Crosstalk between macrophages and fibroblasts contributes to inflammation and damage in giant cell arteritis

OBJECTIVES: Giant cell arteritis (GCA) is a large vessel vasculitis characterized by arterial wall inflammation and remodeling. Macrophages and fibroblasts are abundantly present in arteries affected by GCA, but their crosstalk in GCA pathogenesis is largely unknown. Here we investigated the interaction between macrophages and fibroblasts in GCA-affected arteries and in vitro.

METHODS: Immunostaining was performed to detect macrophages (CD68, CD206, FRβ), fibroblasts (CD90, CD200), GM-CSF, M-CSF, IL-6, MMP-3 and tenascin-C in GCA-positive temporal arteries (n = 9) and aorta tissues (n = 9). Serum tenascin-C levels were measured by ELISA in GCA patients (n = 36) and healthy controls (n = 46). In vitro, monocytes isolated from peripheral blood mononuclear cells (PBMCs) of healthy donors (n = 10) were incubated with GM-CSF or M-CSF for 8 days to induce macrophage differentiation. GM-CSF/M-CSF-macrophage-conditioned medium (MCM) was added to human aortic adventitial fibroblasts (HAoAF) cultures for 24 hours. MRNA expression of proinflammatory cytokines(IL-6, IL-1β), growth factors(GM-CSF, M-CSF), matrix metalloproteinase(MMP-1, MMP-3), chemokines(CCL2, CX3CL1), extracellular matrix proteins(Col1a1, Col1a2, Col3a1, fibronectin-1, tenascin-C) and phenotypic markers (FAP, podoplanin(PDPN), α-SMA, CD200) in cultured fibroblasts were examined by qPCR.

RESULTS: In GCA-affected arteries, pro-inflammatory CD90+IL-6+fibroblasts, but not pro-resolving CD90+CD200+fibroblasts, were spatially associated with macrophages. Adventitial CD90+fibroblasts expressed both GM-CSF and/or M-CSF, which linked to macrophage subsets distribution. In vitro, both GM-CSF- and, to a lesser extent, M-CSF-derived MCM upregulated mRNA expression of IL-6, GM-CSF, M-CSF, CCL2, PDPN and CD200 in fibroblasts. Upregulation of IL-1β, MMP-3, Col3a1 and tenascin-C and downregulation of FAP in fibroblasts was observed with GM-CSF-derived MCM. Adventitial CD90+fibroblasts in GCA-affected temporal arteries also expressed MMP-3 and tenascin-C. Serum levels of tenascin-C in patients with treatment-naïve GCA were significantly higher than those in healthy controls, showing a good diagnostic accuracy (AUC=0.89).

CONCLUSION: The interaction between fibroblasts and macrophages may contribute to the chronicity and progression of GCA and deserves further investigation. Serum tenascin-C is a candidate biomarker for GCA diagnosis.