A central role for vimentin in regulating repair function during healing of the lens epithelium

RGD-Modified Nanofibers Enhance Outcomes in Rats after Sciatic Nerve Injury

Nerve injuries requiring surgery are a significant problem without good clinical alternatives to the autograft. Tissue engineering strategies are critically needed to provide an alternative. In this study, we utilized aligned nanofibers that were click-modified with the bioactive peptide RGD for rat sciatic nerve repair. Empty conduits or conduits filled with either non-functionalized aligned nanofibers or RGD-functionalized aligned nanofibers were used to repair a 13 mm gap in the rat sciatic nerve of animals for six weeks. The aligned nanofibers encouraged cell infiltration and nerve repair as shown by histological analysis. RGD-functionalized nanofibers reduced muscle atrophy. During the six weeks of recovery, the animals were subjected to motor and sensory tests. Sensory recovery was improved in the RGD-functionalized nanofiber group by week 4, while other groups needed six weeks to show improvement after injury. Thus, the use of functionalized nanofibers provides cues that aid in in vivo nerve repair and should be considered as a future repair strategy.

The Cytoskeleton-A Complex Interacting Meshwork

The cytoskeleton of animal cells is one of the most complicated and functionally versatile structures, involved in processes such as endocytosis, cell division, intra-cellular transport, motility, force transmission, reaction to external forces, adhesion and preservation, and adaptation of cell shape. These functions are mediated by three classical cytoskeletal filament types, as follows: Actin, microtubules, and intermediate filaments. The named filaments form a network that is highly structured and dynamic, responding to external and internal cues with a quick reorganization that is orchestrated on the time scale of minutes and has to be tightly regulated. Especially in brain tumors, the cytoskeleton plays an important role in spreading and migration of tumor cells. As the cytoskeletal organization and regulation is complex and many-faceted, this review aims to summarize the findings about cytoskeletal filament types, including substructures formed by them, such as lamellipodia, stress fibers, and interactions between intermediate filaments, microtubules and actin. Additionally, crucial regulatory aspects of the cytoskeletal filaments and the formed substructures are discussed and integrated into the concepts of cell motility. Even though little is known about the impact of cytoskeletal alterations on the progress of glioma, a final point discussed will be the impact of established cytoskeletal alterations in the cellular behavior and invasion of glioma.

Proteomic Analysis Implicates Vimentin in Glioblastoma Cell Migration

We previously showed lithium chloride (LiCl) and other inhibitors of glycogen synthase kinase-3 (GSK-3) including 6-bromo-indirubin-3-oxime (BIO), can block glioblastoma (GBM) cell migration. To investigate the mechanisms involved we used two-dimensional difference in-gel electrophoresis (2D-DIGE) and mass spectrometry to identify proteins altered after treatment of U251 GBM cells with 20 mM LiCl. Downregulation of the intermediate filament protein vimentin was the most significant change identified. Analysis of patient tumor samples revealed that vimentin is expressed abundantly in GBM, and is prognostic especially in lower grade tumors. Additionally, siRNA-mediated vimentin knockdown impaired GBM migration. Western blotting showed that treatment with LiCl or small molecule GSK-3 inhibitors led to the rapid downregulation of detergent soluble vimentin levels across a panel of GBM-derived cells. Fluorescence reactivation after photobleaching (FRAP) microscopy studies showed a significant reduction in the ability of the vimentin cytoskeleton to recover from photo-bleaching in the presence of LiCl or BIO. Biochemical studies revealed that GSK-3 and vimentin directly interact, and analysis of vimentin revealed a GSK-3 consensus phosphorylation site. We conclude that anti-migratory compounds with the ability to inhibit GSK-3 have effects on vimentin cytoskeletal dynamics, which may play a role in their anti-invasive activity.

Effect of Weightlessness on the 3D Structure Formation and Physiologic Function of Human Cancer Cells

With the rapid development of modern medical technology and the deterioration of living environments, cancer, the most important disease that threatens human health, has attracted increasing concerns. Although remarkable achievements have been made in tumor research during the past several decades, a series of problems such as tumor metastasis and drug resistance still need to be solved. Recently, relevant physiological changes during space exploration have attracted much attention. Thus, space exploration might provide some inspiration for cancer research. Using on ground different methods in order to simulate microgravity, structure and function of cancer cells undergo many unique changes, such as cell aggregation to form 3D spheroids, cell-cycle inhibition, and changes in migration ability and apoptosis. Although numerous better experiments have been conducted on this subject, the results are not consistent. The reason might be that different methods for simulation have been used, including clinostats, random positioning machine (RPM) and rotating wall vessel (RWV) and so on. Therefore, we review the relevant research and try to explain novel mechanisms underlying tumor cell changes under weightlessness.

Fibrosis: Shared Lessons From the Lens and Cornea

Regenerative repair in response to wounding involves cell proliferation and migration. This is followed by the reestablishment of cell structure and organization and a dynamic process of remodeling and restoration of the injured cells' extracellular matrix microenvironment and the integration of the newly synthesized matrix into the surrounding tissue. Fibrosis in the lungs, liver, and heart can lead to loss of life and in the eye to loss of vision. Learning to control fibrosis and restore normal tissue function after injury repair remains a goal of research in this area. Here we use knowledge gained using the lens and the cornea to provide insight into how fibrosis develops and clues to how it can be controlled. The lens and cornea are less complex than other tissues that develop life‐threatening fibrosis, but they are well characterized and research using them as model systems to study fibrosis is leading toward an improved understanding of fibrosis. Here we summarize the current state of the literature and how it is leading to promising new treatments. Anat Rec, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Vimentin Diversity in Health and Disease

Vimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn's disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspectives.

