Early Systemic Sclerosis Skin Reveals a Vascular Niche Driving Fibrosis Before Treatment Begins
Early, untreated systemic sclerosis skin is not a passive backdrop to fibrosis. In diffuse cutaneous disease, the earliest tissue events appear to be organized around small vascular neighborhoods where immune cells and fibroblasts meet, exchange signals, and shift the dermis toward a profibrotic state.
This integrated skin analysis in treatment-naive patients with diffuse cutaneous systemic sclerosis used single-nuclei multiome sequencing and two spatial transcriptomic platforms to interrogate fibroblasts, myeloid cells, and their tissue context at once. The approach matters because fibrosis is not driven by one cell type acting in isolation. It emerges from coordinated behavior across vascular, immune, and stromal compartments, and this dataset captured those interactions before therapy could distort the biology.
Macrophages, Fibroblasts, and T Cells Cluster Around the Vasculature
Across papillary dermis, hypodermis, and vascular regions, the tissue showed an immunomodulatory niche enriched for activated myeloid cells and fibroblasts. The most prominent signals included expression of CXCL12, APOE, and C7, genes that fit with a tissue environment built for immune recruitment, metabolic adaptation, and complement-related inflammatory activity.
One sentence captures the spatial logic of the disease: the vascular wall became a meeting place for pathogenic conversation.
Spatial transcriptomic neighborhood analysis showed colocalization of fibroblasts, macrophages, and T cells around blood vessels, rather than a diffuse scattering of inflammatory cells across the dermis. In a fibrosing disorder, that arrangement is biologically persuasive. Blood vessels provide both a structural scaffold and a trafficking route, while perivascular stromal cells can amplify inflammatory cues and translate them into matrix production, cell migration, and persistent tissue remodeling.
Profibrotic Signaling Pathways Were Already Active in Untreated Skin
Pathway analysis pointed to significant enrichment of PI3K/AKT/mTOR signaling within these cellular niches, driven by profibrotic growth factor networks. In practical biologic terms, this pathway sits at the crossroads of proliferation, survival, metabolism, and matrix remodeling. When it is activated in fibroblasts and neighboring immune cells, the tissue gains a durable growth advantage for the very compartments that sustain scarring.
Macrophage subclustering sharpened the signal further. SSc macrophages showed activation of IL-6/JAK/STAT signaling and enrichment of oxidative phosphorylation pathways, suggesting a metabolically active inflammatory state rather than a quiescent infiltrate. The oxidative phosphorylation signature is especially relevant because macrophages can shift their energy use in step with inflammatory polarization and tissue repair programs. In fibrotic skin, that metabolic flexibility may help these cells persist in the dermis and continue feeding pathogenic stromal activation.
PDGF and TGF-β Linked Macrophages to Fibroblast Activation
Ligand-receptor analysis provided the clearest mechanistic bridge between the immune and stromal compartments. SSc macrophages secreted PDGF and TGF-β, and those cues mapped to activation of SSc-dominant fibroblast subclusters. These are not generic inflammatory signals. PDGF is a classic fibroblast mitogen and motility cue, while TGF-β remains one of the central drivers of extracellular matrix deposition and myofibroblast differentiation.
A single finding stands out: monocyte-derived MRC1+ macrophages expressed PDGF near PDGFRhiTHY1hi fibroblasts.
That proximity gives the transcriptomic data a tissue-level mechanism. Perivascular macrophages may not merely accompany fibrosis; they may actively instruct fibroblasts that are already primed to respond. THY1 and PDGFR expression define a fibroblast state with high sensitivity to growth factor input, and the spatial overlap suggests that the conversation is local, repeated, and probably difficult to interrupt once established. In early disease, this kind of cell-to-cell reinforcement can turn a reversible inflammatory insult into a durable fibrotic program.
Why the Vascular Compartment Matters in Early Diffuse Disease
The study’s strongest contribution is not just the identification of inflammatory cells, but the realization that the vascular niche is where the earliest fibroblast-immune interactions concentrate. Systemic sclerosis has long been understood as a disease of vasculopathy, autoimmunity, and fibrosis. These data place the vasculature squarely at the intersection of those processes in untreated skin.
The perivascular location likely matters because endothelial dysfunction can alter leukocyte trafficking, tissue oxygenation, and stromal activation simultaneously. Once macrophages accumulate near vessels, they can amplify chemokine gradients, drive fibroblast activation, and recruit additional immune cells into the same microenvironment. Fibroblasts in that niche then become less like passive structural cells and more like active participants in immune signaling, responding to PDGF, TGF-β, and other growth factor networks with increased fibrotic output.
What This Means for Early Mechanism-Based Intervention
For clinicians and researchers, the practical implication is straightforward: early diffuse systemic sclerosis skin already contains a molecularly organized fibrotic niche before treatment begins. The disease is not waiting for late-stage collagen accumulation to become biologically active. The inflammatory and stromal machinery is already in motion around blood vessels, where macrophages, fibroblasts, and T cells share space and signaling pathways.
This has direct relevance for therapeutic development. Pathways involving PI3K/AKT/mTOR, IL-6/JAK/STAT, PDGF, and TGF-β are not independent observations here; they converge on the same tissue neighborhood and likely reinforce one another. A therapeutic strategy that ignores that spatial convergence risks missing the cells that are actually driving early fibrotic remodeling.
The study also supports a more precise view of skin biopsy biology in systemic sclerosis. Bulk tissue averages can obscure rare but decisive cell states, especially when pathogenic cells are concentrated around vessels. Single-nuclei multiome profiling and spatial transcriptomics together exposed the local architecture of disease and linked transcriptional activation to tissue geography in a way conventional histology cannot.
Even so, this remains a mechanistic tissue study rather than an interventional trial. The findings define early pathogenic circuitry, but they do not establish whether blocking any one pathway would reverse established skin fibrosis or prevent organ progression. They also leave open how these perivascular neighborhoods evolve over time, whether they differ across disease subsets, and how closely they track with clinical severity or treatment response.
What is clear from the tissue itself is the sequence of injury: activated macrophages gather around vessels, fibroblasts adopt a profibrotic state, and signaling networks tied to growth, metabolism, and inflammation converge in a compact dermal niche. In diffuse cutaneous systemic sclerosis, that appears to be one of the earliest places where pathology becomes organized enough to persist.