Akt2 regulates cardiac metabolism and cardiomyocyte survival

High-density lipoprotein protects normotensive and hypertensive rats against ischemia-reperfusion injury through differential regulation of mTORC1 and mTORC2 signaling

Background

High-density lipoprotein (HDL) protects against myocardial ischemia-reperfusion (I/R) injury. Mammalian target of rapamycin complexes 1 and 2 (mTORC1 and mTORC2) play opposing roles in protecting against I/R injury, whereby mTORC1 appears to be detrimental while mTORC2 is protective. However, the role of HDL and mTORC signaling in protecting against I/R in hypertensive rodents is not clearly understood. In this study, we investigated the involvement of mTORC1 and mTORC2 in HDL-mediated protection against myocardial I/R injury in normotensive Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHR).

Methods

Hearts from WKY and SHR were subjected to I/R injury using a modified Langendorff system. Hemodynamics data were collected, and infarct size was measured. Rapamycin and JR-AB2-011 were used to test the role of mTORC1 and mTORC2, respectively. MK-2206 was used to test the role of Akt in HDL-mediated cardiac protection. The expression levels and the activation states of mediators of mTORC1 and mTORC2 signaling and myocardial apoptosis were measured by immunoblotting and/or enzyme-linked immunosorbent assay (ELISA).

Results

HDL protected hearts from WKY and SHR against I/R injury as indicated by significant improvements in cardiac hemodynamics and reduction in infarct size. HDL induced greater protection in WKY compared to SHR. HDL treatment attenuated mTORC1 signaling in WKY by reducing the phosphorylation of P70S6K (mTORC1 substrate). In SHR however, HDL attenuated mTORC1 signaling by reducing the levels of phospho-mTORC1, Rag C (mTORC1 activator), and phospho-PRAS40 (mTORC1 inhibitor). HDL increased the phosphorylation of mTORC2 substrate Akt, specifically the Akt2 isoform in SHR and to a greater extent in WKY. HDL-induced protection was abolished in the presence of Akt antagonist and involved attenuation of GSK, caspases 7 and 8 activation, and cytochrome C release.

Conclusion

HDL mediates cardiac protection via attenuation of mTORC1, activation of mTORC2-Akt2, and inhibition of myocardial apoptosis. HDL regulates mTORC1 and mTORC2 signaling via distinct mechanisms in normotensive and hypertensive rats. HDL attenuation of mTORC1 and activation of mTORC2-Akt2 signaling could be a mechanism by which HDL protects against myocardial I/R injury in hypertension.

Exosomal Preconditioning of Human iPSC-Derived Cardiomyocytes Beneficially Alters Cardiac Electrophysiology and Micro RNA Expression

Experimental evidence, both in vitro and in vivo, has indicated cardioprotective effects of extracellular vesicles (EVs) derived from various cell types, including induced pluripotent stem cell-derived cardiomyocytes. The biological effects of EV secretion, particularly in the context of ischemia and cardiac electrophysiology, remain to be fully explored. Therefore, the goal of this study was to unveil the effects of exosome (EXO)-mediated cell-cell signaling during hypoxia by employing a simulated preconditioning approach on human-induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CMs). Electrophysiological activity of hIPSC-CMs was measured using a multielectrode array (MEA) system. A total of 16 h of hypoxic stress drastically increased the beat period. Moreover, hIPSC-CMs preconditioned with EXOs displayed significantly longer beat periods compared with non-treated cells after 16 h of hypoxia (+15.7%, p < 0.05). Furthermore, preconditioning with hypoxic EXOs resulted in faster excitation-contraction (EC) coupling compared with non-treated hIPSC-CMs after 16 h of hypoxia (-25.3%, p < 0.05). Additionally, microRNA (miR) sequencing and gene target prediction analysis of the non-treated and pre-conditioned hIPSC-CMs identified 10 differentially regulated miRs and 44 gene targets. These results shed light on the intricate involvement of miRs, emphasizing gene targets associated with cell survival, contraction, apoptosis, reactive oxygen species (ROS) regulation, and ion channel modulation. Overall, this study demonstrates that EXOs secreted by hIPSC-CM during hypoxia beneficially alter electrophysiological properties in recipient cells exposed to hypoxic stress, which could play a crucial role in the development of targeted interventions to improve outcomes in ischemic heart conditions.

Insulin-Heart Axis: Bridging Physiology to Insulin Resistance

Insulin signaling is vital for regulating cellular metabolism, growth, and survival pathways, particularly in tissues such as adipose, skeletal muscle, liver, and brain. Its role in the heart, however, is less well-explored. The heart, requiring significant ATP to fuel its contractile machinery, relies on insulin signaling to manage myocardial substrate supply and directly affect cardiac muscle metabolism. This review investigates the insulin-heart axis, focusing on insulin's multifaceted influence on cardiac function, from metabolic regulation to the development of physiological cardiac hypertrophy. A central theme of this review is the pathophysiology of insulin resistance and its profound implications for cardiac health. We discuss the intricate molecular mechanisms by which insulin signaling modulates glucose and fatty acid metabolism in cardiomyocytes, emphasizing its pivotal role in maintaining cardiac energy homeostasis. Insulin resistance disrupts these processes, leading to significant cardiac metabolic disturbances, autonomic dysfunction, subcellular signaling abnormalities, and activation of the renin-angiotensin-aldosterone system. These factors collectively contribute to the progression of diabetic cardiomyopathy and other cardiovascular diseases. Insulin resistance is linked to hypertrophy, fibrosis, diastolic dysfunction, and systolic heart failure, exacerbating the risk of coronary artery disease and heart failure. Understanding the insulin-heart axis is crucial for developing therapeutic strategies to mitigate the cardiovascular complications associated with insulin resistance and diabetes.

Novel biomarkers of preterm brain injury from blood transcriptome in sheep model of intrauterine asphyxia

BACKGROUND

Infants born preterm have a higher incidence of neurological deficits. A key step in finding effective treatments is to identify biomarkers that reliably predict outcome.

METHODS

Following umbilical cord occlusion (UCO) in pregnant sheep, whole fetal blood RNA was sequenced pre- and post-UCO, brain injury outcome was determined by battery of neuropathology scoring and the transcriptome signature correlated to the degree of brain injury. Additionally, we developed a novel analytical procedure to deduce cell blood composition over time.

RESULTS

Sixty-one genes were identified with significant altered expression after UCO. In pre-UCO blood, the level of three mRNAs (Trex2, Znf280b, novel miRNA) and in post-UCO, four mRNAs (Fam184a, Angptl2, novel lincRNA and an unknown protein-coding gene) were associated to brain injury (FDR < 0.01). Several of these mRNAs are related to inflammation and angiogenesis. Pathway analysis highlighted genes playing a role in perinatal death and growth failure. Results also indicate that several leukocyte populations undergo significant changes after UCO.

CONCLUSION

We have used a whole transcriptomic approach to uncover novel biomarkers in fetal blood that correlate to neuropathology in the preterm sheep brain. The current data forms a basis for future studies to investigate mechanisms of these mRNAs in the injury progression.

IMPACT

Trend analysis of genes following asphyxia reveal a group of genes associated with perinatal death and growth failure. Several pre-asphyxia transcripts were associated to brain injury severity suggesting genomic susceptibility to injury. Several post-asphyxia transcripts were correlated to brain injury severity, thus, serve as potential novel biomarkers of injury outcome. Successfully adaptation of cell profiling algorithms suggests significant changes in blood cell composition following asphyxia.

MiR-378 Inhibits Angiotensin II-Induced Cardiomyocyte Hypertrophy by Targeting AKT2

Cardiomyocyte hypertrophy plays a crucial role in heart failure development, potentially leading to sudden cardiac arrest and death. Previous studies suggest that micro-ribonucleic acids (miRNAs) show promise for the early diagnosis and treatment of cardiomyocyte hypertrophy.To investigate the miR-378 expression in the cardiomyocyte hypertrophy model, reverse transcription-polymerase chain reaction (RT-qPCR), Western blot, and immunofluorescence tests were conducted in angiotensin II (Ang II)-induced H9c2 cells and Ang II-induced mouse model of cardiomyocyte hypertrophy. The functional interaction between miR-378 and AKT2 was studied by dual-luciferase reporter, RNA pull-down, Western blot, and RT-qPCR assays.The results of RT-qPCR analysis showed the downregulated expression of miR-378 in both the cell and animal models of cardiomyocyte hypertrophy. It was observed that the introduction of the miR-378 mimic inhibited the hypertrophy of cardiomyocytes induced by Ang II. Furthermore, the co-transfection of AKT2 expression vector partially mitigated the negative impact of miR-378 overexpression on Ang II-induced cardiomyocytes. Molecular investigations provided evidence that miR-378 negatively regulated AKT2 expression by interacting with the 3' untranslated region (UTR) of AKT2 mRNA.Decreased miR-378 expression and AKT2 activation are linked to Ang II-induced cardiomyocyte hypertrophy. Targeting miR-378/AKT2 axis offers therapeutic opportunity to alleviate cardiomyocyte hypertrophy.

Identification of the metabolic state of surviving cardiomyocytes in the human infarcted heart by spatial single-cell transcriptomics

The metabolic status of surviving cardiomyocytes (CM) in the myocardial tissues of patients who sustained myocardial infarction (MI) is largely unknown. Spatial single-cell RNA-sequencing (scRNA-seq) is a novel tool that enables the unbiased analysis of RNA signatures within intact tissues. We employed this tool to assess the metabolic profiles of surviving CM in the myocardial tissues of patients post-MI.

