Mammalian fetal cardiac regeneration after myocardial infarction is associated with differential gene expression compared with the adult

Abstract

Background: In adults, myocardial infarction (MI) results in a brisk inflammatory response, myocardium loss, and scar formation. We have recently reported the first mammalian large-animal model of cardiac regeneration after MI in fetal sheep. We hypothesize that the ability of the fetus to regenerate functional myocardium after MI is owing to differential gene expression regulating the response to MI in the fetus compared with the adult.

Methods: Myocardial infarction was created in adult (n=4) or early gestation fetal (n=4) sheep. Tissue was harvested after 3 or 30 days, and RNA was extracted for microarray, followed by principal component analysis and global gene expression analysis for the following gene ontology terms: response to wounding, inflammatory response, extracellular matrix, cell cycle, cell migration, cell proliferation, and apoptosis.

Results: Principal component analysis demonstrated that the global gene expression pattern in adult infarcts was distinctly different from the uninfarcted region at 3 days and remained different at 30 days after MI. In contrast, gene expression in the fetal infarct was different from the uninfarcted region at 3 days, but by 30 days it returned to a baseline expression pattern similar to the uninfarcted region. Three days after MI there was an increase in the expression of genes related to all gene ontology terms in fetal and adult infarcts, but this increase was much more pronounced in adults. By 30 days, the fetal gene expression returned to baseline, whereas in the adult it remained significantly elevated.

Conclusions: These data demonstrate that the global gene expression pattern is dramatically different in the fetal regenerative response to MI compared with the adult response and may partly be responsible for the regeneration.

Figure 1

PCA analysis of microarray data. Open markers correspond to fetal heart and closed markers correspond to adult heart. Box markers correspond to 3 days after infarction and diamond markers correspond to 30 days after infarction. Blue indicates remote and red indicates infarct. PCA two-dimensional scatter plot represent the differential gene expression patterns of infarct and remote zone of adult and fetal hearts at 3 and 30 days post-MI. Axis: X=PC1: PCA Component 1 (32.2% variance); Y=PC2: PCA Component 2 (23.7% variance).

Figure 2

Violin plots for the genes related to the GO term “response to wounding”. The y-axis represents the log2 of the ratio of the infarct to remote region average gene expression. The violin shapes represent the distribution of the log2 ratios in each group. The adult infarcts demonstrated increased expression of “response to wounding” genes at day 3 and persistence of the expression at 30 days, whereas the fetal infarct gene expression of “response to wounding” genes returned to baseline by 30 days. (29 genes; p<0.005, student’s t test).

Figure 3

(A) Violin plots for the genes related to the GO term “inflammatory response”. The y-axis represents the log2 of the ratio of the infarct to remote region average gene expression. The violin shapes represent the distribution of the log2 ratios in each group. The adult infarcts demonstrated increased expression of “inflammatory response” genes at day 3 and persistence of the expression at 30 days, whereas the fetal infarct gene expression of “response to wounding” genes returned to baseline by 30 days. (162 genes; p<0.005, student’s t test). (B) Real-time quantitative RT-PCR analysis of mRNA for IL-6 and IL-8 in fetal and adult hearts at 3 and 30 days after MI.

Figure 4

Violin plots for the genes related to the GO term “extracellular matrix”. The y-axis represents the log2 of the ratio of the infarct to remote region average gene expression. The violin shapes represent the distribution of the log2 ratios in each group. The adult infarcts demonstrated increased expression of “extracellular matrix” genes at day 3 and persistence of the expression at 30 days, whereas the fetal infarct gene expression of “response to wounding” genes returned to baseline by 30 days. (20 genes; p<0.005, student’s t test).

Figure 5

Violin plots for the genes related to the GO term “cell cycle (254 genes), proliferation (161 genes) and migration (33 genes)”. The y-axis represents the log2 of the ratio of the infarct to remote region average gene expression. The violin shapes represent the distribution of the log2 ratios in each group. The adult infarcts demonstrated increased expression of “cell cycle, proliferation and migration” genes at day 3 and persistence of the expression at 30 days, whereas the fetal infarct gene expression of “response to wounding” genes returned to baseline by 30 days. (p<0.005, student’s t test).

Figure 6

Violin plots for the genes related to the GO term “apoptosis”. The y-axis represents the log2 of the ratio of the infarct to remote region average gene expression. The violin shapes represent the distribution of the log2 ratios in each group. The adult infarcts demonstrated increased expression of “apoptosis” genes at day 3 and persistence of the expression at 30 days, whereas the fetal infarct gene expression of “response to wounding” genes returned to baseline by 30 days. (235 genes; p<0.005, student’s t test).