Platelets, thrombospondin-1 and human dermal fibroblasts cooperate for stimulation of endothelial cell tubulogenesis through VEGF and PAI-1 regulation

Trilayer composite scaffold for urethral reconstruction:in vitroevaluation of mechanical, biological, and angiogenic properties

Regeneration of damaged urethral tissue remains a major challenge in the field of lower urinary tract reconstruction. To address this issue, various synthetic and natural biodegradable biomaterials are currently being explored for the fabrication of scaffolds that promote urethral regeneration and healing. In this study, we present an approach to fabricate a trilayer hybrid scaffold comprising a central layer of poly(lactic acid) (PLA) between two layers of chitosan. The chitosan/PLA/chitosan (CPC) scaffolds were fabricated by a sequential electrospinning process and their properties were evaluated for their suitability for urethral tissue engineering. The physical and biological properties of the CPC scaffolds were evaluated in comparison to electrospun PLA scaffolds and acellular dermis (Alloderm) as controls for a synthetic and a natural scaffold, respectively. Compared to the controls, the CPC scaffolds exhibited higher elastic modulus and ultimate tensile strength, while maintaining extensibility and suture retention strength appropriate for clinical use. The CPC scaffolds displayed significant hydrophilicity, which was associated with a higher water absorption capacity of the chitosan nanofibres. The degradation products of the CPC scaffolds did not exhibit cytotoxicity and promoted wound closure by fibroblastsin vitro. In addition, CPC scaffolds showed increased growth of smooth muscle cells, an essential component for functional regeneration of urethral tissue. Furthermore, in a chicken embryo-based assay, CPC scaffolds demonstrated significantly higher angiogenic potential, indicating their ability to promote vascularisation, a crucial aspect for successful urethral reconstruction. Overall, these results suggest that CPC hybrid scaffolds containing both natural and synthetic components offer significant advantages over conventional acellular or synthetic materials alone. CPC scaffolds show promise as potential candidates for further research into the reconstruction of the urethrain vivo.

Advances in Intercellular Communication Mediated by Exosomal ncRNAs in Cardiovascular Disease

Cardiovascular diseases are a leading cause of worldwide mortality, and exosomes have recently gained attention as key mediators of intercellular communication in these diseases. Exosomes are double-layered lipid vesicles that can carry biomolecules such as miRNAs, lncRNAs, and circRNAs, and the content of exosomes is dependent on the cell they originated from. They can be involved in the pathophysiological processes of cardiovascular diseases and hold potential as diagnostic and monitoring tools. Exosomes mediate intercellular communication, stimulate or inhibit the activity of target cells, and affect myocardial hypertrophy, injury and infarction, ventricular remodeling, angiogenesis, and atherosclerosis. Exosomes can be released from various types of cells, including endothelial cells, smooth muscle cells, cardiomyocytes, fibroblasts, platelets, adipocytes, immune cells, and stem cells. In this review, we highlight the communication between different cell-derived exosomes and cardiovascular cells, with a focus on the roles of RNAs. This provides new insights for further exploring targeted therapies in the clinical management of cardiovascular diseases.

VEGF-Encoding, Gene-Activated Collagen-Based Matrices Promote Blood Vessel Formation and Improved Wound Repair

Disruption in vascularization during wound repair can severely impair healing. Proangiogenic growth factor therapies have shown great healing potential; however, controlling growth factor activity and cellular behavior over desired healing time scales remains challenging. In this study, we evaluated collagen-mimetic peptide (CMP) tethers for their capacity to control growth factor gene transfer and growth factor activity using our recently developed gene-activated hyaluronic acid-collagen matrix (GAHCM). GAHCM was comprised of DNA/polyethyleneimine (PEI) polyplexes that were retained on hyaluronic acid (HA)-collagen hydrogels using CMPs. We hypothesized that using CMP-collagen tethers to control vascular endothelial growth factor-A (VEGF-A) gene delivery in fibroblasts would provide a powerful strategy to modulate the proangiogenic behaviors of endothelial cells (ECs) for blood vessel formation, resulting in enhanced wound repair. In co-culture experiments, we observed that CMP-modified GAHCM induced tunable gene delivery in fibroblasts as predicted, and correspondingly, VEGF-A produced by the fibroblasts led to increased growth and persistent migration of ECs for at least 7 days, as compared to non-CMP-modified GAHCM. Moreover, when ECs were exposed to fibroblast-containing VEGF-GAHCM with higher levels of CMP modification (50% CMP-PEI, or 50 CP), high CD31 expression was stimulated, resulting in the formation of an interconnected EC network with a significantly higher network volume and a larger diameter network structure than controls. Application of VEGF-GAHCM with 50 CP in murine splinted excisional wounds facilitated prolonged prohealing and proangiogenic responses resulting in increased blood vessel formation, improved granulation tissue formation, faster re-epithelialization, and overall enhanced repair. These findings suggest the benefits of CMP-collagen tethers as useful tools to control gene transfer and growth factor activity for improved treatment of wounds.

Peptide nanogels as a scaffold for fabricating dermal grafts and 3D vascularized skin models

Millions of people worldwide suffer from skin injuries, which create significant problems in their lives and are costly to cure. Tissue engineering is a promising approach that aims to fabricate functional organs using biocompatible scaffolds. We designed ultrashort tetrameric peptides with promising properties required for skin tissue engineering. Our work aimed to test the efficacy of these scaffolds for the fabrication of dermal grafts and 3D vascularized skin tissue models. We found that the direct contact of keratinocytes and fibroblasts enhanced the proliferation of the keratinocytes. Moreover, the expression levels of TGF-β1, b-FGF, IL-6, and IL-1α is correlated with the growth of the fibroblasts and keratinocytes in the co-culture. Furthermore, we successfully produced a 3D vascularized skin co-culture model using these peptide scaffolds. We believe that the described results represent an advancement in the fabrication of skin tissue equivalent, thereby providing the opportunity to rebuild missing, failing, or damaged parts.

