Engineering surfaces for site-specific vascular differentiation of mouse embryonic stem cells

Harnessing the Power of Induced Pluripotent Stem Cells and Gene Editing Technology: Therapeutic Implications in Hematological Malignancies

In vitro modeling of hematological malignancies not only provides insights into the influence of genetic aberrations on cellular and molecular mechanisms involved in disease progression but also aids development and evaluation of therapeutic agents. Owing to their self-renewal and differentiation capacity, induced pluripotent stem cells (iPSCs) have emerged as a potential source of short in supply disease-specific human cells of the hematopoietic lineage. Patient-derived iPSCs can recapitulate the disease severity and spectrum of prognosis dictated by the genetic variation among patients and can be used for drug screening and studying clonal evolution. However, this approach lacks the ability to model the early phases of the disease leading to cancer. The advent of genetic editing technology has promoted the generation of precise isogenic iPSC disease models to address questions regarding the underlying genetic mechanism of disease initiation and progression. In this review, we discuss the use of iPSC disease modeling in hematological diseases, where there is lack of patient sample availability and/or difficulty of engraftment to generate animal models. Furthermore, we describe the power of combining iPSC and precise gene editing to elucidate the underlying mechanism of initiation and progression of various hematological malignancies. Finally, we discuss the power of iPSC disease modeling in developing and testing novel therapies in a high throughput setting.

Induced cell migration based on a bioactive hydrogel sheet combined with a perfused microfluidic system

Endothelial cell migration is a crucial step in the process of new blood vessel formation-a necessary process to maintain cell viability inside thick tissue constructs. Here, we report a new method for maintaining cell viability and inducing cell migration using a perfused microfluidic platform based on collagen gel and a gradient hydrogel sheet. Due to the helpful role of the extracellular matrix components in cell viability, we developed a hydrogel sheet from decellularized tissue (DT) of the bovine heart and chitosan (CS). The results showed that hydrogel sheets with an optimum weight ratio of CS/DT = 2 possess a porosity of around 75%, a mechanical strength of 23 kPa, and display cell viability up to 78%. Then, we immobilized a radial gradient of vascular endothelial growth factor (VEGF) on the hydrogel sheet to promote human umbilical vein endothelial cell migration. Finally, we incorporated the whole system as an entirety on the top of the microfluidic platform and studied cell migration through the hydrogel sheet in the presence of soluble and immobilized VEGF. The results demonstrated that immobilized VEGF stimulated cell migration in the hydrogel sheet at all depths compared with soluble VEGF. The results also showed that applying a VEGF gradient in both soluble and immobilized states had a significant effect on cell migration at limited depths (<100 μm). The main finding of this study is a significant improvement in cell migration using an in vivo imitating, cost-efficient and highly reproducible platform, which may open up a new perspective for tissue engineering applications.

Biomaterial Engineering for Controlling Pluripotent Stem Cell Fate

Pluripotent stem cells (PSCs) represent an exciting cell source for tissue engineering and regenerative medicine due to their self-renewal and differentiation capacities. The majority of current PSC protocols rely on 2D cultures and soluble factors to guide differentiation; however, many other environmental signals are beginning to be explored using biomaterial platforms. Biomaterials offer new opportunities to engineer the stem cell niches and 3D environments for exploring biophysical and immobilized signaling cues to further our control over stem cell fate. Here, we review the biomaterial platforms that have been engineered to control PSC fate. We explore how altering immobilized biochemical cues and biophysical cues such as dimensionality, stiffness, and topography can enhance our control over stem cell fates. Finally, we highlight biomaterial culture systems that assist in the translation of PSC technologies for clinical applications.

Control of stem cell fate by engineering their micro and nanoenvironment

Stem cells are capable of long-term self-renewal and differentiation into specialised cell types, making them an ideal candidate for a cell source for regenerative medicine. The control of stem cell fate has become a major area of interest in the field of regenerative medicine and therapeutic intervention. Conventional methods of chemically inducing stem cells into specific lineages is being challenged by the advances in biomaterial technology, with evidence highlighting that material properties are capable of driving stem cell fate. Materials are being designed to mimic the clues stem cells receive in their in vivo stem cell niche including topographical and chemical instructions. Nanotopographical clues that mimic the extracellular matrix (ECM) in vivo have shown to regulate stem cell differentiation. The delivery of ECM components on biomaterials in the form of short peptides sequences has also proved successful in directing stem cell lineage. Growth factors responsible for controlling stem cell fate in vivo have also been delivered via biomaterials to provide clues to determine stem cell differentiation. An alternative approach to guide stem cells fate is to provide genetic clues including delivering DNA plasmids and small interfering RNAs via scaffolds. This review, aims to provide an overview of the topographical, chemical and molecular clues that biomaterials can provide to guide stem cell fate. The promising features and challenges of such approaches will be highlighted, to provide directions for future advancements in this exciting area of stem cell translation for regenerative medicine.

