Kei Ohnuma

Diet-Induced Adipose Tissue Inflammation and Liver Steatosis Are Prevented by DPP-4 Inhibition in Diabetic Mice

OBJECTIVE Diet composition alters the metabolic states of adipocytes and hepatocytes in diabetes. The effects of dipeptidyl peptidase-4 (DPP-4) inhibition on adipose tissue inflammation and fatty liver have been obscure. We investigated the extrapancreatic effects of DPP-4 inhibition on visceral fat and the liver. RESEARCH DESIGN AND METHODS We investigated diet-induced metabolic changes in β-cell–specific glucokinase haploinsufficient (Gck+/−) diabetic mice. We challenged animals with a diet containing a combination of sucrose and oleic acid (SO) or sucrose and linoleic acid (SL). Next, we assessed the effects of a DPP-4 inhibitor, des-fluoro-sitagliptin, on adipose tissue inflammation and hepatic steatosis. RESULTS The epididymal fat weight and serum leptin level were significantly higher in Gck+/− mice fed SL than in mice fed SO, although no significant differences in body weight or adipocyte size were noted. Compared with SO, SL increased the numbers of CD11c+ M1 macrophages and CD8+ T-cells in visceral adipose tissue and the expression of E-selectin, P-selectin, and plasminogen activator inhibitor-1 (PAI-1). DPP-4 inhibition significantly prevented adipose tissue infiltration by CD8+ T-cells and M1 macrophages and decreased the expression of PAI-1. The production of cytokines by activated T-cells was not affected by DPP-4 inhibition. Furthermore, DPP-4 inhibition prevented fatty liver in both wild-type and Gck+/− mice. DPP-4 inhibition also decreased the expressions of sterol regulatory element–binding protein-1c, stearoyl-CoA desaturase-1, and fatty acid synthase, and increased the expression of peroxisome proliferator–activated receptor-α in the liver. CONCLUSIONS Our findings indicated that DPP-4 inhibition has extrapancreatic protective effects against diet-induced adipose tissue inflammation and hepatic steatosis.

CD26-mediated signaling for T cell activation occurs in lipid rafts through its association with CD45RO

CD26 is a T cell activation antigen that contains dipeptidyl peptidase IV activity and is known to bind adenosine deaminase. The mechanism by which CD26 costimulation potentiates T cell receptor-mediated T cell activation, leading to subsequent exertion of T cell effector function, is still not clearly defined. In this article, we demonstrate that CD26 localizes into lipid rafts, and targeting of CD26 to rafts is necessary for signaling events through CD26. Importantly, aggregation of CD26 by anti-CD26 mAb crosslinking also causes coaggregation of CD45 into rafts. Moreover, we show that CD26 directly binds to the cytoplasmic domain of CD45. Our results therefore indicate a mechanism whereby CD26 engagement promotes aggregation of lipid rafts and facilitates colocalization of CD45 to T cell receptor signaling molecules p56Lck, ZAP-70, and TCRζ, thereby enhancing protein tyrosine phosphorylation of various signaling molecules and subsequent interleukin-2 production.

The role of CD26/dipeptidyl peptidase IV in cancer.

CD26/DPPIV is a multifunctional cell surface protein that is widely expressed in most cell types including T lymphocytes, on which it is a marker of activation. It is also present in serum and other body fluids in a truncated form (sCD26/DPPIV). It preferentially cleaves N-terminal dipeptides from polypeptides with proline or alanine in the penultimate position, and in doing so, regulates the activities of a number of cytokines and chemokines. Due in part to this ability to regulate the activity of biopeptides, it can act as a tumor suppressor or activator. It can associate with several proteins, among them fibroblast activating protein-alpha (FAP-alpha), plasminogen, adenosine deaminase (ADA), the tyrosine phosphatase CD45, and the chemokine receptor CXCR4. It can also bind to the extracellular matrix (ECM) and depending on the presence of other ligands, this process can either lead to increased or decreased invasive activity of the cells on which it is expressed. As a result of these characteristics, CD26/DPPIV plays an important role in tumor biology, and is useful as a marker for various cancers, with its levels either on the cell surface or in the serum being increased in some neoplasms and decreased in others. Our group has shown that CD26/DPPIV can be manipulated by such agents as CD26 cDNA-carrying plasmids, siRNA and monoclonal antibodies, resulting in both in vitro and in vivo inhibition of cell growth, enhanced sensitivity to selected chemotherapeutic agents, and enhanced survival of mouse xenograft models. These studies have demonstrated the utility of these tools as potential targeted therapies for specific cancers expressing CD26/DPPIV.

