Bone marrow derived pluripotent cells are pericytes which contribute to vascularization

Implantable 3D printed hydrogels with intrinsic channels for liver tissue engineering

This study presents the design, fabrication, and evaluation of a general platform for the creation of three-dimensional printed devices (3DPDs) for tissue engineering applications. As a demonstration, we modeled the liver with 3DPDs consisting of a pair of parallel millifluidic channels that function as portal-venous (PV) and hepatobiliary (HB) structures. Perfusion of medium or whole blood through the PV channel supports the hepatocyte-containing HB channel. Device computer-aided design was optimized for structural stability, after which 3DPDs were 3D printed in a polyethylene(glycol) diacrylate photoink by digital light processing and evaluated in vitro. The HB channels were subsequently seeded with hepatic cells suspended in a collagen hydrogel. Perfusion of 3DPDs in bioreactors enhanced the viability and function of rat hepatoma cells and were maintained over time, along with improved liver-specific functions. Similar results were observed with primary rat hepatocytes, including significant upregulation of cytochrome p450 activity. Additionally, coculture experiments involving primary rat hepatocytes, endothelial cells, and mesenchymal stem cells in 3DPDs showed enhanced viability, broad liver-specific gene expression, and histological features indicative of liver tissue architecture. In vivo implantation of 3DPDs in a rat renal shunt model demonstrated successful blood flow through the devices without clot formation and maintenance of cell viability. 3D printed designs can be scaled in 3D space, allowing for larger devices with increased cell mass. Overall, these findings highlight the potential of 3DPDs for clinical translation in hepatic support applications.

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

Versatile subtypes of pericytes and their roles in spinal cord injury repair, bone development and repair

Vascular regeneration is a challenging topic in tissue repair. As one of the important components of the neurovascular unit (NVU), pericytes play an essential role in the maintenance of the vascular network of the spinal cord. To date, subtypes of pericytes have been identified by various markers, namely the PDGFR-β, Desmin, CD146, and NG2, each of which is involved with spinal cord injury (SCI) repair. In addition, pericytes may act as a stem cell source that is important for bone development and regeneration, whilst specific subtypes of pericyte could facilitate bone fracture and defect repair. One of the major challenges of pericyte biology is to determine the specific markers that would clearly distinguish the different subtypes of pericytes, and to develop efficient approaches to isolate and propagate pericytes. In this review, we discuss the biology and roles of pericytes, their markers for identification, and cell differentiation capacity with a focus on the potential application in the treatment of SCI and bone diseases in orthopedics.

RNA-sequencing profiling analysis of pericyte-derived extracellular vesicle-mimetic nanovesicles-regulated genes in primary cultured fibroblasts from normal and Peyronie's disease penile tunica albuginea

BACKGROUND

Peyronie's disease (PD) is a severe fibrotic disease of the tunica albuginea that causes penis curvature and leads to penile pain, deformity, and erectile dysfunction. The role of pericytes in the pathogenesis of fibrosis has recently been determined. Extracellular vesicle (EV)-mimetic nanovesicles (NVs) have attracted attention regarding intercellular communication between cells in the field of fibrosis. However, the global gene expression of pericyte-derived EV-mimetic NVs (PC-NVs) in regulating fibrosis remains unknown. Here, we used RNA-sequencing technology to investigate the potential target genes regulated by PC-NVs in primary fibroblasts derived from human PD plaque.

METHODS

Human primary fibroblasts derived from normal and PD patients was cultured and treated with cavernosum pericytes isolated extracellular vesicle (EV)-mimetic nanovesicles (NVs). A global gene expression RNA-sequencing assay was performed on normal fibroblasts, PD fibroblasts, and PD fibroblasts treated with PC-NVs. Reverse transcription polymerase chain reaction (RT-PCR) was used for sequencing data validation.

RESULTS

A total of 4135 genes showed significantly differential expression in the normal fibroblasts, PD fibroblasts, and PD fibroblasts treated with PC-NVs. However, only 91 contra-regulated genes were detected among the three libraries. Furthermore, 20 contra-regulated genes were selected and 11 showed consistent changes in the RNA-sequencing assay, which were validated by RT-PCR.

CONCLUSION

The gene expression profiling results suggested that these validated genes may be good targets for understanding potential mechanisms and conducting molecular studies into PD.

New Insights into Profibrotic Myofibroblast Formation in Systemic Sclerosis: When the Vascular Wall Becomes the Enemy

In systemic sclerosis (SSc), abnormalities in microvessel morphology occur early and evolve into a distinctive vasculopathy that relentlessly advances in parallel with the development of tissue fibrosis orchestrated by myofibroblasts in nearly all affected organs. Our knowledge of the cellular and molecular mechanisms underlying such a unique relationship between SSc-related vasculopathy and fibrosis has profoundly changed over the last few years. Indeed, increasing evidence has suggested that endothelial-to-mesenchymal transition (EndoMT), a process in which profibrotic myofibroblasts originate from endothelial cells, may take center stage in SSc pathogenesis. While in arterioles and small arteries EndoMT may lead to the accumulation of myofibroblasts within the vessel wall and development of fibroproliferative vascular lesions, in capillary vessels it may instead result in vascular destruction and formation of myofibroblasts that migrate into the perivascular space with consequent tissue fibrosis and microvessel rarefaction, which are hallmarks of SSc. Besides endothelial cells, other vascular wall-resident cells, such as pericytes and vascular smooth muscle cells, may acquire a myofibroblast-like synthetic phenotype contributing to both SSc-related vascular dysfunction and fibrosis. A deeper understanding of the mechanisms underlying the differentiation of myofibroblasts inside the vessel wall provides the rationale for novel targeted therapeutic strategies for the treatment of SSc.

Mesenchymal stem cell as a novel approach to systemic sclerosis; current status and future perspectives

Systemic sclerosis is a rare chronic autoimmune disease with extensive microvascular injury, damage of endothelial cells, activation of immune responses, and progression of tissue fibrosis in the skin and various internal organs. According to epidemiological data, women's populations are more susceptible to systemic sclerosis than men. Until now, various therapeutic options are employed to manage the symptoms of the disease. Since stem cell-based treatments have developed as a novel approach to rescue from several autoimmune diseases, it seems that stem cells, especially mesenchymal stem cells as a powerful regenerative tool can also be advantageous for systemic sclerosis treatment via their remarkable properties including immunomodulatory and anti-fibrotic effects. Accordingly, we discuss the contemporary status and future perspectives of mesenchymal stem cell transplantation for systemic sclerosis.

