The Mobilization and Effect of Endogenous Bone Marrow Progenitor Cells in Diabetic Wound Healing

Adipose stem cells-derived small extracellular vesicles transport Thrombospondin 1 cargo to promote insulin resistance in gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus (GDM) is a highly prevalent disease and poses a significant risk to the health of pregnant women. Abdominal adipose tissue (AT) contributes to insulin resistance (IR) associated with GDM. However, the underlying mechanisms remain unclear.

METHODS

In this study, we developed a mouse model of GDM by subjecting mice to a high-fat diet. We collected adipose-derived stem cells (ADSCs) from the abdominal and inguinal regions and examined their role in inducing IR in normal tissues through the secretion of small extracellular vesicles (sEVs). The sEVs derived from ADSCs isolated from GDM mice (ADSC/GDM) were found to inhibit cell viability and insulin sensitivity in AML12, a normal mouse liver cell line.

RESULTS

Through proteomic analysis, we identified high levels of the thrombospondin 1 (Thbs1) protein in the sEVs derived from ADSC/GDM. Subsequent overexpression of Thbs1 protein in AML12 cells demonstrated similar IR as observed with ADSC/GDM-derived sEVs. Mechanistically, the Thbs1 protein within the sEVs interacted with CD36 and transforming growth factor (Tgf) β receptors in AML12 cells, leading to the activation of Tgfβ/Smad2 signaling. Furthermore, the administration of LSKL, an antagonistic peptide targeting Thbs1, suppressed Thbs1 expression in ADSC/GDM-derived sEVs, thereby restoring insulin sensitivity in AML12 cells and GDM mice in vivo.

CONCLUSIONS

These findings shed light on the intercellular transmission mechanism through which ADSCs influence hepatic insulin sensitivity and underscore the therapeutic potential of targeting the Thbs1 protein within sEVs.

Adhesive, injectable, and ROS-responsive hybrid polyvinyl alcohol (PVA) hydrogel co-delivers metformin and fibroblast growth factor 21 (FGF21) for enhanced diabetic wound repair

As conventional treatments for diabetic wounds often fail to achieve rapid satisfactory healing, the development of effective strategies to accelerate diabetic wound repair is highly demanded. Herein, fibroblast growth factor 21 (FGF21) and metformin co-loaded multifunctional polyvinyl alcohol (PVA) hydrogel were fabricated for improved diabetic wound healing. The in vitro results proved that the hydrogel was adhesive and injectable, and that it could particularly scavenge reactive oxygen species (ROSs), while the in vivo data demonstrated that the hydrogel could promote angiogenesis by recruiting endothelial progenitor cells (EPCs) through upregulation of Ang-1. Both ROSs’ removal and EPCs’ recruitment finally resulted in enhanced diabetic wound healing. This work opens a strategy approach to diabetic wound management by combining biological macromolecules and small chemical molecules together using one promising environmental modulating drug delivery system.

Wound Healing Impairment in Type 2 Diabetes Model of Leptin-Deficient Mice—A Mechanistic Systematic Review

Type II diabetes mellitus (T2DM) is one of the most prevalent diseases in the world, associated with diabetic foot ulcers and impaired wound healing. There is an ongoing need for interventions effective in treating these two problems. Pre-clinical studies in this field rely on adequate animal models. However, producing such a model is near-impossible given the complex and multifactorial pathogenesis of T2DM. A leptin-deficient murine model was developed in 1959 and relies on either dysfunctional leptin (ob/ob) or a leptin receptor (db/db). Though monogenic, this model has been used in hundreds of studies, including diabetic wound healing research. In this study, we systematically summarize data from over one hundred studies, which described the mechanisms underlying wound healing impairment in this model. We briefly review the wound healing dynamics, growth factors’ dysregulation, angiogenesis, inflammation, the function of leptin and insulin, the role of advanced glycation end-products, extracellular matrix abnormalities, stem cells’ dysregulation, and the role of non-coding RNAs. Some studies investigated novel chronic diabetes wound models, based on a leptin-deficient murine model, which was also described. We also discussed the interventions studied in vivo, which passed into human clinical trials. It is our hope that this review will help plan future research.

Protective Effects of Engineered Lactobacillus crispatus on Intrauterine Adhesions in Mice via Delivering CXCL12

Endometrial injury is the main cause of intrauterine adhesions (IUA), and there is currently no effective prevention and treatment. Immune cells play an important role in damage repair by sensing the change in the microenvironment. Exogenous CXCL12 can promote tissue regeneration and repair by recruiting immune cells, but its effect and possible mechanism on endometrial regeneration and repair have not been reported. In the present study, we constructed an engineered a Lactobacillus crispatus strain by transforming a pMG36e plasmid carrying a CXCL12 gene into the bacterium, and developed two animal models, the intrauterine adhesion mice with or without diabetes to evaluate the positive effects of this strain on the prevention of IUA after accepting intrauterine surgery in normal and diabetic mice. The results showed that vaginal application of L. crispatus-pMG36e-mCXCL12 strains significantly diminished the levels of pro-inflammatory factors interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α) in serum and uterine tissues of IUA mice, and resulted in the inhibition of the inflammatory (toll-like receptor 4/nuclear factor-κb, TLR4/NF-κB) and fibrotic (transforming growth factor-β1/smads, TGF-β1/Smads) signalling pathways in the uterine tissues. The high-throughput sequencing results further indicated that treatment with L. crispatus-pMG36e-mCXCL12 strains greatly increased the abundance of Lactobacillus spp. and reduced that of the pathogenic Klebsiella spp. in IUA mice. Furthermore, among intrauterine adhesion mice with diabetes, we obtained similar results to non-diabetic mice, that is, L.crispatus-pMG36e-mCXCL12 significantly improved fibrosis and inflammation in the uterine cavity of diabetic mice, and restored the vaginal microbiota balance in diabetic mice. Therefore, we speculated that vaginal administration of L. crispatus-pMG36e-mCXCL12 strains can effectively alleviate intrauterine adhesions by restoring the microbial balance and reducing inflammation and fibrosis caused by surgery.

Pharmacologic targeting of the diabetic stem cell mobilopathy

Diabetes is a chronic metabolic disease characterized by hyperglycemia and several associated biochemical abnormalities. Diabetes leads to multiorgan complications that collectively reduce life expectancy. Hematopoietic stem cells (HSCs) are nested within bone marrow (BM) niches whence they can be mobilized to the peripheral circulation. Clinically, this is done for HSC collection and autologous or allogenic transplantation. A great amount of data from basic and clinical studies support that diabetic patients are poor HSC mobilizers owing to BM remodeling. Dysfunction of the BM shares pathophysiological features and pathways with typical chronic diabetic complications that affect other issues (e.g. the retina and the kidney). From a clinical perspective, impaired HSC mobilization translates into the failure to collect a minimum number of CD34⁺ cells to achieve a safe engraftment after transplantation. Furthermore, blunted mobilization is associated with reduced steady-state levels of circulating HSCs, which have been consistently described in diabetic patients and associated with increased risk of adverse outcomes, including cardiovascular events and death. In this review, we discuss the most clinically relevant pharmacological options to overcome impaired HSC mobilization in diabetes. These therapeutic strategies may result in an improved outcome of diabetic patients undergoing HSC transplantation and restore circulating HSC levels, thereby protecting from adverse cardiovascular outcomes.

