Non-obstructive CAD was identified by a reduced GLS measured by 2D STE in rest images with similar accuracy to the traditional WMSI measured in stress echocardiography.

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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...

Protein kinase C (PKC)-mediated phosphorylation of cardiac myofilament (MF) proteins has been shown to depress the actomyosin interaction and may be important during heart failure. Biochemical studies indicate that phosphorylation of Ser43 and Ser45 of cardiac troponin I (cTnI) plays a substantial role in the PKC-mediated depression. We studied intact and detergent-extracted papillary muscles from nontransgenic (NTG) and transgenic (TG) mouse hearts that express a mutant cTnI (Ser43Ala, Ser45Ala) that lacks specific PKC-dependent phosphorylation sites. Treatment of NTG papillary muscles with phenylephrine (PE) resulted in a transient increase and a subsequent 62% reduction in peak twitch force. TG muscles showed no transient increase and only a 45% reduction in force. There was a similar difference in maximum tension between NTG and TG fiber bundles that had been treated with a phorbol ester and had received subsequent detergent extraction. Although levels of cTnI phosphorylation correlated with these differences, the TG fibers also demonstrated a decrease in phosphorylation of cardiac troponin T. The PKC-specific inhibitor chelerythrine inhibited these responses. Our data provide evidence that specific PKC-mediated phosphorylation of Ser43 and Ser45 of cTnI plays an important role in regulating force development in the intact myocardium.

Familial hypertrophic cardiomyopathy (FHC) is a disease of the sarcomere (Bonne et al. 1998). Mutations in several sarcomeric proteins are the cause of FHC and play a key role in the evolution of the systemic effects of this disease (Maron et al. 1987; Geisterfer-Lowrance et al. 1990). Two of the most lethal mutations associated with human FHC involve changes in cardiac troponin T (cTnT). A mutation that results in a C-terminal truncation of cTnT (cTnT DEL ) and another in which there is a charge change at position 92 in cTnT (R92Q) both result in a hypercontractile phenotype in transgenic (TG) mice and a high frequency of sudden cardiac death in humans. Although previous studies have indicated that mutations linked to FHC function via a dominant-negative mode, a growing body of evidence supports the idea that a gain of function (that is, hypercontractility) may play a significant role in the complications associated with FHC. Hypercontractility (hypercontractile systolic function) is common in humans with FHC-associated mutations (Maron et al. 1987;Schaub et al. 1997 2. We measured steady-state isometric force and ATPase activity in detergent-skinned cardiac fibre bundles from three transgenic (TG) mouse hearts in which 50, 92 and 6 % of the native cTnT was replaced by the wild type (WT) cTnT, R92Q mutant cTnT (R92Q) and the C-terminal deletion mutant of cTnT (cTnT DEL ), respectively.3. Normalized pCa-tension relationships of R92Q and cTnT DEL fibres demonstrated a significant increase in sensitivity to Ca 2+ at short (2.0 µm) and long (2.3 µm) sarcomere lengths (SL). At short SL, the pCa 50 values, representing the midpoint of the pCa-tension relationship, were 5.69 ± 0.01, 5.96 ± 0.01 and 5.81 ± 0.01 for WT, R92Q and cTnT DEL fibres, respectively. At long SL, the pCa 50 values were 5.81 ± 0.01, 6.08 ± 0.01 and 5.95 ± 0.01 for WT, R92Q and cTnT DEL fibres, respectively. 4. The difference in pCa required for half-maximal activation (∆pCa 50 ) at short and long SL was 0.12 ± 0.01 for the R92Q (92 %) TG fibres, which is significantly less than the previously reported ∆pCa 50 value of 0.29 ± 0.02 for R92Q (67 %) TG fibres. At short SL, Ca 2+-activated maximal tension in both R92Q and cTnT DEL fibres decreased significantly (24 and 21 %, respectively; P < 0.005), with no corresponding decrease in Ca 2+ -activated maximal ATPase activity. Therefore, at short SL, the tension cost in R92Q and cTnT DEL fibres increased by 35 and 29 %, respectively (P < 0.001).6. The fibre bundles reconstituted with the recombinant mutant cTnT DEL protein developed only 37 % of the Ca 2+ -activated maximal force developed by recombinant WT cTnT reconstituted fibre bundles, with no apparent changes in Ca 2+ sensitivity.7. Our data indicate that an important mutation-linked effect on cardiac function is the result of an inefficient use of ATP at the myofilament level. Furthermore, the extent of the mutationinduced dysfunction depends not only on the nature of the mutation, but also on the concentration of the mutant protein in the sarcom...