Nerve outgrowth and neuropeptide expression during the remodeling of human burn wound scars. A 7-month follow-up study of 22 patients

Quantifying innervation facilitated by deep learning in wound healing

The peripheral nerves (PNs) innervate the dermis and epidermis, and are suggested to play an important role in wound healing. Several methods to quantify skin innervation during wound healing have been reported. Those usually require multiple observers, are complex and labor-intensive, and the noise/background associated with the immunohistochemistry (IHC) images could cause quantification errors/user bias. In this study, we employed the state-of-the-art deep neural network, Denoising Convolutional Neural Network (DnCNN), to perform pre-processing and effectively reduce the noise in the IHC images. Additionally, we utilized an automated image analysis tool, assisted by Matlab, to accurately determine the extent of skin innervation during various stages of wound healing. The 8 mm wound is generated using a circular biopsy punch in the wild-type mouse. Skin samples were collected on days 3, 7, 10 and 15, and sections from paraffin-embedded tissues were stained against pan-neuronal marker- protein-gene-product 9.5 (PGP 9.5) antibody. On day 3 and day 7, negligible nerve fibers were present throughout the wound with few only on the lateral boundaries of the wound. On day 10, a slight increase in nerve fiber density appeared, which significantly increased on day 15. Importantly, we found a positive correlation (R2 = 0.926) between nerve fiber density and re-epithelization, suggesting an association between re-innervation and re-epithelization. These results established a quantitative time course of re-innervation in wound healing, and the automated image analysis method offers a novel and useful tool to facilitate the quantification of innervation in the skin and other tissues.

Quantifying innervation facilitated by deep learning in wound healing

The peripheral nerves (PNs) innervate the dermis and epidermis, which have been suggested to play an important role in wound healing. Several methods to quantify skin innervation during wound healing have been reported. Those usually require multiple observers, are complex and labor-intensive, and noise/background associated with the Immunohistochemistry (IHC) images could cause quantification errors/user bias. In this study, we employed the state-of-the-art deep neural network, DnCNN, to perform pre-processing and effectively reduce the noise in the IHC images. Additionally, we utilized an automated image analysis tool, assisted by Matlab, to accurately determine the extent of skin innervation during various stages of wound healing. The 8mm wound is generated using a circular biopsy punch in the wild-type mouse. Skin samples were collected on days 3,7,10 and 15, and sections from paraffin-embedded tissues were stained against pan-neuronal marker- protein-gene-product 9.5 (PGP 9.5) antibody. On day 3 and day 7, negligible nerve fibers were present throughout the wound with few only on the lateral boundaries of the wound. On day 10, a slight increase in nerve fiber density appeared, which significantly increased on day 15. Importantly we found a positive correlation (R 2  = 0.933) between nerve fiber density and re-epithelization, suggesting an association between re-innervation and re-epithelization. These results established a quantitative time course of re-innervation in wound healing, and the automated image analysis method offers a novel and useful tool to facilitate the quantification of innervation in the skin and other tissues.

Quantifying innervation facilitated by deep learning in wound healing

The peripheral nerves (PNs) innervate the dermis and epidermis, which have been suggested to play an important role in wound healing. Several methods to quantify skin innervation during wound healing have been reported. Those usually require multiple observers, are complex and labor-intensive, and noise/background associated with the Immunohistochemistry (IHC) images could cause quantification errors/user bias. In this study, we employed the state-of-the-art deep neural network, DnCNN, to perform pre-processing and effectively reduce the noise in the IHC images. Additionally, we utilized an automated image analysis tool, assisted by Matlab, to accurately determine the extent of skin innervation during various stages of wound healing. The 8mm wound is generated using a circular biopsy punch in the wild-type mouse. Skin samples were collected on days 3,7,10 and 15, and sections from paraffin-embedded tissues were stained against pan-neuronal marker- protein-gene-product 9.5 (PGP 9.5) antibody. On day 3 and day 7, negligible nerve fibers were present throughout the wound with few only on the lateral boundaries of the wound. On day 10, a slight increase in nerve fiber density appeared, which significantly increased on day 15. Importantly we found a positive correlation (R- 2 = 0.933) between nerve fiber density and re-epithelization, suggesting an association between re-innervation and re-epithelization. These results established a quantitative time course of re-innervation in wound healing, and the automated image analysis method offers a novel and useful tool to facilitate the quantification of innervation in the skin and other tissues.