Surface density of vascular endothelial growth factor modulates endothelial proliferation and differentiation

Therapeutic strategies aim to regulate vasculature either by encouraging vessel growth for tissue engineering or inhibiting vascularization around a tumor. Vascular endothelial growth factor (VEGF) is essential to these processes, and there are several strategies that manipulate VEGF signaling. Here we develop a method to control the surface density of VEGF, which is covalently attached to tissue culture polystyrene (TCPS), and explore cellular responses to surfaces with varying VEGF densities. We show that the crosslinker reduces but does not eliminate the biological activity of soluble VEGF as measured by endothelial proliferation. However, endothelial cells cultured on surfaces of covalently bound VEGF did not proliferate in response to surface cues. Interestingly, compared to cells incubated with soluble VEGF (10 ng/ml) and cultured on TCPS, lower cell proliferation was observed when endothelial cells were cultured on high VEGF surface densities (5.9 ng/cm(2)), whereas higher cell proliferation occurred when cells were cultured on low surface densities (0.04 ng/cm(2)). High density surfaces (5.9 ng/cm(2)) also acted in synergy with an inhibitor of VEGF receptors to further suppress endothelial cell proliferation. We also examined the effect of VEGF surfaces on endothelial differentiation of mesenchymal stem cells. No effect was observed when cells were cultured on VEGF surfaces; however, the VEGF surfaces acted in synergy with an inhibitor of VEGF receptors to decrease the ability of differentiated cells to form vascular networks. Together, these results suggest that surface density of bound VEGF can be used to modulate cell behavior and inhibit an angiogenic response.

Inhibition of apoptosis in human induced pluripotent stem cells during expansion in a defined culture using angiopoietin-1 derived peptide QHREDGS

Adhesion molecule signaling is critical to human pluripotent stem cell (hPSC) survival, self-renewal, and differentiation. Thus, hPSCs are grown as clumps of cells on feeder cell layers or poorly defined extracellular matrices such as Matrigel. We sought to define a small molecule that would initiate adhesion-based signaling to serve as a basis for a defined substrate for hPSC culture. Soluble angiopoeitin-1 (Ang-1)-derived peptide QHREDGS added to defined serum-free media increased hPSC colony cell number and size during long- and short-term culture when grown on feeder cell layers or Matrigel, i.e. on standard substrates, without affecting hPSC morphology, growth rate or the ability to differentiate into multiple lineages both in vitro and in vivo. Importantly, QHREDGS treatment decreased hPSC apoptosis during routine passaging and single-cell dissociation. Mechanistically, the interaction of QHREDGS with β1-integrins increased expression of integrin-linked kinase (ILK), increased expression and activation of extracellular signal-regulated kinases 1/2 (ERK1/2), and decreased caspase-3/7 activity. QHREDGS immobilization to polyethylene glycol hydrogels significantly increased cell adhesion in a dose-dependent manner. We propose QHREDGS as a small molecule inhibitor of hPSC apoptosis and the basis of an affordable defined substrate for hPSC maintenance.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part II: challenges on the evolution from single to multiple bioactive factor delivery

The development of controlled release systems for the regeneration of bone, cartilage, and osteochondral interface is one of the hot topics in the field of tissue engineering and regenerative medicine. However, the majority of the developed systems consider only the release of a single growth factor, which is a limiting step for the success of the therapy. More recent studies have been focused on the design and tailoring of appropriate combinations of bioactive factors to match the desired goals regarding tissue regeneration. In fact, considering the complexity of extracellular matrix and the diversity of growth factors and cytokines involved in each biological response, it is expected that an appropriate combination of bioactive factors could lead to more successful outcomes in tissue regeneration. In this review, the evolution on the development of dual and multiple bioactive factor release systems for bone, cartilage, and osteochondral interface is overviewed, specifically the relevance of parameters such as dosage and spatiotemporal distribution of bioactive factors. A comprehensive collection of studies focused on the delivery of bioactive factors is also presented while highlighting the increasing impact of platelet-rich plasma as an autologous source of multiple growth factors.

