Figure 1.

Hypoxia promotes postinfarction myocardial repair in mice. (A) Mice were exposed to 10% O₂ after LAD ligation-induced MI, which was then maintained for 7 days, and then, the mice were subjected to normoxia (21% O₂) for 21 days. Hearts were harvested 28 days after MI. (B) Cumulative survival curve (Kaplan-Meier survival plot) of MI mice under hypoxia, normoxia and hyperoxia and sham-operated mice (n = 30 for the MI + hypoxia group, n = 30 for the MI + normoxia mice group, n = 30 for the MI + hyperoxia group, and n = 10 for the sham-operated group). (C) Representative results of trichrome staining of longitudinal heart sections after MI. Scale bar: 1 mm. (D) Heart weight-to-body weight (HW/BW) ratio in sham, MI + normoxic, MI + hypoxic and MI + hyperoxic mice. (E) Left ventricular ejection fraction (LVEF), fractional shortening (LVFS), left ventricular internal diameter at end-systole (LVID, s) and left ventricular volume at end-systole (LV Vol; s) were measured by echocardiography and are presented. (F) Schematic representation of left ventricle (LV) sampling 8 mm from the apical region to the section. Trichrome staining of the transverse section is presented. (n = at least 3 per group). Scale bar: 1 mm. (G) Quantification of the fibrotic area relative to the myocardium in transverse sections. (H) Representative images of infarct areas stained with picrosirius red and visualized under polarized light. Scale bar: 100 μm. (I) Quantification of picrosirius red polarized light analysis in the infarct areas of MI mice. Dot-plots represent data from individual mice. Statistical significance was determined by log-rank test (B), ANOVA followed by Sidak's multiple comparisons test (D, E) or Kruskal-Wallis test followed by Dunn's posttest to correct for multiple comparisons (G, I). *P < 0.05, **P < 0.01 and ***P < 0.001 compared to the corresponding control.