Keratinocyte differentiation is highly regulated to produce the stratified structure of the epidermis and must be balanced with cell proliferation. Our prior studies revealed that hairless mice that cannot synthesize vitamin C (VC) exhibit epidermal atrophy. VC is a cofactor for the DNA demethylation (TET) enzyme, but the role of VC in DNA demethylation during keratinocyte differentiation remains unclear. In this study, we evaluated the role of VC in epigenetic regulation of epidermal proliferation and differentiation in a human epidermal equivalent model. Our findings demonstrated that intracellular VC uptake increased epidermal thickness, cell proliferation, and global levels of 5-hydroxymethylcytosine (5-hmC) DNA. Notably, these effects of VC were attenuated by an inhibitor of the TET enzyme. DNA microarray and whole-genome bisulfite sequencing (WGBS) analyses revealed that twelve genes related to cell proliferation were significantly upregulated by VC. Further, hypomethylated DNA regions associated with these genes were revealed in the presence of VC. Collectively, our findings provide insight into how VC increases epidermal thickness by promoting keratinocyte proliferation via the DNA demethylation of proliferation-related genes. VC is a promising molecule that can be used as developing treatment for epidermal thinning, including in aging.

Environmental stressors such as low temperature, low relative humidity (RH), and airborne particulate matter (PM2.5) can promote tear film (TF) instability and dry eye disease. Because the lipid layer is the first TF component exposed to these challenges, this study investigates how such conditions alter the interfacial behavior of meibomian gland secretion (MGS) films in vitro. A second objective is to evaluate the capacity of Rohto Dry Aid (RDA), a tear-mimetic nanoemulsion, to suppress the impact of environmental stressors on MGS. Pseudobinary MGS/RDA films were studied with a Langmuir trough and Brewster angle microscopy to assess molecular-level interactions at the air–water interface under adverse ambient conditions, including 20 °C aqueous subphase, 20% RH, and PM2.5 exposure. It was found that despite their distinct nature, the environmental stressors exert similar impacts, disrupting the multilayer structure and the reorganization and rheological properties of MGS layers at blink-like area deformations. These adverse effects were moderated by the supplementation with RDA which resulted in partial recovery of the mebomian film structure and isothermal reversibility. Thus, although they cannot fully replicate the complexity of native meibum, tear-mimetic nanoemulsions represent a potent tool to mitigate the impact of environmental stressors on tear film functionality.

Environmental stressors like low temperature, low relative humidity (RH), and particulate matter (PM2.5), promote tear film instability and dry eye disease. This study investigates how these conditions alter the interfacial behavior of meibomian gland secretion (MGS) films in vitro and evaluates the capacity of mucomimetic polymers (0.5% hyaluronic acid [HA], polyvinylpyrrolidone [PVP], and chondroitin sulfate [CHS]) to suppress these impacts. MGS films over polymer-containing aqueous subphases were analyzed using a Langmuir trough and Brewster angle microscopy under adverse conditions (20 °C subphase, 20% RH, PM2.5 exposure). A sophisticated analytical framework was developed to evaluate MGS duplex multilayers: (i) a Volmer equation-based 2D-VES model to probe interfacial molecular properties (limiting area, compressibility, cohesion pressure) and (ii) a combined Maxwell viscoelastic and diffusion-relaxation model to quantify the dilatational relaxation modulus. Results indicate that despite their distinct nature, environmental stressors similarly disrupt the multilayer structure, reorganization, and rheological properties of MGS layers during blink-like deformations. Polymer supplementation moderated these adverse effects, yielding partial recovery of film structure and isothermal reversibility. Distinct mechanisms of action for HA, PVP, and CHS at the film/aqueous interface are elucidated.