Cyclic stretch of cardiac myocytes causes an amplitude-dependent increase in reactive oxygen species, which mediates hypertrophic and apoptotic responses via differential kinase activation.
Does oxidative stress mediate hypertrophy and apoptosis in cyclically stretched ventricular myocytes?
Cyclic mechanical stretch induces amplitude-dependent increases in reactive oxygen species, which mediate hypertrophic responses at both low and high amplitudes and apoptotic responses specifically at high amplitudes in neonatal rat ventricular myocytes.
Oxidative stress stimulates both growth and apoptosis in cardiac myocytes in vitro. We investigated whether oxidative stress mediates hypertrophy and apoptosis in cyclically stretched ventricular myocytes. Neonatal rat ventricular myocytes cultured on laminin-coated silastic membranes were stretched cyclically (1 Hz) at low (nominal 5%) and high (nominal 25%) amplitudes for 24 hours. Stretch caused a graded increase in superoxide anion production as assessed by superoxide dismutase (SOD)-inhibitable cytochrome c reduction or electron paramagnetic resonance spectroscopy. The role of reactive oxygen species (ROS) was assessed using the cell-permeable SOD/catalase mimetics Mn(II/III)tetrakis(1-methyl-4-peridyl) (MnTMPyP) and EUK-8. Stretch-induced increases in protein synthesis ((3)H-leucine incorporation) and cellular protein content were completely inhibited by MnTMPyP (0.05 mmol/L) at both low and high amplitudes of stretch. In contrast, while MnTMPyP inhibited basal atrial natriuretic factor (ANF) mRNA expression, the stretch-induced increase in ANF mRNA expression was not inhibited by MnTMPyP. In contrast to hypertrophy, only high-amplitude stretch increased myocyte apoptosis, as reflected by increased DNA fragmentation on gel electrophoresis and an approximately 3-fold increase in the number of TUNEL-positive myocytes. Similarly, only high-amplitude stretch increased the expression of bax mRNA. Myocyte apoptosis and bax expression stimulated by high-amplitude stretch were inhibited by MnTMPyP. Both low- and high-amplitude stretch caused rapid phosphorylation of ERK1/2, while high-, but not low-, amplitude stretch caused phosphorylation of JNKs. Activation of both ERK1/2 and JNKs was ROS-dependent. Thus, cyclic strain causes an amplitude-related increase in ROS, associated with differential activation of kinases and induction of hypertrophic and apoptotic phenotypes.
Pimentel et al. (2001) studied Neonatal rat ventricular myocytes. Cyclic stretch and oxidative stress inhibition (MnTMPyP) vs. Unstretched cells or cells without MnTMPyP was evaluated on Hypertrophic and apoptotic responses (superoxide anion production, protein synthesis, DNA fragmentation). Cyclic stretch of cardiac myocytes causes an amplitude-dependent increase in reactive oxygen species, which mediates hypertrophic and apoptotic responses via differential kinase activation.