Mustn1 is a smooth muscle cell-secreted microprotein that modulates skeletal muscle extracellular matrix composition

OBJECTIVE

Skeletal muscle plasticity and remodeling are critical for adapting tissue function to use, disuse, and regeneration. The aim of this study was to identify genes and molecular pathways that regulate the transition from atrophy to compensatory hypertrophy or recovery from injury. Here, we have used a mouse model of hindlimb unloading and reloading, which causes skeletal muscle atrophy, and compensatory regeneration and hypertrophy, respectively.

METHODS

We analyzed mouse skeletal muscle at the transition from hindlimb unloading to reloading for changes in transcriptome and extracellular fluid proteome. We then used qRT-PCR, immunohistochemistry, and bulk and single-cell RNA sequencing data to determine Mustn1 gene and protein expression, including changes in gene expression in mouse and human skeletal muscle with different challenges such as exercise and muscle injury. We generated Mustn1-deficient genetic mouse models and characterized them in vivo and ex vivo with regard to muscle function and whole-body metabolism. We isolated smooth muscle cells and functionally characterized them, and performed transcriptomics and proteomics analysis of skeletal muscle and aorta of Mustn1-deficient mice.

RESULTS

We show that Mustn1 (Musculoskeletal embryonic nuclear protein 1, also known as Mustang) is highly expressed in skeletal muscle during the early stages of hindlimb reloading. Mustn1 expression is transiently elevated in mouse and human skeletal muscle in response to intense exercise, resistance exercise, or injury. We find that Mustn1 expression is highest in smooth muscle-rich tissues, followed by skeletal muscle fibers. Muscle from heterozygous Mustn1-deficient mice exhibit differences in gene expression related to extracellular matrix and cell adhesion, compared to wild-type littermates. Mustn1-deficient mice have normal muscle and aorta function and whole-body glucose metabolism. We show that Mustn1 is secreted from smooth muscle cells, and that it is present in arterioles of the muscle microvasculature and in muscle extracellular fluid, particularly during the hindlimb reloading phase. Proteomics analysis of muscle from Mustn1-deficient mice confirms differences in extracellular matrix composition, and female mice display higher collagen content after chemically induced muscle injury compared to wild-type littermates.

CONCLUSIONS

We show that, in addition to its previously reported intracellular localization, Mustn1 is a microprotein secreted from smooth muscle cells into the muscle extracellular space. We explore its role in muscle ECM deposition and remodeling in homeostasis and upon muscle injury. The role of Mustn1 in fibrosis and immune infiltration upon muscle injury and dystrophies remains to be investigated, as does its potential for therapeutic interventions.

Multivalent insulin receptor activation using insulin-DNA origami nanostructures

Insulin binds the insulin receptor (IR) and regulates anabolic processes in target tissues. Impaired IR signalling is associated with multiple diseases, including diabetes, cancer and neurodegenerative disorders. IRs have been reported to form nanoclusters at the cell membrane in several cell types, even in the absence of insulin binding. Here we exploit the nanoscale spatial organization of the IR to achieve controlled multivalent receptor activation. To control insulin nanoscale spatial organization and valency, we developed rod-like insulin-DNA origami nanostructures carrying different numbers of insulin molecules with defined spacings. Increasing the insulin valency per nanostructure markedly extended the residence time of insulin-DNA origami nanostructures at the receptors. Both insulin valency and spacing affected the levels of IR activation in adipocytes. Moreover, the multivalent insulin design associated with the highest levels of IR activation also induced insulin-mediated transcriptional responses more effectively than the corresponding monovalent insulin nanostructures. In an in vivo zebrafish model of diabetes, treatment with multivalent-but not monovalent-insulin nanostructures elicited a reduction in glucose levels. Our results show that the control of insulin multivalency and spatial organization with nanoscale precision modulates the IR responses, independent of the insulin concentration. Therefore, we propose insulin nanoscale organization as a design parameter in developing new insulin therapies.

Soluble and multivalent Jag1 DNA origami nanopatterns activate Notch without pulling force

The Notch signaling pathway has fundamental roles in embryonic development and in the nervous system. The current model of receptor activation involves initiation via a force-induced conformational change. Here, we define conditions that reveal pulling force-independent Notch activation using soluble multivalent constructs. We treat neuroepithelial stem-like cells with molecularly precise ligand nanopatterns displayed from solution using DNA origami. Notch signaling follows with clusters of Jag1, and with chimeric structures where most Jag1 proteins are replaced by other binders not targeting Notch. Our data rule out several confounding factors and suggest a model where Jag1 activates Notch upon prolonged binding without appearing to need a pulling force. These findings reveal a distinct mode of activation of Notch and lay the foundation for the development of soluble agonists.

