Kunihiro Tsuchida

Mesenchymal progenitors distinct from satellite cells contribute to ectopic fat cell formation in skeletal muscle

Ectopic fat deposition in skeletal muscle is closely associated with several disorders, however, the origin of these adipocytes is not clear, nor is the mechanism of their formation. Satellite cells function as adult muscle stem cells but are proposed to possess multipotency. Here, we prospectively identify PDGFRα+ mesenchymal progenitors as being distinct from satellite cells and located in the muscle interstitium. We show that, of the muscle-derived cell populations, only PDGFRα+ cells show efficient adipogenic differentiation both in vitro and in vivo. Reciprocal transplantations between regenerating and degenerating muscles, and co-culture experiments revealed that adipogenesis of PDGFRα+ cells is strongly inhibited by the presence of satellite cell-derived myofibres. These results suggest that PDGFRα+ mesenchymal progenitors are the major contributor to ectopic fat cell formation in skeletal muscle, and emphasize that interaction between muscle cells and PDGFRα+ mesenchymal progenitors, not the fate decision of satellite cells, has a considerable impact on muscle homeostasis.

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.

Expressions of PDGF receptor alpha, c-Kit and Flk1 genes clustering in mouse chromosome 5 define distinct subsets of nascent mesodermal cells.

In gastrulating embryos, various types of cells are generated before differentiation into specific lineages. The mesoderm of the gastrulating mouse embryo represents a group of such intermediate cells. PDGF receptor alpha (PDGFRα), c‐Kit and fetal liver kinase 1 (Flk1) are expressed in distinctive mesodermal derivatives of post‐gastrulation embryos. Their expressions during gastrulation were examined by whole mount immunostaining with monoclonal antibodies against these three receptors. The antibodies stained different mesodermal subsets in gastrulating embryos. Flow cytometry of head fold stage embryos revealed that Flk1+ mesodermal cells could be further classified by the level of c‐Kit expression. To examine the possibility that hematopoietic cell differentiation is initiated from the Flk1+ mesoderm, embryonic stem (ES) cells were cultured on the OP9 or PA6 stromal cell layer; the former but not the latter supported in vitro hematopoiesis from ES cells. Flk1+ cells were detected only on the OP9 cell layer from day 3 of differentiation before the appearance of hematopoietic cells. Thus, Flk1+ cells will be required for in vitro ES cell differentiation into hematopoietic cells. The results suggest that these three receptor tyrosine kinases will be useful for defining and sorting subsets of mesodermal cells from embryos or in vitro cultured ES cells.

Fabrication of ZnPc/protein nanohorns for double photodynamic and hyperthermic cancer phototherapy

Multifunctionalization of carbon nanotubules is easily achieved by attaching functional molecules that provide specific advantages for microscopic applications. We fabricated a double photodynamic therapy (PDT) and photohyperthermia (PHT) cancer phototherapy system that uses a single laser. Zinc phthalocyanine (ZnPc) was loaded onto single-wall carbon nanohorns with holes opened (SWNHox), and the protein bovine serum albumin (BSA) was attached to the carboxyl groups of SWNHox. In this system, ZnPc was the PDT agent, SWNHox was the PHT agent, and BSA enhanced biocompatibility. The double phototherapy effect was confirmed in vitro and in vivo. When ZnPc-SWNHox-BSA was injected into tumors that were subcutaneously transplanted into mice, the tumors almost disappeared upon 670-nm laser irradiation. In contrast, the tumors continued to grow when only ZnPc or SWNHox-BSA was injected. We conclude that carbon nanotubules may be a valuable new tool for use in cancer phototherapy.

