Vascular morphogenesis of adipose-derived stem cells is mediated by heterotypic cell-cell interactions.
ABSTRACT Adipose-derived stromal/stem cells (ASCs) are a promising cell source for vascular-based approaches to clinical therapeutics, as they have been shown to give rise to both endothelial and perivascular cells. While it is well known that ASCs can present a heterogeneous phenotypic profile, spontaneous interactions among these subpopulations that result in the formation of complex tissue structures have not been rigorously demonstrated. Our study reports the novel finding that ASCs grown in monolayers in the presence of angiogenic cues are capable of self-assembling into complex, three-dimensional vascular structures. This phenomenon is only apparent when the ASCs are seeded at a high density (20,000 cells/cm(2)) and occur through orchestrated interactions among three distinct subpopulations: CD31-positive cells (CD31+), α-smooth muscle actin-positive cells (αSMA+), and cells that are unstained for both these markers (CD31-/αSMA-). Investigations into the kinetics of the process revealed that endothelial vessel-like structures initially arose from individual CD31+ cells through proliferation and their interactions with CD31-/αSMA- cells. During this period, αSMA+ cells proliferated and appeared to migrate toward the vessel structures, eventually engaging in cell-cell contact with them after 1 week. By 2 weeks, the lumen-containing CD31+ vessels grew greater than a millimeter in length, were lined with vascular basement membrane proteins, and were encased within a dense, three-dimensional cluster of αSMA+ and CD31-/αSMA- cells. The recruitment of αSMA+ cells was largely due to platelet-derived growth factor (PDGF) signaling, as the inhibition of PDGF receptors substantially reduced αSMA+ cell growth and vessel coverage. Additionally, we found that while hypoxia increased endothelial gene expression and vessel width, it also inhibited the growth of the αSMA+ population. Together, these findings underscore the potential use of ASCs in forming mature vessels in vitro as well as the need for a further understanding of the heterotypic interactions among ASC subpopulations.
- SourceAvailable from: Ayca Zeynep İlter
Chapter: Stem Cells in Wound Healing[Show abstract] [Hide abstract]
ABSTRACT: Cutaneous wound healing encompasses a well-organized process with related but distinct phases, namely, as infl ammatory response, proliferative phase, and remodeling. These interrelated events are orchestrated by different types of cells, chemokines, and hormones to repair the injured area and support the integrity of the tissue. During the wound healing, the cellular responses against the injury are mainly coordinated by mesenchymal stem cells which generate paracrine signals and invoke hemopoietic stem cells, hair follicle stem cells, endothelial precursor cells, and epidermal stem cells to differentiate into resident tissue cells. These cell types have a particular role in each step of healing phases and accelerate the wound closure. This chapter focuses on the involvement of stem cells in various phases of wound healing and recent therapeutic strategies utilizing stem cell therapy and technology for the treatment of tissue injury.Stem Cells: Current Challenges and New Directions, Edited by Kursad Turksen, 01/2013: chapter Stem Cells in Wound Healing: pages 175-197; Humana Press., ISBN: 978-1-4614-8065-5
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ABSTRACT: The innate immune response following bone injury plays an important role in promoting cellular recruitment, revascularization, and other repair mechanisms. Tumor necrosis factor-α (TNF) is a prominent pro-inflammatory cytokine in this cascade, and has been previously shown to improve bone formation and angiogenesis in a dose- and timing-dependent manner. This ability to positively impact both osteogenesis and vascular growth may benefit bone tissue engineering, as vasculature is essential to maintaining cell viability in large grafts after implantation. Here, we investigated the effects of exogenous TNF on the induction of adipose-derived stem/stromal cells (ASCs) to engineer pre-vascularized osteogenic tissue in vitro with respect to dose, timing, and co-stimulation with other inflammatory mediators. We found that acute (2-day), low-dose exposure to TNF promoted vascularization, whereas higher doses and continuous exposure inhibited vascular growth. Co-stimulation with platelet-derived growth factor (PDGF), another key factor released following bone injury, increased vascular network formation synergistically with TNF. ASC-seeded grafts were then cultured within polycaprolactone-fibrin composite scaffolds and implanted in nude rats for 2 weeks, resulting in further tissue maturation and increased angiogenic ingrowth in TNF-treated grafts. VEGF-A expression levels were significantly higher in TNF-treated grafts immediately prior to implantation, indicating a long-term pro-angiogenic effect. These findings demonstrate that TNF has the potential to promote vasculogenesis in engineered osteogenic grafts both in vitro and in vivo. Thus, modulation and/or recapitulation of the immune response following bone injury may be a beneficial strategy for bone tissue engineering.PLoS ONE 09/2014; 9(9):e107199. · 3.53 Impact Factor
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ABSTRACT: We used a combination of strategies to stimulate the vascularization of tissue engineered constructs in vivo including a modular approach to build larger tissues from individual building blocks ('modules') mixed together. Each building block included vascular cells by design: modules were submillimeter-sized collagen gels with an outer layer of endothelial cells (EC), and with embedded adipose-derived mesenchymal stem cells (adMSC) to support EC survival and blood vessel maturation in vivo. We transduced the EC coating the modules with a lentiviral construct to overexpress the angiogenic extracellular matrix (ECM) protein Developmental endothelial locus-1 (Del-1). Upon injection of modules in a subcutaneous SCID/Bg mouse model, there was an increase in the number of blood vessels for implants with EC transduced to overexpress Del-1 compared to control implants (with eGFP transduced EC) over the 21 day duration of the study. The greatest difference between Del-1 and eGFP implants and the highest number of blood vessels was observed seven days after transplantation. The day 7 Del-1 implants also had increased SMA+ staining compared to control, suggesting increased blood vessel maturation through recruitment of SMA+ smooth muscle cells or pericytes to stabilize the newly formed blood vessels. Perfusion studies (microCT, ultrasound imaging, and systemic injection of fluorescent UEA-1 or dextran) showed that some of the newly formed blood vessels (both donor-derived and host-derived, in both Del-1 and eGFP implants) were perfused and connected to the host vasculature as early as seven days after transplantation, and at later time points as well. Nevertheless, perfusion of the implants was limited in some cases, suggesting further improvements are necessary to normalize the vasculature at the implant site.Tissue Engineering Part A 10/2013; · 4.64 Impact Factor