Development of new anti-rheumatic drugs

2011 Fiscal Year Final Research Report

• Project/Area Number: 21249060
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 膠原病・アレルギー・感染症内科学
• Research Institution: Tokyo Medical and Dental University
• Principal Investigator: KOHSAKA Hitoshi 東京医科歯科大学, 大学院・医歯学総合研究科, 准教授 (00251554)
• Project Period (FY): 2009 – 2011
• Keywords: リウマチ学 / 内科 / 臨床 / 薬学 / 免疫学 / 病理学

Research Abstract

Up-regulated expression of cyclin-dependent kinase inhibitor(CDKI) p16^<INK4a>, which inhibits CDK4/6, in the synovial tissues as well as systemic administration of small molecule(sm) CDK4/6 inhibitors suppress animal models of rheumatoid arthritis. Although both inhibit cell cycle progression, they exert differential effects especially in modulating inflammatory mediator production. This part of the present studies was conducted to investigate how p16^<INK4a> expression modulates inflammatory cytokine production from macrophages in relation to simple CDK4/6 kinase inhibition. Forced expression of p16^<INK4a> in bone marrow-derived macrophages(BMM) suppressed LPS-induced expression of IL-6 but not TNFα. This was not observed in RSF. A sm CDK4/6 inhibitor and shRNA to knock down CDK4 failed to suppress IL-6 production, demonstrating that the inhibition did not depend on decrease in CDK4/6 kinase activity. The p16INK4a expression accelerated LPS-induced IRAK1 degradation, and suppressed the p38 MAPK/AP-1 pathway but not the NFκB pathway. Direct down-regulation of IRAK1 with small hairpin RNA also induced specific inhibition of the AP-1 pathway. The accelerated IRAK-1 degradation should be mediated by proteasomal degradation because a proteosome inhibitor restored p38 MAPK activation in p16INK4a-expressing BMM. Also, IRAK1 gene overexpression restored IL-6 production in p16INK4a-expressing THP-1 macrophage cell line. Finally, p16INK4a knock down with si RNA enhanced IL-6 production from senescent BMM that expressed endogenous p16INK4a. These results showed that p16INK4a suppressed IL-6 production from macrophages in a CDK4/6-independent manner. This was due to proteosome-mediated IRAK1 degradation and following suppression of the AP-1 pathway. Thus, unlike sm CDK inhibitors, p16INK4a could exert anti-inflammatory effects on synovial macrophages.
Triggering receptor expressed on myeloid cells(TREM)-1 is the other therapeutic target we are pursuing. It is expressed by macrophages and neutrophils. Its activation augments inflammatory cytokine production triggered by Toll-like receptor engagement. In a mouse sepsis model, blockade of TREM-1 by administration of a TREM-1 extracellular domain/Ig Fc domain fusion protein(TREM-1-Ig) prolonged survival of affected mice. This indicated TREM-1 blockade suppressed pathological inflammation with maintaining minimal inflammatory cytokine production for anti-microbial defense. We reported previously that TREM-1 is expressed on synovial macrophages in the rheumatoid joints and that TREM-1 blockade ameliorated mouse collagen(CII)-induced arthritis(CIA), which is an animal model of rheumatoid arthritis. However, since a ligand for TREM-1 was unknown, physiological roles of TREM-1-ligand and interactions between TREM-1 and TREM-1-ligand remained to be clarified. This part of the studies was conducted to identify the TREM-1-ligand molecule for discerning its involvement in arthritis. To search for cells expressing the TREM-1-ligand, various types of cells were incubated with TREM-1-Ig. It bound to mouse B cells and A20 B-cell lymphoma cells. Expression cloning using A20 cell cDNA library led us to identify a gene encoding the TREM-1-ligand. Furthermore, we raised anti-TREM-1-ligand blocking monoclonal antibody(mAb). Administration of this antibody to CIA mice ameliorated the disease. Anti-TREM-1-ligand mAb treatment exerted no apparent effects on T and B cell responses to CII. Thus, in analogous to the effect of TREM-1-Ig, this effect appeared attributable to attenuation of the inflammatory responses rather than prevention of the adaptive immune responses. Identification of the human TREM-1-ligand in the future study will warrant establishment of a new anti-rheumatic therapy that is not associated with a risk of serious infection.