Compromised Tissue Renewal in the Ageing Human Colonic Epithelium

BACKGROUND: The intestinal epithelium is the most rapidly renewing tissue in the body. It is widely believed that this attribute minimises the accumulation of age-related molecular damage. Increasing evidence suggests that this protective mechanism is undermined by agerelated molecular changes that accumulate in long-lived stem/progenitor cells. Age-related molecular damage in the intestinal epithelium of flies and rodents manifests as a hyperproliferative state that exhibits a greater degree of apoptosis, clonogen/stem cell number and reduced regenerative potential following damage. Furthermore, the human colonic epithelium is subject to age-related accumulation of mutations in mitochondrial DNA. Given that ageing is a major risk factor for cancer, it is surprising that the status of tissue renewal in the ageing human colonic epithelium has received little attention. AIM: To investigate age-related changes in the renewal of the human colonic epithelium.METHODS: Tissue biopsies obtained at sigmoidoscopy (Ethical approval) from young ( 70 years, N= 12) individuals with no apparent pathology were immediately fixed or processed for crypt isolation. Isolated crypts were observed in 3D culture by digital time-lapse microscopy. Native crypts obtained by microdissection of fixed biopsy tissue were subjected to morphometric analysis and immunofluorescence for detection of Ki67 (proliferation marker), beta catenin, c-Myc and axin2 (all markers for Wnt signals), and OLFM4 (an intestinal stem cell marker). RESULTS: Crypts from young subjects (n=116 crypts) were significantly longer (p< 0.05) than those derived from the older cohort (117 crypts), 375± 10 um versus 330 ± 10 um, respectively. The percentage of Ki67 positive cells in all regions along the cryptaxis was significantly greater (p<0.05) in tissue from older subjects : e.g. crypt base 35% (young) versus 52% (old); mid region 42%% (young) versus 62% (old) and upper region 10% (young) versus 17% (old). The number of cell divisions observed under timelapse microscopy was reduced for crypts derived from older subjects suggesting that the increased Ki67 labelling index in the older group reflected a slower cell cycle time. Although the nature of the proliferating cell type is not known at this stage, an increase in OLFM4+ (stem) cell number was observed along the axis of crypts derived from older subjects. The above traits were associated with a trend towards an extended profile of immunolabelling intensity for nuclear beta catenin and Wnt target gene expression along the crypt-axis of tissue derived from older subjects. CONCLUSIONS: Age-related changes in crypt length, cell proliferation and markers for intestinal stem cells and Wnt signalling components along the crypt-axis suggest that tissue renewal is compromised in the ageing human colonic epithelium.