Small and large intestinal stem cells and their relation to cancer

The epithelial layers of the small intestine (SI) and large intestine (LI) are generated via self-renewal and differentiation of tissue-specific stem cells (SCs). Failure of intestinal SCs to respond properly to proliferation and differentiation signals can lead to the formation of cancer, almost exclusively found in the LI in humans. We hypothesize that there are distinct resident SCs in the SI versus LI leading to an increased frequency of human LI (colon) cancer. While fleeting observations of differences between SI and LI have been made in the past, a robust study of the origin of their differences has yet to be done. Here we show dramatic intrinsic differences between normal human SI and LI SCs that may have important implications for the disparity in their susceptibilities to cancer. Primary human fetal SI and LI cells were isolated and expanded in vitro using conditions that selected for SCs. Flow cytometry and limiting dilution analysis indicated differential SC marker expression as well as disparate populations of colony-forming cells. Gene array analysis showed separate hierarchical clustering and differential expression of transcripts involved in differentiation, proliferation and disease pathways of the SI and LI. Using a three-dimensional in vitro differentiation assay, SI and LI SCs formed organoids with architecture and cellular hierarchy similar to that found in vivo. Immunostaining and real-time PCR indicated that both SI and LI SCs retain the ability to differentiate into mature cells of the intestine. We also found that well-known proliferation and differentiation pathways in SI- and LI-derived organoids responded differently when exposed to the same exogenous stimuli. Notably, upon exposure to differentiation cues, an expected decrease in SC marker LGR5 in SI SCs was met with an unexpected increase in LI SCs. We also demonstrate similarities between human LI SCs and colon cancer SCs not present in SI SCs, supporting the notion that normal intestinal SCs are the cell of origin of cancer. Our characterization of human fetal SI and LI SCs revealed critical intrinsic differences that may affect their susceptibility to diseases such as cancer. Further elucidation of pathway differences may allow the exploitation of protective mechanisms to prevent or treat human colon cancer