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1.  Immortalization of human adipose-derived stromal cells: production of cell lines with high growth rate, mesenchymal marker expression and capability to secrete high levels of angiogenic factors 
Human adipose-derived stromal cells (hASCs), due to their relative feasibility of isolation and ability to secrete large amounts of angiogenic factors, are being evaluated for regenerative medicine. However, their limited culture life span may represent an obstacle for both preclinical investigation and therapeutic use. To overcome this problem, hASCs immortalization was performed in order to obtain cells with in vitro prolonged life span but still maintain their mesenchymal marker expression and ability to secrete angiogenic factors.
hASCs were transduced with the human telomerase reverse transcriptase (hTERT) gene alone or in combination with either SV-40 or HPV E6/E7 genes. Mesenchymal marker expression on immortalized hASCs lines was confirmed by flow cytometry (FC), differentiation potential was evaluated by immunocytochemistry and ELISA kits were used for evaluation of angiogenic factors. Green fluorescent protein (GFP) gene transduction was used to obtain fluorescent cells.
We found that hTERT alone failed to immortalize hASCs (hASCs-T), while hTERT/SV40 (hASCs-TS) or hTERT/HPV E6/E7 (hASCs-TE) co-transductions successfully immortalized cells. Both hASCs-TS and hASCs-TE were cultured for up to one year with a population doubling level (PDL) up to 100. Comparative studies between parental not transduced (hASCs-M) and immortalized cell lines showed that both hASCs-TS and hASCs-TE maintained a mesenchymal phenotypic profile, whereas differentiation properties were reduced particularly in hASCs-TS. Interestingly, hASCs-TS and hASCs-TE showed a capability to secrete significant amount of HGF and VEGF. Furthermore, hASCs-TS and hASCs-TE did not show tumorigenic properties in vitro although some chromosomal aberrations were detected. Finally, hASCs-TS and hASCs-TE lines were stably fluorescent upon transduction with the GFP gene.
Here we demonstrated, for the first time, that hASCs, upon immortalization, maintain a strong capacity to secrete potent angiogenic molecules. By combining hASCs immortalization and their paracrine characteristics, we have developed a “hybridoma-like model” of hASCs that could have potential applications for discovering and producing molecules to use in regenerative medicine (process scale-up).
In addition, due to the versatility of these fluorescent-immortalized cells, they could be employed in in vivo cell-tracking experiments, expanding their potential use in laboratory practice.
PMCID: PMC4055112  PMID: 24887516
2.  Human Adipose-Derived Stromal Cells Stimulate Autogenous Skeletal Repair via Paracrine Hedgehog Signaling with Calvarial Osteoblasts 
Stem Cells and Development  2010;20(2):243-257.
Human adipose-derived stromal cells (hASCs) have the proven capacity to ossify skeletal defects. The mechanisms whereby hASCs stimulate bone repair are not fully understood. In this study, we examined the potential for hASCs to stimulate autogenous repair of a mouse calvarial defect. Immunofluoresence, osteogenic stains, and surface electron microscopy were used to demonstrate osteogenic differentiation of hASCs. hASCs were engrafted into 4 mm calvarial defects in athymic mice using an osteoconductive scaffold. Analysis included microcomputed tomography, histology, in situ hybridization, and quantitative real-time–polymerase chain reaction. Next, the in vitro interaction between hASCs and mouse calvarial osteoblasts (mOBs) was assessed by the conditioned medium and coculture assays. The medium was supplemented with Hedgehog signaling modifiers, including recombinant N-terminal Sonic hedgehog, smoothened agonist, and cyclopamine. Finally, cyclopamine was delivered in vivo to hASC-engrafted defects. Significant calvarial healing was observed among hASC-engrafted defects compared with control groups (no treatment or scaffold alone) (*P < 0.05). hASCs showed evidence of stimulation of host mouse osteogenesis, including (1) increased expression of bone markers at the defect edge by in situ hybridization, and (2) increased host osteogenic gene expression by species-specific quantitative real-time polymerase chain reaction. Using the conditioned medium or coculture assays, hASCs stimulated mOB osteogenic differentiation, accompanied by Hedgehog signaling activation. N-terminal Sonic hedgehog or smoothened agonist replicated, while cyclopamine reversed, the pro-osteogenic effect of the conditioned medium on mOBs. Finally, cyclopamine injection arrested bone formation in vivo. hASCs heal critical-sized mouse calvarial defects, this is, at least in part, via stimulation of autogenous healing of the host defect. Our studies suggest that hASC-derived Hedgehog signaling may play a paracrine role in skeletal repair.
PMCID: PMC3128781  PMID: 20698749
3.  Agent-Based Model of Therapeutic Adipose-Derived Stromal Cell Trafficking during Ischemia Predicts Ability To Roll on P-Selectin 
PLoS Computational Biology  2009;5(2):e1000294.
Intravenous delivery of human adipose-derived stromal cells (hASCs) is a promising option for the treatment of ischemia. After delivery, hASCs that reside and persist in the injured extravascular space have been shown to aid recovery of tissue perfusion and function, although low rates of incorporation currently limit the safety and efficacy of these therapies. We submit that a better understanding of the trafficking of therapeutic hASCs through the microcirculation is needed to address this and that selective control over their homing (organ- and injury-specific) may be possible by targeting bottlenecks in the homing process. This process, however, is incredibly complex, which merited the use of computational techniques to speed the rate of discovery. We developed a multicell agent-based model (ABM) of hASC trafficking during acute skeletal muscle ischemia, based on over 150 literature-based rules instituted in Netlogo and MatLab software programs. In silico, trafficking phenomena within cell populations emerged as a result of the dynamic interactions between adhesion molecule expression, chemokine secretion, integrin affinity states, hemodynamics and microvascular network architectures. As verification, the model reasonably reproduced key aspects of ischemia and trafficking behavior including increases in wall shear stress, upregulation of key cellular adhesion molecules expressed on injured endothelium, increased secretion of inflammatory chemokines and cytokines, quantified levels of monocyte extravasation in selectin knockouts, and circulating monocyte rolling distances. Successful ABM verification prompted us to conduct a series of systematic knockouts in silico aimed at identifying the most critical parameters mediating hASC trafficking. Simulations predicted the necessity of an unknown selectin-binding molecule to achieve hASC extravasation, in addition to any rolling behavior mediated by hASC surface expression of CD15s, CD34, CD62e, CD62p, or CD65. In vitro experiments confirmed this prediction; a subpopulation of hASCs slowly rolled on immobilized P-selectin at speeds as low as 2 µm/s. Thus, our work led to a fundamentally new understanding of hASC biology, which may have important therapeutic implications.