The Modulatory Influence of Plant-Derived Compounds on Human Keratinocyte Function

The plant kingdom is a rich source of secondary metabolites with numerous properties, including the potential to modify keratinocyte biology. Keratinocytes are important epithelial cells that play a protective role against various chemical, physical and biological stimuli, and participate in reactive oxygen scavenging and inflammation and wound healing processes. The epidermal cell response may be modulated by phytochemicals via changes in signal transduction pathways. Plant extracts and single secondary compounds can possess a high antioxidant capacity and may suppress reactive oxygen species release, inhibit pro-apoptotic proteins and apoptosis and activate antioxidant enzymes in keratinocytes. Moreover, selected plant extracts and single compounds also exhibit anti-inflammatory properties and exposure may result in limited production of adhesion molecules, pro-inflammatory cytokines and chemokines in keratinocytes. In addition, plant extracts and single compounds may promote keratinocyte motility and proliferation via the regulation of growth factor production and enhance wound healing. While such plant compounds may modulate keratinocyte functions, further in vitro and in vivo studies are needed on their mechanisms of action, and more specific toxicity and clinical studies are needed to ensure their effectiveness and safety for use on human skin.

Calcitonin gene-related peptide alleviates hypertrophic scar formation by inhibiting the inflammation

The present study aims to explore the roles of calcitonin gene-related peptide (CGRP) in the hypertrophic scar and its underlying mechanism. The levels of CGRP were determined in human hypertrophic scar and mouse cutaneous scar using ELISA and Western blot. In in vivo studies, A cutaneous excision mouse model was established and treated with exogenous CGRP or CGRP antagonist. In in vitro studies, bone marrow-derived macrophages (BMDMs) were isolated and treated with exogenous CGRP in the presence of lipopolysaccharide (LPS). qRT-PCR and Western blot were applied to determine the mRNA and protein levels of scar formation and inflammation-related genes, respectively. Flow cytometry was operated to determine the populations of macrophages in the scar. Elevated levels of CGRP were observed in the hypertrophic scar. In the cutaneous excision mouse model, treatment of exogenous CGRP or CGRP antagonist-affected scar formation-related genes including Col1, Tgfb1, and α-SMA, inflammation-related genes including Il1b, Il6, Tnfa, and Ccl2, and CD45⁺F4/80⁺ macrophage. In LPS-induced BMDMs, treatment of exogenous CGRP also altered inflammation-related genes by regulating NF-κB and ERK signaling pathways. The ameliorated effects of CGRP on inflammation in hypertrophic scar formation are associated with its regulative effects on NF-κB and ERK signaling pathways.

Sensory neurons from dorsal root ganglia regulate endothelial cell function in extracellular matrix remodelling

BACKGROUND

Recent physiological and experimental data highlight the role of the sensory nervous system in bone repair, but its precise role on angiogenesis in a bone regeneration context is still unknown. Our previous work demonstrated that sensory neurons (SNs) induce the osteoblastic differentiation of mesenchymal stem cells, but the influence of SNs on endothelial cells (ECs) was not studied.

METHODS

Here, in order to study in vitro the interplay between SNs and ECs, we used microfluidic devices as an indirect co-culture model. Gene expression analysis of angiogenic markers, as well as measurements of metalloproteinases protein levels and enzymatic activity, were performed.

RESULTS

We were able to demonstrate that two sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), were involved in the transcriptional upregulation of angiogenic markers (vascular endothelial growth factor, angiopoietin 1, type 4 collagen, matrix metalloproteinase 2) in ECs. Co-cultures of ECs with SNs also increased the protein level and enzymatic activity of matrix metalloproteinases 2 and 9 (MMP2/MMP9) in ECs.

CONCLUSIONS

Our results suggest a role of sensory neurons, and more specifically of CGRP and SP, in the remodelling of endothelial cells extracellular matrix, thus supporting and enhancing the angiogenesis process. Video abstract.

Physical Management of Scar Tissue: A Systematic Review and Meta-Analysis

Objective: The aim of this systematic review with meta-analysis was to describe the status on the effects of physical scar treatments on pain, pigmentation, pliability, pruritus, scar thickening, and surface area.

Design: Systematic review and meta-analysis.

Subjects: Adults with any kind of scar tissue.

Interventions: Physical scar management versus control or no scar management.

Outcome measures: Pain, pigmentation, pliability, pruritus, surface area, scar thickness.

Results: The overall results revealed that physical scar management is beneficial compared with the control treatment regarding the management of pain (p = 0.012), pruritus (p < 0.001), pigmentation (p = 0.010), pliability (p < 0.001), surface area (p < 0.001), and thickness (p = 0.022) of scar tissue in adults. The observed risk of bias was high for blinding of participants and personnel (47%) and low for other bias (100%).

Conclusions: Physical scar management demonstrates moderate-to-strong effects on improvement of scar issues as related to signs and symptoms. These results show the importance of specific physical management of scar tissue.

