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Immunomodulation in the local tissue microenvironment is pivotal for the determination of macrophage phenotypes and regulation of functions necessary for pro-healing effects. Herein, we demonstrate that a lymph node extracellular matrix (LNEM) prepared by the decellularization of lymph node tissues can mimic lymph node microenvironments for immunomodulation in two-dimensional (2D) and three-dimensional (3D) formats. The LNEM exhibits strengthened immunomodulatory effects in comparison to conventional collagen-based platforms. A 3D LNEM hydrogel is more effective than the 2D LNEM coating in inducing M2 macrophage polarization. The 3D LNEM induces macrophage elongation and enhances the M2-type marker expression and the secretion of anti-inflammatory cytokines. Additionally, the phagocytic function of macrophages is improved upon exposure to the intricate 3D LNEM environment. We demonstrate the reduced susceptibility of liver organoids to a hepatotoxic drug when co-cultured with macrophages in a 3D LNEM. This effect could be attributed to the enhanced anti-inflammatory functions and indicates its potential as a drug-testing platform that enables drug responses similar to those observed in vivo. Finally, the implantation of an LNEM hydrogel in a mouse volumetric muscle loss model facilitates the recruitment of host macrophages to the site of injury and enhances macrophage polarization toward the M2 phenotype for tissue healing in vivo. Therefore, 3D immune system-mimicking biomaterials could serve as useful platforms for tissue modeling and regenerative medicine development.

INTRODUCTION: Mesenchymal stem cells (MSCs) are promising candidates for cell therapy owing to their therapeutic effect in various diseases. In general, MSCs grow efficiently in serum-containing culture media, indicating an essential role of adhesion in their mesenchymal lineage-specific propagation. Nevertheless, the use of non-human supplements in culture (xeno-free issue) in addition to the lack of control over unknown factors in the serum hampers the clinical transition of MSCs. METHODS: In this study, embryonic stem cell derived mesenchymal stem cells (ES-MSCs) were used owing to their scalable production, and they expressed a series of MSC markers same as adipose-derived MSCs. The affinity of the culture matrix was increased by combining fibronectin coating with its adjuvant peptide, gelatin, or both (FNGP) on tissue culture polystyrene to compare the regenerative, therapeutic activities of ES-MSCs with a cell binding plate as a commercial control. RESULTS: The FNGP culture plate promoted pivotal therapeutic functions of ES-MSCs as evidenced by their increased stemness as well as anti-inflammatory and proangiogenic effects in vitro. Indeed, after culturing on the FNGP plates, ES-MSCs efficiently rescued the necrotic damages in mouse ischemic hindlimb model. CONCLUSIONS: This study suggests a potential solution by promoting the surface affinity of culture plates using a mixture of human fibronectin and its adjuvant PHSRN peptide in gelatin. The FNGP plate is expected to serve as an effective alternative for serum-free MSC expansion for bench to clinical transition.

Cell-cell interactions regulate intracellular signaling via reciprocal contacts of cell membranes in tissue regeneration and cancer growth, indicating a critical need of membrane-derived tools in studying these processes. Hence, cell-membrane-derived nanoparticles (CMNPs) are produced using tonsil-derived mesenchymal stem cells (TMSCs) from children owing to their short doubling time. As target cell types, laryngeal cancer cells are compared to bone-marrow-derived MSCs (BMSCs) because of their cartilage damaging and chondrogenic characteristics, respectively. Treating spheroids of these cell types with CMNPs exacerbates interspheroid hypoxia with robust maintenance of the cell-cell interaction signature for 7 days. Both cell types prefer a hypoxic environment, as opposed to blood vessel formation that is absent in cartilage but is required for cancer growth. Hence, angiogenesis is inhibited by displaying the Notch-1 aptamer on CMNPs. Consequently, laryngeal cancer growth is suppressed efficiently in contrast to improved chondroprotection observed in a series of cell and animal experiments using a xenograft mouse model of laryngeal cancer. Altogether, CMNPs execute a two-edged sword function of inducing hypoxic cell-cell packing, followed by suppressing angiogenesis to promote laryngeal cancer death and chondrogenesis simultaneously. This study presents a previously unexplored therapeutic strategy for anti-cancer and chondroprotective treatment using CMNPs.

Gene therapy is a promising method for the treatment of vascular disease; however, successful strategies depend on the development of safe and effective delivery technologies with specific targeting to a diseased point of vasculature. Reactive oxygen species (ROS) are overproduced by vascular smooth muscle cells (VSMCs) at critical stages of atherosclerosis progression. Therefore, ROS were exploited as a stimulus for vascular targeted gene delivery in this study. A combination of bio-conjugation methods and controlled reverse addition-fragmentation chain-trasfer (RAFT) polymerization was utilized to synthesize a new ROS-cleavable, pH-responsive mPEG113-b-CP5K-b-PDMAEMA42-b-P(DMAEMA22-co-BMA40-co-PAA24) (PPDDBP) polymer as a nanocarrier for plasmid DNA (pDNA) delivery. The ros degradability of PPDDBP polymers was confirmed by SIN-1-mediated cleavage of CP5K peptide linkers through a shift in GPC chromatogram with an appearance of mPEG shoulder peak and an increase in zeta potential (ζ). The polyplex nanocarrier also demonstrated effective PDNA loading, serum stability, and hemocompatibility, indicating its excellent performance under physiological conditions. The polyplexes demonstrated ideal pH responsiveness for endosomal escape and effective ROS responsiveness for improved targeting in an in vitro model of pathogenic VSMCs in terms of both uptake and expression of reporter gene. These data suggest this novel nanocarrier polyplex system is a promising gene delivery tool for preventing or treating areas of high ROS, such as atherosclerotic lesions.

