Stem cell-based cardiovascular tissue engineering

Cardiovascular diseases, including myocardial infarction, are the leading cause of death worldwide for both men and women. Current therapies are limited by the restricted intrinsic regeneration capacity of the heart and by the lack of organs for transplantation. Human embryonic stem (hES) cells have the capacity to differentiate into various cell types, including vascular cells for forming de novo blood vessels to potentially repair the infarcted heart after myocardial infarction. Our goal was to improve cardiac function after myocardial infarction through hES-based cardiovascular tissue engineering. Our findings summarized: Improved cardiac performance, attenuated left ventricular dilation and decreased infarct size in infarcted rats can be attained after co-injection of hES-derived vascular cells and Thymosin β4 (Tβ4) in matrix metalloproteinase (MMP)-responsive hydrogels. Enhanced vascular cell adhesion, survival and organization can be achieved when coencapsulating bioactive peptide Tβ4 in MMP-responsive matrix in vitro. Directed cardiac differentiation of pluripotent cells can be influenced by matrix elasticity, adhesion ligand concentration and MMP-sensitivity in vitro. We first systematically modulated a three-dimensional (3D) MMP-responsive hydrogel, mimicking key biochemical characteristics of natural collagenous matrices, the major constituent of cardiac extracellular matrices. We found that these synthetic poly(ethylene glycol) (PEG)-based hydrogels can direct differentiation of pluripotent cardioprogenitors, using P19 embryonal carcinoma (EC) cells as a model, along a cardiac lineage in vitro. In order to systematically probe 3D matrix effects on P19 EC differentiation, matrix elasticity, MMP-sensitivity and the concentration of a matrix-bound RGDSP peptide, which is relevant in early cardiac developments were modulated. Soft matrices (E = 320 ± 64 Pa), mimicking the elasticity of embryonic cardiac tissue, increased the fraction of cells expressing the early cardiac transcription factor Nkx2.5 around 2-fold compared to embryoid bodies (EB) in suspension. In contrast, stiffer matrices (E = 4040 ± 420 Pa) decreased the number of Nkx2.5-positive cells significantly. Further indicators of cardiac maturation were promoted by ligation of integrins relevant in early cardiac development (α5β1, αvβ3) by the RGDSP ligand in combination with the MMP-sensitivity of the matrix, with a 6-fold increased amount of myosin heavy chain (MHC)-positive cells as compared to EB in suspension. This precisely controlled 3D culture system thus may serve as a potential alternative to natural matrices for engineering cardiac tissue structures for cell culture and potentially therapeutic applications. Neovascularization of infarcted tissue is a promising alternative strategy to potentially restoring lost contractile performance by cardiac cells. Vascular cells and cytokines are known to contribute to the protection of cardiomyocytes from death after myocardial infarction, but also in endogenous recruitment of vascular cells and even cardiomyocytes. The in vitro potential of the synthetic MMP-responsive PEG-hydrogel as a bioactive co-encapsulation system for vascular cells and a small bioactive peptide, Tβ4, was then examined. Tβ4 was previously shown to enhance survival of vascular cells and cardiomyocytes in ischemic environments, stimulate neovascularization after cardiac injury by inducing endogenous endothelial cell migration to the ischemic site, as well as play a key role in down-regulating expression of inflammatory molecules. We show that the physical incorporation of Tβ4 in this bioactive matrix creates a 3D environment conducive for human umbilical vein endothelial cell (HUVEC) adhesion, survival, migration and organization. Gels with entrapped Tβ4 increased the survival of HUVEC compared to gels without Tβ4 (p < 0.05), and significantly up-regulated the endothelial genes vascular endothelial-cadherin and angiopoietin-2, whereas the von Willebrand factor was significantly down-regulated (all p < 0.05). Incorporation of Tβ4 significantly increased MMP-2 and MMP-9 secretion of encapsulated HUVEC (p < 0.05). The gel acts as a controlled Tβ4-release system, as MMP-2 and MMP-9 enzymes trigger the release. In addition, Tβ4 facilitated HUVEC attachment and induced vascular-like network formation upon the PEG-hydrogels. These MMP-responsive PEG-hydrogels may thus serve as controlled co-encapsulation system of vascular cells and bioactive factors for in situ regeneration of ischemic tissues. Finally, we employed these injectable MMP-responsive bioactive hydrogels with vasculo-typic adhesion molecule as a provisional in situ reservoir of vascular cells derived from hES cells and Tβ4 peptide, in infarcted hearts. Typically, after myocardial infarction, the performance-generating contractile cardiac tissue is partially replaced by non-contractile fibrotic tissue, driven by upregulated enzymes such as MMP. Here, magnetic resonance imaging (MRI) revealed enhanced contractile performance 3 days and 6 weeks after myocardial infarction (both p < 0.001), attenuated left ventricular dilation (p < 0.05) and decreased infarct size at 6 weeks (p < 0.05) as compared to infarcted rats with PBS injection. . We found the gel substituting the native degrading extracellular matrix in the infarcted myocardium and promoting structural organization of endothelial cells and cardiomyocytes, while the delivered hES-derived vascular cells formed de novo capillaries in the infarct zone.