Genetic influence on scar height and pliability after burn injury in individuals of European ancestry: A prospective cohort study

After similar extent of injury there is considerable variability in scarring between individuals, in part due to genetic factors. This study aimed to identify genetic variants associated with scar height and pliability after burn injury. An exome-wide array association study and gene pathway analysis were performed on a prospective cohort of 665 patients treated for burn injury. Outcomes were scar height (SH) and scar pliability (SP) sub-scores of the modified Vancouver Scar Scale (mVSS). DNA was genotyped using the Infinium^® HumanCoreExome-24 BeadChip. Associations between genetic variants (single nucleotide polymorphisms) and SH and SP were estimated using an additive genetic model adjusting for age, sex, number of surgical procedures and % total body surface area of burn in subjects of European ancestry. No individual genetic variants achieved the cut-off threshold of significance. Gene regions were analysed for spatially correlated single nucleotide polymorphisms and significant regions identified using comb-p software. This gene list was subject to gene pathway analysis to find which biological process terms were over-represented. Using this approach biological processes related to the nervous system and cell adhesion were the predominant gene pathways associated with both SH and SP. This study suggests genes associated with innervation may be important in scar fibrosis. Further studies using similar and larger datasets will be essential to validate these findings.

Complex regional pain syndrome in burn pathological scarring: A case report and review of the literature

Chronic pain in burn pathological scarring is not an uncommon occurrence. The mechanisms of pain are not clearly understood and hence the management approach is often a daunting task. However, meticulous physical examination of these patients may classify them as complex regional pain syndrome, type I. We present a patient with classic signs and symptoms of complex regional pain syndrome associated with burn pathological scarring of her left forearm that had a favourable response to a thoracoscopic sympathectomy. The possible pathological mechanisms of burn pathological scarring, mechanisms of pain, and complex regional pain syndrome are reviewed.

Myelinated and unmyelinated nerve fibers reinnervate tissue-engineered dermo-epidermal human skin analogs in an in vivo model

PURPOSE

The clinical application of autologous tissue-engineered skin analogs is an important strategy to cover large skin defects. Investigating biological dynamics, such as reinnervation after transplantation, is essential to improve the quality of such skin analogs. Previously, we have examined that our skin substitutes are reinnervated by host peripheral nerve fibers as early as 8 weeks after transplantation. Here, we wanted to investigate the presence and possible differences regarding myelinated and unmyelinated host nerve fibers 15 weeks after the transplantation of light and dark human tissue-engineered skin analogs.

METHODS

Human epidermal keratinocytes, melanocytes, and dermal fibroblasts were isolated from human light and dark skin biopsies. Keratinocytes and melanocytes were seeded on fibroblast-containing collagen type I hydrogels after expansion in culture. After additional culturing, the tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds created on the back of immuno-incompetent rats. Skin substitutes were excised and analyzed 15 weeks after transplantation. Histological sections were examined with regard to the ingrowth pattern of myelinated and unmyelinated nerve fibers into the skin analogs using markers, such as Substance P, NF200, and S100-Beta.

RESULTS

We found myelinated and unmyelinated peripheral host nerve fibers 15 weeks after transplantation in the dermal part of our human skin substitutes. In particular, we identified large-diameter-myelinated Aβ- and Aδ-fibers, and small-diameter C-fibers. Furthermore, we observed myelinated nerves in close proximity to CD31-positive blood capillaries. In the long run, both types of ingrown host fibers showed an identical pattern in both light and dark skin analogs.

CONCLUSION

Our data suggest that myelinated and unmyelinated peripheral nerves reinnervate human skin substitutes in a long-term in vivo transplantation assay. Our tissue-engineered skin analogs attract A- and C-fibers to supply both light and dark skin analogs. Potentially, this process restores skin sensitivity and has, therefore, a significant relevance with regard to future application of autologous pigmented dermo-epidermal skin substitutes onto patients.

Current concepts related to hypertrophic scarring in burn injuries

Scarring following burn injury and its accompanying aesthetic and functional sequelae still pose major challenges. Hypertrophic scarring (HTS) can greatly impact patients' quality of life related to appearance, pain, pruritus and even loss of function of the injured body region. The identification of molecular events occurring in the evolution of the burn scar has increased our knowledge; however, this information has not yet translated into effective treatment modalities. Although many of the pathophysiologic pathways that bring about exaggerated scarring have been identified, certain nuances in burn scar formation are starting to be recognized. These include the effects of neurogenic inflammation, mechanotransduction, and the unique interactions of burn wound fluid with fat tissue in the deeper dermal layers, all of which may influence scarring outcome. Tension on the healing scar, pruritus, and pain all induce signaling pathways that ultimately result in increased collagen formation and myofibroblast phenotypic changes. Exposure of the fat domes in the deep dermis is associated with increased HTS, possibly on the basis of altered interaction of adipose-derived stem cells and the deep burn exudate. These pathophysiologic patterns related to stem cell-cytokine interactions, mechanotransduction, and neurogenic inflammation can provide new avenues of exploration for possible therapeutic interventions.