Affinity Maturated Transferrin Receptor Apical Domain Blocks Machupo Virus Glycoprotein Binding

Transferrin receptor 1 (TfR) delivers iron across cellular membranes by shuttling the ion carrier protein transferrin. This ability to deliver large protein ligands inside cells is taken advantage of by pathogens to infiltrate human cells. Notably, the receptor's outermost ectodomain, the apical domain, is used as a point of attachment for several viruses including hemorrhagic arenaviruses. To better understand interactions with the receptor it would be advantageous to probe sequence determinants in the apical domain with viral spike proteins. Here, we carried out affinity maturation of our computationally designed apical domain from human TfR to identify underlying driving forces that lead to better binding. The improved variants were confirmed by in vitro surface plasmon resonance measurements with dissociation constants obtained in the lower nanomolar range. It was found that the strong binding affinities for the optimized variants matched the strength of interactions with the native receptor. The structure of the best variant was determined experimentally indicating that the conformational change in the hairpin binding motif at the protein-protein interface plays a crucial role. The experimental methodology can be straightforwardly applied to other arenavirus or pathogens that use the apical domain. It can further be useful to probe host-virus compatibility or therapeutic strategies based on the transferrin receptor decoys.

Live Detection of Neural Progenitors and Glioblastoma Cells by an Oligothiophene Derivative

There is an urgent need for simple and non-invasive identification of live neural stem/progenitor cells (NSPCs) in the developing and adult brain as well as in disease, such as in brain tumors, due to the potential clinical importance in prognosis, diagnosis, and treatment of diseases of the nervous system. Here, we report a luminescent conjugated oligothiophene (LCO), named p-HTMI, for non-invasive and non-amplified real-time detection of live human patient-derived glioblastoma (GBM) stem cell-like cells and NSPCs. While p-HTMI stained only a small fraction of other cell types investigated, the mere addition of p-HTMI to the cell culture resulted in efficient detection of NSPCs or GBM cells from rodents and humans within minutes. p-HTMI is functionalized with a methylated imidazole moiety resembling the side chain of histidine/histamine, and non-methylated analogues were not functional. Cell sorting experiments of human GBM cells demonstrated that p-HTMI labeled the same cell population as CD271, a proposed marker for stem cell-like cells and rapidly migrating cells in glioblastoma. Our results suggest that the LCO p-HTMI is a versatile tool for immediate and selective detection of neural and glioma stem and progenitor cells.

STEM-19. LIVE DETECTION OF NEURAL STEM AND GLIOBLASTOMA CELLS BY A LUMINESCENT CONJUGATED OLIGOTHIOPHENE DERIVATIVE

Glioblastoma (GBM) is an aggressive nervous system tumor with a mean survival time of 12-14 months. Cells with neural stem cell-like properties can be derived from GBM tumors. These cells seem to escape conventional irradiation treatment, chemotherapy, and surgery, and may play a crucial role for relapse. It is therefore urgent to develop novel approaches for reliable detection of neural stem cell-like cells in GBM. Here we report a luminescent conjugated oligothiophene (LCO), named GlioStem (p-HTMI), for non-invasive and non-amplified real-time detection of live human patient-derived GBM cells and embryonic neural stem/progenitor cells (NSPCs). Within a maximum of 10 minutes after administration of the molecule in vitro, in the existing media, fluorescence emission was observed without any modulation of the cells or additional vehicle, resulting in efficient detection of cytoplasmic luminescent signal in NSPCs or GBM cells from rodents and humans, detectable at Alexa488/GFP wavelength. GlioStem is functionalized with a methylated imidazole moiety resembling the side chain of histidine/histamine, and non-methylated analogues were not functional. In vitro, GlioStem was shown to identify fetal cortical NSPCs from rat (FGF2-expanded), embryonic stem cell-derived NSPCs from mouse (FGF2/EGF-expanded), and FGF2-exposed C6 glioma cell cultures from rat, but not any other cell types investigated. Cell sorting experiments of patient-derived, FGF2/EGF-expanded GBM cells demonstrated that GlioStem in addition to NSPC-markers like Nestin and Sox2 labeled the same population (overlap > 90%) of cells as CD271, a proposed marker for stem cell-like cells and rapidly migrating cells in glioblastoma. Our results suggest that the LCO GlioStem is a versatile tool for immediate and selective detection of subpopulations of neural stem and glioma cells.

