Kazutake Tsujikawa

Fibrosis and adipogenesis originate from a common mesenchymal progenitor in skeletal muscle

Accumulation of adipocytes and collagen type-I-producing cells (fibrosis) is observed in muscular dystrophies. The origin of these cells had been largely unknown, but recently we identified mesenchymal progenitors positive for platelet-derived growth factor receptor alpha (PDGFRα) as the origin of adipocytes in skeletal muscle. However, the origin of muscle fibrosis remains largely unknown. In this study, clonal analyses show that PDGFRα+ cells also differentiate into collagen type-I-producing cells. In fact, PDGFRα+ cells accumulated in fibrotic areas of the diaphragm in the mdx mouse, a model of Duchenne muscular dystrophy. Furthermore, mRNA of fibrosis markers was expressed exclusively in the PDGFRα+ cell fraction in the mdx diaphragm. Importantly, TGF-β isoforms, known as potent profibrotic cytokines, induced expression of markers of fibrosis in PDGFRα+ cells but not in myogenic cells. Transplantation studies revealed that fibrogenic PDGFRα+ cells mainly derived from pre-existing PDGFRα+ cells and that the contribution of PDGFRα− cells and circulating cells was limited. These results indicate that mesenchymal progenitors are the main origin of not only fat accumulation but also fibrosis in skeletal muscle.

Suppression of macrophage functions impairs skeletal muscle regeneration with severe fibrosis

When damaged, skeletal muscle regenerates. In the early phases of regeneration, inflammatory cells such as neutrophils/granulocytes and macrophages infiltrate damaged muscle tissue. To reveal the roles of macrophages during skeletal muscle regeneration, we injected an antibody, AFS98 that blocks the binding of M-CSF to its receptor into normal mice that received muscle damages. Anti-M-CSF receptor administration suppressed macrophage but not neutrophil infiltration. Histological study indicated that suppression of macrophages function leads to the incomplete muscle regeneration. In addition FACS and immunohistochemical study showed that the acute lack of macrophages delayed proliferation and differentiation of muscle satellite cells in vivo. Furthermore, mice injected with the anti-M-CSF receptor antibody exhibited not only adipogenesis, but also significant collagen deposition, i.e., fibrosis and continuous high expression of connective tissue growth factor. Finally we indicate that these fibrosis markers were strongly enriched in CD90(+) cells that do not include myogenic cells. These results indicate that macrophages directly affect satellite cell proliferation and that a macrophage deficiency severely impairs skeletal muscle regeneration and causes fibrosis.

Localization of metallothionein in nuclei of growing primary cultured adult rat hepatocytes

In primary cultured adult rat hepatocytes stimulated by epidermal growth factor and insulin, dramatic changes in the subcellular distribution of metallothionein were clarified by indirect immunofluorescence using antisera specific for this protein. Metallothionein was detected only in the cytoplasm of cultured hepatocytes in the G0 and G1 phases, but was concentrated in the cell nuclei in the early S phase. The strongest staining pattern in the nuclei was observed 12 h after stimulation. Subsequently, the intensity of metallothionein staining in the nuclei decreased. These results suggests that primary cultured hepatocytes are suitable for examining the relation between subcellular localization of metallothionein and cell growth.

Role of γδT Cells in the Inflammatory Response of Experimental Colitis Mice

We examined the severity of experimental colitis induced by dextran sulfate sodium (DSS) using immunologically manipulated mice. C57BL/6 mice showed more severe colitis than BALB/c mice, but mice of both strains recovered fully from the disease after the removal of DSS from their drinking water. The infiltrated cells at the lesions were mainly granulocytes in normal littermates. However, C.B-17 scid, IL-7Rα deficient, and TCR-Cβδ double-deficient mice showed severe colitis and did not recover from the disease even after the removal of DSS. It was found that the infiltrated cells at the lesions in the lethal strains were monocytes. Although both TCR-Cδ−/− and TCR-Cβ−/− mice showed severe colitis phenotypes, infiltration in the former is monocyte-dominant while that in the latter is granulocyte-dominant. Thus the type of cells that infiltrate at the lesions of DSS-induced experimental colitis may be controlled by functional T cell subsets. Immunohistological and RT-PCR analyses of the inflamed colon revealed that the murine homologue of human GROα released by some cells under the control of γδT cells is a possible candidate determining the severity of DSS-induced experimental colitis.

