Xiu-Hong Meng

Melatonin alleviates cadmium‐induced cellular stress and germ cell apoptosis in testes

Abstract:  Increasing evidence demonstrates that melatonin has an anti‐apoptotic effect in somatic cells. However, whether melatonin can protect against germ cell apoptosis remains obscure. Cadmium (Cd) is a testicular toxicant and induces germ cell apoptosis. In this study, we investigated the effects of melatonin on Cd‐evoked germ cell apoptosis in testes. Male ICR mice were intraperitoneally (i.p.) injected with melatonin (5 mg/kg) every 8 hr, beginning at 8 hr before CdCl2 (2.0 mg/kg, i.p.). As expected, acute Cd exposure resulted in germ cell apoptosis in testes, as determined by terminal dUTP nick‐end labeling (TUNEL) staining. Melatonin significantly alleviated Cd‐induced testicular germ cell apoptosis. An additional experiment showed that spliced form of XBP‐1, the target of the IRE‐1 pathway, was significantly increased in testes of mice injected with CdCl2. GRP78, an endoplasmic reticulum (ER) chaperone, and CHOP, a downstream target of the PERK pathway, were upregulated in testes of Cd‐treated mice. In addition, acute Cd exposure significantly increased testicular eIF2α and JNK phosphorylation, indicating that the unfolded protein response (UPR) pathway was activated by CdCl2. Interestingly, melatonin almost completely inhibited Cd‐induced ER stress and the UPR in testes. In addition, melatonin obviously attenuated Cd‐induced heme oxygenase (HO)‐1 expression and protein nitration in testes. Taken together, these results suggest that melatonin alleviates Cd‐induced cellular stress and germ cell apoptosis in testes. Melatonin may be useful as pharmacological agents to protect against Cd‐induced testicular toxicity.

Cadmium-induced teratogenicity: association with ROS-mediated endoplasmic reticulum stress in placenta.

The placenta is essential for sustaining the growth of the fetus. An increased endoplasmic reticulum (ER) stress has been associated with the impaired placental and fetal development. Cadmium (Cd) is a potent teratogen that caused fetal malformation and growth restriction. The present study investigated the effects of maternal Cd exposure on placental and fetal development. The pregnant mice were intraperitoneally injected with CdCl(2) (4.5mg/kg) on gestational day 9. As expected, maternal Cd exposure during early limb development significantly increased the incidences of forelimb ectrodactyly in fetuses. An obvious impairment in the labyrinth, a highly developed tissue of blood vessels, was observed in placenta of mice treated with CdCl(2). In addition, maternal Cd exposure markedly repressed cell proliferation and increased apoptosis in placenta. An additional experiment showed that maternal Cd exposure significantly upregulated the expression of GRP78, an ER chaperone. Moreover, maternal Cd exposure induced the phosphorylation of placental eIF2α, a downstream molecule of PERK signaling. In addition, maternal Cd exposure significantly increased the level of placental CHOP, another target of PERK signaling, indicating that the unfolded protein response (UPR) signaling was activated in placenta of mice treated with CdCl(2). Interestingly, alpha-phenyl-N-t-butylnitrone, a free radical spin-trapping agent, significantly alleviated Cd-induced placental ER stress and UPR. Taken together, these results suggest that reactive oxygen species (ROS)-mediated ER stress might be involved in Cd-induced impairment on placental and fetal development. Antioxidants may be used as pharmacological agents to protect against Cd-induced fetal malformation and growth restriction.

Endoplasmic reticulum stress is involved in hepatic SREBP-1c activation and lipid accumulation in fructose-fed mice.

A link between fructose drinking and nonalcoholic fatty liver disease (NAFLD) has been demonstrated in human and rodent animals. The aim of the present study was to investigate whether endoplasmic reticulum (ER) stress is mediated in the development of fructose-induced NAFLD. Female CD-1 mice were fed with 30% fructose solution for eight weeks. Hepatic lipid accumulation was assessed. Hepatic nuclear sterol regulatory element-binding protein (SREBP)-1c was measured. Results showed that hepatic SREBP-1c was activated in mice fed with fructose solution. Fatty acid synthase (fas) and acetyl-CoA carboxylase (acc), two target genes of SREBP-1c, were up-regulated. Fructose-evoked hepatic SREBP-1c activation seemed to be associated with insulin-induced gene (Insig)-1 depletion. An ER stress and unfolded protein response (UPR), as determined by an increased glucose-regulated protein (GRP78) expression and an increased eIF2α and PERK phosphorylation, were observed in liver of mice fed with fructose solution. Phenylbutyric acid (PBA), an ER chemical chaperone, not only significantly attenuated ER stress, but also alleviated fructose-induced hepatic Insig-1 depletion. PBA inhibited fructose-evoked hepatic SREBP-1c activation and the expression of SREBP-1c target genes, and protected against hepatic lipid accumulation. In conclusion, ER stress contributes, at least in part, to hepatic SREBP-1c activation and lipid accumulation in fructose-evoked NAFLD.

