Peripheral Blood Fibrocytes: Enhancement of Wound Healing by Cell Proliferation, Re-Epithelialization, Contraction, and Angiogenesis

Basic Fibroblast Growth Factor Induces Angiogenic Properties of Fibrocytes to Stimulate Vascular Formation during Wound Healing

The role of fibrocytes in wound angiogenesis remains unclear. We therefore demonstrated the specific changes in fibrocyte accumulation for angiogesis in basic fibroblast growth factor (bFGF)-treated wounds. bFGF-treated wounds exhibited marked formation of arterioles and inhibition of podoplanin⁺ lymph vessels that were lacking in vascular endothelial growth factor-A-treated wounds. Real-time PCR in bFGF-treated wounds manifested enhanced expression of CD34, CD31, and bFGF mRNA and reduced expression of podoplanin and collagen type I, III, and IV mRNA. Double immunofluorescence staining focusing on fibrocyte detection in bFGF-treated wounds showed increased formation of capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, with a lack of capillary-like structures formed by CD45⁺/procollagen I⁺ or CD11b⁺/procollagen I⁺ fibrocytes. However, vascular endothelial growth factor-A-treated wounds lacked capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, with increased numbers of CD34⁺/fetal liver kinase-1⁺ endothelial progenitor cells. Furthermore, fibroblast growth factor receptor 1 siRNA injection into wounds, followed by bFGF, inhibited the formation of capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, together with inhibited mRNA expression of CD34 and CD31 and enhanced mRNA expression of collagen type I, indicating the requirements of bFGF/fibroblast growth factor receptor 1 system for capillary structure formation. This study highlights the angiogenic properties of CD34⁺/procollagen I⁺ fibrocytes specifically induced by bFGF, providing new insight into the active contribution of fibrocytes for vascular formation during wound healing.

Phylogenetic analysis of otospiralin protein

Background:

Fibrocyte-specific protein, otospiralin, is a small protein, widely expressed in the central nervous system as neuronal cell bodies and glia. The increased expression of otospiralin in reactive astrocytes implicates its role in signaling pathways and reparative mechanisms subsequent to injury. Indeed, otospiralin is considered to be essential for the survival of fibrocytes of the mesenchymal nonsensory regions of the cochlea. It seems that other functions of this protein are not yet completely understood.

Materials and Methods:

Amino acid sequences of otospiralin from 12 vertebrates were derived from National Center for Biotechnology Information database. Phylogenetic analysis and phylogeny estimation were performed using MEGA 5.0.5 program, and neighbor-joining tree was constructed by this software.

Results:

In this computational study, the phylogenetic tree of otospiralin has been investigated. Therefore, dendrograms of otospiralin were depicted. Alignment performed in MUSCLE method by UPGMB algorithm. Also, entropy plot determined for a better illustration of amino acid variations in this protein.

Conclusion:

In the present study, we used otospiralin sequence of 12 different species and by constructing phylogenetic tree, we suggested out group for some related species.

Biphasic presence of fibrocytes in a porcine hypertrophic scar model

The duroc pig has been described as a promising animal model for use in the study of human wound healing and scar formation. However, little is known about the presence and chronology of the fibrocyte cell population in the healing process of these animals. Wounds known to form scar were created on red duroc swine (3" x 3") with a dermatome to a total depth of either 0.06 inches or 0.09 inches. These wounds were allowed to heal completely and biopsies were done at scheduled time points during the healing process. Biopsies were formalin fixed and paraffin embedded for immunohistochemical analysis. Porcine reactive antibodies to CD-45 and procollagen-1 and a human reactive antibody to LSP-1 were used to detect the presence of fibrocytes in immunohistochemistry, an immunocytochemistry. Initial immunohistochemical studies showed evidence of a biphasic presence of fibrocytes. Pigs with 0.06 inches deep wounds showed positive staining for CD-45 and LSP-1 within highly cellular areas at days 2 and 4 after wounding. Additional animals with 0.09 inches deep wounds showed positive staining within similar areas at days 56, 70, and 113 after wounding. There was no immunohistochemical evidence of fibrocytes in skin biopsies taken at days 14, 28, or 42. Procollagen-1 staining was diffused in all samples. Cultured cells were stained for CD-45, LSP-1, and procollagen-1 by immunocytochemistry. These data confirm that fibrocytes are indeed present in this porcine model. We conclude that these cells are present after initial wounding and later during scar formation and remodeling. We believe that this is an evidence of a biphasic presence of fibrocytes, first as an acute response to skin wounding followed by later involvement in the remodeling process, prompted by continued inflammation in a deep partial thickness wound.

Fibrocytes participate in the development of heterotopic ossification

Heterotopic ossification (HO) is a complication of musculoskeletal injury characterized by the formation of mature bone in soft tissues. The etiology of HO is unknown. We investigated the role of bone marrow derived progenitor cells in HO pathophysiology. We isolated the cells from HO specimens by cell explantation. Using flow cytometry and immunofluorescence microscopy, we found that 35 to 65% of the HO cells exhibit a bone marrow derived fibrocyte profile consisting in spindle-shaped morphology associated with type 1 pro-collagen and LSP1 expression. When cultured in osteogenic differentiation medium, active machinery for bone mineralization (high gene expression of Anx2, TNAP, and Pit-1), and calcium/phosphate deposits were found. Interestingly, interferon-alpha 2b significantly reduced the proliferation rate and COL1 gene expression in HO cells. We have characterized a novel subset of bone marrow derived progenitor cells in the HO specimens. The findings from this research study will provide new insights into the development of HO in burn patients.

