (CaMKK), an upstream kinase of AMPK, made ghrelin fail to activate AMPK and simultaneously reversed ghrelin's promotion of autophagy. In conclusion, ghrelin could exert its cardioprotective effects on cardiac hypertrophy by promoting autophagy, possibly via CaMKK/AMPK signaling pathway.

TMEM173 protects against pressure overload-induced cardiac hypertrophy by modulating autophagy

TMEM173 has been reported to participate in endoplasmic reticulum stress, inflammation and immunology, all of which closely involved with cardiac hypertrophy. But its role in autophagy is not fully figured out. In our research, Tmem173 global knockout (KO) mice manifested more deteriorated hypertrophy, fibrosis, inflammatory infiltration and cardiac malfunction compared with wild type C57BL/6 mice after 6 weeks of transverse aortic constriction. And KO mice showed inhibited autophagosome degradation in myocardium observed under transmission electron microscope and in protein level. In in vitro experiments conducted in neonatal rat cardiomyocytes under phenylephrine treatment, the abundance of Tmem173 gene was negatively related to the abundance of LC3-Ⅱ and the number of red and yellow fluorescent dots, of which reflected the capacity of autophagosome degradation. These results indicated that TMEM173 might be a promoter of autophagic flux and protected against pressure overload-induced cardiac hypertrophy. It may serve as a potential therapeutic target for cardiac hypertrophy in the future.

Autophagy Inhibition Enables Nrf2 to Exaggerate the Progression of Diabetic Cardiomyopathy in Mice

Nuclear factor-erythroid factor 2-related factor 2 (Nrf2) may either ameliorate or worsen diabetic cardiomyopathy. However, the underlying mechanisms are poorly understood. Herein we report a novel mechanism of Nrf2-mediated myocardial damage in type 1 diabetes (T1D). Global Nrf2 knockout (Nrf2KO) hardly affected the onset of cardiac dysfunction induced by T1D but slowed down its progression in mice independent of sex. In addition, Nrf2KO inhibited cardiac pathological remodeling, apoptosis, and oxidative stress associated with both onset and advancement of cardiac dysfunction in T1D. Such Nrf2-mediated progression of diabetic cardiomyopathy was confirmed by a cardiomyocyte-restricted (CR) Nrf2 transgenic approach in mice. Moreover, cardiac autophagy inhibition via CR knockout of autophagy-related 5 gene (CR-Atg5KO) led to early onset and accelerated development of cardiomyopathy in T1D, and CR-Atg5KO-induced adverse phenotypes were rescued by additional Nrf2KO. Mechanistically, chronic T1D leads to glucolipotoxicity inhibiting autolysosome efflux, which in turn intensifies Nrf2-driven transcription to fuel lipid peroxidation while inactivating Nrf2-mediated antioxidant defense and impairing Nrf2-coordinated iron metabolism, thereby leading to ferroptosis in cardiomyocytes. These results demonstrate that diabetes over time causes autophagy deficiency, which turns off Nrf2-mediated defense while switching on an Nrf2-operated pathological program toward ferroptosis in cardiomyocytes, thereby worsening the progression of diabetic cardiomyopathy.

Role of Exercise on Alleviating Pressure Overload-Induced Left Ventricular Dysfunction and Remodeling via AMPK-Dependent Autophagy Activation

Cardiac hypertrophy is one of the significant risk factors that result in maladaptive cardiac remodeling and heart failure, and exercise is known to exert cardioprotection. In this research, the cardioprotective function and exercise mechanisms were explored.The rats underwent transverse aortic constriction (TAC) or a sham operation. The rats that received TAC were randomly assigned to five groups: (1) rats subjected to a sham operation as control group (SC), (2) rats that underwent TAC group (TC), (3) TAC and moderate-intensity exercise group (TE), (4) TE plus 3-MA group (TEM), and (5) TE plus Compound C group (TEC). The heart function was measured via echocardiography. Histological analysis and relative protein testing were conducted to analyze collagen deposition and apoptosis. Furthermore, western blot was employed to measure the protein expression of relevant signaling pathways. Impaired cardiac function, interstitial fibrosis, enhanced apoptosis, and ER stress were observed in the TAC-induced left ventricular hypertrophy. Exercise attenuated TAC-induced cardiac dysfunction, interstitial fibrosis, and ER stress-related apoptosis. In addition, exercise significantly improved autophagy and upregulated AMPK phosphorylation. Furthermore, AMPK inhibitor Compound C repressed the activation of AMPK, and autophagy inhibitor 3-methyladenine reversed exercise-induced autophagy. All of these abolished the protection of exercise against cardiac dysfunction and fibrosis induced by TAC.Our results indicated that 4 weeks of treadmill exercise could alleviate pressure overload-induced LV dysfunction and remodeling via an autophagy-dependent mechanism, which was induced by enhancing autophagy through the activation of AMPK.

Osteoprotegerin prompts cardiomyocyte hypertrophy via autophagy inhibition mediated by FAK/BECLIN1 pathway

AIM

It has been reported that Osteoprotegerin (OPG) induces cardiomyocyte hypertrophy, but the mechanism remains unclear. This study was to investigate the role of Focal Adhesion Kinase (FAK) pathway in the OPG induced hypertrophy in cultured cardiomyocytes.

