Background Right ventricular hypertrophy (RVH) and RV failure contribute to morbidity and mortality in pulmonary arterial hypertension (PAH). The cause of RV dysfunction and the feasibility of therapeutically targeting the RV are uncertain. We hypothesized that RV dysfunction and electrical remodeling in RVH result, in part, from a glycolytic-shift in the myocyte, caused by activation of pyruvate dehydrogenase kinase (PDK). Methods and Results We studied 2 complementary rat models: RVH+PAH (induced by monocrotaline) and RVH+without PAH (induced by pulmonary artery banding, PAB). Monocrotaline-RVH reduced RV O2-consumption and enhanced glycolysis. RV 2-fluoro-2-deoxy-glucose uptake, Glut-1 expression and pyruvate dehydrogenase phosphorylation increased in monocrotaline-RVH. The RV monophasic action potential duration and QTc-interval were prolonged due to decreased expression of repolarizing voltage-gated K+ channels (Kv1.5, Kv4.2). In the RV working-heart model, the PDK inhibitor, dichloroacetate, acutely increased glucose oxidation and cardiac work in monocrotaline-RVH. Chronic dichloroacetate therapy improved RV repolarization and RV function in vivo and in the RV Langendorff model. In PAB-induced RVH, a similar reduction in cardiac output and glycolytic shift occurred and it too improved with dichloroacetate. In PAB-RVH the benefit of dichloroacetate on cardiac output was ~1/3 that in monocrotaline-RVH. The larger effects in monocrotaline-RVH likely reflect dichloroacetate’s dual metabolic benefits in that model: regression of vascular disease and direct effects on the RV. Conclusion Reduction in RV function and electrical remodeling in 2 models of RVH relevant to human disease (PAH and pulmonic stenosis) result, in part, from a PDK-mediated glycolytic shift in the RV. PDK inhibition partially restores RV function and regresses RVH by restoring RV repolarization and enhancing glucose oxidation. Recognition that a PDK-mediated metabolic shift contributes to contractile and ionic dysfunction in RVH offers insight into the pathophysiology and treatment of RVH.

High-frequency echocardiography and high-field-strength magnetic resonance imaging (MRI) are new noninvasive methods for quantifying pulmonary arterial hypertension (PAH) and right ventricular (RV) hypertrophy (RVH). We compared these noninvasive methods of assessing the pulmonary circulation to the gold standard, cardiac catheterization (micromanometer-tipped catheters), in rats with monocrotaline-induced PAH and normal controls. Closed-chest, Sprague-Dawley rats were anesthetized with inhaled isoflurane (25 monocrotaline, 6 age-matched controls). Noninvasive studies used 37.5-MHz ultrasound (Vevo 770; VisualSonics) or a 9.4-T MRI (Bruker BioSpin). Catheterization used a 1.4-F micromanometer-tipped Millar catheter and a thermodilution catheter to measure cardiac output (CO). We compared noninvasive measures of pulmonary artery (PA) pressure (PAP) using PA acceleration time (PAAT) and CO, using the geometric PA flow method and RV free wall (RVFW) thickness/mass with cardiac catheterization and/or autopsy. Blinded operators performed comparisons using each method within 2 days of another. In a subset of rats with monocrotaline PAH, weekly echocardiograms, catheterization, and autopsy data assessed disease progression. Heart rate was similar during all studies (>323 beats/min). PAAT shortened, and the PA flow envelope displayed systolic "notching," reflective of downstream vascular remodeling/stiffening, within 3 wk of monocrotaline. MRI and echocardiography measures of PAAT were highly correlated (r(2) = 0.87) and were inversely proportional to invasive mean PAP (r(2) = 0.72). Mean PAP by echocardiography was estimated as 58.7 - (1.21 x PAAT). Invasive and noninvasive CO measurement correlated well (r(2) >or= 0.75). Noninvasive measures of RVFW thickness/mass correlated well with postmortem measurements. We conclude that high-resolution echocardiography and MRI accurately determine CO, PAP, and RV thickness/mass, offering similar results as high-fidelity right heart catheterization and autopsy, and that PAAT accurately estimates PAP and permits serial monitoring of experimental PAH. These tools are useful for assessment of the rodent pulmonary circulation and RVH.