Atherosclerosis development leads to irreversible cascades, highlighting the unmet need for improved methods of early diagnosis and prevention. Disturbed flow formation is one of the earliest atherogenic events, resulting in increased endothelial permeability and subsequent monocyte recruitment. Here, a mesenchymal stem cell (MSC)-derived nanovesicle (NV) that can target disturbed flow sites with the peptide GSPREYTSYMPH (PREY) (PMSC-NVs) is presented which is selected through phage display screening of a hundred million peptides. The PMSC-NVs are effectively produced from human MSCs (hMSCs) using plasmid DNA designed to functionalize the cell membrane with PREY. The potent anti-inflammatory and pro-endothelial recovery effects are confirmed, similar to those of hMSCs, employing mouse and porcine partial carotid artery ligation models as well as a microfluidic disturbed flow model with human carotid artery-derived endothelial cells. This nanoscale platform is expected to contribute to the development of new theragnostic strategies for preventing the progression of atherosclerosis.

The cytoskeleton provides structure and plays an important role in cellular function such as migration, resisting compression forces, and transport. The cytoskeleton also reacts to physical cues such as fluid shear stress or extracellular matrix remodeling by reorganizing filament associations, most commonly focal adhesions and cell-cell cadherin junctions. These mechanical stimuli can result in genome-level changes, and the physical connection of the cytoskeleton to the nucleus provides an optimal conduit for signal transduction by interfacing with nuclear envelope proteins, called nesprins, within the LINC (linker of the nucleus to the cytoskeleton) complex. Using single-molecule on single nuclei assays, we report that the interactions between the nucleus and the cytoskeleton, thought to be nesprin-cytoskeleton interactions, are highly sensitive to force magnitude and direction depending on whether cells are historically interfaced with the matrix or with cell aggregates. Application of ~10-30 pN forces to these nesprin linkages yielded structural transitions, with a base transition size of 5-6 nm, which are speculated to be associated with partial unfoldings of the spectrin domains of the nesprins and/or structural changes of histones within the nucleus., This research work was funded and supported by NSF DMR BMAT under 1506717 and NIH EB under 019509 (D.A.B. and H.J.S.). H.J.S. was also supported by the Faculty Research Assistance Program of Yonsei University College of Medicine for 2000 (6–2016–0031). U.H.K was supported by the National Research Foundation of Korea (NRF) under MEST-2015M3A9B3028216. This work was also supported, in part, by Singapore-MIT Alliance for Research and Technology – BioSym, NSF under 1330792, and GAANN under P200A090323 (S.K.B and M.J.L).

Stem and progenitor cells that exhibit significant regenerative potential and critical roles in cancer initiation and progression remain difficult to characterize. Cell fates are determined by reciprocal signaling between the cell microenvironment and the nucleus; hence parameters derived from nuclear remodeling are ideal candidates for stem/progenitor cell characterization. Here we applied high-content, single cell analysis of nuclear shape and organization to examine stem and progenitor cells destined to distinct differentiation endpoints, yet undistinguishable by conventional methods. Nuclear descriptors defined through image informatics classified mesenchymal stem cells poised to either adipogenic or osteogenic differentiation, and oligodendrocyte precursors isolated from different regions of the brain and destined to distinct astrocyte subtypes. Nuclear descriptors also revealed early changes in stem cells after chemical oncogenesis, allowing the identification of a class of cancer-mitigating biomaterials. To capture the metrology of nuclear changes, we developed a simple and quantitative "imaging-derived" parsing index, which reflects the dynamic evolution of the high-dimensional space of nuclear organizational features. A comparative analysis of parsing outcomes via either nuclear shape or textural metrics of the nuclear structural protein NuMA indicates the nuclear shape alone is a weak phenotypic predictor. In contrast, variations in the NuMA organization parsed emergent cell phenotypes and discerned emergent stages of stem cell transformation, supporting a prognosticating role for this protein in the outcomes of nuclear functions.

hMSC source-specific behaviors in 3D NO gel represent EC-like differentiation of ADSCs and pericyte-like characteristics of BMSCs., Angiogenesis is stimulated by nitric oxide (NO) production in endothelial cells (ECs). Although proangiogenic actions of human mesenchymal stem cells (hMSCs) have been extensively studied, the mechanistic role of NO in this action remains obscure. Here, we used a gelatin hydrogel that releases NO upon crosslinking by a transglutaminase reaction (“NO gel”). Then, the source-specific behaviors of bone marrow versus adipose tissue-derived hMSCs (BMSCs versus ADSCs) were monitored in the NO gels. NO inhibition resulted in significant decreases in their angiogenic activities. The NO gel induced pericyte-like characteristics in BMSCs in contrast to EC differentiation in ADSCs, as evidenced by tube stabilization versus tube formation, 3D colocalization versus 2D coformation with EC tube networks, pericyte-like wound healing versus EC-like vasculogenesis in gel plugs, and pericyte versus EC marker production. These results provide previously unidentified insights into the effects of NO in regulating hMSC source-specific angiogenic mechanisms and their therapeutic applications.

