Abstract Body: Background: BNP is a clinical biomarker of heart failure that is prognostic in cardiac amyloid. It is unknown whether BNP reflects a diffuse response of all cardiomyocytes or a spatially restricted subset.
Hypothesis: Amyloid deposits mechanically stress neighboring cardiomyocytes, creating a distinct amyloid borderzone characterized by high NPPB expression and BNP release. If true, BNP may reflect borderzone surface area.
Methods: We analyzed 66 histologic sections from patients with cardiac amyloidosis (3 serial sections at 3-5 locations, from 7 patients - 3 ATTR, 4 AL). Sections were stained for H&E, Congo red (A), NPPB (N), and TNNT2 (T). Slides were scanned, registered, segmented into 133k tiles (245x245 µm), and quantified using a machine learning histology foundation model, spatial gene expression, and amyloid staining. We also performed spatial transcriptomics (n = 2, Xenium) and single-nuclei RNA-seq (n=4), and integrated with published data (108,225 nuclei; 26,612 cardiomyocytes).
Results: NPPB showed marked spatial heterogeneity, with 40% of NPPB+ cardiomyocytes within 20 µm of amyloid and >90% within 100 µm. Structural embeddings defined a continuum of tiles mapping to a remote zone (T+, N-, A-), border zone (T+, N+,A+), and amyloid zone (T-, N-, A+). Single nuclei RNA-seq independently identified this distinct NPPB+ cardiomyocyte subset (~20%), enriched for natriuretic peptides, as well as mitochondrial, cytoskeletal, and mechanotransduction programs. Spatial transcriptomics confirmed localization to amyloid border zones.
Conclusions: Cardiac amyloidosis contains a spatially restricted amyloid-associated border zone where neighboring cardiomyocytes activate a distinct NPPB-defined stress program. Circulating natriuretic peptides may reflect the extent of myocardium exposed to amyloid-adjacent stress.