Rapid initiation of cell cycle reentry processes protects neurons from amyloid-ß toxicity.

Neurons are postmitotic cells. Reactivation of the cell cycle by neurons has been reported in Alzheimer's disease (AD) brains and models. This gave rise to the hypothesis that reentering the cell cycle renders neurons vulnerable and thus contributes to AD pathogenesis. Here, we use the fluorescent ubiquitination-based cell cycle indicator (FUCCI) technology to monitor the cell cycle in live neurons. We found transient, self-limited cell cycle reentry activity in naive neurons, suggesting that their postmitotic state is a dynamic process. Furthermore, we observed a diverse response to oligomeric amyloid-ß (oAß) challenge; neurons without cell cycle reentry activity would undergo cell death without activating the FUCCI reporter, while neurons undergoing cell cycle reentry activity at the time of the oAß challenge could maintain and increase FUCCI reporter signal and evade cell death. Accordingly, we observed marked neuronal FUCCI positivity in the brains of human mutant Aß precursor protein transgenic (APP23) mice together with increased neuronal expression of the endogenous cell cycle control protein geminin in the brains of 3-mo-old APP23 mice and human AD brains. Taken together, our data challenge the current view on cell cycle in neurons and AD, suggesting that pathways active during early cell cycle reentry in neurons protect from Aß toxicity.

From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland function.

Spider webs that serve as snares are one of the most fascinating and abundant type of animal architectures. In many cases they include an adhesive coating of silk lines-so-called viscid silk-for prey capture. The evolutionary switch from silk secretions forming solid fibres to soft aqueous adhesives remains an open question in the understanding of spider silk evolution. Here we functionally and chemically characterized the secretions of two types of silk glands and their behavioural use in the cellar spider, Pholcus phalangioides. Both being derived from the same ancestral gland type that produces fibres with a solidifying glue coat, the two types produce respectively a quickly solidifying glue applied in thread anchorages and prey wraps, or a permanently tacky glue deployed in snares. We found that the latter is characterized by a high concentration of organic salts and reduced spidroin content, showing up a possible pathway for the evolution of viscid properties by hygroscopic-salt-mediated hydration of solidifying adhesives. Understanding the underlying molecular basis for such radical switches in material properties not only helps to better understand the evolutionary origins and versatility of ecologically impactful spider web architectures, but also informs the bioengineering of spider silk-based products with tailored properties.

Glyphosate-induced stiffening of HaCaT keratinocytes, a Peak Force Tapping study on living cells.

The skin is the first physiological barrier, with a complex constitution, that provides defensive functions against multiple physical and chemical aggressions. Glyphosate is an extensively used herbicide that has been shown to increase the risk of cancer. Moreover there is increasing evidence suggesting that the mechanical phenotype plays an important role in malignant transformation. Atomic force microscopy (AFM) has emerged within the last decade as a powerful tool for providing a nanometer-scale resolution imaging of biological samples. Peak Force Tapping (PFT) is a newly released AFM-based investigation technique allowing extraction of chemical and mechanical properties from a wide range of samples at a relatively high speed and a high resolution. The present work uses the PFT technology to investigate HaCaT keratinocytes, a human epidermal cell line, and offers an original approach to study chemically-induced changes in the cellular mechanical properties under near-physiological conditions. These experiments indicate glyphosate induces cell membrane stiffening, and the appearance of cytoskeleton structures at a subcellular level, for low cytotoxic concentrations whereas cells exposed to IC50 (inhibitory concentration 50%) treatment exhibit control-like mechanical behavior despite obvious membrane damages. Quercetin, a well-known antioxidant, reverses the glyphosate-induced mechanical phenotype.

Nutritionally induced nanoscale variations in spider silk structural and mechanical properties.

Spider major ampullate (MA) silk is characterized by high strength and toughness and is adaptable across environments. Experiments depriving spiders of protein have enabled researchers to examine nutritionally induced changes in gene expression, protein structures, and bulk properties of MA silk. However, it has not been elucidated if it varies in a similar way at a nanoscale. Here we used Atomic Force Microscopy (AFM) to simultaneously examine the topographic, structural, and mechanical properties of silks spun by two species of spider, Argiope keyserlingi and Latrodectus hasselti, at a nanoscale when protein fed or deprived. We found height, a measure of localized width, to substantially vary across species and treatments. We also found that Young's modulus, which may be used as an estimate of localized stiffness, decreased with protein deprivation in both species' silk. Our results suggest that nanoscale skin-core structures of A. keyserlingi's MA silk varied significantly across treatments, whereas only slight structural and functional variability was found for L. hasselti's silk. These results largely agreed with examinations of the bulk properties of each species' silk. However, we could not directly attribute the decoupling between protein structures and bulk mechanics in L. hasselti's silk to nanoscale features. Our results advance the understanding of processes inducing skin and core structural variations in spider silks at a nanoscale, which serves to enhance the prospect of developing biomimetic engineering programs.

