Adhesion maturation of neutrophils on nanoscopically presented platelet glycoprotein Ibα

Tissue inhibitors of metalloproteinases (TIMPs) modulate platelet ADAM10 activity

Platelet-specific collagen receptor glycoprotein (GP)VI is stable on the surface of circulating platelets but undergoes ectodomain cleavage on activated platelets. Activation-dependent GPVI metalloproteolysis is primarily mediated by A Disintegrin And Metalloproteinase (ADAM) 10. Regulation of platelet ADAMs activity is not well-defined however Tissue Inhibitors of Metalloproteinases (TIMPs) may play a role. As levels of TIMPs on platelets and the control of ADAMs-mediated shedding by TIMPs has not been evaluated, we quantified the levels of TIMPs on the surface of resting and activated platelets from healthy donors by flow cytometry and multiplex ELISA. Variable levels of all TIMPs could be detected on platelets. Plasma contained significant quantities of TIMP1 and TIMP2, but only trace amounts of TIMP3 and TIMP4. Recombinant TIMP3 strongly ablated resting and activated platelet ADAM10 activity, when monitored using a quenched fluorogenic peptide substrate with ADAM10 specificity. Whilst ADAM10-specific inhibitor GI254023X or ethylenediamine tetraacetic acid (EDTA) could modulate ligand-initiated shedding of GPVI, only recombinant TIMP2 achieved a modest (~20%) inhibition. We conclude that some platelet TIMPs are able to modulate platelet ADAM10 activity but none strongly regulate ligand-dependent shedding of GPVI. Our findings provide new insights into the regulation of platelet receptor sheddase activity.

Research and Clinical Approaches to Assess Platelet Function in Flowing Blood

Platelet adhesion and activation is fundamental to the formation of a hemostatic response to limit loss of blood and instigate wound repair to seal a site of vascular injury. The process of platelet aggregate formation is supported by the coagulation system driving injury-proximal formation of thrombin, which converts fibrinogen to insoluble fibrin. This highly coordinated series of molecular and membranous events must be routinely achieved in flowing blood, at vascular fluid shear rates that place significant strain on molecular and cellular interactions. Platelets have long been recognized to be able to slow down and adhere to sites of vascular injury and then activate and recruit more platelets that forge and strengthen adhesive ties with the vascular wall under these conditions. It has been a major challenge for the Platelet Research Community to construct experimental conditions that allow precise definition of the molecular steps occurring under flow. This brief review will discuss work to date from our group, as well as others that has furthered our understanding of platelet function in flowing blood.

Recent Insights into NIR-Light-Responsive Materials for Photothermal Cell Treatments

Controlling cells using photo-responsive materials is highly indispensable in the current biomedical sector. Considering the potential side effects of nanoparticles, it has become a challenge to control cells with photo-responsive materials. Recent studies have described several methods for controlling cell behavior using nanoparticles subjected to the near-infrared (NIR) laser light operating at the wavelength of 808 nm to 980 nm and at the power densities of 0.33 to 0.72 W·cm^-2. The challenge here is the preparation of biocompatible nanoparticles for both in vivo and in vitro studies and understanding cell behavior with an external light source recommended for biological application. Earlier studies have well documented many approaches and associated mechanisms for controlling cell behavior and the interaction between nanoparticles, cells, and appropriate external light sources. In this review, various nanomaterials such as metal nanomaterials and carbon-based nanomaterials are compared systematically regarding the effects of controlling cell behavior and inflammation by studying their mechanisms, route of administration, dose, and adverse effects such as toxicity and the interaction of nanoparticles with a specific wavelength of the light. Future directions should focus on stable and efficient light-responsive materials with minimal cytotoxicity.

MD Simulations on a Well-Built Docking Model Reveal Fine Mechanical Stability and Force-Dependent Dissociation of Mac-1/GPIbα Complex

Interaction of leukocyte integrin macrophage-1 antigen (Mac-1) to platelet glycoprotein Ibα (GPIbα) is critical for platelet-leukocyte crosstalk in hemostasis and inflammatory responses to vessel injuries under hemodynamic environments. The mechano-regulation and its molecular basis for binding of Mac-1 to GPIbα remain unclear, mainly coming from the lack of crystal structure of the Mac-1/GPIbα complex. We herein built a Mac-1/GPIbα complex model through a novel computer strategy, which included a flexible molecular docking and system equilibrium followed by a "force-ramp + snapback" molecular dynamics (MD) simulation. With this model, a series of "ramp-clamp" steered molecular dynamics (SMD) simulations were performed to examine the GPIbα-Mac-1 interaction under various loads. The results demonstrated that the complex was mechano-stable for both the high rupture force (>250 pN) at a pulling velocity of 3 Å/ns and the conformational conservation under various constant tensile forces (≤75 pN); a catch-slip bond transition was predicted through the dissociation probability, examined with single molecular AFM measurements, reflected by the interaction energy and the interface H-bond number, and related to the force-induced allostery of the complex; besides the mutation-identified residues D222 and R218, the residues were also dominant in the binding of Mac-1 to GPIbα. This study recommended a valid computer strategy for building a likely wild-type docking model of a complex, provided a novel insight into the mechanical regulation mechanism and its molecular basis for the interaction of Mac-1 with GPIbα, and would be helpful for understanding the platelet-leukocyte interaction in hemostasis and inflammatory responses under mechano-microenvironments.

Transport and programmed release of nanoscale cargo from cells by using NETosis

Cells can take up nanoscale materials, which has important implications for understanding cellular functions, biocompatibility as well as biomedical applications. Controlled uptake, transport and triggered release of nanoscale cargo is one of the great challenges in biomedical applications of nanomaterials. Here, we study how human immune cells (neutrophilic granulocytes, neutrophils) take up nanomaterials and program them to release this cargo after a certain time period. For this purpose, we let neutrophils phagocytose DNA-functionalized single-walled carbon nanotubes (SWCNTs) in vitro that fluoresce in the near infrared (980 nm) and serve as sensors for small molecules. Cells still migrate, follow chemical gradients and respond to inflammatory signals after uptake of the cargo. To program release, we make use of neutrophil extracellular trap formation (NETosis), a novel cell death mechanism that leads to chromatin swelling, subsequent rupture of the cellular membrane and release of the cell's whole content. By using the process of NETosis, we can program the time point of cargo release via the initial concentration of stimuli such as phorbol 12-myristate-13-acetate (PMA) or lipopolysaccharide (LPS). At intermediate stimulation, cells continue to migrate, follow gradients and surface cues for around 30 minutes and up to several hundred micrometers until they stop and release the SWCNTs. The transported and released SWCNT sensors are still functional as shown by subsequent detection of the neurotransmitter dopamine and reactive oxygen species (H2O2). In summary, we hijack a biological process (NETosis) and demonstrate how neutrophils transport and release functional nanomaterials.