Prevalence and prediction of prolonged pruritus after severe burns

Years after injury, pruritus is a common and severe problem for many burn patients. However, its characteristics and consequences are often only partially described. The authors therefore performed a prospective detailed examination of burn- and individual-related factors and considered those in relation to pruritus severity. Sixty-seven consecutive burn patients were assessed during acute care, and at 3 and 12 months postburn regarding preburn psychiatric disorders, health-related quality of life, post traumatic stress disorder, and personality traits. Postburn pruritus was subsequently assessed 2 to 7 years postburn using the Questionnaire for Pruritus Assessment. Fifty-one individuals, 76% of the participants, reported burn pruritus any time after the burn. Thirty-three individuals, 49% of the participants, reported ongoing pruritus the last 2 months. Information on the characteristics of pruritus was obtained from 32 of these individuals. Most perceived pruritus as bothersome or annoying and as present every day, 16 (50%) were considered to have severe pruritus, and 11 (34 %) scratched themselves to the point of bleeding. In logistic regressions, this was independently related to TBSA full-thickness burn and health-related quality of life at 3 months, and to TBSA full thickness burn and the personality trait impulsiveness, respectively. About half of the previous burn patients experienced ongoing pruritus on an average of 4.5 years after injury, and half of them had severe pruritus. Scratching oneself to the point of bleeding is linked both to a certain personality and to pruritus. It is suspected that many patients are left without access to the best available treatment.

The role of Eph receptors and Ephrins in the skin

Eph receptors and Ephrin ligands are widely expressed in the skin. Various studies have been carried out to identify the effects of these molecules on many aspects of skin development. Here we summarize the literature that has identified roles for Eph receptors and Ephrins in the skin, focusing mainly on the epidermis, hair follicles, and cutaneous innervation. This review may help direct and focus further investigations into the role of Eph receptors and Ephrins in the development, maintenance, and repair processes in cutaneous biology.

Radiation dermatitis, burns, and recall phenomena: Meaningful instances of immunocompromised district

Ionizing and ultraviolet radiations, as well as burns, can selectively damage and immunologically mark the cutaneous area they act on through direct and indirect mechanisms. After the causal event has disappeared, the affected skin district may appear clinically normal, but its immune behavior is often compromised forever. In fact, irradiated or burned skin areas undergo a destabilization of the immune control, which can lead to either a reduction of immunity (as suggested by the facilitated local occurrence of tumors and infections) or an excess of it (as suggested by the possible local onset of disorders with exaggerated immune response). In other words, these areas become typical immunocompromised districts (ICD). Also, in recall phenomena the damaged skin area usually behaves as an ICD with an exaggerated immune response toward a wide range of drugs (especially chemotherapeutic agents) that prove to be harmless on the undamaged skin surface. The occurrence of any skin disorder on an irradiated, photoexposed, or burned skin area can be defined as an isoradiotopic, isophototopic, or isocaumatopic response, respectively; however, the opposite may also occur when elsewhere generalized cutaneous diseases or eruptions selectively spare irradiated, photoexposed, or burned skin sites (isoradiotopic, isophototopic, and isocaumatopic nonresponse, respectively). The pathomechanisms involved in any secondary disorder occurring on irradiated or burned skin areas may be linked to locally decreased or altered lymph flow (with dysfunction of lymph drainage) on the one hand, and to fibrotic throttling or reduction of peptidergic nerve fibers (with dysfunction of neuroimmune signaling) on the other hand, resulting in a significant dysregulation of the local immune response. Future clinical observations and experimental investigations on radiation dermatitis, sunburns, and thermal or chemical skin injuries should shed new light on the mechanisms regulating regional resistance to infectious agents, local oncogenesis, and district propensity to dysimmune reactions.

