The impact of ageing on the structural compositions of the mucosa of human colon

The increased prevalence of chronic constipation, faecal impaction and incontinence among older individuals have been linked in part, to age-related degenerative changes within the bowel. In aged laboratory animals, increased mucosal permeability has been associated with overall loss of mucosal integrity, but equivalent studies have not been conducted for the human colon. We address this knowledge gap by examining the number of intestinal stem cells and epithelial tight junction proteins, and densities of connective tissues, namely total collagen and elastin, on macroscopically normal ascending (AC; adults: 30-52 years and elderly: 70 - 89 years) and descending (DC; adults: 42-60 years and elderly: 67 - 82 years) colon using immunohistochemistry and tinctorial staining techniques. The results demonstrated that in the ageing AC but not clearly in the DC, there was a significant decline in anti-junctional adhesion molecule-A, anti- occludin and anti-zonula occluden-1 tight junction protein expressions within the epithelium per mucosal unit area. Compared to younger adults, there was no consistent change in anti-claudin-2 protein in the DC from older adults (p = 0.068), but the level of expression tended to increase in the AC (p = 0.059). The number of olfactomedin-4 positive cells tended to be smaller (mean value: AC; 5.2 ± 0.6 vs. 4.9 ± 0.2/ crypt and DC: 5.6 ± 0.8 vs. 5.1 ± 0.3) but were not statistically significant with increasing age in both regions. Ageing increased the amount of elastin fibres within the muscularis mucosae in AC and DC, and there was a tendency for total collagen fibres to increase in the mucosa of the older adults DC (p = 0.061). These structural changes in the aged mucosa have potential to impact colonic functions and may contribute to the development of lower bowel disorders in a region-specific manner.