Infiltrating CCR2+ monocytes and their progenies, fibrocytes, contribute to colon fibrosis by inhibiting collagen degradation through the production of TIMP-1

Naoki Kuroda,Yoshiyuki Takei,Isao Tawara,Masahiro Masuya,Hiroshi Miwa,Takuma Kato,Yuki Kageyama,Kyosuke Tanaka,Kohshi Ohishi,Kensuke Hachiya,Junya Tsuboi,Naoyuki Katayama,Reiko Yamada,Yasuhiko Hamada,Kenichiro Nishikawa,Misao Yoneda

doi:10.1038/s41598-019-45012-6

Abstract

Intestinal fibrosis is a serious complication in inflammatory bowel disease (IBD). Despite the remarkable success of recent anti-inflammatory therapies for IBD, incidence of intestinal fibrosis and need for bowel resection have not significantly changed. To clarify the contribution of haematopoietic-derived cells in intestinal fibrosis, we prepared bone marrow (BM) chimeric mice (chimeras), which were reconstituted with BM cells derived from enhanced green fluorescent protein (EGFP)-transgenic mice or CC chemokine receptor 2 (CCR2)-deficient mice. After 2 months of transplantation, BM chimeras were treated with azoxymethane/dextran sodium sulphate. During chronic inflammation, CCR2+ BM-derived monocyte and fibrocyte infiltration into the colon and CC chemokine ligand 2 production increased, leading to colon fibrosis in EGFP BM chimeras. In CCR2-deficient BM chimeras, monocyte and fibrocyte numbers in the colonic lamina propria significantly decreased, and colon fibrosis was attenuated. In colon tissue, mRNA expression of tissue inhibitor of metalloproteinase (TIMP)-1 but not of collagen I, transforming growth factor-β1 or matrix metalloproteinases was significantly different between the two chimeras. CCR2+ monocytes and fibrocytes showed high Timp1 mRNA expression. Our results suggest that infiltrating CCR2+ monocytes and their progenies, fibrocytes, promote colon fibrosis by inhibiting collagen degradation through TIMP-1 production.

Highlights

Fibrosis is characterised by extensive deposition of extracellular matrix (ECM), mainly collagen I (Col I) and is caused by recurrent epithelial injuries that induce the accumulation and activation of mesenchymal cells, such as fibroblasts and myofibroblasts, as well as infiltration of inflammatory cells, such as macrophages[3,4,5,6]
We used bone marrow (BM) chimeras, which were transplanted with BM-total nucleated cells (TNCs) obtained from enhanced green fluorescent protein (EGFP) or CCR2RFP/RFP mice, to investigate which cells are precursors of fibrocytes in the colon, how they migrate into the inflamed colon and how they contribute to colon fibrosis
We identified two types of fibrocytes, chemokine receptor 2 (CCR2)+ and CCR2− fibrocytes, in the colonic lamina propria (LP) of mice chronically treated with dextran sodium sulphate (DSS)

Summary

Introduction

Fibrosis is characterised by extensive deposition of extracellular matrix (ECM), mainly collagen I (Col I) and is caused by recurrent epithelial injuries that induce the accumulation and activation of mesenchymal cells, such as fibroblasts and myofibroblasts, as well as infiltration of inflammatory cells, such as macrophages[3,4,5,6]. Fibroblasts are widely distributed in the interstitial space of all organs and play a critical role in regulating the turnover of ECM under normal conditions They produce several chemokines and cytokines, such as TNF-α, transforming growth factor-β1 (TGF-β1) and interleukin-1β in response to tissue injury[4,5,6]. Fibrocytes are derived from a subset of monocytes and express mesenchymal markers, such as Col I, and haematopoietic markers, such as CD45 and CD11b13 They express several chemokine receptors, such as CC chemokine receptor (CCR)[1], CCR2, CCR5, CCR7, CXC chemokine receptor 4 (CXCR4) and CX3 chemokine receptor 1 (CX3CR1)[12,14,15,16]. MMPs are triggered by various activators, including other MMPs and proteinases, and are inactivated by specific endogenous inhibitors, such as TIMPs

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