The Protective Role and Underlying Mechanism of Hydrogen Sulfide against glaucomatous injuries in vitro and in vivo

Abstract

Glaucoma, one of the leading causes of irreversible blindness worldwide and is characterized by progressive optic nerve and retinal ganglion cell (RGC) degeneration. Hydrogen sulfide (H2S) plays a role as a potent neurotransmitter and has been proven to protect RGCs against glaucomatous injury in vitro and in vivo, although the exact mechanism is unclear. The main objective of this doctoral thesis was to reveal the potential roles of H2S in glaucoma pathophysiology and to better understand the mechanism of H2S in neuroprotection. In the process of aging, RGCs and β-synuclein (SNCB) are significantly changed in old animals. Under chronic IOP elevation there is a significant RGC loss in old animals, whereas no significant change in young animals; SNCB is significantly downregulated and 3-mercaptosulfurtransferase, a H2S producing enzyme, showed a 3-fold up-regulation within the retina in young animals after IOP elevation, while no significant changes in old ones are notable. GYY4137, a H2S slow-releasing donor, was observed to protect RGC against elevated pressure and oxidative stress in vitro depending on the concentration used (p<0.005). In vivo, intravitreal administration of GYY4137 preserved RGCs from acute ischemic injury and optic nerve crush (p<0.0001). Under acute ischemic injury, exogenous H2S also significantly downregulated SNCB levels. Furthermore, retinal vessel diameters enlarged after intravitreal GYY4137 injection (p<0.0001). As final part of this doctoral thesis, we examined the potential protective mechanisms activated by H2S in a glaucoma animal model. We used mass spectrometry-based proteomics to elucidate how protein expression changes at the cellular level. In total 1115 proteins were identified, 48 proteins were significantly differentially expressed due to I/R. Abundance of 18 key proteins were restored by H2S. Another 11 proteins were differentially expressed following H2S. Proteomic and ingenuity pathway analysis (IPA) revealed a significant H2S-mediated activation of pathways related to mitochondrial function, iron homeostasis and vasodilation. In conclusion, the present doctoral thesis is the first study to analyse the effect of H2S in the pathogenesis of experimental glaucoma and provide an overall insight into the mainstay retinal proteins and pivotal signaling pathways that interact with H2S to maintain retinal homeostasis against glaucomatous injury. These results form the basis for further research of H2S as an innovative treatment strategy for glaucoma.