The effect of the RACK1 signalling protein on the regulation of cell adhesion and cell contact guidance on nanometric grooves

Response of preosteoblasts on micromachined Ti-6Al-4V surface to microstructure dimension

The cell incubation depends on the cultured surface, but various machining methods produce different surface topographies, but it has not been clear how it is related to the topographic feature until now. Hence, the machined Ti-6Al-4V surface is characterized for preosteoblasts incubation via different mechanical fabrication. The relationship between surface topography created by various machining methods and cell incubation behaviour was explored. The objective is to control the surface preosteoblasts growth in machining of biological titanium alloy. According to the cell growth kinetic, the cell incubation behaviour was first proposed and modelled in relation to microstructural dimension and culture duration. Then, the topological cultured microstructure surface was fabricated via mechanical fabrication. Finally, the cell initial adhesion and incubation behaviour on microstructured surface was investigated. It is shown that the surface undulation on machined microstructure is conducive to controlling the direction and distribution of cell incubation from cell growth kinetic model. The cell culture can be controlled on the peak with a small undulation, while it is concentred on the sidewall with a high aspect ratio. Increasing the aspect ratio extends cell growth, while low aspect ratio promotes initial cell adhesion and growth rate. Within the optimal cultured duration, the microstructured surface is more favourable for cell survival, and the cell growth keep positive beyond critical aspect ratio. As a result, the cell adhesion ability is topologically controlled to 5.4 times higher and the growth rate can be improved by 101.7% on milled microgrooved surface. It may be applied to the rapid production of biomedical Ti-6Al-4V implant.

Soft topographical patterns trigger a stiffness-dependent cellular response to contact guidance

Topographical patterns are a powerful tool to study directional migration. Grooved substrates have been extensively used as in vitro models of aligned extracellular matrix fibers because they induce cell elongation, alignment, and migration through a phenomenon known as contact guidance. This process, which involves the orientation of focal adhesions, F-actin, and microtubule cytoskeleton along the direction of the grooves, has been primarily studied on hard materials of non-physiological stiffness. But how it unfolds when the stiffness of the grooves varies within the physiological range is less known. Here we show that substrate stiffness modulates the cellular response to topographical contact guidance. We find that for fibroblasts, while focal adhesions and actin respond to topography independently of the stiffness, microtubules show a stiffness-dependent response that regulates contact guidance. On the other hand, both clusters and single breast carcinoma epithelial cells display stiffness-dependent contact guidance, leading to more directional and efficient migration when increasing substrate stiffness. These results suggest that both matrix stiffening and alignment of extracellular matrix fibers cooperate during directional cell migration, and that the outcome differs between cell types depending on how they organize their cytoskeletons.

Functionalization of TiO2 for Better Performance as Orthopedic Implants

This review mainly focuses on the surface functionalization approaches of titanium dioxide (TiO₂) to prevent bacterial infections and facilitate osteointegration simultaneously for titanium (Ti)-based orthopedic implants. Infection is one of the major causes of implant failure. Meanwhile, it is also critical for the bone-forming cells to integrate with the implant surface. TiO₂ is the native oxide layer of Ti which has good biocompatibility as well as enriched physical, chemical, electronic, and photocatalytic properties. The formed nanostructures during fabrication and the enriched properties of TiO₂ have enabled various functionalization methods to combat the micro-organisms and enhance the osteogenesis of Ti implants. This review encompasses the various modifications of TiO₂ in aspects of topology, drug loading, and element incorporation, as well as the most recently developed electron transfer and electrical tuning approaches. Taken together, these approaches can endow Ti implants with better bactericidal and osteogenic abilities via the functionalization of TiO₂.

The Influence of the Surface Topographical Cues of Biomaterials on Nerve Cells in Peripheral Nerve Regeneration: A Review

The surface topographies of artificial implants including surface roughness, surface groove size and orientation, and surface pore size and distribution have a great influence on the adhesion, migration, proliferation, and differentiation of nerve cells in the nerve regeneration process. Optimizing the surface topographies of biomaterials can be a key strategy for achieving excellent cell performance in various applications such as nerve tissue engineering. In this review, we offer a comprehensive summary of the surface topographies of nerve implants and their effects on nerve cell behavior. This review also emphasizes the latest work progress of the layered structure of the natural extracellular matrix that can be imitated by the material surface topology. Finally, the future development of surface topographies on nerve regeneration was prospectively remarked.

