Significant efforts have been directed to understanding the factors that influence the lineage commitment of stem cells. This paper demonstrates that cell shape, independent of soluble factors, has a ...strong influence on the differentiation of human mesenchymal stem cells (MSCs) from bone marrow. When exposed to competing soluble differentiation signals, cells cultured in rectangles with increasing aspect ratio and in shapes with pentagonal symmetry but with different subcellular curvature—and with each occupying the same area—display different adipogenesis and osteogenesis profiles. The results reveal that geometric features that increase actomyosin contractility promote osteogenesis and are consistent with in vivo characteristics of the microenvironment of the differentiated cells. Cytoskeletal-disrupting pharmacological agents modulate shape-based trends in lineage commitment verifying the critical role of focal adhesion and myosin-generated contractility during differentiation. Microarray analysis and pathway inhibition studies suggest that contractile cells promote osteogenesis by enhancing c-Jun N-terminal kinase (JNK) and extracellular related kinase (ERK1/2) activation in conjunction with elevated wingless-type (Wnt) signaling. Taken together, this work points to the role that geometric shape cues can play in orchestrating the mechanochemical signals and paracrine/autocrine factors that can direct MSCs to appropriate fates.
Abstract Human mesenchymal stem cells (MSCs) have broad therapeutic potential due to their ability to differentiate into multiple cell types. However, when cultured ex vivo MSCs will spontaneously ...differentiate and have been shown to lose multipotency after prolonged passaging. Cell culture conditions that promote maintenance of multipotency during in vitro expansion are a critical need to fully realize the therapeutic potential of MSCs. Here we show that by confining MSCs to small islands, we can restrict inappropriate lineage specification and enhance the expression of mesenchymal stem cell markers Stro-1 and Endoglin. Even when released from the islands and reseeded, cells previously cultured in patterns maintain higher expression of MSC markers compared to cells cultured on plastic, while maintaining their ability to differentiate into adipocytes and osteoblasts. Exposure of non-patterned cells to inhibitors of myosin and Rho-associated protein kinase (ROCK) leads to increased expression of stem cell markers. Our findings suggest that maintenance of MSC “stemness” requires a low state of actomyosin contractility. This work will prove useful in the development of culture conditions for the maintenance of multipotent MSCs in vitro and for the design of niche-mimetic biomaterials.
Historically the culture of mammalian cells in the laboratory has been performed on planar substrates with media cocktails that are optimized to maintain phenotype. However, it is becoming ...increasingly clear that much of biology discerned from 2D studies does not translate well to the 3D microenvironment. Over the last several decades, 2D and 3D microengineering approaches have been developed that better recapitulate the complex architecture and properties of in vivo tissue. Inspired by the infrastructure of the microelectronics industry, lithographic patterning approaches have taken center stage because of the ease in which cell‐sized features can be engineered on surfaces and within a broad range of biocompatible materials. Patterning and templating techniques enable precise control over extracellular matrix properties including: composition, mechanics, geometry, cell–cell contact, and diffusion. In this review article we explore how the field of engineered extracellular matrices has evolved with the development of new hydrogel chemistry and the maturation of micro‐ and nano‐ fabrication. Guided by the spatiotemporal regulation of cell state in developing tissues, techniques for micropatterning in 2D, pseudo‐3D systems, and patterning within 3D hydrogels will be discussed in the context of translating the information gained from 2D systems to synthetic engineered 3D tissues.
Mammalian cells have historically been cultured in the laboratory on rigid, planar substrates. However, cell signaling in 2D environments often fails to recapitulate the complex dynamic processes that occur in vivo. Here we explore how the field of engineered extracellular matrices has evolved from 2D cell culture to 3D microengineered systems that better reflect the complexity of native tissue.