Pubertal cadmium exposure impairs testicular development and spermatogenesis via disrupting testicular testosterone synthesis in adult mice

Cadmium (Cd) is a well-known testicular toxicant. However, the effects of pubertal Cd exposure on testicular development and spermatogenesis remained to be elucidated. The present study investigated the effects of pubertal Cd exposure on testicular development and spermatogenesis. Male CD-1 mice were intraperitoneally injected with CdCl(2) (1mg/kg) daily from postnatal day 35 (PND35) to PND70. As expected, pubertal Cd exposure significantly decreased the number of spermatozoa in epididymides. In addition, pubertal Cd exposure markedly reduced the weights of testes, epididymides and prostate and seminal vesicle in adult mice. A significant decrease in serum and testicular testosterone (T) was observed in mice exposed to Cd during puberty. Moreover, pubertal Cd exposure markedly reduced mRNA and protein levels of testicular StAR, P450scc, P450(17alpha) and 17beta-HSD. Taken together, these results suggest that the decreased testicular T synthesis might partially contribute to pubertal Cd-induced impairment on testicular development and spermatogenesis in mice.

Melatonin alleviates lipopolysaccharide-induced placental cellular stress response in mice.

Abstract:  Melatonin protects mice from lipopolysaccharide (LPS)‐induced fetal death and intra‐uterine growth retardation. Nevertheless, its molecular mechanism remains obscure. In the present study, we investigated the effects of melatonin on LPS‐induced cellular stress in placenta. Pregnant mice were given with melatonin [5.0 mg/kg, intraperitoneal (i.p.)] 30 min before and 150 min after LPS (300 μg/kg, i.p.) on gestational day 15. Oxidative stress, endoplasmic reticulum (ER) stress, hypoxic stress, and heat stress in placenta were analyzed at 4 hr after LPS. As expected, maternal LPS administration resulted in placental glutathione (GSH) depletion and up‐regulated the expression of placental antioxidative enzymes. In addition, LPS significantly increased the level of inducible nitric oxide synthase (iNOS) and enhanced the intensity of placental 3‐nitrotyrosine residues. An ER stress, as determined by a decreased GRP78 expression, an obvious eIF2α and JNK phosphorylation, and an increased CHOP expression, were observed in placenta of pregnant mice injected with LPS. In addition, LPS significantly increased mRNA level of placental HIF‐1α, VEGF, and ET‐1, the markers of hypoxic stress. Heme oxygenase (HO)‐1, a marker of heat stress, was also up‐regulated in placenta of LPS‐treated pregnant mice. Interestingly, LPS‐induced placental oxidative stress, hypoxic stress, and ER stress were significantly alleviated when pregnant mice were given with melatonin, whereas melatonin had little effect on LPS‐evoked placental HO‐1 expression. In conclusion, maternally administered melatonin alleviates LPS‐induced cellular stress in the placenta. Melatonin may be useful as pharmacological agents to protect the fetuses against LPS‐induced intra‐uterine fetal death and intra‐uterine growth restriction.

Age- and gender-dependent impairments of neurobehaviors in mice whose mothers were exposed to lipopolysaccharide during pregnancy.

Lipopolysaccharide (LPS)-induced intrauterine infection has been associated with neurodevelopmental injury in rodents. The purpose of the present study was to analyze the dynamic changes of neurobehaviors in mice whose mothers were exposed to LPS during pregnancy. The pregnant mice were intraperitoneally (i.p.) injected with LPS (8 microg/kg) daily from gestational day (gd) 8 to gd 15. A battery of neurobehavioral tasks was performed in mice at postnatal day (PND) 70, 200, 400 and 600. Results showed that the spatial learning and memory ability, determined by radial six-arm water maze (RAWM), were obviously impaired in two hundred-day-old female mice and four hundred-day-old male mice whose mothers were exposed to LPS during pregnancy. Open field test showed that the number of squares crossed and peripheral time, a marker of anxiety and exploration activity, were markedly increased in two hundred-day-old female mice following prenatal LPS exposure. In addition, prenatal LPS exposure significantly shortened the latency to the first grid crossing in six hundred-day-old female offspring. Moreover, sensorimotor impairment in the beam walking was observed in two hundred-day-old female mice whose mothers were exposed to LPS during pregnancy. Species-typical behavior examination showed that prenatal LPS exposure markedly increased weight burrowed in seventy-day-old male offspring and six hundred-day-old female offspring. Correspondingly, prenatal LPS exposure significantly reduced weight hoarded in two hundred-day-old female offspring. Taken together, these results suggest that prenatal LPS exposure induces neurobehavioral impairments at adulthood in an age- and gender-dependent manner.