Uveal Melanoma Cells Elicit Retinal Pericyte Phenotypical and Biochemical Changes in an in Vitro Model of Coculture

Vascular pericytes are an important cellular component in the tumor microenvironment, however, their role in supporting cancer invasion is poorly understood. We hypothesized that PDGF-BB could be involved in the transition of human retinal pericytes (HRPC) in cancer-activated fibroblasts (CAF), induced by the 92.1 uveal melanoma (UM) cell line. In our model system, HRPC were conditioned by co-culturing with 92.1UM for 6 days (cHRPC), in the presence or absence of imatinib, to block PDGF receptor-β (PDGFRβ). The effects of the treatments were tested by wound healing assay, proliferation assay, RT-PCR, high-content screening, Western blot analysis, and invasion assay. Results showed profound changes in cHRPC shape, with increased proliferation and motility, reduction of NG2 and increase of TGF-β1, α-SMA, vimentin, and FSP-1 protein levels, modulation of PDGF isoform mRNA levels, phospho-PDGFRβ, and PDGFRβ, as well as phospho-STAT3 increases. A reduction of IL-1β and IFNγ and an increase in TNFα, IL10, and TGF-β1, CXCL11, CCL18, and VEGF mRNA in cHRPC were found. Imatinib was effective in preventing all the 92.1UM-induced changes. Moreover, cHRPC elicited a significant increase of 92.1UM cell invasion and active MMP9 protein levels. Our data suggest that retinal microvascular pericytes could promote 92.1UM growth through the acquisition of the CAF phenotype.

The therapeutic potential of mesenchymal stem cells for cardiovascular diseases

Mesenchymal stem cells (MSCs) are derived from a wide range of sources and easily isolated and cultured. MSCs have the capacity for in vitro amplification and self-renewal, low immunogenicity and immunomodulatory properties, and under certain conditions, MSCs can be differentiated into a variety of cells. In the cardiovascular system, MSCs can protect the myocardium by reducing the level of inflammation, promoting the differentiation of myocardial cells around infarct areas and angiogenesis, increasing apoptosis resistance, and inhibiting fibrosis, which are ideal qualities for cardiovascular repair. Preclinical studies have shown that MSCs can be transplanted and improve cardiac repair, but challenges, such as their low rate of migration to the ischemic myocardium, low tissue retention, and low survival rate after transplantation, remain. This article reviews the potential and methods of MSC transplantation in the treatment of cardiovascular diseases (CVDs) and the challenges of the clinical use of MSCs.

Concise Review: The Regenerative Journey of Pericytes Toward Clinical Translation

Coronary artery disease (CAD) is the single leading cause of death worldwide. Advances in treatment and management have significantly improved patient outcomes. On the other hand, although mortality rates have decreased, more people are left with sequelae that require additional treatment and hospitalization. Moreover, patients with severe nonrevascularizable CAD remain with only the option of heart transplantation, which is limited by the shortage of suitable donors. In recent years, cell-based regenerative therapy has emerged as a possible alternative treatment, with several regenerative medicinal products already in the clinical phase of development and others emerging as competitive preclinical solutions. Recent evidence indicates that pericytes, the mural cells of blood microvessels, represent a promising therapeutic candidate. Pericytes are abundant in the human body, play an active role in angiogenesis, vessel stabilization and blood flow regulation, and possess the capacity to differentiate into multiple cells of the mesenchymal lineage. Moreover, early studies suggest a robustness to hypoxic insult, making them uniquely equipped to withstand the ischemic microenvironment. This review summarizes the rationale behind pericyte-based cell therapy and the progress that has been made toward its clinical application. We present the different sources of pericytes and the case for harvesting them from tissue leftovers of cardiovascular surgery. We also discuss the healing potential of pericytes in preclinical animal models of myocardial ischemia (MI) and current practices to upgrade the production protocol for translation to the clinic. Standardization of these procedures is of utmost importance, as lack of uniformity in cell manufacturing may influence clinical outcome. Stem Cells 2018;36:1295-1310.

Angiogenesis in a 3D model containing adipose tissue stem cells and endothelial cells is mediated by canonical Wnt signaling

Adipose-derived stromal cells (ASCs) have gained great attention in regenerative medicine. Progress in our understanding of adult neovascularization further suggests the potential of ASCs in promoting vascular regeneration, although the specific cues that stimulate their angiogenic behavior remain controversial. In this study, we established a three-dimensional (3D) angiogenesis model by co-culturing ASCs and endothelial cells (ECs) in collagen gel and found that ASC-EC-instructed angiogenesis was regulated by the canonical Wnt pathway. Furthermore, the angiogenesis that occurred in implants collected after injections of our collagen gel-based 3D angiogenesis model into nude mice was confirmed to be functional and also regulated by the canonical Wnt pathway. Wnt regulation of angiogenesis involving changes in vessel length, vessel density, vessel sprout, and connection numbers occurred in our system. Wnt signaling was then shown to regulate ASC-mediated paracrine signaling during angiogenesis through the nuclear translocation of β-catenin after its cytoplasmic accumulation in both ASCs and ECs. This translocation enhanced the expression of nuclear co-factor Lef-1 and cyclin D1 and activated the angiogenic transcription of vascular endothelial growth factor A (VEGFA), basic fibroblast growth factor (bFGF), and insulin-like growth factor 1 (IGF-1). The angiogenesis process in the 3D collagen model appeared to follow canonical Wnt signaling, and this model can help us understand the importance of the canonical Wnt pathway in the use of ASCs in vascular regeneration.

Enhancing engineered vascular networks in vitro and in vivo: The effects of IGF1 on vascular development and durability

OBJECTIVES

Creation of functional, durable vasculature remains an important goal within the field of regenerative medicine. Engineered biological vasculature has the potential to restore or improve human tissue function. We hypothesized that the pleotropic effects of insulin-like growth factor 1 (IGF1) would enhance the engineering of capillary-like vasculature.

MATERIALS AND METHODS

The impact of IGF1 upon vasculogenesis was examined in in vitro cultures for a period of up to 40 days and as subcutaneous implants within immunodeficient mice. Co-cultures of human umbilical vein endothelial cells and human bone marrow-derived mesenchymal stem cells in collagen-fibronectin hydrogels were supplemented with either recombinant IGF1 protein or genetically engineered cells to provide sustained IGF1. Morphometric analysis was performed on the vascular networks that formed in four concentrations of IGF1.

RESULTS

IGF1 supplementation significantly enhanced de novo vasculogenesis both in vitro and in vivo. Effects were long-term as they lasted the duration of the study period, and included network density, vessel length, and diameter. Bifurcation density was not affected. However, the highest concentrations of IGF1 tested were either ineffective or even deleterious. Sustained IGF1 delivery was required in vivo as the inclusion of recombinant IGF1 protein had minimal impact.

CONCLUSION

IGF1 supplementation can be used to produce neovasculature with significantly enhanced network density and durability. Its use is a promising methodology for engineering de novo vasculature to support regeneration of functional tissue.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Perivascular Cells in Diffuse Cutaneous Systemic Sclerosis Overexpress Activated ADAM12 and Are Involved in Myofibroblast Transdifferentiation and Development of Fibrosis

Objective.