Differential effects of Hsp90 inhibition on corneal cells in vitro and in vivo

The transformation of quiescent keratocytes to activated fibroblasts and myofibroblasts (KFM transformation) largely depends on transforming growth factor beta (TGFβ) signaling. Initiation of the TGFβ signaling cascade results from binding of TGFβ to the labile type I TGFβ receptor (TGFβRI), which is stabilized by the 90 kDa heat shock protein (Hsp90). Since myofibroblast persistence within the corneal stroma can result in stromal haze and corneal fibrosis in patients undergoing keratorefractive therapy, modulation of TGFβ signaling through Hsp90 inhibition would represent a novel approach to prevent myofibroblast persistence. In vitro, rabbit corneal fibroblasts (RCFs) or stratified immortalized human corneal epithelial cells (hTCEpi) were treated with a Hsp90 inhibitor (17AAG) in the presence/absence of TGFβ1. RCFs were cultured either on tissue culture plastic, anisotropically patterned substrates, and hydrogels of varying stiffness. Cellular responses to both cytoactive and variable substrates were assessed by morphologic changes to the cells, and alterations in expression patterns of key keratocyte and myofibroblast proteins using PCR, Western blotting and immunocytochemistry. Transepithelial electrical resistance (TEER) measurements were performed to establish epithelial barrier integrity. In vivo, the corneas of New Zealand White rabbits were wounded by phototherapeutic keratectomy (PTK) and treated with 17AAG (3× or 6× daily) either immediately or 7 days after wounding for 28 days. Rabbits underwent clinical ophthalmic examinations, SPOTS scoring and advanced imaging on days 0, 1, 3, 7, 10, 14, 21 and 28. On day 28, rabbits were euthanized and histopathology/immunohistochemistry was performed. In vitro data demonstrated that 17AAG inhibited KFM transformation with the de-differentiation of spindle shaped myofibroblasts to dendritic keratocyte-like cells accompanied by significant upregulation of corneal crystallins and suppression of myofibroblast markers regardless of TGFβ1 treatment. RCFs cultured on soft hydrogels or patterned substrates exhibited elevated expression of α-smooth muscle actin (αSMA) in the presence of 17AAG. Treatment of hTCEpi cells disrupted zonula occludens 1 (ZO-1) adherens junction formation. In vivo, there were no differences detected in nearly all clinical parameters assessed between treatment groups. However, rabbits treated with 17AAG developed greater stromal haze formation compared with controls, irrespective of frequency of administration. Lastly, there was increased αSMA positive myofibroblasts in the stroma of 17AAG treated animals when compared with controls. Hsp90 inhibition promoted reversion of the myofibroblast to keratocyte phenotype, although this only occurred on rigid substrates. By contrast, in vivo Hsp90 inhibition was detrimental to corneal wound healing likely due to impairment in corneal epithelial closure and barrier function restoration. Collectively, our data demonstrated a strong interplay in vitro between biophysical cues and soluble signaling molecules in determining corneal stromal cell phenotype.

From Shape to Function: The Next Step in Bioprinting

In 2013, the "biofabrication window" was introduced to reflect the processing challenge for the fields of biofabrication and bioprinting. At that time, the lack of printable materials that could serve as cell-laden bioinks, as well as the limitations of printing and assembly methods, presented a major constraint. However, recent developments have now resulted in the availability of a plethora of bioinks, new printing approaches, and the technological advancement of established techniques. Nevertheless, it remains largely unknown which materials and technical parameters are essential for the fabrication of intrinsically hierarchical cell-material constructs that truly mimic biologically functional tissue. In order to achieve this, it is urged that the field now shift its focus from materials and technologies toward the biological development of the resulting constructs. Therefore, herein, the recent material and technological advances since the introduction of the biofabrication window are briefly summarized, i.e., approaches how to generate shape, to then focus the discussion on how to acquire the biological function within this context. In particular, a vision of how biological function can evolve from the possibility to determine shape is outlined.

Treatment of volumetric muscle loss in mice using nanofibrillar scaffolds enhances vascular organization and integration

Traumatic skeletal muscle injuries cause irreversible tissue damage and impaired revascularization. Engineered muscle is promising for enhancing tissue revascularization and regeneration in injured muscle. Here we fabricated engineered skeletal muscle composed of myotubes interspersed with vascular endothelial cells using spatially patterned scaffolds that induce aligned cellular organization, and then assessed their therapeutic benefit for treatment of murine volumetric muscle loss. Murine skeletal myoblasts co-cultured with endothelial cells in aligned nanofibrillar scaffolds form endothelialized and aligned muscle with longer myotubes, more synchronized contractility, and more abundant secretion of angiogenic cytokines, compared to endothelialized engineered muscle formed from randomly-oriented scaffolds. Treatment of traumatically injured muscle with endothelialized and aligned skeletal muscle promotes the formation of highly organized myofibers and microvasculature, along with greater vascular perfusion, compared to treatment of muscle derived from randomly-oriented scaffolds. This work demonstrates the potential of endothelialized and aligned engineered skeletal muscle to promote vascular regeneration following transplantation.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Hierarchical "As-Electrospun" Self-Assembled Fibrous Scaffolds Deconvolute Impacts of Chemically Defined Extracellular Matrix- and Cell Adhesion-Type Interactions on Stem Cell Haptokinesis

