Full-thickness tissue engineered skin constructed with autogenic bone marrow mesenchymal stem cells

An Overview of Recent Developments in the Management of Burn Injuries

According to the World Health Organization (WHO), around 11 million people suffer from burns every year, and 180,000 die from them. A burn is a condition in which heat, chemical substances, an electrical current or other factors cause tissue damage. Burns mainly affect the skin, but can also affect deeper tissues such as bones or muscles. When burned, the skin loses its main functions, such as protection from the external environment, pathogens, evaporation and heat loss. Depending on the stage of the burn, the patient's condition and the cause of the burn, we need to choose the most appropriate treatment. Personalization and multidisciplinary collaboration are key to the successful management of burn patients. In this comprehensive review, we have collected and discussed the available treatment options, focusing on recent advances in topical treatments, wound cleansing, dressings, skin grafting, nutrition, pain and scar tissue management.

IGF-1-Expressing Placenta-Derived Mesenchymal Stem Cells Promote Scalding Wound Healing

BACKGROUND

Stem cell-based regenerative therapy is a novel approach to severe damaged skin. Perinatal tissues such as placenta are considered as promising alternatives. The present study aimed to investigate the effect of insulin-like growth factor-1 (IGF-1)-expressing placenta-derived mesenchymal stem cells (hPMSCs) on healing of burn wounds.

MATERIALS AND METHODS

hPMSCs were isolated from human placenta, and IGF-1 was transducted into hPMSCs via lentivirus. Flow cytometry and MTT assay were performed to assess cell apoptosis and viability, respectively. Immunostaining of CK19 and ki67 was for evaluating epithelial differentiation ability and cell proliferation. For in vivo studies, we established a mouse model of scalding and performed local administration of IGF-1-expressing hPMSCs via subcutaneous injection. Wound histology was analyzed with H&E staining. The expression of fibrogenic cytokines was detected by western blot. The production of pro-inflammatory factors was measured by ELISA.

RESULTS

Overexpression of IGF-1 promoted cell proliferation and epithelial differentiation of hPMSCs in vitro and in vivo. Mice with burn injury displayed increased wound contraction and healing rates following treatment with IGF-1-expressing hPMSCs. There was less inflammatory infiltration and reduced collagen disposition in the presence of IGF-1 at the wound site. Administration of IGF-1-expressing hPMSCs suppressed inflammation by decreasing the levels of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, and interleukin-6. Besides, IGF-1 increased VEGF expression, and decreased TGF-β1, collagen I and collagen III expressions in vivo.

CONCLUSIONS

IGF-1-expressing PMSCs promotes cell proliferation and epithelial differentiation, inhibits inflammation and collagen deposition, and thus contributes to wound healing.

Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries

Wound healing is an important function of skin; however, after significant skin injury (burns) or in certain dermatological pathologies (chronic wounds), this important process can be deregulated or lost, resulting in severe complications. To avoid these, studies have focused on developing tissue-engineered skin substitutes (TESSs), which attempt to replace and regenerate the damaged skin. Autologous cultured epithelial substitutes (CESs) constituted of keratinocytes, allogeneic cultured dermal substitutes (CDSs) composed of biomaterials and fibroblasts and autologous composite skin substitutes (CSSs) comprised of biomaterials, keratinocytes and fibroblasts, have been the most studied clinical TESSs, reporting positive results for different pathological conditions. However, researchers' purpose is to develop TESSs that resemble in a better way the human skin and its wound healing process. For this reason, they have also evaluated at preclinical level the incorporation of other human cell types such as melanocytes, Merkel and Langerhans cells, skin stem cells (SSCs), induced pluripotent stem cells (iPSCs) or mesenchymal stem cells (MSCs). Among these, MSCs have been also reported in clinical studies with hopeful results. Future perspectives in the field of human-TESSs are focused on improving in vivo animal models, incorporating immune cells, designing specific niches inside the biomaterials to increase stem cell potential and developing three-dimensional bioprinting strategies, with the final purpose of increasing patient's health care. In this review we summarize the use of different human cell populations for preclinical and clinical TESSs under research, remarking their strengths and limitations and discuss the future perspectives, which could be useful for wound healing purposes.

