Dissecting the Impact of Genetic Background on Oncogenic Response to Radiation Exposure in the Ptch1^+/- Mouse Model

Medulloblastoma (MB) is a common primary brain cancer in children. The sonic hedgehog (SHH) pathway is indispensable for the normal development of the cerebellum, and MB is often caused by persistent SHH activation owing to mutations in pathway components. Patched1 (PTCH1) is the primary receptor for the SHH ligand and a negative regulator of the SHH signal transduction pathway. Mice heterozygous for the Ptch1 gene (Ptch1^+/-) are predisposed to MB development. Irradiation of newborn Ptch1^+/- mice dramatically increases MB occurrence. A genetic background carrying the Ptch1 mutation significantly influences the risk of developing MB. This study aims to investigate the genetic background-related mechanisms that regulate radiation-induced cellular response and oncogenesis in the cerebellum. We employed multiple approaches, including: (a) analysis of cellular radiosensitivity in granule cell precursors (GCPs), the MB cells of origin, derived from Ptch1 mice with a genetic background that is sensitive (CD1) or resistant (C57Bl/6) to the induction of radiogenic MB; (b) identification of genes differentially expressed in spontaneous and radiation-induced MBs from these two mouse strains; (c) bioinformatic analysis to correlate the expression of radiation-induced genes with survival in MB patients; and (d) examining the expression of these genes in ex vivo MBs induced by single or repeated radiation doses. We have identified a potential gene expression signature-Trp53bp1, Bax, Cyclin D1, p21, and Nanog-that influences tumor response. In ex vivo cultured spontaneous MBs, the expression levels of these genes increase after irradiation in CD1 mice, but not in mice with a C57Bl/6 genetic background, suggesting that this signature could predict tumor response to radiation therapy and help develop strategies for targeting DNA damage repair in tumors. A detailed understanding of the mechanisms behind genetic background-related susceptibility to radiation-induced oncogenic responses is crucial for translational research.