Cytoplasmic Intermediate Filaments in Cell Biology

Intermediate filaments (IFs) are one of the three major elements of the cytoskeleton. Their stability, intrinsic mechanical properties, and cell type-specific expression patterns distinguish them from actin and microtubules. By providing mechanical support, IFs protect cells from external forces and participate in cell adhesion and tissue integrity. IFs form an extensive and elaborate network that connects the cell cortex to intracellular organelles. They act as a molecular scaffold that controls intracellular organization. However, IFs have been revealed as much more than just rigid structures. Their dynamics is regulated by multiple signaling cascades and appears to contribute to signaling events in response to cell stress and to dynamic cellular functions such as mitosis, apoptosis, and migration.

Epithelial Keratins Modulate cMet Expression and Signaling and Promote InlB-Mediated Listeria monocytogenes Infection of HeLa Cells

The host cytoskeleton is a major target for bacterial pathogens during infection. In particular, pathogens usurp the actin cytoskeleton function to strongly adhere to the host cell surface, to induce plasma membrane remodeling allowing invasion and to spread from cell to cell and disseminate to the whole organism. Keratins are cytoskeletal proteins that are the major components of intermediate filaments in epithelial cells however, their role in bacterial infection has been disregarded. Here we investigate the role of the major epithelial keratins, keratins 8 and 18 (K8 and K18), in the cellular infection by Listeria monocytogenes. We found that K8 and K18 are required for successful InlB/cMet-dependent L. monocytogenes infection, but are dispensable for InlA/E-cadherin-mediated invasion. Both K8 and K18 accumulate at InlB-mediated internalization sites following actin recruitment and modulate actin dynamics at those sites. We also reveal the key role of K8 and K18 in HGF-induced signaling which occurs downstream the activation of cMet. Strikingly, we show here that K18, and at a less extent K8, controls the expression of cMet and other surface receptors such TfR and integrin β1, by promoting the stability of their corresponding transcripts. Together, our results reveal novel functions for major epithelial keratins in the modulation of actin dynamics at the bacterial entry sites and in the control of surface receptors mRNA stability and expression.

In wound repair vimentin mediates the transition of mesenchymal leader cells to a myofibroblast phenotype

Following injury, mesenchymal repair cells are activated to function as leader cells that modulate wound healing. These cells have the potential to differentiate to myofibroblasts, resulting in fibrosis and scarring. The signals underlying these differing pathways are complex and incompletely understood. The ex vivo mock cataract surgery cultures are an attractive model with which to address this question. With this model we study, concurrently, the mechanisms that control mesenchymal leader cell function in injury repair within their native microenvironment and the signals that induce this same cell population to acquire a myofibroblast phenotype when these cells encounter the environment of the adjacent tissue culture platform. Here we show that on injury, the cytoskeletal protein vimentin is released into the extracellular space, binds to the cell surface of the mesenchymal leader cells located at the wound edge in the native matrix environment, and supports wound closure. In profibrotic environments, the extracellular vimentin pool also links specifically to the mesenchymal leader cells and has an essential role in signaling their fate change to a myofibroblast. These findings suggest a novel role for extracellular, cell-surface–associated vimentin in mediating repair-cell function in wound repair and in transitioning these cells to a myofibroblast phenotype.

Site-specific glycosylation regulates the form and function of the intermediate filament cytoskeleton

Intermediate filaments (IF) are a major component of the metazoan cytoskeleton and are essential for normal cell morphology, motility, and signal transduction. Dysregulation of IFs causes a wide range of human diseases, including skin disorders, cardiomyopathies, lipodystrophy, and neuropathy. Despite this pathophysiological significance, how cells regulate IF structure, dynamics, and function remains poorly understood. Here, we show that site-specific modification of the prototypical IF protein vimentin with O-linked β-N-acetylglucosamine (O-GlcNAc) mediates its homotypic protein-protein interactions and is required in human cells for IF morphology and cell migration. In addition, we show that the intracellular pathogen Chlamydia trachomatis, which remodels the host IF cytoskeleton during infection, requires specific vimentin glycosylation sites and O-GlcNAc transferase activity to maintain its replicative niche. Our results provide new insight into the biochemical and cell biological functions of vimentin O-GlcNAcylation, and may have broad implications for our understanding of the regulation of IF proteins in general.

Like the body's skeleton, the cytoskeleton gives shape and structure to the inside of a cell. Yet, unlike a skeleton, the cytoskeleton is ever changing. The cytoskeleton consists of many fibers each made from chains of protein molecules. One of these proteins is called vimentin and it forms intermediate filaments in the cytoskeleton. Many different types of cells contain vimentin and a lot of it is found in cancer cells that have spread beyond their original location to other sites in the body.

Cells use chemical modifications to regulate cytoskeleton proteins. For example, through a process called glycosylation, cells can reversibly attach a sugar modification called O-GlcNAc to vimentin. O-GlcNAc can be attached to several different parts of vimentin and each location may have a different effect. It is not currently clear how cells control their vimentin filaments or what role O-GlcNAc plays in this process.

Using genetic engineering, Tarbet et al. produced human cells in the laboratory with modified vimentin proteins. These altered proteins lacked some of the sites for O-GlcNAc attachment. The goal was to see whether the loss of O-GlcNAc at a specific location would affect fiber formation and cell behavior. The results showed one site where vimentin needs O-GlcNAc to form fibers. Without O-GlcNAc at this site, cells could not migrate towards chemical signals. In addition, in normal human cells, Chlamydia bacteria hijack vimentin and rearrange the filaments to form a cage around themselves for protection. However, the cells lacking O-GlcNAc on vimentin were resistant to infection by Chlamydia bacteria.