Identification of biomarkers involved in differential profiling of hypertrophic and keloid scars versus normal skin

Among raised dermal scar types, keloid (KS) and hypertrophic scars (HS) are considered to present clinical similarities, but there are no known specific biomarkers that allow both scar types to be easily distinguished. Development and progression of raised dermal scars comprises the activation of several molecular pathways and cell defence mechanisms leading to elevated extracellular matrix component synthesis, delayed apoptosis, altered migration and differentiation. Therefore, the aim here was to identify biomarkers that may differentiate between KS and HS compared to normal skin (NS). To achieve this aim, NS (n = 14), KS (n = 14) and HS (n = 14) biopsies were evaluated using histology by H&E staining. Tissue biopsies and primary fibroblasts (passages 0-4) were employed to assess the gene expression levels of 21 biomarkers selected from our previous microarray studies using qRT-PCR. Finally, protein expression was evaluated using In-Cell Western Blotting in primary fibroblasts (p 0-4). Our results demonstrated that out of the 21 biomarkers screened at mRNA and protein levels, α2β1-integrin, Hsp27, PAI-2, MMP-19 and CGRP showed significantly higher expression (p < 0.05) in KS compared to NS and HS. Additionally, these five key biomarkers were found to be significantly higher (p < 0.05) at mRNA level in KS taken from the sternum, a region known to be subjected to high mechanical forces in the body during the performance of daily movements. In conclusion, our findings offer potential molecular targets in raised dermal scars differentiation. Future targeted research may allow provision of diagnostic and prognostic markers in keloid versus hypertrophic scars.

Mechanical tension promotes skin nerve regeneration by upregulating nerve growth factor expression

This study aimed to explore the role of mechanical tension in hypertrophic scars and the change in nerve density using hematoxylin-eosin staining and S100 immunohistochemistry, and to observe the expression of nerve growth factor by western blot analysis. The results demonstrated that mechanical tension contributed to the formation of a hyperplastic scar in the back skin of rats, in conjunction with increases in both nerve density and nerve growth factor expression in the scar tissue. These experimental findings indicate that the cutaneous nervous system plays a role in hypertrophic scar formation caused by mechanical tension.

Tissue-engineered dermo-epidermal skin analogs exhibit de novo formation of a near natural neurovascular link 10 weeks after transplantation

PURPOSE

Human autologous tissue-engineered skin grafts are a promising way to cover skin defects. Clearly, it is mandatory to study essential biological dynamics after transplantation, including reinnervation. Previously, we have already shown that human tissue-engineered skin analogs are reinnervated by host nerve fibers as early as 8 weeks after transplantation. In this study, we tested the hypothesis that there is a de novo formation of a "classical" neurovascular link in tissue-engineered and then transplanted skin substitutes.

METHODS

Keratinocytes, melanocytes, and fibroblasts were isolated from human skin biopsies. After expansion in culture, keratinocytes and melanocytes were seeded on dermal fibroblast-containing collagen type I hydrogels. These human tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds on the back of immuno-incompetent rats. Grafts were analyzed after 3 and 10 weeks. Histological sections were examined with regard to the ingrowth pattern of myelinated and unmyelinated nerve fibers into the skin analogs using markers such as PGP9.5, NF-200, and NF-160. Blood vessels were identified with CD31, lymphatic vessels with Lyve1. In particular, we focused on alignment patterns between nerve fibers and either blood and/or lymphatic vessels with regard to neurovascular link formation.

RESULTS

3 weeks after transplantation, blood vessels, but no nerve fibers or lymphatic vessels could be observed. 10 weeks after transplantation, we could detect an ingrowth of myelinated and unmyelinated nerve fibers into the skin analogs. Nerve fibers were found in close proximity to CD31-positive blood vessels, but not alongside Lyve1-positive lymphatic vessels.

CONCLUSION

These data suggest that host-derived innervation of tissue-engineered dermo-epidermal skin analogs is initiated by and guided alongside blood vessels present early post-transplantation. This observation is consistent with the concept of a cross talk between neurovascular structures, known as the neurovascular link.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

Neuropathic mechanisms in the pathophysiology of burns pruritus: redefining directions for therapy and research

Pruritus in burn wounds is a common symptom affecting patient rehabilitation. Over the last decades, there has been a resurgence of interest into more effective strategies to combat this distressing problem; nevertheless, no reports exist in the literature to propose pathophysiological mechanisms responsible for the generation and persistence of pruritic symptoms in the late phases of burns rehabilitation. Neuronal pathways mediating pruritic and painful stimuli share striking similarities, which allows the comparative exploration of the less extensively studied pruritic mechanisms using pain models. Furthermore, emerging anatomical, neurophysiological, and pharmacological evidence supports the involvement of neuropathic mechanisms in chronic burns pruritus. This work updates the conceptual framework for the pathophysiology of burns itch by embracing the contribution of the central nervous system in the maintenance of symptoms into a chronic state. The proposed pathophysiological model paves new avenues in burns pruritus research and is likely to have implications in the quest for more effective therapeutic regimens in clinical practice.

