Glia U87 cells protect neuronal SH-SY5Y cells from indirect effect of radiation by reducing oxidative stress and apoptosis
Saeed Y1, Xie B1, Xu J1, Rehman A1, Hong M1, Hong Q1, Deng Y2.
Acta Biochim Biophys Sin (Shanghai). 2015 Apr;47(4):250-7. doi: 10.1093/abbs/gmv004. Epub 2015 Feb 27.
Abstract: Indirect effect of radiation increase oxidative stress enhances expression of apoptotic proteins leading to neuronal cell death. Irradiated cell-conditioned medium induced reactive oxygens species levels to be reduced in co-cultures of SH-SY5Y and U87MG cells. In co-cultures superoxide dismutase and glutathione antioxidant levels were increased. Co-cultures also inhibited expression of apoptotic proteins in irradiated cell conditioned media. This suggests glia may protect neuron cells by reducing oxidative stress and apoptotic death.
Introduction: Reactive oxygen species are major culprits prompting indirect effects of radiation resulting in neurodegerneration. Neurons are susceptible to stress but glia provide functional support to cope with hostile conditions including oxidative stress in vivo. Astrocytes provide trophic support and modulate synaptic activity. While glia have been previously reported as more resistant to oxidative stress than neurons. Therefore are neuron-astrocyte interactions enough to cope with oxidative stress and apoptotic damage induced by the indirect effect of radiation. Irradiated cell culture medium-induced reactive oxygen species were reduced in neurons when co-cultured with glia protecting mitochondrial integrity and inhibiting apoptotic proteins that cause neurodegeneration.
Methods: To study the protective effect of glia on irradiated neurons co-cultures grown in trans-well system with 0.4um pores. They measured cell viability by MTT method, which is a colorimetric assay based on mitochondrial ability to reduce MTT to a soluble formazan product with a purple colour with an absorbance at 490nm. In addition, they measured mitochondrial membrane potential using cell permeable mito-specific fluorescent probe JC-1. While they measured reactive oxygen species, nitric oxide, superoxide dismutase and glutathione using ELISA kits which read at 450 nm.
Results: Irradiated cell culture media (ICCM) reduced neuronal viability. However, glia were more stable at higher doses of ICCM. This suggests neurons are more sensitive. There was a decreased number of TUNEL-positive neurones when neuron-glia co-cultures were exposed to ICCM compared to ICCM exposed neurons only. This indicates glia may relieve neuronal stress. Also found in co-cultures neuronal cells were relieved from ICCM-induced mitochondrial depolarization relative to just ICCM-treated neurons. Neurons-glia co-cultures when exposed to ICCM exhibited a reduction in nitric oxide concentration and increased superoxide dismutase and glutathione concentration relative to neuronal cells only which may be due to glia producing antioxidants. Pro-apoptotic proteins increased in ICCM exposed neurons while these had reduced expression in co-cultures with U87MG cells. While anti-apoptotic proteins increased in co-cultures while expression decreased in ICCM exposed neuronal cells only. So high anti and low pro-apoptotic proteins in co-culture infers glia help relieve oxidative stress in neurons.
Discussion: Neurons supported with metabolic and trophic support from glia that may protect neurons from oxidative stress. U87 shown to protect SK-N-SH cells against neurodegerative assault. OS may elevate apoptotic protein expression similar to Bak and Noxa in SK-N-SH neurons exhibiting similar pathological features to Parkinson’s disease. Therefore oxidative stress may be critical for cytotoxicity in neurons and neurodegeneration. Furthermore, glia appear to be more resistant to oxidative stress and apoptotic damage compared to neurons. Glia more resistant to oxidative stress than neurons. However the exact role of glia in neuroprotection unclear. This study demonstrated ICCM-induced oxidative stress was reduced in neurons in co-cultures with glia suggesting glia help reduce oxidative stress. Antioxidant enzymes produced by glia to protect neurons from oxidative stress. This study suggests glia may help neurons cope with cytotoxic effect of ICCM by reducing oxidative stress protecting neurons from apoptosis. Further research is required to understand the underlying mechanism of how glia protect neurons.