Influences Of Low Dose Irradiation On Reactive Astrocytic Proliferation After Spinal Cord Injury In Beagle Dogs

Objective: Astrocytes are significantly activated after spinal cord injury andproduce a large number of pro-inflammatory cytokines which are detrimental to thecord tissue and the main reason of neuronal apoptosis. Since astrocytes have beenreported to undergo cell division following CNS injury, cell cycle control systemseems to play a critical role in cell proliferation and division. In the present study, wesought to determine the influence of low dose irradiation on astrocytes proliferationwith associated inflammatory response after spinal cord injury, and provide theexperimental basis for the neuroprotection of cell cycle modulation in CNS trauma.Materials and Methods: All animals were divided into three groups: shamoperated group, SCI group and low dose irradiation group. Spinal cordhemi-transection injury model was carried out. All Beagle dogs were killed at3d,6d,14d,30d and60d post injury, respectively and then the samples were harvested forfurther use. Tissue edema formation, astrocytic response and neuronal cell death werequantified in dogs subjected to spinal cord hemisection. Astrocytic proliferation andneuronal apoptosis were observed by immunofluorescence, level of astrocyticproliferation related proteins (GFAP and Ki67) expression in the injured cord wasdetermined by western blot analysis, the flow cytometry technique was used forastrocytic cell cycle, TUNEL method was used for neuronal apoptosis，and nissl stainwere carried to count number of anterior horn motor neuron.Results: Our results showed that low dose irradiation significantly decreasedexpression levels of astrocytic proliferation related proteins (GFAP and Ki67),suppressed astrocytic proliferation and produced a remarkable reduction of tissueedema formation. In the low dose irradiation group, a significant reduction of S andG2/M phase astrocyte showed by flow cytometry. Moreover, low dose irradiation evidently attenuated the number of apoptotic neurons after SCI.Conclusion: Modulation of astrocytic proliferation with associatedproinflammatory edema expression may be a mechanism of cell cycleinhibition-mediated neuroprotections in the CNS trauma.