Reduced scar maturation and contractility lead to exaggerated left ventricular dilation after myocardial infarction in mice lacking AMPKα1

Simvastatin attenuates silica-induced pulmonary inflammation and fibrosis in rats via the AMPK-NOX pathway

BACKGROUND

Simvastatin (Sim), a hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, has been widely used in prevention and treatment of cardiovascular diseases. Studies have suggested that Sim exerts anti-fibrotic effects by interfering fibroblast proliferation and collagen synthesis. This study was to determine whether Sim could alleviate silica-induced pulmonary fibrosis and explore the underlying mechanisms.

METHODS

The rat model of silicosis was established by the tracheal perfusion method and treated with Sim (5 or 10 mg/kg), AICAR (an AMPK agonist), and apocynin (a NOX inhibitor) for 28 days. Lung tissues were collected for further analyses including pathological histology, inflammatory response, oxidative stress, epithelial mesenchymal transformation (EMT), and the AMPK-NOX pathway.

RESULTS

Sim significantly reduced silica-induced pulmonary inflammation and fibrosis at 28 days after administration. Sim could reduce the levels of interleukin (IL)-1β, IL-6, tumor necrosis factor-α and transforming growth factor-β1 in lung tissues. The expressions of hydroxyproline, α-SMA and vimentin were down-regulated, while E-cad was increased in Sim-treated rats. In addition, NOX4, p22pox, p40phox, p-p47phox/p47phox expressions and ROS levels were all increased, whereas p-AMPK/AMPK was decreased in silica-induced rats. Sim or AICAR treatment could notably reverse the decrease of AMPK activity and increase of NOX activity induced by silica. Apocynin treatment exhibited similar protective effects to Sim, including down-regulating of oxidative stress and inhibition of the EMT process and inflammatory reactions.

CONCLUSIONS

Sim attenuates silica-induced pulmonary inflammation and fibrosis by downregulating EMT and oxidative stress through the AMPK-NOX pathway.

CYP2J2-derived epoxyeicosatrienoic acids protect against doxorubicin-induced cardiotoxicity by reducing oxidative stress and apoptosis via activation of the AMPK pathway

Objective

Despite the widespread use of doxorubicin (DOX) in chemotherapy, it can cause cardiotoxicity, which severely limits its potential clinical use. CYP2J2-derived epoxyeicosatrienoic acids (EETs) exert cardioprotective effects by maintaining cardiac homeostasis. The roles and latent mechanisms of EETs in DOX cardiotoxicity remain uncertain. We investigated these aspects using mouse tissue and cell culture models.

Methods

C57BL/6J mice were injected with rAAV9-CYP2J2 or a control vector via the caudal vein. A five-week intraperitoneal course of DOX (5 mg/kg per week) was administered. After pretreatment with 14,15-EET, H9C2 cells were treated for 24-h with DOX, to use as a cell model to verify the role of EETs in cardiotoxicity in vitro.

Results

CYP2J2 overexpression mitigated DOX-induced cardiotoxicity, as shown by the diminished cardiac injury marker levels, improved heart function, reduced oxidative stress, and inhibition of myocardial apoptosis in vivo. These protective roles are associated with the enhancement of antioxidant and anti-apoptotic abilities and the activation of the AMPK pathway. 14,15-EET suppresses DOX-induced oxidative stress, mitochondrial dysfunction, and apoptosis in H9C2 cells. AMPK knockdown partially abolished the cardioprotective effects of 14,15-EET against oxidative damage and apoptosis in DOX-treated cells, suggesting that AMPK is responsible for EET-mediated protection against cardiotoxicity.

Conclusion

CYP2J2-derived EETs confer myocardial protection against DOX-induced toxicity by activating the AMPK pathway, which reduces oxidative stress, mitochondrial dysfunction, and apoptosis.

S-nitrosylation of AMPKγ impairs coronary collateral circulation and disrupts VSMC reprogramming

Collateral circulation is essential for blood resupply to the ischemic heart, which is dictated by the contractile phenotypic restoration of vascular smooth muscle cells (VSMC). Here we investigate whether S-nitrosylation of AMP-activated protein kinase (AMPK), a key regulator of the VSMC phenotype, impairs collateral circulation. In rats with collateral growth and development, nitroglycerin decreases coronary collateral blood flow (CCBF), inhibits vascular contractile phenotypic restoration, and increases myocardial infarct size, accompanied by reduced AMPK activity in the collateral zone. Nitric oxide (NO) S-nitrosylates human recombinant AMPKγ1 at cysteine 131 and decreases AMP sensitivity of AMPK. In VSMCs, exogenous expression of S-nitrosylation-resistant AMPKγ1 or deficient NO synthase (iNOS) prevents the disruption of VSMC reprogramming. Finally, hyperhomocysteinemia or hyperglycemia increases AMPKγ1 S-nitrosylation, prevents vascular contractile phenotypic restoration, reduces CCBF, and increases the infarct size of the heart in Apoe-/- mice, all of which is rescued in Apoe-/-/iNOSsm-/- mice or Apoe-/- mice with enforced expression of the AMPKγ1-C130A mutant following RI/MI. We conclude that nitrosative stress disrupts coronary collateral circulation during hyperhomocysteinemia or hyperglycemia through AMPK S-nitrosylation.

Exercise Training Attenuates Acute β-Adrenergic Receptor Activation-Induced Cardiac Inflammation via the Activation of AMP-Activated Protein Kinase

Exercise has proven cardiac benefits, but the underlying mechanisms of exercise that protect the heart from acute sympathetic stress injuries remain unknown. In this study, adult C57BL/6J mice and their AMP-activated protein kinase α2 knockout (AMPKα2^-/-) littermates were either subjected to 6 weeks of exercise training or housed under sedentary conditions and then treated with or without a single subcutaneous injection of the β-adrenergic receptor (β-AR) agonist isoprenaline (ISO). We investigated the differences in the protective effects of exercise training on ISO-induced cardiac inflammation in wild-type (WT) and AMPKα2^-/- mice using histology, enzyme-linked immunosorbent assay (ELISA) and Western blotting analyses. The results indicated that exercise training alleviated ISO-induced cardiac macrophage infiltration, chemokines and the expression of proinflammatory cytokines in wild-type mice. A mechanism study showed that exercise training attenuated the ISO-induced production of reactive oxygen species (ROS) and the activation of NLR Family, pyrin domain-containing 3 (NLRP3) inflammasomes. In cardiomyocytes, the ISO-induced effects on these processes were inhibited by AMP-activated protein kinase (AMPK) activator (metformin) pretreatment and reversed by the AMPK inhibitor (compound C). AMPKα2^-/- mice showed more extensive cardiac inflammation following ISO exposure than their wild-type littermates. These results indicated that exercise training could attenuate ISO-induced cardiac inflammation by inhibiting the ROS-NLRP3 inflammasome pathway in an AMPK-dependent manner. Our findings suggested the identification of a novel mechanism for the cardioprotective effects of exercise.

Cardiac System during the Aging Process

The aging process is accompanied by a continuous decline of the cardiac system, disrupting the homeostatic regulation of cells, organs, and systems. Aging increases the prevalence of cardiovascular diseases, thus heart failure and mortality. Understanding the cardiac aging process is of pivotal importance once it allows us to design strategies to prevent age-related cardiac events and increasing the quality of live in the elderly. In this review we provide an overview of the cardiac aging process focus on the following topics: cardiac structural and functional modifications; cellular mechanisms of cardiac dysfunction in the aging; genetics and epigenetics in the development of cardiac diseases; and aging heart and response to the exercise.

Metformin reduces myogenic contracture and myofibrosis induced by rat knee joint immobilization via AMPK-mediated inhibition of TGF-β1/Smad signaling pathway

PURPOSE

The two structural components contributing to joint contracture formation are myogenic and arthrogenic contracture, and myofibrosis is an important part of myogenic contracture. Myofibrosis is a response to long-time immobilization and is described as a condition with excessive deposition of endomysial and perimysial connective tissue components in skeletal muscle. The purpose of this study was to confirm whether metformin can attenuate the formation of myogenic contracture and myofibrosis through the phosphorylation level of adenosine monophosphate-activated protein kinase (AMPK) and inhabitation of subsequent transforming growth factor beta (TGF-β) 1/Smad signaling pathway.

MATERIALS AND METHODS

An immobilized rat model was used to determine whether metformin could inhibit myogenic contracture and myofibrosis. The contents of myogenic contracture of knee joint was calculated by measuring instrument of range of motion (ROM), and myofibrosis of rectus femoris were determined by ultrasound shear wave elastography and Masson staining. Protein expression of AMPK and subsequent TGF-β1/Smad signaling pathway were determined by western blot. Subsequently, Compound C, a specific AMPK inhibitor, was used to further clarify the role of the AMPK-mediated inhibition of TGF-β1/Smad signaling pathway.

