UV irradiation induces MMP-1, MMP-3, and MMP-9 in human skin in vivo. Sun-protected buttock skin of healthy adult human volunteers was exposed to twice the minimum erythema dose of solar-simulated UV irradiation (SPEC 450W xenon arc solar simulator). Full thickness (4mm) biopsies were obtained 8 and 24 hours post irradiation. Total RNA was extracted and MMP-1, MMP-3, and MMP-9 mRNA levels were determined by real-time RT-PCR, as described in figure 1 legend. Results are means±SEM of MMPs mRNA normalized to 36B4 (internal control) mRNA. N=8, p<0.05.