Platelet-derived growth factor receptors regulate mesenchymal stem cell fate: implications for neovascularization

Biogenesis, Composition and Potential Therapeutic Applications of Mesenchymal Stem Cells Derived Exosomes in Various Diseases

Exosomes are nanovesicles with a wide range of chemical compositions used in many different applications. Mesenchymal stem cell-derived exosomes (MSCs-EXOs) are spherical vesicles that have been shown to mediate tissue regeneration in a variety of diseases, including neurological, autoimmune and inflammatory, cancer, ischemic heart disease, lung injury, and liver fibrosis. They can modulate the immune response by interacting with immune effector cells due to the presence of anti-inflammatory compounds and are involved in intercellular communication through various types of cargo. MSCs-EXOs exhibit cytokine storm-mitigating properties in response to COVID-19. This review discussed the potential function of MSCs-EXOs in a variety of diseases including neurological, notably epileptic encephalopathy and Parkinson's disease, cancer, angiogenesis, autoimmune and inflammatory diseases. We provided an overview of exosome biogenesis and factors that regulate exosome biogenesis. Additionally, we highlight the functions and potential use of MSCs-EXOs in the treatment of the inflammatory disease COVID-19. Finally, we covered a strategies and challenges of MSCs-EXOs. Finally, we discuss conclusion and future perspectives of MSCs-EXOs.

The Combined Use of Platelet-Rich Plasma Clot Releasate and Allogeneic Human Umbilical Cord Mesenchymal Stem Cells Rescue Glucocorticoid-Induced Osteonecrosis of the Femoral Head

Glucocorticoid-induced osteonecrosis of the femoral head (ONFH) is a refractory disease. The treatment options for ONFH, especially nonsurgical ones, merit further investigation. To evaluate the combinatorial therapeutic effects of platelet-rich plasma clot releasate (PRCR) and umbilical cord mesenchymal stem cells (UC-MSCs) on glucocorticoid-induced ONFH, a dexamethasone (DEX)-treated cell model and a high-dose methylprednisolone (MPS)-treated rat model were established. Cell counting kit-8 (CCK-8) assay was performed in vitro to determine the optimum dosage of PRCR for UC-MSC viability. The effects of PRCR, UC-MSCs, and PRCR + UC-MSCs on cell viability, apoptosis, migration, and differentiation capacities of DEX-treated bone marrow mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cell (HUVECs) were explored via Transwell assays. Western blotting was conducted to evaluate the expression levels of RUNX2, VEGF, caspase-3, and Bcl-2 in the coculture systems. Ultrasound-guided intra-articular PRCR, UC-MSCs, and PRCR + UC-MSC injections were performed on the ONFH model rats. Microcomputed tomography, histological and immunohistochemical analyses, tartrate-resistant acid phosphatase (TRAP) staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to assess the therapeutic effects of PRCR and UC-MSCs on bone loss and necrosis induced by high-dose MPS. Results of this study revealed that the in vitro application of PRCR, UC-MSCs, and PRCR + UC-MSCs reversed the impaired proliferation and migration capacities and resisted apoptosis of BMSCs and HUVECs induced by DEX. Moreover, the PRCR and UC-MSC application significantly improved the alkaline phosphatase (ALP) and alizarin red (ALR) staining of BMSCs and tube formation capacity of HUVECs and promoted the protein expression of RUNX2 in BMSCs and VEGF in HUVECs. Similarly, in the ONFH rat model, the intra-articular injection of UC-MSCs and PRCR improved the subchondral bone mass parameters; promoted the expression of ALP, RUNX2, and VEGF; suppressed osteoclast overactivity; and resisted cell apoptosis. The combination of PRCR and UC-MSCs shows promising therapeutic effects in treating glucocorticoid-induced ONFH. The current study provides important information on intra-articular therapy, paving the way for the clinical management of ONFH in the future.

Angiogenic Effects and Crosstalk of Adipose-Derived Mesenchymal Stem/Stromal Cells and Their Extracellular Vesicles with Endothelial Cells

Adipose-derived mesenchymal stem/stromal cells (ASCs) are an adult stem cell population able to self-renew and differentiate into numerous cell lineages. ASCs provide a promising future for therapeutic angiogenesis due to their ability to promote blood vessel formation. Specifically, their ability to differentiate into endothelial cells (ECs) and pericyte-like cells and to secrete angiogenesis-promoting growth factors and extracellular vesicles (EVs) makes them an ideal option in cell therapy and in regenerative medicine in conditions including tissue ischemia. In recent angiogenesis research, ASCs have often been co-cultured with an endothelial cell (EC) type in order to form mature vessel-like networks in specific culture conditions. In this review, we introduce co-culture systems and co-transplantation studies between ASCs and ECs. In co-cultures, the cells communicate via direct cell-cell contact or via paracrine signaling. Most often, ASCs are found in the perivascular niche lining the vessels, where they stabilize the vascular structures and express common pericyte surface proteins. In co-cultures, ASCs modulate endothelial cells and induce angiogenesis by promoting tube formation, partly via secretion of EVs. In vivo co-transplantation of ASCs and ECs showed improved formation of functional vessels over a single cell type transplantation. Adipose tissue as a cell source for both mesenchymal stem cells and ECs for co-transplantation serves as a prominent option for therapeutic angiogenesis and blood perfusion in vivo.

Effects of cryopreservation and long-term culture on biological characteristics and proteomic profiles of human umbilical cord-derived mesenchymal stem cells

Background

Human umbilical cord-derived MSCs (hUC-MSCs) have been identified as promising seeding cells in tissue engineering and clinical applications of regenerative medicine due to their advantages of simple acquisition procedure and the capability to come from a young tissue donor over the other MSCs sources. In clinical applications, large scale production is required and optimal cryopreservation and culture conditions are essential to autologous and allogeneic transplantation in the future. However, the influence of cryopreserved post-thaw and long-term culture on hUC-MSCs remains unknown, especially in terms of specific protein expression. Therefore, biological characteristics and proteomic profiles of hUC-MSCs after cryopreserving and long-term culturing were investigated.

