G蛋白偶联受体91对早期糖尿病大鼠血视网膜屏障的影响及机制

The effects and mechanisms of G protein-coupled receptor 91 on blood-retinal barrier in diabetic rats

目的观察G蛋白偶联受体9l（GPR91）对早期糖尿病大鼠血视网膜屏障（BRB）的影响及可能的作用机制。方法构建GPR9l小发夹RNA（shRNA）慢病毒载体pGCSIL-GFP-shGPR91及相应的慢病毒空载体pGCSIL-GFP-shSerambled。健康雄性Sprague-Dawley大鼠60只，随机分为对照组（A组）、糖尿病链脲佐菌素（STZ）组（B组）、空病毒LV．shScrambled组（C组）、病毒LV．shGPR91组（D组），每组均为15只大鼠。大鼠STZ腹腔注射2周后，C组大鼠玻璃体腔注射浓度为1×10^8TU／m1的空载体病毒1肛1；D组大鼠玻璃体腔注射浓度为1×10^8 Tu／m1的pGCSIL-GFP-shGPR91慢病毒1μl。注射后12周，免疫组织化学染色和蛋白免疫印迹法（Western blot）检测各组大鼠视网膜中GPR91及丝裂原活化蛋白激酶（MAPK）的表达和激活情况。苏木精一伊红染色和伊凡思蓝（EB）渗漏试验观察大鼠视网膜微血管结构改变和渗漏情况。酶联免疫吸附试验（ELISA）检测视网膜中血管内皮生长因子（VEGF）表达情况。结果免疫组织化学染色可见GPR91主要表达于大鼠视网膜神经节细胞层；Western blot检测结果显示，D组GPR91表达较C组显著降低，差异有统计学意义（F=39．31，P〈0．01）。光学显微镜观察发现，B、C组大鼠视网膜内层毛细血管较A组大鼠视网膜内层毛细血管明显扩张，D组大鼠视网膜内层扩张的毛细血管显著改善。EB渗漏试验结果显示，D组大鼠视网膜EB渗漏量较C组下降（33．8±4．11）％，差异有统计学意义（F=30．35，PG0．05）。ELISA检测结果显示，B、C组大鼠视网膜VEGF蛋白表达较A组明显增加；D组大鼠视网膜VEGF蛋白表达较C组显著下降，差异有统计学意义（F=253．15，P〈0．05）。Western blot检测结果显示，B组大鼠视网膜细胞外信号调节激酶（ERK）1／2、c-jun氨基末端激酶、p38MAPK通路均激活，B组各比值与A组比较，差异有统计学意义（q=6．38、2．94、3．45，P〈0．05）。D组中p-ERK1／2与t-ERK1／2的比值较C组显著降低，差异有统计学意义（F=22．50，P〈0．05）。结论GPR91受体shRNA玻璃体腔注射可改善早期糖尿病大鼠视网膜BRB损伤；GPR91受体可能通过激活ERK1／2信号通路参与调控早期糖尿病视网膜中VEGF的表达及BRB的损伤。

Objective To investigate the effects and mechanisms of G protein-coupled receptor 91 （GPR91） on blood-retinal barrier （BRB） in diabetic rats. Methods A lentiviral vector of shRNA targeting rat GPR91 and scrambled shRNA were constructed. Healthy male Sprague-Dawley （SD） rats were selected in this study. The 60 rats were randomized into 4 groups and treated as follows： （1） control group （Group A, n= 15）, the rats received injections of an equal volume of 0.1 % citrate buffer; （2） streptozocin （STZ） group （Group B, n=15）, the rats received injections of STZ; （3） LV. shScrambled group （Group C,n= 15）, diabetic rats received an intravitreal injection of 1 /21 1 ×10^8 TU/ml scrambled shRNA lentiviral particles at 2 weeks after the induction of diabetes; （4） LV. shGPR91 group （Group D, n= 15）, diabetic rats received an intravitreal injection of 1 μl 1 × 10^8 TU/ml pGCSIL-GFP-shGPR91 lentiviral particles. At 12 weeks after intravitreal injection, immunohistochemistry and Western blot were used to assess the expression of GPR91, p-extracellular signal-regulated kinase（ERK）1/2, t-ERK1/2, p-Jun N-terminal kinase （JNK）, t-JNK, p-p38 mitogen-activated protein kinase （MAPK） and t-p38 MAPK. Haematoxylin and eosin （HE） staining and Evans blue dye were used to assess the structure and function of the retinal vessel. Immunohistochemistry enzyme-linked immunosorbent assay （ELISA） was used to test the protein level of VEGF. Results Immunohistochemistry staining showed that GPR91 was predominantly localized to the cell bodies of the ganglion cell layer. Western blot showed that GPR91 expression in Group D decreased significantly compared with Group C （F= 39.31,P〈0.01）. HE staining showed that the retina tissue in Group B and C developed telangiectatic vessels in the inner layer of retina, while the telangiectatic vessels attenuated in Group D. It was also demonstrated in Evans blue dye that the microvascular leakage in Group D decreased by （33.8±4.11）% compared with Group C and there was significant difference （F=30.35, P〈0.05）. The results of ELISA showed the VEGF secretion of Group B and C increased compared with Group A and the VEGF expression in Group D was significantly down regulated after silencing GPR91 gene （F= 253.15, P〈0.05）. The results of Western blot indicated that compared with Group A, the expressions of p-ERK1/2 , p-JNK and p-p38 MAPK were significantly upregulated （q=6.38, 2.94, 3.45; P〈0.05）. Meanwhile, the activation of ERK1/2 was inhibited by GPR91 shRNA and the difference was statistically significant （F=22.50, P〈0.05）. Conclusions The intravitreal injection of GPR91 shRNA attenuated the leakage of BRB in diabetic rats. GPR91 regulated the VEGF release and the leakage of BRB possibly through the ERK1/2 signaling pathway.