Liver specification of human iPSC-derived endothelial cells transplanted into mouse liver.

Background & Aims: Liver sinusoidal endothelial cells (LSECs) are important in liver development, regeneration, and pathophysiology, but the differentiation process underlying their tissue-specific phenotype is poorly understood and difficult to study because primary human cells are scarce. The aim of this study was to use human induced pluripotent stem cell (hiPSC)-derived LSEC-like cells to investigate the differentiation process of LSECs. Methods: hiPSC-derived endothelial cells (iECs) were transplanted into the livers of Fah-/-/Rag2-/-/Il2rg-/- mice and assessed over a 12-week period. Lineage tracing, immunofluorescence, flow cytometry, plasma human factor VIII measurement, and bulk and single cell transcriptomic analysis were used to assess the molecular and functional changes that occurred following transplantation. Results: Progressive and long-term repopulation of the liver vasculature occurred as iECs expanded along the sinusoids between hepatocytes and increasingly produced human factor VIII, indicating differentiation into LSEC-like cells. To chart the developmental profile associated with LSEC specification, the bulk transcriptomes of transplanted cells between 1 and 12 weeks after transplantation were compared against primary human adult LSECs. This demonstrated a chronological increase in LSEC markers, LSEC differentiation pathways, and zonation. Bulk transcriptome analysis suggested that the transcription factors NOTCH1, GATA4, and FOS have a central role in LSEC specification, interacting with a network of 27 transcription factors. Novel markers associated with this process included EMCN and CLEC14A. Additionally, single cell transcriptomic analysis demonstrated that transplanted iECs at 4 weeks contained zonal subpopulations with a region-specific phenotype. Conclusions: Collectively, this study confirms that hiPSCs can adopt LSEC-like features and provides insight into LSEC specification. This humanised xenograft system can be applied to further interrogate LSEC developmental biology and pathophysiology, bypassing current logistical obstacles associated with primary human LSECs. Impact and implications: Liver sinusoidal endothelial cells (LSECs) are important cells for liver biology, but better model systems are required to study them. We present a pluripotent stem cell xenografting model that produces human LSEC-like cells. A detailed and longitudinal transcriptomic analysis of the development of LSEC-like cells is included, which will guide future studies to interrogate LSEC biology and produce LSEC-like cells that could be used for regenerative medicine.

PI(4,5)P2-dependent regulation of endothelial tip cell specification contributes to angiogenesis.

Dynamic positioning of endothelial tip and stalk cells, via the interplay between VEGFR2 and NOTCH signaling, is essential for angiogenesis. VEGFR2 activates PI3K, which phosphorylates PI(4,5)P2 to PI(3,4,5)P3, activating AKT; however, PI3K/AKT does not direct tip cell specification. We report that PI(4,5)P2 hydrolysis by the phosphoinositide-5-phosphatase, INPP5K, contributes to angiogenesis. INPP5K ablation disrupted tip cell specification and impaired embryonic angiogenesis associated with enhanced DLL4/NOTCH signaling. INPP5K degraded a pool of PI(4,5)P2 generated by PIP5K1C phosphorylation of PI(4)P in endothelial cells. INPP5K ablation increased PI(4,5)P2, thereby releasing ß-catenin from the plasma membrane, and concurrently increased PI(3,4,5)P3-dependent AKT activation, conditions that licensed DLL4/NOTCH transcription. Suppression of PI(4,5)P2 in INPP5K-siRNA cells by PIP5K1C-siRNA, restored ß-catenin membrane localization and normalized AKT signaling. Pharmacological NOTCH or AKT inhibition in vivo or genetic ß-catenin attenuation rescued angiogenesis defects in INPP5K-null mice. Therefore, PI(4,5)P2 is critical for ß-catenin/DLL4/NOTCH signaling, which governs tip cell specification during angiogenesis.

Engineering transplantable human lymphatic and blood capillary networks in a porous scaffold.

