Unbiased and quantitative proteomics reveals highly increased angiogenesis induction by the secretome of mesenchymal stromal cells isolated from fetal rather than adult skin

Proteomic analysis and functional validation reveal distinct therapeutic capabilities related to priming of mesenchymal stromal/stem cells with IFN-γ and hypoxia: potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) are a heterogeneous population of multipotent cells that can be obtained from various tissues, such as dental pulp, adipose tissue, bone marrow and placenta. MSCs have gained importance in the field of regenerative medicine because of their promising role in cell therapy and their regulatory abilities in tissue repair and regeneration. However, a better characterization of these cells and their products is necessary to further potentiate their clinical application. In this study, we used unbiased high-resolution mass spectrometry-based proteomic analysis to investigate the impact of distinct priming strategies, such as hypoxia and IFN-γ treatment, on the composition and therapeutic functionality of the secretome produced by MSCs derived from the amniotic membrane of the human placenta (hAMSCs). Our investigation revealed that both types of priming improved the therapeutic efficacy of hAMSCs, and these improvements were related to the secretion of functional factors present in the conditioned medium (CM) and exosomes (EXOs), which play crucial roles in mediating the paracrine effects of MSCs. In particular, hypoxia was able to induce a pro-angiogenic, innate immune response-activating, and tissue-regenerative hAMSC phenotype, as highlighted by the elevated production of regulatory factors such as VEGFA, PDGFRB, ANGPTL4, ENG, GRO-γ, IL8, and GRO-α. IFN-γ priming, instead, led to an immunosuppressive profile in hAMSCs, as indicated by increased levels of TGFB1, ANXA1, THBS1, HOMER2, GRN, TOLLIP and MCP-1. Functional assays validated the increased angiogenic properties of hypoxic hAMSCs and the enhanced immunosuppressive activity of IFN-γ-treated hAMSCs. This study extends beyond the direct priming effects on hAMSCs, demonstrating that hypoxia and IFN-γ can influence the functional characteristics of hAMSC-derived secretomes, which, in turn, orchestrate the production of functional factors by peripheral blood cells. This research provides valuable insights into the optimization of MSC-based therapies by systematically assessing and comparing the priming type-specific functional features of hAMSCs. These findings highlight new strategies for enhancing the therapeutic efficacy of MSCs, particularly in the context of multifactorial diseases, paving the way for the use of hAMSC-derived products in clinical practice.

Modulating the release of bioactive molecules of human mesenchymal stromal cell secretome: Heparinization of hyaluronic acid-based hydrogels

An amine derivative of hyaluronic acid (HA) was crosslinked to obtain a 3D dried sponge. The sponge was subsequently rehydrated using secretome from human mesenchymal stromal cells (MSCs), resulting in the formation of a hydrogel. The release kinetics analysis demonstrated that the hydrogel effectively sustained secretome release, with 70% of the initially loaded wound-healing-associated cytokines being released over a 12-day period. Tuning the hydrogel properties through heparin crosslinking resulted in a biomaterial with a distinct mechanism of action. Specifically, the presence of heparin enhanced water uptake capacity of the hydrogel and increased its sensitivity to enzymatic degradation. Notably, the heparin crosslinking also led to a significant retention of cytokines within the hydrogel matrix. Overall, the secretome-rehydrated HA hydrogel holds promise as a versatile device for regenerative medicine applications: the non-heparinized hydrogel may function as a biomaterial with low reabsorption rates, sustaining the release of bioactive molecules contained in MSC secretome. In contrast, the heparinized hydrogel may serve as a depot of bioactive molecules with faster reabsorption rates. Given its patch-like characteristic, the HA-based hydrogel appears suitable as topical treatment for external organs, such as the skin.

