Unravelling the mechanisms of transcriptional dysregulation in spinal and bulbar muscular atrophy

脊髓延髓肌萎缩症（SBMA）是一种影响全球成年男性的神经肌肉疾病，可导致进行性但无法治疗的运动功能障碍和严重残疾。我的小组和其他人以前的研究表明，骨骼肌在这种疾病中主要受到影响，专门针对恢复肌肉萎缩的治疗足以挽救动物模型中的疾病表型。SBMA是由雄激素受体（AR）突变引起的，雄激素受体是一种蛋白质，对保持骨骼肌年轻和强壮至关重要，其功能是结合DNA并打开或关闭特定基因。像AR这样的蛋白质被称为“转录因子”。这种转录因子如何发挥这种作用以及为什么SBMA中的肌肉变得虚弱和萎缩是关键的未回答和相互关联的问题：对健康和疾病中控制肌肉功能的这些机制缺乏了解正是SBMA患者和大多数以骨骼肌损失为特征的疾病尚无治疗方法的原因。在这个奖学金的过程中，我的计划是了解SBMA突变如何劫持AR指示细胞的能力（即协调转录），导致肌肉萎缩和虚弱。为了实现这一目标，我们将使用相关的疾病模型，例如来自患者的骨骼肌细胞和肌肉活检，这是生成有意义数据的关键，并采用最先进的分子生物学工具，可以研究这些非常具体的功能。特别是，我们最近在实验室建立了一种强大的创新显微镜技术，称为单分子跟踪，它可以在活细胞中以高分辨率研究转录因子的动态，提供有关这些蛋白质在其自身环境中的扩散和结合行为的重要信息。这项研究最令人兴奋的是其潜在的治疗影响。使用遗传方法来增强或抑制AR调节转录的能力，我们的目的是测试突变体AR转录活性的恢复是否足以治疗SBMA。为了进行这些实验，我们设计了一个在3D束（muscle-on-a-chip）中生长肌肉的平台，它概括了肌肉的结构和结构复杂性，有效地代表了体外骨骼肌的复制品。最后，将在SBMA小鼠模型中对关键发现进行体内功能验证。通过在人类和模型系统中应用这些创新和完全整合的细胞和分子生物学技术，这些研究将在理解疾病机制方面取得实质性进展，并提供靶向转录活性作为SBMA和其他以骨骼肌损失为特征的疾病的治疗策略的原理性证据。

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease affecting adult males worldwide, resulting in progressive and yet untreatable motor dysfunction and severe disability. Previous studies from my group and others have shown that skeletal muscle is primarily affected in this disease and therapies exclusively directed at restoring the muscle atrophy are sufficient to rescue the disease phenotype in animal models. SBMA is caused by mutations in the Androgen Receptor (AR), a protein that is critical in maintaining skeletal muscle young and strong and whose functions is to bind DNA and turn specific genes on or off. Proteins like AR are called 'Transcription Factors'. How this transcription factor exerts such effects and why muscles become weak and atrophic in SBMA are key unanswered and interconnected questions: such lack of understanding of these mechanisms of control of muscle function in health and disease is precisely the reason why no treatments are yet available for SBMA patients and, as a matter of fact, for most diseases characterised by skeletal muscle loss. During the course of this Fellowship, my plan is to understand how the SBMA mutation hijacks AR ability to instruct the cell (i.e. coordinate transcription), leading to muscle atrophy and weakness. To achieve this goal, we will use relevant disease models, such as skeletal muscle cells and muscle biopsies derived from patients, which is key to generate meaningful data, and employ state-of-the-art molecular biology tools which allow the investigation of these very specific functions. In particular, we have recently set up in the lab a powerful and innovative microscopy technique, called single-molecule tracking, which enables the study of transcription factor dynamics in living cells and at high resolution, giving important information regarding the diffusion and binding behaviour of these proteins in their own environment.What's most exciting about this research is its potential for therapeutic impact. Using genetic approaches to either enhance or suppress AR ability to regulate transcription, we aim to test whether restoration of mutant AR transcriptional activity is sufficient to treat SBMA. To perform these experiments, we have devised a platform to grow muscle in a 3D bundle (muscle-on-a-chip), which recapitulates the architectural and structural complexities of muscle, effectively representing a replica of skeletal muscle outside of the body. Lastly, key findings will be functionally validated in vivo in a SBMA mouse model. Through application of these innovative and fully integrated cell and molecular biology techniques in humans and model systems, these studies will provide a substantial advancement in the understanding of the mechanisms of disease and provide proof-of-principle evidence of targeting transcriptional activity as a treatment strategy for SBMA and other diseases characterized by skeletal muscle loss.