Due to a relative paucity of studies on human lymphatic assembly in vitro and subsequent in vivo transplantation, capillary formation and survival of primary human lymphatic (hLEC) and blood endothelial cells (hBEC) ± primary human vascular smooth muscle cells (hvSMC) were evaluated and compared in vitro and in vivo. hLEC ± hvSMC or hBEC ± hvSMC were seeded in a 3D porous scaffold in vitro, and capillary percent vascular volume (PVV) and vascular density (VD)/mm2 assessed. Scaffolds were also transplanted into a sub-cutaneous rat wound with morphology/morphometry assessment. Initially hBEC formed a larger vessel network in vitro than hLEC, with interconnected capillaries evident at 2 days. Interconnected lymphatic capillaries were slower (3 days) to assemble. hLEC capillaries demonstrated a significant overall increase in PVV (p = 0.0083) and VD (p = 0.0039) in vitro when co-cultured with hvSMC. A similar increase did not occur for hBEC + hvSMC in vitro, but hBEC + hvSMC in vivo significantly increased PVV (p = 0.0035) and VD (p = 0.0087). Morphology/morphometry established that hLEC vessels maintained distinct cell markers, and demonstrated significantly increased individual vessel and network size, and longer survival than hBEC capillaries in vivo, and established inosculation with rat lymphatics, with evidence of lymphatic function. The porous polyurethane scaffold provided advantages to capillary network formation due to its large (300-600 µm diameter) interconnected pores, and sufficient stability to ensure successful surgical transplantation in vivo. Given their successful survival and function in vivo within the porous scaffold, in vitro assembled hLEC networks using this method are potentially applicable to clinical scenarios requiring replacement of dysfunctional or absent lymphatic networks.

Liver sinusoidal endothelial cells promote the differentiation and survival of mouse vascularised hepatobiliary organoids.

The structural and physiological complexity of currently available liver organoids is limited, thereby reducing their relevance for drug studies, disease modelling, and regenerative therapy. In this study we combined mouse liver progenitor cells (LPCs) with mouse liver sinusoidal endothelial cells (LSECs) to generate hepatobiliary organoids with liver-specific vasculature. Organoids consisting of 5x103 cells were created from either LPCs, or a 1:1 combination of LPC/LSECs. LPC organoids demonstrated mild hepatobiliary differentiation in vitro with minimal morphological change; in contrast LPC/LSEC organoids developed clusters of polygonal hepatocyte-like cells and biliary ducts over a 7 day period. Hepatic (albumin, CPS1, CYP3A11) and biliary (GGT1) genes were significantly upregulated in LPC/LSEC organoids compared to LPC organoids over 7 days, as was albumin secretion. LPC/LSEC organoids also had significantly higher in vitro viability compared to LPC organoids. LPC and LPC/LSEC organoids were transplanted into vascularised chambers created in Fah-/-/Rag2-/-/Il2rg-/- mice (50 LPC organoids, containing 2.5x105 LPCs, and 100 LPC/LSEC organoids, containing 2.5x105 LPCs). At 2 weeks, minimal LPCs survived in chambers with LPC organoids, but robust hepatobiliary ductular tissue was present in LPC/LSEC organoids. Morphometric analysis demonstrated a 115-fold increase in HNF4α+ cells in LPC/LSEC organoid chambers (17.26 ± 4.34 cells/mm2 vs 0.15 ± 0.15 cells/mm2, p = 0.018), and 42-fold increase in Sox9+ cells in LPC/LSEC organoid chambers (28.29 ± 6.05 cells/mm2 vs 0.67 ± 0.67 cells/mm2, p = 0.011). This study presents a novel method to develop vascularised hepatobiliary organoids, with both in vitro and in vivo results confirming that incorporating LSECs with LPCs into organoids significantly increases the differentiation of hepatobiliary tissue within organoids and their survival post-transplantation.