Methods

A spatial scRNA-seq dataset was used to compare the genetic profiles of CM from patients with MI and control patients; we analyzed the metabolic adaptations of surviving CM within the ischemic niche. A standard pipeline in Seurat was used for data analysis, including normalization, feature selection, and identification of highly variable genes using principal component analysis (PCA). Harmony was used to remove batch effects and integrate the CM samples based on annotations. Uniform manifold approximation and projection (UMAP) was used for dimensional reduction. The Seurat "FindMarkers" function was used to identify differentially expressed genes (DEGs), which were analyzed by the Gene Ontology (GO) enrichment pathway. Finally, the scMetabolism R tool pipeline with parameters method = VISION (Vision is a flexible system that utilizes a high-throughput pipeline and an interactive web-based report to annotate and explore scRNA-seq datasets in a dynamic manner) and metabolism.type = Kyoto Encyclopedia of Genes and Genomes (KEGG) was used to quantify the metabolic activity of each CM.

Results

Analysis of spatial scRNA-seq data showed fewer surviving CM in infarcted hearts than in control hearts. GO analysis revealed repressed pathways in oxidative phosphorylation, cardiac cell development, and activated pathways in response to stimuli and macromolecular metabolic processes. Metabolic analysis showed downregulated energy and amino acid pathways and increased purine, pyrimidine, and one-carbon pool by folate pathways in surviving CM.

Conclusions

Surviving CM within the infarcted myocardium exhibited metabolic adaptations, as evidenced by the downregulation of most pathways linked to oxidative phosphorylation, glucose, fatty acid, and amino acid metabolism. In contrast, pathways linked to purine and pyrimidine metabolism, fatty acid biosynthesis, and one-carbon metabolism were upregulated in surviving CM. These novel findings have implications for the development of effective strategies to improve the survival of hibernating CM within the infarcted heart.

Scalable Generation of Nanovesicles from Human-Induced Pluripotent Stem Cells for Cardiac Repair

Extracellular vesicles (EVs) from stem cells have shown significant therapeutic potential to repair injured cardiac tissues and regulate pathological fibrosis. However, scalable generation of stem cells and derived EVs for clinical utility remains a huge technical challenge. Here, we report a rapid size-based extrusion strategy to generate EV-like membranous nanovesicles (NVs) from easily sourced human iPSCs in large quantities (yield 900× natural EVs). NVs isolated using density-gradient separation (buoyant density 1.13 g/mL) are spherical in shape and morphologically intact and readily internalised by human cardiomyocytes, primary cardiac fibroblasts, and endothelial cells. NVs captured the dynamic proteome of parental cells and include pluripotency markers (LIN28A, OCT4) and regulators of cardiac repair processes, including tissue repair (GJA1, HSP20/27/70, HMGB1), wound healing (FLNA, MYH9, ACTC1, ILK), stress response/translation initiation (eIF2S1/S2/S3/B4), hypoxia response (HMOX2, HSP90, GNB1), and extracellular matrix organization (ITGA6, MFGE8, ITGB1). Functionally, NVs significantly promoted tubule formation of endothelial cells (angiogenesis) (p < 0.05) and survival of cardiomyocytes exposed to low oxygen conditions (hypoxia) (p < 0.0001), as well as attenuated TGF-β mediated activation of cardiac fibroblasts (p < 0.0001). Quantitative proteome profiling of target cell proteome following NV treatments revealed upregulation of angiogenic proteins (MFGE8, MYH10, VDAC2) in endothelial cells and pro-survival proteins (CNN2, THBS1, IGF2R) in cardiomyocytes. In contrast, NVs attenuated TGF-β-driven extracellular matrix remodelling capacity in cardiac fibroblasts (ACTN1, COL1A1/2/4A2/12A1, ITGA1/11, THBS1). This study presents a scalable approach to generating functional NVs for cardiac repair.

Application of network pharmacology and molecular docking approach to explore active compounds and potential pharmacological mechanisms of Aconiti Lateralis Radix Praeparata and Lepidii Semen Descurainiae Semen for treatment of heart failure

BACKGROUND

Heart failure (HF) is the end stage of the development of heart disease, whose prognosis is poor. The previous research of our team indicated that the formulae containing Aconiti Lateralis Radix Praeparata and Lepidii Semen Descurainiae Semen (ALRP-LSDS) could inhibit myocardial hypertrophy, inhibit cardiomyocyte apoptosis, delay myocardial remodeling (REM), and improve the prognosis of patients with HF effectively. In order to explore the mechanism of ALRP-LSDS for the treatment of HF, a combined approach of network pharmacology and molecular docking was conducted.

METHODS

Public database TCMSP was used to screen the active compounds of ALRP-LSDS. The targets of screened active compounds were obtained from the TCMSP database and predicted using the online analysis tool PharmMapper. The targets of HF were obtained from 6 databases including GeneCards, OMIM, DrugBank, TTD, PharmGKB, and DisGeNET. Protein-protein interaction and enrichment analysis were performed, respectively, by STRING and Metascape online tools after merging the targets of active compounds and HF. Cytoscape software was used to conduct networks. Finally, molecular docking was performed by Vina to verify the correlation between key targets and active compounds.

RESULTS

Final results indicated that the active compounds including β-sitosterol, isorhamnetin, quercetin, kaempferol, and (R)-norcoclaurine, the targets including AKT1, CASP3, and MAPK1 might be the main active compounds and key targets of ALRP-LSDS for the treatment of HF separately. The binding ability of AKT1 to the main active compounds was better compared with the other 2 key targets, which means it might be more critical. The pathways including AGE-RAGE signaling pathway in diabetic complications, Pathways in cancer, and Fluid shear stress and atherosclerosis might play important roles in the treatment of HF with ALRP-LSDS. In general, ALRP-LSDS could inhibit cardiomyocyte apoptosis, delay REM, and improve cardiac function through multicompound, multitarget, and multipathway, which contributes to the treatment of HF.

CONCLUSIONS

Based on the combined approach of network pharmacology and molecular docking, this study screened out the main active compounds, key targets, and main pathways of ALRP-LSDS for the treatment of HF, and revealed its potential mechanisms, providing a theoretical basis for further research.

Therapeutic Effects of Retinoic Acid in Lipopolysaccharide-Induced Cardiac Dysfunction: Network Pharmacology and Experimental Validation

Purpose

Sepsis, which is deemed as a systemic inflammation reaction syndrome in the face of infectious stimuli, is the primary cause of death in ICUs. Sepsis-induced cardiomyopathy (SIC) may derive from systemic inflammation reaction and oxidative stress. Retinoic acid (RA) is recognized by its beneficial roles in terms of the immunoresponse to infections and antioxygen actions. However, the treatment efficacy and potential causal links of RA in SIC are still elusive.

Methods

By virtue of the STITCH database, we identified the targets of RA. Differentially expressed genes in SIC were acquired from the GEO database. The PPI network of intersected targets was established. GO and KEGG pathway enrichment analysis was completed. Hub genes were analyzed by cytoHubba plug-in. In the process of experimental validation, a mouse sepsis model was established by lipopolysaccharide (LPS), and the treated mice were intraperitoneally injected with RA or Dexamethasone (DEX) 60 min prior to LPS injections. Survival conditions, cardiac functions and antioxidant levels of the mice were assessed. Cardiac inflammation and injury were detected by HE and TUNEL. The levels of key genes and signal pathway expression were analyzed by RT-PCR and Western blot.

Results

PPARA, ITGAM, VCAM-1, IGF-1 and IL-6 were identified as key therapeutic targets of RA by network pharmacology. PI3K-Akt signaling pathway is the main regulatory pathway of RA. In vivo researches unraveled that RA can improve the survival rate and cardiac function of LPS-treated mice, inhibit inflammatory factors and myocardial injury, and regulate the expression of key therapeutic targets and key pathways, which is PI3K-Akt signaling pathway.

Conclusion

Network pharmacological method offers a predicative strategy to explore the treatment efficacy and causal links of RA in endotoxemic myocarditis. Through experimental verification, we discover that RA can reduce lipopolysaccharide-induced cardiac dysfunction by regulating the PI3K-Akt signaling pathway and key genes.

Different activation of MAPKs and Akt/GSK3β after preload vs. afterload elevation

Aims

Pressure overload (PO) and volume overload (VO) lead to concentric or eccentric hypertrophy. Previously, we could show that activation of signalling cascades differ in in vivo mouse models. Activation of these signal cascades could either be induced by intrinsic load sensing or neuro‐endocrine substances like catecholamines or the renin‐angiotensin‐aldosterone system.

Methods and results

We therefore analysed the activation of classical cardiac signal pathways [mitogen‐activated protein kinases (MAPKs) (ERK, p38, and JNK) and Akt‐GSK3β] in in vitro of mechanical overload (ejecting heart model, rabbit and human isolated muscle strips). Selective elevation of preload in vitro increased AKT and GSK3β phosphorylation after 15 min in isolated rabbit muscles strips (AKT 49%, GSK3β 26%, P < 0.05) and in mouse ejecting hearts (AKT 51%, GSK49%, P < 0.05), whereas phosphorylation of MAPKs was not influenced by increased preload. Selective elevation of afterload revealed an increase in ERK phosphorylation in the ejecting heart (43%, P < 0.05), but not in AKT, GSK3β, and the other MAPKs. Elevation of preload and afterload in the ejecting heart induced a significant phosphorylation of ERK (95%, P < 0.001) and showed a moderate increased AKT (P = 0.14) and GSK3β (P = 0.21) phosphorylation, which did not reach significance. Preload and afterload elevation in muscles strips from human failing hearts showed neither AKT nor ERK phosphorylation changes.

Conclusions

Our data show that preload activates the AKT–GSK3β and afterload the ERK pathway in vitro, indicating an intrinsic mechanism independent of endocrine signalling.

