c-Kit+ progenitors generate vascular cells for tissue-engineered grafts through modulation of the Wnt/Klf4 pathway

Keratose Hydrogel Drives Differentiation of Cardiac Vascular Smooth Muscle Progenitor Cells: Implications in Ischemic Treatment

Peripheral artery disease (PAD) is a common vascular disorder in the extremity of limbs with limited clinical treatments. Stem cells hold great promise for the treatment of PAD, but their therapeutic efficiency is limited due to multiple factors, such as poor engraftment and non-optimal selection of cell type. To date, stem cells from a variety of tissue sources have been tested, but little information is available regarding vascular smooth muscle cells (VSMCs) for PAD therapy. The present study examines the effects of keratose (KOS) hydrogels on c-kit+/CD31- cardiac vascular smooth muscle progenitor cell (cVSMPC) differentiation and the therapeutic potential of the resultant VSMCs in a mouse hindlimb ischemic model of PAD. The results demonstrated that KOS but not collagen hydrogel was able to drive the majority of cVSMPCs into functional VSMCs in a defined Knockout serum replacement (SR) medium in the absence of differentiation inducers. This effect could be inhibited by TGF-β1 antagonists. Further, KOS hydrogel increased expression of TGF-β1-associated proteins and modulated the level of free TGF-β1 during differentiation. Finally, transplantation of KOS-driven VSMCs significantly increased blood flow and vascular densities of ischemic hindlimbs. These findings indicate that TGF-β1 signaling is involved in KOS hydrogel-preferred VSMC differentiation and that enhanced blood flow are likely resulted from angiogenesis and/or arteriogenesis induced by transplanted VSMCs.

Treatment with imatinib was useful to delay the neointimal hyperplasia of aortocaval fistula in adenine-induced renal failure rats

PURPOSE

The study was conducted to investigate the effect of the treatment with imatinib, a c-kit specific inhibitor, on the neointimal hyperplasia (NIH) of aortocaval fistula (ACF) in adenine-induced renal failure rats.

MATERIALS AND METHODS

All rats were randomly assigned to 4 groups: rats were fed on a normal diet (normal group); rats were fed on a 0.75% adenine-rich diet (renal failure group). The remaining rats underwent ACF after receiving a 0.75% adenine-rich diet and received daily saline gavage (model group) or imatinib gavage (imatinib group) for 7 days after surgery. Immunohistochemical method was used to detect c-kit expression, and Elastomeric Verhoeff-Van Gieson (EVG) staining was used to observe morphological changes of the ACF. The Pearson correlation analysis was used to evaluate the correlations of c-kit expression with intimal thickness and the percentage of stenosis, respectively.

RESULTS

The renal failure group showed positive c-kit expression on the intima of the inferior vena cava (IVC), whereas the normal group did not. Compared to the model group, intimal thickness (P = 0.001), the percentage of stenosis (P = 0.006) and c-kit expression (P = 0.04) were decreased in the imatinib group at 8 weeks postoperatively. C-kit expression was positively correlated with both intimal thickness and percentage of stenosis (intimal thickness: R = 0.650, P = 0.003; the percentage of stenosis: R = 0.581, P = 0.011) in both the model and imatinib groups.

CONCLUSION

Treatment with imatinib, a c-kit specific inhibitor, was useful to delay the NIH of ACF in adenine-induced renal failure rats.

Krüppel-like factors in tumors: Key regulators and therapeutic avenues

Krüppel-like factors (KLFs) are a group of DNA-binding transcriptional regulators with multiple essential functions in various cellular processes, including proliferation, migration, inflammation, and angiogenesis. The aberrant expression of KLFs is often found in tumor tissues and is essential for tumor development. At the molecular level, KLFs regulate multiple signaling pathways and mediate crosstalk among them. Some KLFs may also be molecular switches for specific biological signals, driving their transition from tumor suppressors to promoters. At the histological level, the abnormal expression of KLFs is closely associated with tumor cell stemness, proliferation, apoptosis, and alterations in the tumor microenvironment. Notably, the role of each KLF in tumors varies according to tumor type and different stages of tumor development rather than being invariant. In this review, we focus on the advances in the molecular biology of KLFs, particularly the regulations of several classical signaling pathways by these factors, and the critical role of KLFs in tumor development. We also highlight their strong potential as molecular targets in tumor therapy and suggest potential directions for clinical translational research.