RESULTS

We revealed that the levels of myogenic contracture and myofibrosis were gradually increased during immobilization, and overexpression of TGF-β1-induced formation of myofibrosis by activating Smad2/3 phosphorylation. Activation of AMPK by metformin suppressed overexpression of TGF-β1 and TGF-β1-induced Smad2/3 phosphorylation, further reducing myogenic contracture and myofibrosis during immobilization. In contrast, inhibition of AMPK by Compound C partially counteracted the inhibitory effect of TGF-β1/Smad signaling pathway by metformin.

CONCLUSION

Notably, we first illustrated the therapeutic effect of metformin through AMPK-mediated inhibition of TGF-β1/Smad signaling pathway in myofibrosis, which may provide a new therapeutic strategy for myogenic contracture.

IMM-H007 attenuates isoprenaline-induced cardiac fibrosis through targeting TGFβ1 signaling pathway

Upon chronic stress, β-adrenergic receptor activation induces cardiac fibrosis and leads to heart failure. The small molecule compound IMM-H007 has demonstrated protective effects in cardiovascular diseases via activation of AMP-activated protein kinase (AMPK). This study aimed to investigate IMM-H007 effects on cardiac fibrosis induced by β-adrenergic receptor activation. Because adenosine analogs also exert AMPK-independent effects, we assessed AMPK-dependent and -independent IMM-H007 effects in murine models of cardiac fibrosis. Continual subcutaneous injection of isoprenaline for 7 days caused cardiac fibrosis and cardiac dysfunction in mice in vivo. IMM-H007 attenuated isoprenaline-induced cardiac fibrosis, diastolic dysfunction, α-smooth muscle actin expression, and collagen I deposition in both wild-type and AMPKα2-/- mice. Moreover, IMM-H007 inhibited transforming growth factor β1 (TGFβ1) expression in wild-type, but not AMPKα2-/- mice. By contrast, IMM-H007 inhibited Smad2/3 signaling downstream of TGFβ1 in both wild-type and AMPKα2-/- mice. Surface plasmon resonance and molecular docking experiments showed that IMM-H007 directly interacts with TGFβ1, inhibits its binding to TGFβ type II receptors, and downregulates the Smad2/3 signaling pathway downstream of TGFβ1. These findings suggest that IMM-H007 inhibits isoprenaline-induced cardiac fibrosis via both AMPKα2-dependent and -independent mechanisms. IMM-H007 may be useful as a novel TGFβ1 antagonist.

Natural AMPK Activators in Cardiovascular Disease Prevention

Cardiovascular diseases (CVD), as a life-threatening global disease, is receiving worldwide attention. Seeking novel therapeutic strategies and agents is of utmost importance to curb CVD. AMP-activated protein kinase (AMPK) activators derived from natural products are promising agents for cardiovascular drug development owning to regulatory effects on physiological processes and diverse cardiometabolic disorders. In the past decade, different therapeutic agents from natural products and herbal medicines have been explored as good templates of AMPK activators. Hereby, we overviewed the role of AMPK signaling in the cardiovascular system, as well as evidence implicating AMPK activators as potential therapeutic tools. In the present review, efforts have been made to compile and update relevant information from both preclinical and clinical studies, which investigated the role of natural products as AMPK activators in cardiovascular therapeutics.

Effects of Metformin in Heart Failure: From Pathophysiological Rationale to Clinical Evidence

Type 2 diabetes mellitus (T2DM) is a worldwide major health burden and heart failure (HF) is the most common cardiovascular (CV) complication in affected patients. Therefore, identifying the best pharmacological approach for glycemic control, which is also useful to prevent and ameliorate the prognosis of HF, represents a crucial issue. Currently, the choice is between the new drugs sodium/glucose co-transporter 2 inhibitors that have consistently shown in large CV outcome trials (CVOTs) to reduce the risk of HF-related outcomes in T2DM, and metformin, an old medicament that might end up relegated to the background while exerting interesting protective effects on multiple organs among which include heart failure. When compared with other antihyperglycemic medications, metformin has been demonstrated to be safe and to lower morbidity and mortality for HF, even if these results are difficult to interpret as they emerged mainly from observational studies. Meta-analyses of randomized controlled clinical trials have not produced positive results on the risk or clinical course of HF and sadly, large CV outcome trials are lacking. The point of force of metformin with respect to new diabetic drugs is the amount of data from experimental investigations that, for more than twenty years, still continues to provide mechanistic explanations of the several favorable actions in heart failure such as, the improvement of the myocardial energy metabolic status by modulation of glucose and lipid metabolism, the attenuation of oxidative stress and inflammation, and the inhibition of myocardial cell apoptosis, leading to reduced cardiac remodeling and preserved left ventricular function. In the hope that specific large-scale trials will be carried out to definitively establish the metformin benefit in terms of HF failure outcomes, we reviewed the literature in this field, summarizing the available evidence from experimental and clinical studies reporting on effects in heart metabolism, function, and structure, and the prominent pathophysiological mechanisms involved.

Identification of the distinctive role of DPT in dilated cardiomyopathy: a study based on bulk and single-cell transcriptomic analysis

Background

Dilated cardiomyopathy (DCM) is a common cause of heart failure. Cardiac remodeling is the main pathological change in DCM, yet the molecular mechanism is still unclear. Therefore, the present study aims to find potential crucial genes and regulators through bulk and single-cell transcriptomic analysis.

Methods

Three microarray datasets of DCM (GSE57338, GSE42955, GSE79962) were chosen from gene expression omnibus (GEO) to analyze the differentially expressed genes (DEGs). LASSO regression, SVM-RFE, and PPI network methods were then carried out to identify key genes. Another dataset (GSE116250) was used to validate these findings. To further identify DCM-associated specific cell types, transcription factors, and cell-cell interaction networks, GSEA, SCENIC, and CellPhoneDB were conducted on public datasets for single-cell RNA sequencing analysis of DCM (GSE109816 and GSE121893). Finally, reverse transcription-polymerase chain reaction (RT-PCR), western blot, and immunohistochemical were performed to validate DPT expression in fibroblasts and DCM.

Results

There were 281 DEGs between DCM and non-failing donors. CCL5 and DPT were identified to be key genes and both genes had a 0.844 area under the receiver operating curve (AUC) in the validation dataset. Further single-cell sequencing analysis revealed three main findings: (I) DPT was mainly expressed in fibroblasts and was significantly upregulated in DCM fibroblasts; (II) DPT⁺ fibroblasts were involved in the organization of the extracellular matrix (ECM) and collagen fibrils and were regulated by the transcription factor STAT3; and (III) DPT⁺ fibroblasts had high interactions with endothelial cells through including Ephrin-Eph, ACKR-CXCL, and JAG-NOTCH signal pathways. RT-PCR, western blot, and immunohistochemical confirmed that DPT was highly expressed and co-localized with Vimentin and p-STAT3 in DCM patients. STAT3 inhibitor S3I-201 reduced the expression of DPT in mouse cardiac fibroblasts.

Conclusions

DPT could be used as a diagnostic marker and therapeutic target of DCM. DPT⁺ fibroblasts could be a novel regulator of the cardiac remodeling process in DCM.

Spatiotemporal AMPKα2 deletion in mice induces cardiac dysfunction, fibrosis and cardiolipin remodeling associated with mitochondrial dysfunction in males only

Background

The AMP-activated protein kinase (AMPK) is a major regulator of cellular energetics which plays key role in acute metabolic response and in long-term adaptation to stress. Recent works have also suggested non-metabolic effects.

Methods

To decipher AMPK roles in the heart, we generated a cardio-specific inducible model of gene deletion of the main cardiac catalytic subunit of AMPK (Ampkα2) in mice. This allowed us to avoid the eventual impact of AMPK-KO in peripheral organs.

Results

Cardio-specific Ampkα2 deficiency led to a progressive left ventricular systolic dysfunction and the development of cardiac fibrosis in males. We observed a reduction in complex I-driven respiration without change in mitochondrial mass or in vitro complex I activity, associated with a rearrangement of the cardiolipins and reduced integration of complex I into the electron transport chain supercomplexes. Strikingly, none of these defects were present in females. Interestingly, suppression of estradiol signaling by ovariectomy partially mimicked the male sensitivity to AMPK loss, notably the cardiac fibrosis and the rearrangement of cardiolipins, but not the cardiac function that remained protected.