The organization and composition of the extracellular matrix (ECM) have been shown to impact the propagation of electrical signals in multiple tissue types. To date, many studies with electroactive biomaterial substrates have relied upon passive electrical stimulation of the ionic media to affect cell behavior. However, development of cell culture systems in which stimulation can be directly applied to the material – thereby isolating the signal to the cell-material interface and cell–cell contracts – would provide a more physiologically-relevant paradigm for investigating how electrical cues modulate lineage-specific stem cell differentiation. In the present study, we have employed unmodified, directly-stimulated, (un)patterned graphene as a cell culture substrate to investigate how extrinsic electrical cycling influences the differentiation of naïve human mesenchymal stem cells (hMSCs) without the bias of exogenous biochemicals. We first demonstrated that cyclic stimulation does not deteriorate the cell culture media or result in cytotoxic pH, which are critical experiments for correct interpretation of changes in cell behavior. We then measured how the expression of osteogenic and neurogenic lineage-specific markers were altered simply by exposure to electrical stimulation and/or physical patterns. Expression of the early osteogenic transcription factor RUNX2 was increased by electrical stimulation on all graphene substrates, but the mature marker osteopontin was only modulated when stimulation was combined with physical patterns. In contrast, the expression of the neurogenic markers MAP2 and β3-tubulin were enhanced in all electrical stimulation conditions, and were less responsive to the presence of patterns. These data indicate that specific combinations of non- biological inputs – material type, electrical stimulation, physical patterns – can regulate hMSC lineage specification. This study represents a substantial step in understanding how the interplay of electrophysical stimuli regulate stem cell behavior and helps to clarify the potential for graphene substrates in tissue engineering applications.

Cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs) hold great promise for modeling human heart diseases. However, iPSC-CMs studied to date resemble immature embryonic myocytes and therefore do not adequately recapitulate native adult cardiomyocyte phenotypes. Since extracellular matrix plays an essential role in heart development and maturation in vivo , we sought to develop a synthetic culture matrix that could enhance functional maturation of iPSC-CMs in vitro . In this study, we employed a library of combinatorial polymers comprising of three functional subunits – poly-e-caprolacton (PCL), polyethylene glycol (PEG), and carboxylated PCL (cPCL) – as synthetic substrates for culturing human iPSC-CMs. Of these, iPSC-CMs cultured on 4%PEG-96%PCL (each % indicates the corresponding molar ratio) exhibit the greatest contractility and mitochondrial function. These functional enhancements are associated with increased expression of cardiac myosin light chain-2v, cardiac troponin I and integrin alpha-7. Importantly, iPSC-CMs cultured on 4%PEG-96%PCL demonstrate troponin I (TnI) isoform switch from the fetal slow skeletal TnI (ssTnI) to the postnatal cardiac TnI (cTnI), the first report of such transition in vitro . Finally, culturing iPSC-CMs on 4%PEG-96%PCL also significantly increased expression of genes encoding intermediate filaments known to transduce integrin-mediated mechanical signals to the myofilaments. In summary, our study demonstrates that synthetic culture matrices engineered from combinatorial polymers can be utilized to promote in vitro maturation of human iPSC-CMs through the engagement of critical matrix-integrin interactions.

To date, bone tissue regeneration strategies lack an approach that effectively provides an osteogenic and angiogenic environment conducive to bone growth. In the current study, we evaluated the osteogenic and angiogenic response of human mesenchymal stem cells (hMSCs) and green fluorescent protein-expressing human umbilical vein endothelial cells (GFP-HUVECs) cocultured on a self-assembled, peptide amphiphile nanomatrix functionalized with the cell adhesive ligand RGDS (PA-RGDS). Analysis of alkaline phosphatase activity, von Kossa staining, Alizarin Red quantification, and osteogenic gene expression, indicates a significant synergistic effect between the PA-RGDS nanomatrix and coculture that promoted hMSC osteogenesis. In addition, coculturing on PA-RGDS resulted in enhanced HUVEC network formation and upregulated vascular endothelial growth factor gene and protein expression. Though PA-RGDS and coculturing hMSCs with HUVECs were each previously reported to individually enhance hMSC osteogenesis, this study is the first to demonstrate a synergistic promotion of HUVEC angiogenesis and hMSC osteogenesis by integrating coculturing with the PA-RGDS nanomatrix. We believe that using the combination of hMSC/HUVEC coculture and PA-RGDS substrate is an efficient method for promoting osteogenesis and angiogenesis, which has immense potential as an efficacious, engineered platform for bone tissue regeneration.

Stem cells have recently emerged as an important candidate for cell therapy. However, some major limitations still exist such as a small quantity of cell supply, senescence, and insufficient differentiation efficiency. Therefore, there is an unmet need to control stem cell behavior for better clinical performance. Since native microenvironment factors including stem cell niche, genetic factors, and growth factors direct stem cell fate cooperatively, user-specified in vitro settings are required to understand the regulatory roles and effects of each factor, thereby applying the factors for improved cell therapy. Among others, various types of biomaterials and transfection method have been employed as key tools for development of the in vitro settings. This review focuses on the current strategies to improve stemness maintenance, direct differentiation, and reprogramming using biomaterials and genetic factors without any aids from additional biochemicals and growth factors.