Correlation between stem cell molecular phenotype and atherosclerotic plaque neointima formation and analysis of stem cell signal pathways

Vascular stem cells exist in the three-layer structure of blood vessel walls and play an indispensable role in angiogenesis under physiological conditions and vascular remodeling under pathological conditions. Vascular stem cells are mostly quiescent, but can be activated in response to injury and participate in endothelial repair and neointima formation. Extensive studies have demonstrated the differentiation potential of stem/progenitor cells to repair endothelium and participate in neointima formation during vascular remodeling. The stem cell population has markers on the surface of the cells that can be used to identify this cell population. The main positive markers include Stem cell antigen-1 (Sca1), Sry-box transcription factor 10 (SOX10). Stromal cell antigen 1 (Stro-1) and Stem cell growth factor receptor kit (c-kit) are still controversial. Different parts of the vessel have different stem cell populations and multiple markers. In this review, we trace the role of vascular stem/progenitor cells in the progression of atherosclerosis and neointima formation, focusing on the expression of stem cell molecular markers that occur during neointima formation and vascular repair, as well as the molecular phenotypic changes that occur during differentiation of different stem cell types. To explore the correlation between stem cell molecular markers and atherosclerotic diseases and neointima formation, summarize the differential changes of molecular phenotype during the differentiation of stem cells into smooth muscle cells and endothelial cells, and further analyze the signaling pathways and molecular mechanisms of stem cells expressing different positive markers participating in intima formation and vascular repair. Summarizing the limitations of stem cells in the prevention and treatment of atherosclerotic diseases and the pressing issues that need to be addressed, we provide a feasible scheme for studying the signaling pathways of vascular stem cells involved in vascular diseases.

Endothelial repair by stem and progenitor cells

The integrity of the endothelial barrier is required to maintain vascular homeostasis and fluid balance between the circulatory system and surrounding tissues and to prevent the development of vascular disease. However, the origin of the newly developed endothelial cells is still controversial. Stem and progenitor cells have the potential to differentiate into endothelial cell lines and stimulate vascular regeneration in a paracrine/autocrine fashion. The one source of new endothelial cells was believed to come from the bone marrow, which was challenged by the recent findings. By administration of new techniques, including genetic cell lineage tracing and single cell RNA sequencing, more solid data were obtained that support the concept of stem/progenitor cells for regenerating damaged endothelium. Specifically, it was found that tissue resident endothelial progenitors located in the vessel wall were crucial for endothelial repair. In this review, we summarized the latest advances in stem and progenitor cell research in endothelial regeneration through findings from animal models and discussed clinical data to indicate the future direction of stem cell therapy.

Progenitor/Stem Cells in Vascular Remodeling during Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by an important occlusive vascular remodeling with the production of new endothelial cells, smooth muscle cells, myofibroblasts, and fibroblasts. Identifying the cellular processes leading to vascular proliferation and dysfunction is a major goal in order to decipher the mechanisms leading to PAH development. In addition to in situ proliferation of vascular cells, studies from the past 20 years have unveiled the role of circulating and resident vascular in pulmonary vascular remodeling. This review aims at summarizing the current knowledge on the different progenitor and stem cells that have been shown to participate in pulmonary vascular lesions and on the pathways regulating their recruitment during PAH. Finally, this review also addresses the therapeutic potential of circulating endothelial progenitor cells and mesenchymal stem cells.