Vascular Pedicle and Microchannels: Simple Methods Toward Effective In Vivo Vascularization of 3D Scaffolds.

Poor vascularization remains a key limiting factor in translating advances in tissue engineering to clinical applications. Vascular pedicles (large arteries and veins) isolated in plastic chambers are known to sprout an extensive capillary network. This study examined the effect vascular pedicles and scaffold architecture have on vascularization and tissue integration of implanted silk scaffolds. Porous silk scaffolds with or without microchannels are manufactured to support implantation of a central vascular pedicle, without a chamber, implanted in the groin of Sprague Dawley rats, and assessed morphologically and morphometrically at 2 and 6 weeks. At both time points, blood vessels, connective tissue, and an inflammatory response infiltrate all scaffold pores externally, and centrally when a vascular pedicle is implanted. At week 2, vascular pedicles significantly increase the degree of scaffold tissue infiltration, and both the pedicle and the scaffold microchannels significantly increase vascular volume and vascular density. Interestingly, microchannels contribute to increased scaffold vascularity without affecting overall tissue infiltration, suggesting a direct effect of biomaterial architecture on vascularization. The inclusion of pedicles and microchannels are simple and effective proangiogenic techniques for engineering thick tissue constructs as both increase the speed of construct vascularization in the early weeks post in vivo implantation.

Bio-engineering a tissue flap utilizing a porous scaffold incorporating a human induced pluripotent stem cell-derived endothelial cell capillary network connected to a vascular pedicle.

Tissue flaps are used to cover large/poorly healing wounds, but involve complex surgery and donor site morbidity. In this study a tissue flap is assembled using the mammalian body as a bioreactor to functionally connect an artery and vein to a human capillary network assembled from induced pluripotent stem cell-derived endothelial cells (hiPSC ECs). In vitro: Porous NovoSorb™ scaffolds (3 mm × 1.35 mm) were seeded with 200,000 hiPSC ECs ±â€¯100,000 human vascular smooth muscle cells (hvSMC), and cultured for 1-3 days, with capillaries formed by 24 h which were CD31+, VE-Cadherin+, EphB4+, VEGFR2+ and Ki67+, whilst hvSMCs (calponin+) attached abluminally. In vivo: In SCID mice, bi-lateral epigastric vascular pedicles were isolated in a silicone chamber for a 3 week 'delay period' for pedicle capillary sprouting, then reopened, and two hiPSC EC ±â€¯hvSMCs seeded scaffolds transplanted over the pedicle. The chamber was either resealed (Group 1), or removed and surrounding tissue secured around the pedicle + scaffolds (Group 2), for 1 or 2 weeks. Human capillaries survived in vivo and were CD31+, VE-Cadherin+ and VEGFR2+. Human vSMCs remained attached, and host mesenchymal cells also attached abluminally. Systemically injected FITC-dextran present in human capillary lumens indicated inosculation to host capillaries. Human iPSC EC capillary morphometric parameters at one week in vivo were equal to or higher than the same parameters measured in human abdominal skin. This 'proof of concept' study has demonstrated that bio-engineering an autologous human tissue flap based on hiPSC EC could minimize the use of donor flaps and has potential applications for complex wound coverage. STATEMENT OF SIGNIFICANCE: Tissue flaps, used for surgical reconstruction of wounds, require complex surgery, often associated with morbidity. Bio-engineering a simpler alternative, we assembled a human induced pluripotent stem cell derived endothelial cell (hiPSC ECs) capillary network in a porous scaffold in vitro, which when transplanted over a mouse vascular pedicle in vivo formed a functional tissue flap with mouse blood flow in the human capillaries. Therefore it is feasible to form an autologous tissue flap derived from a hiPSC EC capillary network assembled in vitro, and functionally connect to a vascular pedicle in vivo that could be utilized in complex wound repair for chronic or acute wounds.

Methods for Assessing Scaffold Vascularization In Vivo.

