内质网应激凋亡通路中Caspase12激活介导的肝纤维化大鼠肝细胞凋亡

Effect of liraglutide on endoplasmic reticulum stress in the renal tissue of type 2 diabetic rats

BACKGROUND

Liraglutide is a glucagon-like peptide 1 receptor agonist analog that has been found to have a therapeutic effect in diabetes. In addition to its ability to treat diabetes, liraglutide has beneficial effects on the cardiovascular system and kidney as well as other beneficial effects, but its specific mechanism is not clear. In this study, a rat model of type 2 diabetes was established by administration of a high-sugar, high-fat diet combined with low-dose streptozotocin (STZ) to observe the effect of liraglutide on the kidneys of type 2 diabetes rats and the possible underlying mechanisms.

AIM

To explore whether liraglutide has a protective effect on type 2 diabetic rat kidneys and the underlying mechanisms.

METHODS

Eight-week-old male Sprague-Dawley rats were randomly divided into a control group, model group, low-dose liraglutide group, and high-dose liraglutide group. Control rats were fed a standard diet, while model group and intervention group rats were fed high-sugar, high-fat feed for 1 mo and then intraperitoneally injected with 40 mg/kg STZ to induce type 2 diabetes. The low-dose and high-dose intervention groups received 100 µg/kg and 200 µg/kg liraglutide, respectively, once daily by subcutaneous injection. The control and model groups were given an equivalent volume of physiological saline for 8 wk. Pathological changes in renal tissues were observed by hematoxylin and eosin staining and periodic acid-Schiff staining, and GRP78 and caspase-12 expression was detected by Western blot and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Western blot analysis showed that GRP78 and caspase-12 protein expression in kidney tissue was significantly higher in model rats than in normal rats and lower in the liraglutide-treated groups than in the model group, with a more significant decrease being observed in the high-dose group than in the low-dose group. RT-PCR showed that the mRNA expression of GRP78 and caspase-12 was higher in model rats than in control rats and lower in the liraglutide-treated groups than in the model group, with the high-dose group exhibiting a more significant decrease than the low-dose group.

CONCLUSION

Liraglutide may delay the progression of diabetic nephropathy by reducing endoplasmic reticulum stress and protect the kidneys in a dose-dependent manner.

Calpain-2 activity promotes aberrant endoplasmic reticulum stress-related apoptosis in hepatocytes

BACKGROUND

Calpain-2 is a Ca²⁺-dependent cysteine protease, and high calpain-2 activity can enhance apoptosis mediated by multiple triggers.

AIM

To investigate whether calpain-2 can modulate aberrant endoplasmic reticulum (ER) stress-related apoptosis in rat hepatocyte BRL-3A cells.

METHODS

BRL-3A cells were treated with varying doses of dithiothreitol (DTT), and their viability and apoptosis were quantified by 3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2-H-tetrazolium bromide and flow cytometry. The expression of ER stress- and apoptosis-related proteins was detected by Western blot analysis. The protease activity of calpain-2 was determined using a fluorescent substrate, N-succinyl-Leu-Leu-Val-Tyr-AMC. Intracellular Ca²⁺ content, and ER and calpain-2 co-localization were characterized by fluorescent microscopy. The impact of calpain-2 silencing by specific small interfering RNA on caspase-12 activation and apoptosis of BRL-3A cells was quantified.

RESULTS

DTT exhibited dose-dependent cytotoxicity against BRL-3A cells and treatment with 2 mmol/L DTT triggered BRL-3A cell apoptosis. DTT treatment significantly upregulated 78 kDa glucose-regulated protein, activating transcription factor 4, C/EBP-homologous protein expression by >2-fold, and enhanced PRKR-like ER kinase phosphorylation, caspase-12 and caspase-3 cleavage in BRL-3A cells in a trend of time-dependence. DTT treatment also significantly increased intracellular Ca²⁺ content, calpain-2 expression, and activity by >2-fold in BRL-3A cells. Furthermore, immunofluorescence revealed that DTT treatment promoted the ER accumulation of calpain-2. Moreover, calpain-2 silencing to decrease calpain-2 expression by 85% significantly mitigated DTT-enhanced calpain-2 expression, caspase-12 cleavage, and apoptosis in BRL-3A cells.

CONCLUSION

The data indicated that Ca²⁺-dependent calpain-2 activity promoted the aberrant ER stress-related apoptosis of rat hepatocytes by activating caspase-12 in the ER.