A novel interaction between CX(3)CR(1) and CCR(2) signalling in monocytes constitutes an underlying mechanism for persistent vincristine-induced pain

BACKGROUND: A dose-limiting side effect of chemotherapeutic agents such as vincristine (VCR) is neuropathic pain, which is poorly managed at present. Chemokine-mediated immune cell/neuron communication in preclinical VCR-induced pain forms an intriguing basis for the development of analgesics. In a murine VCR model, CX(3)CR(1) receptor-mediated signalling in monocytes/macrophages in the sciatic nerve orchestrates the development of mechanical hypersensitivity (allodynia). CX(3)CR(1)-deficient mice however still develop allodynia, albeit delayed; thus, additional underlying mechanisms emerge as VCR accumulates. Whilst both patrolling and inflammatory monocytes express CX(3)CR(1), only inflammatory monocytes express CCR(2) receptors. We therefore assessed the role of CCR(2) in monocytes in later stages of VCR-induced allodynia. METHODS: Mechanically evoked hypersensitivity was assessed in VCR-treated CCR(2)- or CX(3)CR(1)-deficient mice. In CX(3)CR(1)-deficient mice, the CCR(2) antagonist, RS-102895, was also administered. Immunohistochemistry and Western blot analysis were employed to determine monocyte/macrophage infiltration into the sciatic nerve as well as neuronal activation in lumbar DRG, whilst flow cytometry was used to characterise monocytes in CX(3)CR(1)-deficient mice. In addition, THP-1 cells were used to assess CX(3)CR(1)-CCR(2) receptor interactions in vitro, with Western blot analysis and ELISA being used to assess expression of CCR(2) and proinflammatory cytokines. RESULTS: We show that CCR(2) signalling plays a mechanistic role in allodynia that develops in CX(3)CR(1)-deficient mice with increasing VCR exposure. Indeed, the CCR(2) antagonist, RS-102895, proves ineffective in mice possessing functional CX(3)CR(1) receptors but reduces VCR-induced allodynia in CX(3)CR(1)-deficient mice, in which CCR(2)(+) monocytes are elevated by VCR. We suggest that a novel interaction between CX(3)CR(1) and CCR(2) receptors in monocytes accounts for the therapeutic effect of RS-102895 in CX(3)CR(1)-deficient mice. Indeed, we observe that CCR(2), along with its ligand, CCL(2), is elevated in the sciatic nerve in CX(3)CR(1)-deficient mice, whilst in THP-1 cells (human monocytes), downregulating CX(3)CR(1) upregulates CCR(2) expression via p38 MAP kinase signalling. We also show that the CX(3)CR(1)-CCR(2) interaction in vitro regulates the release of pronociceptive cytokines TNF-α and IL1β. CONCLUSIONS: Our data suggests that CCL(2)/CCR(2) signalling plays a crucial role in VCR-induced allodynia in CX(3)CR(1)-deficient mice, which arises as a result of an interaction between CX(3)CR(1) and CCR(2) in monocytes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12974-018-1116-6) contains supplementary material, which is available to authorized users.