Abstract-We report characterization of a transgenic mouse that overexpresses constitutively active protein kinase C⑀ in the heart and slowly develops a dilated cardiomyopathy with failure. The hemodynamic, mechanical, and biochemical properties of these hearts demonstrate a series of temporal events that mark the progression of the disease. In the 3-month transgenic (TG) animals, contractile properties and gene expression measurements are normal, but an increase in myofibrillar Ca 2ϩ sensitivity and thin filament protein phosphorylation is noted. At 6 months, there is a decrease in the myofibrillar Ca 2ϩ sensitivity, a significant increase in ␤-myosin heavy chain mRNA and protein, normal cardiac function, but a blunted response to an inotropic challenge. The transition at 9 months is especially interesting because age-related changes appear to contribute to the decline in function seen in the TG heart. At this point, there is a decline in baseline function and maximum tension produced by the myofibrils, which is coincident with the onset of atrial myosin light chain isoform re-expression in the ventricles. In the 12-month TG mice, there is clear hemodynamic and geometric evidence of failure. Alterations in the composition of the myofibrils persist but the phosphorylation of myosin light chain 2v is dramatically different at this age compared with all others. We interpret these data to implicate the disruption of the myofibrillar proteins and their interactions in the propagation of dilated cardiac disease. (Circ Res. 2004;95:424-432.)Key Words: contractile proteins Ⅲ heart failure Ⅲ protein kinase C H eart disease is the most frequent cause of death in the general population, with a dramatically increasing incidence in the elderly. 1 As with the aging heart, many pathologic features of heart failure are related to structural and functional alterations in cardiac muscle cells. However, the molecular mechanisms underlying the progression of heart failure at the level of cardiac muscle function are largely unknown.A number of diverse lines of evidence have suggested that activation of protein kinase C (PKC) plays a central role in the physiologic and pathophysiologic adaptation of the heart. Studies in vitro and in vivo have shown that PKC phosphorylates a number of important cardiac proteins, including myofilament proteins, 2 as well as proteins involved in Ca 2ϩ homeostasis. 3 Clearly, one hypothesis concerning PKC activation is that increased myofilament phosphorylation results in contractile dysfunction, which diminishes cardiac output, which results in a compensatory enlargement of the heart. This is supported by evidence showing that PKC-mediated phosphorylation of the myofilaments is associated with depressed myofilament activity in reconstituted systems. 4 Multiple isoforms of PKC are expressed in the heart during development, with the predominant isoforms in the adult being the Ca 2ϩ -dependent (␣) and the Ca 2ϩ -independent (␦, ⑀) isoforms. 5 Protein kinase C⑀, an isoform that translocates to the myofi...

(LVH) or congestive heart failure (CHF). To address this issue, we studied pressure overload-induced LV hypertrophy (POLVH) and myocardial infarction-elicited congestive heart failure (MICHF) in rats. LV myocytes were isolated from control, POLVH, and MICHF hearts by mechanical homogenization, skinned with Triton, and attached to micropipettes that projected from a sensitive force transducer and high-speed motor. sensitivity toward levels observed in control cells. In contrast, integration of cTn purified from failing ventricles into control myocytes increased EC50 to levels observed in failing myocytes. The Fmax parameter was not markedly affected by troponin exchange. cTnI phosphorylation was increased in both POLVH and MICHF left ventricles. We conclude that depressed myofilament Ca 2ϩ sensitivity in experimental LVH and CHF is due, in part, to a decreased functional role of cTn that likely involves augmented phosphorylation of cTnI. left ventricle; troponin; phosphorylation; cardiac disease CONGESTIVE HEART FAILURE (CHF) is characterized by reduced ventricular pump function, which is due, in part, to cardiac myocyte dysfunction. It has been widely reported that Ca 2ϩ homeostasis is impaired in CHF (14). However, whether depressed myofilament function contributes to reduced ventricular myocyte contractility in CHF is less clear (5). Studies probing myofilament activation in failing human myocardium must be interpreted with caution because tissue quality, pharmacological treatment, and brain death of donors may confound experimental findings (15,30,44). For these reasons, investigators have employed animal models that allow for the study of myofilament function under more carefully controlled circumstances. For instance, studies in the pacing-induced canine model of CHF indicate that the myofilaments generate more force for a given level of activator Ca 2ϩ (increased Ca 2ϩ sensitivity) compared with controls (45). Examination of myofilament activity in the spontaneously hypertensive heart failure prone (SHHF) rat demonstrates that myofilament function is either augmented or unchanged depending on when studies are performed during the disease progression (32). In contrast, Pérez and coworkers (31) found reduced myofilament function in right ventricular (RV) trabeculae of the SHHF rat. Similarly, de Tombe et al. (7) have also shown reduced myofilament function in RV trabeculae obtained from rats with large left ventricular (LV) infarcts and in skinned RV myocytes isolated from rats with chronic RV hypertrophy induced by pulmonary artery banding (9). However, the impact of experimental LV hypertrophy (LVH) or CHF on myofilament function in the more clinically relevant left ventricle has not been carefully studied. The molecular basis for altered myofilament function in LVH and CHF likely involves changes in thick and thin filament proteins. It has been reported that protein kinase C (PKC) is upregulated in cardiac disease (6,13,43). In addition, recent work from our group indicates that PKC-mediated phosphoryla...

