BACKGROUND: Ultraviolet light (UVA) has a close relationship with photoaging, and mitochondrial damage is a basis of coil senescence and death.OBJECTIVE: To explore the influence of UVA on the mitochondrial deoxyribonucleic acid of human skin fibroblasts, in addition, to discuss whether transforming growth factor β1 (TGF-β1) could relieve mitochondrial DNA (mtDNA) deletion. DESIGN, TIME AND SETTING: The experiment was performed at Department of Plastic Surgery, the First Affiliated Hospital of Fourth Military Medical University from March 2007 to April 2008.MATERIALS: TGF-β1 was purchased from PerProtech Company; rnitochondrial DNA 4 977 bp primer was synthesized by Shanghai Sangon Biological Engineering Technology & Services Co., Ltd; UVA light was produced by Beijing Optical Instruments Factory; and the ultraviolet radiation meter was provided by Photoelectric Instrument Factory of Beijing Normal University.METHODS: Young adult's fibroblasts were obtained from 12 cases with posthectomy. Then the cells were divided into control,UVA irradiation (30, 60, 90 J/cm~2) groups. The mitochondrial DNA 4 977 bp deletion was detected by semi-quantitative PCR. After that, TGF-β1 with different doses (0.1, 1, 10 βg/L) were used to interfere the cells with UVA 90 J/cm~2 irradiation.MAIN OUTCOME MEASURES: DNA 4 977 bp deletion under different doses cumulative irradiation, as well as the effect of TGF-β1 on mtDNA 4 977bp deletion after irradiates UVA90 J/cm~2 were observed.RESULTS: Mitochondrial DNA 4 977 bp had deleted when irradiated with cumulative dose of 60 J/cm~2 UVA, the deletion was aggravated when the UVA dose arrived at 90 J/cm~2, The absorbance value, PCR electrophoresis and band scanning showed that the deletion of mitochondrial DNA 4 977 bp was reduced after adding TGF-β1 at 2 hours prior to irritation in the large dose (10 μg/L) group. However, the difference between the medium and small dose groups had no obviously significance.CONCLUSION: A certain dose of TGF-β1 (10 μg/L) has protective effect on mtDNA 4 977 bp deletion.