Human bone marrow derived mesenchymal stem cells (hMSCs) hold great promise for regenerative medicine due to their multipotent differentiation capacity and immunomodulatory capabilities. Substantial research has elucidated mechanisms by which extracellular cues regulate hMSC fate decisions, but considerably less work has addressed how material properties can be leveraged to maintain undifferentiated stem cells. Here, we show that synthetic culture substrates designed to exhibit moderate cell-repellency promote high stemness and low oxidative stress—two indicators of naïve, healthy stem cells—in commercial and patient-derived hMSCs. Furthermore, the material-mediated effect on cell behavior can be tuned by altering the molar percentage (mol %) and/or chain length of poly(ethylene glycol) (PEG), the repellant block linked to hydrophobic poly(ε-caprolactone) (PCL) in the copolymer backbone. Nano- and angstrom-scale characterization of the cell-material interface reveals that PEG interrupts the adhesive PCL domains in a chain-length-dependent manner; this prevents hMSCs from forming mature focal adhesions and subsequently promotes cell–cell adhesions that require connexin-43. This study is the first to demonstrate that intrinsic properties of synthetic materials can be tuned to regulate the stemness and redox capacity of hMSCs and provides new insight for designing highly scalable, programmable culture platforms for clinical translation.

Remarkable achievements have been made in the clinical application of mechanical circulatory support and cardiac transplantation for patients with end-stage heart failure. Despite the successes, complications associated with these therapies continue to drive cardiac regenerative research utilizing stem cell based therapies. Multiple stem cell lineages hold clinical promise for cardiac regeneration—mostly through cellular differentiation, cellular fusion, and paracrine signaling mechanisms. Bone marrow-derived endothelial progenitor cells are among the most intriguing and controversial cell types currently being investigated. Formidable barriers exist, however, in finding the ideal cardiac regenerative stem cell, such as identifying specific lineage markers, optimizing in vitro cellular expansion and improving methods of stem cell delivery. Hybrid approaches of cardiac regeneration using stem cell therapies in conjunction with immunomodulation after cardiac transplantation or with mechanical circulatory support produce cutting edge stem cell technologies. This review summarizes the current knowledge and therapeutic applications of stem cells in patients with end-stage heart failure, including stem cell therapy after implantation of mechanical circulatory support and cardiac transplantation. J. Cell. Biochem. 115: 1217–1224, 2014. © 2014 Wiley Periodicals, Inc.

Circulating monocytes undergo spontaneous apoptosis when there is no activation stimulus, which is critical to population control for proper host response to implants. As activation and apoptosis of monocytes/macrophages are regulated by cell-cell and cell-matrix interactions, their regulatory mechanism was investigated in this study using polyethylene glycol (PEG)-containing polyurethane films in which PEG-rich and polyester-rich domains were phase separated. Human blood monocyte-derived macrophages (HBMs) preferentially adhered to PEG domains (cell-matrix interaction) due to the low molecular weight (600 g mol⁻¹), resulting in increased HBM density (cell-cell interaction). As both cell-cell and cell-matrix interactions were promoted, HBM apoptosis increased, while their activation as measured by phagocytosis, intracellular reactive oxygen species (ROS) level and matrix metalloproteinase-9 production decreased compared to PEG-free films. When cell seeding density and cell-adhesive gelatin coating on silicone films were controlled, a cooperative role of cell-matrix (adhesion) and cell-cell (density) interactions in inducing HBM apoptosis was observed. Expression of the macrophage adhesion molecule CD11b caused apoptosis in this context, which was mediated by tissue necrosis factor-α signaling but down-regulated by the ROS inhibitor diphenylene iodonium and the anti-inflammatory peptide Ac-SDKP, suggesting a new concept for the design of biomaterials that allows for cell adhesion without excessive inflammatory activation.

Recently, significant progress has been made in developing “stimuli-sensitive” biomaterials as a new therapeutic approach to interact with dynamic physiological conditions. Reactive oxygen species (ROS) production has been implicated in important pathophysiological events, such as atherosclerosis, aging, and cancer. ROS are often overproduced locally in diseased cells and tissues, and they individually and synchronously contribute to many of the abnormalities associated with local pathogenesis. Therefore, the advantages of developing ROS-responsive materials extend beyond site-specific targeting of therapeutic delivery, and potentially include navigating, sensing, and repairing the cellular damages via programmed changes in material properties. Here we review the mechanism and development of biomaterials with ROS-induced solubility switch or degradation, as well as their performance and potential for future biomedical applications.

Material-induced cell aggregation drives a proangiogenic expression profile. Copolymer substrates containing cell-repellent and cell-adhesive domains force the aggregation of human mesenchymal stem cells, which results in enhanced tubulogenesis in vitro and stabilization of vasculature in vivo. These findings can be used to design instructive biomaterial scaffolds for clinical use.

Human mesenchymal stem cells (hMSCs) have been widely studied for therapeutic development in tissue engineering and regenerative medicine. They can be harvested from human donors via tissue biopsies, such as bone marrow aspiration, and cultured to reach clinically relevant cell numbers. However, an unmet issue lies in the fact that the hMSC donors for regenerative therapies are more likely to be of advanced age. Their stem cells are not as potent compared to those of young donors, and continue to lose healthy, stemness-related activities when the hMSCs are serially passaged in tissue culture plates. Here, we have developed a cheap, scalable, and effective copolymer film to culture hMSCs obtained from aged human donors over several passages without loss of reactive oxygen species (ROS) handling or differentiation capacity. Assays of cell morphology, reactive oxygen species load, and differentiation potential demonstrate the effectiveness of copolymer culture on reduction in senescence-related activities of aging donor-derived hMSCs that could hinder the therapeutic potential of autologous stem cell therapies.

