Background Endoplasmic reticulum stress (ERS) specific caspase-12 dependent pathway plays a key role in cell apoptosis,and apoptosis is an important characteristic of diabetic retinal neuron degeneration.Sericin is a potentially effective therapy for retinal neuron apoptosis.However,whether sericin has neuroprotection effects on caspase-12 pathway-associated retinal cells in diabetic retinopathy (DR) process is not unelucidated.Objective This study was to investigate the effects of sericin on the inhibition of retinal neuron apoptosis-associated with ERS specific caspase-12 dependent pathway in diabetic rat.Methods The diabetic models were established by feeding high lipid foods and intraperitoneal injection of streptozotocin for 3 consecutive days in 30 SPF SD rats aged 2-3 months.Twenty-four successful model rats were randomized into sericin-treated group and diabetic model group according to computer number allocation,and another 12 matched rats served as normal control group.The normal saline solution and sericin solution dissolved with normal saline solution 2.4 g/(kg · d) was used for 35 days in gavage method in the diabetic model group and sericin-treated group,respectively.The rats were sacrificed and retinal sections were prepared.TUNEL staining was employed to detect retinal neuron apoptosis.The expressions of glucose regulated protein 78 (GRP78),an ERS marker,and caspase-12 and caspase-3 in retinas in protein and transcription levels were detected by Western blot and reverse transcription PCR,respectively.The use and care of the rats complied with Regulations for the Administration of Affairs Concerning Experimental Animals by State Science and Technology Commission and ARVO Statement.Results Diabetic models were successfully established in 24 of total 30 rats,with the successful rate of 80％.Apoptotic cells were found in the rats of various groups,mostly locating in retinal ganglion cell layer and inner nuclear layer.The apoptotic index (AI) was 0.028 4±0.002 3,0.215 1 ± 0.020 9 and 0.115 0±0.018 1 in the normal control group,diabetic model group and sericin-treated group,respectively,and the AI was significantly lower in the sericin-treated group than that in the diabetic control group (P＜ 0.05).Compared with the diabetic model group,the relative expression levels of GRP78,caspase-12 and caspase-3 proteins in rat retinas were significantly elevated in the sericin-treated group (0.523±0.029 vs.0.924±0.039,1.118 ± 0.051 vs.1.468±0.037,0.315±0.024 vs.0.554±0.032) (all at P＜0.05),and the relative expression levels of GRP78,caspase-12 and caspase-3 mRNA in rat retinas were significantly reduced in the sericin-treated group (0.816± 0.022 vs.1.218±0.033,0.216±0.023 vs.0.407±0.012,0.322±0.022 vs.0.531 ±0.029) (all at P＜0.05).Conclusions Sericin can inhibit ERS-related retinal neuron apoptosis by down-regulating the expressions of GRP78,caspase-12 and caspase-3 in ERS specific caspase-12 dependent pathway in diabetic rats.%背景 内质网应激(ERS)特异性caspase-12凋亡途径在细胞凋亡过程中发挥重要作用,细胞凋亡是糖尿病视网膜神经退行性病变的重要特征.研究证实,丝胶对视网膜神经细胞的凋亡具有保护作用,但其对糖尿病视网膜病变(DR)过程中与caspase-12凋亡途径相关的视网膜神经细胞是否具有保护作用仍有待研究证实. 目的 探讨丝胶是否能够通过影响ERS特异性caspase-12凋亡途径对糖尿病大鼠视网膜细胞凋亡发挥抑制作用.方法 采用高脂高糖饲料喂养联合链脲佐菌素(STZ)连续腹腔内注射3d对30只2～3月龄SPF级SD大鼠制备糖尿病模型,以大鼠空腹血糖≥16.7 mmol/L及出现多饮、多食、多尿特点为造模成功.将24只造模成功的糖尿病模型大鼠按照计算机数字随机分配法分为丝胶治疗组和糖尿病模型组,每组12只,另取同周龄12只正常大鼠作为正常对照组.丝胶治疗组大鼠于成模后给予丝胶溶液2.4 g/(kg·d)灌胃,连续35 d.各组大鼠采用过量麻醉法处死并制备视网膜标本,采用TUNEL法检测并计算各组大鼠视网膜神经细胞的凋亡指数(AI);分别采用Western blot法和逆转录PCR技术检测大鼠视网膜中ERS标志物葡萄糖调节蛋白78(GRP78)、ERS特异性caspase-12凋亡途径和easpase-3蛋白及其mRNA的相对表达量,并对各组检测结果进行比较. 结果 大鼠糖尿病造模成功率为80％(24/36).正常对照组、糖尿病模型组和丝胶治疗组大鼠均可见视网膜神经细胞凋亡,阳性产物主要位于视网膜神经节细胞(RGCs)层和内核层,AI分别为0.028 4±0.002 3、0.215 1±0.020 9和0.1150±0.018 1,糖尿病模型组大鼠视网膜AI明显高于对照组,丝胶治疗组AI明显低于糖尿病模型组,差异均有统计学意义(均P＜0.05).丝胶治疗组大鼠视网膜中GRP78、caspase-12和easpase-3蛋白的相对表达量分别为0.523±0.029、1.118±0.051和0.315±0.024,较糖尿病模型组的0.924±0.039、1.468±0.037和0.554±0.032均明显下降,差异均有统计学意义(均P＜0.05),丝胶治疗组大鼠视网膜中GRP78、easpase-12和caspase-3 mRNA的相对表达量分别为0.816±0.022、0.216±0.023和0.322±0.022,较糖尿病模型组的1.218±0.033、0.407±0.012和0.531±0.029均明显下降,差异均有统计学意义(均P＜0.05). 结论 丝胶可以通过下调糖尿病模型大鼠视网膜中GRP78、caspase-12和caspase-3的表达改善内质网ERS,减少视网膜神经细胞的凋亡.
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