Skin is continuously exposed to external stimuli including ultraviolet radiation, which is
a major cause of skin photoaging. According to recent discoveries, UVA with a lower
energy but deep-penetrating properties, compared to UVB, is likely to play a major part
in causing skin photoaging. The clinical and histochemical changes of photoaging are
well characterized, but the biochemical mechanism are poorly understood partly due to
the lack of suitable experimental systems.
Un this work, three-dimensional, reconstituted skin culture models were prepared. After
certain period of maturation, the equivalent models were shown to be similar in
structure and biochemical characteristics to normal skin. Mature dermal and skin
equivalent models were exposed to sub-lethal doses of UVA, and the effects of UVA
relevant to dermal photoaging were monitored, including the production of elastin,
collagen, collagenase(MMP-1), and tissue inhibitor of metalloproteinases-1(TIMP-1).
Interestingly, dermal and skin equivalents reacted differently to acute and chronic
exposure to UVA. Elastin production was increased as soon as one week after
commencing UVA irradiation by chronic exposure, although a single exposure failed to
do so. this early response could be an important advantage of equivalent models in
studying elastosis in photoaged skin. Collagenase activity was increased by acute UVA
irradiation, but returned to control levels after repeated exposure. On the other hand,
collagen biosynthesis, which was increased by a single exposure, decreased slightly
during 5 weeks of prolonged UVA exposure. Collagenase has been thought to be
responsible for collagen degeneration in dermal photoaging. However, according to the
results obtained in this study, elevated collagenase activity is not likely to be
responsible for the degeneration of collagen in dermal photoaging, while reduced
production of collagen may be the main reason.
It can be concluded that reconstituted skin culture models can serve as useful
experimental tools for the study of skin photoaging. These culture models are relatively
simple to construct, easy to handle, and are reproducible. Moreover, the changes of
dermal photoaging can be observed within 1∼4 weeks of exposure to ultraviolet light
compared to 4 months to 2 years for human or animal studies.
These models will be useful for biochemical and mechanistic studies in a large number
of fields including dermatology, toxicology, and pharmacology.
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