Background The excitotoxicity to retinal neurons caused by abnormal elevation of glutamate in retina is a common pathology concomitant with major blind-causing eye diseases.However,an effective approach to protect retinal neurons from glutamate-induced excitotoxicity is still lack.Intraperitoneal administration of α-melanocyte stimulating hormone(α-MSH)has been shown to protect hippocampal neurons from glutamate-induced excitotoxicity.Objective This study was to investigate the protective effect of α-MSH on glutamate-induced excitotoxicity in a chicken embryonic retinal explant culture system.Methods The retinas were isolated from chick embryos at embryonic day 9(E9) and cultured as explants.The explants at 3,5 and 7 days in vitro and the retinas at corresponding embryonic day 12,14 and 16(E12,E14,E16)were collected.The morphology of explant cultures was examined by hematoxylin and eosin staining,and the expression of melanocortin receptors (MCRs)was analyzed by real-time PCR.In the experiment of glutamate-induced excitotoxicity,the retinal explants at 4 days in vitro were treated with glutamate for 48 hours,α-MSH was incubated with the explants 30 minutes before and during the glutamate treatment period.Then the apoptotic cells were detected by TUNEL staining and quantified.The glutamate alone treated-explants and those treated with culture media were included as controls.The expression of glial fibrillary acidic protein(GFAP) at 48 hours after treatment in all retinal explants was analyzed by real-time PCR.Results Hematoxylin and eosin staining showed that the retinal explants exhibited similar morphology to those observed in the retinas from chick embryos at the corresponding developmental stages.The real-time PCR analyses of chick retinas showed that MC1R mRNA level at E9,E12,E14 and E16 was significantly lower than that in post-hatch day 1 (all P=0.000) ;whereas the transcript level of MC5R was significantly increased from E9 to E12 and E14 (both P =0.000),and then gradually decreased from E14 to P1.The expression of these genes showed similar temporal patterns in the retinal explant cultures.TUNEL staining revealed that treatment of the retinal explant cultures with α-MSH substantially and significantly reduced number of apoptotic cells induced by glutamate (P =0.000),which was accompanied by significant suppression of glutamate-induced GFAP up-regulation (P =0.000).Conclusions Application of α-MSH dramatically ameliorated glutamate-induced cell death in retinal explant cultures.This protective effect may be due to α-MSH-mediated suppression of astrogliosis caused by abnormal elevation of glutamate.%背景 视网膜中谷氨酸异常增高是主要致盲性眼病的基本病理机制之一,但目前仍缺乏一种针对谷氨酸诱导的视网膜兴奋性毒性的有效保护措施.研究证明腹腔注射α-黑素细胞刺激素(α-MSH)可拮抗谷氨酸诱导的大脑海马区神经元的凋亡,但其对视网膜疾病的保护作用尚未证实. 目的 研究α-MSH对谷氨酸引起的视网膜兴奋性毒性的保护作用. 方法 用胚胎第9天(E9)的鸡视网膜建立组织块培养体系.分别收集体外培养第3、5、7天的视网膜组织块及第12、14、16天(E12、E14、E16)的鸡胚视网膜各3块,进行常规苏木精-伊红染色,观察各标本的视网膜形态及组织结构,并用real-time PCR法分别检测不同培养时间点视网膜组织块中α-MSH受体(MCRs)表达量的动态变化.将视网膜组织块分为谷氨酸刺激组、α-MSH+谷氨酸刺激组以及正常培养组,分别用谷氨酸及α-MSH+谷氨酸处理48 h,正常培养组未做处理,用TUNEL染色法检测各组视网膜组织块中细胞凋亡情况,并进行定量分析；real-time PCR法检测各组视网膜组织块中胶质纤维酸性蛋白(GFAP)的表达. 结果 培养3、5、7d视网膜组织块中各层组织结构与E12、E14和E16的视网膜组织结构相似.MC1R mRNA在E9、E12、E14和E16鸡视网膜中的表达量明显低于出生后第1天(P1),差异均有统计学意义(均P=0.000)；MC5R mRNA在E9的表达量明显低于E12及E14,差异均有统计学意义(均P=0.000),从E14至P1则逐渐降低；而MC1R mRNA和MC5R mRNA在培养不同时间视网膜组织块中的表达呈现同样的规律.TUNEL染色显示,谷氨酸刺激鸡胚视网膜组织48 h后,视网膜内核层和神经节细胞层细胞大量凋亡,外核层亦有少量凋亡细胞.DAPI染色结果表明,视网膜各层排列紊乱,但α-MSH+谷氨酸刺激组视网膜结构比较规则.定量分析结果表明,谷氨酸刺激组鸡胚视网膜每张切片的平均凋亡细胞数量为(601±24)个,α-MSH+谷氨酸刺激组为(62±16)个,正常对照组为(72±13)个,各组凋亡细胞数量总体比较差异有统计学意义(F=1422.890,P=0.000)；α-MSH+谷氨酸刺激组凋亡细胞数量明显少于谷氨酸刺激组,差异有统计学意义(P=0.000).谷氨酸刺激组视网膜组织块中GFAP mRNA的相对表达量为2.23±0.06,α-MSH+谷氨酸刺激组为1.14±0.15,正常对照组为1.05±0.04,组间总体差异有统计学意义(F=82.216,P=0.000).谷氨酸刺激组GFAP mRNA的表达量是正常对照组的2.1倍,差异有统计学意义(P=0.000).α-MSH+谷氨酸刺激组的GFAP的表达量较谷氨酸刺激组显著下调,差异有统计学意义(P=0.000),但与正常对照组相比差异无统计学意义(P=0.553). 结论 α-MSH在视网膜组织块中大幅度降低谷氨酸诱导的兴奋性毒性,这种保护作用可能是通过抑制谷氨酸诱导的胶质细胞反应性增生而引起的.
展开▼