Low-intensity treadmill exercise promotes rat dorsal wound healing

In order to investigate the promoting effect of low-intensity treadmill exercise on rat dorsal wound healing and the mechanism, 20 Sprague-Dawley rats were randomly divided into two groups: exercise group (Ex) and non-exercise group (non-ex). The rats in Ex group were given treadmill exercise for one month, and those in non-ex group raised on the same conditions without treadmill exercise. Both groups received dorsal wound operation with free access to food and water. By two-week continuous observation and recording of the wound area, the healing rate was analyzed. The blood sample was collected at day 14 post-operation via cardiac puncture for determination of the number of endothelial progenitor cells (EPCs) by flow cytometry, and the concentrations of relevant cytokines such as basic fibroblast growth factor (bFGF), endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) were measured by ELISA. The skin tissue around the wound was dissected to observe the vascular density under the microscope after HE staining, to detect the mRNA level of VEGFR2 and angiopoietin-1 (Ang-1) receptor using RT-qPCR, and protein expression of a-smooth muscle actin (αSMA) and type III collagen (ColIII) using Western blotting. It was found that the wound area in Ex group was smaller at the same time point than in non-ex group. The number of circulating EPCs was greater and the concentrations of vasoactive factors such as VEGF, eNOS and bFGF were higher in Ex group than in non-ex group. HE staining displayed a higher vessel density in Ex group than in non-ex group. Moreover, the mRNA expression of VEGFR2 and Ang-1 detected in the wound tissue in Ex group was higher than in non-ex group. Meanwhile, the protein expression of αSMA and ColIII was more abundant in Ex group than in non-ex group. Conclusively, the above results demonstrate Ex rats had a higher wound healing rate, suggesting low-intensity treadmill exercise accelerates wound healing. The present work may provide some hint for future study of treating refractory wound.

Human fibrocyte-derived exosomes accelerate wound healing in genetically diabetic mice

Diabetic ulcers represent a substantial societal and healthcare burden worldwide and scarcely respond to current treatment strategies. This study was addressed to evaluate the therapeutic potential of exosomes secreted by human circulating fibrocytes, a population of mesenchymal progenitors involved in normal wound healing via paracrine signaling. The exosomes released from cells sequentially stimulated with platelet-derived growth factor-BB and transforming growth factor-β1, in the presence of fibroblast growth factor 2, did not show potential immunogenicity. These exosomes exhibited in-vitro proangiogenic properties, activated diabetic dermal fibroblasts, induced the migration and proliferation of diabetic keratinocytes, and accelerated wound closure in diabetic mice in vivo. Important components of the exosomal cargo were heat shock protein-90α, total and activated signal transducer and activator of transcription 3, proangiogenic (miR-126, miR-130a, miR-132) and anti-inflammatory (miR124a, miR-125b) microRNAs, and a microRNA regulating collagen deposition (miR-21). This proof-of-concept study demonstrates the feasibility of the use of fibrocytes-derived exosomes for the treatment of diabetic ulcers.

The role of adult tissue-derived stem cells in chronic leg ulcers: a systematic review focused on tissue regeneration medicine

Wound healing is an articulated process that can be impaired in different steps in chronic wounds. Chronic leg ulcers are a special type of non-healing wounds that represent an important cause of morbidity and public cost in western countries. Because of their common recurrence after conventional managements and increasing prevalence due to an ageing population, newer approaches are needed. Over the last decade, the research has been focused on innovative treatment strategies, including stem-cell-based therapies. After the initial interest in embryonic pluripotent cells, several different types of adult stem cells have been studied because of ethical issues. Specific types of adult stem cells have shown a high potentiality in tissue healing, in both in vitro and in vivo studies. Aim of this review is to clearly report the newest insights on tissue regeneration medicine, with particular regard for chronic leg ulcers.

Cells from the hematopoietic lineage are only present transiently during healing in a mouse model of non-severe burn injury

Introduction

The aim of our study is to identify the contribution of hematopoietic-derived cells to burn-wound healing in a non-severe injury. There are many conflicting reports of the contribution of bone marrow-derived cells to wound healing and whether these are hematopoietic or mesenchymal in origin. The role of hematopoietic lineage cells is investigated in this study in the context of the response to burn injury.

Methods

Transgenic mice expressing the LacZ reporter gene in all cells of the hematopoietic lineage underwent a non-severe full-thickness burn injury (8 % of total body surface area). Wounds were assessed for LacZ-positive cells at days 7, 14, and 28 post-injury by using whole-mount staining. Cells were also cultured from the wounds at each time point and analysed for expression of fibroblast and myofibroblast markers.

Results

At day 7, positive cells were identified in the wounds representing the inflammatory response. Some dermal cells were also identified at this early stage. At day 14, positive cells were also identified and were cultured from the wound tissue samples. However, by day 28, no positive cells could be detected or cultured from the healed wound tissue. Isolated LacZ-positive cells did not express collagen 1 or α-smooth muscle actin proteins, indicating that they had not differentiated into dermal fibroblast-type cells.

Conclusions

In this model of burn injury, hematopoietic lineage cells were present in the healing wound only transiently and did not appear to contribute to the long-term scar population. This is in contrast with reports demonstrating that fibrocytes contribute a long-term sustained population in scar tissue. This work demonstrates that in a non-severe burn injury model there is a sustained transient contribution of hematopoietic cells to the healed wound. Further characterisation of the types and extent of wounding required to establish a long-term hematopoietic response will be important in determining future cell-based therapies.

