DAMAGE to skin collagen and elastin (extracellular matrix) is the hall
mark of long-term exposure to solar ultraviolet irradiation(1-3), and
is believed to be responsible for the wrinkled appearance of sun-expos
ed skin(4,5). We report here that matrix-degrading metalloproteinase m
essenger RNAs, proteins and activities are induced in human skin in vi
vo within hours of exposure to ultraviolet-B irradiation (UVB). Induct
ion of metalloproteinase proteins and activities occurred at UVB doses
well below those that cause skin reddening. Within minutes, low-dose
UVB upregulated the transcription factors AP-1 and NF-kappa B, which a
re known to be stimulators of metalloproteinase genes(6,7). All-trans
retinoic acid, which transrepresses AP-1 (ref. 8), applied before irra
diation with UVB, substantially reduced AP-1 and metalloproteinase ind
uction, We propose that elevated metalloproteinases, resulting from ac
tivation of AP-1 and NF-kappa B by low dose solar irradiation, degrade
collagen and elastin in skin, Such damage, if imperfectly repaired wo
uld result in solar scars, which through accumulation from a lifetime
of repeated low-dose sunlight exposure could cause premature skin agei
ng (photoageing).