Differentiation and Proliferation of Human Osteoblasts

临床上重要的骨丢失是I型骨质疏松症、II型骨质疏松症及其继发性原因的总和。在女性中，最大骨量是在35岁之前达到的，骨小梁丢失的证据在40岁，也就是绝经开始之前就已经很明显了。在绝经后，骨丢失的速度会增加(I型)大约5-10年，在此之后，由于II型骨质疏松症，骨丢失的速度继续下降。在男性中，骨丢失的速度没有女性那么快，它是持续的，完全是由于II型骨质疏松症以及次要原因。对脊椎骨质丢失的纵向研究显示，骨质疏松的速度相对较快，接近女性。骨质疏松症类型之间的区别很明显，但相对重要性不太清楚。如果估计是正确的，那么到90岁时，每3名女性中就有1人患有髋部骨折，而男性的这一比例为1/6。75岁以上男性髋部骨折的死亡率为30%，是女性报告死亡率的三倍。因此，II型骨质疏松症是一个非常重要的公共卫生问题，不仅对男性的健康寿命有影响，而且对女性也有附加作用。在这种骨丢失的情况下，破骨活性正常到轻微降低，同时骨形成能力也大大降低。这种形式的骨质疏松症被认为是由成骨细胞活性/功能降低引起的，并被归因于各种因素，如这些细胞在所需部位的招募、增殖和分化不足，以及其他与年龄相关的过程导致的环境变化。研究表明，编码骨钙素转录因子(只在成骨细胞中表达的基因)OSF2/Cbfal的基因已经失活，小鼠没有骨形成。我们在这里提出的假设是，随着成骨细胞的衰老，细胞衰老导致的分化功能缺陷和/或增殖能力下降，并导致年龄相关性骨质疏松症。我们将通过检测OSF2/Cbfal的表达，年轻和老年供者骨组织中衰老相关基因的表达，以及骨来源的成骨细胞中这些基因的增殖能力来测试这一点。我们还将确定成骨细胞是否可以在体内移植模型系统中形成组织。结果将提供初步数据和证据，表明我们可以为R01提案执行这些技术。

Clinically important bone loss is a sum of Type I osteoporosis, Type II osteoporosis and the secondary causes. In women, maximum bone mass is attained before age 35 and evidence of trabecular bone loss is already apparent at age 40, before the onset of menopause. During the post- menopausal period, the rate of bone loss is increased (Type I) for approximately 5-10 years, and after this period, bone loss continues at a decreased rate due to Type II osteoporosis. In men, the rate of bone loss is not as rapid as that of women, it is persistent and due solely to Type II osteoporosis as well as secondary causes. Longitudinal studies of vertebral bone loss reveal relatively rapid rates of osteoporosis, approaching that seen in women. The differences between the types of osteoporosis is clear but the relative importance is less clear. If estimates are correct then 1 in every 3 women will have had a hip fracture by age ninety compared to 1 in 6 men. The mortality associated with hip fracture in men aged greater than 75 years is 30%, triple that reported for women. Therefore Type II osteoporosis is a very important public health issue, not only for the impact on the healthspan of men, but also for the additive role it plays in women as well. In this condition of bone loss there is normal to slightly decreased osteoclastic activity in conjunction with greatly decreased bone forming ability. This form of osteoporosis is thought to be caused by decreased osteoblast activity/function and has been attributed to various factors such as deficits in recruitment, proliferation and differentiation of these cells at needed sites, as well as changes in the milieu as a result of other age- related processes. It has been shown that there is no bone formation in mice in which the gene encoding the transcription factor for osteocalcin (a gene expressed only in osteoblasts) OSF2/Cbfal has been inactivated. We here propose to test the hypothesis that deficits in differentiated function and/or decreased proliferative ability due to cell senescence occurs with aging in osteoblast cells and contributes to age related osteoporosis. We will test this by determining OSF2/Cbfal expression, and expression of senescence related genes in bone tissue from young and old donors and proliferation potential as well as expression of these genes in osteoblasts derived from the bone. We will also determine whether osteoblasts can form tissue in a transplatation model system in vivo. The results will provide the preliminary data and evidence that we can perform these techniques for an R01 proposal.