These findings highlight the importance of O-GlcNAc on vimentin in healthy cells and during infection. Vimentin’s contribution to cell migration may also help to explain its role in the spread of cancer. The importance of O-GlcNAc suggests it could be a new target for therapies. Yet, it also highlights the need for caution due to the delicate balance between the activity of vimentin in healthy and diseased cells. In addition, human cells produce about 70 other vimentin-like proteins and further work will examine if they are also affected by O-GlcNAc.

Role of Corneal Stromal Cells on Epithelial Cell Function during Wound Healing

Following injury, corneal stromal keratocytes transform into repair-phenotype of activated stromal fibroblasts (SFs) and participate in wound repair. Simultaneously, ongoing bi-directional communications between corneal stromal-epithelial cells also play a vital role in mediating the process of wound healing. Factors produced by stromal cells are known to induce proliferation, differentiation, and motility of corneal epithelial cells, which are also subsequently the main processes that occur during wound healing. In this context, the present study aims to investigate the effect of SFs conditioned medium (SFCM) on corneal epithelial cell function along with substance P (SP). Antibody microarrays were employed to profile differentially expressed cell surface markers and cytokines in the presence of SFCM and SP. Antibody microarray data revealed enhanced expression of the ITGB1 in corneal epithelial cells following stimulation with SP whereas SFCM induced abundant expression of IL-8, ITGB1, PD1L1, PECA1, IL-15, BDNF, ICAM1, CD8A, CD44 and NTF4. All these proteins have either direct or indirect roles in epithelial cell growth, movement and adhesion related signaling cascades during tissue regeneration. We also observed activation of MAPK signaling pathway along with increased expression of focal adhesion kinase (FAK), paxillin, vimentin, β-catenin and vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Additionally, epithelial-to-mesenchymal transition (EMT) regulating transcription factors Slug and ZEB1 expression were enhanced in the presence of SFCM. SP enriched the expression of integrin subunits α4, α5, αV, β1 and β3 whereas SFCM increased α4, α5, αV, β1 and β5 integrin subunits. We also observed increased expression of Serpin E1 following SP and SFCM treatment. Wound healing scratch assay revealed enhanced migration of epithelial cells following the addition of SFCM. Taken together, we conclude that SFCM-mediated sustained activation of ZEB1, Slug in combination with upregulated migration-associated integrins and ERK (Extracellular signal-regulated kinase)-FAK-paxillin axis, may lead to induce type 2 EMT-like changes during corneal epithelial wound healing.

Damage-induced reactive oxygen species regulate vimentin and dynamic collagen-based projections to mediate wound repair

Tissue injury leads to early wound-associated reactive oxygen species (ROS) production that mediate tissue regeneration. To identify mechanisms that function downstream of redox signals that modulate regeneration, a vimentin reporter of mesenchymal cells was generated by driving GFP from the vimentin promoter in zebrafish. Early redox signaling mediated vimentin reporter activity at the wound margin. Moreover, both ROS and vimentin were necessary for collagen production and reorganization into projections at the leading edge of the wound. Second harmonic generation time-lapse imaging revealed that the collagen projections were associated with dynamic epithelial extensions at the wound edge during wound repair. Perturbing collagen organization by burn wound disrupted epithelial projections and subsequent wound healing. Taken together our findings suggest that ROS and vimentin integrate early wound signals to orchestrate the formation of collagen-based projections that guide regenerative growth during efficient wound repair.

Expression of Vimentin in hair follicle growth cycle of inner Mongolian Cashmere goats

Background

The growth of Inner Mongolian Cashmere goat skin hair follicle exhibits a periodic growth pattern. The hair growth cycle is distinguished as telogen, anagen, and catagen stages. The role of vimentin in the growth process of hair follicles is evident. To elucidate the mechanism underlying the vimentin activity in the growth cycle of hair follicles, transcriptome sequencing and liquid chromatography-tandem mass spectrometry were used to obtain the nucleic acid and amino acid sequences of VIIM gene and vimentin. The amino acid and nucleic acid sequences were analyzed by comparison. Real-time quantitative PCR, Western blot, and immunohistochemistry analyzed the expression level and sites of vimentin in the three growth stages of the Inner Mongolia Cashmere goat skin samples.

Results

VIM gene cDNA, obtained by transcriptome sequencing, was aligned against that of the Capra hircus VIM gene. The amino acid sequence of vimentin revealed a high similarity rate across other species. The expressions of both VIM gene and vimentin were highest during the growth period and lowest in the rest period. Furthermore, vimentin was primarily expressed in the outer root sheath of the hair follicle as assessed by staining.

Conclusions

The sequences of the gene and protein are similar to that of other species and identical to Capra hircus. However, the expression of VIM and vimentin was proportional to that of the growth of hair follicles. And vimentin expressed only in the outer root sheath of hair follicles. Thus, vimentin was speculated to participate in the regulation of the hair follicle growth cycle by affecting the outer root sheath.

Induction of Immune Surveillance of the Dysmorphogenic Lens

The lens has been considered to be an immune privileged site not susceptible to the immune processes normally associated with tissue injury and wound repair. However, as greater insight into the immune surveillance process is gained, we have reevaluated the concept of immune privilege. Our studies using an N-cadherin lens-specific conditional knockout mouse, N-cad^Δlens, show that loss of this cell-cell junctional protein leads to lens degeneration, necrosis and fibrotic change, postnatally. The degeneration of this tissue induces an immune response resulting in immune cells populating the lens that contribute to the development of fibrosis. Additionally, we demonstrate that the lens is connected to the lymphatic system, with LYVE(+) labeling reaching the lens along the suspensory ligaments that connect the lens to the ciliary body, providing a potential mechanism for the immune circulation. Importantly, we observe that degeneration of the lens activates an immune response throughout the eye, including cornea, vitreous humor, and retina, suggesting a coordinated protective response in the visual system to defects of a component tissue. These studies demonstrate that lens degeneration induces an immune response that can contribute to the fibrosis that often accompanies lens dysgenesis, a consideration for understanding organ system response to injury.

