Pro-inflammatory effect induced by endoplasmic reticulum stress in placental trophoblast cells participates in genesis of gestational diabetes mellitus

Abstract

Objective To explore whether the pro-inflammatory effect of endoplasmic reticulum stress in placental tissues involves in the genesis of gestational diabetes mellitus (GDM). Methods Forty gravidas who underwent regular prenatal examinations and delivered at Tongji Hospital were recruited from January to December, 2016. Among them, 20 were GDM women (GDM group), and the remaining twenty were served as the control, which were selected from those without GDM and matched for age and gestational weeks to the GDM group. Placental tissues were collected from the two groups. The ultrastructure of endoplasmic reticulum in trophoblast cells was observed under transmission electron microscope. The expression of glucose-regulated protein-78 (GRP-78), a marker protein for endoplasmic reticulum stress, and C/EBP homologous protein (CHOP) were detected using Western blotting. Five placental tissue samples were collected from normal gravidas for explant culture. Three subgroups were set up according to different culturing methods including culturing with IL-1β (5 ng/ml) for 20 h (IL-1β model group), 30 μmol/L thapsigargin (TG, an endoplasmic reticulum stress agonist) for 2 h after treating with IL-1β (5 ng/ml) for 18 h (IL-1β+TG intervention group) or with no stimulation (blank control group). Western blotting was used to detect the expressions of GRP-78, CHOP and glucose transporter 4 (GLUT4) in placenta explants. The mRNA expressions of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were determined by real-time fluorescence quantitative polymerase chain reaction (RT-PCR). Statistical analysis was performed using one-way analysis of variance, LSD and t test. Results (1) In the GDM group, increased number and size of endoplasmic reticulum cisternae were observed in trophoblast cells. Moreover, obviously dilated endoplasmic reticulum and different size of fragments and vesicles were also seen under electron microscope. While the endoplasmic reticulum in the placental tissues of the control group showed no obvious swelling. (2) The expression of GRP-78 and CHOP protein in the GDM group were higher than those in the control group (0.90±0.17 vs 0.48±0.08, t=2.24; 0.85±0.13 vs 0.46±0.12, t=2.10; both P<0.05). (3) Compared with the blank control group, the expression of GRP-78 and CHOP protein in the IL-1β model group increased significantly (0.87±0.18 vs 0.36±0.07, t=2.67; 1.14±0.09 vs 0.78±0.06, t=3.20; both P<0.05); but the expression of GLUT4 protein significantly decreased (1.00±0.14 vs 2.21±0.49, t=2.40, P<0.05); the expressions of IL-6 and TNF-α mRNA significantly increased (0.89±0.23 vs 0.30±0.06, t=2.31; 0.62±0.16 vs 0.17±0.09, t=2.29; both P<0.05). Compared with the IL-1β model group, the expression of GRP-78 and CHOP protein significantly increased in IL-1β+TG group (2.02±0.32 vs 0.87±0.18, t=3.11; 2.18±0.31 vs 1.14±0.09, t=3.16; both P<0.05); the expression of GLUT4 protein significantly decreased (0.39±0.19 vs 1.00±0.14, t=2.66, P<0.05); the expression of IL-6 and TNF-α mRNA increased significantly (1.67±0.25 vs 0.89±0.23, t=2.26; 1.42±0.27 vs 0.62±0.16, t=2.51; both P<0.05). Conclusions Endoplasmic reticulum stress may be associated with increased release of pro-inflammatory cytokines in placental tissues of some GDM women and involved in the onset and development of GDM. Key words: Diabetes, gestational; Endoplasmic reticulum stress; Placenta; Cytokines; Inflammation