Inhibitors of BMP-1/TLD proteases as novel therapeutics for muscular dystrophy

描述（由申请人提供）：肌生长抑制素（MSTN）是一种分泌蛋白，通常作用于抑制肌肉生长。由于肌纤维肥大和纤维数量增加的共同作用，经过基因工程改造而缺乏MSTN活性的小鼠肌肉质量显著增加。此外，对野生型小鼠使用多种不同的MSTN抑制剂也可以促进肌肉生长，这表明MSTN在调节成年动物肌肉生长中起着关键作用。因此，人们对MSTN信号抑制剂可能有效增强肌肉退行性疾病患者的肌肉力量和再生的可能性非常感兴趣。在MSTN前体蛋白加工后，成熟的c端二聚体仍然与n端前肽非共价结合，这使MSTN处于无活性的潜伏状态。各种生物化学和遗传学研究表明，BMP-1/tolloid金属蛋白酶家族成员通过切割并使前肽失活，在调节MSTN潜伏期中发挥关键作用。因此，抑制这些蛋白酶可能是一种有效的治疗策略，以防止潜在MSTN的激活，从而促进肌肉生长。此外，靶向这些蛋白酶的潜在益处可能远远超出MSTN抑制，因为已知这些蛋白酶还作用于MSTN之外的其他底物，这些底物可能在肌肉退行性疾病中发挥作用。特别是，这些蛋白酶能够切割TGF-ss结合蛋白LTBP-1，从而使TGF-ss从潜伏状态激活，鉴于抑制TGF-ss信号传导已被证明可以改善mdx小鼠的肌肉再生，这可能对治疗发展具有重要意义。此外，BMP-1/tolloid蛋白酶似乎是负责将前胶原加工成能够形成胶原原纤维的成熟物种的酶，这提高了这些酶可能在各种疾病情况下纤维化的发展中发挥作用的可能性。因此，BMP-1/tolloid蛋白酶抑制剂有潜力通过靶向几种不同的分子途径为肌肉退行性疾病患者提供临床益处。该项目的总体目标是验证在肌肉变性的情况下抑制BMP-1/tolloid蛋白酶的有益作用，并启动能够靶向这些酶的生物制剂的开发。具体目的是：评估在mdx小鼠中靶向BMP-1/tolloid metalloproteases的潜在有益效果，并确定BMP-1/tolloid inhibitor sFRP2在骨骼肌中作为转基因表达或全身给药时是否可以促进肌肉生长。如果成功，这些研究将确定一种新的治疗药物，具有促进肌肉生长和改善肌肉萎缩症患者临床结果的潜力。

DESCRIPTION (provided by applicant): Myostatin (MSTN) is a secreted protein that normally acts to suppress muscle growth. Mice genetically engineered to lack MSTN activity have dramatic increases in muscle mass as a result of a combination of muscle fiber hypertrophy and increased fiber numbers. Moreover, administration of a number of different MSTN inhibitors to wild type mice can also promote muscle growth, demonstrating that MSTN plays a critical role in regulating muscle growth in adult animals. As a result, there has been considerable interest in the possibility that inhibitors of MSTN signaling might be effective in enhancing muscle strength and regeneration in patients with muscle degenerative diseases. Following processing of the MSTN precursor protein, the mature C-terminal dimer remains non-covalently bound to the N-terminal propeptide, which maintains MSTN in an inactive, latent state. A variety of biochemical and genetic studies have demonstrated that members of the BMP-1/tolloid family of metalloproteases play a critical role in regulating MSTN latency by cleaving and thereby inactivating the propeptide. Hence, inhibition of these proteases could be an effective therapeutic strategy to prevent activation of latent MSTN and thereby promote muscle growth. Moreover, the potential benefits of targeting these proteases could extend well beyond just MSTN inhibition, as these proteases are also known to act on other substrates besides MSTN that may play a role in muscle degenerative diseases. In particular, these proteases are capable of cleaving the TGF-ss binding protein, LTBP-1, thereby activating TGF-ss from its latent state, which may be significant with respect to therapeutic development given that inhibition of TGF-ss signaling has been shown to improve muscle regeneration in mdx mice. Furthermore, the BMP-1/tolloid proteases appear to be the enzymes responsible for processing procollagens into the mature species capable of forming collagen fibrils, raising the possibility that these enzymes may play a role in the development of fibrosis in a variety of disease settings. Hence, inhibitors of BMP-1/tolloid proteases have the potential to provide clinical benefit in patients with muscle degenerative diseases by targeting several different molecular pathways. The overall aims of this project are to validate the beneficial effects of inhibiting BMP-1/tolloid proteases in the setting of muscle degeneration and to initiate the development of a biologic agent capable of targeting these enzymes. The Specific Aims are: to assess the potential beneficial effects of targeting BMP-1/tolloid metalloproteases in mdx mice and to determine whether the BMP-1/tolloid inhibitor, sFRP2, can increase muscle growth either when expressed as a transgene in skeletal muscle or when administered systemically to mice. If successful, these studies will identify a novel therapeutic agent with the potential to promote muscle growth and improve clinical outcome in patients with muscular dystrophy. PUBLIC HEALTH RELEVANCE: Myostatin is a protein that normally acts to limit muscle growth. The goal of this project is to develop therapeutic agents capable of blocking myostatin activity and promoting muscle growth in patients with muscle degenerative diseases.