Stem cells are a promising cell source for regenerative medicine due to their differentiation and self-renewal capacities. In the field of regenerative medicine and tissue engineering, a variety of biomedical technologies have been tested to improve proangiogenic activities of stem cells. However, their therapeutic effect is found to be limited in the clinic because of cell loss, senescence, and insufficient therapeutic activities. To address this type of issue, advanced techniques for biomaterial synthesis and fabrication have been approached to mimic proangiogenic microenvironment and to direct proangiogenic activities. This review highlights the types of polymers and design strategies that have been studied to promote proangiogenic activities of stem cells. In particular, scaffolds, hydrogels, and surface topographies, as well as insight into their underlying mechanisms to improve proangiogenic activities are the focuses. The strategy to promote angiogenic activities of hMSCs by controlling substrate repellency is introduced, and the future direction is proposed.

Despite recent advances in biomimetic substrates, there is still only limited understanding of how the extracellular matrix (ECM) functions in the maintenance of cardiomyocyte (CM) phenotype. In this study, we designed electrospun substrates inspired by morphologic features of non-failing and failing human heart ECM, and examined how these substrates regulate phenotypes of adult and neonatal rat ventricular CMs (ARVM and NRVM, respectively). We found that poly(e-caprolactone) fiber substrates designed to mimic the organized ECM of a non-failing human heart maintained healthy CM phenotype (evidenced by cell morphology, organized actin/myomesin bands and expression of β-MYH7 and SCN5A.1 and SCN5A.2) compared to both failing heart ECM-mimetic substrates and tissue culture plates. Moreover, culture of ARVMs and NRVMs on aligned substrates showed differences in m- and z-line alignment; with ARVMs aligning parallel to the ECM fibers and the NRVMs aligning perpendicular to the fibers. The results provide new insight into cardiac tissue engineering by illustrating the importance models that mimic the cardiac ECM microenvironment in vitro.

Primary dilated cardiomyopathy (DCM) is a non-ischemic heart disease with impaired pumping function of the heart. In this study, we used human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a healthy volunteer and a primary DCM patient to investigate the impact of DCM on iPSC-CMs׳ responses to different types of anisotropic strain. A bioreactor system was established that generates cardiac-mimetic forces of 150 kPa at 5% anisotropic cyclic strain and 1 Hz frequency. After confirming cardiac induction of the iPSCs, it was determined that fibronectin was favorable to other extracellular matrix protein coatings (gelatin, laminin, vitronectin) in terms of viable cell area and density, and was therefore selected as the coating for further study. When iPSC-CMs were exposed to three strain conditions (no strain, 5% static strain, and 5% cyclic strain), the static strain elicited significant induction of sarcomere components in comparison to other strain conditions. However, this induction occurred only in iPSC-CMs from a healthy volunteer ("control iPSC-CMs"), not in iPSC-CMs from the DCM patient ("DCM iPSC-CMs"). The donor type also significantly influenced gene expressions of cell-cell and cell-matrix interaction markers in response to the strain conditions. Gene expression of connexin-43 (cell-cell interaction) had a higher fold change in healthy versus diseased iPSC-CMs under static and cyclic strain, as opposed to integrins α-5 and α-10 (cell-matrix interaction). In summary, our iPSC-CM-based study to model the effects of different strain conditions suggests that intrinsic, genetic-based differences in the cardiomyocyte responses to strain may influence disease manifestation in vivo.

In regions of the circulation where vessels are straight and unbranched, blood flow is laminar and unidirectional. In contrast, at sites of curvature, branch points, and regions distal to stenoses, blood flow becomes disturbed. Atherosclerosis preferentially develops in these regions of disturbed blood flow. Current therapies for atherosclerosis are systemic and may not sufficiently target these atheroprone regions. In this study, we sought to leverage the alterations on the luminal surface of endothelial cells caused by this atheroprone flow for nanocarrier targeting. In vivo phage display was used to discover unique peptides that selectively bind to atheroprone regions in the mouse partial carotid artery ligation model. The peptide GSPREYTSYMPH (PREY) was found to bind 4.5-fold more avidly to the region of disturbed flow and was used to form targeted liposomes. When administered intravenously, PREY-targeted liposomes preferentially accumulated in endothelial cells in the partially occluded carotid artery and other areas of disturbed flow. Proteomic analysis and immunoblotting indicated that fibronectin and Filamin-A were preferentially bound by PREY nanocarriers in vessels with disturbed flow. In additional experiments, PREY nanocarriers were used therapeutically to deliver the nitric oxide synthase cofactor tetrahydrobiopterin (BH4), which we have previously shown to be deficient in regions of disturbed flow. This intervention increased vascular BH4 and reduced vascular superoxide in the partially ligated artery in wild-type mice and reduced plaque burden in the partially ligated left carotid artery of fat fed atheroprone mice (ApoE(-/-)). Targeting atheroprone sites of the circulation with functionalized nanocarriers provides a promising approach for prevention of early atherosclerotic lesion formation.

Phenotypic modulation of vascular smooth muscle cells (VSMC) and reactive oxygen species (ROS) is important in vascular pathogenesis. Understanding how these factors relate to cell migration can improve design of therapeutic interventions to control vascular disease. We compared the proliferation, protein content and migration of cultured aortic VSMC from wild type (WT) versus transgenic mice (Tgp22phox), in which overexpression of p22phox was targeted to VSMC. Also, we compared H2O2 generation and expression of specific phenotypic markers of non-migrating with migrating WT versus Tgp22phox VSMC in an in vitro wound scratch model. Enhanced H2O2 production in Tgp22phox versus WT VSMC (p < 0.005) significantly correlated with increased protein content, proliferation, and migration. VSMC migrating across the wound edge produced more H2O2 than non-migrating VSMC (p < 0.05). The expression of synthetic phenotypic markers, tropomyosin 4 and myosin heavy chain embryonic (SMemb), was enhanced significantly, while the expression of contractile marker, smooth muscle alpha-actin, was reduced significantly in migrating versus non-migrating cells, and also in Tgp22phox versus WT (p < 0.005) VSMC. These results are consistent with increased production of ROS accelerating the switch from the contractile to the synthetic phenotype, characterized by increases in proliferation, migration, and expression of TM4 and SMemb and decreased alpha-actin.

