Mitochondria play an essential role in cellular energy metabolism and apoptosis. Previous studies have demonstrated that decreased mitochondrial biogenesis is associated with cancer progression. In mitochondrial biogenesis, peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) regulates the activities of multiple nuclear receptors and transcription factors involved in mitochondrial proliferation. Previously, we showed that overexpression of PGC-1α leads to mitochondrial proliferation and induces apoptosis in human malignant fibrous histiocytoma (MFH) cells in vitro. We also demonstrated that transcutaneous application of carbon dioxide (CO2) to rat skeletal muscle induces PGC-1α expression and causes an increase in mitochondrial proliferation. In this study, we utilized a murine model of human MFH to determine the effect of transcutaneous CO2 exposure on PGC-1α expression, mitochondrial proliferation and cellular apoptosis. PGC-1α expression was evaluated by quantitative real-time PCR, while mitochondrial proliferation was assessed by immunofluorescence staining and the relative copy number of mitochondrial DNA (mtDNA) was assessed by real-time PCR. Immunofluorescence staining and DNA fragmentation assays were used to examine mitochondrial apoptosis. We also evaluated the expression of mitochondrial apoptosis related proteins, such as caspases, cytochorome c and Bax, by immunoblot analysis. We show that transcutaneous application of CO2 induces PGC-1α expression, and increases mitochondrial proliferation and apoptosis of tumor cells, significantly reducing tumor volume. Proteins involved in the mitochondrial apoptotic cascade, including caspase 3 and caspase 9, were elevated in CO2 treated tumors compared to control. We also observed an enrichment of cytochrome c in the cytoplasmic fraction and Bax protein in the mitochondrial fraction of CO2 treated tumors, highlighting the involvement of mitochondria in apoptosis. These data indicate that transcutaneous application of CO2 may represent a novel therapeutic tool in the treatment of human MFH.

A number of studies have reported that decreased mitochondrial numbers are linked with neoplastic transformation and/or tumor progression, including resistance to apoptosis. Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1a) is a multi-functional transcriptional coactivator that regulates the activities of multiple nuclear receptors and transcriptional factors involved in mitochondrial biogenesis. In this study, we observed that the number of mitochondria in sarcoma tissues, such as osteosarcoma and malignant fibrous histiocytoma, is significantly lower than that in normal muscle tissue or benign tumors, and that increasing the number of mitochondria by PGC-1a overexpression induces mitochondrial apoptosis in human sarcoma cell lines. The findings suggest that decreased mitochondrial numbers may contribute to musculoskeletal tumor progression, and that regulation of mitochondrial numbers by PGC-1a could be a potent therapeutic tool for human malignancies.M usculoskeletal malignancies are clinically aggressive and have high metastatic behavior in various organs. Although many chemotherapeutic protocols are used for human sarcomas, the current chemotherapeutic strategies for high-grade sarcomas have been ineffective, and the prognoses of patients can be extremely poor because of local recurrence and distant metastases 1 . Therefore, new therapeutic strategies against high-grade sarcomas need to be established. We have previously reported several therapeutic strategies against high-grade sarcomas [2][3][4] . Mitochondria are cytoplasmic organelles that play essential roles in cellular energy metabolism and programmed cell death 5 . Although the majority of mitochondrial proteins are synthesized by nuclear DNA (nDNA), mitochondria possess their own genome, called mitochondrial DNA (mtDNA) 6 . Thousands of mitochondria are found in each cell, and the number of mitochondria per cell is known to vary with cell or tissue origin, and to change under different internal or external microenvironments, such as hypoxia, and stimulation by steroid hormones 7,8 . Quantitative changes in mitochondrial numbers have been observed in many cancers as a decrease in hepatocellular carcinoma, renal cell carcinoma, advanced gastric cancer and breast cancer [9][10][11][12][13][14] , or an increase in head and neck cancers, ovarian cancer, and esophageal squamous cell carcinoma [15][16][17]

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Background: Tumor hypoxia is a common feature of various human malignancies. Hypoxia contributes to tumor progression, and is a major cause of tumor resistance to chemotherapy. Hypoxia-inducible factor (HIF)-1 is a key transcription factor in hypoxic responses, and regulates the transcription of genes that are involved in crucial aspects of cancer biology, including angiogenesis, cell survival, and invasion. We previously demonstrated that transcutaneous application of carbon dioxide (CO 2 ) induced oxygenation in the treated tissue in vivo, therefore, we hypothesized that transcutaneous CO 2 exposure could enhance the chemosensitivity by reducing hypoxia in a tumor tissue. The aim of this study was to examine the effect of oxygenation by transcutaneous application of CO 2 on the therapeutic efficacy of doxorubicin (DOX) to treat human malignant fibrous histiocytoma (MFH) in vivo. Methods:In this study, we utilized a murine model of human MFH, and mice were randomly divided into four groups: control, CO 2 , DOX and combination (CO 2 + DOX) treatment groups to examine the effect of transcutaneous application of CO 2 on the hypoxic condition, and to assess the therapeutic effect of combination therapy using transcutaneous CO 2 and DOX treatment in vivo.Results: Transcutaneous application of CO 2 treatment decreased HIF-1α expression in human MFH tumor tissues, suggesting that our transcutaneous CO 2 treatment reduced the hypoxic conditions. Furthermore, transcutaneous CO 2 treatment alone had an antitumoral effect, and increased the chemotherapeutic effect of DOX on MFH tumor growth in vivo, with no observable effects on body weight. Conclusions:Our findings in this study strongly indicate that our transcutaneous CO 2 system has antitumor effects and can enhance the chemosensitivity of tumor cells by reducing the local hypoxic conditions.

Waste heat energy could be effectively used if the accumulated thermal energy could be conserved. However, neither typical sensible heat-storage materials such as brick and concrete nor latent heat-storage materials...