Patterned Carboxymethyl-Dextran Functionalized Surfaces Using Organic Mixed Monolayers for Biosensing Applications

The deposition of biomolecules on biosensing surface platforms plays a key role in achieving the required sensitivity and selectivity for biomolecular interactions analysis. Controlling the interaction between the surface and biomolecules is increasingly becoming a crucial design tool to modulate the surface properties needed to improve the performance of the assay and the detection outcome. Carboxymethyl-dextran (CMD) coating can be exploited to promote chemical grafting of proteins, providing a hydrophilic, bioinert, nonfouling surface and a high surface density of immobilized proteins. In the present work, we developed and optimized a technique to produce a cost-effective CMD-based patterned surface for the immobilization of biomolecules to be used on standard protocols optimization. They consist of silicon or glass substrates with patterned bioactive areas able to efficiently confine the sampling solution by simply exploiting hydrophilic/hydrophobic patterning of the surface. The fabrication process involves the use of low-cost instruments and techniques, compatible with large scale production. The devices were validated through a chemiluminescence assay we recently developed for the analysis of binding of DNA nanoassemblies modified with an affinity binder to target proteins immobilized on the bioactive areas. Through this assay we were able to characterize the chemical reactivity of two target proteins toward a dextran matrix on patterned surfaces and to compare it with model CMD-based surface plasmon resonance (SPR) surfaces. We found a high reproducibility and selectivity in molecular recognition, consistent with results obtained on SPR sensor surfaces. The suggested approach is straightforward, cheap, and provides the means to assess patterned functionalized surfaces for bioanalytical platforms.

Motif-driven protein binder design towards transferrin receptor helical domain

Human transferrin receptor 1 (TfR) is necessary for the delivery of the iron carrier protein transferrin into cells and can be utilized for targeted delivery across cellular membranes. Binding of transferrin to the receptor is regulated by hereditary hemochromatosis protein (HFE), an iron regulatory protein that partly shares a binding site with transferrin on TfR. Here, we derived essential binding interactions from HFE and computationally grafted these into a library of small protein scaffolds. One of the designed proteins, TB08, was further optimized computationally and experimentally to identify variants with improved binding to TfR. The optimized variant, TB08 S3.1, expressed well in the E. coli expression system and had an affinity to TfR in the low micromolar range, K_d  ≈ 1 μm, as determined by surface plasmon resonance. A binding competition assay with transferrin further confirmed the interaction of the evolved variant to TfR at the shared binding surface. Additionally, the GFP-tagged evolved variant of TB08 demonstrated cellular internalization as determined by fluorescent and confocal microscopy in HeLa cells. The designed protein is small, allows for robust cargo tagging, and interacts specifically with TfR, thus making it a valuable tool for the characterization of TfR-mediated cellular transport mechanisms and for the assessment of engineering strategies for cargo delivery across cell membranes.

Effects of topological constraints on the alignment and maturation of multinucleated myotubes

Microfluidic-based technologies enable the development of cell culture systems that provide tailored microenvironmental inputs to mammalian cells. Primary myoblasts can be induced to differentiate into multinucleated skeletal muscle cells, myotubes, which are a relevant model system for investigating skeletal muscle metabolism and physiology in vitro. However, it remains challenging to differentiate primary myoblasts into mature myotubes in microfluidics devices. Here we investigated the effects of integrating continuous (solid) and intermittent (dashed) walls in microfluidic channels as topological constraints in devices designed to promote the alignment and maturation of primary myoblast-derived myotubes. The topological constraints caused alignment of the differentiated myotubes, mimicking the native anisotropic organization of skeletal muscle cells. Interestingly, dashed walls facilitated the maturation of skeletal muscle cells, as measured by quantifying myotube cell area and the number of nuclei per myotube. Together, our results suggest that integrating dashed walls as topographic constraints in microfluidic devices supports the alignment and maturation of primary myoblast-derived myotubes.

Spatial Regulation of T-Cell Signaling by Programmed Death-Ligand 1 on Wireframe DNA Origami Flat Sheets

Programmed Death-1 (PD-1) is a coinhibitory receptor expressed on activated T cells that suppresses T-cell signaling and effector functions. It has been previously shown that binding to its ligand PD-L1 induces a spatial reorganization of PD-1 receptors into microclusters on the cell membrane. However, the roles of the spatial organization of PD-L1 on PD-1 clustering and T-cell signaling have not been elucidated. Here, we used DNA origami flat sheets to display PD-L1 ligands at defined nanoscale distances and investigated their ability to inhibit T-cell activation in vitro. We found that DNA origami flat sheets modified with CD3 and CD28 activating antibodies (FS-α-CD3-CD28) induced robust T-cell activation. Co-treatment with flat sheets presenting PD-L1 ligands separated by ∼200 nm (FS-PD-L1-200), but not 13 nm (FS-PD-L1-13) or 40 nm (FS-PD-L1-40), caused an inhibition of T-cell signaling, which increased with increasing molar ratio of FS-PD-L1-200 to FS-α-CD3-CD28. Furthermore, FS-PD-L1-200 induced the formation of smaller PD-1 nanoclusters and caused a larger reduction in IL-2 expression compared to FS-PD-L1-13. Together, these findings suggest that the spatial organization of PD-L1 determines its ability to regulate T-cell signaling and may guide the development of future nanomedicine-based immunomodulatory therapies.

