Early Fetal Healing as a Model for Adult Organ Regeneration

Dual gene-activated dermal scaffolds regulate angiogenesis and wound healing by mediating the coexpression of VEGF and angiopoietin-1

The vascularization of dermal substitutes is a key challenge in efforts to heal deep skin defects. In this study, dual gene-activated dermal scaffolds (DGADSs-1) were fabricated by loading nanocomposite particles of polyethylenimine (PEI)/multiple plasmid DNAs (pDNAs) encoding vascular endothelial growth factor and angiopoietin-1 at a ratio of 1:1. In a similar manner, DGADSs-2 were loaded with a chimeric plasmid encoding both VEGF and Ang-1. In vitro studies showed that both types of DGADSs released PEI/pDNA nanoparticles in a sustained manner; they demonstrated effective transfection ability, leading to upregulated expression of VEGF and Ang-1. Furthermore, both types of DGADSs promoted fibroblast proliferation and blood vessel formation, although DGADSs-1 showed a more obvious promotion effect. A rat full-thickness skin defect model showed that split-thickness skin transplanted using a one-step method could achieve full survival at the 12th day after surgery in both DGADSs-1 and DGADSs-2 groups, and the vascularization time of dermal substitutes was significantly shortened. Compared with the other three groups of scaffolds, the DGADSs-1 group had significantly greater cell infiltration, collagen deposition, neovascularization, and vascular maturation, all of which promoted wound healing. Thus, compared with single-gene-activated dermal scaffolds, DGADSs show greater potential for enhancing angiogenesis. DGADSs with different loading modes also exhibited differences in terms of angiogenesis; the effect of loading two genes (DGADSs-1) was better than the effect of loading a chimeric gene (DGADSs-2). In summary, DGADSs, which continuously upregulate VEGF and Ang-1 expression, offer a new functional tissue-engineered dermal substitute with the ability to activate vascularization.

Macrophages play a key role in tissue repair and regeneration

Tissue regeneration after body injury has always been a complex problem to resolve for mammals. In adult mammals, the repair process after tissue injury is often accompanied by continuous and extensive fibrosis, which leads to scars. This process has been shown to severely hinder regeneration. Macrophages, as widely distributed innate immune cells, not only play an important role in various pathological processes, but also participate in the repair process before tissue regeneration and coordinate the regeneration process after repair. This review will discuss the various forms and indispensability of macrophages involved in repair and regeneration, and how macrophages play a role in the repair and regeneration of different tissues.

Recapitulation of normal collagen architecture in embryonic wounded corneas

Wound healing is characterized by cell and extracellular matrix changes mediating cell migration, fibrosis, remodeling and regeneration. We previously demonstrated that chick fetal wound healing shows a regenerative phenotype regarding the cellular and molecular organization of the cornea. However, the chick corneal stromal structure is remarkably complex in the collagen fiber/lamellar organization, involving branching and anastomosing of collagen bundles. It is unknown whether the chick fetal wound healing is capable of recapitulating this developmentally regulated organization pattern. The purpose of this study was to examine the three-dimensional collagen architecture of wounded embryonic corneas, whilst identifying temporal and spatial changes in collagen organization during wound healing. Linear corneal wounds that traversed the epithelial layer, Bowman´s layer, and anterior stroma were generated in chick corneas on embryonic day 7. Irregular thin collagen fibers are present in the wounded cornea during the early phases of wound healing. As wound healing progresses, the collagen organization dramatically changes, acquiring an orthogonal arrangement. Fourier transform analysis affirmed this observation and revealed that adjacent collagen lamellae display an angular displacement progressing from the epithelium layer towards the endothelium. These data indicate that the collagen organization of the wounded embryonic cornea recapitulate the native macrostructure.

Design Considerations for Hydrogel Wound Dressings: Strategic and Molecular Advances

Wound dressings are traditionally used to protect a wound and to facilitate healing. Currently, their function is expanding. There is an urgent need for new smart products that not only act as a protective barrier but also actively support the wound healing process. Hydrogel dressings are an example of such innovative products and typically facilitate wound healing by providing a hospitable and moist environment in which cells can thrive, while the wound can still breathe and exudate can be drained. These dressings also tend to be less painful or have a soothing effect and allow for additional drug delivery. In this review, various strategic and molecular design considerations are discussed that are relevant for developing a hydrogel into a wound dressing product. These considerations vary from material choice to ease of use and determine the dressing's final properties, application potential, and benefits for the patient. The focus of this review lies on identifying and explaining key aspects of hydrogel wound dressings and their relevance in the different phases of wound repair. Molecular targets of wound healing are discussed that are relevant when tailoring hydrogels toward specific wound healing scenarios. In addition, the potential of hydrogels is reviewed as medicine advances from a repair-based wound healing approach toward a regenerative-based one. Hydrogels can play a key role in the transition toward personal wound care and facilitating regenerative medicine strategies by acting as a scaffold for (stem) cells and carrier/source of bioactive molecules and/or drugs. Impact statement Improved wound healing will lead to a better quality of life around the globe. It can be expected that this coincides with a reduction in health care spending, as the duration of treatment decreases. To achieve this, new and modern wound care products are desired that both facilitate healing and improve comfort and outcome for the patient. It is proposed that hydrogel wound dressings can play a pivotal role in improving wound care, and to that end, this review aims to summarize the various design considerations that can be made to optimize hydrogels for the purpose of a wound dressing.