Human embryonic stem cell-derived microvascular grafts for cardiac tissue preservation after myocardial infarction

Jeffrey Alan Hubbell

We present use of a synthetic, injectable matrix metalloproteinase (MMP)- responsive, bioactive hydrogel as an in situ forming scaffold to deliver thymosin beta 4 (T beta 4), a pro-angiogenic and pro-survival factor, along with vascular cells derived from human embryonic stem cells (hESC) in ischemic injuries to the heart in a rat model. The gel was found to substitute the degrading extracellular matrix in the infarcted myocardium of rats and to promote structural organization of native endothelial cells, while some of the delivered hESC-derived vascular cells formed de novo capillaries in the infarct zone. Magnetic resonance imaging (MRI) revealed that the microvascular grafts effectively preserved contractile performance 3 d and 6 wk after myocardial infarction, attenuated left ventricular dilation, and decreased infarct size as compared to infarcted rats treated with PBS injection as a control (3 d ejection fraction, + similar to 7%, P < 0.001; 6 wk ejection faction, + similar to 12%, P < 0.001). Elevation in vessel density was observed in response to treatment, which may be due in part to elevations in human (donor)-derived cytokines EGF, VEGF and HGF (1 d). Thus, a clinically relevant matrix for dual delivery of vascular cells and drugs may be useful in engineering sustained tissue preservation and potentially regenerating ischemic cardiac tissue. (c) 2010 Elsevier Ltd. All rights reserved.