Graphical abstract

Spatio-temporal immunolocalization of VEGF-A, Runx2, and osterix during the early steps of intramembranous ossification of the alveolar process in rat embryos

Vascular endothelial growth factor A (VEGF-A) is expressed by several cell types and is a crucial factor for angiogenic-osteogenic coupling. However, the immunolocalization of VEGF-A during the early stages of the alveolar process formation remains underexplored. Thus, we analyzed the spatio-temporal immunolocalization of VEGF-A and its relationship with Runt-related transcription factor 2 (Runx2) and osterix (Osx) during the early steps of intramembranous ossification of the alveolar process in rat embryos. Embryo heads (E) of 16, 18 and 20-day-old rats were processed for paraffin embedding. Histomorphometry and immunohistochemistry to detect VEGF-A, Runx2, and Osx (osteoblast differentiation markers) were performed. The volume density of bone tissue including bone cells and blood vessels increased significantly in E18 and E20. Cells showing high VEGF-A immunoreactivity were initially observed within a perivascular niche in the ectomesenchyme; afterwards, these cells were diffusely located near bone formation sites. Runx2-and Osx-immunopositive cells were observed in corresponded regions of cells showing strong VEGF-A immunoreactivity. Although these immunostained cells were observed in all specimens, this immunolocalization pattern was more evident in E16 specimens and gradually decreased in E18 and E20 specimens. Double immunofluorescence labelling showed intracellular co-localization of Osx and VEGF-A in cells surrounding the developing alveolar process, indicating a crucial role of VEGF-A in osteoblast differentiation. Our results showed VEGF-A immunoexpression in osteoblasts and its precursors during the maxillary alveolar process formation of rat embryos. Moreover, the VEGF-A-positive cells located within a perivascular niche at the early stages of the alveolar process development suggest a crosstalk between endothelium and ectomesenchymal cells, reinforcing the angiogenic-osteogenic coupling in this process.

"Crawling Attachment" during Periodontally Accelerated Osteogenic Orthodontics Procedure

The present clinical case reports an increased zone of keratinized gingiva that was generated following surgical excision of the gingiva during periodontally accelerated osteogenic orthodontics. The present case consists of angle Class I with mal-aligned teeth and impacted #11. The patient was evaluated up to 2 years and 1 month (2.1) showing a stable increased zone of keratinized tissue. Possible causes for this event are discussed in this case report. Additional long-term clinical studies are necessary to support these results.

Microvascular Tissue Engineering-A Review

Tissue engineering and regenerative medicine have come a long way in recent decades, but the lack of functioning vasculature is still a major obstacle preventing the development of thicker, physiologically relevant tissue constructs. A large part of this obstacle lies in the development of the vessels on a microscale-the microvasculature-that are crucial for oxygen and nutrient delivery. In this review, we present the state of the art in the field of microvascular tissue engineering and demonstrate the challenges for future research in various sections of the field. Finally, we illustrate the potential strategies for addressing some of those challenges.

Myofibroblast-Derived Exosome Induce Cardiac Endothelial Cell Dysfunction

Background: Endothelial cells (ECs) play a critical role in the maintenance of vascular homeostasis and in heart function. It was shown that activated fibroblast-derived exosomes impair cardiomyocyte function in hypertrophic heart, but their effect on ECs is not yet clear. Thus, we hypothesized that activated cardiac fibroblast-derived exosomes (FB-Exo) mediate EC dysfunction, and therefore modulation of FB-exosomal contents may improve endothelial function. Methods and Results: Exosomes were isolated from cardiac fibroblast (FB)-conditioned media and characterized by nanoparticle tracking analysis and electron microscopy. ECs were isolated from mouse heart. ECs were treated with exosomes isolated from FB-conditioned media, following FB culture with TGF-β1 (TGF-β1-FB-Exo) or PBS (control) treatment. TGF-β1 significantly activated fibroblasts as shown by increase in collagen type1 α1 (COL1α1), periostin (POSTN), and fibronectin (FN1) gene expression and increase in Smad2/3 and p38 phosphorylation. Impaired endothelial cell function (as characterized by a decrease in tube formation and cell migration along with reduced VEGF-A, Hif1α, CD31, and angiopoietin1 gene expression) was observed in TGF-β1-FB-Exo treated cells. Furthermore, TGF-β1-FB-Exo treated ECs showed reduced cell proliferation and increased apoptosis as compared to control cells. TGF-β1-FB-Exo cargo analysis revealed an alteration in fibrosis-associated miRNAs, including a significant increase in miR-200a-3p level. Interestingly, miR-200a-3p inhibition in activated FBs, alleviated TGF-β1-FB-Exo-mediated endothelial dysfunction. Conclusions: Taken together, this study demonstrates an important role of miR-200a-3p enriched within activated fibroblast-derived exosomes on endothelial cell biology and function.

Alendronate and omeprazole in combination reduce angiogenic and growth signals from osteoblasts

Objective

Due to gastrointestinal side effects of oral bisphosphonates (BPs), proton pump inhibitors (PPIs) are often prescribed. PPIs may enhance the risk of osteonecrosis of the jaw, a rare side effect of BPs. Therefore, the objective of this study was to evaluate the effects of the oral BP alendronate (ALN) and the PPI omeprazole (OME) alone and in combination on primary human osteoblasts and gingival fibroblasts in vitro.

Methods

Human gingival fibroblasts and normal human osteoblasts were incubated with either 5 μM of ALN or 1 μM of OME, or ALN + OME for 1, 3, 7 or 14 days. Effect on viability was evaluated by the lactate dehydrogenase activity in the medium and on proliferation by quantifying 3H-thymidin incorporation. Multianalyte profiling of proteins in cell culture media was performed using the Luminex 200TM system to assess the effect on selected bone markers and cytokines.

Results

The proliferation of osteoblasts and fibroblasts was reduced upon exposure to ALN + OME. ALN induced an early, temporary rise in markers of inflammation, and OME and ALN + OME promoted a transient decline. An initial increase in IL-13 occurred after exposure to all three options, whereas ALN + OME promoted IL-8 release after 7 days. OME and ALN + OME promoted a transient reduction in vascular endothelial growth factor (VEGF) from osteoblasts, whereas ALN and ALN + OME induced a late rise in VEGF from fibroblasts. Osteoprotegerin release was enhanced by ALN and suppressed by OME and ALN + OME.

Conclusions

ALN + OME seemed to exaggerate the negative effects of each drug alone on human osteoblasts and gingival fibroblasts. The anti-proliferative effects, modulation of inflammation and impairment of angiogenesis, may induce unfavorable conditions in periodontal tissue facilitating development of osteonecrosis.

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Alendronate and omeprazole reduce proliferation in osteoblasts and fibroblasts.

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Unchanged viability after exposure to either drug or the combination

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Omeprazole, alone and combined with alendronate, cause impairment of angiogenesis.

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Alendronate promotes an initial, transient increase in pro-inflammatory cytokines.