Controlled self-assembly of diblock copolymers offers the possibility of fabricating multilength scale, three-dimensional (3D) porous/fibrous structures (or scaffolds) with defined internal nano- or microstructure, with opportunities for application in a variety of fields, ranging from energy storage to bioengineering. Traditional methods by which such 3D constructs are produced are time-consuming and tedious, hindering their broader exploitation within larger-scale industrial processes. We report the development of a one-step process to fabricate "as-electrospun" self-assembled diblock copolymer micro- to nanometer-sized fibers incorporating core-shell or lamellar, closely packed spheres or bicontinuous gyroid nanosized structures. Isotropic and anisotropic (aligned) porous mats presenting spatially controlled chemistries, including bioactive (peptide-based) motifs, were successfully made from these hierarchical fibers. When functionalized with peptide sequences derived from a cell adhesion molecule (E-cadherin) and an extracellular matrix glycoprotein (laminin), these novel materials provided new insight into the impacts of such exquisitely tailored contact-guidance cues on the haptokinesis of human mesenchymal stem cells.

Curcumin modulates chronic myelogenous leukemia exosomes composition and affects angiogenic phenotype via exosomal miR-21

Tumor derived exosomes are vesicles which contain proteins and microRNAs that mediate cell-cell communication and are involved in angiogenesis and tumor progression. Curcumin derived from the plant Curcuma longa, shows anticancer effects. Exosomes released by CML cells treated with Curcumin contain a high amount of miR-21 that is shuttled into the endothelial cells in a biologically active form. The treatment of HUVECs with CML Curcu-exosomes reduced RhoB expression and negatively modulated endothelial cells motility. We showed that the addition of CML control exosomes to HUVECs caused an increase in IL8 and VCAM1 levels, but Curcu-exosomes reversed these effects thus attenuating their angiogenic properties. This antiangiogenic effect was confirmed with in vitro and in vivo vascular network formation assays. SWATH analysis of the proteomic profile of Curcu-exosomes revealed that Curcumin treatment deeply changes their molecular properties, in particular, Curcumin induces a release of exosomes depleted in pro-angiogenic proteins and enriched in proteins endowed with anti-angiogenic activity. Among the proteins differential expressed we focused on MARCKS, since it was the most modulated protein and a target of miR-21. Taken together our data indicated that also Curcumin attenuates the exosome's ability to promote the angiogenic phenotype and to modulate the endothelial barrier organization.

The cyclic AMP phosphodiesterase 4D5 (PDE4D5)/receptor for activated C-kinase 1 (RACK1) signalling complex as a sensor of the extracellular nano-environment

The cyclic AMP and protein kinase C (PKC) signalling pathways regulate a wide range of cellular processes that require tight control, including cell proliferation and differentiation, metabolism and inflammation. The identification of a protein complex formed by receptor for activated C kinase 1 (RACK1), a scaffold protein for protein kinase C (PKC), and the cyclic AMP-specific phosphodiesterase, PDE4D5, demonstrates a potential mechanism for crosstalk between these two signalling routes. Indeed, RACK1-bound PDE4D5 is activated by PKCα, providing a route through which the PKC pathway can control cellular cyclic AMP levels. Although RACK1 does not appear to affect the intracellular localisation of PDE4D5, it does afford structural stability, providing protection against denaturation, and increases the susceptibility of PDE4D5 to inhibition by cyclic AMP-elevating pharmaceuticals, such as rolipram. In addition, RACK1 can recruit PDE4D5 and PKC to intracellular protein complexes that control diverse cellular functions, including activated G protein-coupled receptors (GPCRs) and integrins clustered at focal adhesions. Through its ability to regulate local cyclic AMP levels in the vicinity of these multimeric receptor complexes, the RACK1/PDE4D5 signalling unit therefore has the potential to modify the quality of incoming signals from diverse extracellular cues, ranging from neurotransmitters and hormones to nanometric topology. Indeed, PDE4D5 and RACK1 have been found to form a tertiary complex with integrin-activated focal adhesion kinase (FAK), which localises to cellular focal adhesion sites. This supports PDE4D5 and RACK1 as potential regulators of cell adhesion, spreading and migration through the non-classical exchange protein activated by cyclic AMP (EPAC1)/Rap1 signalling route.

Mesenchymal Stem Cell Fate: Applying Biomaterials for Control of Stem Cell Behavior

The materials pipeline for biomaterials and tissue engineering applications is under continuous development. Specifically, there is great interest in the use of designed materials in the stem cell arena as materials can be used to manipulate the cells providing control of behavior. This is important as the ability to "engineer" complexity and subsequent in vitro growth of tissues and organs is a key objective for tissue engineers. This review will describe the nature of the materials strategies, both static and dynamic, and their influence specifically on mesenchymal stem cell fate.