Angiotensin II inhibitor facilitates epidermal wound regeneration in diabetic mice

Tissue regeneration and wound healing are severely impaired in diabetes and are associated with poor circulation and dysfunctional blood vessels. Angiotensin II inhibitors are anti-hypertensive drugs used in clinical practice to regulate blood pressure and could affect tissue remodeling. We hypothesize that blocking angiotensin II, using Losartan, could facilitate tissue regeneration in diabetic mice. To this end, we established an experimental model of wound healing in streptozotocin-induced diabetic mice. Our data demonstrated that Losartan accelerates wound repair and normalizes wound stromal responses, having a beneficial role in wounds of diabetic individuals. Our findings highlight a potential therapeutic use of Losartan in improving wound repair in diabetic conditions.

Effect of local injection of mesenchymal stem cells on healing of sutured gastric perforation in an experimental model

BACKGROUND

Mesenchymal stem cells are proposed to facilitate repair of organ injuries. The aim of this study was to investigate whether local injection of mesenchymal stem cells could accelerate healing of sutured gastric perforations.

METHODS

Sutured gastric perforations in rats were treated either with local injection of mesenchymal stem cells (injected MSC group) or by topically spraying with fibrin glue containing mesenchymal stem cells (sprayed MSC group). Controls were treated by local injection of saline or topical spray of fibrin glue without mesenchymal stem cells. Healing of sutured gastric perforations was assessed on days 3, 5 and 7.

RESULTS

Local injection of mesenchymal stem cells significantly promoted the healing of gastric perforations, with the highest pneumatic bursting pressure (mean(s.e.m.) 112·3(30·2) mmHg on day 5 versus 71·2(17·4) mmHg in saline controls; P = 0·001), minimal wound adhesions, and lowest incidence of wound dehiscence (3, 6, 5 and 1 animal on day 5 in control, fibrin, sprayed MSC and injected MSC groups respectively; n = 10 per group) and abdominal abscess (2, 2, 1 and no animals respectively on day 5). Histological examination showed that gastric perforations in the injected MSC group displayed reduced inflammation, and increased granulation and re-epithelialization. Sutured gastric perforations in the injected MSC group showed decreased expression of interleukin 6, and increased expression of transforming growth factor β1 and epithelial proliferating cell nuclear antigen, compared with the other groups.

CONCLUSION

Local injection of mesenchymal stem cells was more effective than topical application, and enhanced the healing of sutured gastric perforations by an anti-inflammatory process, enhanced cellular proliferation and earlier onset of granulation. Surgical relevance Abnormal healing of gastric perforation may cause morbidity and increase the risk of death. Adipose tissue-derived mesenchymal stem cells have been found to promote the healing of organ injuries through cellular differentiation and secretion of cytokines that stimulate cellular proliferation and angiogenesis, and suppress inflammation. This study explored the therapeutic potential of such mesenchymal stem cells for promotion of the healing of sutured gastric perforations. Mesenchymal stem cells delivered by local injection significantly enhanced the healing of gastric perforations with reduced severity of wound adhesion, and a decreased incidence of wound dehiscence and abdominal abscess. The increased expression of transforming growth factor β1, proliferating cell nuclear antigen and reduced level of interleukin 6 provide evidence for enhancement of the healing process. Engrafted mesenchymal stem cells expressed α-smooth muscle actin as a marker of myofibroblasts. This preclinical study indicates that local injection of allogeneic adipose tissue-derived mesenchymal stem cells may have a potential therapeutic role in enhancing the healing of peptic ulcer disease and prevention of ulcer-related complications.

Gingival wound healing: an essential response disturbed by aging?

Gingival wound healing comprises a series of sequential responses that allow the closure of breaches in the masticatory mucosa. This process is of critical importance to prevent the invasion of microbes or other agents into tissues, avoiding the establishment of a chronic infection. Wound healing may also play an important role during cell and tissue reaction to long-term injury, as it may occur during inflammatory responses and cancer. Recent experimental data have shown that gingival wound healing is severely affected by the aging process. These defects may alter distinct phases of the wound-healing process, including epithelial migration, granulation tissue formation, and tissue remodeling. The cellular and molecular defects that may explain these deficiencies include several biological responses such as an increased inflammatory response, altered integrin signaling, reduced growth factor activity, decreased cell proliferation, diminished angiogenesis, reduced collagen synthesis, augmented collagen remodeling, and deterioration of the proliferative and differentiation potential of stem cells. In this review, we explore the cellular and molecular basis of these defects and their possible clinical implications.

A novel subpopulation of peripheral blood mononuclear cells presents in major burn patients

Hypertrophic scars (HTS) are generally believed to result from proliferation and activation of resident connective tissue fibroblasts after burns. To demonstrate a potential role of blood-borne cells, the peripheral blood mononuclear cells (PBMCs) and the effect of PBMCs on dermal fibroblast behavior was investigated. Flow cytometry was used to analyze the surface and intracellular protein expression of PBMCs and fibroblasts. Transwell migration assay, enzyme-linked immunosorbent assay and real-time reverse transcription polymerase chain reaction was performed to assess fibroblast functions. We identified a novel subpopulation of PBMCs in burn patients in vivo that appears at an early stage following major thermal injuries, which primarily express procollagen 1, leukocyte specific protein 1, CD204, toll-like receptor 4 and stromal cell-derived factor 1 (SDF-1) receptor CXCR4. In vitro, the conditioned media from burn patient PBMCs up-regulated the expression of fibrotic growth factors and extracellular matrix molecules, down-regulated antifibrotic factor decorin, enhanced cell chemotaxis and promoted cell differentiation into contractile myofibroblasts in dermal fibroblasts. After thermal injury, this novel subpopulation of PBMCs is systemically triggered and attracted to the wounds under SDF-1/CXCR4 signaling where they appear to modulate the functions of resident connective tissue cells and thus contribute to the development of HTS.