Spatio-temporal analysis of nanoparticles in live tumor spheroids impacted by cell origin and density.

Nanoparticles hold great preclinical promise in cancer therapy but continue to suffer attrition through clinical trials. Advanced, three dimensional (3D) cellular models such as tumor spheroids can recapitulate elements of the tumor environment and are considered the superior model to evaluate nanoparticle designs. However, there is an important need to better understand nanoparticle penetration kinetics and determine how different cell characteristics may influence this nanoparticle uptake. A key challenge with current approaches for measuring nanoparticle accumulation in spheroids is that they are often static, losing spatial and temporal information which may be necessary for effective nanoparticle evaluation in 3D cell models. To overcome this challenge, we developed an analysis platform, termed the Determination of Nanoparticle Uptake in Tumor Spheroids (DONUTS), which retains spatial and temporal information during quantification, enabling evaluation of nanoparticle uptake in 3D tumor spheroids. Outperforming linear profiling methods, DONUTS was able to measure silica nanoparticle uptake to 10 µm accuracy in both isotropic and irregularly shaped cancer cell spheroids. This was then extended to determine penetration kinetics, first by a forward-in-time, center-in-space model, and then by mathematical modelling, which enabled the direct evaluation of nanoparticle penetration kinetics in different spheroid models. Nanoparticle uptake was shown to inversely relate to particle size and varied depending on the cell type, cell stiffness and density of the spheroid model. The automated analysis method we have developed can be applied to live spheroids in situ, for the advanced evaluation of nanoparticles as delivery agents in cancer therapy.

Interfacial Curvature in Confined Coculture Directs Stromal Cell Activity with Spatial Corralling of Pancreatic Cancer Cells.

Interfacial cues in the tumor microenvironment direct the activity and assembly of multiple cell types. Pancreatic cancer, along with breast and prostate cancers, is enriched with cancer-associated fibroblasts (CAFs) that activate to coordinate the deposition of the extracellular matrix, which can comprise over 90% of the tumor mass. While it is clear that matrix underlies the severity of the disease, the relationship between stromal-tumor cell assembly and cell-matrix dynamics remains elusive. Micropatterned hydrogels deconstruct the interplay between matrix stiffness and geometric confinement, guiding heterotypic cell populations and matrix assembly in pancreatic cancer. Interfacial cues at the perimeter of microislands guide CAF migration and direct cancer cell assembly. Computational modeling shows curvature-stress dependent cellular localization for cancer and CAFs in coculture. Regions of convex curvature enhance edge stress that activates a myofibroblast phenotype in the CAFs with migration and increased collagen I deposition, ultimately leading to a central "corralling" of cancer cells. Inhibiting mechanotransduction pathways decreases CAF activation and the associated corralling phenotype. Together, this work reveals how interfacial biophysical cues underpin aspects of stromal desmoplasia, a hallmark of disease severity and chemoresistance in the pancreatic, breast, and prostate cancers, thereby providing a tool to expand stroma-targeting therapeutic strategies.

Morphological damages of a glyphosate-treated human keratinocyte cell line revealed by a micro- to nanoscale microscopic investigation.

Among the molecules to which the human skin is exposed, glyphosate is used as an herbicide. Glyphosate has been shown to induce in vitro cutaneous cytotoxic effects, concomitant with oxidative disorders. In this following study, we focused on dynamic events of the loss of HaCaT cell integrity appearing after a glyphosate treatment. In these conditions, we showed that glyphosate is able to disrupt HaCaT cells and to induce intracellular oxidative cascade. In this aim, we optimized the conditions of cell treatment playing on exposure time (from 24 h to 30 min), which directly modify the cell viability profile (glyphosate 50% inhibition concentration from 28 to 53 mM) and allow to track cells along the treatment as an "induction and visualization" process. The combination of atomic force and fluorescence microscopic approaches offered opportunities to lead in parallel an investigation of the membrane surface and of the intracellular disorders, through cytoskeleton, nuclear, and oxidative stress marker targeting. The originality of our approach relies on monitoring all events derived from oxidative stress in process and performed by simultaneous cytotoxic induction and nanoscale cell visualization. We revealed a transition from spread and globular to elongated cell morphology, with a drastic cell size reduction, after a dose- and time-dependent glyphosate treatment; a redistribution of cell surface protrusions was also pointed out. All these membrane damages, added to observations of disorganized cytoskeleton, condensed chromatin, and overproduction of oxidative reactive species, lead us to conclude that glyphosate acts in induction of apoptotic process.

