Functional consequences of caspase activation in cardiac myocytes

Abstract

Cardiomyocyte apoptosis is present in many cardiac disease states, including heart failure and ischemic heart disease. Apoptosis is associated with the activation of caspases that mediate the cleavage of vital and structural proteins. However, the functional contribution of apoptosis to these conditions is not known. Furthermore, in cardiac myocytes, apoptosis may not be complete, allowing the cells to persist for a prolonged period within the myocardium. Therefore, we examined whether caspase-3 cleaved cardiac myofibrillar proteins and, if so, whether it affects contractile function. The effects of caspase-3 were studied in vitro on individual components of the cardiac myofilament including ␣-actin, ␣-actinin, myosin heavy chain, myosin light chain 1͞2, tropomyosin, cardiac troponins (T, I, C), and the trimeric troponin complex. Exposure of the myofibrillar protein (listed above) to caspase-3 for 4 h resulted in the cleavage of ␣-actin and ␣-actinin, but not myosin heavy chain, myosin light chain 1͞2, and tropomyosin, into three fragments (30, 20, and 15 kDa) and one major fragment (45 kDa), respectively. When cTnT, cTnI, and cTnC were incubated individually with caspase-3, there was no detectable cleavage. However, when the recombinant troponin complex was exposed to caspase-3, cTnT was cleaved, resulting in fragments of 25 kDa. Furthermore, rat cardiac myofilaments exposed to caspase-3 exhibited similar patterns of myofibrillar protein cleavage. Treatment with the caspase inhibitor DEVD-CHO or z-VAD-fmk abolished the cleavage. Myofilaments, isolated from adult rat ventricular myocytes after induction of apoptotic pathway by using ␤-adrenergic stimulation, displayed a similar pattern of actin and TnT cleavage. Exposure of skinned fiber to caspase-3 decreased maximal Ca 2؉ -activated force and myofibrillar ATPase activity. Our results indicate that caspase-3 cleaved myofibrillar proteins, resulting in an impaired force͞Ca 2؉ relationship and myofibrillar ATPase activity. Induction of apoptosis in cardiac cells was associated with similar cleavage of myofilaments. Therefore, activation of apoptotic pathways may lead to contractile dysfunction before cell death.

Neutral sphingomyelinase inhibition participates to the benefits of N-acetylcysteine treatment in post-myocardial infarction failing heart rats

“…Thus, this study provided evidence that partial activation of caspase-3 was compatible with life. Likewise, in isolated adult rat cardiomyocytes, Communal et al [54] have observed that, in the early phase of apoptosis when no major DNA cleavage occurred, caspase-3 activation elicited the cleavage of myofibrillar proteins. Hence, under conditions where the apoptotic response is not completed, caspase-3 activation is likely to damage nuclear and myofibrillar proteins, which will prompt contractile dysfunction before cell death.…”

Cardiomyocyte Apoptosis Triggered by RAFTK/pyk2 via Src Kinase Is Antagonized by Paxillin

“…Based upon our prior report of paxillin cleavage in failing hearts (7) we proposed that caspase-mediated cleavage of paxillin may contribute to the pathogenesis of heart failure. Caspase-mediated cleavage of paxillin has been linked to apoptosis (51), caspase activation leads to focal adhesion dissolution (52,53), and caspase activity is associated with myocardial apoptosis and myofibrillar remodeling (54). Degradation of focal adhesion proteins is prevented by pretreatment with caspase inhibitors (55)(56)(57).…”

The Subunit CSN6 of the COP9 Signalosome Is Cleaved during Apoptosis

“…Caspase-dependent cleavage can activate proteins to become proapoptotic, such as PAK2, MEKK1, and gelsolin (40 -42), or inactivate proteins involved in repair mechanisms of the cell cycle, such as PARP1, Rb, and protein kinase C␦ (43)(44)(45), or lead to degradation of structural proteins, such as lamins and actin (46,47). In data not reported here, we checked whether CSN6 cleavage could alter the apoptotic response in cells.…”