Explore the vast range of titles available.

Endothelial progenitor cell (EPC) nomenclature remains ambiguous and there is a general lack of concordance in the stem cell field with many distinct cell subtypes continually grouped under the term \"EPC.\" It would be highly advantageous to agree on standards to confirm an endothelial progenitor phenotype and this should include detailed immunophenotyping, potency assays, and clear separation from hematopoietic angiogenic cells which are not endothelial progenitors. In this review, we seek to discourage the indiscriminate use of \"EPCs,\" and instead propose precise terminology based on defining cellular phenotype and function. Endothelial colony forming cells and myeloid angiogenic cells are examples of two distinct and well‐defined cell types that have been considered EPCs because they both promote vascular repair, albeit by completely different mechanisms of action. It is acknowledged that scientific nomenclature should be a dynamic process driven by technological and conceptual advances; ergo the ongoing \"EPC\" nomenclature ought not to be permanent and should become more precise in the light of strong scientific evidence. This is especially important as these cells become recognized for their role in vascular repair in health and disease and, in some cases, progress toward use in cell therapy. Stem Cells Translational Medicine 2017;6:1316–1320

Islet transplantation has shown promise as a curative therapy for type 1 diabetes (T1D). However, the side effects of systemic immunosuppression and limited long‐term viability of engrafted islets, together with the scarcity of donor organs, highlight an urgent need for the development of new, improved, and safer cell‐replacement strategies. Induction of local immunotolerance to prevent allo‐rejection against islets and stem cell derived β cells has the potential to improve graft function and broaden the applicability of cellular therapy while minimizing adverse effects of systemic immunosuppression. In this mini review, recent developments in non‐encapsulation, local immunomodulatory approaches for T1D cell replacement therapies, including islet/β cell modification, immunomodulatory biomaterial platforms, and co‐transplantation of immunomodulatory cells are discussed. Key advantages and remaining challenges in translating such technologies to clinical settings are identified. Although many of the studies discussed are preliminary, the growing interest in the field has led to the exploration of new combinatorial strategies involving cellular engineering, immunotherapy, and novel biomaterials. Such interdisciplinary research will undoubtedly accelerate the development of therapies that can benefit the whole T1D population. An overview of different local immunomodulatory approaches in β cell replacement therapies is provided. Strategies in islet/β cell modification with immunomodulatory proteins immobilized on the cell surface or released to the local microenvironment, biomaterial platforms presenting or delivering immunomodulatory signals, and co‐transplantation of immunomodulatory cells are discussed.

Effective bone regeneration remains a significant challenge in surgical practice, particularly due to the limitations associated with autologous bone grafting, such as donor site morbidity and limited bone availability. This study investigated the potential of human bone‐derived endothelial cells (b‐ECs) in mediating bone regeneration, especially in conjunction with bone marrow‐derived mesenchymal stem cells (bm‐MSCs). It is demonstrated that b‐ECs retain unique osteoinductive properties post‐isolation, crucial for promoting bone formation in vivo. Utilizing ectopic and orthotopic xenograft models in immunodeficient mice, these findings revealed that the synergistic interaction of b‐ECs and bm‐MSCs induced rapid and substantial bone formation, highlighting the therapeutic potential of b‐ECs in bone repair strategies. The distinct expression of KIT ligand (KITLG) in b‐ECs emerged as a key factor in these processes. KITLG expression by b‐ECs facilitated the recruitment of c‐Kit+/CD34+ hematopoietic progenitor cells to the osteovascular niche, leading to robust osteogenic differentiation of bm‐MSCs, a process regulated by Notch signaling. Moreover, inducing KITLG expression in non‐bone‐derived endothelial cells conferred similar osteoinductive capabilities. These findings not only enhance the understanding of the intricate interplay between vascular and bone tissues but also open avenues for developing innovative cell‐based approaches for bone regeneration therapy. Bone‐specific endothelial cells (b‐ECs) uniquely express KITLG, which recruits c‐Kit+/CD34+ hematopoietic progenitors (HPCs) to the osteovascular niche, initiating a cascade that culminates in the osteogenic differentiation of bone marrow‐derived mesenchymal stem cells (bm‐MSCs) and subsequent ossification. This process underscores the potential of b‐ECs to enhance bone regeneration and repair by establishing an osteoinductive microenvironment.

