Masanori Iseki

SH2-B Is Required for Both Male and Female Reproduction

ABSTRACT Many growth factors and hormones modulate the reproductive status in mammals. Among these, insulin and insulin-like growth factor I (IGF-I) regulate the development of gonadal tissues. SH2-B has been shown to interact with insulin and IGF-I receptors, although the role of SH2-B in these signals has not been clarified. To investigate the role of SH2-B, we generated mice with a targeted disruption of the SH2-B gene. Both male and female SH2-B−/− mice showed slight retardation in growth and impaired fertility. Female knockout mice possess small, anovulatory ovaries with reduced numbers of follicles and male SH2-B−/− mice have small testes with a reduced number of sperm. SH2-B−/− cumulus cells do not respond to either follicle-stimulating hormone or IGF-I. These data suggest that SH2-B plays a critical role in the IGF-I-mediated reproductive pathway in mice.

TWEAK/Fn14 pathway promotes a T helper 2-type chronic colitis with fibrosis in mice.

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a TNF superfamily member, induces damage of the epithelial cells (ECs) and production of inflammatory mediaters through its receptor Fn14 in a model of acute colitis. In our current study of chronic colitis induced by repeated rectal injection of a hapten, we found that inflammation, fibrosis, and T helper 2 (Th2)-type immunity were significantly reduced in Fn14 gene knockout (KO) mice when compared with wild-type (WT) control mice. Expression of thymic stromal lymphopoietin (TSLP) was lower in Fn14 KO colon ECs than in WT ECs. TWEAK potentiates the induction of TSLP by interleukin-13 (IL-13) in colon explants from WT but not in Fn14 KO tissue. TSLP receptor KO mice exhibit milder chronic colitis, similar to that in Fn14 KO mice. TWEAK and IL-13 synergistically promote fibroblast proliferation. Thus we propose an IL-13-TWEAK/Fn14-TSLP axis as a key mechanism underlying chronic colitis with fibrosis.

Increased Numbers of B-1 Cells and Enhanced Responses against TI-2 Antigen in Mice Lacking APS, an Adaptor Molecule Containing PH and SH2 Domains

ABSTRACT APS (adaptor molecule containing PH and SH2 domains) is an intracellular adaptor protein that forms an adaptor family along with Lnk and SH2-B. While experiments using cultured cell lines have demonstrated that APS is phosphorylated in response to various stimuli, its in vivo functions remain unclear. We attempted to determine the physiological roles of APS by generating APS-deficient (APS−/− ) mice. APS−/− mice were viable and fertile and showed no abnormalities or growth retardation. Immunologically, APS−/− mice showed normal development and distribution of lymphocytes and myeloid cells, except for increased numbers of B-1 cells in the peritoneal cavity. APS−/− mice exhibited an enhanced humoral immune response against trinitrophenol-Ficoll, a thymus-independent type 2 antigen, while APS−/− B-2 cells exhibited normal proliferative responses and tyrosine phosphorylation of intracellular proteins upon B-cell receptor (BCR) cross-linking. APS colocalized with filamentous actin (F-actin) accumulated during the capping of BCRs in APS-transgenic B cells. After BCR stimulation, F-actin contents were lower in APS−/− B-1 cells than in wild-type B-1 cells. Our results indicate that APS might have a novel regulatory role in actin reorganization and control of B-1 cell compartment size.

Lnk/Sh2b3 Controls the Production and Function of Dendritic Cells and Regulates the Induction of IFN-γ–Producing T Cells

Dendritic cells (DCs) are proficient APCs that play crucial roles in the immune responses to various Ags and pathogens and polarize Th cell immune responses. Lnk/SH2B adaptor protein 3 (Sh2b3) is an intracellular adaptor protein that regulates B lymphopoiesis, megakaryopoiesis, and expansion of hematopoietic stem cells by constraining cytokine signals. Recent genome-wide association studies have revealed a link between polymorphism in this adaptor protein and autoimmune diseases, including type 1 diabetes and celiac disease. We found that Lnk/Sh2b3 was also expressed in DCs and investigated its role in the production and function of DC lineage cells. In Lnk−/− mice, DC numbers were increased in the spleen and lymph nodes, and growth responses of bone marrow–derived DCs to GM-CSF were augmented. Mature DCs from Lnk−/− mice were hypersensitive and showed enhanced responses to IL-15 and GM-CSF. Compared to normal DCs, Lnk−/− DCs had enhanced abilities to support the differentiation of IFN-γ–producing Th1 cells from naive CD4+ T cells. This was due to their elevated expression of IL-12Rβ1 and increased production of IFN-γ. Lnk−/− DCs supported the appearance of IFN-γ–producing T cells even under conditions in which normal DCs supported induction of regulatory T cells. These results indicated that Lnk/Sh2b3 plays a regulatory role in the expansion of DCs and might influence inflammatory immune responses in peripheral lymphoid tissues.

Lnk prevents inflammatory CD8+ T-cell proliferation and contributes to intestinal homeostasis

The intracellular adaptor Lnk (also known as SH2B3) regulates cytokine signals that control lymphohematopoiesis, and Lnk−/− mice have expanded B‐cell, megakaryocyte, and hematopoietic stem‐cell populations. Moreover, mutations in the LNK gene are found in patients with myeloproliferative disease, whereas LNK polymorphisms have recently been associated with inflammatory and autoimmune diseases, including celiac disease. Here, we describe a previously unrecognized function of Lnk in the control of inflammatory CD8+ T‐cell proliferation and in intestinal homeostasis. Mature T cells from newly generated Lnk–Venus reporter mice had low but substantial expression of Lnk, whereas Lnk expression was downregulated during homeostatic T‐cell proliferation under lymphopenic conditions. The numbers of CD44hiIFN‐γ+CD8+ effector or memory T cells were found to be increased in Lnk−/− mice, which also exhibited shortening of villi in the small intestine. Lnk−/− CD8+ T cells survived longer in response to stimulation with IL‐15 and proliferated even in nonlymphopenic hosts. Transfer of Lnk−/− CD8+ T cells together with WT CD4+ T cells into Rag2‐deficient mice recapitulated a sign of villous abnormality. Our results reveal a link between Lnk and immune cell‐mediated intestinal tissue destruction.

Cyclosporin A indirectly attenuates activation of group 2 innate lymphoid cells in papain-induced lung inflammation

Cyclosporin A (CsA) is a well-known immunosuppressant that is used against steroid-resistant asthma. Group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells produce Th2 cytokines including IL-5 and play important roles in asthma pathogenesis. Here, we studied the effects of CsA in allergen-induced lung inflammation in mice and found that CsA decreased the number of lung ILC2s and attenuated papain-induced activation of ILC2s accompanied with IL-5 expression. The ILC2 suppression mediated by CsA was not observed in culture or in lymphocyte-deficient Rag2-/- mice. Thus, we propose a new suppressive effect of CsA, i.e., administration of CsA indirectly suppresses maintenance and activation of lung ILC2s in addition to direct suppression of T-cell activation and cytokine production.