DAR 16-II Primes Endothelial Cells for Angiogenesis Improving Bone Ingrowth in 3D-Printed BCP Scaffolds and Regeneration of Critically Sized Bone Defects

Bone is a highly vascularized tissue and relies on the angiogenesis and response of cells in the immediate environmental niche at the defect site for regeneration. Hence, the ability to control angiogenesis and cellular responses during osteogenesis has important implications in tissue-engineered strategies. Self-assembling ionic-complementary peptides have received much interest as they mimic the natural extracellular matrix. Three-dimensional (3D)-printed biphasic calcium phosphate (BCP) scaffolds coated with self-assembling DAR 16-II peptide provide a support template with the ability to recruit and enhance the adhesion of cells. In vitro studies demonstrated prompt the adhesion of both human umbilical vein endothelial cells (HUVEC) and human mesenchymal stem cells (hMSC), favoring endothelial cell activation toward an angiogenic phenotype. The SEM-EDS and protein micro bicinchoninic acid (BCA) assays demonstrated the efficacy of the coating. Whole proteomic analysis of DAR 16-II-treated HUVECs demonstrated the upregulation of proteins involved in cell adhesion (HABP2), migration (AMOTL1), cytoskeletal re-arrangement (SHC1, TMOD2), immuno-modulation (AMBP, MIF), and morphogenesis (COL4A1). In vivo studies using DAR-16-II-coated scaffolds provided an architectural template, promoting cell colonization, osteogenesis, and angiogenesis. In conclusion, DAR 16-II acts as a proactive angiogenic factor when adsorbed onto BCP scaffolds and provides a simple and effective functionalization step to facilitate the translation of tailored 3D-printed BCP scaffolds for clinical applications.

Galectin-9 and Interferon-Gamma Are Released by Natural Killer Cells upon Activation with Interferon-Alpha and Orchestrate the Suppression of Hepatitis C Virus Infection

Natural killer (NK) cells mount an immune response against hepatitis C virus (HCV) infection and can be activated by several cytokines, including interleukin-2 (IL-2), IL-15, and interferon-alpha (IFN-α). By exploiting the Huh7.5 hepatoma cell line infected with the HCV JFH1 genome, we provide novel insights into the antiviral effector functions of human primary NK cells after cytokine stimulation. NK cells activated with IFN-α (IFNα-NKs) had enhanced contact-dependent and -independent responses as compared with NK cells activated with IL-2/IL-15 (IL2/IL15-NKs) and could inhibit HCV replication both in vitro and in vivo. Importantly, IFN-α, but not IL-2/IL-15, protected NK cells from the functional inhibition exerted by HCV. By performing flow cytometry, multiplex cytokine profiling, and mass-spectrometry-based proteomics, we discovered that IFNα-NKs secreted high levels of galectin-9 and interferon-gamma (IFN-γ), and by conducting neutralization assays, we confirmed the major role of these molecules in HCV suppression. We speculated that galectin-9 might act extracellularly to inhibit HCV binding to host cells and downstream infection. In silico approaches predicted the binding of HCV envelope protein E2 to galectin-9 carbohydrate-recognition domains, and co-immunoprecipitation assays confirmed physical interaction. IFN-γ, on the other hand, triggered the intracellular expressions of two antiviral gate-keepers in target cells, namely, myxovirus-1 (MX1) and interferon-induced protein with tetratricopeptide repeats 1 (IFIT1). Collectively, our data add more complexity to the antiviral innate response mediated by NK cells and highlight galectin-9 as a key molecule that might be exploited to neutralize productive viral infection.

Conditioned media derived from human fetal progenitor cells improves skin regeneration in burn wound healing