Cellular remodeling of fibrotic conduit as vascular graft

The replacement of small-diameter arteries remains an unmet clinical need. Here we investigated the cellular remodeling of fibrotic conduits as vascular grafts. The formation of fibrotic conduit around subcutaneously implanted mandrels involved not only fibroblasts but also the trans-differentiation of inflammatory cells such as macrophages into fibroblastic cells, as shown by genetic lineage tracing. When fibrotic conduits were implanted as vascular grafts, the patency was low, and many fibrotic cells were found in neointima. Decellularization and anti-thrombogenic coating of fibrotic conduits produced highly patent autografts that remodeled into neoarteries, offering an effective approach to obtain autografts for clinical therapy. While autografts recruited mostly anti-inflammatory macrophages for constructive remodeling, allogenic DFCs had more T cells and pro-inflammatory macrophages and lower patency. Endothelial progenitors and endothelial migration were observed during endothelialization. Cell infiltration into DFCs was more efficient than decellularized arteries, and infiltrated cells remodeled the matrix and differentiated into smooth muscle cells (SMCs). This work provides insight into the remodeling of fibrotic conduits, autologous DFCs and allogenic DFCs, and will have broad impact on using fibrotic matrix for regenerative engineering.

Human Peripheral Blood-Derived Endothelial Colony-Forming Cells Are Highly Similar to Mature Vascular Endothelial Cells yet Demonstrate a Transitional Transcriptomic Signature

Endothelial colony-forming cells (ECFC) are currently considered as a promising cell population for the pre-endothelialization or pre-vascularization of tissue-engineered constructs, including small-diameter biodegradable vascular grafts. However, the extent of heterogeneity between ECFC and mature vascular endothelial cells (EC) is unclear. Here, we performed a transcriptome-wide study to compare gene expression profiles of ECFC, human coronary artery endothelial cells (HCAEC), and human umbilical vein endothelial cells (HUVEC). Characterization of the abovementioned cell populations was carried out by immunophenotyping, tube formation assay, and evaluation of proliferation capability while global gene expression profiling was conducted by means of RNA-seq. ECFC were similar to HUVEC in terms of immunophenotype (CD31⁺vWF⁺KDR⁺CD146⁺CD34^-CD133^-CD45^-CD90^-) and tube formation activity yet had expectedly higher proliferative potential. HCAEC and HUVEC were generally similar to ECFC with regards to their global gene expression profile; nevertheless, ECFC overexpressed specific markers of all endothelial lineages (NRP2, NOTCH4, LYVE1), in particular lymphatic EC (LYVE1), and had upregulated extracellular matrix and basement membrane genes (COL1A1, COL1A2, COL4A1, COL4A2). Proteomic profiling for endothelial lineage markers and angiogenic molecules generally confirmed RNA-seq results, indicating ECFC as an intermediate population between HCAEC and HUVEC. Therefore, gene expression profile and behavior of ECFC suggest their potential to be applied for a pre-endothelialization of bioartificial vascular grafts, whereas in terms of endothelial hierarchy they differ from HCAEC and HUVEC, having a transitional phenotype.

Vascular Wall as Source of Stem Cells Able to Differentiate into Endothelial Cells

The traditional view of the vascular biology is changed by the discovery of vascular progenitor cells in bone marrow or peripheral blood Further complexity is due to the findings that the vessel walls harbor progenitor and stem cells, called vascular wall-resident vascular stem cells (VW-VSCs), able to differentiate to mature vascular wall cells. These immature stem/progenitor cell populations and multipotent mesenchymal lineage participate in postnatal neovascularization and vascular wall remodeling. Further studies are necessary to deepen the knowledge on characterization and biology of VW-VSCs, in particular of endothelial progenitor cells (EPCs) in order to improve their use in clinical settings for regenerative approaches.