The power from within - understanding the driving forces of neutrophil extracellular trap formation

Neutrophil extracellular traps (NETs) are one of the most intriguing discoveries in immunological research of the past few years. After their first description in 2004, the number of research articles on how NETs affect immunodefense, and also how they contribute to an ever-growing number of diseases, has skyrocketed. However, tempting as it may seem to plunge into pharmaceutical approaches to tamper with NET formation, our understanding of this complex process is still incomplete. Important concepts such as the context-dependent dual functions of NETs, in that they are both inflammatory and anti-inflammatory, or the major intra- and extracellular forces driving NET formation, are only emerging. In this Review, we summarize key aspects of our current understanding of NET formation (also termed NETosis), emphasize biophysical aspects and focus on three key principles - rearrangement and destabilization of the plasma membrane and the cytoskeleton, alterations and disassembly of the nuclear envelope, and chromatin decondensation as a driving force of intracellular reorganization.

Modulating Tumor Cell Functions by Tunable Nanopatterned Ligand Presentation

Cancer comprises a large group of complex diseases which arise from the misrouted interplay of mutated cells with other cells and the extracellular matrix. The extracellular matrix is a highly dynamic structure providing biochemical and biophysical cues that regulate tumor cell behavior. While the relevance of biochemical signals has been appreciated, the complex input of biophysical properties like the variation of ligand density and distribution is a relatively new field in cancer research. Nanotechnology has become a very promising tool to mimic the physiological dimension of biophysical signals and their positive (i.e., growth-promoting) and negative (i.e., anti-tumoral or cytotoxic) effects on cellular functions. Here, we review tumor-associated cellular functions such as proliferation, epithelial-mesenchymal transition (EMT), invasion, and phenotype switch that are regulated by biophysical parameters such as ligand density or substrate elasticity. We also address the question of how such factors exert inhibitory or even toxic effects upon tumor cells. We describe three principles of nanostructured model systems based on block copolymer nanolithography, electron beam lithography, and DNA origami that have contributed to our understanding of how biophysical signals direct cancer cell fate.

Blue and Long-Wave Ultraviolet Light Induce in vitro Neutrophil Extracellular Trap (NET) Formation

Neutrophil Extracellular Traps (NETs) are produced by neutrophilic granulocytes and consist of decondensed chromatin decorated with antimicrobial peptides. They defend the organism against intruders and are released upon various stimuli including pathogens, mediators of inflammation, or chemical triggers. NET formation is also involved in inflammatory, cardiovascular, malignant diseases, and autoimmune disorders like rheumatoid arthritis, psoriasis, or systemic lupus erythematosus (SLE). In many autoimmune diseases like SLE or dermatomyositis, light of the ultraviolet-visible (UV-VIS) spectrum is well-known to trigger and aggravate disease severity. However, the underlying connection between NET formation, light exposure, and disease exacerbation remains elusive. We studied the effect of UVA (375 nm), blue (470 nm) and green (565 nm) light on NETosis in human neutrophils ex vivo. Our results show a dose- and wavelength-dependent induction of NETosis. Light-induced NETosis depended on the generation of extracellular reactive oxygen species (ROS) induced by riboflavin excitation and its subsequent reaction with tryptophan. The light-induced NETosis required both neutrophil elastase (NE) as well as myeloperoxidase (MPO) activation and induced histone citrullination. These findings suggest that NET formation as a response to light could be the hitherto missing link between elevated susceptibility to NET formation in autoimmune patients and photosensitivity for example in SLE and dermatomyositis patients. This novel connection could provide a clue for a deeper understanding of light-sensitive diseases in general and for the development of new pharmacological strategies to avoid disease exacerbation upon light exposure.

Effect of Adhesion and Substrate Elasticity on Neutrophil Extracellular Trap Formation

Neutrophils are the most abundant type of white blood cells. Upon stimulation, they are able to decondense and release their chromatin as neutrophil extracellular traps (NETs). This process (NETosis) is part of immune defense mechanisms but also plays an important role in many chronic and inflammatory diseases such as atherosclerosis, rheumatoid arthritis, diabetes, and cancer. For this reason, much effort has been invested into understanding biochemical signaling pathways in NETosis. However, the impact of the mechanical micro-environment and adhesion on NETosis is not well-understood. Here, we studied how adhesion and especially substrate elasticity affect NETosis. We employed polyacrylamide (PAA) gels with distinctly defined elasticities (Young's modulus E) within the physiologically relevant range from 1 to 128 kPa and coated the gels with integrin ligands (collagen I, fibrinogen). Neutrophils were cultured on these substrates and stimulated with potent inducers of NETosis: phorbol 12-myristate 13-acetate (PMA) and lipopolysaccharide (LPS). Interestingly, PMA-induced NETosis was neither affected by substrate elasticity nor by different integrin ligands. In contrast, for LPS stimulation, NETosis rates increased with increasing substrate elasticity (E > 20 kPa). LPS-induced NETosis increased with increasing cell contact area, while PMA-induced NETosis did not require adhesion at all. Furthermore, inhibition of phosphatidylinositide 3 kinase (PI3K), which is involved in adhesion signaling, completely abolished LPS-induced NETosis but only slightly decreased PMA-induced NETosis. In summary, we show that LPS-induced NETosis depends on adhesion and substrate elasticity while PMA-induced NETosis is completely independent of adhesion.

Novel Stenotic Microchannels to Study Thrombus Formation in Shear Gradients: Influence of Shear Forces and Human Platelet-Related Factors

Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s⁻¹, and peak wall shears of 3700 to 29,000 s⁻¹ within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions.

