S-nitrosoglutathione prevents cognitive impairment through epigenetic reprogramming in ovariectomised mice.

The epigenetic signatures associated with cognitive decline driven by lack of estrogen in post-menopausal state, is not well-understood. The present study is an attempt to unravel the epigenetic mechanisms involved in cognitive impairment preceding ovariectomy in mice and evaluate the protective effects of S-nitrosoglutathione (GSNO). A significant decline in cognitive functions was observed in mice following ovariectomy as assessed by Morris water maze and Novel object recognition test. Administration of GSNO (100 µg/kg body weight, orally) daily for 4 weeks was found to ameliorate cognitive deficits observed in ovariectomised (OVX) mice. The activity of histone acetyl-transferase (HAT) was significantly disrupted in cortex and hippocampus of OVX mice. This was accompanied by increased activity of histone deacetylase (HDAC) and increased levels of HDAC-2, HDAC-3 causing lowered acetylated histone (H)3 levels. Reduced H3 acetylation triggers epigenetic repression of brain derived neurotrophic factor (BDNF) in cortex and hippocampus of OVX mice that may be responsible for neuronal damage and cognitive impairment. GSNO supplementation to OVX mice was able to reinstate HAT(CBP/p300) and HDAC balance through S-nitrosylation. GSNO restored histone acetylation at BDNF promoters (pII, pIV) thereby ameliorating BDNF levels and improving brain morphology and cognition. The study suggests that GSNO improves cognitive function in OVX mice by modulating epigenetic programming.