Current Advanced Therapies Based on Human Mesenchymal Stem Cells for Skin Diseases

Skin disease may be related with immunological disorders, external aggressions, or genetic conditions. Injuries or cutaneous diseases such as wounds, burns, psoriasis, and scleroderma among others are common pathologies in dermatology, and in some cases, conventional treatments are ineffective. In recent years, advanced therapies using human mesenchymal stem cells (hMSCs) from different sources has emerged as a promising strategy for the treatment of many pathologies. Due to their properties; regenerative, immunomodulatory and differentiation capacities, they could be applied for the treatment of cutaneous diseases. In this review, a total of thirteen types of hMSCs used as advanced therapy have been analyzed, considering the last 5 years (2015-2020). The most investigated types were those isolated from umbilical cord blood (hUCB-MSCs), adipose tissue (hAT-MSCs) and bone marrow (hBM-MSCs). The most studied diseases were wounds and ulcers, burns and psoriasis. At preclinical level, in vivo studies with mice and rats were the main animal models used, and a wide range of types of hMSCs were used. Clinical studies analyzed revealed that cell therapy by intravenous administration was the advanced therapy preferred except in the case of wounds and burns where tissue engineering was also reported. Although in most of the clinical trials reviewed results have not been posted yet, safety was high and only local slight adverse events (mild nausea or abdominal pain) were reported. In terms of effectiveness, it was difficult to compare the results due to the different doses administered and variables measured, but in general, percentage of wound's size reduction was higher than 80% in wounds, Psoriasis Area and Severity Index and Severity Scoring for Atopic Dermatitis were significantly reduced, for scleroderma, parameters such as Modified Rodnan skin score (MRSC) or European Scleroderma Study Group activity index reported an improvement of the disease and for hypertrophic scars, Vancouver Scar Scale (VSS) score was decreased after applying these therapies. On balance, hMSCs used for the treatment of cutaneous diseases is a promising strategy, however, the different experimental designs and endpoints stablished in each study, makes necessary more research to find the best way to treat each patient and disease.

Novel pre-vascularized tissue-engineered dermis based on stem cell sheet technique used for dermis-defect healing

Insufficient donor dermis and the shortage of three-dimensional vascular networks are the main limitations in the tissue-engineered dermis (TED). To solve these problems, we initially constructed pre-vascularized bone marrow mesenchymal stem cell sheet (PBMCS) and pre-vascularized fibroblasts cell sheet (PFCS) by cell sheet technology, and then superimposed or folded them together to construct a pre-vascularized TED (PTED), aiming to mimic the real dermis structure. The constructed PTED was implanted in nude mice dorsal dermis-defect wound and the wound-healing effect was quantified at Days 1, 7 and 14 via the methods of histochemistry and immunohistochemistry. The results showed that PTED could rapidly promote the wound closure, especially at Day 14, and the wound-healing rate of three-layer PTED could reach 97.2% (P < 0.01), which was faster than the blank control group (89.1%), PBMCS (92.4%), PFCS (93.8%) and six-layer PTED (92.3%). In addition, the vessel density in the PTED group was higher than the other groups on the 14th day. Taken together, it is proved that the PTED, especially three-layer PTED, is more conducive to the full-thickness dermis-defect repair and the construction of the three-dimensional vascular networks, indicating its potential application in dermis-defect repair.

Evaluation of different commercial hyaluronic acids as a vehicle for injection of human adipose-derived mesenchymal stem cells

Objective

The main purpose of this study is to evaluate, in vitro, the cytotoxicity of different commercial brands of hyaluronic acids to be used as a vehicle for injection of human adipose-derived mesenchymal stem cells (AD-MSCs).

Methods

AD-MSCs were divided into seven groups: one control group where AD-MSCs were cultivated with phosphate-buffered saline (PBS) and six other groups where AD-MSCs were cultivated with different commercial brands of hyaluronic acid. AD-MSC viability analysis was performed after 4, 24, and 48 h in contact with each treatment, using the trypan staining method on a Countess automated cell counter (Thermo Fisher Scientific).

Results

The results clearly demonstrated a significant difference in cell viability when AD-MSCs were exposed to different hyaluronic acids when compared with the control group.

Conclusion

These data suggest that hyaluronic acid can be used as a vehicle for injection of human AD-MSCs, but caution is needed to choose the best product, aiming at its future therapeutic application.

Skin Diseases Modeling using Combined Tissue Engineering and Microfluidic Technologies

In recent years, both tissue engineering and microfluidics have significantly contributed in engineering of in vitro skin substitutes to test the penetration of chemicals or to replace damaged skins. Organ-on-chip platforms have been recently inspired by the integration of microfluidics and biomaterials in order to develop physiologically relevant disease models. However, the application of organ-on-chip on the development of skin disease models is still limited and needs to be further developed. The impact of tissue engineering, biomaterials and microfluidic platforms on the development of skin grafts and biomimetic in vitro skin models is reviewed. The integration of tissue engineering and microfluidics for the development of biomimetic skin-on-chip platforms is further discussed, not only to improve the performance of present skin models, but also for the development of novel skin disease platforms for drug screening processes.

