Biology subjects

Karonitsch, T.

Publications and source records attributed to Karonitsch, T..

3 recordsLinked to original sources

bioRxiv2026

Synovitis in systemic sclerosis is an interferon-driven stromal condition distinct from rheumatoid arthritis

Joint involvement is a major driver of disability in systemic sclerosis (SSc), yet its pathophysiology remains poorly understood. In the absence of specific evidence, SSc synovitis is treated by analogy with rheumatoid arthritis (RA). Here, we present the first comprehensive molecular characterization of SSc synovitis, integrating histology, single-cell RNA sequencing, and spatial multi-omics of synovial biopsies from SSc patients, RA patients, and non-inflammatory controls with in vitro validation. We show that SSc synovitis is characterized by distinct pathomechanisms from RA. Histologically, most SSc biopsies displayed a pauci-immune pathotype with sparse immune infiltrates and predominant stromal cells. At molecular level, synovial fibroblasts in SSc were characterized by a disease-specific type I interferon (IFN) response program, in contrast to the TNF-dominant profile of RA, accompanied by dysregulation of the complement cascade. This IFN program extended across multiple synovial cell types, including monocyte-derived macrophages and endothelial cells, and was spatially organized into focal myeloid niches and a diffuse stromal program. Systemically, elevated serum IFN-2a levels were associated with the presence of clinical synovitis in an independent cohort of SSc patients. We furthermore show that similar IFN-driven programs are shared between skin and synovium in SSc. Genes downregulated by IFNAR1 blockade in SSc skin were enriched in SSc synovium, supporting IFN receptor blockade as a multi-organ target therapeutic strategy. These findings reframe SSc synovitis as a less destructive, IFN-driven stromal condition distinct from RA and provide a mechanistic basis for dedicated clinical trials for joint inflammation in SSc. One Sentence SummarySSc synovitis is a pauci-immune, IFN-driven stromal condition distinct from RA, supporting IFNAR1 blockade as a therapeutic strategy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/733140v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@d85bb5org.highwire.dtl.DTLVardef@6cffe6org.highwire.dtl.DTLVardef@148eb4org.highwire.dtl.DTLVardef@1a4cd83_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2025

Nicotinamide N-Methyltransferase drives fibroblast activation and skin fibrosis in systemic sclerosis

BackgroundIn systemic sclerosis (SSc), an autoimmune response leads to progressive fibrosis of the skin and internal organs, driven by aberrant activation of fibroblasts. The mechanisms dictating persistent dermal fibroblast (DF) activation and production of extracellular matrix (ECM) remain poorly understood. Nicotinamide N-methyltransferase (NNMT), a SAM-consuming enzyme that modulates cellular methylation potential, has been implicated in fibrotic tissue remodelling in metabolic and malignant diseases. Here, we identify NNMT as a key determinant in DF activation and fibrosis in SSc. MethodsWe analyzed bulk, single-cell RNA-Seq and spatial transcriptomics datasets from SSc skin. Functional studies were performed in TGF{beta}-activated primary human DFs using siRNA-mediated NNMT knockdown (KD) combined with RNA-Seq, metabolite profiling, ELISA, and western blotting. The role of NNMT-regulated transcription factors was assessed by QuantSeq 3' RNA-Seq following ATF4, SOX9, or SRF KD. FindingsNNMT was markedly upregulated in SSc skin and enriched in disease-expanded SFRP2/COL8A1 myofibroblast states. NNMT KD restored methylation balance by increasing the SAM/SAH ratio and H3K27me3 levels, and abrogated TGF{beta}-induced profibrotic programs regulating ECM production and collagen synthesis. Mechanistically, NNMT was required for TGF{beta}-induced upregulation of the transcription factors ATF4, SOX9, and SRF, which together orchestrate ECM gene expression and COL1A1 secretion. InterpretationThese findings define a previously unrecognized TGF{beta}-NNMT-ATF4/SOX9/SRF axis that coordinates profibrotic transcriptional programs in DFs. Accordingly, NNMT functions as a central effector linking TGF{beta} signaling to DF activation and ECM remodelling. Targeting NNMT may thus represent a promising therapeutic strategy to attenuate skin fibrosis in SSc.

immunology↗

bioRxiv2025

Time-resolved immune dynamics in rheumatoid arthritis under Methotrexate therapy

Rheumatoid arthritis (RA) is characterized by immune dysregulation, including alterations in peripheral blood mononuclear cell (PBMC) populations and aberrant cytokine signaling. Methotrexate (MTX) is the preferred first-line treatment for RA, yet its precise mechanisms of action remain incompletely understood. This study employed a multi-omics strategy--combining single-cell RNA sequencing (scRNA-seq) and immunophenotyping--to identify key effector peripheral immune cells and their cellular responses in RA patients over 12 weeks of MTX treatment. In our study, MTX was associated with significant immune modulation, including the restoration of naive T and B cells and reductions in T cell memory subsets with these effects detectable as early as three weeks post-treatment. Plasmablast levels also emerged as a potential biomarker for early therapeutic response, reflecting MTXs impact on immune homeostasis. Transcriptional analysis revealed modulation of key pathways, including TNF- signaling, B cell receptor signaling, and T cell receptor-mediated apoptosis. Network analysis identified critical regulatory hubs, such as EGR1, JAK2, and SOCS1, in monocytes and CD4 memory T cells, highlighting these cell types as key mediators of MTXs effects. In conclusion, these findings advance our understanding of MTXs effects on immune cell dynamics at different stages of treatment, showing for the first time the early cellular changes leading to immune modulation in RA. Altogether, our results provide the foundation for further mechanistic investigations into MTX.

genomics↗