Isolation and Characterisation of Mesenchymal Stem Cells from Rat Bone Marrow and the Endosteal Niche: A Comparative Study

Within bone, mesenchymal stromal cells (MSCs) exist within the bone marrow stroma (BM-MSC) and the endosteal niche, as cells lining compact bone (CB-MSCs). This study isolated and characterised heterogeneous MSC populations from each niche and subsequently investigated the effects of extensive cell expansion, analysing population doublings (PDs)/cellular senescence, colony-forming efficiencies (CFEs), MSC cell marker expression, and osteogenic/adipogenic differentiation. CB-MSCs and BM-MSCs demonstrated similar morphologies and PDs, reaching 100 PDs. Both populations exhibited consistent telomere lengths (12-17 kb), minimal senescence, and positive telomerase expression. CB-MSCs (PD15) had significantly lower CFEs than PD50. CB-MSCs and BM-MSCs both expressed MSC (CD73/CD90/CD105); embryonic (Nanog) and osteogenic markers (Runx2, osteocalcin) but no hematopoietic markers (CD45). CB-MSCs (PD15) strongly expressed Oct4 and p16INK4A. At early PDs, CB-MSCs possessed a strong osteogenic potency and low potency for adipogenesis, whilst BM-MSCs possessed greater overall bipotentiality for osteogenesis and adipogenesis. At PD50, CB-MSCs demonstrated reduced potency for both osteogenesis and adipogenesis, compared to BM-MSCs at equivalent PDs. This study demonstrates similarities in proliferative and mesenchymal cell characteristics between CB-MSCs and BM-MSCs, but contrasting multipotentiality. Such findings support further comparisons of human CB-MSCs and BM-MSCs, facilitating selection of optimal MSC populations for regenerative medicine purposes.

Glycoprotein Nonmelanoma Clone B Regulates the Crosstalk between Macrophages and Mesenchymal Stem Cells toward Wound Repair

The process of wound repair requires the coordinated participation of multiple types of cells, which are sequentially recruited during the healing process. In response to tissue injury, both macrophages and mesenchymal stem cells (MSCs) are recruited to the site of injury, where they participate in the repair process. Despite considerable understanding of the role of each cell type in the process of wound repair, the nature of the dynamic interplay between these two cell types and how this interaction influences the process of wound repair are not well understood. Here, using an in vivo model of cutaneous wound healing in mice, we provide evidence that GPNMB is functionally important in promoting the recruitment of MSCs to the site of skin injury, which in turn modulates inflammatory responses by directing the M2 polarization of macrophages in acute wound healing. Furthermore, we show that GPNMB activity is impaired in a diabetic wound environment, which is associated with impaired MSC recruitment that is reversed by the topical administration of recombinant GPNMB protein to the wounds of diabetic mice. Our study provides important insight into the crosstalk between macrophages and endogenous MSCs toward wound repair.

Diabetes and Wound Angiogenesis

Diabetes Mellitus Type II (DM2) is a growing international health concern with no end in sight. Complications of DM2 involve a myriad of comorbidities including the serious complications of poor wound healing, chronic ulceration, and resultant limb amputation. In skin wound healing, which has definite, orderly phases, diabetes leads to improper function at all stages. While the etiology of chronic, non-healing diabetic wounds is multi-faceted, the progression to a non-healing phenotype is closely linked to poor vascular networks. This review focuses on diabetic wound healing, paying special attention to the aberrations that have been described in the proliferative, remodeling, and maturation phases of wound angiogenesis. Additionally, this review considers therapeutics that may offer promise to better wound healing outcomes.

The role of bone marrow mesenchymal stromal cell derivatives in skin wound healing in diabetic mice

Mesenchymal stromal cells (MSCs) have shown to be a promising tool in cell therapies to treat different conditions. Several pre-clinical and clinical studies have proved that the transplantation of MSCs improves wound healing. Here, we compare the beneficial effects of mouse bone marrow-derived allogeneic MSCs (allo-mBM-MSCs) and their acelullar derivatives (allo-acd-mMSCs) on skin wound healing in Non-Obese Diabetic (NOD) mice. One dose of allo-mBM-MSCs (1×106 cells) or one dose of allo-acd-mMSCs (1X) were intradermally injected around wounds in 8-10 week old female NOD mice. Wound healing was evaluated macroscopically (wound closure) every two days, and microscopically (reepithelialization, dermoepidermal junction, skin appendage regeneration, leukocyte infiltration, vascularization, granulation tissue formation, and density of collagen fibers in the dermis) after 16 days of MSC injection. In addition, we measured growth factors and specific proteins that were present in the allo-acd-mMSCs. Results showed significant differences in the wound healing kinetics of lesions that received allo-acd-mMSCs compared to lesions that received vehicle or allo-mBM-MSCs. In particular, mice treated with allo-acd-mMSCs reached significantly higher percentages of wound closure at day 4, 6 and 8, relative to the allo-mBM-MSCs and vehicle groups (p < 0.05), while wound closure percentages could not be statistically distinguished between the allo-mBM-MSCs and vehicle groups. Also, allo-acd-mMSCs had a greater influence in the skin would healing process. Specifically, they caused a less pronounced inflammatory severe response (p < 0.0001), more granulation tissue formation at an advanced stage (p < 0.0001), and higher density of collagen fibers (p < 0.05) compared to the other groups. Nevertheless, at day 16, both allo-mBM-MSCs and allo-acd-mMSCs revealed a higher effect on the recovery of the quality skin (continuous epidermis; regular dermoepidermal junction and skin appendages) relative to untreated lesions (p < 0.0001), but not between them. On the other hand, ELISA analyses indicated that the allo-acd-mMSCs contained growth factors and proteins relevant to wound healing such as IGF-1, KGF, HGF, VEGF, ANG-2, MMP-1, CoL-1 and PGE2. Compared to allo-acd-mMSCs, the administration of allo-mBM-MSCs is insufficient for wound healing in diabetic mice and delays the therapeutic effect, which maybe explained by the fact that trophic factors secreted by MSCs are critical for skin regeneration, and not the cells per se, suggesting that MSCs may require some time to secrete these factors after their administration.

