Figure 6: Myofibroblast-specific Smad3, but not Smad2 signaling is critical for organization of myofibroblast arrays in infarcted hearts.
After 7 days of coronary occlusion, infarct myofibroblasts in wildtype mice (identified through α-SMA immunofluorescence-white arrows), are typically aligned along the direction of the left ventricular wall (red arrow-A, C). In contrast to the perturbed alignment of infarct myofibroblasts in FS3KO mice (C-D, white arrows), FS2KO animals exhibited well-organized myofibroblast arrays (white arrows, A-B). E: Quantitative analysis showed that infarct myofibroblasts in FS3KO mice had a much lower major to minor axis ratio than Smad3 fl/fl cells, suggesting round morphology. In contrast, FS2KO mice had an increase in the major to minor axis ratio of infarct myofibroblasts, reflecting a more elongated morphology (*p<0.05, ****p<0.0001, n=3–9/group). The average angle of the myofibroblasts (white arrows) to the direction of the left ventricle (red arrow) was assessed as a quantitative indicator of cell alignment. The mean angle was significantly higher in FS3KO mice than in FS2KO animals, (F) (****p<0.0001, n=3–9/group), suggesting that formation of aligned arrays of polarized infarct myofibroblasts is dependent on Smad3, and not on Smad2 signaling. Statistical analysis was performed using ANOVA followed by Tukey’s multiple comparison test. Please note that due to the very high mortality of male FS3KO mice following infarction, comparative analysis in this study was limited to female mice.