AMP-activated protein kinase influences metabolic remodeling in H9c2 cells hypertrophied by arginine vasopressin

Reactivation of fatty acid oxidation by medium chain fatty acid prevents myocyte hypertrophy in H9c2 cell line

Metabolic shift is an important contributory factor for progression of hypertension-induced left ventricular hypertrophy into cardiac failure. Under hypertrophic conditions, heart switches its substrate preference from fatty acid to glucose. Prolonged dependence on glucose for energy production has adverse cardiovascular consequences. It was reported earlier that reactivation of fatty acid metabolism with medium chain triglycerides ameliorated cardiac hypertrophy, oxidative stress and energy level in spontaneously hypertensive rat. However, the molecular mechanism mediating the beneficial effect of medium chain triglycerides remained elusive. It was hypothesized that reduction of cardiomyocyte hypertrophy by medium chain fatty acid (MCFA) is mediated by modulation of signaling pathways over expressed in cardiac hypertrophy. The protective effect of medium chain fatty acid (MCFA) was evaluated in cellular model of myocyte hypertrophy. H9c2 cells were stimulated with Arginine vasopressin (AVP) for the induction of hypertrophy. Cell volume and secretion of brain natriuretic peptide (BNP) were used for assessment of cardiomyocyte hypertrophy. Cells were pretreated with MCFA (Caprylic acid) and metabolic modulation was assessed from the expression of medium-chain acyl-CoA dehydrogenase (MCAD), cluster of differentiation-36 (CD36) and peroxisome proliferator-activated receptor (PPAR)-α mRNA. The signaling molecules modified by MCFA was evaluated from protein expression of mitogen activated protein kinases (MAPK: ERK1/2, p38 and JNK) and Calcineurin A. Pretreatment with MCFA stimulated fatty acid metabolism in hypertrophic H9c2, with concomitant reduction of cell volume and BNP secretion. MCFA reduced activated ERK1/2, JNK and calicineurin A expression mediated by AVP. In conclusion, the beneficial effect of MCFA is possibly mediated by stimulation of fatty acid metabolism and modulation of MAPK and Calcineurin A.

Metoprolol alleviates arginine vasopressin-induced cardiomyocyte hypertrophy by upregulating the AKT1-SERCA2 cascade in H9C2 cells

BACKGROUND

Arginine vasopressin (AVP) is elevated in patients with heart failure, and the increase in the AVP concentration in plasma is positively correlated with disease severity and mortality. Metoprolol (Met) is a beta blocker that is widely used in the clinic to treat pathological cardiac hypertrophy and to improve heart function. However, the specific mechanism by which Met alleviates AVP-induced pathological cardiac hypertrophy is still unknown. Our current study aimed to evaluate the inhibitory effects of Met on AVP-induced cardiomyocyte hypertrophy and the underlying mechanisms.

METHODS

AVP alone or AVP plus Met was added to the wild type or AKT1-overexpressing rat cardiac H9C2 cell line. The cell surface areas and ANP/BNP/β-MHC expressions were used to evaluate the levels of hypertrophy. Western bolting was used to analyze AKT1/P-AKT1, AKT2/P-AKT2, total AKT, SERCA2, and Phospholamban (PLN) expression. Fluo3-AM was used to measure the intracellular Ca2+ stores.

RESULTS

In the current study, we found that AKT1 but not AKT2 mediated the pathogenesis of AVP-induced cardiomyocyte hypertrophy. Sustained stimulation (48 h) with AVP led to hypertrophy in the H9C2 rat cardiomyocytes, resulting in the downregulation of AKT1 (0.48 fold compared to control) and SERCA2 (0.62 fold), the upregulation of PLN (1.32 fold), and the increase in the cytoplasmic calcium concentration (1.52 fold). In addition, AKT1 overexpression increased the expression of SERCA2 (1.34 fold) and decreased the expression of PLN (0.48 fold) in the H9C2 cells. Moreover, we found that Met could attenuate the AVP-induced changes in AKT1, SERCA2 and PLN expression and decreased the cytoplasmic calcium concentration in the H9C2 cells.

CONCLUSIONS

Our results demonstrated that the AKT1-SERCA2 cascade served as an important regulatory pathway in AVP-induced pathological cardiac hypertrophy.