Comparison of In-Vitro and Ex-Vivo Wound Healing Assays for the Investigation of Diabetic Wound Healing and Demonstration of a Beneficial Effect of a Triterpene Extract

Diabetes mellitus is a frequent cause for chronic, difficult-to-treat wounds. New therapies for diabetic wounds are urgently needed and in-vitro or ex-vivo test systems are essential for the initial identification of new active molecules. The aim of this study is to compare in-vitro and ex-vivo test systems for their usability for early drug screening and to investigate the efficacy of a birch bark triterpene extract (TE) that has been proven ex-vivo and clinically to accelerate non-diabetic wound healing (WH), in a diabetic context. We investigated in-vitro models for diabetic WH, i.e. scratch assays with human keratinocytes from diabetic donors or cultured under hyperglycaemic conditions and a newly developed porcine ex-vivo hyperglycaemic WH model for their potential to mimic delayed diabetic WH and for the influence of TE in these test systems. We show that keratinocytes from diabetic donors often fail to exhibit significantly delayed WH. For cells under hyperglycaemic conditions significant decrease is observed but is influenced by choice of medium and presence of supplements. Also, donor age plays a role. Interestingly, hyperglycaemic effects are mainly hyperosmolaric effects in scratch assays. Ex-vivo models under hyperglycaemic conditions show a clear and substantial decrease of WH, and here both glucose and hyperosmolarity effects are involved. Finally, we provide evidence that TE is also beneficial for ex-vivo hyperglycaemic WH, resulting in significantly increased length of regenerated epidermis to 188±16% and 183±11% (SEM; p<0.05) compared to controls when using two different TE formulations. In conclusion, our results suggest that microenvironmental influences are important in WH test systems and that therefore the more complex hyperglycaemic ex-vivo model is more suitable for early drug screening. Limitations of the in-vitro and ex-vivo models are discussed. Furthermore our data recommend TE as a promising candidate for in-vivo testings in diabetic wounds.

Hyaluronic acid-laminin hydrogels increase neural stem cell transplant retention and migratory response to SDF-1α

The chemokine SDF-1α plays a critical role in mediating stem cell response to injury and disease and has specifically been shown to mobilize neural progenitor/stem cells (NPSCs) towards sites of neural injury. Current neural transplant paradigms within the brain suffer from low rates of retention and engraftment after injury. Therefore, increasing transplant sensitivity to injury-induced SDF-1α represents a method for increasing neural transplant efficacy. Previously, we have reported on a hyaluronic acid-laminin based hydrogel (HA-Lm gel) that increases NPSC expression of SDF-1α receptor, CXCR4, and subsequently, NPSC chemotactic migration towards a source of SDF-1α in vitro. The study presented here investigates the capacity of the HA-Lm gel to promote NPSC response to exogenous SDF-1α in vivo. We observed the HA-Lm gel to significantly increase NPSC transplant retention and migration in response to SDF-1α in a manner critically dependent on signaling via the SDF-1α-CXCR4 axis. This work lays the foundation for development of a more effective cell therapy for neural injury, but also has broader implications in the fields of tissue engineering and regenerative medicine given the essential roles of SDF-1α across injury and disease states.

Concise Review: Perspectives and Clinical Implications of Bone Marrow and Circulating Stem Cell Defects in Diabetes

Diabetes mellitus is a complex systemic disease characterized by severe morbidity and excess mortality. The burden of its multiorgan complications relies on an imbalance between hyperglycemic cell damage and defective endogenous reparative mechanisms. Inflammation and abnormalities in several hematopoietic components are typically found in diabetes. The discovery that diabetes reduces circulating stem/progenitor cells and impairs their function has opened an entire new field of study where diabetology comes into contact with hematology and regenerative medicine. It is being progressively recognized that such rare circulating cell populations mirror finely regulated processes involved in hematopoiesis, immunosurveillance, and peripheral tissue homeostasis. From a clinical perspective, pauperization of circulating stem cells predicts adverse outcomes and death. Furthermore, studies in murine models and humans have identified the bone marrow (BM) as a previously neglected site of diabetic end-organ damage, characterized by microangiopathy, neuropathy, fat deposition, and inflammation. As a result, diabetes impairs the mobilization of BM stem/progenitor cells, a defect known as mobilopathy or myelokathexis, with negative consequences for physiologic hematopoiesis, immune regulation, and tissue regeneration. A better understanding of the molecular and cellular processes that govern the BM stem cell niche, cell mobilization, and kinetics in peripheral tissues may uncover new therapeutic strategies for patients with diabetes. This concise review summarizes the current knowledge on the interplay between the BM, circulating stem cells, and diabetes, and sets the stages for future developments in the field. Stem Cells 2017;35:106-116.

Cell recruiting chemokine-loaded sprayable gelatin hydrogel dressings for diabetic wound healing

In this study, we developed horseradish peroxidase (HRP)-catalyzed sprayable gelatin hydrogels (GH) as a bioactive wound dressing that can deliver cell-attracting chemotactic cytokines to the injured tissues for diabetic wound healing. We hypothesized that topical administration of chemokines using GH hydrogels might improve wound healing by inducing recruitment of the endogenous cells. Two types of chemokines (interleukin-8; IL-8, macrophage inflammatory protein-3α; MIP-3α) were simply loaded into GH hydrogels during in situ cross-linking, and then their wound-healing effects were evaluated in streptozotocin-induced diabetic mice. The incorporation of chemokines did not affect hydrogels properties including swelling ratio and mechanical stiffness, and the bioactivities of IL-8 and MIP-3α released from hydrogel matrices were stably maintained. In vivo transplantation of chemokine-loaded GH hydrogels facilitated cell infiltration into the wound area, and promoted wound healing with enhanced re-epithelialization/neovascularization and increased collagen deposition, compared with no treatment or the GH hydrogel alone. Based on our results, we suggest that cell-recruiting chemokine-loaded GH hydrogel dressing can serve as a delivery platform of various therapeutic proteins for wound healing applications.

STATEMENT OF SIGNIFICANCE

Despite development of materials combined with therapeutic agents for diabetic wound treatment, impaired wound healing by insufficient chemotactic responses still remain as a significant problem. In this study, we have developed enzyme-catalyzed gelatin (GH) hydrogels as a sprayable dressing material that can deliver cell-attracting chemokines for diabetic wound healing. The chemotactic cytokines (IL-8 and MIP-3α) were simply loaded within hydrogel during in situ gelling, and wound healing efficacy of chemokine-loaded GH hydrogels was investigated in STZ-induced diabetic mouse model. These hydrogels significantly promoted wound-healing efficacy with faster wound closure, neovascularization, and thicker granulation. Therefore, we expect that HRP-catalyzed in situ forming GH hydrogels can serve as an injectable/sprayable carrier of various therapeutic agents for wound healing applications.

Plerixafor improves the endothelial health balance. The effect of diabetes analysed by polychromatic flow cytometry

BACKGROUND AND AIMS

Diabetes damages the endothelium and reduces the availability of bone marrow (BM)-derived endothelial progenitor cells (EPCs). The mobilization of hematopoietic stem cells (HSCs) and EPCs in response to G-CSF is impaired by diabetes, owing to CXCL12 dysregulation. We have previously shown that the CXCR4/CXCL12 disruptor plerixafor rescues HSC and EPC mobilization in diabetes. We herein explored the effects of plerixafor on HSCs, EPCs, and circulating endothelial cells (CECs) in patients with and without diabetes.

