Fibroblast activation protein in aortic stenosis: integrating in vivo imaging with a bioinformatics approach

Abstract Introduction Aortic stenosis has no medical therapy to attenuate disease progression. The underlying pathogenesis is unknown with a lack of delineation of responsible cellular subtypes and pathways driving disease initiation and progression. High-resolution transcriptomic profiling of explanted tissue can enable the identification of disease driving pathways and novel therapeutic targets. Positron emission tomography (PET) may be able to label and to track such pathways in vivo. Methods Bulk- and single nucleus RNA-sequencing was performed on diseased aortic valves from deceased patients with a spectrum of aortic stenosis severity and normal aortic valves from patients undergoing transplant for ischaemic cardiomyopathy. In a linked prospective observational cohort, patients with aortic stenosis and matched controls underwent PET and cardiac computed tomography (CT) at baseline and ≥1 year later. Results Bulk RNA expression (control, n=12; mild/moderate aortic stenosis, n=9; severe aortic stenosis, n=18) revealed a disease-specific gene signature for valvular interstitial cells. A specific cluster of these cells expressing chrondo- and osteo-genic profiles were associated with disease severity, with specific upregulation of fibroblast activation protein (FAP) (Figure 1). Eighty-six patients (11 with aortic sclerosis, and 25 each with mild, moderate or severe aortic stenosis; 72±11 years, 32% female) and 9 control subjects (71±8 years, 33% female) underwent PET with the novel positron emitting radiotracer gallium-68 fibroblast activation protein inhibitor ([68Ga]FAPI, which binds specifically to FAP. [68Ga]FAPI uptake was seen in all patients with aortic sclerosis or stenosis with no uptake seen in the control population. [68Ga]FAPI uptake increased with disease severity (ANOVA p