Potential Neuroprotective Effects of an LSD1 Inhibitor in Retinal Ganglion Cells via p38 MAPK Activity

Abstract

Citation: Tsutsumi T, Iwao K, Hayashi H, et al. Potential neuroprotective effects of an LSD1 inhibitor in retinal ganglion cells via p38 MAPK activity. Invest Ophthalmol Vis Sci. 2016;57:6461-6473. DOI:10.1167/ iovs.16-19494 PURPOSE. The epigenetic mechanisms associated with ocular neurodegenerative diseases remain unclear. The present study aimed to determine the role of lysine-specific demethylase 1 (LSD1), which represses transcription by removing the methyl group from methylated lysine 4 of histone H3, in retinal ganglion cell (RGC) survival, and to investigate the details of the neuroprotective mechanism of tranylcypromine, a major LSD1 inhibitor. METHODS.The authors evaluated whether tranylcypromine contributes to neuronal survival following stress-induced damage using primary cultured rat RGCs and in vivo N-methyl-Daspartate (NMDA)-induced excitotoxicity. Additionally, the molecules associated with tranylcypromine treatment were assessed by microarray and immunoblot analysis. RESULTS.Tranylcypromine significantly suppressed neuronal cell death following glutamate neurotoxicity and oxidative stress. Microarray and immunoblot analyses revealed that p38 mitogen-activated protein kinase (MAPK)c was a key molecule involved in the neuroprotective mechanisms induced by tranylcypromine because the significant suppression of p38 MAPKc by glutamate was reversed by tranylcypromine. Moreover, although pharmacologic inhibition of the phosphorylation of the total p38 MAPKs interfered with neuroprotective effects of tranylcypromine, the specific inhibition of p38 MAPKa and p38 MAPKb did not influence RGC survival. This suggests that the non-p38 MAPKa/b isoforms have important roles in neuronal survival by tranylcypromine. Additionally, the intravitreal administration of tranylcypromine significantly saved RGC numbers in an in vivo glaucoma model employing NMDA-induced excitotoxicity.CONCLUSIONS. These findings indicate that tranylcypromine-induced transcriptional and epigenetic regulation modulated RGC survival via the promotion of p38 MAPKc activity. Therefore, pharmacologic treatments that suppress LSD1 activity may be a novel therapeutic strategy that can be used to treat neurodegenerative diseases.

Targeting Polyamine Oxidase to Prevent Excitotoxicity-Induced Retinal Neurodegeneration

“…Loss of RGCs is a major feature of retinal excitotoxicity (Tsutsumi et al, 2016; Ishimaru et al, 2017). In the present study, NMDA-induced RGC loss was studied (7 days post-NMDA treatment) using retinal flatmount analysis.…”

“…Retinal excitotoxicity was induced using NMDA (N-Methyl-D-Aspartate, Sigma) according to the published methods with minor modifications (Tsutsumi et al, 2016; Ishimaru et al, 2017). Briefly, mice were anesthetized with ketamine/xylazine (73 mg/kg ketamine hydrochloride and 7.3 mg/kg xylaxine hydrochloride, i.p., intraperitoneally), pupils were dilated with 1% tropicamide (Akorn, Lake Forest, IL, United States), and topical anesthesia (1 drop of proparacaine hydrochloride, Akorn) was applied to the cornea.…”

Characterization of LSD1 Expression Within the Murine Eye

“…Recently, Popova and colleagues21 found that Lsd1 is highly expressed in late progenitor retinal cells as they become postmitotic and begin to differentiate and that inhibition of LSD1 blocks the differentiation of the retinoblast into rod photoreceptors. Tsutsumi et al22 found potential neuroprotective effects of an LSD1 inhibitor that may protect retinal ganglion cells (RGCs), which may have implications in glaucoma. These studies have examined the effects of LSD1 inhibition in the retina, and we aimed to extend the current understanding of endogenous LSD1 expression spatially and temporally and compare and contrast our work with theirs.…”

Retinal Cell Protection in Ocular Excitotoxicity Diseases. Possible Alternatives Offered by Microparticulate Drug Delivery Systems and Future Prospects

“…Other compounds have shown antiapoptotic effects in several animal models of ocular excitotoxicity. Between them, it is necessary to highlight I) apelin-36 and apelin-17 involved on the activation of Akt and ERK1/2 signaling pathways required for neuronal survival and inhibition of apoptosis in the retina [68], II) cannabinoids via a mechanism involving the CB1 receptors, the PI3K/Akt and MEK/ERK1/2 signaling pathways [69], III) capsaicin, a transient receptor potential vanilloid type1 agonist that activates opioid receptors, calcitonin gene-related peptide receptor and the tachykinin NK1 receptor involved in the protective effect against the NMDA receptor induced neuronal death [70], IV) pituitary adenylate cyclase-activating polypeptide through phosphatidylcholine-specific PLC pathway and cAMP production [71], V) compounds acting on adenosine A 3 receptor that attenuates the rise in calcium in RGC after activation of glutamate and P2X receptors protecting retinal cells, particularly RGC [72], VI) geranylgeranylacetone involved on the reduction in the activities of caspase-9 and -3, achieving protective results using a normal tension glaucoma mouse model which lacks GLAST [73], VII) CYM-5442 a known sphingosine 1-phosphate receptor agonist that administrated systemically in rats protected RGC from apoptotic death and preserve neuronal function after ET-1 induced RGC loss [19], VIII) adamantane derivatives such as memantine that blocks excessive activation of NMDARs without disrupting normal activity and has recently demonstrated significant preservation of RGCs density in a rodent ocular model of ocular hypertension when administrated in PLGA-polyethylene glycol (commonly PLGA-PEGylated) biodegradable nanoparticles [25], IX) tetramethylpyrazines, commonly known as TMPs, compounds able to block L-type voltage-gated calcium channels [7], X) tranylcypromine, a major lysine-specific demethylase 1 (LSD-1) and monoamine oxidase (MAO) inhibitor, that enhances expression of p38 MAPK and KEGG pathway genes [74], XI) melatonin, an autocrine or paracrine neuromodulator that regulates the local circadian physiology, that can be an effective antioxidant and antiapoptotic compound in the retina, acting as a direct and indirect free radical scavenger [75], XII) serotonin receptor (5-HT1A) agonists via the inhibition of cAMP-PKA signaling pathway that modulates GABAergic presynaptic activity [76], XIII) mTOR pathway stimulating APIs such as ciliary neurotrophic factors, lipopeptide N-fragment osteopontin mimic or lipopeptide phosphatase tension homologue inhibitors [77] or XIV) curcumin that modulates NMDA receptor subunit composition [78]. Finally, compounds with dual mechanism of action could be of special interest in multifactorial diseases as those related with RGC loss.…”

“…[7] Tranylcypromine P38 MAPK and KEGG pathway genes expression. [74] Dual compounds (e.g., Mg acetyltaurate) NMDAR inhibition + antioxidant effect. [79] Melatonin Direct and indirect free radical scavenger.…”