Foxo3a and cardiac myofibroblast transdifferentiation after myocardial infarction

Abstract Background Fibroblast/ myofibroblast differentiation following acute myocardial infarction (MI) is important for myocardial scar formation but also causes adverse remodeling and stiffening of the myocardium leading to cardiac dysfunction and heart failure. Transdifferentiation of myofibroblasts are characterized by periostin, and extracellular matrix protein expression. The transcription factor forkhead box O 3 (FOXO3a) has been recently shown to inhibit hypertrophic cardiac remodeling. Purpose We hypothesized that FOXO3a, a key regulator of cell size, immunity, and cell differentiation, might inhibit transdifferentiation of fibroblasts into myofibroblasts and therefore cardiac fibrosis after MI. Methods Acute MI was induced in Foxo3a-/- mice and wild-type littermates by permanent LAD ligation. Cardiac function was determined by transthoracic echocardiography (TTE) at baseline as well as on days 4 and 14 post-MI. Immune histochemistry was performed with collagen and periostin. Finally, fibroblast differentiation was investigated by single nucleus RNA-sequencing (snRNA-seq). Results Foxo3a-/- mice showed significantly improved survival despite similar infarct size post-MI (p<0.01). The survival advantage was in part due to reduced cardiac ruptures on autopsy. TTE showed reduced LV function, cardiac output, and global strain 4 days post-MI that did not differ between both groups of animals. However, systolic LV function was significantly attenuated in Foxo3a-/- mice 14 days post-MI indicating enhanced wall stiffness. In line with these findings, sn-RNAseq on day 4 post-MI revealed significantly increased numbers of periostin positive myofibroblasts (Myo) (p<0.05) important for stabilizing matrix interactions that transdifferentiated mainly from progenitor-like state fibroblasts (PLS) and homeostatic epicardial derived fibroblasts (HEpiD) in Foxo3a-/- mice. Myo differentially expressed, i.e. upregulated genes important for extracellular matrix structure and organization, cell migration and collagen organization. Moreover, an upregulation of pro-fibrotic genes was observed in other fibroblast clusters such as in HEpiD (i.e., Col1a1, Col1a2, Col3a1), PLS (i.e., fgf10, il1r1), late response fibroblasts (LR-F) (i.e., Col14a1, Rin2) and in activated fibroblasts (F-ACT) (i.e., Gpc6, Slt2) in Foxo3a-/- mice. These changes were corroborated by significantly elevated collagen type 1 and 3 as well as periostin protein expression in Foxo3a-/- mice. Cell chat analysis indicated enhanced number of interactions and interaction strength of myeloid cells with fibroblasts in Foxo3a-/- mice. Conclusion Our data identify Foxo3a as a master regulator of cardiac remodeling attenuating myofibroblast transdifferentiation after acute MI. These findings suggest that deficiency of Foxo3a promotes early scar formation preventing rupture but also contributes to adverse remodeling in later stages resulting in impaired cardiac function and enhanced fibrosis after MI.