Low temperature and mTOR inhibition favor stem cell maintenance in human keratinocyte cultures.

Adult autologous human epidermal stem cells can be extensively expanded ex vivo for cell and gene therapy. Identifying the mechanisms involved in stem cell maintenance and defining culture conditions to maintain stemness is critical, because an inadequate environment can result in the rapid conversion of stem cells into progenitors/transient amplifying cells (clonal conversion), with deleterious consequences on the quality of the transplants and their ability to engraft. Here, we demonstrate that cultured human epidermal stem cells respond to a small drop in temperature through thermoTRP channels via mTOR signaling. Exposure of cells to rapamycin or a small drop in temperature induces the nuclear translocation of mTOR with an impact on gene expression. We also demonstrate by single-cell analysis that long-term inhibition of mTORC1 reduces clonal conversion and favors the maintenance of stemness. Taken together, our results demonstrate that human keratinocyte stem cells can adapt to environmental changes (e.g., small variations in temperature) through mTOR signaling and constant inhibition of mTORC1 favors stem cell maintenance, a finding of high importance for regenerative medicine applications.

Two-dimensional impedance imaging of cell migration and epithelial stratification.

We present a miniaturized impedance imaging system, developed for 2D imaging of cell and tissue culture. The system is based on 16 microelectrodes (5 microm x 4 mm). An equivalent circuit for four-point (tetrapolar) impedance spectra was developed and validated. The system uses an Agilent 4294A impedance analyser combined with a front-end amplifier for the impedance measurements. Human epithelial stem cells (YF 29) were grown on the device surface. Cell migration speeds of 300 nm min(-1) following a "scratch" wound closure assay could be established. Using a commercial software developed for geophysical prospecting, we could generate impedance tomography images at 10 kHz revealing cell migration, increase of epithelial thickness and changes in tissue resistivity over a time course of several days.

Influence of calcium on the proteolytic degradation of the calmodulin-like skin protein (calmodulin-like protein 5) in psoriatic epidermis.

The calmodulin-like skin protein (CLSP) or so-called calmodulin-like protein 5, a recently discovered skin-specific calcium-binding protein, is closely related to keratinocyte differentiation. The 16-kDa protein is proteolytically degraded in the upper layers of the stratum corneum (SC) of healthy skin. With the use of specific new monoclonal antibodies to CLSP, we were able to demonstrate that the abnormal elevated levels of CLSP, characteristic of psoriatic epidermis, were probably not due to an overexpression of the protein, but most likely the result of its non-degradation. Further in vitro experiments using recombinant CLSP and in situ data clearly showed that calcium protected and chelator accelerated CLSP degradation. These data indicate that CLSP degradation in the SC of psoriatic skin might be hindered by the abnormally elevated calcium concentration. No degradation of CLSP in psoriatic epidermis keeping its ability to bind protein as transglutaminase 3 may have a physiological role in skin diseases such as psoriasis.

Controlling skin morphogenesis: hope and despair.

To master tissue and organ morphogenesis necessitates a thorough understanding of the cellular and molecular events involved in development, renewal, repair and regeneration. Skin reconstruction is the paradigm of tissue engineering. The transplantation of autologous adult epidermal stem cells is a life-saving procedure as it regenerates the indispensable barrier function of the skin, but the reconstruction of fully functional skin has been hampered by the complexity of the process. The recent identification of multipotent epithelial stem cells in adult hair follicles and of multipotent stem cells in dermis raises new hopes.

Basal cell carcinoma of the earlobe after auricular acupuncture.

The genesis of familial and sporadic basal cell carcinomas involves activation of the Sonic hedgehog signal transduction pathway. Other known factors for the development of basal cell carcinoma are ultraviolet exposure, X-rays, race, age, gender and decreased DNA repair capacity. We here report the case of a right earlobe sporadic basal cell carcinoma in a 65-year-old woman. This case is unusual because of its earlobe localization and its association with multiple auricular acupuncture treatments. This observation suggests a connection between local traumas, which occur in the course of acupuncture treatment and ear piercing, and the genesis of basal cell carcinoma. The incidence of minor adverse events associated with acupuncture is high, but serious events are uncommon. Acupuncture is not known to date for promoting the development of tumors. This connection remains to be elucidated.