Junko Morimoto

Interleukin-17A Deficiency Accelerates Unstable Atherosclerotic Plaque Formation in Apolipoprotein E-Deficient Mice

Objective—Interleukin(IL)-17A, an inflammatory cytokine, has been implicated in atherosclerosis, in which inflammatory cells within atherosclerotic plaques express IL-17A. However, its role in the development of atheroscelrosis remains to be controversial. Methods and Results—To directly examine the role of IL-17A in atherosclerosis, we generated apolipoprotein E (ApoE)/IL-17A double-deficient (ApoE−/−IL-17A−/−) mice. Mice were fed with high-fat diet (HFD) for either 8 or 16 weeks, both starting at ages of 6 to 8 weeks. We found that splenic CD4+ T-cells produced high amounts of IL-17A in ApoE−/− mice after HFD feeding for 8 weeks. Atherosclerosis was significantly accelerated in HFD-fed ApoE−/−IL-17A−/− mice compared with ApoE−/− mice. Splenic CD4+ T-cells of ApoE−/−IL-17A−/− mice after HFD feeding for 8 weeks, but not for 16 weeks, exhibited increased interferon gamma and decreased IL-5 production. Importantly, formation of vulnerable plaque as evidenced by reduced numbers of vascular smooth muscle cells and reduced type I collagen deposition in the plaque was detected in ApoE−/−IL-17A−/− mice after HFD feeding for 8 weeks. Conclusion—These results suggest that IL-17A regulates the early phase of atherosclerosis development after HFD feeding and plaque stability, at least partly if not all by modulating interferon gamma and IL-5 production from CD4+ T-cells.

Syndecan-4 Prevents Cardiac Rupture and Dysfunction After Myocardial Infarction

Rationale: Syndecan-4 (Syn4), a cell-surface heparan sulfate proteoglycan, has been detected in the infarct region after myocardial infarction (MI), but its functional significance has not been elucidated. Objective: We examined whether and how Syn4 regulates the cardiac healing process after MI. Methods and Results: Although the heart in Syn4-deficient (Syn4−/−) mice was morphologically and functionally normal, Syn4−/− mice exhibited impaired heart function and increased mortality rate as a result of cardiac ruptures after MI. Cardiac ruptures in Syn4−/− mice were associated with reduced inflammatory reaction and impaired granulation tissue formation during the early phase of MI, as evidenced by reduced numbers of leukocytes, fibroblasts, myofibroblasts, macrophages, and capillary vessels, along with reduced extracellular matrix protein deposition in the infarct region after MI. Transforming growth factor-&bgr;1–dependent cell signaling was preserved, whereas cell migration, fibronectin-induced cell signaling, and differentiation into myofibroblasts were defective in Syn4−/− cardiac fibroblasts. We also found that Syn4 was involved in basic fibroblast growth factor–dependent endothelial cell signaling, cell proliferation, and tube formation. Finally, overexpression of the shed form of Syn4 before MI creation led to an increase in mortality due to cardiac rupture via its action as a dominant-negative inhibitor of endogenous Syn4 signaling, which suggested a protective role of Syn4 signaling in MI. Conclusions: These results suggest that Syn4 plays an important role in the inflammatory response and granulation tissue formation, thereby preventing cardiac rupture and dysfunction after MI.

Osteopontin; as a target molecule for the treatment of inflammatory diseases.

It has been well recognized that inflammatory responses are part of pathogenesis for various disorders such as autoimmune diseases. For example, multiple sclerosis (MS) is an inflammatory demyelinating disease of central nervous system that is presumably caused by activated T cells specific for myelin antigens. Rheumatoid arthritis (RA) is also a chronic inflammatory disease characterized by synovial inflammation in which several inflammatory cytokines are involved. On the other hand, Osteopontin (Opn) is a pleiotropic cytokine expressed by activated T cells, dendritic cells (DCs) and macrophages and its expression is up-regulated during inflammation. Secreted form of Opn (s-Opn), which is modified by phosphorylation, glycosylation and proteolytic cleavage with thrombin, has activities as a T helper type 1 (Th1) cytokine and as a chemoattractant for many types of cells through integrin receptors and CD44. Recently, it has been uncovered that intracellular form of Opn (i-Opn) is a critical regulator for Toll like receptor-9 (TLR-9), TLR-7-dependent interferon-alpha (IFN-alpha) expression by plasmacytoid DCs and Th17 development. In this review, we have summarized recent progress in understanding of Opns role in variety of inflammatory disorders.