The success of tissue engineering hinges on the rapid and sufficient vascularization of the neotissue. For efficient vascular network formation within three-dimensional (3D) constructs, biomaterial scaffolds that can support survival of endothelial cells as well as formation and maturation of a capillary network in vivo are highly sought after. Here, we outline a method to biofabricate 3D porous collagen scaffolds that can support extrinsic and intrinsic vascularization using two different in vivo animal models-the mouse subcutaneous implant model (extrinsic vascularization, capillary growth within the scaffold originating from host tissues outside the scaffold) and the rat tissue engineering chamber model (intrinsic vascularization, capillary growth within the scaffold derived from a centrally positioned vascular pedicle). These in vivo vascular tissue engineering approaches hold a great promise for the generation of clinically viable vascularized constructs. Moreover, the 3D collagen scaffolds can also be employed for 3D cell culture and for in vivo delivery of growth factors and cells.

Epigenetic and Transcriptome Profiling Identifies a Population of Visceral Adipose-Derived Progenitor Cells with the Potential to Differentiate into an Endocrine Pancreatic Lineage.

Type 1 diabetes (T1D) is characterized by the loss of insulin-producing ß-cells in the pancreas. T1D can be treated using cadaveric islet transplantation, but this therapy is severely limited by a lack of pancreas donors. To develop an alternative cell source for transplantation therapy, we carried out the epigenetic characterization in nine different adult mouse tissues and identified visceral adipose-derived progenitors as a candidate cell population. Chromatin conformation, assessed using chromatin immunoprecipitation (ChIP) sequencing and validated by ChIP-polymerase chain reaction (PCR) at key endocrine pancreatic gene promoters, revealed similarities between visceral fat and endocrine pancreas. Multiple techniques involving quantitative PCR, in-situ PCR, confocal microscopy, and flow cytometry confirmed the presence of measurable (2-1000-fold over detectable limits) pancreatic gene transcripts and mesenchymal progenitor cell markers (CD73, CD90 and CD105; >98%) in visceral adipose tissue-derived mesenchymal cells (AMCs). The differentiation potential of AMCs was explored in transgenic reporter mice expressing green fluorescent protein (GFP) under the regulation of the Pdx1 (pancreatic and duodenal homeobox-1) gene promoter. GFP expression was measured as an index of Pdx1 promoter activity to optimize culture conditions for endocrine pancreatic differentiation. Differentiated AMCs demonstrated their capacity to induce pancreatic endocrine genes as evidenced by increased GFP expression and validated using TaqMan real-time PCR (at least 2-200-fold relative to undifferentiated AMCs). Human AMCs differentiated using optimized protocols continued to produce insulin following transplantation in NOD/SCID mice. Our studies provide a systematic analysis of potential islet progenitor populations using genome-wide profiling studies and characterize visceral adipose-derived cells for replacement therapy in diabetes.

The Vascularised Chamber as an In Vivo Bioreactor.

Vascularisation is key to developing large transplantable tissue constructs capable of providing therapeutic benefits. The vascularised tissue engineering chamber originates from surgical concepts in tissue prefabrication and microsurgery. It serves as an in vivo bioreactor in the form of a closed, protected space surgically created and embedded within the body by fitting a noncollapsible chamber around major blood vessels. This creates a highly angiogenic environment which facilitates the engraftment and survival of transplanted cells and tissue constructs. This article outlines the chamber concept and explores its application in the context of recent advances in biomedical engineering, and how this can play a role in the future of cell therapies and regenerative medicine.

Melatonin promotes survival of nonvascularized fat grafts and enhances the viability and migration of human adipose-derived stem cells via down-regulation of acute inflammatory cytokines.

