C5L2 不再是孤儿受体——进展与展望

C5a Like Receptor2--C5L2,又称G蛋白偶联受体77(GPR77),是 C5aR(CD88)亚家族成员,在氨基酸序列上与C5aR(CD88)有35%的同源性.广泛分布于全身各组织细胞,在粒细胞和未成熟树突状细胞(immature dendritic)及脾脏中有大量的表达.由于长期以来未发现其生理性配体而被称为孤儿受体(orphan receptor).当前大量研究表明C5L2能与C5a,C3a,C4a,去精 C5a(C5a des-Arg74)和去精 C3a(C3a des-Arg77) 结合,且与C5a des-Arg74结合能力比CD88与C5a des-Arg74高10倍.在结构、功能等方面与CD88也有很多相似之处.与CD 88不同的是由于C5L2第三跨膜片断末端的DRY序列上精氨酸被亮氨酸替代,有一个更短的胞内第三环,缺乏丝氨酸/苏氨酸残基,所以不能强有力地与G蛋白偶联,和C5a结合后仅诱导转染细胞发生微弱的磷酸化,不引起细胞内钙的流动及转染细胞脱颗粒;C5L2与配体结合后不发生内化,并具有与配体缓慢的结合与解离的特性.作为过敏毒素受体,C5L2在过敏毒素C5a参与的相关疾病,如脓毒症(sepsis)、急性肺损伤(ALI)、急性呼吸窘迫综合征(ARDS)等的发生、发展以及对G蛋白偶联受体的研究都具有重要的意义.     

C5a受体（C5aR,CD88）

Ｃ５ａ是一个重要的炎症介质，但其作用的机制是在对其受体Ｃ５ａＲ（ＣＤ８８）近年来有了较明确的认识后才得以阐明的。本文就Ｃ５ａＲ的结构、作用的分子机理、作用后的信号转导机制、Ｃ５ａＲ的脱敏与内移，以及Ｃ５ａＲ的基因结构及其表达调控等的一些新进展加以介绍。     

C5aR1促进神经干细胞增殖作用的实验研究

目的研究C5aR1在新生小鼠脑内及体外培养神经干细胞内的表达规律,探索C5aR1对神经干细胞增殖调节的作用。方法以免疫组化方法检测在新生小鼠脑内及体外培养的神经干细胞内C5aR1的表达;培养C5aR基因敲除小鼠来源的神经干细胞,同时利用C5aR拮抗剂处理正常小鼠来源的神经干细胞,分别观察神经干细胞的增殖状态,分析C5aR1对神经干细胞增殖的调节作用。结果 1)在新生小鼠脑内,C5aR1主要表达于海马和室下区等神经干细胞分布区域;2)C5aR1与nestin共表达于体外培养的神经干细胞内;3)C5aR特异性拮抗肽下调体外培养的神经干细胞内nestin表达并抑制其增殖;C5aR1基因敲除,神经干细胞的成球能力明显降低。结论 C5aR1在脑内以及神经干细胞内均有表达,对神经干细胞的增殖具有促进作用,其具体机制还有待进一步的实验研究。     