Methods

Firstly, hUC-MSCs were isolated from human umbilical cord tissues and identified through morphology, surface markers and tri-lineage differentiation potential at passage 3, and then the biological characteristics and proteomic profiles were detected and compared after cryopreserving and long-term culturing at passage 4 and continuously cultured to passage 10 with detection occurring here as well. The proteomic profiles were tested by using the isobaric tags for relative and absolute quantification (iTRAQ) labeling technique and differential protein were confirmed by mass spectrometry.

Results

The results showed no significant differences in phenotypes including morphology, surface marker and tri-lineage differentiation potential but have obvious changes in translation level, which is involved in metabolism, cell cycle and other pathways.

Conclusion

This suggests that protein expression may be used as an indicator of hUC-MSCs security testing before applying in clinical settings, and it is also expected to provide the foundation or standardization guide of hUC-MSCs applications in regenerative medicine.

Characterization and therapeutic applications of mesenchymal stem cells for regenerative medicine

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent, genomic stable, self-renewable, and culturally expandable adult stem cells. MSCs facilitate tissue development, maintenance and repair, and produce secretory factors that support engraftment and trophic functions, marking them an attractive option in cell therapy, regenerative medicine and tissue engineering.

METHOD

In this review, we summarize the recent researches regarding the isolation and characterization of MSCs, therapeutic applications and advanced engineering techniques. We also discuss the advantages and limitations that remain to be overcome for MSCs based therapy.

RESULTS

It has been demonstrated that MSCs are able to modulate endogenous tissue and immune cells. Preclinical studies and early phase clinical trials have shown their great potential for tissue engineering of bone, cartilage, marrow stroma, muscle, fat, and other connective tissues.

CONCLUSIONS

MSC-based therapy show considerable promise to rebuild damaged or diseased tissues, which could be a promising therapeutic method for regeneration medicine.

A vessel subtype beneficial for osteogenesis enhanced by strontium-doped sodium titanate nanorods by modulating macrophage polarization

Early vascularization plays an important role in bone healing, especially in interfacial bone formation.

Promoting in vivo early angiogenesis with sub-micrometer strontium-contained bioactive microspheres through modulating macrophage phenotypes

Early vascularization capacity of biomaterials plays an essential role in efficient wound healing and tissue regeneration, especially in large tissue tension implanting position such as bone augmentation. Strontium-contained silica-based bioactive materials have shown the role of promoting angiogenesis by stimulating osteoblasts to secrete angiogenesis related cytokines. However, osteoblasts have little effect on early angiogenesis due to the inflammatory reaction of implantation site. Here, for the first time, we found that the monodispersed strontium-contained bioactive glasses microspheres (SrBGM) could significantly promote the early angiogenesis through regulating macrophage phenotypes. After being stimulated with SrBGM in vitro, RAW cells (macrophages) presented a trend towards to M2 phenotype and expressed high level of platelet-derived growth factor-BB (PDGF-BB). Moreover, the RAW conditioned medium of SrBGM significantly enhanced the angiogenic capacity of HUVECs. The in vivo early vascularization studies showed that significant new vessels were observed at the center of SrBGM-based scaffolds after implantation for 1 week in a bone defect model of rats, suggesting their enhanced early vascularization. Due to the efficient vascularization, the in vivo new bone formation was promoted significantly. Our study may provide a novel strategy to promote the early vascularization of biomaterials through modulating the microphage phenotypes, which has wide applications in various tissue regeneration and wound healing.

RXRα provokes tumor suppression through p53/p21/p16 and PI3K-AKT signaling pathways during stem cell differentiation and in cancer cells

The retinoid X receptor alpha (RXRα) is an important therapeutic target impacting diverse biological processes. Activation of RXRα is known to suppress cancer cell growth. However, the cellular mechanism has been elusive. In the present study, we addressed its role during stem cell differentiation and the underlying connections with carcinogenesis. RXRα was significantly upregulated following the differentiation of human mesenchymal stem cell (hMSC) toward the formation of endothelial cell (EC). However, overexpression of RXRα in hMSC provoked a senescence-like phenotype accompanied by the elevation of tumor suppressor p53, p21, and p16. Consistently, RXRα level was suppressed in cancer cells (~five times lower compared to differentiated hMSC), and its elevation could inhibit the proliferation, migration, and angiogenesis of cancer cells. We further demonstrated that these inhibitory effects were related to RXRα’s interaction with estrogen receptor α (ERα) as well as EGF and ANGPTL3 through modulating PI3K/AKT signaling pathway by AKT and FAK phosphorylation. Moreover, RXRα inhibited glycolytic metabolism in cancer cells, which might be underlying its inhibition of differentiation and carcinogenic features. These data suggest that RXRα acts as a suppressor rather than a driving force during stem cell differentiation, and unbalanced RXRα can trigger multiple yet connected signaling pathways in preventing carcinogenesis.

Biomimetic Approaches for Bone Tissue Engineering

Although autologous bone grafts are considered a gold standard for the treatment of bone defects, they are limited by donor site morbidities and geometric requirements. We propose that tissue engineering technology can overcome such limitations by recreating fully viable and biological bone grafts. Specifically, we will discuss the use of bone scaffolds and autologous cells with bioreactor culture systems as a tissue engineering paradigm to grow bone in vitro. We will also discuss emergent vascularization strategies to promote graft survival in vivo, as well as the role of inflammation during bone repair. Finally, we will highlight some recent advances and discuss new solutions to bone repair inspired by endochondral ossification.

