Redox Homeostasis Regulates The Proliferation Of Brain Cells In The Development Of Rat Brain

BackgroundAs the development of nervous system is an important part of the bodydevelopment, the study on the regulation of neural cells proliferation in the braindevelopment has a wider and far-reaching significance. Reactive oxygen species(ROS) is a class of important signaling molecules and playscritical roles duringtissuedevelopment. The role of ROS in liver development has been proved in ourprevious studies. In the present study, we further explore the role and mechanism ofROS in the development of nervous system.ObjectiveBy studying the redox homeostasis variation of brain tissue and exploring therelationship between ROS levels and the activity of antioxidant system at different developmental stages of brain, we hypothesised that ROS were involved in theproliferation of neural cells. Then we usedPC12cells as an in vitro research modelof nerve cells to elucidate the mechanism of ROS in regulating the proliferation ofnerve cells and to seek new targets for further study of ROS on nerve cellsproliferation.Methods1. Observe the redox system variation of brain tissue at different developmentalstages of rats and preliminarily study the regulation of ROS on nerve cellsproliferation.（1） We used primary cultured neurons at different developmental stages of ratsto detect cell cycles, levels of ROS and the changes of proliferativeproteins such as PCNA, CyclinD and Rb.（2） Detect the protein expression and activities of antioxidant enzymes such asNrf2.（3） Separate the brain tissue of rats at different developmental stages, extractand detect the activity of mitochondria and the changes of ROS.2. Study the dose-effect relationship between ROS and neural cells proliferation invitro andthe mechanism of ROS in regulating the proliferation of PC12cell.（1） The growth character of the PC12cells was observed to make the growthcurve.（2） PC12cells were applied to oxidants and antioxidants separately. Then thedose-effect relationship between ROS levels and PC12cell proliferationwas studied.（3） The proliferation of PC12cells was interfered and the expression of cellcycle protein such as CyclinD, PCNA and Rb were observed to explore therole of ROS in the regulation of cell proliferation. Results1. There was a burst growth period during the development of SD rat’s brain,which was between the7thto the15thdays postnatal. During this period, the rate ofgrowth and development accelerated, the metabolic activity was strong and theROS generation and antioxidant defense system were in an active but balancedstate.2. Mitochondrial activityand function were gradually increased accompanyingthe development process of brain. While in the “brain burst growth period”, themitochondrialactivityrose sharply and then fell gradually.3. ROS is involved in the regulation of nerve cell proliferation. During theembryonic development of SD rat brain, ROS level wasfrom high to low while theantioxidant activitieswere from low to high. These results indicatedthat the changeof ROS levels plays an important role in the proliferation and differentiation ofnerve cells. From the embryonic stage to the postnatal maturation, the brainmaintained a dynamic redox balance and the ROS wascontrolled in the “right”range. The transcription factor Nrf2could regulate the redox homeostasis viaregulating the level of ROS. The activity of SOD gradually decreased and theexpression of antioxidant enzymesCAT, GPx and GRgradually increased, so thatthe redox homeostasis is maintained stable. Consequently,the level of ROSin braintissue was adjusted by the redox system to participate in the regulation of nervoussystem development.4. PC12cells were treated with oxidant (t-BHP) or antioxidant (NAC) during thelogarithmic growth phase. An appropriate dose of t-BHP(1μM) couldpromote cellsproliferation by activating the ERK signaling pathway. The antioxidant NACexposure significantly reduced ROS levels, inhibited cell proliferation of PC12cells and activated p38, whereas p38inhibitors significantly reversed this. Thus weconcluded that the changes of ROS levels promote or inhibit cell proliferation viaactivating the ERK or p38pathway. ConclusionThis subject showed a contradictory phenomenon that the change of ROS leveland the antioxidant defense system are converse in the development of rat brain. Sowe propose a hypothesis that the redox homeostasis in brain tissue adjusted thelevel of ROS to participate in the regulation of nervous system development. Thenby exploying the in vitro model of nerve cells we get the conclusion that thechanges of ROS levels could promote or inhibit cell proliferation via activating theERK or p38signaling pathway. This discovery provides a base fordemonstratingthe role of ROS in regulating neural cell proliferation and a newdirection for future study of brain development.