Follistatin-like 3 mediates paracrine fibroblast activation by cardiomyocytes

Follistatins are extracellular inhibitors of the TGF-β family ligands including activin A, myostatin and bone morphogenetic proteins. Follistatin-like 3 (FSTL3) is a potent inhibitor of activin signalling and antagonises the cardioprotective role of activin A in the heart. FSTL3 expression is elevated in patients with heart failure and is upregulated in cardiomyocytes by hypertrophic stimuli, but its role in cardiac remodelling is largely unknown. Here, we show that the production of FSTL3 by cardiomyocytes contributes to the paracrine activation of cardiac fibroblasts, inducing changes in cell adhesion, promoting proliferation and increasing collagen production. We found that FSTL3 is necessary for this response and for the induction of cardiac fibrosis. However, full activation requires additional factors, and we identify connective tissue growth factor as a FSTL3 binding partner in this process. Together, our data unveil a novel mechanism of paracrine communication between cardiomyocytes and fibroblasts that may provide potential as a therapeutic target in heart remodelling.British Heart Foundation [PG/08/084/25827]; Heart Research UK; National Institute for Health Research Cardiovascular Biomedical Research Unit at the Royal Brompton; Harefield NHS Foundation Trust; Imperial College; European Union [ERG-239158, ITN-289600]; Spanish Ministry of Science and Innovation [BFU2009-10016, CP08/00144]; Regional Government of Madrid [S2010/BMD-2321 'Fibroteam']S

Activin A and Follistatin-Like 3 Determine the Susceptibility of Heart to Activin A and Follistatin-Like 3 Determine the Susceptibility of Heart to Ischemic Injury

Background-Transforming growth factor-␤ family cytokines have diverse actions in the maintenance of cardiac homeostasis. Activin A is a member of this family whose regulation and function in heart are not well understood at a molecular level. Follistatin-like 3 (Fstl3) is an extracellular regulator of activin A protein, and its function in the heart is also unknown. Methods and Results-We analyzed the expression of various transforming growth factor-␤ superfamily cytokines and their binding partners in mouse heart. Activin ␤A and Fstl3 were upregulated in models of myocardial injury. Overexpression of activin A with an adenoviral vector (Ad-act␤A) or treatment with recombinant activin A protein protected cultured myocytes from hypoxia/reoxygenation-induced apoptosis. Systemic overexpression of activin A in mice by intravenous injection of Ad-act␤A protected hearts from ischemia/reperfusion injury. Activin A induced the expression of Bcl-2, and ablation of Bcl-2 by small interfering RNA abrogated its protective action in myocytes. The protective effect of activin A on cultured myocytes was abolished by treatment with Fstl3 or by a pharmacological activin receptor-like kinase inhibitor. Cardiac-specific Fstl3 knockout mice showed significantly smaller infarcts after ischemia/reperfusion injury that was accompanied by reduced apoptosis. Conclusions-Activin A and Fstl3 are induced in heart by myocardial stress. Activin A protects myocytes from death, and this activity is antagonized by Fstl3. Thus, the relative expression levels of these factors after injury is a determinant of cell survival in the heart. (Circulation. 2009;120:1606-1615.