Vascular progenitor cell senescence in patients with Marfan syndrome

Vascular progenitor cells (VPCs) present in the adventitia of the vessel wall play a critical role in the regulation of vascular repair following injury. This study aimed to assess the function of VPCs isolated from patients with Marfan syndrome (MFS). VPCs were isolated from control and MFS donors and characterized. Compared with control‐VPCs, MFS‐VPCs exhibited cellular senescence as demonstrated by increased cell size, higher SA‐β‐gal activity and elevated levels of p53 and p21. RNA sequencing showed that several cellular process‐related pathways including cell cycle and cellular senescence were significantly enriched in MFP‐VPCs. Notably, the expression level of TGF‐β1 was much higher in MFS‐VPCs than control‐VPCs. Treatment of control‐VPCs with TGF‐β1 significantly enhanced mitochondrial reactive oxidative species (ROS) and induced cellular senescence whereas inhibition of ROS reversed these effects. MFS‐VPCs displayed increased mitochondrial fusion and decreased mitochondrial fission. Treatment of control‐VPCs with TGF‐β1 increased mitochondrial fusion and reduced mitochondrial fission. Nonetheless, treatment of mitofusin2 (Mfn2)‐siRNA inhibited TGF‐β1‐induced mitochondrial fusion and cellular senescence. Furthermore, TGF‐β1‐induced mitochondrial fusion was mediated by the AMPK signalling pathway. Our study shows that TGF‐β1 induces VPC senescence in patients with MFS by mediating mitochondrial dynamics via the AMPK signalling pathway.

Histone Deacetylase 7-Derived Peptides Play a Vital Role in Vascular Repair and Regeneration

Cardiovascular disease is a leading cause of morbidity and mortality globally. Accumulating evidence indicates that local resident stem/progenitor cells play an important role in vascular regeneration. Recently, it is demonstrated that a histone deacetylase 7-derived 7-amino acid peptide (7A, MHSPGAD) is critical in modulating the mobilization and orientated differentiation of these stem/progenitor cells. Here, its therapeutic efficacy in vascular repair and regeneration is evaluated. In vitro functional analyses reveal that the 7A peptide, in particular phosphorylated 7A (7Ap, MH[pSer]PGAD), could increase stem cell antigen-1 positive (Sca1+) vascular progenitor cell (VPC) migration and differentiation toward an endothelial cell lineage. Furthermore, local delivery of 7A as well as 7Ap could enhance angiogenesis and ameliorate vascular injury in ischaemic tissues; these findings are confirmed in a femoral artery injury model and a hindlimb ischaemia model, respectively. Importantly, sustained delivery of 7A, especially 7Ap, from tissue-engineered vascular grafts could attract Sca1+-VPC cells into the grafts, contributing to endothelialization and intima/media formation in the vascular graft. These results suggest that this novel type of peptides has great translational potential in vascular regenerative medicine.

Genetic lineage tracing analysis of c-kit+ stem/progenitor cells revealed a contribution to vascular injury-induced neointimal lesions

AIMS

Accumulating evidence indicates the presence of vascular stem/progenitor cells that may play a role in endothelial repair and lesion formation in the injured artery, in which c-kit⁺ stem/progenitor cells have been reported to differentiate into endothelial and smooth muscle cells in vitro and in ischemic tissue. In this study, we investigated whether and how endogenous c-kit⁺ stem/progenitor cells contribute to vascular injury and neointima formation in vivo.

METHODS AND RESULTS

We created Kit-CreERxRosa26-RFP mice and performed genetic lineage tracing analysis of c-kit⁺ stem/progenitor cells in injury-induced neointima formation in vivo. We provide direct evidence that endogenous c-kit⁺ stem/progenitor cells minimally differentiate into endothelial or smooth muscle cells facilitating vascular repair, but predominantly generate monocytes/macrophages and granulocytes contributing to vascular immuno-inflammatory response to endothelial injury. Although c-kit⁺ cells reside in both bone marrow and vessel wall, bone marrow transplantation data indicate that bone marrow-derived c-kit⁺ cells are the main source for enhancing neointima formation. Furthermore, treatment of ACK2, a c-kit receptor antagonizer, attenuates neointimal hyperplasia after injury at least in part by depleting c-kit⁺ cells and their generated progeny.

CONCLUSIONS

c-kit⁺ stem/progenitor cells are not a main source for endothelial regeneration and smooth muscle accumulation of the large artery injury, but a plausible interventional approach to reduce vascular immuno-inflammatory response and subsequently to ameliorate vascular lesions.