In Vivo Type 2 Diabetes and Wound-Healing Effects of Antioxidant Gold Nanoparticles Synthesized Using the Insulin Plant Chamaecostus cuspidatus in Albino Rats

BACKGROUND

Gold nanoparticles are known for their many applications in the fields of therapeutics and diagnosis.

METHODS

This article focuses mainly on the green method of synthesizing gold nanoparticles by using the leaf powder extract of the insulin plant Chamaecostus cuspidatus and on the characterization of developed plant-mediated synthesis of gold nanoparticles. Furthermore, we investigated the free-radical scavenging activity of green-synthesized gold nanoparticles.

RESULTS

The free radicals were exhibited in a dose-dependent manner. The 50% inhibition of free radicals by gold nanoparticles showed that it was similar to that of the standard inhibition. Toxicity studies generally examine changes in blood serum chemistry and cell populations in tissue morphology through histologic analysis without inducing any lethal effects in the mouse model, thereby accomplishing sustained control over the progression of diabetes mellitus, which plays a leading role in vascular complications in patients. The treatment by gold nanoparticles of the mice with diabetes for a period of 21 days restored their blood glucose, glycogen and insulin levels.

CONCLUSIONS

The use of gold nanoparticles as antidiabetes materials has been achieved. Further studies are required before gold nanoparticle-based drugs are more widely used.

A gene-activating skin substitute comprising PLLA/POSS nanofibers and plasmid DNA encoding ANG and bFGF promotes in vivo revascularization and epidermalization

A gene-activated porous nanofibrous scaffold for effectively promoting vascularization, epidermalization and dermal wound healing by sustained release of dual plasmid DNAs.

Decellularized scaffolds containing hyaluronic acid and EGF for promoting the recovery of skin wounds

There is no effective therapy for the treatment of deep and large area skin wounds. Decellularized scaffolds can be prepared from animal tissues and represent a promising biomaterial for investigation in tissue regeneration studies. In this study, MTT assay showed that epidermal growth factor (EGF) increased NIH3T3 cell proliferation in a bell-shaped dose response, and the maximum cell proliferation was achieved at a concentration of 25 ng/ml. Decellularized scaffolds were prepared from pig peritoneum by a series of physical and chemical treatments. Hyaluronic acid (HA) increased EGF adsorption to the scaffolds. Decellularized scaffolds containing HA sustained the release of EGF compared to no HA. Rabbits contain relatively large skin surface and are less expensive and easy to be taken care, so that a rabbit wound healing model was use in this study. Four full-thickness skin wounds were created in each rabbit for evaluation of the effects of the scaffolds on the skin regeneration. Wounds covered with scaffolds containing either 1 or 3 μg/ml EGF were significantly smaller than with vaseline oil gauzes or with scaffolds alone, and the wounds covered with scaffolds containing 1 μg/ml EGF recovered best among all four wounds. Hematoxylin-Eosin staining confirmed these results by demonstrating that significantly thicker dermis layers were also observed in the wounds covered by the decellularized scaffolds containing HA and either 1 or 3 μg/ml EGF than with vaseline oil gauzes or with scaffolds alone. In addition, the scaffolds containing HA and 1 μg/ml EGF gave thicker dermis layers than HA and 3 μg/ml EGF and showed the regeneration of skin appendages on day 28 post-transplantation. These results demonstrated that decellularized scaffolds containing HA and EGF could provide a promising way for the treatment of human skin injuries.

Acceleration of wound healing in acute full-thickness skin wounds using a collagen-binding peptide with an affinity for MSCs

Mesenchymal stem cells (MSCs) have been accepted as a promising cell source in tissue repair and regeneration. However, the inability to enrich MSCs in target areas limits their wide application. As a result, it has been a major goal to induce MSCs to be abundantly and specifically recruited to the injury site. In this study, a peptide with a specific affinity for MSCs (E7 peptide) was immobilized to a collagen scaffold via a collagen-binding domain (CBD) to construct a functional collagen scaffold. In addition, the hypothesis that this method could recruit MSCs specifically was evaluated in a porcine model. In vivo investigations indicated that due to the immunore-action, the CBD-MSC-peptide collagen scaffold enhanced MSC adhesion and infiltration and promoted wound healing. At day 7 after surgery, we found more infiltrating cells and capillaries in the Collagen/CBD-E7 peptide group compared to the Scaffold group. At day 14, 21 and 28, a faster healing process was observed in the Collagen/CBD-E7 peptide group, with significant differences compared with the other groups (P < 0.05, P < 0.01). The results demonstrate the potential use of targeted therapy to rapidly heal skin wounds.