Directing angiogenic differentiation of mesenchymal stem cells (MSCs) still remains challenging for successful tissue engineering. Without blood vessel formation, stem cell-based approaches are unable to fully regenerate damaged tissues due to limited support for cell viability and desired tissue/organ functionality. Herein, we report in situ cross-linkable gelatin−hydroxyphenyl propionic acid (GH) hydrogels that can induce pro-angiogenic profiles of MSCs via purely material-driven effects. This hydrogel directed endothelial differentiation of mouse and human patient-derived MSCs through integrin-mediated interactions at the cell-material interface, thereby promoting perfusable blood vessel formation in vitro and in vivo. The causative roles of specific integrin types (α1 and αvβ3) in directing endothelial differentiation were verified by blocking the integrin functions with chemical inhibitors. In addition, to verify the material-driven effect is not species-specific, we confirmed in vitro endothelial differentiation and in vivo blood vessel formation of patient-derived human MSCs by this hydrogel. These findings provide new insight into how purely material-driven effects can direct endothelial differentiation of MSCs, thereby promoting vascularization of scaffolds towards tissue engineering and regenerative medicine applications in humans.

Clinical trials utilizing mesenchymal stem cells (MSCs) for severe vascular diseases have highlighted the need to effectively engraft cells and promote pro-angiogenic activity. A functional material accomplishing these two goals is an ideal solution as spatiotemporal and batch-to-batch variability in classical therapeutic delivery can be minimized, and tissue regeneration would begin rapidly at the implantation site. Gelatin may serve as a promising biomaterial due to its excellent biocompatibility, biodegradability, and non-immuno/antigenicity. However, the dissolution of gelatin at body temperature and quick enzymatic degradation in vivo have limited its use thus far. To overcome these challenges, an injectable, in situ crosslinkable gelatin was developed by conjugating enzymatically-crosslinkable hydroxyphenyl propionic acid (GHPA). When MSCs are cultured in 3D in vitro or injected in vivo in GHPA, spontaneous endothelial differentiation occurs, as evidenced by marked increases in endothlelial cell marker expressions (Flk1, Tie2, ANGPT1, vWF) in addition to forming an extensive perfusable vascular network after 2-week subcutaneous implantation. Additionally, favorable host macrophage response is achieved with GHPA as shown by decreased iNOS and increased MRC1 expression. These results indicate GHPA as a promising soluble factor-free cell delivery template which induces endothelial differentiation of MSCs with robust neovasculature formation and favorable host response.

Over the last fifteen years, basic science and clinical studies have aimed to identify cancer stem cells (CSCs) in multiple types of cancer in order to unravel their mechanistic roles in cancer recurrence for therapeutic exploitation. Exposure of cells and tissues to hypoxia, or sub-atmospheric concentrations of oxygen (< 21% O2), stimulates various stress response pathways that bias the cells towards a self-preserving, anti-apoptotic phenotype. Despite major advances in our understanding of hypoxia, CSCs, and their interrelated nature, some of the most promising cancer therapies have shown limited efficacy in clinic for the past few years, in part due to the inherently hypoxic nature of growing tumors. In the present article, we discuss recent findings regarding the behavior of breast and brain CSCs under hypoxia, as well as the mechanisms that have been shown to drive their chemo-/radioresistance and metastatic potential.

Vascularization of a tissue-engineered construct enables efficient transport of nutrients and waste products; it is necessary for successful long-term tissue growth and host integration. Although significant progress has been made, sufficient vascularization of engineered constructs is still a major challenge, limiting clinical applications of tissue engineering (TE) approaches [1]. Successful vascularization promotes the interactions of TE implants with host tissues, leading to efficient tissue regeneration. Therefore, there is an unmet need to develop a more efficient method to vascularize TE constructs. In particular, obtaining a reliable source of endothelial cells (ECs) that line all blood vessels is a critical and challenging step towards successful vascularization of TE constructs, empowering TE to be applied in a larger scale and scope.

Graphene is a novel material whose application in the biomedical sciences has only begun to be realized. In the present study, we have employed three-dimensional graphene foams as culture substrates for human mesenchymal stem cells and provide evidence that these materials can maintain stem cell viability and promote osteogenic differentiation.

