The regulation of collagen (I) homotrimer synthesis and its role in musculoskeletal dysfunction

骨关节炎、骨质疏松症和软组织损伤等肌肉骨骼疾病以及组织和器官纤维化造成了巨大的医疗负担，特别是在老龄化人口中。因此，了解异常胶原蛋白（I）合成的调节及其在骨和关节功能中的作用对于开发针对这些使人衰弱的疾病的策略至关重要。胶原蛋白（I型）是体内最丰富的结构蛋白，是骨和关节组织的主要成分。I型胶原形成纤维，包围细胞，使组织对机械负荷有弹性。I型胶原蛋白的天然形式可以通过细胞使用生物酶降解和重组，并且该过程允许骨骼组织适应机械负荷的变化。当组织结构不足以抵抗外部载荷时，可能发生组织损伤，包括骨折和破裂。在一般人群中，这些问题表现为包括骨质疏松症（骨质疏松）、骨关节炎（软骨损失和骨过度生长）和软组织损伤在内的疾病。I型胶原蛋白的过度产生（称为纤维化）进一步限制了组织功能，导致残疾和发病率和死亡率增加。遗传和生物化学研究发现，一种异常形式的I型胶原蛋白，称为胶原蛋白（I）同源三聚体，存在于退行性疾病和纤维化疾病中。这种异常的胶原蛋白改变了胶原蛋白原纤维的生物物理性质，并且对酶促分解具有抗性。因此，胶原蛋白（I）同源三聚体可能影响组织响应变化的机械负荷和抵抗纤维化的能力。本研究的目的是确定是否有相关的胶原（I）mRNA（COL 1A 1和COL 1A 2）水平指导胶原（I）同源三聚体合成，并且如果胶原（I）同源三聚体产生不充分但持久的纤维基质，导致年龄相关的肌肉骨骼疾病和纤维化，或者病理学是否可以解释为胶原蛋白α-1（I）过度产生引起的细胞应激一系列复杂的细胞相互作用通常会导致胶原蛋白（I）异源三聚体，但本项目将测试以下假设：COL 1A 1 mRNA水平的增加会抑制细胞控制异源三聚体合成的能力，并导致异常胶原蛋白（I）的同时产生。同三聚体。细胞包含一个精心设计的控制系统，调节基因活性和蛋白质产生，称为microRNA的小RNA分子似乎特别重要。MicroRNA与mRNA中间体（基因活性和蛋白质产生之间）结合，通常会降低其有效性。已知miR-133靶向COL 1A 1而不是COL 1A 2，并且在几种纤维化中丰度较低。该项目将测试增加或减少miR-133活性如何影响胶原蛋白（I）同源三聚体的合成，并将确定它是否可以成为肌肉骨骼和纤维化疾病的新靶点。同源三聚体影响肌肉骨骼组织将在缺乏COL 1A 2的小鼠中进行硬和软胶原组织中的结构和生物力学改变的综合分析基因初步表型数据（IMPC）表明，这些小鼠有异常的骨形态和软胶原组织的缺陷。将产生胶原（I）同源三聚体沿着有截短的α-2（I）链的良好表征的骨生成Bastata小鼠模型（“oim”）用作对照。明显更严重的oim表型可能由细胞应激引起，因此将在遗传操作的细胞培养物和小鼠组织中评价细胞应激。细胞应激可以被几种药物靶向，因此可能会被降低以帮助治疗这些疾病。

Musculoskeletal diseases such as osteoarthritis, osteoporosis and soft-tissue injuries together with tissue and organ fibrosis impose a huge healthcare burden, particularly in the ageing population. Therefore understanding the regulation of abnormal collagen (I) synthesis and its role in bone and joint function is of critical importance in order to develop strategies to target these debilitating diseases.Collagen (type I) is the most abundant structural protein in the body and is the major component of bone and joint tissues. Type I collagen forms fibres that surround cells and make tissues resilient to mechanical loading. The natural form of type I collagen can be degraded and reformed by cells using biological enzymes and this process allows skeletal tissues to adapt to changes in mechanical loading. When the tissue structure is inadequate to resist external loads, tissue injury including fractures and ruptures can occur. In the general population such problems are manifested as diseases including osteoporosis (weak bone), osteoarthritis (cartilage loss and bone overgrowth) and soft tissue injuries. Over-production of type I collagen (termed fibrosis) furthermore restricts tissue function leading to disability and increased morbidity and mortality. Genetic and biochemical studies have found that an abnormal form of type I collagen, termed collagen (I) homotrimer, is present in both degenerative and fibrotic diseases. This abnormal collagen alters the biophysical properties of collagen fibrils and is resistant to enzymatic breakdown. Collagen (I) homotrimer may therefore affect the ability of tissues to respond to changing mechanical loads and to counteract fibrosis. The aim of this project is to determine whether relative collagen (I) mRNA (COL1A1 and COL1A2) levels direct collagen (I) homotrimer synthesis and if collagen (I) homotrimer produces an inadequate but persistent fibrillar matrix that leads to age-related musculoskeletal disease and fibrosis, or whether pathology could be accounted for by cellular stress caused by over-production of the collagen alpha-1(I) chain.A complex series of cellular interactions normally results in collagen (I) heterotrimer but this project will test the hypothesis that increased levels of the COL1A1 mRNA overwhelms the ability of the cells to control heterotrimer synthesis and results in the concurrent production of abnormal collagen (I) homotrimer. Cells contain an elaborate system of controls that regulate gene activity and protein production and small RNA molecules termed microRNAs appear to be particularly important. MicroRNAs bind to the mRNA intermediates (between gene activity and protein production) often decreasing their effectiveness. miR-133 is known to target COL1A1 rather than COL1A2 and is less abundant in several fibroses. This project will test how increasing or decreasing miR-133 activity affects collagen (I) homotrimer synthesis and will determine whether it could be a novel target for musculoskeletal and fibrotic diseases.To reveal how collagen fibrils containing collagen (I) homotrimer affect musculoskeletal tissues a comprehensive analysis of the structural and biomechanical alterations in hard and soft collagenous tissues will be performed in mice lacking the COL1A2 gene. Preliminary phenotyping data (IMPC) indicates that these mice have abnormal bone morphology and defects in soft collagenous tissues. A well-characterised osteogenesis imperfecta mouse model ('oim') that produces collagen (I) homotrimer along with truncated alpha-2(I) chains will be used as a control. The apparently more severe oim phenotype may result from cellular stress, therefore cellular stress will be evaluated in genetically manipulated cell cultures and mouse tissues. Cellular stress can be targeted by several pharmaceuticals so could potentially be reduced to help treat these diseases.