BACKGROUND: Growth differentiation factor 15 (GDF15) is a stress-responsive cytokine and biomarker that is produced after myocardial infarction and that is related to prognosis in acute coronary syndrome (ACS). We hypothesized that secreted proteins that activate GDF15 production may represent new ACS biomarkers.
METHODS: We expressed clones from an infarcted mouse heart cDNA library in COS1 cells and assayed for activation of a luciferase reporter gene controlled by a 642-bp fragment of the mouse growth differentiation factor 15 (GDF15) gene promoter. We measured the circulating concentrations of follistatin-like 1 (FSTL1) and GDF15 in 1369 patients with ACS.
RESULTS: One cDNA clone that activated the GDF15 promoter-luciferase reporter encoded the secreted protein FSTL1. Treatment with FSTL1 activated GDF15 production in cultured cardiomyocytes. Transgenic production of FSTL1 stimulated GDF15 production in the murine heart, whereas cardiomyocyte-selective deletion of FSTL1 decreased production of GDF15 in cardiomyocytes, indicating that FSTL1 is sufficient and required for GDF15 production. In ACS, FSTL1 emerged as the strongest independent correlate of GDF15 (partial R(2) = 0.26). A total of 106 patients died of a cardiovascular cause during a median follow-up of 252 days. Patients with an FSTL1 concentration in the top quartile had a 3.7-fold higher risk of cardiovascular death compared with patients in the first 3 quartiles (P < 0.001). FSTL1 remained associated with cardiovascular death after adjustment for clinical, angiographic, and biochemical variables.
CONCLUSIONS: Our study is the first to use expression cloning for biomarker discovery upstream of a gene of interest and to identify FSTL1 as an independent prognostic biomarker in ACS.

Widera C et al. Clin Chem. 2012 Aug;58(8):1233-41. Epub 2012 Jun 6.

Therapeutic Impact of Follistatin-like 1 on Myocardial Ischemic Injury in Preclinical Animal Models

BACKGROUND: Acute coronary syndrome (ACS) is a leading cause of death in developed countries. Follistatin-like 1 (FSTL1) is a myocyte-derivedsecreted protein, which is upregulated in the heart in response to ischemic insult. Here, we investigated the therapeutic impact of FSTL1 on acute cardiac injury in small and large preclinical animal models of ischemia/reperfusion (I/R) and dissected its molecular mechanism. METHODS AND RESULTS: Administration of human FSTL1 protein significantly attenuated myocardial infarct size in a mouse or pig model of I/R, which was associated with reduction of apoptosis and inflammatory responses in the ischemic heart. Administration of FSTL1 enhanced the phosphorylation of AMP-activated protein kinase (AMPK) in the I/R-injured heart. In cultured cardiac myocytes, FSTL1 suppressed apoptosis in response to hypoxia/reoxygenation and LPS-stimulated expression of pro-inflammatory genes through its ability to activate AMPK. I/R led to enhancement of bone morphogenetic protein-4 (BMP-4) expression and Smad1/5/8 phosphorylation in the heart, and FSTL1 suppressed the increased phosphorylation of Smad1/5/8 in ischemic myocardium. Treatment of cardiac myocytes with FSTL1 abolished the BMP-4-stimulated increase in apoptosis, Smad1/5/8 phosphorylation and pro-inflammatory gene expression. In cultured macrophages, FSTL1 diminished LPS-stimulated expression of pro-inflammatory genes via activation of AMPK, and also abolished BMP-4-dependent induction of pro-inflammatory mediators. CONCLUSIONS: Our data indicate that FSTL1 can prevent myocardial I/R injury by inhibiting apoptosis and inflammatory response through modulation of AMPK- and BMP-4-dependent mechanisms, suggesting that FSTL1 could represent a novel therapeutic target for ACS.

Ogura Y, et al. Circulation. 2012 Aug 28. [Epub ahead of print]