Silk fibroin photo-lyogels containing microchannels as a biomaterial platform for in situ tissue engineering.

The biophysical properties of biomaterials are key to directing the biological responses and biomaterial integration and function in in situ tissue engineering approaches. We present silk photo-lyogels, a biomaterial format fabricated using a new combinatorial approach involving photo-initiated crosslinking of silk fibroin via di-tyrosine bonds followed by lyophilization to generate 3D, porous lyogels showing physical properties distinct to those of lyophilized silk sponges or silk hydrogels. This fabrication approach allowed introduction of microchannels into 3D constructs via biofabrication approaches involving silk crosslinking around an array of 3D printed photocurable resin pillars to generate parallel channels or around a 3D printed sacrificial thermosensitive gel to generate interconnected channels in a rapid manner and without the need for chemical modification of silk fibroin. The presence of interconnected microchannels significantly improved migration of endothelial cells into 3D photo-lyogels in vitro, and tissue infiltration, photo-lyogel integration, and vascularization when implanted in vivo in a mouse subcutaneous model. Taken together, these findings demonstrate the feasibility and utility of a new combinatorial fabrication approach for generation of silk biomaterials that support cell interactions and implant integration for in situ tissue engineering approaches.

PIEZO1-Mediated Currents Are Modulated by Substrate Mechanics.

PIEZO1 is a bona fide mammalian mechanically activated channel that has recently been shown to provide instructive cues during neuronal specification, texture sensing, and cell migration where mechanical inputs arise at the interface between the cells and their substrate. Here, we have investigated whether the mechanical properties of the substrate alone can modulate PIEZO1 activity, in response to exogenously applied stimuli, using elastomeric pillar arrays as force transducers. This methodology enables application of mechanical stimuli at cell-substrate contact points by deflecting individual pili. We found that PIEZO1 is more sensitive to substrate deflections with increased spacing between pili (reducing surface roughness) but not on more stiff substrates. Cellular contractility was required for the sensitization of PIEZO1 but was not essential for PIEZO1 activation. Computational modeling suggested that the membrane tension changes generated by pillar deflections were below the membrane tension changes that arise from cellular indentation or high-speed pressure clamp assays. We conclude that the mechanics of the microenvironment can modulate PIEZO1 signaling, highlighting the importance of studying channel activation directly at the cell-substrate interface. We propose that forces arising from actin-mediated contractility and within the lipid bilayer act synergistically to regulate PIEZO1 activation by stimuli applied at contacts between cells and their surroundings.

Controlling self-assembly of diphenylalanine peptides at high pH using heterocyclic capping groups.

Using small angle neutron scattering (SANS), it is shown that the existence of pre-assembled structures at high pH for a capped diphenylalanine hydrogel is controlled by the selection of N-terminal heterocyclic capping group, namely indole or carbazole. At high pH, changing from a somewhat hydrophilic indole capping group to a more hydrophobic carbazole capping group results in a shift from a high proportion of monomers to self-assembled fibers or wormlike micelles. The presence of these different self-assembled structures at high pH is confirmed through NMR and circular dichroism spectroscopy, scanning probe microscopy and cryogenic transmission electron microscopy.

Transient tissue priming via ROCK inhibition uncouples pancreatic cancer progression, sensitivity to chemotherapy, and metastasis.

The emerging standard of care for patients with inoperable pancreatic cancer is a combination of cytotoxic drugs gemcitabine and Abraxane, but patient response remains moderate. Pancreatic cancer development and metastasis occur in complex settings, with reciprocal feedback from microenvironmental cues influencing both disease progression and drug response. Little is known about how sequential dual targeting of tumor tissue tension and vasculature before chemotherapy can affect tumor response. We used intravital imaging to assess how transient manipulation of the tumor tissue, or "priming," using the pharmaceutical Rho kinase inhibitor Fasudil affects response to chemotherapy. Intravital Förster resonance energy transfer imaging of a cyclin-dependent kinase 1 biosensor to monitor the efficacy of cytotoxic drugs revealed that priming improves pancreatic cancer response to gemcitabine/Abraxane at both primary and secondary sites. Transient priming also sensitized cells to shear stress and impaired colonization efficiency and fibrotic niche remodeling within the liver, three important features of cancer spread. Last, we demonstrate a graded response to priming in stratified patient-derived tumors, indicating that fine-tuned tissue manipulation before chemotherapy may offer opportunities in both primary and metastatic targeting of pancreatic cancer.

Translating Periosteum's Regenerative Power: Insights From Quantitative Analysis of Tissue Genesis With a Periosteum Substitute Implant.

