Abstract Colorectal cancer (CRC) incidence increases with advanced age, yet how aging affects early epithelial responses to oncogenic mutations remains poorly understood. BrafV600E mutation is a major driver of serrated pathway of CRC, but the initial molecular events caused by BrafV600E activation in aged intestinal stem cells are largely undefined. In the present study, we used proximal colon organoids (COs) derived from young (2 months) and aged (22 months) male and female mice carrying heterozygous Cre-activable BrafV600E (termed Braf+/LSL) transgene at the endogenous Braf locus and Cre-activable gene encoding red fluorescence marker protein, TdTom (termed TdTom+/LSL) to model age-dependent responses to oncogenic BrafV600E. We found that BrafV600E activation differentially affects epithelial growth depending on age. Following Cre-mediated BrafV600E induction, young male and female COs exhibited a pronounced proliferative burst, followed by a sharp growth collapse later passage, indicating an initial oncogene-induced senescence (OIS) response. In contrast, aged COs showed sustained growth across serial passages, indicating a failure to mount an OIS program. qPCR analysis aligned with these phenotypes: in young organoids, senescence-associated genes (p21, p16, Cxcl2, Il6) showed strong induction specifically at passage 4, coinciding with growth attenuation. Aged COs showed markedly reduced or absent induction of these transcripts at all passages, supporting an age-related loss of senescence competence. Loss of senescence competence is specific to oncogene response, not to general DNA damaging agents. The secretary profile further distinguished these responses with increases in CXCL2 and IL-6 secretion in young BrafV600E activated COs, reflecting SASP activation, whereas aged COs produced minimal amounts of these cytokines. Additionally, IGF2 secretion was significantly diminished in aged COs compared to young counterparts, suggesting altered growth factor signaling that may facilitate continued proliferation under oncogenic stress. Genome wide transcriptome and epigenome analyses indicate emergence of pro-tumorigenic epigenetic states in colon epithelium, which includes disrupted senescence and metabolic pathways. These findings are especially significant given the widely held view that aging is accompanied by increased stem cell senescence. Our studies reveal a paradox: aged epithelial cells exhibit a diminished senescence response when exposed to oncogenes. This novel observation reveals that the ability of aged cells to bypass OIS, together with a reduced inflammatory response, plays a key role in the increased susceptibility to tumor initiation observed with aging. Citation Format: Shilpa Bisht, Kaavya Mahadevan Iyer, Akash Sureshkumar, Rachael Powers, Ying Cui, Jinxiao Liang, Lijing Yang, Daniel Petkovich, Damilola Killanin, Ray-Whay C. Yen, Tina Largent, Stephen B. Baylin, Rafael de Cabo, Hariharan P. Easwaran. Aging reprograms early oncogenic responses to Braf V600E activation in colon organoids through altered growth phenotype, senescence, and secretory signaling abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2461.
Bisht et al. (Fri,) studied this question.