A DNA-nanoassembly-based approach to map membrane protein nanoenvironments

Most proteins at the plasma membrane are not uniformly distributed but localize to dynamic domains of nanoscale dimensions. To investigate their functional relevance, there is a need for methods that enable comprehensive analysis of the compositions and spatial organizations of membrane protein nanodomains in cell populations. Here we describe the development of a non-microscopy-based method for ensemble analysis of membrane protein nanodomains. The method, termed nanoscale deciphering of membrane protein nanodomains (NanoDeep), is based on the use of DNA nanoassemblies to translate membrane protein organization information into a DNA sequencing readout. Using NanoDeep, we characterized the nanoenvironments of Her2, a membrane receptor of critical relevance in cancer. Importantly, we were able to modulate by design the inventory of proteins analysed by NanoDeep. NanoDeep has the potential to provide new insights into the roles of the composition and spatial organization of protein nanoenvironments in the regulation of membrane protein function.

Spatial organization-dependent EphA2 transcriptional responses revealed by ligand nanocalipers

Ligand binding induces extensive spatial reorganization and clustering of the EphA2 receptor at the cell membrane. It has previously been shown that the nanoscale spatial distribution of ligands modulates EphA2 receptor reorganization, activation and the invasive properties of cancer cells. However, intracellular signaling downstream of EphA2 receptor activation by nanoscale spatially distributed ligands has not been elucidated. Here, we used DNA origami nanostructures to control the positions of ephrin-A5 ligands at the nanoscale and investigated EphA2 activation and transcriptional responses following ligand binding. Using RNA-seq, we determined the transcriptional profiles of human glioblastoma cells treated with DNA nanocalipers presenting a single ephrin-A5 dimer or two dimers spaced 14, 40 or 100 nm apart. These cells displayed divergent transcriptional responses to the differing ephrin-A5 nano-organization. Specifically, ephrin-A5 dimers spaced 40 or 100 nm apart showed the highest levels of differential expressed genes compared to treatment with nanocalipers that do not present ephrin-A5. These findings show that the nanoscale organization of ephrin-A5 modulates transcriptional responses to EphA2 activation.

Solution-Controlled Conformational Switching of an Anchored Wireframe DNA Nanostructure

Self-assembled DNA origami nanostructures have a high degree of programmable spatial control that enables nanoscale molecular manipulations. A surface-tethered, flexible DNA nanomesh is reported herein which spontaneously undergoes sharp, dynamic conformational transitions under physiological conditions. The transitions occur between two major macrostates: a spread state dominated by the interaction between the DNA nanomesh and the BSA/streptavidin surface and a surface-avoiding contracted state. Due to a slow rate of stochastic transition events on the order of tens of minutes, the dynamic conformations of individual structures can be detected in situ with DNA PAINT microscopy. Time series localization data with automated imaging processing to track the dynamically changing radial distribution of structural markers are combined. Conformational distributions of tethered structures in buffers with elevated pH exhibit a calcium-dependent domination of the spread state. This is likely due to electrostatic interactions between the structures and immobilized surface proteins (BSA and streptavidin). An interaction is observed in solution under similar buffer conditions with dynamic light scattering. Exchanging between solutions that promote one or the other state leads to in situ sample-wide transitions between the states. The technique herein can be a useful tool for dynamic control and observation of nanoscale interactions and spatial relationships.

Neurturin is a PGC-1α1-controlled myokine that promotes motor neuron recruitment and neuromuscular junction formation

OBJECTIVE

We examined whether skeletal muscle overexpression of PGC-1α1 or PGC-1α4 affected myokine secretion and neuromuscular junction (NMJ) formation.

METHODS

A microfluidic device was used to model endocrine signaling and NMJ formation between primary mouse myoblast-derived myotubes and embryonic stem cell-derived motor neurons. Differences in hydrostatic pressure allowed for fluidic isolation of either cell type or unidirectional signaling in the fluid phase. Myotubes were transduced to overexpress PGC-1α1 or PGC-1α4, and myokine secretion was quantified using a proximity extension assay. Morphological and functional changes in NMJs were measured by fluorescent microscopy and by monitoring muscle contraction upon motor neuron stimulation.

