Toru Miyazaki

Tetraspanins CD9 and CD81 function to prevent the fusion of mononuclear phagocytes

Tetraspanins CD9 and CD81 facilitate the fusion between gametes, myoblasts, or virus-infected cells. Here, we investigated the role of these tetraspanins in the fusion of mononuclear phagocytes. Expression of CD9 and CD81 and their complex formation with integrins were up-regulated when blood monocytes were cultured under normal conditions. Under fusogenic conditions in the presence of Con A, CD9 and CD81 up-regulation was inhibited, and their complex formation with integrins was down-regulated. Anti-CD9 and -CD81 antibodies, which were previously shown to inhibit the fusion of gametes, myoblasts, and virus-infected cells, unexpectedly promoted the fusion of monocytes and alveolar macrophages. However, these effects were not due to altered cell adhesion, aggregation, or cytokine production. When stimulated in vitro or in vivo, alveolar macrophages and bone marrow cells of CD9- and CD81-null mice formed larger numbers of multinucleated cells than those of wild-type mice. Finally, CD9/CD81 double-null mice spontaneously developed multinucleated giant cells in the lung and showed enhanced osteoclastogenesis in the bone. These results suggest that CD9 and CD81 coordinately prevent the fusion of mononuclear phagocytes.

AIM inhibits apoptosis of T cells and NKT cells in corynebacterium-induced granuloma formation in mice

Apoptosis inhibitor expressed by macrophages (AIM) inhibits apoptosis of CD4(+)CD8(+) (CD4/CD8) double-positive thymocytes, and supports the viability of these cells on the thymic selection. However, pleiotropic functions of AIM have been suggested. In this study, heat-killed Corynebacterium parvum (C. parvum) was injected into mice carrying the homozygous mutation (AIM(-/-)) and wild-type (AIM(+/+)) mice, to investigate the role of AIM in the formation of hepatic granulomas. In AIM(-/-) mice, the size and the number of hepatic granulomas were larger, and the resorption of granulomas was more delayed than in AIM(+/+) mice. The production of interleukin-12 was more prominent in AIM(-/-) mice than in AIM(+/+) mice. In the liver of AIM(+/+) mice, expression of AIM messenger ribonucleic acid (mRNA) increased after C. parvum injection. In situ hybridization demonstrated that AIM mRNA was expressed in Kupffer cells and exudate macrophages in the liver, especially in granulomas. Larger numbers of T cells and natural killer T (NKT) cells underwent apoptosis in the granulomas of AIM(-/-) mice, suggesting that AIM prevents apoptosis of NKT cells and T cells in C. parvum-induced inflammation. Recombinant AIM (rAIM) protein significantly inhibited apoptosis of NKT cells and T cells obtained from C. parvum-stimulated livers in vitro. These results indicate that AIM functions to induce resistance to apoptosis within NKT cells and T cells, and supports the host defense in granulomatous inflammation.

Fatal Propionic Acidemia in Mice Lacking Propionyl-CoA Carboxylase and Its Rescue by Postnatal, Liver-specific Supplementation via a Transgene

Propionic acidemia (PA) is an inborn error of metabolism caused by the genetic deficiency of propionyl-CoA carboxylase (PCC). By disrupting the α-subunit gene of PCC, we created a mouse model of PA (PCCA−/−), which died in 24–36 h after birth due to accelerated ketoacidosis. A postnatal, liver-specific PCC expression via a transgene in a far lower level than that in wild-type liver, allowed PCCA−/− mice to survive the newborn and early infant periods, preventing a lethal fit of ketoacidosis (SAP+PCCA−/− mice). Interestingly, SAP+PCCA−/− mice, in which the transgene expression increased after the late infant period, continued to grow normally while mice harboring a persistent low level of PCC died in the late infant period due to severe ketoacidosis, clearly suggesting the requirement of increased PCC supplementation in proportion to the animal growth. Based on these results, we propose a two-step strategy to achieve an efficient PA prevention in human patients: a partial PCC supplementation in the liver during the newborn and early infant periods, followed by a larger amount of supplementation in the late infant period.

The BTB-kelch Protein KLHL6 Is Involved in B-Lymphocyte Antigen Receptor Signaling and Germinal Center Formation

ABSTRACT BTB-kelch proteins can elicit diverse biological functions but very little is known about the physiological role of these proteins in vivo. Kelch-like protein 6 (KLHL6) is a BTB-kelch protein with a lymphoid tissue-restricted expression pattern. In the B-lymphocyte lineage, KLHL6 is expressed throughout ontogeny, and KLHL6 expression is strongly upregulated in germinal center (GC) B cells. To analyze the role of KLHL6 in vivo, we have generated mouse mutants of KLHL6. Development of pro- and pre-B cells was normal but numbers of subsequent stages, transitional 1 and 2, and mature B cells were reduced in KLHL6-deficient mice. The antigen-dependent GC reaction was blunted (smaller GCs, reduced B-cell expansion, and reduced memory antibody response) in the absence of KLHL6. Comparison of mutants with global loss of KLHL6 to mutants lacking KLHL6 specifically in B cells demonstrated a B-cell-intrinsic requirement for KLHL6 expression. Finally, B-cell antigen receptor (BCR) cross-linking was less sensitive in KLHL6-deficient B cells compared to wild-type B cells as measured by proliferation, Ca2+ response, and activation of phospholipase Cγ2. Our results strongly point to a role for KLHL6 in BCR signal transduction and formation of the full germinal center response.