Bioengineering Vascular Networks to Study Angiogenesis and Vascularization of Physiologically Relevant Tissue Models in Vitro

Angiogenesis assays are essential for studying aspects of neovascularization and angiogenesis and investigating drugs that stimulate or inhibit angiogenesis. To date, there are several in vitro and in vivo angiogenesis assays that are used for studying different aspects of angiogenesis. Although in vivo assays are the most representative of native angiogenesis, they raise ethical questions, require considerable technical skills, and are expensive. In vitro assays are inexpensive and easier to perform, but the majority of them are only two-dimensional cell monolayers which lack the physiological relevance of three-dimensional structures. Thus, it is important to look for alternative platforms to study angiogenesis under more physiologically relevant conditions in vitro. Accordingly, in this study, we developed polymeric vascular networks to be used to study angiogenesis and vascularization of a 3D human skin model in vitro. Our results showed that this platform allowed the study of more than one aspect of angiogenesis, endothelial migration and tube formation, in vitro when combined with Matrigel. We successfully reconstructed a human skin model, as a representative of a physiologically relevant and complex structure, and assessed the suitability of the developed in vitro platform for studying endothelialization of the tissue-engineered skin model.

Microvessel Network Formation and Interactions with Pancreatic Islets in Three-Dimensional Chip Cultures

The pancreatic islet is a highly vascularized micro-organ, and rapid revascularization postislet transplantation is important for islet survival and function. However, the various mechanisms involved in islet revascularization are not fully understood, and we currently lack good in vitro platforms to explore this. Our aim for this study was to generate perfusable microvascular networks in a microfluidic chip device, in which islets could be easily integrated, to establish an in vitro platform for investigations on islet-microvasculature interactions. We compared the ability of mesenchymal stem cells (MSCs) and fibroblasts to support microvascular network formation by human umbilical vein endothelial cells (HUVECs) and human induced pluripotent stem cell-derived endothelial colony-forming cell in two-dimensional and three-dimensional models of angiogenesis, and tested the effect of different culture media on microvessel formation. HUVECs that were supported by MSCs formed patent and perfusable networks in a fibrin gel, whereas networks supported by fibroblasts rapidly regressed. Network morphology could be controlled by adjusting relative cell numbers and densities. Incorporation of isolated rat islets demonstrated that islets recruit local microvasculature in vitro, but that the microvessels did not invade islets, at least during the course of these studies. This in vitro microvascularization platform can provide a useful tool to study how various parameters affect islet integration with microvascular networks and could also be utilized for studies of vascularization of other organ systems. Impact statement To improve pancreatic islet graft survival and function posttransplantation, rapid and adequate revascularization is critical. Efforts to improve islet revascularization are demanding due to an insufficient understanding of the mechanisms involved in the process. We have applied a microfluidics platform to generate microvascular networks, and by incorporating pancreatic islets, we were able to study microvasculature-islet interactions in real time. This platform can provide a useful tool to study islet integration with microvascular networks, and could be utilized for studies of vascularization of other organ systems. Moreover, this work may be adapted toward developing a prevascularized islet construct for transplantation.

Role of thrombospondin‑1 and thrombospondin‑2 in cardiovascular diseases (Review)

Thrombospondin (TSP)-1 and TSP-2 are matricellular proteins in the extracellular matrix (ECM), which serve a significant role in the pathological processes of various cardiovascular diseases (CVDs). The multiple effects of TSP-1 and TSP-2 are due to their ability to interact with various ligands, such as structural components of the ECM, cytokines, cellular receptors, growth factors, proteases and other stromal cell proteins. TSP-1 and TSP-2 regulate the structure and activity of the aforementioned ligands by interacting directly or indirectly with them, thereby regulating the activity of different types of cells in response to environmental stimuli. The pathological processes of numerous CVDs are associated with the degradation and remodeling of ECM components, and with cell migration, dysfunction and apoptosis, which may be regulated by TSP-1 and TSP-2 through different mechanisms. Therefore, investigating the role of TSP-1 and TSP-2 in different CVDs and the potential signaling pathways they are associated with may provide a new perspective on potential therapies for the treatment of CVDs. In the present review, the current understanding of the roles TSP-1 and TSP-2 serve in various CVDs were summarized. In addition, the interacting ligands and the potential pathways associated with these thrombospondins in CVDs are also discussed.

Endothelial Progenitor Cells inhibit jaw osteonecrosis in a rat model: A major adverse effect of bisphosphonate therapy

Medication-related osteonecrosis of the jaw (MRONJ) is a serious adverse effect of antiresorptive and antiangiogenic therapies. MRONJ is identified by chronic wounds in the oral mucosa associated with exposed necrotic bone. We hypothesized that zoledronic acid (ZOL) impairs keratinocyte and fibroblast function and reduces soft tissue vascularization; therefore, treating MRONJ with proangiogenic cells may benefit MRONJ patients. The effect of ZOL and dexamethasone (DEX) on gingival fibroblasts and keratinocytes was investigated. In-vitro, ZOL inhibited fibroblast and keratinocyte proliferation, delaying scratch healing. In-vivo, exposed bone was detected at tooth extraction sites, mainly in ZOL(+)/DEX(+) rats; and was associated with significantly decreased soft tissue vascularization, serum-VEGF, and tissue-VEGF. Local injection of early and late endothelial progenitor cells (EPCs) healed 13 of 14 MRONJ lesions compared with 2/7 lesions in the mesenchymal stem cells, and 2/6, in culture-medium group. The EPCs reduced necrotic bone area, increased serum and tissue VEGF levels. EPCs engraftment was minimal, suggesting their paracrine role in MRONJ healing. The EPC-conditioned medium improved scratch healing of keratinocytes and fibroblasts via VEGF pathway and elevated mRNA of VEGFA and collagen1A1. In conclusion, a novel MRONJ treatment with EPCs, increased vascularization and improved epithelial and fibroblast functions as well as cured the lesion.