METHODS

We re-analysed data gathered in the NCT02056210 trial, wherein patients with (n = 10) and without diabetes (n = 10) received plerixafor to test stem/progenitor cell mobilization. We applied a novel and very specific polychromatic flow cytometry (PFC) approach to identify and quantify HSCs, EPCs, and CECs.

RESULTS

We found that 7-AAD(-)Syto16(+)CD34(+)CD45(dim) HSC levels determined by PFC strongly correlated to the traditional enumeration of CD34(+) cells, whereas 7-AAD(-)Syto16(+)CD34(+)CD45(neg)KDR(+) EPCs were unrelated to the traditional enumeration of CD34(+)KDR(+) cells. Using PFC, we confirmed that plerixafor induces rapid mobilization of HSCs and EPCs in both groups, with a marginally significant defect in patients with diabetes. Plerixafor reduced live (7-AAD(-)) and dead (7-AAD(+)) Syto16(+)CD34(bright)CD45(neg)CD146(+) CECs more in patients without than in those with diabetes. The EPC/CEC ratio, a measure of the vascular health balance, was increased by plerixafor, but less prominently in patients with that in those without diabetes.

CONCLUSIONS

In addition to rescuing defective mobilization associated with diabetes, plerixafor improves the balance between EPCs and CECs, but the latter effect is blunted in patients with diabetes.

The use of hematopoietic stem cells in autoimmune diseases

Hematopoietic stem cells (HSCs) have been shown recently to hold much promise in curing autoimmune diseases. Newly diagnosed Type 1 diabetes individuals have been successfully reverted to normoglycemia by administration of autologous HSCs in association with a nonmyeloablative regimen (antithymocyte globulin + cyclophasmide). Furthermore, recent trials reported positive results by using HSCs in treatment of systemic sclerosis, multiple sclerosis and rheumatoid arthritis as well. Early data suggested that HSCs possess immunological properties that may be harnessed to alleviate the symptoms of individuals with autoimmune disorders and possibly induce remission of autoimmune diseases. Mechanistically, HSCs may facilitate the generation of regulatory T cells, may inhibit the function of autoreactive T-cell function and may reshape the immune system.

Substance P combined with epidermal stem cells promotes wound healing and nerve regeneration in diabetes mellitus

Exogenous substance P accelerates wound healing in diabetes, but the mechanism remains poorly understood. Here, we established a rat model by intraperitoneally injecting streptozotocin. Four wounds (1.8 cm diameter) were drilled using a self-made punch onto the back, bilateral to the vertebral column, and then treated using amniotic membrane with epidermal stem cells and/or substance P around and in the middle of the wounds. With the combined treatment the wound-healing rate was 100% at 14 days. With prolonged time, type I collagen content gradually increased, yet type III collagen content gradually diminished. Abundant protein gene product 9.5- and substance P-immunoreactive nerve fibers regenerated. Partial nerve fiber endings extended to the epidermis. The therapeutic effects of combined substance P and epidermal stem cells were better than with amniotic membrane and either factor alone. Our results suggest that the combination of substance P and epidermal stem cells effectively contributes to nerve regeneration and wound healing in diabetic rats.

Heme Oxygenase-1 Promotes Delayed Wound Healing in Diabetic Rats

Diabetic ulcers are one of the most serious and costly chronic complications for diabetic patients. Hyperglycemia-induced oxidative stress may play an important role in diabetes and its complications. The aim of the study was to explore the effect of heme oxygenase-1 on wound closure in diabetic rats. Diabetic wound model was prepared by making an incision with full thickness in STZ-induced diabetic rats. Wounds from diabetic rats were treated with 10% hemin ointment for 21 days. Increase of HO-1 protein expression enhanced anti-inflammation and antioxidant in diabetic rats. Furthermore, HO-1 increased the levels of VEGF and ICAM-1 and expressions of CBS and CSE protein. In summary, HO-1 promoted the wound closure by augmenting anti-inflammation, antioxidant, and angiogenesis in diabetic rats.

Cinnamtannin B-1 Promotes Migration of Mesenchymal Stem Cells and Accelerates Wound Healing in Mice

Substances that enhance the migration of mesenchymal stem cells to damaged sites have the potential to improve the effectiveness of tissue repair. We previously found that ethanol extracts of Mallotus philippinensis bark promoted migration of mesenchymal stem cells and improved wound healing in a mouse model. We also demonstrated that bark extracts contain cinnamtannin B-1, a flavonoid with in vitro migratory activity against mesenchymal stem cells. However, the in vivo effects of cinnamtannin B-1 on the migration of mesenchymal stem cells and underlying mechanism of this action remain unknown. Therefore, we examined the effects of cinnamtannin B-1 on in vivo migration of mesenchymal stem cells and wound healing in mice. In addition, we characterized cinnamtannin B-1-induced migration of mesenchymal stem cells pharmacologically and structurally. The mobilization of endogenous mesenchymal stem cells into the blood circulation was enhanced in cinnamtannin B-1-treated mice as shown by flow cytometric analysis of peripheral blood cells. Whole animal imaging analysis using luciferase-expressing mesenchymal stem cells as a tracer revealed that cinnamtannin B-1 increased the homing of mesenchymal stem cells to wounds and accelerated healing in a diabetic mouse model. Additionally, the cinnamtannin B-1-induced migration of mesenchymal stem cells was pharmacologically susceptible to inhibitors of phosphatidylinositol 3-kinase, phospholipase C, lipoxygenase, and purines. Furthermore, biflavonoids with similar structural features to cinnamtannin B-1 also augmented the migration of mesenchymal stem cells by similar pharmacological mechanisms. These results demonstrate that cinnamtannin B-1 promoted mesenchymal stem cell migration in vivo and improved wound healing in mice. Furthermore, the results reveal that cinnamtannin B-1-induced migration of mesenchymal stem cells may be mediated by specific signaling pathways, and the flavonoid skeleton may be relevant to its effects on mesenchymal stem cell migration.

Nestin Positive Bone Marrow Derived Cells Responded to Injury Mobilize into Peripheral Circulation and Participate in Skin Defect Healing

Exogenously infused mesenchymal stem cells (MSCs) are thought to migrate to injury site through peripheral blood stream and participate in tissue repair. However, whether and how endogenous bone marrow MSCs mobilized to circulating and targeted to tissue injury has raised some controversy, and related studies were restricted by the difficulty of MSCs identifying in vivo. Nestin, a kind of intermediate filament protein initially identified in neuroepithelial stem cells, was recently reported as a credible criteria for MSCs in bone marrow. In this study, we used a green fluorescent protein (GFP) labeled bone marrow replacement model to trace the nestin positive bone marrow derived cells (BMDCs) of skin defected-mice. We found that after skin injured, numbers of nestin⁺ cells in peripheral blood and bone marrow both increased. A remarkable concentration of nestin⁺ BMDCs around skin wound was detected, while few of these cells could be observed in uninjured skin or other organs. This recruitment effect could not be promoted by granulocyte colony-stimulating factor (G-CSF), suggests a different mobilization mechanism from ones G-CSF takes effect on hematopoietic cells. Our results proposed nestin⁺ BMDCs as mobilized candidates in skin injury repair, which provide a new insight of endogenous MSCs therapy.