Microvascular damage is pivotal in the pathogenesis of systemic sclerosis (SSc), preceding fibrosis, and whose trigger is not still fully understood. Perivascular progenitor cells, with profibrotic activity and function, are identified by the expression of the isoform 12 of ADAM (ADAM12) and this molecule may be upregulated by transforming growth factor-β (TGF-β). The goal of this work was to evaluate whether pericytes in the skin of patients with diffuse cutaneous SSc (dcSSc) expressed ADAM12, suggesting their potential contribution to the fibrotic process, and whether TGF-β might modulate this molecule.

Methods.

After ethical approval, mesenchymal stem cells (MSC) and fibroblasts (FB) were isolated from bone marrow and skin samples collected from 20 patients with dcSSc. ADAM12 expression was investigated in the skin and in isolated MSC and FB treated with TGF-β by immunofluorescence, quantitative real-time PCR, and western blot. Further, we silenced ADAM12 expression in both dcSSc-MSC and -FB to confirm the TGF-β modulation.

Results.

Pericytes and FB of dcSSc skin showed an increased expression of ADAM12 when compared with healthy control skin. TGF-β in vitro treatment induced a significant increase of ADAM12 in both SSc-MSC and -FB, with the higher levels observed in dcSSc cells. After ADAM12 silencing, the TGF-β ability to upregulate α-smooth muscle actin in both SSc-MSC and SSc-FB was inhibited.

Conclusion.

Our results suggest that in SSc, pericytes that transdifferentiate toward activated FB are present in the vascular tree, and TGF-β, while increasing ADAM12 expression, may modulate this transdifferentiation.

Amniotic Mesenchymal Stem Cells Can Enhance Angiogenic Capacity via MMPs In Vitro and In Vivo

The aim of this study was to evaluate the angiogenic capacity and proteolytic mechanism of coculture using human amniotic mesenchymal stem cells (hAMSCs) with human umbilical vein endothelial cells (HUVECs) in vivo and in vitro by comparing to those of coculture using bone marrow mesenchymal stem cells with HUVEC. For the in vivo experiment, cells (HUVEC-monoculture, HUVEC-hAMSC coculture, and HUVEC-BMMSC coculture) were seeded in fibrin gels and injected subcutaneously in nude mice. The samples were collected on days 7 and 14 and histologically analyzed by H&E and CD31 staining. CD31-positive staining percentage and vessel-like structure (VLS) density were evaluated as quantitative parameters for angiogenesis. The increases of CD31-positive staining area and VLS density in both HUVEC-hAMSC group and HUVEC-BMMSC group were found between two time points, while obvious decline of those was observed in HUVEC-only group. For the in vitro experiment, we utilized the same 3D culture model to investigate the proteolytic mechanism related to capillary formation. Intensive vascular networks formed by HUVECs were associated with hAMSCs or BMMSCs and related to MMP2 and MMP9. In conclusion, hAMSCs shared similar capacity and proteolytic mechanism with BMMSCs on neovascularization.

Analyzing Structure and Function of Vascularization in Engineered Bone Tissue by Video-Rate Intravital Microscopy and 3D Image Processing

Vascularization is a key challenge in tissue engineering. Three-dimensional structure and microcirculation are two fundamental parameters for evaluating vascularization. Microscopic techniques with cellular level resolution, fast continuous observation, and robust 3D postimage processing are essential for evaluation, but have not been applied previously because of technical difficulties. In this study, we report novel video-rate confocal microscopy and 3D postimage processing techniques to accomplish this goal. In an immune-deficient mouse model, vascularized bone tissue was successfully engineered using human bone marrow mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) in a poly (D,L-lactide-co-glycolide) (PLGA) scaffold. Video-rate (30 FPS) intravital confocal microscopy was applied in vitro and in vivo to visualize the vascular structure in the engineered bone and the microcirculation of the blood cells. Postimage processing was applied to perform 3D image reconstruction, by analyzing microvascular networks and calculating blood cell viscosity. The 3D volume reconstructed images show that the hMSCs served as pericytes stabilizing the microvascular network formed by HUVECs. Using orthogonal imaging reconstruction and transparency adjustment, both the vessel structure and blood cells within the vessel lumen were visualized. Network length, network intersections, and intersection densities were successfully computed using our custom-developed software. Viscosity analysis of the blood cells provided functional evaluation of the microcirculation. These results show that by 8 weeks, the blood vessels in peripheral areas function quite similarly to the host vessels. However, the viscosity drops about fourfold where it is only 0.8 mm away from the host. In summary, we developed novel techniques combining intravital microscopy and 3D image processing to analyze the vascularization in engineered bone. These techniques have broad applicability for evaluating vascularization in other engineered tissues as well.

Use of mesenchymal stem cells for therapy of cardiac disease

Despite substantial clinical advances over the past 65 years, cardiovascular disease remains the leading cause of death in America. The past 15 years has witnessed major basic and translational interest in the use of stem and precursor cells as a therapeutic agent for chronically injured organs. Among the cell types under investigation, adult mesenchymal stem cells are widely studied, and in early stage, clinical studies show promise for repair and regeneration of cardiac tissues. The ability of mesenchymal stem cells to differentiate into mesoderm- and nonmesoderm-derived tissues, their immunomodulatory effects, their availability, and their key role in maintaining and replenishing endogenous stem cell niches have rendered them one of the most heavily investigated and clinically tested type of stem cell. Accumulating data from preclinical and early phase clinical trials document their safety when delivered as either autologous or allogeneic forms in a range of cardiovascular diseases, but also importantly define parameters of clinical efficacy that justify further investigation in larger clinical trials. Here, we review the biology of mesenchymal stem cells, their interaction with endogenous molecular and cellular pathways, and their modulation of immune responses. Additionally, we discuss factors that enhance their proliferative and regenerative ability and factors that may hinder their effectiveness in the clinical setting.

Pericytes at the intersection between tissue regeneration and pathology

Perivascular multipotent cells, pericytes, contribute to the generation and repair of various tissues in response to injury. They are heterogeneous in their morphology, distribution, origin and markers, and elucidating their molecular and cellular differences may inform novel treatments for disorders in which tissue regeneration is either impaired or excessive. Moreover, these discoveries offer novel cellular targets for therapeutic approaches to many diseases. This review discusses recent studies that support the concept that pericyte subtypes play a distinctive role in myogenesis, neurogenesis, adipogenesis, fibrogenesis and angiogenesis.

Impaired endothelium-mesenchymal stem cells cross-talk in systemic sclerosis: a link between vascular and fibrotic features

INTRODUCTION

To assess if an impaired cross-talk between endothelial cells (ECs) and perivascular/multipotent mesenchymal stem cells (MSCs) might induce a perturbation of vascular repair and leading to a phenotypic switch of MSC toward myofibroblast in Systemic Sclerosis (SSc).

METHODS

We investigated different angiogenic and profibrotic molecules in a tridimentional matrigel assay, performing co-cultures with endothelial cells (ECs) and bone marrow derived MSCs from patients and healthy controls (HC). After 48 hours of co-culture, cells were sorted and analyzed for mRNA and protein expression.

