Lysosomal phospholipase A2 in autoimmune disease

描述（由申请人提供）：系统性红斑狼疮在历史上一直是并且仍然是一种知之甚少的自身免疫性疾病。最近的进展已经确定狼疮促进单基因改变，表现型狼疮在人类的许多方面。尽管有这些进展，仍然没有统一的假设，也没有新的机制为基础，针对这种疾病的免疫疗法。近年来，一些临床和实验研究指出，凋亡细胞的清除障碍是狼疮的一个共同特征。由于巨噬细胞识别、结合和摄取凋亡细胞的分子基础已被更好地定义，与吞噬细胞受体表达受损相关的基因改变与狼疮鼠模型相关。例子包括乳脂球EGF因子8和c-mer原癌基因酪氨酸激酶。磷脂溶血磷脂酰胆碱已被确定为参与清除凋亡细胞的巨噬细胞募集的重要“找到我”信号。然而，溶血磷脂酰胆碱是如何作为一个发现我的信号产生是未知的，并在编码酶或酶参与溶血PC的形成，将导致狼疮表型的基因中的类似的变化的鉴定尚未报道。本实验室发现、克隆并鉴定了一种新的磷脂酶A2，命名为溶酶体磷脂酶A2。这种酶在磷脂酶A2家族中是独特的。溶酶体磷脂酶A2的特征在于酸性pH最适值，转酰化神经酰胺的能力，以及它响应于吞噬刺激如酵母聚糖从巨噬细胞分泌。缺乏溶酶体磷脂酶A2表达的基因敲除小鼠的特征在于模仿狼疮的大多数方面的迟发性自身免疫表型。这些小鼠发生淋巴细胞增生，伴有肝脾肿大、消瘦和肾衰竭。小鼠表现出显著阳性ANA、抗dsDNA滴度、高循环免疫球蛋白水平和肾小球肾炎。脾脏和淋巴结的特征在于与驻留巨噬细胞相关的高水平凋亡小体的持续存在，这与凋亡细胞清除的缺陷一致。根据这些观察，提出了以下主要假设。溶酶体磷脂酶A2是巨噬细胞消化和清除凋亡细胞所必需的。提出以下具体目标来检验这一假设：1）免疫表型LPLA 2敲除小鼠。2)确定溶酶体磷脂酶A2缺失抑制或消除巨噬细胞清除凋亡细胞的机制。3)确定溶酶体磷脂酶A2是否足以或必须挽救LPLA 2缺失小鼠中的狼疮表型。4)确定肼苯哒嗪、奎尼丁和普鲁卡因胺对溶酶体磷脂酶A2的抑制是否是药物诱导狼疮的基础。 公共卫生相关性：我们发现并鉴定了一种新的溶酶体磷脂酶A2。基因敲除小鼠缺乏这种酶的活性，会产生迟发性自身免疫表型，其特征类似于系统性红斑狼疮。了解磷脂降解受损导致自身免疫表型的机制可能为狼疮的发病机制和潜在的治疗新靶点提供新的见解。

DESCRIPTION (provided by applicant): Systemic lupus erythematosus historically has been and still remains a poorly understood autoimmune disorder. Recent advances have been made in identifying lupus promoting single gene alterations that phenocopy many aspects of lupus in humans. Despite these advances there remains no unifying hypothesis and no new mechanism based, directed immunotherapy for this disease. In recent years several clinical and experimental studies have pointed to the impairment in the clearance of apoptotic cells as a common feature of lupus. As the molecular basis for the recognition, binding, and uptake of apoptotic cells by macrophages has become better defined, gene alterations associated with the impaired expression of phagocytic receptors for "eat me" signals are associated with murine models of lupus. Examples include the milk fat globule-EGF factor 8 and the c-mer proto-oncogene tyrosine kinase. The phospholipid lyso- phosphatidylcholine has been identified as an important "find me" signal for the recruitment of macrophages involved in the clearance of apoptotic cells. However, how lyso-phosphatidylcholine is generated as a find me signal is unknown and the identification of comparable alterations in the genes encoding the enzyme or enzymes involved in lyso-PC formation that would result in a lupus phenotype have not been reported. Our laboratory discovered, cloned, and characterized a novel phospholipase A2 named lysosomal phospholipase A2. This enzyme is distinct among the family of phospholipase A2s. Lysosomal phospholipase A2 is characterized by an acidic pH optimum, the ability to transacylate ceramide, and it secretion from macrophages in response to phagocytic stimuli such as zymosan. A knockout mouse, lacking the expression of lysosomal phospholipase A2 is characterized by a late onset autoimmune phenotype that mimics most aspects of lupus. These mice develop lymphoproliferation with hepatosplenomegaly, wasting, and renal failure. The mice exhibit markedly positive ANAs, anti-dsDNA titers, high circulating immunoglobulin levels, and glomerulonephritis. The spleens and lymph nodes are characterized by the persistence of high levels of apoptotic bodies in association with resident macrophages, consistent with a defect in the clearance of apoptotic cells. Based on these observations, the following primary hypothesis is proposed. Lysosomal phospholipase A2 is necessary for the digestion and clearance of apoptotic cells by macrophages. The following specific aims are proposed to test this hypothesis: 1) To immunologically phenotype LPLA2 null mice. 2) To determine the mechanism by which the absence of lysosomal phospholipase A2 inhibits or eliminates the clearance of apoptotic cells by macrophages. 3) To determine lysosomal phospholipase A2 is either sufficient or necessary to rescue the lupus phenotype in the LPLA2 null mice. 4) To determine whether inhibition of lysosomal phospholipase A2 by hydralazine, quinidine, and procainamide is the basis for drug induced lupus. PUBLIC HEALTH RELEVANCE: We have discovered and characterized a new lysosomal phospholipase A2. Knockout mice, deficient in the activity of this enzyme, develop a late onset autoimmune phenotype with features similar to systemic lupus erythematosus. Understanding the mechanisms whereby impaired degradation of phospholipids result in the autoimmune phenotype may provide new insights into the pathogenesis of lupus and potential new targets for therapy.