Author Summary
Ischemic pathologies, such as acute myocardial infarction and peripheral vascular disease, continue to be associated with high morbidities and mortalities. Recently, therapies wherein adult stem cells are injected into the circulation have been shown to increase blood flow and help to restore tissue function following injury. Pre-clinical animal models and human trials have shown successes utilizing this approach, but variable trafficking efficiencies and low incorporation of cells into the injured tissue severely limit effectiveness and may preclude clinical adoption. To address this, we sought to study the complex process of how injected stem cells traffic through the microcirculation and home to sites of injury, in an effort to identify bottlenecks in this process that could be manipulated for therapeutic gain. We developed an agent-based computer model to speed the rate of discovery, and we identified a key cell–cell adhesion interaction that could be targeted to enhance stem cell homing efficiencies during injectable stem cell therapies.
PMCID: PMC2636895  PMID: 19247427
4.  Human Adipose Tissue-Derived SSEA-4 Subpopulation Multi-Differentiation Potential Towards the Endothelial and Osteogenic Lineages 
Tissue Engineering. Part A  2012;19(1-2):235-246.
Human adipose tissue has been recently recognized as a potential source of stem cells for regenerative medicine applications, including bone tissue engineering (TE). Despite the gathered knowledge regarding the differentiation potential of human adipose tissue-derived stem cells (hASCs), in what concerns the endothelial lineage many uncertainties are still present. The existence of a cell subpopulation within the human adipose tissue that expresses a SSEA-4 marker, usually associated to pluripotency, raises expectations on the differentiation capacity of these cells (SSEA-4+hASCs). In the present study, the endothelial and osteogenic differentiation potential of the SSEA-4+hASCs was analyzed, aiming at proposing a single-cell source/subpopulation for the development of vascularized bone TE constructs. SSEA-4+hASCs were isolated using immunomagnetic sorting and cultured either in α-MEM, in EGM-2 MV (endothelial growth medium), or in osteogenic medium. SSEA-4+hASCs cultured in EGM-2 MV formed endothelial cell-like colonies characterized by a cobblestone morphology and expression of CD31, CD34, CD105, and von Willebrand factor as determined by quantitative reverse transcriptase (RT)-polymerase chain reaction, immunofluorescence, and flow cytometry. The endothelial phenotype was also confirmed by their ability to incorporate acetylated low-density lipoprotein and to form capillary-like structures when seeded on Matrigel. SSEA-4+hASCs cultured in α-MEM displayed fibroblastic-like morphology and exhibited a mesenchymal surface marker profile (>90% CD90+/CD73+/CD105+). After culture in osteogenic conditions, an overexpression of osteogenic-related markers (osteopontin and osteocalcin) was observed both at molecular and protein levels. Matrix mineralization detected by Alizarin Red staining confirmed SSEA-4+hASCs osteogenic differentiation. Herein, we demonstrate that from a single-cell source, human adipose tissue, and by selecting the appropriate subpopulation it is possible to obtain microvascular-like endothelial cells and osteoblasts, the most relevant cell types for the creation of vascularized bone tissue-engineered constructs.
PMCID: PMC3530944  PMID: 22924692
5.  Enhancement of Human Adipose-Derived Stromal Cell Angiogenesis through knockdown of a BMP-2 inhibitor 
When employing tissue engineering approaches to clinical problems, cells are often transplanted to a distant site on a scaffold into an environment different from their original niche. Previous studies have demonstrated the role of Noggin, a BMP inhibitor in vascular development and angiogenesis. We hypothesized that noggin suppression in human adipose derived stromal cells (hASCs) would enhance VEGF secretion and angiogenesis in vitro and in vivo to a greater extent than BMP-2 alone.
hASCs were isolated from human lipoaspirate (n=6) and transfected with a Noggin shRNA construct. Knockdown was confirmed and angiogenesis was assessed by tubule formation and qRT-PCR. Cells were seeded on scaffolds with or without BMP-2 and implanted into a 4mm critical size calvarial defect. In vivo angiogenic signaling was assessed by immunofluoresence and immunohistochemistry.
hASCs with noggin suppression secreted significantly higher amounts of VEGF protein on ELISA (*p<0.05). hASCs with noggin knockdown expressed higher levels of angionegic gene markers by qRT-PCR (VE-cadherein, VEGFA, and HIF1A), and displayed enhanced vascular tubule formation in vitro. In vivo, calvarial defects seeded with noggin shRNA hASCs exhibited a significantly higher number of vessels in the defect site than controls by immunohistochemistry (*p<0.05). Additionally, BMP-2 releasing scaffolds significantly enhanced VEGF and PECAM protein levels in the defect site.
hASCs demonstrate significant increases in angiogenesis both in vitro and in vivo both with noggin suppression and BMP-2 supplementation. By creating a cell with noggin suppressed and by using a scaffold with increased BMP-2, we can create a more angiogenic niche.
PMCID: PMC3246067  PMID: 21915082
Angiogenesis; vasculogenesis; Skeletal tissue engineering; Tissue regeneration; Multipotent stromal cells; Calvarial defect; Noggin; Bone morphogenetic protein; scaffold; adipose-derived stromal cells
6.  Microarray Analysis of Human Adipose-Derived Stem Cells in Three-Dimensional Collagen Culture: Osteogenesis Inhibits Bone Morphogenic Protein and Wnt Signaling Pathways, and Cyclic Tensile Strain Causes Upregulation of Proinflammatory Cytokine Regulators and Angiogenic Factors 
Tissue Engineering. Part A  2011;17(21-22):2615-2627.