Immunoregulation of macrophages by dynamic ligand presentation via ligand-cation coordination

Macrophages regulate host responses to implants through their dynamic adhesion, release, and activation. Herein, we employ bisphosphonate (BP)-coated gold nanoparticle template (BNP) to direct the swift and convertible formation of Mg²⁺-functional Mg²⁺-BP nanoparticle (NP) on the BP-AuNP surface via reversible Mg²⁺-BP coordination, thus producing (Mg²⁺-BP)-Au dimer (MgBNP). Ethylenediaminetetraacetic acid-based Mg²⁺ chelation facilitates the dissolution of Mg²⁺-BP NP, thus enabling the reversion of the MgBNP to the BNP. This convertible nanoassembly incorporating cell-adhesive Mg²⁺ moieties directs reversible attachment and detachment of macrophages by BP and EDTA, without physical scraping or trypsin that could damage cells. The swift formation of RGD ligand- and Mg²⁺-bifunctional RGD-Mg²⁺-BP NP that yields (RGD-Mg²⁺-BP)-Au dimer (RGDBNP) further stimulates the adhesion and pro-regenerative M2-type polarization of macrophages, both in vitro and in vivo, including rho-associated protein kinase. This swift and non-toxic dimer formation can include diverse bio-functional moieties to regulate host responses to implants.

Control of macrophage adhesion and phenotype is important to biomaterial applications. Here, the authors report on the use of bisphosphonate coated gold nanoparticles by magnesium coordination for the controlled adhesion and polarisation of macrophages in vitro and in vivo and controlled cell release.

Anisotropic Ligand Nanogeometry Modulates the Adhesion and Polarization State of Macrophages

Material implants trigger host reactions generated by cells, such as macrophages, which display dynamic adhesion and polarization including M1 inflammatory state and M2 anti-inflammatory state. Creating materials that enable diverse nanoscale display of integrin-binding groups, such as RGD ligand, can unravel nanoscale recruitment and ligation of integrin, which modulate cellular adhesion and activation. Here, we synthesized gold nanorods (GNRs) with various nanoscale anisotropies (i.e., aspect ratios, ARs), but in similar surface areas, and controlled their substrate conjugation to display an anisotropic ligand nanogeometry without modulating ligand density. Using nanoscale immunolabeling, we demonstrated that highly anisotropic ligand-coated GNRs ("AR4" and "AR7") facilitated the recruitment of integrin β1 on macrophages to their nanoscale surfaces. Consequently, highly anisotropic GNRs (e.g., "AR4" and "AR7") elevated the adhesion and M2 state of macrophages, with the inhibition of their M1 state in the culture and mice, entailing rho-associated protein kinase. This nanoscale anisotropic nanogeometry provides a novel and critical parameter to be considered in the generation of biomaterials to potentially modulate host reactions to the implants for immunomodulatory tissue regeneration.

Bicyclic RGD Peptides with Exquisite Selectivity for the Integrin αvβ3 Receptor Using a "Random Design" Approach

We describe the identification of bicyclic RGD peptides with high affinity and selectivity for integrin α_vβ₃ via high-throughput screening of partially randomized libraries. Peptide libraries (672 different compounds) comprising the universal integrin-binding sequence Arg-Gly-Asp (RGD) in the first loop and a randomized sequence XXX (X being one of 18 canonical l-amino acids) in the second loop, both enclosed by either an l- or d-Cys residue, were converted to bicyclic peptides via reaction with 1,3,5-tris(bromomethyl)benzene (T3). Screening of first-generation libraries yielded lead bicyclic inhibitors displaying submicromolar affinities for integrin α_vβ₃ (e.g., C_T3HEQc_T3RGDc_T3, IC₅₀ = 195 nM). Next generation (second and third) libraries were obtained by partially varying the structure of the strongest lead inhibitors and screening for improved affinities and selectivities. In this way, we identified the highly selective bicyclic α_vβ₃-binders C_T3HPQc_T3RGDc_T3 (IC₅₀ = 30 nM), C_T3HPQC_T3RGDc_T3 (IC₅₀ = 31 nM), and C_T3HSQC_T3RGDc_T3 (IC₅₀ = 42 nM) with affinities comparable to that of a knottin-RGD-type peptide (32 amino acids, IC₅₀ = 38 nM) and outstanding selectivities over integrins α_vβ₅ (IC₅₀ > 10000 nM) and α₅β₁ (IC₅₀ > 10000 nM). Affinity measurements using surface plasmon-enhanced fluorescence spectroscopy (SPFS) yielded K_d values of 0.4 and 0.6 nM for the Cy5-labeled bicycle C_T3HPQc_T3RGDc_T3 and RGD "knottin" peptide, respectively. In vitro staining of HT29 cells with Cy5-labeled bicycles using confocal microscopy revealed strong binding to integrins in their natural environment, which highlights the high potential of these peptides as markers of integrin expression.

Serum and Serum Albumin Inhibit in vitro Formation of Neutrophil Extracellular Traps (NETs)

The formation of neutrophil extracellular traps (NETs) is an immune defense mechanism of neutrophilic granulocytes. Moreover, it is also involved in the pathogenesis of autoimmune, inflammatory, and neoplastic diseases. For that reason, the process of NET formation (NETosis) is subject of intense ongoing research. In vitro approaches to quantify NET formation are commonly used and involve neutrophil stimulation with various activators such as phorbol 12-myristate 13-acetate (PMA), lipopolysaccharides (LPS), or calcium ionophores (CaI). However, the experimental conditions of these experiments, particularly the media and media supplements employed by different research groups, vary considerably, rendering comparisons of results difficult. Here, we present the first standardized investigation of the influence of different media supplements on NET formation in vitro. The addition of heat-inactivated (hi) fetal calf serum (FCS), 0.5% human serum albumin (HSA), or 0.5% bovine serum albumin (BSA) efficiently prevented NET formation of human neutrophils following stimulation with LPS and CaI, but not after stimulation with PMA. Thus, serum components such as HSA, BSA and hiFCS (at concentrations typically found in the literature) inhibit NET formation to different degrees, depending on the NETosis inducer used. In contrast, in murine neutrophils, NETosis was inhibited by FCS and BSA, regardless of the inducer employed. This shows that mouse and human neutrophils have different susceptibilities toward the inhibition of NETosis by albumin or serum components. Furthermore, we provide experimental evidence that albumin inhibits NETosis by scavenging activators such as LPS. We also put our results into the context of media supplements most commonly used in NET research. In experiments with human neutrophils, either FCS (0.5–10%), heat-inactivated (hiFCS, 0.1–10%) or human serum albumin (HSA, 0.05–2%) was commonly added to the medium. For murine neutrophils, serum-free medium was used in most cases for stimulation with LPS and CaI, reflecting the different sensitivities of human and murine neutrophils to media supplements. Thus, the choice of media supplements greatly determines the outcome of experiments on NET-formation, which must be taken into account in NETosis research.

