ABSTRACT
objectiveTo explore the specific molecular mechanism of neuronal apoptosis induced by ATM inactivation. MethodsCGNs matured 7 days in vitro were cultured 8 h with 25 K， 5 K or 25 K medium containing ATM-specific inhibitors （Ku55933， 10 µmol/L； Ku60019， 15 µmol/L） for Hoechst stain and apoptosis analysis， or cultured for different lengths of time （2， 4， 8 h） to detect the protein expression levels of ATM， caspase-3 and cleaved caspase-3 by Western blotting. ATM and GADD45α specific siRNA was transfected into C6 cells and CGNs， and its interference efficiency was verified by q-PCR and Western blotting. CGNs matured for 5 days in vitro were transfected with ATM specific siRNA and pCMV-EGFP by calcium phosphate for 48 h， Hoechst staining and apoptosis analysis were performed. CGNs matured for 7 days in vitro were treated with 25 K medium containing ATM specific inhibitors for 8 h， transcriptome sequencing， differential expression gene identification and pathway enrichment analysis were performed. CGNs matured for 5 days in vitro were co-transfected with GADD45α specific siRNA and pCMV-EGFP by calcium phosphate for 48 h， then treated with 5 K or 25 K medium containing 15 µmol/L Ku6 for 8 h. Hoechst staining and apoptosis analysis were performed. ResultsCompared with the 25 K， CGNs nuclear pyknosis rate， cleaved Caspase-3 and ATM protein expression level were increased in the 5 K and ATM-specific inhibitor groups. The mRNA and protein expression levels of ATM and GADD45α were effectively reduced after transfection of ATM and GADD45α specific siRNA in C6 cells and CGNs. Compared with control， CGNs transfected with ATM specific siRNA showed a higher nuclear pyknosis rate. Totally 835 genes were identified to be up-regulated and 848 genes to be down-regulated in the Ku55933 treatment group； 454 genes were identified to be up-regulated and 314 genes to be down-regulated in the Ku6 treatment group； 274 genes were co-up regulated in the Ku5 and Ku60019 treatment groups， while 179 genes were co-down-regulated in the Ku5 and Ku6 treatment groups and the expression of ATM downstream target GADD45α was upregulated. The enrichment results showed that TNF signaling pathway， NF-κB signaling pathway and Apoptosis signaling pathway were significantly enriched. Compared with control， mRNA and protein expression levels of GADD45α were increased in inhibitor treatment and 5 K， while knocking down GADD45α resulted in a decrease in nuclear pyknosis rate in the Ku60019 and 5 K treatment group. ConclusionLoss of ATM activity induces GADD45α-dependent cerebellar granular neuronal apoptosis.