Cardioprotective Effects of Palmitoleic Acid (C16:1n7) in a Mouse Model of Catecholamine-Induced Cardiac Damage Are Mediated by PPAR Activation

Palmitoleic acid (C16:1n7) has been identified as a regulator of physiological cardiac hypertrophy. In the present study, we aimed to investigate the molecular pathways involved in C16:1n7 responses in primary murine cardiomyocytes (PCM) and a mouse model of isoproterenol (ISO)-induced cardiac damage. PCMs were stimulated with C16:1n7 or a vehicle. Afterwards, RNA sequencing was performed using an Illumina HiSeq sequencer. Confirmatory analysis was performed in PCMs and HL-1 cardiomyocytes. For an in vivo study, 129 sv mice were orally treated with a vehicle or C16:1n7 for 22 days. After 5 days of pre-treatment, the mice were injected with ISO (25 mg/kg/d s. c.) for 4 consecutive days. Cardiac phenotyping was performed using echocardiography. In total, 129 genes were differentially expressed in PCMs stimulated with C16:1n7, including Angiopoietin-like factor 4 (Angptl4) and Pyruvate Dehydrogenase Kinase 4 (Pdk4). Both Angptl4 and Pdk4 are proxisome proliferator-activated receptor α/δ (PPARα/δ) target genes. Our in vivo results indicated cardioprotective and anti-fibrotic effects of C16:1n7 application in mice. This was associated with the C16:1n7-dependent regulation of the cardiac PPAR-specific signaling pathways. In conclusion, our experiments demonstrated that C16:1n7 might have protective effects on cardiac fibrosis and inflammation. Our study may help to develop future lipid-based therapies for catecholamine-induced cardiac damage.

Cardiac expression of microRNA-7 is associated with adverse cardiac remodeling

Although microRNA-7 (miRNA-7) is known to regulate proliferation of cancer cells by targeting Epidermal growth factor receptor (EGFR/ERBB) family, less is known about its role in cardiac physiology. Transgenic (Tg) mouse with cardiomyocyte-specific overexpression of miRNA-7 was generated to determine its role in cardiac physiology and pathology. Echocardiography on the miRNA-7 Tg mice showed cardiac dilation instead of age-associated physiological cardiac hypertrophy observed in non-Tg control mice. Subjecting miRNA-7 Tg mice to transverse aortic constriction (TAC) resulted in cardiac dilation associated with increased fibrosis bypassing the adaptive cardiac hypertrophic response to TAC. miRNA-7 expression in cardiomyocytes resulted in significant loss of ERBB2 expression with no changes in ERBB1 (EGFR). Cardiac proteomics in the miRNA-7 Tg mice showed significant reduction in mitochondrial membrane structural proteins compared to NTg reflecting role of miRNA-7 beyond the regulation of EGFR/ERRB in mediating cardiac dilation. Consistently, electron microscopy showed that miRNA-7 Tg hearts had disorganized rounded mitochondria that was associated with mitochondrial dysfunction. These findings show that expression of miRNA-7 in the cardiomyocytes results in cardiac dilation instead of adaptive hypertrophic response during aging or to TAC providing insights on yet to be understood role of miRNA-7 in cardiac function.

Casein Kinase-2 Interacting Protein-1 Regulates Physiological Cardiac Hypertrophy via Inhibition of Histone Deacetylase 4 Phosphorylation

Different kinds of mechanical stimuli acting on the heart lead to different myocardial phenotypes. Physiological stress, such as exercise, leads to adaptive cardiac hypertrophy, which is characterized by a normal cardiac structure and improved cardiac function. Pathological stress, such as sustained cardiac pressure overload, causes maladaptive cardiac remodeling and, eventually, heart failure. Casein kinase-2 interacting protein-1 (CKIP-1) is an important regulator of pathological cardiac remodeling. However, the role of CKIP-1 in physiological cardiac hypertrophy is unknown. We subjected wild-type (WT) mice to a swimming exercise program for 21 days, which caused an increase in myocardial CKIP-1 protein and mRNA expression. We then subjected CKIP-1 knockout (KO) mice and myocardial-specific CKIP-1-overexpressing mice to the 21-day swimming exercise program. Histological and echocardiography analyses revealed that CKIP-1 KO mice underwent pathological cardiac remodeling after swimming, whereas the CKIP-1-overexpressing mice had a similar cardiac phenotype to the WT controls. Histone deacetylase 4 (HDAC4) is a key molecule in the signaling cascade associated with pathological hypertrophy; the phosphorylation levels of HDAC4 were markedly higher in CKIP-1 KO mouse hearts after the swimming exercise program. The phosphorylation levels of HDAC4 did not change after swimming in the hearts of CKIP-1-overexpressing or WT mice. Our results indicate that swimming, a mechanical stress that leads to physiological hypertrophy, triggers pathological cardiac remodeling in CKIP-1 KO mice. CKIP-1 is necessary for physiological cardiac hypertrophy in vivo, and for modulating the phosphorylation level of HDAC4 after physiological stress. Genetically engineering CKIP-1 expression affected heart health in response to exercise.

