DNA damage response associated miRNA dysregulation in Ataxia-telangiectasia

Background Ataxia-telangiectasia (A-T) is a rare autosomal recessive genome-instability disorder due to pathogenic vari-ants in ATM, a central kinase of the DNA double-strand break signaling, checkpoint activation and stress-response pathways.Although microRNAs (miRNAs) regulate DNA damage response (DDR), apoptosis, senescence and cell-cycle control, thestress-responsive behavior of selected ATM/DDR-associated miRNAs remains incompletely characterized in A-T fibroblastmodels.Methods and Results Four predefined ATM/DDR-associated candidate miRNAs (hsa-miR-34a-5p, hsa-miR-26a-5p, hsa-miR-106b-5p and hsa-miR-20a-5p) were quantified in one ATM-proficient fibroblast control and three A-T fibroblast celllines both under basal and bleomycin exposed conditions. The relative expression of selected miRNAs was measured byRT-qPCR. miR-34a-5p and miR-26a-5p levels were lower in each of the three bleomycin-treated A-T lines relative to thesingle bleomycin-treated WT control line. miR-34a-5p and miR-26a-5p levels were lower in bleomycin-treated three A-Tlines relative to the single control WT line. Within-cell-line analysis showed significant miR-34a-5p induction after bleo-mycin in WT, AT648 and AT9607, whereas significant miR-26a-5p induction was observed only in AT648. AT648 showedthe broadest within-cell-line response, with significant induction of all four tested miRNAs after bleomycin. Target-basedenrichment and network analyses of the predefined candidate panel identified annotations related to cell-cycle regulation,G1/S transition, RB/E2F signaling, p53 signaling, apoptosis, senescence, PI3K-Akt signaling, and DNA damage-associatedprocesses. Network analysis revealed a number of shared candidate targets such as CCND1, CCND2, E2F1, E2F3, RB1,WEE1, PTEN, SMAD4, MYC and VEGFA.Conclusions In this fibroblast panel, miR-34a-5p and miR-26a-5p showed the most consistent baseline alterations, whereasbleomycin responsiveness was cell-line specific and heterogeneou