The role of vascular endothelial growth inhibitor in wound healing

TNFSF15 facilitates the differentiation of CD11b+ myeloid cells into vascular pericytes in tumors

OBJECTIVE

Immature vasculature lacking pericyte coverage substantially contributes to tumor growth, drug resistance, and cancer cell dissemination. We previously demonstrated that tumor necrosis factor superfamily 15 (TNFSF15) is a cytokine with important roles in modulating hematopoiesis and vascular homeostasis. The main purpose of this study was to explore whether TNFSF15 might promote freshly isolated myeloid cells to differentiate into CD11b+ cells and further into pericytes.

METHODS

A model of Lewis lung cancer was established in mice with red fluorescent bone marrow. After TNFSF15 treatment, CD11b+ myeloid cells and vascular pericytes in the tumors, and the co-localization of pericytes and vascular endothelial cells, were assessed. Additionally, CD11b+ cells were isolated from wild-type mice and treated with TNFSF15 to determine the effects on the differentiation of these cells.

RESULTS

We observed elevated percentages of bone marrow-derived CD11b+ myeloid cells and vascular pericytes in TNFSF15-treated tumors, and the latter cells co-localized with vascular endothelial cells. TNFSF15 protected against CD11b+ cell apoptosis and facilitated the differentiation of these cells into pericytes by down-regulating Wnt3a-VEGFR1 and up-regulating CD49e-FN signaling pathways.

CONCLUSIONS

TNFSF15 facilitates the production of CD11b+ cells in the bone marrow and promotes the differentiation of these cells into pericytes, which may stabilize the tumor neovasculature.

nWASP Inhibition Increases Wound Healing via TrKb/PLCγ Signalling

(1) Background: Chronic wounds represent a major burden to patients and healthcare systems and identifying new therapeutic targets to encourage wound healing is a significant challenge. This study evaluated nWASP as a new therapeutic target in human wound healing and determined how this can be regulated. (2) Methods: Clinical cohorts from patients with chronic wounds were tested for the expression of nWASP and cell models were employed to evaluate the influence of nWASP on cellular functions that are key to the healing process following knockdown and/or the use of nWASP-specific inhibitors. (3) Results: nWASP was significantly elevated at transcript levels in human non-healing chronic wounds versus healing tissues. nWASP inhibitors, wiskostatin and 187-1, along with the knockdown of nWASP, modified both HaCaT and HECV cell behaviour. We then identified two signalling pathways affected by nWASP inhibition: TrkB signalling and downstream PLCγ1 phosphorylation were impaired by nWASP inhibition in HaCaT cells. The healing of wounds in a diabetic murine model was significantly improved with an nWASP inhibitor treatment. (4) Conclusions: This study showed that nWASP activity was related to the non-healing behaviour of chronic wounds and together with the findings in the in vivo models, it strongly suggested nWASP as a therapeutic target in non-healing wounds that are regulated via TrkB and PLCγ1 signalling.

VEGI Improves Outcomes in the Early Phase of Experimental Traumatic Brain Injury

Excessive expression of vascular endothelial growth factor (VEGF) is a common cause of blood-brain barrier (BBB) breakdown that triggers severe complications following traumatic brain injury (TBI). It has been shown that inhibition of VEGF activities may attenuate cerebral edema in pathological conditions. Vascular endothelial growth inhibitor (VEGI; also known as TNFSF15), a cytokine produced largely by vascular endothelial cells, is capable of downregulating VEGF expression and inhibiting VEGF receptor-2 (VEGFR2) activation. In this study we found that TBI can cause breakdown of BBB and sharp increases of VEGF/VEGI and Angpt2/Angpt1 ratios in the injured tissues. VEGI treatment resulted in a marked decrease of BBB permeability and concomitant restoration of normal ratios of VEGF/VEGI and Angpt2/Angpt1. Consistently, alleviated edema, decreased neuron cell death, and improved neurological functions were observed when the experimental animals were treated with VEGI in the early phase of TBI. Our findings suggest that administration of VEGI recombinant protein at early phases of TBI is beneficial to stabilization of the disease conditions.