Concise review: tissue-engineered skin and nerve regeneration in burn treatment

Burns not only destroy the barrier function of the skin but also alter the perceptions of pain, temperature, and touch. Different strategies have been developed over the years to cover deep and extensive burns with the ultimate goal of regenerating the barrier function of the epidermis while recovering an acceptable aesthetic aspect. However, patients often complain about a loss of skin sensation and even cutaneous chronic pain. Cutaneous nerve regeneration can occur from the nerve endings of the wound bed, but it is often compromised by scar formation or anarchic wound healing. Restoration of pain, temperature, and touch perceptions should now be a major challenge to solve in order to improve patients' quality of life. In addition, the cutaneous nerve network has been recently highlighted to play an important role in epidermal homeostasis and may be essential at least in the early phase of wound healing through the induction of neurogenic inflammation. Although the nerve regeneration process was studied largely in the context of nerve transections, very few studies have been aimed at developing strategies to improve it in the context of cutaneous wound healing. In this concise review, we provide a description of the characteristics of and current treatments for extensive burns, including tissue-engineered skin approaches to improve cutaneous nerve regeneration, and describe prospective uses for autologous skin-derived adult stem cells to enhance recovery of the skin's sense of touch.

Rebuild, restore, reinnervate: do human tissue engineered dermo-epidermal skin analogs attract host nerve fibers for innervation?

PURPOSE

Tissue engineered skin substitutes are a promising tool to cover large skin defects, but little is known about reinnervation of transplants. In this experimental study, we analyzed the ingrowth of host peripheral nerve fibers into human tissue engineered dermo-epidermal skin substitutes in a rat model. Using varying cell types in the epidermal compartment, we wanted to assess the influence of epidermal cell types on reinnervation of the substitute.

METHODS

We isolated keratinocytes, melanocytes, fibroblasts, and eccrine sweat gland cells from human skin biopsies. After expansion, epidermal cells were seeded on human dermal fibroblast-containing collagen type I hydrogels as follows: (1) keratinocytes only, (2) keratinocytes with melanocytes, (3) sweat gland cells. These substitutes were transplanted into full-thickness skin wounds on the back of immuno-incompetent rats and were analyzed after 3 and 8 weeks. Histological sections were examined with regard to myelinated and unmyelinated nerve fiber ingrowth using markers such as PGP9.5, NF-200, and NF-145.

RESULTS

After 3 weeks, the skin substitutes of all three epidermal cell variants showed no neuronal ingrowth from the host into the transplant. After 8 weeks, we could detect an innervation of all three types of skin substitutes. However, the nerve fibers were restricted to the dermal compartment and we could not find any unmyelinated fibers in the epidermis. Furthermore, there was no distinct difference between the constructs resulting from the different cell types used to generate an epidermis.

CONCLUSION

Our human tissue engineered dermo-epidermal skin substitutes demonstrate a host-derived innervation of the dermal compartment as early as 8 weeks after transplantation. Thus, our substitutes apparently have the capacity to attract nerve fibers from adjacent host tissues, which also grow into grafts and thereby potentially restore skin sensitivity.

The reinnervation and revascularisation pattern of scarless murine fetal wounds

Fetal wounds can heal without scarring. There is evidence that the sensory nervous system plays a role in mediating inflammation and healing, and that the reinnervation pattern of adult wounds differs from that of unwounded skin. Ectoderm is required for development of the cutaneous nerve plexus in early gestation. It was hypothesised that scarless fetal wounds might completely regenerate their neural and vascular architecture. Wounds were made on mouse fetuses at embryonic day 16.5 of a 19.5-day gestation, which healed without visible scars. Immunohistochemical analysis of wound sites was performed to assess reinnervation, using antibodies to the pan neuronal marker PGP9.5 as well as to the neuropeptides calcitonin gene-related peptide (CGRP) and substance P (SP). Staining for the endothelial marker von Willebrand factor (VWF) allowed comparison of reinnervation and revascularisation. Wounds were harvested at timepoints from day 1 after wounding to postnatal day 6. Quantification of wound reinnervation and revascularisation was performed for timepoints up to 6 days post-wounding. Hypervascularisation of the wounds occurred within 24 h, and blood vessel density within the wounds remained significantly elevated until postnatal day 2 (4 days post- wounding), after which VWF immunoreactivity was similar between wound and control groups. Wound nerve density returned to a level similar to that of unwounded skin within 48 h of wounding, and PGP9.5 immunoreactive nerve fibre density remained similar to control skin thereafter. CGRP and SP immunoreactivity followed a similar pattern to that of PGP9.5, although wound levels did not return to those of control skin until postnatal day 1. Scarless fetal wounds appeared to regenerate their nerve and blood vessel microanatomy perfectly after a period of hypervascularisation.

