Comparative characterization of stromal vascular cells derived from three types of vascular wall and adipose tissue

The Characteristics and Survival Potential Under Sub-lethal Stress of Mesenchymal Stromal/Stem Cells Isolated from the Human Vascular Wall

Mesenchymal stromal/stem cells (MSCs) have been identified in multiple human tissues, including the vascular wall. High proliferative potential, multilineage, and immunomodulatory properties make vascular MSCs promising candidates for regenerative medicine. Indeed, their location is strategic for controlling vascular and extra-vascular tissue homeostasis. However, the clinical application of MSCs, and in particular vascular MSCs, is still challenging. Current studies are focused on developing strategies to improve MSC therapeutic applications, like priming MSCs with stress conditions (hypoxia, nutrient deprivation) to achieve a higher therapeutic potential. The goal of the present study is to review the main findings regarding the MSCs isolated from the human vascular wall. Further, the main priming strategies tested on MSCs from different sources are reported, together with the experience on vascular MSCs isolated from healthy cryopreserved and pathological arteries. Stress induction can be a priming approach able to improve MSC effectiveness through several mechanisms that are discussed in this review. Nevertheless, these issues have not been completely explored in vascular MSCs and potential side effects need to be investigated.

Effects of non-vascularized adipose tissue transplantation on its genetic profile

Subcutaneous adipose tissue (SAT) is recognized as a highly active metabolic and inflammatory tissue. Interestingly, adipose tissue transplantation is widely performed in plastic surgery via lipofilling, yet little is known about the gene alteration of adipocytes after transplantation. We performed an RNA-expression analysis of fat transplants before and after fat transplantation.In C57BL/6 N mice SAT was autologously transplanted. Samples of SAT were analysed before transplantation, 7, and 15 days after transplantation and gene expression profiles were measured.Analysis revealed that lipid metabolism-related genes were downregulated while inflammatory and extracellular matrix related genes were up-regulated 7 and 15 days after transplantation. When comparing gene expression profile 7 days after transplantation to 15 days after transplantation developmental pathways showed most changes.

Telocytes in the human ascending aorta: Characterization and exosome-related KLF-4/VEGF-A expression

Telocytes (TCs), a novel interstitial cell entity promoting tissue regeneration, have been described in various tissues. Their role in inter‐cellular signalling and tissue remodelling has been reported in almost all human tissues. This study hypothesizes that TC also contributes to tissue remodelling and regeneration of the human thoracic aorta (HTA). The understanding of tissue homeostasis and regenerative potential of the HTA is of high clinical interest as it plays a crucial role in pathogenesis from aortic dilatation to lethal dissection. Therefore, we obtained twenty‐five aortic specimens of heart donors during transplantation. The presence of TCs was detected in different layers of aortic tissue and characterized by immunofluorescence and transmission electron microscopy. Further, we cultivated and isolated TCs in highly differentiated form identified by positive staining for CD34 and c‐kit. Aortic‐derived TC was characterized by the expression of PDGFR‐α, PDGFR‐β, CD29/integrin β‐1 and αSMA and the stem cell markers Nanog and KLF‐4. Moreover, TC exosomes were isolated and characterized for soluble angiogenic factors by Western blot. CD34⁺/c‐kit⁺ TCs shed exosomes containing the soluble factors VEGF‐A, KLF‐4 and PDGF‐A. In summary, TC occurs in the aortic wall. Correspondingly, exosomes, derived from aortic TCs, contain vasculogenesis‐relevant proteins. Understanding the regulation of TC‐mediated aortic remodelling may be a crucial step towards designing strategies to promote aortic repair and prevent adverse remodelling.

The angiogenic potential of CD271+ human adipose tissue-derived mesenchymal stem cells

BACKGROUND

Autologous fat grafting is often a crucial aspect of reconstructive and aesthetic surgeries, yet poor graft retention is a major issue with this technique. Enriching fat grafts with adipose tissue-derived mesenchymal stem cells (AD-MSCs) improves graft survival-however, AD-MSCs represent a heterogeneous population. Selection of subpopulations of AD-MSCs would allow the targeting of specific AD-MSCs that may benefit fat graft survival more than the general AD-MSC population.

METHODS

Human AD-MSCs were selected for the surface marker CD271 using magnetic-activated cell sorting and compared to the CD271 negative phenotype.  These subpopulations were analysed for gene expression using Real-Time qPCR and RNA sequencing; surface marker characteristics using immunostaining; ability to form tubules when cultured with endothelial cells; and gene and protein expression of key angiogenic mediators when cultured with ex-vivo adipose tissue.

