マウス胸腺における脂肪化および脂肪細胞分化

Abstract

The mouse thymus locates on a position close to the pericardial cavity and consists of two lobes. The lobes surrouded by a capsule are subdivided into many lobules by connective tissue trabeculae. Each lobule consists of lymphocytes-accumulated regions, cortex and medulla. In the previous study, since only lymphocytes in many kinds of thymus-constructing cell expressed the long type leptin receptor (OBRL), it was suggested that thymocytes were regulated with leptin produced by adipocytes differenciated and proliferated through thymic age involution. Then it is naturally interested in studying when lipogenesis and adipogenesis begin in the thymus either in embryogenesis or in postnatal growth. We extracted and measured the quantity of total lipid of the thymus and found that that began to increase at the period of 5 to 8 week-old after birth. The quantity of DNA of the thymus was little changed for this period. Then we directly observed histologically HE-stained sections under light microscope. The small number of adipocytes was observed at surrouding connective tissue, but never found in trabeculae of thymus of neonatal. In 5 week-old thymus adipocytes were first observed in small groups in the trabeculae. Secondly, we detected FGF10,PPARγ and leptin mENA expressions by the RTPCR method as the indication of adipogenesis in the thymus from embryo just before birth to 6 month-old. Both FGF10 and PPARγmRNA were detected in all specimens. The expression of PPARγ is slightly less than that of FGF10 in the embryonic thymus, but with incresing age it incresed and apparently more than that of FGF10 in the 6 moth-old thymus. These results suggest that adipogenesis in the thymus begins just before birth at the latest and that lipogenesis in the thymus does at 5 week-old after birth.