MK5 haplodeficiency decreases collagen deposition and scar size during post-myocardial infarction wound repair

MK5 is a protein serine/threonine kinase activated by p38, ERK3, and ERK4 MAPKs. MK5 mRNA and immunoreactivity are detected in mouse cardiac fibroblasts, and MK5 haplodeficiency attenuates the increase in collagen 1-α1 mRNA evoked by pressure overload. The present study examined the effect of MK5 haplodeficiency on reparative fibrosis following myocardial infarction (MI). Twelve-week-old MK5^+/- and wild-type littermate (MK5^+/+) mice underwent ligation of the left anterior descending coronary artery (LADL). Surviving mice were euthanized 8 or 21 days post-MI. Survival rates did not differ significantly between MK5^+/+ and MK5^+/- mice, with rupture of the LV wall being the primary cause of death. Echocardiographic imaging revealed similar increases in LV end-diastolic diameter, myocardial performance index, and wall motion score index in LADL-MK5^+/+ and LADL-MK5^+/- mice. Area at risk did not differ between LADL-MK5^+/+ and LADL-MK5^+/- hearts. In contrast, infarct size, scar area, and scar collagen content were reduced in LADL-MK5^+/- hearts. Immunohistochemical analysis of mice experiencing heart rupture revealed increased MMP-9 immunoreactivity in the infarct border zone of LADL-MK5^+/- hearts compared with LADL-MK5^+/+. Although inflammatory cell infiltration was similar in LADL-MK5^+/+ and LADL-MK5^+/- hearts, angiogenesis was more pronounced in the infarct border zone of LADL-MK5^+/- mice. Characterization of ventricular fibroblasts revealed reduced motility and proliferation in fibroblasts isolated from MK5^-/- mice compared with those from both wild-type and haplodeficient mice. siRNA-mediated knockdown of MK5 in fibroblasts from wild-type mice also impaired motility. Hence, reduced MK5 expression alters fibroblast function and scar morphology but not mortality post-MI. NEW & NOTEWORTHY MK5/PRAK is a protein serine/threonine kinase activated by p38 MAPK and/or atypical MAPKs ERK3/4. MK5 haplodeficiency reduced infarct size, scar area, and scar collagen content post-myocardial infarction. Motility and proliferation were reduced in cultured MK5-null cardiac myofibroblasts.

Current Challenges of Bioprinted Tissues Toward Clinical Translation

IMPACT STATEMENT

This review has a broad overview of the current challenges of bioprinted tissues towards clinical translations and future directions to overcome those challenges. The development of this field has a huge impact on the situation of an insufficient number of organ donors for life-saving organ transplantations.

Long term culture and differentiation of endothelial progenitor like cells from rat adipose derived stem cells

The procedure of obtaining qualified endothelial progenitor cells (EPCs) is still unclear and there has been some controversy on their biological properties and time of emergence. In this study, we used long-term culture of Adipose Derived Stem Cells (ADSCs) in an endothelial induction medium to obtain endothelial progenitor-like cells, and investigated the features of a few surface markers and the physiologic functions of the cells produced. In order to achieve our aim, rat ADSCs were isolated and cultured in an endothelial basal medium (EBM2), supplemented with an endothelial growth medium (EGM2). The cells were cultured 1 week for short-time, 2 weeks for mid-time, and 3 weeks for long-time cultures. Morphological changes were monitored by phase contrast and electron microscopy. The expressions of a few endothelial progenitor cells markers were analyzed by real-time RT-PCR. Low-density lipoprotein uptake and lectin binding assay were also performed for functional characterization. After induction, ADSCs showed changes in morphology from spindle-shaped in the first week to cobblestone-shaped during the next 2 weeks. Then, endothelial cell phenotype was defined by the presence of Weibel-Palade bodies in the cytoplasm and tube formation, without the use of Matrigel in the third week. In keeping with gene expression analysis, VEGFR-2 showed significant expression during early stages of endothelial differentiation for up to 3 weeks. A significantly increased expression of Tie2 was observed on day 21. Likewise, VE-Cadherin, CD34, CD133, WVF and CD31 were not significantly expressed within the same period of time. Endothelial differentiated cells also showed little LDL uptake and little to no lectin binding during the first 2 weeks of induction. However, high LDL uptake and lectin binding were observed in the third week. It appears that long term culture of ADSCs in EGM2 leads to significantly increased expression of some endothelial progenitor cells markers, strong DiI-ac-LDL uptake, lectin binding and tube-like structure formation in endothelial differentiated cells. Therefore, selection of an appropriate culture time and culture medium is crucial for establishing an efficient route to obtain sufficient numbers of EPCs with optimized quantity and quality.

Results of Experimental Ligation of the Main Vein with the Use of Cell Technologies

Autologous multipotent mesenchymal stromal cells (MMSC) of bone marrow origin with transfected GFP gene and additionally stained cell membranes were injected to rats through the skin in the projection of ligated femoral vein. The results were evaluated by fluorescent microscopy. No signs of MMSC incorporation into the wall of ligated vessel or reorganized collaterals were detected. Angiogenesis processes involving MMSC were detected in experimental rats within just 4 days and progressed until week 2 postinjection, mainly in granulations at the site of surgical intervention and the cicatrix forming there. Injected MMSC completely formed all tunics of the new vessels and incorporated in the vessels forming from the recipient cells. MMSC and the objects created from them were gradually eliminated with participation of macrophages and replaced by structures formed from the recipient cells.

Biological Interaction Between Human Gingival Fibroblasts and Vascular Endothelial Cells for Angiogenesis: A Co-culture Perspective

Advancement in cell culture protocols, multidisciplinary research approach, and the need of clinical implication to reconstruct damaged or diseased tissues has led to the establishment of three-dimensional (3D) test systems for regeneration and repair. Regenerative therapies, including dental tissue engineering, have been pursued as a new prospect to repair and rebuild the diseased/lost oral tissues. Interactions between the different cell types, growth factors, and extracellular matrix components involved in angiogenesis are vital in the mechanisms of new vessel formation for tissue regeneration. In vitro pre-vascularization is one of the leading scopes in the tissue-engineering field. Vascularization strategies that are associated with co-culture systems have proved that there is communication between different cell types with mutual beneficial effects in vascularization and tissue regeneration in two-dimensional or 3D cultures. Endothelial cells with different cell populations, including osteoblasts, smooth muscle cells, and fibroblasts in a co-culture have shown their ability to advocate pre-vascularization. In this review, a co-culture perspective of human gingival fibroblasts and vascular endothelial cells is discussed with the main focus on vascularization and future perspective of this model in regeneration and repair.