Conclusion

Our results confirm the close link between AMPK and cardiac mitochondrial function, but also highlight links with cardiac fibrosis. Importantly, we show that AMPK is differently involved in these processes in males and females, which may have clinical implications for the use of AMPK activators in the treatment of heart failure.

AMPK is a metabolic sensor of cellular energy which regulates energy homeostasis.

We generated a cardiac-specific inducible deletion of Ampkα2 and demonstrated that this deletion induces mild cardiac dysfunction in male only.

Cardiac dysfunction observed in males was associated with cardiac fibrosis and cardiac cardiolipin remodeling that are not seen in females.

Although no significant cardiac function alteration was noticed in ovariectomized female Ampkα2ciKO mice, these latter exhibited cardiac fibrosis and mild cardiolipins remodeling.

Our results show a higher dependence on AMPK signaling fibrosis and cardiolipin biosynthesis/maturation in males, either due to the absence of female hormones protection or/and to the action of male hormones. This may contribute to the known difference in cardiovascular risk and outcome between sexes.

Dynamic Regulation of Cysteine Oxidation and Phosphorylation in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury significantly alters heart function following infarct and increases the risk of heart failure. Many studies have sought to preserve irreplaceable myocardium, termed cardioprotection, but few, if any, treatments have yielded a substantial reduction in clinical I/R injury. More research is needed to fully understand the molecular pathways that govern cardioprotection. Redox mechanisms, specifically cysteine oxidations, are acute and key regulators of molecular signaling cascades mediated by kinases. Here, we review the role of reactive oxygen species in modifying cysteine residues and how these modifications affect kinase function to impact cardioprotection. This exciting area of research may provide novel insight into mechanisms and likely lead to new treatments for I/R injury.

Lysyl oxidase inhibitors attenuate cyclosporin A-induced nephropathy in mouse

Calcineurin inhibitors, such as Cyclosporin (CsA), are the mainstay of anti-rejection therapy in solid organ transplants but can paradoxically induce progressive nephropathy characterised by renal dysfunction and interstitial fibrosis. Lysyl oxidases (LOXs), a group of enzymes that catalyse extracellular matrix (ECM) crosslinking, were shown to implicate in tissue scarring. It is hypothesized that inhibition of these enzymes may render therapeutic effects against CsA-induced nephropathy. In this study, 6-to-8 weeks old C57BL/6 J mice were administered saline or CsA (30 mg/kg/day s.c) for 16 weeks. At 8 weeks, CsA-treated animals were divided into 5 groups respectively treated with: (1) vehicle, (2) PXS-5505 (Pan-LOX inhibitor), (3) PXS-5382 (LOX-like 2 inhibitor), (4) PXS-5505 for 4 weeks then PXS-5382 for 4 weeks (sequential therapy), and (5) Telmisartan (standard therapy). Our results indicate that CsA administration significantly increased the levels of blood urea nitrogen, glomerular and tubular injury, tubulointerstitial fibrosis, inflammation and oxidative stress in mouse kidney. These changes were associated with upregulated mRNA expression of LOX and LOXL2. Administration of Pan-LOX or LOXL2 inhibitors or the sequential therapy suppressed the expression of ECM proteins (α-SMA, FN and COL1A), matrix metalloproteases (MMP)2 and 9, inflammatory markers (TNFα and MCP-1) and TGF-β1-Smad3 signalling. Among all regimens including telmisartan, only Pan-LOX inhibitor PXS-5505 was able to attenuate uraemia. Collectively, our study suggests that Pan-LOX and LOXL2 inhibition can attenuate progressive nephropathy due to CsA administration.

The novel ginsenoside AD2 prevents angiotensin II-induced connexin 40 and connexin 43 dysregulation by activating AMP kinase signaling in perfused beating rat atria

Connexin-40 (Cx40) and Cx43 are the principal components of gap junctions. Dysregulation of connexin expression is clinically related to cardiac pathologies. 25-Hydroxy protopanaxadiol [25-OH-PPD, 20 (R)-dammarane-3β, 12β, 20, 25-tetrol], known as AD2, is a novel protopanaxadiol extracted from Panax ginseng that exhibits many pharmacological activities, but its effects on cardiac gap junctions are poorly understood. The aim of this study was to evaluate the effects of AD2 on angiotensin II (Ang II)-induced Cx40 and Cx43 dysregulation. In this study, isolated beating rat atria were perfused with Ang II (5 μM) for 1 h to induce Cx40 and Cx43 dysregulation. The effects of AD2 (1.6, 16, and 160 μg/100 g body weight) on Ang II-induced hemodynamics in rats were analyzed by biological recorder, and changes in proteins levels were analyzed by western blotting. The results showed that AD2 ameliorated Ang II-induced hyper hemodynamics and abnormal P-waves, and prevented fibrotic collagen deposition (3.77% ± 1.64%-26.31% ± 1.64% with Ang II, 5.76% ± 0.94% with AD2). Ang II upregulated expression of nuclear factor kappa B, activator protein 1, and transforming growth factor β1, and downregulated of Cx40 and Cx43 expression, which were inhibited by AD2 concomitantly with increased of AMP-activated protein kinase (AMPK) expression via liver kinase B1 activation. The present findings suggest that AD2 inhibited Ang II-induced dysregulation of Cx40 and Cx43 via activation of AMPK signaling, thus highlighting the promise and utility of AD2 for treatment of connexin dysregulation-related heart disease.

Limb-bud and Heart (LBH) mediates proliferation, fibroblast-to-myofibroblast transition and EMT-like processes in cardiac fibroblasts

Cardiac fibrosis is an important pathological change after myocardial infarction (MI). Its progression is essential for post-MI infarct healing, during which transforming growth factor beta1 (TGF-β1) plays a critical role. Limb-bud and Heart (LBH), a newly discovered target gene of TGF-β1, was shown to promote normal cardiogenesis. αB-crystallin (CRYAB), an LBH-interacting protein, was demonstrated to be involved in TGF-β1-induced fibrosis. The roles and molecular mechanisms of LBH and CRYAB during cardiac fibrosis remain largely unexplored. In this study, we investigated the alterations of LBH and CRYAB expression in mouse cardiac tissue after MI. LBH and CRYAB were upregulated in activated cardiac fibroblasts (CFs), while in vitro TGF-β1 stimulation induced the upregulation of LBH, CRYAB, and fibrogenic genes in primary CFs of neonatal rats. The results of the ectopic expression of LBH proved that LBH accelerated CF proliferation under hypoxia, mediated the expression of CRYAB and fibrogenic genes, and promoted epithelial-mesenchymal transition (EMT)-like processes in rat CFs, while subsequent CRYAB silencing reversed the effects induced by elevated LBH expression. We also verified the protein-protein interaction (PPI) between LBH and CRYAB in fibroblasts. In summary, our work demonstrated that LBH promotes the proliferation of CFs, mediates TGF-β1-induced fibroblast-to-myofibroblast transition and EMT-like processes through CRYAB upregulation, jointly functioning in post-MI infarct healing. These findings suggest that LBH could be a promising potential target for the study of cardiac repair and cardiac fibrosis.

Fibrosis after Myocardial Infarction: An Overview on Cellular Processes, Molecular Pathways, Clinical Evaluation and Prognostic Value

The ischemic injury caused by myocardial infarction activates a complex healing process wherein a powerful inflammatory response and a reparative phase follow and balance each other. An intricate network of mediators finely orchestrate a large variety of cellular subtypes throughout molecular signaling pathways that determine the intensity and duration of each phase. At the end of this process, the necrotic tissue is replaced with a fibrotic scar whose quality strictly depends on the delicate balance resulting from the interaction between multiple actors involved in fibrogenesis. An inflammatory or reparative dysregulation, both in term of excess and deficiency, may cause ventricular dysfunction and life-threatening arrhythmias that heavily affect clinical outcome. This review discusses cellular process and molecular signaling pathways that determine fibrosis and the imaging technique that can characterize the clinical impact of this process in-vivo.

AMPKα1 deletion in myofibroblasts exacerbates post-myocardial infarction fibrosis by a connexin 43 mechanism

We have previously demonstrated that systemic AMP-activated protein kinase α1 (AMPKα1) invalidation enhanced adverse LV remodelling by increasing fibroblast proliferation, while myodifferentiation and scar maturation were impaired. We thus hypothesised that fibroblastic AMPKα1 was a key signalling element in regulating fibrosis in the infarcted myocardium and an attractive target for therapeutic intervention. The present study investigates the effects of myofibroblast (MF)-specific deletion of AMPKα1 on left ventricular (LV) adaptation following myocardial infarction (MI), and the underlying molecular mechanisms. MF-restricted AMPKα1 conditional knockout (cKO) mice were subjected to permanent ligation of the left anterior descending coronary artery. cKO hearts exhibit exacerbated post-MI adverse LV remodelling and are characterised by exaggerated fibrotic response, compared to wild-type (WT) hearts. Cardiac fibroblast proliferation and MF content significantly increase in cKO infarcted hearts, coincident with a significant reduction of connexin 43 (Cx43) expression in MFs. Mechanistically, AMPKα1 influences Cx43 expression by both a transcriptional and a post-transcriptional mechanism involving miR-125b-5p. Collectively, our data demonstrate that MF-AMPKα1 functions as a master regulator of cardiac fibrosis and remodelling and might constitute a novel potential target for pharmacological anti-fibrotic applications.

