Differential regulation of osteoclastogenesis by Notch2/Delta-like 1 and Notch1/Jagged1 axes.

INTRODUCTION: Osteoclastogenesis plays an important role in the bone erosion of rheumatoid arthritis (RA). Recently, Notch receptors have been implicated in the development of osteoclasts. However, the responsible Notch ligands have not been identified yet. This study was undertaken to determine the role of individual Notch receptors and ligands in osteoclastogenesis. METHODS: Mouse bone marrow-derived macrophages or human peripheral blood monocytes were used as osteoclast precursors and cultured with receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage-colony stimulating factor (M-CSF) to induce osteoclasts. Osteoclasts were detected by tartrate-resistant acid phosphatase (TRAP) staining. K/BxN serum-induced arthritic mice and ovariectomized mice were treated with anti-mouse Delta-like 1 (Dll1) blocking monoclonal antibody (mAb). RESULTS: Blockade of a Notch ligand Dll1 with mAb inhibited osteoclastogenesis and, conversely, immobilized Dll1-Fc fusion protein enhanced it in both mice and humans. In contrast, blockade of a Notch ligand Jagged1 enhanced osteoclastogenesis and immobilized Jagged1-Fc suppressed it. Enhancement of osteoclastogenesis by agonistic anti-Notch2 mAb suggested that Dll1 promoted osteoclastogenesis via Notch2, while suppression by agonistic anti-Notch1 mAb suggested that Jagged1 suppressed osteoclastogenesis via Notch1. Inhibition of Notch signaling by a gamma-secretase inhibitor suppressed osteoclastogenesis, implying that Notch2/Dll1-mediated enhancement was dominant. Actually, blockade of Dll1 ameliorated arthritis induced by K/BxN serum transfer, reduced the number of osteoclasts in the affected joints and suppressed ovariectomy-induced bone loss. CONCLUSIONS: The differential regulation of osteoclastogenesis by Notch2/Dll1 and Notch1/Jagged1 axes may be a novel target for amelioration of bone erosion in RA patients.

Gain-of-function mutations and copy number increases of Notch2 in diffuse large B-cell lymphoma.

Signaling through the Notch1 receptor has a pivotal role in early thymocyte development. Gain of Notch1 function results in the development of T-cell acute lymphoblastic leukemia in a number of mouse experimental models, and activating Notch1 mutations deregulate Notch1 signaling in the majority of human T-cell acute lymphoblastic leukemias. Notch2, another member of the Notch gene family, is preferentially expressed in mature B cells and is essential for marginal zone B-cell generation. Here, we report that 5 of 63 (approximately 8%) diffuse large B-cell lymphomas, a subtype of mature B-cell lymphomas, have Notch2 mutations. These mutations lead to partial or complete deletion of the proline-, glutamic acid-, serine- and threonine-rich (PEST) domain, or a single amino acid substitution at the C-terminus of Notch2 protein. Furthermore, high-density oligonucleotide microarray analysis revealed that some diffuse large B-cell lymphoma cases also have increased copies of the mutated Notch2 allele. In the Notch activation-sensitive luciferase reporter assay in vitro, mutant Notch2 receptors show increased activity compared with wild-type Notch2. These findings implicate Notch2 gain-of-function mutations in the pathogenesis of a subset of B-cell lymphomas, and suggest broader roles for Notch gene mutations in human cancers.

Jagged1 suppresses collagen-induced arthritis by indirectly providing a negative signal in CD8+ T cells.

Distinct Notch ligands possess a characteristic ability in terms of functional T cell differentiation. However, the precise role or the therapeutic potential of each Notch ligand in autoimmune diseases is largely unknown. In this study, we examined whether Jagged1 modulates a collagen-induced rheumatoid arthritis (CIA) model by altering T cell responses. The injection of a soluble Jagged1-encoding plasmid, sJag1-P, before or even after initial type II collagen (CII) immunization suppressed the disease severity of CIA. However, this treatment did not suppress CII-specific CD4(+) T cell proliferation and CII-specific Ab production. Depletion of either CD4(+) or CD8(+) T cells ameliorated CIA severity and sJag1-P further improved CIA in CD4(+) but not CD8(+) T cell-depleted mice. Injection of OVA and Jagged1-encoding plasmids inhibited proliferation of OVA-specific granzyme B-producing CD8(+) T cells, although Jagged1 could not directly inhibit CD8(+) T cell proliferation in vitro. The blockade of Jagged1 by an anti-Jagged1 Ab exacerbated CIA, whereas this effect was not observed in the absence of CD8(+) T cells. These data indicate that Jagged1 is able to deliver an indirect negative signal into CD8(+) T cells in vivo, which suggests its therapeutic potential in the treatment of CD8(+) T cell-mediated diseases, including rheumatoid arthritis.