title: UV decreases the synthesis of free fatty acids and triglycerides in the epidermis of human skin in vivo, contributing to development of skin photoaging.
abstract: BACKGROUND
  Although fatty acids are known to be important in various skin functions, their roles on photoaging in human skin are poorly understood.
  
  
  OBJECTIVE
  We investigated the alteration of lipid metabolism in the epidermis by photoaging and acute UV irradiation in human skin.
  
  
  METHODS
  UV irradiated young volunteers (21-33 years, n=6) and elderly volunteers (70-75 years, n=7) skin samples were obtained by punch biopsy. Then the epidermis was separated from dermis and lipid metabolism was investigated.
  
  
  RESULTS
  We observed that the amounts of free fatty acids (FFA) and triglycerides (TG) in the epidermis of photoaged or acutely UV irradiated human skin were significantly decreased. The expressions of genes related to lipid synthesis, including acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD), sterol regulatory element binding proteins (SREBPs), and peroxisome proliferator-activated receptors (PPARgamma) were also markedly decreased. To elucidate the significance of these changes of epidermal lipids in human skin, we investigated the effects of TG or various inhibitors for the enzymes involved in TG synthesis on the expression of matrix metalloproteinase-1 (MMP-1) in cultured human epidermal keratinocytes. We demonstrated that triolein (TG) reduced basal and UV-induced MMP-1 mRNA expression. In addition, each inhibitor for various lipid synthesis enzymes, such as TOFA (ACC inhibitor), cerulenin (FAS inhibitor) and trans-10, cis-12-CLA (SCD inhibitor), increased the MMP-1 expression significantly in a dose-dependent manner. We also demonstrated that triolein could inhibit cerulenin-induced MMP-1 expression. Furthermore, topical application of triolein (10%) significantly prevented UV-induced MMP-13, COX-2, and IL-1beta expression in hairless mice.
  
  
  CONCLUSIONS
  Our results suggest that TG and FFA may play important roles in photoaging of human skin.
authors.affiliation: Department of Dermatology, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Eun Ju
authors.initials: EJ
authors.lastname: Kim
authors.forename: Xing-Ji
authors.initials: XJ
authors.lastname: Jin
authors.forename: Yeon Kyung
authors.initials: YK
authors.lastname: Kim
authors.forename: In Kyung
authors.initials: IK
authors.lastname: Oh
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Chi-Hyun
authors.initials: CH
authors.lastname: Park
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Chung
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D000818:Animals; D004817:Epidermis / Q000473:pathology / Q000502:physiology* / Q000528:radiation effects*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005260:Female; D006801:Humans; D050356:Lipid Metabolism; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D012867:Skin / Q000473:pathology*; D015595:Skin Aging; D014280:Triglycerides / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D005230:Fatty Acids, Nonesterified; D014280:Triglycerides