Human adipose-derived stem cells (hASC) have shown great potential for bone tissue engineering. However, the molecular mechanisms underlying this potential are not yet known, in particular the separate and combined effects of three-dimensional (3D) culture and mechanical loading on hASC osteogenesis. Mechanical stimuli play a pivotal role in bone formation, remodeling, and fracture repair. To further understand hASC osteogenic differentiation and response to mechanical stimuli, gene expression profiles of proliferating or osteogenically induced hASC in 3D collagen I culture in the presence and absence of 10% uniaxial cyclic tensile strain were examined using microarray analysis. About 847 genes and 95 canonical pathways were affected during osteogenesis of hASC in 3D culture. Pathway analysis indicated the potential roles of Wnt/β-catenin signaling, bone morphogenic protein (BMP) signaling, platelet-derived growth factor (PDGF) signaling, and insulin-like growth factor 1 (IGF-1) signaling in hASC during osteogenic differentiation. Application of 10% uniaxial cyclic tensile strain suggested synergistic effects of strain with osteogenic differentiation media on hASC osteogenesis as indicated by significantly increased calcium accretion of hASC. There was no significant further alteration in the four major pathways (Wnt/β-catenin, BMP, PDGF, and IGF-1). However, 184 transcripts were affected by 10% cyclic tensile strain. Function and network analysis of these transcripts suggested that 10% cyclic tensile strain may play a role during hASC osteogenic differentiation by upregulating two crucial factors in bone regeneration: (1) proinflammatory cytokine regulators interleukin 1 receptor antagonist and suppressor of cytokine signaling 3; (2) known angiogenic inductors fibroblast growth factor 2, matrix metalloproteinase 2, and vascular endothelial growth factor A. This is the first study to investigate the effects of both 3D culture and mechanical load on hASC osteogenic differentiation. A complete microarray analysis investigating both the separate effect of soluble osteogenic inductive factors and the combined effects of chemical and mechanical stimulation was performed on hASC undergoing osteogenic differentiation. We have identified specific genes and pathways associated with mechanical response and osteogenic potential of hASC, thus providing significant information toward improved understanding of our use of hASC for functional bone tissue engineering applications.
PMCID: PMC3204199  PMID: 21767168
7.  Flow Cytometric Cell Sorting and In Vitro Pre-Osteoinduction Are Not Requirements for In Vivo Bone Formation by Human Adipose-Derived Stromal Cells 
PLoS ONE  2013;8(2):e56002.
Human adipose-derived stromal cells (hASCs) are a promising cell source for bone tissue engineering. However, before the clinical application of hASCs for the treatment of bone defects, key questions require answers, including whether pre-osteoinduction (OI) and flow cytometric cell purification are indispensible steps for in vivo bone formation by hASCs. In this study, hASCs were purified by flow cytometric cell sorting (FCCS). The osteogenic capabilities of hASCs and purified hASCs with or without pre-osteoinduction were examined through in vitro and in vivo experiments. We found that pre-OI enhanced the in vitro osteogenic capacity of hASCs. However, 8 weeks after in vivo implantation, there were no significant differences between hASCs and hASCs that had undergone OI (hASCs+OI) or between purified hASCs and purified hASCs+OI (P>0.05). Interestingly, we also found that purified hASCs had an osteogenic potential similar to that of unpurified hASCs in vitro and in vivo. These results suggest that FCCS and in vitro pre-OI are not requirements for in vivo bone formation by hASCs.
PMCID: PMC3569421  PMID: 23409111
8.  Pericytes Derived from Adipose-Derived Stem Cells Protect against Retinal Vasculopathy 
PLoS ONE  2013;8(5):e65691.
Retinal vasculopathies, including diabetic retinopathy (DR), threaten the vision of over 100 million people. Retinal pericytes are critical for microvascular control, supporting retinal endothelial cells via direct contact and paracrine mechanisms. With pericyte death or loss, endothelial dysfunction ensues, resulting in hypoxic insult, pathologic angiogenesis, and ultimately blindness. Adipose-derived stem cells (ASCs) differentiate into pericytes, suggesting they may be useful as a protective and regenerative cellular therapy for retinal vascular disease. In this study, we examine the ability of ASCs to differentiate into pericytes that can stabilize retinal vessels in multiple pre-clinical models of retinal vasculopathy.
Methodology/Principal Findings
We found that ASCs express pericyte-specific markers in vitro. When injected intravitreally into the murine eye subjected to oxygen-induced retinopathy (OIR), ASCs were capable of migrating to and integrating with the retinal vasculature. Integrated ASCs maintained marker expression and pericyte-like morphology in vivo for at least 2 months. ASCs injected after OIR vessel destabilization and ablation enhanced vessel regrowth (16% reduction in avascular area). ASCs injected intravitreally before OIR vessel destabilization prevented retinal capillary dropout (53% reduction). Treatment of ASCs with transforming growth factor beta (TGF-β1) enhanced hASC pericyte function, in a manner similar to native retinal pericytes, with increased marker expression of smooth muscle actin, cellular contractility, endothelial stabilization, and microvascular protection in OIR. Finally, injected ASCs prevented capillary loss in the diabetic retinopathic Akimba mouse (79% reduction 2 months after injection).
ASC-derived pericytes can integrate with retinal vasculature, adopting both pericyte morphology and marker expression, and provide functional vascular protection in multiple murine models of retinal vasculopathy. The pericyte phenotype demonstrated by ASCs is enhanced with TGF-β1 treatment, as seen with native retinal pericytes. ASCs may represent an innovative cellular therapy for protection against and repair of DR and other retinal vascular diseases.
PMCID: PMC3669216  PMID: 23741506
9.  The Effects of Cyclic Hydrostatic Pressure on Chondrogenesis and Viability of Human Adipose- and Bone Marrow-Derived Mesenchymal Stem Cells in Three-Dimensional Agarose Constructs 
Tissue Engineering. Part A  2012;19(1-2):299-306.