RESULTS

ECs-SSc showed a decreased tube formation ability which is not improved by co-cultures with different MSCs. After sorting, we showed: i. an increased production of vascular endothelial growth factor A (VEGF-A) in SSc-MSCs when co-cultured with SSc-ECs; ii. an increased level of transforming growth factor beta (TGF-β) and platelet growth factor BB (PDGF-BB) in SSc-ECs when co-cultured with both HC- and SSc-MSCs; iii. an increase of TGF-β, PDGF-R, alpha smooth muscle actin (α-SMA) and collagen 1 (Col1) in both HC- and SSc-MSCs when co-cultured with SSc-ECs.

CONCLUSION

We showed that during SSc, the ECs-MSCs crosstalk resulted in an altered expression of different molecules involved in the angiogenic processes, and mainly SSc-ECs seem to modulate the phenotypic switch of perivascular MSCs toward a myofibroblast population, thus supporting the fibrotic process.

Impaired Cav-1 expression in SSc mesenchymal cells upregulates VEGF signaling: a link between vascular involvement and fibrosis

BACKGROUND

Systemic sclerosis (SSc) is characterized by vascular alteration and fibrosis, the former probably leading to fibrosis via the ability of both endothelial cells and pericytes to differentiate toward myofibroblast. It is well known that vascular endothelial growth factor A (VEGF-A, hereafter referred to as VEGF) may induce a profibrotic phenotype on perivascular cells. Caveolin-1 (Cav-1) is involved in the regulation of VEGF signaling, playing a role in the transport of internalized VEGF receptor 2 (VEGFR2) toward degradation, thus decreasing VEGF signaling. In this work, we assessed the levels of Cav-1 in SSc bone marrow mesenchymal stem cells (SSc-MSCs), a pericyte surrogate, and correlate these results with VEGF signaling, focusing onpotential pathogenic pathways leading to fibrosis.

RESULTS

WE EXPLORED THE VEGF SIGNALING ASSESSING: (1) Cav-1 expression; (2) its co-localization with VEGFR2; (3) the activity of VEGFR2, by IF, immunoprecipitation, and western blot. In SSc-MSCs, Cav-1 levels were lower when compared to healthy controls (HC)-MSCs. Furthermore, the Cav-1/VEGFR2 co-localization and the ubiquitination of VEGFR2 were impaired in SSc-MSCs, suggesting a decreased degradation of the receptor and, as a consequence, the tyrosine phosphorylation of VEGFR2 and the PI3-kinase-Akt pathways were significantly increased when compared to HC. Furthermore, an increased connective tissue growth factor (CTGF) expression was observed in SSc-MSCs. Taken together, these data suggested the upregulation of VEGF signaling in SSc-MSCs. Furthermore, after silencing Cav-1 expression in HC-MSCs, an increased CTGF expression in HC-MSCs was observed, mirroring the results obtained in SSc-MSCs, and confirming the potential role that the lack of Cav-1 may play in the persistent VEGF signaling .

CONCLUSIONS

During SSc, the lower levels of Cav-1 may contribute to the pathogenesis of fibrosis via an upregulation of the VEGF signaling in perivascular cells which are shifted to a profibrotic phenotype.

The role of pericyte detachment in vascular rarefaction

BACKGROUND

Pericytes surround endothelial cells at the perivascular interface. Signaling between endothelial cells and pericytes is crucial for capillary homeostasis, as pericytes stabilize vessels and regulate many microvascular functions. Recently it has been shown that pericytes are able to detach from the vascular wall and contribute to fibrosis by becoming scar-forming myofibroblasts in many organs including the kidney. At the same time, the loss of pericytes within the perivascular compartment results in vulnerable capillaries which are prone to instability, pathological angiogenesis, and, ultimately, rarefaction.

AIMS

This review will give an overview of pericyte-endothelial cell interactions, summarize the signaling pathways that have been identified to be involved in pericyte detachment from the vascular wall, and present pathological endothelial responses in the context of disease of the kidney.

Liver cell therapy and tissue engineering for transplantation

Liver transplantation remains the only definitive treatment for liver failure and is available to only a tiny fraction of patients with end-stage liver diseases. Major limitations for the procedure include donor organ shortage, high cost, high level of required expertise, and long-term consequences of immune suppression. Alternative cell-based liver therapies could potentially greatly expand the number of patients provided with effective treatment. Investigative research into augmenting or replacing liver function extends into three general strategies. Bioartificial livers (BALs) are extracorporeal devices that utilize cartridges of primary hepatocytes or cell lines to process patient plasma. Injection of liver cell suspensions aims to foster organ regeneration or provide a missing metabolic function arising from a genetic defect. Tissue engineering recreates the organ in vitro for subsequent implantation to augment or replace patient liver function. Translational models and clinical trials have highlighted both the immense challenges involved and some striking examples of success.

The role of pericytes in neurovascular unit remodeling in brain disorders

Neurons are extremely vulnerable cells that tightly rely on the brain’s highly dynamic and complex vascular network that assures an accurate and adequate distribution of nutrients and oxygen. The neurovascular unit (NVU) couples neuronal activity to vascular function, controls brain homeostasis, and maintains an optimal brain microenvironment adequate for neuronal survival by adjusting blood-brain barrier (BBB) parameters based on brain needs. The NVU is a heterogeneous structure constituted by different cell types that includes pericytes. Pericytes are localized at the abluminal side of brain microvessels and contribute to NVU function. Pericytes play essential roles in the development and maturation of the neurovascular system during embryogenesis and stability during adulthood. Initially, pericytes were described as contractile cells involved in controlling neurovascular tone. However, recent reports have shown that pericytes dynamically respond to stress induced by injury upon brain diseases, by chemically and physically communicating with neighboring cells, by their immune properties and by their potential pluripotent nature within the neurovascular niche. As such, in this paper, we would like to review the role of pericytes in NVU remodeling, and their potential as targets for NVU repair strategies and consequently neuroprotection in two pathophysiologically distinct brain disorders: ischemic stroke and Alzheimer’s disease (AD).

BMP4 promotes vascularization of human adipose stromal cells and endothelial cells in vitro and in vivo

OBJECTIVES

Vascularization is a major obstacle to clinical application of regenerative medicine. Engineered tissues must be able to generate an early vascular network that can quickly connect with the host vasculature. Recent research demonstrates that natural adipose tissues contain abundant stromal cells, which can give rise to pericytes. In this study, we aimed to investigate the application of human adipose stromal cells (ASCs) to vascularization, and the function of BMP4 protein during vascularization.

MATERIALS AND METHODS

Immunofluorescence staining for α-SMA and PDGFR-β were utilized to identify characteristics of ASCs/pericytes. They were then loaded into a collagen-fibronectin gel with endothelial cells to assess their vascularization ability, both in vitro and in vivo.

RESULTS

We showed that the ASCs expressed some of the essential markers of pericytes and they were able to promote vascularization with endothelial cells in 3D culture, both in vitro and in vivo. BMP4 protein further promoted this vascularization.