Protein Kinase B2 (PKB2/AKT2) Is Essential for Host Protection in CVB3-Induced Acute Viral Myocarditis

Protein kinase B2 (AKT2) is involved in various cardiomyocyte signaling processes, including those important for survival and metabolism. Coxsackievirus B3 (CVB3) is one of the most common pathogens that cause myocarditis in humans. The role of AKT2 in CVB3 infection is not yet well understood. We used a cardiac-specific AKT2 knockout (KO) mouse to determine the role of AKT2 in CVB3-mediated myocarditis. CVB3 was injected intraperitoneally into wild-type (WT) and KO mice. The mice’s survival rate was recorded: survival in KO mice was significantly decreased compared with WT mice (WT vs. KO: 73.3 vs. 27.1%). Myocardial damage and inflammation were significantly increased in the hearts of KO mice compared with those of WT mice. Moreover, from surface ECG, AKT2 KO mice showed a prolonged atria and ventricle conduction time (PR interval, WT vs. KO: 47.27 ± 1.17 vs. 64.79 ± 7.17 ms). AKT2 deletion induced severe myocarditis and cardiac dysfunction due to CVB3 infection. According to real-time PCR, the mRNA level of IL-1, IL-6, and TNF-α decreased significantly in KO mice compared with WT mice on Days 5 after infection. In addition, innate immune response antiviral effectors, Type I interferon (interferon-α and β), and p62, were dramatically suppressed in the heart of KO mice. In particular, the adult cardiac myocytes isolated from the heart showed high induction of TLR4 protein in KO mice in comparison with WT. AKT2 deletion suppressed the activation of Type I interferon and p62 transcription in CVB3 infection. In cardiac myocytes, AKT2 is a key signaling molecule for the heart from damage through the activation of innate immunity during acute myocarditis.

Role of PI3K/Akt signaling pathway in cardiac fibrosis

Heart failure (HF) is considered as a severe health problem worldwide, while cardiac fibrosis is one of the main driving factors for the progress of HF. Cardiac fibrosis was characterized by changes in cardiomyocytes, cardiac fibroblasts, ratio of collagen (COL) I/III, and the excessive production and deposition of extracellular matrix (ECM), thus forming a scar tissue, which leads to pathological process of cardiac structural changes and systolic as well as diastolic dysfunction. Cardiac fibrosis is a common pathological change of many advanced cardiovascular diseases including ischemic heart disease, hypertension, and HF. Accumulated studies have proven that phosphoinositol-3 kinase (PI3K)/Akt signaling pathway is involved in regulating the occurrence, progression and pathological formation of cardiac fibrosis via regulating cell survival, apoptosis, growth, cardiac contractility and even the transcription of related genes through a series of molecules including mammalian target of rapamycin (mTOR), glycogen synthase kinase 3 (GSK-3), forkhead box proteins O1/3 (FoxO1/3), and nitric oxide synthase (NOS). Thus, the review focuses on the role of PI3K/Akt signaling pathway in the cardiac fibrosis. The information reviewed here should be significant in understanding the role of PI3K/Akt in cardiac fibrosis and contribute to the design of further studies related to PI3K/Akt and the cardiac fibrotic response, as well as sought to shed light on a potential treatment for cardiac fibrosis.

Insulin signaling in the heart

Insulin receptors are highly expressed in the heart and vasculature. Insulin signaling regulates cardiac growth, survival, substrate uptake, utilization, and mitochondrial metabolism. Insulin signaling modulates the cardiac responses to physiological and pathological stressors. Altered insulin signaling in the heart may contribute to the pathophysiology of ventricular remodeling and heart failure progression. Myocardial insulin signaling adapts rapidly to changes in the systemic metabolic milieu. What may initially represent an adaptation to protect the heart from carbotoxicity may contribute to amplifying the risk of heart failure in obesity and diabetes. This review article presents the multiple roles of insulin signaling in cardiac physiology and pathology and discusses the potential therapeutic consequences of modulating myocardial insulin signaling.

Adiponectin Attenuates Lipopolysaccharide-induced Apoptosis by Regulating the Cx43/PI3K/AKT Pathway

Cardiomyocyte apoptosis is a crucial factor leading to myocardial dysfunction. Adiponectin (APN) has a cardiomyocyte-protective impact. Studies have shown that the connexin43 (Cx43) and phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) signaling pathways play an important role in the heart, but whether APN plays a protective role by regulating these pathways is unclear. Our study aimed to confirm whether APN protects against lipopolysaccharide (LPS)-induced cardiomyocyte apoptosis and to explore whether it plays an important role through regulating the Cx43 and PI3K/AKT signaling pathways. In addition, our research aimed to explore the relationship between the Cx43 and PI3K/AKT signaling pathways. In vitro experiments: Before H9c2 cells were treated with LPS for 24 h, they were pre-treated with APN for 2 h. The cytotoxic effect of APN on H9c2 cells was evaluated by a CCK-8 assay. The protein levels of Bax, Bcl2, cleaved caspase-3, cleaved caspase-9, Cx43, PI3K, p-PI3K, AKT and p-AKT were evaluated by Western blot analysis, and the apoptosis rate was evaluated by flow cytometry. APN attenuated the cytotoxicity induced by LPS. LPS upregulated Bax, cleaved caspase-3 and cleaved caspase-9 and downregulated Bcl2 in H9c2 cells; however, these effects were attenuated by APN. In addition, LPS upregulated Cx43 expression, and APN downregulated Cx43 expression and activated the PI3K/AKT signaling pathway. LPS induced apoptosis and inhibited PI3K/AKT signaling pathway in H9c2 cells, and these effects were attenuated by Gap26 (a Cx43 inhibitor). Moreover, the preservation of APN expression was reversed by LY294002 (a PI3K/AKT signaling pathway inhibitor). In vivo experiments: In C57BL/6J mice, a sepsis model was established by intraperitoneal injection of LPS, and APN was injected into enterocoelia. The protein levels of Bax, Bcl2, cleaved caspase-3, and Cx43 were evaluated by Western blot analysis, and immunohistochemistry was used to detect Cx43 expression and localization in myocardial tissue. LPS upregulated Bax and cleaved caspase-3 and downregulated Bcl2 in sepsis; however, these effects were attenuated by APN. In addition, the expression of Cx43 was upregulated in septic myocardial tissue, and APN downregulated Cx43 expression in septic myocardial tissue. In conclusion, both in vitro and in vivo, the data demonstrated that APN can protect against LPS-induced apoptosis during sepsis by modifying the Cx43 and PI3K/AKT signaling pathways.

Cyanide Poisoning Compromises Gene Pathways Modulating Cardiac Injury in Vivo

Smoke inhalation from a structure fire is a common route of cyanide poisoning in the U.S. Cyanide inhibits cellular respiration, often leading to death. Its rapid distribution throughout the body can result in injuries to multiple organs, and cyanide victims were reported to experience myocardial infarction and other cardiac complications. However, molecular mechanisms of such complications are yet to be elucidated. While FDA-approved CN antidotes such as sodium thiosulfate and hydroxocobalamin are clinically used, they have foreseeable limitations during mass casualty situations because they require intravenous administration. To facilitate the development of better antidotes and therapeutic treatments, a global view of molecular changes induced by cyanide exposure is necessary. As an exploratory pursuit, we performed oligonucleotide microarrays to establish cardiac transcriptomes of an animal model of nose-only inhalation exposure to hydrogen cyanide (HCN), which is relevant to smoke inhalation. We also profiled cardiac transcriptomes after subcutaneous injection of potassium cyanide (KCN). Although the KCN injection model has often been used to evaluate medical countermeasures, this study demonstrated that cardiac transcriptomes are largely different from that of the HCN inhalation model at multiple time points within 24 h after exposure. Pathway analysis identified that HCN-induced transcriptomes were enriched with genes encoding mediators of pathways critical in modulation of cardiac complications and that a large number of such genes were significantly decreased in expression. We utilized the upstream regulatory analysis to propose drugs that can be potentially employed to treat cyanide-induced cardiac complications.

Bcl-2 Is Involved in Cardiac Hypertrophy through PI3K-Akt Pathway

Cardiac hypertrophy (CH) is a common cause of sudden cardiac death and heart failure, resulting in a significant medical burden. The present study is aimed at exploring potential CH-related pathways and the key downstream effectors. The gene expression profile of GSE129090 was obtained from the Gene Expression Omnibus database (GEO), and 1325 differentially expressed genes (DEGs) were identified, including 785 upregulated genes and 540 downregulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome pathway enrichment analysis of DEGs were then performed. Although there were no pathways enriched by downregulated genes, many CH-related pathways were identified by upregulated genes, including PI3K-Akt signaling pathway, extracellular matrix- (ECM-) receptor interaction, regulation of actin cytoskeleton, and hypertrophic cardiomyopathy (HCM). In the deeper analysis of PI3K-Akt signaling pathway, we found all the signaling transduction pointed to B cell lymphoma-2- (Bcl-2-) mediated cell survival. We then demonstrated that PI3K-Akt signaling pathway was indeed activated in cardiac hypertrophy. Furthermore, no matter LY294002, an inhibitor of the PI3K/AKT signaling pathway, or Venetoclax, a selective Bcl-2 inhibitor, protected against cardiac hypertrophy. In conclusion, these data indicate that Bcl-2 is involved in cardiac hypertrophy as a key downstream effector of PI3K-Akt signaling pathway, suggesting a potential therapeutic target for the clinical management of cardiac hypertrophy.