Molecular Mechanisms of Nigella sativa- and Nigella sativa Exercise-Induced Cardiac Hypertrophy in Rats

Background. In our lab, we demonstrated cardiac hypertrophy induced by long-term administration of Nigella sativa (Ns) with enhanced function. Therefore, we aim to investigate the molecular mechanisms of Ns-induced cardiac hypertrophy, compare it with that induced by exercise training, and explore any possible synergistic effect of these two interventions. Method. Twenty adult Wistar male rats were divided into control (C), Ns-fed (N.s.), exercise-trained (Ex.), Ns-fed exercise-trained (N.s.Ex.) groups. 800 mg/kg of Ns was administered orally to N.s. rats. Ex. rats were trained on a treadmill with speed 18 m/min and grade 32° for two hours daily, and the N.s.Ex. group underwent both interventions. After 8 weeks, Immunohistochemical slides of the left ventricles were prepared using rat growth hormone (GH), insulin-like growth factor I (IGF-I), angiotensin-II receptors 1 (AT-I), endothelin-I (ET-1), Akt-1, and Erk-1. Cell diameter and number of nuclei were measured. Results. Cardiomyocyte diameter, number of nuclei, GH, and Akt were significantly higher in N.s, Ex., and N.s.Ex groups compared with the controls. IGF-I, AT-1, and ET-1 were significantly higher in Ex. rats only compared with the controls. Erk-1 was lower in N.s., Ex., and N.s.Ex. compared with the controls. Conclusion. We can conclude that Ns-induced cardiac hypertrophy is mediated by the GH-IGF I-PI3P-Akt pathway. Supplementation of Ns to exercise training protocol can block the upregulation of AT-I and ET-1. The combined N.s. exercise-induced cardiac hypertrophy might be a superior model of physiological cardiac hypertrophy and be used as a prophylactic therapy for athletes who are engaged in vigorous exercise activity.

Cardiac Oxidative Signaling and Physiological Hypertrophy in the Na/K-ATPase α1s/sα2s/s Mouse Model of High Affinity for Cardiotonic Steroids

The Na/K-ATPase is the specific receptor for cardiotonic steroids (CTS) such as ouabain and digoxin. At pharmacological concentrations used in the treatment of cardiac conditions, CTS inhibit the ion-pumping function of Na/K-ATPase. At much lower concentrations, in the range of those reported for endogenous CTS in the blood, they stimulate hypertrophic growth of cultured cardiac myocytes through initiation of a Na/K-ATPase-mediated and reactive oxygen species (ROS)-dependent signaling. To examine a possible effect of endogenous concentrations of CTS on cardiac structure and function in vivo, we compared mice expressing the naturally resistant Na/K-ATPase α1 and age-matched mice genetically engineered to express a mutated Na/K-ATPase α1 with high affinity for CTS. In this model, total cardiac Na/K-ATPase activity, α1, α2, and β1 protein content remained unchanged, and the cardiac Na/K-ATPase dose–response curve to ouabain shifted to the left as expected. In males aged 3–6 months, increased α1 sensitivity to CTS resulted in a significant increase in cardiac carbonylated protein content, suggesting that ROS production was elevated. A moderate but significant increase of about 15% of the heart-weight-to-tibia-length ratio accompanied by an increase in the myocyte cross-sectional area was detected. Echocardiographic analyses did not reveal any change in cardiac function, and there was no fibrosis or re-expression of the fetal gene program. RNA sequencing analysis indicated that pathways related to energy metabolism were upregulated, while those related to extracellular matrix organization were downregulated. Consistent with a functional role of the latter, an angiotensin-II challenge that triggered fibrosis in the α1r/rα2s/s mouse failed to do so in the α1s/sα2s/s. Taken together, these results are indicative of a link between circulating CTS, Na/K-ATPase α1, ROS, and physiological cardiac hypertrophy in mice under baseline laboratory conditions.

