Epithelial stem cells

Generation of folliculogenic human epithelial stem cells from induced pluripotent stem cells

Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling. The isolation and propagation of human EpSCs for tissue engineering purposes remains a challenge. Here we develop a strategy to differentiate human iPSCs (hiPSCs) into CD200⁺/ITGA6⁺ EpSCs that can reconstitute the epithelial components of the hair follicle and interfollicular epidermis. The hiPSC-derived CD200⁺/ITGA6⁺ cells show a similar gene expression signature as EpSCs directly isolated from human hair follicles. Human iPSC-derived CD200⁺/ITGA6⁺ cells are capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths in skin reconstitution assays. The regenerated hair follicles possess a KRT15⁺ stem cell population and produce hair shafts expressing hair specific keratins. These results suggest an approach for generating large numbers of human EpSCs for tissue engineering and new treatments for hair loss, wound healing and other degenerative skin disorders.

The spatial distribution of LGR5+ cells correlates with gastric cancer progression

In this study we tested the prevalence, histoanatomical distribution and tumour biological significance of the Wnt target protein and cancer stem cell marker LGR5 in tumours of the human gastrointestinal tract. Differential expression of LGR5 was studied on transcriptional (real-time polymerase chain reaction) and translational level (immunohistochemistry) in malignant and corresponding non-malignant tissues of 127 patients comprising six different primary tumour sites, i.e. oesophagus, stomach, liver, pancreas, colon and rectum. The clinico-pathological significance of LGR5 expression was studied in 100 patients with gastric carcinoma (GC). Non-neoplastic tissue usually harboured only very few scattered LGR5⁺ cells. The corresponding carcinomas of the oesophagus, stomach, liver, pancreas, colon and rectum showed significantly more LGR5⁺ cells as well as significantly higher levels of LGR5-mRNA compared with the corresponding non-neoplastic tissue. Double staining experiments revealed a coexpression of LGR5 with the putative stem cell markers CD44, Musashi-1 and ADAM17. Next we tested the hypothesis that the sequential changes of gastric carcinogenesis, i.e. chronic atrophic gastritis, intestinal metaplasia and invasive carcinoma, are associated with a reallocation of the LGR5⁺ cells. Interestingly, the spatial distribution of LGR5 changed: in non-neoplastic stomach mucosa, LGR5⁺ cells were found predominantly in the mucous neck region; in intestinal metaplasia LGR5⁺ cells were localized at the crypt base, and in GC LGR5⁺ cells were present at the luminal surface, the tumour centre and the invasion front. The expression of LGR5 in the tumour centre and invasion front of GC correlated significantly with the local tumour growth (T-category) and the nodal spread (N-category). Furthermore, patients with LGR5⁺ GCs had a shorter median survival (28.0±8.6 months) than patients with LGR5⁻ GCs (54.5±6.3 months). Our results show that LGR5 is differentially expressed in gastrointestinal cancers and that the spatial histoanatomical distribution of LGR5⁺ cells has to be considered when their tumour biological significance is sought.

Engineered whole organs and complex tissues

End-stage organ failure is a key challenge for the medical community because of the ageing population and the severe shortage of suitable donor organs available. Equally, injuries to or congenital absence of complex tissues such as the trachea, oesophagus, or skeletal muscle have few therapeutic options. A new approach to treatment involves the use of three-dimensional biological scaffolds made of allogeneic or xenogeneic extracellular matrix derived from non-autologous sources. These scaffolds can act as an inductive template for functional tissue and organ reconstruction after recellularisation with autologous stem cells or differentiated cells. Such an approach has been used successfully for the repair and reconstruction of several complex tissues such as trachea, oesophagus, and skeletal muscle in animal models and human beings, and, guided by appropriate scientific and ethical oversight, could serve as a platform for the engineering of whole organs and other tissues.