Dermal Fibroblasts from Different Layers of Pig Skin Exhibit Different Profibrotic and Morphological Characteristics

Transdermal Delivery of High Molecular Weight Antibiotics to Deep Tissue Infections via Droplette Micromist Technology Device (DMTD)

Wound infection by multidrug-resistant (MDR) bacteria is a major disease burden. Systemic administration of broad-spectrum antibiotics colistin methanesulfonate (CMS) and vancomycin are the last lines of defense against deep wound infections by MDR bacteria. However, systemic administration of CMS and vancomycin are linked to life-threatening vital organ damage. Currently there are no effective topical application strategies to deliver these high molecular weight antibiotics across the stratum corneum. To overcome this difficulty, we tested if high molecular weight antibiotics delivered by Droplette micromist technology device (DMTD), a transdermal delivery device that generates a micromist capable of packaging large molecules, could attenuate deep skin tissue infections. Using green fluorescent protein-tagged E. coli and live tissue imaging, we show that (1) the extent of attenuation of deep-skin E. coli infection was similar when treated with topical DMTD- or systemic IP (intraperitoneal)-delivered CMS; (2) DMTD-delivered micromist did not spread the infection deeper; (3) topical DMTD delivery and IP delivery resulted in similar levels of vancomycin in the skin after a 2 h washout period; and (4) IP-delivered vancomycin was about 1000-fold higher in kidney and plasma than DMTD-delivered vancomycin indicating systemic toxicity. Thus, topical DMTD delivery of these antibiotics is a safe treatment for the difficult-to-treat deep skin tissue infections by MDR bacteria.

Dermal fibroblast from superficial layers of pig skin exhibits more proliferative capacity than that from deep layers

OBJECTIVE

To further examine the feasibility of using pigs as an animal model for the study of dermal fibroblast heterogeneity and to explore the proliferative capacity of dermal fibroblasts from different layers of pig skin in vitro and in vivo.

MATERIAL AND METHODS

Cultured superficial and deep dermal fibroblasts were subjected to cell growth assay, cell cycle analysis, immunocytochemical staining and western blotting for proliferating cell nuclear antigens. Moreover, skin samples autografted with superficial/deep dermal fibroblasts were subjected to immunohistochemical staining and western blotting for proliferating cell nuclear antigen.

RESULTS

The cell growth assay showed that the growth curve of the superficial dermal fibroblast was progressively higher than that of the deep layer. The cell cycle analysis showed that the (G2+S) percentage of the superficial dermal fibroblasts was significantly higher than that of the deep layer fibroblasts. The immunocytochemical staining and western blotting showed that the expression of proliferating cell nuclear antigen in the cultured superficial dermal fibroblast was significantly higher than that of the deep layer cells. The immunohistochemical staining showed that the positive rate of proliferating cell nuclear antigen in the skin samples autografted with the superficial dermal fibroblast was significantly higher than that of the deep layer.

CONCLUSIONS

This study has demonstrated that similar to human dermal fibroblasts, dermal fibroblasts from different layers of pig skin exhibit distinct proliferative capacity, which increases the feasibility of using pigs as an animal model for future studies on the heterogeneity of dermal fibroblasts.

The pig as a model system for investigating the recruitment and contribution of myofibroblasts in skin healing

In the skin-healing field, porcine models are regarded as a useful analogue for human skin due to their numerous anatomical and physiological similarities. Despite the widespread use of porcine models in skin healing studies, the initial origin, recruitment and transition of fibroblasts to matrix-secreting contractile myofibroblasts are not well defined for this model. In this review, we discuss the merit of the pig as an animal for studying myofibroblast origin, as well as the challenges associated with assessing their contributions to skin healing. Although a variety of wound types (incisional, partial thickness, full thickness, burns) have been investigated in pigs in attempts to mimic diverse injuries in humans, direct comparison of human healing profiles with regards to myofibroblasts shows evident differences. Following injury in porcine models, which often employ juvenile animals, myofibroblasts are described in the developing granulation tissue at 4 days, peaking at Days 7-14, and persisting at 60 days post-wounding, although variations are evident depending on the specific pig breed. In human wounds, the presence of myofibroblasts is variable and does not correlate with the age of the wound or clinical contraction. Our comparison of porcine myofibroblast-mediated healing processes with those in humans suggests that further validation of the pig model is essential. Moreover, we identify several limitations evident in experimental design that need to be better controlled, and standardisation of methodologies would be beneficial for the comparison and interpretation of results. In particular, we discuss anatomical location of the wounds, their size and depth, as well as the healing microenvironment (wet vs. moist vs. dry) in pigs and how this could influence myofibroblast recruitment. In summary, although a widespread model used in the skin healing field, further research is required to validate pigs as a useful analogue for human healing with regards to myofibroblasts.