Addition of autologous mesenchymal stem cells to whole blood for bioenhanced ACL repair has no benefit in the porcine model

BACKGROUND

Coculture of mesenchymal stem cells (MSCs) from the retropatellar fat pad and peripheral blood has been shown to stimulate anterior cruciate ligament (ACL) fibroblast proliferation and collagen production in vitro. Current techniques of bioenhanced ACL repair in animal studies involve adding a biologic scaffold, in this case an extracellular matrix-based scaffold saturated with autologous whole blood, to a simple suture repair of the ligament. Whether the enrichment of whole blood with MSCs would further improve the in vivo results of bioenhanced ACL repair was investigated.

HYPOTHESIS

The addition of MSCs derived from adipose tissue or peripheral blood to the blood-extracellular matrix composite, which is used in bioenhanced ACL repair to stimulate healing, would improve the biomechanical properties of a bioenhanced ACL repair after 15 weeks of healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-four adolescent Yucatan mini-pigs underwent ACL transection followed by (1) bioenhanced ACL repair, (2) bioenhanced ACL repair with the addition of autologous adipose-derived MSCs, and (3) bioenhanced ACL repair with the addition of autologous peripheral blood derived MSCs. After 15 weeks of healing, the structural properties of the ACL (yield load, failure load, and linear stiffness) were measured. Cell and vascular density were measured in the repaired ACL via histology, and its tissue structure was qualitatively evaluated using the advanced Ligament Maturity Index.

RESULTS

After 15 weeks of healing, there were no significant improvements in the biomechanical or histological properties with the addition of adipose-derived MSCs. The only significant change with the addition of peripheral blood MSCs was an increase in knee anteroposterior laxity when measured at 30° of flexion.

CONCLUSION

These findings suggest that the addition of adipose or peripheral blood MSCs to whole blood before saturation of an extracellular matrix carrier with the blood did not improve the functional results of bioenhanced ACL repair after 15 weeks of healing in the pig model.

CLINICAL RELEVANCE

Whole blood represents a practical biologic additive to ligament repair, and any other additive (including stem cells) should be demonstrated to be superior to this baseline before clinical use is considered.

Kruppel-like factor KLF4 facilitates cutaneous wound healing by promoting fibrocyte generation from myeloid-derived suppressor cells

Pressure ulcers (PUs) are serious skin injuries whereby the wound healing process is frequently stalled in the inflammatory phase. Myeloid-derived suppressor cells (MDSCs) accumulate as a result of inflammation and promote cutaneous wound healing by mechanisms not fully understood. Recently, MDSCs have been shown to differentiate into fibrocytes which serve as emerging effector cells that enhance cell proliferation in wound healing. We postulate that in wound healing, MDSCs not only execute their immunosuppressive function to regulate inflammation, but also stimulate cell proliferation once they differentiate into fibrocytes. In the current study, using full thickness and pressure ulcer mouse models, we found that KLF4 deficiency resulted in decreased accumulation of MDSCs and fibrocytes and wound healing was significantly delayed. Conversely, KLF4 activation by the plant-derived product, Mexicanin I, increased the numbers of MDSCs and fibrocytes and accelerated wound healing. Collectively, our study revealed a previously unreported function of MDSCs in cutaneous wound healing and identified Mexicanin I as a potential agent to accelerate PU wound healing.

Cooperation between human fibrocytes and endothelial colony-forming cells increases angiogenesis via the CXCR4 pathway

Fibrotic diseases of the lung are associated with a vascular remodelling process. Fibrocytes (Fy) are a distinct population of blood-borne cells that co-express haematopoietic cell antigens and fibroblast markers, and have been shown to contribute to organ fibrosis. The purpose of this study was to determine whether fibrocytes cooperate with endothelial colony-forming cells (ECFC) to induce angiogenesis. We isolated fibrocytes from blood of patient with idiopathic pulmonary fibrosis (IPF) and characterised them by flow cytometry, quantitative reverse transcriptase PCR (RTQ-PCR), and confocal microscopy. We then investigated the angiogenic interaction between fibrocytes and cord-blood-derived ECFC, both in vitro and in an in vivo Matrigel implant model. Compared to fibroblast culture medium, fibrocyte culture medium increased ECFC proliferation and differentiation via the SDF-1/CXCR4 pathway. IPF-Fy co-implanted with human ECFC in Matrigel plugs in immunodeficient mice formed functional microvascular beds, whereas fibroblasts did not. Evaluation of implants after two weeks revealed an extensive network of erythrocyte-containing blood vessels. CXCR4 blockade significantly inhibited this blood vessel formation. The clinical relevance of these data was confirmed by strong CXCR4 expression in vessels close to fibrotic areas in biopsy specimens from patients with IPF, by comparison with control lungs. In conclusion, circulating fibrocytes might contribute to the intense remodelling of the pulmonary vasculature in patients with idiopathic pulmonary fibrosis.