RESULTS

Skeletal muscle transduction with PGC-1α1, but not PGC-1α4, increased NMJ formation and size. PGC-1α1 increased muscle secretion of neurturin, which was sufficient and necessary for the effects of muscle PGC-1α1 on NMJ formation.

CONCLUSIONS

Our findings indicate that neurturin is a mediator of PGC-1α1-dependent retrograde signaling from muscle to motor neurons.

Computer-Aided Production of Scaffolded DNA Nanostructures from Flat Sheet Meshes

The use of DNA as a nanoscale construction material has been a rapidly developing field since the 1980s, in particular since the introduction of scaffolded DNA origami in 2006. Although software is available for DNA origami design, the user is generally limited to architectures where finding the scaffold path through the object is trivial. Herein, we demonstrate the automated conversion of arbitrary two‐dimensional sheets in the form of digital meshes into scaffolded DNA nanostructures. We investigate the properties of DNA meshes based on three different internal frameworks in standard folding buffer and physiological salt buffers. We then employ the triangulated internal framework and produce four 2D structures with complex outlines and internal features. We demonstrate that this highly automated technique is capable of producing complex DNA nanostructures that fold with high yield to their programmed configurations, covering around 70 % more surface area than classic origami flat sheets.

Autologous Peripheral Blood Mononuclear Cells as Treatment in Refractory Acute Respiratory Distress Syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a devastating disorder. Despite enormous efforts in clinical research, effective treatment options are lacking, and mortality rates remain unacceptably high.

OBJECTIVES

A male patient with severe ARDS showed no clinical improvement with conventional therapies. Hence, an emergent experimental intervention was performed.

METHODS

We performed intratracheal administration of autologous peripheral blood-derived mononuclear cells (PBMCs) and erythropoietin (EPO).

RESULTS

We found that after 2 days of initial PBMC/EPO application, lung function improved and extracorporeal membrane oxygenation (ECMO) support was reduced. Bronchoscopy and serum inflammatory markers revealed reduced inflammation. Additionally, serum concentration of miR-449a, b, c and miR-34a, a transient upregulation of E-cadherin and associated chromatin marks in PBMCs indicated airway epithelial differentiation. Extracellular vesicles from PBMCs demonstrated anti-inflammatory capacity in a TNF-α-mediated nuclear factor-x03BA;B in vitro assay. Despite improving respiratory function, the patient died of multisystem organ failure on day 38 of ECMO treatment.

CONCLUSIONS

This case report provides initial encouraging evidence to use locally instilled PBMC/EPO for treatment of severe refractory ARDS. The observed clinical improvement may partially be due to the anti-inflammatory effects of PBMC/EPO to promote tissue regeneration. Further studies are needed for more in-depth understanding of the underlying mechanisms of in vivo regeneration.

Neural stem cell differentiation is dictated by distinct actions of nuclear receptor corepressors and histone deacetylases

Signaling factors including retinoic acid (RA) and thyroid hormone (T3) promote neuronal, oligodendrocyte, and astrocyte differentiation of cortical neural stem cells (NSCs). However, the functional specificity of transcriptional repressor checkpoints controlling these differentiation programs remains unclear. Here, we show by genome-wide analysis that histone deacetylase (HDAC)2 and HDAC3 show overlapping and distinct promoter occupancy at neuronal and oligodendrocyte-related genes in NSCs. The absence of HDAC3, but not HDAC2, initiated a neuronal differentiation pathway in NSCs. The ablation of the corepressor NCOR or HDAC2, in conjunction with T3 treatment, resulted in increased expression of oligodendrocyte genes, revealing a direct HDAC2-mediated repression of Sox8 and Sox10 expression. Interestingly, Sox10 was required also for maintaining the more differentiated state by repression of stem cell programming factors such as Sox2 and Sox9. Distinct and nonredundant actions of NCORs and HDACs are thus critical for control of lineage progression and differentiation programs in neural progenitors.

