Technical characteristics of the original method, the 6-well plate and the 12-well plate modifications.
Abstract
Tissue engineering of the skin is used for various applications. However, to develop treatments for skin pathologies such as psoriasis, robust pathological skin models are needed. The purpose of the work presented in this chapter was to optimize the production of more reproducible psoriatic skin substitutes by modifying the original self-assembly method. Substitutes were produced according to the self-assembly method partially modified. The culture flasks of 25 cm2 were replaced by 6-well and 12-well plates. Fibroblasts were cultured in 6-well and 12-well plates with ascorbic acid until they form manipulable sheets, which were superimposed and incubated for 7 days to form a dermal layer. Afterwards, keratinocytes were seeded on the dermal layer forming an epidermal layer. Then, the substitutes were raised to the air-liquid interface and cultured 21 days before being analyzed. Analyses demonstrated that psoriatic substitutes have a significantly thicker epidermis than healthy substitutes and the persistence of nuclear structures in corneocytes, with original and both modified methods. Immunofluorescence markers such as filaggrin, loricrin, and keratin 14 have confirmed these results. However, some differences were observed in substitutes produced with 12-well plates. Modifications made to the original method for the production of psoriatic substitutes are effective and lead to highly reproducible substitutes more suitable for pharmacological testing.
Keywords
- tissue engineering
- cell culture
- skin substitutes
- psoriasis
- self-assembly approach
- in vitro
1. Introduction
1.1. Skin
The integumentary system is the largest and heaviest organ of the body [1, 2]. This organ is divided into three distinct layers: the epidermis (superficial layer), the dermis (intermediate layer), and the hypodermis (deepest layer). Its main function is to protect the body from external aggressions, such as chemical, mechanical, thermal, microbial, and UV rays [3, 4]. It is therefore a physical, biological, and immunological barrier. The epidermis, the outer layer of the skin, predominantly ensures this barrier function by a constant renewal of keratinocytes, the epidermal cells. Keratinocytes differentiated into five layers: from the
1.2. Psoriasis
Psoriasis is an erythematous-squamous dermatosis touching both men and women. This chronic skin pathology affects 2–3% of the world’s population [6, 7], which correspond to approximately 125 M people [8]. This pathology is characterized by a hyperproliferation and an abnormal differentiation of keratinocytes resulting in reddish and whitish plaques [5]. At a cellular level, histopathological characteristics consist of acanthosis, parakeratosis, hyperkeratosis, agranulose, and papillomatosis [9, 10]. The disease’s etiology is still unknown. However, environmental and immune factors, as well as genetic predispositions, would act together to trigger psoriasis [10, 11]. This disease seriously affects the quality of life of patients due to the appearance of their skin and the side effects of drugs. Existing treatments cause many severe side effects such as nephrotoxicity, hepatotoxicity, immunosuppression, teratogenicity, and no curable treatments have been found [12, 13, 14]. Moreover, several comorbidities may be related to psoriasis, such as major cardiac events, type 2 diabetes, and psoriatic arthritis [6].
1.3. In vivo and in vitro psoriatic skin models
The skin is a complex organ. Thus, the production of representative and reproducible skin models is a constant challenge. The use of
1.3.1. In vivo models
Many approaches are used to obtain animal models as representative as possible to the human pathology. Spontaneous mutations, like the homozygous asebia, xenotransplantation, like the severe combined immunodeficient mice (SCID) and the athymic nude mouse, and genetic models, such as the CD18 hypomorphic mice model, the K14/TGF-α, and the involucrin/INF-γ, have been used over the years to study psoriasis but all of them displayed some limitations [21, 22, 23]. Animal models are mostly used to study specific aspects of the pathology. The development of a representative animal model can be expensive.
1.3.2. In vitro models
There are two types of models: monolayer models (dermal or epidermal) and bilayer substitutes. Monolayer models use only one cell type, keratinocytes or fibroblasts, and will be used to study a specific characteristic or to understand the role of a certain cell type in pathologies such as psoriasis. However, these models exclude interactions between different cell types. Bilayer models displayed two layers of skin: dermis and epidermis, which allow the study of skin complexity more representatively. The challenge of skin engineering is to reproduce the complexity and the functionalities of a pathological skin. There are different
Our team has developed a psoriatic skin model based on a self-assembly method, which is free of exogenous material [31]. This model has been characterized towards its permeability, lipid organization and response to antipsoriatic drugs [32, 33]. This basic model has also been improved by the addition of other cell types such as endothelial cells in order to reproduce the angiogenesis observed
2. Modified self-assembly methodology
As mentioned previously, our team has developed a model of
Self-assembly method | Culture surface area (cm2) | Final size of substitute (usable) (cm2) | Volume of medium by fibroblast sheet (ml) | Anchoring papers |
---|---|---|---|---|
Original | 25 | 3.87 | 5 | Day 42 |
6-well plates | 9.6 | 3.87 | 2 | Day 0 |
12-well plates | 3.8 | 1.27 | 2 | Day 0 |
Table 1.