Harnessing nanotopography and integrin-matrix interactions to influence stem cell fate

Stem cells respond to nanoscale surface features, with changes in cell growth and differentiation mediated by alterations in cell adhesion. The interaction of nanotopographical features with integrin receptors in the cells' focal adhesions alters how the cells adhere to materials surfaces, and defines cell fate through changes in both cell biochemistry and cell morphology. In this Review, we discuss how cell adhesions interact with nanotopography, and we provide insight as to how materials scientists can exploit these interactions to direct stem cell fate and to understand how the behaviour of stem cells in their niche can be controlled. We expect knowledge gained from the study of cell-nanotopography interactions to accelerate the development of next-generation stem cell culture materials and implant interfaces, and to fuel discovery of stem cell therapeutics to support regenerative therapies.

The role of filopodia in the recognition of nanotopographies

Substrate-exploring functions of filopodia were previously suggested based on cell studies on flat surfaces, but their role in topography sensing especially within nanofibrillar environments remained elusive. Here we have grown highly flexible hairy silicon nanowires on micropatterned islands on otherwise flat glass surfaces and coated them both with the extracellular matrix (ECM) protein fibronectin. This allowed us to visualize how filopodia steer fundamental cell functions such as cell adhesion, spreading, migration and division in the absence of lamellipodia. Shortly after seeding, transient filopodia protrude from the still spherical cells. Once filopodia contact nanowires, they bend and align them, while most filopodia peel off from flat surfaces. A zipping mechanism regulated by traction forces is proposed to explain how force-induced changes in filopodia-substrate contact angles enable topography sensing, including the still elusive phenomenon of contact guidance. Filopodia thus play a central role in steering transient topographic preferences.

Lower extent but similar rhythm of osteogenic behavior in hBMSCs cultured on nanofibrous scaffolds versus induced with osteogenic supplement

Nanotopographic cues from biomaterials exert powerful effects on the osteogenic differentiation of mesenchymal stem cells because of their niche-mimicking features. However, the biological mechanisms underlying cell lineage determination by surface nanotopography have not been clearly elucidated. Here, we explored the osteogenic behavior of human bone marrow mesenchymal stem cells (hBMSCs) on poly-l-lactide nanofibers with different orientations and monitored the dynamic changes in global gene expression triggered by topographical cues. RT-PCR analysis of osteogenic marker genes and ALP activity assays demonstrated that hBMSCs cultured on random nanofibers showed enhanced osteogenic-specific fate compared with those on aligned nanofibers. Microarray analysis demonstrated a similar temporal change in gene expression patterns between hBMSCs cultured on random nanofibers and those induced with an osteogenic supplement (OS). However, the extent of osteogenic differentiation on the fibrous scaffold was much lower than that driven by chemical OS. In-depth pathway analysis revealed that focal adhesion kinase, TGF-β, Wnt, and MAPK pathways were involved in the activation of osteogenic differentiation in hBMSCs on random nanofibers. These findings suggested that a lower extent but similar rhythm of dynamic cellular behavior was induced on random nanofibers when compared with the OS condition and that mechanotransduction could trigger nonspecific and multilevel responses in hBMSCs. This study provides insight into the regulation of osteogenesis directed by substratum surfaces.

Direct observation of CD4 T cell morphologies and their cross-sectional traction force derivation on quartz nanopillar substrates using focused ion beam technique

Direct observations of the primary mouse CD4 T cell morphologies, e.g., cell adhesion and cell spreading by culturing CD4 T cells in a short period of incubation (e.g., 20 min) on streptavidin-functionalized quartz nanopillar arrays (QNPA) using a high-content scanning electron microscopy method were reported. Furthermore, we first demonstrated cross-sectional cell traction force distribution of surface-bound CD4 T cells on QNPA substrates by culturing the cells on top of the QNPA and further analysis in deflection of underlying QNPA via focused ion beam-assisted technique.

RACK1 is involved in endothelial barrier regulation via its two novel interacting partners

Background

RACK1, receptor for activated protein kinase C, serves as an anchor in multiple signaling pathways. TIMAP, TGF-β inhibited membrane-associated protein, is most abundant in endothelial cells with a regulatory effect on the endothelial barrier function. The interaction of TIMAP with protein phosphatase 1 (PP1cδ) was characterized, yet little is known about its further partners.

Results

We identified two novel interacting partners of RACK1, namely, TGF-β inhibited membrane-associated protein, TIMAP, and farnesyl transferase. TIMAP is most abundant in endothelial cells where it is involved in the regulation of the barrier function. WD1-4 repeats of RACK1 were identified as critical regions of the interaction both with TIMAP and farnesyl transferase. Phosphorylation of TIMAP by activation of the cAMP/PKA pathway reduced the amount of TIMAP-RACK1 complex and enhanced translocation of TIMAP to the cell membrane in vascular endothelial cells. However, both membrane localization of TIMAP and transendothelial resistance were attenuated after RACK1 depletion. Farnesyl transferase, the enzyme responsible for prenylation and consequent membrane localization of TIMAP, is present in the RACK1-TIMAP complex in control cells, but it does not co-immunoprecipitate with TIMAP after RACK1 depletion.

Conclusions

Transient parallel linkage of TIMAP and farnesyl transferase to RACK1 could ensure prenylation and transport of TIMAP to the plasma membrane where it may attend in maintaining the endothelial barrier as a phosphatase regulator.

