Wounds Inhibit Tumor Growth In Vivo.

OBJECTIVE: The aim of this study was to determine the interaction of full thickness excisional wounds and tumors in vivo. SUMMARY OF BACKGROUND DATA: Tumors have been described as wounds that do not heal due to similarities in stromal composition. On the basis of observations of slowed tumor growth after ulceration, we hypothesized that full thickness excisional wounds would inhibit tumor progression in vivo. METHODS: To determine the interaction of tumors and wounds, we developed a tumor xenograft/allograft (human head and neck squamous cell carcinoma SAS/mouse breast carcinoma 4T1) wound mouse model. We examined tumor growth with varying temporospatial placement of tumors and wounds or ischemic flap. In addition, we developed a tumor/wound parabiosis model to understand the ability of tumors and wounds to recruit circulating progenitor cells. RESULTS: Tumor growth inhibition by full thickness excisional wounds was dose-dependent, maintained by sequential wounding, and relative to distance. This effect was recapitulated by placement of an ischemic flap directly adjacent to a xenograft tumor. Using a parabiosis model, we demonstrated that a healing wound was able to recruit significantly more circulating progenitor cells than a growing tumor. Tumor inhibition by wound was unaffected by presence of an immune response in an immunocompetent model using a mammary carcinoma. Utilizing functional proteomics, we identified 100 proteins differentially expressed in tumors and wounds. CONCLUSION: Full thickness excisional wounds have the ability to inhibit tumor growth in vivo. Further research may provide an exact mechanism for this remarkable finding and new advances in wound healing and tumor biology.

Macrophage Subpopulation Dynamics Shift following Intravenous Infusion of Mesenchymal Stromal Cells.

Intravenous infusion of mesenchymal stromal cells (MSCs) is thought to be a viable treatment for numerous disorders. Although the intrinsic immunosuppressive ability of MSCs has been credited for this therapeutic effect, their exact impact on endogenous tissue-resident cells following delivery has not been clearly characterized. Moreover, multiple studies have reported pulmonary sequestration of MSCs upon intravenous delivery. Despite substantial efforts to improve MSC homing, it remains unclear whether MSC migration to the site of injury is necessary to achieve a therapeutic effect. Using a murine excisional wound healing model, we offer an explanation of how sequestered MSCs improve healing through their systemic impact on macrophage subpopulations. We demonstrate that infusion of MSCs leads to pulmonary entrapment followed by rapid clearance, but also significantly accelerates wound closure. Using single-cell RNA sequencing of the wound, we show that following MSC delivery, innate immune cells, particularly macrophages, exhibit distinctive transcriptional changes. We identify the appearance of a pro-angiogenic CD9+ macrophage subpopulation, whose induction is mediated by several proteins secreted by MSCs, including COL6A1, PRG4, and TGFB3. Our findings suggest that MSCs do not need to act locally to induce broad changes in the immune system and ultimately treat disease.

The Plane of Mesh Placement Does Not Impact Abdominal Donor Site Complications in Microsurgical Breast Reconstruction.

BACKGROUND: Reinforcement of the abdominal wall with synthetic mesh in autologous breast reconstruction using abdominal free tissue transfer decreases the risk of bulging and herniation. However, the impact of the plane of mesh placement on donor site complications has not yet been investigated. METHODS: We performed a retrospective analysis of 312 patients who had undergone autologous breast reconstruction with muscle-sparing transverse rectus abdominis myocutaneous (MS-TRAM) flaps or deep inferior epigastric perforator (DIEP) flaps as well as polypropylene mesh implantation at the donor site. Donor site complications were compared among patients with different flap types and different mesh positions including overlay (n = 90), inlay and overlay (I-O; n = 134), and sublay (n = 88). RESULTS: Abdominal hernias occurred in 2.86% of patients who had undergone MS-TRAM reconstructions and in 2.63% of patients who had undergone DIEP reconstructions. When comparing patients with different mesh positions, donor site complications occurred in 14.4% of patients with overlay mesh, 13.4% of patients with I-O mesh, and 10.2% of patients with sublay mesh (P = 0.68). Abdominal hernias occurred in 4.44% of patients with overlay mesh, 2.24% of patients with I-O mesh, and 2.27% of patients with sublay mesh (P = 0.69). Multivariable logistic regression analysis did not identify a significant association between mesh position and hernia rates as well as wound complications. CONCLUSIONS: Our data indicate that the plane of synthetic mesh placement in relation to the rectus abdominis muscle does not impact the rate of postoperative donor site complications in patients undergoing breast reconstruction with MS-TRAM or DIEP flaps.

