A comparison of apoptosis levels in keloid tissue, physiological scars and normal skin

Apoptosis is a process of programmed cell death that occurs in multicellular organisms. The mitochondrial pathway plays a paramount role in apoptosis. In this study, the expression levels of key factors in the mitochondrial pathway and the cell proliferation factor (PCNA) were measured to evaluate the level of apoptosis and proliferation in keloid scars, physiological scars and normal skin tissue. Thirty samples were taken from 30 patients: 10 keloid patients, 10 physiological scar patients and 10 patients without obvious scarring. All 30 patients were selected randomly from the Department of Plastic Surgery at Peking Union Medical College Hospital from June 2016 to December 2016. Hematoxylin and eosin staining and Masson staining were used to observe the differences in histology and fiber tissue content. Mitochondrial pathway factors (caspase-3, caspase-8, caspase-9, Bcl-2, Bax, cytochrome-c) and PCNA expression levels were detected by immunohistochemistry and were analyzed as the percentage of positively stained cells in the epidermis and dermis. Relative protein expression levels were measured by western blotting. Compared with physiological scars and normal skin tissue, keloid tissue had an increase in fiber number and decrease in cell content. In our immunohistochemical and western blot analyses, all tissue types showed similar expression levels of the mitochondrial pathway factors. However, the percentage of PCNA-positive cells and the relative protein expression level of PCNA were significantly higher in keloid tissue. Keloid has a similar apoptosis level as physiological scars and normal skin but has a higher expression of PCNA, indicating that keloid scars have high levels of proliferation and normal apoptosis.