A large body of literature is available on wound healing in humans. Nonetheless, a standardized ex vivo wound model without disruption of the dermal compartment has not been put forward with compelling justification. Here, we present a novel wound model based on application of negative pressure and its effects for epidermal regeneration and immune cell behaviour. Importantly, the basement membrane remained intact after blister roof removal and keratinocytes were absent in the wounded area. Upon six days of culture, the wound was covered with one to three-cell thick K14+Ki67+ keratinocyte layers, indicating that proliferation and migration were involved in wound closure. After eight to twelve days, a multi-layered epidermis was formed expressing epidermal differentiation markers (K10, filaggrin, DSG-1, CDSN). Investigations about immune cell-specific manners revealed more T cells in the blister roof epidermis compared to normal epidermis. We identified several cell populations in blister roof epidermis and suction blister fluid that are absent in normal epidermis which correlated with their decrease in the dermis, indicating a dermal efflux upon negative pressure. Together, our model recapitulates the main features of epithelial wound regeneration, and can be applied for testing wound healing therapies and investigating underlying mechanisms.

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Re-epithelialization and immune cell behaviour in an ex vivo human skin model.

The cellular and molecular mechanisms underpinning tissue repair and its failure to heal are still poorly understood, and current therapies are limited. Poor wound healing after trauma, surgery, acute illness, or chronic disease conditions affects millions of people worldwide each year and is the consequence of poorly regulated elements of the healthy tissue repair response, including inflammation, angiogenesis, matrix deposition, and cell recruitment. Failure of one or several of these cellular processes is generally linked to an underlying clinical condition, such as vascular disease, diabetes, or aging, which are all frequently associated with healing pathologies. The search for clinical strategies that might improve the body’s natural repair mechanisms will need to be based on a thorough understanding of the basic biology of repair and regeneration. In this review, we highlight emerging concepts in tissue regeneration and repair, and provide some perspectives on how to translate current knowledge into viable clinical approaches for treating patients with wound-healing pathologies.

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Wound repair and regeneration: Mechanisms, signaling, and translation

Wound healing is one of the most complex processes in the human body. It involves the spatial and temporal synchronization of a variety of cell types with distinct roles in the phases of hemostasis...

Wound Healing: A Cellular Perspective.

Significance: Keratinocytes, a major cellular component of the epidermis, are responsible for restoring the epidermis after injury through a process termed epithelialization. This review will focus on the pivotal role of keratinocytes in epithelialization, including cellular processes and mechanisms of their regulation during re-epithelialization, and their cross talk with other cell types participating in wound healing. Recent Advances: Discoveries in epidermal stem cells, keratinocyte immune function, and the role of the epidermis as an independent neuroendocrine organ will be reviewed. Novel mechanisms of gene expression regulation important for re-epithelialization, including microRNAs and histone modifications, will also be discussed. Critical Issues: Epithelialization is an essential component of wound healing used as a defining parameter of a successful wound closure. A wound cannot be considered healed in the absence of re-epithelialization. The epithelialization process is impaired in all types o...

Epithelialization in Wound Healing: A Comprehensive Review

Background: The integrity of healthy skin plays a crucial role in maintaining physiological homeostasis of the human body. The skin is the largest organ system of

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Skin Wound Healing: An Update on the Current Knowledge and Concepts.

Understanding the pathology resulting from Staphylococcus aureus and Pseudomonas aeruginosa polymicrobial wound infections is of great importance due to their ubiquitous nature, increasing prevalence, growing resistance to antimicrobial agents, and ability to delay healing. Methicillin-resistant S. aureus USA300 is the leading cause of community-associated bacterial infections resulting in increased morbidity and mortality. We utilized a well-established porcine partial thickness wound healing model to study the synergistic effects of USA300 and P. aeruginosa on wound healing. Wound re-epithelialization was significantly delayed by mixed-species biofilms through suppression of keratinocyte growth factor 1. Pseudomonas showed an inhibitory effect on USA300 growth in vitro while both species co-existed in cutaneous wounds in vivo. Polymicrobial wound infection in the presence of P. aeruginosa resulted in induced expression of USA300 virulence factors Panton-Valentine leukocidin and α-hemolysin. These results provide evidence for the interaction of bacterial species within mixed-species biofilms in vivo and for the first time, the contribution of virulence factors to the severity of polymicrobial wound infections.

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Interactions of methicillin resistant Staphylococcus aureus USA300 and Pseudomonas aeruginosa in polymicrobial wound infection.

Effective method to remove wound bacteria: comparison of various debridement modalities in an in vivo porcine model.

The epidermis is maintained by epidermal stem cells (ESCs) that reside in distinct niches and contribute to homeostasis and wound closure. Keratinocytes at the nonhealing edges of venous ulcers (VUs) are healing-incompetent, hyperproliferative, and nonmigratory, suggesting deregulation of ESCs. To date, genes which regulate ESC niches have been studied in mice only. Utilizing microarray analysis of VU nonhealing edges, we identified changes in expression of genes harboring regulation of ESCs and their fate. In a prospective clinical study of 10 VUs, we confirmed suppression of the bone morphogenetic protein receptor (BMPR) and GATA binding protein 3 (GATA3) as well as inhibitors of DNA-binding proteins 2 and 4 (ID2 and ID4). We also found decreased levels of phosphorylated glycogen synthase kinase 3 (GSK3), nuclear presence of β-catenin, and overexpression of its transcriptional target, c-myc, indicating activation of the Wnt pathway. Additionally, we found down-regulation of leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1), a gene important for maintaining ESCs in a quiescent state, and absence of keratin 15 (K15), a marker of the basal stem cell compartment suggesting local depletion of ESCs. Our study shows that loss of genes important for regulation of ESCs and their fate along with activation of β-catenin and c-myc in the VU may contribute to ESC deprivation and a hyperproliferative, nonmigratory healing incapable wound edge.

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Deregulation of epidermal stem cell niche contributes to pathogenesis of nonhealing venous ulcers

Frontal fibrosing alopecia (FFA) is characterized by scarring alopecia of the frontotemporal hairline that may occasionally extend as far as the mid-scalp. The affected areas show pale discoloration of the skin, with loss of follicular orifices and variable degrees of perifollicular erythema and scaling. Thinning of the eyebrows accompanies the frontotemporal recession. Although the histologic features of FFA are comparable with those of lichen planopilaris (LPP), clinically, multifocal areas of scarring alopecia as seen in LPP are absent. Recommended therapies include topical corticosteroids and tacrolimus, intralesional triamcinolone, oral antimalarials, and finasteride. Although Kossard originally described FFA in postmenopausal women in 1994 and termed it ‘‘postmenopausal frontal fibrosing alopecia,’’ it has subsequently been reported in premenopausal women. To our knowledge, this is the fourth male case reported in the literature and the first reported attempt at hair transplantation in a patient with this disease.

Aron G. Nusbaum

Papers

Epithelialization in Wound Healing: A Comprehensive Review

Interactions of methicillin resistant Staphylococcus aureus USA300 and Pseudomonas aeruginosa in polymicrobial wound infection.

Effective method to remove wound bacteria: comparison of various debridement modalities in an in vivo porcine model.

Deregulation of epidermal stem cell niche contributes to pathogenesis of nonhealing venous ulcers

Frontal Fibrosing Alopecia in a Man: Results of Follicular Unit Test Grafting