Abstract 594: Identification of Cell Cycle Regulatory and Inflammatory Genes as Predominant Targets of p38 MAPK in the Heart
Mitogen-activated protein kinases (MAPKs) regulate cardiomyocyte growth and apoptosis in response to extracellular stimulation, but the downstream effectors that mediate their pathophysiological effects remain poorly understood. We determined the targets and role of p38 MAPK in the heart in vivo by using local adenovirus-mediated gene transfer of constitutively active upstream kinase mitogen-activated protein kinase kinase 3b (MKK3bE) and wild-type p38α in rats. DNA microarray analysis of animals with cardiac-specific overexpression of p38 MAPK revealed that 264 genes were upregulated and 2 genes were down-regulated more than 2-fold. A large number of previously unknown p38 target genes were found, such as cell cycle regulators cyclins A2, and B1 as well as transcription factors Runx1 and Krox20. Many fundamental inflammation-associated genes like interleukin-6 (IL-6) and toll-like receptor-2 as well as cell adhesion genes selectin E and osteopontin were also elevated in p38 MAPK overexpressing hearts. The complete list of 266 differentially expressed genes was loaded into PathwayAssist to build the interaction map showing potential connections among genes regulated by p38 MAPK overexpression in the heart. A central signaling molecule in this pathway was IL-6, which has been implicated in the regulation of 20 genes found to be affected by p38 MAPK. Further, using gel mobility shift assays we identified several cardiac transcription factors including serum response factor (SRF), activator protein-1 (AP-1), nuclear factor κB (NF-κB) that were directly activated by p38 MAPK overexpression. Finally, we determined the functional significance of the altered cardiac gene expression profile by histological analysis and echocardiographic measurements, which indicated that p38 MAPK overexpression induced gene expression results in myocardial cell proliferation, inflammation and fibrosis. In conclusion, we defined the novel target genes and transcription factors as well as the functional effects of p38 MAPK in the heart. Our results demonstrate that the pathophysiological consequence of p38 MAPK overexpression is myocardial cell proliferation and inflammation associated with fibrosis in the adult heart.