Left ventricular myofilament dysfunction in rat experimental hypertrophy and congestive heart failure

Abstract

(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...

Protein Kinase C Contributes to the Maintenance of Contractile Force in Human Ventricular Cardiomyocytes

“…In particular, Belin et al recently reported (12) that heart failure is accompanied by increased PKC-dependent myofibrillar protein phosphorylation and decreased contractility in the rat. Moreover, this effect of PKC was probably mediated by increased phosphorylation of troponin proteins (19). The differences in the experimental set-ups provide a plausible explanation for the controversial findings (increase versus decrease in contractility).…”

“…The differences in the experimental set-ups provide a plausible explanation for the controversial findings (increase versus decrease in contractility). In the earlier reports the effects of PKC were tested under conditions, where PKC activity was several times higher than the control, like heart failure or transgenic models (16,19,21,34), or phosphorylation of myofibrillar proteins by in vitro kinase treatments (12,20,37), or target proteins altered by site directed mutagenesis (20,22,24,25,35,36). In contrast we used reconstituted cardiomyocytes containing physiological levels of PKC isoforms, in addition to the endogenous mixture of myofibrillar substrates and the respective targeting proteins.…”

Cardiac thin filament regulation

“…Although it is well recognized that disturbances in calcium regulation constitute an important mechanism in this process [7], it is now clear that heart failure is also associated with a decline in myofilament response to activator Ca 2+ [15,16,27,37,67,72]. Although isoform distribution and proteolytic cleavage of contractile proteins may play a role, (inappropriate) contractile protein phosphorylation has emerged as an important determinant of depressed myofilament function in various etiologies of heart failure [5,6,27,67]. For example, in experimental heart failure in the rat, we found a depression in myofilament function that was causally linked to alterations in Tn; a follow-up study demonstrated that this was due to, most likely, up-regulation of PKC-α activity and the subsequent phosphorylation of cardiac contractile proteins [5,6].…”

“…Although isoform distribution and proteolytic cleavage of contractile proteins may play a role, (inappropriate) contractile protein phosphorylation has emerged as an important determinant of depressed myofilament function in various etiologies of heart failure [5,6,27,67]. For example, in experimental heart failure in the rat, we found a depression in myofilament function that was causally linked to alterations in Tn; a follow-up study demonstrated that this was due to, most likely, up-regulation of PKC-α activity and the subsequent phosphorylation of cardiac contractile proteins [5,6]. Likewise, studies by van der Velden et al indicate that depressed myofilament function in human heart failure is associated with alterations in Tn phosphorylation, as well as other contractile proteins such as myosin light chain and myosin-binding protein C [27].…”

“…Recent investigations have provided new insights into the molecular mechanisms that underlie thin filament activation and the role of contractile protein phosphorylation in modulating myofilament function in the heart [37,67]. Moreover, contractile protein phosphorylation has emerged as an important determinant of depressed myofilament function in cardiac diseases such as the syndrome of congestive heart failure, cardiac hypertrophy, and diabetic cardiomyopathy [5,6,27,67]. Accordingly, this review is focused on the cardiac thin filament and its role in regulating cardiac myofilament dynamics both in health and disease.…”