Mechanical offloading of incisional wounds is associated with transcriptional downregulation of inflammatory pathways in a large animal model

Cutaneous scarring is a major source of morbidity and current therapies to mitigate scar formation remain ineffective. Although wound fibrosis and inflammation are highly linked, only recently have mechanical forces been implicated in these pathways. Our group has developed a topical polymer device that significantly reduces post-injury scar formation via the manipulation of mechanical forces. Here we extend these studies to examine the genomewide transcriptional effects of mechanomodulation during scar formation using a validated large animal model, the red Duroc pig. We demonstrate that mechanical loading of incisional wounds upregulates expression of genes associated with inflammatory and fibrotic pathways, and that device-mediated offloading of these wounds reverses these effects. Validation studies are needed to clarify the clinical significance of these findings.

Wounded embryonic corneas exhibit nonfibrotic regeneration and complete innervation

PURPOSE

Wound healing in adult corneas is characterized by activation of keratocytes and extracellular matrix (ECM) synthesis that results in fibrotic scar formation and loss of transparency. Since most fetal wounds heal without scaring, we investigated the regenerative potential of wounded embryonic corneas.

METHODS

On embryonic day (E) 7 chick corneas were wounded by making a linear incision traversing the epithelium and anterior stroma. Wounded corneas were collected between E7 and E18, and analyzed for apoptosis, cell proliferation, staining of ECM components, and corneal innervation.

RESULTS

Substantial wound retraction was observed within 16-hours postwounding (hpw) and partial re-epithelialized by 5-days postwounding (dpw). Corneal wounds were fully re-epithelialized by 11 dpw with no visible scars. There was no difference in the number of cells undergoing apoptosis between wounded and control corneas. Cell proliferation was reduced in the wounded corneas, albeit mitotic cells in the regenerating epithelium. Staining for alpha-smooth muscle actin (α-SMA), tenascin, and fibronectin was vivid but transient at the wound site. Staining for procollagen I, perlecan, and keratan sulfate proteoglycan was reduced at the wound site. Wounded corneas were fully regenerated by 11 dpw and showed similar patterns of staining for ECM components, albeit an increase in perlecan staining. Corneal innervation was inhibited during wound healing, but regenerated corneas were innervated similar to controls.

CONCLUSIONS

These data show that minimal keratocyte activation, rapid ECM reconstruction, and proper innervation occur during nonfibrotic regeneration of the embryonic cornea.

Proteoglycans of uterine fibroids and keloid scars: similarity in their proteoglycan composition

Fibrosis is the formation of excess and abnormal fibrous connective tissue as a result of either a reparative or reactive process. A defining feature of connective tissue is its extracellular matrix, which provides structural support and also influences cellular activity. Two common human conditions that result from fibrosis are uterine fibroids (leiomyomas) and keloid scars. Because these conditions share a number of similarities and because their growth is due primarily to excessive extracellular matrix deposition, we compared the proteoglycans of uterine fibroids and keloid scars with corresponding normal tissues. Our analysis indicates that uterine fibroids and keloid scars contain higher amounts of glycosaminoglycans relative to normal myometrium and normal adult skin respectively. Proteoglycan composition is also different in the fibrotic tissues. Compared with unaffected tissues, uterine fibroids and keloid scars contain higher relative amounts of versican and lower relative amounts of decorin. There is also evidence for a higher level of versican catabolism in the fibrotic tissues compared with unaffected tissues. These qualitative and quantitative proteoglycan differences may play a role in the expansion of these fibroses and in their excessive matrix deposition and matrix disorganization, due to effects on cell proliferation, TGF (transforming growth factor)-β signalling and/or collagen fibril formation.

Effects of nanofiber/stem cell composite on wound healing in acute full-thickness skin wounds

Acute full-thickness skin wounds (FTSW) caused by extensive burns or high-energy trauma are not adequately addressed by current clinical treatments. This study hypothesized that biomimetic nanofiber scaffolds (NFSs) functionalized with rich attachment of bone-marrow-derived mesenchymal stem cells (BM-MSCs) can promote wound healing in acute FTSW. Results in a rat model showed that both NFS and BM-MSCs contributed to the wound healing. Wounds in NFS group with a higher density of BM-MSCs achieved complete closure 8 days earlier than the control group. Implanted BM-MSCs were found to promote epithelial edge ingrowth and collagen synthesis. The colocation of BM-MSCs (tagged with quantum-dots) with the expression of keratin 10 and filaggrin indicated the participation of BM-MSCs in epidermal differentiation at early and intermediate stages under the local wounding environment. Overall, this study suggests a great potential of using NFS/BM-MSC composites for the treatment of acute FTSW.