Stem cells are known to have excellent regenerative ability, which is primarily facilitated by indirect paracrine factors, rather than via direct cell replacement. The regenerative process is mediated by the release of extracellular matrix molecules, cytokines, and growth factors, which are also present in the media during cultivation. Herein, we aimed to demonstrate the functionality of key factors and mechanisms in skin regeneration through the analysis of conditioned media derived from fetal stem cells. A series of processes, including 3D pellet cultures, filtration and lyophilization is developed to fabricate human fetal cartilage-derived progenitor cells-conditioned media (hFCPCs-CM) and its useful properties are compared with those of human bone marrow-derived MSCs-conditioned media (hBMSCs-CM) in terms of biochemical characterization, and in vitro studies of fibroblast behavior, macrophage polarization, and burn wound healing. The hFCPCs-CM show to be devoid of cellular components but to contain large amounts of total protein, collagen, glycosaminoglycans, and growth factors, including IGFBP-2, IGFBP-6, HGF, VEGF, TGF β3, and M-CSF, and contain a specific protein, collagen alpha-1(XIV) compare with hBMSCs-CM. The therapeutic potential of hFCPCs-CM observes to be better than that of hBMSCs-CM in the viability, proliferation, and migration of fibroblasts, and M2 macrophage polarization in vitro, and efficient acceleration of wound healing and minimization of scar formation in third-degree burn wounds in a rat model. The current study shows the potential therapeutic effect of hFCPCs and provides a rationale for using the secretome released from fetal progenitor cells to promote the regeneration of skin tissues, both quantitatively and qualitatively. The ready-to-use product of human fetal cartilage-derived progenitor cells-conditioned media (hFCPCs-CM) are fabricated via a series of techniques, including a 3D culture of hFCPCs, filtration using a 3.5 kDa cutoff dialysis membrane, and lyophilization of the CM. hFCPCs-CM contains many ECM molecules and biomolecules that improves wound healing through efficient acceleration of M2 macrophage polarization and reduction of scar formation.

Secretome from Human Mesenchymal Stem Cells-Derived Endothelial Cells Promotes Wound Healing in a Type-2 Diabetes Mouse Model

Tissue regeneration is often impaired in patients with metabolic disorders such as diabetes mellitus and obesity, exhibiting reduced wound repair and limited regeneration capacity. We and others have demonstrated that wound healing under normal metabolic conditions is potentiated by the secretome of human endothelial cell-differentiated mesenchymal stem cells (hMSC-EC). However, it is unknown whether this effect is sustained under hyperglycemic conditions. In this study, the wound healing effect of secretomes from undifferentiated human mesenchymal stem cells (hMSC) and hMSC-EC in a type-2 diabetes mouse model was analyzed. hMSC were isolated from human Wharton’s jelly and differentiated into hMSC-EC. hMSC and hMSC-EC secretomes were analyzed and their wound healing capacity in C57Bl/6J mice fed with control (CD) or high fat diet (HFD) was evaluated. Our results showed that hMSC-EC secretome enhanced endothelial cell proliferation and wound healing in vivo when compared with hMSC secretome. Five soluble proteins (angiopoietin-1, angiopoietin-2, Factor de crecimiento fibroblástico, Matrix metallopeptidase 9, and Vascular Endothelial Growth Factor) were enriched in hMSC-EC secretome in comparison to hMSC secretome. Thus, the five recombinant proteins were mixed, and their pro-healing property was evaluated in vitro and in vivo. Functional analysis demonstrated that a cocktail of these proteins enhanced the wound healing process similar to hMSC-EC secretome in HFD mice. Overall, our results show that hMSC-EC secretome or a combination of specific proteins enriched in the hMSC-EC secretome enhanced wound healing process under hyperglycemic conditions.

Neuroprotection and Axonal Regeneration Induced by Bone Marrow Mesenchymal Stromal Cells Depend on the Type of Transplant