Inflammation and angiogenesis are inevitable in vivo responses to biomaterial implants. Continuous progress has been made in biomaterial design to improve tissue interactions with an implant by either reducing inflammation or promoting angiogenesis. However, it has become increasingly clear that the physiological processes of inflammation and angiogenesis are interconnected through various molecular mechanisms. Hence, there is an unmet need for engineering functional tissues by simultaneous activation of pro-angiogenic and anti-inflammatory responses to biomaterial implants. In this work, the modulus and fibrinogen adsorption of porous scaffolds were tuned to meet the requirements (i.e., ~100 kPa and ~10 nm, respectively), for soft tissue regeneration by employing tyrosine-derived combinatorial polymers with polyethylene glycol crosslinkers. Two types of functional peptides (i.e., pro-angiogenic laminin-derived C16 and anti-inflammatory thymosin β4-derived Ac-SDKP) were loaded in porous scaffolds through collagen gel embedding so that peptides were released in a controlled fashion, mimicking degradation of the extracellular matrix. The results from (1) in vitro coculture of human umbilical vein endothelial cells and human blood-derived macrophages and (2) in vivo subcutaneous implantation revealed the directly proportional relationship between angiogenic activities (i.e., tubulogenesis and perfusion capacity) and inflammatory activities (i.e., phagocytosis and F4/80 expression) upon treatment with either type of peptide. Interestingly, cotreatment with both types of peptides upregulated the angiogenic responses, while downregulating the inflammatory responses. Also, anti-inflammatory Ac-SDKP peptides reduced production of pro-inflammatory cytokines (i.e., interleukin [IL]-1β, IL-6, IL-8, and tumor necrosis factor alpha) even when treated in combination with pro-angiogenic C16 peptides. In addition to independent regulation of angiogenesis and inflammation, this study suggests a promising approach to improve soft tissue regeneration (e.g., blood vessel and heart muscle) when inflammatory diseases (e.g., ischemic tissue fibrosis and atherosclerosis) limit the regeneration process.

The role of reactive oxygen species (ROS)-mediated cell signal transduction pathways emanating from engineered cell substrates remains unclear. To elucidate the role, polymers derived from the amino acid L-tyrosine were used as synthetic matrix substrates. Variations in their chemical properties were created by co-polymerizing hydrophobic L-tyrosine derivatives with uncharged hydrophilic poly(ethylene glycol) (PEG, Mw = 1,000 Da), and negatively charged desaminotyrosyl-tyrosine (DT). These substrates were characterized for their intrinsic ability to generate ROS, as well as their ability to elicit Saos-2 cell responses in terms of intracellular ROS production, actin remodeling, and apoptosis. PEG-containing substrates induced both exogenous and intracellular ROS production, whereas the charged substrates reduced production of both types, indicating a coupling of exogenous ROS generation and intracellular ROS production. Furthermore, PEG-mediated ROS induction caused nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase and an increase in caspase-3 activity, confirming a link with apoptosis. PEG-rich pro-oxidant substrates caused cytoskeletal actin remodeling through β-actin cleavage by caspase-3 into fractins. The fractins co-localized to the mitochondria and reduced the mitochondrial membrane potential. The remnant cytosolic β-actin was polymerized and condensed, events consistent with apoptotic cell shrinkage. The cytoskeletal remodeling was integral to the further augmentation of intracellular ROS production. Conversely, the anti-oxidant DT-containing charged substrates suppressed the entire cascade of apoptotic progression. We demonstrate that ROS activity serves an important role in “outside-in” signaling for cells grown on substrates: the ROS activity couples exogenous stress, driven by substrate composition, to changes in intracellular signaling. This signaling causes cell apoptosis, which is mediated by actin remodeling. J. Cell. Physiol. 218: 549–557, 2009. © 2008 Wiley-Liss, Inc.

Cell-based, high-throughput screening has revolutionized the development of small-molecule pharmaceuticals. A similar paradigm for the accelerated development of biomaterials for cell and tissue engineering involves the iterative use of combinatorial biomaterial synthesis, rapid cellular response screens, and computational modeling methods. However, assays to probe cell responses to biomaterials are frequently subjective, lack dynamic responsiveness, and are limited to low-throughput experimentation. In this report, we highlight the use of high-resolution imaging of cell-based fluororeporters to establish and correlate quantifiable metrics of cell functional end points (e.g., cell growth, cell adhesion, cell attachment strength), as well as of intracellular cytoskeletal features (e.g., descriptors of actin organization) on a set of model biomaterial substrates synthesized by combinatorial variations. Selected mammalian cell lines were genetically engineered with a series of green fluorescent protein (GFP) fusion genes to allow for live cell imaging on biomaterials. We demonstrate that high-content imaging yields a large number of quantifiable morphometric descriptors of ultrastructural cell features (e.g., cell cytoskeleton) in conjunction with densitometric descriptors of cell behaviors (e.g., cell apoptosis). We illustrate how such descriptors can be used to discern combinatorial variations in substrate composition, and how living GFP reporters are uniquely suited to generate such descriptors unlike fixed tissue preparations. This quantitative approach of live fluororeporter cell imaging could be valuable for metrology of cell-material interactions.

The phenotype of endothelial cells (ECs) is specific to the vascular bed from which they originate. To examine how mechanical forces alter the phenotype of different ECs, we compared the effects of cyclic strain and motion control on reactive oxygen species (ROS) production and metabolism and cell adhesion molecule expression in human umbilical vein endothelial cells (HUVEC) vs. human aortic endothelial cells (HAEC). HUVEC and HAEC were subjected to cyclic strain (10% or 20%, 1 Hz), to a motion control that simulated fluid agitation over the cells without strain, or to static conditions for 24 h. We measured H2O2production with dichlorodihydrofluorescein acetate and superoxide with dihydroethidium fluorescence changes; superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) activities spectrophotometrically; and vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 protein expression with Western blot analyses. HUVEC under cyclic strain showed 1) higher intracellular H2O2levels, 2) increased SOD, catalase, and GPx activities, and 3) greater VCAM-1 and ICAM-1 protein expression, compared with motion control or static conditions. However, in HAEC, motion control induced higher levels of ROS, enzyme activities associated with ROS defense, and VCAM-1 and ICAM-1 expression than cyclic strain. The opposite responses obtained with these two human EC types may reflect their vessels of origin, in that HAEC are subjected to higher cyclic strain deformations in vivo than HUVEC.