Identification and Characterization of a Novel Follistatin-like Protein as a Binding Protein for the TGF-β Family

Follistatin is an activin-binding protein that prevents activin from binding to its receptors and neutralizes its activity. Follistatin also binds bone morphogenetic proteins (BMPs). In this study, we report the identification of a novel follistatin-like protein from mouse. The mouse cDNA encodes a 256-residue precursor and most likely a mouse homologue of human FLRG, which was found at the breakpoint of the chromosomal rearrangement in a B-cell line. Whereas follistatin has three follistatin domains, which are presumed to be growth factor binding motifs, FLRG possesses only two follistatin domains. Northern blotting revealed that mRNAs for FLRG were abundantly expressed in heart, lung, kidney, and testis in mouse. The recombinant mouse FLRG proteins were found to have binding activity for both activin and bone morphogenetic protein-2. Like follistatin, FLRG has higher affinity for activin than for BMP-2. The FLRG protein inhibited activin-induced and BMP-2-induced transcriptional responses in a dose-dependent manner. GlutathioneS-transferase fusion proteins encoding various regions of FLRG were produced and studied. Ligand blotting using125I-activin revealed that the COOH-terminal region containing the second follistatin domain was able to bind activin. Our finding implies that cellular signaling by activin and BMPs is tightly regulated by multiple members of the follistatin family.

Enhancement of In Vivo Anticancer Effects of Cisplatin by Incorporation Inside Single-Wall Carbon Nanohorns

Cisplatin (CDDP) was incorporated inside single-wall carbon nanohorns with holes opened (SWNHox) by a nanoprecipitation method that involved dispersion of CDDP and SWNHox in a solvent followed by the solvent evaporation. The incorporated CDDP quantity increased from the previously reported value of 15 to 46%, and the total released quantity of CDDP also increased from 60 to 100% by changing the solvent from dimethylformamide to water. Concurrently, in vitro anticancer efficiency of CDDP@SWNHox increased to 4-6 times greater than that of the intact CDDP. In vivo, CDDP@SWNHox intratumorally injected to transplanted tumors of mice suppressed the tumor growth more than the intact CDDP. We observed that CDDP@SWNHox adhered to the cell surfaces in vitro and stayed within the tumor tissues in vivo. Therefore, we think that the CDDP released from SWNHox realized high concentrations locally at the cells in vitro and in the tissues in vivo and could efficiently attack the tumor cells. We also found that SWNHox itself had an in vivo anticancer effect, which might increase the anticancer activities of CDDP@SWNHox.

Tumor-stroma interaction of human pancreatic cancer: acquired resistance to anticancer drugs and proliferation regulation is dependent on extracellular matrix proteins.

Introduction Pancreatic cancer is one of the major causes of cancer-related deaths in industrialized countries. It is known that pancreatic cancer is resistant to chemotherapy and that cancer cells are surrounded by extracellular matrix (ECM) proteins including collagen I, collagen IV, fibronectin, and laminin. Aims To examine the role of ECM proteins in acquired resistance to anticancer drugs and proliferation regulation in pancreatic cancers. Methodology and Results We used an in vitro model of ECM-induced chemoresistance and cell proliferation of cancer cell lines (MIA PaCa-2, PANC-1, and Capan-1) with 3 different malignancy grades and found that resistance to cytotoxic drugs and proliferation regulation was dependent on ECM proteins. Pancreatic cancer cell lines, especially MIA PaCa-2 cells, adhering to any of the ECM proteins showed decreased cytotoxicity of anticancer drugs, except for gemcitabine. PANC-1 and Capan-1 cells adhering to fibronectin, collagen I, and collagen IV proliferated more than the controls. Conclusion ECM proteins have important roles in acquired resistance to anticancer drugs and cell proliferation regulation of pancreatic cancer cells. Therefore, the expression of ECM proteins in pancreatic cancer specimens could provide valuable information to aid anticancer drug cytotoxicity, and gemcitabine would be useful for treatment of patients with pancreatic cancer.