Scarless healing of oral mucosa is characterized by faster resolution of inflammation and control of myofibroblast action compared to skin wounds in the red Duroc pig model

BACKGROUND

Scar formation following skin trauma can have devastating consequences causing physiological and psychosocial concerns. Currently, there are no accepted predictable treatments to prevent scarring which emphasizes a need for a better understanding of the wound healing and scar formation process.

OBJECTIVES

Previously it was shown that healing of small experimental wounds in the oral mucosa of red Duroc pigs results in significantly reduced scar formation as compared with equivalent full-thickness skin wounds. In the present study, scar formation was assessed in 17 times larger experimental wounds in both oral mucosa and skin of the red Duroc pigs.

METHODS

Equivalent experimental wounds were created in the oral mucosa and dorsal skin of red Duroc pigs, and scar formation, localization and abundance of key wound healing cells, transforming growth factor-beta (TGF-beta) and phosphorylated Smad3 (pSmad3) were assessed.

RESULTS

Oral mucosal wounds displayed significantly less clinical and histological scar formation than did the corresponding skin wounds. The number of macrophages, mast cells, TGF-beta and pSmad3 immunopositive cells was significantly reduced in the oral mucosal wounds as compared with skin wounds during the maturation stage of the healing process. Although the number of myofibroblasts was significantly elevated, the oral mucosal wounds showed significantly less contraction than did the skin wounds over time.

CONCLUSIONS

Earlier resolution of the inflammatory reaction and reduced wound contraction may promote scarless oral mucosal wound healing. In addition, scar formation likely depends not only on the number of myofibroblasts but also on the extracellular environment which regulates their function.

Using hair-follicle stem cells for urinary bladder-wall regeneration

There are many diseases in which autologous urothelial and muscle cells cannot be used for in vitro construction of the urinary bladder wall for augmentation (cystoplasty). These diseases are the most frequent indications for bladder augmentation. The present paper focuses on the idea of harvesting potentially multipotent stem cells out of hair follicles in order to use them for regeneration of the urinary bladder wall. Current clinical practice suggests the use of cultures enriched with progenitors. The hair follicle stem cell niche gives an opportunity to reduce the invasiveness of harvesting these cells. Both epithelial and dermal multipotent stem cells populations within hair follicles raise new possibilities for tissue engineering of the urinary bladder. The hypothesis is that hair-follicle stem cells can be used, with the guarantee of the sufficient cell number, for a construction in vitro of the urinary bladder wall replacement.

Memory encoded throughout our bodies: molecular and cellular basis of tissue regeneration

When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field. When a sheep loses its tail, it cannot regenerate it in the manner of lizards. On the other hand, it is possible to clone mammals from somatic cells, showing that a complete developmental program is intact in a wounded sheep's tail the same way it is in a lizard. Thus, there is a requirement for more than only the presence of the entire genetic code in somatic cells for regenerative abilities. Thoughts like this have motivated us to assemble more than just a factographic synopsis on tissue regeneration. As a model, we review skin wound healing in chronological order, and when possible, we use that overview as a framework to point out possible mechanisms of how damaged tissues can restore their original structure. This article postulates the existence of tissue structural memory as a complex distributed homeostatic mechanism. We support such an idea by referring to an extremely fragmented literature base, trying to synthesize a broad picture of important principles of how tissues and organs may store information about their own structure for the purposes of regeneration. Selected developmental, surgical, and tissue engineering aspects are presented and discussed in the light of recent findings in the field.

Novel therapies for scar reduction and regenerative healing of skin wounds

Fibrotic scars deposited during skin wound healing can cause disfiguration and loss of dermal function. Scar differentiation involves inputs from multiple cell types in a predictable and overlapping sequence of cellular events that includes inflammation, migration/proliferation and extracellular matrix deposition. Research into the molecular mechanisms underpinning these processes in embryonic and adult wounds has contributed to the development of a growing number of novel therapeutic approaches for improving scar appearance. This review discusses some of these emerging strategies for shifting the balance of healing from scarring to regeneration in the context of non-pathological wounds. Particular focus is given to potential therapies based on transforming growth factor (TGF)-beta signaling and recent unexpected findings involving targeting of gap junctional connexins. Lessons learned in promoting scarless healing of cutaneous injuries might provide a basis for regenerative healing in other scenarios, such as spinal cord rupture or myocardial infarction.