Feedback regulation of Nrf2 on cadmium chloride-induced endoplasmic reticulum stress in testicles and ovaries of rats

Objective To investigate the feedback regulatory effects of nuclear factor erythroid 2-related factor 2 (Nrf2) on cadmium chloride (CdCl₂)-induced endoplasmic reticulum stress in the testicles and ovaries of rats.

Methods Forty-eight Sprague-Dawley rats were randomly divided into eight groups (six rats in each group) according to the cadmium chloride exposure dose and whether to administer tert-butylhydroquinone (tBHQ): control group (intraperitoneal injection of 0.9% normal saline); low-dose, medium-dose, and high-dose CdCl₂ groups (intraperitoneal injected of CdCl₂ solution at 1.14, 2.28, and 4.56 mg/kg, respectively); tBHQ group (intraperitoneal injection of 20 mg/kg tBHQ solution); and tBHQ+low-dose, tBHQ+medium-dose, and tBHQ+high-dose CdCl₂ groups (pretreatment with 20 mg/kg tBHQ solution 120 minutes before intraperitoneal injection of 1.14, 2.28, and 4.56 mg/kg CdCl₂ solution, respectively). After 48 hours of exposure, the rats were sacrificed to collect the testicles and ovaries, and the mRNA and protein expression levels of 78 kDa glucose-regulated protein (Bip), PKR-like endoplasmic reticulum kinase (PERK), Nrf2 was determined by RT-PCR and Western blot.

Results Compared with tBHQ group, the expression of Nrf2 mRNA and protein in the testicles in the tBHQ+medium-dose CdCl₂ group was significantly increased (F were 144.47 and 302.88, respectively, P < 0.05); the expression of Nrf2 mRNA and protein in the ovaries in the tBHQ+low-dose, medium-dose, and high-dose CdCl₂ groups was all significantly increased (F were 55.97 and 80.08, respectively, P < 0.05). Compared with the same dose of CdCl₂ group, the tBHQ+medium-dose CdCl₂ group showed significantly increased expression of Nrf2 protein in the testicles (F=74.66, P < 0.05), with no significant differences in the expression of Bip and PERK in the testicles; the tBHQ+high-dose CdCl₂ group showed a significant increase in the expression of Nrf2 protein in the ovaries(F=30.58, P < 0.05) and varying degrees of reductions in the expression of Bip mRNA and protein (F were 33.13, 25.28, and 30.24, respectively, P < 0.05), and PERK mRNA in the ovaries, and the expression of Nrf2 protein was negatively correlated with the expression of Bip mRNA and PERK mRNA in the ovaries (r were -0.783 and -0.817, respectively, P < 0.05); the tBHQ+high-dose CdCl₂ group showed significant decreases in the mRNA expression of PERK and Nrf2, and the protein expression of Bip, PERK, and Nrf2 in the testicles(F were 19.73, 53.63, 25.28, 99.98 and 74.66, respectively, P < 0.05).

Conclusion Pretreatment with tBHQ can induce varying degrees of Nrf2 expression in the testicles and ovaries of rats exposed to different doses of CdCl₂. The up-regulation of Nrf2 expression in the ovaries of rats can reduce the level of endoplasmic reticulum stress through the PERK/Nrf2 pathway, thereby alleviating the damage of cadmium to the ovaries.