Mechanistic study of copper nanoparticle (CuNP) toxicity on the mouse uterus via apelin signaling

Copper nanoparticles (CuNPs) have been widely utilized in various applications. Due to its wider application, humans are at risk of its exposure. It has been reported that the exposure of CuNPs can lead to organ accumulation and affect organ toxicity. Recent study suggested that CuNPs can translocate into the uterus and affect uterine injury in rat, whereas uterine toxicity still remains unclear. The uterus is an important female organ which is required to sustain pregnancy. Thus, uterine structure and physiology are important. Therefore, this study hypothesized that CuNPs might have a toxic effect on the uterine features of mice. In this study, we have investigated the potential effects of CuNPs on the uterus of mice both in vivo and in vitro. In in vivo study, two groups of female mice were exposed to 5 and 50 mg/kg/day via oral exposure. In vivo results showed that CuNP treatment decreases the body weight and uterus weight and changes in antioxidant status with low estrogen and progesterone levels. Furthermore, CuNPs up-regulated the expression of caspase3 and down-regulated the expression of apelin receptor (APJ). Immunolocalization of apelin showed low abundance in the CuNP-treated uterus. These results suggest a poor apelin signaling in the uterus after CuNP treatment. The in vivo findings were further supported by the in vitro studies. Firstly, the uterus was cultured with 5 and 40 μg of CuNPs, and in the second in vitro experiment, the uterus was divided into 4 groups: control, 40 μg of CuNPs, 40 μg of CuNPs with apelin, and 40 μg of CuNPs with apelin receptor antagonist (ML221). In vitro study showed that CuNPs could directly induce the oxidative stress and apoptosis as well as changing antioxidant status in the uterus. The in vitro apelin 13 (APLN 13) treatments alleviated the expression of BCL2 and improved the antioxidant markers in CuNP-treated uterus. These results also provided an evidence of apelin-mediated signaling in the CuNP-treated uterus. In summary, our results present evidence that CuNPs can stimulate apoptotic pathways which may lead to uterine impairment due to weak apelin signaling.