The Role of Cellular Receptors Involved in Inflammation

我们小组一直致力于研究细胞受体在炎症反应和肿瘤进展中的作用。我们对与细菌和宿主来源的趋化肽相互作用的甲酰肽受体特别感兴趣。在人类中，有三种功能性的FMLF受体，即FPRR、FPRL1和FPRL2。Fpr基因突变的小鼠对细菌感染的抵抗力降低，提示该受体可能参与宿主对微生物感染的防御。最近，我们的实验室和其他实验室发现了一些针对FPR和FPRL1的新型趋化激动剂。这些激动剂包括来自多肽文库的小肽，来自HIV-1包膜蛋白的多肽域，以及更重要的与肿瘤以及炎症性和神经退行性疾病相关的多肽激动剂。这些发现扩大了甲酰肽受体的功能范围。我们已经鉴定出一种中性粒细胞颗粒蛋白组织蛋白G(CAG)，它具有杀菌作用，能裂解许多蛋白质，在小鼠体内注射时能促进抗体反应，并能趋化人的粒细胞和单核细胞，是一种新型的受体fpr的趋化激动剂。这一发现为CAG的许多生物学活性提供了重要的分子基础，并将有助于根据CAG的结构和功能设计促进宿主防御的药物。我们还研究了甲醛多肽受体fpr在促进肿瘤进展中的作用。我们发现高度恶性的人脑胶质瘤细胞，包括来自已建立的肿瘤细胞系和原代胶质瘤标本的细胞，都表达FPR。Fpr介导高度恶性的人脑胶质瘤细胞对坏死性肿瘤组织提取物中所含的配体的反应。激活的FPR还促进肿瘤细胞生长和产生对肿瘤新血管形成至关重要的血管内皮生长因子。我们利用短RNA干扰从胶质瘤细胞中删除了FPR，与表达FPR的肿瘤细胞相比，这种肿瘤细胞在裸鼠体内形成致命肿瘤的能力大大降低。因此，FPRR可能是高度恶性的人脑胶质瘤细胞侵袭行为的一个重要因素，因此它可以被认为是抗胶质瘤治疗药物开发的靶点。我们揭示了另一种甲酰化多肽受体FPRL1在阿尔茨海默病的炎症和神经变性中的潜在重要作用，其特征是脑内Abeta42肽的过度产生与脑巨噬细胞(小胶质细胞)的聚集和激活有关。我们发现，FPRL1不仅介导了Abeta42的趋化活性，而且还促进了Abeta42在巨噬细胞中的内化和随后的细胞内聚集。FPRL1与Abeta42相互作用，但不与巨噬细胞和神经细胞中的非淀粉样肽激动剂相互作用，增加了细胞的凋亡。与FPRL1类似的小鼠mFPR2也介导了Abeta42刺激的髓系细胞的趋化和超氧化物释放，并通过Toll样受体的配体等促炎信号增强了该受体在小鼠原代小胶质细胞中的表达。尽管阿尔茨海默病患者有进行性的神经退行性变，但患者大脑的枕叶很少受到影响。这导致了编码一种小的神经保护多肽人(HN)的基因的鉴定。在对HN神经保护机制的研究中，我们发现HN与Abeta42共享甲酰肽受体FPRL1和小鼠mFPR2。通过共享FPRL1，HN减少了Abeta42在巨噬细胞中的聚集及其对神经细胞的毒性。这些发现为我们提出的使用阿尔茨海默病小鼠模型的研究提供了理论基础，以进一步阐明FPRL1和mFPR2在阿尔茨海默病发病机制中的作用。

Our group has been pursuing the studies of the role of cellular receptors in inflammatory responses and tumor progression.We are especially interested in formyl peptide receptors that interact with bacterial and host-derived chemotactic peptids. In humans, there are three functional fMLF receptors, FPR, FPRL1, and FPRL2. Mice with disrupted FPR gene showed reduced resistance to bacterial infection, suggesting this receptor may be involved in host defense against microbial infection. Recently our laboratory and other laboratories identified a number of novel chemotactic agonists for both FPR and FPRL1. These agonists include small peptides derived from peptide libraries, peptide domains derived from HIV-1 envelope proteins, and more importantly, peptide agonists associated with tumor as well as inflammatory and neurodegenerative diseases. These findings expanded the functional scope of formylpeptide receptors. We have identified a neutrophil granule protein Cathepsin G (CaG), which is bactericidal, cleaves a number of proteins, promotes antibody responses when injected in mice, and chemoattracts human granulocytes and monocytes, as a novel chemotatic agonist for the receptor FPR. This finding provides important molecular basis for many biological activities of CaG and will assist in the design of agents that promote host defense based on the structure and function of CaG. We also studied the role of formalpeptide receptor FPR in promoting tumor progression. We found that highly malignant human glioma cells, including those from established tumor cell lines and primary glioma specimens, express FPR. FPR mediates the migration of high malignant human glioma cells in response to ligands contained in the extracts of necrotic tumor tissues. Activated FPR also promotes tumor cell growth and production of VEGF that is crucial for formation of new blood vessels in tumors. We utilized short RNA-interference to delete FPR from glioma cells, and such tumor cells exhibited greatly reduced capacity to form deadly tumors in nude mice, as compared with tumor cells that express FPR. Thus, FPR may act as an important contributor to the aggressive behavior of highly malignant human glioma cells thus it can be considered as a target for the development of anti-glioma therapeutics.We have revealed a potentially important role of another formylpeptide receptor FPRL1 in the inflammation and neurodegeneration in Alzheimer's disease, which is characterized by over-production of Abeta42 peptides in the brain in association with accumulation and activation of brain macrophages (microglia). We found that FPRL1 not only mediates the chemotactic activity of Abeta42 but also promotes the internalization and subsequent intracellular aggregation of Abeta peptides in macrophages. The interaction of FPRL1 with Abeta42, but not with non-amyloidogenic peptide agonists in macrophages and neuronal cells increased apoptosis of the cells. The mouse counterpart of FPRL1, namely mFPR2, also mediates the chemotaxis and super oxide release in myeloid cell stimulated by Abeta42 and the expression of this receptor was enhanced in mouse primary microglial cells by proinflammatory signals such as ligands by Toll-like receptors. Despite the progressive neurodegenration in AD, the occipital lobes of the patient brains are rarely affected. This has led to the identification of a gene coding for a small neuroprotective polypeptide Humanin (HN). In studies of the mechanisms of HN in neuroprotection, we found that HN shares the formylpeptide receptor FPRL1 and mouse mFPR2 with Abeta42. By sharing FPRL1, HN reduces the aggregation of Abeta42 in macrophages and its toxicity for neuronal cells. These findings provide the rationale for our proposed studies using mouse models of Alzheimer's disease to further elucidate the contribution of FPRL1 and mFPR2 to the pathogenesis of Alzheimer's disease.