Transgenic expression of a myostatin inhibitor derived from follistatin increases skeletal muscle mass and ameliorates dystrophic pathology in mdx mice

Myostatin is a potent negative regulator of skeletal muscle growth. Therefore, myostatin inhibition offers a novel therapeutic strategy for muscular dystrophy by restoring skeletal muscle mass and suppressing the progression of muscle degeneration. The known myostatin inhibitors include myostatin propeptide, follistatin, follistatin‐related proteins, and myostatin antibodies. Although follistatin shows potent myostatin‐inhibiting activities, it also acts as an efficient inhibitor of activins. Because activins are involved in multiple functions in various organs, their blockade by follistatin would affect multiple tissues other than skeletal muscles. In the present study, we report the characterization of a myostatin inhibitor derived from follistatin, which does not affect activin signaling. The dissociation constants (Kd) of follistatin to activin and myostatin are 1.72 nM and 12.3 nM, respectively. By contrast, the dissociation constants (Kd) of a follistatin‐derived myostatin inhibitor, designated FS I‐I, to activin and myostatin are 64.3 μM and 46.8 nM, respectively. Transgenic mice expressing FS I‐I, under the control of a skeletal muscle‐specific promoter showed increased skeletal muscle mass and strength. Hyperplasia and hypertrophy were both observed. We crossed FS I‐I transgenic mice with mdx mice, a model for Duchenne muscular dystrophy. Notably, the skeletal muscles in the mdx/FS I‐I mice showed enlargement and reduced cell infiltration. Muscle strength is also recovered in the mdx/FS I‐I mice. These results indicate that myostatin blockade by FS I‐I has a therapeutic potential for muscular dystrophy.—Nakatani, M., Takehara, Y., Sugino, H., Matsumoto, M., Hashimoto, O., Hasegawa, Y., Murakami, T., Uezumi, A., Takeda, S., Noji, S., Sunada, Y., Tsuchida, K. Transgenic expression of a myostatin inhibitor derived from follistatin increases skeletal muscle mass and ameliorates dystrophic pathology in mdx mice. FASEB J. 22, 477–487 (2008)

Follistatin induces muscle hypertrophy through satellite cell proliferation and inhibition of both myostatin and activin

Follistatin (FS) inhibits several members of the TGF-beta superfamily, including myostatin (Mstn), a negative regulator of muscle growth. Mstn inhibition by FS represents a potential therapeutic approach of muscle atrophy. The aim of our study was to investigate the mechanisms of the FS-induced muscle hypertrophy. To test the role of satellite cells in the FS effect, we used irradiation to destroy their proliferative capacity. FS overexpression increased the muscle weight by about 37% in control animals, but the increase reached only 20% in irradiated muscle, supporting the role of cell proliferation in the FS-induced hypertrophy. Surprisingly, the muscle hypertrophy caused by FS reached the same magnitude in Mstn-KO as in WT mice, suggesting that Mstn might not be the only ligand of FS involved in the regulation of muscle mass. To assess the role of activin (Act), another FS ligand, in the FS-induced hypertrophy, we electroporated FSI-I, a FS mutant that does not bind Act with high affinity. Whereas FS electroporation increased muscle weight by 32%, the muscle weight gain induced by FSI-I reached only 14%. Furthermore, in Mstn-KO mice, FSI-I overexpression failed to induce hypertrophy, in contrast to FS. Therefore, these results suggest that Act inhibition may contribute to FS-induced hypertrophy. Finally, the role of Act as a regulator of muscle mass was supported by the observation that ActA overexpression induced muscle weight loss (-15%). In conclusion, our results show that satellite cell proliferation and both Mstn and Act inhibition are involved in the FS-induced muscle hypertrophy.

Activin isoforms signal through type I receptor serine/threonine kinase ALK7.

Activins play a fundamental role in cell differentiation and development. Activin A signaling is mediated through a combination of activin type II receptors (ActRIIs) and the activin type IB receptor, ALK4. Signaling receptors of other activin isoforms remain to be elucidated. Here, we found that activin AB and activin B are ligands for ALK7. ALK7 is an orphan receptor serine/threonine kinase expressed in neuroendocrine tissues including pancreatic islets. The combination of ActRIIA and ALK7, preferred by activin AB and activin B but not by activin A, is responsible for activin-mediated secretion of insulin from pancreatic beta cell line, MIN6. In contrast, all activins activate a combination of ActRIIA and ALK4 with various levels of potency. Thus, variation in activin signaling through type I receptors is dependent upon homo- and heterodimeric assembly of activin isoforms. Thus, the differential combination of receptor heterodimers mediates variation in activin isoform signaling.