肾癌荷瘤小鼠组织中补体 C5a / C5aR 通路活化与肿瘤高凝状态 的关系及其机制研究

目的 研究肾癌荷瘤小鼠组织中补体 C5a / C5aR 通路活化与肿瘤高凝状态的关系及其机制。 方法 收集 2016 年 7 月至 2019 年 10 月于唐山市人民医院收治的 32 例经病理学活检确诊的肾癌患者的癌组织和 癌旁组织。 采用 Western 印迹法检测组织中 C5a / C5aR 通路活化相关蛋白表达情况。 于 BALB/ c-nu / nu 裸鼠 前肢腋窝皮下接种人 ACHN 肾癌细胞株, 接种成功后随机分为干预组、 模型组, 其中干预组尾静脉注射 C5a 联合 C5aR 阻断剂 (C5aR antagonist, C5aRA), 模型组等体积注射生理盐水, 另取 6 只空白小鼠作为对 照组。 观察小鼠肿瘤生长情况, 检测高凝状态相关指标水平。 脱颈处死小鼠, 收集癌组织, 采用 Western 印迹法检测组织中 C5a / C5aR 通路活化相关蛋白表达情况。 结果 两组小鼠肿瘤体积于荷瘤 6 ~ 21 d 差异具 有统计学意义, 且干预组的肿瘤体积明显低于模型组 ( P< 0. 05)。 3 组小鼠于荷瘤第 1 天的血清 D-D、 vWF、 TF 水平差异无统计学意义, 荷瘤第 14 天、 第 21 天干预组、 模型组血清凝血指标水平明显增加, 其 中干预组均明显低于模型组 (P< 0. 05)。 干预组癌组织中 C5aR、 C5b-9、 FGL2、 P38、 p-P38 的表达水平均 明显低于模型组 (P< 0. 05)。 肾癌患者癌组织中 C5aR、 C5b-9、 FGL2、 P38、 p-P38 的表达水平均明显高于 癌旁组织 (P< 0. 05)。 32 例肾癌患者中高凝状态患者 14 例, 非高凝状态患者 18 例, 高凝状态组癌组织中 C5aR、 C5b-9、 FGL2、 P38、 p-P38 的表达水平均明显高于非高凝状态组 (P< 0. 05)。 结论 补体 C5a / C5aR 通路可通过调控 FGL2 的表达而诱导肾癌的高凝状态, 进而参与肾癌的发病过程。     

C5a/C5aR通路对约氏疟原虫增殖和小鼠生存的影响

目的观察C5a/C5aR通路对约氏疟原虫17XL（P.y17XL）的增殖及其对BALB/c小鼠致死率的影响。结论将实验小鼠分为正常BALB/c组和C5aR-/-BALB/c组,每组5只,相同剂量的P.y17XL（2×105）分别感染正常BALB/c组小鼠和C5aR-/-BALB/c组小鼠,于感染后0、2、4和6d观察两组小鼠原虫血症和存活率的变化,并且采用ELISA检测感染P.y17XLBALB/c小鼠血清中C5a的水平。结果与正常组小鼠相比,C5aR-/-组小鼠生存期缩短,P.y17XL在C5aR-/-组小鼠的原虫血症较野生株小鼠高（P〈0.05）,而P.y17XL感染小鼠的血清中C5a含量低于未感染的小鼠。结论 C5a/C5aR能够抑制P.y17XL的增殖,并能延长感染小鼠的生存期。     

人C5aR（CD88）序列结构及其B细胞表位预测

采用ＫｙｔｅＤｏｏｌｉｔｔｌｅ氨基酸亲水性标准及Ｂａｉｒｏｃｈ的ＧＧＢＳＭ方案对人Ｃ５ａＲ分子的亲水性基序、Ｂ细胞表位及二级结构进行了预测，并用吴氏建立的Ｂ细胞表位预测方法进行评述。     

C5a/C5aR信号在约氏疟原虫肝期发育及遗传减毒子孢子诱导小鼠保护性免疫中的作用

目的探讨C5a/C5a R信号在约氏疟原虫肝期自然感染和遗传减毒子孢子诱导小鼠保护性免疫中的作用。方法遗传减毒子孢子免疫Balb/c小鼠2、4、6 d后,ELISA检测补体C5a的活化情况;然后利用C5a R-/-Balb/c小鼠,通过定量PCR检测和吉姆萨染色比较子孢子攻击免疫或未免疫2种小鼠的肝脏虫荷和原虫血症。结果子孢子攻击免疫或未免疫的野生与C5a R-/-小鼠的肝脏虫荷和原虫血症之间无统计学差异(P>0.05)。结论遗传减毒子孢子免疫能够成功诱导小鼠产生完全保护性免疫,但补体C5a R缺失对减毒子孢子的免疫保护效果和肝期自然感染均无明显影响,说明C5a/C5a R信号通路并不参与调节约氏疟原虫肝期发育和遗传减毒子孢子诱导小鼠产生的保护性免疫。     