CONCLUSION

Adipose stromal cells promoted vascularization by endothelial cells and BMP4 protein further enhanced this effect.

In vitro and in vivo angiogenic capacity of BM-MSCs/HUVECs and AT-MSCs/HUVECs cocultures

The aim of this study was to comparatively evaluate the angiogenic capacity of cocultures using either human bone marrow- or human adipose tissue-derived mesenchymal stem cells (MSCs) (BM- or AT-MSCs) with human umbilical vein endothelial cells (HUVECs) both in vitro and in vivo at early time points (i.e. days 3 and 7). In vitro, cells were either monocultured (i.e. BM-MSCs, AT-MSCs or HUVECs) or cocultured (i.e. BM-MSCs/HUVECs and AT-MSCs/HUVECs) on Thermanox® (2-dimensional, 2D) or in collagen gels (3-dimensional, 3D). For the in vivo experiment, cells (cocultures) were embedded in collagen gels and implanted subcutaneously in nude mice. For both in vitro and in vivo experiments, samples were collected on days 3 and 7 and histologically processed for hematoxylin-eosin and platelet endothelial cell adhesion molecule (PECAM-1; CD31) staining. For in vivo samples, quantitative parameters for evaluating angiogenesis included CD31-positive staining percentage, total vessel-like structure (VLS) area percentage, VLS density, and average VLS area (i.e. the size of per VLS). In vitro results showed the formation of VLS in both cocultures, while none of the monocultures showed VLS formation, irrespective of 2D or 3D culture condition. Although VLS formation occurred after in vivo implantation, no significant difference in angiogenic capacity was observed between the two cocultures, either on day 3 or on day 7. Further, VLS density decreased and anastomosis of the new human vessels with the murine host vasculature occurred over time. In conclusion, this study demonstrated that AT-MSCs/HUVECs and BM-MSCs/HUVECs have equal angiogenic capacity both in vitro and in vivo, and that vessels from donor origin can anastomose with the host vasculature within seven days of implantation.

Comparison of Effects of Mechanical Stretching on Osteogenic Potential of ASCs and BMSCs

Mechanical forces play critical roles in the development and remodeling processes of bone. As an alternative cell source for bone engineering, adipose-derived stem cells (ASCs) should be fully investigated for their responses to mechanical stress. Similarly, the osteogenic potential, stimulated by mechanical stress, should be compared with bone marrow stromal cells (BMSCs), which have been clinically used for bone tissue engineering. In this study, ASCs and BMSCs were osteogenic-induced for 48 hours, and then subjected to uniaxial mechanical stretching for 2 or 6 hours. Cell orientation, osteogenic regulatory genes, osteogenic genes and ALP activities were measured and compared between ASCs and BMSCs. ASCs could align in a perpendicular way to the direction of stretching stress, while BMSCs did not present a specific alignment. Both 2 and 6 hours mechanical stretching could enhance the mRNA expression of Osx and Runx2 in BMSCs and ASCs, while OCN mRNA only increased in ASCs after 6 hours mechanical loading. Mechanical stretching enhanced the BMP-2 mRNA expression in ASCs, while only after 6 hours of mechanical loading significantly increased the BMP-2 gene expression in BMSCs. Significant differences only exist between ASCs and BMSCs loaded at 2 hours of mechanical stretching. It is concluded that ASCs are more rapid responders to mechanical stress, and have greater potential than BMSCs in osteogenesis when stimulated by mechanical stretching, indicating their usefulness for bone study in a rat model.

Role of pericytes in skeletal muscle regeneration and fat accumulation

Stem cells ensure tissue regeneration, while overgrowth of adipogenic cells may compromise organ recovery and impair function. In myopathies and muscle atrophy associated with aging, fat accumulation increases dysfunction, and after chronic injury, the process of fatty degeneration, in which muscle is replaced by white adipocytes, further compromises tissue function and environment. Some studies suggest that pericytes may contribute to muscle regeneration as well as fat formation. This work reports the presence of two pericyte subpopulations in the skeletal muscle and characterizes their specific roles. Skeletal muscle from Nestin-GFP/NG2-DsRed mice show two types of pericytes, Nestin-GFP-/NG2-DsRed+ (type-1) and Nestin-GFP+/NG2-DsRed+ (type-2), in close proximity to endothelial cells. We also found that both Nestin-GFP-/NG2-DsRed+ and Nestin-GFP+/NG2-DsRed+ cells colocalize with staining of two pericyte markers, PDGFRβ and CD146, but only type-1 pericyte express the adipogenic progenitor marker PDGFRα. Type-2 pericytes participate in muscle regeneration, while type-1 contribute to fat accumulation. Transplantation studies indicate that type-1 pericytes do not form muscle in vivo, but contribute to fat deposition in the skeletal muscle, while type-2 pericytes contribute only to the new muscle formation after injury, but not to the fat accumulation. Our results suggest that type-1 and type-2 pericytes contribute to successful muscle regeneration which results from a balance of myogenic and nonmyogenic cells activation.

Pericytes in the eye

Pericytes in the retina differ from pericytes in many other organs by their high density and their cooperative role in the neurovascular unit. Their diverse ontogeny and the fact that not one pericyte marker identifies the entire population suggest also functional plurality in the retina, including invading cells of mesenchymal origin. Further, to establish factors determining pericyte recruitment, modifiers of pericyte adhesion and homeostasis, such as notch-3 and angptl-4, have been recently identified, expanding the understanding of pericyte function in the retina. Also, the role of pericytes as part of the neurovascular unit has been appreciated, given that the neuroglia determines pericyte survival and motility under disease conditions. Pericyte dropout is not unique in the diabetic retina, and non-diabetic animal models may prove useful in the search for mechanisms involved in disease-associated dysfunction of the neurovascular unit.

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

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

Enhanced mobilization of the bone marrow-derived circulating progenitor cells by intracoronary freshly isolated bone marrow cells transplantation in patients with acute myocardial infarction

Autologous bone marrow cell transplantation (BMCs-Tx) is a promising novel option for treatment of cardiovascular disease. We analysed in a randomized controlled study the influence of the intracoronary autologous freshly isolated BMCs-Tx on the mobilization of bone marrow–derived circulating progenitor cells (BM-CPCs) in patients with acute myocardial infarction (AMI). Sixty-two patients with AMI were randomized to either freshly isolated BMCs-Tx or to a control group without cell therapy. Peripheral blood (PB) concentrations of CD34/45⁺- and CD133/45⁺-circulating progenitor cells were measured by flow cytometry in 42 AMI patients with cell therapy as well as in 20 AMI patients without cell therapy as a control group on days 1, 3, 5, 7, 8 and 3, 6 as well as 12 months after AMI. Global ejection fraction (EF) and the size of infarct area were determined by left ventriculography. We observed in patients with freshly isolated BMCs-Tx at 3 and 12 months follow up a significant reduction of infarct size and increase of global EF as well as infarct wall movement velocity. The mobilization of CD34/45⁺ and CD133/45⁺ BM-CPCs significantly increased with a peak on day 7 as compared to baseline after AMI in both groups (CD34/45⁺: P < 0.001, CD133/45⁺: P < 0.001). Moreover, this significant mobilization of BM-CPCs existed 3, 6 and 12 months after cell therapy compared to day 1 after AMI. In control group, there were no significant differences of CD34/45⁺ and CD133/45⁺ BM-CPCs mobilization between day 1 and 3, 6 and 12 months after AMI. Intracoronary transplantation of autologous freshly isolated BMCs by use of point of care system in patients with AMI may enhance and prolong the mobilization of CD34/45⁺ and CD133/45⁺ BM-CPCs in PB and this might increase the regenerative potency after AMI.