Vascular Network Formation by Human Microvascular Endothelial Cells in Modular Fibrin Microtissues

Microvascular endothelial cells (MVEC) are a preferred cell source for autologous revascularization strategies, since they can be harvested and propagated from small tissue biopsies. Biomaterials-based strategies for therapeutic delivery of cells are aimed at tailoring the cellular microenvironment to enhance the delivery, engraftment, and tissue-specific function of transplanted cells. In the present study, we investigated a modular tissue engineering approach to therapeutic revascularization using fibrin-based microtissues containing embedded human MVEC and human fibroblasts (FB). Microtissues were formed using a water-in-oil emulsion process that produced populations of spheroidal tissue modules with a diameter of 100-200 µm. The formation of MVEC sprouts within a fibrin matrix over 7 days in culture was dependent on the presence of FB, with the most robust sprouting occurring at a 1:3 MVEC:FB ratio. Cell viability in microtissues was high (>90%) and significant FB cell proliferation was observed over time in culture. Robust sprouting from microtissues was evident, with larger vessels developing over time and FB acting as pericyte-like cells by enveloping endothelial tubes. These neovessels were shown to form an interconnected vascular plexus over 14 days of culture when microtissues were embedded in a surrounding fibrin hydrogel. Vessel networks exhibited branching and inosculation of sprouts from adjacent microtissues, resulting in MVEC-lined capillaries with hollow lumens. Microtissues maintained in suspension culture aggregated to form larger tissue masses (1-2 mm in diameter) over 7 days. Vessels formed within microtissue aggregates at a 1:1 MVEC:FB ratio were small and diffuse, whereas the 1:3 MVEC:FB ratio produced large and highly interconnected vessels by day 14. This study highlights the utility of human MVEC as a cell source for revascularization strategies, and suggests that the ratio of endothelial to support cells can be used to tailor vessel characteristics. The modular microtissue format may allow minimally invasive delivery of populations of prevascularized microtissues for therapeutic applications.

Aging impairs VEGF-mediated, androgen-dependent regulation of angiogenesis

There is a progressive impairment of vascular repair mechanisms with advancing age concomitant with a steady decline in circulating androgen levels in men. Emerging evidence indicates androgens regulate angiogenesis; however, little research has focused on the impact of age upon androgen-mediated regulation of angiogenic mechanisms. Human dermal fibroblasts from young (<30 years) and older (>65 years) men were incubated with DHT, with or without androgen receptor antagonist hydroxyflutamide, or phosphoinositide 3-kinase inhibitor. Fibroblast-conditioned medium was used to stimulate angiogenic functions in human umbilical vein endothelial cells. Nuclear fractionation and fluorescence microscopy were used to study androgen receptor (AR) distribution. Conditioned medium from fibroblasts of young men, but not old men, treated with DHT produced a 3-fold increase in human umbilical vein endothelial cell tubulogenesis and 2-fold increase in migration via increased vascular endothelial growth factor (VEGF) expression and secretion, predominantly of VEGF145. DHT-induced VEGF secretion from fibroblasts of young men was AR-dependent and increased AKT phosphorylation, which was abrogated by phosphoinositide 3-kinase inhibition. By contrast, fibroblasts from older men were unresponsive to DHT and lacked androgen-mediated enhancement in VEGF production. These findings were associated with reduced AR nuclear translocation in old fibroblasts. The failure of DHT-induced paracrine stimulation of angiogenesis in fibroblasts from older men is likely due to defective nuclear translocation of AR. This first demonstration of androgen resistance (or insensitivity) acquired by human fibroblasts with aging suggests that pharmacological testosterone therapy for old men may be less effective in enhancing angiogenesis and facilitating tissue regeneration mechanisms reliant on paracrine release of VEGF.

Alteration of skin properties with autologous dermal fibroblasts

Dermal fibroblasts are mesenchymal cells found between the skin epidermis and subcutaneous tissue. They are primarily responsible for synthesizing collagen and glycosaminoglycans; components of extracellular matrix supporting the structural integrity of the skin. Dermal fibroblasts play a pivotal role in cutaneous wound healing and skin repair. Preclinical studies suggest wider applications of dermal fibroblasts ranging from skin based indications to non-skin tissue regeneration in tendon repair. One clinical application for autologous dermal fibroblasts has been approved by the Food and Drug Administration (FDA) while others are in preclinical development or various stages of regulatory approval. In this context, we outline the role of fibroblasts in wound healing and discuss recent advances and the current development pipeline for cellular therapies using autologous dermal fibroblasts. The microanatomic and phenotypic differences of fibroblasts occupying particular locations within the skin are reviewed, emphasizing the therapeutic relevance of attributes exhibited by subpopulations of fibroblasts. Special focus is provided to fibroblast characteristics that define regional differences in skin, including the thick and hairless skin of the palms and soles as compared to hair-bearing skin. This regional specificity and functional identity of fibroblasts provides another platform for developing regional skin applications such as the induction of hair follicles in bald scalp or alteration of the phenotype of stump skin in amputees to better support their prosthetic devices.

Zoledronic acid and geranylgeraniol regulate cellular behaviour and angiogenic gene expression in human gingival fibroblasts

The mevalonate pathway (MVP) and the anti-angiogenic effect of bisphosphonates have been shown to play a role in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (BRONJ). This study determined the effect of the bisphosphonate, zoledronic acid and the replenishment of the MVP by geranylgeraniol on human gingival fibroblasts. Cell viability, apoptosis, morphological analysis using transmission electron microscopy, and gene expression for vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B, epiregulin and interferon-alpha were conducted. Results showed cellular viability was decreased in the presence of zoledronic acid and the co-addition of zoledronic acid with geranylgeraniol restored cell viability to control levels. Caspase 3/7 was detected in zoledronic-acid-treated cells indicating apoptosis. Transmission electron microscopy revealed dilation of the rough endoplasmic reticulum with zoledronic acid and the appearance of multiple lipid-like vesicles following the addition of geranylgeraniol. Zoledronic acid significantly (P < 0.05, FR > ± 2) up-regulated vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B and epiregulin at one or more time points but not interferon-alpha. Addition of geranylgeraniol resulted in a reduction in the expression of all five genes compared with zoledronic-acid-treated human gingival fibroblasts. The study concluded geranylgeraniol partially reversed the effects of zoledronic acid in human gingival fibroblasts both at the cellular and genetic levels, suggesting the regulation of these genes is mediated via the mevalonate pathway.