Nanotopography induced contact guidance of the F11 cell line during neuronal differentiation: a neuronal model cell line for tissue scaffold development

The F11 hybridoma, a dorsal root ganglion-derived cell line, was used to investigate the response of nociceptive sensory neurons to nanotopographical guidance cues. This established this cell line as a model of peripheral sensory neuron growth for tissue scaffold design. Cells were seeded on substrates of cyclic olefin copolymer (COC) films imprinted via nanoimprint lithography (NIL) with a grating pattern of nano-scale grooves and ridges. Different ridge widths were employed to alter the focal adhesion formation, thereby changing the cell/substrate interaction. Differentiation was stimulated with forskolin in culture medium consisting of either 1 or 10% fetal bovine serum (FBS). Per medium condition, similar neurite alignment was achieved over the four day period, with the 1% serum condition exhibiting longer, more aligned neurites. Immunostaining for focal adhesions found the 1% FBS condition to also have fewer, less developed focal adhesions. The robust response of the F11 to guidance cues further builds on the utility of this cell line as a sensory neuron model, representing a useful tool to explore the design of regenerative guidance tissue scaffolds.

Matrix nanotopography as a regulator of cell function

The architecture of the extracellular matrix (ECM) directs cell behavior by providing spatial and mechanical cues to which cells respond. In addition to soluble chemical factors, physical interactions between the cell and ECM regulate primary cell processes, including differentiation, migration, and proliferation. Advances in microtechnology and, more recently, nanotechnology provide a powerful means to study the influence of the ECM on cell behavior. By recapitulating local architectures that cells encounter in vivo, we can elucidate and dissect the fundamental signal transduction pathways that control cell behavior in critical developmental, physiological, and pathological processes.

Poly-lactic-glycolic-acid surface nanotopographies selectively decrease breast adenocarcinoma cell functions

The ability of poly(lactic-co-glycolic acid) (PLGA, 50:50 PLG/PGA, wt%) nanotopographies to decrease lung epithelial carcinoma cell functions (including adhesion, proliferation, apoptosis and vascular endothelial growth factor (VEGF) secretion) has been previously reported. Specifically, results demonstrated decreased lung epithelial carcinoma cell VEGF synthesis on 23 nm surface-featured PLGA compared to traditional nanosmooth PLGA. However, clearly, different cell lines could have different behaviors on similar biomaterials. Thus, to investigate the universality of nanopatterned PLGA substrates to inhibit numerous cancer cell functions, here, breast epithelial adenocarcinoma cell (MCF-7) adhesion, proliferation, apoptosis and VEGF secretion were determined on different PLGA nanometer surface topographies. To isolate surface nanotopographical effects from all other surface properties, PLGA surfaces with various nanotopographies but similar chemistry and hydrophobicity were fabricated here. Atomic force microscopy (AFM) verified the varied nanotopographies on the PLGA surfaces prepared in this study. Importantly, results demonstrated for the first time significantly decreased breast adenocarcinoma cell functions (including decreased proliferation rate, increased apoptosis and decreased VEGF synthesis) on 23 nm featured PLGA surfaces compared to all other PLGA surface topographies fabricated (specifically, nanosmooth, 300 and 400 nm surface-featured PLGA surfaces). In contrast, healthy breast epithelial cells proliferated more (24%) on the 23 nm featured PLGA surfaces compared to all other PLGA samples. In summary, these results provided further insights into understanding the role PLGA surface nanotopographies can have on cancer cell functions and, more importantly, open the possibility of using polymer nanotopographies for a wide range of anticancer regenerative medicine applications (without resorting to the use of chemotherapeutics).

Receptor for activated C kinase 1 (RACK1): a regulator for migration and invasion in oral squamous cell carcinoma cells

PURPOSE

Receptor of activated protein kinase C 1 (RACK1) has been identified as an anchoring or adaptor protein in multiple intracellular signal transduction pathways. Our previous study has showed that the expression of RACK1 was paralleled with proliferation and correlated with metastasis and clinical outcome. However, the underlined mechanism has not been uncovered.

MATERIALS AND METHODS

We first selected a most effective siRNA among three siRNAs (siRNA-1, siRNA-2 and siRNA-3) targeting different regions in the RACK1 mRNA and re-evaluated the anticancer effect of RACK1 silencing on HSC-3 and Cal-27 cell lines by cell growth inhibition. And then, we investigated whether knockdown of RACK1 could inhibit cell adhesion, migration and invasion in these two cell lines. To further understand the molecular mechanism of RACK1 in these processes, the expressions of EGFR, pEGFR, HER2, MMP-2 and MMP-9 were detected by western blot.

RESULTS

We verified that the silence of RACK1 gene in two OSCC cell lines could not only inhibit cell proliferation but also decrease the invasion, migration and adhesion capability of the tumor cells. Further, western blot analysis deduced that it might be related to the decrease in protein expression of EGFR, pEGFR, HER2, MMP-2 and MMP-9.

