Millions of Californians suffer from epidermal derived skin disorders, which range from psoriasis, squamous cell carcinomas, basal cell carcinomas to chronic wounds. These diseases are characterized by abnormalities in epidermal stem and progenitor cell growth and differentiation. For example, increased proliferation and failure to properly differentiate can lead to skin carcinomas whereas diabetes patients often suffer from chronic skin ulcers. Currently not much is known about the mechanisms that govern epidermal stem cell growth and differentiation. This proposal seeks to understand the fundamental mechanisms of epidermal stem cell self-renewal and differentiation through the study of epigenetic factors, which may yield insights in the development of therapies for epidermal disorders. Epigenetic modifications can potentially be modified either through inhibition or activation of epigenetic factors. Thus diseases stemming from deregulation of epigenetics may potentially be reversible or ameliorated. Our proposed research will benefit California in several ways: 1) our research should provide epigenetic targets that can be modulated by small molecules that can potentially treat epidermal disorders; 2) provide a thorough understanding of how adult somatic stem cells regenerate tissue.
Tissue specific stem and progenitor cells exist to replenish the tissue it resides during normal homeostasis or during regeneration from a wound. Disease and aging leads to a depletion of these stem and progenitor cells, which can impede the ability of the body to regenerate itself. Thus, an understanding of the mechanisms of how tissue specific stem and progenitor cells self-renew and differentiates is key to being able to maintain these cells for life and to use these cells therapeutically. Stem and progenitor cells reside in specific niches in our bodies, which interact with neighboring cells and extracellular proteins. Unfortunately, this type of interaction is difficult to model in cultured cells. We have previously developed methods to regenerate 3D intact human epidermis on immune compromised mice, which allows us to investigate the factors important for tissue regeneration. Potential regulators of epidermal stem cell self-renewal and differentiation include epigenetic factors. Epigenetic factors are proteins that modify either DNA or histone. Alterations in DNA or histone can lead to heritable changes in gene expression, which may lead to a stem cell determining whether to differentiate or proliferate. In the past year, we have found that epigenetic factors such as histone and DNA demethylases are important for epidermal stem and progenitor cell self-renewal and differentiation. Specifically, DNA demethylases are important for promoting epidermal differentiation by removing repressive DNA methylation marks that are a barrier to efficient expression of differentiation genes. We have also found that the H3K36 demethylase has an important role in maintaining the self-renewal of epidermal progenitor cells. Without expression of this factor the cells spontaneously differentiated and stopped proliferation. Loss of the H3K36 demethylase prevented methylation on this epigenetic mark. In turn, this prevented the expression of key self-renewal genes leading to premature cellular differentiation. Our results show that the differentiation status of the epidermis is mediated by both histone and DNA demethylases.