Fibroblast activation protein alpha expression identifies activated fibroblasts after myocardial infarction.

INTRODUCTION: Fibroblast activation protein α (FAP) is a membrane-bound serine protease expressed by activated fibroblasts during wound healing in the skin. Expression of FAP after myocardial infarction (MI) and potential effects on cardiac wound healing are largely unknown. METHODS: MI was induced in rats and FAP expression was analyzed at 3, 7 and 28 days post-MI by microarray, Western blot and immunohistochemistry. In human hearts after MI, a FAP(+) fibroblast population was identified, and characterized by immunohistochemistry for prolyl-4-hydroxylase ß, α-smooth muscle actin, Thy-1 and vimentin. Signaling pathways leading to FAP expression were studied in human cardiac fibroblasts by Western blot and ELISA using TGFß1, TGF-beta type I-receptor (TGFbR1)-inhibitor SB431542 or the MAPK-inhibitor U0126 as well as siRNA targeting SMAD2 and SMAD3. Finally, fibroblasts were assayed for FAP-dependent migration (modified Boyden-chamber), proliferation (BrdU-assay) and gelatinolytic activity by gelatin zymography. RESULTS: In rats, FAP expression was increased after MI especially in the peri-infarct area peaking at 7 days post-MI. Co-localization analysis identified the majority of FAP(+) cells as activated proto-myofibroblasts and myofibroblasts. Concordantly, FAP(+) fibroblasts were abundant in ischemic tissue of human hearts after MI, but not in healthy control hearts. In vitro, FAP was induced by TGFß1 via the canonical SMAD2/SMAD3 pathway. Depletion of FAP in fibroblasts reduced migratory capacity, while proliferation was not affected. Gelatin zymography revealed gelatinase activity by fibroblast-derived FAP. CONCLUSION: In this study, we show for the first time the expression of FAP in activated fibroblasts after MI and its activation by TGFß1. Effects of FAP on fibroblast migration and gelatinolytic activity indicate a potential role in cardiac wound healing and remodeling.

Circulating concentrations of fibroblast activation protein α in apparently healthy individuals and patients with acute coronary syndrome as assessed by sandwich ELISA.

BACKGROUND: Fibroblast activation protein α (FAP) is a membrane glycoprotein with dipeptidyl-peptidase and collagenase activity and is expressed in cancer, arthritis, and atherosclerotic plaques. We hypothesized that FAP can be measured quantitatively in the circulation and provide prognostic information in acute coronary syndrome (ACS). METHODS: We assessed the performance of a commercially available FAP ELISA and the pre-analytic characteristics of the marker. We determined FAP concentrations in EDTA plasma samples from 101 apparently healthy blood donors and 407 patients with ACS. Patients were followed for 12 months regarding all-cause mortality and non-fatal myocardial infarction (MI). RESULTS: FAP was stable at room temperature (for 1 day) and 4°C (3 days) and resistant to 3 freeze/thaw cycles. Recovery of recombinant human FAP ranged from 78 to 103% and serial dilutions of spiked samples resulted in measurements within 91 to 120% of expected values. Patients with ACS had lower plasma FAP concentrations compared with blood donors [median (25th-75th percentiles): 84 (69-101) ng/mL vs. 108 (87-124) ng/mL, P < 0.001]. Patients presenting with FAP concentrations in the first quartile had a 3.0-fold higher risk of death (95% confidence interval 1.4-6.2) compared with patients in the second to fourth quartiles (P = 0.004). FAP concentration was not related to the risk of MI. CONCLUSIONS: Our study is the first to associate FAP with prognosis in ACS. The favorable pre-analytic characteristics of FAP will facilitate future studies of the marker in other disease settings associated with altered FAP expression.