Impaired maturation of myeloid progenitors in mice lacking novel Polycomb group protein MBT-1

Polycomb group (PcG) proteins participate in DNA‐binding complexes with gene‐repressing activity, many of which have been highlighted for their involvement in hematopoiesis. We have identified a putative PcG protein, termed MBT‐1, that is associated with Rnf2, an in vivo interactor of PcG proteins. MBT‐1 structurally resembles the H‐L(3)MBT protein, whose deletion is predicted to be responsible for myeloid hematopoietic malignancies. The human MBT‐1 gene is located on chromosome 6q23, a region frequently deleted in leukemia cells, and shows a transient expression spike in response to maturation‐inducing stimuli in myeloid leukemia cells. MBT‐1−/− myeloid progenitor cells exhibit a maturational deficiency but maintain normal proliferative activities. This results in the accumulation of immature myeloid progenitors and hence, a marked decrease of mature myeloid blood cells, causing the MBT‐1−/− mice to die of anemia during a late embryonic stage. Together, we conclude that MBT‐1 specifically regulates the maturational advancement of myeloid progenitor cells during transitions between two developmental stages. We also show that MBT‐1 appears to influence myelopoiesis by transiently enhancing p57KIP2 expression levels.

The lck promoter-driven expression of the Wilms tumor gene WT1 blocks intrathymic differentiation of T-lineage cells.

In the thymi of WT1-transgenic (Tg) mice with the 17AA+/KTS- spliced form of the Wilms tumor gene WT1 driven by the lck promoter, the frequencies of CD4-CD8- double-negative (DN) thymocytes were significantly increased relative to those in normal littermates. Of the 4 subsets of CD4-CD8- DN thymocytes, the DN1 (CD44+CD25-) subset increased in both frequency and absolute cell number, whereas the DN2 (CD44+CD25+) and DN3 (CD44-CD25+) subsets decreased, indicating the blocking of thymocyte differentiation from the DN1 to the DN2 subsets. Furthermore, CD4-CD8+ T-cell receptor (TCR) γδ T-cells increased in both frequency and absolute cell number in the spleen and peripheral blood of the WT1-Tg mice relative to those of normal littermates. The CD8 molecules of these CD4-CD8+ TCR78 T-cells were CD8aß, suggesting that they originated from the thymus. These results are the first direct evidence demonstrating that the WT1 gene is involved in the development and differentiation of T-lineage cells.IntJHematol. 2003;77:463-470.

Improved Experimental Procedures for Achieving Efficient Germ Line Transmission of Nonobese Diabetic (NOD)-Derived Embryonic Stem Cells

The manipulation of a specific gene in NOD mice, the best animal model for insulin-dependent diabetes mellitus (IDDM), must allow for the precise characterization of the functional involvement of its encoded molecule in the pathogenesis of the disease. Although this has been attempted by the cross-breeding of NOD mice with many gene knockout mice originally created on the 129 or C57BL/6 strain background, the interpretation of the resulting phenotype(s) has often been confusing due to the possibility of a known or unknown disease susceptibility locus (e.g., Idd locus) cosegregating with the targeted gene from the diabetes-resistant strain. Therefore, it is important to generate mutant mice on a pure NOD background by using NOD-derived embryonic stem (ES) cells. By using the NOD ES cell line established by Nagafuchi and colleagues in 1999 (FEBSLett., 455, 101–104), the authors reexamined various conditions in the context of cell culture, DNA transfection, and blastocyst injection, and achieved a markedly improved transmission efficiency of these NOD ES cells into the mouse germ line. These modifications will enable gene targeting on a “pure” NOD background with high efficiency, and contribute to clarifying the physiological roles of a variety of genes in the disease course of IDDM.

Positive selection by the pre-TCR yields mature CD8+ T cells.

It has been of much interest whether there is functional redundancy between the constitutively signaling pre-Tα/TCRβ (pre-TCR) and ligated TCRαβ complexes, which independently operate the two distinct checkpoints during thymocyte development, i.e., the pre-TCR involved in β-selection at the CD4−CD8− double-negative stage and the TCRαβ being crucial for positive/negative selection at the CD4+CD8+ double-positive stage. We found that the pre-TCR expressed on double-positive cells in TCRα-deficient (TCRα−/−) mice produced a small number of mature CD8+ T cells. Surprisingly, when pre-Tα was overexpressed, resulting in augmentation of pre-TCR expression, there was a striking increase of the CD8+ T cells. In addition, even in the absence of up-regulation of pre-TCR expression, a similar increase of CD8+ T cells was also observed in TCRα−/− mice overexpressing Egr-1, which lowers the threshold of signal strength required for positive selection. In sharp contrast, the CD8+ T cells drastically decreased in the absence of pre-Tα on a TCRα−/− background. Thus, the pre-TCR appears to functionally promote positive selection of CD8+ T cells. The biased production of CD8+ T cells via the pre-TCR might also support the potential involvement of signal strength in CD4/CD8 lineage commitment.

Role of AIM in Corynebacterium-induced granuloma formation in mice

Apoptosis inhibitor expressed by macrophages (AIM) is a murine macrophage-specific protein and belongs to the macrophage scavenger receptor cysteine-rich domain superfamily. AIM has been introduced as the inducer of resistance to thymocyte apoptosis [1]. Because apoptosis of inflammatory cells plays a pivotal role in inflammation [2], we have applied a mouse model to address potential involvement of AIM in the process of granulomatous inflammation in vivo.