METHODS

The H9C2 line of rat cardiomyocytes were treated with OPG at different concentrations and the cellular hypertrophy was evaluated. Meanwhile, the activity of FAK and other the phosphorylation kinases were detected. Autophagy flux assay was performed in absence and presence OPG. The interaction between proteins was analyses using Co-Immunoprecipitation assay.

RESULTS

We found that OPG induced cardiomyocyte hypertrophic response, indicated by increased cellular size and protein content per cell. OPG increases the heart/body weight ratio in vivo. Also OPG inhibits autophagy and induces FAK phosphorylation. FAK silencing using si-RNA abrogates the effect of OPG on autophagy and cellular hypertrophy. Furthermore, Co-immunoprecipitation assay reveals that OPG inhibits autophagy through enhancing the binding of FAK and Beclin1.

CONCLUSION

The FAK/Beclin1 signal pathway is essential for the OPG induced autophagy inhibition and hypertrophic response in cultured H9C2 cells.

Activated FMS-like tyrosine kinase 3 ameliorates angiotensin II-induced cardiac remodelling

AIM

FMS-like receptor tyrosine kinase 3 (Flt3) has been reported to be increased in cardiomyocytes responding to ischaemic stress. This study was to determine whether Flt3 activation could ameliorate pressure overload-induced heart hypertrophy and fibrosis, and to elucidate the mechanisms of action.

METHODS

In vivo cardiac hypertrophy and remodelling experiments were conducted by infusing angiotensin II (Ang II) chronically in male C57BL/6 mice. Flt3-specific ligand (FL) was administered intraperitoneally every two days (5 µg/mouse). In vitro experiments on hypertrophy, apoptosis and autophagy mechanism were performed in neonatal rat cardiomyocytes (NRCMs) and H9c2 cells with adenovirus vector-mediated overexpression of Flt3.

RESULTS

Our results demonstrated that following chronic Ang II infusion for 4 weeks, the mice exhibited heart hypertrophy, fibrosis, apoptosis and contractile dysfunction. Meanwhile, Ang II induced autophagic responses in mouse hearts, as evidenced by increased LC3 II and decreased P62 expression. These pathological alterations in Ang II-treated mice were significantly ameliorated by Flt3 activation with FL administration. In NRCMs and Flt3-overexpressed H9c2 cells, FL attenuated Ang II-induced pathological autophagy and inactivated AMPK/mTORC1/FoxO3a signalling, thereby efficiently mitigating cell hypertrophy and apoptosis. Conversely, the AMPK activator metformin or the mTORC1 inhibitor rapamycin reversed the effects of FL on the alterations of autophagy, hypertrophy and apoptosis in cardiomyocytes induced by Ang II.

CONCLUSION

Flt3 activation ameliorates cardiac hypertrophy, fibrosis and contractile dysfunction in the mouse model of chronic pressure overload, most likely via suppressing AMPK/mTORC1/FoxO3a-mediated autophagy. These results provide new evidence supporting Flt3 as a novel therapeutic target in maladaptive cardiac remodelling.

Corosolic acid ameliorates cardiac hypertrophy via regulating autophagy

Aim: In this work, we explored the role of corosolic acid (CRA) during pressure overload-induced cardiac hypertrophy. Methods and results: Cardiac hypertrophy was induced in mice by aortic banding. Four weeks post-surgery, CRA-treated mice developed blunted cardiac hypertrophy, fibrosis, and dysfunction, and showed increased LC3 II and p-AMPK expression. In line with the in vivo studies, CRA also inhibited the hypertrophic response induced by PE stimulation accompanying with increased LC3 II and p-AMPK expression. It was also found that CRA blunted cardiomyocyte hypertrophy and promoted autophagy in Angiotensin II (Ang II)-treated H9c2 cells. Moreover, to further verify whether CRA inhibits cardiac hypertrophy by the activation of autophagy, blockade of autophagy was achieved by CQ (an inhibitor of the fusion between autophagosomes and lysosomes) or 3-MA (an inhibitor of autophagosome formation). It was found that autophagy inhibition counteracts the protective effect of CRA on cardiac hypertrophy. Interestingly, AMPK knockdown with AMPKα2 siRNA-counteracted LC3 II expression increase and the hypertrophic response inhibition caused by CRA in PE-treated H9c2 cells. Conclusion: These results suggest that CRA may protect against cardiac hypertrophy through regulating AMPK-dependent autophagy.

The Dark Side of Nrf2 in the Heart

Nuclear factor-erythroid factor 2-related factor 2 (Nrf2) is a critical transcription factor that regulates the expression of over 1000 genes in the cell under normal and stressed conditions. These transcripts can be categorized into different groups with distinct functions, including antioxidative defense, detoxification, inflammatory responses, transcription factors, proteasomal and autophagic degradation, and metabolism. Nevertheless, Nrf2 has been historically considered as a crucial regulator of antioxidant defense to protect against various insult-induced organ damage and has evolved as a promising drug target for the treatment of human diseases, such as heart failure. However, burgeoning evidence has revealed a detrimental role of Nrf2 in cardiac pathological remodeling and dysfunction toward heart failure. In this mini-review, we outline recent advances in structural features of Nrf2 and regulation of Nrf2 activity and discuss the emerging dark side of Nrf2 in the heart as well as the potential mechanisms of Nrf2-mediated myocardial damage and dysfunction.