Autologous adipose-derived mesenchymal stem cells improve healing of coiled experimental saccular aneurysms: an angiographic and histopathological study

PURPOSE

Long-term occlusion of coiled aneurysms frequently fails, probably because of poor intrasaccular healing and inadequate endothelialization across the aneurysm neck. The purpose of this study was to determine if attachment of autologous mesenchymal stem cells (MSCs) to platinum coils would improve the healing response in an elastase-induced aneurysm model in rabbits.

MATERIALS AND METHODS

With approval from the institutional animal care and use committee, aneurysms were created in rabbits and embolized with control platinum coils (Axium; Medtronic) (n=6) or coils seeded ex vivo with autologous adipose-tissue MSCs (n=7). Aneurysmal occlusion after embolization was evaluated at 1 month with angiography. Histological samples were analyzed by gross imaging and graded on the basis of neck and dome healing on H&E staining. Fibrosis was evaluated using a ratio of the total area presenting collagen. Endothelialization of the neck was quantitatively analyzed using CD31 immunohistochemistry. χ² and Student's t-test were used to compare groups.

RESULTS

Healing score (11.5 vs 8.0, p=0.019), fibrosis ratio (10.3 vs 0.13, p=0.006) and endothelialization (902 262 μm² vs 31 810 μm², p=0.041) were significantly greater in the MSC group. The MSC group showed marked cellular proliferation and thrombus organization, with a continuous membrane bridging the neck of the aneurysm. Angiographic stable or progressive occlusion rate was significantly lower in the MSC group (0.00, 95% CI 0.00 to 0.41) compared with controls (0.67, 95% CI 0.22 to 0.96) (p=0.02).

CONCLUSIONS

Autologous MSCs attached to platinum coils significantly improve histological healing, as they result in improved neck endothelialization and collagen matrix formation within the aneurysm sac.

Acute Hypoxic Stress Affects Migration Machinery of Tissue O2-Adapted Adipose Stromal Cells

The ability of mesenchymal stromal (stem) cells (MSCs) to be mobilised from their local depot towards sites of injury and to participate in tissue repair makes these cells promising candidates for cell therapy. Physiological O₂ tension in an MSC niche in vivo is about 4-7%. However, most in vitro studies of MSC functional activity are performed at 20% O₂. Therefore, this study focused on the effects of short-term hypoxic stress (0.1% O₂, 24 h) on adipose tissue-derived MSC motility at tissue-related O₂ level. No significant changes in integrin expression were detected after short-term hypoxic stress. However, O₂ deprivation provoked vimentin disassembly and actin polymerisation and increased cell stiffness. In addition, hypoxic stress induced the downregulation of ACTR3, DSTN, MACF1, MID1, MYPT1, NCK1, ROCK1, TIAM1, and WASF1 expression, the products of which are known to be involved in leading edge formation and cell translocation. These changes were accompanied by the attenuation of targeted and nontargeted migration of MSCs after short-term hypoxic exposure, as demonstrated in scratch and transwell migration assays. These results indicate that acute hypoxic stress can modulate MSC function in their native milieu, preventing their mobilisation from sites of injury.

Human Mesenchymal Stem Cells of Diverse Origins Support Persistent Infection with Kaposi's Sarcoma-Associated Herpesvirus and Manifest Distinct Angiogenic, Invasive, and Transforming Phenotypes

Kaposi's sarcoma (KS), a highly angiogenic and invasive tumor often involving different organ sites, including the oral cavity, is caused by infection with Kaposi's sarcoma-associated herpesvirus (KSHV). Diverse cell markers have been identified on KS tumor cells, but their origin remains an enigma. We previously showed that KSHV could efficiently infect, transform, and reprogram rat primary mesenchymal stem cells (MSCs) into KS-like tumor cells. In this study, we showed that human primary MSCs derived from diverse organs, including bone marrow (MSCbm), adipose tissue (MSCa), dental pulp, gingiva tissue (GMSC), and exfoliated deciduous teeth, were permissive to KSHV infection. We successfully established long-term cultures of KSHV-infected MSCa, MSCbm, and GMSC (LTC-KMSCs). While LTC-KMSCs had lower proliferation rates than the uninfected cells, they expressed mixtures of KS markers and displayed differential angiogenic, invasive, and transforming phenotypes. Genetic analysis identified KSHV-derived microRNAs that mediated KSHV-induced angiogenic activity by activating the AKT pathway. These results indicated that human MSCs could be the KSHV target cells in vivo and established valid models for delineating the mechanism of KSHV infection, replication, and malignant transformation in biologically relevant cell types.

IMPORTANCE

Kaposi's sarcoma is the most common cancer in AIDS patients. While KSHV infection is required for the development of Kaposi's sarcoma, the origin of KSHV target cells remains unclear. We show that KSHV can efficiently infect human primary mesenchymal stem cells of diverse origins and reprogram them to acquire various degrees of Kaposi's sarcoma-like cell makers and angiogenic, invasive, and transforming phenotypes. These results indicate that human mesenchymal stem cells might be the KSHV target cells and establish models for delineating the mechanism of KSHV-induced malignant transformation.

