Studies on differentiation‐dependent expression and activity of distinct transglutaminases by specific substrate peptides using three‐dimensional reconstituted epidermis

Analysis on promotive effect of rocking culture on keratinocyte differentiation in 3-dimensional reconstitution human epidermis

A 3-dimensional culture system of keratinocytes achieves cornification as a terminal differentiation that can mimic the formation of stratified epidermis. At the onset of keratinocyte differentiation, air-exposure treatment is essential for promotion. We have previously reported that the stimulation of differentiation is accompanied by downregulation of the transcriptional activity of the hypoxia-inducible factor (HIF) and also found that rocking treatment of cultured keratinocytes in the submerged condition restored their differentiation. A comparative study of cultured keratinocytes with and without rocking was then carried out to investigate the characteristics of the recovered differentiation by morphological and biochemical analyses. In addition, transcriptome analysis revealed the expected similar pattern between air-exposed and rocking cultures, including HIF-regulating transcripts. Furthermore, the promotive effect of rocking treatment was impaired under hypoxic culture conditions (1% O2). We showed that the restored promotion of differentiation by rocking culture is mainly due to the abrogation of transcriptional events by hypoxia.

Involvement of hypoxia-inducible factor activity in inevitable air-exposure treatment upon differentiation in a three-dimensional keratinocyte culture

Formation of the human skin epidermis can be reproduced by a three-dimensional (3D) keratinocyte culture system, in which air-exposure is inevitable upon initiation of differentiation. In the continuous submerged culture without air-exposure, even with a differentiation-compatible medium, several keratinocyte-specific proteins were not induced resulting in the formation of aberrant epidermal layers. To clarify the mechanism by which air-exposure promotes keratinocyte differentiation, we performed a comparative analysis on biological properties between submerged and air-liquid interphase culture systems. By transcriptomic analysis, hypoxia-inducible factor (HIF)-related genes appeared to significantly change in these cultured cells. In submerged culture, the transcriptional activity of HIF on its canonical response element was enhanced, while air-exposure treatment drastically reduced the transcriptional activity despite the high HIF protein level. Regulating HIF activity through reagents and genetic manipulation revealed that the reduced but retained HIF-transcriptional activity was essentially involved in differentiation. Furthermore, we showed, for the first time, that artificial supplementation of oxygen in the submerged culture system could restore keratinocyte differentiation as observed in the air-exposed culture. Thus, we mechanistically evaluated how HIF regulates the air-exposure-dependent differentiation of keratinocytes in a 3D culture system.

Investigation of mouse amniotic fluid for stimulating ability of keratinocyte differentiation depending on the fetal stage

During fetal development, the barrier function of the fetal skin is developed under specific conditions for epidermis formation. In keratinocyte differentiation, the well-orchestrated production and modification of various structural proteins are induced. We assessed the epidermal barrier function in different fetal stages by evaluating the enzymatic activity of cross-linking proteins, transglutaminases, and the permeation of fluorescence dye in the stained epidermal sections. During days 15.5-17.5 in gestation, the enzymatic activities in the epidermis appeared to increase significantly; meanwhile, dye permeation was substantially decreased, suggesting the formation of a protective barrier. For the fetal epidermis formation in the earlier stage, unclarified stimulating factors in the amniotic fluid (AF) are possible to promote barrier function by stimulating keratinocyte differentiation. Thus, we performed proteomic spectrometric (MS) analysis on the components in the AF at different fetal stages. Also, we investigated the promotive ability of the components using a cultured keratinocyte differentiation system. According to the MS analysis, the AF components appeared to exhibit stage-specific variations, where possible unique functions have been identified. We also found that adding the AF from each stage to the medium for cultured keratinocytes specifically enhanced the levels of the differentiation markers. These results provide information on the possible role of AF that contains regulatory factors on keratinocyte differentiation.

Human skin equivalents: Impaired barrier function in relation to the lipid and protein properties of the stratum corneum

To advance drug development representative reliable skin models are indispensable. Animal skin as test model for human skin delivery is restricted as their properties greatly differ from human skin. In vitro 3D-human skin equivalents (HSEs) are valuable tools as they recapitulate important aspects of the human skin. However, HSEs still lack the full barrier functionality as observed in native human skin, resulting in suboptimal screening outcome. In this review we provide an overview of established in-house and commercially available HSEs and discuss in more detail to what extent their skin barrier biology is mimicked in vitro focusing on the lipid properties and cornified envelope. Further, we will illustrate how underlying factors, such as culture medium improvements and environmental factors affect the barrier lipids. Lastly, potential improvements in skin barrier function will be proposed aiming at a new generation of HSEs that may replace animal skin delivery studies fully.

Identification and characterization of substrates crosslinked by transglutaminases in liver and kidney fibrosis

The transglutaminase (TGase) family consists of eight isozymes that catalyze Ca²⁺-dependent crosslink formation between glutamine and lysine residues of proteins. In the pathogenesis of various chronic diseases, among the TGase isozymes, TG2 in particular is upregulated and contributes to a critical role in fibrosis development and progression via the stabilization of extracellular matrix proteins and activation of TGF-β. Although TG2 has been considered a key enzyme in fibrosis, the causative role of TG2 and involvement of other isozymes remain unclear. We have recently developed a comprehensive analysis method targeting the isozyme-specific substrates of TGase in liver and kidney fibrosis. In this review article, we introduce a previously developed method for determining the activity and tissue distribution of TGase and for the detecting and identification of TGase substrates in an isozyme-specific manner. Using our comprehensive analysis method, we newly characterized the overlapping profile data regarding potential substrates of TG1 and TG2 that have been identified in liver and kidney fibrosis to date. Our results obtained by comparing the specificity and similarity of potential TGase substrates between different tissue fibrosis models provide a deeper understanding regarding the specific and common pathways in disease pathogenesis and progression.