The application of three-dimensional collagen-scaffolds seeded with myoblasts to repair skeletal muscle defects

Three-dimensional (3D) engineered tissue constructs are a novel and promising approach to tissue repair and regeneration. 3D tissue constructs have the ability to restore form and function to damaged soft tissue unlike previous methods, such as plastic surgery, which are able to restore only form, leaving the function of the soft tissue often compromised. In this study, we seeded murine myoblasts (C2C12) into a collagen composite scaffold and cultured the scaffold in a roller bottle cell culture system in order to create a 3D tissue graft in vitro. The 3D graft created in vitro was then utilized to investigate muscle tissue repair in vivo. The 3D muscle grafts were implanted into defect sites created in the skeletal muscles in mice. We detected that the scaffolds degraded slowly over time, and muscle healing was improved which was shown by an increased quantity of innervated and vascularized regenerated muscle fibers. Our results suggest that the collagen composite scaffold seeded with myoblasts can create a 3D muscle graft in vitro that can be employed for defect muscle tissue repair in vivo.

Micro- and nanotechnology in cardiovascular tissue engineering

While in nature the formation of complex tissues is gradually shaped by the long journey of development, in tissue engineering constructing complex tissues relies heavily on our ability to directly manipulate and control the micro-cellular environment in vitro. Not surprisingly, advancements in both microfabrication and nanofabrication have powered the field of tissue engineering in many aspects. Focusing on cardiac tissue engineering, this paper highlights the applications of fabrication techniques in various aspects of tissue engineering research: (1) cell responses to micro- and nanopatterned topographical cues, (2) cell responses to patterned biochemical cues, (3) controlled 3D scaffolds, (4) patterned tissue vascularization and (5) electromechanical regulation of tissue assembly and function.

Bioactive scaffolds for engineering vascularized cardiac tissues

Functional vascularization is a key requirement for the development and function of most tissues, and most critically cardiac muscle. Rapid and irreversible loss of cardiomyocytes during cardiac infarction directly results from the lack of blood supply. Contractile cardiac grafts, engineered using cardiovascular cells in conjunction with biomaterial scaffolds, are an actively studied method for cardiac repair. In this article, we focus on biomaterial scaffolds designed to mediate the development and maturation of vascular networks, by immobilized growth factors. The interactive effects of multiple vasculogenic factors are discussed in the context of cardiac tissue engineering.

Photocrosslinkable chitosan modified with angiopoietin-1 peptide, QHREDGS, promotes survival of neonatal rat heart cells

Myocardial infarction (MI) results in the death of cardiomyocytes (CM), which causes scar formation and pathological remodeling of the heart. The delivery of healthy myocytes or bone marrow cells reduces pathological remodeling after MI, however, current cell injection methods have low cell survival rates and high cell loss. The main objective of this work was to develop a novel hydrogel that can promote survival of CMs. Photocrosslinkable azidobenzoic acid modified chitosan (Az-chitosan) was conjugated with the angiopoietin-1-derived peptide, QHREDGS. This novel peptide is thought to mediate attachment and survival responses of CM to angiopoietin-1 via integrin binding. Thin layers of Az-chitosan, Az-chitosan-QHREDGS, and Az-chitosan-DGQESHR (scrambled peptide control) were spin coated on glass slides and photocrosslinked with application of UV light (365 nm). Neonatal rat heart cells cultured up to 5 days, demonstrated significantly higher attachment and viability on Az-chitosan-QHREDGS compared to cells on other hydrogel controls. Surfaces were also stained for the CM-specific marker troponin I, demonstrating significantly higher percentage of CMs on Az-chitosan-QHREDGS compared to Az-chitosan. The cells cultivated on Az-chitosan-QHREDGS demonstrated significantly lower levels of caspase 3/7 activation after taxol treatment in comparison to cells cultivated on the control hydrogels, glass substrate, or Az-chitosan linked to RGD, an established integrin binding peptide that did not protect against apoptosis. Thus, Az-chitosan-QHREDGS supports attachment and survival of neonatal rat heart cells.