不同遗传背景对C5aR在银屑病病理中作用的影响

目的:建立咪喹莫特诱导的银屑病样动物模型,通过比较BALB/c和C57BL/6两种遗传背景的C5aR^+/+和C5aR^-/-小鼠的病理表现及相关指标的变化,探讨不同遗传背景对C5aR在银屑病病理发生中的作用。方法:小鼠分为4组:C5aR^+/+BALB/c、C5aR^-/-BALB/c、C5aR^+/+ C57BL/6和C5aR^-/-C57BL/6小鼠组。咪喹莫特涂抹小鼠背部皮肤,诱导银屑病动物模型。依据PASI(psoriasis area severity index)评价各组小鼠的皮损程度;HE染色观察皮损组织的病理学变化;qRT-PCR检测皮损组织中IL-17A mRNA水平;流式细胞术分析引流淋巴结和皮损局部组织中分泌IL-17A的γδT细胞亚群的百分比。结果:与同背景C5aR^+/+小鼠相比,C5aR^-/-小鼠银屑病样表型显著减小;相比BALB/c背景的C5aR^+/+(或C5aR^...     

补体裂解产物C5a的研究进展

C5a由C5裂解而来,由74个氨基酸构成,是一种潜在的前炎症因子。C5a在羧肽酶的作用下迅速变成C5adesArg,通过G蛋白受体经典的通路与C5aR结合后在天然免疫中和适应性免疫中均发挥着重要的作用,非G蛋白受体通路目前的研究还不明朗。研究发现,C5a是许多自身免疫性疾病的重要病原起始物,所以抑制C5a的释放在未来的治疗中是一个很好的策略和方向。     

人C5aR(CD88)序列结构分析及其B细胞表位预测

采用ＫｙｔｅＤｏｏｌｉｔｔｌｅ氨基酸亲水性标准及Ｂａｉｒｏｃｈ的ＧＧＢＳＭ方案对人Ｃ５ａＲ分子的亲水性基序、Ｂ细胞表位及二级结构进行了预测，并用吴氏建立的Ｂ细胞表位预测方法进行评述。结果显示，不同的预测方案所得结果一致，人Ｃ５ａＲ分子中，构成螺旋结构，伸展构象及无规卷曲的氨基酸残基数比例分别为３３．７％，３４．６％，３１．７％。三个高亲水性区域为第１５～１８位的ＤＤＫＤ，第１９５～２００位的ＤＫＲＲＥＲ和第３３０～３３３位的ＲＥＳＫ，其Ａｈ值分别为３．０、３．０、２．３２。其平均抗原性指数ＡＩ值分别为０．０６４、０．０９１、０．０７０。Ｎ－端第９～３０氨基酸序列的ＡＩ＝０．０４２，是Ｂ细胞优势表位区，以此制作短肽单克隆抗体是可行的。     

短发夹状RNA基因沉默补体受体C5aR及抑制LPS诱导的肾脏上皮细胞凋亡

目的:探讨短发夹状RNA基因沉默补体受体C5aR及抑制LPS诱导的肾脏上皮细胞凋亡的作用效果。方法:构建针对大鼠补体受体C5aR基因编码区的短发夹状RNA(shRNA)真核表达载体质粒pRNAT-U6.1-C5aR shRNA,采用电穿孔的方法转染RK3E细胞,经G418筛选后,形成稳定的表达C5aR shRNA的细胞系。实验分为3组,①正常对照组:未转染的RK3E细胞;②阴性对照组:转染空载体pRNAT-U6.1的RK3E细胞系;③实验组:转染C5aR shRNA的RK3E细胞系。经脂多糖(LPS)孵育12小时后,流式细胞仪检测各组细胞凋亡率,RT-PCR检测mRNA的表达,γ计数仪测定125I标记的C5a与RK3E的结合情况。结果:与正常对照组和阴性对照组相比,实验组的细胞凋亡率显著降低(P0.01),C5aR mRNA水平显著降低(P0.01),125I标记的C5a与RK3E结合活性显著下降。结论:针对C5aR的特异性短发夹RNA可以明显引起靶基因的沉默,进而抑制LPS诱导的肾脏上皮细胞凋亡的发生。     

Functional identification of the stable transfection C5aR cell line Molt-4

The complement C5 anaphylatoxin receptor is a member of the seven transmembrane-spanning G protein-coupled receptor superfamily that signals through Gcxi and Gtz16. C5aR is mostly expressed on neutrophils, macrophages and endothelial cells. C5a and C5aR interaction plays an important role in numerous biological effects such as in vivo cytokine storm which results in inflammatory damage. Considering the limitation of collection of human peripheral blood neutrophils and their short half life, the stably transfected cell line for studying the biological effects of C5aR is needed. In this study, we transfected C5aR gene into Molt-4 cell line and examined the function of ectopic C5aR. Our results showed stable expression of the C5aR in Molt-4 cell line and their interaction with human C5a induced ERKI/2 phosphorylation, Ca＋＋ influx. This stable transfected cell line may provide a useful tool for studying signal pathways related to C5a and C5aR interplay and antibody development specific for C5aR. Cellular ＆ Molecular Immunology.     