Overexpression of FNTB and the activation of Ras induce hypertrophy and promote apoptosis and autophagic cell death in cardiomyocytes

Farnesyltransferase (FTase) is an important enzyme that catalyses the modification of protein isoprene downstream of the mevalonate pathway. Previous studies have shown that the tissue of the heart in the suprarenal abdominal aortic coarctation (AAC) group showed overexpression of FTaseβ (FNTB) and the activation of the downstream protein Ras was enhanced. FTase inhibitor (FTI) can alleviate myocardial fibrosis and partly improve cardiac remodelling in spontaneously hypertensive rats. However, the exact role and mechanism of FTase in myocardial hypertrophy and remodelling are not fully understood. Here, we used recombinant adenovirus to transfect neonatal rat ventricular cardiomyocytes to study the effect of FNTB overexpression on myocardial remodelling and explore potential mechanisms. The results showed that overexpression of FNTB induces neonatal rat ventricular myocyte hypertrophy and reduces the survival rate of cardiomyocytes. FNTB overexpression induced a decrease in mitochondrial membrane potential and increased apoptosis in cardiomyocytes. FNTB overexpression also promotes autophagosome formation and the accumulation of autophagy substrate protein, LC3II. Transmission electron microscopy (TEM) and mCherry‐GFP tandem fluorescent‐tagged LC3 (tfLC3) showed that FNTB overexpression can activate autophagy flux by enhancing autophagosome conversion to autophagolysosome. Overactivated autophagy flux can be blocked by bafilomycin A1. In addition, salirasib (a Ras farnesylcysteine mimetic) can alleviate the hypertrophic phenotype of cardiomyocytes and inhibit the up‐regulation of apoptosis and autophagy flux induced by FNTB overexpression. These results suggest that FTase may have a potential role in future treatment strategies to limit the adverse consequences of cardiac hypertrophy, cardiac dysfunction and heart failure.

COP9 Signalosome Suppresses RIPK1-RIPK3-Mediated Cardiomyocyte Necroptosis in Mice

BACKGROUND

Mechanisms governing the induction of heart failure by the impairment of autophagy and the ubiquitin-proteasome system and the molecular pathways to cardiomyocyte necrosis remain incompletely understood. COPS8 is an essential subunit of the COP9 (COnstitutive Photomorphogenesis 9) signalosome, a key regulator of ubiquitination. Mice with cardiomyocyte-restricted knockout of Cops8 (Cops8-cko) show autophagic and ubiquitin-proteasome system malfunction and massive cardiomyocyte necrosis followed by acute heart failure and premature death, providing an excellent animal model to address the mechanistic gaps specified above. This study was conducted to determine the nature and underlying mechanisms of the cardiomyocyte necrosis in Cops8-cko mice.

METHODS AND RESULTS

Compared with littermate control mice, myocardial protein levels of key factors in the necroptotic pathway (RIPK1 [receptor-interacting protein kinase 1], RIPK3, MLKL [mixed lineage kinase-like], the RIPK1-bound RIPK3), protein carbonyls, full-length Casp8 (caspase 8), and BCL2, as well as histochemical staining of superoxide anions were significantly higher but the cleaved Casp8 and the Casp8 activity were significantly lower in Cops8-cko mice. In vivo cardiomyocyte uptake of Evan's blue dye was used as an indicator of necrosis. Cops8-cko mice treated with a RIPK1 kinase inhibitor (Nec-1 [Necrostatin-1]) showed less Evans blue dye uptake (0.005% versus 0.20%; P<0.0001) and longer median lifespan (32.5 versus 27 days; P<0.01) than those treated with vehicle control. RIPK3 haploinsufficiency showed similar rescuing effects on Cops8-cko but Cyclophilin D deficiency did the opposite.

CONCLUSIONS

Cardiac Cops8/COP9 signalosome malfunction causes RIPK1-RIPK3 dependent, but mitochondrial permeability transition pore independent, cardiomyocyte necroptosis in mice and the COP9 signalosome plays an indispensable role in suppressing cardiomyocyte necroptosis.

Sophocarpine ameliorates cardiac hypertrophy through activation of autophagic responses

Mounting evidences indicate that autophagy is an essential homeostatic mechanism to maintain the global cardiac structure function. Sophocarpine (SOP), a major bioactive compound derived from the natural plant Sophora flavescens. However, the role of SOP in cardiac hypertrophy remain to be fully elucidated. In the present study, we tested the hypothesis that SOP protects against Ang II-induced cardiac hypertrophy by mediating the regulation of autophagy. The results demonstrated that SOP attenuated the Ang II-induced cardiac hypertrophy, as assessed by measurements of echocardiography parameters, the ratios of heart weight/body weight and left ventricle weight/body weight, histopathological staining, cross-sectional cardiomyocyte area, and the expression levels of cardiac hypertrophic markers. The anti-hypertrophic effect of SOP was mediated by activating autophagy-related pathway, as revealed by reversal of the increased autophagy marker protein expression. These findings reveal a novel mechanism of SOP attenuating cardiac hypertrophy via activating autophagy-related signaling pathways.