Metabolic Aspects of Anthracycline Cardiotoxicity

OPINION STATEMENT

Heart failure (HF) is increasingly recognized as the major complication of chemotherapy regimens. Despite the development of modern targeted therapies such as monoclonal antibodies, doxorubicin (DOXO), one of the most cardiotoxic anticancer agents, still remains the treatment of choice for several solid and hematological tumors. The insurgence of cardiotoxicity represents the major limitation to the clinical use of this potent anticancer drug. At the molecular level, cardiac side effects of DOXO have been associated to mitochondrial dysfunction, DNA damage, impairment of iron metabolism, apoptosis, and autophagy dysregulation. On these bases, the antioxidant and iron chelator molecule, dexrazoxane, currently represents the unique FDA-approved cardioprotectant for patients treated with anthracyclines.A less explored area of research concerns the impact of DOXO on cardiac metabolism. Recent metabolomic studies highlight the possibility that cardiac metabolic alterations may critically contribute to the development of DOXO cardiotoxicity. Among these, the impairment of oxidative phosphorylation and the persistent activation of glycolysis, which are commonly observed in response to DOXO treatment, may undermine the ability of cardiomyocytes to meet the energy demand, eventually leading to energetic failure. Moreover, increasing evidence links DOXO cardiotoxicity to imbalanced insulin signaling and to cardiac insulin resistance. Although anti-diabetic drugs, such as empagliflozin and metformin, have shown interesting cardioprotective effects in vitro and in vivo in different models of heart failure, their mechanism of action is unclear, and their use for the treatment of DOXO cardiotoxicity is still unexplored.This review article aims at summarizing current evidence of the metabolic derangements induced by DOXO and at providing speculations on how key players of cardiac metabolism could be pharmacologically targeted to prevent or cure DOXO cardiomyopathy.

Titin and CK2α are New Intracellular Targets in Acute Insulin Application-Associated Benefits on Electrophysiological Parameters of Left Ventricular Cardiomyocytes From Insulin-Resistant Metabolic Syndrome Rats

BACKGROUND

Previous studies have demonstrated that a high-carbohydrate intake could induce metabolic syndrome (MetS) in male rats with marked cardiac functional abnormalities. In addition, studies mentioned some benefits of insulin application on these complications, but there are considerable disagreements among their findings. Therefore, we aimed to extend our knowledge on the in-vitro influence of insulin on left ventricular dysfunction and also in the isolated cardiomyocytes from MetS rats.

RESULTS

At the organ function level, an acute insulin application (100-nM) provided an important beneficial effect on the left ventricular developed pressure in MetS rats. Furthermore, to treat the freshly isolated cardiomyocytes from MetS rats with insulin provided marked recoveries in elevated resting intracellular Ca²⁺-level, as well as significant prevention of prolonged action potential through an augmentation in depressed K⁺-channel currents. Insulin also normalized the cellular levels of increased ROS and phosphorylation of PKCα, together with normalizations of apoptotic markers in MetS cardiomyocytes through the insulin-mediated regulation of phospho-Akt. Since not only elevated PKCα-activity but also reductions in phospho-Akt are key modulators of titin-based cardiomyocyte stiffening in hyperglycemia, insulin treatment of the cardiomyocytes prevented the activation of titin via the above pathways. Furthermore, CK2α-activation and NOS-phosphorylation could be prevented with insulin treatment. Mechanistically, we found that impaired insulin signaling and elevated PKCα and CK2α activities, as well as depressed Akt phosphorylation, are key modulators of titin-based cardiomyocyte stiffening in MetS rats.

CONCLUSION

We propose that restoring normal kinase activities and also increases in phospho-Akt by insulin can contribute marked recoveries in MetS heart function, indicating a promising approach to modulate titin-associated factors in heart dysfunction associated with type-2 diabetes mellitus. Graphical Abstract.

Overexpression of miR-150-5p Alleviates Apoptosis in Sepsis-Induced Myocardial Depression

Sepsis-induced myocardial depression has high mortality and is very common in intensive care units. Previous studies have found that microRNAs play an important role in regulating sepsis-induced myocardial depression. miR-150-5p is involved in many biological processes; however, the mechanism underlying its role in sepsis-induced myocardial depression is still unclear. In this study, we generated rat models of septic shock induced by lipopolysaccharide. Whole genomic RNA sequencing was performed on 12 left ventricles collected after LPS treatment to identify miRNAs. Most of the target genes of the differently expressed microRNAs were involved in apoptosis, according to Gene Ontology. We also observed apoptosis in the heart tissue and in H9C2 cardiomyocytes stimulated with lipopolysaccharide, indicating that cell apoptosis may be an important mechanism in sepsis-induced myocardial depression. Furthermore, the expression of miR-150-5p was reduced, and overexpression of miR-150-5p with mimics resulted in a decrease in apoptosis, decreased expression of cleaved caspase3 and Bax, and increased expression of Bcl-2. Additionally, after H9C2 cells were transfected with miR-150-5p mimics or an inhibitor, the expression of Akt2 decreased or increased, respectively. These findings suggest that miR-150-5p can alleviate apoptosis and may be a novel therapeutic target for sepsis-induced myocardial depression.

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.

Insulin receptor substrates differentially exacerbate insulin-mediated left ventricular remodeling

Pressure overload (PO) cardiac hypertrophy and heart failure are associated with generalized insulin resistance and hyperinsulinemia, which may exacerbate left ventricular (LV) remodeling. While PO activates insulin receptor tyrosine kinase activity that is transduced by insulin receptor substrate 1 (IRS1), the present study tested the hypothesis that IRS1 and IRS2 have divergent effects on PO-induced LV remodeling. We therefore subjected mice with cardiomyocyte-restricted deficiency of IRS1 (CIRS1KO) or IRS2 (CIRS2KO) to PO induced by transverse aortic constriction (TAC). In WT mice, TAC-induced LV hypertrophy was associated with hyperactivation of IRS1 and Akt1, but not IRS2 and Akt2. CIRS1KO hearts were resistant to cardiac hypertrophy and heart failure in concert with attenuated Akt1 activation. In contrast, CIRS2KO hearts following TAC developed more severe LV dysfunction than WT controls, and this was prevented by haploinsufficiency of Akt1. Failing human hearts exhibited isoform-specific IRS1 and Akt1 activation, while IRS2 and Akt2 activation were unchanged. Kinomic profiling identified IRS1 as a potential regulator of cardioprotective protein kinase G-mediated signaling. In addition, gene expression profiling revealed that IRS1 signaling may promote a proinflammatory response following PO. Together, these data identify IRS1 and Akt1 as critical signaling nodes that mediate LV remodeling in both mice and humans.

In vivo glucoregulation and tissue-specific glucose uptake in female Akt substrate 160 kDa knockout rats

The Rab GTPase activating protein known as Akt substrate of 160 kDa (AS160 or TBC1D4) regulates insulin-stimulated glucose uptake in skeletal muscle, the heart, and white adipose tissue (WAT). A novel rat AS160-knockout (AS160-KO) was created with CRISPR/Cas9 technology. Because female AS160-KO versus wild type (WT) rats had not been previously evaluated, the primary objective of this study was to compare female AS160-KO rats with WT controls for multiple, important metabolism-related endpoints. Body mass and composition, physical activity, and energy expenditure were not different between genotypes. AS160-KO versus WT rats were glucose intolerant based on an oral glucose tolerance test (P<0.001) and insulin resistant based on a hyperinsulinemic-euglycemic clamp (HEC; P<0.001). Tissue glucose uptake during the HEC of female AS160-KO versus WT rats was: 1) significantly lower in epitrochlearis (P<0.05) and extensor digitorum longus (EDL; P<0.01) muscles of AS160-KO compared to WT rats; 2) not different in soleus, gastrocnemius or WAT; and 3) ~3-fold greater in the heart (P<0.05). GLUT4 protein content was reduced in AS160-KO versus WT rats in the epitrochlearis (P<0.05), EDL (P<0.05), gastrocnemius (P<0.05), soleus (P<0.05), WAT (P<0.05), and the heart (P<0.005). Insulin-stimulated glucose uptake by isolated epitrochlearis and soleus muscles was lower (P<0.001) in AS160-KO versus WT rats. Akt phosphorylation of insulin-stimulated tissues was not different between the genotypes. A secondary objective was to probe processes that might account for the genotype-related increase in myocardial glucose uptake, including glucose transporter protein abundance (GLUT1, GLUT4, GLUT8, SGLT1), hexokinase II protein abundance, and stimulation of the AMP-activated protein kinase (AMPK) pathway. None of these parameters differed between genotypes. Metabolic phenotyping in the current study revealed AS160 deficiency produced a profound glucoregulatory phenotype in female AS160-KO rats that was strikingly similar to the results previously reported in male AS160-KO rats.

Ablating the Rab-GTPase activating protein TBC1D1 predisposes rats to high-fat diet-induced cardiomyopathy

KEY POINTS

Although the role of TBC1D1 within the heart remains unknown, expression of TBC1D1 increases in the left ventricle following an acute infarction, suggesting a biological importance within this tissue. We investigated the mechanistic role of TBC1D1 within the heart, aiming to establish the consequences of attenuating TBC1D1 signalling in the development of diabetic cardiomyopathy, as well as to determine potential sex differences. TBC1D1 ablation increased plasma membrane fatty acid binding protein content and myocardial palmitate oxidation. Following high-fat feeding, TBC1D1 ablation dramatically increased fibrosis and induced end-diastolic dysfunction in both male and female rats in the absence of changes in mitochondrial bioenergetics. Altogether, independent of sex, ablating TBC1D1 predisposes the left ventricle to pathological remodelling following high-fat feeding, and suggests TBC1D1 protects against diabetic cardiomyopathy.