Cardiac fibroblast-dependent extracellular matrix accumulation is associated with diastolic stiffness in type 2 diabetes

Cardiovascular complications are a leading cause of death in patients with type 2 diabetes mellitus (T2DM). Diastolic dysfunction is one of the earliest manifestations of diabetes-induced changes in left ventricular (LV) function, and results from a reduced rate of relaxation and increased stiffness. The mechanisms responsible for increased stiffness are not completely understood. Chronic hyperglycemia, advanced glycation endproducts (AGEs), and increased levels of proinflammatory and profibrotic cytokines are molecular pathways known to be involved in regulating extracellular matrix (ECM) synthesis and accumulation resulting in increased LV diastolic stiffness. Experiments were conducted using a genetically-induced mouse model of T2DM generated by a point mutation in the leptin receptor resulting in nonfunctional leptin receptors (db/db murine model). This study correlated changes in LV ECM and stiffness with alterations in basal activation of signaling cascades and expression of profibrotic markers within primary cultures of cardiac fibroblasts from diabetic (db/db) mice with nondiabetic (db/wt) littermates as controls. Primary cultures of cardiac fibrobroblasts were maintained in 25 mM glucose (hyperglycemic-HG; diabetic db/db) media or 5 mM glucose (normoglycemic-NG, nondiabetic db/wt) media. The cells then underwent a 24-hour exposure to their opposite (NG; diabetic db/db) media or 5 mM glucose (HG, nondiabetic db/wt) media. Protein analysis demonstrated significantly increased expression of type I collagen, TIMP-2, TGF-β, PAI-1 and RAGE in diabetic db/db cells as compared to nondiabetic db/wt, independent of glucose media concentration. This pattern of protein expression was associated with increased LV collagen accumulation, myocardial stiffness and LV diastolic dysfunction. Isolated diabetic db/db fibroblasts were phenotypically distinct from nondiabetic db/wt fibroblasts and exhibited a profibrotic phenotype in normoglycemic conditions.

Analysis of stromal cell secretomes reveals a critical role for stromal cell-derived hepatocyte growth factor and fibronectin in angiogenesis

OBJECTIVE

Angiogenesis requires tightly coordinated crosstalk between endothelial cells (ECs) and stromal cells, such as fibroblasts and smooth muscle cells. The specific molecular mechanisms moderating this process are still poorly understood.

METHODS AND RESULTS

Stromal cell-derived factors are essential for EC sprouting and lumen formation. We therefore compared the abilities of 2 primary fibroblast isolates and a primary smooth muscle cell isolate to promote in vitro angiogenesis, and analyzed their secretomes using a combination of nano liquid chromatography-mass spectrometry/mass spectrometry, quantitative PCR, and ELISA. Each isolate exhibited a different level of angiogenic ability. Using quantitative MS, we then compared the secretomes of a fibroblast isolate exhibiting low angiogenic activity, a fibroblast isolate exhibiting high angiogenic activity, and human umbilical vein ECs. High angiogenic fibroblast supernatants exhibited an overabundance of proteins associated with extracellular matrix constituents compared with low angiogenic fibroblasts or ECs. Finally, small interfering RNA technology and purified protein were used to confirm a role for stromal cell-derived hepatocyte growth factor and fibronectin in inducing EC sprouting.

CONCLUSIONS

Differences in stromal cell ability to induce angiogenesis are a result of differences in the secreted proteomes of both extracellular matrix proteins and proangiogenic growth factors.

Lack of haptoglobin results in unbalanced VEGFα/angiopoietin-1 expression, intramural hemorrhage and impaired wound healing after myocardial infarction

Decreased haptoglobin (Hp) functionality due to allelic variations is associated with worsened outcome in patients after myocardial infarction (MI). However, mechanisms through which haptoglobin deficiency impairs cardiac repair remain to be elucidated. In the present study, we identified novel molecular alterations mediated by Hp involved in early and late cardiac repair responses after left coronary artery ligation in Hp(-/-) and wild-type (WT) mice. We observed a higher mortality rate in Hp(-/-) mice despite similar infarct size between groups. Deaths were commonly caused by cardiac rupture in Hp(-/-) animals. Histological analysis of 3 and 7days old non-ruptured infarcted hearts revealed more frequent and more severe intramural hemorrhage and increased leukocyte infiltration in Hp(-/-) mice. Analyses of non-ruptured hearts revealed increased oxidative stress, reduced PAI-1 activity and enhanced VEGFα transcription in Hp(-/-) mice. In line with these observations, we found increased microvascular permeability in Hp(-/-) hearts 3days after infarction. In vitro, haptoglobin prevented hemoglobin-induced oxidative stress and restored VEGF/Ang-1 balance in endothelial cell cultures. During long-term follow-up of the surviving animals, we observed altered matrix turnover, impaired scar formation and worsened cardiac function and geometry in Hp(-/-)mice. In conclusion, haptoglobin deficiency severely deteriorates tissue repair and cardiac performance after experimental MI. Haptoglobin plays a crucial role in both short- and long-term cardiac repair responses by reducing oxidative stress, maintaining microvascular integrity, myocardial architecture and proper scar formation.

Gene expression profiling in dermatitis herpetiformis skin lesions

Dermatitis herpetiformis (DH) is an autoimmune blistering skin disease associated with gluten-sensitive enteropathy (CD). In order to investigate the pathogenesis of skin lesions at molecular level, we analysed the gene expression profiles in skin biopsies from 6 CD patients with DH and 6 healthy controls using Affymetrix HG-U133A 2.0 arrays. 486 genes were differentially expressed in DH skin compared to normal skin: 225 were upregulated and 261 were downregulated. Consistently with the autoimmune origin of DH, functional classification of the differentially expressed genes (DEGs) indicates a B- and T-cell immune response (LAG3, TRAF5, DPP4, and NT5E). In addition, gene modulation provides evidence for a local inflammatory response (IL8, PTGFR, FSTL1, IFI16, BDKRD2, and NAMPT) with concomitant leukocyte recruitment (CCL5, ENPP2), endothelial cell activation, and neutrophil extravasation (SELL, SELE). DEGs also indicate overproduction of matrix proteases (MMP9, ADAM9, and ADAM19) and proteolytic enzymes (CTSG, ELA2, CPA3, TPSB2, and CMA1) that may contribute to epidermal splitting and blister formation. Finally, we observed modulation of genes involved in cell growth inhibition (CGREF1, PA2G4, and PPP2R1B), increased apoptosis (FAS, TNFSF10, and BASP1), and reduced adhesion at the dermal epidermal junction (PLEC1, ITGB4, and LAMA5). In conclusion, our results identify genes that are involved in the pathogenesis of DH skin lesions.