Follistatin-Like 3 Enhances the Function of Endothelial Cells Derived from Pluripotent Stem Cells by Facilitating β-Catenin Nuclear Translocation Through Inhibition of Glycogen Synthase Kinase-3β Activity

The fight against vascular disease requires functional endothelial cells (ECs) which could be provided by differentiation of induced Pluripotent Stem Cells (iPS Cells) in great numbers for use in the clinic. However, the great promise of the generated ECs (iPS-ECs) in therapy is often restricted due to the challenge in iPS-ECs preserving their phenotype and function. We identified that Follistatin-Like 3 (FSTL3) is highly expressed in iPS-ECs, and, as such, we sought to clarify its possible role in retaining and improving iPS-ECs function and phenotype, which are crucial in increasing the cells' potential as a therapeutic tool. We overexpressed FSTL3 in iPS-ECs and found that FSTL3 could induce and enhance endothelial features by facilitating β-catenin nuclear translocation through inhibition of glycogen synthase kinase-3β activity and induction of Endothelin-1. The angiogenic potential of FSTL3 was also confirmed both in vitro and in vivo. When iPS-ECs overexpressing FSTL3 were subcutaneously injected in in vivo angiogenic model or intramuscularly injected in a hind limb ischemia NOD.CB17-Prkdcscid/NcrCrl SCID mice model, FSTL3 significantly induced angiogenesis and blood flow recovery, respectively. This study, for the first time, demonstrates that FSTL3 can greatly enhance the function and maturity of iPS-ECs. It advances our understanding of iPS-ECs and identifies a novel pathway that can be applied in cell therapy. These findings could therefore help improve efficiency and generation of therapeutically relevant numbers of ECs for use in patient-specific cell-based therapies. In addition, it can be particularly useful toward the treatment of vascular diseases instigated by EC dysfunction. Stem Cells 2018;36:1033-1044.

Role of Resident Stem Cells in Vessel Formation and Arteriosclerosis

Vascular, resident stem cells are present in all 3 layers of the vessel wall; they play a role in vascular formation under physiological conditions and in remodeling in pathological situations. Throughout development and adult early life, resident stem cells participate in vessel formation through vasculogenesis and angiogenesis. In adults, the vascular stem cells are mostly quiescent in their niches but can be activated in response to injury and participate in endothelial repair and smooth muscle cell accumulation to form neointima. However, delineation of the characteristics and of the migration and differentiation behaviors of these stem cells is an area of ongoing investigation. A set of genetic mouse models for cell lineage tracing has been developed to specifically address the nature of these cells and both migration and differentiation processes during physiological angiogenesis and in vascular diseases. This review summarizes the current knowledge on resident stem cells, which has become more defined and refined in vascular biology research, thus contributing to the development of new potential therapeutic strategies to promote endothelial regeneration and ameliorate vascular disease development.

Smooth muscle cells differentiated from mesenchymal stem cells are regulated by microRNAs and suitable for vascular tissue grafts

Tissue-engineered vascular grafts with long-term patency are greatly needed in the clinical settings, and smooth muscle cells (SMCs) are a critical graft component. Human mesenchymal stem cells (MSCs) are used for generating SMCs, and understanding the underlying regulatory mechanisms of the MSC-to-SMC differentiation process could improve SMC generation in the clinic. Here, we found that in response to stimulation of transforming growth factor-β1 (TGFβ1), human umbilical cord-derived MSCs abundantly express the SMC markers α-smooth muscle actin (αSMA), smooth muscle protein 22 (SM22), calponin, and smooth muscle myosin heavy chain (SMMHC) at both gene and protein levels. Functionally, MSC-derived SMCs displayed contracting capacity in vitro and supported vascular structure formation in the Matrigel plug assay in vivo More importantly, SMCs differentiated from human MSCs could migrate into decellularized mouse aorta and give rise to the smooth muscle layer of vascular grafts, indicating the potential of utilizing human MSC-derived SMCs to generate vascular grafts. Of note, microRNA (miR) array analysis and TaqMan microRNA assays identified miR-503 and miR-222-5p as potential regulators of MSC differentiation into SMCs at early time points. Mechanistically, miR-503 promoted SMC differentiation by directly targeting SMAD7, a suppressor of SMAD-related, TGFβ1-mediated signaling pathways. Moreover, miR-503 expression was SMAD4-dependent. SMAD4 was enriched at the miR-503 promoter. Furthermore, miR-222-5p inhibited SMC differentiation by targeting and down-regulating ROCK2 and αSMA. In conclusion, MSC differentiation into SMCs is regulated by miR-503 and miR-222-5p and yields functional SMCs for use in vascular grafts.