Intermediate Filaments at the Junction of Mechanotransduction, Migration, and Development

Mechanically induced signal transduction has an essential role in development. Cells actively transduce and respond to mechanical signals and their internal architecture must manage the associated forces while also being dynamically responsive. With unique assembly-disassembly dynamics and physical properties, cytoplasmic intermediate filaments play an important role in regulating cell shape and mechanical integrity. While this function has been recognized and appreciated for more than 30 years, continually emerging data also demonstrate important roles of intermediate filaments in cell signal transduction. In this review, with a particular focus on keratins and vimentin, the relationship between the physical state of intermediate filaments and their role in mechanotransduction signaling is illustrated through a survey of current literature. Association with adhesion receptors such as cadherins and integrins provides a critical interface through which intermediate filaments are exposed to forces from a cell's environment. As a consequence, these cytoskeletal networks are posttranslationally modified, remodeled and reorganized with direct impacts on local signal transduction events and cell migratory behaviors important to development. We propose that intermediate filaments provide an opportune platform for cells to both cope with mechanical forces and modulate signal transduction.

Intermediate Filaments and the Regulation of Cell Motility during Regeneration and Wound Healing

SUMMARYIntermediate filaments (IFs) comprise a diverse group of flexible cytoskeletal structures, the assembly, dynamics, and functions of which are regulated by posttranslational modifications. Characteristically, the expression of IF proteins is specific for tissues, differentiation stages, cell types, and functional contexts. Recent research has rapidly expanded the knowledge of IF protein functions. From being regarded as primarily structural proteins, it is now well established that IFs act as powerful modulators of cell motility and migration, playing crucial roles in wound healing and tissue regeneration, as well as inflammatory and immune responses. Although many of these IF-associated functions are essential for tissue repair, the involvement of IF proteins has been established in many additional facets of tissue healing and regeneration. Here, we review the recent progress in understanding the multiple functions of cytoplasmic IFs that relate to cell motility in the context of wound healing, taking examples from studies on keratin, vimentin, and nestin. Wound healing and regeneration include orchestration of a broad range of cellular processes, including regulation of cell attachment and migration, proliferation, differentiation, immune responses, angiogenesis, and remodeling of the extracellular matrix. In this respect, IF proteins now emerge as multifactorial and tissue-specific integrators of tissue regeneration, thereby acting as essential guardian biopolymers at the interface between health and disease, the failing of which contributes to a diverse range of pathologies.

Intracellular Motility of Intermediate Filaments

SUMMARYThe establishment and continuous cell type-specific adaptation of cytoplasmic intermediate filament (IF) networks are linked to various types of IF motility. Motor protein-driven active transport, linkage to other cellular structures, diffusion of small soluble subunits, and intrinsic network elasticity all contribute to the motile behavior of IFs. These processes are subject to regulation by multiple signaling pathways. IF motility is thereby connected to and involved in many basic cellular processes guarding the maintenance of cell and tissue integrity. Disturbances of IF motility are linked to diseases that are characterized by cytoplasmic aggregates containing IF proteins together with other cellular components.

Cultivation and characterization of pterygium as an ex vivo study model for disease and therapy

PURPOSE

Development of ex vivo model to study pathogenesis, inflammation and treatment modalities for pterygium.

METHODS

Pterygium obtained from surgery was cultivated (3 months). Gravitational attachment method using viscoelastic facilitated adherence of graft and outgrowing cells. Medium contained serum as the only growth supplement with no use of scaffolds. Surface profiling of the multi-layered cells for hematopoietic- and mesenchymal stem cell markers was performed. Examination of cells by immunohistochemistry using pluripotency, oxidative stress, stemness, migration and proliferation, epithelial and secretory markers was performed. The effect of anti-proliferative agent Mitomycin C upon secretion of pro-inflammatory cytokines IL-6 and IL-8 was assessed.

RESULTS

Cells showed high expression of migration- (CXCR4), secretory- (MUC1, MUC4) and oxidative damage- (8-OHdG) markers, and low expression of hypoxia- (HIF-1α) and proliferation- (Ki-67) markers. Moderate and low expression of the pluripotency markers (Vimentin and ΔNp63) was present, respectively, while the putative markers of stemness (Sox2, Oct4, ABCG-2) and epithelial cell markers- (CK19, CK8-18) were weak. The surface marker profile of the outgrowing cells revealed high expression of the hematopoietic marker CD47, mesenchymal markers CD90 and CD73, minor or less positivity for the hematopoietic marker CD34, mesenchymal marker CD105, progenitor marker CD117 and attachment protein markers while low levels of IL-6 and IL-8 secretion ex vivo, were inhibited upon Mitomycin C treatment.

CONCLUSION

Ex vivo tissue engineered pterygium consists of a mixture of cells of different lineage origin, suitable for use as a disease model for studying pathogenesis ex vivo, while opening possibilities for new treatment and prevention modalities.

Crosstalk of cell polarity signaling pathways

Cell polarity, the asymmetric organization of cellular components along one or multiple axes, is present in most cells. From budding yeast cell polarization induced by pheromone signaling, oocyte polarization at fertilization to polarized epithelia and neuronal cells in multicellular organisms, similar mechanisms are used to determine cell polarity. Crucial role in this process is played by signaling lipid molecules, small Rho family GTPases and Par proteins. All these signaling circuits finally govern the cytoskeleton, which is responsible for oriented cell migration, cell shape changes, and polarized membrane and organelle trafficking. Thus, typically in the process of cell polarization, most cellular constituents become polarized, including plasma membrane lipid composition, ion concentrations, membrane receptors, and proteins in general, mRNA, vesicle trafficking, or intracellular organelles. This review gives a brief overview how these systems talk to each other both during initial symmetry breaking and within the signaling feedback loop mechanisms used to preserve the polarized state.