Tracking the elusive fibrocyte: identification and characterization of collagen-producing hematopoietic lineage cells during murine wound healing

Fibrocytes are a unique population of circulating cells reported to exhibit characteristics of both hematopoietic and mesenchymal cells, and play an important role in wound healing. However, putative fibrocytes have been found to lose expression of hematopoietic surface markers such as CD45 during differentiation, making it difficult to track these cells in vivo with conventional methodologies. In this study, to distinguish hematopoietic and nonhematopoietic cells without surface markers, we took advantage of the gene vav 1, which is expressed solely on hematopoietic cells but not on other cell types, and established a novel transgenic mouse, in which hematopoietic cells are irreversibly labeled with green fluorescent protein and nonhematopoietic cells with red fluorescent protein. Use of single-cell transcriptional analysis in this mouse model revealed two discrete types of collagen I (Col I) expressing cells of hematopoietic lineage recruited into excisional skin wounds. We confirmed this finding on a protein level, with one subset of these Col I synthesizing cells being CD45+ and CD11b+, consistent with the traditional definition of a fibrocyte, while another was CD45- and Cd11b-, representing a previously unidentified population. Both cell types were found to initially peak, then reduce posthealing, consistent with a disappearance from the wound site and not a loss of identifying surface marker expression. Taken together, we have unambiguously identified two cells of hematopoietic origin that are recruited to the wound site and deposit collagen, definitively confirming the existence and natural time course of fibrocytes in cutaneous healing.

Novel anti-microbial peptide SR-0379 accelerates wound healing via the PI3 kinase/Akt/mTOR pathway

We developed a novel cationic antimicrobial peptide, AG30/5C, which demonstrates angiogenic properties similar to those of LL-37 or PR39. However, improvement of its stability and cost efficacy are required for clinical application. Therefore, we examined the metabolites of AG30/5C, which provided the further optimized compound, SR-0379. SR-0379 enhanced the proliferation of human dermal fibroblast cells (NHDFs) via the PI3 kinase-Akt-mTOR pathway through integrin-mediated interactions. Furthermore SR-0379 promoted the tube formation of human umbilical vein endothelial cells (HUVECs) in co-culture with NHDFs. This compound also displays antimicrobial activities against a number of bacteria, including drug-resistant microbes and fungi. We evaluated the effect of SR-0379 in two different would-healing models in rats, the full-thickness defects under a diabetic condition and an acutely infected wound with full-thickness defects and inoculation with Staphylococcus aureus. Treatment with SR-0379 significantly accelerated wound healing when compared to fibroblast growth factor 2 (FGF2). The beneficial effects of SR-0379 on wound healing can be explained by enhanced angiogenesis, granulation tissue formation, proliferation of endothelial cells and fibroblasts and antimicrobial activity. These results indicate that SR-0379 may have the potential for drug development in wound repair, even under especially critical colonization conditions.

Low-level laser therapy with 810 nm wavelength improves skin wound healing in rats with streptozotocin-induced diabetes

OBJECTIVE

The aim of present study was to evaluate whether low-level laser therapy (LLLT) can reverse the impaired wound healing process in diabetic rats.

BACKGROUND DATA

Impaired wound healing in diabetic patients represents a major health problem. Recent studies have indicated that LLLT may improve wound healing in diabetic rats, but the optimal treatment parameters are still unknown.

MATERIALS AND METHODS

Male Sprague-Dawley rats (n=21) were randomly divided into three groups: a healthy control group, a diabetic sham-treated group, and a diabetic LLLT-treated group. Diabetes mellitus was then induced by streptozotocin administration to the two diabetic groups. One 4 cm long full thickness skin incision and one full thickness circular excision (diameter=4 mm) were performed on the back of each rat. An infrared 810 nm laser with an output of 30 mW, a power density of 30 mW/cm(2), and a spot size of 1 cm(2) was used to irradiate each wound for 30 sec (daily dose of 0.9 J/cm(2)/wound/day).

RESULTS

In diabetic rats, the histology of LLLT-treated excisions revealed a similar healing response to that in nondiabetic controls, with significantly more mature granulation tissue than in the sham-treated diabetic control group. LLLT reduced the loss of tensile strength, and increased the incision wound stiffness significantly compared with sham-irradiated rats, but this did not achieve the same level as in the nondiabetic controls.

CONCLUSIONS

Our study demonstrates that infrared LLLT can improve wound healing in diabetic rats. Nevertheless, further research needs to be performed to evaluate the exact underlying mechanism and to further optimize LLLT parameters for clinical use.

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.

Paracrine functions of fibrocytes to promote lung fibrosis

Fibrocytes are derived from the bone marrow and are found in the circulation. They can be recruited to sites of injury and contribute to repair/remodeling. In vitro evidence suggests that fibrocytes may differentiate into fibroblasts to promote lung fibrosis. However, in vivo evidence for this is sparse. This review summarizes recent literature which may suggest that fibrocytes function to promote fibrosis via paracrine actions. In this way, secretion of growth factors, proteases and matricellular proteins may strongly influence the actions of resident epithelial and mesenchymal cells to promote repair and resolution or to tip the scale toward pathologic remodeling.

