Mechanosensitivity of osteoporotic stem cells for diagnosis and treatment of osteoporosis

骨质疏松症是人类最常见的骨骼疾病，影响超过四分之一的50岁以上的人。这种情况主要影响绝经后妇女，在英国每年有超过500，000例脆性相关骨折。日常活动导致的骨折风险增加，是我们老龄化人口面临的一个重大挑战。目前的药物治疗选择，如双膦酸盐，被证明不足以提供长期的骨折保护。为了确保老年人的骨骼健康，需要新的治疗方式，这为生物工程策略提供了机会。机械负荷是维持骨骼健康的关键因素。骨密度的稳态是成骨细胞和破骨细胞活性平衡的结果，两者都是机械敏感的。缺乏负荷（例如，在零g航天飞行或长期卧床期间）已被证明会导致骨吸收增加和骨密度损失。在与年龄相关的骨质疏松症中，这种疾病不一定是由于缺乏负荷本身，但可能是骨细胞对机械信号的反应不足。因此，由此产生的一个假设是，骨质疏松症直接导致改变mechanotransductive信号机制在cellularlevel.Prior研究集中在体外机械刺激细胞的方法，如使用纳米振幅振动。某些振动参数（1 kHz，30 nm振幅）的使用已显示出对源自骨髓和脂肪组织的成体间充质干细胞（MSC）的有效成骨刺激。这种刺激方法包括通过ROCK信号传导和机械敏感性离子通道激活机械转导途径，其对振动幅度具有潜在依赖性。该过程通过增加肌动蛋白-肌球蛋白收缩性改变粘着斑构象并增加细胞张力，还可能改变通过体外技术（例如AFM、细胞变形）测量的细胞机械性质。在MSC的情况下，这导致向高收缩性成骨细胞表型和增加的矿化分化，而不依赖于成骨试剂或生长因子。然而，健康和老年/骨质疏松MSC之间的机械转导反应的差异还有待研究。除了体外细胞刺激研究，可以直接向患者施加纳米振动的可穿戴设备的开发已经开始。在这项技术可以应用于骨质疏松症的临床挑战之前，需要进一步了解与骨髓腔内的健康成骨细胞相比，骨质疏松骨细胞的机械转导反应。此外，对于患病状态下的骨细胞，可能需要重新考虑振动疗法（在持续时间、振幅和频率方面）的合适给药方案的确定。研究不同年龄组大鼠骨髓间充质干细胞在不同水平机械负荷下的表型变化.确定细胞力学特性（例如刚度、变形性）是否可用作骨形成能力和骨质疏松症发作或机械传导信号减少的诊断。使用体外数据开发可通过可穿戴振动设备实际应用的治疗纳米振动方案

Osteoporosis is the most common bone disease in humans, affecting over a quarter of people aged 50+ years. The condition predominantly affects post-menopausal women and results in over 500,000 fragility related fractures p/a within the UK. The elevated fracture risk from everyday activities, due to weakened bones, is a major challenge for our aging population. Current pharmaceutical treatment options, such as bisphosphonates, are proving insufficient to provide long term fracture protection. To ensure bone health into older age, new treatment modalities are required, representing an opportunity for bioengineering strategies. Mechanical loading is a key factor in maintaining bone health. Homeostasis of bone density is a result of balance in the activities of osteoblasts and osteoclasts, which are both mechanically sensitive. A lack of loading (e.g. during zero-g spaceflight or extended bed rest) has been show to result in increased bone resorption and a loss of bone density. In age-related osteoporosis, the disease is not necessarily due to a lack of loading per se, but can be a failure of bone cells to respond sufficiently to mechanical signals. Therefore, one resulting hypothesis is that osteoporosis directly results from altered mechanotransductive signalling mechanisms at the cellular level.Prior research has focussed on methods of mechanically stimulating cells in vitro, such as the use of nanoamplitude vibration. The use of certain vibration parameters (1 kHz, 30 nm amplitude) has shown effective osteogenic stimulation of adult mesenchymal stem cells (MSCs) derived from bone marrow and adipose tissue. This stimulation method includes activation of mechanotransductive pathways via ROCK signalling and mechanosensitive ion channels with a potential dependence on vibration amplitude. The process alters focal adhesion conformation and increases cellular tension through increased actin-myosin contractility, potentially also changing cellular mechanical properties as measured by in vitro techniques (e.g. AFM, cell deformation). In the case of MSCs, this leads to differentiation towards a high contractility osteoblastic phenotype and increased mineralisation, without recourse to osteogenic reagents or growth factors. However, the differences in mechanotransductive response between healthy and aged/osteoporotic MSCs are yet to be studied. Alongside in vitro cell stimulation studies, development of wearable devices which can apply nanovibration directly to patients has begun. Before this technology can be applied to the clinical challenge of osteoporosis, there needs to be further understanding of the mechanotransductive response of osteoporotic bone cells compared to healthy osteogenic cells residing within the bone marrow cavity. In addition, the identification of suitable administration options for a vibrational therapy (in terms of duration, amplitude and frequency) may need to be reconsidered for bone cells in the diseased state.RESEARCH OBJECTIVES1. To study phenotypic changes of osteoporotic stem cells under various levels of mechanical loading across different age groups.2. To determine if cellular mechanical properties (e.g. stiffness, deformability) could be used as a diagnostic of bone forming capacity and onset of osteoporosis or reduced mechanotransductive signalling.3. Use in vitro data to develop therapeutic nanovibration protocols which could be applied practically via wearable vibration devices