Roles of AMP-Activated Protein Kinase (AMPK) in Mammalian Reproduction

Reproduction is an energy demanding function and only take place in case of sufficient available energy status in mammals. Metabolic diseases such as anorexia nervosa are clinically associated with reduced fertility. AMP-activated protein kinase (AMPK), as a major regulator of cellular energy homeostasis, is activated in limited energy reserves to ensure the orderly progress of various physiological activities. In recent years, mounting evidence shows that AMPK is involved in the regulation of reproductive function through multiple mechanisms. AMPK is likely to be a metabolic sensor integrating central and peripheral signals. In this review, we aim to explore the preclinical studies published in the last decade that investigate the role of AMP-activated protein kinase in the reproductive field, and its role as a target for drug therapy of reproductive system-related diseases. We also emphasized the emerging roles of AMPK in transcriptional regulation of reproduction processes and metabolisms, which are tightly related to the energy state and fertility of an organism.

Glucose transporters in cardiovascular system in health and disease

Glucose transporters are essential for the heart to sustain its function. Due to its nature as a high energy-consuming organ, the heart needs to catabolize a huge quantity of metabolic substrates. For optimized energy production, the healthy heart constantly switches between various metabolites in accordance with substrate availability and hormonal status. This metabolic flexibility is essential for the maintenance of cardiac function. Glucose is part of the main substrates catabolized by the heart and its use is fine-tuned via complex molecular mechanisms that include the regulation of the glucose transporters GLUTs, mainly GLUT4 and GLUT1. Besides GLUTs, glucose can also be transported by cotransporters of the sodium-glucose cotransporter (SGLT) (SLC5 gene) family, in which SGLT1 and SMIT1 were shown to be expressed in the heart. This SGLT-mediated uptake does not seem to be directly linked to energy production but is rather associated with intracellular signalling triggering important processes such as the production of reactive oxygen species. Glucose transport is markedly affected in cardiac diseases such as cardiac hypertrophy, diabetic cardiomyopathy and heart failure. These alterations are not only fingerprints of these diseases but are involved in their onset and progression. The present review will depict the importance of glucose transport in healthy and diseased heart, as well as proposed therapies targeting glucose transporters.

α1AMP-Activated Protein Kinase Protects against Lipopolysaccharide-Induced Endothelial Barrier Disruption via Junctional Reinforcement and Activation of the p38 MAPK/HSP27 Pathway

Vascular hyperpermeability is a determinant factor in the pathophysiology of sepsis. While, AMP-activated protein kinase (AMPK) is known to play a role in maintaining endothelial barrier function in this condition. Therefore, we investigated the underlying molecular mechanisms of this protective effect. α1AMPK expression and/or activity was modulated in human dermal microvascular endothelial cells using either α1AMPK-targeting small interfering RNA or the direct pharmacological AMPK activator 991, prior to lipopolysaccharide (LPS) treatment. Western blotting was used to analyze the expression and/or phosphorylation of proteins that compose cellular junctions (zonula occludens-1 (ZO-1), vascular endothelial cadherin (VE-Cad), connexin 43 (Cx43)) or that regulate actin cytoskeleton (p38 MAPK; heat shock protein 27 (HSP27)). Functional endothelial permeability was assessed by in vitro Transwell assays, and quantification of cellular junctions in the plasma membrane was assessed by immunofluorescence. Actin cytoskeleton remodeling was evaluated through actin fluorescent staining. We consequently demonstrate that α1AMPK deficiency is associated with reduced expression of CX43, ZO-1, and VE-Cad, and that the drastic loss of CX43 is likely responsible for the subsequent decreased expression and localization of ZO-1 and VE-Cad in the plasma membrane. Moreover, α1AMPK activation by 991 protects against LPS-induced endothelial barrier disruption by reinforcing cortical actin cytoskeleton. This is due to a mechanism that involves the phosphorylation of p38 MAPK and HSP27, which is nonetheless independent of the small GTPase Rac1. This results in a drastic decrease of LPS-induced hyperpermeability. We conclude that α1AMPK activators that are suitable for clinical use may provide a specific therapeutic intervention that limits sepsis-induced vascular leakage.

Lower Body Weight in Rats Under Hypobaric Hypoxia Exposure Would Lead to Reduced Right Ventricular Hypertrophy and Increased AMPK Activation

Background

Both chronic hypoxia (CH) and long-term chronic intermittent hypoxia (CIH) exposure lead to right ventricular hypertrophy (RVH). Weight loss is an effective intervention to improve cardiac function and energy metabolism in cardiac hypertrophy. Likewise, caloric restriction (CR) also plays an important role in this cardioprotection through AMPK activation. We aimed to determine the influence of body weight (BW) on RVH, AMPK and related variables by comparing rats exposed to both hypoxic conditions.

Methods

Sixty male adult rats were separated into two groups (n = 30 per group) according to their previous diet: a caloric restriction (CR) group and an ad libitum (AL) group. Rats in both groups were randomly assigned to 3 groups: a normoxic group (NX, n = 10), a CIH group (2 days hypoxia/2 days normoxia; n = 10) and a CH group (n = 10). The CR group was previously fed 10 g daily, and the other was fed ad libitum. Rats were exposed to simulated hypobaric hypoxia in a hypobaric chamber set to 428 Torr (the equivalent pressure to that at an altitude of 4,600 m above sea level) for 30 days. Measurements included body weight; hematocrit; serum insulin; glycemia; the degree of RVH (Fulton's index and histology); and AMPK, mTOR, and PP2C expression levels in the right ventricle determined by western blotting.

Results

A lower degree of RVH, higher AMPK activation, and no activation of mTOR were found in the CR groups exposed to hypobaric hypoxia compared to the AL groups (p < 0.05). Additionally, decreased glycemia and serum insulin levels were observed. Interestingly, PP2C expression showed an increase in the AL groups but not in the CR groups (p < 0.05).

Conclusion

Maintaining a low weight before and during exposure to high-altitude hypoxia, during either CH or CIH, could prevent a major degree of RVH. This cardioprotection would likely be due to the activation of AMPK. Thus, body weight is a factor that might contribute to RVH at high altitudes.

A functional role for AMPK in female fertility and endometrial regeneration

Adenosine monophosphate-activated protein kinase (AMPK) is a highly conserved heterotrimeric complex that acts as an intracellular energy sensor. Based on recent observations of AMPK expression in all structures of the female reproductive system, we hypothesized that AMPK is functionally required for maintaining fertility in the female. This hypothesis was tested by conditionally ablating the two catalytic alpha subunits of AMPK, Prkaa1 and Prkaa2, using Pgr-cre mice. After confirming the presence of PRKAA1, PRKAA2 and the active phospho-PRKAA1/2 in the gravid uterus by immunohistochemistry, control (Prkaa1/2 fl/fl ) and double conditional knockout mice (Prkaa1/2 d/d ) were placed into a six-month breeding trial. While the first litter size was comparable between Prkaa1/2 fl/fl and Prkaa1/2 d/d female mice (P = 0.8619), the size of all subsequent litters was dramatically reduced in Prkaa1/2 d/d female mice (P = 0.0015). All Prkaa1/2 d/d female mice experienced premature reproductive senescence or dystocia by the fourth parity. This phenotype manifested despite no difference in estrous cycle length, ovarian histology in young and old nulliparous or multiparous animals, mid-gestation serum progesterone levels or uterine expression of Esr1 or Pgr between Prkaa1/2 fl/fl and Prkaa1/2 d/d female mice suggesting that the hypothalamic-pituitary-ovary axis remained unaffected by PRKAA1/2 deficiency. However, an evaluation of uterine histology from multiparous animals identified extensive endometrial fibrosis and disorganized stromal-glandular architecture indicative of endometritis, a condition that causes subfertility or infertility in most mammals. Interestingly, Prkaa1/2 d/d female mice failed to undergo artificial decidualization. Collectively, these findings suggest that AMPK plays an essential role in endometrial regeneration following parturition and tissue remodeling that accompanies decidualization.