CONCLUSION

Our results clearly showed the significance of RACK1-induced OSCC cell migration, invasion and adhesion, which could explain the underlined mechanism of the effect of the gene on metastasis and clinical outcome. Also, our results confirmed its role to be a prognostic indicator and a promising drug target for OSCC cell metastasis.

Effect of nanogroove geometry on adipogenic differentiation

We present the effect of nanotopographically defined surfaces on adipocyte differentiation using various nanogroove patterns. Parallel nanogroove arrays with equal inter-groove distance (400, 550, 800 nm width) and varying distances (550 nm width with three different spacings of 550, 1100, and 2750 nm) were fabricated by UV-assisted capillary force lithography (CFL) on 18 mm diameter glass coverslips using biocompatible polyurethane (PU)-based material. After coating with fibronectin and subsequent culture of 3T3-L1 preadipocytes, the degree of adipocyte differentiation was determined by Oil Red O staining and adipogenic gene expression. We observed that adipocyte differentiation was slightly but substantially affected by culture on various nanogrooved surfaces. In particular, the cell crawling into nanogrooves contributed substantially to an enhanced level of differentiation with higher contact guidance, suggesting that cell-to-surface interactions would play a role for the adipocyte differentiation.

Biomimetic microtopography to enhance osteogenesis in vitro

Biomimicry is being used in the next generation of biomaterials. Tuning material surface features such as chemistry, stiffness and topography allow the control of cell adhesion, proliferation, growth and differentiation. Here, microtopographical features with nanoscale depths, similar in scale to osteoclast resorption pits, were used to promote in vitro bone formation in basal medium. Primary human osteoblasts were used to represent an orthopaedically relevant cell type and analysis of adhesions, cytoskeleton, osteospecific proteins (phospho-Runx2 and osteopontin) and mineralisation (alizarin red) was performed. The results further demonstrate the potential for biomimicry in material design and show that the osteoblast response can be tuned from changes in feature size.

Structure of the RACK1 dimer from Saccharomyces cerevisiae

Receptor for activated C-kinase 1 (RACK1) serves as a scaffolding protein in numerous signaling pathways involving kinases and membrane-bound receptors from different cellular compartments. It exists simultaneously as a cytosolic free form and as a ribosome-bound protein. As part of the 40S ribosomal subunit, it triggers translational regulation by establishing a direct link between protein kinase C and the protein synthesis machinery. It has been suggested that RACK1 could recruit other signaling molecules onto the ribosome, providing a signal-specific modulation of the translational process. RACK1 is able to dimerize both in vitro and in vivo. This homodimer formation has been observed in several processes including the regulation of the N-methyl-d-aspartate receptor by the Fyn kinase in the brain and the oxygen-independent degradation of hypoxia-inducible factor 1. The functional relevance of this dimerization is, however, still unclear and the question of a possible dimerization of the ribosome-bound protein is still pending. Here, we report the first structure of a RACK1 homodimer, as determined from two independent crystal forms of the Saccharomyces cerevisiae RACK1 protein (also known as Asc1p) at 2.9 and 3.9 Å resolution. The structure reveals an atypical mode of dimerization where monomers intertwine on blade 4, thus exposing a novel surface of the protein to potential interacting partners. We discuss the significance of the dimer structure for RACK1 function.

Fibronectin distribution on demixed nanoscale topographies

PURPOSE

It is known that surface nanotopography influences cell adhesion and differentiation. Our aim is to analyze the effect of nanoscale topography on fibronectin adsorption and, afterwards, on cell adhesion in order to rationalize the cell-material interaction by focusing on the state of the intermediate layer of adsorbed fibronectin at the material interphase.

METHODS

Nanotopographic surfaces were produced by demixing of thin film polymer blends - PLLA and PS - during a high speed spin-casting process. Fibronectin (FN) was adsorbed on the different nanotopographies and the protein distribution was directly observed by atomic force microscopy (AFM). The fraction of the surface covered by the protein was quantified by image analysis, as well as the distribution of FN between peaks and valleys. Focal adhesion protein -vinculin- was immunostained and quantified by image analysis on the different nanoscale surfaces.

RESULTS

Different nanoscale domains were obtained by changing the composition of the system within a height range of 3 nm to 30 nm. FN tends to adsorb on the peaks of nanoisland topographies, especially in compositions that did not enhance cell adhesion. Moreover, protein distribution between valleys and peaks alters the size of focal adhesion plaques, which grew larger on surfaces with an even distribution of fibronectin.

CONCLUSIONS

Our results suggest that the surface nanotopography is a key material property capable of influencing protein adsorption. Additionally, the distribution of the protein on the different samples was correlated to the initial ability of cells to adhere in terms of the size of the focal plaques.