Role of Neuropilin-1 in Diabetic Nephropathy

Diabetic nephropathy (DN) often develops in patients suffering from type 1 or type 2 diabetes mellitus. DN is characterized by renal injury resulting in proteinuria. Neuropilin-1 (NRP-1) is a single-pass transmembrane receptor protein devoid of enzymatic activity. Its large extracellular tail is structured in several domains, thereby allowing the molecule to interact with multiple ligands linking NRP-1 to different pathways through its signaling co-receptors. NRP-1’s role in nervous system development, immunity, and more recently in cancer, has been extensively investigated. Although its relation to regulation of apoptosis and cytoskeleton organization of glomerular vascular endothelial cells was reported, its function in diabetes mellitus and the development of DN is less clear. Several lines of evidence demonstrate a reduced NRP-1 expression in glycated-BSA cultured differentiated podocytes as well as in glomeruli from db/db mice (a model of type 2 Diabetes) and in diabetic patients diagnosed with DN. In vitro studies of podocytes implicated NRP-1 in the regulation of podocytes’ adhesion to extracellular matrix proteins, cytoskeleton reorganization, and apoptosis via not completely understood mechanisms. However, the exact role of NRP-1 during the onset of DN is not yet understood. This review intends to shed more light on NRP-1 and to present a link between NRP-1 and its signaling complexes in the development of DN.

Rho/MRTF-A-Induced Integrin Expression Regulates Angiogenesis in Differentiated Multipotent Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are known to undergo endothelial differentiation in response to treatment with vascular endothelial growth factor (VEGF), but their angiogenic ability is poorly characterized. In the present study, we aimed to further investigate the role of Rho/MRTF-A in angiogenesis by MSCs and the effect of the Rho/MRTF-A pathway on the expression of integrins α1β1 and α5β1, which are known to mediate physiological and pathological angiogenesis. Our results showed that increased expression of α1, α5, and β1 was observed during angiogenesis of differentiated MSCs, and the Rho/MRTF-A signaling pathway was demonstrated to be involved in regulating the expression of integrins α1, α5, and β1. Luciferase reporter assay and ChIP assay determined that MRTF-A could bind to and transactivate the integrin α1 and α5 promoters. Treatment with the Rho inhibitor C3 transferase, the Rho-associated protein kinase (ROCK) inhibitor Y27632 or with shMRTF-A inhibited both the upregulation of α1, α5, and β1 as well as angiogenesis. Furthermore, in human umbilical vein endothelial cells (HUVECs), MRTF-A deletion led to marked reductions in cell migration and vessel network formation compared with the control. These data demonstrate that Rho/MRTF-A signaling is an important mediator that controls integrin gene expression during MSC-mediated angiogenic processes.

Nanotherapy for Cancer: Targeting and Multifunctionality in the Future of Cancer Therapies

Cancer continues to be a prevalent and lethal disease, despite advances in tumor biology research and chemotherapy development. Major obstacles in cancer treatment arise from tumor heterogeneity, drug resistance, and systemic toxicities. Nanoscale delivery systems, or nanotherapies, are increasing in importance as vehicles for antineoplastic agents because of their potential for targeting and multifunctionality. We discuss the current field of cancer therapy and potential strategies for addressing obstacles in cancer treatment with nanotherapies. Specifically, we review the strategies for rationally designing nanoparticles for targeted, multimodal delivery of therapeutic agents.

Grafting and early expression of growth factors from adipose-derived stem cells transplanted into the cochlea, in a Guinea pig model of acoustic trauma

Noise exposure causes damage of multiple cochlear cell types producing permanent hearing loss with important social consequences. In mammals, no regeneration of either damaged hair cells or auditory neurons has been observed and no successful treatment is available to achieve a functional recovery. Loads of evidence indicate adipose-derived stem cells (ASCs) as promising tools in diversified regenerative medicine applications, due to the high degree of plasticity and trophic features. This study was aimed at identifying the path of in vivo cell migration and expression of trophic growth factors, upon ASCs transplantation into the cochlea, following noise-induced injury. ASCs were isolated in primary culture from the adipose tissue of a guinea pig, transduced using a viral vector to express the green fluorescent protein, and implanted into the scala tympani of deafened animals. Auditory function was assessed 3 and 7 days after surgery. The expression of trophic growth factors was comparatively analyzed using real-time PCR in control and noise-injured cochlear tissues. Immunofluorescence was used to assess the in vivo localization and expression of trophic growth factors in ASCs and cochleae, 3 and 7 days following homologous implantation. ASC implantation did not modify auditory function. ASCs migrated from the perilymphatic to the endolymphatic compartment, during the analyzed time course. Upon noise exposure, the expression of chemokine ligands and receptors related to the PDGF, VEGF, and TGFbeta pathways, increased in the cochlear tissues, possibly guiding in vivo cell migration. Immunofluorescence confirmed the increased expression, which appeared to be further strengthened by ASCs’ implantation. These results indicated that ASCs are able to migrate at the site of tissue damage and express trophic factors, upon intracochlear implantation, providing an original proof of principle, which could pave the way for further developments of ASC-based treatments of deafness.

Platelet-derived growth factor regulates the secretion of extracellular vesicles by adipose mesenchymal stem cells and enhances their angiogenic potential

BACKGROUND

Several studies demonstrate the role of adipose mesenchymal stem cells (ASCs) in angiogenesis. The angiogenic mechanism has been ascribed to paracrine factors since these cells secrete a plenty of signal molecules and growth factors. Recently it has been suggested that besides soluble factors, extracellular vesicles (EVs) that include exosomes and microvesicles may play a major role in cell-to-cell communication. It has been shown that EVs are implicated in the angiogenic process.

RESULTS

Herein we studied whether EVs released by ASCs may mediate the angiogenic activity of these cells. Our results demonstrated that ASC-derived EVs induced in vitro vessel-like structure formation by human microvascular endothelial cells (HMEC). EV-stimulated HMEC when injected subcutaneously within Matrigel in SCID mice formed vessels. Treatment of ASCs with platelet-derived growth factor (PDGF) stimulated the secretion of EVs, changed their protein composition and enhanced the angiogenic potential. At variance of EVs released in basal conditions, PDGF-EVs carried c-kit and SCF that played a role in angiogenesis as specific blocking antibodies inhibited in vitro vessel-like structure formation. The enhanced content of matrix metalloproteinases in PDGF-EVs may also account for their angiogenic activity.