CYLD exaggerates pressure overload-induced cardiomyopathy via suppressing autolysosome efflux in cardiomyocytes

Deubiquitinating enzymes (DUBs) appear to be a new class of regulators of cardiac homeostasis and disease. However, DUB-mediated signaling in the heart is not well understood. Herein we report a novel mechanism by which cylindromatosis (CYLD), a DUB mediates cardiac pathological remodeling and dysfunction. Cardiomyocyte-restricted (CR) overexpression of CYLD (CR-CYLD) did not cause gross health issues and hardly affected cardiac function up to age of one year in both female and male mice at physiological conditions. However, CR-CYLD overexpression exacerbated pressure overload (PO)-induced cardiac dysfunction associated with suppressed cardiac hypertrophy and increased myocardial apoptosis in mice independent of the gender. At the molecular level, CR-CYLD overexpression enhanced PO-induced increases in poly-ubiquitinated proteins marked by lysine (K)48-linked ubiquitin chains and autophagic vacuoles containing undegraded contents while suppressing autophagic flux. Augmentation of cardiac autophagy via CR-ATG7 overexpression protected against PO-induced cardiac pathological remodeling and dysfunction in both female and male mice. Intriguingly, CR-CYLD overexpression switched the CR-ATG7 overexpression-dependent cardiac protection into myocardial damage and dysfunction associated with increased accumulation of autophagic vacuoles containing undegraded contents in the heart. Genetic manipulation of Cyld in combination with pharmacological modulation of autophagic functional status revealed that CYLD suppressed autolysosomal degradation and promoted cell death in cardiomyocytes. In addition, Cyld gene gain- and/or loss-of-function approaches in vitro and in vivo demonstrated that CYLD mediated cardiomyocyte death associated with impaired reactivation of mechanistic target of rapamycin complex 1 (mTORC1) and upregulated Ras genes from rat brain 7 (Rab7), two key components for autolysosomal degradation. These results demonstrate that CYLD serves as a novel mediator of cardiac pathological remodeling and dysfunction by suppressing autolysosome efflux in cardiomyocytes. Mechanistically, it is most likely that CYLD suppresses autolysosome efflux via impairing mTORC1 reactivation and interrupting Rab7 release from autolysosomes in cardiomyocytes.

Sestrin2 as a potential therapeutic target for cardiovascular diseases

Sestrin2 is a cysteine sulfinyl reductase that plays crucial roles in regulation of antioxidant actions. Sestrin2 provides cytoprotection against multiple stress conditions, including hypoxia, endoplasmic reticulum (ER) stress and oxidative stress. Recent research reveals that upregulation of Sestrin2 is induced by various transcription factors such as p53 and activator protein 1 (AP-1), which further promotes AMP-activated protein kinase (AMPK) activation and inhibits mammalian target of rapamycin protein kinase (mTOR) signaling. Sestrin2 triggers autophagy activity to reduce cellular reactive oxygen species (ROS) levels by promoting nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) activation and Kelch-like ECH-associated protein 1 (Keap1) degradation, which plays a pivotal role in homeostasis of metabolic regulation. Under hypoxia and ER stress conditions, elevated Sestrin2 expression maintains cellular homeostasis through regulation of antioxidant genes. Sestrin2 is responsible for diminishing cellular ROS accumulation through autophagy via AMPK activation, which displays cardioprotection effect in cardiovascular diseases. In this review, we summarize the recent understanding of molecular structure, biological roles and biochemical functions of Sestrin2, and discuss the roles and mechanisms of Sestrin2 in autophagy, hypoxia and ER stress. Understanding the precise functions and exact mechanism of Sestrin2 in cellular homeostasis will provide the evidence for future experimental research and aid in the development of novel therapeutic strategies for cardiovascular diseases.

Melatonin ameliorates pressure overload-induced cardiac hypertrophy by attenuating Atg5-dependent autophagy and activating the Akt/mTOR pathway

Cardiac hypertrophy, including hypertension and valvular dysfunction, is a pathological feature of many cardiac diseases that ultimately leads to heart failure. Melatonin confers a protective role against pathological cardiac hypertrophy, but the underlying mechanisms remain elusive. In the present study, we hypothesized that melatonin protects against pressure overload-induced cardiac hypertrophy by attenuating Atg5-dependent autophagy and activating the Akt/mTOR pathway. Male C57BL/6 mice that received adenovirus carrying cardiac-specific Atg5 (under the cTNT promoter; Ad-cTNT-Atg5) underwent transverse aortic constriction (TAC) or sham operation and received an intraperitoneal injection of melatonin (10 mg/kg/d), vehicle or LY294002 (10 mg/kg/d) for 8 weeks. Melatonin treatment for 8 weeks markedly attenuated cardiac hypertrophy and restored impaired cardiac function, as indicated by a decreased HW/BW ratio, reduced cell cross-sectional area and fibrosis, downregulated the mRNA levels of ANP, BNP, and β-MHC and ameliorated adverse effects on the LVEF and LVFS. Melatonin treatment also inhibited apoptosis and alleviated autophagy dysfunction. Furthermore, melatonin inhibited Akt/mTOR pathway activation, while these effects were blocked by LY294002. In addition, the effect of melatonin regulation on TAC-induced autophagy dysfunction was inhibited by LY294002 or cardiac-specific Atg5 overexpression. As expected, Akt/mTOR pathway inhibition or cardiac-specific Atg5 overexpression restrained melatonin alleviation of pressure overload-induced cardiac hypertrophy. These results demonstrated that melatonin ameliorated pressure overload-induced cardiac hypertrophy by attenuating Atg5-dependent autophagy and activating the Akt/mTOR pathway.

