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

Giant cell arteritis (GCA) is a large vessel vasculitis characterized by arterial wall inflammation and remodelling. 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.

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 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 fibroblast (HAoAF) cultures for 24 h. 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 (fibroblast activation protein [FAP], podoplanin [PDPN], α-smooth muscle actin, CD200) in cultured fibroblasts were examined by qPCR.

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 GM-CSF and/or M-CSF, which linked to macrophage subset 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 (area under the curve 0.89).

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.