Degradation of the extracellular matrix, facilitated by matrix metalloproteinases (MMPs), can lead to mechanical failure of vascular constructs, suggesting that MMP inhibition could improve survival of constructs. Therefore, we investigated the role of MMP-9 in collagen remodeling in vitro, focusing on the three major steps of production, degradation, and organization. Because an adequate blood supply is essential for survival of tissue-engineered constructs, we also evaluated the influence of MMP-9 deficiency on angiogenesis in vivo by implantation of thin biodegradable polymer scaffolds. Using aortic smooth muscle cells (SMCs) from wild-type and genetically deficient (9KO) mice, we examined the role of MMP-9 in collagen mRNA expression and protein accumulation, both with and without ascorbic acid treatment. We measured collagen assembly in a fibrillogenesis assay. We investigated in vivo angiogenesis and cell invasion, using fluorescence microangiography and histology. MMP-9 deficiency did not affect collagen mRNA production or polymer scaffold degradation, but collagen accumulation was greater in cultures of 9KO SMCs than in wild-type SMCs. Both MMP-9 deficiency and chemical inhibition impaired collagen degradation. Ascorbic acid treatment enhanced collagen production by 9KO SMCs compared with wild-type SMCs at 3 days, but by 7 days this effect was reversed. MMP-9 improved fibrillogenesis of collagen, significantly more on ascorbic acid treatment. MMP-9 deficiency dramatically decreased inflammatory cell invasion, but also capillary formation within biodegradable polymer scaffolds in vivo. Our data suggest that MMP inhibition, by impairing collagen organization and angiogenesis, might have detrimental effects on the survival of vascular constructs.

The blood-brain barrier (BBB) dynamically controls exchange between the brain and the body, but this interaction cannot be studied directly in the intact human brain or sufficiently represented by animal models. Most existing in vitro BBB models do not include neurons and glia with other BBB elements and do not adequately predict drug efficacy and toxicity. Under the National Institutes of Health Microtissue Initiative, we are developing a three-dimensional, multicompartment, organotypic microphysiological system representative of a neurovascular unit of the brain. The neurovascular unit system will serve as a model to study interactions between the central nervous system neurons and the cerebral spinal fluid (CSF) compartment, all coupled to a realistic blood-surrogate supply and venous return system that also incorporates circulating immune cells and the choroid plexus. Hence all three critical brain barriers will be recapitulated: blood-brain, brain-CSF, and blood-CSF. Primary and stem cell-derived human cells will interact with a variety of agents to produce critical chemical communications across the BBB and between brain regions. Cytomegalovirus, a common herpesvirus, will be used as an initial model of infections regulated by the BBB. This novel technological platform, which combines innovative microfluidics, cell culture, analytical instruments, bioinformatics, control theory, neuroscience, and drug discovery, will replicate chemical communication, molecular trafficking, and inflammation in the brain. The platform will enable targeted and clinically relevant nutritional and pharmacologic interventions for or prevention of such chronic diseases as obesity and acute injury such as stroke, and will uncover potential adverse effects of drugs. If successful, this project will produce clinically useful technologies and reveal new insights into how the brain receives, modifies, and is affected by drugs, other neurotropic agents, and diseases.

Poly(ethylene glycol) (PEG) is one of the most widely used compounds across a variety of platforms and is increasingly found in medical applications. Polycarbonates containing varying mol% of PEG (Mw 1000) were used to probe the effects of PEG on cell adhesion, proliferation, spreading, and survival. Two contrasting PEG-mediated cell signaling elements affected these cellular behaviors: (i) integrin α5 receptor mediated cellular focal adhesions to the biomaterial surface and (ii) modulation of cellular redox and apoptosis through generation of reactive oxygen species (ROS). At lower PEG1k mol% (5% and 8%) cell attachment and spreading decreased concomitantly due to ROS, whereas at the higher PEG1k mol% studied (10% and 20%) an unusual super-adhesive behavior was observed. At higher PEG1k mol% cells exhibited greatly enhanced spreading, which was confirmed through immunolocalization of integrin α5 receptors and enhanced mRNA expression of the integrin α5 gene. These cellular responses on higher PEG1k mol% co-polymers were sufficient to overcome the ROS-driven effects on caspase activation and cell shrinkage, which dominated at lower PEG1k mol%. These studies elucidate PEG-mediated cellular signaling with the implication that the adhesion and apoptotic activity of PEG-rich materials can be sensitively controlled by anti-oxidant addition. Moreover, this study shows that biomaterials can drive the cell fate in opposing directions through concurrent property changes.

Background The interaction of stem cells with their culture substrates is critical in controlling their fate and function. Declining stemness of adult-derived human mesenchymal stem cells (hMSCs) during in vitro expansion on tissue culture polystyrene (TCPS) severely limits their therapeutic efficacy prior to cell transplantation into damaged tissues. Thus, various formats of natural and synthetic materials have been manipulated in attempts to reproduce in vivo matrix environments in which hMSCs reside. Results We developed a series of patterned polymer matrices for cell culture by hot-pressing poly(ε-caprolactone) (PCL) films in femtosecond laser-ablated nanopore molds, forming nanofibers on flat PCL substrates. hMSCs cultured on these PCL fiber matrices significantly increased expression of critical self-renewal factors, Nanog and OCT4A, as well as markers of cell-cell interaction PECAM and ITGA2. The results suggest the patterned polymer fiber matrix is a promising model to maintain the stemness of adult hMSCs. Conclusion This approach meets the need for scalable, highly repeatable, and tuneable models that mimic extracellular matrix features that signal for maintenance of hMSC stemness.