Potential risk of hyperuricemia: leading cardiomyocyte hypertrophy by inducing autophagy

BACKGROUND

Clinical studies have shown that hyperuricemia is associated with many cardiovascular diseases; however, the mechanisms involved remain unclear. In this study, we investigated the effect of uric acid on cardiomyocytes and the underlying mechanism.

METHODS AND RESULTS

H9c2 cardiomyocytes were treated with various concentrations of uric acid. 3-Methyladenine (3-MA) or Compound C was added before treatment with uric acid. The expression of myocardial hypertrophy-related genes was measured using polymerase chain reaction (PCR). The cell surface area was calculated using ImageJ Software. Western blotting was used to measure the protein levels. Uric acid increased the gene expression of Nppa, Nppb, and Myh5, which are involved in myocardial hypertrophy, and the relative cell surface area of cardiomyocytes in a dose-dependent manner. Consistently, the ratio of LC3II/I, which is a biomarker of autophagy, increased dose-dependently, whereas the protein level of p62, a protein that is degraded by autophagy, decreased. 3-MA, an autophagy inhibitor, rescued uric acid-induced myocardial hypertrophy. Treatment with uric acid increased the level of phosphorylated adenosine monophosphate kinase (AMPK), as well as its downstream effector unc-51-like kinase (ULK1). Pharmacological inhibition of AMPK by Compound C attenuated the uric acid-induced activation of autophagy and myocardial hypertrophy.

CONCLUSIONS

Uric acid induces myocardial hypertrophy by activating autophagy via the AMPK-ULK1 signaling pathway. Decreasing the serum uric acid level may therefore be clinically beneficial in alleviating cardiac hypertrophy.

The Calcineurin-TFEB-p62 Pathway Mediates the Activation of Cardiac Macroautophagy by Proteasomal Malfunction

RATIONALE

The ubiquitin-proteasome system (UPS) and the autophagic-lysosomal pathway are pivotal to proteostasis. Targeting these pathways is emerging as an attractive strategy for treating cancer. However, a significant proportion of patients who receive a proteasome inhibitor-containing regime show cardiotoxicity. Moreover, UPS and autophagic-lysosomal pathway defects are implicated in cardiac pathogenesis. Hence, a better understanding of the cross-talk between the 2 catabolic pathways will help advance cardiac pathophysiology and medicine.

OBJECTIVE

Systemic proteasome inhibition (PSMI) was shown to increase p62/SQSTM1 expression and induce myocardial macroautophagy. Here we investigate how proteasome malfunction activates cardiac autophagic-lysosomal pathway.

METHODS AND RESULTS

Myocardial macroautophagy, TFEB (transcription factor EB) expression and activity, and p62 expression were markedly increased in mice with either cardiomyocyte-restricted ablation of Psmc1 (an essential proteasome subunit gene) or pharmacological PSMI. In cultured cardiomyocytes, PSMI-induced increases in TFEB activation and p62 expression were blunted by pharmacological and genetic calcineurin inhibition and by siRNA-mediated Molcn1 silencing. PSMI induced remarkable increases in myocardial autophagic flux in wild type mice but not p62 null (p62-KO) mice. Bortezomib-induced left ventricular wall thickening and diastolic malfunction was exacerbated by p62 deficiency. In cultured cardiomyocytes from wild type mice but not p62-KO mice, PSMI induced increases in LC3-II flux and the lysosomal removal of ubiquitinated proteins. Myocardial TFEB activation by PSMI as reflected by TFEB nuclear localization and target gene expression was strikingly less in p62-KO mice compared with wild type mice.

CONCLUSIONS

(1) The activation of cardiac macroautophagy by proteasomal malfunction is mediated by the Mocln1-calcineurin-TFEB-p62 pathway; (2) p62 unexpectedly exerts a feed-forward effect on TFEB activation by proteasome malfunction; and (3) targeting the Mcoln1 (mucolipin1)-calcineurin-TFEB-p62 pathway may provide new means to intervene cardiac autophagic-lysosomal pathway activation during proteasome malfunction.

Cilostazol alleviate nicotine induced cardiomyocytes hypertrophy through modulation of autophagy by CTSB/ROS/p38MAPK/JNK feedback loop

Nicotine is proved to be an important factor for cardiac hypertrophy. Autophagy is important cell recycling system involved in the regulation of cardiac hypertrophy. Cilostazol, which is often used in the management of peripheral vascular disease. However, the effects of cilostazol on nicotine induced autophagy and cardiac hypertrophy are unclear. Here, we aim to determine the role and molecular mechanism of cilostazol in alleviating nicotine-induced cardiomyocytes hypertrophy through modulating autophagy and the underlying mechanisms. Our results clarified that nicotine stimulation caused cardiomyocytes hypertrophy and autophagy flux impairment significantly in neonatal rat ventricular myocytes (NRVMs), which were evidenced by augments of LC3-II and p62 levels, and impaired autophagosomes clearance. Interestingly, cathepsin B (CTSB) activity decreased dramatically after stimulation with nicotine in NRVMs, which was crucial for substrate degradation in the late stage of autophagy process, and cilostazol could reverse this effect dramatically. Intracellular ROS levels were increased significantly after nicotine exposure. Meanwhile, p38MAPK and JNK were activated after nicotine treatment. By using ROS scavenger N-acetyl-cysteine (NAC) could reverse the effects of nicotine by down-regulation the phosphorylation of p38MAPK and JNK pathways, and pretreatment of specific inhibitors of p38MAPK and JNK could restore the autophagy impairment and cardiomyocytes hypertrophy induced by nicotine. Moreover, CTSB activity of lysosome regained after the treatment with cilostazol. Cilostazol also inhibited the ROS accumulation and the activation of p38MAPK and JNK, which providing novel connection between lysosome CTSB and ROS/p38MAPK/JNK related oxidative stress pathway. This is the first demonstration that cilostazol could alleviate nicotine induced cardiomyocytes hypertrophy through restoration of autophagy flux by activation of CTSB and inhibiting ROS/p38/JNK pathway, exhibiting a feedback loop on regulation of autophagy and cardiomyocytes hypertrophy.

