Expression and Role of IL-1β Signaling in Chondrocytes Associated with Retinoid Signaling during Fracture Healing.

Tsuyoshi Shimo,Saki Fujii,Soichiro Ibaragi,Yuki Kunisada,Hiroaki Takebe,Karnoon Shamsoon,Kazuharu Irie,Naito Kurio,Tatsuo Okui,Akira Sasaki,Kyoichi Obata,Masahiro Iwamoto,Akihiro Hosoya

doi:10.3390/ijms21072365

Abstract

The process of fracture healing consists of an inflammatory reaction and cartilage and bone tissue reconstruction. The inflammatory cytokine interleukin-1β (IL-1β) signal is an important major factor in fracture healing, whereas its relevance to retinoid receptor (an RAR inverse agonist, which promotes endochondral bone formation) remains unclear. Herein, we investigated the expressions of IL-1β and retinoic acid receptor gamma (RARγ) in a rat fracture model and the effects of IL-1β in the presence of one of several RAR inverse agonists on chondrocytes. An immunohistochemical analysis revealed that IL-1β and RARγ were expressed in chondrocytes at the fracture site in the rat ribs on day 7 post-fracture. In chondrogenic ATDC5 cells, IL-1β decreases the levels of aggrecan and type II collagen but significantly increased the metalloproteinase-13 (Mmp13) mRNA by real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. An RAR inverse agonist (AGN194310) inhibited IL-1β-stimulated Mmp13 and Ccn2 mRNA in a dose-dependent manner. Phosphorylated extracellular signal regulated-kinases (pERK1/2) and p-p38 mitogen-activated protein kinase (MAPK) were increased time-dependently by IL-1β treatment, and the IL-1β-induced p-p38 MAPK was inhibited by AGN194310. Experimental p38 inhibition led to a drop in the IL-1β-stimulated expressions of Mmp13 and Ccn2 mRNA. MMP13, CCN2, and p-p38 MAPK were expressed in hypertrophic chondrocytes near the invaded vascular endothelial cells. As a whole, these results point to role of the IL-1β via p38 MAPK as important signaling in the regulation of the endochondral bone formation in fracture healing, and to the actions of RAR inverse agonists as potentially relevant modulators of this process.

Highlights

Fracture healing consists of three major stages: a reaction stage, a repair stage, and a remodeling stage [1]
We first evaluated the expressions of IL-1β and RARγ in chondrocytes in a rat bone fracture model, making observations at day 7 after rib fracture
The immunohistochemical analysis revealed that IL-1β was distridbauyte7dselcatrigonelsyisinshcohwonndinroFcigyuteres 1aAnd,B.thTehesuimrrmouunnodheidstomcheesmeniccahlyamnaallycsiesllrsevineatlhede bthoanteILm-1aβrrwoaws cells (Figudreist1rCib,uDte),dalnadrgtehlyatinRcAhoRnγdwroacystexs panredsstheedsiunrrcohuonndderdomcyetseesnacht ythmeaflrcaeclltsuirnetshietebionnethmearrirboswocfemllsice on day 7(Faifgtuerrefr1aCc,tDu)r,ean(FdigthuarteR1AER,Fγ).was expressed in chondrocytes at the fracture site in the ribs of mice on day 7 after fracture (Figure 1E,F)

Summary

Introduction

Fracture healing consists of three major stages: a reaction stage, a repair stage, and a remodeling stage [1]. The repair process begins with a hematoma and an inflammatory response at the fracture site. Endochondral bone formation is an indispensable process during the healing phase of fracture healing, beginning with the differentiation of bone marrow stem cells into chondrocytes, and chondrocyte proliferation, differentiation, maturation, apoptosis, and vascular invasion [1]. IL-1β enhanced calcium deposition and the expression of bone morphogenetic protein (BMP)-2 mRNA by differential activations of Nuclear factor-κB(NF-κB) and ERK signaling in osteogenic and higher productions of matrix metallopeptidase (MMP)-13 in cultured bone marrow MSCs [4]. The expression pattern of IL-1β during endochondral fracture repair is bimodal, peaking during the initial inflammatory phase and again during the later remodeling phase [6]. Little is known about the exact nature of the inflammatory response in chondrocytes

Methods

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Discussion

Conclusion