Counterbalance: modulation of VEGF/VEGFR activities by TNFSF15

Vascular hyperpermeability occurs in angiogenesis and several pathobiological conditions, producing elevated interstitial fluid pressure and lymphangiogenesis. How these closely related events are modulated is a fundamentally important question regarding the maintenance of vascular homeostasis and treatment of disease conditions such as cancer, stroke, and myocardial infarction. Signals mediated by vascular endothelial growth factor receptors, noticeably VEGFR-1, −2, and −3, are centrally involved in the promotion of both blood vessel and lymphatic vessel growth. These signaling pathways are counterbalanced or, in the case of VEGFR3, augmented by signals induced by tumor necrosis factor superfamily-15 (TNFSF15). TNFSF15 can simultaneously downregulate membrane-bound VEGFR1 and upregulate soluble VEGFR1, thus changing VEGF/VEGFR1 signals from pro-angiogenic to anti-angiogenic. In addition, TNFSF15 inhibits VEGF-induced VEGFR2 phosphorylation, thereby curbing VEGFR2-mediated enhancement of vascular permeability. Third, and perhaps more interestingly, TNFSF15 is capable of stimulating VEGFR3 gene expression in lymphatic endothelial cells, thus augmenting VEGF-C/D-VEGFR3-facilitated lymphangiogenesis. We discuss the intertwining relationship between the actions of TNFSF15 and VEGF in this review.

The ability of tumor necrosis factor superfamily-15 (TNFSF15) protein to balance the actions of vascular endothelial growth factors (VEGFs) highlights new therapeutic strategies for the treatment of diseases that disrupt the circulatory system. Gui-Li Yang at the Tianjin Neurological Institute and Lu-Yuan Li at Nankai University describe the mechanisms through which TNFSF15 inhibits blood vessel growth mediated by VEGF receptor-1 (VEGFR1) and counterbalances the increase in vascular permeability mediated by VEGFR2. Interestingly, TNFSF15 enhances the effects of VEGFR3 on the formation of lymphatic vessels by promoting VEGFR3 gene expression in lymphatic endothelial cells. Further research will determine whether TNFSF15′s unique capacity to regulate the properties of both blood and lymph vessels can be harnessed to improve the treatment of conditions such as cancer, stroke, myocardial infarction and lymphoedema.

TNFSF15 suppresses VEGF production in endothelial cells by stimulating miR-29b expression via activation of JNK-GATA3 signals

Vascular endothelial cell growth factor (VEGF) plays a pivotal role in promoting neovascularization. VEGF gene expression in vascular endothelial cells in normal tissues is maintained at low levels but becomes highly up-regulated in a variety of disease settings including cancers. Tumor necrosis factor superfamily 15 (TNFSF15; VEGI; TL1A) is an anti-angiogenic cytokine prominently produced by endothelial cells in a normal vasculature. We report here that VEGF production in mouse endothelial cell line bEnd.3 can be inhibited by TNFSF15 via microRNA-29b (miR-29b) that targets the 3'-UTR of VEGF transcript. Blocking TNFSF15 activity by using either siRNA against the TNFSF15 receptor known as death domain-containing receptor-3 (DR3; TNFRSF25), or a neutralizing antibody 4-3H against TNFSF15, led to inhibition of miR-29b expression and reinvigoration of VEGF production. In addition, we found that TNFSF15 activated the JNK signaling pathway as well as the transcription factor GATA3, resulting in enhanced miR-29b production. Treatment of the cells either with SP600125, an inhibitor of JNK, or with JNK siRNA, led to eradication of TNFSF15-induced GATA3 expression. Moreover, GATA3 siRNA suppressed TNFSF15-induced miR-29b expression. These findings suggest that VEGF gene expression can be suppressed by TNFSF15-stimulated activation of the JNK-GATA3 signaling pathway which gives rise to up-regulation of miR-29b.

