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Background: Radiation-induced skin injury is a serious concern during radiotherapy and accidental exposure to radiation., Objective: This study aims to investigate the molecular events in early response to ionizing radiation of skin tissues and underlying mechanism., Methods: Mice and rats were irradiated with an electron beam. Skin tissues were used for liquid chromatography-mass spectrometry (LC-MS)-based metabolomics, mRNA-Seq and single-cell RNA sequencing (scRNA-Seq). Human keratinocytes (HaCaT) and skin fibroblasts (WS1) were used for functional studies., Results: The integrated analysis of metabolomics and transcriptomics showed that 6 key fatty acid-associated metabolites, 9 key fatty acid-associated genes and multiple fatty acid-associated pathways were most obviously enriched and increased in the irradiated skins. Among them, acyl-CoA dehydrogenase very long chain (ACADVL) was investigated in greater detail due to its most obvious expression difference and significance in fatty acid metabolism. ScRNA-Seq of rat skin from irradiated individuals revealed that ACADVL was expressed in all subpopulations of skin tissues, with variations at different timepoints after radiation. Immunohistochemistry confirmed an increased ACADVL expression in the epidermis from human sample and various animal models, including monkeys, rats and mice. The knockdown of ACADVL increased the radiosensitivity of human keratinocytes and human skin fibroblasts. Silencing of ACADVL facilitated the expression of apoptosis and pyroptosis-related proteins following ionizing radiation., Conclusion: This study illustrated that cutaneous fatty acid metabolism was altered in the early response of ionizing radiation, and fatty acid metabolism-associated ACADVL is involved in radiation-induced cell death., Competing Interests: Conflict of interest The authors state no conflict of interest., (Copyright © 2023 Japanese Society for Investigative Dermatology. Published by Elsevier B.V. All rights reserved.)

Background: Radiation-induced skin injury is a serious concern during radiotherapy and radiation accidents. Skin fat represents the dominant architectural component of the human skin. However, the interplay between skin fat and the progression of radiation-induced skin injury remains largely unexplored., Objective: This study aims to elucidate the interplay between skin fat and the progression of radiation-induced skin injury., Methods: SD rats were irradiated with an electron beam. mRNA profiles were determined by RNA-Seq. The skin lipid mass was monitored by magnetic resonance imaging (MRI) and lipid profiles were measured by liquid chromatography-mass spectrometry (LC-MS). Human mature adipocytes isolated from dermal and subcutaneous white adipose tissues (WATs) were co-cultured with human keratinocytes (HaCaT) and skin fibroblasts (WS1) in the transwell culture system. Cell migration ability was measured by migration assay., Results: Radiation modulated cutaneous lipid metabolism by downregulating multiple pathways. Moreover, radiation decreased skin fat mass with altered lipid metabolite profiles. The rats fed with a high-fat diet showed resistance to radiogenic skin injury compared with that with a control diet, indicating that skin lipid plays a radioprotective role. Mature adipocytes promoted the migration but not the proliferation of co-cultured skin keratinocytes and fibroblasts. Palmitic acid, the most abundant fatty acid in skin tissues, facilitated the migration of WS1 cells. Moreover, fatty acid-binding protein 4 (FABP4) could be incorporated into skin cells and promote DNA damage repair in irradiated skin fibroblasts., Conclusion: Radiation induces cutaneous lipid remolding, and skin adipocytes confer a protective role against radiation-induced skin injury., Competing Interests: Declaration of Competing Interest The authors state no conflict of interest., (Copyright © 2020 Japanese Society for Investigative Dermatology. Published by Elsevier B.V. All rights reserved.)