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ChIP-seq reveals distinct and overlapping occupancy of HDAC2 and HDAC3 in NSCs

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Absence of NCOR promotes oligodendrocyte differentiation of NSCs

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HDAC2 controls Sox10 expression in OL differentiation via a SOX2-occupied enhancer

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Sox10 is required for maintaining the differentiated state in late OL precursors

CtBPs sense microenvironmental oxygen levels to regulate neural stem cell state

Bone morphogenetic proteins (BMPs) secreted by the dorsal neural tube and overlying ectoderm are key signals for the specification of the roof plate and dorsal interneuron populations. However, the signals that confer nonneurogenic character to the roof plate region are largely unknown. We report that the roof plate region shows elevated oxygen levels compared to neurogenic regions of the neural tube. These high oxygen levels are required for the expression of the antineuronal transcription factor Hes1 in the roof plate region. The transcriptional corepressor CtBP is a critical mediator of the oxygen-sensing response. High oxygen promotes a decrease in the CtBP occupancy of the promoter of Hes1. Furthermore, under conditions of high oxygen and BMP, CtBP associates with HES1 and represses neurogenesis. We propose that CtBP integrates signals originating from microenvironmental levels of oxygen and BMP to confer nonneurogenic character to the roof plate region.

Preservation of aortic root architecture and properties using a detergent-enzymatic perfusion protocol

Aortic valve degeneration and dysfunction is one of the leading causes for morbidity and mortality. The conventional heart-valve prostheses have significant limitations with either life-long anticoagulation therapeutic associated bleeding complications (mechanical valves) or limited durability (biological valves). Tissue engineered valve replacement recently showed encouraging results, but the unpredictable outcome of tissue degeneration is likely associated to the extensive tissue processing methods. We believe that optimized decellularization procedures may provide aortic valve/root grafts improved durability. We present an improved/innovative decellularization approach using a detergent-enzymatic perfusion method, which is both quicker and has less exposure of matrix degenerating detergents, compared to previous protocols. The obtained graft was characterized for its architecture, extracellular matrix proteins, mechanical and immunological properties. We further analyzed the engineered aortic root for biocompatibility by cell adhesion and viability in vitro and heterotopic implantation in vivo. The developed decellularization protocol was substantially reduced in processing time whilst maintaining tissue integrity. Furthermore, the decellularized aortic root remained bioactive without eliciting any adverse immunological reaction. Cell adhesion and viability demonstrated the scaffold's biocompatibility. Our optimized decellularization protocol may be useful to develop the next generation of clinical valve prosthesis with a focus on improved mechanical properties and durability.

Electrochemical control of growth factor presentation to steer neural stem cell differentiation

Let it grow: The conjugated polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was synthesized with heparin as the counterion to form a cell culture substrate. The surface of PEDOT:heparin in the neutral state associated biologically active growth factors. Electrochemical in situ oxidation of PEDOT during live cell culture decreased the bioavailability of the growth factor and created an exact onset of neural stem cell differentiation.

Control of neural stem cell survival by electroactive polymer substrates

Stem cell function is regulated by intrinsic as well as microenvironmental factors, including chemical and mechanical signals. Conducting polymer-based cell culture substrates provide a powerful tool to control both chemical and physical stimuli sensed by stem cells. Here we show that polypyrrole (PPy), a commonly used conducting polymer, can be tailored to modulate survival and maintenance of rat fetal neural stem cells (NSCs). NSCs cultured on PPy substrates containing different counter ions, dodecylbenzenesulfonate (DBS), tosylate (TsO), perchlorate (ClO₄) and chloride (Cl), showed a distinct correlation between PPy counter ion and cell viability. Specifically, NSC viability was high on PPy(DBS) but low on PPy containing TsO, ClO₄ and Cl. On PPy(DBS), NSC proliferation and differentiation was comparable to standard NSC culture on tissue culture polystyrene. Electrical reduction of PPy(DBS) created a switch for neural stem cell viability, with widespread cell death upon polymer reduction. Coating the PPy(DBS) films with a gel layer composed of a basement membrane matrix efficiently prevented loss of cell viability upon polymer reduction. Here we have defined conditions for the biocompatibility of PPy substrates with NSC culture, critical for the development of devices based on conducting polymers interfacing with NSCs.

Inkjet printing of macromolecules on hydrogels to steer neural stem cell differentiation

Inkjet printing allows for the rapid and inexpensive printing of cells, materials, and protein molecules. However, the combination of inkjet printing and control of neural stem cell (NSC) multipotency and differentiation has remained unexplored. We used an inkjet printer (Canon BJC-2100) to print biologically active macromolecules on poly-acrylamide-based hydrogels (HydroGel(TM)), which were subsequently seeded with primary fetal NSCs. NSCs cultured on areas printed with fibroblast growth factor-2 (FGF2) remained undifferentiated, consistent with the effects of FGF2 when administered in solution. NSCs cultured in parallel on the same hydrogels but in areas printed with ciliary neurotrophic factor (CNTF) or fetal bovine serum (FBS) displayed a rapid induction of markers for astrocytic (glial fibrillary acidic protein, GFAP) or smooth muscle (smooth muscle actin, SMA) differentiation, respectively. These results are consistent with known actions of CNTF and FBS on NSCs. Importantly, NSCs cultured on a printed gradient of increasing levels of CNTF showed a linear increase in numbers of cells expressing GFAP, demonstrating a functional gradient of CNTF. Lastly, genetically modified NSCs proved to respond properly to printed macromolecules, suggesting that inkjet printing can successfully be combined with gene delivery to achieve effective control of stem cell differentiation.