CONCLUSIONS

Our findings indicate that EVs released by ASCs may contribute to the ASC-induced angiogenesis and suggest that PDGF may trigger the release of EVs with an enhanced angiogenic potential.

The paracrine effects of mesenchymal stem cells stimulate the regeneration capacity of endogenous stem cells in the repair of a bladder-outlet-obstruction-induced overactive bladder

Overactive bladder (OAB), which is characterized by the sudden and uncomfortable need to urinate with or without urinary leakage, is a challenging urological condition. The insufficient efficacy of current pharmacotherapies that uses antimuscarinic agents has increased the demand for novel long-term/stable therapeutic strategies. Here, we report the superior therapeutic efficacy of using mesenchymal stem cells (MSCs) for the treatment of OAB and a novel therapeutic mechanism that activates endogenous Oct4(+) primitive stem cells. We induced OAB using bladder-outlet-obstruction (BOO) in a rat model and either administered a single transplantation of human adipose-derived MSCs or daily intravenous injections of solifenacin, an antimuscarinic agent, for 2 weeks. Within 2 weeks, both the MSC- and solifenacin-treated groups similarly demonstrated relief from BOO-induced detrusor overactivity, hypertrophic smooth muscle, and neurological injuries. In contrast with the solifenacin-treated groups, a single transplantation of MSCs improved most OAB parameters to normal levels within 4 weeks. Although the transplanted human MSCs were hardly engrafted into the damaged bladders, the bladder tissues transplanted with MSCs increased rat sequence-specific transcription of Oct4, Sox2, and Stella, which are surrogate markers for primitive pluripotent stem cells. In addition, MSCs enhanced the expression of several genes, responsible for stem cell trafficking, including SDF-1/CXCR4, HGF/cMet, PDGF/PDGFR, and VEGF/VEGFR signaling axis. These changes in gene expression were not observed in the solifenacin-treated group. Therefore, we suggest the novel mechanisms for the paracrine effect of MSCs as unleashing/mobilizing primitive endogenous stem cells, which could not only explain the long-term/stable therapeutic efficacy of MSCs, but also provide promising new therapies for the treatment of OAB.

Perivascular cells in blood vessel regeneration

Vascular engineering seeks to design and construct functional blood vessels comprising endothelial cells (ECs) and perivascular cells (PCs), with the ultimate goal of clinical translation. While EC behavior has been extensively investigated, PCs play an equally significant role in the development of novel regenerative strategies, providing functionality and stability to vessels. The two major classes of PCs are vascular smooth muscle cells (vSMCs) and pericytes; vSMCs can be further sub-classified as either contractile or synthetic. The inclusion of these cell types is crucial for successful regeneration of blood vessels. Furthermore, understanding distinctions between vSMCs and pericytes will enable improved therapeutics in a tissue-specific manner. Here we focus on the approaches and challenges facing the use of PCs in vascular regeneration, including their characteristics, stem cell sources, and interactions with ECs. Finally, we discuss biochemical and microRNA (miR) regulators of PC behavior and engineering approaches that mimic various cues affecting PC function.

Comparative proteome approach demonstrates that platelet-derived growth factor C and D efficiently induce proliferation while maintaining multipotency of hMSCs

This is the first study that comprehensively describes the effects of the platelet-derived growth factor (PDGF) isoforms C and D during in vitro expansion of human mesenchymal stem cells (hMSCs). Our results show that PDGFs can enhance proliferation of hMSCs without affecting their multipotency. It is of great value to culture and expand hMSCs in a safe and effective manner without losing their multipotency for manipulation and further development of cell-based therapies. Moreover, differential effects of PDGF isoforms have been observed on lineage-specific differentiation induced by BMP2 and Vitamin D3. Based on label-free LC-based quantitative proteomics approach we have furthermore identified specific pathways induced by PDGFs during the proliferation process, showing the importance of bioinformatics tools to study cell function.

Repression of Zeb1 and hypoxia cause sequential mesenchymal-to-epithelial transition and induction of aid, Oct4, and Dnmt1, leading to immortalization and multipotential reprogramming of fibroblasts in spheres

In this study, we demonstrate that sphere formation triggers immortalization and stable reprogramming of mouse fibroblasts. Cell contact signaling in spheres causes downregulation of the epithelial-to-mesenchymal transition transcription factor Zeb1 leading to rapid mesenchymal-to-epithelial transition. Hypoxia within spheres together with loss of Zeb1 repression synergize to cause superinduction of Hif1a, which in turn leads to induction of the DNA demethylase Aid/Aicda, demethylation of the Oct4 promoter/enhancer and multipotency. Oct4 and Nanog expression diminish when cells are removed from the hypoxic environment of spheres and placed in monolayer culture, but the cells retain multipotential capacity, demonstrating stable reprogramming and a gene expression pattern resembling adult stem cells. Oct4 has been shown to induce Dnmt1 in mesenchymal stem cells, and we link Oct4 and Dnmt1 to silencing of cell cycle inhibitory cyclin dependent kinase inhibitors and Arf, and immortalization of the reprogrammed fibroblasts. Sphere formation then represents a novel and rapid protocol for immortalization and stable reprogramming of fibroblasts to multipotency that does not require exogenous expression of a stem cell factor or a lineage-specifying transcription factor.