What's new in regenerative medicine: split up of the mesenchymal stem cell family promises new hope for cardiovascular repair

Coronary artery disease (CAD) is exceedingly prevalent and requires care optimization. Regenerative medicine holds promise to improve the clinical outcome of CAD patients. Current approach consists in subsidizing the infarcted heart with boluses of autologous stem cells from the bone marrow. Moreover, mesenchymal stem cells (MSCs) are in the focus of intense research owing to an apparent superiority in plasticity and regenerative capacity compared with hematopoietic stem cells. In this review, we report recent findings indicating the presence, within the heterogeneous MSC population, of perivascular stem cells expressing typical pericyte markers. Moreover, we focus on recent research showing the presence of similar cells in the adventitia of large vessels. These discoveries were fundamental to shape a roadmap toward clinical application in patients with myocardial ischemia. Adventitial stem cells are ideal candidates for promotion of cardiac repair owing to their ease of accessibility and expandability and potent vasculogenic activity.

Characterization of α-smooth muscle actin positive cells during multilineage differentiation of dental pulp stem cells

OBJECTIVES

Dental pulp tissue contains stem cells that can differentiate into multiple lineages under specific culture conditions; the origin of these dental pulp stem cells, however, is still unknown.

MATERIALS AND METHODS

Here we have utilized an α-SMA-GFP transgenic mouse model to characterize expression of a-smooth muscle actin (SMA)-GFP in subpassages of pulp-tissue-derived dental pulp cells, as perivascular cells express α-SMA.

RESULTS

During subculturing, percentages of cells expressing a-SMA increased significantly from passage 1 to 3. α-SMA-GFP-positive cells expanded faster than α-SMA-GFP-negative cells. The dental pulp cells at passage 3 were induced towards osteogenic, adipogenic or chondrogenic differentiation. All three differentiated cell lines expressed high levels of α-SMA (mineralized nodules, lipid droplets and chondrocyte pellets). GFP expression colocalized with differentiated osteoblasts, adipocytes and chondrocytes. Co-culturing the α-SMA-GFP-positive cells with human endothelial cells promoted formation of tube-like structures and robust vascular networks, in 3-D culture.

CONCLUSIONS

Taken together, the a-SMA-GFP-positive cells were shown to have multilieange differentiation ability and to promote vascularization in a co-culture system with endothelial cells.

Spontaneous fibroblast-derived pericyte recruitment in a human tissue-engineered angiogenesis model in vitro

Cooperation between endothelial cells and pericytes is essential to the stabilization and maturation of blood microvessels. We developed a unique in vitro tissue-engineered model to study angiogenesis. The human endothelialized reconstructed connective tissue model promotes the formation of a three-dimensional branching network of capillary-like tubes (CLT) with closed lumens. The purpose of this work was to investigate whether pericytes were spontaneously recruited around CLT in the model. We demonstrated that smooth muscle α-actin (SMA)-positive cells were found closely associated with PECAM-1-positive capillaries in the model. Twelve percent (±2.6) of SMA-positive cells were detected along with 15% (±1.64) von Willebrand factor-positive endothelial cells in the culture system after 31 days of in vitro maturation. Conversely, no SMA-positive cells were detected in reconstructed connective tissues made solely of fibroblasts. Knowing that PDGF is a major factor in the recruitment of pericytes, we showed that blockade of the PDGFB receptor using the inhibitor AG1296 induced an overall 5, 2.6, and 2.4-fold decrease in the SMA-positive cells, von Willebrand factor-positive cells, and number of capillaries, respectively. Using combinations of human GFP-positive fibroblasts and endothelial cells, we demonstrated that pericytes were recruited from the fibroblast population in the model. In conclusion, our tissue-engineered culture system promotes the spontaneous formation of a network of capillaries and the recruitment of pericytes derived from fibroblasts. Since pericytes are essential components of the blood microvasculature, this culture system is a powerful model to study angiogenesis and endothelial cell/pericyte interactions in vitro.

Pericyte TIMP3 and ADAMTS1 modulate vascular stability after kidney injury

Kidney pericytes are progenitors of scar-forming interstitial myofibroblasts that appear after injury. The function of kidney pericytes as microvascular cells and how these cells detach from peritubular capillaries and migrate to the interstitial space, however, are poorly understood. Here, we used an unbiased approach to identify genes in kidney pericytes relevant to detachment and differentiation in response to injury in vivo, with a particular focus on genes regulating proteolytic activity and angiogenesis. Kidney pericytes rapidly activated expression of a disintegrin and metalloprotease with thrombospondin motifs-1 (ADAMTS1) and downregulated its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3) in response to injury. Similarly to brain pericytes, kidney pericytes bound to and stabilized capillary tube networks in three-dimensional gels and inhibited metalloproteolytic activity and angiogenic signaling in endothelial cells. In contrast, myofibroblasts did not have these vascular stabilizing functions despite their derivation from kidney pericytes. Pericyte-derived TIMP3 stabilized and ADAMTS1 destabilized the capillary tubular networks. Furthermore, mice deficient in Timp3 had a spontaneous microvascular phenotype in the kidney resulting from overactivated pericytes and were more susceptible to injury-stimulated microvascular rarefaction with an exuberant fibrotic response. Taken together, these data support functions for kidney pericytes in microvascular stability, highlight central roles for regulators of extracellular proteolytic activity in capillary homoeostasis, and identify ADAMTS1 as a marker of activation of kidney pericytes.