Morphological Plasticity of Human Melanoma Cells Is Determined by Nanoscopic Patterns of E- and N-Cadherin Interactions

Loss of E-cadherin and concomitant upregulation of N-cadherin is known as the cadherin switch, and has been implicated in melanoma progression. Mechanistically, homophilic ligation of N-cadherin-expressing melanoma cells with N-cadherin presented within the microenvironment is thought to facilitate invasion. However, the biophysical aspects governing molecular specificity and function of such interactions remain unclear. By using precisely defined nano-patterns of N- or E-cadherin (with densities tunable by more than one order of magnitude from 78 to 1,128 ligands/μm²), we analyzed adhesion and spreading of six different human melanoma cell lines with distinct constitutive cadherin expression patterns. Cadherin-mediated homophilic cell interactions (N/N and E/E) with cadherin-functionalized nano-matrices revealed an unexpected functional dichotomy inasmuch as melanoma cell adhesion was cadherin density-dependent, while spreading and lamellipodia formation were independent of cadherin density. Surprisingly, E-cadherin-expressing melanoma cells also interacted with N-cadherin-presenting nano-matrices, suggesting heterophilic (N/E) interactions. However, cellular spreading in these cases occurred only at high densities of N-cadherin (i.e., >285 ligands/μm²). Overall, our approach using nano-patterned biomimetic surfaces provides a platform to further refine the roles of cadherins in tumor cell behavior and it revealed an intriguing flexibility of mutually compensating N- and E-cadherin interactions relevant for melanoma progression.

Chromatin swelling drives neutrophil extracellular trap release

Neutrophilic granulocytes are able to release their own DNA as neutrophil extracellular traps (NETs) to capture and eliminate pathogens. DNA expulsion (NETosis) has also been documented for other cells and organisms, thus highlighting the evolutionary conservation of this process. Moreover, dysregulated NETosis has been implicated in many diseases, including cancer and inflammatory disorders. During NETosis, neutrophils undergo dynamic and dramatic alterations of their cellular as well as sub-cellular morphology whose biophysical basis is poorly understood. Here we investigate NETosis in real-time on the single-cell level using fluorescence and atomic force microscopy. Our results show that NETosis is highly organized into three distinct phases with a clear point of no return defined by chromatin status. Entropic chromatin swelling is the major physical driving force that causes cell morphology changes and the rupture of both nuclear envelope and plasma membrane. Through its material properties, chromatin thus directly orchestrates this complex biological process.

Magnetic Manipulation of Reversible Nanocaging Controls In Vivo Adhesion and Polarization of Macrophages

Macrophages are key immune cells that perform various physiological functions, such as the maintenance of homeostasis, host defense, disease progression, and tissue regeneration. Macrophages adopt distinctly polarized phenotypes, such as pro-inflammatory M1 phenotype or anti-inflammatory (pro-healing) M2 phenotype, to execute disparate functions. The remotely controlled reversible uncaging of bioactive ligands, such as Arg-Gly-Asp (RGD) peptide, is an appealing approach for temporally regulating the adhesion and resultant polarization of macrophages on implants in vivo. Here, we utilize physical and reversible uncaging of RGD by a magnetic field that allows facile tissue penetration. We first conjugated a RGD-bearing gold nanoparticle (GNP) to the substrate and then a magnetic nanocage (MNC) to the GNP via a flexible linker to form the heterodimeric nanostructure. We magnetically manipulated nanoscale displacement of MNC and thus its proximity to the GNP to reversibly uncage and cage RGD. The uncaging of RGD temporally promoted the adhesion and subsequent M2 polarization of macrophages while inhibiting their M1 polarization both in vitro and in vivo. The RGD uncaging-mediated adhesion and M2 polarization of macrophages involved rho-associated protein kinase signaling. This study demonstrates physical and reversible uncaging of RGD to regulate the adhesion and polarization of host macrophages in vivo. This approach of magnetically regulating the heterodimer conformation for physical and reversible uncaging of RGD offers the promising potential to manipulate inflammatory or tissue-regenerative immune responses to the implants in vivo.

Control of Integrin Affinity by Confining RGD Peptides on Fluorescent Carbon Nanotubes

Integrins are transmembrane receptors that mediate cell-adhesion, signaling cascades and platelet-mediated blood clotting. Most integrins bind to the common short peptide Arg-Gly-Asp (RGD). The conformational freedom of the RGD motif determines how strong and to which integrins it binds. Here, we present a novel approach to tune binding constants by confining RGD peptide motifs via noncovalent adsorption of single-stranded DNA (ssDNA) anchors onto single-walled carbon nanotubes (SWCNTs). Semiconducting SWCNTs display fluorescence in the near-infrared (nIR) region and are versatile fluorescent building blocks for imaging and biosensing. The basic idea of this approach is that the DNA adsorbed on the SWCNT surface determines the conformational freedom of the RGD motif and affects binding affinities. The RGD motif was conjugated to different ssDNA sequences in both linear ssDNA-RGD and bridged ssDNA-RGD-ssDNA geometries. Molecular dynamics (MD) simulations show that the RGD motif in all the synthesized systems is mostly exposed to solvent and thus available for binding, but its flexibility depends on the exact geometry. The affinity for the human platelet integrin α_IIbβ₃ could be modulated up to 15-fold by changing the ssDNA sequence. IC₅₀ values varied from 309 nM for (C)₂₀-RGD/SWCNT hybrids to 29 nM for (GT)₁₅-RGD/SWCNT hybrids. When immobilized onto surface adhesion of epithelial cells increased 6-fold for (GT)₁₅-RGD/SWCNTs. (GT)₁₅-RGD/SWCNTs also increased the number of adhering human platelets by a factor of 4.8. Additionally, α_IIbβ₃ integrins on human platelets were labeled in the nIR by incubating them with these ssDNA-peptide/SWCNT hybrids. In summary, we show that ssDNA-peptide hybrid structures noncovalently adsorb onto SWCNTs and serve as recognition units for cell surface receptors such as integrins. The DNA sequence affects the overall RGD affinity, which is a versatile and straightforward approach to tune binding affinities. In combination with the nIR fluorescence properties of SWCNTs, these new hybrid materials promise many applications in integrin targeting and bioimaging.