This study investigates the effects of cyclic hydrostatic pressure (CHP) on chondrogenic differentiation of human adipose-derived stem cells (hASCs) in three-dimensional (3-D) agarose constructs maintained in a complete growth medium without soluble chondrogenic inducing factors. hASCs were seeded in 2% agarose hydrogels and exposed to 7.5 MPa CHP for 4 h per day at a frequency of 1 Hz for up to 21 days. On days 0, 7, 14, and 21, the expression levels of collagen II, Sox9, aggrecan, and cartilage oligomeric matrix protein (COMP) were examined by real-time reverse transcriptase–polymerase chain reaction analysis. Gene expression analysis found collagen II mRNA expression in only the CHP-loaded construct at day 14 and at no other time during the study. CHP-loaded hASCs exhibited upregulated mRNA expression of Sox9, aggrecan, and COMP at day 7 relative to unloaded controls, suggesting that CHP initiated chondrogenic differentiation of hASCs in a manner similar to human bone marrow-derived mesenchymal stem cells (hMSC). By day 14, however, loaded hASC constructs exhibited significantly lower mRNA expression of the chondrogenic markers than unloaded controls. Additionally, by day 21, the samples exhibited little measurable mRNA expression at all, suggesting a decreased viability. Histological analysis validated the lack of mRNA expression at day 21 for both the loaded and unloaded control samples with a visible decrease in the cell number and change in morphology. A comparative study with hASCs and hMSCs further examined long-term cell viability in 3-D agarose constructs of both cell types. Decreased cell metabolic activity was observed throughout the 21-day experimental period in both the CHP-loaded and control constructs of both hMSCs and hASCs, suggesting a decrease in cell metabolic activity, alluding to a decrease in cell viability. This suggests that a 2% agarose hydrogel may not optimally support hASC or hMSC viability in a complete growth medium in the absence of soluble chondrogenic inducing factors over long culture durations. This is the first study to examine the ability of mechanical stimuli alone, in the absence of chondrogenic factors transforming growth factor beta (TGF-β)3, TGF-β1 and/or bone morphogenetic protein 6 (BMP6) to induce hASC chondrogenic differentiation. The findings of this study suggest that CHP initiates hASC chondrogenic differentiation, even in the absence of soluble chondrogenic inductive factors, confirming the importance of considering both mechanical stimuli and appropriate 3-D culture for cartilage tissue engineering using hASCs.
PMCID: PMC3530937  PMID: 22871265
10.  Angiopoietin-1-expressing adipose stem cells genetically modified with baculovirus nanocomplex: investigation in rat heart with acute infarction 
The objective of this study was to develop angiopoietin-1 (Ang1)-expressing genetically modified human adipose tissue derived stem cells (hASCs) for myocardial therapy. For this, an efficient gene delivery system using recombinant baculovirus complexed with cell penetrating transactivating transcriptional activator TAT peptide/deoxyribonucleic acid nanoparticles (Bac-NP), through ionic interactions, was used. It was hypothesized that the hybrid Bac- NPAng1 system can efficiently transduce hASCs and induces favorable therapeutic effects when transplanted in vivo. To evaluate this hypothesis, a rat model with acute myocardial infarction and intramyocardially transplanted Ang1-expressing hASCs (hASC-Ang1), genetically modified by Bac-NPAng1, was used. Ang1 is a crucial pro-angiogenic factor for vascular maturation and neovasculogenesis. The released hAng1 from hASC-Ang1 demonstrated profound mitotic and anti-apoptotic activities on endothelial cells and cardiomyocytes. The transplanted hASC-Ang1 group showed higher cell retention compared to hASC and control groups. A significant increase in capillary density and reduction in infarct sizes were noted in the infarcted hearts with hASC-Ang1 treatment compared to infarcted hearts treated with hASC or the untreated group. Furthermore, the hASC-Ang1 group showed significantly higher cardiac performance in echocardiography (ejection fraction 46.28% ± 6.3%, P < 0.001 versus control, n = 8) than the hASC group (36.35% ± 5.7%, P < 0.01, n = 8), 28 days post-infarction. The study identified Bac-NP complex as an advanced gene delivery vehicle for stem cells and demonstrated its potential to treat ischemic heart disease with high therapeutic index for combined stem cell-gene therapy strategy.
PMCID: PMC3278230  PMID: 22334788
combined stem cell-gene therapy; baculovirus; nanoparticle; myocardial therapy; angiogenesis; tissue engineering
11.  Deleterious Effects of Freezing on Osteogenic Differentiation of Human Adipose-Derived Stromal Cells In Vitro and In Vivo 
Stem Cells and Development  2010;20(3):427-439.
Human adipose-derived stromal cells (hASCs) represent a multipotent stromal cell type with a proven capacity to undergo osteogenic differentiation. Many hurdles exist, however, between current knowledge of hASC osteogenesis and their potential future use in skeletal tissue regeneration. The impact of frozen storage on hASC osteogenic differentiation, for example, has not been studied in detail. To examine the effects of frozen storage, hASCs were harvested from lipoaspirate and either maintained in standard culture conditions or frozen for 2 weeks under standard conditions (90% fetal bovine serum, 10% dimethyl sulfoxide). Next, in vitro parameters of cell morphology (surface electron microscopy [EM]), cell viability and growth (trypan blue; bromodeoxyuridine incorporation), osteogenic differentiation (alkaline phosphatase, alizarin red, and quantitative real-time (RT)–polymerase chain reaction), and adipogenic differentiation (Oil red O staining and quantitative RT–polymerase chain reaction) were performed. Finally, in vivo bone formation was assessed using a critical-sized cranial defect in athymic mice, utilizing a hydroxyapatite (HA)-poly(lactic-co-glycolic acid) scaffold for ASC delivery. Healing was assessed by serial microcomputed tomography scans and histology. Freshly derived ASCs differed significantly from freeze–thaw ASCs in all markers examined. Surface EM showed distinct differences in cellular morphology. Proliferation, and osteogenic and adipogenic differentiation were all significantly hampered by the freeze–thaw process in vitro (*P < 0.01). In vivo, near complete healing was observed among calvarial defects engrafted with fresh hASCs. This was in comparison to groups engrafted with freeze–thaw hASCs that showed little healing (*P < 0.01). Finally, recombinant insulin-like growth factor 1 or recombinant bone morphogenetic protein 4 was observed to increase or rescue in vitro osteogenic differentiation among frozen hASCs (*P < 0.01). The freezing of ASCs for storage significantly impacts their biology, both in vitro and in vivo. The ability of ASCs to successfully undergo osteogenic differentiation after freeze–thaw is substantively muted, both in vitro and in vivo. The use of recombinant proteins, however, may be used to mitigate the deleterious effects of the freeze–thaw process.
PMCID: PMC3128779  PMID: 20536327
12.  Acute Skeletal Injury is Necessary for Human Adipose-Derived Stromal Cell Mediated Calvarial Regeneration 
Plastic and reconstructive surgery  2011;127(3):1118-1129.
Studies have demonstrated that human adipose derived stromal cells (hASCs) are able to repair acute calvarial injuries. However, the more clinically relevant repair of an established skeletal defect has not been addressed. We sought to determine whether hASCs could heal chronic (established) calvarial defects.
Critical-sized (4mm) mouse parietal defects were created. hASCs were either engrafted immediately postoperatively (acute defect), or 8 weeks following defect creation (established defect). Methods of analysis included microCT scans, histology, and in situ hybridization. Finally, hASCs were treated in vitro with PRP to simulate an acute wound environment; proliferation and osteogenic differentiation were assessed (Alkaline phosphatase, Alizarin red, and qRT-PCR).