ABSTRACT

TBC1D1, a Rab-GTPase activating protein, is involved in the regulation of glucose handling and substrate metabolism within skeletal muscle, and is essential for maintaining pancreatic β-cell mass and insulin secretion. However, the function of TBC1D1 within the heart is largely unknown. Therefore, we examined the role of TBC1D1 in the left ventricle and the functional consequence of ablating TBC1D1 on the susceptibility to high-fat diet-induced abnormalities. Since mutations within TBC1D1 (R125W) display stronger associations with clinical parameters in women, we further examined possible sex differences in the predisposition to diabetic cardiomyopathy. In control-fed animals, TBC1D1 ablation did not alter insulin-stimulated glucose uptake, or echocardiogram parameters, but increased accumulation of a plasma membrane fatty acid transporter and the capacity for palmitate oxidation. When challenged with an 8 week high-fat diet, TBC1D1 knockout rats displayed a four-fold increase in fibrosis compared to wild-type animals, and this was associated with diastolic dysfunction, suggesting a predisposition to diet-induced cardiomyopathy. Interestingly, high-fat feeding only induced cardiac hypertrophy in male TBC1D1 knockout animals, implicating a possible sex difference. Mitochondrial respiratory capacity and substrate sensitivity to pyruvate and ADP were not altered by diet or TBC1D1 ablation, nor were markers of oxidative stress, or indices of overt heart failure. Altogether, independent of sex, ablation of TBC1D1 not only increased the susceptibility to high-fat diet-induced diastolic dysfunction and left ventricular fibrosis, independent of sex, but also predisposed male animals to the development of cardiac hypertrophy. These data suggest that TBC1D1 may exert cardioprotective effects in the development of diabetic cardiomyopathy.

Metabolic syndrome diminishes insulin-induced Akt activation and causes a redistribution of Akt-interacting proteins in cardiomyocytes

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors, with insulin resistance as a critical component for its development. Insulin signaling in the heart leads to Akt (also known as PKB) activation, a serine/threonine protein kinase, which regulates cardiac glucose metabolism and growth. Cardiac metabolic inflexibility, characterized by impaired insulin-induced glucose uptake and oxidation, has been reported as an early and consistent change in the heart of different models of MetS and diabetes; however, the evaluation of Akt activation has yielded variable results. Here we report in cardiomyocytes of MetS rats, diminished insulin-induced glucose uptake and Akt activation, evaluated by its impaired mobilization towards the plasma membrane and phosphorylation, and reflected in a re-distribution of its interacting proteins, assessed by label-free mass spectrometry (data are available via ProteomeXchange with identifier PXD013260). We report 45 proteins with diminished abundance in Akt complex of MetS cardiomyocytes, mainly represented by energy metabolism-related proteins, and also, 31 Akt-interacting proteins with increased abundance, which were mainly related to contraction, endoplasmic reticulum stress, and Akt negative regulation. These results emphasize the relevance of Akt in the regulation of energy metabolism in the heart and highlight Akt-interacting proteins that could be involved in the detrimental effects of MetS in the heart.

Cardiac Contractility Modulation Attenuates Chronic Heart Failure in a Rabbit Model via the PI3K/AKT Pathway

The Akt plays an important role in regulating cardiac growth, myocardial angiogenesis, and cell death in cardiac myocytes. However, there are few studies to focus on the responses of the Akt pathway to cardiac contractility modulation (CCM) in a chronic heart failure (HF) model. In this study, the effects of CCM on the treatment of HF in a rabbit model were investigated. Thirty six-month-old rabbits were randomly separated into control, HF, and CCM groups. The rabbits in HF and CCM groups were pressure uploaded, which can cause an aortic constriction. Then, CCM was gradually injected to the myocardium of rabbits in the CCM group, and this process lasted for four weeks with six hours per day. Rabbit body weight, heart weight, and heart beating rates were recorded during the experiment. To assess the CCM impacts, rabbit myocardial histology was examined as well. Additionally, western blot analysis was employed to measure the protein levels of Akt, FOXO3, Beclin, Pi3k, mTOR, GSK-3β, and TORC2 in the myocardial histology of rabbits. Results showed that the body and heart weight of rabbits decreased significantly after suffering HF when compared with those in the control group. However, they gradually recovered after CCM application. The CCM significantly decreased collagen volume fraction in myocardial histology of HF rabbits, indicating that CCM therapy attenuated myocardial fibrosis and collagen deposition. The levels of Akt, FOXO3, Beclin, mTOR, GSK-3β, and TORC2 were significantly downregulated, but Pi3k concentration was greatly upregulated after CCM utilization. Based on these findings, it was concluded that CCM could elicit positive effects on HF therapy, which was potentially due to the variation in the Pi3k/Akt signaling pathway.

Qishen Yiqi Drop Pill, a novel compound Chinese traditional medicine protects against high glucose-induced injury in cardiomyocytes

OBJECTIVE

Qishen Yiqi Drop Pill (QSYQ) has been recognized as a potential protective agent for various cardiovascular diseases. However, the effect of QSYQ in cardiac complications associated with diabetes is not clear currently. In this study, we investigate whether QSYQ could exert cardiac protective effects against high glucose-induced injuries in cardiac H9c2 cells.

METHODS

H9c2 cells were exposed to 24 hours of high glucose in presence or absence of QSYQ and LY294002. Cell cytotoxicity, apoptosis, reactive oxygen species (ROS) generation, mitochondrial membrane potential and mitochondrial permeability transition pore (mPTP) opening were determined. Levels of bax, bcl-2, p53, cleaved caspase-3, PI3K and Akt were evaluated by Western blot.

RESULTS

Our data indicated that QSYQ significantly increased the cell viability and decreased cytotoxicity. By analysing the apoptotic rate as well as the expression levels of cytoapoptosis-related factors including cleaved caspase-3, bax, bcl-2, and p53, we found that QSYQ could remarkably suppress apoptosis of cardiomyoblasts caused by high glucose. In addition, it also showed that QSYQ reduced the generation of ROS. We further found that QSYQ treatment could inhibit the loss of mitochondrial membrane potential and mPTP opening. Moreover, Western blot analysis showed enhanced phosphorylation of PI3K/Akt. The specific inhibitor of PI3K, LY294002 not only inhibited QSYQ induced PI3K/Akt signalling pathway activation, but alleviated its protective effects.

CONCLUSIONS

In summary, these findings demonstrated that QSYQ effectively protected H9c2 cells against the series injuries due to high glucose at least partially by activating the PI3K/Akt signalling pathway.

Modulation of PTEN by hexarelin attenuates coronary artery ligation-induced heart failure in rats

Background/aim

Hexarelin is a synthetic growth hormone-releasing peptide that exerts cardioprotective effects. However, its cardioprotective effect against heart failure (HF) is yet to be explained. This study investigated the therapeutic role of hexarelin and the mechanisms underlying its cardioprotective effects against coronary artery ligation (CAL)-induced HF in rats.

Materials and methods

Rats with four weeks of permanent CAL, induced myocardial infarction, and HF were randomly separated into four groups: the control group (Ctrl), sham group (Sham), hexarelin treatment group (HF + Hx), and heart failure group (HF). The rats were treated with subcutaneous injection of hexarelin (100 µg/kg) in the treatment group or saline in the other groups twice a day for 30 days. Left ventricular (LV) function, oxidative stress, apoptosis, molecular analyses, and cardiac structural and pathological changes in rats were assessed.

Results

The treatment of HF rats with hexarelin significantly induced the upregulation of phosphatase and tensin homologue (PTEN) expression and inhibited the phosphorylation of protein kinase B (Akt) and mammalian target of rapamycin (mTOR) to significantly improve LV function, ameliorate myocardial remodeling, and reduce oxidative stress.

Conclusion

These findings indicate that hexarelin attenuates CAL-induced HF in rats by ameliorating myocardial remodeling, LV dysfunction, and oxidative stress via the upmodulation of PTEN signaling and downregulation of the Akt/mTOR signaling pathway.

Deletion of protein kinase B2 preserves cardiac function by blocking interleukin-6-mediated injury and restores blood pressure during angiotensin II/high-salt-diet-induced hypertension

OBJECTIVE

Protein kinase B2 (AKT2) is implicated in cardiomyocyte survival during various stress conditions. However, the role of AKT2 in heart function, cardiac hypertrophy and blood pressure (BP) control during hypertension is not fully understood. Therefore, we sought to determine whether the deletion of AKT2 protects cardiac function during angiotensin II/high-salt-diet (AngII/HSD) treatment and find out the signaling pathway.

METHODS

Male C57BL/6J (wild type), AKT2 knockout and interleukin (IL)-6 knockout mice were fed a 4% NaCl diet for 5 weeks. In the last week, mice were split in two groups and infused subcutaneously with either vehicle or AngII (1.5 μg/h per mouse) for 1 week. Then, BP and cardiac function were assessed. Immunohistology of IL-6 and monocyte chemoattractant protein 1 was performed to detect inflammation in the heart. Masson's trichrome staining was performed to evaluate cardiac fibrosis. Heart tissue homogenates and neonatal mice cardiomyocytes were collected to analyze oxidative stress.

RESULTS

Compared with wild-type mice, AKT2 knockout mice maintained BP and showed better left ventricle ejection fraction, lower level of fibrosis, reduced oxidative stress, reduced IL-6 expression and less macrophage infiltration, when treated with AngII/HSD. IL-6 knockout mice treated with AngII/HSD also showed alleviated left ventricular function, fibrosis, oxidative stress and macrophage infiltration compared with wild type.

CONCLUSION

AKT2 deficiency prevents the development of AngII/HSD-induced hypertension, cardiac dysfunction and myocardial injury including oxidative stress, fibrosis and inflammation by suppressing IL-6 expression. These data reveal an important role of the AKT2-IL-6 pathway in mediating AngII/HSD-induced hypertension and cardiomyopathy.