Remote Control of Heterodimeric Magnetic Nanoswitch Regulates the Adhesion and Differentiation of Stem Cells

Remote, noninvasive, and reversible control over the nanoscale presentation of bioactive ligands, such as Arg-Gly-Asp (RGD) peptide, is highly desirable for temporally regulating cellular functions in vivo. Herein, we present a novel strategy for physically uncaging RGD using a magnetic field that allows safe and deep tissue penetration. We developed a heterodimeric nanoswitch consisting of a magnetic nanocage (MNC) coupled to an underlying RGD-coated gold nanoparticle (AuNP) via a long flexible linker. Magnetically controlled movement of MNC relative to AuNP allowed reversible uncaging and caging of RGD that modulate physical accessibility of RGD for integrin binding, thereby regulating stem cell adhesion, both in vitro and in vivo. Reversible RGD uncaging by the magnetic nanoswitch allowed temporal regulation of stem cell adhesion, differentiation, and mechanosensing. This physical and reversible RGD uncaging utilizing heterodimeric magnetic nanoswitch is unprecedented and holds promise in the remote control of cellular behaviors in vivo.

Proteolytic processing of platelet receptors

Platelets have a major role in hemostasis and an emerging role in biological processes including inflammation and immunity. Many of these processes require platelet adhesion and localization at sites of tissue damage or infection and regulated platelet activation, mediated by platelet adheso-signalling receptors, glycoprotein (GP) Ib-IX-V and GPVI. Work from a number of laboratories has demonstrated that levels of these receptors are closely regulated by metalloproteinases of the A Disintegrin And Metalloproteinase (ADAM) family, primarily ADAM17 and ADAM10. It is becoming increasingly evident that platelets have important roles in innate immunity, inflammation, and in combating infection that extends beyond processes of hemostasis. This overview will examine the molecular events that regulate levels of platelet receptors and then assess ramifications for these events in settings where hemostasis, inflammation, and infection processes are triggered.

Nanoscale Tuning of VCAM-1 Determines VLA-4-Dependent Melanoma Cell Plasticity on RGD Motifs

The biophysical fine-tuning of cancer cell plasticity is crucial for tumor progression but remains largely enigmatic. Although vascular cell adhesion molecule-1 (VCAM-1/CD106) has been implicated in melanoma progression, here its presentation on endothelial cells was associated with diminished melanoma cell spreading. Using a specific nanoscale modulation of VCAM-1 (tunable from 70 to 670 ligands/μm²) next to integrin ligands (RGD motifs) in a bifunctional system, reciprocal regulation of integrin α4 (ITGA4/VLA-4/CD49d)-dependent adhesion and spreading of melanoma cells was found. As the VCAM-1/VLA-4 receptor pair facilitated adhesion, while at the same time antagonizing RGD-mediated spreading, melanoma cell morphogenesis on these bifunctional matrices was directly regulated by VCAM-1 in a dichotomic and density-dependent fashion. This was accompanied by concordant regulation of F-actin cytoskeleton remodeling, Rac1-expression, and paxillin-related adhesion formation. The novel function of VCAM-1 was corroborated in vivo using two murine models of pulmonary metastasis. The regulation of melanoma cell plasticity by VCAM-1 highlights the complex regulation of tumor-matrix interactions.Implications: Nanotechnology has revealed a novel dichotomic function of the VCAM-1/VLA-4 interaction on melanoma cell plasticity, as nanoscale tuning of this interaction reciprocally determines adhesion and spreading in a ligand density-dependent manner. Mol Cancer Res; 16(3); 528-42. ©2017 AACR.

Remote Manipulation of Ligand Nano-Oscillations Regulates Adhesion and Polarization of Macrophages in Vivo

Macrophages play crucial roles in various immune-related responses, such as host defense, wound healing, disease progression, and tissue regeneration. Macrophages perform distinct and dynamic functions in vivo, depending on their polarization states, such as the pro-inflammatory M1 phenotype and pro-healing M2 phenotype. Remote manipulation of the adhesion of host macrophages to the implants and their subsequent polarization in vivo can be an attractive strategy to control macrophage polarization-specific functions but has rarely been achieved. In this study, we grafted RGD ligand-bearing superparamagnetic iron oxide nanoparticles (SPIONs) to a planar matrix via a long flexible linker. We characterized the nanoscale motion of the RGD-bearing SPIONs grafted to the matrix, in real time by in situ magnetic scanning transmission electron microscopy (STEM) and in situ atomic force microscopy. The magnetic field was applied at various oscillation frequencies to manipulate the frequency-dependent ligand nano-oscillation speeds of the RGD-bearing SPIONs. We demonstrate that a low oscillation frequency of the magnetic field stimulated the adhesion and M2 polarization of macrophages, whereas a high oscillation frequency suppressed the adhesion of macrophages but promoted their M1 polarization, both in vitro and in vivo. Macrophage adhesion was also temporally regulated by switching between the low and high frequencies of the oscillating magnetic field. To the best of our knowledge, this is the first demonstration of the remote manipulation of the adhesion and polarization phenotype of macrophages, both in vitro and in vivo. Our system offers the promising potential to manipulate host immune responses to implanted biomaterials, including inflammation or tissue reparative processes, by regulating macrophage adhesion and polarization.