Near complete osseous healing was observed when calvarial defects were immediately engrafted with hASCs. In contrast, when hASCs were engrafted into established defects, little bone formation occurred. Histological analysis affirmed findings by microCT, showing more robust staining for alkaline phosphatase and picrosirius red in an acute than in a established hASC engrafted defect. In situ hybridization and qRT PCR showed an increase in BMP expression (Bmp2, Bmp4 and Bmp7) acutely following calvarial defect creation. Finally, in vitro treatment of hASCs with PRP enhanced osteogenic differentiation and increased Bmp2 expression.
While hASCs can be utilized to heal an acute mouse calvarial defect, hASCs do not enhance healing of an established (or chronic) defect. Endogenous BMP signaling activated post-injury may explain these differences in healing. Platelet rich plasma enhances osteogenic differentiation of hASCs in vitro and may prove a promising therapy for future skeletal tissue engineering efforts.
PMCID: PMC3073240  PMID: 21364415
Osteogenesis; Adipose derived mesenchymal cells; Multipotent stromal cells; Platelet rich plasma, Bone morphogenetic protein, Adult Stem Cells
13.  Locally applied VEGFA increases the osteogenic healing capacity of human adipose derived stem cells by promoting osteogenic and endothelial differentiation 
Stem Cells (Dayton, Ohio)  2011;29(2):286-296.
Human adipose derived stem cells (hASCs) are known for their capability to promote bone healing when applied to bone defects. For bone tissue regeneration, both sufficient angiogenesis and osteogenesis is desirable. Vascular endothelial growth factor A (VEGFA) has the potential to promote differentiation of common progenitor cells to both lineages. To test this hypothesis, the effects of VEGFA on hASCs during osteogenic differentiation were tested in vitro. In addition, hASCs were seeded in murine critical-sized calvarial defects locally treated with VEGFA. Our results suggest that VEGFA improves osteogenic differentiation in vitro as indicated by alkaline phosphatase activity, alizarin red staining, and QRT-PCR analysis. Moreover, local application of VEGFA to hASCs significantly improved healing of critical sized calvarial defects in vivo. This repair was accompanied by a striking enhancement of angiogenesis. Both paracrine and, to a lesser degree, cell-autonomous effects of VEGFA treated hASCs were accountable for angiogenesis. These data were confirmed by utilization of CD31-/CD45- mouse ASCsGFP+ cells. In summary, we demonstrated that VEGFA increased osteogenic differentiation of hASCS in vitro and in vivo, which was accompanied by an enhancement of angiogenesis. Additionally, we showed that during bone regeneration, the increase in angiogenesis of hASCs upon treatment with VEGFA was attributable to both paracrine and cell-autonomous effects. Thus, locally applied VEGFA might prove to be a valuable growth factor that can mediate both osteogenesis and angiogenesis of multipotent hASCs in the context of bone regeneration.
PMCID: PMC3400547  PMID: 21732486
VEGFA; Bone Regeneration; Angiogenesis; Endothel; Calvaria
14.  Regulation of Human Adipose-Derived Stromal Cell Osteogenic Differentiation by Insulin-like Growth Factor-1 and Platelet-Derived Growth Factor-Alpha 
Human adipose-derived stromal cells (hASCs) possess a great potential for tissue engineering purposes. Our laboratory is interested in harnessing hASCs for skeletal tissue regeneration and identifying those factors that enhance hASC osteogenic differentiation. We hypothesized that Insulin-Like Growth Factor (IGF) and Platelet Derived Growth Factor (PDGF) would stimulate hASC osteogenesis and that IGF would stimulate adipogenesis.
Materials and Methods
ASCs were harvested from human lipoaspirate. Previously, a microarray analysis examined gene expression throughout osteogenic differentiation. In a candidate fashion we added recombinant Insulin-Like Growth Factor (IGF-1) and Platelet-Derived Growth Factor (PDGF)-α individually as well as in combination. Osteogenesis and adipogenesis were assessed by alkaline phosphatase, Alizarin red, and Oil red O staining, as well as qRT-PCR (RUNX2, ALP, OCN, IGF1, PPARG, LPL, AP2, GCP1). Finally, intersection between IGF and PDGF signaling pathways was evaluated.
IGF-1 was observed to increase osteogenic differentiation by all markers (*p<0.01). However, PDGF-α when added alone primarily did not effect osteogenic markers. PDGF-α positively regulated transcription of IGF1. Addition of PDGF-α in combination with or prior to IGF-1 enhanced osteogenesis more than either alone. IGF-1 increased while PDGF-α diminished hASC adipogenesis.
IGF signaling significantly increased osteogenesis in human ASCs and may be used for tissue engineering purposes. The combination of PDGF and IGF may be more beneficial than either alone in driving ASC osteogenesis. Future in vivo applications will focus on the combination of ASCs, biomimetic scaffolds and recombinant IGF.
PMCID: PMC3016898  PMID: 20220555
Adipose derived stromal cells; Skeletal tissue engineering; Tissue regeneration; Multipotent stromal cells; IGF; PDGF
15.  Primary Cilia: The Chemical Antenna Regulating Human Adipose-Derived Stem Cell Osteogenesis 
PLoS ONE  2013;8(5):e62554.
Adipose-derived stem cells (ASC) are multipotent stem cells that show great potential as a cell source for osteogenic tissue replacements and it is critical to understand the underlying mechanisms of lineage specification. Here we explore the role of primary cilia in human ASC (hASC) differentiation. This study focuses on the chemosensitivity of the primary cilium and the action of its associated proteins: polycystin-1 (PC1), polycystin-2 (PC2) and intraflagellar transport protein-88 (IFT88), in hASC osteogenesis. To elucidate cilia-mediated mechanisms of hASC differentiation, siRNA knockdown of PC1, PC2 and IFT88 was performed to disrupt cilia-associated protein function. Immunostaining of the primary cilium structure indicated phenotypic-dependent changes in cilia morphology. hASC cultured in osteogenic differentiation media yielded cilia of a more elongated conformation than those cultured in expansion media, indicating cilia-sensitivity to the chemical environment and a relationship between the cilium structure and phenotypic determination. Abrogation of PC1, PC2 and IFT88 effected changes in both hASC proliferation and differentiation activity, as measured through proliferative activity, expression of osteogenic gene markers, calcium accretion and endogenous alkaline phosphatase activity. Results indicated that IFT88 may be an early mediator of the hASC differentiation process with its knockdown increasing hASC proliferation and decreasing Runx2, alkaline phosphatase and BMP-2 mRNA expression. PC1 and PC2 knockdown affected later osteogenic gene and end-product expression. PC1 knockdown resulted in downregulation of alkaline phosphatase and osteocalcin gene expression, diminished calcium accretion and reduced alkaline phosphatase enzymatic activity. Taken together our results indicate that the structure of the primary cilium is intimately associated with the process of hASC osteogenic differentiation and that its associated proteins are critical players in this process. Elucidating the dynamic role of the primary cilium and its associated proteins will help advance the application of hASC in generating autologous tissue engineered therapies in critical defect bone injuries.