An expedient method for the synthesis of cyclic carbonates from homoallylic carbonic acid esters by means of photo‐aerobic selenium‐π‐acid multicatalysis is reported. Until now, conceptually related ...methods commonly relied either on the stoichiometric addition of electrophiles onto the substrate's alkene moiety or the presence of pre‐installed leaving groups in allylic position of said alkene to – in part, catalytically – initiate an intramolecular attack by an adjacent carbonic acid ester group. In sharp contrast, the current study shows that the C−C double bond of homoallylic carbonic acid esters can be directly activated by the catalytic interplay of a pyrylium dye and a diselane using ambient air as the sole oxidant and visible light as an energy source.
A useful protocol to synthesize 1,3‐dioxan‐2‐ones from homoallylic carbonates by photo‐aerobic selenium‐π‐acid multicatalysis is reported. Previous methods predominantly relied on stoichiometric additions of electrophiles onto alkenes or the presence of nucleofuges in allylic position of the olefin. In contrast, the C−C double bond can also be directly activated by the catalytic interplay of a pyrylium dye and a diselane.
The dynamic epigenetic landscape directs gene expression patterns that dictate cellular form and function, and drive the assembly of cells into tissues. The high degree of plasticity in the ...epigenetic landscape of mammalian cells is directed by materials, which provide the context in which cells receive and integrate multivariate signals to programme the chromatin state towards specific functional outcomes. In this Review, we explore how materials guide the cellular epigenetic landscape and discuss how engineered materials target cell plasticity, particularly through dynamic changes in histone methylation and acetylation. After discussing findings in developmental biology and cancer research that link materials parameters to chromatin state, we highlight how cell culture materials that control ligand presentation, mechanics, topography and geometry have shown how materials cues and context influence chromatin state through mechanotransduction. Finally, we describe how tissue fabrication can control cellular plasticity to drive meaningful biological activities that may facilitate the assembly of cells and tissues into functional architectures.The dynamic epigenetic landscape directs gene expression patterns that regulate cellular form and function. Designer cell culture materials have shed light on how materials cues influence cellular plasticity through the epigenome and directed tissue-fabrication approaches that drive biological activities.
In this study femtosecond and nanosecond time-resolved transient absorption spectroscopy was used to investigate the influence of ionic strength and complexity on the excited state dynamics of a ...Ru(II)-based metal–organic dyad. The bis-heteroleptic complex Ru(bpy)2(ippy)2+ (1), where bpy = 2,2′-bipyridine and ippy = 2-(1-pyrenyl-1H-imidazo4,5-f1,10phenanthroline, is a potent photosensitizer for in vitro photodynamic therapy (PDT) and photodynamic inactivation (PDI) of microorganisms owing to a long-lived triplet excited state derived from a metal-to-ligand charge-transfer (3MLCT) state that is equilibrium with an intraligand (3IL) state. The prolonged lifetime provides ample opportunity for bimolecular quenching of this state by oxygen; thus singlet oxygen (1O2) sensitization is very efficient. In simple aqueous solution, fast cooling within the 3MLCT manifold is followed by energy transfer to an 3IL state, which is facilitated by rotation of a pyrenyl unit about the imidazo–pyrenyl (ip) coannular bond. For solutions of 1 in high ionic strength simulated biological fluid (SBF), a more physiologically relevant solvent that contains a complex mixture of ions at pH 7.4, femtosecond studies revealed an additional excited state, possibly based on an ion–ligand interaction. This new state appearing in high ionic strength SBF was not observable in water, simple buffers, or low ionic strength SBF. These photoinduced dynamics were also affected by the presence of biomolecules such as DNA in simple buffer, whereby relaxation on the picosecond time scale was accelerated from 39 to 18 ps with DNA intercalation by 1. The increased rate of coplanarization of the pyrene and the imidazole units was attributed to DNA-induced conformational restriction of the pyrenyl unit relative to the ip bond. Quantitative changes to excited state decay rates of 1 in solutions of high ionic strength were also observed when probed on the microsecond time scale. Notably, the thermalized excited state decay pathways were altered substantially with DNA intercalation, with access to some states being completely blocked. Experimentally, this manifested in the absence of the slowest microsecond decay channel, which is normally observed for 1 in solution. The quantitative and qualitative observations from this study highlight the importance of employing biologically relevant solvents and potential biomolecule targets when the excited state dynamics and photophysical properties (under cell-free conditions) responsible for the potent photobiological effects are assessed in the context of photodynamic therapy and photodynamic inactivation.