: An abundance of surgical studies during the past 2 centuries provide empirical evidence of periosteum's regenerative power for reconstructing tissues as diverse as trachea and bone. This study aimed to develop quantitative, efficacy-based measures, thereby providing translational guidelines for the use of periosteum to harness the body's own healing potential and generate target tissues. The current study quantitatively and qualitatively demonstrated tissue generation modulated by a periosteum substitute membrane that replicates the structural constituents of native periosteum (elastin, collagen, progenitor cells) and its barrier, extracellular, and cellular properties. It shows the potentiation of the periosteum's regenerative capacity through the progenitor cells that inhabit the tissue, biological factors intrinsic to the extracellular matrix of periosteum, and mechanobiological factors related to implant design and implementation. In contrast to the direct intramembranous bone generated in defects surrounded by patent periosteum in situ, tissue generation in bone defects bounded by the periosteum substitute implant occurred primarily via endochondral mechanisms whereby cartilage was first generated and then converted to bone. In addition, in defects treated with the periosteum substitute, tissue generation was highest along the major centroidal axis, which is most resistant to prevailing bending loads. Taken together, these data indicate the possibility of designing modular periosteum substitute implants that can be tuned for vectorial and spatiotemporal delivery of biological agents and facilitation of target tissue genesis for diverse surgical scenarios and regenerative medicine approaches. It also underscores the potential to develop physical therapy protocols to maximize tissue genesis via the implant's mechanoactive properties. SIGNIFICANCE: In the past 2 centuries, the periosteum, a niche for stem cells and super-smart biological material, has been used empirically in surgery to repair tissues as diverse as trachea and bone. In the past 25 years, the number of articles indexed in PubMed for the keywords "periosteum and tissue engineering" and "periosteum and regenerative medicine" has burgeoned. Yet the biggest limitation to the prescriptive use of periosteum is lack of easy access, giving impetus to the development of periosteum substitutes. Recent studies have opened up the possibility to bank periosteal tissues (e.g., from the femoral neck during routine resection for implantation of hip replacements). This study used an interdisciplinary, quantitative approach to assess tissue genesis in modular periosteum substitute implants, with the aim to provide translational strategies for regenerative medicine and tissue engineering.

Cell elasticity is regulated by the tropomyosin isoform composition of the actin cytoskeleton.

The actin cytoskeleton is the primary polymer system within cells responsible for regulating cellular stiffness. While various actin binding proteins regulate the organization and dynamics of the actin cytoskeleton, the proteins responsible for regulating the mechanical properties of cells are still not fully understood. In the present study, we have addressed the significance of the actin associated protein, tropomyosin (Tpm), in influencing the mechanical properties of cells. Tpms belong to a multi-gene family that form a co-polymer with actin filaments and differentially regulate actin filament stability, function and organization. Tpm isoform expression is highly regulated and together with the ability to sort to specific intracellular sites, result in the generation of distinct Tpm isoform-containing actin filament populations. Nanomechanical measurements conducted with an Atomic Force Microscope using indentation in Peak Force Tapping in indentation/ramping mode, demonstrated that Tpm impacts on cell stiffness and the observed effect occurred in a Tpm isoform-specific manner. Quantitative analysis of the cellular filamentous actin (F-actin) pool conducted both biochemically and with the use of a linear detection algorithm to evaluate actin structures revealed that an altered F-actin pool does not absolutely predict changes in cell stiffness. Inhibition of non-muscle myosin II revealed that intracellular tension generated by myosin II is required for the observed increase in cell stiffness. Lastly, we show that the observed increase in cell stiffness is partially recapitulated in vivo as detected in epididymal fat pads isolated from a Tpm3.1 transgenic mouse line. Together these data are consistent with a role for Tpm in regulating cell stiffness via the generation of specific populations of Tpm isoform-containing actin filaments.

A step further toward glyphosate-induced epidermal cell death: involvement of mitochondrial and oxidative mechanisms.

A deregulation of programmed cell death mechanisms in human epidermis leads to skin pathologies. We previously showed that glyphosate, an extensively used herbicide, provoked cytotoxic effects on cultured human keratinocytes, affecting their antioxidant capacities and impairing morphological and functional cell characteristics. The aim of the present study, carried out on the human epidermal cell line HaCaT, was to examine the part of apoptosis plays in the cytotoxic effects of glyphosate and the intracellular mechanisms involved in the apoptotic events. We have conducted different incubation periods to reveal the specific events in glyphosate-induced cell death. We observed an increase in the number of early apoptotic cells at a low cytotoxicity level (15%), and then, a decrease, in favor of late apoptotic and necrotic cell rates for more severe cytotoxicity conditions. At the same time, we showed that the glyphosate-induced mitochondrial membrane potential disruption could be a cause of apoptosis in keratinocyte cultures.