Epithelial-mesenchymal transition, and collective and individual cell migration regulate epithelial changes in the amikacin-damaged organ of Corti

Characterizing the microenvironment of a damaged organ of Corti and identifying the basic mechanisms involved in subsequent epithelial reorganization are critical for improving the outcome of clinical therapies. In this context, we studied the expression of a variety of cell markers related to cell shape, cell adhesion and cell plasticity in the rat organ of Corti poisoned with amikacin. Our results indicate that, after severe outer hair cell losses, the cytoarchitectural reorganization of the organ of Corti implicates epithelial-mesenchymal transition mechanisms and involves both collective and individual cell migratory processes. The results also suggest that both root cells and infiltrated fibroblasts participate in the homeostasis of the damaged epithelium, and that the flat epithelium that may emerge offers biological opportunities for late regenerative therapies.

Evaluation of dynamic changes in interstitial fluid proteome following microdialysis probe insertion trauma in trapezius muscle of healthy women

Microdialysis (MD) has been shown to be a promising technique for sampling of biomarkers. Implantation of MD probe causes an acute tissue trauma and provokes innate response cascades. In order to normalize tissue a two hours equilibration period for analysis of small molecules has been reported previously. However, how the proteome profile changes due to this acute trauma has yet to be fully understood. To characterize the early proteome events induced by this trauma we compared proteome in muscle dialysate collected during the equilibration period with two hours later in "post-trauma". Samples were collected from healthy females using a 100 kDa MW cut off membrane and analyzed by high sensitive liquid chromatography tandem mass spectrometry. Proteins involved in stress response, immune system processes, inflammatory responses and nociception from extracellular and intracellular fluid spaces were identified. Sixteen proteins were found to be differentially abundant in samples collected during first two hours in comparison to "post-trauma". Our data suggests that microdialysis in combination with mass spectrometry may provide potentially new insights into the interstitial proteome of trapezius muscle, yet should be further adjusted for biomarker discovery and diagnostics. Moreover, MD proteome alterations in response to catheter injury may reflect individual innate reactivity.

Paxillin: a crossroad in pathological cell migration

Paxilllin is a multifunctional and multidomain focal adhesion adapter protein which serves an important scaffolding role at focal adhesions by recruiting structural and signaling molecules involved in cell movement and migration, when phosphorylated on specific Tyr and Ser residues. Upon integrin engagement with extracellular matrix, paxillin is phosphorylated at Tyr31, Tyr118, Ser188, and Ser190, activating numerous signaling cascades which promote cell migration, indicating that the regulation of adhesion dynamics is under the control of a complex display of signaling mechanisms. Among them, paxillin disassembly from focal adhesions induced by extracellular regulated kinase (ERK)-mediated phosphorylation of serines 106, 231, and 290 as well as the binding of the phosphatase PEST to paxillin have been shown to play a key role in cell migration. Paxillin also coordinates the spatiotemporal activation of signaling molecules, including Cdc42, Rac1, and RhoA GTPases, by recruiting GEFs, GAPs, and GITs to focal adhesions. As a major participant in the regulation of cell movement, paxillin plays distinct roles in specific tissues and developmental stages and is involved in immune response, epithelial morphogenesis, and embryonic development. Importantly, paxillin is also an essential player in pathological conditions including oxidative stress, inflammation, endothelial cell barrier dysfunction, and cancer development and metastasis.

Targeting Microtubules for Wound Repair

Significance: Fast and seamless healing is essential for both deep and chronic wounds to restore the skin and protect the body from harmful pathogens. Thus, finding new targets that can both expedite and enhance the repair process without altering the upstream signaling milieu and causing serious side effects can improve the way we treat wounds. Since cell migration is key during the different stages of wound healing, it presents an ideal process and intracellular structural machineries to target. Recent Advances and Critical Issues: The microtubule (MT) cytoskeleton is rising as an important structural and functional regulator of wound healing. MTs have been reported to play different roles in the migration of the various cell types involved in wound healing. Specific microtubule regulatory proteins (MRPs) can be targeted to alter a section or subtype of the MT cytoskeleton and boost or hinder cell motility. However, inhibiting intracellular components can be challenging in vivo, especially using unstable molecules, such as small interfering RNA. Nanoparticles can be used to protect these unstable molecules and topically deliver them to the wound. Utilizing this approach, we recently showed that fidgetin-like 2, an uncharacterized MRP, can be targeted to enhance cell migration and wound healing. Future Directions: To harness the full potential of the current MRP therapeutic targets, studies should test them with different delivery platforms, dosages, and skin models. Screening for new MT effectors that boost cell migration in vivo would also help find new targets for skin repair.

Pharmacologic inhibition of reactive gliosis blocks TNF-α-mediated neuronal apoptosis

Reactive gliosis is an early pathological feature common to most neurodegenerative diseases, yet its regulation and impact remain poorly understood. Normally astrocytes maintain a critical homeostatic balance. After stress or injury they undergo rapid parainflammatory activation, characterized by hypertrophy, and increased polymerization of type III intermediate filaments (IFs), particularly glial fibrillary acidic protein and vimentin. However, the consequences of IF dynamics in the adult CNS remains unclear, and no pharmacologic tools have been available to target this mechanism in vivo. The mammalian retina is an accessible model to study the regulation of astrocyte stress responses, and their influence on retinal neuronal homeostasis. In particular, our work and others have implicated p38 mitogen-activated protein kinase (MAPK) signaling as a key regulator of glutamate recycling, antioxidant activity and cytokine secretion by astrocytes and related Müller glia, with potent influences on neighboring neurons. Here we report experiments with the small molecule inhibitor, withaferin A (WFA), to specifically block type III IF dynamics in vivo. WFA was administered in a model of metabolic retinal injury induced by kainic acid, and in combination with a recent model of debridement-induced astrocyte reactivity. We show that WFA specifically targets IFs and reduces astrocyte and Müller glial reactivity in vivo. Inhibition of glial IF polymerization blocked p38 MAPK-dependent secretion of TNF-α, resulting in markedly reduced neuronal apoptosis. To our knowledge this is the first study to demonstrate that pharmacologic inhibition of IF dynamics in reactive glia protects neurons in vivo.

