RESUMO
BACKGROUND & AIMS: Colorectal cancer (CRC) is thought to arise when the cumulative mutational burden within colonic crypts exceeds a certain threshold that leads to clonal expansion and ultimately neoplastic transformation. Therefore, quantification of the fixation and subsequent expansion of somatic mutations in normal epithelium is key to understanding colorectal cancer initiation. The aim of the present study was to determine how advantaged expansions can be accommodated in the human colon. METHODS: Immunohistochemistry was used to visualize loss of the cancer driver KDM6A in formalin-fixed paraffin-embedded (FFPE) normal human colonic epithelium. Combining microscopy with neural network-based image analysis, we determined the frequencies of KDM6A-mutant crypts and fission/fusion intermediates as well as the spatial distribution of clones. Mathematical modeling then defined the dynamics of their fixation and expansion. RESULTS: Interpretation of the age-related behavior of KDM6A-negative clones revealed significant competitive advantage in intracrypt dynamics as well as a 5-fold increase in crypt fission rate. This was not accompanied by an increase in crypt fusion. Mathematical modeling of crypt spacing identifies evidence for a crypt diffusion process. We define the threshold fission rate at which diffusion fails to accommodate new crypts, which can be exceeded by KRAS activating mutations. CONCLUSIONS: Advantaged gene mutations in KDM6A expand dramatically by crypt fission but not fusion. The crypt diffusion process enables accommodation of the additional crypts up to a threshold value, beyond which polyp growth may occur. The fission rate associated with KRAS mutations offers a potential explanation for KRAS-initiated polyps.
Assuntos
Proliferação de Células , Transformação Celular Neoplásica/genética , Pólipos do Colo/genética , Neoplasias Colorretais/genética , Células Epiteliais/patologia , Histona Desmetilases/genética , Mucosa Intestinal/patologia , Mutação , Células-Tronco Neoplásicas/patologia , Proteínas Proto-Oncogênicas p21(ras)/genética , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Transformação Celular Neoplásica/metabolismo , Transformação Celular Neoplásica/patologia , Pólipos do Colo/metabolismo , Pólipos do Colo/patologia , Neoplasias Colorretais/metabolismo , Neoplasias Colorretais/patologia , Difusão , Células Epiteliais/metabolismo , Feminino , Histona Desmetilases/metabolismo , Humanos , Mucosa Intestinal/metabolismo , Masculino , Pessoa de Meia-Idade , Modelos Biológicos , Células-Tronco Neoplásicas/metabolismo , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Adulto JovemRESUMO
Obesity is a major risk factor for many common diseases and has a substantial heritable component. To identify new genetic determinants, we performed exome-sequence analyses for adult body mass index (BMI) in up to 587,027 individuals. We identified rare loss-of-function variants in two genes (BSN and APBA1) with effects substantially larger than those of well-established obesity genes such as MC4R. In contrast to most other obesity-related genes, rare variants in BSN and APBA1 were not associated with normal variation in childhood adiposity. Furthermore, BSN protein-truncating variants (PTVs) magnified the influence of common genetic variants associated with BMI, with a common variant polygenic score exhibiting an effect twice as large in BSN PTV carriers than in noncarriers. Finally, we explored the plasma proteomic signatures of BSN PTV carriers as well as the functional consequences of BSN deletion in human induced pluripotent stem cell-derived hypothalamic neurons. Collectively, our findings implicate degenerative processes in synaptic function in the etiology of adult-onset obesity.