The requirement for fibroblasts in angiogenesis: fibroblast-derived matrix proteins are essential for endothelial cell lumen formation

A role for fibroblasts in physiological and pathological angiogenesis is now well recognized; however, the precise mechanisms underlying their action have not been determined. Using an in vitro angiogenesis model in combination with a candidate gene approach, column chromatography, and mass spectrometry, we identify two classes of fibroblast-derived factors--one that supports vessel sprouting but not lumen formation, and one that promotes lumen formation. In the absence of fibroblasts a combination of angiopoietin-1, angiogenin, hepatocyte growth factor, transforming growth factor-α, and tumor necrosis factor drives robust endothelial cell (EC) sprouting; however, lumens fail to form. Subsequent addition of fibroblast-conditioned medium restores lumenogenesis. Using small interfering RNA-mediated knockdown, we show that five genes expressed in fibroblasts--collagen I, procollagen C endopeptidase enhancer 1, secreted protein acidic and rich in cysteine, transforming growth factor-β-induced protein ig-h3, and insulin growth factor-binding protein 7--are necessary for lumen formation. Moreover, lumen formation can be rescued by addition of purified protein to knockdown cultures. Finally, using rheology, we demonstrate that the presence of these matricellular proteins results in significantly stiffer gels, which correlates with enhanced lumen formation. These findings highlight the critical role that fibroblast-derived extracellular matrix components play in EC lumen formation and provide potential insight into the role of fibroblasts in the tumor microenvironment.

Both actin and polyproline interactions of profilin-1 are required for migration, invasion and capillary morphogenesis of vascular endothelial cells

The objective of the present study was to evaluate how different ligand interactions of profilin-1 (Pfn1), an actin-binding protein that is upregulated during capillary morphogenesis of vascular endothelial cells (VEC), contribute to migration and capillary forming ability of VEC. We adopted a knockdown-knockin experimental system to stably express either fully functional form or mutants of Pfn1 that are impaired in binding to two of its major ligands, actin (H119E mutant) and proteins containing polyproline domains (H133S mutant), in a human dermal microvascular cell line (HmVEC) against near-null endogenous Pfn1 background. We found that silencing endogenous Pfn1 expression in HmVEC leads to slower random migration, reduced velocity of membrane protrusion and a significant impairment in matrigel-induced cord formation. Only re-expression of fully functional but not any of the two ligand-binding deficient mutants of Pfn1 rescues the above defects. We further show that loss of Pfn1 expression in VEC inhibits three-dimensional capillary morphogenesis, MMP2 secretion and ECM invasion. VEC invasion through ECM is also inhibited when actin and polyproline interactions of Pfn1 are disrupted. Together, these experimental data demonstrate that Pfn1 regulates VEC migration, invasion and capillary morphogenesis through its interaction with both actin and proline-rich ligands.

Proliferation-promoting effect of platelet-rich plasma on human adipose-derived stem cells and human dermal fibroblasts

BACKGROUND

This study evaluated changes in platelet-derived growth factor (PDGF)-AB and transforming growth factor (TGF)-beta1 release from platelets by platelet-rich plasma activation, and the proliferation potential of activated platelet-rich plasma and platelet-poor plasma on human adipose-derived stem cells and human dermal fibroblasts.

METHODS

Platelet-rich plasma was prepared using a double-spin method, with the number of platelets counted in each preparation stage. Platelet-rich and platelet-poor plasma were activated with autologous thrombin and calcium chloride, and levels of platelet-released PDGF-AB and TGF-beta1 were determined by enzyme-linked immunosorbent assay. Cells were cultured for 1, 4, or 7 days in serum-free Dulbecco's Modified Eagle Medium supplemented with 5% whole blood plasma, nonactivated platelet-rich plasma, nonactivated platelet-poor plasma, activated platelet-rich plasma, or activated platelet-poor plasma. In parallel, these cells were cultured for 1, 4, or 7 days in serum-free Dulbecco's Modified Eagle Medium supplemented with 1%, 5%, 10%, or 20% activated platelet-rich plasma. The cultured human adipose-derived stem cells and human dermal fibroblasts were assayed for proliferation.

RESULTS

Platelet-rich plasma contained approximately 7.9 times as many platelets as whole blood, and its activation was associated with the release of large amounts of PDGF-AB and TGF-beta1. Adding activated platelet-rich or platelet-poor plasma significantly promoted the proliferation of human adipose-derived stem cells and human dermal fibroblasts. Adding 5% activated platelet-rich plasma to the medium maximally promoted cell proliferation, but activated platelet-rich plasma at 20% did not promote it.

CONCLUSIONS

Platelet-rich plasma can enhance the proliferation of human adipose-derived stem cells and human dermal fibroblasts. These results support clinical platelet-rich plasma application for cell-based, soft-tissue engineering and wound healing.

Characterization of the acute temporal changes in excisional murine cutaneous wound inflammation by screening of the wound-edge transcriptome

This work represents a maiden effort to systematically screen the transcriptome of the healing wound-edge tissue temporally using high-density GeneChips. Changes during the acute inflammatory phase of murine excisional wounds were characterized histologically. Sets of genes that significantly changed in expression during healing could be segregated into the following five sets: up-early (6-24 h; cytokine-cytokine receptor interaction pathway), up-intermediary (12-96 h; leukocyte-endothelial interaction pathway), up-late (48-96 h; cell-cycle pathway), down-early (6-12 h; purine metabolism) and down-intermediary (12-96 h; oxidative phosphorylation pathway). Results from microarray and real-time PCR analyses were consistent. Results listing all genes that were significantly changed at any specific time point were further mined for cell-type (neutrophils, macrophages, endothelial, fibroblasts, and pluripotent stem cells) specificity. Candidate genes were also clustered on the basis of their functional annotation, linking them to inflammation, angiogenesis, reactive oxygen species (ROS), or extracellular matrix (ECM) categories. Rapid induction of genes encoding NADPH oxidase subunits and downregulation of catalase in response to wounding is consistent with the fact that low levels of endogenous H2O2 is required for wound healing. Angiogenic genes, previously not connected to cutaneous wound healing, that were induced in the healing wound-edge included adiponectin, epiregulin, angiomotin, Nogo, and VEGF-B. This study provides a digested database that may serve as a valuable reference tool to develop novel hypotheses aiming to elucidate the biology of cutaneous wound healing comprehensively.

Endothelial-stromal interactions in angiogenesis

PURPOSE OF REVIEW

Angiogenesis often occurs in the context of a wound or tumor stroma. This review will focus on the recent findings on the interactions between angiogenic endothelial cells and the other components of the stroma - fibroblasts, pericytes and extracellular matrix.

