Investigation of mechanism of bone formation associated with aging

1)大鼠骨组织中骨基质蛋白mRNA的增龄性减少采用不脱钙骨切片原位杂交的方法，分析单个成骨细胞中骨基质蛋白mRNA表达的增龄性变化。在8周龄雄性大鼠股骨，I型胶原和骨钙素的mRNAs在骨表面的立方成骨细胞中有较强的表达。在骨吸收表面的部分单核细胞和破骨细胞中检测到骨桥蛋白基因的表达。在60周龄和100周龄雄性大鼠股骨中，这些骨基质蛋白mRNAs的表达显著减少。老年大鼠骨髓中骨祖细胞的特性为了探讨与衰老相关的骨丢失的机制，我们检测了大鼠骨髓细胞的特性，包括含有骨祖细胞的集落形成单位-成纤维细胞(CFU-F)。结果表明：1)小鼠骨髓细胞碱性磷酸酶(ALP)活性和甲状旁腺激素反应随增龄而降低。2)CFU-F总数和ALP阳性CFU-F数均随年龄增长而减少。3)从4周龄大鼠体内分离的10个CFU-F中，有9个在扩散腔中移植到大鼠的腹膜腔内形成了骨样组织。然而，从60周龄大鼠分离的6个CFU-F中，只有3个形成了骨样组织。这些结果表明，骨祖细胞数量的减少至少部分参与了老年性骨质疏松症的发病机制。

To investigate the mechanism involved in the changes in bone tissues associated with aging, we conducted the following experiments.1)Age-related reduction in bone matrix protein mRNA in rat bone tissueAge-related changes in the expression of bone matrix protein mRNAs in individual osteoblastic cells were analyzed in vivo by in situ hybridization using undecalcified bone sections. In the femurs of 8-week-old male rats, strong expression of type I collagen and osteocalcin mRNAs was detected in cuboidal osteoblasts on the bone surface. Osteopontin mRNA was detected in some of the mononuclear cells and osteoclasts on the bone resorption surface. In the femurs of 60-week-old and 100-week-old male rats, expression these bone matrix protein mRNAs was markedly decreased. These results indicate age-related reductions in both biological activity and numbers of osteoblasts.Properties of osteoprogenitor cells in bone marrow of aged ratsTo investigate the mechanism of bone loss associated woth aging, we examined the properties of rat bone marrow cells including Colony Forming Unit-Fibroblastic (CFU-F) which contains osteoprogenitor cells. The following results were obtained.1)Both alkaline phosphatase (ALP) activity and parathyroid hormone response in bone marrow cells were decreased with age. 2) Both the total number of CFU-F and the ALP-positive CFU-F were decreased with age. 3) Nine out of 10 CFU-Fs isolated from 4-week-old rats form bone-like tissues when they were transplanted into rat peritoneal cavity using diffusion chambers. However, only 3 out of 6 CFU-Fs isolated from 60-week-old rats form bone-like tissues. These results suggest that decrease in number of osteoprogenitor cells is involed, at least in part, in the mechanizm of senile osteoporosis.