CHANGES IN COLLAGEN MESSENGER-RNA EXPRESSION IN THE SKIN OF HAIRLESS MICE DURING AGING OR INDUCED BY ULTRAVIOLET-B RADIATION

We demonstrated that the ratio of type III to type I collagen increase s during chronological aging. This increase became even more significa nt in hairless mice receiving chronic ultra-violet B irradiation. We i nvestigated the regulation of these processes at the transcriptional l evel by extraction and quantification of mRNAs coding for fibrillar co llagens. Total RNA from non-irradiated or irradiated mice was analysed by RNA-DNA hybridization on slot-blots. We observed changes in the tr anscription rate of these specific genes during aging and induced ''ph otoaging''. During chronological aging, we found a decrease of mRNA co ding for type I collagen without any alteration in the amount of mRNA coding for type III collagen. In ultraviolet B-treated mouse skin, we found a significant increase of mRNA coding for type III collagen with no change in the amount of mRNA coding for type I collagen. These dat a are in agreement with the results obtained at the translational leve l. Comparison between chronological aging and induced ''photoaging'' a t the transcriptional level shows evidence for a separate regulation o f the expression of the genes coding for these two procollagens and sh ows also differences in the modifications of collagen gene expression between chronological aging and photoaging.