Heart failure is characterized by initial compensatory changes, including the myocyte hypertrophy, chamber dilation, and matrix remodeling, that proceed until progressive dysfunction produces end stage heart failure and mortality. Recently, the roles of secreted factors in the heart that could regulate pathological hypertrophy, including follistatin (FST) and related molecules, have been examined by various investigators. FST is a molecule that blocks secretion of follicle-stimulating hormone from the pituitary and regulates members of the transforming growth factor beta (TGF-β) family including myostatin. Here we tested the effects of a particular FST isoform, FST288, on heart function in mice. The gene encoding FST produces three isoforms that differ in biological activities and cell surface binding capabilities. The FST315 isoform contains all six exons, and proteolytic cleavage of the FST315 C-terminal tail results in production of FST303. The lack of exon 6, which codes for the acidic C-terminal tail of the putative full-length protein, results in FST288. The missing acidic C-terminal tail region found in soluble FST315 allows FST288 to bind cell surface heparin-sulfated proteoglycans, accounting for the differential actions of these FST isoforms. Since mice that are null for the FST gene die embryonically, we used genetically modified mice that express only the FST288 isoform to test the role of FST315 in adult heart. Examination of these animals suggests that the loss of FST315 expression has limited effects on the heart at the resting state. When these mice are subjected to pressure overload through transverse aortic constriction (TAC) surgery they appear to be resistant to the compensatory cardiac hypertrophy present in wild type mice by 4 weeks post surgery. Both cardiac structure (examined by histology) and function (as measured by echocardiography and pressure/volume loops) following TAC are improved in the genetically modified mice when compared to wild type mice. This response is likely due to modification of the myostatin signaling pathway, one of the major targets of FST315. Overall, our data illustrates that FST315 is an important contributor to the progression of pressure overload induced cardiac hypertrophy.
Essential role of CPI-17 for muscle force generation in urinary bladder using CPI-17 genetically modified mice