Stevens-Johnson syndrome and toxic epidermal necrolysis: a 10-year experience in a burns unit.

OBJECTIVE: Stevens-Johnson syndrome (SJS) and its more severe counterpart, toxic epidermal necrolysis (TEN), are skin hypersensitivity reactions defined by epidermal blistering and necrosis. The exact pathophysiology of SJS/TEN is yet to be deciphered, but a number of risk factors have been identified including adverse drug reactions. The diagnosis of SJS/TEN is made on a clinical basis, and treatment consists of supportive care and occasionally immunosuppressants, such as cyclosporin, high-dose intravenous immunoglobulins and/or corticosteroids. Mortality rates can reach 20-25% in adults but are reduced with early intervention. To identify optimal treatment regimens, to better understand the patient cohort affected, and to help identify key risk factors for mortality, we report our experience with the treatment and management of SJS/TEN patients. METHODS: A retrospective review of consecutive patients with SJS and/or TEN admitted to a single burns centre in Germany, between 2008 and 2018, was conducted. The primary outcomes of demographics, clinical course, treatment and patient-reported outcomes were recorded and compared with a control group of patients with burns without a diagnosis of SJS/TEN. RESULTS: A total of 23 patients with SJS/TEN met the inclusion criteria: 17 (74%) with TEN; four (17%) with SJS/TEN overlap; and two (9%) with SJS. Of the patients, 14 (61%) were female and nine (39%) were male. Patient age ranged from 32-78 years (mean: 52 years). A matched cohort of 23 patients with burns served as the control group. All patients received standard of care with a multidisciplinary team. Compared with the control group, SJS/TEN patients had higher mortality rates (n=6, 26% versus n=8, 35%, respectively). The average age of death was 69 years in SJS/TEN patients versus 63 years in control group patients. Age and SCORTEN scores were significant predictors of mortality. CONCLUSIONS: SJS and TEN are rare but extreme reactions of the skin and mucosa, associated with high disease mortality rates. This 10-year single-centre retrospective review contributes to the bank of information for reviews evaluating the management of SJS/TEN patients.

Stevens-Johnson syndrome and toxic epidermal necrolysis: a systematic review and meta-analysis.

OBJECTIVE: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare and severe skin and mucosal reactions that are associated with high mortality. Despite the severity, an evidence-based treatment protocol for SJS/TEN is still lacking. METHOD: In this systematic review and meta-analysis, the PubMed database was searched using the following terms: [Stevens-Johnson syndrome] OR [toxic epidermal necrolysis] AND [therapy] OR [treatment] over a 20-year period (1999-2019) in the German and English language. All clinical studies reporting on the treatment of SJS/TEN were included, and epidemiological and diagnostic aspects of treatment were analysed. A meta-analysis was conducted on all comparative clinical studies that met the inclusion criteria. RESULTS: A total of 88 studies met the inclusion criteria, reporting outcomes in 2647 patients. Treatment was either supportive or used systemic corticosteroid, intravenous immunoglobulin, plasmapheresis, cyclosporine, thalidomide or cyclophosphamide therapy. The meta-analysis included 16 (18%) studies, reporting outcomes in 976 (37%) patients. Systemic glucocorticoids showed a survival benefit for SJS/TEN patients in all analyses compared with other forms of treatment. Cyclosporine treatment also showed promising results, despite being used in a small cohort of patients. No beneficial effects on mortality could be demonstrated for intravenous immunoglobulins. CONCLUSION: Glucocorticoids and cyclosporine may be tentatively recommended as the most promising immunomodulatory therapies for SJS/TEN, but these results should be investigated in future prospective controlled trials.

Molecular Mechanisms of Hair Growth and Regeneration: Current Understanding and Novel Paradigms.