PMCID: PMC3656889  PMID: 23690943
16.  Endothelial Differentiation of Human Stem Cells Seeded onto Electrospun Polyhydroxybutyrate/Polyhydroxybutyrate-Co-Hydroxyvalerate Fiber Mesh 
PLoS ONE  2012;7(4):e35422.
Tissue engineering is based on the association of cultured cells with structural matrices and the incorporation of signaling molecules for inducing tissue regeneration. Despite its enormous potential, tissue engineering faces a major challenge concerning the maintenance of cell viability after the implantation of the constructs. The lack of a functional vasculature within the implant compromises the delivery of nutrients to and removal of metabolites from the cells, which can lead to implant failure. In this sense, our investigation aims to develop a new strategy for enhancing vascularization in tissue engineering constructs. This study's aim was to establish a culture of human adipose tissue-derived stem cells (hASCs) to evaluate the biocompatibility of electrospun fiber mesh made of polyhydroxybutyrate (PHB) and its copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-HV) and to promote the differentiation of hASCs into the endothelial lineage. Fiber mesh was produced by blending 30% PHB with 70% PHB-HV and its physical characterization was conducted using scanning electron microscopy analysis (SEM). Using electrospinning, fiber mesh was obtained with diameters ranging 300 nm to 1.3 µm. To assess the biological performance, hASCs were extracted, cultured, characterized by flow cytometry, expanded and seeded onto electrospun PHB/PHB-HV fiber mesh. Various aspects of the cells were analyzed in vitro using SEM, MTT assay and Calcein-AM staining. The in vitro evaluation demonstrated good adhesion and a normal morphology of the hASCs. After 7, 14 and 21 days of seeding hASCs onto electrospun PHB/PHB-HV fiber mesh, the cells remained viable and proliferative. Moreover, when cultured with endothelial differentiation medium (i.e., medium containing VEGF and bFGF), the hASCs expressed endothelial markers such as VE-Cadherin and the vWF factor. Therefore, the electrospun PHB/PHB-HV fiber mesh appears to be a suitable material that can be used in combination with endothelial-differentiated cells to improve vascularization in engineered bone tissues.
PMCID: PMC3327675  PMID: 22523594
17.  Ovarian cancer-derived lysophosphatidic acid stimulates secretion of VEGF and stromal cell-derived factor-1α from human mesenchymal stem cells 
Experimental & Molecular Medicine  2010;42(4):280-293.
Lysophosphatidic acid (LPA) stimulates growth and invasion of ovarian cancer cells and tumor angiogenesis. Cancer-derived LPA induces differentiation of human adipose tissue-derived mesenchymal stem cells (hASCs) to α-smooth muscle actin (α-SMA)-positive cancer-associated fibroblasts. Presently, we explored whether cancer-derived LPA regulates secretion of pro-angiogenic factors from hASCs. Conditioned medium (CM) from the OVCAR-3 and SKOV3 ovarian cancer cell lines stimulated secretion angiogenic factors such as stromal-derived factor-1α (SDF-1α) and VEGF from hASCs. Pretreatment with the LPA receptor inhibitor Ki16425 or short hairpin RNA lentiviral silencing of the LPA1 receptor abrogated the cancer CM-stimulated expression of α-SMA, SDF-1, and VEGF from hASCs. LPA induced expression of myocardin and myocardin-related transcription factor-A, transcription factors involved in smooth muscle differentiation, in hASCs. siRNA-mediated depletion of endogenous myocardin and MRTF-A abrogated the expression of α-SMA, but not SDF-1 and VEGF. LPA activated RhoA in hASCs and pretreatment with the Rho kinase inhibitor Y27632 completely abrogated the LPA-induced expression of α-SMA, SDF-1, and VEGF in hASCs. Moreover, LPA-induced α-SMA expression was abrogated by treatment with the ERK inhibitor U0126 or the phosphoinositide-3-kinase inhibitor LY294002, but not the PLC inhibitor U73122. LPA-induced VEGF secretion was inhibited by LY294002, whereas LPA-induced SDF-1 secretion was markedly attenuated by U0126, U73122, and LY294002. These results suggest that cancer-secreted LPA induces differentiation of hASCs to cancer-associated fibroblasts through multiple signaling pathways involving Rho kinase, ERK, PLC, and phosphoinositide-3-kinase.
PMCID: PMC2859327  PMID: 20177148
carcinoma; fibroblasts; lysophosphatidic acid; ovarian neoplasms; receptors, lysophosphatidic acid; rho-associated kinases; vascular endothelial growth factor A
18.  Proteomic Identification of ADAM12 as a Regulator for TGF-β1-Induced Differentiation of Human Mesenchymal Stem Cells to Smooth Muscle Cells 
PLoS ONE  2012;7(7):e40820.
Transforming growth factor-β1 (TGF-β1) induces the differentiation of human adipose tissue-derived mesenchymal stem cells (hASCs) into smooth muscle cells. Lipid rafts are cholesterol-rich microdomains in cell membranes that reportedly play a key role in receptor-mediated signal transduction and cellular responses. In order to clarify whether lipid rafts are involved in TGF-β1-induced differentiation of hASCs into smooth muscle cells, we analyzed the lipid raft proteome of hASCs.
