Background/Purpose: Alternatively activated macrophages expressing CD206 are believed to promote fibrosis in a range of disorders including systemic sclerosis (SSc). Novel therapeutic peptides (RP) which enter the cell by binding CD206 may selectively inhibit this population of cells. We investigated the potential for RP peptides to suppress fibrosis in experimental mice and in model systems using SSc derived macrophages. sCD206 and CD206 cell surface expression were evaluated as biomarkers in SSc.

Methods: RP therapeutic peptides 10mg/kg were administered by twice daily subcutaneous injection during dermal and lung bleomycin fibrosis models, in wild type C57BL/6 female mice (n=10 mice per group). SSc macrophage viability was assayed by Presto Blue assay. SSc macrophage-fibroblast cross-talk was modelled using transfer of media followed by qPCR for collagen I. sCD206 was assayed by ELISA in plasma (n=40 healthy control (HC) and 40 diffuse SSc) and blister fluid (BF) (n=12 HC and 13 SSc). SSc monocyte-derived macrophages (n=17 SSc & 9 HC) were profiled by flow cytometry for CD206 (M2) and P2X7 (ATP receptor) expression, and by qPCR for arginase (M2) and IFNg (M1).

Results: In mouse models, RP peptides inhibited both the dermal and lung fibrosis induced by bleomycin, and reduced plasma cytokines to basal levels (skin model; dermal thickness in controls 343, bleo 402, bleo +RP 345 um, p<0.0009, plasma IL-6 in bleo 101 pg/ml, bleo+RP 24, p<0.00018, plasma IL12p40 bleo 38, bleo+RP 0, p<01.5×10^-7) (lung model; Ashcroft score bleomycin 5.8, bleo+RP 2.8, p<0.0024, plasma IL6 bleo 58, bleo+RP 7 p<0.0005, IL12p40 bleo 152, bleo+RP0, p<0.00014).

As a biomarker, sCD206 was elevated in SSc plasma (SSc median 683, HC 583 pg/ml, p<0.024), and BF (SSc median sCD206 42, HC 31 pg/ml, p<0.041). Both CD206 and P2X₇ were highly expressed by SSc macrophages (mean fluorescence SSc, 776.1 SD=409.1, 724.4 SD=455.3 vs HC 632.2 SD=73.7, 472.9 SD=25.4), correlating with modified Rodnan skin score (p<0.05, r=0.51). Double positive P2X7 and CD206 cells were seen in a subgroup with higher skin scores. SSc macrophages had elevated arginase:IFNg ratio (11.4 vs 5.9, p=0.03 ).

RP therapeutic peptides suppressed viability in SSc macrophage cultures with raised arginase:IFNγ ratio >8, but had no effect on macrophages with lower arginase:IFNγ. Treatment of SSc macrophages with RP832c, as the lead candidate, effectively abolished macrophage-fibroblast cross-talk, reducing collagen I to basal levels (collagen I, basal 2830, TGFbeta stimulated 3026, SSc macrophage media treated 4186, RP832c 10µM macrophage media 3519, RP832c 100uM macrophage media 2475, relative expression to TBP, p<0.0039).

Conclusion: These data confirm the presence of activated CD206 positive macrophages in SSc, and demonstrate the potential for these cells to directly stimulate fibroblasts, inducing collagen I. Furthermore, the RP peptides suppress fibrosis and cytokines in mouse models and selectively inhibit highly activated SSc macrophages. RP832c, the lead compound, blocked SSc macrophage-fibroblast cross-talk and will be developed as a GLP therapeutic for clinical trials.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/novel-therapeutic-peptides-which-target-cd206-inhibit-macrophage-dependent-fibroblast-activation-in-scleroderma/