Vascular stem/progenitor cells: functions and signaling pathways

Vascular stem/progenitor cells (VSCs) are an important source of all types of vascular cells needed to build, maintain, repair, and remodel blood vessels. VSCs, therefore, play critical roles in the development, normal physiology, and pathophysiology of numerous diseases. There are four major types of VSCs, including endothelial progenitor cells (EPCs), smooth muscle progenitor cells (SMPCs), pericytes, and mesenchymal stem cells (MSCs). VSCs can be found in bone marrow, circulating blood, vessel walls, and other extravascular tissues. During the past two decades, considerable progress has been achieved in the understanding of the derivation, surface markers, and differentiation of VSCs. Yet, the mechanisms regulating their functions and maintenance under normal and pathological conditions, such as in eye diseases, remain to be further elucidated. Owing to the essential roles of blood vessels in human tissues and organs, understanding the functional properties and the underlying molecular basis of VSCs is of critical importance for both basic and translational research.

Mesenchymal stem cells and vascular regeneration

In recent years, MSCs have emerged as a promising therapeutic cell type in regenerative medicine. They hold great promise for treating cardiovascular diseases, such as myocardial infarction and limb ischemia. MSCs may be utilized in both cell-based therapy and vascular graft engineering to restore vascular function, thereby providing therapeutic benefits to patients. The efficacy of MSCs lies in their multipotent differentiation ability toward vascular smooth muscle cells, endothelial cells and other cell types, as well as their capacity to secrete various trophic factors, which are potent in promoting angiogenesis, inhibiting apoptosis and modulating immunoreaction. Increasing our understanding of the mechanisms of MSC involvement in vascular regeneration will be beneficial in boosting present therapeutic approaches and developing novel ones to treat cardiovascular diseases. In this review, we aim to summarize current progress in characterizing the in vivo identity of MSCs, to discuss mechanisms involved in cell-based therapy utilizing MSCs, and to explore current and future strategies for vascular regeneration.

Use of human aortic extracellular matrix as a scaffold for construction of a patient-specific tissue engineered vascular patch

Synthetic or biologic materials are usually used to repair vascular malformation in congenital heart defects; however, non-autologous materials show both mismatch compliance and antigenicity, as well as a lack of recellularization on its surface. Here, we constructed a tissue-engineered vascular patch (TEVP) using decellularized extracellular matrix (ECM) scaffold obtained from excised human aorta during surgery, which was seeded with patient-derived bone marrow CD34-positive (CD34+) progenitor cells. While cellular components were removed, the decellularized ECM scaffold retained native ECM composition, similar mechanical performance to undecellularized aortic tissue, and supported the adhesion, survival and proliferation of CD34+ progenitor cells. Interestingly, after in vitro seeding of decellularized aortic ECM scaffold for 21 d, CD34+ progenitor cells differentiated into mature vascular endothelial cells without addition of any growth factors, as confirmed by the increased levels of endothelial surface markers (CD31, Von Willebrand factor (VWF), VE-cadherin and ICAM-2) and upregulated gene levels (CD31, VWF and eNOS) concurrently with decreased expression of stem cell markers (CD133 and CD34), thus, resulting in surface endothelialization of decellularized ECM scaffold. Consequently, the patient-specific TEVP constructed in this study holds great potential for clinical use in pediatric patients with vascular malformation.