Neuropeptide substance P attenuates hyperoxia-induced oxidative stress injury in type II alveolar epithelial cells via suppressing the activation of JNK pathway

Hyperoxia-induced oxidative stress plays a key role in many pulmonary diseases. In an earlier study we found the protective effect of the neuropeptide substance P (SP) on type II alveolar epithelial cells (AECIIs) after hyperoxia exposure. Then, we investigated c-Jun N-terminal kinase (C-JNK) signal transduction pathways in AECIIs before and after hyperoxia exposure. Primary AECIIs were isolated and purified from premature rats. Subsequently, the cells were treated with air (21% oxygen), hyperoxia (95% oxygen), SP+ air, and SP+ hyperoxia. SP was added in advance to reach a final concentration 1 x 10(-6) mol/l. The cells were then exposed to air and hyperoxia for 12, 24, and 48 h. XTT cell proliferation assay and fluorescence-activated cell sorting (FACS) were employed to detect cell growth and apoptosis. Phosphorylated JNK (p-JNK) levels were measured using Western blot assay. The morphological alteration of AECIIs was observed using a transmission electron microscope (TEM). Compared with the simple hyperoxia treatment, the cell growth and apoptosis percentage was significantly increased and decreased after adding additional SP. Meanwhile, the reduced levels of p-JNKs could be found after adding SP. Furthermore, the morphological damage of AECIIs was greatly improved. These data suggest that SP can promote AECII proliferation and inhibit apoptosis by suppressing JNK signal pathways after hyperoxia exposure, which attenuates hyperoxia-induced oxidative stress damage in AECIIs. It might be a potential therapy for acute pulmonary injury under hyperoxia-induced oxidative stress.

Postburn Scars: An Update

Burn wounds give rise to the largest scars we can find in human pathology, influencing patients' quality of life. Despite the improved knowledge on pathophysiology, efficacy of the various treatments remains unsatisfactory. In this short review recent literature is examined with a focus on recent data on postburn pathological scars epidemiology and risk factors, which underline the high prevalence and the long evolution, pointing to identify this illness as a systemic inflammatory one, more frequent in women and in those of younger age, regulated by local factors relevant in wound healing.

Dexamethasone treatment of post-MI rats attenuates sympathetic innervation of the infarct region

Sympathetic fiber innervation of the damaged region following injury represents a conserved event of wound healing. The present study tested the hypothesis that impaired scar healing in post-myocardial infarction (post-MI) rats was associated with a reduction of sympathetic fibers innervating the infarct region. In 1-wk post-MI rats, neurofilament-M-immunoreactive fibers (1,116 ± 250 μm2/mm2) were detected innervating the infarct region and observed in close proximity to a modest number of endothelial nitric oxide synthase-immunoreactive scar-residing vessels. Dexamethasone (Dex) treatment (6 days) of post-MI rats led to a significant reduction of scar weight (Dex + MI 38 ± 4 mg vs. MI 63 ± 2 mg) and a disproportionate nonsignificant decrease of scar surface area (Dex + MI 0.54 ± 0.06 cm2vs. MI 0.68 ± 0.06 cm2). In Dex-treated post-MI rats, the density of neurofilament-M-immunoreactive fibers (125 ± 47 μm2/mm2) innervating the infarct region was significantly reduced and associated with a decreased expression of nerve growth factor (NGF) mRNA (Dex + MI 0.80 ± 0.07 vs. MI 1.11 ± 0.08; P < 0.05 vs. MI). Previous studies have demonstrated that scar myofibroblasts synthesize NGF and may represent a cellular target of Dex. The exposure of 1st passage scar myofibroblasts to Dex led to a dose-dependent suppression of [3H]thymidine uptake and a concomitant attenuation of NGF mRNA expression (untreated 3.47 ± 0.35 vs. Dex treated 2.28 ± 0.40; P < 0.05 vs. untreated). Thus the present study has demonstrated that impaired scar healing in Dex-treated post-MI rats was associated with a reduction of neurofilament-M-immunoreactive fibers innervating the infarct region. The attenuation of scar myofibroblast proliferation and NGF mRNA expression may represent underlying mechanisms contributing to the diminished neural response in the infarct region of Dex-treated post-MI rats.

Itching following burns: epidemiology and predictors

BACKGROUND

Itching (pruritus) following burns is a well-known clinical problem. However, there are no long-term prospective studies that document the course and the extent of the problem. Studies on risk factors are anecdotal.