Accelerated development of aging-associated and instability-induced osteoarthritis in osteopontin-deficient mice

OBJECTIVEnTo investigate the role of osteopontin (OPN) in the development of osteoarthritis (OA) under in vivo and in vitro conditions.nnnMETHODSnBoth instability-induced and aging-associated OA models were generated using OPN-deficient (OPN-/-) and control wild-type (WT) mice. An in vitro cartilage degradation model was also used, to evaluate the effect of OPN on proteoglycan loss from joint cartilage.nnnRESULTSnOPN deficiency exacerbated both aging-associated and instability-induced OA. Both structural changes and an increased loss of proteoglycan from cartilage tissue were augmented in the absence of OPN. OPN deficiency also led to the induction of matrix metalloproteinase 13 (MMP-13), which degrades a major component of the cartilage matrix protein type II collagen. Both the loss of proteoglycan and the induction of the collagen-degrading enzyme MMP-13 facilitated the development of OA.nnnCONCLUSIONnOPN plays a pivotal role in the progression of both instability-induced and aging-associated spontaneous OA. OPN is a critical intrinsic regulator of cartilage degradation via its effects on MMP-13 expression and proteoglycan loss.

Role of matricellular proteins in cardiac tissue remodeling after myocardial infarction

After onset of myocardial infarction (MI), the left ventricle (LV) undergoes a continuum of molecular, cellular, and extracellular responses that result in LV wall thinning, dilatation, and dysfunction. These dynamic changes in LV shape, size, and function are termed cardiac remodeling. If the cardiac healing after MI does not proceed properly, it could lead to cardiac rupture or maladaptive cardiac remodeling, such as further LV dilatation and dysfunction, and ultimately death. Although the precise molecular mechanisms in this cardiac healing process have not been fully elucidated, this process is strictly coordinated by the interaction of cells with their surrounding extracellular matrix (ECM) proteins. The components of ECM include basic structural proteins such as collagen, elastin and specialized proteins such as fibronectin, proteoglycans and matricellular proteins. Matricellular proteins are a class of non-structural and secreted proteins that probably exert regulatory functions through direct binding to cell surface receptors, other matrix proteins, and soluble extracellular factors such as growth factors and cytokines. This small group of proteins, which includes osteopontin, thrombospondin-1/2, tenascin, periostin, and secreted protein, acidic and rich in cysteine, shows a low level of expression in normal adult tissue, but is markedly upregulated during wound healing and tissue remodeling, including MI. In this review, we focus on the regulatory functions of matricellular proteins during cardiac tissue healing and remodeling after MI.

CSF-1–Dependent Red Pulp Macrophages Regulate CD4 T Cell Responses

The balance between immune activation and suppression must be regulated to maintain immune homeostasis. Tissue macrophages (MΦs) constitute the major cellular subsets of APCs within the body; however, how and what types of resident MΦs are involved in the regulation of immune homeostasis in the peripheral lymphoid tissues are poorly understood. Splenic red pulp MΦ (RPMs) remove self-Ags, such as blood-borne particulates and aged erythrocytes, from the blood. Although many scattered T cells exist in the red pulp of the spleen, little attention has been given to how RPMs prevent harmful T cell immune responses against self-Ags. In this study, we found that murine splenic F4/80hiMac-1low MΦs residing in the red pulp showed different expression patterns of surface markers compared with F4/80+Mac-1hi monocytes/MΦs. Studies with purified cell populations demonstrated that F4/80hiMac-1low MΦs regulated CD4+ T cell responses by producing soluble suppressive factors, including TGF-β and IL-10. Moreover, F4/80hiMac-1low MΦs induced the differentiation of naive CD4+ T cells into functional Foxp3+ regulatory T cells. Additionally, we found that the differentiation of F4/80hiMac-1low MΦs was critically regulated by CSF-1, and in vitro-generated bone marrow-derived MΦs induced by CSF-1 suppressed CD4+ T cell responses and induced the generation of Foxp3+ regulatory T cells in vivo. These results suggested that splenic CSF-1–dependent F4/80hiMac-1low MΦs are a subpopulation of RPMs and regulate peripheral immune homeostasis.

Syndecan-4 Deficiency Limits Neointimal Formation After Vascular Injury by Regulating Vascular Smooth Muscle Cell Proliferation and Vascular Progenitor Cell Mobilization

Objective—Syndecan-4 (Syn4) is a heparan sulfate proteoglycan and works as a coreceptor for various growth factors. We examined whether Syn4 could be involved in the development of neointimal formation in vivo. Methods and Results—Wild-type (WT) and Syn4-deficient (Syn4−/−) mice were subjected to wire-induced femoral artery injury. Syn4 mRNA was upregulated after vascular injury in WT mice. Neointimal formation was attenuated in Syn4−/− mice, concomitantly with the reduction of Ki67-positive vascular smooth muscle cells (VSMCs). Basic-fibroblast growth factor– or platelet-derived growth factor-BB–induced proliferation, extracellular signal-regulated kinase activation, and expression of cyclin D1 and Bcl-2 were impaired in VSMCs from Syn4−/− mice. To examine the role of Syn4 in bone marrow (BM)–derived vascular progenitor cells (VPCs) and vascular walls, we generated chimeric mice by replacing the BM cells of WT and Syn4−/− mice with those of WT or Syn4−/− mice. Syn4 expressed by both vascular walls and VPCs contributed to the neointimal formation after vascular injury. Although the numbers of VPCs were compatible between WT and Syn4−/− mice, mobilization of VPCs from BM after vascular injury was defective in Syn4−/− mice. Conclusion—Syn4 deficiency limits neointimal formation after vascular injury by regulating VSMC proliferation and VPC mobilization. Therefore, Syn4 may be a novel therapeutic target for preventing arterial restenosis after angioplasty.