The Role of Lysyl Oxidase Enzymes in Cardiac Function and Remodeling

Lysyl oxidase (LOX) proteins comprise a family of five copper-dependent enzymes (LOX and four LOX-like isoenzymes (LOXL1-4)) critical for extracellular matrix (ECM) homeostasis and remodeling. The primary role of LOX enzymes is to oxidize lysyl and hydroxylysyl residues from collagen and elastin chains into highly reactive aldehydes, which spontaneously react with surrounding amino groups and other aldehydes to form inter- and intra-catenary covalent cross-linkages. Therefore, they are essential for the synthesis of a mature ECM and assure matrix integrity. ECM modulates cellular phenotype and function, and strikingly influences the mechanical properties of tissues. This explains the critical role of these enzymes in tissue homeostasis, and in tissue repair and remodeling. Cardiac ECM is mainly composed of fibrillar collagens which form a complex network that provides structural and biochemical support to cardiac cells and regulates cell signaling pathways. It is now becoming apparent that cardiac performance is affected by the structure and composition of the ECM and that any disturbance of the ECM contributes to cardiac disease progression. This review article compiles the major findings on the contribution of the LOX family to the development and progression of myocardial disorders.

P2Y12 antagonists and cardiac repair post-myocardial infarction: global and regional heart function analysis and molecular assessments in pigs

Aims

P2Y12 antagonists are the standard in antiplatelet therapy but their potential effects on functional myocardial recovery and cardioprotection post-myocardial infarction (MI) are unknown. We investigated in a preclinical model of MI whether ticagrelor and clopidogrel differently affect cardiac repair post-MI.

Methods and results

Pigs either received: (i) clopidogrel (600 mg; 75 mg/qd); (ii) ticagrelor (180 mg; 90 mg/bid); and (iii) placebo control. MI was induced by mid-left anterior descending coronary artery balloon occlusion (60 min) and animals received the maintenance doses for the following 42 days. Serial cardiac magnetic resonance was performed at Day 3 and Day 42 for the assessment of global and regional cardiac parameters. We determined cardiac AMP-activated protein kinase (AMPK), Akt/PKB, aquaporin-4, vascular density, and fibrosis. In comparison to controls, both P2Y12 antagonists limited infarct expansion at Day 3, although ticagrelor induced a further 5% reduction (P < 0.05 vs. clopidogrel) whereas oedema was only reduced by ticagrelor (≈23% P < 0.05). Scar size decreased at Day 42 in ticagrelor-treated pigs vs. controls but not in clopidogrel-treated pigs. Left ventricular ejection fraction was higher 3 days post-MI in ticagrelor-treated pigs and persisted up to Day 42 (P < 0.05 vs. post-MI). Regional analysis revealed that control and clopidogrel-treated pigs had severe and extensive wall motion abnormalities in the jeopardized myocardium and a reduced myocardial viability that was not as evident in ticagrelor-treated pigs (χ2P < 0.05 vs. ticagrelor). Only ticagrelor enhanced myocardial AMPK and Akt/PKB activation and reduced aquaporin-4 levels (P < 0.05 vs. control and clopidogrel). No differences were observed in vessel density and fibrosis markers among groups.

Conclusions

Ticagrelor is more efficient than clopidogrel in attenuating myocardial structural and functional alterations post-MI and in improving cardiac healing. These benefits are associated with persistent AMPK and Akt/PKB activation.

Spermidine-enhanced autophagic flux improves cardiac dysfunction following myocardial infarction by targeting the AMPK/mTOR signalling pathway

BACKGROUND AND PURPOSE

Spermidine, a natural polyamine, is abundant in mammalian cells and is involved in cell growth, proliferation, and regeneration. Recently, oral spermidine supplements were cardioprotective in age-related cardiac dysfunction, through enhancing autophagic flux. However, the effect of spermidine on myocardial injury and cardiac dysfunction following myocardial infarction (MI) remains unknown.

EXPERIMENTAL APPROACH

We determined the effects of spermidine in a model of MI, Sprague-Dawley rats with permanent ligation of the left anterior descending artery, and in cultured neonatal rat cardiomyocytes (NRCs) exposed to angiotensin II (Ang II). Cardiac function in vivo was assessed with echocardiography. In vivo and in vitro studies used histological and immunohistochemical techniques, along with western blots.

KEY RESULTS

Spermidine improved cardiomyocyte viability and decreased cell necrosis in NRCs treated with angiotensin II. In rats post-MI, spermidine reduced infarct size, improved cardiac function, and attenuated myocardial hypertrophy. Spermidine also suppressed the oxidative damage and inflammatory cytokines induced by MI. Moreover, spermidine enhanced autophagic flux and decreased apoptosis both in vitro and in vivo. The protective effects of spermidine on cardiomyocyte apoptosis and cardiac dysfunction were abolished by the autophagy inhibitor chloroquine, indicating that spermidine exerted cardioprotective effects at least partly through promoting autophagic flux, by activating the AMPK/mTOR signalling pathway.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that spermidine improved MI-induced cardiac dysfunction by promoting AMPK/mTOR-mediated autophagic flux.

Cardiac fibrosis: new insights into the pathogenesis

Cardiac fibrosis is defined as the imbalance of extracellular matrix (ECM) production and degradation, thus contributing to cardiac dysfunction in many cardiac pathophysiologic conditions. This review discusses specific markers and origin of cardiac fibroblasts (CFs), and the underlying mechanism involved in the development of cardiac fibrosis. Currently, there are no CFs-specific molecular markers. Most studies use co-labelling with panels of antibodies that can recognize CFs. Origin of fibroblasts is heterogeneous. After fibrotic stimuli, the levels of myocardial pro-fibrotic growth factors and cytokines are increased. These pro-fibrotic growth factors and cytokines bind to its receptors and then trigger the activation of signaling pathway and transcriptional factors via Smad-dependent or Smad independent-manners. These fibrosis-related transcriptional factors regulate gene expression that are involved in the fibrosis to amplify the fibrotic response. Understanding the mechanisms responsible for initiation, progression, and amplification of cardiac fibrosis are of great clinical significance to find drugs that can prevent the progression of cardiac fibrosis.

Effect of Endoplasmic Reticulum Stress and Autophagy in the Regulation of Post-infarct Cardiac Repair

BACKGROUND

Acute myocardial infarction (AMI) is reported to be accompanied by endoplasmic reticulum (ER) stress and autophagy induction. Nevertheless, the roles of ER stress and autophagy in post-infarct reparative fibrosis remain to be elucidated.

AIM

To investigate the effects of ER stress and autophagy on the regulation of post-infarct reparative fibrosis.

METHODS

The expression of GRP78 and LC3 in cardiac fibroblasts in human heart tissues obtained from patients with or without AMI was assessed by immunofluorescence. In vitro, human cardiac fibroblasts (HCFs) were stimulated by various agents, the expression of GRP78, LC3 and fibronectin in these was evaluated by immunoblot and/or immunofluorescence.

RESULTS

After AMI, HCFs expressed significantly higher levels of GRP78 and LC3. ER stress inducer, tunicamycin (200 ng/mL) significantly increased the level of autophagy and reduced expression of fibronectin in HCFs, both of which were reversed by 4 Phenylbutyric acid. Under the condition of ER stress, the expression of fibronectin in HCFs was regulated by different levels of autophagy. LC3 co-localized with fibronectin when stimulated HCFs with tunicamycin.

CONCLUSION

AMI induces ER stress in cardiac fibroblasts, down-regulating fibronectin via enhanced autophagy. These findings suggest that ER stress and autophagy may be a therapeutic target to improve prognosis of patients with AMI.

