Elsevier

Burns

Volume 41, Issue 4, June 2015, Pages 843-847
Burns

Epidermal aquaporin-3 is increased in the cutaneous burn wound

https://doi.org/10.1016/j.burns.2014.10.033Get rights and content

Highlights

  • In the skin, AQPs permit rapid, regulated, and selective water permeability and have been demonstrated to play a role in skin hydration, cell proliferation, migration, immunity, and wound healing.

  • The burn wound edge demonstrates a partial loss of the epidermal architecture representing a partial thickness burn.

  • In the burn wound center there is a complete loss of the epidermis and dermis representing a full thickness burn.

  • Aquaporin-3 expression is absent in the burn wound center.

  • There is a significant increase in the quantity of aquaporin-3 expression along the burn wound edge compared to the burn wound center.

Abstract

Introduction

Aquaporins (AQP) are a family of transmembrane proteins that transport water and small solutes such as glycerol across cell membranes. It is a mediator of transcellular water flow and plays an important role in maintaining intra/extracellular fluid homeostasis by facilitating water transport in response to changing osmotic gradients. In the skin, AQPs permit rapid, regulated, and selective water permeability and have been demonstrated to play a role in skin hydration, cell proliferation, migration, immunity, and wound healing. However, the expression of AQP-3 in the cutaneous burn wound has never been elucidated. We sought to assess the expression of AQP-3 in patients with burn wounds.

Methods

A fresh full thickness biopsy sample was taken from the center of the burn wound, the burn wound edge, and the graft donor site in 7 patients (n = 21), approximately 3–7 days post injury. Fixed, paraffin embedded sections were stained using AQP-3 specific antibody and examined by immunofluorescence. Fresh samples were processed to quantify AQP-3 protein expression with Western blot analysis.

Results

The central portion of the burn wound revealed destruction of the epidermis and dermis with no AQP-3 present. Along the burn wound edge where the epidermal architecture was disrupted, there was robust AQP-3 staining. Western blot analysis demonstrated deeper staining along the burn wound edge compared to unburned skin (control). Quantification of the protein shows a significant amount of AQP-3 expression along the burn wound edge (3.6 ± 0.34) compared to unburned skin (2.1 ± 0.28, N = 7, *p < 0.05). There is no AQP-3 expression in the burn wound center.

Conclusion

AQP-3 expression is increased in the burn wound following injury. While its role in wound healing has been defined, we report for the first time the effect of cutaneous burns on AQP-3 expression. Our data provides the first step in determining its functional role in burn wounds. We hypothesize that development of AQP3 targeted therapies may improve burn wound healing.

Introduction

Aquaporins (AQP) are a family of transmembrane proteins that transport water and small solutes such as glycerol across cell membranes [1]. It is a mediator of transcellular water flow and plays an important role in maintaining intra/extracellular fluid homeostasis by facilitating water transport in response to changing osmotic gradients [2]. AQPs are found in the major systems of the human body such as the nervous, renal, cardiovascular, respiratory, reproductive, digestive, musculoskeletal, and integumentary systems [2].

In the skin, AQPs permit rapid, regulated, and selective water permeability and have been demonstrated to play a role in skin hydration, cell proliferation, migration, immunity, and wound healing [3], [4], [5]. Overall, 6 skin AQPs have been identified. At the epidermal level, the most important and abundant of these proteins is AQP-3. It is a member of the aquaglyceroporin subfamily and is found primarily in the plasma membrane of keratinocytes and dermal fibroblasts [6], [7]. AQP-3 has function in the transportation of water and glycerol, a natural moisturizing factor that keeps the skin hydrated, in the interstitial space and intracellularly [8].

In the epidermis, AQP3 is organized to create a highly selective permeability gradient (Fig. 1). For example, epidermal permeability progressively increases from the stratum corneum to the stratum basale. Not coincidentally, this difference in cell permeability is proportional to the concentration of AQP3 within each epidermal layer, with high concentrations being found in the stratum basale and absent in the stratum corneum and granulosum. In fact, it is this proportionate increase in membrane permeability to AQP3 expression that forms the biologic rationale for an AQP3 mediated water clamp or gate phenomenon, a regulatory mechanism by which water moves across cellular membranes dependent on the conformation of the protein channel in the open or closed position [9].

Wound healing in the skin is a multi-step process that involves several cell types, including epidermal keratinocytes, fibroblasts, endothelial cells, and peripheral nerve cells [10]. In addition to cellular involvement, a number of cell signaling molecules and proteins are involved in this process as well. AQP-3 is integral to wound healing by facilitating water and glycerol transport and therefore keratinocyte migration and proliferation respectively [3]. In fact, the absence of AQP3 regulated transport of water and glycerol has been shown to impair wound healing in animal models [11].

While the role of role of AQP-3 in cutaneous wound healing has been defined, its activity in the burn wound has not previously been determined. The aim of our study was to determine the effect of a cutaneous burn on AQP-3 expression within the wound.

Section snippets

Materials and methods

Following institutional review board approval (IRB), a total of 7 patients were selected for our study. Full thickness biopsy samples were taken from 3 locations on each patient; the burn wound center, edge, and graft donor sites for a total of 21 specimens (3 per patient) approximately 3–7 days post injury. The areas of burn to be biopsied were determined from physical examination by an experienced burn surgeon. The samples were immediately processed and stored in alloprotect reagent (Qiagen).

Results

A total of 20 patients were enrolled into our study (N = 7) over a 5-month period. The mean age of the patients selected was 51 years (22–82 years) with 43% male and 57% female. African-Americans accounted for 29% (N = 2) of the patient population, Caucasian 57% (N = 4), Asian 14% (N = 1). The average total body surface area (TBSA) that was burned on these patients was 11.6%. The mechanism of each burn was 57% flame (N = 4), 29% scald (N = 2), and 14% grease (N = 1) (Table 1). Light microscopy of biopsied

Discussion

We sought to determine the effect of a cutaneous burn on AQP-3 expression in humans using tissue samples from patients admitted to our unit with deep burns to skin. Full thickness biopsy samples were taken from the wound edge (defined clinically as a partial thickness burn), the donor site (normal skin), and wound center (full thickness burn). We evaluated the location and the degree of AQP-3 expression in the skin using immunofluorescence and western blot analysis respectively.

In the center of

Disclosures

The authors report no proprietary or commercial interest in any product mentioned or concept discussed in this article.

Author contributions

R. Sebastian, E. Chau, P. Fillmore participated in the development of the study, conducted the experiments, assisted in interpreting the data and writing the manuscript. J. Matthews served in interpreting the data, determining its clinical significance and writing the manuscript. L.A. Price and V. Sidhaye assisted in the design of the experiments and determining its clinical significance. S. Milner oversaw all aspects of the study and obtained the grant that provided funding for the study.

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