Study of Skin Cells That Stop Replicating (Senescent) During Wound Healing

Background: Cellular senescence is the aging of cells. It is a complex process that may be connected with aging and age-related diseases. It is unknown if these cells appear around wound sites in humans a few days after skin injury and if there are differences in young and old individuals. This study is being done to look at how cells in your body respond to small skin wounds. This information may help treat age-related diseases. Objective: To study how cells in the body respond to small skin wounds. Eligibility: Healthy adults ages 20-39 or 70+ Design: Participants will be screened with medical history, physical exam, and blood sample. They will fast before the screening visit. Women will have a urine pregnancy test. Participants will have 3 study visits over about 3 weeks. Visits 1 and 2: Participants will fast before and have blood taken. Women will have a urine test. All participants will have 2 skin biopsies. A spot on the upper arm will be numbed. Two small pieces of skin will be removed. They will keep the area covered until the next visit. Visit 3: Participants will have their vital signs taken. Their biopsy wounds will be measured and photographed.

Objectives and Specific Aims: The objective of this proof-of-concept study is to understand the physiological role of senescent cells in humans during the aging process using a model of wound healing. Cellular senescence is the phenomenon by which normal cells cease to divide in response to a stress. We aim to determine if in healthy humans: (1) senescent cells appear around wound sites a few days after skin injury; (2) the number of senescent cells induced by skin injury increases with age; (3) the wound healing process, as determined by the size of the healed wounds, is altered with aging; (4) biomarkers of senescence-associated secretory phenotype (SASP) increase significantly in the tissue around the wound a few days after skin injury, and the magnitude of increase is higher in older compared to younger persons; (5) ethnic differences in the dynamics of the appearance of senescent cells and whether such a difference is associated with wound healing. We also want to describe changes that occur with aging in DNA methylation and histone acetylation, gene expression, and protein expression within senescent cells in comparison to normal tissue. Experimental Design and Methods: One hundred and twenty-eight healthy participants, sixty-four between the ages of 20-39 years and sixty-four 70 years old or older will be recruited for this pilot study. Of the sixty-four participants in each age group, thirty-two will be men and thirty-two will be women and sixteen will be Caucasian and sixteen will be African American. Each participant will have two 3mm skin biopsies on the inner upper arm during baseline visit (Visit 1) and two 6mm skin biopsies concentric to the previous site during Visit 2. Visit 2 will be scheduled on 8 different days (day 3, 5, 7, 9, 11, 13, 21 and 30) after the baseline visit with two men and two woman from each age/ethnic group for each of the days. A follow-up visit will be scheduled at the discretion of the medical staff. Senescent cells will be visualized by confocal microscopy based on a number of senescent markers described in the literature. Senescent biomarkers will be measured in the tissue and systemically at baseline and follow-up. Medical Relevance and Expected Outcome: Cellular senescence is a complex process characterized by arrest in replication that is thought to be intrinsically connected with aging and age-related diseases. Recently, researchers have suggested that senescent cells may play a role in the pathogenesis of type 2 diabetes and its associated complications. Therefore, understanding the physiological role of senescent cells is critically important for understanding aging and age-related diseases such as type 2 diabetes. Preclinical data have shown that senescent cells were inducible during cutaneous wound healing. Our preliminary results showed that there may be a difference in rate of granulation tissue formation with ethnicity. Therefore, this method can be used to quantify senescent cell response after a standard stimulus and to verify whether the magnitude of senescence response correlate with aging and ethnicity. In the future this method could be used to test interventions that can modify the senescence response, and may be an invaluable method for assessing novel treatments of type 2 diabetes involving senescent cells.