Figure 1.
Schematic representation of the self-assembly method. (A) Original self-assembly method: fibroblasts were cultured 28 days in 25 cm2 flasks for the production of fibroblast sheets. At day 28, flasks were opened with a soldering iron, and two sheets were superimposed to form a dermal equivalent. After one week, a metal ring was deposited on substitutes, and keratinocytes were seeded into the ring. Then, substitutes were cultured one more week in submerged conditions. At day 42, substitutes were placed on an anchoring paper and were raised to the air-liquid interface for three weeks. (B) Modified self-assembly method: fibroblasts were seeded in 6-well or 12-well plates in which anchoring paper have been previously placed. After 28 days of culture, two fibroblast sheets were easily superimposed and solidified with Ligaclip®. Dermal equivalents were cultured seven days before keratinocytes seeding. At day 42, substitutes were raised to the air-liquid interface and cultured for three weeks.
2.1. Results
2.1.1. Macroscopic results
Healthy skin substitutes reconstructed using either the original or modified methods (Figure 2A–C) showed a uniform and opaque epidermis recovering all the seeding area within the anchoring paper (white contours). For substitutes produced with psoriatic cells, those reconstructed according to the original method and the 6-well plate modifications (Figure 2D–E) showed an irregular and contracted epidermis. Psoriatic skin substitutes produced using the 12-well plate modification (Figure 2F) demonstrated a more uniform epidermis compared to other methods.

Figure 2.
Macroscopic analyses. Macroscopic appearance of healthy substitutes (A–C) and psoriatic substitutes (D–F). Substitutes were produced according to the original method (A and D), 6-well plate modification (B and E), and 12-well plate modification (C and F). Three substitutes of each condition were analyzed, and the results were confirmed with three independent experiments. Cells from two different healthy patients and three different psoriatic patients were used (scale bar = 1 cm).
2.1.2. Histology
Healthy skin substitutes reconstructed according to the original method, and the 6-well plate modification (Figure 3A and B) demonstrated a well-differentiated epidermis and similar characteristics. A thickening of the living epidermis was observed in substitutes produced with psoriatic cells using the original method, as well as in those reconstructed according to the modified protocols (Figure 3D–F). A less differentiated epidermis was observed in psoriatic substitutes produced according to the original method and the 6-well plate modification (Figure 3D–E), compared with the substitutes produced according to the 12-well plate modification (Figure 3F). The substitutes reconstructed according to the 12-well plate modification (Figure 3C and F) demonstrated a greater cell differentiation which results in a thickening of the

Figure 3.
Histological analyses. Masson’s trichrome staining of healthy substitutes (A–C), psoriatic substitutes (D–F) and substitutes produced with the original method (A and D), 6-well plate modification (B and E), and 12-well plate modification (C and F). Three substitutes of each condition were analyzed, and the results were confirmed with three independent experiments. Cells from two different healthy patients and three different psoriatic patients were used (scale bar = 100 μm).
2.1.3. Epidermal thickness
Thickness of skin substitutes’ living epidermis was measured with the AxioVision software. No significant differences were observed between the skin substitutes reconstructed with healthy cells according to the original method or the two new modifications (65.6 ± 13.9 vs. 69.0 ± 6.8 vs. 78.39 ± 18.69 μm; Figure 4A). Measurements of psoriatic substitutes thickness reconstructed according to the original method, and the 6-well plate modification did not show any significant differences between these two methods (93.50 ± 18.9 μm vs. 106.7 ± 23.7 μm; Figure 4B), while psoriatic substitutes produced with the 12-well plate modification demonstrated a significant difference compared with the original method (130.8 ± 18.8 vs. 93.50 ± 18.9 μm).

Figure 4.
Thickness of the living part of epidermis. (A) Measurements of healthy substitutes produced with the original method, the 6-well plate modification, and the 12-well plate modification. (B) Measurements of psoriatic substitutes produced according to the original method, the 6-well plate modification, and the 12-well plate modification. The statistical significance was determined using ANOVA test (
2.1.4. Immunofluorescence analyses
Immunofluorescent markers were used to compare protein expression. Late differentiation markers, such as filaggrin and loricrin, were observed in order to compare the different skin substitute models. The

Figure 5.
Filaggrin and loricrin staining. Expression of filaggrin (red) in healthy substitutes (A–C), psoriatic substitutes (D–F) and substitutes produced according to the original method (A and D), the 6-well plate modification (B and E), and the 12-well plate modification (C and F). Expression of loricrin (green) in healthy substitutes (G–I), psoriatic substitutes (J–L) and substitutes produced according to the original method (G and J), the 6-well plate modification (H and K), and the 12-well plate modification (I and L). The nuclei were stained with Hoechst (blue). Three substitutes of each condition were analyzed, and the results were confirmed with three independent experiments. Cells from two different healthy patients and three different psoriatic patients were used (scale bar = 100 μm).
Other markers, such as keratin 14, keratin 1, and laminin, were also observed. Keratin 14 (K14) is expressed in the basal layer of the epidermis and is gradually reduced until keratins 1 (K1) and 10 (K10) are synthesized. In healthy substitutes produced according to the original method and the 6-well plate modification, keratin 14 was normally expressed (Figure 6A and B), whereas in healthy substitutes produced according to the 12-well plate modification, this keratin was still present in the

