As a major component of the epidermal tissue, a primary keratinocyte has served as an essential tool not only for the study of pathogenesis of skin-related diseases but also for the assessment of potential toxicities of various chemicals used in cosmetics. However, its short lifespan in ex vivo setting has been a great hurdle for many practical applications. Therefore, a number of immortalization attempts have been made with success to overcome this limitation. In order to understand the immortalization process of a primary keratinocyte, several key biological phenomena governing its lifespan will be reviewed first. Then, various immortalization methods for the establishment of stable keratinocyte cell lines will be explained. Finally, its application to a three-dimensional skin culture system will be described.
Aging ; Biological Phenomena ; Cell Line ; Keratinocytes* ; Skin*

In spite of frequent usage of primary human foreskin keratinocytes (HFKs) in the study of skin biology, senescence-induced blockage of in vitro proliferation has been a big hurdle for their effective utilization. In order to overcome this passage limitation, we first isolated ten HFK lines from circumcision patients and successfully immortalized four of them via a retroviral transduction of high-risk human papillomavirus (HPV) E6 and E7 oncogenes. We confirmed expression of a keratinocyte marker protein, keratin 14 and two viral oncoproteins in these immortalized HFKs. We also observed their robust responsiveness to various exogenous stimuli, which was evidenced by increased mRNA expression of epithelial differentiation markers and pro-inflammatory genes in response to three reactive chemicals. In addition, their applicability to cytotoxicity assessment turned out to be comparable to that of HaCaT cells. Finally, we confirmed their differentiation capacity by construction of well-stratified three dimensional skin cultures. These newly established immortalized HFKs will be valuable tools not only for generation of in vitro skin disease models but also for prediction of potential toxicities of various cosmetic chemicals.
Antigens, Differentiation ; Biology ; Foreskin* ; Humans* ; In Vitro Techniques ; Keratin-14 ; Keratinocytes* ; Oncogene Proteins ; Oncogenes ; RNA, Messenger ; Skin Diseases ; Skin* ; Zidovudine

Purpose: This study investigated hand-washing practice among community-dwelling older adults during the coronavirus disease 2019 (COVID-19) pandemic and aimed to identify the impact of COVID-19-related concerns and depression on hand-washing practice. Methods: This was a secondary analysis of data extracted from the 2020 Community Health Survey. The primary data were collected through self-reporting from August 10 to September 8, 2020 in a cross-sectional study. The subjects consisted of 1,350 adults aged 65 or older living in J Province who participated in the 2020 Community Health Survey. Results: The factors affecting hand-washing practice among older adults were male gender (β = –.18, p < .001), age (β = –.07, p = .001), no education (β = –.20, p < .001) and elementary, middle, and high school graduation (β = –.15, p < .001) compared to a college or higher education, poor health perception (β = –.13, p < .001), COVID-19-related concerns (β = .08, p = .005), and depression (β = –.07, p = .001). To summarize, the factors negatively affecting hand-washing practice included male gender, lower education level, poor health perception, and depression, while the factors positively associated with hand-washing practice included COVID-19-related concerns. Conclusion These findings show the importance of considering these multifaceted determinants when designing targeted interventions and educational programs aimed at promoting hand-washing among older adults. Additionally, based on the relationship between hand-washing practice and COVID-19-related concerns and depression, interventions that can alleviate mental problems along with providing proper education are required.