Vimentin Intermediate Filaments Template Microtubule Networks to Enhance Persistence in Cell Polarity and Directed Migration

Increased expression of vimentin intermediate filaments (VIFs) enhances directed cell migration, but the mechanism behind VIFs' effect on motility is not understood. VIFs interact with microtubules, whose organization contributes to polarity maintenance in migrating cells. Here, we characterize the dynamic coordination of VIF and microtubule networks in wounded monolayers of retinal pigment epithelial cells. By genome editing, we fluorescently labeled endogenous vimentin and α-tubulin, and we developed computational image analysis to delineate architecture and interactions of the two networks. Our results show that VIFs assemble an ultrastructural copy of the previously polarized microtubule network. Because the VIF network is long-lived compared to the microtubule network, VIFs template future microtubule growth along previous microtubule tracks, thus providing a feedback mechanism that maintains cell polarity. VIF knockdown prevents cells from polarizing and migrating properly during wound healing. We suggest that VIFs' templating function establishes a memory in microtubule organization that enhances persistence in cell polarization in general and migration in particular.

Citrullination of glial intermediate filaments is an early response in retinal injury

PURPOSE

A hallmark of retinal gliosis is the increased detection and modification of the type III intermediate filament (IF) proteins vimentin and glial fibrillary acidic protein (GFAP). Here, we investigated vimentin and GFAP in Müller glia in a mouse model of alkali injury, focusing on the posttranslational modification of citrullination.

METHODS

Mice were injured by corneal exposure to 1.0 N NaOH, and eyes were enucleated at different time points following injury. The levels of soluble and cytoskeletal forms of IF proteins and citrullination were measured using western blot analysis. Citrullinated GFAP was identified by immunoprecipitation followed by two-dimensional (2D) isoelectric focusing-polyacrylamide gel electrophoresis (IEF-PAGE) western blotting using a specific antibody that recognizes citrullinated GFAP. Vimentin, GFAP, and citrullinated proteins were localized in the retina by immunohistochemistry (IHC). Drug treatments were investigated in retinal explant cultures of posterior eyecups obtained from mouse eyes that were injured in vivo.

RESULTS

Detection of GFAP in injured retinas increased over a period of 1 to 7 days, showing increased levels in both soluble and cytoskeletal forms of this IF protein. The global level of citrullinated proteins was also induced over this period, with low-salt buffer extraction showing the most abundant early changes in citrullination. Using IHC, we found that GFAP filaments assembled at Müller glial end feet, growing in size with time through the inner layers of the retina at 1-3 h postinjury. Interestingly, over this early time period, levels of soluble citrullinated proteins also increased within the retina, as detected by western blotting, coincident with the localization of the citrullinated epitopes on growing GFAP filaments and existing vimentin filaments by 3 h after injury. Taking advantage of the in vivo injury model to promote a robust gliotic response, posterior eyecups from 7-day postinjured eyes were treated in explant cultures with the peptidyl arginine deiminase inhibitor Cl-amidine, which was found to reduce global citrullination. Surprisingly, the detection of injury-induced high-molecular-weight GFAP species containing citrullinated epitopes was also reduced by Cl-amidine treatment. Using a low dose of the potent type III IF drug withaferin A (WFA), we showed that Cl-amidine treatment in combination with WFA reduced global protein citrullination further, suggesting that GFAP may be a key component of pathological citrullinated targets.

CONCLUSIONS

Our findings illuminate citrullination as a potential novel target for trauma-induced retinal gliosis. We also propose that strategies for combining drugs targeting type III IFs and citrullination may potentiate tissue repair, which is an idea that needs to be validated in vivo.

Lack of vimentin impairs endothelial differentiation of embryonic stem cells

The cytoskeletal filament vimentin is inherent to the endothelial phenotype and is critical for the proper function of endothelial cells in adult mice. It is unclear, however, if the presence of vimentin is necessary during differentiation to the endothelial phenotype. Here we evaluated gene and protein expression of differentiating wild type embryonic stem cells (WT ESCs) and vimentin knockout embryonic stem cells (VIM −/− ESCs) using embryoid bodies (EBs) formed from both cell types. Over seven days of differentiation VIM −/− EBs had altered morphology compared to WT EBs, with a rippled outer surface and a smaller size due to decreased proliferation. Gene expression of pluripotency markers decreased similarly for EBs of both cell types; however, VIM −/− EBs had impaired differentiation towards the endothelial phenotype. This was quantified with decreased expression of markers along the specification pathway, specifically the early mesodermal marker Brachy-T, the lateral plate mesodermal marker FLK1, and the endothelial-specific markers TIE2, PECAM, and VE-CADHERIN. Taken together, these results indicate that the absence of vimentin impairs spontaneous differentiation of ESCs to the endothelial phenotype in vitro.