RESULTS

Human AD-MSCs with the surface marker CD271 express angiogenic genes at higher levels, and inflammatory genes at lower levels, than the CD271- AD-MSC population. A greater proportion of CD271+ AD-MSCs also possess the typical complement of stem cell surface markers and are more likely to promote effective neoangiogenesis, compared to CD271- AD-MSCs.

CONCLUSION

Enriching grafts with the CD271+ AD-MSC subpopulation holds potential for the improvement of reconstructive and aesthetic surgeries involving adipose tissue.

Vessel Wall-Derived Mesenchymal Stromal Cells Share Similar Differentiation Potential and Immunomodulatory Properties with Bone Marrow-Derived Stromal Cells

Purpose

This study is aimed at investigating the phenotype, differentiation potential, immunomodulatory properties, and responsiveness of saphenous vein vessel wall-derived mesenchymal stromal cells (SV-MSCs) to various TLR ligands and proinflammatory cytokines, as well as comparing their features to those of their bone marrow-derived counterparts (BM-MSCs).

Methods

SV-MSCs were isolated by enzymatic digestion of the saphenous vein vessel wall. Phenotype analysis was carried out by flow cytometry and microscopy, whereas adipogenic, chondrogenic, and osteogenic differentiation potentials were tested in in vitro assays. For comparative analysis, the expression of different stemness, proliferation, and differentiation-related genes was determined by Affymetrix gene array. To compare the immunomodulatory properties of SV-MSCs and BM-MSCs, mixed lymphocyte reaction was applied. To investigate their responses to various activating stimuli, MSCs were treated with TLR ligands (LPS, PolyI:C) or proinflammatory cytokines (TNFα, IL-1β, IFNγ), and the expression of various early innate immune response-related genes was assessed by qPCR, while secretion of selected cytokines and chemokines was measured by ELISA.

Results

The isolated SV-MSCs were able to differentiate into bone, fat, and cartilage cells/direction in vitro. SV-MSCs expressed the most important MSC markers (CD29, CD44, CD73, CD90, and CD105) and shared almost identical phenotypic characteristics with BM-MSCs. Their gene expression pattern and activation pathways were close to those of BM-MSCs. SV-MSCs showed better immunosuppressive activity inhibiting phytohemagglutinin-induced T lymphocyte proliferation in vitro than BM-MSCs. Cellular responses to treatments mimicking inflammatory conditions were comparable in the bone marrow- and saphenous vein-derived MSCs. Namely, similar to BM-MSCs, SV-MSCs secreted increased amount of IL-6 and IL-8 after 12- or 24-hour treatment with LPS, PolyI:C, TNFα, or IL-1β, compared to untreated controls. Interestingly, a different CXCL-10/IP-10 secretion pattern could be observed under inflammatory conditions in the two types of MSCs.

Conclusion

Based on our results, cells isolated from saphenous vein vessel wall fulfilled the ISCT's (International Society for Cellular Therapy) criteria for multipotent mesenchymal stromal cells, and no significant differences in the phenotype, gene expression pattern, and responsiveness to inflammatory stimuli could be observed between BM-MSCs and SV-MSCs, while the latter cells have more potent immunosuppressive activity in vitro. Further functional assays have to be performed to reveal whether SV-MSCs could be useful for certain regenerative therapeutic applications or tissue engineering purposes.

Vasculogenic properties of adventitial Sca-1+CD45+ progenitor cells in mice: a potential source of vasa vasorum in atherosclerosis

The cellular origins of vasa vasorum are ill-defined and may involve circulating or local progenitor cells. We previously discovered that murine aortic adventitia contains Sca-1⁺CD45⁺ progenitors that produce macrophages. Here we investigated whether they are also vasculogenic. In aortas of C57BL/6 mice, Sca-1⁺CD45⁺ cells were localised to adventitia and lacked surface expression of endothelial markers (<1% for CD31, CD144, TIE-2). In contrast, they did show expression of CD31, CD144, TIE-2 and VEGFR2 in atherosclerotic ApoE^-/- aortas. Although Sca-1⁺CD45⁺ cells from C57BL/6 aorta did not express CD31, they formed CD31⁺ colonies in endothelial differentiation media and produced interconnecting vascular-like cords in Matrigel that contained both endothelial cells and a small population of macrophages, which were located at branch points. Transfer of aortic Sca-1⁺CD45⁺ cells generated endothelial cells and neovessels de novo in a hindlimb model of ischaemia and resulted in a 50% increase in perfusion compared to cell-free control. Similarly, their injection into the carotid adventitia of ApoE^-/- mice produced donor-derived adventitial and peri-adventitial microvessels after atherogenic diet, suggestive of newly formed vasa vasorum. These findings show that beyond its content of macrophage progenitors, adventitial Sca-1⁺CD45⁺ cells are also vasculogenic and may be a source of vasa vasorum during atherogenesis.