On the role of RhoA/ROCK signaling in contact guidance of bone-forming cells on anisotropic Ti6Al4V surfaces

Patterned surfaces direct cell spatial dynamics, yielding cells oriented along the surface geometry, in a process known as contact guidance. The Rho family of GTPases controls the assembly of focal adhesions and cytoskeleton dynamics, but its role in modulating bone-cell alignment on patterned surfaces remains unknown. This article describes the interactions of two human cell types involved in osseointegration, specifically mesenchymal stem cells and osteoblasts, with submicron- or nano-scale Ti6Al4V grooved surfaces generated by mechanical abrasion. The surface chemistry of the alloy was not affected by grinding, ensuring that the differences found in cellular responses were exclusively due to changes in topography. Patterned surfaces supported cell growth and stimulated mesenchymal stem cell viability. Anisotropic surfaces promoted cell orientation and elongation along the grates. Both cell types oriented on nanometric surfaces with grooves of 150 nm depth and 2 μm width. The number of aligned cells increased by approximately 30% on submicrometric grooves with sizes of about 1 μm depth and 10 μm width. Cells were treated with drugs that attenuate the activities of the GTPase RhoA and one of its downstream effectors, Rho-associated kinase (ROCK), and contact guidance of treated cells on the grooved surfaces was investigated. The data indicate that the RhoA/ROCK pathway is a key modulator of both mesenchymal stem cell and osteoblast orientation on nanometric surface features. RhoA and its effector participate in the alignment of mesenchymal stem cells on submicrometric grooves, but not of osteoblasts. These findings show that RhoA/ROCK signaling is involved in contact guidance of bone-related cells on metallic substrates, although to a varying extent depending on the specific cell type and the dimensions of the pattern.

Exploring cellular contact guidance using gradient nanogratings

Nanoscale surface features that mimic extracellular matrix are critical environmental cues for cell contact guidance and are vital in advanced medical devices in order to manipulate cell behaviors. Among them, nanogratings (line-and-space gratings) are common platforms to study geometric effects on cell contact guidance, especially cell alignment, but generally are one pattern height per platform. In this study, we developed a strategy to fabricate controlled substrates with a wide range of pattern shapes and surface chemistries and to separate surface chemistry and topography effects. As a demonstration of this strategy, six nanograting platforms on three materials were fabricated and applied to examine and differentiate the effects of surface topography and surface chemistry on cell contact guidance of murine preosteoblasts. All of the six platforms contained the same gradient in pattern height (0 to ≈350 nm). They were prepared using nanoimprint lithography and annealing for thermoplastic materials (low molecular weight polystyrene (PS) and polymethylmethacrylate (PMMA)) and photoimprint for a thermoset material (a cross-linked dimethacrylate (DMA)). Each material contains two platforms that are only different in line-and-space pitch (420 or 800 nm). The DMA nanogratings had a reverse line-and-space profile to those of the PS and PMMA nanogratings. Using these platforms, a full range of cell alignment, from randomly orientated to completely parallel to the grating direction was achieved. Results from focal adhesion assays and scanning electronic microscopy indicated a change in cell-substrate contact from a noncomposite state (full contact) to a composite state (partial contact between cell and substrate) as pattern height increased. These gradient platforms allowed for the separation of surface chemistry and surface topography to provide insight into the mechanisms responsible for cell contact guidance on nanopatterned surfaces.

Nanotopographical modification: a regulator of cellular function through focal adhesions

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

FROM THE CLINICAL EDITOR

In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

The interaction of cells and bacteria with surfaces structured at the nanometre scale

The current development of nanobiotechnologies requires a better understanding of cell-surface interactions on the nanometre scale. Recently, advances in nanoscale patterning and detection have allowed the fabrication of appropriate substrates and the study of cell-substrate interactions. In this review we discuss the methods currently available for nanoscale patterning and their merits, as well as techniques for controlling the surface chemistry of materials at the nanoscale without changing the nanotopography and the possibility of truly characterizing the surface chemistry at the nanoscale. We then discuss the current knowledge of how a cell can interact with a substrate at the nanoscale and the effect of size, morphology, organization and separation of nanofeatures on cell response. Moreover, cell-substrate interactions are mediated by the presence of proteins adsorbed from biological fluids on the substrate. Many questions remain on the effect of nanotopography on protein adsorption. We review papers related to this point. As all these parameters have an influence on cell response, it is important to develop specific studies to point out their relative influence, as well as the biological mechanisms underlying cell responses to nanotopography. This will be the basis for future research in this field. An important topic in tissue engineering is the effect of nanoscale topography on bacteria, since cells have to compete with bacteria in many environments. The limited current knowledge of this topic is also discussed in the light of using topography to encourage cell adhesion while limiting bacterial adhesion. We also discuss current and prospective applications of cell-surface interactions on the nanoscale. Finally, based on questions raised previously that remain to be solved in the field, we propose future directions of research in materials science to help elucidate the relative influence of the physical and chemical aspects of nanotopography on bacteria and cell response with the aim of contributing to the development of nanobiotechnologies.