Aims To compare the biometric data from partial coherence interferometry (PCI) and swept-source OCT (SS-OCT) in patients with age-related cataract and epiretinal membrane (ERM): ERM, ERM with ...foveoschisis and macular pseudohole. Methods 49 eyes of 49 subjects including 36 ERM, 9 ERM foveoschisis and 4 macular pseudohole were analysed to evaluate the axial length (AL) measurements and the presence of AL measurement errors, defined basing on the shape of the biometric output graphs and on the concordance of AL values between instruments. Eyes with ERM were divided in four stages according to OCT features (i.e. presence/absence of the foveal pit, presence of ectopic inner foveal layers, disrupted retinal layers). Results The devices provided similar mean AL measurements in all subgroups, with differences <0.1 mm in 41/49 cases (83.6%). AL measurement errors were observed in ERM stages 3 and 4, characterized by ectopic inner foveal layers, and were significantly more frequent with the PCI (8/17, 47%) as compared with the SS-OCT device (2/17, 12%), p = 0.02. The refractive prediction error in cases with AL measurement errors was significantly greater using the PCI compared to the SS-OCT device (p<0.05). Conclusion Both devices provide reliable biometric data in the majority of patients and can be used in the preoperative assessment of patients with age-related cataract and ERM. In eyes with ectopic inner foveal layers, attention should be paid as AL measurement and refractive prediction errors may occur, more frequently with the PCI device.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract Cells sense and transduce the chemical and mechanical properties of their microenvironment through cell surface integrin receptors. Traction stress exerted by cells on the extracellular ...matrix mediates focal adhesion stabilization and regulation of the cytoskeleton for directing biological activity. Understanding how stem cells integrate biomaterials properties through focal adhesions during differentiation is important for the design of soft materials for regenerative medicine. In this paper we use micropatterned hydrogels containing fluorescent beads to explore force transmission through integrins from single mesenchymal stem cells (MSCs) during differentiation. When cultured on polyacrylamide gels, MSCs will express markers associated with osteogenesis and myogenesis in a stiffness dependent manner. The shape of single cells and the composition of tethered matrix protein both influence the magnitude of traction stress applied and the resultant differentiation outcome. We show how geometry guides the spatial positioning of focal adhesions to maximize interaction with the matrix, and uncover a relationship between αvβ3, α5β1 and mechanochemical regulation of osteogenesis.
The class of cyclic lipopeptide natural products consists of compounds with a diverse range of bioactivities. In this study, we elucidated the structure of the cyclic lipopeptide anikasin using X-ray ...crystallography, analyzed its biosynthetic gene cluster, and investigated its natural role in the interaction between the producer strain Pseudomonas fluorescens HKI0770 and protozoal predators. These results led to the conclusion that anikasin has dual functionality enabling swarming motility and acting as a niche amoebicide, which effectively inhibits the social amoeba Polysphondylium violaceum and protects the producer strain from protozoal grazing.
The ease of fabricating high quality photonic crystals from porous silicon and its biocompatibility have inspired the conception of various biosensing schemes using this material. However, the ...instability of porous silicon has significantly slowed progress in this area. Here we discuss the potential of different porous silicon photonic crystals for biosensing in the context of its surface chemistry and nanostructure, both of which need to be optimized to obtain sensitive and stable devices. Of particular promise are recent approaches that use porous silicon as sensors for enzymatic activity, for cell capture and concentration devices.
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