Genetic profiles of the bladder
Depending on the environment of the individual, the human bladder can be exposed to carcinogens as they are flushed through the body. Lawson et al. and Li et al. examined the genetic composition of laser-dissected microbiopsies from normal and cancer cells collected from the urothelium, a specialized epithelium lining the lower urinary tract (see the Perspective by Rozen). These complementary studies identified the mutational landscape of bladder urothelium through various sequencing strategies and identified high mutational heterogeneity within and between individuals and tumors. Both studies identified mutational profiles related to specific carcinogens such as aristolochic acid and the molecules found in tobacco. These studies present a comprehensive description of the diverse mutational landscape of the human bladder in health and disease, unraveling positive selection for cancer-causing mutations, a diversity of mutational processes, and large differences across individuals.
Abstract
The extent of somatic mutation and clonal selection in the human bladder remains unknown. We sequenced 2097 bladder microbiopsies from 20 individuals using targeted (n = 1914 microbiopsies), whole-exome (n = 655), and whole-genome (n = 88) sequencing. We found widespread positive selection in 17 genes. Chromatin remodeling genes were frequently mutated, whereas mutations were absent in several major bladder cancer genes. There was extensive interindividual variation in selection, with different driver genes dominating the clonal landscape across individuals. Mutational signatures were heterogeneous across clones and individuals, which suggests differential exposure to mutagens in the urine. Evidence of APOBEC mutagenesis was found in 22% of the microbiopsies. Sequencing multiple microbiopsies from five patients with bladder cancer enabled comparisons with cancer-free individuals and across histological features. This study reveals a rich landscape of mutational processes and selection in normal urothelium with large heterogeneity across clones and individuals.