Whole body glucoregulation and tissue-specific glucose uptake in a novel Akt substrate of 160 kDa knockout rat model

Akt substrate of 160 kDa (also called AS160 or TBC1D4) is a Rab GTPase activating protein and key regulator of insulin-stimulated glucose uptake which is expressed by multiple tissues, including skeletal muscle, white adipose tissue (WAT) and the heart. This study introduces a novel rat AS160-knockout (AS160-KO) model that was created using CRISPR/Cas9 technology. We compared male AS160-KO versus wildtype (WT) rats for numerous metabolism-related endpoints. Body mass, body composition, energy expenditure and physical activity did not differ between genotypes. Oral glucose intolerance was detected in AS160-KO versus WT rats (P<0.005). A hyperinsulinemic-euglycemic clamp (HEC) revealed insulin resistance for glucose infusion rate (P<0.05) with unaltered hepatic glucose production in AS160-KO versus WT rats. Genotype-effects on glucose uptake during the HEC: 1) was significantly lower in epitrochlearis (P<0.01) and extensor digitorum longus (P<0.05) of AS160-KO versus WT rats, and tended to be lower for AS160-KO versus WT rats in the soleus (P<0.06) and gastrocnemius (P<0.08); 2) tended to be greater for AS160-KO versus WT rats in white adipose tissue (P = 0.09); and 3) was significantly greater in the heart (P<0.005) of AS160-KO versus WT rats. GLUT4 protein abundance was significantly lower for AS160-KO versus WT rats in each tissue analyzed (P<0.01–0.001) except the gastrocnemius. Ex vivo insulin-stimulated glucose uptake was significantly lower (P<0.001) for AS160-KO versus WT rats in isolated epitrochlearis or soleus. Insulin-stimulated Akt phosphorylation (in vivo or ex vivo) did not differ between genotypes for any tissue tested. Ex vivo AICAR-stimulated glucose uptake by isolated epitrochlearis was significantly lower for AS160-KO versus WT rats (P<0.01) without genotype-induced alteration in AMP-activated protein phosphorylation. This unique AS160-KO rat model, which elucidated striking genotype-related modifications in glucoregulation, will enable future research aimed at understanding AS160’s roles in numerous physiological processes in response to various interventions (e.g., diet and/or exercise).

Molecular mechanism of lipid-induced cardiac insulin resistance and contractile dysfunction

Long-chain fatty acids are the main cardiac substrates from which ATP is generated continually to serve the high energy demand and sustain the normal function of the heart. Under healthy conditions, fatty acid β-oxidation produces 50-70% of the energy demands with the remainder largely accounted for by glucose. Chronically increased dietary lipid supply often leads to excess lipid accumulation in the heart, which is linked to a variety of maladaptive phenomena, such as insulin resistance, cardiac hypertrophy and contractile dysfunction. CD36, the predominant cardiac fatty acid transporter, has a key role in setting the heart on a road to contractile dysfunction upon the onset of chronic lipid oversupply by translocating to the cell surface and opening the cellular 'doors' for fatty acids. The sequence of events after the CD36-mediated myocellular lipid accumulation is less understood, but in general it has been accepted that the excessively imported lipids cause insulin resistance, which in turn leads to contractile dysfunction. There are several gaps of knowledge in this proposed order of events which this review aims to discuss. First, the molecular mechanisms underlying lipid-induced insulin resistance are not yet completely disclosed. Specifically, several mediators have been proposed, such as diacylglycerols, ceramides, peroxisome proliferator-activated receptors (PPAR), inflammatory kinases and reactive oxygen species (ROS), but their relative contributions to the onset of insulin resistance and their putatively synergistic actions are topics of controversy. Second, there are also pieces of evidence that lipids can induce contractile dysfunction independently of insulin resistance. Perhaps, a more integrative view is needed, in which several lipid-induced pathways operate synergistically or in parallel to induce contractile dysfunction. Unraveling of these processes is expected to be important in designing effective therapeutic strategies to protect the lipid-overloaded heart.

Mitochondrial genome modulates myocardial Akt/Glut/HK salvage pathway in spontaneously hypertensive rats adapted to chronic hypoxia

Recently we have shown that adaptation to continuous normobaric hypoxia (CNH) decreases myocardial ischemia/reperfusion injury in spontaneously hypertensive rats (SHR) and in a conplastic strain (SHR-mt^BN). The protective effect was stronger in the latter group characterized by a selective replacement of the SHR mitochondrial genome with that of a more ischemia-resistant Brown Norway strain. The aim of the present study was to examine the possible involvement of the hypoxia inducible factor (HIF)-dependent pathway of the protein kinase B/glucose transporters/hexokinase (Akt/GLUT/HK) in this mitochondrial genome-related difference of the cardioprotective phenotype. Adult male rats were exposed for 3 wk to CNH ([Formula: see text] 0.1). The expression of dominant isoforms of Akt, GLUT, and HK in left ventricular myocardium was determined by real-time RT-PCR and Western blotting. Subcellular localization of GLUTs was assessed by quantitative immunofluorescence. Whereas adaptation to hypoxia markedly upregulated protein expression of HK2, GLUT1, and GLUT4 in both rat strains, Akt2 protein level was significantly increased in SHR-mt^BN only. Interestingly, a higher content of HK2 was revealed in the sarcoplasmic reticulum-enriched fraction in SHR-mt^BN after CNH. The increased activity of HK determined in the mitochondrial fraction after CNH in both strains suggested an increase of HK association with mitochondria. Interestingly, HIF1a mRNA increased and HIF2a mRNA decreased after CNH, the former effect being more pronounced in SHR-mt^BN than in SHR. Pleiotropic effects of upregulated Akt2 along with HK translocation to mitochondria and mitochondria-associated membranes can potentially contribute to a stronger CNH-afforded cardioprotection in SHR-mt^BN compared with progenitor SHR.

Metallothionein Preserves Akt2 Activity and Cardiac Function via Inhibiting TRB3 in Diabetic Hearts

Cardiac insulin resistance is a key pathogenic factor for diabetic cardiomyopathy (DCM), but the mechanism remains largely unclear. We found that diabetic hearts exhibited decreased phosphorylation of total Akt and isoform Akt2 but not Akt1 in wild-type (WT) male FVB mice, which was accompanied by attenuation of Akt downstream glucose metabolic signal. All of these signal changes were not observed in metallothionein cardiac-specific transgenic (MT-TG) hearts. Furthermore, insulin-induced glucose metabolic signals were attenuated only in WT diabetic hearts. In addition, diabetic hearts exhibited increased Akt-negative regulator tribbles pseudokinase 3 (TRB3) expression only in WT mice, suggesting that MT may preserve Akt2 function via inhibiting TRB3. Moreover, MT prevented tert-butyl hydroperoxide (tBHP)-reduced insulin-stimulated Akt2 phosphorylation in MT-TG cardiomyocytes, which was abolished by specific silencing of Akt2. Specific silencing of TRB3 blocked tBHP inhibition of insulin-stimulated Akt2 phosphorylation in WT cardiomyocytes, whereas overexpression of TRB3 in MT-TG cardiomyocytes and hearts abolished MT preservation of insulin-stimulated Akt2 signals and MT prevention of DCM. Most importantly, supplementation of Zn to induce MT preserved cardiac Akt2 signals and prevented DCM. These results suggest that diabetes-inhibited cardiac Akt2 function via TRB3 upregulation leads to aberrant cardiac glucose metabolism. MT preservation of cardiac Akt2 function by inhibition of TRB3 prevents DCM.

Downregulation of Akt2 attenuates ER stress-induced cytotoxicity through JNK-Wnt pathway in cardiomyocytes

Akt, also known as protein kinase B (PKB), is a serine/threonine kinase that promotes survival and growth in response to extracellular signals. Akt1 has been demonstrated to play vital roles in cardiovascular diseases, but the role of Akt2 in cardiomyocytes is not fully understood. This study investigated the effect of Akt2 knockdown on tunicamycin (TM)-induced cytotoxicity in cardiomyocytes and the underlying mechanisms with a focus on the JNK-Wnt pathway. TM treatment significantly increased the expression of Akt2 at both mRNA and protein levels, which was shown to be mediated by the induction of reactive oxygen species (ROS). Knockdown of Akt2 expression via siRNA transfection markedly increased cell viability, decreased lactate dehydrogenase (LDH) release and reduced cell apoptosis after TM exposure. The results of western blot showed that downregulation of Akt2 also attenuated the TM-induced activation of the unfolded protein response (UPR) factors and ER stress associated pro-apoptotic proteins. In addition, Si-Akt2 transfection partially prevented the TM-induced decrease in nuclear localization of β-catenin. By using the selective inhibitor SP-600,125 to inhibit JNK phosphorylation, we found that knockdown of Akt2-induced protection and inhibition of ER stress was mediated by reversing TM-induced decrease of Wnt through the JNK pathway. In summary, these data suggested that Akt2 play a pivotal role in regulating cardiomyocyte survival during ER stress by modulating the JNK-Wnt pathway.

Connexin43 and zonula occludens-1 are targets of Akt in cardiomyocytes that correlate with cardiac contractile dysfunction in Akt deficient hearts

While deletion of Akt1 results in a smaller heart size and Akt2^-/- mice are mildly insulin resistant, Akt1^-/-/Akt2^-/- mice exhibit perinatal lethality, indicating a large degree of functional overlap between the isoforms of the serine/threonine kinase Akt. The present study aimed to determine the cooperative contribution of Akt1 and Akt2 on the structure and contractile function of adult hearts. To generate an inducible, cardiomyocyte-restricted Akt2 knockout (KO) model, Akt2^flox/flox mice were crossed with tamoxifen-inducible MerCreMer transgenic (MCM) mice and germline Akt1^-/- mice to generate the following genotypes:Akt1^+/+; Akt2^flox/flox (WT), Akt2^flox/flox; α-MHC-MCM (iAkt2 KO), Akt1^-/-, and Akt1^-/-; Akt2^flox/flox; α-MHC-MCM mice (Akt1^-/-/iAkt2 KO). At 28 days after the first tamoxifen injection, Akt1^-/-/iAkt2 KO mice developed contractile dysfunction paralleling increased atrial and brain natriuretic peptide (ANP and BNP) levels, and repressed mitochondrial gene expression. Neither cardiac fibrosis nor apoptosis were detected in Akt1^-/-/iAkt2 KO hearts. To explore potential molecular mechanisms for contractile dysfunction, we investigated myocardial microstructure before the onset of heart failure. At 3 days after the first tamoxifen injection, Akt1^-/-/iAkt2 KO hearts showed decreased expression of connexin43 (Cx43) and connexin-interacting protein zonula occludens-1 (ZO-1). Furthermore, Akt1/2 silencing significantly decreased both Cx43 and ZO-1 expression in cultured neonatal rat cardiomyocytes in concert with reduced beating frequency. Akt1 and Akt2 are required to maintain cardiac contraction. Loss of Akt signaling disrupts gap junction protein, which might precipitate early contractile dysfunction prior to heart failure in the absence of myocardial remodeling, such as hypertrophy, fibrosis, or cell death.