Vascular precursor cells in tissue injury repair

Vascular precursor cells include stem cells and progenitor cells giving rise to all mature cell types in the wall of blood vessels. When tissue injury occurs, local hypoxia and inflammation result in the generation of vasculogenic mediators which orchestrate migration of vascular precursor cells from their niche environment to the site of tissue injury. The intricate crosstalk among signaling pathways coordinates vascular precursor cell proliferation and differentiation during neovascularization. Establishment of normal blood perfusion plays an essential role in the effective repair of the injured tissue. In recent years, studies on molecular mechanisms underlying the regulation of vascular precursor cell function have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches to treat chronic wounds and ischemic diseases in vital organ systems. Verification of safety and establishment of specific guidelines for the clinical application of vascular precursor cell-based therapy remain major challenges in the field.

Molecular and cellular impact of Psoriasin (S100A7) on the healing of human wounds

Psoriasin, which is also known as S100A7, is a member of the S100 protein family, a group of calcium-responsive signalling proteins. Psoriasin expression remains high in patients with psoriasis, whereas it is downregulated in patients with invasive breast carcinoma. This observation suggests that this protein may be a notable marker of keratinocyte function and differentiation during wound healing. The aim of the present study was to determine the cellular impact of Psoriasin in keratinocytes, which are the primary cell type associated with wound healing. Psoriasin expression in wound tissues was examined using reverse transcription-quantitative polymerase chain reaction and immunochemical staining. Knockdown of Psoriasin in HaCaT cells was performed using anti-Psoriasin ribozyme transgenes and the effect on growth, adhesion and migration of keratinocytes was subsequently determined using in vitro cellular functional assays. Psoriasin expression is upregulated in wounds, particularly at the wound edges. The present study demonstrated that Psoriasin is expressed in keratinocytes and is a fundamental regulator of keratinocyte migration. Significant increases in the rate of keratinocyte adhesion, migration and growth were observed in Psoriasin-deficient cells (P<0.01 vs. control). Application of small inhibitors identified the potential association of neural Wiskott-Aldrich syndrome protein, focal adhesion primase and rho-associated protein kinase signalling pathways with Psoriasin-regulated cell adhesion and motility. In conclusion, Psoriasin serves an important role in the wound healing process, suggesting that it may be utilized as a potential wound healing biomarker.

TNFSF15 Inhibits Blood Retinal Barrier Breakdown Induced by Diabetes

Tumor necrosis factor superfamily 15 (TNFSF15) is an endogenous neovascularization inhibitor and an important negative regulator of vascular homeostasis. This study aimed to explore the potential role of TNFSF15 in diabetic retinopathy. Vitreous TNFSF15 and VEGF levels in proliferative diabetic retinopathy (PDR) patients were detected by ELISA. Retinal expression of TNFSF15 and the content of tight junction proteins (TJPs) in rats were detected by immunohistochemistry and Western blot, respectively. The blood retinal barrier (BRB) permeability was evaluated using Evans Blue (EB) dye. The TNFSF15/VEGF ratio was decreased in the vitreous fluid of patients with PDR relative to the controls, even though the expression levels of TNFSF15 were higher. TNFSF15 was dramatically decreased one month later after diabetes induction (p < 0.001), and then increased three months later and thereafter. TNFSF15 treatment significantly protected the BRB in the diabetic animals. Diabetes decreased TJPs levels in the retina, and these changes were inhibited by TNFSF15 treatment. Moreover, TNFSF15 decreased activation of VEGF both in mRNA and protein levels caused by diabetes. These results indicate that TNFSF15 is an important inhibitor in the progression of DR and suggest that the regulation of TNFSF15 shows promise for the development of diabetic retinopathy treatment strategies.