Hair is a defining feature of mammals and has critical functions, including protection, production of sebum, apocrine sweat and pheromones, social and sexual interactions, thermoregulation, and provision of stem cells for skin homeostasis, regeneration, and repair. The hair follicle (HF) is considered a "mini-organ," consisting of intricate and well-organized structures which originate from HF stem and progenitor cells. Dermal papilla cells are the main components of the mesenchymal compartments in the hair bulb and are instrumental in generating signals to regulate the behavior of neighboring epithelial cells during the hair cycle. Mesenchymal-epithelial interactions within the dermal papilla niche drive HF embryonic development as well as the postnatal hair growth and regeneration cycle. This review summarizes the current understanding of HF development, repair, and regeneration, with special focus on cell signaling pathways governing these processes. In particular, we discuss emerging paradigms of molecular signaling governing the dermal papilla-epithelial cellular interactions during hair growth and maintenance and the recent progress made towards tissue engineering of human hair follicles.

Burns: modified metabolism and the nuances of nutrition therapy.

OBJECTIVE: To review the effects of burn injury on nutritional requirements and how this can best be supported in a healthcare setting. METHOD: A literature search for articles discussing nutrition and/or metabolism following burn injury was carried out. PubMed, Embase and Web of Science databases were searched using the key search terms 'nutrition' OR 'metabolism' AND 'burn injury' OR 'burns'. There was no limitation on the year of publication. RESULTS: A total of nine articles met the inclusion criteria, the contents of which are discussed in this manuscript. CONCLUSION: Thermal injury elicits the greatest metabolic response, among all traumatic events, in critically ill patients. In order to ensure burn patients can meet the demands of their increased metabolic rate and energy expenditure, adequate nutritional support is essential. Burn injury results in a unique pathophysiology, involving alterations in endocrine, inflammatory, metabolic and immune pathways and nutritional support needed during the inpatient stay varies depending on burn severity and idiosyncratic patient physiologic parameters.

Cryopreserved human skin allografts promote angiogenesis and dermal regeneration in a murine model.

Cryopreserved human skin allografts (CHSAs) are used for the coverage of major burns when donor sites for autografts are insufficiently available and have clinically shown beneficial effects on chronic non-healing wounds. However, the biologic mechanisms behind the regenerative properties of CHSA remain elusive. Furthermore, the impact of cryopreservation on the immunogenicity of CHSA has not been thoroughly investigated and raised concerns with regard to their clinical application. To investigate the importance and fate of living cells, we compared cryopreserved CHSA with human acellular dermal matrix (ADM) grafts in which living cells had been removed by chemical processing. Both grafts were subcutaneously implanted into C57BL/6 mice and explanted after 1, 3, 7, and 28 days (n = 5 per group). A sham surgery where no graft was implanted served as a control. Transmission electron microscopy (TEM) and flow cytometry were used to characterise the ultrastructure and cells within CHSA before implantation. Immunofluorescent staining of tissue sections was used to determine the immune reaction against the implanted grafts, the rate of apoptotic cells, and vascularisation as well as collagen content of the overlaying murine dermis. Digital quantification of collagen fibre alignment on tissue sections was used to quantify the degree of fibrosis within the murine dermis. A substantial population of live human cells with intact organelles was identified in CHSA prior to implantation. Subcutaneous pockets with implanted xenografts or ADMs healed without clinically apparent rejection and with a similar cellular immune response. CHSA implantation largely preserved the cellularity of the overlying murine dermis, whereas ADM was associated with a significantly higher rate of cellular apoptosis, identified by cleaved caspase-3 staining, and a stronger dendritic cell infiltration of the murine dermis. CHSA was found to induce a local angiogenic response, leading to significantly more vascularisation of the murine dermis compared with ADM and sham surgery on day 7. By day 28, aggregate collagen-1 content within the murine dermis was greater following CHSA implantation compared with ADM. Collagen fibre alignment of the murine dermis, correlating with the degree of fibrosis, was significantly greater in the ADM group, whereas CHSA maintained the characteristic basket weave pattern of the native murine dermis. Our data indicate that CHSAs promote angiogenesis and collagen-1 production without eliciting a significant fibrotic response in a xenograft model. These findings may provide insight into the beneficial effects clinically observed after treatment of chronic wounds and burns with CHSA.

Age-associated intracellular superoxide dismutase deficiency potentiates dermal fibroblast dysfunction during wound healing.

