Dedifferentiation of Human Epidermal Keratinocytes Induced by UV In Vitro

Abstract

Dedifferentiation is an important biological phenomenon and is understood as a process in which cells develop in a reverse order from a more differentiated to a less differentiated state. In the present study, we observed that after UV treatment, the surviving keratinocytes underwent the reversion from differentiated state to dedifferentiated state, evidenced by the changes from three levels, including phenotype, morphology and function. First, the mature keratinocytes acquired a dedifferentiated phenotype indicated by reexpression of transit-amplifying (TA) cell markers, including CK14 and β1 integrin. Second, the cells experienced morphological changes during the process of dedifferentiation. Cells treated with UV were small and had a high nuclear to cytoplasmic ratio, whereas cells without treatment had well-developed cellular organelles and abundant tonofilaments. Third, after UV treatment, the cells regained strong proliferation capacity. These dedifferentiation-derived stem cells formed colonies with defined edges developed and presented multiple-layer growing profile under three-dimensional culture condition. The skin equivalent (SE) produced with UV-treated keratinocytes also showed a well-organized structure with four stratifications. We also report the signaling pathway involved in the dedifferentiation process. The extracellular signal-regulated kinase (ERK) pathway regulates the phenotype reversion of keratinocytes into progenitor cells. Inhibition of ERK kinase activities with a specific inhibitor (PD98059) substantially blocked phosphorylation of ERK1/2 and human keratinocyte dedifferentiation. These data collectively provide a proof-of-concept that UV treatment of HEKs is capable of inducing a phenotype reversion from an adult differentiated state to an immature-like dedifferentiated state via ERK Mitogen-Activated Protein Kinases (MAPK)-dependent pathway. It may offer the direct evidence for the existence of dedifferentiation and the underlying mechanisms involved in the process, which may bring a new insight for the regenerative medicine.