Background:Fos-like 2 (Fosl-2) is a transcription factor of the AP-1 family and has a broad range in inducing cellular changes affecting fibrosis and inflammatory responses. Pathological effects of Fosl-2 have been associated with systemic sclerosis (SSc). In addition, increased expression of Fosl-2 has been detected in human SSc monocyte-derived macrophages [1]. Monocytes and macrophages play a central role in activating and propagating acute inflammation followed by pathological fibrosis and organ dysfunction. The classification of the macrophage polarization phenotype can be assigned based on the stimulus, for example into classically-activated M(LPS), and alternatively-activated M(IL-4) macrophages [2]. However, the role of the Fosl-2 transcription factor in macrophage polarization remains elusive.Objectives:To investigate the role of Fosl-2 in macrophage polarization in SSc using Fosl-2 overexpressing transgenic (Fosl-2 tg) mice and human blood-derived macrophages from SSc patients.Methods:Thiogylcolate-elicited peritoneal macrophages were isolated from wild-type (wt) and Fosl-2 tg mice. Human peripheral CD14+ blood-derived monocytes were isolated and differentiated to macrophages (hMDM) from healthy controls and SSc patients. Murine and human macrophages were polarized with LPS (10 ng/ml), LPS + recombinant mouse IFN-γ (10 ng/ml), recombinant mouse, resp. human IL-4 (10 ng/ml) or remained untreated. Macrophage surface marker expression was assessed by flow cytometry using a mouse (F4/80, CD11b, CD86, CD80, CD38, MHCII, CD206, PD-L1, PD-L2, CD36) or human (CD38, CD40, CD86, PD-L2, PD-L1, CD163, CD206) designed polarization panel. Phagocytic activity was detected with pHrodo Red E.coli particles by flow cytometry. Gene expression and secretion of pro- and anti-inflammatory markers were measured by RT-qPCR, standard ELISAs and Griess Assay for nitric oxide production.Results:After LPS stimulation, mRNA levels of IL-1β (p<0.01, n=11-12), TNF-α (p=0.05, n=11-12) and IFN-γ (p<0.05, n=7) were reduced, whereas expression of IL-10 (p<0.05, n=11-12) was enhanced in Fosl-2 tg peritoneal macrophages in comparison to wt cells. Secretion of TNF-α (p<0.01, n=9-11) and nitric oxide (p<0.01, n=9) was impaired in Fosl-2 tg peritoneal macrophages compared to wt cells after LPS stimulation. Peritoneal macrophages were analyzed directly after isolation for macrophage polarization cell surface marker expression. Fosl-2 tg peritoneal macrophages showed an increase in the F4/80+CD11b+PD-L2+CD36+ cell population (p<0.01, n=3-6) compared to peritoneal macrophages from wt mice.The expression of cell surface markers of non-polarized and IL-4 stimulated SSc hMDM (n=17) showed an increased percentage of CD40+CD86+CD206+PD-L2+CD163+ cells (p<0.05) compared to healthy control hMDM (n=7). Phagocytic activity was enhanced in SSc hMDM (n=7) compared to healthy untreated (p<0.05), LPS (p=0.05) and IL-4 (p<0.05) hMDM (n=5).Conclusion:Our animal data indicates a role of Fosl-2 in regulating macrophage polarization with a shift from a classically-activated to an alternatively-activated phenotype. Similarly, SSc hMDM resemble a functional M(IL-4) alternative macrophage phenotype.Thus, maintaining a balanced proportion of classically- and alternatively-activated macrophage phenotypes may be an effective tool to control macrophage function in SSc.References:[1]Moreno-Moral, A., et al., Changes in macrophage transcriptome associate with systemic sclerosis and mediate GSDMA contribution to disease risk. Ann Rheum Dis, 2018. 77(4): p. 596-601.[2]Kania, G., M. Rudnik, and O. Distler, Involvement of the myeloid cell compartment in fibrogenesis and systemic sclerosis. Nat Rev Rheumatol, 2019. 15(5): p. 288-302.Disclosure of Interests:Amela Hukara: None declared, Michal Rudnik: None declared, Chantal Brigitta Rufer: None declared, Oliver Distler Speakers bureau: Actelion, Bayer, Boehringer Ingelheim, Medscape, Novartis, Roche, Menarini, Mepha, MSD, iQone, Pfizer, Consultant of: Abbvie, Actelion, Acceleron Pharma, Amgen, AnaMar, Arxx Therapeutics, Bayer, Baecon Discovery, Blade Therapeutics, Boehringer, CSL Behring, ChemomAb, Corpuspharma, Curzion Pharmaceuticals, Ergonex, Galapagos NV, GSK, Glenmark Pharmaceuticals, Inventiva, Italfarmaco, iQvia, Kymera, Medac, Medscape, Mitsubishi Tanabe Pharma, MSD, Roche, Sanofi, UCB, Lilly, Target BioScience, Pfizer, Grant/research support from: Actelion, Bayer, Boehringer Ingelheim, Kymera Therapeutics, Mitsubishi Tanabe, Przemyslaw Blyszczuk: None declared, Gabriela Kania: None declared
IFN-γ selectively suppresses a subset of TLR4-activated genes and enhancers to potentiate M1-like macrophage polarization