Expression of the anaphylatoxin receptors C3aR and C5aR is increased in fatal asthma

BACKGROUND: The mechanisms leading to death from asthma are not completely understood. Recent studies suggest the involvement of the anaphylatoxins C3a and C5a, generated during complement activation, and their receptors C3aR and C5aR in the pathogenesis of asthma. OBJECTIVE: The aim of our study was to investigate the expression of C3aR and C5aR in fatal asthma. METHODS: We analyzed lung tissue from 14 subjects who died of asthma (fatal asthma; FA) and 14 subjects who died of nonpulmonary causes (controls) and bronchial biopsy specimens from 16 subjects with mild intermittent asthma (MIA). C3aR and C5aR expression was evaluated by immunohistochemistry, and a semiquantitative analysis of the intensity of staining was performed according to a visual analogue scale (score, 0-3). RESULTS: C3aR was expressed on airway epithelium, smooth muscle, submucosal, and parenchymal vessels. C5aR was expressed on myeloid cells infiltrating the submucosa and on airway epithelium. Statistical analysis demonstrated higher expression of C3aR on submucosal vessels in FA compared with controls and MIA (median [minimum-maximum], controls, 0.24 [0-1.48]; MIA, 0.0 [0-1.00]; FA, 1.56 [0.13-3]; P = .002). C3aR was also increased on parenchymal vessels in FA (controls, 0.56 [0-2.00]; FA, 1.81 [0.5-3]; P = .0004). C5aR expression on airway epithelium was increased in FA compared with controls and MIA (controls, 1.25 [0.25-3]; MIA, 1.00 [0-2.00]; FA, 3.00 [1.13-3.00]; P = .001). CONCLUSION: The results of our study suggest a role of complement in FA.     

Functions of C5a receptors

The split product of the complement protein, C5, is C5a and is an extremely potent pro-inflammatory peptide that interacts with two C5a receptors, C5aR and C5L2, present on surfaces of phagocytes as well as other cell types. The former is a well-established receptor that initiates G-protein-coupled signaling via mitogen-activated protein kinase pathways. Its in vivo blockade greatly reduces inflammatory injury. Much less is known about C5L2, occupancy of which by C5a does not initiate increased intracellular Ca²⁺. There are numerous conflicting reports suggesting that C5L2 is a “default receptor” that attenuates C5a-dependent biological responses by competing with C5aR for binding of C5a. However, there are other reports suggesting that C5L2 plays an active, positive role in inflammatory responses. Better definition of C5L2 is needed if its in vivo blockade, along with C5aR, is to be considered in complement-dependent inflammatory diseases.     

C5a- and ASP-mediated C5L2 activation, endocytosis and recycling are lost in S323I-C5L2 mutation

C5L2, a G-protein-coupled receptor (GPCR), has been identified as an ASP (C3adesArg) and C5a receptor. Controversy exists regarding both ligand binding and functionality. ASP activation of C5L2 is proposed to regulate fat storage. C5L2 is also proposed as a decoy receptor for C5a, an inflammatory mediator, based on absence of Ca²⁺ or chemotaxis changes.

Aims

(i) to evaluate C5L2 receptor activation and recycling using recombinant ASP (rASP) and rC5a and (ii) assess receptor trafficking of S323I-C5L2 mutation previously identified in a family and demonstrated to have altered functionality.