2011

Tissue engineering of the bladder

Catharina Adelöw

Stem cell use in bladder tissue engineering is a recently addressed area of investigation that has generated excitement as a novel way to restore and regenerate lost or damaged urinary bladder tissue. The remodelling of smooth muscle plays a significant role in bladder repair and regeneration. De-differentiation of smooth muscle cells from a contractile phenotype to a synthetic proliferative phenotype is characterised by smooth muscle hypertrophy and fibrosis, and leads to a poorly compliant bladder. To elucidate the underlying mechanisms of such phenomena, recent efforts in bladder tissue engineering have focused on understanding smooth muscle biology and associated mechanisms of bladder diseases. In this thesis we have designed a synthetic poly (ethylene glycol) (PEG) hydrogel for stem cell and drug delivery aimed to enhance control smooth muscle cell phenotype and thus assist in bladder repair and regeneration. We began by developing a method for isolation of cells from the bladder wall. Traditionally urothelium and smooth muscle cells are separated by dissection, and primary cultures are initiated in distinctly different medium formulations to obtain homogenous cultures and limit contaminating cells. However, the bladder wall harbours, apart from urothelial and smooth muscle cells, fibroblasts that have similar nutritional requirements and are likely candidates to contaminate smooth muscle cell cultures. Isolation of these three cell types by conjugation to magnetic beads and repeated separations allowed us to obtain pure cell populations. Furthermore, this technique permitted us to freely choose any specific medium formulation we wished to utilise. We then turned our attentions to engineering a materials system, by chemically and physically tuning a PEG hydrogel in terms of ligand concentration and matrix stiffness, to provide a three-dimensional environment for optimal spreading of human smooth muscle cells and mesenchymal stem cells. Cell viability, proliferation and differentiation were assessed in optimised hydrogels. Compared to cultures on traditional two-dimensional plastic, mesenchymal stem cells cultured within our three-dimensional hydrogels acquired a smooth muscle cell-like phenotype and smooth muscle cells obtained a less de-differentiated phenotype. In addition, we demonstrated cell-demanded gel degradation and deposition of newly synthesised extracellular matrix proteins. In order to modulate cell phenotypes further, we hypothesised that cell differentiation could be directed by the adhesion ligands made available within the matrix. In this manner, cells that were exposed to a matrix presenting certain integrin-binding ligands would begin expressing the corresponding integrins in order to adhere to the matrix. Consequently, we explored the effect of various specific integrin-binding ligands on mesenchymal stem cell integrin expression and differentiation. Fibronectin (FN) fragments engineered to demonstrate specificity to different integrins, namely α5β1 (FNIII910) and αvβ3 (FNIII10), were conjugated to PEG functionalised with vinyl sulfone and compared to fibronectin wild type (FNIIIWT) fragment and the RGD peptide, which both provide binding sites for a range of integrins. We found that assembly of focal adhesions and formation of stress fibres were altered due to the specific fragments provided, and expression of integrin- and smooth muscle cell specific genes varied in mesenchymal stem cells cultured within hydrogels functionalised with different fragments. Moreover, these fibronectin fragments turned out to be especially helpful for improved attachment of urothelial cells on top of hydrogels. With this biomaterial system in hand, we sought to develop a co-culture model of the bladder wall that permitted mesenchymal stem cells and urothelial cells cultured within / on top of PEG hydrogels, and to explore the combinatorial effect of ligand binding and cell-cell interactions on mesenchymal stem cell fate. Interestingly, we found that co-culturing with urothelial cells influenced gene expression of mesenchymal stem cells differently, depending on the protein fragment to which they were adhering. Mesenchymal stem cells cultured within PEG-FNIIIWT hydrogels were shown to up-regulate smooth muscle cell specific genes, while down-regulation was demonstrated in PEG-RGD, PEG-FNIII910 and PEG-FNIII10 hydrogels. Again, mesenchymal stem cells cultured within PEG-FNIIIWT hydrogels were shown to up-regulate integrin expressions α5, αv, β1 and β3, while down-regulation of the same genes was demonstrated for cells cultured within PEG-FNIII9*10 hydrogels, and a more complex pattern of integrin regulation was found for cells cultured within PEG-RGD and PEG-FNIII10 hydrogels. Finally, we investigated a novel approach to growth factor delivery in a controlled release manner, by providing cell- and growth factor binding protein fragments. In this system we show that transforming growth factor beta 1 (TGF-β1) release from PEG hydrogels influence smooth muscle cell specific gene expressions differently depending on the integrin- and growth factor binding proteins available within the hydrogel. Delivery of TGF-β1 within PEG-FNIIIWT hydrogels was shown to up-regulate smooth muscle specific genes in mesenchymal stem cells, while the other conditions displayed more complex patterns of gene expression. Further experiments are required to characterise the conjugation of PEGprotein-growth factor, and the release profiles for the growth factor in the different conditions. In conclusion, this thesis investigates the effect of various chemical and physical signals on mesenchymal stem cell-to-smooth muscle cell differentiation in an in vitro model to further understand cell-cell and cell-extracellular matrix interactions and create improved artificial microenvironments for directing and / or maintaining cell differentiation. The PEG hydrogel that we designed permits the co-culture of cells as well as the incorporation of peptides and proteins such as cell adhesion- and growth factor binding ligands, and growth factors for directing the differentiation of human mesenchymal stem cells into smooth muscle cells. Here, we explore these features and their effects on cell differentiation in vitro. Hence, our PEG hydrogel system can serve both as an in vitro model for studying basic cell biology, and as a cell delivery vehicle for improved bladder tissue regeneration.

EPFL2009

Tissue engineering of the bladder

Catharina Adelöw

EPFL2009