Until now, the glycation reaction was considered to be a nonspecific reaction between reducing sugars and amino groups of random proteins. We were able to identify the intermediate filament vimentin as the major target for the AGE modification N ⑀ -(carboxymethyl)lysine (CML) in primary human fibroblasts. This glycation of vimentin is neither based on a slow turnover of this protein nor on an extremely high intracellular expression level, but remarkably it is based on structural properties of this protein. Glycation of vimentin was predominantly detected at lysine residues located at the linker regions using nanoLC-ESI-MS/MS. This modification results in a rigorous redistribution of vimentin into a perinuclear aggregate, which is accompanied by the loss of contractile capacity of human skin fibroblasts. CMLinduced rearrangement of vimentin was identified as an aggresome. This is the first evidence that CML-vimentin represents a damaged protein inside the aggresome, linking the glycation reaction directly to aggresome formation. Strikingly, we were able to prove that the accumulation of modified vimentin can be found in skin fibroblasts of elderly donors in vivo, bringing AGE modifications in human tissues such as skin into strong relationship with loss of organ contractile functions.

Extracellular matrix (ECM) organization is a complex process that requires the coordinated efforts of many molecules. For the regulation of collagen fiber diameter, the proteoglycan decorin appears to be of major relevance. To investigate the role of decorin in the process of (photo-)aging in more detail, full-thickness punch biopsies were isolated from human buttock skin. Single exposure with two minimal erythemal doses of solar simulated irradiation caused down-regulation of decorin mRNA in young (n = 5) and old subjects (n = 5) after 24 h. Interestingly, decorin mRNA was elevated with age. To test the hypothesis that a decreased collagen-to-decorin-ratio impairs collagen structure we also investigated collagens I and III gene expression. Both were down-regulated with increasing age and after single UV-irradiation. As determined by laser capture microdissection-quantitative real time-Polymerase chain reaction (n = 11), decorin is mostly present in the reticular dermis while being absent from the papillary dermis. Minor expression was also observed in the epidermis. However, in contrast to full-thickness skin biopsies age-dependent changes in collagens I, III, and decorin expression could not be observed with this methodology indicating technical limitations. Together with our finding that collagens I and III mRNA are similarly expressed in the reticular and papillary dermis and are down-regulated by UV, our studies support the idea of a major role of decorin in ECM organization. Altered expression of decorin mRNA in the different dermal strata and a decrease in the collagen-to-decorin ratio inflicted by both age and ultraviolet irradiation possibly affect collagen bundle diameter and subsequently the mechanical properties of human skin.