| Budget Amount *help |
¥3,850,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥450,000)
Fiscal Year 2007: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2006: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Osteocytes are thought to play crucial roles in bone metabolism, although limited information has been available on their specific products and physiological function. To isolate genes expressed in osteocytes, we employed subtractive suppression PCR method using RNA from osteocyte-enriched bone fraction. A genes isolated by the method encodes a novel enzyme involved in phospholipid metabolism, which has been found as a sphingomyelin synthase(SMS2 : Huitema, et. al.(2004) ; Yamaoka, et. al.(2004)). To determine the expression of Sms2 in vivo, LacZ gene was introduced into mouse Sms2 locus to monitor the expression of Sms2. At E13.5, the expression, as monitored by X-gal staining, was detected only in skeletal elements, especially in the areas enriched in osteoblasts. The expression was observed not only in osteoblasts but also in osteocytes of E16.5 embryo. Sms2 was expressed in some differentiated chondrocytes of long bones, but not detected in rib or articular cartilages which remain uncalcified. In adult, although the expression was detected in non-skeletal tissues, it is markedly expressed in osteocytes. It has been reported that sphingomyelinase activity was detected in matrix vesicles, which play a pivotal role in matrix mineralization, and that sphingomyelin was hydrolyzed upon mineralization. Furthermore, mice carrying mutations in SmpdS, a gene encoding neutral sphingomyelinase, exhibited skeletal malformation and delayed calcification. Indeed, it prompted us to hypothesize that sphingomyelin may have some inhibitory effects on mineralization. In fact, when Sms2 gene was overexpressed in osteoblasts, mineralization was significantly suppressed. Thus, Sms2 may play a role in terminal differentiation of osteoblast and/or matrix mineralization in bone.
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