Production of factors involved into fibrosis regulation by various types of human macrophages

Abstract

Macrophages (Mφ) play a key role in regulation of fibrogenesis, including proliferation of fibroblasts and myofibroblasts, differentiation of progenitor cells into myofibroblasts, as well as synthesis and secretion of the extracellular matrix, mainly collagen. The direction of the Mφ effects (stimulation or suppression) is determined by a number of factors, including the stage of the fibrotic process and the Mφ functional phenotype dependent on the signals of microenvironment. One of the feasible ways of the fibrogenesis regulating is the secretion of pro- or antifibrotic factors such as matrix metalloproteinases, inhibitors of metalloproteinases and some cytokines. However, existing data on ability to secrete these factors by various subpopulations of human Mφ are rare and controversial. The aim of this study was to characterize the ability of human M1, M2a, and M2c Mφ differentiating in the presence of GM-CSF to produce matrix metalloproteinases (MMP-9) and their tissue inhibitors (TIMP-1), as well as some cytokines and growth factors. As compared to M2 macrophages, the M1 macrophages polarized by lipopolysaccharide produced significantly more TNFα, IL-6 and IL-2 that have pro-inflammatory activity and are able to initiate a fibrotic process. In turn, M2a Mφ stimulated by IL-4 were characterized by a high level of VEGF production and, at the same time, low levels of TNFα and IL-6, which may determine the important role of these cells at the proliferative stage of fibrosis and stimulation of extracellular matrix deposition. Finally, M2c Mφ polarized by dexamethasone, exhibited the М2а-like cytokine profile, i.e., VEGF was actively produced against the background of low TNFα and IL-6 synthesis. Moreover, all three Mφ subpopulations did actively secrete MMP-9 and TIMP-1, without significant difference in production of these factors. However, M2c Mφ differed by a significantly higher MMP-9/TIMP-1 ratio index compared to M1 and M2a Mφ, and it is crucial at the rearrangement stage of the fibrotic process. Thus, the production of MMP-9 and TIMP-1, together with other pleiotropic cytokines and growth factors by various Mφ subtypes may reflect their role in regulation of fibrotic process at various stages.

Keywords

• macrophages
• polarization
• cytokines
• matrix metalloproteinases
• inhibitors of matrix metalloproteinases
• fibrosis