Granulocyte-Macrophage Colony-Stimulating Factor (CSF) and Macrophage CSF-Dependent Macrophage Phenotypes Display Differences in Cytokine Profiles and Transcription Factor Activities: Implications for CSF Blockade in Inflammation

TLDR

GM‑CSF and M‑CSF expand macrophage numbers and alter their differentiation, and blocking them in animal models reduces inflammatory disease activity. The study aims to determine the specific actions of GM‑CSF and M‑CSF on macrophages during inflammation. Murine bone‑marrow macrophages were differentiated with GM‑CSF or M‑CSF, stimulated with LPS, and cytokine secretion and NF‑κB/AP‑1 activation were measured, with cross‑pretreatment to assess phenotype switching. GM‑CSF‑derived macrophages produced pro‑inflammatory cytokines (TNF‑α, IL‑6, IL‑12p70, IL‑23) and rapidly activated NF‑κB/AP‑1, whereas M‑CSF‑derived cells produced anti‑inflammatory IL‑10 and CCL2, lacked IL‑12p70/IL‑23, and exhibited slower signaling, indicating opposing roles that could inform CSF‑targeted therapies.

Abstract

Abstract GM-CSF and M-CSF (CSF-1) can enhance macrophage lineage numbers as well as modulate their differentiation and function. Of recent potential significance for the therapy of inflammatory/autoimmune diseases, their blockade in relevant animal models leads to a reduction in disease activity. What the critical actions are of these CSFs on macrophages during inflammatory reactions are unknown. To address this issue, adherent macrophages (GM-BMM and BMM) were first derived from murine bone marrow precursors by GM-CSF and M-CSF, respectively, and stimulated in vitro with LPS to measure secreted cytokine production, as well as NF-κB and AP-1 activities. GM-BMM preferentially produced TNF-α, IL-6, IL-12p70, and IL-23 whereas, conversely, BMM generated more IL-10 and CCL2; strikingly the latter population could not produce detectable IL-12p70 and IL-23. Following LPS stimulation, GM-BMM displayed rapid IκBα degradation, RelA nuclear translocation, and NF-κB DNA binding relative to BMM, as well as a faster and enhanced AP-1 activation. Each macrophage population was also pretreated with the other CSF before LPS stimulation and found to adopt the phenotype of the other population to some extent as judged by cytokine production and NF-κB activity. Thus, GM-CSF and M-CSF demonstrate, at the level of macrophage cytokine production, different and even competing responses with implications for their respective roles in inflammation, including a possible dampening or suppressive role for M-CSF in certain circumstances.