Significance of CXCL12 in type 2 diabetes mellitus and its associated complications

Immune responses are extensively accepted as primitive etiological leading causes involved in immune system diseases. It is now well established that chemokines as the main arms of the immune system play critical roles in the regulation of immune responses in the pathogenesis of different diseases. Several environmental and genetic elements of the immune system are also believed to potentially affect both the onsets of immunological diseases. The stromal cell-derived factor-1 alpha (SDF-1α) which in new nomenclature is nominated as C-X-C motif ligand 12 (CXCL12) is involved in the development and progression of immune responses. The CXCL12 is an extensively active chemokine that serves as a recruiter for migration and trafficking of leukocytes and hematopoietic progenitor cells. Patients suffering type 2 diabetes (T2D) that ascribe heterozygous SDF-1 3'A genotype (801G/A in the 3' untranslated region) have increased insulin-dependent mobilization of adult progenitor cells, which are known to participate in angiogenesis and vascular repair. Conversely, homing of progenitor cells contributes to the diabetes vascular complications. Because carriers of the SDF-1 3'A genotype show increased levels of the CXCL12 messenger RNA (mRNA) in their peripheral blood mononuclear cells. Genetic variations of CXCL12 gene might affect trafficking of inflammatory cells or defected precursors and hence induced tendency to diabetic complications. The SDF-1 3'A genetic variation of CXCL12 influences the development of late vascular diabetic complications, and previous studies reported that this genetic variation regulates the expression of CXCL12. Therefore, the main goal of the present study was to collect the most recent reports regarding the relation between serum concentrations and SDF-1 3'A genetic variation of CXCL12 in T2D.

Adipose tissue-derived mesenchymal stem cells and platelet-rich plasma: stem cell transplantation methods that enhance stemness

Because of their ease of isolation and relative abundance, adipose-derived mesenchymal stem cells (ASCs) are a particularly attractive autologous cell source for various therapeutic purposes. ASCs retain a high proliferation capacity in vitro and have the ability to undergo extensive differentiation into multiple cell lineages. Moreover, ASCs secrete a wide range of growth factors that can stimulate tissue regeneration. Therefore, the clinical use of ASCs is feasible. However, the potential of ASCs differs depending on the donor's medical condition, including diseases such as diabetes. Recent studies demonstrated that ASCs from diabetic donors exhibit reduced proliferative potential and a smaller proportion of stem cell marker-positive cells. Therefore, to ensure the success of regenerative medicine, tissue engineering methods must be improved by the incorporation of factors that increase the proliferation and differentiation of stem/progenitor cells when autologous cells are used. Platelet-rich plasma (PRP), which contains high levels of diverse growth factors that can stimulate stem cell proliferation and cell differentiation in the context of tissue regeneration, has recently been identified as a biological material that could be applied to tissue regeneration. Thus, co-transplantation of ASCs and PRP represents a promising novel approach for cell therapy in regenerative medicine. In this review, we describe the potential benefits of adding PRP to ASCs and preclinical and clinical studies of this approach in various medical fields. We also discuss the mechanisms of PRP action and future cell-based therapies using co-transplantation of ASCs and PRP.

Sensory neuropathy hampers nociception-mediated bone marrow stem cell release in mice and patients with diabetes

AIMS/HYPOTHESIS

Upon tissue injury, peripheral sensory neurons release nociceptive factors (e.g. substance P [SP]), which exert local and systemic actions including the recruitment of bone marrow (BM)-derived haematopoietic stem and progenitor cells (HSPCs) endowed with paracrine pro-angiogenic properties. We herein explore whether diabetic neuropathy interferes with these phenomena.

METHODS

We first investigated the presence of sensory neuropathy in the BM of patients with type 2 diabetes by immunohistochemistry and morphometry analyses of nerve size and density and assessment of SP release by ELISA. We next analysed the association of sensory neuropathy with altered HSPC release under ischaemia or following direct stimulation with granulocyte colony-stimulating factor (G-CSF). BM and circulating HSPCs expressing the neurokinin 1 receptor (NK1R), which is the main SP receptor, were measured by flow cytometry. We finally assessed whether an altered modulation of SP secretion interferes with the mobilisation and homing of NK1R-HSPCs in a mouse model of type 2 diabetes after limb ischaemia (LI).

RESULTS

Nociceptive fibres were reduced in the BM of patients and mice with type 2 diabetes. Patients with neuropathy showed a remarkable reduction in NK1R-HSPC mobilisation under ischaemia or upon G-CSF stimulation. Following LI, diabetic mice manifested an altered SP gradient between BM, peripheral blood and limb muscles, accompanied by a depressed recruitment of NK1R-HSPCs to the ischaemic site.

CONCLUSIONS/INTERPRETATION

Sensory neuropathy translates into defective liberation and homing of reparative HSPCs. Nociceptors may represent a new target for treatment of diabetic complications.

Wound healing: an update

Wounds, both chronic and acute, continue to be a tremendous socioeconomic burden. As such, technologies drawn from many disciplines within science and engineering are constantly being incorporated into innovative wound healing therapies. While many of these therapies are experimental, they have resulted in new insights into the pathophysiology of wound healing, and in turn the development of more specialized treatments for both normal and abnormal wound healing states. Herein, we review some of the emerging technologies that are currently being developed to aid and improve wound healing after cutaneous injury.

The role of mast cells in cutaneous wound healing in streptozotocin-induced diabetic mice

Mast cells (MCs) reside in cutaneous tissue, and an increment of MCs is suggested to induce vascular regression in the process of wound healing. To clarify participation of MCs in diabetic cutaneous wound healing, we created an excisional wound on diabetic mice 4 weeks after streptozotocin injections and subsequently investigated the healing processes for 49 days, comparing them with control mice. The rate of wound closure was not markedly different between the diabetic and control mice. In the proliferative phase at days 7 and 14, neovascularization in the wound was weaker in diabetic mice than in control mice. In the remodeling phase at day 21 and afterward, rapid vascular regression occurred in control mice; however, neovascularization was still observed in diabetic mice where the number of vessels in granulation tissues was relatively higher than in control mice. In the remodeling phase of the control mice, MCs within the wound began to increase rapidly and resulted in considerable accumulation, whereas the increment of MCs was delayed in diabetic mice. In addition, the number of fibroblast growth factor (FGF)- or vascular endothelial growth factor (VEGF)-immunopositive hypertrophic fibroblast-like spindle cells and c-Kit-positive/VEGFR2-positive/FcεRIα-negative endothelial progenitor cells (EPCs) were higher in diabetic wounds. In conclusion, neovascularization in the proliferative phase and vascular regression in the remodeling phase were impaired in diabetic mice. The delayed increment of MCs and sustained angiogenic stimuli by fibroblast-like spindle cells and EPCs may inhibit vascular regression in the remodeling phase and impair the wound-healing process in diabetic mice.