The aging heart

As the elderly segment of the world population increases, it is critical to understand the changes in cardiac structure and function during the normal aging process. In this review, we outline the key molecular pathways and cellular processes that underlie the phenotypic changes in the heart and vasculature that accompany aging. Reduced autophagy, increased mitochondrial oxidative stress, telomere attrition, altered signaling in insulin-like growth factor, growth differentiation factor 11, and 5'- AMP-activated protein kinase pathways are among the key molecular mechanisms underlying cardiac aging. Aging promotes structural and functional changes in the atria, ventricles, valves, myocardium, pericardium, the cardiac conduction system, and the vasculature. We highlight the factors known to accelerate and attenuate the intrinsic aging of the heart and vessels in addition to potential preventive and therapeutic avenues. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

κ-opioid receptor activation protects against myocardial ischemia-reperfusion injury via AMPK/Akt/eNOS signaling activation

This study aims to investigate the effect of κ-opioid receptor activation on myocardial ischemia and reperfusion(I/R) injury and elucidate the underlying mechanisms. Myocardial I/R rat model and simulated I/R cardiomyocytes model were established. In vivo study showed that U50,488 H improved cardiac function, reduced myocardial infarct size and serum cTnT significantly. The effect of U50,488 H was abolished by nor-BNI(a κ-opioid receptor antagonist), Compound C(an AMPK inhibitor), Akt inhibitor and L-NAME(an eNOS inhibitor). AICAR, an AMPK activator, mimicked the effect of U50,488 H. U50,488 H up-regulated p-AMPK, p-Akt, and p-eNOS, which were abolished by nor-BNI. AICAR increased p-Akt and p-eNOS, which was abolished by Compound C. In vitro study showed that U50,488 H increased p-AMPK, p-Akt, and p-eNOS via κ-OR activation. The effect of U50,488 H on p-AMPK was abolished by compound C, but not Akt inhibitor and L-NAME. The effect of U50,488 H on p-Akt was abolished by compound C and Akt inhibitor, but not L-NAME. AICAR increased p-Akt and p-eNOS, which was abolished by Akt inhibitor, but not L-NAME. U50,488 H and AICAR also increased the viability of cardiomyocytes subjected to simulated I/R, the effects of U50,488 H and AICAR were blocked by nor-BNI, Compound C, Akt inhibitor, and L-NAME, respectively. In conclusion, κ-OR activation confers cardioprotection via AMPK/Akt/eNOS signaling.

AMPK activation counteracts cardiac hypertrophy by reducing O-GlcNAcylation

AMP-activated protein kinase (AMPK) has been shown to inhibit cardiac hypertrophy. Here, we show that submaximal AMPK activation blocks cardiomyocyte hypertrophy without affecting downstream targets previously suggested to be involved, such as p70 ribosomal S6 protein kinase, calcineurin/nuclear factor of activated T cells (NFAT) and extracellular signal-regulated kinases. Instead, cardiomyocyte hypertrophy is accompanied by increased protein O-GlcNAcylation, which is reversed by AMPK activation. Decreasing O-GlcNAcylation by inhibitors of the glutamine:fructose-6-phosphate aminotransferase (GFAT), blocks cardiomyocyte hypertrophy, mimicking AMPK activation. Conversely, O-GlcNAcylation-inducing agents counteract the anti-hypertrophic effect of AMPK. In vivo, AMPK activation prevents myocardial hypertrophy and the concomitant rise of O-GlcNAcylation in wild-type but not in AMPKα2-deficient mice. Treatment of wild-type mice with O-GlcNAcylation-inducing agents reverses AMPK action. Finally, we demonstrate that AMPK inhibits O-GlcNAcylation by mainly controlling GFAT phosphorylation, thereby reducing O-GlcNAcylation of proteins such as troponin T. We conclude that AMPK activation prevents cardiac hypertrophy predominantly by inhibiting O-GlcNAcylation.

AMPK and cardiac remodelling

Cardiac remodelling is generally accepted as a critical process in the progression of heart failure. Myocyte hypertrophy, inflammatory responses and cardiac fibrosis are the main pathological changes associated with cardiac remodelling. AMP-activated protein kinase (AMPK) is known as an energy sensor and a regulator of cardiac metabolism under normal and ischaemic conditions. Additionally, AMPK has been shown to play roles in cardiac remodelling extending well beyond metabolic regulation. In this review, we discuss the currently defined roles of AMPK in cardiac remodelling and summarize the effects of AMPK on cardiac hypertrophy, inflammatory responses and fibrosis and the molecular mechanisms underlying these effects. In addition, we discuss some pharmacological activators of AMPK that are promising treatments for cardiac remodelling.

Global fibroblast activation throughout the left ventricle but localized fibrosis after myocardial infarction

Fibroblast (Fb) differentiation and interstitial fibrosis contribute to cardiac remodeling and loss of function after myocardial infarction (MI). We investigated regional presence and regulation of fibrosis in a pig MI model. In vivo analysis of regional function and perfusion defined three regions: the scar, the myocardium adjacent to the scar (MI_adjacent, reduced function, reduced perfusion reserve), and the remote myocardium (MI_remote, minimal functional deficit, maintained perfusion). Interstitial and perivascular fibrosis, and increase of collagen type I, was only observed in the MI_adjacent. Fb activated protein-alpha (FAP-α) was enriched in MI_adjacent compared to MI_remote. TGF-β1, which triggers Fb differentiation, was upregulated in both MI_adjacent and MI_remote, whereas lysyl oxidase, a regulator of collagen cross-linking, and the proteoglycans decorin and biglycan were only increased in the MI_adjacent. Fb isolated and cultured for 4 days had myoFb characteristics with little difference between MI_remote and MI_adjacent, although RNA sequencing revealed differences in gene expression profiles. Fbs from all regions maintained proliferative capacity, and induced contraction of 3-D collagen matrices but scar myoFb was more effective. These data suggest that after MI, signaling through TGF-β1, possibly related to increased mechanical load, drives Fb activation throughout the left ventricle while regional signaling determines further maturation and extracellular matrix remodeling after MI.

AMPK orchestrates an elaborate cascade protecting tissue from fibrosis and aging

Fibrosis is a common process characterized by excessive extracellular matrix (ECM) accumulation after inflammatory injury, which is also a crucial cause of aging. The process of fibrosis is involved in the pathogenesis of most diseases of the heart, liver, kidney, lung, and other organs/tissues. However, there are no effective therapies for this pathological alteration. Annually, fibrosis represents a huge financial burden for the USA and the world. 5'-AMP-activated protein kinase (AMPK) is a pivotal energy sensor that alleviates or delays the process of fibrogenesis. In this review, we first present basic background information on AMPK and fibrogenesis and describe the protective roles of AMPK in three fibrogenic phases. Second, we analyze the protective action of AMPK during fibrosis in myocardial, hepatic, renal, pulmonary, and other organs/tissues. Third, we present a comprehensive discussion of AMPK during fibrosis and draw a conclusion. This review highlights recent advances, vital for basic research and clinical drug design, in the regulation of AMPK during fibrosis.

Metformin effects on the heart and the cardiovascular system: A review of experimental and clinical data

BACKGROUND

Metformin, the eldest and most widely used glucose lowering drug, is likely to be effective also on cardiac and vascular disease prevention. Nonetheless, uncertainty still exists with regard to its effects on the cardiovascular system as a whole and specifically on the myocardium, both at the organ and cellular levels.

METHODS

We reviewed the available data on the cardiac and vascular effects of metformin, encompassing both in vitro, either tissue or isolated organ, and in vivo studies in experimental animals and humans, as well as the evidence generated by major clinical trials.

RESULTS

At the cellular level metformin's produces both AMP-activated kinase (AMPK) dependent and independent effects. At the systemic level, possibly also through other pathways, this drug improves endothelial function, protects from oxidative stress and inflammation, and from the negative effects of angiotensin II. On the myocardium it attenuates ischemia-reperfusion injury and prevents adverse remodeling induced by humoral and hemodynamic factors. The effects on myocardial cell metabolism and contractile function being not evident at rest or in more advanced stages of cardiac dysfunction, could be relevant during transient ischemia, during an acute increase in workload and in the early stages of diabetic/hypertensive cardiomyopathy as confirmed by few small clinical trials and some observational studies. The overall evidence emerging from both clinical trials and real world registry is in favor of a protective effect of metformin with respect to both coronary events and progression to heart failure.

CONCLUSIONS

Given this potential, its efficacy and its safety (and also its low cost) metformin remains the central pillar of the therapy of diabetes.

YiQiFuMai Powder Injection attenuates coronary artery ligation-induced myocardial remodeling and heart failure through modulating MAPKs signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

YiQiFuMai Powder Injection (YQFM), a traditional Chinese medicine prescription re-developed based on Sheng-Mai-San, is a classical and traditional therapeutic for clinical heart failure (HF) and angina. However, its potential mechanism against HF remains unclear.

AIM OF THE STUDY

The present study observes the therapeutic role of YQFM and mechanisms underlying its effects on coronary artery ligation (CAL)-induced myocardial remodeling (MR) and HF.

METHODS

MR and HF were induced by permanent CAL for 2 weeks in ICR mice. Then mice were treated with YQFM (0.13g/kg, 0.26g/kg and 0.53g/kg) once a day until 2 weeks later. Cardiac structure and function were evaluated by echocardiography. Serum lactate dehydrogenase (LDH), creatine kinase (CK) and malondialdehyde (MDA) were measured by biochemical kits and cardiomyocyte morphology was assessed by hematoxylin-eosin (HE) staining. Myocardial hydroxyproline (HYP), serum amino-terminal pro-peptide of pro-collagen type III (PIIINP), and Masson's trichrome staining were employed to evaluate cardiac fibrosis. Circulating level of N-terminal pro-B-type natriuretic peptide (NT-proBNP) was tested by ELISA kit to predict prognosis of CAL-induced HF. Effects of YQFM on the mitogen-activated protein kinases (MAPKs) pathway after CAL operation was evaluated by Western blotting and immunohistochemistry assay.