Radiation-induced skin fibrosis is a detrimental and chronic disorder that occurs after radiation exposure. DNA methylation has been characterized as an important regulatory mechanism of multiple pathological processes. In this study, we compared the genome-wide DNA methylation status in radiation-induced fibrotic skin and adjacent normal tissues of rats by methylated DNA immunoprecipitation sequencing. Radiation-induced fibrotic skin showed differentially methylated regions associated with 3,650 protein-coding genes, 72 microRNAs, 5,836 long noncoding RNAs and 3 piwi-interacting RNAs. By integrating the mRNA and methylation profiles, the zinc transporter SLC39A9/ZIP9 was investigated in greater detail. The protein level of ZIP9 was increased in irradiated skin tissues of humans, monkeys, and rats, especially in radiogenic fibrotic skin tissues. Radiation induced the demethylation of a CpG dinucleotide in exon 1 of ZIP9 that resulted in recruitment of the transcriptional factor Sp1 and increased ZIP9 expression. Overexpression of ZIP9 resulted in activation of the profibrotic transforming growth factor-β signaling pathway through protein kinase B in human fibroblasts. In addition, radiation-induced skin fibrosis was associated with increased zinc accumulation. The zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethylenediamine abrogated ZIP9-induced activation of the transforming growth factor-β signaling pathway and attenuated radiation-induced skin fibrosis in a rat model. In summary, our findings illustrate epigenetic regulation of ZIP9 and its critical role in promoting radiation-induced skin fibrosis., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Radiation-induced acute skin injury and consequent fibrosis are common complications of cancer radiotherapy and radiation accidents. Stromal cell-derived factor-1α (SDF-1α) and its receptor, CXC chemokine receptor 4 (CXCR4) have been shown to be involved in multiple cellular events. However, the role of SDF-1α/CXCR4 axis in radiation-induced acute injury and fibrosis of skin has not been reported. In this study, we found that the expression of SDF-1α and CXCR4 was significantly increased in irradiated skin tissues of humans, monkeys and rats, compared to their nonirradiated counterparts. Mice with keratinocyte-specific ablation of CXCR4 showed less severe skin damage than wild-type mice after receiving a 35 Gy dose of radiation. Consistently, subcutaneous injection of AMD3100, an FDA approved SDF-1α/CXCR4 inhibitor, attenuated skin injury and fibrosis induced by exposure to radiation in a rat model. Mechanically, the SDF-1α/CXCR4 axis promotes pro-fibrotic TGF-b/Smad signaling through the PI3K-MAPK signaling cascade in human keratinocyte HaCaT cells and skin fibroblast WS1 cells. AMD3100 inhibited Smad2 nuclear translocation and transcriptional activity of Smad2/3 induced by radiation, which suppressed the pro-fibrotic TGF-b/Smad signaling pathway activated by exposure. Taken together, these findings demonstrate the involvement of SDF-1α/CXCR4 axis in radiation-induced acute injury and fibrosis of skin, and indicate that AMD3100 would be an effective countermeasure against these diseases.

Radiation-induced skin fibrosis is a detrimental and chronic disorder that occurs after radiation exposure. The molecular changes underlying the pathogenesis of radiation-induced fibrosis of human skin have not been extensively reported. Technical advances in proteomics have enabled exploration of the biomarkers and molecular pathogenesis of radiation-induced skin fibrosis, with the potential to broaden our understanding of this disease. In this study, we compared protein expression in radiation-induced fibrotic human skin and adjacent normal tissues using iTRAQ-based proteomics technology. We identified 186 preferentially expressed proteins (53 upregulated and 133 downregulated) between radiogenic fibrotic and normal skin tissues. The differentially expressed proteins included keratins (KRT5, KRT6A, KRT16 and KRT17), caspase-14, fatty acid-binding protein 5 (FABP5), SLC2A14 and resistin. Through bioinformatic analysis of the proximal promoters, common motifs and corresponding transcriptional factors were identified that associate with the dysregulated proteins, including PAX5, TBX1, CLOCK and AP2D. In particular, FABP5 (2.15-fold increase in fibrotic skin tissues), a transporter of hydrophobic fatty acids, was investigated in greater detail. Immunohistochemistry confirmed that the protein level of FABP5 was increased in fibrotic human skin tissues, especially in the epidermis. Overexpression of FABP5 resulted in nuclear translocation of SMAD2 and significant activation of the profibrotic TGF-β signaling pathway in human fibroblast WS1 cells. Moreover, exogenous FABP5 (FABP5-EGFP) could be incorporated by skin cells and intensify TGF-β signaling, indicating a communication between the microenvironment and skin fibrosis. Taken together, our findings illustrate the molecular changes during radiation-induced human skin fibrosis and the critical role of FABP5 in activating the TGF-β signaling pathway.