Tuning Selectivity of Fluorescent Carbon Nanotube-Based Neurotransmitter Sensors

Detection of neurotransmitters is an analytical challenge and essential to understand neuronal networks in the brain and associated diseases. However, most methods do not provide sufficient spatial, temporal, or chemical resolution. Near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWCNTs) have been used as building blocks for sensors/probes that detect catecholamine neurotransmitters, including dopamine. This approach provides a high spatial and temporal resolution, but it is not understood if these sensors are able to distinguish dopamine from similar catecholamine neurotransmitters, such as epinephrine or norepinephrine. In this work, the organic phase (DNA sequence) around SWCNTs was varied to create sensors with different selectivity and sensitivity for catecholamine neurotransmitters. Most DNA-functionalized SWCNTs responded to catecholamine neurotransmitters, but both dissociation constants (K_d) and limits of detection were highly dependent on functionalization (sequence). K_d values span a range of 2.3 nM (SWCNT-(GC)₁₅ + norepinephrine) to 9.4 μM (SWCNT-(AT)₁₅ + dopamine) and limits of detection are mostly in the single-digit nM regime. Additionally, sensors of different SWCNT chirality show different fluorescence increases. Moreover, certain sensors (e.g., SWCNT-(GT)₁₀) distinguish between different catecholamines, such as dopamine and norepinephrine at low concentrations (50 nM). These results show that SWCNTs functionalized with certain DNA sequences are able to discriminate between catecholamine neurotransmitters or to detect them in the presence of interfering substances of similar structure. Such sensors will be useful to measure and study neurotransmitter signaling in complex biological settings.

Surface Patterning of Gold Nanoparticles on PEG-Based Hydrogels to Control Cell Adhesion

We report on a versatile and easy approach to micro-pattern gold nanoparticles (Au NPs) on 8-arm poly(ethylene glycol)-vinyl sulfone thiol (8PEG-VS-SH) hydrogels, and the application of these patterned Au NPs stripes in controlling cell adhesion. Firstly, the Au NPs were patterned on silicon wafers, and then they were transferred onto reactive, multifunctional 8PEG-VS-SH hydrogels. The patterned, micrometer-sized Au NPs stripes with variable spacings ranging from 20 μm to 50 μm were created by our recently developed micro-contact deprinting method. For this micro-contact deprinting approach, four different PEG-based stamp materials have been tested and it was found that the triblock copolymer PEG-PPG-PEG-(3BC) stamp established the best transfer efficiency and has been used in the ongoing work. After the successful creation of micro-patterns of Au NPs stripes on silicon, the patterns can be transferred conveniently and accurately to 8PEG-VS-SH hydrogel films. Subsequently these Au NPs patterns on 8PEG-VS-SH hydrogels have been investigated in cell culture with murine fibroblasts (L-929). The cells have been observed to adhere to and spread on those nano-patterned micro-lines in a remarkably selective and ordered manner.

Kinetic Requirements for Spatiotemporal Chemical Imaging with Fluorescent Nanosensors

Fluorescent nanosensors are powerful tools for basic research and bioanalytical applications. Individual nanosensors are able to detect single molecules, while ensembles of nanosensors can be used to measure the bulk concentration of an analyte. Collective imaging of multiple nanosensors could provide both spatial and temporal chemical information from the nano- to the microscale. This type of chemical imaging with nanosensors would be very attractive to study processes such as chemical signaling between cells (e.g., neurons). So far, it is not understood what processes are resolvable (concentration, time, space) and how optimal sensors should be designed. Here, we develop a theoretical framework to simulate the fluorescence image of arrays of nanosensors in response to a concentration gradient. For that purpose, binding and unbinding of the analyte is simulated for each single nanosensor by using a Monte Carlo simulation and varying rate constants (k_on, k_off). Multiple nanosensors are arranged on a surface and exposed to a concentration pattern c_A(x,y,t) of an analyte. We account for the resolution limit of light microscopy (Abbe limit) and the acquisition speed and resolution of optical setups and determine the resulting response images ΔI(x,y,t). Consequently, we introduce terms for the spatial and temporal resolution and simulate phase diagrams for different rate constants that allow us to predict how a sensor should be designed to provide a desired spatial and temporal resolution. Our results show, for example, that imaging of neurotransmitter release requires rate constants of k_on = 10⁶ M^-1 s^-1and k_off = 10² s^-1 in many scenarios, which corresponds to high dissociation constants of K_d > 100 μM. This work predicts if a given fluorescent nanosensor array (rate constants, size, shape, geometry, density) is able to resolve fast concentration changes such as neurotransmitter release from cells. Additionally, we provide rational design principles to engineer nanosensors for chemical imaging.

Uniform Distance Scaling Behavior of Planet-Satellite Nanostructures Made by Star Polymers

Planet-satellite nanostructures from RAFT star polymers and larger (planet) as well as smaller (satellite) gold nanoparticles are analyzed in experiments and computer simulations regarding the influence of arm number of star polymers. A uniform scaling behavior of planet-satellite distances as a function of arm length was found both in the dried state (via transmission electron microscopy) after casting the nanostructures on surfaces and in the colloidally dispersed state (via simulations and small-angle X-ray scattering) when 2-, 3-, and 6-arm star polymers were employed. This indicates that the planet-satellite distances are mainly determined by the arm length of star polymers. The observed discrepancy between TEM and simulated distances can be attributed to the difference of polymer configurations in dried and dispersed state. Our results also show that these distances are controlled by the density of star polymers end groups, and the number of grabbed satellite particles is determined by the magnitude of the corresponding density. These findings demonstrate the feasibility to precisely control the planet-satellite structures at the nanoscale.

Sexy again: the renaissance of neutrophils in psoriasis

Notwithstanding their prominent presence in psoriatic skin, the functional role of neutrophilic granulocytes still remains somewhat enigmatic. Sparked by exciting scientific discoveries regarding neutrophil functions within the last years, the interest in these short-lived cells of the innate immune system has been boosted recently. While it had been known for some time that neutrophils produce and respond to a number of inflammatory mediators, recent research has linked neutrophils with the pathogenic functions of IL-17, possibly in conjunction with the formation of NETs (neutrophil extracellular traps). Antipsoriatic therapies exert their effects, at least in part, through interference with neutrophils. Neutrophils also appear to connect psoriasis with comorbid diseases. However, directly tampering with neutrophil functions is not trivial as evinced by the failure of therapeutic approaches targeting redundantly regulated cellular communication networks. It has also become apparent that neutrophils link important pathogenic functions of the innate and the adaptive immune system and that they are intricately involved in regulatory networks underlying the pathophysiology of psoriasis. In order to advocate intensified research into the role of this interesting cell population, we here highlight some features of neutrophils and put them into perspective with our current view of the pathophysiology of psoriasis.