3D bioprinting for skin tissue engineering: Current status and perspectives

Skin and skin appendages are vulnerable to injury, requiring rapidly reliable regeneration methods. In recent years, 3D bioprinting has shown potential for wound repair and regeneration. 3D bioprinting can be customized for skin shape with cells and other materials distributed precisely, achieving rapid and reliable production of bionic skin substitutes, therefore, meeting clinical and industrial requirements. Additionally, it has excellent performance with high resolution, flexibility, reproducibility, and high throughput, showing great potential for the fabrication of tissue-engineered skin. This review introduces the common techniques of 3D bioprinting and their application in skin tissue engineering, focusing on the latest research progress in skin appendages (hair follicles and sweat glands) and vascularization, and summarizes current challenges and future development of 3D skin printing.

Utilizing Human Dermal Fibroblast Heterogeneity in Autologous Dermal Fibroblast Therapy: An Overcomplicated Strategy or a Promising Approach?

Although human dermal fibroblast heterogeneity has been acknowledged for several decades and a large body of in vitro studies has been performed with zonal dermal fibroblast, current autologous dermal fibroblast therapies do not reflect human dermal fibroblast heterogeneity. To determine if the utilization of human dermal fibroblast heterogeneity in autologous dermal fibroblast therapy is more of a translational perspective that may thus be more likely to make it to the clinic, this article critically reviews the previous studies on dermal fibroblast heterogeneity performed to date. We found that in vitro studies of human dermal fibroblast heterogeneity have run nearly parallel to the in vivo study of autologous dermal fibroblast therapy. Although several human to nude mice xenotransplantation experiments have been performed in different layers of human dermal fibroblast, their clinical significance remains to be considered. We conclude that there is still a great gap between basic experiments and the clinical employment of human dermal fibroblast heterogeneity. To overcome this, it is necessary to conduct clinical trials, which might be restricted by ethical issues. Alternatively, it might be easier to conduct in vivo studies in animal models. Based on our previous study of dermal fibroblast heterogeneity in pigs, we propose the use of pigs as a good animal model for dermal fibroblast heterogeneity. Time will show whether the utilization of human dermal fibroblast heterogeneity in autologous dermal fibroblast therapy is an overcomplicated strategy or a promising approach. Anat Rec, 302:2126-2131, 2019. © 2019 American Association for Anatomy.

Dermis, acellular dermal matrix, and fibroblasts from different layers of pig skin exhibit different profibrotic characteristics: evidence from in vivo study

To explore the profibrotic characteristics of the autografted dermis, acellular dermal matrix, and dermal fibroblasts from superficial/deep layers of pig skin, 93 wounds were established on the dorsa of 7 pigs. 72 wounds autografted with the superficial/deep dermis and acellular dermal matrix served as the superficial/deep dermis and acellular dermal matrix group, respectively, and were sampled at 2, 4, and 8 weeks post-wounding. 21 wounds autografted with/without superficial/deep dermal fibroblasts served as the superficial/deep dermal fibroblast group and the control group, respectively, and were sampled at 2 weeks post-wounding. The hematoxylin and eosin staining showed that the wounded skin thicknesses in the deep dermis group (superficial acellular dermal matrix group) were significantly greater than those in the superficial dermis group (deep acellular dermal matrix group) at each time point, the thickness of the cutting plane in the deep dermal fibroblast group was significantly greater than that in the superficial dermal fibroblast group and the control group. The western blots showed that the α-smooth muscle actin expression in the deep dermis group (superficial acellular dermal matrix group) was significantly greater than that in the superficial dermis group (deep acellular dermal matrix group) at each time point. In summary, the deep dermis and dermal fibroblasts exhibited more profibrotic characteristics than the superficial ones, on the contrary, the deep acellular dermal matrix exhibited less profibrotic characteristics than the superficial one.