Melatonin reduces OGD/R-induced neuron injury by regulating redox/inflammation/apoptosis signaling

To investigate the roles and underlying mechanisms of melatonin in oxygen-glucose deprivation/reoxygenation (OGD/R)-insulted SH SY5Y cells.

SH SY5Y cells were cultured for OGD/R stimulation. Cell viability and cytotoxicity were measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, lactate dehydrogenase (LDH), and Hoechst 33258/propidium iodide (PI) staining assays. The mRNA levels of high mobility group box-1 (HMGB1), tumor necrosis factor α (TNF-α), and inducible nitric oxide synthase (iNOS) were analyzed by quantitative Real Time-PCR assays. Nitric oxide (NO) production was assessed by Griess reagent. Reactive oxygen species (ROS) production was detected by fluorescent probe. Malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were examined by commercial kits. Cell apoptosis was analyzed by flow cytometry and caspase-3 activity. The protein levels were detected by Western blot.

Melatonin enhanced the viability and reduced the death and LDH release of OGD/R exposed SH SY5Y cells. Melatonin repressed the HMGB1, TNF-α, and iNOS mRNA expression, NO production, and nuclear factor κB (NF-κB) activation in OGD/R challenged SH SY5Y cells. Melatonin reduced the ROS, MDA, 4-HNE, and 8-OHdG contents but further enhanced the levels of the nuclear factor E2-related factor-2 (Nrf2) and heme oxygenase (HO-1). Melatonin-increased viability and melatonin-decreased LDH release were also mediated by the blockage of NF-κB or reversed by Nrf2 or HO-1 knockdown. Melatonin exerted antiapoptotic effect on OGD/R treated SH SY5Y cells partly by activating Akt signaling. OGD/R challenged SH SY5Y cell autophagy was also repressed by melatonin, as evidenced by the decreased levels of LC-II and beclin-1 and the increased phosphorylation of mammalian target of rapamycin (mTOR), p70 ribosomal protein S6 kinase (p70S6K), and eukaryotic initiation factor 4E binding protein 1 (4E-BP-1).

Melatonin protected SH SY5Y cells from OGD/R induced oxidative stress, inflammation, apoptosis, and autophagy by blocking NF-κB signaling and activating Nrf2/HO-1, Akt, and mTOR/p70S6K/4E-BP-1 pathways, thereby indicating that melatonin is a potential and novel therapeutic drug for ischemic stroke.