Background/Purpose: Single-cell transcriptomic data has shown that fibroblasts exhibit heterogeneity, with subpopulations that have diverse functional characteristics. However, the conventional single-cell methods are unable to provide spatial information, which is critical for unraveling disease-specific cellular interactions. Fibroblasts, which play a crucial role in fibrotic diseases such as systemic sclerosis (SSc), have not been spatially defined at the cellular level. In this study, our objective was to examine different subsets of fibroblasts  and investigate the spatial organization and cellular niches of these fibroblast subsets in SSc skin using imaging mass cytometry (IMC).

Methods: We employed IMC to analyze the diversity of fibroblasts in 18 skin samples obtained from patients with systemic sclerosis (SSc) and healthy individuals at the single-cell level. Based on known activation markers, we identified several types of fibroblast subsets. We then examined how these subsets were distributed within the tissues and investigated the distinct cellular local environments present in the skin of SSc.

Results: Our analysis found 13 distinct subsets of fibroblasts in both SSc and control skin. Among these subsets, we observed an increase of fibroblast subpopulations in SSc, including myofibroblasts,  FAP^high-, S1PR⁺-, Thy1⁺;ADAM12^high;PU.1^high-, and ADAM12⁺;GLI1⁺-fibroblasts. Three of the subpopulations were decreased in SSc, including TFAM^high-, PI16⁺;FAP⁺-, and Thy1⁺;ADAM12^low-fibroblasts. We also detected spatial reorganization and altered cellular interactions between fibroblasts subsets in SSc. The presence of S1PR⁺ fibroblast was associated with the severity and progression of skin fibrosis, while a higher quantity of PI16⁺;FAP^– fibroblasts was linked to milder skin fibrosis. The abundance of S1PR⁺ fibroblast-interacting ADAM12⁺;GLI1⁺ fibroblasts correlates with the extent of skin fibrosis, while no association was found when examining ADAM12⁺;GLI1⁺ fibroblasts alone regardless of their interaction partners. The frequencies of S1PR⁺ fibroblasts in the upper dermis are elevated in patients with the progression of skin fibrosis.

Conclusion: We utilized IMC to demonstrate significant alterations in the abundance and spatial distribution of fibroblast subsets in SSc skin. These changes in spatial distribution and cellular interactions among fibroblasts correlate differently with clinical parameters of SSc. These findings suggest that spatial localization and interacting partners may functionally impact the phenotype of fibroblasts. Targeting these dysregulations could provide additional therapeutic benefits. Monitoring the alteration in abundance, localization, and cellular interaction for fibroblasts in SSc skin may offer further insights into patient stratification.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterization-of-fibroblast-subpopulations-and-their-cellular-local-environments-in-systemic-sclerosis-using-imaging-mass-cytometry/