Crosstalk Between Endoplasmic Reticulum Stress and Mitochondrial Pathway Mediates Cadmium-Induced Germ Cell Apoptosis in Testes

Cadmium (Cd) is associated with male infertility and poor semen quality in humans. Increasing evidence demonstrates that Cd induces testicular germ cell apoptosis in rodent animals. However, the molecular mechanisms of Cd-induced testicular germ cell apoptosis remain poorly understood. In the present study, we investigated the role of endoplasmic reticulum (ER) stress on Cd-evoked germ cell apoptosis in testes. We show that spliced form of XBP-1, the target of the IRE1 pathway, was significantly increased in testes of mice injected with CdCl(2). GRP78, an ER chaperone, and CHOP, a downstream target of the PERK pathway, were upregulated in testes of Cd-treated mice. In addition, acute Cd exposure significantly caused eIF2α and JNK phosphorylation in testes, indicating that the unfolded protein response pathway in testes was activated by Cd. Interestingly, phenylbutyric acid (PBA), an ER chemical chaperone, attenuated Cd-induced ER stress and protected against germ cell apoptosis in testes. In addition, PBA significantly attenuated Cd-evoked release of cytochrome c from mitochondria to cytoplasm in testes. Taken together, these results suggest that crosstalk between ER stress signaling and mitochondrial pathway mediates Cd-induced testicular germ cell apoptosis.

Maternal cypermethrin exposure during lactation impairs testicular development and spermatogenesis in male mouse offspring

Within the last decade, numerous epidemiological studies have demonstrated that endocrine disruptors are a possible cause for a decline in semen quality. Cypermethrin is a widely used pyrethroid insecticide, but little is known about its potentially adverse effects on male reproduction. In the present study, we investigated the effects of maternal cypermethrin exposure during lactation on testicular development and spermatogenesis in male offspring. Maternal mice were administered with cypermethrin (25 mg/kg) by gavage daily from postnatal day 0 (PND0) to PND21. Results showed that the weight of testes at PND21 was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Maternal cypermethrin exposure during lactation markedly decreased the layers of spermatogenic cells, increased the inside diameter of seminiferous tubules, and disturbed the array of spermatogenic cells in testes of pups at PND21. In addition, maternal cypermethrin exposure during lactation markedly reduced mRNA and protein levels of testicular P450scc, a testosterone (T) synthetic enzyme. Correspondingly, the level of serum and testicular T at weaning was significantly decreased in pups whose mothers were exposed to cypermethrin during lactation. Although the expression of testicular T synthetic enzymes and serum and testicular T in adulthood had restored to control level, the decreased testicular weight and histological changes were irreversible. Importantly, the number of spermatozoa was significantly decreased in adult male offspring whose mothers were exposed to cypermethrin during lactation. In conclusion, maternal cypermethrin exposure during lactation permanently impairs testicular development and spermatogenesis in male offspring, whereas cypermethrin‐induced endocrine disruption is reversible.

Ascorbic acid protects against cadmium-induced endoplasmic reticulum stress and germ cell apoptosis in testes

Cadmium (Cd) is a testicular toxicant which induces endoplasmic reticulum (ER) stress and germ cell apoptosis in testes. This study investigated the effects of ascorbic acid on Cd-evoked ER stress and germ cell apoptosis in testes. Male mice were intraperitoneally injected with CdCl(2) (2.0 mg/kg). As expected, a single dose of Cd induced testicular germ cell apoptosis. Interestingly, Cd-triggered testicular germ cell apoptosis was almost completely inhibited in mice treated with ascorbic acid. Interestingly, ascorbic acid significantly attenuated Cd-induced upregulation of GRP78 in testes. In addition, ascorbic acid significantly attenuated Cd-triggered testicular IRE1α and eIF2α phosphorylation and XBP-1 activation, indicating that this antioxidant counteracts Cd-induced unfolded protein response (UPR) in testes. Finally, ascorbic acid significantly attenuated Cd-evoked upregulation of CHOP and JNK phosphorylation, two components in ER stress-mediated apoptotic pathway. In conclusion, ascorbic acid protects mice from Cd-triggered germ cell apoptosis via inhibiting ER stress and UPR in testes.

Pubertal and early adult exposure to fenvalerate disrupts steroidogenesis and spermatogenesis in mice at adulthood

Fenvalerate, a pyrethroid insecticide used worldwide, has been shown to have a potentially adverse effect on male reproduction. Our earlier study showed that maternal fenvalerate exposure during lactation impaired testicular development in male offspring. In this study, we investigated the effects of pubertal and early adult exposure to fenvalerate on steroidogenesis and spermatogenesis in mice. Male mice were administered fenvalerate (60 mg/kg) by gavage daily from postnatal day 35 (PND35) to PND63. Results showed that sperm count was significantly decreased in fenvalerate‐treated mice. In addition, fenvalerate markedly decreased the layers of spermatogenic cells, disturbed the array of spermatogenic cells and increased the number of apoptotic cells in testes. The adverse effects of fenvalerate on male reproduction seemed to be associated with a decrease in serum and testicular testosterone (T). Although pubertal and early adult exposure to fenvalerate had little effect on the number of Leydig cells in testes, mRNA and protein levels of testicular T biosynthetic enzymes including P45017α and P450scc were significantly downregulated in fenvalerate‐treated mice. In conclusion, pubertal and early adult fenvalerate exposure induces a deleterious effect on steroidogenesis and spermatogenesis in adulthood. The decreased testicular T synthesis partially contributes to fenvalerate‐induced impairment on spermatogenesis. Copyright