The effect of endoplasmic reticulum stress on detrusor muscle apoptosis in diabetic cystopathy

Abstract

Objective To observe the effect of Endoplasmic Reticulum Stress (ERS) on detrusor muscle apoptosis in Streptozotocin (STZ)-induced diabetic rats. Methods At 4, 8, 12, and 16 weeks after induction of diabetic rat models, the sections of detrusor muscle tissue were made and were stained with Van Gieson solution, the collagen fibers of each group were observed and their proportions were calculated; the sub-cellular ultrastructure was observed by Transmission Electron Microscopy (TEM). Proliferating Cell Nuclear Antigen (PCNA) assay kit and Strept Avidin-Biotin Complex (SABC) staining were used for the evaluation of Detrusor Smooth Muscle (DSM) cell proliferation. Moreover, the expression of three hallmarks of ERS-associated apoptosis, including Glucose-regulated protein 78 (GRP78), CCAAT/enhancer-binding protein homologous protein (CHOP), and cysteinyl aspartate-specific protease (Caspase)-12, was detected by Real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting. Results The proportion of collagen fibers showed a significant climbing trend [(13.38±2.65)%, (18.14±1.93)%, (19.71±3.05)% vs. (7.86±0.72)%, P<0.05] since DM8w group, except DM4w group [(8.02±0.43)%]. With the time prolonged, the swelled and fused cisternaes started to show; the mild particle fusion and degranulation also could be seen in the zone of ER; the distorted or pyknotic nucleus contained clusters of unidentified dark-stained granules that could be observed. Compared with the control group, the increased PCNA-positive percentages [(20.34±4.55)%, (46.88±7.12)%, (39.78±1.93)%, (22.15±5.64)% vs. (16.26±2.43)%, P<0.05] and apoptosis indexes [(17.12±2.78)%, (28.12±4.09)%, (28.12±4.09)%, (43.39±6.82)% vs. (6.32±1.23)%, P<0.05] can be seen in model groups. Elevated expression of GRP78, CHOP, and Caspase-12 at both protein and mRNA levels in a time-dependent fashion were detected (P<0.05). Conclusion Morphological and ultrastructural damages to the DSM as well as the cell proliferation and apoptosis indicate the time-dependent alterations. The occurrence of ERS may be involved in the development of diabetic cystopathy (DCP) and may contribute to the diabetic detrusor muscle apoptosis. Key words: Endoplasmic reticulum stress; Diabetic cystopathy; Detrusor; Apoptosis