Epigenetic and genetic dissections of UV-induced global gene dysregulation in skin cells through multi-omics analyses

To elucidate the complex molecular mechanisms underlying the adverse effects UV radiation (UVR) on skin homeostasis, we performed multi-omics studies to characterize UV-induced genetic and epigenetic changes. Human keratinocytes from a single donor treated with or without UVR were analyzed by RNA-seq, exome-seq, and H3K27ac ChIP-seq at 4 h and 72 h following UVR. Compared to the relatively moderate mutagenic effects of UVR, acute UV exposure induced substantial epigenomic and transcriptomic alterations, illuminating a previously underappreciated role of epigenomic and transcriptomic instability in skin pathogenesis. Integration of the multi-omics data revealed that UVR-induced transcriptional dysregulation of a subset of genes was attributable to either genetic mutations or global redistribution of H3K27ac. H3K27ac redistribution further led to the formation of distinctive super enhancers in UV-irradiated cells. Our analysis also identified several new UV target genes, including CYP24A1, GJA5, SLAMF7 and ETV1, which were frequently dysregulated in human squamous cell carcinomas, highlighting their potential as new molecular targets for prevention or treatment of UVR-induced skin cancers. Taken together, our concurrent multi-omics analyses provide new mechanistic insights into the complex molecular networks underlying UV photobiological effects, which have important implications in understanding its impact on skin homeostasis and pathogenesis

207-nm UV Light—A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. II: In-Vivo Safety Studies

Background UVC light generated by conventional germicidal lamps is a well-established anti-microbial modality, effective against both bacteria and viruses. However, it is a human health hazard, being both carcinogenic and cataractogenic. Earlier studies showed that single-wavelength far-UVC light (207 nm) generated by excimer lamps kills bacteria without apparent harm to human skin tissue in vitro. The biophysical explanation is that, due to its extremely short range in biological material, 207 nm UV light cannot penetrate the human stratum corneum (the outer dead-cell skin layer, thickness 5–20 μm) nor even the cytoplasm of individual human cells. By contrast, 207 nm UV light can penetrate bacteria and viruses because these cells are physically much smaller. Aims To test the biophysically-based hypothesis that 207 nm UV light is not cytotoxic to exposed mammalian skin in vivo. Methods Hairless mice were exposed to a bactericidal UV fluence of 157 mJ/cm2 delivered by a filtered Kr-Br excimer lamp producing monoenergetic 207-nm UV light, or delivered by a conventional 254-nm UV germicidal lamp. Sham irradiations constituted the negative control. Eight relevant cellular and molecular damage endpoints including epidermal hyperplasia, pre-mutagenic UV-associated DNA lesions, skin inflammation, and normal cell proliferation and differentiation were evaluated in mice dorsal skin harvested 48 h after UV exposure. Results While conventional germicidal UV (254 nm) exposure produced significant effects for all the studied skin damage endpoints, the same fluence of 207 nm UV light produced results that were not statistically distinguishable from the zero exposure controls. Conclusions As predicted by biophysical considerations and in agreement with earlier in vitro studies, 207-nm light does not appear to be significantly cytotoxic to mouse skin. These results suggest that excimer-based far-UVC light could potentially be used for its anti-microbial properties, but without the associated hazards to skin of conventional germicidal UV lamps

Epidermal thickness in hairless mice skin exposed to UVC light.

<p>A) Representative cross-sectional images of H&E-stained mouse dorsal skin comparing the epidermal thickness in sham-exposed mice (top panel), in mice exposed to 254-nm light (middle panel) or to 207-nm light (bottom panel). B) Quantification of epidermal thickness; values represent the average ± SD of epidermal thickness measured in nine randomly selected fields of view per mouse (n = 3).* p<0.0001.</p

Top view of the custom-designed mouse UV irradiation box.

<p>The UV lamp is located above the irradiation box, which has separate compartments to house up to eight mice. A metal-mesh cover (not shown) allows UV light transmission (74% transparency) from above. As shown, during both acclimatization and irradiation, the mice have ad-libitum access to food and water.</p

Expression of the proliferative marker Ki-67 in keratinocytes of hairless mice skin exposed to UVC.

<p>A) Ki-67-positive keratinocytes (dark-stained cells) in typical cross-sections of skin of sham-exposed mice (top panel), of mice exposed to 254-nm light (middle panel) or to 207-nm light (bottom panel). B) Quantification of the percentage of keratinocytes expressing Ki-67 antigen; values represent the average ± SD of Ki-67-positive cells measured in six randomly selected fields of view per mouse (n = 3). * p<0.0001.</p

Summary of the combined results for each endpoint.

<p>Summary of the combined results for each endpoint.</p

Tissue differentiation in UVC-exposed hairless mouse skin.

<p><b>A)</b> Representative cross-sectional images of mouse dorsal epidermis expressing (brown stained area) K6A with B) relative quantification. Mice were sham-exposed (top panel), exposed to 254-nm light (middle panel) or to 207-nm light (bottom panel). Values represent the average ± SD of the percentage of keratin optical density measured in nine randomly selected fields of view per mouse (n = 3). * p <0.0001.</p

UVC-induced pre-mutagenic DNA lesions in hairless mice skin.

<p>A) Representative cross-sectional images of dorsal skin samples comparing pre-mutagenic skin lesions CPD (top row, dark-stained cells) and 6-4PP (bottom row, dark stained cells) in the epidermis of sham-exposed mice (left column), of mice exposed to 254-nm light (middle column) or to 207-nm light (right column). Quantification of the percentage of keratinocytes showing B) CPD or C) 6-4PP dimers; values represent the average ± SD of cells exhibiting dimers measured in nine randomly selected fields of view per mouse (n = 3). * p<0.0001.</p

UVC-induced inflammation in hairless mice skin.

<p>Density of A) mast cells and B) cells expressing the myeloperoxidase (MPO) enzyme (i.e. neutrophils) in the epidermis of sham-exposed mice, of mice exposed to 254-nm light or to 207-nm light. Values represent the average ± SD of the number of cells / m² measured in six randomly selected fields of view per mouse (n = 3). * p <0.0001.</p

Parenchymal and stromal tissue regeneration of tooth organ by pivotal signals reinstated in decellularized matrix

Cells are transplanted to regenerate an organs' parenchyma, but how transplanted parenchymal cells induce stromal regeneration is elusive. Despite the common use of a decellularized matrix, little is known as to the pivotal signals that must be restored for tissue or organ regeneration. We report that Alx3, a developmentally important gene, orchestrated adult parenchymal and stromal regeneration by directly transactivating Wnt3a and vascular endothelial growth factor. In contrast to the modest parenchyma formed by native adult progenitors, Alx3-restored cells in decellularized scaffolds not only produced vascularized stroma that involved vascular endothelial growth factor signalling, but also parenchymal dentin via the Wnt/β-catenin pathway. In an orthotopic large-animal model following parenchyma and stroma ablation, Wnt3a-recruited endogenous cells regenerated neurovascular stroma and differentiated into parenchymal odontoblast-like cells that extended the processes into newly formed dentin with a structure-mechanical equivalency to native dentin. Thus, the Alx3-Wnt3a axis enables postnatal progenitors with a modest innate regenerative capacity to regenerate adult tissues. Depleted signals in the decellularized matrix may be reinstated by a developmentally pivotal gene or corresponding protein