Nonvascularized fat grafting is a valuable technique for soft tissue reconstruction but poor survival of fat in the host environment remains a problem. A process known as cell-assisted transfer is used to enhance fat graft retention by adding stromal vascular fraction, an adipose-derived stem cell (ASC) rich content to lipoaspirate. We have recently shown that the use of melatonin, a reactive oxygen species scavenger, protects human ASCs from hydrogen peroxide-induced oxidative stress and cell death in vitro but its role as a pharmacological adjunct in clinical fat grafting has not been studied. Herein, the effect of melatonin was examined on human ASCs in vitro using survival and functional assays including the MTT assay, CellTox Green assay, monolayer scratch assay as well as a human cytokine chemoluminescence, and tumour necrosis factor-α assay. Further, the effect of melatonin-treated fat grafts was tested in vivo with a murine model. Haematoxylin and eosin staining, perilipin and CD31 immunostaining were performed with morphometric analysis of adipose tissue. The results demonstrate that, in vitro, the addition of melatonin to ASCs significantly improved their cell-viability, promoted cell migration and preserved membrane integrity as compared to controls. In addition, it induced a potent anti-inflammatory response by downregulating acute inflammatory cytokines particularly tumour necrosis factor-α. For the first time, it is demonstrated in vivo that melatonin enhances fat graft volume retention by reducing inflammation and increasing the percentage of adipose volume within fat grafts with comparable volumes to that of cell-assisted lipotransfer. Based on these novel findings, melatonin may be a useful pharmacological adjunct in clinical fat grafting.

Indomethacin Enhances Fat Graft Retention by Up-Regulating Adipogenic Genes and Reducing Inflammation.

BACKGROUND: Cell-assisted lipotransfer has been promisingly applied to restore soft-tissue defects in plastic surgery; however, the harvesting of stromal vascular fraction increases morbidity and poses potential safety hazards. The authors investigated whether adding indomethacin, an antiinflammatory proadipogenic drug, to the fat graft at the time of transplantation would enhance the final graft volume compared with cell-assisted lipotransfer. METHODS: In vitro, human adipose-derived stem cells were cultured in conditioned growth media supplemented with various doses of indomethacin to investigate adipogenesis and the expression of the adipogenic genes. In vivo, lipoaspirate mixed with stromal vascular fractions or indomethacin was injected into the dorsum of mice. Tissues were harvested at weeks 2, 4, and 12 to evaluate histologic changes. RESULTS: In vitro, polymerase chain reaction analysis revealed that increased up-regulation of adipogenic genes and activation of the peroxisome proliferator-activated receptor-γ pathway. In vivo, the percentage volume of adipocytes in the indomethacin-assisted groups was higher than that in the lipoaspirate-alone (control) group at 12 weeks (p = 0.016), and was equivalent to the volume in the cell-assisted groups (p = 1.000). Indomethacin improved adipose volumes but had no effect on vascularity. A larger number of small adipocytes appeared in the treatment samples than in the controls at 2 weeks (p = 0.044) and 4 weeks (p = 0.021). CONCLUSIONS: Pretreating lipoaspirate with indomethacin enhances the final volume retention of engrafted fat. This result is explained in part by increased adipogenesis and possibly by the inhibition of inflammatory responses.

An adipogenic gel for surgical reconstruction of the subcutaneous fat layer in a rat model.

