Rationale Oxidative stress plays a significant role in the development of heart failure. H2O2 (a physiologically-relevant form of oxidative stress) induces substantial changes in gene expression in cardiomyocytes and modulates apoptosis. It activates three major MAPK cascades [extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNKs), p38-MAPKs] that regulate transcription and gene expression in other cells. The aim is to identify the contribution of each pathway in the gene expression response of cardiomyocytes to H₂O₂.

Methodology Neonatal cardiomyocytes were exposed to H2O2 (0.2 mM, 2h) in the absence/presence of PD184352 (2 µM; inhibits ERK1/2 signalling), JNK-IN-8 (1 µM; inhibits JNKs) or SB203580 (0.7 µM; inhibits p38-MAPK). Expression of transcription factors or redox enzymes was assessed using qPCR.

Results Upregulation of EGR1 and EGR3 by H2O2 (2.8±0.2 and 3.8±0.7 fold, respectively) was significantly inhibited by PD184352, but not JNK-IN-8 or SB203580. In contrast, upregulation of FosB and Fosl1 (80.9±28.4 and 13.1±2.3 fold; one-way ANOVA with SNK post-test, n=3/4) was unaffected by any inhibitor. Atf3 upregulation (14.1±1.9 fold) was reduced by JNK-IN-8 (to 7.8±1.2 fold; p<0.001), but enhanced by PD184352 (to 23.1±0.8 fold; p<0.001). Interestingly, upregulation of HMOX and GCLC (3.7±0.6 and 3.2±0.7 fold) was reduced by SB203580 (to 2.3±0.29 and 2.3±0.35 fold; p<0.05).

Conclusions The data from even this small subset of genes indicate that the MAPKs play a substantial but differential role in regulating cardiomyocyte gene expression in response to H₂O₂. To gain global oversight of the relative contributions of each MAPK cascade, future experiments will use microarrays.