RESULTS

YQFM (0.53g/kg) improved the left ventricular (LV) function and structure impairment after 2 weeks in CAL mice. YQFM administration also decreased LDH and CK activities, circulating levels of MDA, PIIINP, NT-proBNP, and HYP contents. Moreover, YQFM ameliorated cardiac injury and fibrosis. Furthermore, YQFM (0.53g/kg) inhibited the myocardial phosphorylation of MAPKs in HF mice.

CONCLUSION

Our findings suggest that YQFM attenuates CAL-induced HF via improving cardiac function, attenuating structure damage, oxidative stress, necrosis, collagen deposition, and fibrosis. In addition, YQFM ameliorates cardiac remodeling and HF, partially through inhibiting the MAPKs signaling pathways. These data provide insights and mechanisms into the widely application of YQFM in patients with HF, MI and other ischemic heart diseases.

Hypertension-induced remodelling: on the interactions of cardiac risk factors

Hypertension induces considerable cardiac remodelling, such as hypertrophy, interstitial fibrosis, and abnormal activity of the cardiac sympathetic nervous system, which are established risk factors in several highly dangerous heart diseases, such as ventricular fibrillation and congestive heart failure. All these risk factors and heart diseases are studied extensively in isolation, but to our knowledge, there is no comprehensive review of their interactions. At the same time, there is growing evidence suggesting that such interactions are numerous and that a successful therapy against a particular condition may have unexpectedly weak effects on mortality, as treated patients may die of a different cause exacerbated by the therapy. In this article, we present a multiscale review of the literature focusing on the relationships between the above‐mentioned risk factors and heart diseases, and introduce a framework that gives insight into their possible interactions. We use this framework to demonstrate that conditions such as fibrosis and elevated activity of the sympathetic nervous system may be compensatory, rather than purely pathological, mechanisms in certain contexts. Finally, we show why the described mechanisms are relevant not only in hypertension, but also in the case of healed myocardial infarction.

Sodium-myoinositol cotransporter-1, SMIT1, mediates the production of reactive oxygen species induced by hyperglycemia in the heart

Hyperglycemia (HG) stimulates the production of reactive oxygen species in the heart through activation of NADPH oxidase 2 (NOX2). This production is independent of glucose metabolism but requires sodium/glucose cotransporters (SGLT). Seven SGLT isoforms (SGLT1 to 6 and sodium-myoinositol cotransporter-1, SMIT1) are known, although their expression and function in the heart remain elusive. We investigated these 7 isoforms and found that only SGLT1 and SMIT1 were expressed in mouse, rat and human hearts. In cardiomyocytes, galactose (transported through SGLT1) did not activate NOX2. Accordingly, SGLT1 deficiency did not prevent HG-induced NOX2 activation, ruling it out in the cellular response to HG. In contrast, myo-inositol (transported through SMIT1) reproduced the toxic effects of HG. SMIT1 overexpression exacerbated glucotoxicity and sensitized cardiomyocytes to HG, whereas its deletion prevented HG-induced NOX2 activation. In conclusion, our results show that heart SMIT1 senses HG and triggers NOX2 activation. This could participate in the redox signaling in hyperglycemic heart and contribute to the pathophysiology of diabetic cardiomyopathy.

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

AMP-activated protein kinase (AMPK) is a ubiquitously expressed metabolic sensor among various species. Specifically, cellular AMPK is phosphorylated and activated under certain stressful conditions, such as energy deprivation, in turn to activate diversified downstream substrates to modulate the adaptive changes and maintain metabolic homeostasis. Recently, emerging evidences have implicated the potential roles of AMPK signaling in tumor initiation and progression. Nevertheless, a comprehensive description on such topic is still in scarcity, especially in combination of its biochemical features with mouse modeling results to elucidate the physiological role of AMPK signaling in tumorigenesis. Hence, we performed this thorough review by summarizing the tumorigenic role of each component along the AMPK signaling, comprising of both its upstream and downstream effectors. Moreover, their functional interplay with the AMPK heterotrimer and exclusive efficacies in carcinogenesis were chiefly explained among genetically altered mice models. Importantly, the pharmaceutical investigations of AMPK relevant medications have also been highlighted. In summary, in this review, we not only elucidate the potential functions of AMPK signaling pathway in governing tumorigenesis, but also potentiate the future targeted strategy aiming for better treatment of aberrant metabolism-associated diseases, including cancer.

AMP-activated protein kinase α1-sensitive activation of AP-1 in cardiomyocytes

AMP-activated protein kinase (Ampk) regulates myocardial energy metabolism and plays a crucial role in the response to cell stress. In the failing heart, an isoform shift of the predominant Ampkα2 to the Ampkα1 was observed. The present study explored possible isoform specific effects of Ampkα1 in cardiomyocytes. To this end, experiments were performed in HL-1 cardiomyocytes, as well as in Ampkα1-deficient and corresponding wild-type mice and mice following AAV9-mediated cardiac overexpression of constitutively active Ampkα1. As a result, in HL-1 cardiomyocytes, overexpression of constitutively active Ampkα1 increased the phosphorylation of Pkcζ. Constitutively active Ampkα1 further increased AP-1-dependent transcriptional activity and mRNA expression of the AP-1 target genes c-Fos, Il6 and Ncx1, effects blunted by Pkcζ silencing. In HL-1 cardiomyocytes, angiotensin-II activated AP-1, an effect blunted by silencing of Ampkα1 and Pkcζ, but not of Ampkα2. In wild-type mice, angiotensin-II infusion increased cardiac Ampkα1 and cardiac Pkcζ protein levels, as well as c-Fos, Il6 and Ncx1 mRNA expression, effects blunted in Ampkα1-deficient mice. Pressure overload by transverse aortic constriction (TAC) similarly increased cardiac Ampkα1 and Pkcζ abundance as well as c-Fos, Il6 and Ncx1 mRNA expression, effects again blunted in Ampkα1-deficient mice. AAV9-mediated cardiac overexpression of constitutively active Ampkα1 increased Pkcζ protein abundance and the mRNA expression of c-Fos, Il6 and Ncx1 in cardiac tissue. In conclusion, Ampkα1 promotes myocardial AP-1 activation in a Pkcζ-dependent manner and thus contributes to cardiac stress signaling.

Cardioprotective actions of Notch1 against myocardial infarction via LKB1-dependent AMPK signaling pathway

AMP-activated protein kinase (AMPK) signaling pathway plays a pivotal role in intracellular adaptation to energy stress during myocardial ischemia. Notch1 signaling in the adult myocardium is also activated in response to ischemic stress. However, the relationship between Notch1 and AMPK signaling pathways during ischemia remains unclear. We hypothesize that Notch1 as an adaptive signaling pathway protects the heart from ischemic injury via modulating the cardioprotective AMPK signaling pathway. C57BL/6J mice were subjected to an in vivo ligation of left anterior descending coronary artery and the hearts from C57BL/6J mice were subjected to an ex vivo globe ischemia and reperfusion in the Langendorff perfusion system. The Notch1 signaling was activated during myocardial ischemia. A Notch1 γ-secretase inhibitor, dibenzazepine (DBZ), was intraperitoneally injected into mice to inhibit Notch1 signaling pathway by ischemia. The inhibition of Notch1 signaling by DBZ significantly augmented cardiac dysfunctions caused by myocardial infarction. Intriguingly, DBZ treatment also significantly blunted the activation of AMPK signaling pathway. The immunoprecipitation experiments demonstrated that an interaction between Notch1 and liver kinase beta1 (LKB1) modulated AMPK activation during myocardial ischemia. Furthermore, a ligand of Notch1 Jagged1 can significantly reduce cardiac damage caused by ischemia via activation of AMPK signaling pathway and modulation of glucose oxidation and fatty acid oxidation during ischemia and reperfusion. But Jagged1 did not have any cardioprotections on AMPK kinase dead transgenic hearts. Taken together, the results indicate that the cardioprotective effect of Notch1 against ischemic damage is mediated by AMPK signaling via an interaction with upstream LKB1.