A role for L-alpha-lysophosphatidylinositol and GPR55 in the modulation of migration, orientation and polarization of human breast cancer cells

BACKGROUND AND PURPOSE

Increased circulating levels of L-alpha-lysophosphatidylinositol (LPI) are associated with cancer and LPI is a potent, ligand for the G-protein-coupled receptor GPR55. Here we have assessed the modulation of breast cancer cell migration, orientation and polarization by LPI and GPR55.

EXPERIMENTAL APPROACH

Quantitative RT-PCR was used to measure GPR55 expression in breast cancer cell lines. Cell migration and invasion were measured using a Boyden chamber chemotaxis assay and Cultrex invasion assay, respectively. Cell polarization and orientation in response to the microenvironment were measured using slides containing nanometric grooves.

KEY RESULTS

GPR55 expression was detected in the highly metastatic MDA-MB-231 breast cancer cell line. In these cells, LPI stimulated binding of [(35)S]GTPgammaS to cell membranes (pEC(50) 6.47 +/- 0.45) and significantly enhanced cell chemotaxis towards serum. MCF-7 cells expressed low levels of GPR55 and did not migrate or invade towards serum factors. When GPR55 was over-expressed in MCF-7 cells, serum induced a robust migratory and invasive response, which was further enhanced by LPI and prevented by siRNA to GPR55. The physical microenvironment has been identified as a key factor in determining breast tumour cell metastatic fate. LPI endowed MDA-MB-231 cells with the capacity to detect shallow (40 nm deep) grooved slides and induced marked cancer cell polarization on both flat and grooved surfaces.

CONCLUSIONS AND IMPLICATIONS

LPI and GPR55 play a role in the modulation of migration, orientation and polarization of breast cancer cells in response to the tumour microenvironment.

Effect of nanoscale topography on fibronectin adsorption, focal adhesion size and matrix organisation

Phase separation of PLLA/PS (50/50, w/w) solutions during a spin-casting process gives rise to well-defined nanotopographies of 14, 29 and 45 nm deep pits depending on the concentration of the solution. Their influence on the biological activity of fibronectin (FN) was investigated. FN adsorption was quantified by radiolabelling the protein. The amount of adsorbed FN was higher on the 14 nm deep pit nanotopography than on the other two surfaces. FN distribution between valleys and peaks was investigated by AFM combined with image analysis. FN tends to adsorb preferentially on the valleys of the nanotopography only for the 14 nm system and when adsorbed from solutions of concentration lower than 10 microg/ml. Higher concentration of the FN solution leads to evenly distribution of the protein throughout the surface; moreover, there is no difference in the distribution of the protein between valleys and peaks for the other two systems (29 and 45 nm) irrespective of the concentration of the FN solution. The biological activity of the adsorbed protein layer was assessed by investigating MC3T3 osteoblast-like cells adhesion, FN reorganisation and late matrix formation on the different substrates. Even if initial cell adhesion is excellent for every substrate, the size of the focal adhesion plaques increases as the size of the pits in the nanotopography does. This is correlated to FN reorganisation, which only takes places on the 29 and 45 nm deep pits surfaces, where enhanced late matrix production was also found.

Modulation of morphology and functions of human hepatoblastoma cells by nano-grooved substrata

It is known that cellular behavior is affected by nano-patterned topography. For example, many cell types tend to align and extend along the direction of nano-grooves/ridges structures. In this study, we investigated the impact of nano-grooves/ridges on hepatocyte morphology and functions. HepG2/C3A (C3A) cells were cultured on nano-grooved silicon or polystyrene substrata with various widths (from 100 to 500 nm) and depths (from 100 to 380 nm). Nano-grooved substrates induced dramatic changes in C3A cell morphology. The cells formed spheroids on the flat substrates, while C3A cells spread and grew confluently with elongated and aligned morphology along the nano-grooves/ridges. Albumin synthesis was enhanced on the nano-grooved silicon substrates compared to the flat surface, and was decreased with increasing groove depths. Urea conversion on the shallow grooves (400 nm wide and 100 nm deep) remained at the same level of that on the flat surfaces, but was decreased on the deeper grooves. We found that the functions of hepatocytes were enhanced on the substrates with shallow grooves. The nano-grooved substrates may be applied as in vitro culture systems of hepatocytes for both diagnostic and therapeutic applications.

Engineering substrate topography at the micro- and nanoscale to control cell function

The interaction of mammalian cells with nanoscale topography has proven to be an important signaling modality in controlling cell function. Naturally occurring nanotopographic structures within the extracellular matrix present surrounding cells with mechanotransductive cues that influence local migration, cell polarization, and other functions. Synthetically nanofabricated topography can also influence cell morphology, alignment, adhesion, migration, proliferation, and cytoskeleton organization. We review the use of in vitro synthetic cell-nanotopography interactions to control cell behavior and influence complex cellular processes, including stem-cell differentiation and tissue organization. Future challenges and opportunities in cell-nanotopography engineering are also discussed, including the elucidation of mechanisms and applications in tissue engineering.