FoxO1 is required for physiological cardiac hypertrophy induced by exercise but not by constitutively active PI3K

The insulin-like growth factor 1 receptor (IGF1R) and phosphoinositide 3-kinase p110a (PI3K) are critical regulators of exercise-induced physiological cardiac hypertrophy, and provide protection in experimental models of pathological remodeling and heart failure. Forkhead box class O1 (FoxO1) is a transcription factor which regulates cardiomyocyte hypertrophy downstream of IGF1R/PI3K activation in vitro, but its role in physiological hypertrophy in vivo was unknown. We generated cardiomyocyte-specific FoxO1 knockout (cKO) mice and assessed the phenotype under basal conditions and settings of physiological hypertrophy induced by 1) swim training, or 2) cardiac-specific transgenic expression of constitutively active PI3K (caPI3KTg+). Under basal conditions, male and female cKO mice displayed mild interstitial fibrosis compared with control (CON) littermates, but no other signs of cardiac pathology were present. In response to exercise training, female CON mice displayed an increase (~21%) in heart weight normalized to tibia length vs untrained mice. Exercise-induced hypertrophy was blunted in cKO mice. Exercise increased cardiac Akt phosphorylation and IGF1R expression, but was comparable between genotypes. However, differences in Foxo3a, Hsp70 and autophagy markers were identified in hearts of exercised cKO mice. Deletion of FoxO1 did not reduce cardiac hypertrophy in male or female caPI3KTg+ mice. Cardiac Akt and FoxO1 protein expression were significantly reduced in hearts of caPI3KTg+ mice, which may represent a negative feedback mechanism from chronic caPI3K, and negate any further effect of reducing FoxO1 in the cKO. In summary, FoxO1 contributes to exercise-induced hypertrophy. This has important implications when considering FoxO1 as a target for treating the diseased heart.

β-Catenin Regulates Cardiac Energy Metabolism in Sedentary and Trained Mice

The role of canonical Wnt signaling in metabolic regulation and development of physiological cardiac hypertrophy remains largely unknown. To explore the function of β-catenin in the regulation of cardiac metabolism and physiological cardiac hypertrophy development, we used mice heterozygous for cardiac-specific β-catenin knockout that were subjected to a swimming training model. β-Catenin haploinsufficient mice subjected to endurance training displayed a decreased β-catenin transcriptional activity, attenuated cardiomyocytes hypertrophic growth, and enhanced activation of AMP-activated protein kinase (AMPK), phosphoinositide-3-kinase–Akt (Pi3K–Akt), and mitogen-activated protein kinase/extracellular signal-regulated kinases 1/2 (MAPK/Erk1/2) signaling pathways compared to trained wild type mice. We further observed an increased level of proteins involved in glucose aerobic metabolism and β-oxidation along with perturbed activity of mitochondrial oxidative phosphorylation complexes (OXPHOS) in trained β-catenin haploinsufficient mice. Taken together, Wnt/β-catenin signaling appears to govern metabolic regulatory programs, sustaining metabolic plasticity in adult hearts during the adaptation to endurance training.

Mechanisms for the transition from physiological to pathological cardiac hypertrophy

The heart is capable of responding to stressful situations by increasing muscle mass, which is broadly defined as cardiac hypertrophy. This phenomenon minimizes ventricular wall stress for the heart undergoing a greater than normal workload. At initial stages, cardiac hypertrophy is associated with normal or enhanced cardiac function and is considered to be adaptive or physiological; however, at later stages, if the stimulus is not removed, it is associated with contractile dysfunction and is termed as pathological cardiac hypertrophy. It is during physiological cardiac hypertrophy where the function of subcellular organelles, including the sarcolemma, sarcoplasmic reticulum, mitochondria, and myofibrils, may be upregulated, while pathological cardiac hypertrophy is associated with downregulation of these subcellular activities. The transition of physiological cardiac hypertrophy to pathological cardiac hypertrophy may be due to the reduction in blood supply to hypertrophied myocardium as a consequence of reduced capillary density. Oxidative stress, inflammatory processes, Ca2+-handling abnormalities, and apoptosis in cardiomyocytes are suggested to play a critical role in the depression of contractile function during the development of pathological hypertrophy.