Frank Haoning Yu

Fibrotic conditions contribute to significant global morbidity and mortality. Yet the underlying processes that orchestrate fibrosis remain poorly understood due to the cellular and spatial complexity of the stromal, immune, and vascular compartments that regulate fibrotic disease progression. Senescent cells (SnCs) have been implicated in fibrosis, but their roles are unclear, as evidence indicates that they serve both pathogenic and reparative functions. Here, we show that fibrosis-associated SnCs contain functionally divergent senotypes that are organized into distinct spatial niches. Using integrated single-cell and spatial transcriptomics analyses and hierarchical factorization in a murine fibrosis model, we identify fibroblast and perivascular SnC subpopulations that upregulate diverse programs related to extracellular matrix (ECM) production, immune signaling, and vascular remodeling. Fibroblast senotypes localize to discrete microenvironments with distinct tissue architectures, including niches associated with fibrotic signaling, immune activity, and cartilage development. Perivascular SnCs occupy interfaces between fibrotic signaling and immune-active niches and upregulate vascular and fibrotic remodeling pathways. Depletion of pericyte-lineage SnCs increases vascular maturation and fibrotic ECM deposition, providing mechanistic validation of the beneficial role these SnCs play in vascular remodeling and fibrosis modulation. In addition, using a new web-based infrastructure to query our senotype gene signatures in public datasets, we demonstrate that these senotypes are conserved across different murine and human fibrotic conditions. These findings establish senescence as a spatially organized regulator of fibrosis and identify perivascular senescence as a link between vascular remodeling and fibrotic outcomes.

Immune-stromal crosstalk governs tissue fibrosis, which is marked by dysregulated extracellular matrix (ECM) production and aberrant vasculature. Here, we investigate how γδ T cell interactions with stromal cells shape fibrosis in the foreign body response in a murine biomaterial implant model. During the acute reaction, type-1 (γδIFNγ) and type-17 (γδ17) γδ T cell subsets accumulate at the implant site. While γδIFNγ cells decrease as fibrosis progresses, activated γδ17 cells persist as dominant interleukin-17 producers. The γδ17 cell compartment expands with aging and high-fat diet, both factors associated with chronic inflammation and fibrosis. Fibroblasts co-cultured with γδ17 cells exhibit increased expression of collagen genes and intercellular communication inference links γδ T cell ligands to activation of ECM remodeling and vascular development programs in fibroblasts and endothelial cells. Finally, genetic deletion of γδ T cells in mice alters expression of ECM components and increases vessel size within the fibrotic matrix. Altogether, our findings implicate γδ T cells in regulating stromal cell behavior to modulate composition and vascularity of fibrotic tissues.

Fibrosis plays a key role in both chronic disease progression and failure of synthetic biomaterial implants. However, the contribution of adaptive immunity to fibrotic development remains incompletely understood, particularly for regulatory T cells (Tregs). Here, we used single-cell multiomic profiling, integrating transcriptomics with T cell receptor (TCR) sequencing, to map Treg heterogeneity and clonal dynamics in a synthetic material-induced model of fibrosis. We uncovered progressive Treg clonal expansion accompanied by TCR activation signatures and an increasingly immunosuppressive phenotype along a continuous transcriptional trajectory. These Tregs suppressed immune responses and influenced extracellular matrix and vascular gene expression. Cell-cell communication inference predicted Treg-driven activation of pro-fibrotic and vasculogenic transcriptional programs in fibroblasts and endothelial cells, including Sox-family transcription factors. Functional Treg depletion increased inflammation and significantly reduced neovascularization. Together, these findings identify Treg functions in the fibro-vascular niche through stromal cell modulation, highlighting immune-stromal interactions as an important axis in fibrosis.