Vimentin coordinates fibroblast proliferation and keratinocyte differentiation in wound healing via TGF-β-Slug signaling

Vimentin has been shown to be involved in wound healing, but its functional contribution to this process is poorly understood. Here we describe a previously unrecognized function of vimentin in coordinating fibroblast proliferation and keratinocyte differentiation during wound healing. Loss of vimentin led to a severe deficiency in fibroblast growth, which in turn inhibited the activation of two major initiators of epithelial-mesenchymal transition (EMT), TGF-β1 signaling and the Zinc finger transcriptional repressor protein Slug, in vimentin-deficient (VIM(-/-)) wounds. Correspondingly, VIM(-/-) wounds exhibited loss of EMT-like keratinocyte activation, limited keratinization, and slow reepithelialization. Furthermore, the fibroblast deficiency abolished collagen accumulation in the VIM(-/-) wounds. Vimentin reconstitution in VIM(-/-) fibroblasts restored both their proliferation and TGF-β1 production. Similarly, restoring paracrine TGF-β-Slug-EMT signaling reactivated the transdifferentiation of keratinocytes, reviving their migratory properties, a critical feature for efficient healing. Our results demonstrate that vimentin orchestrates the healing by controlling fibroblast proliferation, TGF-β1-Slug signaling, collagen accumulation, and EMT processing, all of which in turn govern the required keratinocyte activation.

Needle-free jet injection of hyaluronic acid improves skin remodeling in a mouse model

PURPOSE

The purpose of this study was to improve methods of jet injection using a mouse model. We investigated the mechanism of action, efficacy, and safety of the pneumatic device using injection of hyaluronic acid (HA) solution into a mouse model.

METHODS

We evaluated the efficacy and safety of an INNOJECTOR™ pneumatic device that pneumatically accelerates a jet of HA solution under high pressure into the dermis of mouse skin. We examined the treatment effects using skin hybrid model jet dispersion experiments, photographic images, microscopy, and histological analyses.

RESULTS

Use of the INNOJECTOR™ successfully increased dermal thickness and collagen synthesis in our mouse model. Jet dispersion experiments were performed using agarose gels and a polyacrylamide gel model to understand the dependence of jet penetration on jet power. The mechanisms by which pneumatic injection using HA solution exerts its effects may involve increased dermal thickening, triggering of a wound healing process, and activation of vimentin and collagen synthesis.

CONCLUSIONS

Collagen synthesis and increased dermal thickening were successfully achieved in our mouse model using the INNOJECTOR™. Pneumatic injection of HA under high pressure provides a safe and effective method for improving the appearance of mouse skin. Our findings indicate that use of the INNOJECTOR™ may induce efficient collagen remodeling with subsequent marked dermal layer thickening by targeting vimentin.

Mechanics of epithelial tissues during gap closure

The closure of gaps is crucial to maintaining epithelium integrity during developmental and repair processes such as dorsal closure and wound healing. Depending on biochemical as well as physical properties of the microenvironment, gap closure occurs through assembly of multicellular actin-based contractile cables and/or protrusive activity of cells lining the gap. This review discusses the relative contributions of 'purse-string' and cell crawling mechanisms regulated by cell-substrate and cell-cell interactions, cellular mechanics and physical constraints from the environment.

Vimentin in Bacterial Infections

Despite well-studied bacterial strategies to target actin to subvert the host cell cytoskeleton, thus promoting bacterial survival, replication, and dissemination, relatively little is known about the bacterial interaction with other components of the host cell cytoskeleton, including intermediate filaments (IFs). IFs have not only roles in maintaining the structural integrity of the cell, but they are also involved in many cellular processes including cell adhesion, immune signaling, and autophagy, processes that are important in the context of bacterial infections. Here, we summarize the knowledge about the role of IFs in bacterial infections, focusing on the type III IF protein vimentin. Recent studies have revealed the involvement of vimentin in host cell defenses, acting as ligand for several pattern recognition receptors of the innate immune system. Two main aspects of bacteria-vimentin interactions are presented in this review: the role of vimentin in pathogen-binding on the cell surface and subsequent bacterial invasion and the interaction of cytosolic vimentin and intracellular pathogens with regards to innate immune signaling. Mechanistic insight is presented involving distinct bacterial virulence factors that target vimentin to subvert its function in order to change the host cell fate in the course of a bacterial infection.

Intermediate filament dynamics: What we can see now and why it matters

The mechanical properties of vertebrate cells are largely defined by the system of intermediate filaments (IF). As part of a dense network, IF polymers are constantly rearranged and relocalized in the cell to fulfill their duty as cells change shape, migrate, or divide. With the development of new imaging technologies, such as photoconvertible proteins and super-resolution microscopy, a new appreciation for the complexity of IF dynamics has emerged. This review highlights new findings about the transport of IF, the remodeling of filaments by a process of severing and re-annealing, and the subunit exchange that occurs between filament precursors and a soluble pool of IF. We will also discuss the unique dynamic features of the keratin IF network. Finally, we will speculate about how the dynamic properties of IF are related to their functions.

Differential Expression of Proteins Associated with the Hair Follicle Cycle - Proteomics and Bioinformatics Analyses

Hair follicle cycling can be divided into the following three stages: anagen, catagen, and telogen. The molecular signals that orchestrate the follicular transition between phases are still unknown. To better understand the detailed protein networks controlling this process, proteomics and bioinformatics analyses were performed to construct comparative protein profiles of mouse skin at specific time points (0, 8, and 20 days). Ninety-five differentially expressed protein spots were identified by MALDI-TOF/TOF as 44 proteins, which were found to change during hair follicle cycle transition. Proteomics analysis revealed that these changes in protein expression are involved in Ca2+-regulated biological processes, migration, and regulation of signal transduction, among other processes. Subsequently, three proteins were selected to validate the reliability of expression patterns using western blotting. Cluster analysis revealed three expression patterns, and each pattern correlated with specific cell processes that occur during the hair cycle. Furthermore, bioinformatics analysis indicated that the differentially expressed proteins impacted multiple biological networks, after which detailed functional analyses were performed. Taken together, the above data may provide insight into the three stages of mouse hair follicle morphogenesis and provide a solid basis for potential therapeutic molecular targets for this hair disease.