Adipose Tissue-Derived Mesenchymal Cells Support Skin Reepithelialization through Secretion of KGF-1 and PDGF-BB: Comparison with Dermal Fibroblasts

Epidermal organization and homeostasis are regulated by mesenchymal influences through paracrine actions. Until today, dermal fibroblasts (DFs) are used in the “dermal” layer to support keratinocyte growth in vitro in dermal and skin substitutes. In the present work, we used human adipose tissue-derived mesenchymal cells (ADMCs) as a support of keratinocyte growth in vitro (in monolayer culture and in 3D skin cell culture models) and in vivo (mouse wound healing models) and compared our findings with those obtained using dermal fibroblasts. ADMCs induce reepithelialization during wound healing more efficiently than DFs, by enhancing keratinocyte proliferation through cell cycle progression, and migration. This effect is mediated (at least partially) by a paracrine action of KGF-1 and PDGF-BB, which are more prominently expressed in ADMCs than in DFs. Furthermore, replacement of DFs by ADMCs in the dermal compartment of organotypic skin cultures leads to an artificial epidermis resembling to that of normal skin, concerning the general histology, although with a higher expression of cytokeratins 5 and 19. In Rag1 knockout mice, ADMCs induced a more rapid reepithelialization and a more effective wound healing, compared to dermal fibroblasts. In conclusion, we provide evidence that ADMCs can serve as supportive cells for primary keratinocyte cultures. In addition, because of their abundance and the great cell yield achieved during ADMC isolation, they represent an interesting cell source, with potential aspects for clinical use.

The mouse dorsal skin fold chamber as a means for the analysis of tissue engineered skin

The therapy of extensive and deep burn wounds is still a challenging task for reconstructive plastic surgery. The outcome is generally not satisfactory, neither from the functional nor from the aesthetic aspect. Several available skin substitutes are used but there is need for optimization of new skin substitutes which have to be tested in vitro as well as in vivo. Here, we show that the dorsal skin fold chamber preparation of mice is well suited for the testing of skin substitutes in vivo. Dermal skin constructs consisting of matriderm(®) covered with a collagen type I gel were inserted into full thickness skin wounds in the skin fold chambers. The skin substitutes integrated well into the adjacent skin and got epithelialized from the wound edges within 11 days. The epithelialization by keratinocytes is the prerequisite that also cell-free dermal substitutes might be used in the case of the lack of sufficient areas to gain split thickness skin grafts. Further advantage of the chambers is the lack of wound contraction, which is common but undesired in rodent wound healing. Furthermore, this model allows a sophisticated histological as well as immunohistochemical analysis. As such, we conclude that this model is well suited for the analysis of tissue engineered skin constructs. Besides epithelialization the mode and extend of neovascularization and contraction of artificial grafts may be studied under standardized conditions.

The possible use of stem cells in regenerative medicine: dream or reality?

Stem cells are one of the most fascinating areas in regenerative medicine today. They play a crucial role in the development and regeneration of human life and are defined as cells that continuously reproduce themselves while maintaining the ability to differentiate into various cell types. Stem cells are found at all developmental stages, from embryonic stem cells that differentiate into all cell types found in the human body to adult stem cells that are responsible for tissue regeneration. The general opinion postulates that clinical therapies based on the properties of stem cells may have the potential to change the treatment of degenerative diseases or important traumatic injuries in the "near" future. We here briefly review the literature in particularly for the liver, heart, kidney, cartilage, and bone regeneration.

Therapeutic potential of stem cells in skin repair and regeneration

Stem cells are defined by their capacity of self-renewal and multilineage differentiation, which make them uniquely situated to treat a broad spectrum of human diseases. Based on a series of remarkable studies in several fields of regenerative medicine, their application is not too far from the clinical practice. Full-thickness burns and severe traumas can injure skin and its appendages, which protect animals from water loss, temperature change, radiation, trauma and infection. In adults, the normal outcome of repair of massive full-thickness burns is fibrosis and scarring without any appendages, such as hair follicles, sweat and sebaceous glands. Perfect skin regeneration has been considered impossible due to the limited regenerative capacity of epidermal keratinocytes, which are generally thought to be the key source of the epidermis and skin appendages. Currently, researches on stem cells, such as epidermal stem cells, dermal stem cells, mesenchymal stem cells from bone marrow, and embryonic stem cells, bring promise to functional repair of skin after severe burn injury, namely, complete regeneration of skin and its appendages. In this study, we present an overview of the most recent advances in skin repair and regeneration by using stem cells.