Induction of Expression of CD271 and CD34 in Mesenchymal Stromal Cells Cultured as Spheroids

Cultured mesenchymal stromal cells (MSCs) are cells that can be used for tissue engineering or cell therapies owing to their multipotency and ability to secrete immunomodulatory and trophic molecules. Several studies suggest that MSCs can become pericytes when cocultured with endothelial cells (ECs) but failed to use pericyte markers not already expressed by MSCs. We hypothesized ECs could instruct MSCs to express the molecules CD271 or CD34, which are expressed by pericytes in situ but not by MSCs. CD271 is a marker of especial interest because it is associated with multipotency, a characteristic that wanes in MSCs as they are culture expanded. Consequently, surface expression of CD271 and CD34 was detected in roughly half of the MSCs cocultured with ECs as spheroids in the presence of insulin-like growth factor 1 (IGF-1). Conversely, expression of CD271 and CD34 was detected in a similar proportion of MSCs cultured under these conditions without ECs, and expression of these markers was low or absent when no IGF-1 was added. These findings indicate that specific culture conditions including IGF-1 can endow cultured MSCs with expression of CD271 and CD34, which may enhance the multipotency of these cells when they are used for therapeutic purposes.

Vascular Stem/Progenitor Cell Migration and Differentiation in Atherosclerosis

SIGNIFICANCE

Atherosclerosis is a major cause for the death of human beings, and it takes place in large- and middle-sized arteries. The pathogenesis of the disease has been widely investigated, and new findings on vascular stem/progenitor cells could have an impact on vascular regeneration. Recent Advances: Recent studies have shown that abundant stem/progenitor cells present in the vessel wall are mainly responsible for cell accumulation in the intima during vascular remodeling. It has been demonstrated that the mobilization and recruitment of tissue-resident stem/progenitor cells give rise to endothelial and smooth muscle cells (SMCs) that participate in vascular repair and remodeling such as neointimal hyperplasia and arteriosclerosis. Interestingly, cell lineage tracing studies indicate that a large proportion of SMCs in neointimal lesions is derived from adventitial stem/progenitor cells.

CRITICAL ISSUES

The influence of stem/progenitor cell behavior on the development of atherosclerosis is crucial. An understanding of the regulatory mechanisms that control stem/progenitor cell migration and differentiation is essential for stem/progenitor cell therapy for vascular diseases and regenerative medicine.

FUTURE DIRECTIONS

Identification of the detailed process driving the migration and differentiation of vascular stem/progenitor cells during the development of atherosclerosis, discovery of the environmental cues, and signaling pathways that control cell fate within the vasculature will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis. Antioxid. Redox Signal. 00, 000-000.

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.

Responses of adventitial CD34+ vascular wall-resident stem/progenitor cells and medial smooth muscle cells to carotid injury in rats

Cell culture and carotid injury studies with SD rats were performed to investigate the roles of CD34⁺ vascular wall-resident stem/progenitor cells (VRS/Pcs) and vascular smooth muscle cells (SMCs) in neointimal formation. In vitro, the media-isolated SM MHC⁺ SMCs occupied 93.92±8.62% of total BrdU⁺ cells, whereas the CD34⁺ cells, only 2.61±0.82%, indicating that the cell expansion in SMC culture was attributed to SM MHC⁺ SMCs. The adventitia-isolated CD34⁺ VRS/Pcs responded to PDGF-BB by differentiating into SMC-like cells which expressed SM22α (an early stage SMC marker), but seldom SM MHC (a late stage SMC marker). In carotid injury model, the CD34⁺ VRS/Pcs differentiated SMC-like cells migrated in very few numbers into only the outer layer of the media, and this was further confirmed by a cell tracking analysis. While the neointimal cells were consistently SM MHC⁺ and CD34^- SMCs during whole course of the post-injury remodeling. Thus it is speculated that the adventitial CD34⁺ VRS/Pcs, at least in rat model, do not directly participate in neointimal formation, but function to maintain homeostasis of the media during injury-induced vascular wall remodeling.