Mesenchymal stromal cell (MSC) therapy to treat neurodegenerative diseases has not been as successful as expected in some preclinical studies. Because preclinical research is so diverse, it is difficult to know whether the therapeutic outcome is due to the cell type, the type of transplant or the model of disease. Our aim here was to analyze the effect of the type of transplant on neuroprotection and axonal regeneration, so we tested MSCs from the same niche in the same model of neurodegeneration in the three transplantation settings: xenogeneic, syngeneic and allogeneic. For this, bone marrow mesenchymal stromal cells (BM-MSCs) isolated from healthy human volunteers or C57/BL6 mice were injected into the vitreous body of C57/BL6 mice (xenograft and syngraft) or BALB/c mice (allograft) right after optic nerve axotomy. As controls, vehicle matched groups were done. Retinal anatomy and function were analyzed in vivo by optical coherence tomography and electroretinogram, respectively. Survival of vision forming (Brn3a⁺) and non-vision forming (melanopsin⁺) retinal ganglion cells (RGCs) was assessed at 3, 5 and 90 days after the lesion. Regenerative axons were visualized by cholera toxin β anterograde transport. Our data show that grafted BM-MSCs did not integrate in the retina but formed a mesh on top of the ganglion cell layer. The xenotransplant caused retinal edema, detachment and folding, and a significant decrease of functionality compared to the murine transplants. RGC survival and axonal regeneration were significantly higher in the syngrafted retinas than in the other two groups or vehicle controls. Melanopsin⁺RGCs, but not Brn3a⁺RGCs, were also neuroprotected by the xenograft. In conclusion, the type of transplant has an impact on the therapeutic effect of BM-MSCs affecting not only neuronal survival but also the host tissue response. Our data indicate that syngrafts may be more beneficial than allografts and, interestingly, that the type of neuron that is rescued also plays a significant role in the successfulness of the cell therapy.

Mesenchymal stromal cells in wound healing applications: role of the secretome, targeted delivery and impact on recessive dystrophic epidermolysis bullosa treatment

Mesenchymal stromal cells (MSCs) are multi-potent stromal-derived cells capable of self-renewal that possess several advantageous properties for wound healing, making them of interest to the field of dermatology. Research has focused on characterizing the unique properties of MSCs, which broadly revolve around their regenerative and more recently discovered immunomodulatory capacities. Because of ease of harvesting and expansion, differentiation potential and low immunogenicity, MSCs have been leading candidates for tissue engineering and regenerative medicine applications for wound healing, yet results from clinical studies have been variable, and promising pre-clinical work has been difficult to reproduce. Therefore, the specific mechanisms of how MSCs influence the local microenvironment in distinct wound etiologies warrant further research. Of specific interest in MSC-mediated healing is harnessing the secretome, which is composed of components known to positively influence wound healing. Molecules released by the MSC secretome can promote re-epithelialization and angiogenesis while inhibiting fibrosis and microbial invasion. This review focuses on the therapeutic interest in MSCs with regard to wound healing applications, including burns and diabetic ulcers, with specific attention to the genetic skin disease recessive dystrophic epidermolysis bullosa. This review also compares various delivery methods to support skin regeneration in the hopes of combating the poor engraftment of MSCs after delivery, which is one of the major pitfalls in clinical studies utilizing MSCs.

Mesenchymal Stem Cell Secretome for Dermatology Application: A Review

Secretome, also known as conditioned medium, is a secreted molecule from mesenchymal stem cells (MSCs) that has a variety of biological activities that can be used in various therapies, especially on the skin applications. A lack of conventional therapies makes secretome as a promising alternative therapy. The presence of growth factors, cytokines, and extracellular vesicles including microvesicles and exosomes in secretome has been widely reported, which serves in improving the proliferation and migration of cells to help in skin regeneration. Therefore, we were able to optimize the use of this secretome in a well-needed special review related to its work in addressing various skin problems. So, in this article, we discussed the benefits and biological activity of secretome on the skin application. This review was compiled based on the approval of several sites, such as Scopus, PubMed, Science Direct, and Google Scholar with the terms "MSC secretome for skin," "secretome for skin," "secretome dermatology," "secretome conditioned medium for skin," "secretome conditioned medium for skin wound," "secretome conditioned medium for aging," "secretome conditioned medium for hair growth," and "secretome conditioned medium for psoriasis." A total of 215 articles were collected for selection, of which 90 articles were used. Based on the results, it was concluded that secretome has a variety of useful activities to regenerate and repair tissue damage that have not been used on the skin, such as for wound healing, photoprotection, promotion of hair growth, psoriasis treatment, and other application as antimicrobial.