Regulatory role of DC-derived osteopontin in systemic allergen sensitization

Osteopontin (OPN) is a secreted phosphoglycoprotein with a wide range of functions, and is involved in various pathophysiological conditions. However, the role of OPN in IgE and Th2‐associated allergic responses remains incompletely defined. The aim of this study was to elucidate the role of OPN in systemic allergen sensitization in mice. When compared with OPN+/+ mice, significantly increased levels of OVA‐induced IgE were found in OPN−/− mice. OPN−/− DC demonstrated an increased capacity to enhance Th2 cytokine production in CD4+ T cells from sensitized OPN+/+ mice. Furthermore, significantly reduced levels of IL‐12p70 expression were seen in LPS‐stimulated OPN−/− DC as compared with the WT DC, and the reduction was reversible by the addition of recombinant OPN (rOPN). rOPN was able to suppress OVA‐induced IL‐13 production in the cultures of CD4 and OPN−/− DC, but this inhibitory activity was neutralized by the addition of anti‐IL‐12 Ab. In addition, administration of rOPN in vivo suppressed OVA‐specific IgE production; however, this suppressive effect was abrogated in IL‐12‐deficient mice. These results indicate that DC‐derived OPN plays a regulatory role in the development of systemic allergen sensitization, which is mediated, at least in part, through the production of endogenous IL‐12.

Prevention of experimental autoimmune uveoretinitis by blockade of osteopontin with small interfering RNA.

Osteopontin (OPN) is elevated during the progression of experimental autoimmune uveoretinitis (EAU) in C57BL/6 (B6) mice. Furthermore, EAU symptoms are ameliorated in OPN knockout mice or in B6 mice treated with anti-OPN antibody (M5). Recently, OPN has been shown to promote the Th1 response not only in the extracellular space as a secretory protein but also in cytosol as a signaling component. Thus, we attempted to reduce OPN in both compartments by using a small interfering RNA (siRNA) targeting the OPN coding sequence (OPN-siRNA). EAU was induced in B6 mice by immunization with human interphotoreceptor retinoid-binding protein (hIRBP) peptide sequence 1-20. The OPN- or control-siRNA was administered with hydrodynamic methods 24 h before and simultaneously with immunization (prevention regimen). When plasma OPN levels were quantified following siRNA administration with the prevention regimen, the level in the OPN-siRNA-treated group was significantly lower than that in the control-siRNA-treated group. Accordingly, the clinical and histopathological scores of EAU were significantly reduced in B6 mice when siRNA caused OPN blockade. Furthermore, TNF-alpha, IFN-gamma, IL-2, GM-CSF and IL-17 levels in the culture supernatants were markedly suppressed in the OPN-siRNA-treated group, whereas the proliferative responses of T lymphocytes from regional lymph nodes against immunogenic peptides was not significantly reduced. On the other hand, the protection was not significant if the mice received the OPN-siRNA treatment on day 7 and day 8 after immunization when the clinical symptoms appeared overt (reversal regimen). Our results suggest that OPN blockade with OPN-siRNA can be an alternative choice for the usage of anti-OPN antibody and controlling uveoretinitis in the preventive regimen.

Osteopontin Modulates the Generation of Memory CD8+ T Cells during Influenza Virus Infection

The adaptive immune system generates memory cells, which induce a rapid and robust immune response following secondary Ag encounter. Memory CD8+ T cells are a critical component of protective immunity against infections and cancers. Therefore, understanding the mechanism whereby memory CD8+ T cells are generated and maintained is important for inducing effective memory CD8+ T cell response. Recent studies have demonstrated that the inflammatory cytokine IL-12 favors the generation of terminal effector CD8+ T cells rather than memory precursor effector CD8+ T cells by regulating the expression of the transcription factor T-bet. In this study, we report that the inflammatory cytokine osteopontin (Opn) modulates memory CD8+ T cell generation during influenza virus infection. Although Opn wild-type and Opn knockout (KO) mice had similar numbers of virus-specific effector CD8+ T cells, virus-specific effector CD8+ T cells generated in Opn KO mice showed low levels of T-bet expression and an increased memory precursor cell population compared with cells generated in Opn wild-type mice. This resulted in the persistently increased number of memory CD8+ T cells in Opn KO mice. Studies with bone marrow-derived dendritic cells demonstrated that Opn deficiency in bone marrow-derived dendritic cells results in low levels of IL-12 production in response to the stimulation with influenza virus. Thus, we hypothesize that Opn modulates the generation of memory precursor effector CD8+ T cells by regulating cytokine milieu during the acute phase of virus infection. This finding may provide new insight into the role of Opn in adaptive immune response.