Circulating fibrocytes stabilize blood vessels during angiogenesis in a paracrine manner

Accumulating evidence supports that circulating fibrocytes play important roles in angiogenesis. However, the specific role of fibrocytes in angiogenesis and the underlying mechanisms remain unclear. In this study, we found that fibrocytes stabilized newly formed blood vessels in a mouse wound-healing model by inhibiting angiogenesis during the proliferative phase and inhibiting blood vessel regression during the remodeling phase. Fibrocytes also inhibited angiogenesis in a Matrigel mouse model. In vitro study showed that fibrocytes inhibited both the apoptosis and proliferation of vascular endothelial cells (VECs) in a permeable support (Transwell) co-culture system. In a three-dimensional collagen gel, fibrocytes stabilized the VEC tubes by decreasing VEC tube density on stimulation with growth factors and preventing VEC tube regression on withdrawal of growth factors. Further mechanistic investigation revealed that fibrocytes expressed many prosurvival factors that are responsible for the prosurvival effect of fibrocytes on VECs and blood vessels. Fibrocytes also expressed angiogenesis inhibitors, including thrombospondin-1 (THBS1). THBS1 knockdown partially blocked the fibrocyte-induced inhibition of VEC proliferation in the Transwell co-culture system and recovered the fibrocyte-induced decrease of VEC tube density in collagen gel. Purified fibrocytes transfected with THBS1 siRNA partially recovered the fibrocyte-induced inhibition of angiogenesis in both the wound-healing and Matrigel models. In conclusion, our findings reveal that fibrocytes stabilize blood vessels via prosurvival factors and anti-angiogenic factors, including THBS1.

Evidence of a role for fibrocyte and keratinocyte-like cells in the formation of hypertrophic scars

Burn injuries affect millions of people every year, and dermal fibrosis is a common complication for the victims. This disfigurement has functional and cosmetic consequences and many research groups have made it the focus of their work to understand the mechanisms that underlie its development. Although significant progress has been made in wound-healing processes, the complexity of events involved makes it very difficult to come up with a single strategy to prevent this devastating fibrotic condition. Inflammation is considered one predisposing factor, although this phase is a necessary aspect of the wound-healing process. Inflammation, driven by infiltrated immune cells, begins minutes after the burn injury and is the prevalent phase of wound healing in the early stages. Accompanying the inflammatory infiltrate, there is evidence that subpopulations of bone marrow-derived cells are also present. These populations include fibrocytes and keratinocyte-like cells, derivatives of CD14 monocytes, a component of the peripheral blood mononuclear cell infiltrate. There is evidence that these cells contribute to regeneration and repair of the wound site, but it is interesting to note that there are also reports that these cells can have adverse effects and may contribute to the development of dermal fibrosis. In this article, the authors present a review of the origin and transdifferentiation of these cells from bone marrow stem cells, the environments that direct this transdifferentiation, and evidence to support their role in fibrosis, as well as potential avenues for therapeutics to control their fibrotic effects.

Wound healing: a paradigm for regeneration

Human skin is a remarkably plastic organ that sustains insult and injury throughout life. Its ability to expeditiously repair wounds is paramount to survival and is thought to be regulated by wound components such as differentiated cells, stem cells, cytokine networks, extracellular matrix, and mechanical forces. These intrinsic regenerative pathways are integrated across different skin compartments and are being elucidated on the cellular and molecular levels. Recent advances in bioengineering and nanotechnology have allowed researchers to manipulate these microenvironments in increasingly precise spatial and temporal scales, recapitulating key homeostatic cues that may drive regeneration. The ultimate goal is to translate these bench achievements into viable bedside therapies that address the growing global burden of acute and chronic wounds. In this review, we highlight current concepts in cutaneous wound repair and propose that many of these evolving paradigms may underlie regenerative processes across diverse organ systems.

Fibrocytes represent a novel MDSC subset circulating in patients with metastatic cancer

Fibrocytes are hematopoietic stem cell-derived fibroblast precursors that are implicated in chronic inflammation, fibrosis, and wound healing. Myeloid-derived suppressor cells (MDSCs) expand in cancer-bearing hosts and contribute to tumor immune evasion. They are typically described as CD11b⁺HLA-DR⁻ in humans. We report abnormal expansions of CD11b⁺HLA-DR⁺ myeloid cells in peripheral blood mononuclear fractions of subjects with metastatic pediatric sarcomas. Like classical fibrocytes, they display cell surface α smooth muscle actin, collagen I/V, and mediate angiogenesis. However, classical fibrocytes serve as antigen presenters and augment immune reactivity, whereas fibrocytes from cancer subjects suppressed anti-CD3-mediated T-cell proliferation, primarily via indoleamine oxidase (IDO). The degree of fibrocyte expansion observed in individual subjects directly correlated with the frequency of circulating GATA3⁺CD4⁺ cells (R = 0.80) and monocytes from healthy donors cultured with IL-4 differentiated into fibrocytes with the same phenotypic profile and immunosuppressive properties as those observed in patients with cancer. We thus describe a novel subset of cancer-induced myeloid-derived suppressor cells, which bear the phenotypic and functional hallmarks of fibrocytes but mediate immune suppression. These cells are likely expanded in response to Th2 immune deviation and may contribute to tumor progression via both immune evasion and angiogenesis.

Functional interaction of cockroach allergens and mannose receptor (CD206) in human circulating fibrocytes

BACKGROUND

The innate pattern recognition C-type-lectin receptors (CLRs), including mannose receptor (MRC1; CD206), have been suggested to functionally interact with allergens and are critical in controlling immune response. Fibrocytes have been considered to play a role in allergic asthma. Here we sought to investigate the functional interaction of cockroach allergens with CD206 in fibrocytes.

METHODS

Profiling of N-linked glycans from natural purified cockroach allergen Bla g 2 was accomplished by MALDI-MS. The binding activity of cockroach allergens to CD206 was determined by solid-phase binding assays. Levels of CD206 expression on human fibrocytes and CD206 mediated signaling and cytokine production in Bla g 2 treated fibrocytes were determined.