The adipose-derived mesenchymal stem cell secretome promotes hepatic regeneration in miniature pigs after liver ischaemia-reperfusion combined with partial resection

Background

Hepatic ischaemia-reperfusion injury (HIRI) is inevitable in complicated liver surgery and is a major factor leading to postoperative complications and liver dysfunction. Studies have shown that the paracrine mechanisms of stem cell may be essential to tissue repair and functional improvement after transplantation. However, the role of the adipose-derived mesenchymal stem cell secretome (ASC-secretome) in liver regeneration in large animals remains to be determined.

Methods

Twenty-four miniature pigs were subjected to laparoscopic liver ischaemia-reperfusion combined with partial hepatectomy and divided into the following four groups: the saline group, the DMEM group, the ASC group and the ASC-secretome group. Serum and liver tissue samples were collected before the operation and at 1, 3 and 7 days after the operation, and changes in tissue pathology, serum inflammation, liver function, angiogenesis-related factors and liver tissue regeneration-related genes and proteins were evaluated.

Results

Detailed histological analysis showed that ASCs and the ASC-secretome changed pathological damage to liver tissue after liver ischaemia-reperfusion combined with partial hepatectomy (1 and 3 days: p < 0.01). Compared with the saline and DMEM control groups, the ASC-secretome group had significantly reduced expression levels of ALP (1 and 3 days: p < 0.05), ALT (1 day: p < 0.01; 3 days: p < 0.05) and AST (1 and 3 days: p < 0.01), which promoted the recovery of liver function. Moreover, detection of the expression levels of TNF-α and IL-1β (1 day: p < 0.01; 3 days: p < 0.05), IL-6 (1 and 3 days: p < 0.05) and IL-10 (1 and 3 days: p < 0.01) in serum confirmed that the ASC-secretome had obvious anti-inflammatory effects. In addition, the ASC-secretome increased the expression levels of ANG-1 (3 days: p < 0.01), ANG-2 (3 and 7 days: p < 0.01) and VEGF (1 and 7 days: p < 0.05; 3 days: p < 0.01) and promoted angiogenesis during liver regeneration. Moreover, it promoted the mRNA expression of HGF and Cyclin D1 (1 and 3 days: p < 0.01); increased the levels of p-STAT3 (1 and 3 days: p < 0.01), PCNA and Ki67 (1 and 3 days: p < 0.01; 7 days: p < 0.05); inhibited the negative feedback of SOCS3 (1 and 3 days: p < 0.01); and decreased the mRNA expression of TGF-β (3 days: p < 0.01). The cytokines and growth factors detected in the ASC-secretome included TNF-α, IL-6, IL-1β, ANG-1, ANG-2, VEGF and b-FGF.

Conclusion

The ASC-secretome alleviates the inflammatory response induced by ischaemia-reperfusion combined with partial hepatectomy in miniature pigs and promotes liver regeneration.

Extracellular Vesicle-Derived microRNAs of Human Wharton's Jelly Mesenchymal Stromal Cells May Activate Endogenous VEGF-A to Promote Angiogenesis

Despite low levels of vascular endothelial growth factor (VEGF)-A, the secretome of human Wharton’s jelly (WJ) mesenchymal stromal cells (MSCs) effectively promoted proangiogenic responses in vitro, which were impaired upon the depletion of small (~140 nm) extracellular vesicles (EVs). The isolated EVs shared the low VEGF-A profile of the secretome and expressed five microRNAs, which were upregulated compared to fetal dermal MSC-derived EVs. These upregulated microRNAs exclusively targeted the VEGF-A gene within 54 Gene Ontology (GO) biological processes, 18 of which are associated with angiogenesis. Moreover, 15 microRNAs of WJ-MSC-derived EVs were highly expressed (Ct value ≤ 26) and exclusively targeted the thrombospondin 1 (THBS1) gene within 75 GO biological processes, 30 of which are associated with the regulation of tissue repair. The relationship between predicted microRNA target genes and WJ-MSC-derived EVs was shown by treating human umbilical-vein endothelial cells (HUVECs) with appropriate doses of EVs. The exposure of HUVECs to EVs for 72 h significantly enhanced the release of VEGF-A and THBS1 protein expression compared to untreated control cells. Finally, WJ-MSC-derived EVs stimulated in vitro tube formation along with the migration and proliferation of HUVECs. Our findings can contribute to a better understanding of the molecular mechanisms underlying the proangiogenic responses induced by human umbilical cord-derived MSCs, suggesting a key regulatory role for microRNAs delivered by EVs.

