The Mechanism Of Ceramide Mediated Radiation-induced Germ Cell Apoptosis In Caenorhabditis Elegans

Researches about radiation damage effect in vivo is very significant for healthy risk assessment as well as cancer therapy at low doses.Ceramide,which has been well proved as a second messenger,could function in various cellular processes.However,the mechanism and processes of signal production and transduction of ceramide in effect of radiation-induced damage,especially in vivo level,is not clear.In this study,with proton microbeam and wide beam irradiation,we investigated the mechanism and processes of signal production and transduction of radiation-induced damage mediated by ceramide,applying germ cell apoptosis in Caenorhabditis elegans(C.elegans)as the main biological endpoint.Main results in this study are as follows:1.Using proton microbeam for fixed-point quantitative irradiation to posterior pharynx bulb of C.elegans,we found that de novo synthesis pathway of ceramide was required for microbeam-induced bystander effect in vivo,which means that radiation to posterior pharynx bulb could not induce increase of germ cell apoptosis anymore after mutating ceramide synthase genes.Based on results of microneam radiation,we further used wide beam/ionizing radiation(IR)for irradiation to whole body of C.elegans and results indicated that ceramide is required for whole-body IR-induced germ cell apoptosis.2.We further explored the signaling mechanism of ceramide.Our results showed that ceramide synthase functioned in radiation-induced germ cell apoptosis with no tissue specificity via RNA interfering gene of ceramide synthetase lagr-1 in RNAi tissue specific strains;We used fluorescent reporter strain HUS::GFP to detect ROS level and fluorescent probe JC-1 to detect change of mitochondrial transmembrane potential(MTP).Results suggested ceramide mediated radiation-induced germ cell apoptosis through regulating production of radical oxygen species(ROS)and ceramide was closely connected with radiation-induced decrease of MTP,indicating a crucial role of ceramide in regulating function of mitochondria.3.Applying genetic mutated strains and exogenous ceramide,data illustrated that p53 homolog CEP-1 may regulate BH3-only protein EGL-1 through ceramide to mediate radiation-induced germ cell apoptosis.And ceramide may regulated DNA damage checkpoint protein HUS-1;besides,we explored the relationship of ceramide and MAPK pathway in radiation-induced germ cell apoptosis.We applied genetic mutated strains and exogenous ceramide and results elucidated that ceramide might function epistatic to pmk-1 and mpk-1 in MAPK pathway to promote radiation-induced apoptosis in C.celegans.This study investigated molecular mechanism of ceramide in radiation-indced apoptosis at living level.Results defined that ceramide play a pivotal role in radiation-indced apoptosis and potentially regulated DNA damage response pathway,MAPK pathway and mitochondrial function.This study could provide experimental data and theoretical basis for radiation protection and oncotherapy.