Overcoming the Roadblocks to Cardiac Cell Therapy Using Tissue Engineering

Transplantations of various stem cells or their progeny have repeatedly improved cardiac performance in animal models of myocardial injury; however, the benefits observed in clinical trials have been generally less consistent. Some of the recognized challenges are poor engraftment of implanted cells and, in the case of human cardiomyocytes, functional immaturity and lack of electrical integration, leading to limited contribution to the heart's contractile activity and increased arrhythmogenic risks. Advances in tissue and genetic engineering techniques are expected to improve the survival and integration of transplanted cells, and to support structural, functional, and bioenergetic recovery of the recipient hearts. Specifically, application of a prefabricated cardiac tissue patch to prevent dilation and to improve pumping efficiency of the infarcted heart offers a promising strategy for making stem cell therapy a clinical reality.

Adventitial SCA-1+ Progenitor Cell Gene Sequencing Reveals the Mechanisms of Cell Migration in Response to Hyperlipidemia

Adventitial progenitor cells, including SCA-1⁺ and mesenchymal stem cells, are believed to be important in vascular remodeling. It has been shown that SCA-1⁺ progenitor cells are involved in neointimal hyperplasia of vein grafts, but little is known concerning their involvement in hyperlipidemia-induced atherosclerosis. We employed single-cell sequencing technology on primary adventitial mouse SCA-1⁺ cells from wild-type and atherosclerotic-prone (ApoE-deficient) mice and found that a group of genes controlling cell migration and matrix protein degradation was highly altered. Adventitial progenitors from ApoE-deficient mice displayed an augmented migratory potential both in vitro and in vivo. This increased migratory ability was mimicked by lipid loading to SCA-1⁺ cells. Furthermore, we show that lipid loading increased miRNA-29b expression and induced sirtuin-1 and matrix metalloproteinase-9 levels to promote cell migration. These results provide direct evidence that blood cholesterol levels influence vascular progenitor cell function, which could be a potential target cell for treatment of vascular disease.

Transdifferentiated Human Vascular Smooth Muscle Cells are a New Potential Cell Source for Endothelial Regeneration

Endothelial dysfunction is widely implicated in cardiovascular pathological changes and development of vascular disease. In view of the fact that the spontaneous endothelial cell (EC) regeneration is a slow and insufficient process, it is of great interest to explore alternative cell sources capable of generating functional ECs. Vascular smooth muscle cell (SMC) composes the majority of the vascular wall and retains phenotypic plasticity in response to various stimuli. The aim of this study is to test the feasibility of the conversion of SMC into functional EC through the use of reprogramming factors. Human SMCs are first dedifferentiated for 4 days to achieve a vascular progenitor state expressing CD34, by introducing transcription factors OCT4, SOX2, KLF4 and c-MYC. These SMC-derived progenitors are then differentiated along the endothelial lineage. The SMC-converted ECs exhibit typical endothelial markers expression and endothelial functions in vitro, in vivo and in disease model. Further comprehensive analysis indicates that mesenchymal-to-epithelial transition is requisite to initiate SMCs reprogramming into vascular progenitors and that members of the Notch signalling pathway regulate further differentiation of the progenitors into endothelial lineage. Together, we provide the first evidence of the feasibility of the conversion of human SMCs towards endothelial lineage through an intermediate vascular progenitor state induced by reprogramming.

Perivascular cells and tissue engineering: Current applications and untapped potential

The recent development of tissue engineering provides exciting new perspectives for the replacement of failing organs and the repair of damaged tissues. Perivascular cells, including vascular smooth muscle cells, pericytes and other tissue specific populations residing around blood vessels, have been isolated from many organs and are known to participate to the in situ repair process and angiogenesis. Their potential has been harnessed for cell therapy of numerous pathologies; however, in this Review we will discuss the potential of perivascular cells in the development of tissue engineering solutions for healthcare. We will examine their application in the engineering of vascular grafts, cardiac patches and bone substitutes as well as other tissue engineering applications and we will focus on their extensive use in the vascularization of engineered constructs. Additionally, we will discuss the emerging potential of human pericytes for the development of efficient, vascularized and non-immunogenic engineered constructs.