Tumour endothelial marker-8 in wound healing and its impact on the proliferation and migration of keratinocytes

Chronic wound management represents a significant burden on healthcare systems and negatively impacts on the quality of patient life. New strategies to understand and identify wounds that will not heal in a normal manner are required. Tumour endothelial marker‑8 (TEM‑8) has been implicated in the wound healing and angiogenesis processes. TEM‑8 expression was examined at the transcript level in a cohort of acute (n=10) and chronic (n=14) wounds and in normal skin (n=10). Protein analysis of TEM‑8 was also undertaken for this cohort using immunohistochemistry (IHC). TEM‑8 impact on keratinocyte cell growth and migration was assessed following TEM‑8 ribozyme transgene transfection of human HaCaT keratinocytes using cell growth and electric cell‑substrate impedance sensing (ECIS)‑based assays. Expression of TEM‑8 was observed to be increased in acute wounds compared to chronic wounds and normal skin using quantitative polymerase chain reaction transcript analysis and IHC staining of wound tissues. Knockdown of TEM‑8 in HaCaT cells, using two independent ribozyme transgenes, resulted in significant decreases in cell growth as well as reductions in the rate of migration assessed using an ECIS‑based system. TEM‑8 may be differentially expressed between wound types and loss of this molecule impacts HaCaT growth and migration, potentially implicating this molecule as a factor involved in successful progression of wound healing.

VEGI attenuates the inflammatory injury and disruption of blood-brain barrier partly by suppressing the TLR4/NF-κB signaling pathway in experimental traumatic brain injury

Acute traumatic brain injury (TBI) tends to cause the over-activation of inflammatory response and disruption of blood brain barrier (BBB), associating with long-term cognitive and behavioral dysfunction. Vascular endothelial growth inhibitor (VEGI), as a suppressor in the angiogenesis specifically by inducing apoptosis in proliferating endothelial cells, has been applied to different diseases, especially the tumors. But rare study had been done in the field of brain injury. So in this study, we investigated the effects and mechanisms associated with VEGI-induced neuroprotection following CNS injury in mice TBI models. We demonstrated that the VEGI treatment reduced the contusion brain tissue loss, the permeation of inflammatory cells (MPO(+)) and the activation of microglia (Iba-1(+)). The treatment up-regulated the tight junction proteins (CLN5, ZO-1 and OCLN), which are vital importance for the integrity of the blood brain barrier (BBB), the B-cell lymphoma 2 (Bcl-2) cell survival factors, while down-regulated the expression of TLR4, NF-κB and inflammatory cytokines (IL-1β, TNF-α, iNOS). The treatment also decreased the expression of reactive astrocytes (GFAP(+)), as well as the VEGF, and lowered the permeability of Evens Blue (EB). These findings suggested that the VEGI-treatment could alleviate the post-traumatic excessive inflammatory response, and maintain the stability of blood vessels, remitting the secondary brain damage.

Interferon-γ produced by tumor-infiltrating NK cells and CD4+ T cells downregulates TNFSF15 expression in vascular endothelial cells

Endothelial cells in an established vasculature secrete tumor necrosis factor superfamily-15 (TNFSF15; VEGI; TL1A) that functions as a negative modulator of neovascularization to maintain blood vessel stability. TNFSF15 gene expression diminishes at angiogenesis and inflammation sites such as in cancers and wounds. We reported previously that vascular endothelial growth factor and monocyte chemotactic protein-1 contribute to TNFSF15 downmodulation in ovarian cancer. Here we show that interferon-γ (IFNγ) suppresses TNFSF15 expression in human umbilical vein endothelial cells. This activity is mediated by IFNγ receptor and the transcription factor STAT1. Immunohistochemical analysis of ovarian cancer clinical specimens indicates that TNFSF15 expression diminishes while tumor vascularity increases in specimens with high-grades of IFNγ expression. Since tumor-infiltrating NK and CD4(+) T cells are the main sources of IFNγ in tumor lesions, we isolated these cells from peripheral blood of healthy individuals, treated the cells with ovarian cancer OVCAR3 cell-conditioned media, and found a onefold and tenfold increase of IFNγ production in NK and CD4(+) T cells, respectively, compared with that in vehicle-treated cells. These findings support the view that tumor-infiltrating NK and CD4(+) T cells under the influence of cancer cells significantly increase the production of IFNγ, which in turn inhibits TNFSF15 expression in vascular endothelial cells, shifting the balance of pro- and anti-angiogenic factors toward escalated angiogenesis potential in the tumor.