High-concentration hydrogen protects mouse heart against ischemia/reperfusion injury through activation of thePI3K/Akt1 pathway

The study investigated the role of Akt1 through the cardioprotection of high-concentration hydrogen (HCH). C57BL/6 mice were randomly divided into the following groups: sham, I/R, I/R + HCH, I/R + HCH + LY294002 (PI3K inhibitor), I/R + HCH + wortmannin (PI3K inhibitor), I/R + LY294002, and I/R + wortmannin. After 45 min of ischemia, HCH (67% H₂ and 33% O₂) was administered to mice during a 90-min reperfusion. To investigate the role of Akt1 in the protective effects of HCH, mice were divided into the following groups: I/R + A-674563 (Akt1 selective inhibitor), I/R + HCH + A-674563, I/R + CCT128930 (Akt2 selective inhibitor), and I/R + HCH + CCT128930. After a 4-h reperfusion, serum biochemistry, histological, western blotting, and immunohistochemical analyses were performed to evaluate the role of the PI3K-Akt1 pathway in the protection of HCH. In vitro, 75% hydrogen was administered to cardiomyocytes during 4 h of reoxygenation after 3-h hypoxia. Several analyses were performed to evaluate the role of the Akt1 in the protective effects of hydrogen. HCH resulted in the phosphorylation of Akt1 but not Akt2, and Akt1 inhibition markedly abolished HCH-induced cardioprotection. Our findings reveal that HCH may exert cardioprotective effects through a PI3K-Akt1-dependent mechanism.

AKT2 deficiency induces retardation of myocyte development through EndoG-MEF2A signaling in mouse heart

Protein kinase B2 (AKT2) is implicated in diverse process of cardiomyocyte signaling including survival and metabolism. However, the role of AKT2 in myocardium development and the signaling pathway is rarely understood. Therefore, we sought to determine the effect of AKT2 deletion on heart development and its downstream targets. By using experimental animal models and neonatal rat cardiomyocytes (NRCMs), we observed that AKT2 deficiency induces retardation of heart development and increased systemic blood pressure (BP) without affecting cardiac function. Further investigation suggested that deficiency of AKT2 in myocardium results in diminished MEF2A abundance, which induced decreased size of cardiomyocytes. We additionally confirmed that EndoG, which is also regulated by AKT2, is a suppressor of MEF2A in myocardium. Finally, our results proved that AKT2 deficiency impairs the response to β-adrenergic stimuli that normally causes hypertrophy in cardiomyocytes by downregulating MEF2A expression. Our data are the first to show the important role of AKT2 in determining the size of myocardium, its deficiency causes retardation of cardiomyocyte development. We also proved a novel pathway of heart development involving EndoG and MEF2A regulated by AKT2.

Heterozygous deletion of AKT1 rescues cardiac contractility, but not hypertrophy, in a mouse model of Noonan Syndrome with Multiple Lentigines

Noonan Syndrome with Multiple Lentigines (NSML) is associated with congenital heart disease in form of pulmonary valve stenosis and hypertrophic cardiomyopathy (HCM). Genetically, NSML is primarily caused by mutations in the non-receptor protein tyrosine phosphatase SHP2. Importantly, certain SHP2 mutations such as Q510E can cause a particularly severe form of HCM with heart failure in infancy. Due to lack of insight into the underlying pathomechanisms, an effective custom-tailored therapy to prevent heart failure in these patients has not yet been found. SHP2 regulates numerous signaling cascades governing cell growth, differentiation, and survival. Experimental models have shown that NSML mutations in SHP2 cause dysregulation of downstream signaling, in particular involving the protein kinase AKT. AKT, and especially the isoform AKT1, has been shown to be a major regulator of cardiac hypertrophy. We therefore hypothesized that hyperactivation of AKT1 is required for the development of Q510E-SHP2-induced HCM. We previously generated a transgenic mouse model of NSML-associated HCM induced by Q510E-SHP2 expression in cardiomyocytes starting before birth. Mice display neonatal-onset HCM with initially preserved contractile function followed by functional decline around 2months of age. As a proof-of-principle study, our current goal was to establish to which extent a genetic reduction in AKT1 rescues the Q510E-SHP2-induced cardiac phenotype in vivo. AKT1 deletion mice were crossed with Q510E-SHP2 transgenic mice and the resulting compound mutant offspring analyzed. Homozygous deletion of AKT1 greatly reduced viability in our NSML mouse model, whereas heterozygous deletion of AKT1 in combination with Q510E-SHP2 expression was well tolerated. Despite normalization of pro-hypertrophic signaling downstream of AKT, heterozygous deletion of AKT1 did not ameliorate cardiac hypertrophy induced by Q510E-SHP2. However, the functional decline caused by Q510E-SHP2 expression was effectively prevented by reducing AKT1 protein. This demonstrates that AKT1 plays an important role in the underlying pathomechanism. Furthermore, the functional rescue was associated with an increase in the capillary-to-cardiomyocyte ratio and normalization of capillary density per tissue area in the compound mutant offspring. We therefore speculate that limited oxygen supply to the hypertrophied cardiomyocytes may contribute to the functional decline observed in our mouse model of NSML-associated HCM.

Phosphoinositide 3-kinase (p110α) gene delivery limits diabetes-induced cardiac NADPH oxidase and cardiomyopathy in a mouse model with established diastolic dysfunction

Phosphoinositide 3-kinase [PI3K (p110α)] is able to negatively regulate the diabetes-induced increase in NADPH oxidase in the heart. Patients affected by diabetes exhibit significant cardiovascular morbidity and mortality, at least in part due to a cardiomyopathy characterized by oxidative stress and left ventricular (LV) dysfunction. Thus, PI3K (p110α) may represent a novel approach to protect the heart from diabetes-induced cardiac oxidative stress and dysfunction. In the present study, we investigated the therapeutic potential of a delayed intervention with cardiac-targeted PI3K gene therapy, administered to mice with established diabetes-induced LV diastolic dysfunction. Diabetes was induced in 6-week-old male mice by streptozotocin (STZ). After 8 weeks of untreated diabetes, LV diastolic dysfunction was confirmed by a reduction in echocardiography-derived transmitral E/A ratio. Diabetic and non-diabetic mice were randomly allocated to receive either recombinant adeno-associated viral vector-6 carrying a constitutively-active PI3K construct (recombinant adeno-associated-virus 6-constitutively active PI3K (p110α) (caPI3K) (rAAV6-caPI3K), single i.v. injection, 2 × 1011 vector genomes) or null vector, and were followed for a further 6 or 8 weeks. At study endpoint, diabetes-induced LV dysfunction was significantly attenuated by a single administration of rAAV6-caPI3K, administered 8 weeks after the induction of diabetes. Diabetes-induced impairments in each of LV NADPH oxidase, endoplasmic reticulum (ER) stress, apoptosis, cardiac fibrosis and cardiomyocyte hypertrophy, in addition to LV systolic dysfunction, were attenuated by delayed intervention with rAAV6-caPI3K. Hence, our demonstration that cardiac-targeted PI3K (p110α) gene therapy limits diabetes-induced up-regulation of NADPH oxidase and cardiac remodelling suggests new insights into promising approaches for the treatment of diabetic cardiomyopathy, at a clinically relevant time point (after diastolic dysfunction is manifested).

Exogenous cathepsin V protein protects human cardiomyocytes HCM from angiotensin Ⅱ-Induced hypertrophy

Angiotensin (Ang) Ⅱ-induced cardiac hypertrophy can deteriorate to heart failure, a leading cause of mortality. Endogenous Cathepsin V (CTSV) has been reported to be cardioprotective against hypertrophy. However, little is known about the effect of exogenous CTSV on cardiac hypertrophy. We used the human cardiomyocytes HCM as a cell model to investigate the effects of exogenous CTSV on Ang Ⅱ-induced cardiac cell hypertrophy. Cell surface area and expression of classical markers of hypertrophy were analyzed. We further explored the mechanism of CTSV cardioprotective by assessing the levels and activities of PI3K/Akt/mTOR and MAPK signaling pathway proteins. We found that pre-treating cardiomyocytes with CTSV could significantly inhibit Ang Ⅱ-induced hypertrophy. The mRNA expression of hypertrophy markers ANP, BNP and β-MHC was obviously elevated in Ang Ⅱ-treated cardiac cells. Whereas, exogenous CTSV effectively halted this elevation. Further study revealed that the protective effects of exogenous CTSV might be mediated by repressing the phosphorylation of proteins in the PI3K/Akt/mTOR and MAPK pathways. Based on our results, we concluded that exogenous CTSV inhibited Ang Ⅱ-induced hypertrophy in HCM cells by inhibiting PI3K/Akt/mTOR. This study provides experimental evidence for the application of CTSV protein for the treatment of cardiac hypertrophy.

