Endothelial microparticles in patients with kidney transplants

描述（由申请人提供）：本提案旨在建立循环内皮微粒（EMP）水平，作为肾移植中异体移植排斥反应的一种新的生物标志物。内皮细胞（EC）在同种异体移植功能障碍和排斥反应的发病机制中起重要作用。随着免疫抑制和手术技术的改进，移植物存活率显著提高。然而，同种异体移植排斥反应仍然是导致同种异体移植失败的主要原因之一。内皮细胞是同种异体移植排斥反应的主要靶点之一，尤其是抗体介导的排斥反应（AMR）。通常，肾移植功能是通过血清肌酐（SC）水平来评估的。不幸的是，SC水平升高是异体肾移植功能障碍的非特异性标志，它可能发生在许多不同的情况下。评估同种异体移植排斥反应的“金标准”测试是肾同种异体移植活检，这是一种侵入性、昂贵且相对危险的程序。急性细胞排斥反应（ACR）的模式是有据可查和广泛认可的。然而，AMR的诊断是肾脏病理学中最具挑战性的问题之一。小管周围毛细血管（PTC） C4d染色是AMR的标志物之一。尽管如此，一些肾活检显示C4d染色，没有AMR或ACR的组织学发现。最近，有证据表明某些形式的AMR可能对PTC C4d染色呈阴性。基于这些数据，我们需要一种可靠且具有临床意义的同种异体移植排斥反应标志物。微颗粒是由不同类型的细胞脱落的小膜泡，其中含有细胞表面蛋白质和原细胞的细胞质成分。微粒的产生是正常细胞功能的一部分，但由于细胞凋亡和细胞应激，微粒的产生增加。其他人和我们之前已经证明，循环EMP水平可以作为EC功能障碍的替代标志物。最近的研究表明，包括肾脏在内的实体器官移植患者的循环EMP水平发生了变化。我们证明了循环EMP水平，最初在丙型肝炎肝硬化患者中升高，在肝移植后两周降至健康人的水平。这一数据表明，循环EMP水平可能有助于作为实体器官移植患者EC功能的生物标志物。基于这些发现，我们假设：1)循环EMP水平升高可能是异体肾移植排斥反应的新标志物；2)同种异体肾移植内皮产生的EMP与受体内皮产生的EMP在蛋白质组成上存在差异；因此，前者可作为异体肾移植EC功能的生物标志物。我们的假设将在两个特定目的下进行测试：1)评估循环内皮微粒水平是否可以作为肾移植患者异体移植排斥反应的标志；2)进行一项初步研究，以调查是否可以进一步分离循环EMP池，以区分受体和同种异体内皮细胞产生的微粒。结论：该R21是推进EMP作为肾移植患者排斥反应新标志物研究的重要一步。

DESCRIPTION (provided by applicant): This proposal seeks to establish levels of circulating endothelial microparticles (EMP) as a novel biomarker of allograft rejection in the setting of kidney transplantation. Endothelial cells (EC) play an important role in the pathogenesis of allograft dysfunction and rejection. With improved immunosuppression and surgical technique, graft survival has significantly increased. Nevertheless, allograft rejection remains one of the main causes for allograft failure. The endothelium is one of the main targets in allograft rejection, especially antibody-mediated rejection (AMR). Typically, renal allograft function is evaluated by serum creatinine (SC) levels. Unfortunately, SC level elevation is a non-specific marker of renal allograft dysfunction, and it may occur in many different conditions. The "gold standard" test for the assessment of allograft rejection is renal allograft biopsy, which is an invasive, expensive and relatively risky procedure. The patterns of acute cellular rejection (ACR) are well-documented and broadly recognized. However, diagnosis of AMR is one of the most challenging in renal pathology. Peritubular capillary (PTC) C4d staining is one of the markers of AMR. Still, some kidney biopsies show C4d staining without histologic findings of AMR or ACR. Recently, evidence that some forms of AMR may be negative for PTC C4d staining has been described. Based on these data, the need for a reliable and clinically significant marker of allograft rejection is emerging. Microparticles are small membrane vesicles shed by different cell types, which contain cell surface proteins and cytoplasmic components of the original cell. The microparticle production is a part of normal cell function, but it increases by apoptotic cells and cells under stress. Others and we had previously demonstrated that levels of circulating EMP may be used as a surrogate marker of EC dysfunction. Recent studies have indicated changes in circulating EMP levels in patients with solid organ transplants, including kidneys. We demonstrated that circulating EMP levels, initially elevated in patients with Hepatitis C cirrhosis, were decreased to the levels seen in healthy people two weeks after liver transplantation. This data suggests that the levels of circulating EMP may be useful as a biomarker of EC function in patients with solid organ transplants. Based on these findings, we hypothesize that 1) an elevation in circulating EMP levels may be a novel marker of renal allograft rejection; 2) EMP produced by the renal allograft endothelium are different by their protein composition from EMP produced by the recipient endothelium; therefore, the former may be used as the biomarker of EC function of the renal allograft. Our hypotheses will be tested under two specific aims: 1) evaluate if the levels of circulating endothelial microparticles can be used as a marker of allograft rejection in patients with kidney transplants; 2) undertake a pilot study to investigate if the pool of circulating EMP may be further separated in order to distinguish between the microparticles produced by the recipient and allograft endothelium. Conclusions: This R21 is the essential step to advance the study of EMP as the novel marker of rejection in renal transplant patients. PUBLIC HEALTH RELEVANCE: Renal transplantation saves thousands of lives and improves quality of life in patients with end stage renal disease. The main cause of renal allograft failure is rejection. The endothelium is the internal layer in blood vessels and it is one of the main targets during allograft rejection. Microparticles are small vesicles shed by many cells when they are functioning abnormally, including the endothelium. We described earlier that the number of endothelial microparticles reflects endothelial cell function in experimental settings in vitro and in animals. We propose that number of microparticles shed by the endothelium in the renal allograft increases during rejection and this may be used as a novel marker for rejection. Our long term goal is to develop a novel, reliable and useful clinical test to recognize rejection in patients with renal transplants.