Peptidylarginine deiminase type 6 in rheumatoid arthritis pathogenesis

项目总结/摘要 瓜氨酸化蛋白是类风湿性关节炎（RA）免疫系统的主要靶点， 这表明增强瓜氨酸的机制与最严重的疾病结果有关。蛋白 瓜氨酸酶是精氨酸残基向瓜氨酸的酶促转化，由钙- 依赖性肽基精氨酸脱亚胺酶（PAD）。在人类中发现了五种PAD成员，PAD 1- 4，和无催化活性的PAD 6。虽然有几种机制与瓜氨酸异常有关， RA，包括在中性粒细胞死亡期间PAD（特别是PAD 4）的过度活化和 增强PAD 4活性的自身抗体、控制瓜氨酸化的调节途径知之甚少。 由于PAD需要超生理浓度的钙才能在体外发挥活性，因此怀疑PAD 体内激活需要调节酶对钙的敏感性的额外因素。这些辅因子， 但尚未查明。我们的初步数据表明，没有瓜氨酸化的PAD 6 活性，和3种新的PAD 6剪接变体首次在该提案中描述，作为辅因子， 降低PAD 4催化所需的钙。此外，我们发现所有的PAD 6变体都是丰富的， 在中性粒细胞中，其被认为是RA关节中瓜氨酸化蛋白的主要来源。总之，我们 假设PAD 6及其变体可能负责调节PAD 4活性的大小， 在生理和病理条件下。我们将在三个人的模型中直接检验这个假设 明确的目标。在目标1中，我们将定义PAD 6变体如何调节PAD 4活性，目的是鉴定PAD 6变体的功能。 PAD 6变体降低PAD 4钙需求的生化机制。目标2将定义 PAD 6及其剪接变体在细胞水平的表达和功能。目标3将研究表达 RA滑液中PAD 6亚型的表达，以阐明其与瓜氨酸 RA中的蛋白质总之，这些研究将定义疾病放大相关的新的相互作用机制， 以维持RA关节中瓜氨酸化蛋白的产生。此外，这些研究还可以提供 靶向PAD 6作为调节PAD 4活性的新治疗策略的证据，这是非常重要的 用于瓜氨酸在致病上有牵连的疾病。

PROJECT SUMMARY/ABSTRACT Citrullinated proteins are major targets of the immune system in rheumatoid arthritis (RA), with recent evidence suggesting that mechanisms that enhance citrullination are associated with the worst disease outcome. Protein citrullination is the enzymatic conversion of arginine residues to citrulline and is mediated by the family of calcium- dependent peptidylarginine deiminase (PAD) enzymes. Five PAD members have been found in humans, PAD1- 4, and the catalytically inactive PAD6. While several mechanisms have been linked to abnormal citrullination in RA, including hyperactivation of PADs (particularly PAD4) during neutrophil death and the production of autoantibodies that enhance PAD4 activity, regulatory pathways that control citrullination are poorly understood. Since PADs require supraphysiologic concentrations of calcium for activity in vitro, it is suspected that PAD activation in vivo requires additional factors that modulate the enzyme’s sensitivity for calcium. Such co-factors, however, have not been identified. Our preliminary data demonstrate that PAD6, which has no citrullinating activity, and 3 novel PAD6 splicing variants described for the first time in this proposal, act as co-factors that decrease the calcium requirement of PAD4 for catalysis. Moreover, we found that all PAD6 variants are abundant in neutrophils, which are considered a major source of citrullinated proteins in the RA joint. Taken together, we hypothesize that PAD6 and its variants may be responsible for modulating the magnitude of PAD4 activity both in physiologic and pathologic conditions. We will examine this hypothesis directly in the human model in three specific aims. In Aim 1, we will define how PAD6 variants regulate PAD4 activity with the goal of identifying the biochemical mechanisms by which PAD6 variants decrease the calcium requirement of PAD4. Aim 2 will define the expression and function of PAD6 and its splicing variants at the cellular level. Aim 3 will study the expression of PAD6 isoforms in RA synovial fluid to address their relationship with the abnormal production of citrullinated proteins in RA. Together, these studies will define novel interacting mechanisms of disease amplification relevant to sustain the production of citrullinated proteins in the RA joints. Furthermore, these studies may provide evidence for targeting PAD6 as a novel therapeutic strategy to modulate PAD4 activity, which is highly significant for diseases in which citrullination has been pathogenically implicated.