RECENT FINDINGS

Large-scale gene expression arrays have provided a remarkable insight into the diversity of fibroblasts in different tissues and under different conditions. These somewhat neglected cells are now understood to play a critical role in tumor growth, regulating not only the phenotype of the tumor cells but also the angiogenic response that supports them. These advances are leading to an understanding of the soil and seed hypothesis at the molecular level. In addition, there is a new focus on the role of pericytes in regulating angiogenesis and their potential as targets for tumor therapy.

SUMMARY

Initiation of new blood vessel formation requires metalloproteinase induction leading to the degradation of the basement membrane, sprouting of endothelial cells and regulation of pericyte attachment. Fibroblasts and their activated counterpart, the myofibroblast, play a large role in synchronizing these events through the expression of numerous extracellular matrix molecules, growth factors and morphogens, including fibroblast growth factors and transforming growth factor beta.

Angiogenesis in inflammatory bowel disease

Both ulcerative colitis and Crohn's disease, the two major forms of inflammatory bowel diseases, are recognized, at the moment, as perplexing and challenging clinical entities, in which several molecules and cell types are implicated. Recent molecular evidence proposes the intestinal microvascular remodelling or angiogenesis, as a phenomenon implicated in the pathogenesis of these chronic inflammatory disorders, together with other proposed theories involved in the pathogenesis of inflammatory bowel diseases, such as genetic, microbacterial and immune factors. Intestinal damage is followed by a physiological angiogenesis, but the abnormal expression of pro- and anti-angiogenic molecules and the changes of vascular cell types could reflect a pathological vascular remodelling. Thus, the inflammation may be favoured and maintained by a pathological angiogenesis. A better understanding of the angiogenic process may facilitate the design of more effective therapies for chronic intestinal inflammation.

Increased VEGFR2 expression during human late endothelial progenitor cells expansion enhances in vitro angiogenesis with up-regulation of integrin alpha(6)

In vitro expansion of late endothelial progenitor cells (EPCs) might yield a cell therapy product useful for myocardial and leg ischaemia, but the influence of EPC expansion on the angiogenic properties of these cells is unknown. In the present study, we investigated the effect of in vitro EPC expansion on vascular endothelial growth factor (VEGF) receptor expression. EPCs were obtained from CD34⁺ cord blood cells and expanded for up to 5 weeks. Real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR) showed that VEGFR2 expression, contrary to VEGFR1 and VEGFR3 expression, was significantly higher on expanded EPCs than on freshly isolated CD34⁺ cells or on human umbilical vein endothelial cells (HUVECs). Quantitative flow cytometry confirmed that VEGFR2 density on EPCs increased during the expansion process and was significantly higher than on HUVECs. The impact of VEGFR2 increase was studied on the three theoretical steps of angiogenesis, i.e., EPC proliferation, migration and differentiation. VEGFR2 up-regulation had no effect on VEGF-induced cell proliferation, but significantly enhanced EPC migration and pseudotubes formation dependent on integrin α₆ subunit overexpression. In vitro expansion of late EPCs increases the expression of VEGFR2, the main VEGF receptor, with possible implications for EPC-based angiogenic therapy.

Thrombospondins use the VLDL receptor and a nonapoptotic pathway to inhibit cell division in microvascular endothelial cells

TSPs 1 and 2 function as endogenous inhibitors of angiogenesis. Although thrombospondins (TSPs) have been shown to induce apoptosis in HMVECs, we reasoned that a homeostatic mechanism would also be needed to inhibit EC growth without causing cell death, e.g., in the maintenance of a normal vascular endothelium. HMVECs, cultured in low serum, responded to VEGF with an increase in [(3)H]thymidine incorporation that was inhibited by TSPs and was accompanied by decreases in the phosphorylation of Akt and MAPK, without an increase in apoptosis. RAP, an inhibitor of the low-density lipoprotein (LDL) family of endocytic receptors, and blocking antibodies to VLDLR were as effective as TSPs in the inhibition of thymidine uptake in response to VEGF, and the effects of these agents were not additive. Supportive evidence for the role of the VLDLR in mediating this inhibition was provided by the demonstration of a high-affinity interaction between TSPs and the VLDLR. We propose that TSP1 and TSP2, together with the VLDLR, initiate a nonapoptotic pathway for maintenance of the normal adult vascular endothelium in a quiescent state, similar to that invoked for the regulation of mitogenesis by PDGF, but involving signaling via the VLDLR rather than LRP1.

Tissue engineering for full-thickness burns: a dermal substitute from bench to bedside

Our aim was to obtain a viable and easily available dermal substitute (DS) for the definitive coverage of full-thickness burns. A DS composed of a collagen-glycosaminoglycan-chitosan dermal matrix (DM) colonized with foreskin fibroblasts (FF) is described. FF-colonized DS were compared to the DM seeded with adult dermal fibroblasts (DF). FF-colonized DS expressed more fibrillin and tropoelastin than that with DF. Reconstructed skin obtained with both FF- and DF-colonized DS similarly expressed laminin-5 and collagen VII at the dermal-epidermal junction. Both FF- and DF-colonized DS produced cutaneous wound healing mediators in a dose-dependent manner in the presence of platelet lysate. After freeze-thawing, the FF-colonized DS were recovered in culture and retained their ability to produce vascular endothelial growth factor. Grafting of DS into nude rats achieved a complete healing of a dermal-epidermal lesion with a good epidermalization.

Delayed and deficient dermal maturation in mice lacking the CXCR3 ELR-negative CXC chemokine receptor

Replacement of wounded skin requires the initially florid cellular response to abate and even regress as the dermal layer returns to a relatively paucicellular state. The signals that direct this "stop and return" process have yet to be deciphered. CXCR3 chemokine receptor and its ligand CXCL11/IP-9/I-TAC are expressed by basal keratinocytes and CXCL10/IP-10 by keratinocytes and endothelial cells during wound healing in mice and humans. In vitro, these ligands limit motility in dermal fibroblasts and endothelial cells. To examine whether this signaling pathway contributes to wound healing in vivo, full-thickness excisional wounds were created on CXCR3 wild-type (+/+) or knockout (-/-) mice. Even at 90 days, long after wound closure, wounds in the CXCR3(-/-) mice remained hypercellular and presented immature matrix components. The CXCR3(-/-) mice also presented poor remodeling and reorganization of collagen, which resulted in a weakened healed dermis. This in vivo model substantiates our in vitro findings that CXCR3 signaling is necessary for inhibition of fibroblast and endothelial cell migration and subsequent redifferentiation of the fibroblasts to a contractile state. These studies establish a pathophysiologic role for CXCR3 and its ligand during wound repair.