H<sub>2</sub>S in the neurodegeneration: a "double-faced Janus"
This paper reviews current literature data on the participation of hydrogen sulfide (H2S) in the pathogenesis of neurodegenerative disorders - Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). In the CNS the level of H2S is determined by the enzymes of its synthesis - cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE). H2S is a gasotransmitter, the action of which is realized through chemical and conformational modification of protein molecules simultaneously in spacious pools of cells - in a «broad field». The effects of H2S are highly divergent when a certain threshold is reached, it moves from the neuroprotection to the neurodegeneration. The neurodegeneration is mediated by both increased (in ALS) and decreased (PD, AD, HD) levels of H2S production, which is determined by the activity of different enzymes of its synthesis - CBS (PD, AD, ALS) or CSE (HD) - depending on the specificity of the certain disorder, that leads to the deployment of the especial pattern of neurological events. The disturbances in sulfur-containing amino acids metabolism and thiol-disulfide homeostasis are an integrative part in H2S-dependent mechanism of the neurodegeneration. The opposite/divergent negative effect of H2S, the involvement of different enzymes of its synthesis and some products of transformation in the pathological process suggest about the dual nature of H2S as a signaling molecule at neurodegenerative disorders.