Understanding regulatory pathways of neovascularization in diabetes

Diabetes mellitus and its associated comorbidities represent a significant health burden worldwide. Vascular dysfunction is the major contributory factor in the development of these comorbidities, which include impaired wound healing, cardiovascular disease and proliferative diabetic retinopathy. While the etiology of abnormal neovascularization in diabetes is complex and paradoxical, the dysregulation of the varied processes contributing to the vascular response are due in large part to the effects of hyperglycemia. In this review, we explore the mechanisms by which hyperglycemia disrupts chemokine expression and function, including the critical hypoxia inducible factor-1 axis. We place particular emphasis on the therapeutic potential of strategies addressing these pathways; as such targeted approaches may one day help alleviate the healthcare burden of diabetic sequelae.

The dipeptidyl peptidase-4 inhibitor saxagliptin improves function of circulating pro-angiogenic cells from type 2 diabetic patients

BACKGROUND

Type 2 diabetes (T2D) is associated with reduction and dysfunction of circulating pro-angiogenic cells (PACs). DPP-4 inhibitors, a class of oral agents for T2D, might possess pleiotropic vasculoprotective activities. Herein, we tested whether DPP-4 inhibition with Saxagliptin affects the function of circulating PACs from T2D and healthy subjects.

METHODS

PACs were isolated from T2D (n = 20) and healthy (n = 20) subjects. Gene expression, clonogenesis, proliferation, adhesion, migration and tubulisation were assessed in vitro by incubating PACs with or without Saxagliptin and SDF-1α. Stimulation of angiogenesis by circulating cells from T2D patients treated with Saxagliptin or other non-incretinergic drugs was assessed in vivo using animal models.

RESULTS

Soluble DPP-4 activity was predominant over cellular activity and was successfully inhibited by Saxagliptin. At baseline, T2D compared to healthy PACs contained less acLDL(+)Lectin(+) cells, and showed altered expression of genes related to adhesion and cell cycle regulation. This was reflected by impaired adhesion and clonogenesis/proliferative response of T2D PACs. Saxagliptin + SDF-1α improved adhesion and tube sustaining capacity of PACs from T2D patients. CD14+ PACs were more responsive to Saxagliptin than CD14- PACs. While Saxagliptin modestly reduced angiogenesis by mature endothelial cells, circulating PACs-progeny cells from T2D patients on Saxagliptin treatment displayed higher growth factor-inducible in vivo angiogenetic activity, compared to cells from T2D patients on non-incretinergic regimen.

CONCLUSIONS

Saxagliptin reverses PACs dysfunction associated with T2D in vitro and improves inducible angiogenesis by circulating cells in vivo. These data add knowledge to the potential pleiotropic cardiovascular effects of DPP-4 inhibition.

Hydrogen sulfide improves wound healing via restoration of endothelial progenitor cell functions and activation of angiopoietin-1 in type 2 diabetes

Impaired angiogenesis and its induced refractory wound lesions are common complications of diabetes. Hydrogen sulfide (H2S) has been reported to have proangiogenic effects. We hypothesize that H2S improves diabetic wound healing by restoring endothelial progenitor cell (EPC) function in type 2 diabetes. db/db Mice were treated with sodium hydrosulfide (NaHS), 4-hydro-xythiobenzamide group (HTB), or saline for 18 days. db/+ Mice were treated with dl-propargylglycine (PAG) or saline for 18 days. Plasma H2S levels were significantly decreased in db/db mice and restored in the NaHS and HTB mice compared with the diabetic control group. Wound-closure rates were significantly faster in the NaHS and HTB groups than in the db/db group, in which the PAG group had slower wound-closure rates. Wound skin capillary densities were enhanced in the NaHS and HTB groups. EPC functions were significantly preserved in the NaHS and HTB groups but were decreased in the PAG group. Meanwhile, EPC functions of the db/+ mice were significantly reduced after in vitro PAG treatment or cystathionine-γ-lyase (CSE) silencing; EPC functions of db/db mice were significantly improved after in vitro NaHS treatment. The expressions of Ang-1 in wound skin tissue and in EPCs were upregulated in the NaHS and HTB groups compared with db/db controls, but were downregulated by in vivo PAG and in vitro siCSE treatment compared with normal controls. Diabetic EPC tube formation capacity was significantly inhibited by Ang-1 small interfering RNA before NaHS treatment compared with db/db EPCs treated with NaHS only. Taken together, these results show that H2S improves wound healing by restoration of EPC functions and activation of Ang-1 in type 2 diabetic mice.

CD34+/CD45-dim stem cell mobilization by hyperbaric oxygen - changes with oxygen dosage

Because hyperbaric oxygen treatment mobilizes bone marrow derived-stem/progenitor cells by a free radical mediated mechanism, we hypothesized that there may be differences in mobilization efficiency based on exposure to different oxygen partial pressures. Blood from twenty consecutive patients was obtained before and after the 1st, 10th and 20th treatment at two clinical centers using protocols involving exposures to oxygen at either 2.0 or 2.5 atmospheres absolute (ATA). Post-treatment values of CD34+, CD45-dim leukocytes were always 2-fold greater than the pre-treatment values for both protocols. Values for those treated at 2.5 ATA were significantly greater than those treated at 2.0 ATA by factors of 1.9 to 3-fold after the 10th and before and after the 20th treatments. Intracellular content of hypoxia inducible factors -1, -2, and -3, thioredoxin-1 and poly-ADP-ribose polymerase assessed in permeabilized CD34+ cells with fluorophore-conjugated antibodies were twice as high in all post- versus pre-treatment samples with no significant differences between 2.0 and 2.5 ATA protocols. We conclude that putative progenitor cell mobilization is higher with 2.5 versus 2.0 ATA treatments, and all newly mobilized cells exhibit higher concentrations of an array of regulatory proteins.

Combination therapy accelerates diabetic wound closure

Background

Non-healing foot ulcers are the most common cause of non-traumatic amputation and hospitalization amongst diabetics in the developed world. Impaired wound neovascularization perpetuates a cycle of dysfunctional tissue repair and regeneration. Evidence implicates defective mobilization of marrow-derived progenitor cells (PCs) as a fundamental cause of impaired diabetic neovascularization. Currently, there are no FDA-approved therapies to address this defect. Here we report an endogenous PC strategy to improve diabetic wound neovascularization and closure through a combination therapy of AMD3100, which mobilizes marrow-derived PCs by competitively binding to the cell surface CXCR4 receptor, and PDGF-BB, which is a protein known to enhance cell growth, progenitor cell migration and angiogenesis.

