Abstract 924: A Transcriptomic Approach to Dissect Regulatory Elements Controlling Transmural Gene Expression in Human Left Ventricular Myocardium in Health and Disease
Background: In human myocardium, substantial differences are observed across the left ventricular free wall in terms of perfusion, energy metabolism and electrophysiological properties. Changes in transmural electrical gradients are believed to play a pivotal role in arrhythmogenesis in heart failure, exemplified by the prominent reduction of the transient outward current (Ito) in subepicardium (EPI), but not in subendocardium (ENDO) in human DCM.
Methods: To identify key transcriptional regulators of these transmural gradients in DCM, we compared gene expression in 1mm thin ENDO and EPI tissue slices of five non-failing (NF) and seven DCM hearts with Affymetrix U133A+B arrays. Differentially expressed genes were identified by SAM analysis with a false discovery rate of 5%. Seven transcripts were validated by real-time RT-PCR.
Results: 273 and 638 transcripts were preferentially expressed in EPI and ENDO, respectively. Consistent with increased wall stress on the inner myocardial wall in DCM, a variety of genes involving pro-fibrotic pathways (most prominently CTGF and TGF-beta1) and extracellular matrix remodelling were selectively up-regulated in ENDO DCM. KChIP2 (β-subunit of Ito channels) displayed the largest transmural gradient from EPI to ENDO (5.7±0.9 -fold in NF; 2.7±0.7 -fold in DCM), whereas BNP showed the steepest gradient from ENDO to EPI (3.3±1.1-fold in NF; 13.9±9.8 -fold in DCM). As BNP and KChIP2 were inversely regulated in DCM (r=0.87), KChIP2 represents a major heart-failure responsive gene in human myocardium. We are currently investigating two transcription factors which are differentially expressed across the human LV and regulated by heart failure, making them potential regulators of KCNIP2. In addition, the transmural gradient of ERK2, known to modulate Ito levels in an animal model of hypertrophy, suggests that post-translational modifications of Ito channel complexes may be operative in the human heart.
Conclusion: Transcriptomic approaches are suitable to identify potential regulatory genes of cardiac ion channel complexes. Transmural gradients in gene expression are profoundly modulated by heart failure, exemplified by transcriptional up-regulation of extracellular matrix components in DCM-ENDO.