Mitochondrial metabolism and bone formation

我们的长期目标是了解线粒体代谢在骨生理学中的作用和调控 和病理不像其他领域，如心血管和肌肉生理学和神经科学，到目前为止， 很少有人致力于骨骼领域的线粒体研究。这是一个巨大的 知识差距和开发新的骨病理学靶向策略的关键障碍， 例如已知与线粒体功能障碍相关的衰老和创伤。这也给 这对我们的计划具有特殊意义。我们的目标是确定 在骨髓基质细胞（BMSC， a.k.a.骨髓间充质干细胞）和测试，如果策略旨在改善线粒体代谢， Lism刺激OB分化和骨形成。我们公布的和新的未公布的数据表明， 在成骨细胞分化过程中，线粒体融合成一个网络，这是一种已知的使成骨细胞的保真度最大化的现象。 氧化磷酸化（OxPhos）。活性OxPhos的危险副产品是氧化应激， 线粒体通透性转换孔（MPTP）的开口。MPTP开放损害mito- 完整性和功能。亲环素D（CypD）是MPTP的关键正调控因子。因此， 对于经历向氧化代谢转变的细胞，例如BMSC分化成OB，以使其转化为氧化代谢。 CypD/MPTP。我们确实发现，随着线粒体在成骨细胞分化过程中融合和活化， CypD在mRNA水平下调，确保对氧化应激的保护并支持OxPhos 和OB计划的进展。此外，我们的数据表明敲除（KO）小鼠中CypD基因缺失 或药理学抑制在支持OB氧化和骨形成功能方面特别有效， 病理性压力，如衰老和骨折。我们最近报道，CypD KO小鼠受到很好的保护， 对抗衰老过程中的骨质流失这与文献显示的脑、心脏和肾组织的变化一致。 CypD K 0小鼠被保护免于老化或缺血性损伤中的退化。所有这些都让我们假设 线粒体融合和CypD下调导致OxPhos的激活和MPTP的抑制， 在成骨细胞分化过程中，为了验证这一假设并实现我们的目标，我们将： 1)描述了在OB分化过程中线粒体被激活的机制，重点是线粒体- 2）描述CypD/MPTP在OB分化过程中的作用和调节; 3）评估 将CypD作为治疗靶点，以改善骨折愈合和衰老中的骨形成。这些研究将 全面了解OB分化过程中线粒体代谢的调节， 开发新的骨靶向治疗策略的基本原理。

Our long-term goal is to understand the role and regulation of mitochondrial metabolism in bone physiology and pathology. Unlike other fields, such as cardiovascular and muscle physiology and neuroscience, to date very little effort has been directed towards mitochondrial research in the bone field. This presents an immense knowledge gap and a critical barrier to developing novel mitochondria-targeted strategies for bone pathologies, such as aging and trauma which are known to be associated with mitochondrial dysfunction. This also gives special significance to our mitochondria-centered proposal. Our objective here is to determine the mechanism controlling mitochondrial activity during osteoblastic (OB) differentiation of bone marrow stromal cells (BMSC, a.k.a. bone marrow mesenchymal stem cells) and test if strategies aimed at improving mitochondrial metabo- lism stimulate OB differentiation and bone formation. Our published and new unpublished data indicate that during OB differentiation, mitochondria fuse into a network, a phenomenon known to maximize the fidelity for oxidative phosphorylation (OxPhos). A dangerous byproduct of active OxPhos is oxidative stress which pro- motes opening of a large Mitochondrial Permeability Transition Pore (MPTP). MPTP opening impairs mito- chondrial integrity and function. Cyclophilin D (CypD) is a key positive regulator of MPTP. It is, thus beneficial for cells undergoing a shift towards oxidative metabolism, e.g. BMSCs differentiating into OBs, to inactivate CypD/MPTP. We indeed found that as mitochondria become fused and activated during OB differentiation, CypD is downregulated at the mRNA level ensuring protection against oxidative stress and supporting OxPhos and progression of OB program. Moreover, our data indicate that CypD genetic deletion in knockout (KO) mice or pharmacological inhibition is especially efficient in supporting OB oxidative and bone forming function under pathological stress, such as in aging and fracture. We recently reported that CypD KO mice are well protected against bone loss in aging. This is consistent with the literature showing that brain, heart, and kidney tissues of CypD KO mice are protected against degeneration in aging or ischemic injury. All this led us to hypothesize that mitochondrial fusion and CypD downregulation leading to activation of OxPhos and inhibition of MPTP dur- ing OB differentiation, are critical for OB differentiation. To test this hypothesis and fulfill our objective, we will: 1) characterize the mechanism by which mitochondria are activated during OB differentiation focusing on mito- chondrial fusion; 2) characterize the role and regulation of CypD/MPTP during OB differentiation; and 3) evalu- ate CypD as a therapeutic target to improve bone formation in fracture healing and aging. These studies will provide comprehensive understanding of regulation of mitochondrial metabolism during OB differentiation and a rationale for developing new mitochondria-targeted therapeutic strategies in bone.