Methods and Results

Wounded mice were assigned to 1 of 5 experimental arms (n = 8/arm): saline treated wild-type, saline treated diabetic, AMD3100 treated diabetic, PDGF-BB treated diabetic, and AMD3100/PDGF-BB treated diabetic. Circulating PC number and wound vascularity were analyzed for each group (n = 8/group). Cellular function was assessed in the presence of AMD3100. Using a validated preclinical model of type II diabetic wound healing, we show that AMD3100 therapy (10 mg/kg; i.p. daily) alone can rescue diabetes-specific defects in PC mobilization, but cannot restore normal wound neovascularization. Through further investigation, we demonstrate an acquired trafficking-defect within AMD3100-treated diabetic PCs that can be rescued by PDGF-BB (2 μg; topical) supplementation within the wound environment. Finally, we determine that combination therapy restores diabetic wound neovascularization and accelerates time to wound closure by 40%.

Conclusions

Combination AMD3100 and PDGF-BB therapy synergistically improves BM PC mobilization and trafficking, resulting in significantly improved diabetic wound closure and neovascularization. The success of this endogenous, cell-based strategy to improve diabetic wound healing using FDA-approved therapies is inherently translatable.

Nanofiber-expanded human umbilical cord blood-derived CD34+ cell therapy accelerates murine cutaneous wound closure by attenuating pro-inflammatory factors and secreting IL-10

Nanofiber-expanded human umbilical cord blood-derived CD34+ cell therapy is under consideration for treating peripheral and cardiac ischemia. However, the therapeutic efficacy of nanofiber-expanded human umbilical cord blood-derived (NEHUCB) CD34+ cell therapy for wound healing and its mechanisms are yet to be established. Using an excision wound model in NOD/SCID mice, we show herein that NEHUCB-CD34+ cells home to the wound site and significantly accelerate the wound-healing process compared to vehicle-treated control. Histological analysis reveals that accelerated wound closure is associated with the re-epithelialization and increased angiogenesis. Additionally, NEHUCB-CD34+ cell-therapy decreases expression of pro-inflammatory cytokines, such as TNF-α, IL-1β, IL-6 and NOS2A in the wound bed, and concomitantly increases expression of IL-10 compared to vehicle-treated control. These findings were recapitulated in vitro using primary dermal fibroblasts and NEHUCB-CD34+ cells. Moreover, NEHUCB-CD34+ cells attenuate NF-κB activation and nuclear translocation in dermal fibroblasts through enhanced secretion of IL-10, which is known to bind to NF-κB and suppress transcriptional activity. Collectively, these data provide novel mechanistic evidence of NEHUCB-CD34+ cell-mediated accelerated wound healing.

Number of circulating pro-angiogenic cells, growth factor and anti-oxidative gene profiles might be altered in type 2 diabetes with and without diabetic foot syndrome

Aims/Introduction

Type 2 diabetes is often complicated by diabetic foot syndrome (DFS). We analyzed the circulating stem cells, growth factor and anti‐oxidant gene expression profiles in type 2 diabetes patients without or with different forms of DFS.

Materials and Methods

Healthy volunteers (n = 13) and type 2 diabetes patients: (i) without DFS (n = 10); or with (ii) Charcot osteoneuropathy (n = 10); (iii) non‐infected (n = 17); (iv) infected (n = 11); and (v) healed ulceration were examined (n = 12). Peripheral blood endothelial progenitor cells (EPC), mesenchymal stem cells (MSC), hematopoietic stem cells (HSC) and very small embryonic‐like (VSEL) cells were phenotyped using flow cytometry. Plasma cytokine concentrations and gene expressions in blood cells were measured by Luminex and quantitative real‐time polymerase chain reaction assays, respectively.

Results

Patients with non‐complicated type 2 diabetes showed reduced HMOX1 expression, accompanied by HMOX2 upregulation, and had less circulating EPC, MSC or HSC than healthy subjects. In contrast, VSEL cells were elevated in the type 2 diabetes group. However, subjects with DFS, even with healed ulceration, had fewer VSEL cells, more CD45‐CD29⁺CD90⁺MSC, and upregulated HMOX1 when compared with the type 2 diabetes group. Patients with Charcot osteopathy had lowered plasma fibroblast growth factor‐2. Elevated plasma tumor necrosis factor‐α and decreased catalase expression was found in all diabetic patients.

Conclusions

Patients with type 2 diabetes and different forms of DFS have an altered number of circulating stem cells. Type 2 diabetes might also be associated with a changed plasma growth factor and anti‐oxidant gene expression profile. Altogether, these factors could contribute to the pathogenesis of different forms of DFS.

Diabetes impairs adipose tissue-derived stem cell function and efficiency in promoting wound healing

Adipose tissue-derived stem cells (ASCs) are gaining increasing consideration in tissue repair therapeutic application. Recent evidence indicates that ASCs enhance skin repair in animal models of impaired wound healing. To assess the therapeutic activity of autologous vs. allogeneic ASCs in the treatment of diabetic ulcers, we functionally characterized diabetic ASCs and investigated their potential to promote wound healing with respect to nondiabetic ones. Adipose tissue-derived cells from streptozotocin-induced type 1 diabetic mice were analyzed either freshly isolated as stromal vascular fraction (SVF), or following a single passage of culture (ASCs). Diabetic ASCs showed decreased proliferative potential and migration. Expression of surface markers was altered in diabetic SVF and cultured ASCs, with a reduction in stem cell marker-positive cells. ASCs from diabetic mice released lower amounts of hepatocyte growth factor, vascular endothelial growth factor (VEGF)-A, and insulin-like growth factor-1, growth factors playing important roles in skin repair. Accordingly, the supernatant of diabetic ASCs manifested reduced capability to promote keratinocyte and fibroblast proliferation and migration. Therapeutic potential of diabetic SVF administered to wounds of diabetic mice was blunted as compared with cells isolated from nondiabetic mice. Our data indicate that diabetes alters ASC intrinsic properties and impairs their function, thus affecting therapeutic potential in the autologous treatment for diabetic ulcers.

Current aspects in the pathophysiology and treatment of chronic wounds in diabetes mellitus

Impaired wound healing is a frequent and very severe problem in patients with diabetes mellitus, yet little is known about the underlying pathomechanisms. In this paper we review the biology of wound healing with particular attention to the pathophysiology of chronic wounds in diabetic patients. The standard treatment of diabetic ulcers includes measures to optimize glycemic control as well as extensive debridement, infection elimination by antibiotic therapy based on wound pathogen cultures, the use of moisture dressings, and offloading high pressure from the wound bed. In this paper we discuss novel adjuvant therapies with particular reference to the use of autologous skin transplants for the treatment of diabetic foot ulcers which do not respond to standard care.

The wound watch: an objective staging system for wounds in the diabetic (db/db) mouse model

As in cancer biology, in wound healing there is a need for objective staging systems to decide for the best treatment and predictors of outcome. We developed in the diabetic (db/db) wound healing model, a staging system, the "wound watch," based on the quantification of angiogenesis and cell proliferation in open wounds. In chronic wounds, there is often a lack of cellular proliferation and angiogenesis that leads to impaired healing. The wound watch addresses this by quantifying the proliferative phase of wound healing in two dimensions (cellular division and angiogenesis). The results are plotted in a two-dimensional graph to monitor the course of healing and compare the response to different treatments.

