Nadia Hedhli

Activation of the Cardiac Proteasome During Pressure Overload Promotes Ventricular Hypertrophy

Background— The adaptation of cardiac mass to hemodynamic overload requires an adaptation of protein turnover, ie, the balance between protein synthesis and degradation. We tested 2 hypotheses: (1) chronic left ventricular hypertrophy (LVH) activates the proteasome system of protein degradation, especially in the myocardium submitted to the highest wall stress, ie, the subendocardium, and (2) the proteasome system is required for the development of LVH. Methods and Results— Gene and protein expression of proteasome subunits and proteasome activity were measured separately from left ventricular subendocardium and subepicardium, right ventricle, and peripheral tissues in a canine model of severe, chronic (2 years) LVH induced by aortic banding and then were compared with controls. Both gene and protein expressions of proteasome subunits were increased in LVH versus control (P<0.05), which was accompanied by a significant (P<0.05) increase in proteasome activity. Posttranslational modification of the proteasome was also detected by 2-dimensional gel electrophoresis. These changes were found specifically in left ventricular subendocardium but not in left ventricular subepicardium, right ventricle, or noncardiac tissues from the same animals. In a mouse model of chronic pressure overload, a 50% increase in heart mass and a 2-fold increase in proteasome activity (both P<0.05 versus sham) were induced. In that model, the proteasome inhibitor epoxomicin completely prevented LVH while blocking proteasome activation. Conclusions— The increase in proteasome expression and activity found during chronic pressure overload in myocardium submitted to higher stress is also required for the establishment of LVH.

Proteasome inhibition decreases cardiac remodeling after initiation of pressure overload

We tested the possibility that proteasome inhibition may reverse preexisting cardiac hypertrophy and improve remodeling upon pressure overload. Mice were submitted to aortic banding and followed up for 3 wk. The proteasome inhibitor epoxomicin (0.5 mg/kg) or the vehicle was injected daily, starting 2 wk after banding. At the end of the third week, vehicle-treated banded animals showed significant (P<0.05) increase in proteasome activity (PA), left ventricle-to-tibial length ratio (LV/TL), myocyte cross-sectional area (MCA), and myocyte apoptosis compared with sham-operated animals and developed signs of heart failure, including increased lung weight-to-TL ratio and decreased ejection fraction. When compared with that group, banded mice treated with epoxomicin showed no increase in PA, a lower LV/TL and MCA, reduced apoptosis, stabilized ejection fraction, and no signs of heart failure. Because overload-mediated cardiac remodeling largely depends on the activation of the proteasome-regulated transcription factor NF-kappaB, we tested whether epoxomicin would prevent this activation. NF-kappaB activity increased significantly upon overload, which was suppressed by epoxomicin. The expression of NF-kappaB-dependent transcripts, encoding collagen types I and III and the matrix metalloprotease-2, increased (P<0.05) after banding, which was abolished by epoxomicin. The accumulation of collagen after overload, as measured by histology, was 75% lower (P<0.05) with epoxomicin compared with vehicle. Myocyte apoptosis increased by fourfold in hearts submitted to aortic banding compared with sham-operated hearts, which was reduced by half upon epoxomicin treatment. Therefore, we propose that proteasome inhibition after the onset of pressure overload rescues ventricular remodeling by stabilizing cardiac function, suppressing further progression of hypertrophy, repressing collagen accumulation, and reducing myocyte apoptosis.

H11 Kinase Prevents Myocardial Infarction by Preemptive Preconditioning of the Heart

Ischemic preconditioning confers powerful protection against myocardial infarction through pre-emptive activation of survival signaling pathways, but it remains difficult to apply to patients with ischemic heart disease, and its effects are transient. Promoting a sustained activation of preconditioning mechanisms in vivo would represent a novel approach of cardioprotection. We tested the role of the protein H11 kinase (H11K), which accumulates by 4- to 6-fold in myocardium of patients with chronic ischemic heart disease and in experimental models of ischemia. This increased expression was quantitatively reproduced in cardiac myocytes using a transgenic (TG) mouse model. After 45 minutes of coronary artery occlusion and reperfusion, hearts from TG mice showed an 82±5% reduction in infarct size compared with wild-type (WT), which was similar to the 84±4% reduction of infarct size observed in WT after a protocol of ischemic preconditioning. Hearts from TG mice showed significant activation of survival kinases participating in preconditioning, including Akt and the 5′AMP-activated protein kinase (AMPK). H11K directly binds to both Akt and AMPK and promotes their nuclear translocation and their association in a multiprotein complex, which results in a stimulation of survival mechanisms in cytosol and nucleus, including inhibition of proapoptotic effectors (glycogen synthase kinase-3β, Bad, and Foxo), activation of antiapoptotic effectors (protein kinase C&egr;, endothelial and inducible NO synthase isoforms, and heat shock protein 70), increased expression of the hypoxia-inducible factor-1α, and genomic switch to glucose utilization. Therefore, activation of survival pathways by H11K preemptively triggers the antiapoptotic and metabolic response to ischemia and is sufficient to confer cardioprotection in vivo equally potent to preconditioning.

