Impact of microstructure on cell behavior and tissue mechanics in collagen and dermal decellularized extra-cellular matrices.

Skin models are used for many applications such as research and development or grafting. Unfortunately, most lack a proper microenvironment producing poor mechanical properties and inaccurate extra-cellular matrix composition and organization. In this report we focused on mechanical properties, extra-cellular matrix organization and cell interactions in human skin samples reconstructed with pure collagen or dermal decellularized extra-cellular matrices (S-dECM) and compared them to native human skin. We found that Full-thickness S-dECM samples presented stiffness two times higher than collagen gel and similar to ex vivo human skin, and proved for the first time that keratinocytes also impact dermal mechanical properties. This was correlated with larger fibers in S-dECM matrices compared to collagen samples and with a differential expression of F-actin, vinculin and tenascin C between S-dECM and collagen samples. This is clear proof of the microenvironment's impact on cell behaviors and mechanical properties. STATEMENT OF SIGNIFICANCE: In vitro skin models have been used for a long time for clinical applications or in vitro knowledge and evaluation studies. However, most lack a proper microenvironment producing a poor combination of mechanical properties and appropriate biological outcomes, partly due to inaccurate extra-cellular matrix (ECM) composition and organization. This can lead to limited predictivity and weakness of skin substitutes after grafting. This study shows, for the first time, the importance of a complex and rich microenvironment on cell behaviors, matrix macro- and micro-organization and mechanical properties. The increased composition and organization complexity of dermal skin decellularized extra-cellular matrix populated with differentiated cells produces in vitro skin models closer to native human skin physiology.

Assessing the Role of Carbonyl Adducts, Particularly Malondialdehyde Adducts, in the Development of Dermis Yellowing Occurring during Skin Photoaging.

Solar elastosis is associated with a diffuse yellow hue of the skin. Photoaging is related to lipid peroxidation leading to the formation of carbonyl groups. Protein carbonylation can occur by addition of reactive aldehydes, such as malondialdehyde (MDA), 4-hydroxy-nonenal (4-HNE), and acrolein. All the proteins concerned with this modification, and the biological consequences of adduct formation, are not completely identified. The link between yellowish skin and dermal carbonylated proteins induced by aldehyde adducts was investigated. The study was carried out on ex vivo skin samples from sun-exposed or sun-protected areas and on in vitro dermal equivalent models incubated with 5 mM MDA, 4-HNE, or acrolein. The yellow color and the level of MDA, 4-HNE, and acrolein adducts were evaluated. Yellowish color differences were detected in the dermis of sun-exposed skin compared to sun-protected skin and in in vitro models following addition of MDA, 4-HNE, or acrolein. The yellowing was correlated with the carbonyl adducts increasing in the dermis and in in vitro models incubated with aldehydes. The stronger yellowing seemed to be mediated more by MDA than 4-HNE and acrolein. These observations suggest that dermal carbonylation especially induced by MDA result in the yellow hue of dermis and is involved, in part, in the yellowing observed during skin photoaging.

Author Correction: Reconstructed Skin Models Revealed Unexpected Differences in Epidermal African and Caucasian Skin.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Reconstructed Skin Models Revealed Unexpected Differences in Epidermal African and Caucasian Skin.

Clinical observations of both normal and pathological skin have shown that there is a heterogeneity based on the skin origin type. Beside external factors, intrinsic differences in skin cells could be a central element to determine skin types. This study aimed to understand the in vitro behaviour of epidermal cells of African and Caucasian skin types in the context of 3D reconstructed skin. Full-thickness skin models were constructed with site matched human keratinocytes and papillary fibroblasts to investigate potential skin type related differences. We report that reconstructed skin epidermis exhibited remarkable differences regarding stratification and differentiation according to skin types, as demonstrated by histological appearance, gene expression analysed by DNA microarray and quantitative proteomic analysis. Signalling pathways and processes related to terminal differentiation and lipid/ceramide metabolism were up-regulated in epidermis constructed with keratinocytes from Caucasian skin type when compared to that of keratinocytes from African skin type. Specifically, the expression of proteins involved in the processing of filaggrins was found different between skin models. Overall, we show unexpected differences in epidermal morphogenesis and differentiation between keratinocytes of Caucasian and African skin types in in vitro reconstructed skin containing papillary fibroblasts that could explain the differences in ethnic related skin behaviour.

The reconstructed skin model as a new tool for investigating in vitro dermal fillers: increased fibroblast activity by hyaluronic acid.

BACKGROUND: Clinical studies on dermal fillers have essentially focused upon visible improvement of skin quality and any eventual side effects, whereas very little is known about their detailed biological effects. OBJECTIVES: New skin equivalent models were created to investigate the biological impact of hyaluronic acid (HA) fillers on the dermal compartment in vitro. MATERIALS AND METHODS: Two different reconstructed skin models were developed to incorporate HA within the collagen fibers. In the mixed model, HA was distributed throughout the whole collagen gel whereas the HA was concentrated in the center of collagen gel in the inclusion model. RESULTS: A comparison of the addition of fillers in two models of reconstructed skin has permitted a better understanding of the biological impact of HA fillers. Protein profiling of supernatants from both models suggested a regulation of MMP-1 secretion by fibroblasts as a function of HA volume, distribution in the dermis and degree of cross-linking. Immunostaining of the inclusion model revealed increased production of type I and III procollagens close to the cross-linked HA. Fibroblasts located in this area showed a fusiform morphology as well as an increase in -smooth actin expression. The observed increase in collagen production may thus result in part from tension in fibroblasts surrounding the cross-linked HA. CONCLUSION: The inclusion reconstructed skin model, as compared to the mixed model, presented here, appears to be a useful tool for investigating the properties of various fillers in vitro and closer to the in vivo situation; our results show that HA fillers promote in vitro remodeling of the dermis by fibroblasts.

In vivo and in vitro approaches in understanding the differences between Caucasian and African skin types: specific involvement of the papillary dermis.

BACKGROUND: Most of the identified differences between Caucasian and African skin types have been related to the superficial part of the skin, the epidermis. We investigated possible implications of the dermal compartment in cutaneous differences observed between Caucasians and Africans. METHODS: In vivo and in vitro comparative studies were carried out using normal human skin biopsies and the corresponding in vitro reconstructed skin. Skin equivalents were developed with papillary fibroblasts isolated from the superficial dermis of both Caucasian and African skin types. Expression of major components of the dermal-epidermal junction (DEJ) was examined as a function of ethnicity. RESULTS: Control histological examinations of skin biopsies showed that the African skin type had greater convoluted appearance of the DEJ than the Caucasian skin type. Immunostainings of type IV and VII collagens, laminin 5, and nidogen proteins at the DEJ were lower in African skin compared with Caucasian skin biopsies. CONCLUSIONS: This study brings together new elements on involvement of the papillary dermis in differences between Caucasian and African skin types. As fibroblasts from the superficial dermis cooperate with epidermal keratinocytes in producing protein of the membrane basal zone, present in vivo results suggest that papillary fibroblasts may play a part in the distinct features observed at the DEJ. In preliminary in vitro experiments, differences in several protein expressions contributing to the DEJ framework were found in reconstructed skin models made with papillary fibroblasts from both Caucasian and African skin types. Therefore, in vitro skin equivalents may be useful for better understanding of ethnic skin differences in the future.