RESULTS

Profiling of N-linked glycans from Bla g 2 revealed a predominance of small, mannose-terminated glycans with and without fucose. Significant binding of Bla g 2 to CD206 was observed, which was inhibited by yeast mannan (a known CD206 ligand), free mannose, and a blocking antibody (anti-hMR). Flow cytometric analyses of human fibrocytes (CD45(+) and collagen-1(+)) showed selective expression of CD206 on fibrocytes. Functionally, a concentration-dependent uptake of FITC labeled Bla g 2 by fibrocytes was observed, but was significantly inhibited by anti-hMR. Bla g 2 can stimulate up-regulation of inflammatory cytokines including TNF-alpha and IL-6 and activation of nuclear factor kappa B (NF-kB/p65), p38 mitogen-activated protein kinase (p38), ERK, and JNK in cultured fibrocytes. This increased secretion of TNF-alpha and IL-6 and activation of NF-kB, ERK, and JNK was significantly inhibited by the addition of either mannan or mannose. Furthermore, Bla g 2 induced increase in TNF-alpha and IL-6 production was also inhibited by the use of NF-kB, ERK, and JNK inhibitors.

CONCLUSION

These results provide evidence supporting the existence of a functional cockroach allergen-CD206 axis in human fibrocytes, suggesting a role for CD206 in regulating allergen induced allergic responses in asthma.

Intradermal adipocytes mediate fibroblast recruitment during skin wound healing

Acute wound healing in the skin involves the communication of multiple cell types to coordinate keratinocyte and fibroblast proliferation and migration for epidermal and dermal repair. Many studies have focused on the interplay between hematopoietic cells, keratinocytes and fibroblasts during skin wound healing, yet the possible roles for other cell types within the skin, such as intradermal adipocytes, have not been investigated during this process. Here, we identify that adipocyte lineage cells are activated and function during acute skin wound healing. We find that adipocyte precursor cells proliferate and mature adipocytes repopulate skin wounds following inflammation and in parallel with fibroblast migration. Functional analysis of mice with defects in adipogenesis demonstrates that adipocytes are necessary for fibroblast recruitment and dermal reconstruction. These data implicate adipocytes as a key component of the intercellular communication that mediates fibroblast function during skin wound healing.

Research progress in the mechanism of effect of PRP in bone deficiency healing

Platelet-rich plasma (PRP) therapy is a recently developed technique that uses a concentrated portion of autologous blood to try to improve and accelerate the healing of various tissues. There is a considerable interest in using these PRP products for the treatment used in bone deficiency healing. Because PRP products are safe and easy to prepare and administer, there has been increased attention toward using PRP in numerous clinical settings. The benefits of PRP therapy appear to be promising, and many investigators are exploring the ways in which this therapy can be used in the clinical setting. At present, the molecular mechanisms of bone defect repair studies have focused on three aspects of the inflammatory cytokines, growth factors and angiogenic factors. The role of PRP works mainly through these three aspects of bone repair. The purpose of this paper is to review the current evidence on the mechanism of the effect of PRP in bone deficiency healing.

Stem cell therapy for lower extremity diabetic ulcers: where do we stand?

The impairment of wound healing in diabetic patients is an important clinical problem affecting millions of patients worldwide. Various clinical and basic science studies show that stem cell therapy, as a regenerative medical therapy, can be a good solution. In this paper, we begin with an introduction of the cellular mechanism of the diabetic ulcer. We will then discuss the advantages and limitations of various stem cell therapies that have been under extensive recent study.

Bone marrow-derived cells from the footprint infiltrate into the repaired rotator cuff

BACKGROUND

Cells from the bone marrow are considered important during the rotator cuff repair process, but the kinetics of bone marrow-derived cells in this process is unknown.

PURPOSE

To analyze the kinetics of bone marrow cells during the rotator cuff repair process, to review whether or not they are histologically involved in rotator cuff healing, and to analyze the biomechanics of the repaired tissues.

METHODS

Bone marrow chimeric rats that express green fluorescent protein (GFP) only in bone marrow- and circulation-derived cells were created. Bilateral supraspinatus tendons were separated from the greater tuberosity of the humeral head to produce a rotator cuff transection model. Drilling into the bone marrow was performed in the greater tuberosity of the right humerus and the supraspinatus tendon was repaired (drilling group), while the supraspinatus tendon was repaired on the left shoulder without drilling (control group). We examined the histology of the rotator cuff, the ultimate force-to-failure, and the proportion of GFP-positive cells in the repaired rotator cuff at 2, 4 and 8 weeks after surgery.

RESULTS

Mesenchymal cells were observed in the repaired rotator cuff at 2 weeks in both groups. There were more GFP-positive cells in the drilling group than the control group at 2, 4 and 8 weeks. The ultimate force-to-failure was significantly higher in the drilling group than the control group at 4 and 8 weeks.

CONCLUSION

Bone marrow-derived cells passed through holes drilled in the humerus footprint, infiltrated the repaired rotator cuff and contributed to postsurgical rotator cuff healing.

Surgical inflammatory stress: the embryo takes hold of the reins again

The surgical inflammatory response can be a type of high-grade acute stress response associated with an increasingly complex trophic functional system for using oxygen. This systemic neuro-immune-endocrine response seems to induce the re-expression of 2 extraembryonic-like functional axes, i.e. coelomic-amniotic and trophoblastic-yolk-sac-related, within injured tissues and organs, thus favoring their re-development. Accordingly, through the up-regulation of two systemic inflammatory phenotypes, i.e. neurogenic and immune-related, a gestational-like response using embryonic functions would be induced in the patient's injured tissues and organs, which would therefore result in their repair. Here we establish a comparison between the pathophysiological mechanisms that are produced during the inflammatory response and the physiological mechanisms that are expressed during early embryonic development. In this way, surgical inflammation could be a high-grade stress response whose pathophysiological mechanisms would be based on the recapitulation of ontogenic and phylogenetic-related functions. Thus, the ultimate objective of surgical inflammation, as a gestational process, is creating new tissues/organs for repairing the injured ones. Since surgical inflammation and early embryonic development share common production mechanisms, the factors that hamper the wound healing reaction in surgical patients could be similar to those that impair the gestational process.