High-resolution imaging of cellular dopamine efflux using a fluorescent nanosensor array

Intercellular communication via chemical signaling proceeds with both spatial and temporal components, but analytical tools, such as microfabricated electrodes, have been limited to just a few probes per cell. In this work, we use a nonphotobleaching fluorescent nanosensor array based on single-walled carbon nanotubes (SWCNTs) rendered selective to dopamine to study its release from PC12 neuroprogenitor cells at a resolution exceeding 20,000 sensors per cell. This allows the spatial and temporal dynamics of dopamine release, following K⁺ stimulation, to be measured at exceedingly high resolution. We observe localized, unlabeled release sites of dopamine spanning 100 ms to seconds that correlate with protrusions but not predominately the positive curvature associated with the tips of cellular protrusions as intuitively expected. The results illustrate how directionality of chemical signaling is shaped by membrane morphology, and highlight the advantages of nanosensor arrays that can provide high spatial and temporal resolution of chemical signaling.

Neutrophil extracellular traps: protagonists of cancer progression?

Neutrophil extracellular traps (NETs) are a defense mechanism first described to trap and kill bacteria and other pathogens. Increasingly, however, their involvement in the pathogenesis of inflammatory and malignant diseases is being recognized. Several recent studies have suggested important roles of NETs in tumor progression, metastasis and tumor-associated thrombosis. Although systematic studies to address the role of NETs in tumor development are still scarce, we will explore the emerging evidence for NETs as potential protagonists in malignant disease and highlight the mechanisms through which these effects may be exerted. Future questions arising from our current knowledge of direct and indirect interactions between NETs and cancer cells will be outlined and we will explore NETs as candidate pharmaceutical targets in cancer patients.

Basic mechanisms of platelet receptor shedding

Proteolytic shedding of the extracellular ectodomain of platelet receptors provides a key mechanism for irreversible loss of ligand-binding capacity, and for regulating platelet function in health and disease. Platelets derived from megakaryocytes are small anucleate cells in peripheral blood, with the ability to rapidly adhere, become activated, and secrete an array of procoagulant and proinflammatory factors at sites of vascular injury or disease, and to form a platelet aggregate (thrombus) which is not only critical in normal hemostasis and wound healing, but in atherothrombotic diseases including myocardial infarction and ischemic stroke. Basic mechanisms of receptor shedding on platelets have important distinctions from how receptors on other cell types might be shed, in that shedding is rapidly initiated (within seconds to minutes) and occurs under altered shear conditions encountered in flowing blood or experimentally ex vivo. This review will consider the key components of platelet receptor shedding, that is, the receptor with relevant cleavage site, the (metallo)proteinase or sheddase and how its activity is regulated, and the range of known regulatory factors that control platelet receptor shedding including receptor-associated molecules such as calmodulin, factors controlling sheddase surface expression and activity, and other elements such as shear stress, plasma membrane properties, cellular activation status or age. Understanding these basic mechanisms of platelet receptor shedding is significant in terms of utilizing receptor surface expression or soluble proteolytic fragments as platelet-specific biomarkers and/or ultimately therapeutic targeting of these mechanisms to control platelet reactivity and function.

Metalloproteolytic receptor shedding…platelets "acting their age"

Whilst significant effort has been focused on development of tools and approaches to clinically modulate activation processes that consume platelets, the platelet receptors that initiate activation processes remain untargeted. The modulation of receptor levels is also linked to underlying platelet aging processes which influence normal platelet lifespan and also the functionality and survival of stored platelets that are used in transfusion. In this review, we will focus on platelet adhesion receptors initiating thrombus formation, and discuss how regulation of levels of these receptors impact platelet function and platelet survival.

Structural basis for the specific inhibition of glycoprotein Ibα shedding by an inhibitory antibody

Ectodomain shedding of glycoprotein (GP) Ibα is thought to mediate the clearance of activated, aged or damaged platelets. A monoclonal antibody, 5G6, has been developed recently to specifically bind to the GPIbα shedding cleavage site and to inhibit its shedding. However, the molecular mechanism underlying antigen recognition and inhibitory specificity is not clear. To elucidate the structural basis for 5G6 binding to GPIbα, we determined the crystal structure of 5G6 Fab fragment in complex with its epitope peptide KL10 (GPIbα residues 461–470, KLRGVLQGHL), to 2.4-Å resolution. Key residues in both 5G6 and KL10 were mutated to validate their effects in antibody binding by using isothermal titration calorimetry. The 5G6 Fab-KL10 peptide complex structure confirmed the direct association of 5G6 with its target GPIbα residues and elucidated the molecular basis underlying its binding specificity and high affinity. The similar binding properties of 5G6 Fab fragment to GPIbα on human platelets as those to KL10 suggests that such an interaction may not be affected by the plasma membrane or nearby GPIbβ. This structural information may facilitate further antibody optimization and humanization.

Effects of shear on P-selectin deposition in microfluidic channels

Traditional leukocyte adhesion assays have provided significant insight into the mechanisms of leukocyte rolling in part through the use of homogeneously coated surfaces. These assays typically involve protein coating of glass coverslips or plastic petri dishes applied via a static drop of protein solution. With this approach, it is difficult to spatially control the location of proteins to fabricate surface-bound protein gradients that mimic in vivo situations. Microfluidic patterning of proteins with microfluidic devices has become a popular technique due to the ability to spatially pattern proteins on a cellular scale. Despite the advantages of microfluidic patterning, few studies have systematically investigated the effects of perfusion time, protein concentration, and perfusion shear stress on protein deposition. Herein, we demonstrated the fabrication of both line and step gradients of P-selectin on glass substrates that support cell rolling and adhesion assays. Investigation of the flow conditions during the microfluidic patterning led to several significant findings. We observed that the protein deposition time of 5 min was sufficient to deposit adequate P-selectin to support neutrophil rolling. We demonstrated that the amount of membrane P-selectin (mP-selectin) or recombinant P-selectin (rP-selectin) deposited showed a dependence on the perfusion shear stress between 4.0 and 32.0 dyn/cm(2), while similar studies with fibronectin or fibrinogen showed no shear stress dependence. Finally, we also created step changes in surface adherent protein concentration of P-selectin to characterize leukocyte-rolling behavior in response to sudden changes in ligand density.