Hesr1 and Hesr3 are essential to generate undifferentiated quiescent satellite cells and to maintain satellite cell numbers

Satellite cells, which are skeletal muscle stem cells, divide to provide new myonuclei to growing muscle fibers during postnatal development, and then are maintained in an undifferentiated quiescent state in adult skeletal muscle. This state is considered to be essential for the maintenance of satellite cells, but their molecular regulation is unknown. We show that Hesr1 (Hey1) and Hesr3 (Heyl) (which are known Notch target genes) are expressed simultaneously in skeletal muscle only in satellite cells. In Hesr1 and Hesr3 single-knockout mice, no obvious abnormalities of satellite cells or muscle regenerative potentials are observed. However, the generation of undifferentiated quiescent satellite cells is impaired during postnatal development in Hesr1/3 double-knockout mice. As a result, myogenic (MyoD and myogenin) and proliferative (Ki67) proteins are expressed in adult satellite cells. Consistent with the in vivo results, Hesr1/3-null myoblasts generate very few Pax7+ MyoD– undifferentiated cells in vitro. Furthermore, the satellite cell number gradually decreases in Hesr1/3 double-knockout mice even after it has stabilized in control mice, and an age-dependent regeneration defect is observed. In vivo results suggest that premature differentiation, but not cell death, is the reason for the reduced number of satellite cells in Hesr1/3 double-knockout mice. These results indicate that Hesr1 and Hesr3 are essential for the generation of adult satellite cells and for the maintenance of skeletal muscle homeostasis.

A Novel Human AlkB Homologue, ALKBH8, Contributes to Human Bladder Cancer Progression

We recently identified a novel human AlkB homologue, ALKBH8, which is expressed in various types of human cancers including human urothelial carcinomas. In examining the role and function of ALKBH8 in human bladder cancer development in vitro, we found that silencing of ALKBH8 through small interfering RNA transfection reduced reactive oxygen species (ROS) production via down-regulation of NAD(P)H oxidase-1 (NOX-1) and induced apoptosis through subsequent activation of c-jun NH(2)-terminal kinase (JNK) and p38. However, we also found that JNK and p38 activation resulted in phosphorylation of H2AX (gammaH2AX), a variant of mammalian histone H2A, which contributes to the apoptosis induced by silencing ALKBH8 and NOX-1. Silencing of ALKBH8 significantly suppressed invasion, angiogenesis, and growth of bladder cancers in vivo as assessed both in the chorioallantoic membrane assay and in an orthotopic mouse model using green fluorescent protein-labeled KU7 human urothelial carcinoma cells. Immunohistochemical examination showed high expression of ALKBH8 and NOX-1 proteins in high-grade, superficially and deeply invasive carcinomas (pT(1) and >pT(2)) as well as in carcinoma in situ, but not in low-grade and noninvasive phenotypes (pT(a)). These findings indicate an essential role for ALKBH8 in urothelial carcinoma cell survival mediated by NOX-1-dependent ROS signals, further suggesting new therapeutic strategies in human bladder cancer by inducing JNK/p38/gammaH2AX-mediated cell death by silencing of ALKBH8.

Hypertension and dysregulated proinflammatory cytokine production in receptor activity-modifying protein 1-deficient mice

Calcitonin gene-related peptide (CGRP) is thought to be a prominent neuropeptide in cardiovascular regulation and neuroimmune modulation. There are two isoforms of CGRP (αCGRP and βCGRP), and the main CGRP receptors are probably composed of a calcitonin receptor-like receptor (CLR) and a receptor activity-modifying protein (RAMP)1. However, the physiological functions of CGRP that are mediated through the CLR/RAMP1 receptors remain to be clarified. For an improved understanding of the functions, we generated mice deficient in RAMP1, a specific subunit of CGRP receptors, by a conditional gene-targeting technique. The RAMP1-deficient mice (RAMP1−/−) exhibited high blood pressure, with no changes in heart rate. αCGRP was found to have a potent vascular relaxant activity compared with βCGRP in the artery of the WT (RAMP1+/+) mice. The activities of both CGRP isoforms were remarkably suppressed in the arteries of the RAMP1−/− mice. The LPS-induced inflammatory responses of the RAMP1−/− mice revealed a transient and significant increase in the serum CGRP levels and high serum levels of proinflammatory cytokines compared with the RAMP1+/+ mice. αCGRP and βCGRP equally suppressed the production of TNF-α and IL-12 in bone marrow-derived dendritic cells stimulated with lipopolysaccharide. Their inhibitory effects were not observed in the bone marrow-derived dendritic cells of the RAMP1−/− mice. These results indicate that CGRP signaling through CLR/RAMP1 receptors plays a crucial role in the regulation of both blood pressure by vascular relaxation and proinflammatory cytokine production from dendritic cells.

