P168 Modelling macrophage-fibroblast interaction in scleroderma to evaluate new treatments
Authors: Lei Linda , Abdi Bahja , Mujkavnovic Amer , Wen Xu Shi , Lopez Henry , Stratton Richard 
Published: April 2020

Abstract

Background
Alternatively-activated M2-like macrophages are known to express CD206 and are thought to have an important role in pathological fibrosis in scleroderma through stimulation of fibroblasts. RP peptides are 10-12 mer synthetic peptides which have been developed to engage with human macrophages via CD206, but the selectivity of this receptor for macrophages requires clarification. In this study, we investigate the relative expression levels of CD206 in SSc macrophages and fibroblasts, and explore two approaches in modelling macrophage-fibroblast interactions to evaluate the efficacy of the RP peptides.

Methods
Macrophages were derived from peripheral blood mononuclear cells by culture of buffy layer cells in RPMI supplemented by M-CSF (4ng/ml) for 7 days. Skin fibroblasts were obtained by explant culture of 4 mm punch biospies from the involved forearm skin of SSc patients and healthy controls, maintained in DMEM with 10-% FCS and studied at passage 3-5. Stimulation with TGFβ (4ng/ml) was used to further enhance the activation state of fibroblasts. Macrophages and skin fibroblast lysates were evaluated using qPCR to determine the level of expression of CD206. Macrophages were co-cultured with fibroblasts within respective monolayers on 50kPa gels (models stiff scleroderma skin) for four days with or without the peptide inhibitors. Collagen mRNA expression from the cellular monolayers were quantified by qPCR and Western blot. In the second approach, macrophages and fibroblasts were co-cultured together with or without the peptide inhibitors in a collagen gel contraction assay. The gel was weighed and imaged after 48 hours of incubation and the collagen gel contraction was then quantified as a measure of fibrotic activity.

Results
Expression of CD206 was specific to macrophages and not seen in fibroblast cultures (relative expression level in macrophages 26.63 versus 0.004 in unstimulated fibroblasts versus 0.04 in TGFβ-stimulated fibroblasts. Fibroblasts co-cultured with macrophages in monolayers show increased CTGF and collagen mRNA by qPCR. There was a dose response reduction in CTGF and collagen mRNA in assays cultured with the RP peptide inhibitor. CTGF mRNA was positively correlated with CD206 expression (r2=0.81). Co-culture of SSc macrophages led to enhanced contraction of collagen gels (0.1g in macrophages, 0.08g in fibroblasts, 0.062 for fibroblasts co-cultured with macrophages) which was fully reversed by the RP peptide treatment (0.1g).

Conclusion
SSc macrophages express CD206 which has potential as a biomarker of ongoing fibrotic activity whereas fibroblasts express very minimal levels of CD206 even when stimulated by the pro-fibrotic TGFβ. RP peptides that are specific for CD206 on macrophages led to a suppression of the macrophage signature and inhibition of the pro-fibrotic cross talk in macrophages and fibroblasts in both monolayer and 3D collagen gels. Both approaches of evaluating macrophage-fibroblast interactions in scleroderma are viable approaches to evaluate new treatments.

Disclosures
L. Lei None. B. Abdi None. A. Mujkavnovic None. X. Shi Wen None. H. Lopez Shareholder/stock ownership; Scientific director at Riptide Biosciences. R. Stratton None.