Differentiation of Vascular Stem Cells Contributes to Ectopic Calcification of Atherosclerotic Plaque

The cellular and molecular basis of vascular calcification (VC) in atherosclerosis is not fully understood. Here, we investigate role of resident/circulating progenitor cells in VC and contribution of inflammatory plaque environment to this process. Vessel-derived stem/progenitor cells (VSCs) and mesenchymal stem cells (MSCs) isolated from atherosclerotic ApoE(-/-) mice showed significantly more in vitro osteogenesis and chondrogenesis than cells generated from control C57BL/6 mice. To assess their ability to form bone in vivo, cells were primed chondrogenically or cultured in control medium on collagen glycosaminoglycan scaffolds in vitro prior to subcutaneous implantation in ApoE(-/-) and C57BL/6 mice using a crossover study design. Atherosclerotic ApoE(-/-) MSCs and VSCs formed bone when implanted in C57BL/6 mice. In ApoE(-/-) mice, these cells generated more mature bone than C57BL/6 cells. The atherosclerotic in vivo environment alone promoted bone formation by implanted C57BL/6 cells. Un-primed C57BL/6 VSCs were unable to form bone in either mouse strain. Treatment of ApoE(-/-) VSC chondrogenic cultures with interleukin (IL)-6 resulted in significantly increased glycosaminoglycan deposition and expression of characteristic chondrogenic genes at 21 days. In conclusion, resident vascular cells from atherosclerotic environment respond to the inflammatory milieu and undergo calcification. IL-6 may have a role in aberrant differentiation of VSCs contributing to vascular calcification in atherosclerosis.

Regenerative Translation of Human Blood-Vessel-Derived MSC Precursors

Mesenchymal stem/stromal cells (MSCs) represent a promising adult progenitor cell source for tissue repair and regeneration. Their mysterious identity in situ has gradually been unveiled by the accumulating evidence indicating an association between adult multipotent stem/progenitor cells and vascular/perivascular niches. Using immunohistochemistry and fluorescence-activated cell sorting, we and other groups have prospectively identified and purified subpopulations of multipotent precursor cells associated with the blood vessels within multiple human organs. The three precursor subsets, myogenic endothelial cells (MECs), pericytes (PCs), and adventitial cells (ACs), are located, respectively, in the three structural tiers of typical blood vessels: intima, media, and adventitia. MECs, PCs, and ACs have been extensively characterized in prior studies and are currently under investigation for their therapeutic potentials in preclinical animal models. In this review, we will briefly discuss the identification, isolation, and characterization of these human blood-vessel-derived stem cells (hBVSCs) and summarize the current status of regenerative applications of hBVSC subsets.

Vascular wall progenitor cells in health and disease

The vasculature plays an indispensible role in organ development and maintenance of tissue homeostasis, such that disturbances to it impact greatly on developmental and postnatal health. Although cell turnover in healthy blood vessels is low, it increases considerably under pathological conditions. The principle sources for this phenomenon have long been considered to be the recruitment of cells from the peripheral circulation and the re-entry of mature cells in the vessel wall back into cell cycle. However, recent discoveries have also uncovered the presence of a range of multipotent and lineage-restricted progenitor cells in the mural layers of postnatal blood vessels, possessing high proliferative capacity and potential to generate endothelial, smooth muscle, hematopoietic or mesenchymal cell progeny. In particular, the tunica adventitia has emerged as a progenitor-rich compartment with niche-like characteristics that support and regulate vascular wall progenitor cells. Preliminary data indicate the involvement of some of these vascular wall progenitor cells in vascular disease states, adding weight to the notion that the adventitia is integral to vascular wall pathogenesis, and raising potential implications for clinical therapies. This review discusses the current body of evidence for the existence of vascular wall progenitor cell subpopulations from development to adulthood and addresses the gains made and significant challenges that lie ahead in trying to accurately delineate their identities, origins, regulatory pathways, and relevance to normal vascular structure and function, as well as disease.

Effects of estrogen on growth and smooth muscle differentiation of vascular wall-resident CD34(+) stem/progenitor cells

OBJECTIVES

To investigate the effects of estrogen on growth and smooth muscle cell (SMC)-differentiation of vascular wall-resident CD34(+) stem/progenitor cells (VRS/Pcs).