Phenotypic characterization and in vivo localization of human adipose-derived mesenchymal stem cells

Human adipose-derived mesenchymal stem cells (hADMSCs) are a potential cell source for autologous cell therapy due to their regenerative ability. However, detailed cytological or phenotypic characteristics of these cells are still unclear. Therefore, we determined and compared cell size, morphology, ultrastructure, and immunohistochemical (IHC) expression profiles of isolated hADMSCs and cells located in human adipose tissues. We also characterized the localization of these cells in vivo. Light microscopy examination at low power revealed that hADMSCs acquired a spindle-shaped morphology after four passages. Additionally, high power views showed that these cells had various sizes, nuclear contours, and cytoplasmic textures. To further evaluate cell morphology, transmission electron microscopy was performed. hADMSCs typically had ultrastructural characteristics similar to those of primitive mesenchymal cells including a relatively high nuclear/cytosol ratio, prominent nucleoli, immature cytoplasmic organelles, and numerous filipodia. Some cells contained various numbers of lamellar bodies and lipid droplets. IHC staining demonstrated that PDGFR and CD10 were constitutively expressed in most hADMSCs regardless of passage number but expression levels of α-SMA, CD68, Oct4 and c-kit varied. IHC staining of adipose tissue showed that cells with immunophenotypic characteristics identical to those of hADMSCs were located mainly in the perivascular adventitia not in smooth muscle area. In summary, hADMSCs were found to represent a heterogeneous cell population with primitive mesenchymal cells that were mainly found in the perivascular adventitia. Furthermore, the cell surface markers would be CD10/PDGFR. To obtain defined cell populations for therapeutic purposes, further studies will be required to establish more specific isolation methods.

Platelet derived growth factor-evoked Ca2+ wave and matrix gene expression through phospholipase C in human pulmonary fibroblast

The primary role of fibroblasts is production and degradation of extracellular matrix, and thus it helps in the structural framework of tissues. The close relation between fibroblast malfunction and many diseases such as chronic obstructive pulmonary disease, asthma, and fibrosis is widely accepted. Fibroblasts are known to respond to different growth factors and cytokines including platelet-derived growth factors (PDGF). However, the intracellular signaling mechanisms are not entirely clear. In addition to complex phosphorylation-driven signaling pathways, PDGF is also known to work through Ca(2+) signaling. We hypothesize that in human pulmonary fibroblasts, Ca(2+) waves play an important role in PDGF-mediated changes. To test this hypothesis, we treated human pulmonary fibroblasts, obtained from the lungs of ten donors, with PDGF acutely or overnight plus/minus a variety of blockers under various conditions. Ca(2+) waves were monitored by confocal [Ca(2+)]i fluorimetry, while gene expression of extracellular matrix genes was assessed via RT-PCR method. We found that both acute and overnight PDGF treatment evoked Ca(2+) waves. Removal of external Ca(2+) or depletion of internal Ca(2+) store using Cyclopiazonic acid (CPA) completely occluded PDGF-evoked Ca(2+) waves. Ryanodine, which blocks ryanodine receptor channels, had no effect on PDGF-evoked Ca(2+) wave, whereas the phospholipase C inhibitor U73122 and Xestospongin C, a potent IP3 receptor blocker, reduced the rapid PDGF-response to a relatively slowly-developing rise in [Ca(2+)]i. We also found that PDGF dramatically increased the expression of fibronectin1 and collagen A1 genes, which was reversed by the use of CPA or U73122. Our study indicates that, in human pulmonary fibroblasts, PDGF acts through IP3-induced Ca(2+)-release to trigger Ca(2+) waves, which in turn modulate gene expression of several matrix proteins.

S-nitrosoglutathione reductase (GSNOR) enhances vasculogenesis by mesenchymal stem cells

Although nitric oxide (NO) signaling promotes differentiation and maturation of endothelial progenitor cells, its role in the differentiation of mesenchymal stem cells (MSCs) into endothelial cells remains controversial. We tested the role of NO signaling in MSCs derived from WT mice and mice homozygous for a deletion of S-nitrosoglutathione reductase (GSNOR(-/-)), a denitrosylase that regulates S-nitrosylation. GSNOR(-/-) MSCs exhibited markedly diminished capacity for vasculogenesis in an in vitro Matrigel tube-forming assay and in vivo relative to WT MSCs. This decrease was associated with down-regulation of the PDGF receptorα (PDGFRα) in GSNOR(-/-) MSCs, a receptor essential for VEGF-A action in MSCs. Pharmacologic inhibition of NO synthase with L-N(G)-nitroarginine methyl ester (L-NAME) and stimulation of growth hormone-releasing hormone receptor (GHRHR) with GHRH agonists augmented VEGF-A production and normalized tube formation in GSNOR(-/-) MSCs, whereas NO donors or PDGFR antagonist reduced tube formation ∼50% by murine and human MSCs. The antagonist also blocked the rescue of tube formation in GSNOR(-/-) MSCs by L-NAME or the GHRH agonists JI-38, MR-409, and MR-356. Therefore, GSNOR(-/-) MSCs have a deficient capacity for endothelial differentiation due to downregulation of PDGFRα related to NO/GSNOR imbalance. These findings unravel important aspects of modulation of MSCs by VEGF-A activation of the PDGFR and illustrate a paradoxical inhibitory role of S-nitrosylation signaling in MSC vasculogenesis. Accordingly, disease states characterized by NO deficiency may trigger MSC-mediated vasculogenesis. These findings have important implications for therapeutic application of GHRH agonists to ischemic disorders.

Derivation and maturation of synthetic and contractile vascular smooth muscle cells from human pluripotent stem cells

AIMS

Embryonic vascular smooth muscle cells (vSMCs) have a synthetic phenotype; in adults, they commit to the mature contractile phenotype. Research shows that human pluripotent stem cells (hPSCs) differentiate into vSMCs, but nobody has yet documented their maturation into the synthetic or contractile phenotypes. This study sought to control the fate decisions of hPSC derivatives to guide their maturation towards a desired phenotype.