'Off-the-shelf' tissue-engineered skin alternatives for epidermal and dermal skin layers are available; however, no such alternative for the subdermal fat layer exists. Without this well-vascularized layer, skin graft take is variable and grafts may have reduced mobility, contracture and contour defects. In this study a novel adipose-derived acellular matrix (Adipogel) was investigated for its properties to generate subdermal fat in a rat model. In a dorsal thoracic site, a 1 × 1 cm Adipogel implant was inserted within a subdermal fat layer defect. In a dorsal lumbar site, an Adipogel implant was inserted in a subfascial pocket. Contralateral control defects remained empty. At 8 weeks wound/implant sites were evaluated histologically, immunohistochemically and morphometrically. Identifiable thoracic Adipogel implants lost volume in vivo over 8 weeks. Neovascularization and adipogenesis were evident within implants and adipocyte percentage volume was 33.07 ± 6.55% (mean ± SEM). A comparison of entire cross-sections of thoracic wounds demonstrated a significant increase in total wound fat in Adipogel-implanted wounds (37.19 ± 4.48%, mean ± SEM) compared to control (16.53 ± 4.60%; p = 0.0092), indicating that some Adipogel had been completely converted to normal fat. At the lumbar site, Adipogel also lost volume, appearing flattened, although fat generation and angiogenesis occurred. At both sites macrophage infiltration was mild, whilst many infiltrating cells were PDGFRß-positive mesenchymal cells. Adipogel is adipogenic and angiogenic and is a promising candidate for subcutaneous fat regeneration; it has the potential to be a valuable adjunct to wound-healing therapy and reconstructive surgery practice. Copyright © 2015 John Wiley & Sons, Ltd.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber.

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

Three Dimensional Collagen Scaffold Promotes Intrinsic Vascularisation for Tissue Engineering Applications.

Here, we describe a porous 3-dimensional collagen scaffold material that supports capillary formation in vitro, and promotes vascularization when implanted in vivo. Collagen scaffolds were synthesized from type I bovine collagen and have a uniform pore size of 80 µm. In vitro, scaffolds seeded with primary human microvascular endothelial cells suspended in human fibrin gel formed CD31 positive capillary-like structures with clear lumens. In vivo, after subcutaneous implantation in mice, cell-free collagen scaffolds were vascularized by host neovessels, whilst a gradual degradation of the scaffold material occurred over 8 weeks. Collagen scaffolds, impregnated with human fibrinogen gel, were implanted subcutaneously inside a chamber enclosing the femoral vessels in rats. Angiogenic sprouts from the femoral vessels invaded throughout the scaffolds and these degraded completely after 4 weeks. Vascular volume of the resulting constructs was greater than the vascular volume of constructs from chambers implanted with fibrinogen gel alone (42.7±5.0 µL in collagen scaffold vs 22.5±2.3 µL in fibrinogen gel alone; p<0.05, n = 7). In the same model, collagen scaffolds seeded with human adipose-derived stem cells (ASCs) produced greater increases in vascular volume than did cell-free collagen scaffolds (42.9±4.0 µL in collagen scaffold with human ASCs vs 25.7±1.9 µL in collagen scaffold alone; p<0.05, n = 4). In summary, these collagen scaffolds are biocompatible and could be used to grow more robust vascularized tissue engineering grafts with improved the survival of implanted cells. Such scaffolds could also be used as an assay model for studies on angiogenesis, 3-dimensional cell culture, and delivery of growth factors and cells in vivo.

Porous PLGA microspheres tailored for dual delivery of biomolecules via layer-by-layer assembly.

Tissue engineering is a complex and dynamic process that requires varied biomolecular cues to promote optimal tissue growth. Consequently, the development of delivery systems capable of sequestering more than one biomolecule with controllable release profiles is a key step in the advancement of this field. This study develops multilayered polyelectrolyte films incorporating alpha-melanocyte stimulating hormone (α-MSH), an anti-inflammatory molecule, and basic fibroblast growth factor (bFGF). The layers were successfully formed on macroporous poly lactic-co-glycolic acid microspheres produced using a combined inkjet and thermally induced phase separation technique. Release profiles could be varied by altering layer properties including the number of layers and concentrations of layering molecules. α-MSH and bFGF were released in a sustained manner and the bioactivity of α-MSH was shown to be preserved using an activated macrophage cell assay in vitro. The system performance was also tested in vivo subcutaneously in rats. The multilayered microspheres reduced the inflammatory response induced by a carrageenan stimulus 6 weeks after implantation compared to the non-layered microspheres without the anti-inflammatory and growth factors, demonstrating the potential of such multilayered constructs for the controlled delivery of bioactive molecules.

Macrophage phenotype in response to implanted synthetic scaffolds: an immunohistochemical study in the rat.