Differentiation of Human Embryonic Stem Cells to Endothelial Progenitor Cells on Laminins in Defined and Xeno-free Systems

A major hurdle for in vitro culturing of primary endothelial cells (ECs) is that they readily dedifferentiate, hampering their use for therapeutic applications. Human embryonic stem cells (hESCs) may provide an unlimited cell source; however, most current protocols deriving endothelial progenitor cells (EPCs) from hESCs use direct differentiation approaches albeit on undefined matrices, yet final yields are insufficient. We developed a method to culture monolayer hESCs on stem cell niche laminin (LN) LN511 or LN521 matrix. Here, we report a chemically defined, xeno-free protocol for differentiation of hESCs to EPCs using LN521 as the main culture substrate. We were able to generate ∼95% functional EPCs defined as VEGFR2⁺CD34⁺CD31⁺VE-Cadherin⁺. RNA-sequencing analyses of hESCs, EPCs, and primary human umbilical vein endothelial cells showed differentiation-related EC expression signatures, regarding basement membrane composition, cell-matrix interactions, and changes in endothelial lineage markers. Our results may facilitate production of stable ECs for the treatment of vascular diseases and in vitro cell modeling.

Vascular Development and Regeneration in the Mammalian Heart

Cardiovascular diseases including coronary artery disease are the leading cause of death worldwide. Unraveling the developmental origin of coronary vessels could offer important therapeutic implications for treatment of cardiovascular diseases. The recent identification of the endocardial source of coronary vessels reveals a heterogeneous origin of coronary arteries in the adult heart. In this review, we will highlight recent advances in finding the sources of coronary vessels in the mammalian heart from lineage-tracing models as well as differentiation studies using pluripotent stem cells. Moreover, we will also discuss how we induce neovascularization in the damaged heart through transient yet highly efficient expression of VEGF-modified mRNAs as a potentially therapeutic delivery platform.

Endothelial Progenitor Cells in Diabetic Microvascular Complications: Friends or Foes?

Despite being featured as metabolic disorder, diabetic patients are largely affected by hyperglycemia-induced vascular abnormality. Accumulated evidence has confirmed the beneficial effect of endothelial progenitor cells (EPCs) in coronary heart disease. However, antivascular endothelial growth factor (anti-VEGF) treatment is the main therapy for diabetic retinopathy and nephropathy, indicating the uncertain role of EPCs in the pathogenesis of diabetic microvascular disease. In this review, we first illustrate how hyperglycemia induces metabolic and epigenetic changes in EPCs, which exerts deleterious impact on their number and function. We then discuss how abnormal angiogenesis develops in eyes and kidneys under diabetes condition, focusing on “VEGF uncoupling with nitric oxide” and “competitive angiopoietin 1/angiopoietin 2” mechanisms that are shared in both organs. Next, we dissect the nature of EPCs in diabetic microvascular complications. After we overview the current EPCs-related strategies, we point out new EPCs-associated options for future exploration. Ultimately, we hope that this review would uncover the mysterious nature of EPCs in diabetic microvascular disease for therapeutics.

Reprogramming towards endothelial cells for vascular regeneration

Endothelial damage and dysfunction are implicated in cardiovascular pathological changes and the development of vascular diseases. In view of the fact that the spontaneous endothelial cell (EC) regeneration is a slow and insufficient process, it is of great significance to explore alternative cell sources capable of generating functional ECs to repair damaged endothelium. Indeed, recent achievements of cell reprogramming to convert somatic cells to other cell types provide new powerful approaches to study endothelial regeneration. Based on progress in the research field, the present review aims to summarize the strategies and mechanisms of generating endothelial cells through reprogramming from somatic cells, and to examine what this means for the potential application of cell therapy in the clinic.