衰老通过改变生长表型、衰老和分泌信号重编程结肠类器官对Braf V600E激活的早期致癌反应

Colorectal cancer (CRC) incidence increases with advanced age, yet how aging affects early epithelial responses to oncogenic mutations remains poorly understood. Braf V600E mutation is a major driver of serrated pathway of CRC, but the initial molecular events caused by Braf V600E 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 Braf V600E (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 Braf V600E . We found that Braf V600E activation differentially affects epithelial growth depending on age. Following Cre-mediated Braf V600E 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 Braf V600E 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.