Cancer-associated fibroblasts contribute to macrophage recruitment in head and neck cancer.

Objectives: To examine and compare the ability of factors secreted from cancer-associated fibroblasts (CAFs) to promote recruitment of monocytes/macrophages, the presence of which is known to be associated with poor disease outcome in a number of solid tumours including head and neck cancers.
Methods: Senescence (a feature of some CAF) was induced in primary human oral fibroblasts using cisplatin, and monitored using senescence associated β-galactosidase assay and by measuring markers of senescence by qPCR. Oral fibroblasts were also transdifferentiated into myofibroblasts (another CAF phenotype) by treating with TGF-β, and the activated phenotype confirmed by qPCR and Western blot of myofibroblast markers. Chemotaxis assays were used to examine the ability of fibroblast secreted factors to recruit monocytic THP1 cells and monocytes isolated from peripheral blood.
Results: Cisplatin treatment induced senescence of oral fibroblasts, while TGF-β transdifferentiated normal oral fibroblasts to myofibroblasts with highest activation seen at 96 h exposure. IL-6 secretion was reduced with increasing TGF-β exposure in myofibroblasts, while secretion of this cytokine was increased 22-fold in cisplatin-induced senescent fibroblasts compared to myofibroblasts. Similarly, higher level of CCL2 (8-fold) was secreted by senescent fibroblast in comparison to myofibroblasts. THP-1 migration was reduced with increasing duration of TGF-β treatment while senescent fibroblasts induced significantly increased migration (~5-fold) compared to conditioned medium from myofibroblasts. Monocytes from peripheral blood migrated more towards both myofibroblasts and senescent fibroblasts with 33-fold and 31.5-fold increases, respectively, compared to untreated controls.
Conclusions: It is likely that different sub-populations of CAFs play different roles in the tumour microenvironment. These data suggest that senescent fibroblasts may promote recruitment of macrophages more than myofibroblasts by secreting a discrete repertoire of factors, including CCL2.