METHODS AND RESULTS

The long-term differentiation of hPSCs, including the integration-free-induced PSC line, in high serum with platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-β1, allowed us to induce the synthetic vSMC (Syn-vSMC) phenotype with increased extracellular matrix (ECM) protein expression and reduced expression of contractile proteins. By monitoring the expression of two contractile proteins, smooth muscle myosin heavy chain (SMMHC) and elastin, we show that serum starvation and PDGF-BB deprivation caused maturation towards the contractile vSMC (Con-vSMC) phenotype. Con-vSMCs differ distinctively from Syn-vSMC derivatives in their condensed morphology, prominent filamentous arrangement of cytoskeleton proteins, production and assembly of elastin, low proliferation, numerous and active caveolae, enlarged endoplasmic reticulum, and ample stress fibres and bundles, as well as their high contractility. When transplanted subcutaneously into nude mice, the human Con-vSMCs aligned next to the host's growing functional vasculature, with occasional circumferential wrapping and vascular tube narrowing.

CONCLUSION

We control hPSC differentiation into synthetic or contractile phenotypes by using appropriate concentrations of relevant factors. Deriving Con-vSMCs from an integration-free hiPSC line may prove useful for regenerative therapy involving blood vessel differentiation and stabilization.

Mediator MED23 plays opposing roles in directing smooth muscle cell and adipocyte differentiation

The Mediator complex functions as a control center, orchestrating diverse signaling, gene activities, and biological processes. However, how Mediator subunits determine distinct cell fates remains to be fully elucidated. Here, we show that Mediator MED23 controls the cell fate preference that directs differentiation into smooth muscle cells (SMCs) or adipocytes. Med23 deficiency facilitates SMC differentiation but represses adipocyte differentiation from the multipotent mesenchymal stem cells. Gene profiling revealed that the presence or absence of Med23 oppositely regulates two sets of genes: the RhoA/MAL targeted cytoskeleton/SMC genes and the Ras/ELK1 targeted growth/adipogenic genes. Mechanistically, MED23 favors ELK1-SRF binding to SMC gene promoters for repression, whereas the lack of MED23 favors MAL-SRF binding to SMC gene promoters for activation. Remarkably, the effect of MED23 on SMC differentiation can be recapitulated in zebrafish embryogenesis. Collectively, our data demonstrate the dual, opposing roles for MED23 in regulating the cytoskeleton/SMC and growth/adipogenic gene programs, suggesting its "Ying-Yang" function in directing adipogenesis versus SMC differentiation.

Cyclic ADP ribose is a novel regulator of intracellular Ca2+ oscillations in human bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) are a promising cell source for regenerative medicine. However, the cellular biology of these cells is not fully understood. The present study characterizes the cyclic ADP-ribose (cADPR)-mediated Ca(2+) signals in human MSCs and finds that externally applied cADPR can increase the frequency of spontaneous intracellular Ca(2+) (Ca(2+) (i) ) oscillations. The increase was abrogated by a specific cADPR antagonist or an inositol trisphosphate receptor (IP3R) inhibitor, but not by ryanodine. In addition, the cADPR-induced increase of Ca(2+) (i) oscillation frequency was prevented by inhibitors of nucleoside transporter or by inhibitors of the transient receptor potential cation melastatin-2 (TRPM2) channel. RT-PCR revealed mRNAs for the nucleoside transporters, concentrative nucleoside transporters 1/2 and equilibrative nucleoside transporters 1/3, IP3R1/2/3 and the TRPM2 channel, but not those for ryanodine receptors and CD38 in human MSCs. Knockdown of the TRPM2 channel by specific short interference RNA abolished the effect of cADPR on the Ca(2+) (i) oscillation frequency, and prevented the stimulation of proliferation by cADPR. Moreover, cADPR remarkably increased phosphorylated extracellular-signal-regulated kinases 1/2 (ERK1/2), but not Akt or p38 mitogen-activated protein kinase (MAPK). However, cADPR had no effect on adipogenesis or osteogenesis in human MSCs. Our results indicate that cADPR is a novel regulator of Ca(2+) (i) oscillations in human MSCs. It permeates the cell membrane through the nucleoside transporters and increases Ca(2+) oscillation via activation of the TRPM2 channel, resulting in enhanced phosphorylation of ERK1/2 and, thereby, stimulation of human MSC proliferation. This study delineates an alternate signalling pathway of cADPR that is distinct from its well-established role of serving as a Ca(2+) messenger for mobilizing the internal Ca(2+) stores. Whether cADPR can be used clinically for stimulating marrow function in patients with marrow disorders remains to be further studied.

Towards the therapeutic use of vascular smooth muscle progenitor cells

Recent advances in the development of alternative proangiogenic and revascularization processes, including recombinant protein delivery, gene therapy, and cell therapy, hold the promise of greater efficacy in the management of cardiovascular disease in the coming years. In particular, vascular progenitor cell-based strategies have emerged as an efficient treatment approach to promote vessel formation and repair and to improve tissue perfusion. During the past decade, considerable progress has been achieved in understanding therapeutic properties of endothelial progenitor cells, while the therapeutic potential of vascular smooth muscle progenitor cells (SMPC) has only recently been explored; the number of the circulating SMPC being correlated with cardiovascular health. Several endogenous SMPC populations with varying phenotypes have been identified and characterized in the peripheral blood, bone marrow, and vascular wall. While the phenotypic entity of vascular SMPC is not fully defined and remains an evolving area of research, SMPC are increasingly recognized to play a special role in cardiovascular biology. In this review, we describe the current approaches used to define vascular SMPC. We further summarize the data on phenotype and functional properties of SMPC from various sources in adults. Finally, we discuss the role of SMPC in cardiovascular disease, including the contribution of SMPC to intimal proliferation, angiogenesis, and atherosclerotic plaque instability as well as the benefits resulting from the therapeutic use of SMPC.