Getting the right stuff: controlling neural stem cell state and fate in vivo and in vitro with biomaterials

Stem cell therapy holds great promises in medical treatment by, e.g., replacing lost cells, re-constitute healthy cell populations and also in the use of stem cells as vehicles for factor and gene delivery. Embryonic stem cells have rightfully attracted a large interest due to their proven capacity of differentiating into any cell type in the embryo in vivo. Tissue-specific stem cells are however already in use in medical practice, and recently the first systematic medical trials involving human neural stem cell (NSC) therapy have been launched. There are yet many obstacles to overcome and procedures to improve. To ensure progress in the medical use of stem cells increased basic knowledge of the molecular mechanisms that govern stem cell characteristics is necessary. Here we provide a review of the literature on NSCs in various aspects of cell therapy, with the main focus on the potential of using biomaterials to control NSC characteristics, differentiation, and delivery. We summarize results from studies on the characteristics of endogenous and transplanted NSCs in rodent models of neurological and cancer diseases, and highlight recent advancements in polymer compatibility and applicability in regulating NSC state and fate. We suggest that the development of specially designed polymers, such as hydrogels, is a crucial issue to improve the outcome of stem cell therapy in the central nervous system.

The effect of environmental factors on the response of human corneal epithelial cells to nanoscale substrate topography

We have previously shown that human corneal epithelial cells sense and react to nanoscale substrate topographic stimuli [Teixeira AI, Abrams GA, Bertics PJ, Murphy CJ, Nealey PF. Epithelial contact guidance on well-defined micro- and nanostructured substrates. J Cell Sci 2003;116(10):1881-92; Karuri NW, Liliensiek S, Teixeira AI, Abrams G, Campbell S, Nealey PF, et al. Biological length scale topography enhances cell-substratum adhesion of human corneal epithelial cells. J Cell Sci 2004;117(15):3153-64]. Here we demonstrate that cellular responses to nanoscale substrate topographies are modulated by the context in which these stimuli are presented to cells. In Epilife medium, cells aligned preferentially in the direction perpendicular to nanoscale grooves and ridges. This is in contrast to a previous study where cells cultured in DMEM/F12 medium aligned in the direction parallel to nanoscale topographic features [Teixeira AI, Abrams GA, Bertics PJ, Murphy CJ, Nealey PF. Epithelial contact guidance on well-defined micro- and nanostructured substrates. J Cell Sci 2003;116(10):1881-92]. Additionally, cell alignment in Epilife medium was dependent on pattern pitch. Cells switched from perpendicular to parallel alignment when the pitch was increased from 400 to 4,000 nm. There was a transition region (between 800 and 1,600 nm pitch) where both parallel and perpendicular alignments were favored compared to all other cellular orientations. Cells formed focal adhesions parallel to the substrate topographies in this transition region. On the nano- and microscale patterns, 400 and 4,000 nm pitch, focal adhesions were almost exclusively oriented obliquely to the topographic patterns.

Recording Notch signaling in real time

Notch signaling is a highly conserved signaling pathway, which is critical for many cell fate decisions. Ligand activation of Notch leads to cleavage of the Notch receptor and liberation of the Notch intracellular domain (ICD) from the membrane-tethered receptor. After translocation to the nucleus, the Notch ICD interacts with the DNA-binding protein CSL to activate gene transcription. To better understand the temporal and spatial aspects of Notch signaling, we here describe a fluorescent protein-based reporter assay that allows Notch activation to be followed in real time in individual cells. We have generated a reporter construct composed of 12 CSL-binding motifs linked to fluorescent proteins with different half-lives: a stabler red fluorescent protein (DsRedExpressDR) and a destabilized form of green fluorescent protein (d1EGFP). The fluorescent reporters reflect the activation status of Notch signaling with single-cell resolution. The reporters rapidly respond to various forms of Notch activation, including ligand activation of full-length Notch receptors. Finally, we use this assay to gain insights into the level of Notch signaling in CNS progenitor cells in culture and in vivo.