Ninjurin1 regulates striated muscle growth and differentiation

Chronic pressure overload due to aortic valve stenosis leads to pathological cardiac hypertrophy and heart failure. Hypertrophy is accompanied by an increase in myocyte surface area, which requires a proportional increase in the number of cell-cell and cell-matrix contacts to withstand enhanced workload. In a proteomic analysis we identified nerve injury-induced protein 1 (Ninjurin1), a 16kDa transmembrane cell-surface protein involved in cell adhesion and nerve repair, to be increased in hypertrophic hearts from patients with aortic stenosis. We hypothesised that Ninjurin1 is involved in myocyte hypertrophy. We analyzed cardiac biopsies from aortic-stenosis patients and control patients undergoing elective heart surgery. We studied cardiac hypertrophy in mice after transverse aortic constriction and angiotensin II infusions, and performed mechanistic analyses in cultured myocytes. We assessed the physiological role of ninjurin1 in zebrafish during heart and skeletal muscle development. Ninjurin1 was increased in hearts of aortic stenosis patients, compared to controls, as well as in hearts from mice with cardiac hypertrophy. Besides the 16kDa Ninjurin1 (Ninjurin1-16) we detected a 24kDa variant of Ninjurin1 (Ninjurin1-24), which was predominantly expressed during myocyte hypertrophy. We disclosed that the higher molecular weight of Ninjurin1-24 was caused by N-glycosylation. Ninjurin1-16 was contained in the cytoplasm of myocytes where it colocalized with stress-fibers. In contrast, Ninjurin1-24 was localized at myocyte membranes. Gain and loss-of-function experiments showed that Ninjurin1-24 plays a role in myocyte hypertrophy and myogenic differentiation in vitro. Reduced levels of ninjurin1 impaired cardiac and skeletal muscle development in zebrafish. We conclude that Ninjurin1 contributes to myocyte growth and differentiation, and that these effects are mainly mediated by N-glycosylated Ninjurin1-24.

The inhibitory subunit of cardiac troponin (cTnI) is modified by arginine methylation in the human heart

BACKGROUND

The inhibitory subunit of cardiac troponin (cTnI) is a gold standard cardiac biomarker and also an essential protein in cardiomyocyte excitation-contraction coupling. The interactions of cTnI with other proteins are fine-tuned by post-translational modification of cTnI. Mutations in cTnI can lead to hypertrophic cardiomyopathy.

METHODS AND RESULTS

Here we report, for the first time, that cTnI is modified by arginine methylation in human myocardium. Using Western blot, we observed reduced levels of cTnI arginine methylation in human hypertrophic cardiomyopathy compared to dilated cardiomyopathy biopsies. Similarly, using a rat model of cardiac hypertrophy we observed reduced levels of cTnI arginine methylation compared to sham controls. Using mass spectrometry, we identified cTnI methylation sites at R74/R79 and R146/R148 in human cardiac samples. R146 and R148 lie at the boundary between the critical cTnI inhibitory and switch peptides; PRMT1 methylated an extended inhibitory peptide at R146 and R148 in vitro. Mutations at R145 that have been associated with hypertrophic cardiomyopathy hampered R146/R148 methylation by PRMT1 in vitro. H9c2 cardiac-like cells transfected with plasmids encoding for a methylation-deficient R146A/R148A cTnI protein developed cell hypertrophy, with a 32% increase in cell size after 72 h, compared to control cells.

DISCUSSION

Our results provide evidence for a novel and significant cTnI post-translational modification. Our work opens the door to translational investigations of cTnI arginine methylation as a biomarker of disease, which can include e.g. cardiomyopathies, myocardial infarction and heart failure, and offers a novel way to investigate the effect of cTnI mutations in the inhibitory/switch peptides.