Regenerative tendon and ligament healing: opportunities with recombinant human platelet-derived growth factor BB-homodimer

Intrinsic tendon healing in response to injury is a reparative process that often results in formation of scar tissue with functional and mechanical properties inferior to those of the native tendon. Development of therapies that can promote regenerative, rather than reparative, healing hold the promise of improving patient recovery from tendon and ligament injuries by producing tissue that is morphologically and functionally equivalent to the native tissue. One therapeutic approach that has been a frequent topic of investigation in the preclinical literature is the use of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) to augment tendon and ligament repair. The chemotactic, mitogenic, and pro-angiogenic properties of rhPDGF-BB have been shown to result in recruitment and proliferation of tenogenic cells and a commensurate boost in extracellular matrix deposition and organization, improving the morphological and biomechanical properties of healing tendons and ligaments. The outcomes of the preclinical studies reviewed here strongly suggest that rhPDGF-BB will provide a new therapeutic opportunity to improve the treatment of injured tendons and ligaments.

Specific glycosaminoglycans modulate neural specification of mouse embryonic stem cells

Mouse embryonic stem (mES) cells express a low sulfated form of heparan sulfate (HS). HS chains displayed by ES cells and their progeny become more complex and more sulfated during progression from pluripotency to neuroectodermal precursors. Sulfated epitopes are important for recognition and binding of a variety of ligands including members of the fibroblast growth factor (FGF) family. We demonstrated previously that mES cells lacking HS cannot undergo neural specification but this activity can be recovered by adding soluble heparin, a highly sulfated glycosaminoglycan (GAG). Therefore, we hypothesized that soluble GAGs might be used to support neural differentiation of HS competent cells and that the mechanisms underlying this activity might provide useful information about the signaling pathways critical for loss of pluripotency and early lineage commitment. In this study, we demonstrate that specific HS/heparin polysaccharides support formation of Sox1(+) neural progenitor cells from wild-type ES cells. This effect is dependent on sulfation pattern, concentration, and length of saccharide. Using a selective inhibitor of FGF signal transduction, we show that heparin modulates signaling events regulating exit from pluripotency and commitment to primitive ectoderm and subsequently neuroectoderm. Interestingly, we were also able to demonstrate that multiple receptor tyrosine kinases were influenced by HS in this system. This suggests roles for additional factors, possibly in cell proliferation or protection from apoptosis, during the process of neural specification. Therefore, we conclude that soluble GAGs or synthetic mimics could be considered as suitable low-cost factors for addition to ES cell differentiation regimes.

bFGF and PDGF-BB have a synergistic effect on the proliferation, migration and VEGF release of endothelial progenitor cells

We have investigated the synergistic effects of bFGF (basic fibroblast growth factor) and PDGF-BB (platelet-derived growth factor-BB) on the proliferation, migration and VEGF (vascular endothelial growth factor) release of EPCs (endothelial progenitor cells). The proliferation of EPCs was assayed by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium]. EPCs migration was detected using the Transwell system. Real-time PCR was used to assess the transcription of PDGFRβ mRNA. PLC-γ (phospholipase C gamma) expression and VEGF release were analysed by Western blot and ELISA. bFGF and PDGF-BB could, respectively, or synergistically, promote the proliferation and migration of EPCs, and these effects of bFGF and PDGF-BB were implemented by enhancing PDGFRβ mRNA, PLC-γ and VEGF expression, while inhibitor of PDGF receptor kinase (AG1296) and the selective PLC inhibitor (U73122) could block these effects of bFGF and PDGF-BB. In the meantime, we proved that the amplification by bFGF and PDGF-BB-stimulated PDGFRβ mRNA, PLC-γ and VEGF expression was abrogated by anti-bFGF antibody, AG1296 and U73122. These results strongly suggest that the proliferation and migration of EPCs may depend on bFGF and/or PDGF-BB by PDGFRβ/PLC-γ signalling pathway, and bFGF and/or PDGF-BB stimulate VEGF release at a point downstream from PDGFRβ/PLC-γ in EPCs.

Scaffolds in tissue engineering of blood vessels

Tissue engineering of small diameter (<5 mm) blood vessels is a promising approach for developing viable alternatives to autologous vascular grafts. It involves in vitro seeding of cells onto a scaffold on which the cells attach, proliferate, and differentiate while secreting the components of extracellular matrix that are required for creating the tissue. The scaffold should provide the initial requisite mechanical strength to withstand in vivo hemodynamic forces until vascular smooth muscle cells and fibroblasts reinforce the extracellular matrix of the vessel wall. Hence, the choice of scaffold is crucial for providing guidance cues to the cells to behave in the required manner to produce tissues and organs of the desired shape and size. Several types of scaffolds have been used for the reconstruction of blood vessels. They can be broadly classified as biological scaffolds, decellularized matrices, and polymeric biodegradable scaffolds. This review focuses on the different types of scaffolds that have been designed, developed, and tested for tissue engineering of blood vessels, including use of stem cells in vascular tissue engineering.

Functional proteomics to dissect tyrosine kinase signalling pathways in cancer

Advances in the generation and interpretation of proteomics data have spurred a transition from focusing on protein identification to functional analysis. Here we review recent proteomics results that have elucidated new aspects of the roles and regulation of signal transduction pathways in cancer using the epidermal growth factor receptor (EGFR), ERK and breakpoint cluster region (BCR)-ABL1 networks as examples. The emerging theme is to understand cancer signalling as networks of multiprotein machines which process information in a highly dynamic environment that is shaped by changing protein interactions and post-translational modifications (PTMs). Cancerous genetic mutations derange these protein networks in complex ways that are tractable by proteomics.