ORIGINAL RESEARCH Cardiac development and physiology are modulated by FGF2 in an isoform- and sex-specific manner

The low-molecular-weight isoform (Lo) of fibroblast growth factor 2 (FGF2) has distinct functions from the high-molecular-weight isoforms (Hi) of FGF2 in the adult stressed heart. However, the specific roles of these isoforms in the unstressed heart were not examined. We investigated whether the FGF2 isoforms modulate cardiac development and physiology in isoform- and sex-specific manners. Young adult male and female mice that were deficient in either Hi FGF2 (Hi KO) or Lo FGF2 (Lo KO) underwent echocardiographic analysis and were compared to their wild-type (WT) counterparts. By com-parison to WT cohorts, female Lo KO hearts display a 33 % larger left ventric-ular (LV) volume and smaller LV mass and wall thickness. Mitral valve flow measurements from these hearts reveal that the early wave to atrial wave ratio (E/A) is higher, the deceleration time is 30 % shorter and the mitral valve E-A velocity–time integral is reduced by 20 % which is consistent with a restrictive filling pattern. The female Hi KO hearts do not demonstrate any significant abnormality. In male Hi KO mice the cardiac output from the LV is 33% greater and the fractional shortening is 29 % greater, indicating enhanced sys-tolic function, while in male Lo KO hearts we observe a smaller E/A ratio and a prolonged isovolumic relaxation time, consistent with an impaired relaxa-tion filling pattern. We conclude that the developmental and physiological functions of FGF2 isoforms in the unstressed heart are isoform specific and nonredundant and that these roles are modulated by sex