Serious methanol crossover of Nafion greatly limits the use of increased fuel concentrations in methanol fuel cells, which results in a decreased power density. To lower the methanol crossover of Nafion, thin layers of PVDF nanofibers were successfully electrospun and impregnated with a Nafion solution to create novel fuel cell membranes. The morphological structures, mechanical properties, thermal stabilities, chemical resistance and proton conductivity were investigated for each composite membrane. The performances of membranes with different layers of PVDF nanofibers were evaluated, using a single cell direct methanol fuel cell with 10M methanol fuel. In comparison with membranes of pure Nafion, the introduction of PVDF fiber mats greatly enhanced the membrane's thermal and oxidation stabilities, suppressed swelling ratios and water uptake, and increase fuel cell performance.
Cells are subjected to a barrage of daily insults that often lead to their cortex being ripped open and requiring immediate repair. An important component of the cell's repair response is the formation of an actomyosin ring at the wound periphery to mediate its closure. Here we show that inhibition of myosin or the linear actin nucleation factors Diaphanous and/or DAAM results in a disrupted contractile apparatus and delayed wound closure. We also show that the branched actin nucleators WASp and SCAR function non-redundantly as scaffolds to assemble and maintain this contractile actomyosin cable. Removing branched actin leads to the formation of smaller circular actin-myosin structures at the cell cortex and slow wound closure. Removing linear and branched actin simultaneously results in failed wound closure. Surprisingly, removal of branched actin and myosin results in the formation of parallel linear F-actin filaments that undergo a chiral swirling movement to close the wound, thereby uncovering a new mechanism of cell wound closure. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text]
To cope with continuous physiological and environmental stresses, cells of all sizes require an effective wound repair process to seal breaches to their cortex. Once a wound is recognized, the cell must rapidly plug the injury site, reorganize the cytoskeleton and the membrane to pull the wound closed, and finally remodel the cortex to return to homeostasis. Complementary studies using various model organisms have demonstrated the importance and complexity behind the formation and translocation of an actin ring at the wound periphery during the repair process. Proteins such as actin nucleators, actin bundling factors, actin-plasma membrane anchors, and disassembly factors are needed to regulate actin ring dynamics spatially and temporally. Notably, Rho family GTPases have been implicated throughout the repair process, whereas other proteins are required during specific phases. Interestingly, although different models share a similar set of recruited proteins, the way in which they use them to pull the wound closed can differ. Here, we describe what is currently known about the formation, translocation, and remodeling of the actin ring during the cell wound repair process in model organisms, as well as the overall impact of cell wound repair on daily events and its importance to our understanding of certain diseases and the development of therapeutic delivery modalities.
Cells are subjected to a barrage of daily insults that often lead to its cortex being ripped open and requiring immediate repair. An important component of the cell′s repair response is the formation of an actomyosin ring at the wound periphery to mediate its closure. Inhibition of linear actin nucleation factors and myosin result in a disrupted contractile apparatus and delayed wound closure. Here we show that branched actin nucleators function as a scaffold to assemble and maintain this contractile actomyosin cable. Removing branched actin leads to the formation of smaller circular actin-myosin structures at the cell cortex and slow wound closure. Removing linear and branched actin results in failed wound closure. Surprisingly, removal of branched actin and myosin results in the formation of parallel linear actin filaments that undergo a chiral swirling movement to close the wound. These results provide insight into actin organization in contractile actomyosin rings and uncover a new mechanism of wound closure.
In many cellular contexts, intracellular actomyosin networks must generate directional forces to carry out cellular tasks such as migration and endocytosis, which play important roles during normal developmental processes. A number of different actin binding proteins have been identified that form linear or branched actin, and that regulate these filaments through activities such as bundling, crosslinking, and depolymerization to create a wide variety of functional actin assemblies. The helical nature of actin filaments allows them to better accommodate tensile stresses by untwisting, as well as to bend to great curvatures without breaking. Interestingly, this latter property, the bending of actin filaments, is emerging as an exciting new feature for determining dynamic actin configurations and functions. Indeed, recent studies using in vitro assays have found that proteins including IQGAP, Cofilin, Septins, Anillin, α-Actinin, Fascin, and Myosins—alone or in combination—can influence the bending or curvature of actin filaments. This bending increases the number and types of dynamic assemblies that can be generated, as well as the spectrum of their functions. Intriguingly, in some cases, actin bending creates directionality within a cell, resulting in a chiral cell shape. This actin-dependent cell chirality is highly conserved in vertebrates and invertebrates and is essential for cell migration and breaking L-R symmetry of tissues/organs. Here, we review how different types of actin binding protein can bend actin filaments, induce curved filament geometries, and how they impact on cellular functions.