Small Extracellular Vesicles from Human Fetal Dermal Cells and Their MicroRNA Cargo: KEGG Signaling Pathways Associated with Angiogenesis and Wound Healing

The use of cell secreted factors in clinical settings could be an alternative to conventional cell therapy, with the advantage of limiting concerns generally associated with traditional cell transplantation, such as tumorigenicity, immunoreactivity, and carrying of infections. Based on our published data, we predict a potential role for extracellular vesicles (EVs) in contributing to the proangiogenic activity of human fetal dermal cell secretome. Depletion of nanosized EVs from secretome significantly impaired its ability to induce formation of mesh-like structures in vitro. The isolated EVs were characterized for size and concentration by nanoparticle tracking analysis, and for protein markers (Rab5⁺, Alix⁺, CD63⁺, and calnexin⁻). The microRNA profile of EVs revealed 87 microRNAs significantly upregulated (≥15-fold increase) in fetal compared to adult dermal cell-derived EVs. Interestingly, these upregulated microRNAs included microRNAs with a validated role in angiogenesis according to literature. Moreover, the DIANA-TarBase v7.0 analysis confirmed enrichment in the KEGG signaling pathways associated with angiogenesis and wound healing, with the identification of putative target genes including thrombospondin 1. To validate the in silico data, EVs were also characterized for total protein contents. When tested in in vitro angiogenesis, fetal dermal cell-derived EVs were more effective than their adult counterpart in inducing formation of complete mesh-like structures. Furthermore, treatment of fibroblasts with fetal dermal-derived EVs determined a 4-fold increase of thrombospondin 1 protein amounts compared with the untreated fibroblasts. Finally, visualization of CSFE-labeled EVs in the cytosol of target cells suggested a successful uptake of these particles at 4-8 hours of incubation. We conclude that EVs are important contributors of the proangiogenic effect of fetal dermal cell secretome. Hence, EVs could also serve as vehicle for a successful delivery of microRNAs or other molecules of therapeutic interest to target cells.

Paracrine Mechanisms of Mesenchymal Stromal Cells in Angiogenesis

The role of the mesenchymal stromal cell- (MSC-) derived secretome is becoming increasingly intriguing from a clinical perspective due to its ability to stimulate endogenous tissue repair processes as well as its effective regulation of the immune system, mimicking the therapeutic effects produced by the MSCs. The secretome is a composite product secreted by MSC in vitro (in conditioned medium) and in vivo (in the extracellular milieu), consisting of a protein soluble fraction (mostly growth factors and cytokines) and a vesicular component, extracellular vesicles (EVs), which transfer proteins, lipids, and genetic material. MSC-derived secretome differs based on the tissue from which the MSCs are isolated and under specific conditions (e.g., preconditioning or priming) suggesting that clinical applications should be tailored by choosing the tissue of origin and a priming regimen to specifically correct a given pathology. MSC-derived secretome mediates beneficial angiogenic effects in a variety of tissue injury-related diseases. This supports the current effort to develop cell-free therapeutic products that bring both clinical benefits (reduced immunogenicity, persistence in vivo, and no genotoxicity associated with long-term cell cultures) and manufacturing advantages (reduced costs, availability of large quantities of off-the-shelf products, and lower regulatory burden). In the present review, we aim to give a comprehensive picture of the numerous components of the secretome produced by MSCs derived from the most common tissue sources for clinical use (e.g., AT, BM, and CB). We focus on the factors involved in the complex regulation of angiogenic processes.