Figure 6.
Keratin 14 and keratin 1 staining. Expression of keratin 14 (green) in healthy substitutes (A–C), psoriatic substitutes (D–F) and substitutes produced with the original method (A and D), the 6-well plate modification (B and E), and the 12-well plate modification (C and F). Expression of keratin 1 (green) in healthy substitutes (G–I), psoriatic substitutes (J–L) and substitutes produced according to the original method (G and J), the 6-well plate modification (H and K), and the 12-well plate modification (I and L). The nuclei were stained with Hoechst (blue). Three substitutes of each condition were analyzed, and the results were confirmed with three independent experiments. Cells from two different healthy patients and three different psoriatic patients were used (scale bar = 100 μm).

Figure 7.
Laminin staining. Expression of laminin (green) in healthy substitutes (A–C), psoriatic substitutes (D–F) and substitutes produced according to the original method (A and D), the 6-well plate modification (B and E), and the 12-well plate modification (C and F). The nuclei were stained with Hoechst (blue). Three substitutes of each condition were analyzed, and the results were confirmed with three independent experiments. Cells from two different healthy patients and three different psoriatic patients were used (scale bar = 100 μm).
2.2. Discussion
With psoriasis etiology still unknown, several
Previous studies of our group have shown that this psoriatic skin model demonstrated phenotypic characteristics of
Differentiation of psoriatic skin is characterized by the altered expression of several epidermal proteins [43]. In a normal differentiation process (approximately 28 days), the basal layer transit amplifying cells differentiate and migrate into upper epidermal layers and synthesize important proteins involved in the differentiation and the skin barrier function such as filaggrin, loricrin, and keratins [36, 37, 44]. Filaggrin is normally synthesized from a precursor, profilaggrin, found in the granular layer. This protein is a key role in the formation of the cornified envelope [37]. In skin disease, such as psoriasis, expression of filaggrin is decreased, such that it is sometimes even absent due to an altered differentiation process and a reduction or an absence of the granular layer (agranulose) [38, 45, 46]. Loricrin, a major component of the cornified envelope, is stored in granules of the
Keratins are intermediate filaments highly involved in epidermal structure and different types are expressed in the varying differentiation stages [48]. K5 and K14 are normally found in the basal layer of the epidermis, and they are progressively replaced by K1 and K10 in suprabasal layers [49]. However,
Some studies suggested that alterations in the basal membrane of psoriatic skin play an important role in the abnormal proliferation and differentiation of psoriatic keratinocytes [53, 54, 55]. Indeed, the expression of proteins such as laminin, which is one of the main proteins that forms the basal membrane, is decreased and disrupted in psoriatic skin unlike in healthy skin. In this last, laminin forms a linear and continuous structure [54]. Laminin expression in our skin substitutes produced with healthy cells regardless of the method (original method and two new modifications) was intense, continuous and more restricted to the basal lamina, demonstrating a good structure of the basal membrane. For psoriatic skin substitutes (original method and 6-well plate modification), the expression of laminin was more distributed through the dermis compared to healthy substitutes, showing disorganization in the basal membrane. For the psoriatic skin substitutes reconstructed according to the 12-well plate modification, laminin staining was more compact and similar to healthy substitute expression. Interestingly, this observation is showing that the basal membrane was more organized, thus less similar to the psoriatic phenotype. These results showed that the 6-well plate modification is more representative of the
2.3. Conclusion
These new modifications to protocol provide several advantages in the production of skin substitutes. Indeed, the 6-well and 12-well plate modifications require almost 3 times fewer fibroblasts and culture medium than the original method for the production of fibroblast sheets, which favorably reduce production costs. In addition, the use of plates and anchoring papers at the beginning of the production greatly facilitate the handling and the superposition of fibroblast sheets increasing the quality of the dermal equivalent. The anchoring papers allow the production of more reproducible and uniform size substitutes within the same experiment and between the different studies, which are essential for pharmaceutical studies. In conclusion, the modifications made to the original self-assembly method for the production of psoriatic substitutes are effective and demonstrate a comparable phenotype. However, the 6-well method is the one that leads to reconstructed substitutes with characteristics more similar to those seen
Acknowledgments
The authors acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institutes of Health Research (CIHR) through their joint Collaborative Health Research Projects (CHRP) program. The “Fonds d’Enseignement et de Recherche (FER)” of the Faculty of Pharmacy, Université Laval, Québec, QC, Canada (Isabelle Gendreau scholarship), the “Fonds de Recherche du Québec—Santé (FRQS)” (Alexe Grenier scholarship) and the support of the “Réseau ThéCell du Québec” are also acknowledged. Moreover, Dr. Pouliot is a FRQS career award scholar.
Conflict of interest
The authors state no conflict of interest. The authors have no relationship with a for-profit or a not-for-profit organization to disclose. There is no financial conflict with the subject or the materials discussed in the manuscript apart from those disclosed.
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