A male Eleutherodactylus Coqui (EC, a frog) expands and contracts its gular skin to a great extent during mating calls, displaying its extraordinarily compliant organ. There are striking similarities between frog gular skin and the human bladder as both organs expand and contract significantly. While the high extensibility of the urinary bladder is attributed to the unique helical ultrastructure of collagen type III, the mechanism behind the gular skin of EC is unknown. We therefore aim to understand the structure–property relationship of gular skin tissues of EC. Our findings demonstrate that the male EC gular tissue can elongate up to 400%, with an ultimate tensile strength (UTS) of 1.7 MPa. Species without vocal sacs, Xenopus Laevis (XL) and Xenopus Muelleri (XM), elongate only up to 80% and 350% with UTS~6.3 MPa and ~4.5 MPa, respectively. Transmission electron microscopy (TEM) and histological staining further show that EC tissues’ collagen fibers exhibit a layer-by-layer arrangement with an uninterrupted, knot-free, and continuous structure. The collagen bundles alternate between a circular and longitudinal shape, suggesting an out-of-plane zig-zag structure, which likely provides the tissue with greater extensibility. In contrast, control species contain a nearly linear collagen structure interrupted by thicker muscle bundles and mucous glands. Meanwhile, in the rat bladder, the collagen is arranged in a helical structure. The bladder-like high extensibility of EC gular skin tissue arises despite it having eight-fold lesser elastin and five times more collagen than the rat bladder. To our knowledge, this is the first study to report the structural and molecular mechanisms behind the high compliance of EC gular skin. We believe that these findings can lead us to develop more compliant biomaterials for applications in regenerative medicine.
Here, we report the design and development of highly stretchable, compliant, and enzymatic-resistant transiently cross-linked decellularized extracellular matrixes (dECMs) (e.g., porcine small intestine submucosa/dSIS, urinary bladder matrix/dUBM, bovine pericardium/dBP, bovine dermis/dBD, and human dermis/dHD). Specifically, these dECMs were modified with long aliphatic chains (C9, C14, and C18). Upon modification, dECMs became significantly resistant to enzymatic degradation for extended periods, showed increased water contact angle (>20%–90%), and stretched >200% than their control counterparts. Modified dECMs are compliant, undergoing 100% elongation at only 0.3–0.5 MPa of applied tensile stress (∼10%–25% of their control counterparts), similar to the control bladder tissue. Furthermore, modified dECMs remain structurally stable at the physiological temperature with increased storage and loss modulus values but decreased tan δ values compared to their control counterparts. Although modification reduces cell adhesion, the gene expressions in polarized macrophages remain unchanged (e.g., TGFβ, CD163, and CD86), except for the modified bovine pericardium (dBP) where a significant decrease in TNFα gene expression is observed. When implanted in the rat subcutaneous model, modified dECMs degraded relatively slowly and did not cause significant fibrotic tissue formation. The numbers of pro-regenerative macrophages increased to several folds in a later time point of evaluation. Modified dECM also supported the bladder wall regeneration with formations of the urothelium, lamina propria, blood vessels, and muscle bundles and reduced the occurrence of calculi formation by 50% in a rat bladder augmentation model. We anticipate that the enhanced stretchability, compliance, and physiological stability of dECMs indicate their suitability for urologic tissue regeneration.
Compared with wild-type mice, lipocalin-2-/-mice have increased interleukin 22 expression, increased adaptation, and less dysbiosis after 75% small-bowel resection. Moreover, the proinflammatory and anti-adaptive effects of lipocalin-2 can be transferred to germ-free mice via a fecal transplant. BACKGROUND & AIMS:In short-bowel syndrome (SBS), inadequate intestinal adaptation is responsible for the majority of complications, including sepsis, liver failure, and death. In this study, we sought to further delineate the adaptive response to identify potential therapeutic targets. METHODS:We performed a 75% small-bowel resection (SBR) or sham operation on C57Bl/6J wild-type (WT), lipocalin-2 (LCN2) -/-, and interleukin 22 (IL22) -/mice. Exogenous IL22 was administered to SBR WT mice. Cecal fecal matter from SBR WT and SBR LCN2 -/mice were transplanted into germ-free mice. Intestinal permeability, inflammation, proliferation, and the microbiome were evaluated 1 week after surgery. CD4 þ IL22 þ laminal propria lymphocytes were sorted by flow cytometry. Naïve T cells were polarized to T-helper cells with or without LCN2.RESULTS: A 75% SBR in a mouse re-creates the increased intestinal permeability, enterocyte proliferation, and intestinal dysbiosis seen in SBS. LCN2 expression increases after 75% SBR, and this increase can be abrogated with broad-spectrum antibiotic treatment. LCN2 -/mice have less intestinal inflammation, increased IL22 expression, and greater adaptation as evidenced by less intestinal permeability, increased carbohydrate enzyme expression, less weight loss, and less dysbiosis after 75% SBR than WT mice. The proinflammatory and anti-adaptive effects of LCN2 can be transferred to germ-free mice via a fecal transplant. Administration of exogenous IL22 improves adaptation and restores the normal microbiome after 75% SBR in WT mice.CONCLUSIONS: LCN2 promotes inflammation and slows intestinal adaptation through changes in the microbiome and IL22 inhibition in a mouse SBS model. Strategies to reduce LCN2 may offer novel therapeutic approaches to enhance adaptation in SBS.
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