MECHANICAL FORCES, OSTEOCYTES VAIBILITY, BONE STRENGTH

机械力、骨细胞可用性、骨强度

• 批准号: 7095002
• 负责人: Teresita M. Bellido
• 金额: $ 16.64万
• 依托单位: UNIV OF ARKANSAS FOR MED SCIS
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7095002
• 关键词: aging; animal old age; apoptosis; biological signal transduction; biomechanics; bone density; caveolas; caveolins; cellular pathology; diphosphonate; estrogen receptors; focal adhesion kinase; genetically modified animals; immobilization of body part; laboratory mouse; mechanical stress; mechanoreceptors; metabolism disorder chemotherapy; mitogen activated protein kinase; molecular pathology; osteocytes; osteogenesis; osteoporosis; physiologic bone resorption; skeletal pharmacology

Osteocytes detect the need for mechanical adaptation and microdamage repair and signal to osteoblasts or osteoclasts, leading to bone gain or loss. Although long-lived, osteocytes undergo apoptosis, and their viability contributes to bone strength by mechanisms dependent and independent of changes in bone mineral density. During the preceding funding period, it was found that, similar to hormonal and pharmacological stimuli, mechanical forces regulate osteocyte lifespan. Thus, mechanical stimulation in vitro prevents osteocyte apoptosis via an integrin/Src/ERK pathway that requires the integrity of caveolae and a ligand-independent function of the estrogen receptor (ER). Conversely, reduced mechanical forces in vivo increase osteocyte apoptosis, and this event temporally precedes, and is spatially associated with, osteoclast-mediated resorption and the subsequent loss of mineral and strength. It was also found that during aging bone strength decreases before a reduction in bone mineral density, and osteocyte apoptosis increases. Based on this knowledge, it is proposed that mechanical stimuli trigger ERK-dependent signals that sustain osteocyte survival via a signalsome assembled in caveolae and composed of integrins and signaling molecules, including the ERs. Conversely, diminished mechanical forces?from reduced physical activity with age?eliminate the signals that maintain osteocyte viability, thereby leading to apoptosis. Dying osteocytes in turn recruit osteoclasts to the vicinity. Both mechanisms, disruption of the integrity of the osteocyte network and increased osteoclastic bone resorption, contribute to the age-related decline in bone strength and mass. To validate these hypotheses, in Aim 1 will be defined in vitro the role of the ER and caveolin-1 in ERK-mediated anti-apoptosis induced by mechanical stimulation; and whether other survival signaling pathways act in concert to control osteocyte death. In Aim 2, it will be determined in vivo whether mechanically induced survival signaling is disrupted by unloading and during aging, and established whether unloading- or aging-induced osteoclast-mediated resorption and loss of bone and strength are ameliorated by inhibiting osteocyte apoptosis by 1) constitutively activating the ERK pathway in OG2- MEK-SP mice, 2) overexpressing the anti-apoptotic protein Bcl-2 in DMP1-Bcl2 mice, and 3) treating with a unique bisphosphonate that inhibits osteocyte apoptosis without affecting osteoclasts. In Aim 3, it will be established whether induction of osteocyte apoptosis is sufficient to trigger osteoclast recruitment and whether the kinetics of the osteoclastogenic response to osteocyte apoptosis are altered with aging. These studies will advance our understanding of the mechanistic basis for the profound role of mechanical forces, or lack of thereof, in skeletal health and disease, and will establish the contribution of osteocyte apoptosis to the loss of bone strength that ensues with aging. We expect that this work will provide new avenues for the treatment of bone fragility in conditions of reduced physical activity, such as in the elderly or during the temporary immobilization of bed rest, space flight, and motor paralysis.

骨细胞检测需要机械适应和微型修复以及对成骨细胞或信号的需求 破骨细胞，导致骨获得或损失。虽然寿命长，但骨细胞会经历凋亡及其生存能力 依赖于骨矿物质密度变化的机制来促进骨骼强度。 在上述资金期间，发现与激素和药理刺激类似 机械力调节骨细胞寿命。因此，体外机械刺激可防止骨细胞凋亡 通过整合素/SRC/ERK途径，需要Caveolae的完整性和与配体无关的功能 雌激素受体（ER）。相反，体内的机械力减少增加了骨细胞的凋亡，这 事件在时间上是前面的，并且在空间上与破骨细胞介导的吸收和后续 矿物质和强度的损失。还发现，在衰老期间，骨骼强度降低了 骨矿物质密度和骨细胞凋亡增加。基于这些知识，提议 机械刺激触发ERK依赖性信号，该信号通过组装的信号群维持骨细胞的存活率 口腔，由整合素和信号分子组成，包括ER。相反，减少了 机械力？随着年龄的增长而减少体育活动？消除维持骨细胞的信号 生存能力，从而导致凋亡。垂死的骨细胞反过来募集了附近的骨细胞。两个都 机制，破坏性骨细胞网络的完整性的破坏以及骨质碎屑骨吸收的增加， 有助于与年龄相关的骨骼强度和质量下降。为了验证这些假设，在AIM 1中将是 在体外定义了ER和小窝蛋白-1在机械诱导的ERK介导的抗凋亡中的作用 刺激；以及其他生存信号通路是否共同控制骨细胞死亡。在AIM 2中，它 将在体内确定机械诱导的生存信号传导是否因卸载而破坏 衰老，并确定是否卸载或衰老诱导的破骨细胞介导的吸收和骨骼的丧失 通过1）组成性激活OG2-的ERK途径来改善强度通过抑制骨细胞的凋亡来改善强度。 MEK-SP小鼠，2）在DMP1-BCL2小鼠中过表达抗凋亡蛋白Bcl-2，3）用A 独特的双膦酸盐抑制骨细胞凋亡而不会影响破骨细胞。在AIM 3中，它将是 确定诱导骨细胞凋亡是否足以触发破骨细胞募集以及是否是否 衰老的骨细胞凋亡对骨细胞细胞凋亡的动力学反应的动力学。这些研究会 促进我们对机械作用或缺乏力量作用的机械基础的理解， 在骨骼健康和疾病中，将建立骨细胞凋亡对骨骼丧失的贡献 随着衰老而随之而来的力量。我们预计这项工作将为骨骼的治疗提供新的途径 在体育锻炼减少的条件下，例如老年人或暂时固定期间的脆弱性 床休息，太空飞行和运动麻痹。