TNFSF15 inhibits vasculogenesis by regulating relative levels of membrane-bound and soluble isoforms of VEGF receptor 1

Mouse bone marrow-derived Lin(-)-Sca-1(+) endothelial progenitor cell (EPC) has pluripotent abilities such as supporting neovascularization. Vascular endothelial growth factor (VEGF) receptor 1 (VEGFR1) (Flt1) recognizes various VEGF isoforms and is critically implicated in a wide range of physiological and pathological settings, including vasculogenesis. Mouse EPC expresses two isoforms of VEGFR1: mFlt1, which transmits ligand-induced signals; and sFlt1, which acts as a negative regulator by sequestering ligands of VEGF receptors. How the relative levels of mFlt1 and sFlt1 are regulated is not yet clear. We report here that tumor necrosis factor superfamily 15 (TNFSF15) (also known as VEGI or TL1A), an endothelial cell-secreted cytokine, simultaneously promotes mFlt1 degradation and up-regulates sFlt1 expression in EPC, giving rise to disruption of VEGF- or PlGF-induced activation of eNOS and MAPK p38 and effective inhibition of VEGF-driven, EPC-supported vasculogenesis in a murine Matrigel implant model. TNFSF15 treatment of EPC cultures facilitates Akt deactivation-dependent, ubiquitin-assisted degradation of mFlt1 and stimulates sFlt1 expression by activating the PKC, Src, and Erk1/2 signaling pathway. Additionally, TNFSF15 promotes alternative splicing of the Flt1 gene in favor of sFlt1 production by down-regulating nuclear protein Jumonji domain-containing protein 6 (Jmjd6), thus alleviating Jmjd6-inhibited sFlt1 expression. These findings indicate that TNFSF15 is a key component of a molecular mechanism that negatively modulates EPC-supported vasculogenesis through regulation of the relative levels of mFlt1 and sFlt1 in EPC.

TNFSF15 Modulates Neovascularization and Inflammation

Tumor necrosis factor superfamily-15 (TNFSF15; also known as VEGI or TL1A) is a unique cytokine that functions in the modulation of vascular homeostasis and inflammation. TNFSF15 is expressed abundantly in established vasculature but is down-regulated at sites of neovascularization such as in cancers and wounds. TNFSF15 inhibits endothelial cell proliferation and endothelial progenitor cell differentiation. Additionally, TNFSF15 stimulates T cell activation, Th1 cytokine production, and dendritic cell maturation. Some of the functions of TNFSF15 are mediated by death receptor-3. We review the experimental evidences on TNFSF15 activities in angiogenesis, vasculogenesis, inflammation, and immune system mobilization.

Down-modulation of TNFSF15 in ovarian cancer by VEGF and MCP-1 is a pre-requisite for tumor neovascularization