TCR Engagement Increases Hypoxia-Inducible Factor-1α Protein Synthesis via Rapamycin-Sensitive Pathway under Hypoxic Conditions in Human Peripheral T Cells

Peripheral T cells encounter rapid decrease in oxygen tension because they are activated by Ag recognition and migrate into inflammatory sites or tumors. Activated T cells, therefore, are thought to have such machineries that enable them to adapt to hypoxic conditions and execute immune regulation in situ. We have recently shown that survival of CD3-engaged human peripheral blood T cells is prolonged under hypoxic conditions and hypoxia-inducible factor-1 (HIF-1) and its target gene product adrenomedullin play a critical role for the process. It is also shown that hypoxia alone is not sufficient, but TCR-mediated signal is required for accumulation of HIF-1α in human peripheral T cells. In the present study, we showed that TCR engagement does not influence hypoxia-dependent stabilization but stimulates protein synthesis of HIF-1α, most possibly via PI3K/mammalian target of rapamycin system, and that expression of HIF-1α and its target genes is blocked by treatment with rapamycin. Since some of those gene products, e.g., glucose transporters and phosphoglycerokinase, are considered to be essential for glycolysis and energy production under hypoxic conditions and adequate immune reaction in T cells, this TCR-mediated synthesis of HIF-1α may play a pivotal role in peripheral immune response. Taken together, our results may highlight a novel aspect of downstream signal from Ag recognition by TCR and a unique pharmacological role of rapamycin as well.

Natural Course of Neuroblastoma Detected by Mass Screening: A 5-Year Prospective Study at a Single Institution

PURPOSE To describe various favorable courses of neuroblastoma (NBL) detected by mass screening and to present our observation program as a temporary treatment option, to be used until a final decision is made regarding the mass screening program for 6-month-old infants. PATIENTS AND METHODS Between October 1993 and November 1999, 26 of 51 patients with NBL detected by mass screening were enrolled in our observation program. The criteria for observation included urinary vanillylmandelic acid (VMA) and homovanillic acid (HVA) levels less than 50 microg/mg creatinine, smaller tumor size (< 5.0 cm), preoperative status, and granted informed consent. Patients were divided into four groups according to changes in urinary VMA and HVA values and tumor size. Patients who no longer fulfilled criteria underwent surgery. RESULTS The observation period ranged from 4 to 73 months. Urinary VMA and HVA levels decreased in 19 of 26 patients, often by age 16 months. Eighteen patients had regressing tumors, and in 10 of these cases, the tumor was undetectable or barely detectable by imaging techniques. Four patients younger than 12 months had increased tumor marker levels and tumor volume, histologically reflecting neuroblastic proliferation. The remaining three patients, all older than 18 months, had varied tumor marker levels but increased tumor volume, histologically reflecting an increase in Schwann cells. No upgrading of tumor stage or unfavorable biologic factor was noted in any patient. CONCLUSION None of our patients showed evidence of transition from favorable to unfavorable prognosis, a finding that points to a reduction in the significance of screening as a public health measure. Until results of ongoing screening trials involving older patients have been evaluated, the observation program can be used as a temporary measure to avoid, with little risk, unnecessary surgical intervention.

Role of CD26/dipeptidyl peptidase IV in human T cell activation and function.

CD26 is a 110 kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) activity that is expressed on numerous cell types and has a multitude of biological functions. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its linkage with signaling pathways and structures involved in T-lymphocyte activation as well as antigen presenting cell (APC)-T-cell interaction. In this paper, we will review emerging data on CD26-mediated T-cell costimulation, suggesting that CD26 may be an appropriate therapeutic target for the treatment of immune disorders. However, the identity of its putative natural ligand had not yet been clearly elucidated. Recently, using protein engineering and proteomic approach, we have recently characterized the putative costimulatory ligand for CD26 in T-cells and the proximal signaling events directly associated with the cytoplasmic region of CD26 in CD26-associated T-cell costimulation, processes that are independent of the CD28 costimulatory pathway. Our work therefore presents novel findings that contribute to the area of T-cell costimulation and signal transduction.

