Origin and development of septoclasts in endochondral ossification of mice.

Septoclasts are mononuclear spindle-shaped phagocytes with their long processes in uncalcified cartilage matrices and locate adjacent to the capillary endothelium at the chondro-osseous junction of the growth plate. We have previously revealed a selective expression of epidermal-type fatty acid-binding protein (E-FABP/FABP5) in septoclasts. Although, pericytes are known to distribute along capillaries and directly surround their endothelial cells in a situation similar to septoclasts, no clear evidence is available on the relationship between septoclasts and pericytes. We investigated the chronological localization and morphological change of septoclasts during development of the tibia of mice to clarify the development of septoclasts and the immune-localization of pericyte markers in septoclasts to clarify the origin of septoclasts. E-FABP-immunoreactive septoclasts emerged at the perichondrium in the middle of the cartilaginous templates of the tibia in prenatal development. Septoclasts migrated to the surface of the cartilage adjacent to invading blood vessels. Processes of septoclasts became longer and their apexes attached to Von Kossa-negative uncalcified matrices during the formation process of the primary ossification center. Not only platelet-derived growth factor receptor beta, but also neuron-glial antigen 2 was localized in septoclasts of mice from E15 (embryonic day 15) to P6w (postnatal 6 week). Our results suggest that septoclasts are originated from pericytes and involved in the blood vessel invasion during formation of the primary ossification center.

Retinoic acid regulates cell-shape and -death of E-FABP (FABP5)-immunoreactive septoclasts in the growth plate cartilage of mice.

Septoclasts, which are mononuclear and spindle-shaped cells with many processes, have been considered to resorb the transverse septa of the growth plate (GP) cartilage at the chondro-osseous junction (COJ). We previously reported the expression of epidermal-type fatty acid-binding protein (E-FABP, FABP5) and localization of peroxisome proliferator-activated receptor (PPAR)ß/δ, which mediates the cell survival or proliferation, in septoclasts. On the other hand, retinoic acid (RA) can bind to E-FABP and is stored abundantly in the GP cartilage. From these information, it is possible to hypothesize that RA in the GP is incorporated into septoclasts during the cartilage resorption and regulates the growth and/or death of septoclasts. To clarify the mechanism of the cartilage resorption induced by RA, we administered an overdose of RA or its precursor vitamin A (VA)-deficient diet to young mice. In mice of both RA excess and VA deficiency, septoclasts decreased in the number and cell size in association with shorter and lesser processes than those in normal mice, suggesting a substantial suppression of resorption by septoclasts in the GP cartilage. Lack of PPARß/δ-expression, TUNEL reaction, RA receptor (RAR)ß, and cellular retinoic acid-binding protein (CRABP)-II were induced in E-FABP-positive septoclasts under RA excess, suggesting the growth arrest/cell-death of septoclasts, whereas cartilage-derived retinoic acid-sensitive protein (CD-RAP) inducing the cell growth arrest or morphological changes was induced in septoclasts under VA deficiency. These results support and do not conflict with our hypothesis, suggesting that endogenous RA in the GP is possibly incorporated in septoclasts and utilized to regulate the activity of septoclasts resorbing the GP cartilage.

Synergism between α-mangostin and TRAIL induces apoptosis in squamous cell carcinoma of the oral cavity through the mitochondrial pathway.

Mangosteen (Garcinia mangostana) is a tree found in South-East Asia and the pericarp of its fruit has been used in folk medicine for the treatment of many human illnesses. Mangosteen fruit rinds contain a high concentration of xanthone, which is a type of polyphenol. One type of xanthone, α-mangostin, has been reported to exert chemopreventive effects against chemically-induced colon cancer through the decrease of c-Myc expression, suppressing tumor growth in a mouse model of mammary cancer. A recent study demonstrated the inhibitive effect of α-mangostin on the growth of prostate cancer. However, it remains unclear whether α-mangostin induces cell death in oral cancer. The present study examined the impact of α-mangostin on human oral squamous cell carcinoma (HOSCC). Firstly we analyzed the expression of c-Myc in five HOSCC cell lines. The highest expression level of c-Myc mRNA was observed in SAS cells and the lowest in HSC-4 cells. Therefore, SAS cells were treated with α-mangostin, which was found to exert a weak cytocidal effect. Since α-mangostin has been reported to exert synergistic effects on cancers when combined with anticancer drugs, we attempted to evaluate such synergistic effects of α-mangostin when used with a cytokine, tumor necrosis factor (TNF)-related apoptosis­inducing ligand (TRAIL). We found that the combination of α-mangostin with TRAIL induced apoptosis of SAS cells through the mitochondrial pathway via activation of caspase-9 and -3/7, following release of cytochrome c. This apoptosis was induced by S/G2/M-phase arrest. Immunopositivity for c-Myc was observed in the cytoplasm of tumor cells in 16 (40%) of the 40 cases of HOSCC. These data revealed that the combination of α-mangostin and TRAIL may have a considerable potential for the treatment of oral cancer.