Priming the Proteasome to Protect against Proteotoxicity

Increased proteotoxic stress (IPTS) resulting from the increased production or decreased removal of abnormally folded proteins is recognized as an important pathogenic factor for a large group of highly disabling and life-threatening human diseases, such as neurodegenerative disorders and many heart diseases. The proteasome is pivotal to the timely removal of abnormal proteins but its functional capacity often becomes inadequate in the disease conditions; consequently, proteasome functional insufficiency in return exacerbates IPTS. Recent research in proteasome biology reveals that the proteasome can be activated by endogenous protein kinases, making it possible to pharmacologically prime the proteasome for treating diseases with IPTS.

Inhibition of Interleukin-6/glycoprotein 130 signalling by Bazedoxifene ameliorates cardiac remodelling in pressure overload mice

The role of IL-6 signalling in hypertensive heart disease and its sequelae is controversial. Our group demonstrated that Bazedoxifene suppressed IL-6/gp130 signalling in cancer cells but its effect on myocardial pathology induced by pressure overload is still unknown. We explored whether Bazedoxifene could confer benefits in wild-type C57BL/6J mice suffering from transverse aortic constriction (TAC) and the potential mechanisms in H9c2 myoblasts. Mice were randomized into three groups (Sham, TAC, TAC+Bazedoxifene, n = 10). Morphological and histological observations suggested TAC aggravated myocardial remodelling while long-term intake of Bazedoxifene (5 mg/kg, intragastric) attenuated pressure overload-induced pathology. Echocardiographic results indicated Bazedoxifene rescued cardiac function in part. We found Bazedoxifene decreased the mRNA expression of IL-6, MMP2, Col1A1, Col3A1 and periostin in murine hearts after 8-week surgery. By Western blot detection, we found Bazedoxifene exhibited an inhibition of STAT3 activation in mice three hours and 8 weeks after TAC. Acute TAC stress (3 hours) led to down-regulated ratio of LC3-Ⅱ/LC3-Ⅰ, while in mice after long-term (8 weeks) TAC this ratio becomes higher than that in Sham mice. Bazedoxifene inverted the autophagic alteration induced by TAC at both two time-points. In H9c2 myoblasts, Bazedoxifene suppressed the IL-6-induced STAT3 activation. Moreover, IL-6 reduced the ratio of LC3-Ⅱ/LC3-Ⅰ, promoted P62 expression but Bazedoxifene reversed both changes in H9c2 cells. Our data suggested Bazedoxifene inhibited IL-6/gp130 signalling and protected against cardiac remodelling together with function deterioration in TAC mice.

Novel Insights into the Role of HDL-Associated Sphingosine-1-Phosphate in Cardiometabolic Diseases

Sphingolipids are key signaling molecules involved in the regulation of cell physiology. These species are found in tissues and in circulation. Although they only constitute a small fraction in lipid composition of circulating lipoproteins, their concentration in plasma and distribution among plasma lipoproteins appears distorted under adverse cardiometabolic conditions such as diabetes mellitus. Sphingosine-1-phosphate (S1P), one of their main representatives, is involved in regulating cardiomyocyte homeostasis in different models of experimental cardiomyopathy. Cardiomyopathy is a common complication of diabetes mellitus and represents a main risk factor for heart failure. Notably, plasma concentration of S1P, particularly high-density lipoprotein (HDL)-bound S1P, may be decreased in patients with diabetes mellitus, and hence, inversely related to cardiac alterations. Despite this, little attention has been given to the circulating levels of either total S1P or HDL-bound S1P as potential biomarkers of diabetic cardiomyopathy. Thus, this review will focus on the potential role of HDL-bound S1P as a circulating biomarker in the diagnosis of main cardiometabolic complications frequently associated with systemic metabolic syndromes with impaired insulin signaling. Given the bioactive nature of these molecules, we also evaluated its potential of HDL-bound S1P-raising strategies for the treatment of cardiometabolic disease.