Persistent inflammation and neovascularization are critical to cancer development. In addition to upregulation of positive control mechanisms such as overexpression of angiogenic and inflammatory factors in the cancer microenvironment, loss of otherwise normally functioning negative control mechanisms is likely to be an important attribute. Insights into the down-modulation of such negative control mechanisms remain largely unclear, however. We show here that tumor necrosis factor superfamily-15 (TNFSF15), an endogenous inhibitor of neovascularization, is a critical component of the negative control mechanism that operates in normal ovary but is missing in ovarian cancer. We show in clinical settings that TNFSF15 is present prominently in the vasculature of normal ovary but diminishes in ovarian cancer as the disease progresses. Vascular endothelial growth factor (VEGF) produced by cancer cells and monocyte chemotactic protein-1 (MCP-1) produced mainly by tumor-infiltrating macrophages and regulatory T cells effectively inhibits TNFSF15 production by endothelial cells in vitro. Using a mouse syngeneic tumor model, we demonstrate that silencing TNFSF15 by topical shRNA treatments prior to and following mouse ovarian cancer ID8 cell inoculation greatly facilitates angiogenesis and tumor growth, whereas systemic application of recombinant TNFSF15 inhibits angiogenesis and tumor growth. Our findings indicate that downregulation of TNFSF15 by cancer cells and tumor infiltrating macrophages and lymphocytes is a pre-requisite for tumor neovascularization.

Influence of interleukin-8 (IL-8) and IL-8 receptors on the migration of human keratinocytes, the role of PLC-γ and potential clinical implications

Interleukin (IL)-8 is a pro-inflammatory cytokine that has a direct effect on immune cells, including polymorphonuclear cells. Keratinocytes are a rich source of IL-8. However, there is little knowledge on the role of IL-8 in clinical wound healing and the direct biological effect of IL-8 on keratinocytes. In this study, the effect of recombinant human IL-8 (rhIL-8) on migration and adhesion was tested using HaCaT keratinocytes as a cell model. The cell functions were evaluated using impedance cell sensing. The expression of IL-8 receptor (IL-8R) transcripts in human skin and wounds (acute and chronic) was assessed using real-time transcript analysis. rhIL-8 significantly increased the migration of keratinocytes (3.5±0.3 for cells treated with IL-8 vs. 2.7±0.6 for controls; p=0.029). It is interesting to note that treatment of keratinocytes with IL-8 resulted in a marked shift in the responsive frequencies. IL-8 only resulted in a marginal increase in cell adhesion, which was particularly noticeable at high frequencies. The PLC-γ inhibitor completely eradicated the action of IL-8 on the migration of HaCaT cells. Using real time PCR, it was found that chronic wounds had significantly lower levels of the B form of the IL-8R (IL-8RB) (p=0.045) and marginally lower levels of the A form, IL-8RA, in comparison with acute wounds. Therefore, IL-8 has a direct and profound stimulatory effect on the migration of human keratinocytes, which is likely to occur via the PLC-γ pathway. Together with a reduced level of IL-8Rs in difficult-healing wounds, IL-8 has a clear prognostic and therapeutic value in wound healing.

Activated leukocyte cell adhesion molecule impacts on clinical wound healing and inhibits HaCaT migration

Activated leukocyte cell adhesion molecule (ALCAM) is a glycoprotein of the immunoglobulin superfamily that has been implicated in the processes of cell adhesion and migration. The current study examines the importance of ALCAM in regulating HaCaT cell growth and migration and its potential to impact on wound healing. ALCAM levels were examined in a range of clinical wound and normal skin samples using Q-PCR and immunohistochemistry. ALCAM expression was targeted in HaCaT keratinocyte cells using a hammerhead ribozyme transgene system. Subsequently, the impact of ALCAM suppression on HaCaT migration and growth was assessed. ALCAM protein was detected mainly in keratinocytes. ALCAM transcript levels were found to be significantly higher in the non-healed chronic wound samples compared with healed samples (P = 0·026). In addition, targeting of ALCAM in HaCaT cells brought about a substantial increase in cellular migration and growth compared with HaCaT control cells.Our results suggest that ALCAM plays an important role in the migration of HaCaT keratinocyte cells. The data also suggests that higher levels of ALCAM may impair healing in chronic wounds. The impact of ALCAM in wound healing may thus be somewhat due to its impact on cell migration and growth.