Proteasome inhibitors and cardiac cell growth

Activation of the ubiquitin-proteasome system has been described in different models of cardiac hypertrophy. Cardiac cell growth in response to pressure or volume overload, as well as physiological adaptive hypertrophy, is accompanied by an increase in protein ubiquitination, proteasome subunit expression, and proteasome activity. Importantly, an inhibition of proteasome activity prevents and reverses cardiac hypertrophy and remodelling in vivo. The focus of this review is to provide an update about the mechanisms by which proteasome inhibitors affect cardiac cell growth in adaptive and maladaptive models of cardiac hypertrophy. In the first part, we summarize how the proteasome affects both proteolysis and protein synthesis in a context of cardiac cell growth. In the second part, we show how proteasome inhibition can prevent and reverse cardiac hypertrophy and remodelling in response to different conditions of overload.

Cardiotoxicity of Molecularly Targeted Agents

Cardiac toxicity of molecularly targeted cancer agents is increasingly recognized as a significant side effect of chemotherapy. These new potent therapies may not only affect the survival of cancer cells, but have the potential to adversely impact normal cardiac and vascular function. Unraveling the mechanisms by which these therapies affect the heart and vasculature is crucial for improving drug design and finding alternative therapies to protect patients predisposed to cardiovascular disease. In this review, we summarize the classification and side effects of currently approved molecularly targeted chemotherapeutics.

Increased expression of H11 kinase stimulates glycogen synthesis in the heart.

Objective. H11 kinase is a serine/threonine kinase preferentially expressed in the heart, which participates in cardiac cell growth and also in cytoprotection during ischemia. A cardiac-specific transgenic mouse overexpressing H11 kinase (2- to 7-fold protein increase) has been generated, and is characterized by cardiac hypertrophy with preserved function and protection against irreversible damage during ischemia/reperfusion. In this study, we tested whether H11 kinase also participates in the metabolic adaptation to cardiac hypertrophy and ischemia. Methods and Results. A yeast two-hybrid screen using H11 kinase as a bait in a human heart library revealed a potential interaction with phosphoglucomutase (PGM), the enzyme converting glucose 6-phosphate into glucose 1-phosphate. Interaction between H11 kinase and PGM was confirmed by co-immunoprecipitation. To test the biochemical relevance of this interaction, PGM activity was measured in the heart from wild type and transgenic mice, showing a 20% increase of Vmax in the transgenic group, without change in KM. Glycogen content was increased proportionately to the expression of the transgene, reaching a 40% increase in high-expression transgenic mice (7-fold increase in H11 kinase protein) versus wild type (p < 0.01). Increased incorporation of glucose into glycogen was coupled to a 3-fold increase in the protein expression of the glucose transporter GLUT1 in plasma membrane of transgenic mice (p < 0.01). Conclusion. H11 kinase promotes the synthesis of glycogen, an essential fuel for the stressed heart in both conditions of overload and ischemia. Therefore, H11 kinase represents an integrative sensor in the cardiac adaptation to stress by coordinating cell growth, survival and metabolism. (Mol Cell Biochem 265: 71–78, 2004)

Cardiovascular Effects of Neuregulin-1/ErbB Signaling: Role in Vascular Signaling and Angiogenesis

The NRG/erbB pathway has emerged as an important therapeutic target for cancer growth as well as cardiac related diseases. This discovery stems back to findings showing that overexpression of erbB2 receptors increases the metastatic potential of breast cancer in patients. Blocking this receptor using a monoclonal antibody (trastuzumab) inhibits tumor growth and offers significantly improved outcomes. However, excitement over this discovery was tempered by data showing that trastuzumab-treated patients have an increased risk of developing cardiac dysfunction, limiting the clinical potential of this novel agent. This finding suggested an important protective effect of the erbB signaling pathway on cardiac survival and homeostasis. Further investigation has shown that endothelial-derived neuregulin (a key ligand for erbB receptors) has a protective paracrine effect on cardiac cells as well as vascular smooth muscle cells in the setting of an injury. Since endothelial cells contain erbB receptors, they are also targets for autocrine signaling via this pathway, an important mediator of vascular preservation and angiogenic responses of endothelium. In this review we summarize important clinical findings as well as animal and cellular models that illustrate the signaling pathways involved in vascular cell regulation of cardiomyocyte survival and angiogenesis via the NRG/erbB pathway.