Ste20-like kinase (SLK), a regulatory kinase for polo-like kinase (Plk) during the G2/M transition in somatic cells.

Activation of the cyclin‐dependent kinase cdc2‐cyclin B1 at the G2/M transition of the cell cycle requires dephosphorylation of threonine‐14 and tyrosine‐15 in cdc2, which in higher eukaryotes is brought about by the Cdc25C phosphatase. In Xenopus, there is evidence that a kinase cascade comprised of xPlkk1 and Plx1, the Xenopus polo‐like kinase 1, plays a key role in the activation of Cdc25C during oocyte maturation. In the mammalian somatic cell cycle, a polo‐like kinase homologue (Plk1) also functions during mitosis, but a kinase upstream of Plk is still unknown.

Genetic Background Affects Properties of Satellite Cells and mdx Phenotypes

Duchenne muscular dystrophy (DMD) is the most common lethal genetic disorder of children. The mdx (C57BL/10 background, C57BL/10-mdx) mouse is a widely used model of DMD, but the histopathological hallmarks of DMD, such as the smaller number of myofibers, accumulation of fat and fibrosis, and insufficient regeneration of myofibers, are not observed in adult C57BL/10-mdx except for in the diaphragm. In this study, we showed that DBA/2 mice exhibited decreased muscle weight, as well as lower myofiber numbers after repeated degeneration-regeneration cycles. Furthermore, the self-renewal efficiency of satellite cells of DBA/2 is lower than that of C57BL/6. Therefore, we produced a DBA/2-mdx strain by crossing DBA/2 and C57BL/10-mdx. The hind limb muscles of DBA/2-mdx mice exhibited lower muscle weight, fewer myofibers, and increased fat and fibrosis, in comparison with C57BL/10-mdx. Moreover, remarkable muscle weakness was observed in DBA/2-mdx. These results indicate that the DBA/2-mdx mouse is a more suitable model for DMD studies, and the efficient satellite cell self-renewal ability of C57BL/10-mdx might explain the difference in pathologies between humans and mice.

Prostate cancer antigen-1 contributes to cell survival and invasion though discoidin receptor 1 in human prostate cancer

A novel gene, prostate cancer antigen (PCA)‐1, was recently reported to be expressed in the prostate; however, its biological roles remain unclear. Knockdown of the PCA‐1 gene by small interfering RNA transfection induced apoptosis through reducing the expression of the anti‐apoptotic molecule Bcl‐xl and cytoplasmic release of cytochrome c in the androgen‐independent prostate cancer cell line PC3. Moreover, in vitro matrigel and in vivo chorioallantoic membrane assays showed that silencing of PCA‐1 significantly downregulated discoidin receptor (DDR)‐1 expression, resulting in suppression of cancer‐cell invasion. Transfection with PCA‐1 increased the levels of both Bcl‐xl and DDR1, which made the cells more invasive through the upregulation of matrix metalloproteinase 9 in DU145. Interestingly, long‐term culture using androgen‐free medium increased the level of PCA‐1 and the related expression of Bcl‐xl and DDR‐1 in the androgen‐sensitive cancer cell line LNCaP, suggesting that PCA‐1 signaling is associated with androgen independence. Immunohistochemical analysis in a series of 169 prostate carcinomas showed that PCA‐1 and DDR1 were strongly expressed in prostate cancer cells, including preneoplastic lesions, but there was little or no expression in normal epithelium. Moreover, the expression of PCA‐1 and DDR‐1 was associated with a hormone‐independent state of prostate cancer. Taken together, we propose that PCA‐1–DDR‐1 signaling is a new important axis involved in malignant potential prostate cancer associated with hormone‐refractory status. (Cancer Sci 2008; 99: 39–45)