Myocyte contractile activity modulates norepinephrine cytotoxicity and survival effects of neuregulin-1beta

Area of Science:

• Cardiology
• Cell Biology
• Physiology

Background:

• Mechanical and electrical activity are crucial for cardiomyocyte function.
• Understanding how these activities influence cell survival pathways is vital for cardiac research.
• Existing models often do not fully replicate the dynamic environment of beating heart cells.

Purpose of the Study:

• To investigate how electrical stimulation and mechanical activity affect adult rat ventricular myocytes (ARVM) responses to pro-apoptotic and pro-survival signals.
• To examine the impact of electrical pacing on myocyte survival, stress signaling, and responses to beta-adrenergic receptor (beta-AR) and neuregulin-1beta (NRG) stimulation.
• To determine if myocyte contractility modulates cellular responses to norepinephrine (NE) and NRG.

Main Methods:

• Adult rat ventricular myocytes (ARVM) were subjected to electrical stimulation at varying frequencies (0, 2, and 5 Hz).
• Cell survival was assessed using trypan blue uptake, creatine phosphokinase (CPK) release, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNL) staining.
• Stress signaling pathways, including heat shock proteins (HSP70, HSP90) and stress kinases (Erk, JNK, p38), were analyzed.
• Responses to beta-adrenergic receptor (beta-AR) stimulation with norepinephrine (NE) and neuregulin-1beta (NRG) were evaluated in both paced and quiescent myocytes.

Main Results:

• Electrical stimulation (pacing) of ARVM did not significantly affect overall cell survival despite increased mitochondrial activity at higher frequencies.
• Pacing did not induce stress responses or activate stress kinases (Erk, JNK, p38) within 24 hours.
• Neuregulin-1beta (NRG) stimulation of Erk and Akt pathways was comparable in paced and quiescent cells.
• Pacing sensitized myocytes to beta-AR-stimulated JNK phosphorylation and cell death, with lower NE concentrations causing significant cytotoxicity in paced cells compared to quiescent cells.
• NRG suppressed beta-AR-induced apoptosis via a phosphatidylinositol-3-kinase (PI3K)-dependent pathway, but this effect was overcome by high NE concentrations in paced cells.

Conclusions:

• Myocyte contractility significantly modulates cellular responses to both cytotoxic (NE) and cytoprotective (NRG) ligands.
• Electrically paced cardiomyocytes in primary culture provide a feasible and relevant model for studying cell survival signaling pathways.
• These findings highlight the importance of incorporating mechanical and electrical activity when investigating cardiomyocyte signaling and survival mechanisms.