A stress-function tradeoff organizes epithelial heterogeneity across spatial scales in the human thyroid

Many organs are organized into repeating anatomical units, yet how cellular heterogeneity is structured within and between these units remains poorly understood. Here we use spatial transcriptomics to dissect multiscale heterogeneity in the human thyroid gland, a tissue composed of hormone-producing follicles. Across human thyroid samples spanning non-inflamed to inflamed states, we develop a follicle-aware analytical framework that separates intra-follicular from inter-follicular variability. We find that heterogeneity among thyrocytes is not dominated by differences in hormone synthesis but instead by two opposing transcriptional programs: an active hormone-producing state and a damage-response thyrocyte (DRT) state enriched for stress, immune, and damage-response pathways. DRTs are spatially clustered, associated with DNA damage markers, and are enriched near immune niches. Notably, the balance between active and damage-response programs constitutes a major axis of variability across cells, follicles, and patients. Our findings highlight a damage-response epithelial thyrocyte state that may be fundamental to follicular function in the human thyroid and provide a general framework for studying heterogeneity in tissues composed of repeating anatomical units.