Caveolin-1 Triggers T-cell Activation via CD26 in Association with CARMA1

CD26 is a widely distributed 110-kDa cell surface glycoprotein with an important role in T-cell costimulation. We demonstrated previously that CD26 binds to caveolin-1 in antigen-presenting cells, and following exogenous CD26 stimulation, Tollip and IRAK-1 disengage from caveolin-1 in antigen-presenting cells. IRAK-1 is then subsequently phosphorylated to up-regulate CD86 expression, resulting in subsequent T-cell proliferation. However, it is unclear whether caveolin-1 is a costimulatory ligand for CD26 in T-cells. Using soluble caveolin-1-Fc fusion protein, we now show that caveolin-1 is the costimulatory ligand for CD26, and that ligation of CD26 by caveolin-1 induces T-cell proliferation and NF-κB activation in a T-cell receptor/CD3-dependent manner. We also demonstrated that the cytoplasmic tail of CD26 interacts with CARMA1 in T-cells, resulting in signaling events that lead to NF-κB activation. Ligation of CD26 by caveolin-1 recruits a complex consisting of CD26, CARMA1, Bcl10, and IκB kinase to lipid rafts. Taken together, our findings provide novel insights into the regulation of T-cell costimulation via the CD26 molecule.

Soluble CD26/Dipeptidyl Peptidase IV Induces T Cell Proliferation Through CD86 Up-Regulation on APCs

CD26 is a T cell costimulatory molecule with dipeptidyl peptidase IV enzyme activity in its extracellular region. We have previously reported that the addition of soluble CD26 (sCD26) resulted in enhanced proliferation of peripheral blood T lymphocytes induced by the recall Ag, tetanus toxoid (TT). However, the mechanism involved in this immune enhancement has not yet been elucidated. In this paper, we demonstrate that the enhancing effect of sCD26 on TT-induced T cell proliferation occurred in the early stages of immune response. The cells directly affected by exogenously added sCD26 are the CD14-positive monocytes in the peripheral blood. Mannose-6 phosphate interfered with the uptake of sCD26 into monocytes, suggesting that mannose-6 phosphate/insulin-like growth factor II receptor plays a role in the transportation of sCD26 into monocytes. When sCD26 was added after Ag presentation had taken place, enhancement in TT-induced T cell proliferation was not observed. In addition, enhancement of TT-mediated T cell proliferation by sCD26 does not result from trimming of the MHC-bound peptide on the surface of monocytes. Importantly, we also showed that exogenously added sCD26 up-regulated the expression of the costimulatory molecule CD86 on monocytes through its dipeptidyl peptidase IV activity, and that this increased expression of CD86 was observed at both protein and mRNA level. Therefore, our findings suggest that sCD26 enhances T cell immune response to recall Ag via its direct effect on APCs.

CD26 Mediates Dissociation of Tollip and IRAK-1 from Caveolin-1 and Induces Upregulation of CD86 on Antigen-Presenting Cells

ABSTRACT CD26 is a T-cell costimulatory molecule with dipeptidyl peptidase IV enzyme activity in its extracellular region. We have previously reported that the addition of recombinant soluble CD26 resulted in enhanced proliferation of human T lymphocytes induced by the recall antigen tetanus toxoid (TT) via upregulation of CD86 on monocytes and that caveolin-1 was a binding protein of CD26, and the CD26-caveolin-1 interaction resulted in caveolin-1 phosphorylation (p-cav-1) as well as TT-mediated T-cell proliferation. However, the mechanism involved in this immune enhancement has not yet been elucidated. In the present work, we perform experiments to identify the molecular mechanisms by which p-cav-1 leads directly to the upregulation of CD86. Through proteomic analysis, we identify Tollip (Toll-interacting protein) and IRAK-1 (interleukin-1 receptor-associated serine/threonine kinase 1) as caveolin-1-interacting proteins in monocytes. We also demonstrate that following stimulation by exogenous CD26, Tollip and IRAK-1 dissociate from caveolin-1, and IRAK-1 is then phosphorylated in the cytosol, leading to the upregulation of CD86 via activation of NF-κB. Binding of CD26 to caveolin-1 therefore regulates signaling pathways in antigen-presenting cells to induce antigen-specific T-cell proliferation.

Soluble CD26/dipeptidyl peptidase IV enhances transendothelial migration via its interaction with mannose 6-phosphate/insulin-like growth factor II receptor

CD26 is a T cell surface molecule with dipeptidyl peptidase IV (DPPIV) enzyme activity in its extracellular region. In addition to its membrane form, CD26 exists in plasma as a soluble form (sCD26), which is the extracellular domain of the molecule thought to be cleaved from the cell surface. In this paper, we demonstrate that sCD26 mediates enhanced transendothelial T cell migration, an effect that requires its intrinsic DPPIV enzyme activity. We also show that sCD26 directly targets endothelial cells and that mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGFIIR) on the endothelial cell surface acts as a receptor for sCD26. Our findings therefore suggest that sCD26 influences T cell migration through its interaction with M6P/IGFIIR.