METHODS AND RESULTS

The existence of CD34(+) VRS/Pcs was confirmed by immunohistochemistry in the adventitia of arteries of young (2-month-old) and old (24-month-old) female SD rats with less CD34(+) adventitial cells detected in the old. The VRS/Pcs isolated from young animals were grown in Stem cell growth medium or induced to differentiate into SMC with PDGF-BB in the presence or absence of 17β-estrodiol (E2). Flow cytometry, RT-qPCR and Western blot showed that E2 promoted Brdu incorporation of the CD34(+) VRS/Pcs growing in Stem cell growth medium; but when the cells were incubated in PDGF-BB, the hormone enhanced their expression of SMC marker SM22. ChIP and IP assays showed that E2 significantly promoted the binding of pELK1-SRF complex to the promoter of c-fos gene in CD34(+) VRS/Pcs growing in the Stem cell growth medium; but when the cells were stimulated with PDGF-BB, an E2-enhanced binding of myocardin-SRF to the promoter of SM22 gene was found with enhanced expression of SRC3 and its binding to myocardin. The effects of E2 above could be blocked by the estrogen receptor antagonist ICI 182,780 or inhibited by SRF-siRNA.

CONCLUSION

Estrogen has dual effects on CD34(+) VRS/Pcs. For the undifferentiated VRS/Pcs, it accelerates their proliferation by enhancing binding of pELK1-SRF complex to c-fos gene; while for the differentiating VRS/Pcs, it promotes their differentiation to SMC through a mechanism of SRC3-mediated interaction of myocardin-SRF complex with SM22 gene.

Concentration-Dependent Vascularization of Adipose Stromal Vascular Fraction Cells

Adipose-derived stromal vascular fraction (SVF) cells have been shown to self-associate to form vascular structures under both in vitro and in vivo conditions. The angiogenic (new vessels from existing vessels) and vasculogenic (new vessels through self-assembly) potential of the SVF cell population may provide a cell source for directly treating (i.e., point of care without further cell isolation) ischemic tissues. However the correct dosage of adipose SVF cells required to achieve a functional vasculature has not been established. Accordingly, in vitro and in vivo dose response assays were performed evaluating the SVF cell vasculogenic potential. Serial dilutions of freshly isolated rat adipose SVF cells were plated on growth factor reduced Matrigel and vasculogenesis, assessed as cellular tube-like network assembly, was quantified after 3 days of culture. This in vitro vasculogenesis assay indicated that rat SVF cells reached maximum network length at a concentration of 2.5 × 10(5) cells/ml and network maintained at the higher concentrations tested. The same concentrations of rat and human SVF cells were used to evaluate vasculogenesis in vivo. SVF cells were incorporated into collagen gels and subcutaneously implanted into Rag1 immunodeficient mice. The 3D confocal images of harvested constructs were evaluated to quantify dose dependency of SVF cell vasculogenesis potential. Rat- and human-derived SVF cells yielded a maximum vasculogenic potential at 1 × 10(6) and 4 × 10(6) cells/ml, respectively. No adverse reactions (e.g., toxicity, necrosis, tumor formation) were observed at any concentration tested. In conclusion, the vasculogenic potential of adipose-derived SVF cell populations is dose dependent.

Inflammatory, metabolic, and genetic mechanisms of vascular calcification

This review centers on updating the active research area of vascular calcification. This pathology underlies substantial cardiovascular morbidity and mortality, through adverse mechanical effects on vascular compliance, vasomotion, and, most likely, plaque stability. Biomineralization is a complex, regulated process occurring widely throughout nature. Decades ago, its presence in the vasculature was considered a mere curiosity and an unregulated, dystrophic process that does not involve biological mechanisms. Although it remains controversial whether the process has any adaptive value or past evolutionary advantage, substantial advances have been made in understanding the biological mechanisms driving the process. Different types of calcific vasculopathy, such as inflammatory versus metabolic, have parallel mechanisms in skeletal bone calcification, such as intramembranous and endochondral ossification. Recent work has identified important regulatory roles for inflammation, oxidized lipids, elastin, alkaline phosphatase, osteoprogenitor cells, matrix γ-carboxyglutamic acid protein, transglutaminase, osteoclastic regulatory factors, phosphate regulatory hormones and receptors, apoptosis, prelamin A, autophagy, and microvesicles or microparticles similar to the matrix vesicles of skeletal bone. Recent work has uncovered fascinating interactions between matrix γ-carboxyglutamic acid protein, vitamin K, warfarin, and transport proteins. And, lastly, recent breakthroughs in inherited forms of calcific vasculopathy have identified the genes responsible as well as an unexpected overlap of phenotypes. Until recently, vascular calcification was considered a purely degenerative, unregulated process. Since then, investigative groups around the world have identified a wide range of causative mechanisms and regulatory pathways, and some of the recent developments are highlighted in this review.