Agrin, a unique growth factor for cartilage regeneration in osteoarthritis

关节软骨是覆盖长骨末端的组织，它允许关节的无摩擦运动。关节软骨的丧失是骨性关节炎的主要特征，会导致关节疼痛和无法行走或执行简单的任务。在英国，骨关节炎是残疾津贴的主要原因，而且与巨额间接成本有关。它影响到60岁以上人口的三分之一以上，因此是影响幸福的主要因素之一，特别是老年人。到目前为止，我们还没有任何可以阻止骨性关节炎进展的治疗方法。可用的治疗仅限于止痛药和关节置换术。虽然关节置换术通常有效，但高达五分之一的患者达不到患者的期望，而且寿命有限，经常需要复杂和具有挑战性的翻修手术。关节置换的这一严重局限性正变得更加突出，因为人们的寿命要长得多，而且越来越多的人在更早的年龄患上了骨关节炎。我们已经发现，软骨细胞产生的一种名为Agin的分子对软骨健康是必不可少的。在骨性关节炎中，这种分子会被降解，然而我们知道，服用AGRIN将有助于形成新的软骨，也会限制软骨降解分子的产生，如基质金属蛋白酶-3。最后，我们发现AGRIN的一种工作方式是通过关闭一种名为WNT的分子信号，该信号已被证明有利于软骨破坏，当过度活跃时，容易导致骨关节炎。在这项研究中，我们打算测试是否确实将AGRIN直接注射到关节中可以治疗骨关节炎。首先，我们将对小鼠进行基因改造，这样当我们使用一种特殊药物时，软骨内就会产生agin。这将确保AGRIN在软骨内以最佳方式输送，并且我们所看到的任何效果都是由于AGRIN对软骨的影响。我们将通过损伤膝关节的半月板来诱导这些小鼠的骨性关节炎，这会导致机械关节不稳定。半月板损伤是骨关节炎发生的常见原因，在人类中也是如此。一旦小鼠患上了骨关节炎，我们就会给小鼠注射一种特殊的药物，这种药物会诱导软骨中产生农业蛋白。然后，我们将看到，与对照组相比，诱导软骨中的农业蛋白是否能导致骨关节炎的愈合。除了这种仅导致软骨中农业蛋白产生增加的遗传方法外，我们还将使用诱导产生农业蛋白的病毒，或在炎症组织中无法降解的更小的农业蛋白片段。这些病毒将被注射到关节内，就像合成农业林将被注射到患者体内一样。因此，agin不仅会进入软骨，还会进入其他关节组织，如骨和关节的内层，称为滑膜。这将使我们能够看到agin对关节所有组织的影响。最后，我们将利用分子手段，研究agin激活软骨细胞的机制。这一目标的实现将使我们能够识别已经存在的化合物，这些化合物可以激活相同途径的相同受体和细胞成分，并可能使我们能够在不必合成农业林素的情况下达到相同的效果。

The articular cartilage is the tissue that covers the ends of the long bones and that allows the frictionless motion of the joint. The loss of the articular cartilage, which is the main feature of osteoarthritis, leads to joint pain and incapacity to walk or perform simple tasks. Osteoarthritis is the leading cause for disability allowance in UK and is associated with huge indirect costs. It affects over 1/3 of the population over the age of 60 and therefore is one of the major factors affecting well-being particularly in the elderly. To-date, we do not have any treatment that stops progression of osteoarthritis. Available treatments are limited to pain killers and joint replacement. Although generally effective, joint replacement does not live up to the patients' expectations in up to one in five patients, and has a limited life span often requiring complex and challenging revision surgery. This serious limitation of joint replacement is becoming more prominent due to the fact that people live much longer and because more people are developing osteoarthritis at an earlier age. We have discovered that a molecule called Agrin, produced by cartilage cells, is essential for cartilage health. In osteoarthritis this molecule is degraded, however we know that administering Agrin will help forming new cartilage and will also limit the production of cartilage-degrading molecules such as MMP-3. Finally, we have discovered that one way that Agrin works is by shutting down a molecular signal called WNT which has been shown to favour cartilage breakdown and, when excessively active, predisposes people to develop osteoarthritis.In this study we intend to test if indeed administering Agrin directly into the joint can treat osteoarthritis. First, we will genetically engineer mice so that Agrin is produced within cartilage when we administer a special drug. This will ensure that Agrin is delivered optimally within the cartilage and that whatever effect we see is due to the effect of Agrin on cartilage. We will induce osteoarthritis in these mice by damaging the meniscus in the knee, which results in mechanical joint instability. Damage to the meniscus is a common cause of osteoarthritis development also in people. Once the mice have developed osteoarthritis we will administer the special drug that will induce Agrin production in the cartilage. We will then see if, compared to controls, Agrin induction in cartilage leads to healing of osteoarthritis.In addition to this genetic approach which leads to increased Agrin production only in cartilage, we will use also viruses that induce the production of Agrin, or smaller fragments of Agrin that cannot be degraded in inflamed tissues. These viruses will be injected into the joint just like synthetic Agrin would be in patients. Therefore Agrin will go not only into cartilage, but also into other joint tissues such as the bone and the internal lining of the joint called synovial membrane. This will enable to see the effects of Agrin administration to all tissues of the joint.Finally, using molecular approaches, we will study the mechanism by which Agrin activates cartilage cells. The delivery of this aim will enable us to identify already existing compounds that can activate the same receptor and cellular components of the same pathway and may enable us to achieve the same effects without having to make synthetic Agrin.