miR-21-5p regulates mitochondrial respiration and lipid content in H9C2 cells

Cardiovascular-related pathologies are the single leading cause of death in patients with chronic kidney disease (CKD). Previously, we found that a 5/6th nephrectomy model of CKD leads to an upregulation of miR-21-5p in the left ventricle, targeting peroxisome proliferator-activated receptor-α and altering the expression of numerous transcripts involved with fatty acid oxidation and glycolysis. In the present study, we evaluated the potential for knockdown or overexpression of miR-21-5p to regulate lipid content, lipid peroxidation, and mitochondrial respiration in H9C2 cells. Cells were transfected with anti-miR-21-5p (40 nM), pre-miR-21-5p (20 nM), or the appropriate scrambled oligonucleotide controls before lipid treatment in culture or as part of the Agilent Seahorse XF fatty acid oxidation assay. Overexpression of miR-21-5p attenuated the lipid-induced increase in cellular lipid content, whereas suppression of miR-21-5p augmented it. The abundance of malondialdehyde, a product of lipid peroxidation, was significantly increased with lipid treatment in control cells but attenuated in pre-miR-21-5p-transfected cells. This suggests that miR-21-5p reduces oxidative stress. The cellular oxygen consumption rate (OCR) was increased in both pre-miR-21-5p- and anti-miR-21-5p-transfected cells. Levels of intracellular ATP were significantly higher in anti-mR-21-5p-transfected cells. Pre-miR-21-5p blocked additional increases in OCR in response to etomoxir and palmitic acid. Conversely, anti-miR-21-5p-transfected cells exhibited reduced OCR with both etomoxir and palmitic acid, and the glycolytic capacity was concomitantly reduced. Together, these results indicate that overexpression of miR-21-5p attenuates both lipid content and lipid peroxidation in H9C2 cells. This likely occurs by reducing cellular lipid uptake and utilization, shifting cellular metabolism toward reliance on the glycolytic pathway. NEW & NOTEWORTHY Both overexpression and suppression of miR-21-5p augment basal and maximal mitochondrial respiration. Our data suggest that reliance on glycolytic and fatty acid oxidation pathways can be modulated by the abundance of miR-21-5p within the cell. miR-21-5p regulation of mitochondrial respiration can be modulated by extracellular lipids.

Arginine vasopressin ameliorates spatial learning impairments in chronic cerebral hypoperfusion via V1a receptor and autophagy signaling partially

Chronic cerebral hypoperfusion (CCH) is a major factor contributing to neurological disorders and cognitive decline. Autophagy activation is believed to provide both beneficial and detrimental roles during hypoxic/ischemic cellular injury. Although arginine vasopressin (AVP) has been strongly involved in many behaviors, especially in learning and memory, the effects of AVP on CCH and their molecular mechanisms remain unclear. Here, to investigate whether there was neuroprotective effects of AVP on CCH through V1a receptor (an AVP receptor) signaling, permanent bilateral carotid arteries occlusion (two vessel occlusion, 2VO) was used to establish a rat model of CCH, and hypertonic saline (5.3%) was injected intraperitoneally to induce the secretion of AVP. Results showed that hypertonic saline effectively alleviated spatial learning and memory deficit, enhanced synaptic plasticity of CA3-CA1 hippocampal synapses, upregulated N-methyl-d-aspartate receptor subunit 2B (NR2B) and postsynaptic density protein 95 (PSD-95) surface expressions, reduced oxidative stress and increased Nissl bodies in 2VO model rats. These phenomena were significantly decreased by V1a receptor antagonist SR49059. Interestingly, hypertonic saline also upregulated autophagy in the hippocampus of 2VO rats partly through V1a receptor. These findings imply that AVP has a beneficial role for the treatment of cognitive impairments partly through V1a receptor signaling in CCH, which is possibly related to improving synaptic plasticity by promoting NR2B and PSD-95 externalization and by enhancing autophagy.

Mapping arginine methylation in the human body and cardiac disease

PURPOSE

Arginine methylation (ArgMe) is one of the most ubiquitous PTMs, and hundreds of proteins undergo ArgMe in, for example, brain. However, the scope of ArgMe in many tissues, including the heart, is currently underexplored. Here, we aimed to (i) identify proteins undergoing ArgMe in human organs, and (ii) expose the relevance of ArgMe in cardiac disease.

EXPERIMENTAL DESIGN

The publicly available proteomic data is used to search for ArgMe in 13 human tissues. To induce H9c2 cardiac-like cell hypertrophy glucose is used.

RESULTS

The results show that ArgMe is mainly tissue-specific; nevertheless, the authors suggest an embryonic origin of core ArgMe events. In the heart, 103 mostly novel ArgMe sites in 58 nonhistone proteins are found. The authors provide compelling evidence that cardiac protein ArgMe is relevant to cardiomyocyte ontology, and important for proper cardiac function. This is highlighted by the fact that genetic mutations affecting methylated arginine positions are often associated with cardiac disease, including hypertrophic cardiomyopathy. The pilot experimental data suggesting significant changes in ArgMe profiles of H9c2 cells upon induction of cell hypertrophy using glucose is provided.

CONCLUSIONS AND CLINICAL RELEVANCE

The work calls for in-depth investigation of ArgMe in normal and diseased tissues using methods including clinical proteomics.