Reactive oxygen species (ROS) impair wound healing through destructive oxidation of intracellular proteins, lipids and nucleic acids. Intracellular superoxide dismutase (SOD1) regulates ROS levels and plays a critical role in tissue homoeostasis. Recent evidence suggests that age-associated wound healing impairments may partially result from decreased SOD1 expression. We investigated the mechanistic basis by which increased oxidative stress links to age-associated impaired wound healing. Fibroblasts were isolated from unwounded skin of young and aged mice, and myofibroblast differentiation was assessed by measuring α-smooth muscle actin and collagen gel contraction. Excisional wounds were created on young and aged mice to study the healing rate, ROS levels and SOD1 expression. A mechanistic link between oxidative stress and fibroblast function was explored by assessing the TGF-ß1 signalling pathway components in young and aged mice. Age-related wounds displayed reduced myofibroblast differentiation and delayed wound healing, consistent with a decrease in the in vitro capacity for fibroblast-myofibroblast transition following oxidative stress. Young fibroblasts with normal SOD1 expression exhibited increased phosphorylation of ERK in response to elevated ROS. In contrast, aged fibroblasts with reduced SOD1 expression displayed a reduced capacity to modulate intracellular ROS. Collectively, age-associated wound healing impairments are associated with fibroblast dysfunction that is likely the result of decreased SOD1 expression and subsequent dysregulation of intracellular ROS. Strategies targeting these mechanisms may suggest a new therapeutic approach in the treatment of chronic non-healing wounds in the aged population.

Optimising management of self-inflicted burns: a retrospective review.

OBJECTIVE: Self-inflicted burns typically result in extensive injuries requiring intensive care and attention in a specialised burn unit. Burn units should be familiar with the optimal management of self-inflicted burns, including the psychological and psychiatric treatment. This paper describes the experiences of managing these challenging injuries in a German burn centre. METHODS: A retrospective review of patients with self-inflicted burns admitted to the burn centre between 2000 and 2017. Demographics, details of injury, presence of psychiatric disorder, clinical course, operative management and patient outcomes were recorded and compared with a control group without self-inflicted burns. Outcome measures included graft take rate, complications and need for further surgery. RESULTS: There were a total of 2055 burn patient admissions, with 17 cases (0.8%) of self-inflicted burns. The mean age was 36±11 years with an mean percentage total body surface area (%TBSA) burned of 43.5±22.5% which was not significantly different from the control group (p=0.184). Schizophrenia and personality disorder were the most common diagnoses in the self-inflicted burns patients (n=11; 65%). Of these, four had sustained previous self-inflicted burns. Length of hospital stay was significantly longer in the self-inflicted burn group than in the control group (49.0±16.7 days, respectively, p=0.002). CONCLUSION: Attempted suicide by self-inflicted burns represents <1% of burn admissions. This population demonstrates a high incidence of prior psychiatric disorders. Successful treatment includes multidisciplinary management of acute medical, surgical, and psychiatric care.

Transdermal deferoxamine prevents pressure-induced diabetic ulcers.

There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation.

Multiple Subsets of Brain Tumor Initiating Cells Coexist in Glioblastoma.

Brain tumor-initiating cells (BTICs) are self-renewing multipotent cells critical for tumor maintenance and growth. Using single-cell microfluidic profiling, we identified multiple subpopulations of BTICs coexisting in human glioblastoma, characterized by distinct surface marker expression and single-cell molecular profiles relating to divergent bulk tissue molecular subtypes. These data suggest BTIC subpopulation heterogeneity as an underlying source of intra-tumoral bulk tissue molecular heterogeneity, and will support future studies into BTIC subpopulation-specific therapies. Stem Cells 2016;34:1702-1707.

Ultrasound-assisted liposuction provides a source for functional adipose-derived stromal cells.

BACKGROUND AIMS: Regenerative medicine employs human mesenchymal stromal cells (MSCs) for their multi-lineage plasticity and their pro-regenerative cytokine secretome. Adipose-derived mesenchymal stromal cells (ASCs) are concentrated in fat tissue, and the ease of harvest via liposuction makes them a particularly interesting cell source. However, there are various liposuction methods, and few have been assessed regarding their impact on ASC functionality. Here we study the impact of the two most popular ultrasound-assisted liposuction (UAL) devices currently in clinical use, VASER (Solta Medical) and Lysonix 3000 (Mentor) on ASCs. METHODS: After lipoaspirate harvest and processing, we sorted for ASCs using fluorescent-assisted cell sorting based on an established surface marker profile (CD34+CD31-CD45-). ASC yield, viability, osteogenic and adipogenic differentiation capacity and in vivo regenerative performance were assessed. RESULTS: Both UAL samples demonstrated equivalent ASC yield and viability. VASER UAL ASCs showed higher osteogenic and adipogenic marker expression, but a comparable differentiation capacity was observed. Soft tissue healing and neovascularization were significantly enhanced via both UAL-derived ASCs in vivo, and there was no significant difference between the cell therapy groups. CONCLUSIONS: Taken together, our data suggest that UAL allows safe and efficient harvesting of the mesenchymal stromal cellular fraction of adipose tissue and that cells harvested via this approach are suitable for cell therapy and tissue engineering applications.

