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.

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.

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.

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).

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.

Sericins/pharmacology; Diabetic retinopathy/physiopathology; Gene expression; Glucose regulating protein 78; Cysteine aspartate kinase 12; Cysteine aspartate kinase 3; Rats, Sprague Dawley