Vascular endothelial growth inhibitor (VEGI; TNFSF15) inhibits bone marrow-derived endothelial progenitor cell incorporation into Lewis lung carcinoma tumors

Bone marrow (BM)-derived endothelial progenitor cells (EPC) have a critical role in tumor neovascularization. Vascular endothelial growth inhibitor (VEGI) is a member of the TNF superfamily (TNFSF15). We have shown that recombinant VEGI suppresses tumor angiogenesis by specifically eliminating proliferating endothelial cells (EC). We report here that treatment of tumor bearing mice with recombinant VEGI leads to a significantly decreased population of BM-derived EPC in the tumors. We transplanted whole bone marrow from green fluorescent protein (GFP) transgenic mice into C57BL/6 recipient mice, which were then inoculated with Lewis lung carcinoma (LLC) cells. Intraperitoneal injection of recombinant VEGI led to significant inhibition of tumor growth and decrease of vasculature density compared to vehicle-treated mice. Tumor implantation yielded a decrease of BM-derived EPC in the peripheral blood, while VEGI-treatment resulted in an initial delay of such decrease. Analysis of the whole bone marrow showed a decrease of Lin(-)-c-Kit(+)-Sca-1(+) hematopoietic stem cell (HSC) population in tumor bearing mice; however, VEGI-treatment caused a significant increase of this cell population. In addition, the number of BM-derived EPC in VEGI-treated tumors was notably less than that in the vehicle-treated group, and most of the apoptotic cells in the VEGI-treated tumors were of bone marrow origin. These findings indicate that VEGI inhibits BM-derived EPC mobilization and prevents their incorporation into LLC tumors by inducing apoptosis specifically of BM-derived cells, resulting in the inhibition of EPC-supported tumor vasculogenesis and tumor growth.

Use of human mesenchymal cells to improve vascularization in a mouse model for scaffold-based dermal regeneration

All engineered bioartificial structures developed for tissue regeneration require oxygen and nutrients to establish proper physiological functions. Aiming to improve vascularization during dermal regeneration, we combined the use of a bioartificial collagen scaffold and a defined human mesenchymal cell (MC) line. This cell line, termed V54/2, exhibits typical morphologic and immunohistochemical characteristics of MC. V54/2 cells seeded in the scaffold were able to survive, proliferate, and secrete significant amounts of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) during 2 weeks in vitro. To induce dermal regeneration, scaffolds with or without cells were transplanted in a nude mice full skin defect model. After 2 weeks of transplantation, scaffolds seeded with V54/2 cells showed more vascularization during the dermal regeneration process than controls, and the presence of human cells in the regenerating tissue was detected by immunohistochemistry. To confirm if local presence of angiogenic growth factors is sufficient to induce neovascularization, scaffolds were loaded with VEGF and bFGF and used to induce dermal regeneration in vivo. Results showed that scaffolds supplemented with growth factors were significantly more vascularized than control scaffolds (scaffolds without growth factors). The present work suggests that combined use of MC and bioartificial scaffolds induces therapeutic angiogenesis during the scaffold-based dermal regeneration process.

Cell model of inflammation

Chemical and physical stimuli trigger a cutaneous response by first inducing the main epidermal cells, keratinocytes, to produce specific mediators that are responsible for the initiation of skin inflammation. Activation modulates cell communication, namely leucocyte recruitment and blood-to-skin extravasation through the selective barrier of the vascular ECs (endothelial cells). In the present study, we describe an in vitro model which takes into account the various steps of human skin inflammation, from keratinocyte activation to the adhesion of leucocytes to dermal capillary ECs. Human adult keratinocytes were subjected to stress by exposure to UV irradiation or neuropeptides, then the conditioned culture medium was used to mimic the natural micro-environmental conditions for dermal ECs. A relevant in vitro model must include appropriate cells from the skin. This is shown in the present study by the selective reaction of dermal ECs compared with EC lines from distinct origins, in terms of leucocyte recruitment, sensitivity to stress and nature of the stress-induced secreted mediators. This simplified model is suitable for the screening of anti-inflammatory molecules whose activity requires the presence of various skin cells.