The Role of Focal Adhesion Kinase in Keratinocyte Fibrogenic Gene Expression.

Abnormal skin scarring causes functional impairment, psychological stress, and high socioeconomic cost. Evidence shows that altered mechanotransduction pathways have been linked to both inflammation and fibrosis, and that focal adhesion kinase (FAK) is a key mediator of these processes. We investigated the importance of keratinocyte FAK at the single cell level in key fibrogenic pathways critical for scar formation. Keratinocytes were isolated from wildtype and keratinocyte-specific FAK-deleted mice, cultured, and sorted into single cells. Keratinocytes were evaluated using a microfluidic-based platform for high-resolution transcriptional analysis. Partitive clustering, gene enrichment analysis, and network modeling were applied to characterize the significance of FAK on regulating keratinocyte subpopulations and fibrogenic pathways important for scar formation. Considerable transcriptional heterogeneity was observed within the keratinocyte populations. FAK-deleted keratinocytes demonstrated increased expression of genes integral to mechanotransduction and extracellular matrix production, including Igtbl, Mmpla, and Col4a1. Transcriptional activities upon FAK deletion were not identical across all single keratinocytes, resulting in higher frequency of a minor subpopulation characterized by a matrix-remodeling profile compared to wildtype keratinocyte population. The importance of keratinocyte FAK signaling gene expression was revealed. A minor subpopulation of keratinocytes characterized by a matrix-modulating profile may be a keratinocyte subset important for mechanotransduction and scar formation.

Suction assisted liposuction does not impair the regenerative potential of adipose derived stem cells.

BACKGROUND: Adipose-derived stem cells (ASCs) have been identified as a population of multipotent cells with promising applications in tissue engineering and regenerative medicine. ASCs are abundant in fat tissue, which can be safely harvested through the minimally invasive procedure of liposuction. However, there exist a variety of different harvesting methods, with unclear impact on ASC regenerative potential. The aim of this study was thus to compare the functionality of ASCs derived from the common technique of suction-assisted lipoaspiration (SAL) versus resection. METHODS: Human adipose tissue was obtained from paired abdominoplasty and SAL samples from three female donors, and was processed to isolate the stromal vascular fraction. Fluorescence-activated cell sorting was used to determine ASC yield, and cell viability was assayed. Adipogenic and osteogenic differentiation capacity were assessed in vitro using phenotypic staining and quantification of gene expression. Finally, ASCs were applied in an in vivo model of tissue repair to evaluate their regenerative potential. RESULTS: SAL specimens provided significantly fewer ASCs when compared to excised fat tissue, however, with equivalent viability. SAL-derived ASCs demonstrated greater expression of the adipogenic markers FABP-4 and LPL, although this did not result in a difference in adipogenic differentiation. There were no differences detected in osteogenic differentiation capacity as measured by alkaline phosphatase, mineralization or osteogenic gene expression. Both SAL- and resection-derived ASCs enhanced significantly cutaneous healing and vascularization in vivo, with no significant difference between the two groups. CONCLUSION: SAL provides viable ASCs with full capacity for multi-lineage differentiation and tissue regeneration, and is an effective method of obtaining ASCs for cell-based therapies.

Extracellular superoxide dismutase deficiency impairs wound healing in advanced age by reducing neovascularization and fibroblast function.

