657  2001 American Society for Photobiology 0031-8655/00 $5.00+0.00 Photochemistry and Photobiology, 2001, 73(6): 657–663 Induction of mRNA for Matrix Metalloproteinase 1 and Tissue Inhibitor of Metalloproteinases 1 in Human Skin in vivo by Solar Simulated Radiation ¶ Christine Lahmann* 1 , Antony R. Young 2 , Klaus-Peter Wittern 1 and Jo ¨ rg Bergemann 1 1 Beiersdorf AG, Paul Gerson Unna Skin Research Center, Hamburg, Germany and 2 Department of Environmental Photobiology, St John’s Institute of Dermatology, King’s College, St Thomas’ Hospital, London, UK Received 21 August 2000; accepted 10 February 2001 ABSTRACT Repeated exposure to solar ultraviolet radiation results in premature skin aging due, in part, to the degradation of dermal collagen by fibroblast collagenase (matrix me- talloproteinase 1 [MMP-1]). We have established TaqMan  reverse transcription (RT) polymerase chain reaction (PCR) systems to quantify the messenger RNA (mRNA) expression of MMP-1 and its specific inhibitor TIMP-1 in human buttock skin exposed in vivo to solar simulated radiation (SSR). A time-course study (n  6) with two minimal erythema doses (MED) of SSR showed maximal induction of MMP-1 and TIMP-1 at 24 h. A dose–response study (n  6) sampled at 24 h revealed that doses of about 1 MED were necessary to induce ex- pression of MMP-1 mRNA, and our data suggest that the response is saturated at about 2 MED. We also investi- gated SSR-induced gene expression in the dermis and epidermis separately (n  5). MMP-1 was present in both tissues, but TIMP-1 was only detected in the dermis. In general, we could only measure MMP-1 mRNA in the nonirradiated control skin of volunteers who were smok- ers. We hypothesize very large interpersonal variation with MMP-1 induction compared with TIMP-1 which was detected in all the control sites. This suggests a lack of relationship between MMP-1 and TIMP-1 mRNA ex- pression. The large donor variability for MMP-1 in all the studies demonstrates that it is important to analyze gene expression individually. INTRODUCTION Long-term solar exposure causes a specific type of prema- ture skin aging, known as photoaging. This is characterized by the appearance of wrinkles, dry, inelastic leathery skin and irregular pigmentation (1,2). Histologically, photodam- aged skin shows marked quantitative and qualitative alter- ¶Posted on the website on 28 February 2001. *To whom correspondence should be addressed at: Beiersdorf AG, Paul Gerson Unna Skin Research Center, 4212 Molecular Biolo- gy, Unnastrasse 48, 20245 Hamburg, Germany. Fax: 49-40-4909- 5814; e-mail: lahmanc@hamburg.beiersdorf.com ations in the dermal connective tissue (3,4). These include elastosis, an accumulation of abnormal elastotic material (5) and proteoglycans (6). Furthermore, the degradation and dis- organization of collagen fibrils, which are responsible for the strength and resilience of the skin (7), have been observed. Biochemical analysis has shown reduced levels of types-I and -III procollagens (8) and crosslinks within the collagen molecules (9). There is also evidence for an increased ratio of type-III to type-I collagen (10) and an enhanced level of elastin gene expression (11) in UV-irradiated skin. Matrix metalloproteinases (MMP)² belong to a family of zinc-dependent endopeptidases capable of degrading struc- tural proteins such as collagens and elastin in connective tissue (12,13). The controlled activity of MMP plays an im- portant role in tissue remodeling during developmental pro- cesses, tissue repair and angiogenesis. MMP have been im- plicated in several diseases that are accompanied by exces- sive breakdown of connective tissue as, e.g. in tumor cell invasion, metastasis and rheumatoid arthritis (14). Recently, it has been hypothesized that MMP are involved in photo- aging (15–17). The proteolytic activity of MMP is regulated by endogenous tissue inhibitors of metalloproteinases (TIMP) which inhibit the active MMP by forming tight non- covalent 1:1 complexes (18). The development of sensitive TaqMan  reverse transcrip- tion (RT) polymerase chain reaction (PCR) systems (19,20) makes it possible to detect and analyze very small amounts of messenger RNA (mRNA) from individual human skin biopsies. In the time-course and dose–response studies re- ported here we have exploited this important advantage to quantify the solar simulating radiation (SSR) induction of mRNA expression of MMP-1 (21), TIMP-1 (22) and the housekeeping gene glyceraldehyde-3-phosphate-dehydroge- nase (GAPDH) (23) in human skin in vivo. GAPDH has been used as a housekeeping gene in several ultraviolet ra- ² Abbreviations: FAM, 6-carboxyfluorescein; GAPDH, glyceralde- hyde-3-phosphate-dehydrogenase; MED, minimal erythema dose; MMP, matrix metalloproteinase; mRNA, messenger RNA; PCR, polymerase chain reaction; RT, reverse transcription; SD, standard deviation; SSR, solar simulated radiation; TAMRA, 6-carboxy- N,N,N',N'-tetramethylrhodamine; TIMP, tissue inhibitor of metal- loproteinases; UNG, uracil N-glycosylase; UVR, ultraviolet radi- ation.