Human pluripotent stem cells (hPSCs) offer an unprecedented opportunity to model diverse cell types and tissues. To enable systematic exploration of the programming landscape mediated by transcription factors (TFs), we present the Human TFome, a comprehensive library containing 1,564 TF genes and 1,732 TF splice isoforms. By screening the library in three hPSC lines, we discovered 290 TFs, including 241 that were previously unreported, that induce differentiation in 4 days without alteration of external soluble or biomechanical cues. We used four of the hits to program hPSCs into neurons, fibroblasts, oligodendrocytes and vascular endothelial-like cells that have molecular and functional similarity to primary cells. Our cell-autonomous approach enabled parallel programming of hPSCs into multiple cell types simultaneously. We also demonstrated orthogonal programming by including oligodendrocyte-inducible hPSCs with unmodified hPSCs to generate cerebral organoids, which expedited in situ myelination. Large-scale combinatorial screening of the Human TFome will complement other strategies for cell engineering based on developmental biology and computational systems biology. A library of human transcription factor genes is screened for differentiation of human pluripotent stem cells.

Endothelial colony-forming cells (ECFCs) are endothelial precursors that circulate in peripheral blood. Studies have demonstrated that human ECFCs have robust vasculogenic properties. However, whether ECFCs can exert trophic functions in support of specific stem cells in vivo remains largely unknown. Here, we sought to determine whether human ECFCs can function as paracrine mediators before the establishment of blood perfusion. We used two xenograft models of human mesenchymal stem cell (MSC) transplantation and studied how the presence of ECFCs modulates MSC engraftment and regenerative capacity in vivo. Human MSCs were isolated from white adipose tissue and bone marrow aspirates and were s.c. implanted into immunodeficient mice in the presence or absence of cord blood-derived ECFCs. MSC engraftment was regulated by ECFC-derived paracrine factors via platelet-derived growth factor BB (PDGF-BB)/platelet-derived growth factor receptor (PDGFR)-β signaling. Cotransplanting ECFCs significantly enhanced MSC engraftment by reducing early apoptosis and preserving stemness-related properties of PDGFR-β ⁺ MSCs, including the ability to repopulate secondary grafts. MSC engraftment was negligible in the absence of ECFCs and completely impaired in the presence of Tyrphostin AG1296, an inhibitor of PDGFR kinase. Additionally, transplanted MSCs displayed fate-restricted potential in vivo, with adipose tissue-derived and bone marrow-derived MSCs contributing exclusive differentiation along adipogenic and osteogenic lineages, respectively. This work demonstrates that blood-derived ECFCs can serve as paracrine mediators and regulate the regenerative potential of MSCs via PDGF-BB/PDGFR-β signaling. Our data suggest the systematic use of ECFCs as a means to improve MSC transplantation.

Here we investigated whether endothelial colony forming cells (ECFC) and mesenchymal progenitor cells (MPC) form vascular networks and restore blood flow in ischemic skeletal muscle, and whether host myeloid cells play a role. ECFC + MPC, ECFC alone, MPC alone, or vehicle alone were injected into the hind limb ischemic muscle one day after ligation of femoral artery and vein. At day 5, hind limbs injected with ECFC + MPC showed greater blood flow recovery compared with ECFC, MPC, or vehicle. Tail vein injection of human endothelial specific Ulex europaeus agglutinin - I demonstrated an increased number of perfused human vessels in ECFC + MPC compared with ECFC. In vivo bioluminescence imaging showed ECFC persisted for 14 days in ECFC + MPC-injected hind limbs. Flow cytometric analysis of ischemic muscles at day 2 revealed increased myeloid lineage cells in ECFC + MPC-injected muscles compared to vehicle-injected muscles. Neutrophils declined by day 7, while the number of myeloid cells, macrophages, and monocytes did not. Systemic myeloid cell depletion with anti-Gr-1 antibody blocked the improved blood flow observed with ECFC + MPC and reduced ECFC and MPC retention. Our data suggest that ECFC + MPC delivery could be used to reestablish blood flow in ischemic tissues, and this may be enhanced by coordinated recruitment of host myeloid cells.