Macrophages predominate among the cells that directly interact with biomaterials and are key orchestrators of host-biomaterial interactions. However, the macrophage response to synthetic scaffolds in particular has not been well studied. The aim of this study was therefore to characterise the macrophage response to several synthetic scaffolds in the rat using immunohistological techniques for a panel of markers of macrophage subclass or activation, including ED1 (CD68), ED2 (CD163), CD80, mannose receptor and inducible nitric oxide synthase (iNOS). Materials were implanted subcutaneously and collected after 6-8 weeks during the chronic phase of the host response. Unmodified polycaprolactone scaffolds uniquely demonstrated a total lack of both macrophage adherence to surfaces and a wider foreign body response compared to scaffolds composed of poly(lactic-co-glycolic acid) (PLGA) and polyurethanes (PURs), with those macrophages present having a clear M2 (MR+, CD80-, iNOS-) phenotype. PLGA scaffolds displayed an M1-dominant (CD80+, iNOS+, MR-) response with substantial foreign body giant cell (FBGC) formation, whilst PUR scaffold FBGCs had a more mixed M1 (CD80+, iNOS+) and M2 (MR+) phenotype. The study also identified that the use of the ED1 antibody in the rat as a pan-macrophage marker is problematic as there is a separate and substantial ED2-positive macrophage population that it does not label, both in response to biomaterials and in normal tissues. The biomaterial-dependent nature of activation for both macrophages and FBGCs was confirmed, and nuanced M1/M2 phenotypes were described.

Isolation of human lymphatic malformation endothelial cells, their in vitro characterization and in vivo survival in a mouse xenograft model.

Human lymphatic vascular malformations (LMs), also known as cystic hygromas or lymphangioma, consist of multiple lymphatic endothelial cell-lined lymph-containing cysts. No animal model of this disease exists. To develop a mouse xenograft model of human LM, CD34(Neg)CD31(Pos) LM lymphatic endothelial cells (LM-LEC) were isolated from surgical specimens and compared to foreskin CD34(Neg)CD31(Pos) lymphatic endothelial cells (LECs). Cells were implanted into a mouse tissue engineering model for 1, 2 and 4 weeks. In vitro LM-LECs showed increased proliferation and survival under starvation conditions (P < 0.0005 at 48 h, two-way ANOVA), increased migration (P < 0.001, two-way ANOVA) and formed fewer (P = 0.029, independent samples t test), shorter tubes (P = 0.029, independent samples t test) than foreskin LECs. In vivo LM-LECs implanted into a Matrigel™-containing mouse chamber model assembled to develop vessels with dilated cystic lumens lined with flat endothelium, morphology similar to that of clinical LMs. Human foreskin LECs failed to survive implantation. In LM-LEC implanted chambers the percent volume of podoplanin(Pos) vessels was 1.18 ± 2.24 % at 1 week, 6.34 ± 2.68 % at 2 weeks and increasing to 7.67 ± 3.60 % at 4 weeks. In conclusion, the significantly increased proliferation, migration, resistance to apoptosis and decreased tubulogenesis of LM-LECs observed in vitro is likely to account for their survival and assembly into stable LM-like structures when implanted into a mouse vascularised chamber model. This in vivo xenograft model will provide the basis of future studies of LM biology and testing of potential pharmacological interventions for patients with lymphatic malformations.

The adipogenic potential of various extracellular matrices under the influence of an angiogenic growth factor combination in a mouse tissue engineering chamber.

