SUMMARY Chronic ulcers, defined as wounds that fail to heal within a three-month period, are associated with age-related dysfunction in skin stem cells that not only has potential to blunt tissue repair, but also accounts for skin fragility, atrophy, and the "aging phenotype" that itself has clinical as well as psychosocial implications. Non-healing ulcers in aging individuals represent a multibillion dollar burden in the United States and to society globally, both through utilization of health care resources as well as through reduction in productivity. Nonetheless, it is recognized that "the basic biology and the influence of age-associated changes on wound healing are poorly understood, and there are numerous research questions still to be answered". To address this important issue, we have 1) assembled a highly collaborative and multidisciplinary team of investigators with established track records in skin pathology, regenerative and stem cell biology, wound healing, bioinformatics, and the pathobiology of aging; 2) leveraged the resources of seven Harvard Institutions to develop a unified and state- of-the-art approach to decipher the role skin stem cell deficiency in age-related defective wound healing; and 3) generated data-based hypotheses and identified inter-project synergies that will maximize productivity and translational focus. Our fundamental hypothesis is that identification and interrogation of three major, inter- related, and therapeutically targetable/reprogrammable pathways relevant to age-related skin stem cell dysfunction, a) metabolic, b) epigenetic, and c) membrane transporter/receptor, will pave the way for combinatorial (multicomponent) therapies necessary for more robust healing and regenerative responses to skin injury. We will pursue this goal through six strategies that have been developed by the key personnel of this PPG: 1) discovery of biomarkers for epidermal and dermal stem cell identification and manipulation; 2) determination of metabolic regulators required for epidermal progenitor activity and maintenance; 3) identification of novel epigenetic pathways that govern skin stem cell function and vitality; 4) development and evaluation of unique murine models that permit study of human wound healing in vivo; 5) deployment of lineage tracking technologies that facilitate detection of experimentally-manipulated stem cell fate in healing wounds; and 6) generation of new animal strains and for epigenomic induction of premature aging and methods for genomic restoration of stem cell youth and pluripotency. Our overall aims seek to answer the following questions: 1) How can one map the key metabolomic, epigenetic, and cell receptor stem cell pathways that drive age-related wound healing dysfunction?; 2) What are the therapeutically-accessible nodes for stem cell-directed multicomponent combinatorial targeting within these pathways?; and 3) What are the agents that likely will affect restoration of robust and regenerativ...