Tanshinone IIA Restores Dynamic Balance of Autophagosome/Autolysosome in Doxorubicin-Induced Cardiotoxicity via Targeting Beclin1/LAMP1

Clinical use of the anti-cancer drug doxorubicin (DOX) is largely limited due to its severe cardiotoxicity. Dysregulation of autophagy is implicated in DOX-induced cardiotoxicity (DIC). Prior studies have indicated that Beclin1 and lysosomal-associated membrane proteins-1 (LAMP1) are critical mediators of autophagy. In this work, by assessing autophagic flux in a DOX-stimulated H9C2 model, we observed autolysosome accumulation caused by interruption of autolysosome degradation. Tanshinone IIA (TSA) is a well-known small molecule that exerts impressive cardioprotective effects on heart failure. Here, we investigated the regulation of TSA in DOX-treated zebrafish, mice, and H9C2 models. Results demonstrated that TSA remarkably improved heart function and reversed pathological changes in vivo, while TSA restored autophagic flux by promoting autolysosome degradation and autophagosome formation. Further experiments demonstrated that these effects were mediated through upregulation of Beclin1 and LAMP1. The mTOR agonist MHY1485 was shown to abrogate the effect of TSA via the UNC-51-like kinase 1 (ULK1)-Beclin1/TFEB-LAMP1 signaling pathway in vitro, demonstrating that TSA protects against DIC by promoting autophagy via the Beclin1/LAMP1 signaling pathway. We further employed a U87 model to assess whether TSA would compromise the antitumor activity of DOX. Intriguingly, the co-treatment of TSA was able to synergistically inhibit proliferative activity. Collectively, in this study we uncover the novel insight that TSA is able to reduce the cardiotoxicity of DOX without compromising antitumor activity.

Highly Dynamic Changes in the Activity and Regulation of Macroautophagy in Hearts Subjected to Increased Proteotoxic Stress

Macroautophagy (referred to as autophagy hereafter) plays an important role in the quality control of cellular proteins and organelles. Transcription Factor EB (TFEB) globally activates the expression of genes in the autophagic-lysosomal pathway (ALP) to replenish lysosomes and ALP machineries. We previously reported that myocardial TFEB signaling was impaired in advanced cardiac proteinopathy; however, myocardial ALP status and TFEB activity at earlier stages of cardiac proteinopathy remain uncharacterized. Here a stable line of CryAB^R120G transgenic (R120G) and non-transgenic (NTG) littermate mice with cardiomyocyte-restricted overexpression of CryAB^R120G were used at 1, 3, and 6 months of age. At 1 month when no cardiac phenotypes other than aberrant protein aggregation are discernible, R120G mice displayed a 5-fold increase in myocardial LC3-II flux. Interestingly, the LC3-II flux increase co-existed with increases in mTOR complex 1 (mTORC1) activities as well as cytoplasmic, but not nuclear, TFEB proteins. This increase in cytoplasmic TFEB proteins occurred without any discernible alteration in TFEB activity as reflected by unchanged mRNA levels of representative TFEB target genes (Mcoln1, M6pr, Sqstm1, Vps18, and Uvrag). At 3 months of age when hypertrophy and diastolic malfunction start to develop, the LC3-II flux remained significantly increased but to a lesser degree (2-fold) than at 1 month. The LC3-II flux increase was associated with decreased mTORC1 activities and with increased nuclear TFEB proteins and TFEB activities. At 6 months of age when congestive heart failure is apparent in R120G mice, both LC3-II flux and TFEB activities were severely suppressed, while mTORC1 activity increased. We conclude that changes in both autophagy and TFEB signaling are highly dynamic during the progression of cardiac proteinopathy. Increases in autophagy occur before increases in TFEB activities but both increase in the compensatory stage of cardiac proteinopathy. Once congestive heart failure develops, both autophagy and TFEB signaling become impaired. Our results suggest that TFEB signaling is regulated by both mTORC1-dependent and -independent mechanisms in hearts subjected to increased proteotoxic stress. For therapeutic exploration, it will be important to test the effect of TFEB stimulation at the early, intermediate, and late stages of cardiac proteinopathy.

Soluble epoxide hydrolase inhibitor, TUPS, attenuates isoproterenol/angiotensin II-induced cardiac hypertrophy through mammalian target of rapamycin-mediated autophagy inhibition

OBJECTIVES

To investigate the potential role and mechanism of TUPS, a soluble epoxide hydrolase inhibitor, in cardiac hypertrophy.

METHODS

Rat and H9C2 cell models of cardiac hypertrophy were induced by isoproterenol and angiotensin II, respectively, followed by TUPS treatment. The expression of hypertrophic markers, ANP and BNP, was determined by quantitative real-time PCR. The abundance of Beclin-1, LC3, p-AMPK and phosphorylated-mammalian target of rapamycin (p-mTOR) proteins was analysed by Western blot and immunohistocytology. Cell morphology and viability were evaluated by F-actin staining and MTS. H9C2 cells were transfected with GFP-LC3 to evaluate autophagy flux.

KEY FINDINGS

TUPS significantly inhibited rat heart size, heart weight-to-body weight ratio, heart wall thickness, hypertrophic H9C2 cell swelling and viability suppression as well as the expression of ANP and BNP genes in hypertrophic models. In addition, autophagic markers Beclin-1 and LC3 were elevated in both cellular and animal models, which were suppressed by TUPS, with corresponding changes of autophagy flux. The abundance of p-AMPK was increased, while p-mTOR was decreased in hypertrophic cells, which were abolished by TUPS. Rapamycin decreased p-mTOR level, increased Beclin-1 and LC3 expression and induced cell size enlargement and cell viability inhibition in hypertrophic H9C2 cells treated with TUPS.

CONCLUSIONS

TUPS inhibits cardiac hypertrophy by regulating mTOR/autophagy axis.