Responses of human keratocytes to micro- and nanostructured substrates

We have previously shown that human corneal epithelial cells respond to synthetic topographic features with dimensions similar to those found in the native human corneal basement membrane. Epithelial cells integrated inputs from substrate topography and soluble factors in the culture medium to generate alignment responses to substrate topographic anisotropies. Human keratocytes are the main cellular components of the stroma, the tissue that underlies the corneal epithelium. Here we report that keratocytes aligned more strongly than epithelial cells along topographic patterns of grooves and ridges. On patterns with pitches of 800 nm and larger approximately 70% of keratocytes were aligned along the patterns compared to 35% for epithelial cells. On 70 nm-wide ridges on a 400-nm pitch, keratocyte alignment dropped to 45%, whereas epithelial cell alignment remained constant. Similarly to epithelial cells, focal adhesions and associated stress fibers in keratocytes were aligned mainly along the substrate topographies, although oblique orientations were also observed. Furthermore, keratocytes cultured on the nanoscale patterns had fewer stress fibers and focal adhesions than cells cultured on microscale patterns or on smooth substrates.

Biological length scale topography enhances cell-substratum adhesion of human corneal epithelial cells

The basement membrane possesses a rich 3-dimensional nanoscale topography that provides a physical stimulus, which may modulate cell-substratum adhesion. We have investigated the strength of cell-substratum adhesion on nanoscale topographic features of a similar scale to that of the native basement membrane. SV40 human corneal epithelial cells were challenged by well-defined fluid shear, and cell detachment was monitored. We created silicon substrata with uniform grooves and ridges having pitch dimensions of 400-4000 nm using X-ray lithography. F-actin labeling of cells that had been incubated for 24 hours revealed that the percentage of aligned and elongated cells on the patterned surfaces was the same regardless of pitch dimension. In contrast, at the highest fluid shear, a biphasic trend in cell adhesion was observed with cells being most adherent to the smaller features. The 400 nm pitch had the highest percentage of adherent cells at the end of the adhesion assay. The effect of substratum topography was lost for the largest features evaluated, the 4000 nm pitch. Qualitative and quantitative analyses of the cells during and after flow indicated that the aligned and elongated cells on the 400 nm pitch were more tightly adhered compared to aligned cells on the larger patterns. Selected experiments with primary cultured human corneal epithelial cells produced similar results to the SV40 human corneal epithelial cells. These findings have relevance to interpretation of cell-biomaterial interactions in tissue engineering and prosthetic design.

Epithelial contact guidance on well-defined micro- and nanostructured substrates

The human corneal basement membrane has a rich felt-like surface topography with feature dimensions between 20 nm and 200 nm. On the basis of these findings, we designed lithographically defined substrates to investigate whether nanotopography is a relevant stimulus for human corneal epithelial cells. We found that cells elongated and aligned along patterns of grooves and ridges with feature dimensions as small as 70 nm, whereas on smooth substrates, cells were mostly round. The percentage of aligned cells was constant on substrate tomographies with lateral dimensions ranging from the nano- to the micronscale, and increased with groove depth. The presence of serum in the culture medium resulted in a larger percentage of cells aligning along the topographic patterns than when no serum was added to the basal medium. When present, actin microfilaments and focal adhesions were aligned along the substrate topographies. The width of the focal adhesions was determined by the width of the ridges in the underlying substrate. This work documents that biologic length-scale topographic features that model features encountered in the native basement membrane can profoundly affect epithelial cell behavior.

Adhesion and proliferation of corneal epithelial cells on self-assembled monolayers

The effect of surface chemistry on the proliferation and adhesion of SV-40 human corneal epithelial cells was investigated. The surface chemistry of substrates was controlled by the deposition of self-assembled monolayers (SAMs) terminated with the following functional groups: -CF3, -CH3, -CO(2)H, and -NH(2). SAMs of alkanethiols on gold and of alkylsiloxanes on SiOx were included in the study. Comparisons are made between different types and functionalities of SAMs and between SAM-covered substrates and tissue culture polystyrene. Adhesion assays were performed after incubation of the cells for 1 h in 10% fetal bovine serum and in serum-free conditions. The cellular response was found to be a function of surface chemistry and the presence of exogenous proteins. The number of cells that adhered to most of the SAMs in 10% serum and in serum-free conditions was not significantly different from the number of cells that adhered to TCPS. Proliferation assays were carried out in 10% serum and in 0.5% serum. Cell behavior was influenced by surface chemistry but did not deviate significantly from the behavior on TCPS for most of the SAMs. Serum level did not play a major role in cell proliferation. Our data establish the expected behaviors for a corneal epithelial cell line under defined conditions on specific surfaces.