Release of promoter-proximally paused RNA polymerase II (RNAPII) is a recently recognized transcriptional regulatory checkpoint. The biological roles of RNAPII pause release and the mechanisms by which extracellular signals control it are incompletely understood. Here we show that VEGF stimulates RNAPII pause release by stimulating acetylation of ETS1 , a master endothelial cell transcriptional regulator. In endothelial cells, ETS1 binds transcribed gene promoters and stimulates their expression by broadly increasing RNAPII pause release. 34 VEGF enhances ETS1 chromatin occupancy and increases ETS1 acetylation, enhancing its binding to BRD4 , which recruits the pause release machinery and increases RNAPII pause release. Endothelial cell angiogenic responses in vitro and in vivo require ETS1 -mediated transduction of VEGF signaling to release paused RNAPII. Our results define an angiogenic pathway in which VEGF enhances ETS1 – BRD4 interaction to broadly promote RNAPII pause release and drive angiogenesis. Promoter proximal RNAPII pausing is a rate-limiting transcriptional mechanism. Chen et al . show that this process is essential in angiogenesis by demonstrating that the endothelial master transcription factor ETS1 promotes global RNAPII pause release, and that this process is governed by VEGF.

Mural cells are central to vascular integrity and function. In this study, we demonstrate the innovative use of the transcription factor NKX3.1 to guide the differentiation of human induced pluripotent stem cells into mural progenitor cells (iMPCs). By transiently activating NKX3.1 in mesodermal intermediates, we developed a method that diverges from traditional growth factor-based differentiation techniques. This approach efficiently generates a robust iMPC population capable of maturing into diverse functional mural cell subtypes, including smooth muscle cells and pericytes. These iMPCs exhibit key mural cell functionalities such as contractility, deposition of extracellular matrix, and the ability to support endothelial cell-mediated vascular network formation in vivo. Our study not only underscores the fate-determining significance of NKX3.1 in mural cell differentiation but also highlights the therapeutic potential of these iMPCs. We envision these insights could pave the way for a broader use of iMPCs in vascular biology and regenerative medicine. Mural progenitor cells are crucial for vascular stability. Here, the authors generate these cells from human pluripotent stem cells using NKX3.1 and show that they can mature into various mural cell types and contribute to blood vessel formation.

Ischaemic diseases such as critical limb ischaemia and myocardial infarction affect millions of people worldwide 1 . Transplanting endothelial cells (ECs) is a promising therapy in vascular medicine, but engrafting ECs typically necessitates co-transplanting perivascular supporting cells such as mesenchymal stromal cells (MSCs), which makes clinical implementation complicated 2 , 3 . The mechanisms that enable MSCs to facilitate EC engraftment remain elusive. Here we show that, under cellular stress, MSCs transfer mitochondria to ECs through tunnelling nanotubes, and that blocking this transfer impairs EC engraftment. We devised a strategy to artificially transplant mitochondria, transiently enhancing EC bioenergetics and enabling them to form functional vessels in ischaemic tissues without the support of MSCs. Notably, exogenous mitochondria did not integrate into the endogenous EC mitochondrial pool, but triggered mitophagy after internalization. Transplanted mitochondria co-localized with autophagosomes, and ablation of the PINK1–Parkin pathway negated the enhanced engraftment ability of ECs. Our findings reveal a mechanism that underlies the effects of mitochondrial transfer between mesenchymal and endothelial cells, and offer potential for a new approach for vascular cell therapy. Under stressful conditions, mesenchymal stromal cells transfer mitochondria to endothelial cells through tunnelling nanotubes, and artificially transplanting mitochondria into endothelial cells improves the ability of these cells to engraft and to revascularize ischaemic tissues.

Tissue engineering holds great promise in regenerative medicine. However, the field of tissue engineering faces a myriad of difficulties. A major challenge is the necessity to integrate vascular networks into bioengineered constructs to enable physiological functions including adequate oxygenation, nutrient delivery, and removal of waste products. The last two decades have seen remarkable progress in our collective effort to bioengineer human-specific vascular networks. Studies have included both in vitro and in vivo investigations, and multiple methodologies have found varying degrees of success. What most approaches to bioengineer human vascular networks have in common, however, is the synergistic use of both (1) endothelial cells (ECs)—the cells used to line the lumen of the vascular structures and (2) perivascular cells—usually used to support EC function and provide perivascular stability to the networks. Here, we have highlighted trends in the use of various cellular sources over the last two decades of vascular network bioengineering research. To this end, we comprehensively reviewed all life science and biomedical publications available at the MEDLINE database up to 2018. Emphasis was put on selective studies that definitively used human ECs and were specifically related to bioengineering vascular networks. To facilitate this analysis, all papers were stratified by publication year and then analyzed according to their use of EC and perivascular cell types. This study provides an illustrating discussion on how each alternative source of cells has come to be used in the field. Our intention was to reveal trends and to provide new insights into the trajectory of vascular network bioengineering with regard to cellular sources.