Oridonin protects against cardiac hypertrophy by promoting P21-related autophagy

Autophagy is an endogenous protective process; the loss of autophagy could destabilize proteostasis and elevate intracellular oxidative stress, which is critically involved in the development of cardiac hypertrophy and heart failure. Oridonin, a natural tetracycline diterpenoid from the Chinese herb Rabdosia, has autophagy activation properties. In this study, we tested whether oridonin protects against cardiac hypertrophy in mice and cardiomyocytes. We implemented aortic banding to induce a cardiac hypertrophy mouse model, and oridonin was given by gavage for 4 weeks. Neonatal rat cardiomyocytes were stimulated with angiotensin II to simulate neurohumoural stress. Both in vivo and in vitro studies suggested that oridonin treatment mitigated pressure overload-induced cardiac hypertrophy and fibrosis, and also preserved heart function. Mice that received oridonin exhibited increased antioxidase activities and suppressed oxidative injury compared with the aortic banding group. Moreover, oridonin enhanced myocardial autophagy in pressure-overloaded hearts and angiotensin II-stimulated cardiomyocytes. Mechanistically, we discovered that oridonin administration regulated myocardial P21, and cytoplasmic P21 activated autophagy via regulating Akt and AMPK phosphorylation. These findings were further corroborated in a P21 knockout mouse model. Collectively, pressure overload-induced autophagy dysfunction causes intracellular protein accumulation, resulting in ROS injury while aggravating cardiac hypertrophy. Thus, our data show that oridonin promoted P21-related autophagic lysosomal degradation, hence attenuating oxidative injury and cardiac hypertrophy.

The immunoproteasome catalytic β5i subunit regulates cardiac hypertrophy by targeting the autophagy protein ATG5 for degradation

Pathological cardiac hypertrophy eventually leads to heart failure without adequate treatment. The immunoproteasome is an inducible form of the proteasome that is intimately involved in inflammatory diseases. Here, we found that the expression and activity of immunoproteasome catalytic subunit β5i were significantly up-regulated in angiotensin II (Ang II)-treated cardiomyocytes and in the hypertrophic hearts. Knockout of β5i in cardiomyocytes and mice markedly attenuated the hypertrophic response, and this effect was aggravated by β5i overexpression in cardiomyocytes and transgenic mice. Mechanistically, β5i interacted with and promoted ATG5 degradation thereby leading to inhibition of autophagy and cardiac hypertrophy. Further, knockdown of ATG5 or inhibition of autophagy reversed the β5i knockout-mediated reduction of cardiomyocyte hypertrophy induced by Ang II or pressure overload. Together, this study identifies a novel role for β5i in the regulation of cardiac hypertrophy. The inhibition of β5i activity may provide a new therapeutic approach for hypertrophic diseases.

Tanshinone IIA protects against heart failure post-myocardial infarction via AMPKs/mTOR-dependent autophagy pathway

Heart failure (HF) leads to an increase in morbidity and mortality globally. Tanshinone IIA is an important traditional Chinese medicine monomer and has been shown to have remarkable protective effect against HF. Autophagy is critically involved in the progression of HF. The effect of Tanshinone IIA on autophagy has not been clarified yet. In this study, left anterior descending (LAD) ligation was used to induce HF model and a hydrogen peroxide-(H₂O₂-)-induced H9C2 cell injury model was established. in vivo, echocardiography results showed that Tanshinone IIA could significantly improve heart function. Western Blot result showed that Tanshinone IIA treatment enhanced autophagy and regulated expressions of key autophagy-related molecules, including protein 1 light chain 3 (LC3), p62 and Beclin1. Tanshinone IIA also inhibited apoptosis and regulated expressions of key apoptotic protein, including B cell lymphoma-2 (Bcl-2) and Bcl-2 Associated X Protein (Bax) and cleaved caspase-3 and -7. Further experiments demonstrated that the effects of Tanshinone IIA were mediated through upregulation of AMP-activated protein kinase (AMPK) and downregulation of mammalian target of rapamycin (mTOR) simultaneously. The mTOR agonist MHY1485 could abrogate the therapeutic effect of Tanshinone IIA in vitro. In conclusion, Tanshinone IIA protects cardiomyocytes and improves cardiac function by inhibiting apoptosis and inducing autophagy via activation of the AMPK-mTOR signaling pathway.

Cyclic peptide RD808 reduces myocardial injury induced by β1-adrenoreceptor autoantibodies

Autoantibodies against the second extracellular loop of β₁-adrenergic receptor (β₁-AA) have been shown to be involved in the development of cardiovascular diseases. Recently, there has been considerable interest in strategies to remove these autoantibodies, particularly therapeutic peptides to neutralize β₁-AA. Researchers are investigating the roles of cyclic peptides that mimic the structure of relevant epitopes on the β₁-AR-EC_II in a number of immune-mediated diseases. Here, we used a cyclic peptide, namely, RD808, to neutralize β₁-AA, consequently alleviating β₁-AA-induced myocardial injury. We investigated the protective effects of RD808 on the myocardium both in vitro and in vivo. RD808 was found to increase the survival rate of cardiomyocytes; furthermore, it decreased myocardial necrosis and apoptosis and improved the cardiac function of BalB/c mice in a β₁-AA transfer model. In vitro and in vivo experiments showed that myocardial autophagy was increased in the presence of RD808, which might contribute to its cardioprotective effects. Our findings indicate that RD808 reduced myocardial injury induced by β₁-AA.