HMGB2 in cartilage homeostasis, aging and osteoarthritis

描述（由申请人提供）：骨关节炎（OA）是最常见的关节疾病，也是导致残疾的主要原因。衰老是骨性关节炎的主要危险因素，骨性关节炎始于软骨浅表带（SZ）的破坏。决定SZ中细胞独特表型的分子机制尚不清楚，关于初始软骨表面缺陷原因的信息有限。我们的初步研究表明，染色质蛋白HMGB2仅在关节软骨的SZ中表达。我们检查了Hmgb2-/-小鼠，发现与野生型（WT）小鼠相比，OA更严重。在人和小鼠关节中，HMGB2的表达随着年龄的增长而减少和丧失，随后在软骨表面发生退行性变化。这些发现支持了我们的假设，即HMGB2参与软骨稳态，衰老相关的HMGB2表达缺失是SZ破坏和早期OA的一种机制。该研究的目的是研究衰老相关的HMGB2减少如何影响软骨完整性，并解决HMGB2的分子和细胞机制。目的1。小鼠和人类关节中HMGB2缺乏。我们将分析Hmgb2-/-小鼠软骨退变的发生、演变和模式，并研究Hmgb2-/-小鼠自发和手术诱导OA的发病机制。这些发现将在人体关节软骨中得到证实。目标2。关节软骨细胞中的HMGB2。我们将描述表达hmgb2的细胞的表型和分化状态。我们将研究HMGB2在培养软骨细胞中的表达调节，并确定HMGB2在调节SZ软骨细胞存活和生物合成反应中的作用。目标3。HMGB2调控细胞功能的机制：与左-1和¿-catenin的相互作用。我们将绘制HMGB2和left -1物理相互作用中涉及的基本基序。我们将研究¿-catenin与HMGB2相互作用的功能，以及在left -1依赖基因、SZP和存活基因表达中的作用。通过关节内注射表达Cre重组酶的腺病毒，有条件地敲除-catenin，获得-catenin的浅表区特异性缺失。所提出的研究有可能对控制SZ软骨细胞独特分化状态的分子机制产生新的见解。这些信息不仅与骨关节炎有关，而且与软骨组织工程有关。拟议的研究将为关节软骨早期退行性改变的机制提供见解，并可能允许OA的预防和治疗策略的发展。公共卫生相关性：骨关节炎是最普遍的关节疾病，是致残的主要原因。目前还没有改善疾病的治疗方法，这在一定程度上与对发病机制的不完全了解有关。具体来说，骨关节炎病变始于关节软骨表面，这对生物力学功能和关节润滑很重要，然后发展为更大的病变，导致软骨完全丧失。关于最初软骨表面缺陷的原因的信息是非常有限的。我们的初步研究表明，染色质蛋白HMGB2仅在人和小鼠关节软骨的浅表区表达。随着年龄的增长，HMGB2表达的减少和丧失，随之而来的是软骨细胞的丧失和软骨表面退行性变化的发生。这些观察结果表明，HMGB2是维持软骨表面完整性的关键因素，其衰老相关的损失是骨关节炎的主要发病机制。提出的研究有可能确定预防和治疗骨关节炎的新途径。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) is the most prevalent joint disease and a major cause of disability. Aging is the major risk factor for OA which begins with disruption of the cartilage superficial zone (SZ). Molecular mechanisms that determine the unique phenotype of cells in the SZ are unknown and information on causes of the initial cartilage surface defects is limited. Our preliminary studies show that the chromatin protein HMGB2 is exclusively expressed in the SZ of articular cartilage. We examined Hmgb2-/- mice and found more severe OA as compared to wild-type (WT) mice. In human and WT mouse joints there is an aging-related reduction and loss of HMGB2 expression followed by degenerative changes in the cartilage surface. These findings support our hypothesis that HMGB2 is involved in cartilage homeostasis and aging-related loss of HMGB2 expression is a mechanism involved in disruption of the SZ and early OA. The goals of the proposed study are to investigate how aging-related reduction of HMGB2 affects cartilage integrity and address molecular and cellular mechanisms of HMGB2. Aim 1. HMGB2 deficiency in murine and human joints. We will analyze onset, evolution and patterns of cartilage degeneration in Hmgb2-/- mice and examine mechanisms of OA pathogenesis in Hmgb2-/- mice involved in spontaneous and surgically induced OA. These findings will be confirmed with human articular cartilage. Aim 2. HMGB2 in articular chondrocytes. We will characterize phenotype and differentiation status of HMGB2-expressing cells. Studies will be performed on regulation of HMGB2 expression in cultured chondrocytes and we will determine the role of HMGB2 in regulating survival and biosynthetic responses in SZ chondrocytes. Aim 3. Mechanisms of HMGB2 regulation of cell function: interactions with Lef-1 and ¿-catenin. We will map essential motifs involved in the physical interaction of HMGB2 and Lef-1. We will address function of ¿-catenin interaction with HMGB2 and in expression of Lef-1 dependent genes, SZP and survival genes. Superficial zone-specific deletion of ¿-catenin will be obtained by conditional knock out of ¿-catenin by intraarticular injection of adenovirus expressing Cre recombinase. The proposed studies have the potential to generate new insight into molecular mechanisms that control the unique differentiation status of SZ chondrocytes. This information will not only be relevant to OA but also to cartilage tissue engineering. The proposed studies will provide insights into mechanisms of early degenerative changes in the articular cartilage and may permit development of preventive and therapeutic strategies for OA. PUBLIC HEALTH RELEVANCE: Osteoarthritis represents the most prevalent joint disease and is a major cause of disability. Disease-modifying therapies are not available and this is in part related to an incomplete understanding of pathogenetic mechanisms. Specifically, osteoarthritic lesions begin at the articular cartilage surface which is important in biomechanical function and joint lubrication and then progress to larger lesions with complete loss of cartilage. Information on the causes of the initial cartilage surface defects is very limited. Our preliminary studies show that the chromatin protein HMGB2 is exclusively expressed in the superficial zone of articular cartilage from human and murine joints. With advancing age there is a reduction and loss of HMGB2 expression that is followed by loss of cartilage cells and the onset of degenerative changes in the cartilage surface. These observations suggest that HMGB2 is a critical factor for maintaining the integrity of the cartilage surface and that its aging-related loss is a central pathogenetic mechanism in osteoarthritis. The proposed research has the potential to identify new avenues for the prevention and treatment of osteoarthritis.