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Cytoprotection by Jun kinase during nitric oxide-induced cardiac myocyte apoptosis
P Andreka1, J Zang, C Dougherty
1Department of Molecular and Cellular Pharmacology, University of Miami, FL, USA.
Abstract:
Nitric oxide (NO) induces apoptosis in cardiac myocytes through an oxidant-sensitive mechanism. However, additional factors appear to modulate the exact timing and rate of NO-dependent apoptosis. In this study, we investigated the role of mitogen-activated protein kinases (MAPKs) (extracellular signal-regulated kinase [ERK] 1/2, c-Jun N-terminal kinase [JNK] 1/2, and p38MAPK) in NO-mediated apoptotic signaling. The NO donor S:-nitrosoglutathione (GSNO) induced caspase-dependent apoptosis in neonatal rat cardiac myocytes, preceded by a rapid (<10-minute) and significant (approximately 50-fold) activation of JNK1/2. Activation of JNK was cGMP dependent and was inversely related to NO concentration; it was maximal at the lowest dose of GSNO (10 micromol/L) and negligible at 1 mmol/L. NO slightly increased ERK1/2 beginning at 2 hours but did not affect p38MAPK activity. Inhibitors of ERK and p38MAPK activation did not affect cell death rates. In contrast, expression of dominant-negative JNK1 or MKK4 mutants significantly increased NO-induced apoptosis at 5 hours (56.77% and 57.37%, respectively, versus control, 40.5%), whereas MEKK1, an upstream activator of JNK, sharply reduced apoptosis in a JNK-dependent manner. Adenovirus-mediated expression of dominant-negative JNK1 both eliminated the rapid activation of JNK by NO and accelerated NO-mediated apoptosis by approximately 2 hours. These data indicate that NO activates JNK as part of a cytoprotective response, concurrent with initiation of apoptotic signaling. Early, transient activation of JNK serves both to delay and to reduce the total extent of apoptosis in cardiac myocytes.
Insights
Nitric oxide (NO) activates c-Jun N-terminal kinase (JNK) in cardiac cells, a process that initially delays and reduces apoptosis. This JNK activation is part of a protective response to NO-induced cell death.
Area of Science:
- Cardiovascular Biology
- Cell Signaling
- Apoptosis Research
Background:
- Nitric oxide (NO) is known to induce apoptosis in cardiac myocytes.
- The precise mechanisms and modulators of NO-dependent apoptosis are not fully understood.
- Mitogen-activated protein kinases (MAPKs) are key signaling molecules in cellular stress responses.
Purpose of the Study:
- To investigate the role of specific MAPKs (ERK1/2, JNK1/2, p38MAPK) in nitric oxide-mediated apoptosis signaling in cardiac myocytes.
- To elucidate the temporal relationship between NO, MAPK activation, and apoptosis.
Main Methods:
- Primary neonatal rat cardiac myocytes were treated with the NO donor S-nitrosoglutathione (GSNO).
- Caspase activity, MAPK phosphorylation (JNK, ERK, p38), and apoptosis rates were measured.
- Pharmacological inhibitors and dominant-negative mutants of MAPKs and their upstream activators were used to assess functional roles.
Main Results:
- GSNO induced rapid, cGMP-dependent JNK1/2 activation, which was inversely related to NO concentration.
- ERK1/2 showed slight activation at later time points, while p38MAPK activity was unaffected.
- Inhibition of JNK signaling accelerated NO-induced apoptosis, whereas inhibition of ERK or p38 had no effect.
- Early, transient JNK activation by NO was found to be cytoprotective, delaying and reducing overall apoptosis.
Conclusions:
- Nitric oxide activates JNK signaling in cardiac myocytes as an early, transient, and cytoprotective response.
- This JNK activation paradoxically delays and reduces the extent of NO-induced apoptosis.
- The findings reveal a complex interplay between NO, JNK signaling, and programmed cell death in the heart.