IL‐4 Stimulated Macrophages Induce a Pro‐Inflammatory Secretome in Fibroblasts

Abstract

The precis continuum manifold of cell state of macrophages and fibroblast cells during skin fibrosis, described as a chronic inflammatory and tissue remodeling microenvironment, is not well understood. Both cell populations respond directly to damage and present a coordinated chain of activation states that dictates the reparative outcome. The spectrum change in phenotype during late remodeling is important, because it is by both cells that autocrine and paracrine communication contribute to the deposition of extracellular matrix (ECM) and chronic inflammation. Here, we provide evidence that the anti‐inflammatory M2‐like (IL‐4 induced) macrophage cell state drives activated fibroblasts to secrete important pro‐inflammatory mediators and thus changing the fibroblast cell state to one that promotes a continuous fibrotic milieu. Indirect and direct co‐culture systems were used to elevate the effects paracrine and autocrine feedback of secreted factors and cell‐contact dependent factors. These studies showed the exposure of TGF‐β‐activated fibroblasts to M2‐like macrophages altered the cytokine/chemokine secretion profile of fibroblasts to express IL‐1β, TNFα, and CXCL10 and enhanced its expression of profibrotic matrix production by using transcriptomic analysis. To understand the necessity of fibroblast‐macrophage crosstalk in the fibrotic process a gain of function approach was used by reconstituting the mice with IL‐4 polarized macrophage in an in vivo sterile wound/fibrosis bleomycin model. Tissue fibroblasts increased expression of pro‐inflammatory cytokines included IL‐10, INF‐γ, and IL‐13, as confirmed by transcriptomic analysis. These analyses additionally identified an imbalance in proteolytic remodeling actions of TIMPs and MMPs. These findings identify an important role of macrophage‐specific cell state and phenotype‐directed crosstalk with tissue remodeling activated fibroblast in signaling to orchestrate a chronic inflammatory and fibrotic microenvironment.Support or Funding InformationThis work was supported by NIH grants R01AR68317, R01AG055564, and R01GM121558.