The wound-healing response and upregulated embryonic mechanisms: brothers-in-arms forever

The cutaneous wound-healing reaction occurs in overlapping but inter-related phases, which ultimately result in fibrosis. The pathophysiological mechanisms involved in fibrotic diseases, including organ-related and even systemic diseases, such as systemic sclerosis, could represent the successive systemic upregulation of extraembryonic-like phenotypes, that is, amniotic and vitelline phenotypes. These two extraembryonic-like phenotypes act on the injured tissue to induce a process similar to gastrulation, which occurs during the early phases of embryo development. The amniotic-like phenotype plays a leading role in the development of neurogenic responses with significant hydroelectrolytic alterations that essentially represent the development of open microcirculation within the injured tissue. In turn, through the overlapping expression of a vitelline-like phenotype, a bone marrow-related response is produced. Interstitial infiltration by molecular and cellular mediators contributed by amniotic- and vitelline-like functions provides the functional and metabolic autonomy needed for inducing new tissue formation through mechanisms similar to those that act in gastrulation during the early phases of embryonic development. Thus, while a new tissue is formed, it quickly evolves into fibrotic tissue because of premature senescence. Mechanisms related to extraembryonic-like functions have been suggested in the following physiological and pathological processes: embryonic development; wound-healing reactions occurring during adult life; and senescence. The existence of this sort of basic self-organizing fractal-like functional pattern is an essential characteristic of our way of life.

Low molecular weight heparin inhibits circulating fibrocytes differentiation by modulating neuronal nitric oxide synthase and TGF-β1/Smad pathway

BACKGROUND/AIMS

Circulating fibrocytes (CFs) have been placed at the center of a number of fibrosing conditions. Recently, attention has been drawn to the non-anticoagulant activities of low molecular weight heparin (LH), especially its anti-fibrotic effects. The purpose of this study was to investigate the effects of LH on CFs differentiation and possible underlying mechanisms.

METHODS/RESULTS

CFs were cultured from human peripheral blood mononuclear cells and identified by dual-immunofluorescence staining. Incubation with LH inhibited CFs trans-differentiation by upregulating CD34 and downregulating pro-Collagen I and a-SMA in a concentration- and time-dependent manner, all of which were detected by flow cytometry. Similar effects were observed after incubation with L-NAME, an inhibitor of NOS. NO production was measured by Griess methods and markedly decreased in CFs treated with LH. Three NOS isoforms were assessed by western blot and nNOS was the predominant isoform involved in this process. Additionally, LH and L-NAME had similar down-regulating effects on the expression of TGF-β1 and pSmad2/3, which indicated that TGF-β/Smad pathway might be a downstream signaling of nNOS/NO during LH treatment.

CONCLUSION

These results suggested that LH could exhibit anti-fibrotic effects by inhibiting CFs transdifferentiation, in which the involvement of nNOS/NO and TGF-β/Smad pathway were identified.

The mandibular ridge oral mucosa model of stromal influences on the endothelial tip cells: an immunohistochemical and TEM study

This study aimed to evaluate by immunohistochemistry and transmission electron microscopy (TEM) the morphological features of the oral mucosa endothelial tip cells (ETCs) and to determine the immune and ultrastructural patterns of the stromal nonimmune cells which could influence healing processes. Immune labeling was performed on bioptic samples obtained from six edentulous patients undergoing surgery for dental implants placement; three normal samples were collected from patients prior to the extraction of the third mandibular molar. The antibodies were tested for CD34, CD117(c-kit), platelet derived growth factor receptor-alpha (PDGFR-α), Mast Cell Tryptase, CD44, vimentin, CD45, CD105, alpha-smooth muscle actin, FGF2, Ki67. In light microscopy, while stromal cells (StrCs) of the reparatory and normal oral mucosa, with a fibroblastic appearance, were found positive for a CD34/CD44/CD45/CD105/PDGFR-α/vimentin immune phenotype, the CD117/c-kit labeling led to a positive stromal reaction only in the reparatory mucosa. In TEM, non-immune StrCs presenting particular ultrastructural features were identified as circulating fibrocytes (CFCs). Within the lamina propria CFCs were in close contact with ETCs. Long processes of the ETCs were moniliform, and hook-like collaterals were arising from the dilated segments, suggestive for a different stage migration. Maintenance and healing of oral mucosa are so supported by extensive processes of angiogenesis, guided by ETCs that, in turn, are influenced by the CFCs that populate the stromal compartment both in normal and reparatory states. Therefore, CFCs could be targeted by specific therapies, with pro- or anti-angiogenic purposes.

Early experiences with stem cells in treating chronic wounds

This review provides a thorough and clear discussion on the outcomes of stem cells in treating chronic wounds. With recent technological developments that now allow isolation and culture of stem cells, researchers are able to perform vigorous studies on somatic or adult stem cells. Human and animal stem cell studies are discussed with a focus on the basic process of stem cells in wound healing and the authors' first-hand clinical experience with stem cells used for chronic wound healing.