Advanced age is characterized by impairments in wound healing, and evidence is accumulating that this may be due in part to a concomitant increase in oxidative stress. Extended exposure to reactive oxygen species (ROS) is thought to lead to cellular dysfunction and organismal death via the destructive oxidation of intra-cellular proteins, lipids and nucleic acids. Extracellular superoxide dismutase (ecSOD/SOD3) is a prime antioxidant enzyme in the extracellular space that eliminates ROS. Here, we demonstrate that reduced SOD3 levels contribute to healing impairments in aged mice. These impairments include delayed wound closure, reduced neovascularization, impaired fibroblast proliferation and increased neutrophil recruitment. We further establish that SOD3 KO and aged fibroblasts both display reduced production of TGF-ß1, leading to decreased differentiation of fibroblasts into myofibroblasts. Taken together, these results suggest that wound healing impairments in ageing are associated with increased levels of ROS, decreased SOD3 expression and impaired extracellular oxidative stress regulation. Our results identify SOD3 as a possible target to correct age-related cellular dysfunction in wound healing.

Stem Cells in Wound Healing: The Future of Regenerative Medicine? A Mini-Review.

The increased risk of disease and decreased capacity to respond to tissue insult in the setting of aging results from complex changes in homeostatic mechanisms, including the regulation of oxidative stress and cellular heterogeneity. In aged skin, the healing capacity is markedly diminished resulting in a high risk for chronic wounds. Stem cell-based therapies have the potential to enhance cutaneous regeneration, largely through trophic and paracrine activity. Candidate cell populations for therapeutic application include adult mesenchymal stem cells, embryonic stem cells and induced pluripotent stem cells. Autologous cell-based approaches are ideal to minimize immune rejection but may be limited by the declining cellular function associated with aging. One strategy to overcome age-related impairments in various stem cell populations is to identify and enrich with functionally superior stem cell subsets via single cell transcriptomics. Another approach is to optimize cell delivery to the harsh environment of aged wounds via scaffold-based cell applications to enhance engraftment and paracrine activity of therapeutic stem cells. In this review, we shed light on challenges and recent advances surrounding stem cell therapies for wound healing and discuss limitations for their clinical adoption.

Injuries to appendage extremities and digit tips: A clinical and cellular update.

BACKGROUND: The regrowth of amputated appendage extremities and the distal tips of digits represent models of tissue regeneration in multiple vertebrate taxa. In humans, digit tip injuries, including traumatic amputation and crush injuries, are among the most common type of injury to the human hand. Despite clinical reports demonstrating natural regeneration of appendages in lower vertebrates and human digits, current treatment options are suboptimal, and are complicated by the anatomical complexities and functions of the different tissues within the digits. RESULTS: In light of these challenges, we focus on recent advancements in understanding appendage regeneration from model organisms. We pay special attention to the cellular programs underlying appendage regeneration, where cumulative data from salamanders, fish, frogs, and mice indicate that regeneration occurs by the actions of lineage-restricted precursors. We focus on pathologic states and the interdependency that exists, in both humans and animal models, between the nail organ and the peripheral nerves for successful regeneration. CONCLUSIONS: The increased understanding of regeneration in animal models may open new opportunities for basic and translational research aimed at understanding the mechanisms that support limb regeneration, as well as amelioration of limb abnormalities and pathologies.

Cell recruitment by amnion chorion grafts promotes neovascularization.

BACKGROUND: Nonhealing wounds are a significant health burden. Stem and progenitor cells can accelerate wound repair and regeneration. Human amniotic membrane has demonstrated efficacy in promoting wound healing, though the underlying mechanisms remain unknown. A dehydrated human amnion chorion membrane (dHACM) was tested for its ability to recruit hematopoietic progenitor cells to a surgically implanted graft in a murine model of cutaneous ischemia. METHODS: dHACM was subcutaneously implanted under elevated skin (ischemic stimulus) in either wild-type mice or mice surgically parabiosed to green fluorescent protein (GFP) + reporter mice. A control acellular dermal matrix, elevated skin without an implant, and normal unwounded skin were used as controls. Wound tissue was harvested and processed for histology and flow cytometric analysis. RESULTS: Implanted dHACMs recruited significantly more progenitor cells compared with controls (*P < 0.05) and displayed in vivo SDF-1 expression with incorporation of CD34 + progenitor cells within the matrix. Parabiosis modeling confirmed the circulatory origin of recruited cells, which coexpressed progenitor cell markers and were localized to foci of neovascularization within implanted matrices. CONCLUSIONS: In summary, dHACM effectively recruits circulating progenitor cells, likely because of stromal derived factor 1 (SDF-1) expression. The recruited cells express markers of "stemness" and localize to sites of neovascularization, providing a partial mechanism for the clinical efficacy of human amniotic membrane in the treatment of chronic wounds.