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.

Evidence that AMP-activated protein kinase can negatively modulate ornithine decarboxylase activity in cardiac myoblasts

The responses of AMP-activated protein kinase (AMPK) and Ornithine decarboxylase (ODC) to isoproterenol have been examined in H9c2 cardiomyoblasts, AMPK represents the link between cell growth and energy availability whereas ODC, the key enzyme in polyamine biosynthesis, is essential for all growth processes and it is thought to have a role in the development of cardiac hypertrophy. Isoproterenol rapidly induced ODC activity in H9c2 cardiomyoblasts by promoting the synthesis of the enzyme protein and this effect was counteracted by inhibitors of the PI3K/Akt pathway. The increase in enzyme activity became significant between 15 and 30min after the treatment. At the same time, isoproterenol stimulated the phosphorylation of AMPKα catalytic subunits (Thr172), that was associated to an increase in acetyl coenzyme A carboxylase (Ser72) phosphorylation. Downregulation of both α1 and α2 isoforms of the AMPK catalytic subunit by siRNA to knockdown AMPK enzymatic activity, led to superinduction of ODC in isoproterenol-treated cardiomyoblasts. Downregulation of AMPKα increased ODC activity even in cells treated with other adrenergic agonists and in control cells. Analogue results were obtained in SH-SY5Y neuroblastoma cells transfected with a shRNA construct against AMPKα. In conclusion, isoproterenol quickly activates in H9c2 cardiomyoblasts two events that seem to contrast one another. The first one, an increase in ODC activity, is linked to cell growth, whereas the second, AMPK activation, is a homeostatic mechanism that negatively modulates the first. The modulation of ODC activity by AMPK represents a mechanism that may contribute to control cell growth processes.

Interrelationship between cardiac hypertrophy, heart failure, and chronic kidney disease: endoplasmic reticulum stress as a mediator of pathogenesis

Synthesis of transmembrane and secretory proteins occurs within the endoplasmic reticulum (ER) and is extremely important in the normal functioning of both the heart and kidney. The dysregulation of protein synthesis/processing within the ER causes the accumulation of unfolded proteins, thereby leading to ER stress and the activation of the unfolded protein response. Sarcoplasmic reticulum/ER Ca2+ disequilibrium can lead to cardiac hypertrophy via cytosolic Ca2+ elevation and stimulation of the Ca2+/calmodulin, calcineurin, NF-AT3 pathway. Although cardiac hypertrophy may be initially adaptive, prolonged or severe ER stress resulting from the increased protein synthesis associated with cardiac hypertrophy can lead to apoptosis of cardiac myocytes and result in reduced cardiac output and chronic heart failure. The failing heart has a dramatic effect on renal function because of inadequate perfusion and stimulates the release of many neurohumoral factors that may lead to further ER stress within the heart, including angiotensin II and arginine-vasopressin. Renal failure attributable to proteinuria and uremia also induces ER stress within the kidney, which contributes to the transformation of tubular epithelial cells to a fibroblast-like phenotype, fibrosis, and tubular cell apoptosis, further diminishing renal function. As a consequence, cardiorenal syndrome may develop into a vicious circle with poor prognosis. New therapeutic modalities to alleviate ER stress through stimulation of the cytoprotective components of the unfolded protein response, including GRP78 upregulation and eukaryotic initiation factor 2α phosphorylation, may hold promise to reduce the high morbidity and mortality associated with cardiorenal syndrome.

AMPK activation, a preventive therapeutic target in the transition from cardiac injury to heart failure

Heart failure is a progressive muscular disorder leading to a deterioration of the heart characterized by a contractile dysfunction and a chronic energy deficit. As a consequence, the failing heart is unable to meet the normal metabolic and energy needs of the body. The transition between compensated left ventricular hypertrophy and the de-compensated heart is multifactorial, although metabolic disturbances are considered to play a significant role. In this respect, the AMP-activated protein kinase (AMPK) could be a potential target in heart failure development. AMPK senses the energy state of the cell and orchestrates a global metabolic response to energy deprivation. We briefly review here the current knowledge about the chronic energy deficit of the failing heart, as well as the role of AMPK in energy homeostasis and in the control of non-metabolic targets in relation to cardiac hypertrophy and heart failure. The relative importance of energetic and non-metabolic effects in the potential cardioprotective action of AMPK is discussed.