Stiffening of human skin fibroblasts with age.

Changes in mechanical properties are an essential characteristic of the aging process of human skin. Previous studies attribute these changes predominantly to the altered collagen and elastin organization and density of the extracellular matrix. Here, we show that individual dermal fibroblasts also exhibit a significant increase in stiffness during aging in vivo. With the laser-based optical cell stretcher we examined the viscoelastic biomechanics of dermal fibroblasts isolated from 14 human donors aged 27 to 80. Increasing age was clearly accompanied by a stiffening of the investigated cells. We found that fibroblasts from old donors exhibited an increase in rigidity of ∼60% with respect to cells of the youngest donors. A FACS analysis of the content of the cytoskeletal polymers shows a shift from monomeric G-actin to polymerized, filamentous F-actin, but no significant changes in the vimentin and microtubule content. The rheological analysis of fibroblast-populated collagen gels demonstrates that cell stiffening directly results in altered viscoelastic properties of the collagen matrix. These results identify a new mechanism that may contribute to the age-related impairment of elastic properties in human skin. The altered mechanical behavior might influence cell functions involving the cytoskeleton, such as contractility, motility, and proliferation, which are essential for reorganization of the extracellular matrix.

Stiffening of human skin fibroblasts with age.

Changes in mechanical properties are an essential characteristic of the aging process of human skin. Previous studies attribute these changes predominantly to the altered collagen and elastin organization and density of the extracellular matrix. Here, we show that individual dermal fibroblasts also exhibit a significant increase in stiffness during aging in vivo. With the laser-based optical cell stretcher we examined the viscoelastic biomechanics of dermal fibroblasts isolated from 14 human donors aged 27 to 80. Increasing age was clearly accompanied by a stiffening of the investigated cells. We found that fibroblasts from old donors exhibited an increase in rigidity of ∼60% with respect to cells of the youngest donors. A FACS analysis of the content of the cytoskeletal polymers shows a shift from monomeric G-actin to polymerized, filamentous F-actin, but no significant changes in the vimentin and microtubule content. The rheological analysis of fibroblast-populated collagen gels demonstrates that cell stiffening directly results in altered viscoelastic properties of the collagen matrix. These results identify a new mechanism that may contribute to the age-related impairment of elastic properties in human skin. The altered mechanical behavior might influence cell functions involving the cytoskeleton, such as contractility, motility, and proliferation, which are essential for reorganization of the extracellular matrix.

Modification of vimentin: a general mechanism of nonenzymatic glycation in human skin.

In a recent study, we were able to show that the intermediate filament protein vimentin aggregates in human dermal fibroblasts because of modification by the advanced glycation endproduct carboxymethyllysine (CML). In this work, we investigated the formation of intracellular CML in relation to the concentration of glucose in the culture medium. The natural degradation product of glucose, methylglyoxal, was able to induce the aggregation of vimentin. This dicarbonyl leads to the formation of the modifications MG-H1 and carboxyethyllysine (CEL) as a result of the reaction with arginine and lysine residues of proteins. Furthermore, we found that the protein vimentin was modified, not only by CML and CEL, but also by pentosidine and pyrraline. These findings underline the special position of vimentin as a preferential target of the Maillard reaction in human skin.

A novel treatment option for photoaged skin.

BACKGROUND: DNA damage as a result of ultraviolet (UV) exposure plays an important role in the progression of cutaneous aging. Both folic acid and creatine have been linked to the process of DNA protection and repair. AIMS: This study aims to investigate the effects of a commercially available folic acid- and creatine-containing formulation to fight the clinical signs of premature skin aging. PATIENTS/METHODS: Both in vitro and in vivo home-in-use studies using a folic acid- and creatine-containing formulation were performed aiming to elucidate the efficacy in terms of improvement of skin regeneration, protection from UV-induced DNA damage (Comet assay), reduction of wrinkle volume, and skin visco-elasticity. Furthermore, clinical evaluation and photography were carried out to determine the improvement of clinically graded parameters after treatment. RESULTS: Cultured full-thickness epidermal skin models supplemented with folic acid and creatine after epithelial perturbation showed an accelerated skin regeneration compared to untreated control models. Similarly, application of a folic acid- and creatine-containing formulation significantly improved epidermal turnover in vivo as evidenced by smaller corneocytes derived from the treated sites relative to the vehicle-treated sides. In addition, topical in vivo application of this formulation significantly protected from UV-induced DNA lesions, increased skin firmness, and reduced wrinkle volume compared to untreated control areas. Expert grading confirmed a significant decrease of fine and coarse wrinkles in the periocular region as well as overall wrinkles, tactile roughness, and laxity. CONCLUSIONS: Taken together, these results show that the combination of folic acid and creatine significantly accelerates epidermal skin regeneration in vitro and in vivo. Together with the finding of improved biomechanical skin properties, we conclude that the described topical formulation provides an effective treatment option for (photo)-aged skin.

Vimentin is the specific target in skin glycation. Structural prerequisites, functional consequences, and role in skin aging.

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(epsilon)-(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. CML-induced 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.