OBJECTIVES

To study self-reported itching in a multicentre cohort among adults with burns at 3, 12 and 24 months postburn. Further, to examine psychological and injury characteristics in relation to itching at these three points in time.

METHODS

Itching was assessed as part of a self-report scar complaint list in a prospective longitudinal cohort study. Injury characteristics, demographics and self-reported post-traumatic stress symptoms were examined as possible risk factors in three linear regression models.

RESULTS

A total of 510 persons participated. The reported prevalence rates of mild to severe itching were as high as 87%, 70% and 67% at the three respective points in time. Significant predictors of itching at all three points in time were deep dermal injury and early post-traumatic stress symptoms. Along with these, total burned surface area and female gender were predictors at 3 months postburn.

CONCLUSIONS

Itching remains a significant problem over a 2-year period. Individuals having undergone surgical procedures and experiencing early post-traumatic distress are more likely to suffer from long-term and persistent itching. Implications regarding practice and research are discussed.

The reinnervation pattern of wounds and scars may explain their sensory symptoms

Anaesthesia, pruritus and pain are common in cutaneous scars. The reinnervation pattern of healing wounds and scars might help to explain these symptoms, as sensory neurotransmitters are known to be mediators of inflammation and healing. We quantified the regeneration patterns of blood vessels and nerves in excisional skin wounds as they matured into scars. Mice underwent 1cm(2) full thickness skin excisions. Wounds were harvested between five and 84 days. Sections underwent immunohistochemical staining for protein gene product 9.5 (PGP9.5) a pan-neuronal marker, and the sensory neuropeptides calcitonin gene related peptide (CGRP) and substance P (SP). The endothelial marker von Willebrand factor (VWF) was used to allow co-localisation and quantification of blood vessels. Nerve fibre density was quantified at multiple sites within wounds. There was no difference in the reinnervation/revascularisation pattern between peripheral and central sites. The density of PGP9.5, CGRP, SP and VWF peaked between 14 and 42 days, and levels of PGP9.5, CGRP and VWF all decreased to approximately those found in unwounded skin by 84 days (mature scar). SP levels, however, remained elevated at approximately twice the density found in unwounded skin. Increased densities of SP and CGRP in healing wounds could explain the unpleasant sensory symptoms of healing wounds.

Nerve quantification in female red Duroc pig (FRDP) scar compared to human hypertrophic scar

A significant impediment to studying hypertrophic scar is the lack of an animal model. We have confirmed similarities between scarring in the female red Duroc pig (FRDP) and human hypertrophic scar and conclude that this model warrants validation. Reports have suggested that the cutaneous nervous system may play a role in hypertrophic scar development and several studies have shown nerve density in hypertrophic scar to be increased. The purpose of this study was to further validate the FRDP model of hypertrophic scar by quantifying nerves in FRDP tissue and comparing the findings to human hypertrophic scar. Wounds of varying depth were created on the backs of two FRDP and tissue samples were harvested at 10 days, 1 month and 5 months post-wounding. Human specimens were obtained from six burn patients. Immunohistochemistry was performed and digital images were captured. Color subtractive computer-assisted image analysis was used to quantify nerve density and nerve area fraction. The results demonstrate that nerve tissue is increased in FRDP scar tissue and is quite similar to that in human hypertrophic scar and to that described in the literature. These data provide additional evidence that the FRDP model may be useful for studying hypertrophic scarring.

Nerve regeneration in a collagen-chitosan tissue-engineered skin transplanted on nude mice

A reconstructed skin made of a collagen-chitosan sponge seeded with human fibroblasts and keratinocytes and grown in vitro for 31 days was developed for the treatment of deep and extensive burns. The aim of this study was to assess whether this tissue-engineered skin could promote nerve regeneration in vivo, since recovery of sensation is a major concern for burnt patients. The human reconstructed skin was transplanted on the back of nude mice and the growth of nerve fibres within it was assessed 40, 60, 90 and 120 days after graft. Nerve growth was monitored by confocal microscopy using immunohistochemical staining of PGP 9.5 and 150 kD neurofilament, while Schwann cell migration was observed using protein S100 expression and laminin deposition. Nerve growth was first detected 60 days after transplantation and was more abundant 90 and 120 days after graft. Linear arrangements of Schwann cells were observed in the graft as early as 40 days after graft. Nerve growth was observed along these Schwann cell extensions 60 days after transplantation. We conclude that the three-dimensional architecture of the collagen-chitosan tissue-engineered skin sponge encourages nerve growth. This result provides new perspectives to increase nerve regeneration within the tissue-engineered skin by linkage of neurotrophic factors in the sponge before transplantation.