Comparative study of the production of soluble factors in human placenta-derived mesenchymal stromal/stem cells grown in adherent conditions or as aggregates in a catheter-like device

Different approaches have been studied in both preclinical and clinical settings to develop cell-based therapies and/or engineered cell-based therapies to better integrate grafts with the host. In these techniques, much attention is addressed to the use of adult stem cells such as mesenchymal stem cells (MSCs), but identifying and obtaining sufficient numbers of therapeutic cells, and the right route of administration, is often a challenge. In this study, we tested the feasibility of encapsulating human amnion-derived MSCs (hAMSCs) in a semipermeable and biocompatible fiber as a new approach for regenerative medicine. Our data showed that hAMSCs aggregated in the device constitutes an effective system for enhancing, or at least for maintaining, the paracrine activity of these cells in order to better promote tissue regeneration in an immune isolated state. In our new experimental approach, the hAMSCs retained their therapeutic potential, as shown by both the production of specific immunomodulatory/angiogenic factors and immunomodulatory and angiogenic ability observed in vitro. Unlike cell infusion methods, the use of encapsulated-cells leads to minimally invasive approaches, avoiding a direct interaction with the host. Therefore, the potentiality of an allograft or xenograft without the need for immunosuppression, and the lack of tumorigenesis is very intriguing.

Human fetal skin-derived stem cell secretome enhances radiation-induced skin injury therapeutic effects by promoting angiogenesis

Background

Radiation dermatitis is a refractory skin injury caused by radiotherapy. Human fetal skin-derived stem cell (hFSSC) is a preferable source for cell therapy and skin tissue regeneration. In the present study, we investigated the repair effect of using hFSSC secretome on a radiation skin injury model in rats.

Methods

We prepared the hFSSC secretome and studied its effects on the proliferation and tube formation of human umbilical vein endothelial cell (HUVEC) in vitro. Furthermore, we used a Sr-90 radiation-induced skin injury model of rats and evaluated the effects of hFSSC secretome on radiation skin injury in vivo.

Results

The results showed that hFSSC secretome significantly promoted the proliferation and tube formation of HUVEC in vitro; in addition, hFSSC secretome-treated rats exhibited higher healing quality and faster healing rate than the other two control groups; the expression level of collagen type III α 1 (Col3A1), transforming growth factor β3 (TGF-β3), angiotensin 1 (Ang-1), angiotensin 2 (Ang-2), vascular endothelial growth factor (VEGF), and placental growth factor (PLGF) was significantly increased, while collagen type I α 2 (Col1A2) and transforming growth factor β1 (TGF-β1) were decreased in hFSSC secretome group.

Conclusions

In conclusion, our results provided the first evidence on the effects of hFSSC secretome towards radiation-induced skin injury. We found that hFSSC secretome significantly enhanced radiation dermatitis angiogenesis, and the therapeutic effects could match with the characteristics of fetal skin. It may act as a kind of novel cell-free therapeutic approach for radiation-induced cutaneous wound healing.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

Proteomic analysis of human mesenchymal stromal cell secretomes: a systematic comparison of the angiogenic potential

Human mesenchymal stromal cell (hMSC) secretomes have shown to influence the microenvironment upon injury, promoting cytoprotection, angiogenesis, and tissue repair. The angiogenic potential is of particular interest for the treatment of ischemic diseases. Interestingly, hMSC secretomes isolated from different tissue sources have shown dissimilarities with respect to their angiogenic profile. This study compares angiogenesis of hMSC secretomes from adipose tissue (hADSCs), bone marrow (hBMSCs), and umbilical cord Wharton’s jelly (hWJSCs). hMSC secretomes were obtained under xenofree conditions and analyzed by liquid chromatography tandem mass spectrometry (LC/MS-MS). Biological processes related to angiogenesis were found to be enriched in the proteomic profile of hMSC secretomes. hWJSC secretomes revealed a more complete angiogenic network with higher concentrations of angiogenesis related proteins, followed by hBMSC secretomes. hADSC secretomes lacked central angiogenic proteins and expressed most detected proteins to a significantly lower level. In vivo all secretomes induced vascularization of subcutaneously implanted Matrigel plugs in mice. Differences in secretome composition were functionally analyzed with monocyte and endothelial cell (EC) in vitro co-culture experiments using vi-SNE based multidimensional flow cytometry data analysis. Functional responses between hBMSC and hWJSC secretomes were comparable, with significantly higher migration of CD14⁺⁺ CD16⁻ monocytes and enhanced macrophage differentiation compared with hADSC secretomes. Both secretomes also induced a more profound pro-angiogenic phenotype of ECs. These results suggest hWJSCs secretome as the most potent hMSC source for inflammation-mediated angiogenesis induction, while the potency of hADSC secretomes was lowest. This systematic analysis may have implication on the selection of hMSCs for future clinical studies.

