M. M. Hodges1, C. Zgheib1, J. Xu1, L. C. Dewberry1, S. A. Hilton1, J. Hu1, K. W. Liechty1 1University Of Colorado-Denver, Anschutz Medical Campus,Department Of General Surgery, Laboratory For Fetal And Regenerative Biology,Aurora, COLORADO, USA
Introduction: The fetal response to myocardial infarction (MI) is regenerative, whereas the adult response to MI is reparative and associated with increased fibrosis. Global gene expression analysis of ovine specific microarray demonstrated significant increase in extracellular matrix (ECM) related gene expression after MI in adult versus fetal ovine hearts. Transforming growth factor beta-1 (TGFB1) is a key regulator of ECM related gene expression in renal and pulmonary fibrosis; however, the expression of TGFB1 in the fetal response to MI has yet to be described. We hypothesize that expression of TGFB1 is downregulated in the regenerative, fetal model of myocardial regeneration following MI when compared to the reparative and fibrotic, adult response to MI.
Methods: Myocardial infarction (MI) was induced in fetal (65-76 days gestation, n=19) and adult (7 months old, n=8) sheep via ligation of the left anterior descending coronary artery. Ovine specific microarray was used to evaluate expression of TGFB1 and related genes (collagen I, collagen III, elastin, and miR-21) in adult and fetal hearts, 3 and 30 days after MI. Gene expression in the infarct area (IA) was compared to gene expression in the remote zone. Student’s t-test was used for statistical comparisons, with p<0.05 considered statistically significant.
Results: Both 3 and 30 days after MI, TGFB1 gene expression was significantly upregulated in the IA of adult hearts (p=0.036 and p=0.003); however, there was no significant change in TGFB1 gene expression in the IA of fetal hearts. At 3 days, the increased TGFB1 gene expression in the IA of adult hearts was associated with a significant increase in collagen I (p=0.009), collagen III (p=0.0003), elastin (p=0.045), and miR-21 (p=0.009) gene expression. While there was a significant increase in collagen III expression in the IA of fetal hearts 3 days after MI (p=0.008), there was no significant difference in the expression of collagen I, and there was a significant reduction in the expression of elastin (p=0.04). MiR-21 was undetectable in fetal hearts. The gene expression of collagen I (p=0.014), collagen III (p=0.047), elastin (p=0.027), and miR-21 (p=0.039) remained elevated in adult IAs 30 days after MI. However, there was no significant difference in collagen I, collagen III, or elastin gene expression in the fetal IA 30 days after MI.
Conclusion: TGFB1 has been described as a master regulator of the fibrotic response in adult hearts after MI. This is the first evaluation of TGFB1 expression in the regenerative, fetal response to MI. We have shown that TGFB1 expression is unchanged in the regenerative, fetal response to MI in contrast to the upregulation of TGFB1 seen in the adult response. While safe and effective therapies directed at reducing fibrosis after MI by decreasingTGFB1 are lacking, these results indicate that promising therapies may be developed by continuing to pursue TGFB1 as a therapeutic target.