Mice lacking S nitrosoglutathione reductase GSNOR a denitros
Mice lacking S-nitrosoglutathione reductase (GSNOR), a denitrosylase that regulates S-nitrosylation, have increased levels of S-nitrosoglutathione (GSNO) and exhibit nitrosative stress. GSNO is in equilibrium with protein S-nitrosylation in cells, and GSNOR controls the cellular concentration of protein S-nitrosylation. GSNOR is a ubiquitous protein found in tissues such as the liver, thymus, spleen, and heart. Loss of GSNOR leads to increased levels of GSNO and subsequent modification of cysteine residues by S-nitrosylation, thereby affecting cellular signaling. We hypothesized that nitrosative stress in Gsnor−/− mice would affect hypothalamic-pituitary-gonadal axis function and spermatogenesis. We characterized testicular and pituitary functions of Gsnor−/− mice. We evaluated fertility, sperm parameters, testis histology, and reproductive hormone levels in Gsnor−/− mice and compared them with adult wild-type (WT) control mice.
Discussion Gsnor−/− mice have smaller testes, subfertility, and decreased levels of testosterone and LH, with preserved FSH. Gsnor−/− mice have intact testicular function, as demonstrated by hCG stimulation leading to increased testosterone levels, and similar patterns of immunofluorescent staining for LHR and 3β-HSD in the testes. Stimulation with GnRH led to increased LH levels in Gsnor−/− mice, suggesting inducible pituitary function. Therefore, the Gsnor−/− mouse is a model of secondary hypogonadism with likely impairment of hypothalamic function from nitrosative stress. We investigated Gsnor−/− mice because of observed subfertility. Our initial investigation began with an evaluation of reproductive hormones. Surprisingly, the Gsnor−/− mice had nearly undetectable testosterone and LH levels with nearly normal FSH levels. Despite nearly castrate levels of testosterone and undetectable LH, the mice remained fertile, albeit less fertile than WT mice. This can be explained by the similar FSH levels between Gsnor−/− mice and WT mice. Previously published studies of differential LH and FSH SU 4312 attribute this to changes in GnRH pulse frequency. LH release is highly dependent on GnRH pulse frequency, with higher frequencies of pulsatile GnRH release favoring LH secretion, whereas slower frequencies of GnRH pulses favor FSH release.15, 16 Furthermore, FSH expression can be constitutive and influenced by other stimulatory and inhibitory inputs such as activin and inhibin. The exact mechanism of how Gsnor−/− mice have very low levels of LH with normal levels of FSH will be important to evaluate mechanisms of GnRH release. Excess nitrosative stress possibly resulting in secondary hypogonadism is an important hypothesis because of its possible implications in reproductive toxicology. Endocrine disrupting compounds, such as bisphenol A and phthalates, are found ubiquitously in food and water and are of toxicologic human health concern, especially in developing children. Mothers exposed to higher bisphenol A levels during early pregnancy and their matching term cord samples displayed increased nitrosative stress. Prenatal and lactational exposure to endosulfan, a compound that increases nitrosative stress, decreases LH levels and therefore has been implicated in delayed puberty. Therefore, Gsnor−/− mice can be used as a model to study the effects of endocrine disruptors on hypothalamic-pituitary-gonadal axis and fertility. Gsnor−/− mice have impaired fertility and a disrupted hypothalamic-pituitary-gonadal axis likely due to nitroso-redox imbalance. RNS are generated through myriad normal cellular process and tissues. The largest generator of RNS is nitric oxide synthase, which is located throughout the body, including the brain. Pathologic states, such as arthritis, diabetes, cancer, and liver damage, lead to pathologic levels of RNS.7, 20, 21 Exogenous sources of ROS and RNS include smoking, air pollution, heavy metals, alcohol, solvents, paracetamol, radiation, and bisphenol A.17, 22 Previous literature has linked RNS and ROS to impaired semen parameters. Currently, antioxidant therapy is used empirically and can improve semen parameters and pregnancy rate.22, 23 Antioxidant therapy such as ascorbate can be targeted at decreasing nitrosative stress and nitroso-redox imbalance and could be used in the treatment of secondary hypogonadism.