Methods and Results
Pretreatment of hASCs with the lipid raft disruptor methyl-β-cyclodextrin abrogated TGF-β1-induced expression of α-smooth muscle actin, a smooth muscle cell marker, suggesting a pivotal role of lipid rafts in TGF-β1-induced differentiation of hASCs to smooth muscle cells. Sucrose density gradient centrifugation along with a shotgun proteomic strategy using liquid chromatography-tandem mass spectrometry identified 1002 individual proteins as the lipid raft proteome, and 242 of these were induced by TGF-β1 treatment. ADAM12, a disintegrin and metalloproteases family member, was identified as the most highly up-regulated protein in response to TGF-β1 treatment. TGF-β1 treatment of hASCs stimulated the production of both ADAM12 protein and mRNA. Silencing of endogenous ADAM12 expression using lentiviral small hairpin RNA or small interfering RNA abrogated the TGF-β1-induced differentiation of hASCs into smooth muscle cells.
These results suggest a pivotal role for lipid raft-associated ADAM12 in the TGF-β1-induced differentiation of hASCs into smooth muscle cells.
PMCID: PMC3396647  PMID: 22808268
19.  Human Adipose Derived Stromal Cells Heal Critical Size Mouse Calvarial Defects 
PLoS ONE  2010;5(6):e11177.
Human adipose-derived stromal cells (hASCs) represent a multipotent cell stromal cell type with proven capacity to differentiate along an osteogenic lineage. This suggests that they may be used to heal defects of the craniofacial or appendicular skeleton. We sought to substantiate the use of undifferentiated hASCs in the regeneration of a non-healing mouse skeletal defect.
Methodology/Principal Findings
Human ASCs were harvested from female lipoaspirate. Critical-sized (4 mm) calvarial defects were created in the parietal bone of adult male nude mice. Defects were either left empty, treated with an apatite coated PLGA scaffold alone, or a scaffold with human ASCs. MicroCT scans were obtained at stratified time points post-injury. Histology, in situ hybridization, and histomorphometry were performed. Near complete healing was observed among hASC engrafted calvarial defects. This was in comparison to control groups that showed little healing (*P<0.01). Human ASCs once engrafted differentiate down an osteogenic lineage, determined by qRT-PCR and histological co-expression assays using GFP labeled cells. ASCs were shown to persist within a defect site for two weeks (shown by sex chromosome analysis and quantified using Luciferase+ ASCs). Finally, rBMP-2 was observed to increase hASC osteogenesis in vitro and osseous healing in vivo.
Human ASCs ossify critical sized mouse calvarial defects without the need for pre-differentiation. Recombinant differentiation factors such as BMP-2 may be used to supplement hASC mediated repair. Interestingly, ASC presence gradually dissipates from the calvarial defect site. This study supports the potential translation for ASC use in the treatment of human skeletal defects.
PMCID: PMC2887361  PMID: 20567510
20.  Adipogenic Human Adenovirus Ad-36 Induces Commitment, Differentiation, and Lipid Accumulation in Human Adipose-Derived Stem Cells 
Stem cells (Dayton, Ohio)  2008;26(4):969-978.
Human adenovirus Ad-36 is causatively and correlatively linked with animal and human obesity, respectively. Ad-36 enhances differentiation of rodent preadipocytes, but its effect on adipogenesis in humans is unknown. To indirectly assess the role of Ad-36-induced adipogenesis in human obesity, the effect of the virus on commitment, differentiation, and lipid accumulation was investigated in vitro in primary human adipose-derived stem/stromal cells (hASC). Ad-36 infected hASC in a time- and dose-dependent manner. Even in the presence of osteogenic media, Ad-36-infected hASC showed significantly greater lipid accumulation, suggestive of their commitment to the adipocyte lineage. Even in the absence of adipogenic inducers, Ad-36 significantly increased hASC differentiation, as indicated by a time-dependent expression of genes within the adipogenic cascade—CCAAT/Enhancer binding protein-β, peroxisome proliferator-activated receptor-γ, and fatty acid-binding protein—and consequentially increased lipid accumulation in a time- and viral dose-dependent manner. Induction of hASC to the adipocyte state by Ad-36 was further supported by increased expression of lipoprotein lipase and the accumulation of its extracellular fraction. hASC from subjects harboring Ad-36 DNA in their adipose tissue due to natural infection had significantly greater ability to differentiate compared with Ad-36 DNA-negative counterparts, which offers a proof of concept. Thus, Ad-36 has the potential to induce adipogenesis in hASC, which may contribute to adiposity induced by the virus.
PMCID: PMC2747294  PMID: 18203674
Obesity; Adiposity; Adipogenesis; Infectobesity; Lipogenesis; Adipocyte progenitors
21.  Systemic Administration of Human Adipose-Derived Stem Cells Reverts Nociceptive Hypersensitivity in an Experimental Model of Neuropathy 
Stem Cells and Development  2012;22(8):1252-1263.
Over the last decade, it has been proved that mesenchymal stem cells (MSCs) elicit anti-inflammatory effects. MSCs from adipose tissue (hASCs) differentiate into cells of the mesodermal lineage and transdifferentiate into ectodermal-origin cells. Although there are various etiologies to chronic pain, one common feature is that painful states are associated with increased inflammation. We believe in hASCs as a therapeutic tool also in pathologies involving neuroinflammation and neuronal tissue damage. We have investigated the effect of hASCs injected in a model of neuropathic pain [(mouse sciatic nerve chronic constriction injury (CCI)]. hASCs from 5 donors were characterized, and no major differences were depicted. hASCs were cryopreserved and grown on demand. About 1×106, 3×106, and 6×106 hASCs were intravenously injected into normal immunocompetent mice. No mouse died, and no macroscopic toxicity or behavioral changes were observed, confirming the safety of hASCs. hASCs, intravenously (i.v.) injected into C57BL/6 mice when the neuropathic pain was already established, induced a significant reduction in mechanical allodynia and a complete reversion of thermal hyperalgesia in a dose–response fashion, already 1 day after administration. Moreover, the hASCs effect can be boosted by repeated administrations, allowing a prolonged therapeutic effect. Treatment decreased the level of the CCI-induced proinflammatory cytokine interleukin (IL)-1β and activated the anti-inflammatory cytokine IL-10 in the lesioned nerve. hASCs treatment also restored normal inducible nitric oxide synthase expression in the spinal cord of CCI animals. Our data suggest that hASCs are worthy of further studies as an anti-inflammatory therapy in the treatment of neuropathic pain or chronic inflammatory diseases.
PMCID: PMC3613970  PMID: 23190263
22.  Differentiation of Human Adipose-derived Stem Cells along the Keratocyte Lineage In vitro 
To evaluate differentiation of human adipose-derived stem cells (hASCs) to the keratocyte lineage by co-culture with primary keratocytes in vitro.
