Spatial FAP Expression as Detected by 68 Ga-FAPI-46 Identifies Myofibroblasts Beyond the Infarct Scar After Reperfusion

Figures

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  Fig. 1. Time course of FAP and CD68 expression on day 0, 3 and 7 after MI/R. (A, B) Co-immunohistochemical analysis for FAP and CD68 in the same sections at day 0, 3, and 7 after MI/R. (E, F) FAP and CD68 expression peaked at day 3 in the infarcted myocardium. (C, D) FAP expressing myofibroblasts and CD68 expressing inflammatory cells were both located in close proximity within the infarcted myocardium, but were identified as distinct cell populations at 3 days (C) and 7 days after MI/R (D). (G) Weak correlation between FAP and CD68 at days 3 (white circles) and 7 (black circles). Bars indicate mean ± SE. MI/R day 0: n = 4; day 3: n = 5; day 7: n = 4, # = p < 0.05 vs. day 0. Scale bar: 200 µm (A, B) and 100 µm (C, D). FAP, green; CD68, red; Nuclei, blue

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  Fig. 2. FAP expression in the AAR at day 3 after MI/R is not correlated with ischemic or hypoxic myocardium. (A, C) Co-immunohistochemistry for perfused myocardium, hypoxic myocardium, and FAP. The border between surviving (“surv.”) and ischemic myocardium (“AAR”) is delineated by dotted lines. FAP expression is predominantly located within the AAR in a non-uniform pattern, with little FAP expression detected in adjacent surviving myocardium (black arrows). (B, D) Quantitative analysis shows FAP expression is not correlated with ischemic (B) or hypoxic area (D). (E) Overview of ischemia, hypoxia and FAP-expression at 3 days after MI/R, demonstrating abundant FAP-expression within the AAR. Hypoxia (Pimonidazole), green; perfused vasculature (lectin), yellow; FAP, red; Nuclei, blue. (B) n = 3; (D) n = 4; Scale bars: 200 μm

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  Fig. 3. Myocardial 68 Ga-FAPI-46 autoradiography and FAP expression at 3 days after MI/R. (A) Representative example of FAP and CD68 expression together with 68 Ga-FAPI-46 autoradiography in nearby sections from the mid-portion of the infarcted heart. High uptake of 68 Ga-FAPI-46 tracer within the infarcted LV free wall as evidenced by hematoxylin–eosin (H/E) staining. Areas of FAP-expression and 68 Ga-FAPI-46 uptake are consistent across the sections. (B, C) 68 Ga-FAPI-46 uptake extends beyond the infarct scar. Masson trichrome staining delineates the collagen containing infarct scar (violet, dotted lines in upper panels), and 68 Ga-FAPI-46 autoradiography in the same sections shows uptake in the infarct area. 68 Ga-FAPI-46 uptake is non-uniformly distributed with spots of highest uptake in the infarct area but extends into the infarct borderzone and is also detected in remote myocardium. The area fraction of.68 Ga-FAPI-46 uptake in relation to the LV is higher than the area fraction of scar identified by Masson trichrome (P = 0.001) (C). CD68, green; FAP, red; Nuclei, blue. Scale bar: 200 μm. Autoradiography, n = 5

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  Fig. 4. 68 Ga-FAPI-46 PET signal exceeds the infarct region after anterior acute myocardial infarction. Depicted are: Myocardial perfusion images using 99mTc-tetrofosmin at rest (first row) and 68 Ga-FAPI PET (second row). Area of perfusion defect after revascularization and area of activated fibroblasts are indicated by dotted lines in 3 representative patient examples

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  Fig. 5. FAP expression exceeds the infarct region after acute MI in patients with reduced LV-function. Upper panels: 7 days post-MI, CD13 and FAP are expressed within the scar, borderzone and adjacent myocardial tissue. FAP is expressed adjacent to CD13-expressing cells in the border zone (arrowheads). Lower panels: 22 days post-MI, CD13 expression is found mostly within the scar, but extends into the granulation tissue of the border zone. FAP expression is non-homogenously distributed within the scar, and also found in clusters within the border zone and also around blood vessels (arrowheads). Scale bars: 500 μM. Bz, Borderzone