SH3BP2 gain-of-function mutation exacerbates inflammation and bone loss in a murine collagen-induced arthritis model.

Tomoyuki Mukai,Mizuho Kittaka,Yasuyoshi Ueki,Keiichiro Nishida,Teruhito Yoshitaka,Shu Ishida,David A Fox,Yoshitaka Morita,Richard Gallant,Cordula M Stover

doi:10.1371/journal.pone.0105518

Abstract

ObjectiveSH3BP2 is a signaling adapter protein which regulates immune and skeletal systems. Gain-of-function mutations in SH3BP2 cause cherubism, characterized by jawbone destruction. This study was aimed to examine the role of SH3BP2 in inflammatory bone loss using a collagen-induced arthritis (CIA) model.MethodsCIA was induced in wild-type (Sh3bp2+/+) and heterozygous P416R SH3BP2 cherubism mutant knock-in (Sh3bp2KI/+) mice, an SH3BP2 gain-of-function model. Severity of the arthritis was determined by assessing the paw swelling and histological analyses of the joints. Micro-CT analysis was used to determine the levels of bone loss. Inflammation and osteoclastogenesis in the joints were evaluated by quantitating the gene expression of inflammatory cytokines and osteoclast markers. Furthermore, involvement of the T- and B-cell responses was determined by draining lymph node cell culture and measurement of the serum anti-mouse type II collagen antibody levels, respectively. Finally, roles of the SH3BP2 mutation in macrophage activation and osteoclastogenesis were determined by evaluating the TNF-α production levels and osteoclast formation in bone marrow-derived M-CSF-dependent macrophage (BMM) cultures.Results Sh3bp2KI/+ mice exhibited more severe inflammation and bone loss, accompanying an increased number of osteoclasts. The mRNA levels for TNF-α and osteoclast marker genes were higher in the joints of Sh3bp2KI/+ mice. Lymph node cell culture showed that lymphocyte proliferation and IFN-γ and IL-17 production were comparable between Sh3bp2+/+ and Sh3bp2KI/+ cells. Serum anti-type II collagen antibody levels were comparable between Sh3bp2+/+ and Sh3bp2KI/+ mice. In vitro experiments showed that TNF-α production in Sh3bp2KI/+ BMMs is elevated compared with Sh3bp2+/+ BMMs and that RANKL-induced osteoclastogenesis is enhanced in Sh3bp2KI/+ BMMs associated with increased NFATc1 nuclear localization.ConclusionGain-of-function of SH3BP2 augments inflammation and bone loss in the CIA model through increased macrophage activation and osteoclast formation. Therefore, modulation of the SH3BP2 expression may have therapeutic potential for the treatment of rheumatoid arthritis.

Highlights

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease resulting in bone loss
The incidence of arthritis at day 42 was comparable between Sh3bp2+/+ and Sh3bp2KI/+ mice (73.3% vs. 71.4%, respectively) (Figure 2B), Sh3bp2KI/+ mice showed a tendency of earlier development compared with Sh3bp2+/+ mice (P = 0.13 at day 28 and P = 0.14 at day 31)
These findings suggest that P416R SH3 domain-binding protein 2 (SH3BP2) mutation does not significantly affect the immune events involved in the induction of arthritis

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease resulting in bone loss. Bone loss is exclusively driven by osteoclasts [1,2], which are bone-resorbing cells derived from myeloid cells. Osteoclast differentiation is regulated mainly by receptor activator of nuclear factor-kB (RANK) and its ligand, RANKL. RANKL is predominantly expressed on osteoblasts and osteocytes [3,4,5]. In pathological conditions, it can be expressed by other cells such as fibroblasts and T cells [6,7,8]. In RA, inflammatory cytokines including tumor necrosis factor (TNF)-a, interleukin (IL)-1b, and IL-6, have been found to enhance

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