Abstract 3773: Myotrophin and the p53 Signaling Cascade in Cardiac Hypertrophy/Heart Failure
Myotrophin (Myo), a 12-kDa protein, stimulates myocyte growth and is a factor in initiating cardiac hypertrophy (CH). Cardiospecific overexpression of Myo in transgenic mice (Myo-Tg) induces hypertrophy that progresses to heart failure (HF). Oligonucleotide gene array revealed upregulation of a p53 homologue gene (EST-AI843106) in Myo-Tg mice during HF, indicating that p53 plays an important role during the transition of hypertrophy to HF. To dissect out the mechanisms of p53-mediated Myo-induced CH/HF, we developed a double-transgenic mouse line (p53−/−/myo+/+) by crossing Myo-Tg mice with p53-null mice. The double transgenic mice showed a significant attenuation of cardiac mass compared to Myo-Tg mice (heart weight:body weight ratio; 5.2 ± 0.21 vs. 7.9 ± 0.58, p < 0.001) associated with improved cardiac function and downregulation of ANF expression, suggesting that hypertrophy induced by Myo overexpression is indeed mediated through p53. To elucidate the relationship between p53 and Myo-induced hypertrophy, we performed a Reverse-Transcription Real-Time PCR pathway array on heart tissues from p53−/−/myo+/+ vs. Myo-Tg mice. A bioinformatic approach, Ingenuity Pathway AnalysisTM (IPA), was used to analyze the selected up-/downregulated genes. The IPA network showed that among the up-/downregulated genes, Bcl2, Brca1, Cdkn1a and Myc occupy the nodal position, whereas E2f1, Pmaip1, Gadd45a and Pttg1 function as peripheral candidates. The expression profiles of some genes of the p53 pathway were validated by immunoblot analysis. Functional assignment of these selected candidate genes showed that Bcl2, E2f1 and FasL are related to CH/HF, but the function of Gadd45a, Pmaip1, and Vcan is still unknown. Apart from these p53 cascade members, we also found that other molecules (e.g., Jnk, Ras, NF-kB, Cyclin L, and Mek) may be involved in an intricate interplay to stimulate p53-mediated Myo-induced CH. Suppression of NF-kB activity (by electrophoresis mobility shift assay) in p53−/−/myo+/+ mice compared to Myo-Tg mice indicated involvement of NF-kB, as predicted by IPA, in Myo/p53 cross-talk. Our data suggest that the p53 signaling cascade actively participates in progression of hypertrophy to HF, triggered by overexpression of myotrophin.