Abstract 508: A Reactive Oxygen Species-mediated PKC-ERK-RSK Pathway Decreases The Cyclic AMP Response Element Binding Protein And May Initiate Transcriptional Changes In Cardiac Memory
Introduction: We previously reported that ventricular pacing (VP) to induce cardiac memory (CM) results in a decreased outward K current Ito and reduced mRNA and protein of the Ito subunit, KChIP2. The transcription factor CREB (cAMP response element binding protein) is integral to the KChIP2 reduction but the basis for the CREB decrease is uncertain. We hypothesized that reactive O2 species (ROS) activate a PKC-ERK-RSK pathway to initiate the CREB decrease in CM.
Methods and Results: Neonatal rat cardiac myocytes (NRCM) were stimulated with H2O2. A gradual decrease of CREB protein began 30m after onset of H2O2: maximum decrease was at 2h (Fig⇓). There were also increases of CREB-pSer133, p-RSK and p-ERK beginning 15m after H2O2 treatment. U0126 (MEK inhibitor) and GF109203X (PKC inhibitor) attenuated the CREB decrease and increased CREB-pSer133, p-RSK and p-ERK. JNK or p38 inhibitors had no effect. To investigate ROS role in CM induction, 10 dogs were AV-sequentially paced for 2h and LV epicardial biopsies were taken before and at 2h VP. T wave vector displacement was .12 mV at 2h indicating CM. Lipid peroxidation (malondialdehyde and 4-hydroxyalkenals levels, used as indicators of oxidative stress) was increased in CM LV tissue homogenates compared to shams (.65+0.05 vs .55+0.02 a.u., P<.05). Western blots showed decreased nuclear CREB (897+115 sham vs 382+110 a.u. CM, p<.05) and increased cytosolic p-RSK (224+47 vs 323+67 a.u., p<.05) and p-ERK (913+154 vs 1122+170 a.u., p<.05). No changes were seen in JNK and p38.
Conclusion: The CREB decrease in CM appears to be regulated by a ROS mediated PKC- ERK-RSK pathway.