Mechanotransduction in neutrophil activation and deactivation

Mechanotransduction refers to the processes through which cells sense mechanical stimuli by converting them to biochemical signals and, thus, eliciting specific cellular responses. Cells sense mechanical stimuli from their 3D environment, including the extracellular matrix, neighboring cells and other mechanical forces. Incidentally, the emerging concept of mechanical homeostasis,long term or chronic regulation of mechanical properties, seems to apply to neutrophils in a peculiar manner, owing to neutrophils' ability to dynamically switch between the activated/primed and deactivated/deprimed states. While neutrophil activation has been known for over a century, its deactivation is a relatively recent discovery. Even more intriguing is the reversibility of neutrophil activation and deactivation. We review and critically evaluate recent findings that suggest physiological roles for neutrophil activation and deactivation and discuss possible mechanisms by which mechanical stimuli can drive the oscillation of neutrophils between the activated and resting states. We highlight several molecules that have been identified in neutrophil mechanotransduction, including cell adhesion and transmembrane receptors, cytoskeletal and ion channel molecules. The physiological and pathophysiological implications of such mechanically induced signal transduction in neutrophils are highlighted as a basis for future work. This article is part of a Special Issue entitled: Mechanobiology.

Primary haemostasis: newer insights

At the same time as biophysical and omics approaches are drilling deeper into the molecular details of platelets and other blood cells, as well as their receptors and mechanisms of regulation, there is also an increasing awareness of the functional overlap between human vascular systems. Together, these studies are redefining the intricate networks linking haemostasis and thrombosis with inflammation, infectious disease, cancer/metastasis and other vascular pathophysiology. The focus of this state-of-the-art review is some of the newer advances relevant to primary haemostasis. Of particular interest, platelet-specific primary adhesion-signalling receptors and associated activation pathways control platelet function in flowing blood and provide molecular links to other systems. Platelet glycoprotein (GP)Ibα of the GPIb-IX-V complex and GPVI not only initiate platelet aggregation and thrombus formation by primary interactions with von Willebrand factor and collagen, respectively, but are also involved in coagulation, leucocyte engagement, bacterial or viral interactions, and are relevant as potential risk markers in a range of human diseases. Understanding these systems in unprecedented detail promises significant advances in evaluation of individual risk, in new diagnostic or therapeutic possibilities and in monitoring the response to drugs or other treatment.

Nanomaterials, inflammation, and tissue engineering

Nanomaterials exhibit unique properties that are absent in the bulk material because decreasing material size leads to an exponential increase in surface area, surface area to volume ratio, and effective stiffness, resulting in altered physiochemical properties. Diverse categories of nanomaterials such as nanoparticles, nanoporous scaffolds, nanopatterned surfaces, nanofibers, and carbon nanotubes can be generated using advanced fabrication and processing techniques. These materials are being increasingly incorporated in tissue engineering scaffolds to facilitate the development of biomimetic substitutes to replace damaged tissues and organs. Long-term success of nanomaterials in tissue engineering is contingent upon the inflammatory responses they elicit in vivo. This review seeks to summarize the recent developments in our understanding of biochemical and biophysical attributes of nanomaterials and the inflammatory responses they elicit, with a focus on strategies for nanomaterial design in tissue engineering applications.

Nanoscale integrin ligand patterns determine melanoma cell behavior

Cells use integrin receptors to adhere onto surfaces by binding to ligands such as the arginine-glycine-aspartic acid (RGD) motif. Cancer cells make use of this adhesion process, which has motivated the development of integrin-directed drugs. However, those drugs may exert paradoxical effects on tumor progression, which raises the question of how integrin function is governed in tumor cells on the nanoscale. We have utilized precisely defined and tunable RGD ligand site densities spanning 1 order of magnitude, i.e., 103 to 1145 ligand sites/μm(2), by using RGD-functionalized gold nanoparticle patterns immobilized on glass by block copolymer (micellar) nanolithography. In an αVβ3 integrin-dependent fashion, human melanoma cells spread, formed focal contacts, and reorganized cytoskeletal fibers on a physiologically relevant RGD density of 349 sites/μm(2). Intriguingly, low doses of solute RGD "shifted" the optimal densities of immobilized ligand along with corresponding melanoma cell integrin clusters and cytoskeletal changes toward those typical for "intermediate" ligand presentation. Consequently, melanoma cells were forced into a "permissive" state, optimizing interactions with suboptimal nanostructured biomimetic surfaces, thus providing an explanation for the seemingly paradoxical effects on tumor progression and a potential clue for individualized antitumoral therapies.

Platelet receptor expression and shedding: glycoprotein Ib-IX-V and glycoprotein VI

Quantity, quality, and lifespan are 3 important factors in the physiology, pathology, and transfusion of human blood platelets. The aim of this review is to discuss the proteolytic regulation of key platelet-specific receptors, glycoprotein(GP)Ib and GPVI, involved in the function of platelets in hemostasis and thrombosis, and nonimmune or immune thrombocytopenia. The scope of the review encompasses the basic science of platelet receptor shedding, practical aspects related to laboratory analysis of platelet receptor expression/shedding, and clinical implications of using the proteolytic fragments as platelet-specific biomarkers in vivo in terms of platelet function and clearance. These topics can be relevant to platelet transfusion regarding both changes in platelet receptor expression occurring ex vivo during platelet storage and/or clinical use of platelets for transfusion. In this regard, quantitative analysis of platelet receptor profiles on blood samples from individuals could ultimately enable stratification of bleeding risk, discrimination between causes of thrombocytopenia due to impaired production vs enhanced clearance, and monitoring of response to treatment prior to change in platelet count.