Perivascular human endometrial mesenchymal stem cells express pathways relevant to self-renewal, lineage specification, and functional phenotype

Human endometrium regenerates on a cyclic basis from candidate stem/progenitors whose genetic programs are yet to be determined. A subpopulation of endometrial stromal cells, displaying key properties of mesenchymal stem cells (MSCs), has been characterized. The endometrial MSC (eMSC) is likely the precursor of the endometrial stromal fibroblast. The goal of this study was to determine the transcriptome and signaling pathways in the eMSC to understand its functional phenotype. Endometrial stromal cells from oocyte donors (n = 20) and patients undergoing benign gynecologic surgery (n = 7) were fluorescence-activated cell sorted into MCAM (CD146)(+)/PDGFRB(+) (eMSC), MCAM (CD146)(-)/PDGFRB(+) (fibroblast), and MCAM (CD146)(+)/PDGFRB(-) (endothelial) populations. The eMSC population contained clonogenic cells with a mesenchymal phenotype differentiating into adipocytes when cultured in adipogenic medium. Gene expression profiling using Affymetrix Human Gene 1.0 ST arrays revealed 762 and 1518 significantly differentially expressed genes in eMSCs vs. stromal fibroblasts and eMSCs vs. endothelial cells, respectively. By principal component and hierarchical clustering analyses, eMSCs clustered with fibroblasts and distinctly from endothelial cells. Endometrial MSCs expressed pericyte markers and were localized by immunofluorescence to the perivascular space of endometrial small vessels. Endometrial MSCs also expressed genes involved in angiogenesis/vasculogenesis, steroid hormone/hypoxia responses, inflammation, immunomodulation, cell communication, and proteolysis/inhibition, and exhibited increased Notch, TGFB, IGF, Hedgehog, and G-protein-coupled receptor signaling pathways, characteristic of adult tissue MSC self-renewal and multipotency. Overall, the data support the eMSC as a clonogenic, multipotent pericyte that displays pathways of self-renewal and lineage specification, the potential to respond to conditions during endometrial desquamation and regeneration, and a genetic program predictive of its differentiated lineage, the stromal fibroblast.

Mesenchymal stem cells and cardiovascular disease: a bench to bedside roadmap

In recent years, the incredible boost in stem cell research has kindled the expectations of both patients and physicians. Mesenchymal progenitors, owing to their availability, ease of manipulation, and therapeutic potential, have become one of the most attractive options for the treatment of a wide range of diseases, from cartilage defects to cardiac disorders. Moreover, their immunomodulatory capacity has opened up their allogenic use, consequently broadening the possibilities for their application. In this review, we will focus on their use in the therapy of myocardial infarction, looking at their characteristics, in vitro and in vivo mechanisms of action, as well as clinical trials.

Improved functional activity of bone marrow derived circulating progenitor cells after intra coronary freshly isolated bone marrow cells transplantation in patients with ischemic heart disease

Objectives

There is growing evidence that intracoronary autologous bone marrow cells transplantation (BMCs-Tx) in patients with chronic myocardial infarction beneficially affects postinfarction remodelling. In this randomized controlled study we analyzed the influence of intracoronary autologous freshly isolated bone marrow cells transplantation by use of point of care system on cardiac function and on the functional activity of bone marrow derived circulating progenitor cells (BM-CPCs) in patients with ischemic heart disease (IHD).

Methods

56 patients with IHD were randomized to either received freshly isolated BMC-Tx or a control group that did not receive cell therapy. The functional activity of BM-CPCs in peripheral blood (PB) was measured by migration assay and colony forming unit assay pre- and 3, 6 as well as 12 months after procedure. Global ejection fraction (EF) and infarct size area were determined by left ventriculography.

Results

Intracoronary transplantation of autologous freshly isolated BMCs led to a significant reduction of infarct size and an increase of global EF as well as infarct wall movement velocity after 3 and 12 months follow-up compared to control group. The colony-forming capacity of BM-CPCs significantly increased 3, 6 and 12 months after cell therapy compared to pre BMCs-Tx and control group (CFU-E: p < 0.001, CFU-GM: p < 0.001). Likewise, we found significant increase of migratory response to stromal cell-derived factor 1 (SDF-1) and vascular endothelial growth factor (VEGF) after cell therapy compared to pre BMCs-Tx (SDF-1: p < 0.001, VEGF: p < 0.001) and to control (SDF-1: p < 0.001, VEGF: p < 0.001). There was no significant difference of migratory- and colony forming capacity between pre- and 3, 6, 12 months after coronary angiography in control group without cell therapy.

Conclusions

Intracoronary transplantation of autologous freshly isolated BMCs by use of point of care system may lead to improvement of BM-CPCs functional activity in peripheral blood, which might increase the regenerative potency in patients with IHD.

Pivotal role of pericytes in kidney fibrosis

1. Kidney pericytes were recently identified as collagen Iα1-producing cells in healthy kidney, but the developmental, physiological and pathological roles of kidney pericytes remain poorly understood. Pericytes are stromal-derived cells that envelop and have intimate connections with adjacent capillary endothelial cells (EC). Recent studies in the eye and brain have revealed that pericytes are crucial for angiogenesis, vascular stability and vessel integrity. 2. In response to kidney injury, pericytes promptly migrate away from the capillary wall into the interstitial space. Here, pericytes are activated and differentiate into scar-forming myofibroblasts. In the absence of pericytes, peritubular capillaries are destabilized, leading to vascular regression. Consequently, capillary loss and fibrosis following kidney injury are intimately linked and hinge centrally around pericyte detachment from EC. 3. Kinetic mathematical modelling has demonstrated that pericytes are the major source of myofibroblasts in the fibrotic kidney. Comprehensive genetic fate mapping studies of nephron epithelia or kidney stroma has demonstrated that epithelial cells do not migrate outside of the epithelial compartment to become myofibroblasts; rather, interstitial pericytes are progenitors of scar-forming myofibroblasts. Bidirectional signalling between pericytes and EC is necessary for pericyte detachment from peritubular capillaries. 4. In the present review, we summarize the pathologically vital roles of kidney pericytes in fibrosis, including our new findings. The study of kidney pericytes and endothelial-pericyte cross-talk will identify novel therapeutic targets for currently incurable chronic kidney diseases.

The Nell-1 growth factor stimulates bone formation by purified human perivascular cells

The search for novel sources of stem cells other than bone marrow mesenchymal stem cells (MSCs) for bone regeneration and repair has been a critical endeavor. We previously established an effective protocol to homogeneously purify human pericytes from multiple fetal and adult tissues, including adipose, bone marrow, skeletal muscle, and pancreas, and identified pericytes as a primitive origin of human MSCs. In the present study, we further characterized the osteogenic potential of purified human pericytes combined with a novel osteoinductive growth factor, Nell-1. Purified pericytes grown on either standard culture ware or human cancellous bone chip (hCBC) scaffolds exhibited robust osteogenic differentiation in vitro. Using a nude mouse muscle pouch model, pericytes formed significant new bone in vivo as compared to scaffold alone (hCBC). Moreover, Nell-1 significantly increased pericyte osteogenic differentiation, both in vitro and in vivo. Interestingly, Nell-1 significantly induced pericyte proliferation and was observed to have pro-angiogenic effects, both in vitro and in vivo. These studies suggest that pericytes are a potential new cell source for future efforts in skeletal regenerative medicine, and that Nell-1 is a candidate growth factor able to induce pericyte osteogenic differentiation.