AMPK in cardiac fibrosis and repair: Actions beyond metabolic regulation

Fibrosis is a general term encompassing a plethora of pathologies that span all systems and is marked by increased deposition of collagen. Injury of variable etiology gives rise to complex cascades involving several cell-types and molecular signals, leading to the excessive accumulation of extracellular matrix that promotes fibrosis and eventually leads to organ failure. Cardiac fibrosis is a dynamic process associated notably with ischemia, hypertrophy, volume- and pressure-overload, aging and diabetes mellitus. It has profoundly deleterious consequences on the normal architecture and functioning of the myocardium and is associated with considerable mortality and morbidity. The AMP-activated protein kinase (AMPK) is a ubiquitously expressed cellular energy sensor and an essential component of the adaptive response to cardiomyocyte stress that occurs during ischemia. Nevertheless, its actions extend well beyond its energy-regulating role and it appears to possess an essential role in regulating fibrosis of the myocardium. In this review paper, we will summarize the main elements and crucial players of cardiac fibrosis. In addition, we will provide an overview of the diverse roles of AMPK in the heart and discuss in detail its implication in cardiac fibrosis. Lastly, we will highlight the recently published literature concerning AMPK-targeting current therapy and novel strategies aiming to attenuate fibrosis.

AMPK in Cardiovascular Diseases

This chapter summarizes the implication of AMP-activated protein kinase (AMPK) in the regulation of various physiological and pathological cellular events of great importance for the maintenance of cardiac function. These include the control of both metabolic and non-metabolic elements targeting the different cellular components of the cardiac tissue, i.e., cardiomyocytes, fibroblasts, and vascular cells. The description of the multifaceted action of the two AMPK catalytic isoforms, α1 and α2, emphasizes the general protective action of this protein kinase against the development of critical pathologies like myocardial ischemia, cardiac hypertrophy, diabetic cardiomyopathy, and heart failure.

Impact of AMP-Activated Protein Kinase α1 Deficiency on Tissue Injury following Unilateral Ureteral Obstruction

Background

AMP-activated protein kinase (Ampk) is a sensor of the cellular energy status and a powerful regulator of metabolism. Activation of Ampk was previously shown to participate in monocyte-to-fibroblast transition and matrix protein production in renal tissue. Thus, the present study explored whether the catalytic Ampkα1 isoform participates in the regulation of the renal fibrotic response following unilateral ureteral obstruction (UUO).

Methods

UUO was induced in gene-targeted mice lacking functional Ampkα1 (Ampkα1^-/-) and in corresponding wild-type mice (Ampkα1^+/+). In the obstructed kidney and, for comparison, in the non-obstructed control kidney, quantitative RT-PCR, Western blotting and immunostaining were employed to determine transcript levels and protein abundance, respectively.

Results

In Ampkα1^+/+ mice, UUO significantly up-regulated the protein abundance of the Ampkα1 isoform, but significantly down-regulated the Ampkα2 isoform in renal tissue. Phosphorylated Ampkα protein levels were significantly increased in obstructed kidney tissue of Ampkα1^+/+ mice but not of Ampkα1^-/- mice. Renal expression of α-smooth muscle actin was increased following UUO, an effect again less pronounced in Ampkα1^-/- mice than in Ampkα1^+/+ mice. Histological analysis did not reveal a profound effect of Ampkα1 deficiency on collagen 1 protein deposition. UUO significantly increased phosphorylated and total Tgf-ß-activated kinase 1 (Tak1) protein, as well as transcript levels of Tak1-downstream targets c-Fos, Il6, Pai1 and Snai1 in Ampkα1^+/+ mice, effects again significantly ameliorated in Ampkα1^-/- mice. Moreover, Ampkα1 deficiency inhibited the UUO-induced mRNA expression of Cd206, a marker of M2 macrophages and of Cxcl16, a pro-fibrotic chemokine associated with myeloid fibroblast formation. The effects of Ampkα1 deficiency during UUO were, however, paralleled by increased tubular injury and apoptosis.

Conclusions

Renal obstruction induces an isoform shift from Ampkα2 towards Ampkα1, which contributes to the signaling involved in cell survival and fibrosis.

CTRP3 attenuates post-infarct cardiac fibrosis by targeting Smad3 activation and inhibiting myofibroblast differentiation

C1q/tumor necrosis factor-related protein-3 (CTRP3) is a novel adipokine with modulation effects on metabolism, inflammation, and cardiovascular system. This study aimed to investigate the effect of CTRP3 on cardiac fibrosis and its underlying mechanism. The myocardial expression of CTRP3 was significantly decreased after myocardial infarction (MI). Adenovirus-delivered CTRP3 supplement attenuated myocardial hypertrophy, improved cardiac function, inhibited interstitial fibrosis, and decreased the number of myofibroblasts post-MI. In cultured adult rat cardiac fibroblasts (CFs), CTRP3 attenuated cell proliferation; migration; and the expression of connective tissue growth factor, collagen I, and collagen III induced by transforming growth factor (TGF)-β1. Moreover, CTRP3 inhibited whereas CTRP3 small interfering RNA (siRNA) facilitated the expression of α-SMA and profibrotic molecules induced by TGF-β1. CTRP3 also attenuated TGF-β1-induced Smad3 phosphorylation, nuclear translocation, and interaction with p300. CTRP3 increased the phosphorylation of AMP-activated protein kinase (AMPK) and Akt in both rat hearts and CFs. Adenine 9-β-D-arabinofuranoside (AraA), an AMPK inhibitor, abolished the protective effect of CTRP3 against TGF-β1-induced profibrotic response and Smad3 activation. Taken together, CTRP3 attenuates cardiac fibrosis by inhibiting myofibroblast differentiation and the subsequent extracellular matrix production. AMPK is required for the anti-fibrotic effect of CTRP3 through targeting Smad3 activation and inhibiting myofibroblast differentiation.

KEY MESSAGE

CTRP3 alleviates cardiac fibrosis in a rat post-MI model and in cardiac fibroblasts. CTRP3 inhibits fibroblast-to-myofibroblast differentiation. CTRP3 exerts anti-fibrotic effect through targeting Smad3 activation. AMPK mediates the anti-fibrotic effect of CTRP3 by inhibition of Smad3 activation.

Beyond energy homeostasis: the expanding role of AMP-activated protein kinase in regulating metabolism

The recent exciting advances in our understanding of the regulation of the energy sensor AMP-activated protein kinase (AMPK), together with renewed appreciation of its importance in maintaining cellular function, brought together leading scientists at a recent FASEB-sponsored meeting in September 2014. Here, we report some of the highlights of this conference.

AMPK deficiency in cardiac muscle results in dilated cardiomyopathy in the absence of changes in energy metabolism

AIMS

AMP-activated protein kinase (AMPK) is thought to be a central player in regulating myocardial metabolism and its activation has been shown to inhibit cardiac hypertrophy. Recently, mice with muscle-specific deletion of AMPK β1/β2 subunits (AMPKβ1β2-deficient mice, β1β2M-KO) have been generated and possess <10% of normal AMPK activity in muscle. However, how/if dramatic AMPK deficiency alters cardiac metabolism, function, or morphology has not been investigated. Therefore, the aim of this study was to determine whether a significant loss of AMPK activity alters cardiac function, metabolism, and hypertrophy, and whether this may play a role in the pathogenesis of heart failure.

METHODS AND RESULTS

β1β2M-KO mice exhibit an approximate 25% reduction in systolic and diastolic function compared with wild-type (WT) littermates. Despite the well-documented role of AMPK in controlling myocardial energy metabolism, there was no difference in basal glucose and fatty acid oxidation rates between β1β2M-KO and WT mice. However, there was reduced AMPK-mediated phosphorylation of troponin I in β1β2M-KO and reduced ventricular cell shortening in the presence of low Ca(2+), which may explain the impaired cardiac function in these mice. Interestingly, β1β2M-KO mice did not display any signs of compensatory cardiac hypertrophy, which could be attributed to impaired activation of p38 MAPK.

CONCLUSIONS

β1β2M-KO mice display evidence of dilated cardiomyopathy. This is the first mouse model of AMPK deficiency that demonstrates cardiac dysfunction in the absence of pathological stress and provides insights into the role of AMPK in regulating myocardial function, metabolism, hypertrophy, and the progression to heart failure.

Metformin: from mechanisms of action to therapies

Metformin is currently the first-line drug treatment for type 2 diabetes. Besides its glucose-lowering effect, there is interest in actions of the drug of potential relevance to cardiovascular diseases and cancer. However, the underlying mechanisms of action remain elusive. Convincing data place energy metabolism at the center of metformin's mechanism of action in diabetes and may also be of importance in cardiovascular diseases and cancer. Metformin-induced activation of the energy-sensor AMPK is well documented, but may not account for all actions of the drug. Here, we summarize current knowledge about the different AMPK-dependent and AMPK-independent mechanisms underlying metformin action.