| Research Abstract |
Peripheral aromatization of androgens exert estrogenic actions in many tissues. Recently in situ production of estrogens by aromatase was detected in human bone and cultured osteoblasts and has been proposed to participate in maintenance of bone mass. We examined aromatase expression by immunohistochemistry and mRNA in situ hybridization in 16 cases of tibia (male 2, female 14,62 (]SY.+-。[) 5.2 year old) and quantified the level of aromatase mRNA in 28 cases of rib, femur and lumbar vertebrae (16 male, 12 female, 58.0 (]SY.+-。[) 11.3 year old) by reverse transcriptase-polymerase chain reaction (RT-PCR) in order to study whether or not and in which cell types aromatase was expressed in human bone tissues. We also studied alternative use of multiple exons 1 of its gene and immunolocalization of type I 17 beta-hydroxysteroid dehydrogenase (HSD), which converts estrone produced by aromatase to estradiol. Strong aromatase immunoreactivity and mRNA hybridization as well as type I 17beta-HSD immunoreactivity were detected in lining cells, osteoblasts, chondrocytes of articular cartilage and adipocytes adjacent to bone trabeculae in all the cases examined. Amounts of aromatase mRNA varied greatly among the subjects (11.25 (]SY.+-。[) 9.77,0.61 to 42.84 attomole/ng total RNA). The amount of aromatase expression was not correlated with age or sex of the subjects but positively correlated with the degree of osteroporotic changes evaluated by radiological findings of lumbar vertebrae. Analysis of multiple exons 1 revealed that 1b or fibroblasts type was predominantly (23/26) utilized as a promoter of aromatase gene expression. These results demonstrated that aromatase is expressed widely in human bone tissue and may play important roles in maintenance of human bone tissue.
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