The stem cell niche should be a key issue for cell therapy in regenerative medicine

Recent advances in stem cell research have highlighted the role played by such cells and their environment (the stem cell niche) in tissue renewal and homeostasis. The control and regulation of stem cells and their niche are remaining challenges for cell therapy and regenerative medicine on several tissues and organs. These advances are important for both, the basic knowledge of stem cell regulation, and their practical translational applications into clinical medicine. This article is primarily concerned with the mesenchymal stem cells (MSCs) and it reviews the current aspects of their own niche. We discuss on the need for a deeper understanding of the identity of this cell type and its microenvironment in order to improve the effectiveness of any cell therapy for regenerative medicine. Ex vivo reproduction of the conditions of the natural stem cell niche, when necessary, would provide success to tissue engineering. The first challenge of regenerative medicine is to find cells able to replace and/or repair the lost function of tissues and organs by disease or aging and the trophic and immunomodulatory effects recently found for MSCs open up for new opportunities. If MSCs are pericytes, as it has been proposed, perhaps it may explain the ubiquity of these cells and their possible role in miscellaneous repairs throughout the body opening for new chances for extensive tissue repair.

Adipose stem cells originate from perivascular cells

Recent research has shown that adipose tissues contain abundant MSCs (mesenchymal stem cells). The origin and location of the adipose stem cells, however, remain unknown, presenting an obstacle to the further purification and study of these cells. In the present study, we aimed at investigating the origins of adipose stem cells. α-SMA (α-smooth muscle actin) is one of the markers of pericytes. We harvested ASCs (adipose stromal cells) from α-SMA-GFP (green fluorescent protein) transgenic mice and sorted them into GFP-positive and GFP-negative cells by FACS. Multilineage differentiation tests were applied to examine the pluripotent ability of the α-SMA-GFP-positive and -negative cells. Immunofluorescent staining for α-SMA and PDGF-Rβ (platelet-derived growth factor receptor β) were applied to identify the α-SMA-GFP-positive cells. Then α-SMA-GFP-positive cells were loaded on a collagen-fibronectin gel with endothelial cells to test their vascularization ability both in vitro and in vivo. Results show that, in adipose tissue, all of the α-SMA-GFP-positive cells congregate around the blood vessels. Only the α-SMA-GFP-positive cells have multilineage differentiation ability, while the α-SMA-GFP-negative cells can only differentiate in an adipogenic direction. The α-SMA-GFP-positive cells maintained expression of α-SMA during multilineage differentiation. The α-SMA-GFP-positive cells can promote the vascularization of endothelial cells in three-dimensional culture both in vitro and in vivo. We conclude that the adipose stem cells originate from perivascular cells and congregate around blood vessels.

Immortalized CNS pericytes are quiescent smooth muscle actin-negative and pluripotent

Despite their identification more than 100 years ago by the French scientist Charles-Marie Benjamin Rouget, microvascular pericytes have proven difficult to functionally characterize, due in part to their relatively low numbers and the lack of specific cell markers. However, recent progress is beginning to shed light on the diverse biological functions of these cells. Pericytes are thought to be involved in regulating vascular homeostasis and hemostasis as well as serving as a local source of adult stem cells. To further define the properties of these intriguing cells, we have isolated pericytes from transgenic mice (Immortomouse®) harboring a temperature-sensitive mutant of the SV40 virus target T-gene. This Immortopericyte (IMP) conditional cell line is stable for long periods of time and, at 33°C in the presence of interferon gamma, does not differentiate. Under these conditions IMPs are alpha muscle actin-negative and exhibit a pluripotent phenotype, but can be induced to differentiate along both mesenchymal and neuronal lineages at 37°C. Alternatively, differentiation of wild type pericytes and IMPs can be induced directly from capillaries in culture. Finally, the addition of endothelial cells to purified IMP cultures augments their rate of self-renewal and differentiation, possibly in a cell-to-cell contact dependent manner.

Diabetes impairs arteriogenesis in the peripheral circulation: review of molecular mechanisms

Patients suffering from both diabetes and PAD (peripheral arterial disease) are at risk of developing critical limb ischaemia and ulceration, and potentially requiring limb amputation. In addition, diabetes complicates surgical treatment of PAD and impairs arteriogenesis. Arteriogenesis is defined as the remodelling of pre-existing arterioles into conductance vessels to restore the perfusion distal to the occluded artery. Several strategies to promote arteriogenesis in the peripheral circulation have been devised, but the mechanisms through which diabetes impairs arteriogenesis are poorly understood. The present review provides an overview of the current literature on the deteriorating effects of diabetes on the key players in the arteriogenesis process. Diabetes affects arteriogenesis at a number of levels. First, it elevates vasomotor tone and attenuates sensing of shear stress and the response to vasodilatory stimuli, reducing the recruitment and dilatation of collateral arteries. Secondly, diabetes impairs the downstream signalling of monocytes, without decreasing monocyte attraction. In addition, EPC (endothelial progenitor cell) function is attenuated in diabetes. There is ample evidence that growth factor signalling is impaired in diabetic arteriogenesis. Although these defects could be restored in animal experiments, clinical results have been disappointing. Furthermore, the diabetes-induced impairment of eNOS (endothelial NO synthase) strongly affects outward remodelling, as NO signalling plays a key role in several remodelling processes. Finally, in the structural phase of arteriogenesis, diabetes impairs matrix turnover, smooth muscle cell proliferation and fibroblast migration. The review concludes with suggestions for new and more sophisticated therapeutic approaches for the diabetic population.

Human embryonic stem cell-derived vascular progenitor cells capable of endothelial and smooth muscle cell function

OBJECTIVE

Previous studies have demonstrated development of endothelial cells (ECs) and smooth muscle cells (SMCs) as separate cell lineages derived from human embryonic stem cells (hESCs). We demonstrate CD34(+) cells isolated from differentiated hESCs function as vascular progenitor cells capable of producing both ECs and SMCs. These studies better define the developmental origin and reveal the relationship between these two cell types, as well as provide a more complete biological characterization.

MATERIALS AND METHODS

hESCs are cocultured on M2-10B4 stromal cells or Wnt1-expressing M2-10B4 for 13 to 15 days to generate a CD34(+) cell population. These cells are isolated using a magnetic antibody separation kit and cultured on fibronectin-coated dishes in EC medium. To induce SMC differentiation, culture medium is changed and a morphological and phenotypic change occurs within 24 to 48 hours.

RESULTS

CD34(+) vascular progenitor cells give rise to ECs and SMCs. The two populations express respective cell-specific transcripts and proteins, exhibit intracellular calcium in response to various agonists, and form robust tube-like structures when cocultured in Matrigel. Human umbilical vein endothelial cells cultured under SMC conditions do not exhibit a change in phenotype or genotype. Wnt1-overexpressing stromal cells produced an increased number of progenitor cells.

CONCLUSIONS

The ability to generate large numbers of ECs and SMCs from a single vascular progenitor cell population is promising for therapeutic use to treat a variety of diseased and ischemic conditions. The stepwise differentiation outlined here is an efficient, reproducible method with potential for large-scale cultures suitable for clinical applications.