Results

stably transfected C5L2-HEK cells were sorted using fluorescent-ASP (Fluos-ASP) binding. Following 2-h serum-free pretreatment, C5L2 was typically localized to the cell-surface. β-Arrestin-2-GFP transiently transfected C5L2-HEK cells demonstrated rASP and rC5a-dependent β-arrestin-2-GFP translocation, which showed time-dependent intracellular colocalization with C5L2. Without ligand or C5L2 transfection, no translocation was identified at any time point. Ligand-dependent (rASP and rC5a) C5L2 endocytosis was time-dependent with a 1-h nadir, and was clathrin- and cholesterol-dependent. Transiently transfected Rab-GFP proteins (Rabs 5, 7 and 11) demonstrated time-dependent colocalization of Rab5, Rab7, and Rab11 with C5L2. In contrast to C5L2, a large proportion of stably transfected S323I-C5L2 did not localize to the cell-surface. While S323I-C5L2 was competent for Fluos-ASP and ¹²⁵I-ASP binding, although at a reduced level, there was no ligand-mediated receptor phosphorylation. Further, there was no ligand-mediated activation of β-arrestin-2-GFP translocation, and no downstream functional activation of glucose transport or triglyceride synthesis.

Conclusion

C5L2 is a functional metabolic receptor, and serine 323 is important for ASP induced functionality.     

Rapid‐onset clinical and mechanistic effects of anti‐C5aR treatment in the mouse collagen‐induced arthritis model

Preclinical evidence supports targeting the C5a receptor (C5aR) in rheumatoid arthritis (RA). To support ongoing clinical development of an anti‐C5aR monoclonal antibody, we have investigated for the first time the mechanism of action and the pharmacodynamics of a blocking anti‐murine C5aR (anti‐mC5aR) surrogate antibody in mouse collagen‐induced arthritis (CIA). First, efficacy was demonstrated in a multiple‐dose treatment study. Almost complete inhibition of clinical disease progression was obtained, including reduced bone and cartilage destruction in anti‐mC5aR‐treated mice. Then, the mechanism of action was examined by looking for early effects of anti‐mC5aR treatment in single‐dose treatment studies. We found that 48 h after single‐dose treatment with anti‐mC5aR, the neutrophil and macrophage infiltration into the paws was already reduced. In addition, several inflammatory markers, including tumour necrosis factor (TNF)‐α, interleukin (IL)‐6 and IL‐17A were reduced locally in the paws, indicating reduction of local inflammation. Furthermore, dose‐setting experiments supported a beneficial clinical effect of dosing above the C5aR saturation level. In conclusion, these preclinical data demonstrated rapid onset effects of antibody blockade of C5aR. The data have translational value in supporting the Novo Nordisk clinical trials of an anti‐C5aR antibody in rheumatoid arthritis patients, by identifying potential biomarkers of treatment effects as well as by providing information on pharmacodynamics and novel insights into the mechanism of action of monoclonal antibody blockade of C5aR.     

Expression of complement C3, C5, C3aR and C5aR1 genes in resting and activated CD4+ T cells

Complement activation is traditionally thought to occur in the extracellular space. However, it has been suggested that complement proteins are activated and function at additional locations. T cells contain intracellular stores of C3 and C5 that can be cleaved into C3a and C5a and bind to intracellular receptors, which have been shown to be of vital importance for the differentiation and function of these cells. However, whether the origin of the complement proteins located within T cells is derived from endogenous produced complement or from an uptake dependent mechanism is unknown.The presence of intracellular C3 in T cells from normal donors was investigated by fluorescence microscopy and flow cytometry. Moreover, mRNA expression levels of several genes encoding for complement proteins with primary focus on C3, C3aR, C5 and C5aR1 during resting state and upon activation of CD4⁺ T cells were investigated by a quantitative PCR technique. Furthermore, the gene expression level was evaluated at different time points.We confirmed the presence of intracellular C3 protein in normal T-cells. However, we could not see any increase in mRNA levels using any activation strategy tested. On the contrary, we observed a slight increase in C3 and C5aR1 mRNA only in the non-activated T-cells compared to the activated T cells, and a decrease in the activated T-cells at different incubation time points.Our results show that there is a baseline intracellular expression of the complement C3, C5, C3aR and C5aR1 genes in normal CD4⁺ T cells, but that expression is not increased during T-cell activation, but rather down regulated. Thus, the pool of intracellular complement in CD4⁺ T cells may either be due to accumulated complement due low-grade expression or arise from the circulation from an uptake dependent mechanism, but these possibilities are not mutually exclusive.