Histone Demethylation and Toll-like Receptor 8–Dependent Cross-Talk in Monocytes Promotes Transdifferentiation of Fibroblasts in Systemic Sclerosis Via Fra-2

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To investigate whether epigenetic changes can modulate monocytes to produce tissue inhibitor of metalloproteinases 1 (TIMP-1) via Fra-2 (an activator protein 1 [AP-1] family member), a novel downstream mediator that promotes fibrogenesis.


AP-1 transcription factors and TIMP-1 expression were measured in monocytes from systemic sclerosis (SSc) patients and healthy controls. Involvement of Fra-2 in the regulation of TIMP-1 following treatment with Toll-like receptor 8 (TLR-8) agonist was investigated using a luciferase activity assay and chromatin immunoprecipitation (ChIP) analysis. Expression of TIMP-1 and Fra-2 was determined in response to TLR-8 treatment and to different histone modifications, including 3′-deazaneplanocin (DZNep) and apicidin. Fibroblasts from healthy controls were cocultured with DZNep plus TLR-8–treated healthy control monocytes.


Up-regulation of Fra-2 was detected in bleomycin-challenged mice and in skin biopsy samples from SSc patients. Enhanced expression of Fra-2 and TIMP-1 was correlated in SSc monocytes (P= 0.021). The expression of Fra-1 was significantly reduced (P= 0.037) in SSc monocytes. Inhibiting AP-1 activity reduced TIMP-1 production in TLR-8–stimulated monocytes from healthy controls and SSc patients. ChIP experiments revealed binding of Fra-2 to the TIMP-1 promoter. Stimulation with DZNep plus TLR-8 enhanced Fra-2 and TIMP-1 expression in healthy control monocytes, whereas TLR-8 plus apicidin repressed Fra-2 and TIMP-1 expression. Finally, healthy control monocytes treated with DZNep plus TLR-8 induced strong production of α-smooth muscle actin in dermal fibroblasts, which was inhibited by TIMP-1–blocking antibody.


These data demonstrate a novel role of histone demethylation induced by DZNep on Fra-2–mediated TIMP-1 production by monocytes in the presence of TLR-8 agonist. This consequently orchestrates the transdifferentiation of fibroblasts, a key event in the pathogenesis of SSc.

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