Materials and Methods
A co-culture system using transwell inserts to grow hASCs on bottom and keratocytes on top in keratocyte differentiating medium (KDM) was developed. hASCs that were cultured in complete culture medium (CCM) and KDM were used as control. After 16 days, hASCs were examined for morphologic changes and proliferation by cell count. qRT-PCR and flow cytometry were used to detect the expression of aldehyde dehydrogenase 3 family, member A1 (ALDH3A1) and keratocan.
hASCs became more dendritic and elongated in co-culture system relative to CCM and KDM. The doubling time of the cells was longer as differentiation progressed. qRT-PCR showed a definite trend towards increased expression of both ALDH3A1 and keratocan in co-culture system despite statistically non-significant p-values. Flow cytometry showed significantly increased protein levels of ALDH3A1 and keratocan in co-culture system relative to CCM group (p < 0.001) and even relative to KDM group (p < 0.001 for ALDH3A1 and p < 0.01 for keratocan).
The co-culture method is a promising approach to induce differentiation of stem cell populations prior to in vivo applications. This study reveals an important potential for bioengineering of corneal tissue using autologous multi-potential stem cells.
PMCID: PMC3737075  PMID: 23936748
Human adipose-derived stem cells; Co-culture system; Keratocyte; Bioengineered cornea
23.  Functional Binding of Human Adipose-Derived Stromal Cells: Effects of Extraction Method & Hypoxia Pretreatment 
Annals of plastic surgery  2008;60(4):437-444.
Human adipose-derived stromal cells (hASCs) were evaluated in vitro for their ability to bind vascular adhesion and extracellular matrix proteins in order to arrest (firmly adhere) under physiological flow conditions. hASCs were flowed through a parallel plate flow chamber containing substrates presenting immobilized Type I Collagen, fibronectin, E-selectin, L-selectin, P-selectin, vascular cell adhesion molecule-1 (VCAM-1), or intercellular adhesion molecule-1 (ICAM-1) under static and laminar flow conditions (wall shear stress = 1 dyn/cm2). hASCs were able to firmly adhere to Type I Collagen, fibronectin, VCAM-1, and ICAM-1 substrates, but not to any of the selectins. Pretreatment with hypoxia increased the ability of hASCs isolated by liposuction to adhere to VCAM-1 and ICAM-1, but this effect was not seen in cells isolated by tissue excision. These results indicate that hASCs possess the ability to adhere key adhesion proteins, illustrate the importance of hASC harvest procedure, and suggest mechanisms for homing in a setting where interaction with inflamed or injured tissue is necessary.
PMCID: PMC2829884  PMID: 18362576
Adipose-derived stromal cells; hypoxia; liposuction; parallel plate flow chamber; adhesion cascade
24.  Elastic Properties of Induced Pluripotent Stem Cells 
Tissue Engineering. Part A  2010;17(3-4):495-502.
The recent technique of transducing key transcription factors into unipotent cells (fibroblasts) to generate pluripotent stem cells (induced pluripotent stem cells [iPSCs]) has significantly changed the stem cell field. These cells have great promise for many clinical applications, including that of regenerative medicine. Our findings show that iPSCs can be derived from human adipose-derived stromal cells (hASCs), a notable advancement in the clinical applicability of these cells. To investigate differences between two iPS cell lines (fibroblast-iPSC and hASC-iPSC), and also the gold standard human embryonic stem cell, we looked at cell stiffness as a possible indicator of cell differentiation-potential differences. We used atomic force microscopy as a tool to determine stem cell stiffness, and hence differences in material properties between cells. Human fibroblast and hASC stiffness was also ascertained for comparison. Interestingly, cells exhibited a noticeable difference in stiffness. From least to most stiff, the order of cell stiffness was as follows: hASC-iPSC, human embryonic stem cell, fibroblast-iPSC, fibroblasts, and, lastly, as the stiffest cell, hASC. In comparing hASC-iPSCs to their origin cell, the hASC, the reprogrammed cell is significantly less stiff, indicating that greater differentiation potentials may correlate with a lower cellular modulus. The stiffness differences are not dependent on cell culture density; hence, material differences between cells cannot be attributed solely to cell–cell constraints. The change in mechanical properties of the cells in response to reprogramming offers insight into how the cell interacts with its environment and might lend clues to how to efficiently reprogram cell populations as well as how to maintain their pluripotent state.
PMCID: PMC3052278  PMID: 20807017
25.  Survival and Biodistribution of Xenogenic Adipose Mesenchymal Stem Cells Is Not Affected by the Degree of Inflammation in Arthritis 
PLoS ONE  2015;10(1):e0114962.
Application of mesenchymal stem/stromal cells (MSCs) in treating different disorders, in particular osteo-articular diseases, is currently under investigation. We have already documented the safety of administrating human adipose tissue-derived stromal MSCs (hASCs) in immunodeficient mice. In the present study, we investigated whether the persistence of MSC is affected by the degree of inflammation and related to the therapeutic effect in two inflammatory models of arthritis.
Methodology/Principal Findings
We used C57BL/6 or DBA/1 mice to develop collagenase-induced osteoarthritis (CIOA) or collagen-induced arthritis (CIA), respectively. Normal and diseased mice were administered 2.5×105 hASCs in the knee joints (IA) or 106 in the tail vein (IV). For CIA, clinical scores were monitored during the time course of the disease while for CIOA, OA scores were assessed by histology at euthanasia. Thirteen tissues were recovered at different time points and processed for real-time PCR and Alu sequence detection. Immunological analyses were performed at euthanasia. After IV infusion, no significant difference in the percentage of hASCs was quantified in the lungs of normal and CIA mice at day 1 while no cell was detected at day 10 taking into account the sensitivity of the assay, indicating that a high level of inflammation did not affect the persistence of cells. In CIOA mice, we reported the therapeutic efficacy of hASCs at reducing OA clinical scores at day 42 when hASCs were not detected in the joints. However, the percentage and distribution of hASCs were similar in osteoarthritic and normal mice at day 1 and 10 after implantation indicating that moderate inflammation does not alter hASC persistence in vivo.
While inflammatory signals are required for the immunosuppressive function of MSCs, they do not enhance their capacity to survive in vivo, as evaluated in two xenogeneic inflammatory pre-clinical models of arthritis.
PMCID: PMC4283953  PMID: 25559623

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