The skin regeneration potential of a pro-angiogenic secretome from human skin-derived multipotent stromal cells

Multipotent stromal cells stimulate skin regeneration after acute or chronic injuries. However, many stem cell therapy protocols are limited by the elevated number of cells required and poor cell survival after transplantation. Considering that the beneficial effects of multipotent stromal cells on wound healing are typically mediated by paracrine mechanisms, we examined whether the conditioned medium from skin-derived multipotent stromal cells would be beneficial for restoring the skin structure of mice after wounding. A proteomic characterization of skin-derived multipotent stromal cell-conditioned medium was performed, and the angiogenic function of this secretome was investigated in vitro using an endothelial cell tube formation assay. We then applied the skin-derived multipotent stromal cell-conditioned medium directly to full-thickness excisional wounds or embedded it into carrageenan or poly(vinyl alcohol) hydrogels to monitor tissue regeneration in mice. Biological processes related to wound healing and angiogenesis were highlighted by the analysis of the skin-derived multipotent stromal cell secretome, and a pro-angiogenic capacity for promoting tubule-like structures was first confirmed in vitro. Skin wounds treated with skin-derived multipotent stromal cell-conditioned medium also displayed increased angiogenesis, independently of the association of the conditioned medium with hydrogels. However, improvements in wound closure and epidermis or decreased inflammatory cell presence were not observed. Hence, the use of the secretome obtained from human skin-derived multipotent stromal cells may be a potential strategy to aid the natural skin repair of full-thickness lesions mainly based on its pro-angiogenic properties.

Mesenchymal stromal cells isolated from human fetal liver release soluble factors with a potential role in liver tissue repair

We isolated a population of proliferating cells from cultured human fetal hepatocytes of 16-22 weeks gestational age. The cells shared a similar phenotype to that of mesenchymal stromal cells (MSCs) according to the International Society for Cellular Therapy (ISCT), including plastic adherence, antigen expression profile, and in vitro multilineage differentiation potential. Fetal liver (FL)-MSCs expressed the albumin gene, and harbored a subpopulation of CK18⁺ cells (20-40%), which defined their hepatic origin. However, when subjected to in vitro hepatic differentiation, FL-MSCs did not acquire significant liver functions. Quantitative analysis of conditioned medium (CM) collected from cultured cells revealed the presence of growth factors and chemokines with potential liver regenerative properties, the most relevant of which (concentration ≥3000 pg/ml) were SDF-1 alpha, IL-6, MCP-1, IL-8, MIP-1 beta, VEGF-A, Gro-alpha, and HGF. Culturing of FL-MSCs as spheroids significantly enhanced the secretion of HGF and bFGF (approximately 5-fold) compared with culture monolayers. Moreover, CM assessed in vitro induced capillary-like organization and migration of human umbilical vein endothelial cells (HUVECs) and fibroblasts as target cells. Interestingly, exosomes isolated from CM induced similar cellular responses in vitro with high efficiency and in a dose-dependent manner. FL-MSCs underwent several in vitro subcultivations, and did not stimulate allogenic T-cell proliferation thus suggesting a low immunogenicity. Furthermore, 5-year cryopreservation did not affect cell viability (approximately 90% of viable post-thawed FL-MSCs). These observations support the feasibility of a cell bank establishment for allogenic transplantation. We concluded that FL-MSCs or they secreted factors may be a valid alternative to hepatocyte transplantation in liver cell-based therapies.