The extracellular matrix (ECM) Matrigel™ has frequently and successfully been used to generate new adipose tissue experimentally, but is unsuitable for human application. This study sought to compare the adipogenic potential of a number of alternative, biologically derived or synthetic ECMs with potential for human application, with and without growth factors and a small fat autograft. Eight groups, with six severe combined immunodeficient (SCID) mice per group, were created with bilateral chambers (silicone tubes) implanted around the epigastric vascular pedicle, with one chamber/animal containing a 5mg fat autograft. Two animal groups were created for each of four ECMs (Matrigel™, Myogel, Cymetra® and PuraMatrix™) which filled the bilateral chambers. One group/ECM had no growth factors added to chambers whilst the other group had growth factors (GFs) (vascular endothelial growth factor-A (VEGF-A) plus fibroblast growth factor-2 (FGF-2) plus platelet-derived growth factor-BB (PDGF-BB)) added to both chambers. At 6weeks, chamber tissue was morphometrically assessed for percent and absolute adipose tissue volume. Overall, the triple GF regime significantly increased percent(∗) and absolute(#) adipose tissue volume (p<0.0005(∗#)) compared to chambers without triple GF treatment. The fat autograft also significantly increased percent (p<0.0005) and absolute (p<0.011) adipose tissue volume. Cymetra® (human collagen) constructs yielded the largest total tissue and absolute adipose tissue volume. We found that the pro-angiogenic FGF-2, VEGF-A and PDGF-BB combination in ECMs of synthetic and biological origin produced an overall significantly increased adipose tissue volume at 6weeks and may have clinical application, particularly with Cymetra.

Enhanced liver progenitor cell survival and differentiation in vivo by spheroid implantation in a vascularized tissue engineering chamber.

Liver tissue engineering is hampered by poor implanted cell survival due to inadequate vascularization and cell-cell/cell-matrix interactions. Here, we use liver progenitor cell (LPC) spheroids to enhance cell-cell/cell-matrix interactions, with implantation into an angiogenic in vivo mouse chamber. Spheroids were generated in vitro in methylcellulose medium. Day 2 spheroids were optimal for implantation (22,407 +/-645 cells/spheroid), demonstrating maximal proliferation (Ki67 immunolabeling) and minimal apoptosis (caspase-3 immunolabelling). In vivo chambers established bilaterally on epigastric vessels of immunodeficient mice were implanted with equivalent numbers of LPCs as a cell suspension (200,000 cells), or spheroids (9 spheroids). At day 14, a trend of increased LPC survival was observed in spheroid-implanted chambers [pan-cytokeratin (panCK+) cells, p = 0.38, 2.4 fold increase)], with significantly increased differentiation [cytokeratin 18 (CK18+) cells, p < 0.002, 5.1 fold increase)] compared to cell suspension-implanted chambers. At day 45, both measures were significantly increased in spheroid-implanted chambers (panCK, p < 0.006, 16 fold increase) (CK18, p < 0.019, 6 fold increase). Hepatic acini/plates of CK18 + cells expressed hepatocyte nuclear factor 4-α and ß-catenin, indicating ongoing hepatic differentiation. Spheroid cell-delivery significantly increased LPC survival and differentiation compared to conventional cell suspensions. This LPC spheroid/vascularized chamber model has clinical potential to generate three-dimensional vascularized liver tissue for liver replacement.

MicroRNAs in insulin resistance and obesity.

MicroRNAs (miRNAs) are a class of short, single-stranded non-protein coding gene products which can regulate the gene expression through post-transcriptional inhibition of messenger RNA (mRNA) translation. They are known to be involved in many essential biological processes including development, insulin secretion, and adipocyte differentiation. miRNAs are involved in complex metabolic processes, such as energy and lipid metabolism, which have been studied in the context of diabetes and obesity. Obesity, hyperlipidemia (elevated levels of blood lipids), and insulin resistance are strongly associated with the onset of type 2 diabetes. These conditions are also associated with aberrant expression of multiple essential miRNAs in pancreatic islets of Langerhans and peripheral tissues, including adipose tissue. A thorough understanding of the physiological role these miRNAs play in these tissues, and changes to their expression under pathological conditions, will allow researchers to develop new therapeutics with the potential to correct the aberrant expression of miRNAs in type 2 diabetes and obesity.