Transglutaminase Promotes CPPD Disease in Aging Joints

描述（由申请人提供）：焦磷酸钙二水合物（CPPD）沉积病是退行性关节炎的一种常见形式，优先针对老年人。受影响的患者患有严重的慢性关节炎，目前尚无治疗方法。随着人口老龄化，CPPD沉积病和其他形式的退行性关节炎将在医疗保健和生活质量成本方面带来越来越大的社会负担。在关节纤维和透明软骨中形成CPPD晶体。它们的形成需要细胞外焦磷酸盐和钙在无序的细胞周围基质环境中相互作用。软骨细胞外基质对CPPD晶体形成的贡献仍然缺乏表征，这是本工作的重点。我们发现转谷氨酰胺酶（Tgase）家族是CPPD晶体形成的重要参与者。酶催化蛋白质之间或蛋白质内部形成独特的交联。关节软骨含有两种Tgase酶，II型Tgase和XIIIA因子（FXIIIA）。在关节软骨中，Tgase活性随着年龄的增长而急剧增加，并且存在于潜在晶体形成部位的细胞周围软骨细胞基质中。在体外实验中，抑制Tgase活性可抑制CPPD晶体的形成，而Tgase过表达可引起基质矿化。我们假设老化软骨细胞外基质中Tgase活性的增加通过将关键的CPPD晶体促进蛋白交联到细胞外基质中来促进CPPD晶体的形成。我们将证明1)细胞外基质Tgase活性参与CPPD晶体形成；2) FXIIIA是软骨细胞外基质中主要的Tgase；3)三种关键的Tgase底物（骨桥蛋白、SPARC和原纤维蛋白1）被Tgase捕获在细胞周基质中，直接参与CPPD晶体的形成。我们将通过使用来自三个年龄组动物的猪软骨，以及来自CPPD沉积疾病或骨关节炎患者的人软骨来探索这些假设。我们将使用两种CPPD晶体形成模型来研究Tgase及其底物蛋白在CPPD晶体形成中的作用。患病人软骨的免疫组织化学研究将用于证实这些发现与CPPD疾病的相关性。这些研究将有助于我们了解CPPD沉积疾病，从而设计出针对这种常见致残性关节炎的有效治疗方法。

DESCRIPTION (provided by applicant): Calcium pyrophosphate dihydrate (CPPD) deposition disease is a common form of degenerative arthritis preferentially targeting the elderly. Affected patients have a severe chronic arthritis for which there are currently no therapies. As the population ages, CPPD deposition disease and other forms of degenerative arthritis will present an increasing societal burden in terms of health care and quality of life costs. CPPD crystals form in articular fibro-and hyaline cartilage. Their formation requires the interaction of extracellular pyrophosphate and calcium in a milieu of disordered pericellular matrix. The contributions of cartilage extracellular matrix to CPPD crystal formation remain poorly characterized and are the focus of this work. We identified the transglutaminase (Tgase) family of enzymes as important participants in CPPD crystal formation. Tgases catalyze the formation of unique crosslinks between or within proteins. Articular cartilage contains two Tgase enzymes, type II Tgase and Factor XIIIA (FXIIIA). Tgase activity dramatically increases with age in articular cartilage, and is present in the pericellular chondrocyte matrix at sites of potential crystal formation. Inhibition of Tgase activity suppresses CPPD crystal formation in vitro, while Tgase overexpression causes matrix mineralization. We hypothesize that increased Tgase activity in the extracellular matrix of aging cartilage contributes to CPPD crystal formation by crosslinking key CPPD crystal-promoting proteins into pericellular matrix. We will show that 1) extracellular matrix Tgase activity participates in CPPD crystal formation; 2) FXIIIA is the predominant Tgase in cartilage extracellular matrix; and 3) three key Tgase substrates (osteopontin, SPARC, and fibrillin 1) are trapped in the pericellular matrix by Tgase and directly participate in CPPD crystal formation. We will explore these hypotheses by using porcine cartilage from animals of three age groups, and human cartilage from patients with CPPD deposition disease or osteoarthritis. We will use two models of CPPD crystal formation to investigate the role of Tgase and its substrate proteins in CPPD crystal formation. Immunohistochemical studies of diseased human cartilage will be used to confirm the relevance of these findings to CPPD disease. These studies will contribute to our understanding of CPPD deposition disease, so that effective therapies for this common and disabling form of arthritis can be designed.