Human mesenchymal stem cell grafts enhance normal and impaired wound healing by recruiting existing endogenous tissue stem/progenitor cells

Mesenchymal stem cells (MSCs) have been investigated as a clinical therapy to promote tissue repair. However, the disappearance of grafted cells soon after engraftment suggests a possible role as initiators of repair rather than effectors. We evaluated the relative contribution of grafted human MSCs and host stem/progenitor cells in promoting wound healing by using a novel asymmetric wound model in normal and impaired healing diabetic (db/db) mice to discriminate between the effect of direct engraftment and the subsequent systemic response. Experimental animals received paired wounds, with one wound receiving human mesenchymal stem cells (hMSCs) and the other wound receiving vehicle to assess local and systemic effects, respectively. Control animals received vehicle in both wounds. Grafted hMSCs significantly improved healing in both normal and impaired healing animals; produced significant elevation of signals such as Wnt3a, vascular endothelial growth factor, and platelet-derived growth factor receptor-α; and increased the number of pre-existing host MSCs recruited to the wound bed. Improvement was also seen in both the grafted and nongrafted sides, suggesting a systemic response to hMSC engraftment. Healing was enhanced despite the rapid loss of hMSCs, suggesting that mobilizing the host response is the major outcome of grafting MSCs to tissue repair. We validate that hMSCs evoke a host response that is clinically relevant, and we suggest that therapeutic efforts should focus on maximizing the mobilization of host MSCs.

The role of stem cells in the treatment of diabetic foot ulcers

Diabetic foot ulcers (DFUs) are a significant and rapidly growing complication of diabetes and its effects on wound healing. Over half of diabetic patients who develop a single ulcer will subsequently develop another ulcer of which the majority will become chronic non-healing ulcers. One-third will progress to lower extremity amputation. Over the past decade, the outcomes for patients with DFUs ulcers have not improved, despite advances in wound care. Successful treatment of diabetic foot ulcers is hindered by the lack of targeted therapy that hones in on the healing processes dysregulated by diabetes. Stem cells are a promising treatment for DFUs as they are capable of targeting, as well as bypassing, the underlying abnormal healing mechanisms and deranged cell signaling in diabetic wounds and promote healing. This review will focus on existing stem cell technologies and their application in the treatment of DFUs.

Regenerative therapies for diabetic microangiopathy

Hyperglycaemia occurring in diabetes is responsible for accelerated arterial remodeling and atherosclerosis, affecting the macro- and the microcirculatory system. Vessel injury is mainly related to deregulation of glucose homeostasis and insulin/insulin-precursors production, generation of advanced glycation end-products, reduction in nitric oxide synthesis, and oxidative and reductive stress. It occurs both at extracellular level with increased calcium and matrix proteins deposition and at intracellular level, with abnormalities of intracellular pathways and increased cell death. Peripheral arterial disease, coronary heart disease, and ischemic stroke are the main causes of morbidity/mortality in diabetic patients representing a major clinical and economic issue. Pharmacological therapies, administration of growth factors, and stem cellular strategies are the most effective approaches and will be discussed in depth in this comprehensive review covering the regenerative therapies of diabetic microangiopathy.

Strategies to reverse endothelial progenitor cell dysfunction in diabetes

Bone-marrow-derived cells-mediated postnatal vasculogenesis has been reported as the main responsible for the regulation of vascular homeostasis in adults. Since their discovery, endothelial progenitor cells have been depicted as mediators of postnatal vasculogenesis for their peculiar phenotype (partially staminal and partially endothelial), their ability to differentiate in endothelial cell line and to be incorporated into the vessels wall during ischemia/damage. Diabetes mellitus, a condition characterized by cardiovascular disease, nephropathy, and micro- and macroangiopathy, showed a dysfunction of endothelial progenitor cells. Herein, we review the mechanisms involved in diabetes-related dysfunction of endothelial progenitor cells, highlighting how hyperglycemia affects the different steps of endothelial progenitor cells lifetime (i.e., bone marrow mobilization, trafficking into the bloodstream, differentiation in endothelial cells, and homing in damaged tissues/organs). Finally, we review preclinical and clinical strategies that aim to revert diabetes-induced dysfunction of endothelial progenitor cells as a means of finding new strategies to prevent diabetic complications.

Impaired therapeutic capacity of autologous stem cells in a model of type 2 diabetes

Endogenous stem cells in the bone marrow respond to environmental cues and contribute to tissue maintenance and repair. In type 2 diabetes, a multifaceted metabolic disease characterized by insulin resistance and hyperglycemia, major complications are seen in multiple organ systems. To evaluate the effects of this disease on the endogenous stem cell population, we used a type 2 diabetic mouse model (db/db), which recapitulates these diabetic phenotypes. Bone marrow-derived mesenchymal stem cells (MSCs) from db/db mice were characterized in vitro using flow cytometric cell population analysis, differentiation, gene expression, and proliferation assays. Diabetic MSCs were evaluated for their therapeutic potential in vivo using an excisional splint wound model in both nondiabetic wild-type and diabetic mice. Diabetic animals possessed fewer MSCs, which were proliferation and survival impaired in vitro. Examination of the recruitment response of stem and progenitor cells after wounding revealed that significantly fewer endogenous MSCs homed to the site of injury in diabetic subjects. Although direct engraftment of healthy MSCs accelerated wound closure in both healthy and diabetic subjects, diabetic MSC engraftment produced limited improvement in the diabetic subjects and could not produce the same therapeutic outcomes as in their nondiabetic counterparts in vivo. Our data reveal stem cell impairment as a major complication of type 2 diabetes in mice and suggest that the disease may stably alter endogenous MSCs. These results have implications for the efficiency of autologous therapies in diabetic patients and identify endogenous MSCs as a potential therapeutic target.

Stem Cell Therapy: A New Treatment for Burns?

Stem cell therapy has emerged as a promising new approach in almost every medicine specialty. This vast, heterogeneous family of cells are now both naturally (embryonic and adult stem cells) or artificially obtained (induced pluripotent stem cells or iPSCs) and their fates have become increasingly controllable, thanks to ongoing research in this passionate new field. We are at the beginning of a new era in medicine, with multiple applications for stem cell therapy, not only as a monotherapy, but also as an adjunct to other strategies, such as organ transplantation or standard drug treatment. Regrettably, serious preclinical concerns remain and differentiation, cell fusion, senescence and signalling crosstalk with growth factors and biomaterials are still challenges for this promising multidisciplinary therapeutic modality. Severe burns have several indications for stem cell therapy, including enhancement of wound healing, replacement of damaged skin and perfect skin regeneration - incorporating skin appendages and reduced fibrosis -, as well as systemic effects, such as inflammation, hypermetabolism and immunosuppression. The aim of this review is to describe well established characteristics of stem cells and to delineate new advances in the stem cell field, in the context of burn injury and wound healing.