Mechanisms of Age-Related Skeletal Resistance to BMP-7 and IGF-I

描述（由申请人提供）：骨形态发生蛋白（BMPs）在几种治疗环境中作为骨合成代谢剂显示出巨大的前景。最重要的潜在临床应用之一是治疗与年龄有关的骨质疏松症。然而，BMP治疗老年性骨质疏松症和相关骨折的效用可能受到老年骨骼中BMP成骨作用的阻力的限制。因此，了解年龄相关的bmp抵抗机制对于恢复老年人骨合成代谢作用敏感性和/或克服抵抗策略的成功至关重要。我们和其他人的研究表明，BMP-2和BMP-7这两种研究最广泛的bmp通过激活IGF-1信号通路来刺激成骨细胞分化。然而，研究还表明，老年动物的骨祖细胞可能对IGF-1的骨合成代谢作用产生抗性，这是由于IGF-1刺激的IGF-1受体磷酸化减少，下游信号通路（包括PI3K/Akt和ERK）的激活减少。我们和其他人发现，通过PKC异构体PKD传递BMP信号可能是刺激成骨细胞分化的IGF-1信号通路中的一个组成部分。根据我们的初步研究表明，来自老年野生型小鼠和来自年轻和老年IGF-1受体杂合小鼠的骨髓基质细胞（BMSC）可能对BMP-7具有抗性，我们假设来自老年小鼠的骨髓基质细胞对BMP-7激活的PI3K/Akt/PKD信号通路以及其他IGF-1信号通路具有抗性。为了验证这一假设，我们建议首先全面检查衰老小鼠BMSC中IGF-1R、PI3K/Akt/PKD和ERK通路对BMP-7活化的抗性。我们将通过对年轻野生型小鼠细胞中的IGF-1R进行RNA沉默，以及在老年野生型小鼠和年轻和老年Igf1r小鼠细胞中表达构成活性形式的IGF-1R和下游效应分子，并分别确定它们是否能抑制和促进成骨细胞分化，从而严格检验这些途径对BMP-7刺激的抵抗是BMSC对BMP-7分化作用的基础。在我们的第二个具体目标中，我们将通过确定年轻的IGF-1受体杂合小鼠和老年野生型小鼠是否对BMP-7的异位成骨作用产生抗性，将这些发现转化为体内环境。我们还将确定IGF-1受体单倍体不足是否会加剧与年龄相关的对BMP-7诱导的骨形成的抵抗。成功的结果将为未来的研究提供基础，旨在通过表达活性形式的IGF-1信号中间体来挽救体内年龄相关的bmp抗性。这些结果可能导致骨质疏松症治疗新模式的发展。

DESCRIPTION (provided by applicant): Bone Morphogenetic proteins (BMPs) show great promise as bone anabolic agents in several therapeutic settings. One of the most important potential clinical applications is in the treatment of age-related osteoporosis. However, the utility of BMP treatment of age-related osteoporosis and related fractures may be limited by resistance to the bone forming actions of BMPs in the aged skeleton. Thus, understanding the mechanisms of age-related resistance to BMPs is critical to the success of strategies aimed at restoring sensitivity and/or overcoming resistance to bone anabolic action in the aged. Our work and that of others indicates that BMP-2 and BMP-7, the two most widely studied BMPs, stimulate osteoblastic differentiation by activating IGF-1 signaling pathways. However, studies also indicated that osteoprogenitor cells from aged animals may be resistant to the bone anabolic effects of IGF-1 due to reduced IGF-1 stimulated IGF-1 receptor phosphorylation and reduced activation of downstream signaling pathways including PI3K/Akt and ERK. We and others have found that BMP signaling via the PKC isoform PKD may be a component in the IGF-1 signaling pathway that stimulates osteoblastic differentiation. Based on our preliminary studies indicating that bone marrow stromal cells (BMSC) from aged wild-type mice and from young and old IGF-1 receptor heterozygous mice may be resistant to BMP-7, we hypothesize that BMSC from aged mice are resistant to BMP-7 activation of PI3K/Akt/PKD signaling and possibly other IGF-1 signaling pathways. We propose to test this hypothesis by first comprehensively examining the IGF-1R, PI3K/Akt/PKD and ERK pathways for resistance to BMP-7 activation in BMSC from aged mice. We will critically test the hypothesis that resistance of these pathways to BMP-7 stimulation underlies the resistance of BMSC to the differentiating effect of BMP-7 by conducting RNA silencing of the IGF-1R in cells from young wild-type mice and by expressing constitutively active forms of the IGF-1R and downstream effector molecules in cells from aged wild-type and young and aged Igf1r mice and determining whether they can inhibit and promote osteoblastic differentiation, respectively. In our second specific aim we will translate these findings to the in-vivo setting by determining whether young IGF-1 receptor heterozygous mice and old wild-type mice are resistant to the ectopic bone forming action of BMP-7. We will also determine whether IGF-1 receptor haplo-insufficiency exacerbates age-related resistance to BMP-7 induced bone formation. Successful outcomes will provide the basis for future studies designed to rescue in vivo age-related resistance to BMPs by expressing active forms of IGF-1 signaling intermediates. These results could lead to the development of new therapeutic modes for treating osteoporosis. PUBLIC HEALTH RELEVANCE: Age related osteoporosis is a major cause of debilitation and morbidity in the gerontological population. The goal of the current study is to provide a molecular basis for the development of novel therapeutic agents that will treat age related osteoporosis by activating signal transduction pathways used by bone anabolic agents.