Induction of Apoptosis in Human Keratinocyte Stem Cells: The Role of Hydrogen Sulfide

Abstract

Apoptosis of epithelial stem cells is currently attracting much attention for the role it could play in cancer development. Because deficiencies in apoptosis mechanisms may be one of the causes of neoplasm formation, targeting cancer stem cells for treatment with keratinocyte stem cells could produce lasting results. However, some aspects of the apoptosis of human keratinocyte stem cells are not well understood. In this chapter, we clarify the relationship between hydrogen sulfide (H2S) and keratinocyte stem cells. H2S is produced in many human tissues and has been shown to cause apoptosis in the cells of epithelial tissue components. In our studies, the percentage of apoptotic cells in a population of keratinocyte stem cells was significantly increased following H2S exposure. The mitochondrial membrane was depolarized, and ROS levels were significantly increased because of both cytochrome c oxidase and superoxide dismutase inhibition by H2S. As a result, mitochondrial apoptotic pathways, including cytochrome c and caspase-9 and -3, were activated, while caspase-8 remained inactive. The p53 and BAX levels also were significantly elevated. We concluded that H2S induces apoptosis in human keratinocyte stem cells through intrinsic pathways. Further, we developed a novel protocol for separating keratinocyte stem cells from human mucosa using magnetic separation, by means of which we found that the α6β4-integrin-positive, CD71-negative fraction was also the keratinocyte stem-cell fraction.