Abstract-Mutations in striated muscle ␣-tropomyosin (␣-TM), an essential thin filament protein, cause both dilated cardiomyopathy (DCM) and familial hypertrophic cardiomyopathy. Two distinct point mutations within ␣-tropomyosin are associated with the development of DCM in humans: Glu40Lys and Glu54Lys. To investigate the functional consequences of ␣-TM mutations associated with DCM, we generated transgenic mice that express mutant ␣-TM (Glu54Lys) in the adult heart. Results showed that an increase in transgenic protein expression led to a reciprocal decrease in endogenous ␣-TM levels, with total myofilament TM protein levels remaining unaltered. Histological and morphological analyses revealed development of DCM with progression to heart failure and frequently death by 6 months. Echocardiographic analyses confirmed the dilated phenotype of the heart with a significant decrease in the left ventricular fractional shortening. Work-performing heart analyses showed significantly impaired systolic, and diastolic functions and the force measurements of cardiac myofibers revealed that the myofilaments had significantly decreased Ca 2ϩ sensitivity and tension generation. Real-time RT-PCR quantification demonstrated an increased expression of ␤-myosin heavy chain, brain natriuretic peptide, and skeletal actin and a decreased expression of the Ca 2ϩ handling proteins sarcoplasmic reticulum Ca 2ϩ -ATPase and ryanodine receptor. Furthermore, our study also indicates that the ␣-TM54 mutation decreases tropomyosin flexibility, which may influence actin binding and myofilament Ca 2ϩ sensitivity. The pathological and physiological phenotypes exhibited by these mice are consistent with those seen in human DCM and heart failure. As such, this is the first mouse model in which a mutation in a sarcomeric thin filament protein, specifically TM, leads to DCM. Key Words: mouse model Ⅲ transgenic Ⅲ myocardial contractility Ⅲ thin filament T ropomyosin (TM) is an ␣ helical coiled-coil fibrous protein that binds actin filaments providing structural stability and modulation of filament function. In striated muscle, TM along with the troponin complex regulates Ca 2ϩ -mediated actin-myosin crossbridges. Numerous mutations in many of the contractile proteins of the cardiac sarcomere have been associated with dilated and hypertrophic cardiomyopathy, where the myocardial performance is compromised. In humans, 2 dilated cardiomyopathy (DCM)-associated mutations (Glu54Lys and Glu40Lys) have been identified in ␣-tropomyosin (␣-TM) (or TPM1), 1 in contrast to the 8 distinct mutations in the same gene that are associated with familial hypertrophic cardiomyopathy (FHC). 2 The DCM mutations in ␣-TM are located in a region (amino acids 40 to 100) where half of the reported human FHC mutations occur (Glu62Gln, Ala63Val, Lys70Thr, Val95Ala); this region does not interact with troponin (Tn)T.Protein-modeling studies on the TM filaments harboring Glu54Lys and Glu40Lys substitutions show that both of them create a strong local increase in the positive cha...