AKT2 Blocks Nucleus Translocation of Apoptosis-Inducing Factor (AIF) and Endonuclease G (EndoG) While Promoting Caspase Activation during Cardiac Ischemia

The AKT (protein kinase B, PKB) family has been shown to participate in diverse cellular processes, including apoptosis. Previous studies demonstrated that protein kinase B2 (AKT2^−/−) mice heart was sensitized to apoptosis in response to ischemic injury. However, little is known about the mechanism and apoptotic signaling pathway. Here, we show that AKT2 inhibition does not affect the development of cardiomyocytes but increases cell death during cardiomyocyte ischemia. Caspase-dependent apoptosis of both the extrinsic and intrinsic pathway was inactivated in cardiomyocytes with AKT2 inhibition during ischemia, while significant mitochondrial disruption was observed as well as intracytosolic translocation of cytochrome C (Cyto C) together with apoptosis-inducing factor (AIF) and endonuclease G (EndoG), both of which are proven to conduct DNA degradation in a range of cell death stimuli. Therefore, mitochondria-dependent cell death was investigated and the results suggested that AIF and EndoG nucleus translocation causes cardiomyocyte DNA degradation during ischemia when AKT2 is blocked. These data are the first to show a previous unrecognized function and mechanism of AKT2 in regulating cardiomyocyte survival during ischemia by inducing a unique mitochondrial-dependent DNA degradation pathway when it is inhibited.

Isorhamnetin protects against cardiac hypertrophy through blocking PI3K-AKT pathway

Isorhamnetin, a flavonoid compound extracted from the Chinese herb Hippophae rhamnoides L., is well known for its anti-inflammatory, anti-oxidative, anti-adipogenic, anti-proliferative, and anti-tumor activities. However, the role of isorhamnetin in cardiac hypertrophy has not been reported. The aims of the present study were to find whether isorhamnetin could alleviate cardiac hypertrophy and to define the underlying molecular mechanisms. Here, we investigated the effects of isorhamnetin (100 mg/kg/day) on cardiac hypertrophy induced by aortic banding in mice. Cardiac hypertrophy was evaluated by echocardiographic, hemodynamic, pathological, and molecular analyses. Our data demonstrated that isorhamnetin could inhibit cardiac hypertrophy and fibrosis 8 weeks after aortic banding. The results further revealed that the effect of isorhamnetin on cardiac hypertrophy was mediated by blocking the activation of phosphatidylinositol 3-kinase-AKT signaling pathway. In vitro studies performed in neonatal rat cardiomyocytes confirmed that isorhamnetin could attenuate cardiomyocyte hypertrophy induced by angiotensin II, which was associated with phosphatidylinositol 3-kinase-AKT signaling pathway. In conclusion, these data indicate for the first time that isorhamnetin has protective potential for targeting cardiac hypertrophy by blocking the phosphatidylinositol 3-kinase-AKT signaling pathway. Thus, our study suggests that isorhamnetin may represent a potential therapeutic strategy for the treatment of cardiac hypertrophy and heart failure.

Zebrafish akt2 is essential for survival, growth, bone development, and glucose homeostasis

As one of three akt isoforms, akt2 plays a key role in the regulation of widely divergent cellular processes in mammals. However, its role and underlying mechanisms in zebrafish remain largely unknown. To elucidate the function of akt2 in zebrafish, we generated zebrafish lacking akt2 gene via CRISPR/Cas9 technology. Akt2-null zebrafish exhibit partial lethality and severe growth deficiency, which is different from those observed in akt2-null mice. Furthermore, akt2-null zebrafish display deficiency in fin ray development, but their cartilage is not affected. Similar to observations in akt2-null mice, akt2-null zebrafish display impaired glucose homeostasis. However, in contrast to that in akt2-null mice, insulin level is lower in akt2-null zebrafish, implicating the symptoms of type I diabetes exhibited in akt2-null zebrafish. In addition, transcriptome analysis reveals that the genes involved in metabolism and osteogenesis are disturbed in akt2-null zebrafish. Taken together, these data not only support an important role of akt2 in zebrafish survival, growth, bone development and glucose homeostasis, but also suggest that akt2 has divergent functions between mice and zebrafish, even though they are evolutionarily conserved.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

Insulin Signaling and Heart Failure

Heart failure is associated with generalized insulin resistance. Moreover, insulin-resistant states such as type 2 diabetes mellitus and obesity increases the risk of heart failure even after adjusting for traditional risk factors. Insulin resistance or type 2 diabetes mellitus alters the systemic and neurohumoral milieu, leading to changes in metabolism and signaling pathways in the heart that may contribute to myocardial dysfunction. In addition, changes in insulin signaling within cardiomyocytes develop in the failing heart. The changes range from activation of proximal insulin signaling pathways that may contribute to adverse left ventricular remodeling and mitochondrial dysfunction to repression of distal elements of insulin signaling pathways such as forkhead box O transcriptional signaling or glucose transport, which may also impair cardiac metabolism, structure, and function. This article will review the complexities of insulin signaling within the myocardium and ways in which these pathways are altered in heart failure or in conditions associated with generalized insulin resistance. The implications of these changes for therapeutic approaches to treating or preventing heart failure will be discussed.

Prolonged hyperinsulinemia affects metabolic signal transduction markers in a tissue specific manner

Insulin dysregulation is common in horses although the mechanisms of metabolic dysfunction are poorly understood. We hypothesized that insulin signaling in striated (cardiac and skeletal) muscle and lamellae may be mediated through different receptors as a result of receptor content, and that transcriptional regulation of downstream signal transduction and glucose transport may also differ between tissues sites during hyperinsulinemia. Archived samples from horses treated with a prolonged insulin infusion or a balanced electrolyte solution were used. All treated horses developed marked hyperinsulinemia and clinical laminitis. Protein expression was compared across tissues for the insulin receptor and insulin-like growth factor 1 receptor (IGF-1R) by immunoblotting. Gene expression of metabolic insulin-signaling markers (insulin receptor substrate 1, Akt2, and glycogen synthase kinase 3 beta [GSK-3β]) and glucose transport (basal glucose transporter 1 and insulin-sensitive glucose transporter 4) was evaluated using real-time reverse transcription polymerase chain reaction. Lamellar tissue contained significantly more IGF-1R protein than skeletal muscle, indicating the potential significance of IGF-1R signaling for this tissue. Gene expression of the selected markers of insulin signaling and glucose transport in skeletal muscle and lamellar tissues was unaffected by prolonged hyperinsulinemia. In contrast, the significant upregulation of Akt2, GSK-3β, GLUT1, and GLUT4 gene expression in cardiac tissue suggested that the prolonged hyperinsulinemia induced an increase in insulin sensitivity and a transcriptional activation of glucose transport. Responses to insulin are tissue-specific, and extrapolation of data across tissue sites is inappropriate.

Nutrient-sensing mTORC1: Integration of metabolic and autophagic signals

The ability of adult cardiomyocytes to regenerate is limited, and irreversible loss by cell death plays a crucial role in heart diseases. Autophagy is an evolutionarily conserved cellular catabolic process through which long-lived proteins and damaged organelles are targeted for lysosomal degradation. Autophagy is important in cardiac homeostasis and can serve as a protective mechanism by providing an energy source, especially in the face of sustained starvation. Cellular metabolism is closely associated with cell survival, and recent evidence suggests that metabolic and autophagic signaling pathways exhibit a high degree of crosstalk and are functionally interdependent. In this review, we discuss recent progress in our understanding of regulation of autophagy and its crosstalk with metabolic signaling, with a focus on the nutrient-sensing mTOR complex 1 (mTORC1) pathway.

Curcumin Protects Neonatal Rat Cardiomyocytes against High Glucose-Induced Apoptosis via PI3K/Akt Signalling Pathway

The function of curcumin on NADPH oxidase-related ROS production and cardiac apoptosis, together with the modulation of protein signalling pathways, was investigated in cardiomyocytes. Primary cultures of neonatal rat cardiomyocytes were exposed to 30 mmol/L high glucose with or without curcumin. Cell viability, apoptosis, superoxide formation, the expression of NADPH oxidase subunits, and potential regulatory molecules, Akt and GSK-3β, were assessed in cardiomyocytes. Cardiomyocytes exposure to high glucose led to an increase in both cell apoptosis and intracellular ROS levels, which were strongly prevented by curcumin treatment (10 μM). In addition, treatment with curcumin remarkably suppressed the increased activity of Rac1, as well as the enhanced expression of gp91(phox) and p47(phox) induced by high glucose. Lipid peroxidation and SOD were reversed in the presence of curcumin. Furthermore, curcumin treatment markedly inhibited the reduced Bcl-2/Bax ratio elicited by high glucose exposure. Moreover, curcumin significantly increased Akt and GSK-3β phosphorylation in cardiomyocytes treated with high glucose. In addition, LY294002 blocked the effects of curcumin on cardiomyocytes exposure to high glucose. In conclusion, these results demonstrated that curcumin attenuated high glucose-induced cardiomyocyte apoptosis by inhibiting NADPH-mediated oxidative stress and this protective effect is most likely mediated by PI3K/Akt-related signalling pathway.

Novel remodeling of the mouse heart mitochondrial proteome in response to acute insulin stimulation

BACKGROUND AND AIM

Mitochondrial dysfunction contributes to the pathophysiology of diabetic cardiomyopathy. The aim of this study was to investigate the acute changes in the mitochondrial proteome in response to insulin stimulation.

METHODS AND RESULTS

Cardiac mitochondria from C57BL/6 mice after insulin stimulation were analyzed using two-dimensional fluorescence difference gel electrophoresis. MALDI-TOF MS/MS was utilized to identify differences. Two enzymes involved in metabolism and four structural proteins were identified. Succinyl-CoA ligase [ADP forming] subunit beta was identified as one of the differentially regulated proteins. Upon insulin stimulation, a relatively more acidic isoform of this protein was increased by 53% and its functional activity was decreased by ∼32%.

CONCLUSIONS

This proteomic remodeling in response to insulin stimulation may play an important role in the normal and diabetic heart.