Assessing the Photoprotective Effects of Fluorescent Sphingomyelin Against UVB Induced DNA Damage in Human Keratinocytes

Abstract

Assessing the Photoprotective Effects of Fluorescent Sphingomyelin Against UVB Induced DNA Damage in Human Keratinocytes Rebecca Marie Kandell Non Melanoma Skin Cancer (NMSC) affects 3.3 million Americans each year and results from Ultra Violet Radiation (UVR) damage to DNA in the form of pyrimidine dimers and photoproducts [1]-[5]. Cells directly detect the damage and initiate apoptosis, cell cycle arrest, or DNA repair by modulating p53 and p21 levels [6]-[9]. Current methods of photoprotection include sunscreen, but controversy over safety of some active ingredients necessitates research into more natural alternatives [10]-[12]. In particular, 24 hour incubation with bovine milk sphingomyelin (BSM) has demonstrated photoprotective potential by reducing p21 and p53 levels in keratinocytes (KRTs) after UV radiation [13], [14]. This thesis aims to expand on past BSM research by exploring the mechanism for photoprotection. Normally, sphingomyelin (SM) is metabolically degraded to ceramide which then leads to cell apoptosis [6]. The goals of this thesis were to characterize a fluorescent SM (FSM) to assess changes in intracellular fluorescence distribution after various incubation and post-UV exposure times. FSM was deemed functionally equivalent to BSM by reducing levels of p21 after UV. Furthermore, quantification demonstrated that FSM trafficking and intracellular fluorescence were independent of continuous incubation time, warranting further investigation into shorter timepoints like 1 hour. Across several post-UV timepoints, the 1 hour incubation had a consistently higher average cytoplasmic mean gray value compared to 24 hour incubation. In addition, the no UV control was significantly lower compared to the 24 hour and 12 hour post-UV timepoints. No post-UV differences were observed for the 24hour incubation, suggesting future work is necessary for the 1 hour incubation, which potentially streamlines future experiments. Two immunofluorescence stains for endogenous SM (lysenin) and ceramide were also optimized for preliminary fluorescence distribution studies and v colocalization with FSM. Finally, a 3T3 fibroblast spheroid model was utilized as proof-ofconcept for future 3D KRT cultures and depth of dye penetration quantification methods. These findings suggest FSM is an appropriate model for BSM trafficking, a shorter FSM incubation time could potentially be adopted in future studies, dual immunofluorescence staining for SM and ceramide is viable, and spheroids provide a promising model for future 3D KRT studies.