Cells activated for wound repair have the potential to direct collective invasion of an epithelium

Mechanisms regulating how groups of cells are signaled to move collectively from their original site and invade surrounding matrix are poorly understood. Here we develop a clinically relevant ex vivo injury invasion model to determine whether cells involved in directing wound healing have invasive function and whether they can act as leader cells to direct movement of a wounded epithelium through a three-dimensional (3D) extracellular matrix (ECM) environment. Similar to cancer invasion, we found that the injured cells invade into the ECM as cords, involving heterotypical cell-cell interactions. Mesenchymal cells with properties of activated repair cells that typically locate to a wound edge are present in leader positions at the front of ZO-1-rich invading cords of cells, where they extend vimentin intermediate filament-enriched protrusions into the 3D ECM. Injury-induced invasion depends on both vimentin cytoskeletal function and MMP-2/9 matrix remodeling, because inhibiting either of these suppressed invasion. Potential push and pull forces at the tips of the invading cords were revealed by time-lapse imaging, which showed cells actively extending and retracting protrusions into the ECM. This 3D injury invasion model can be used to investigate mechanisms of leader cell-directed invasion and understand how mechanisms of wound healing are hijacked to cause disease.

Cell Migration and Invadopodia Formation Require a Membrane-binding Domain of CARMIL2

CARMILs regulate capping protein (CP), a critical determinant of actin assembly and actin-based cell motility. Vertebrates have three conserved CARMIL genes with distinct functions. In migrating cells, CARMIL2 is important for cell polarity, lamellipodial assembly, ruffling, and macropinocytosis. In cells, CARMIL2 localizes with a distinctive dual pattern to vimentin intermediate filaments and to membranes at leading edges and macropinosomes. The mechanism by which CARMIL2 localizes to membranes has not been defined. Here, we report that CARMIL2 has a conserved membrane-binding domain composed of basic and hydrophobic residues, which is necessary and sufficient for membrane localization, based on expression studies in cells and on direct binding of purified protein to lipids. Most important, we find that the membrane-binding domain is necessary for CARMIL2 to function in cells, based on rescue expression with a set of biochemically defined mutants. CARMIL1 and CARMIL3 contain similar membrane-binding domains, based on sequence analysis and on experiments, but other CPI motif proteins, such as CD2AP, do not. Based on these results, we propose a model in which the membrane-binding domain of CARMIL2 tethers this multidomain protein to the membrane, where it links dynamic vimentin filaments with regulation of actin assembly via CP.

The Use of Withaferin A to Study Intermediate Filaments

Withaferin A (WFA), initially identified as a compound that inhibits experimental angiogenesis, has been shown to bind to soluble vimentin (sVim) and other type III intermediate filament (IF) proteins. We review WFA's dose-related activities (Section 1), examining nanomolar concentrations effects on sVim in cell proliferation and submicromolar effects on lamellipodia and focal adhesion formation. WFA effects on polymeric IFs are especially interesting to the study of cell migration and invasion that depend on IF mechanical contractile properties. WFA interferes with NF-κB signaling, though this anti-inflammatory mechanism may occur via perturbation of sVim-protein complexes, and possibly also via targeting IκB kinase β directly. However, micromolar concentrations that induce vimentin cleavage to promote apoptosis may increasingly show off-target effects via targeting other IFs (neurofilaments and keratin) and non-IFs (tubulin, heat-shock proteins, proteasome). Thus, in Section 2, we describe our studies combining cell cultures with animal models of injury to validate relevant type III IF-targeting mechanisms of WFA. In Section 3, we illuminate from investigating myofibroblast differentiation how sVim phosphorylation may govern cell type-selective sensitivity to WFA, offering impetus for exploring vimentin phosphorylation isoforms as targets and biomarkers of fibrosis. These different WFA targets and activities are listed in a summary table.

CARMIL2 is a novel molecular connection between vimentin and actin essential for cell migration and invadopodia formation

CARMIL2 is a novel and direct molecular connection between vimentin filaments and actin assembly during cell migration and invadopodia formation. Through two distinct domains, CARMIL2 localizes to vimentin filaments and regulates actin assembly. The biochemical activities of both domains are necessary for cell migration and invasion.

Cancer cell migration requires the regulation of actin networks at protrusions associated with invadopodia and other leading edges. Carcinomas become invasive after undergoing an epithelial–mesenchymal transition characterized by the appearance of vimentin filaments. While vimentin expression correlates with cell migration, the molecular connections between vimentin- and actin-based membrane protrusions are not understood. We report here that CARMIL2 (capping protein, Arp2/3, myosin-I linker 2) provides such a molecular link. CARMIL2 localizes to vimentin, regulates actin capping protein (CP), and binds to membranes. CARMIL2 is necessary for invadopodia formation, as well as cell polarity, lamellipodial assembly, membrane ruffling, macropinocytosis, and collective cell migration. Using point mutants and chimeras with defined biochemical and cellular properties, we discovered that localization to vimentin and CP binding are both essential for the function of CARMIL2 in cells. On the basis of these results, we propose a model in which dynamic vimentin filaments target CARMIL2 to critical membrane-associated locations, where CARMIL2 regulates CP, and thus actin assembly, to create cell protrusions.

Rap1 GTPase is required for mouse lens epithelial maintenance and morphogenesis

Rap1, a Ras-like small GTPase, plays a crucial role in cell-matrix adhesive interactions, cell-cell junction formation, cell polarity and migration. The role of Rap1 in vertebrate organ development and tissue architecture, however, remains elusive. We addressed this question in a mouse lens model system using a conditional gene targeting approach. While individual germline deficiency of either Rap1a or Rap1b did not cause overt defects in mouse lens, conditional double deficiency (Rap1 cKO) prior to lens placode formation led to an ocular phenotype including microphthalmia and lens opacification in embryonic mice. The embryonic Rap1 cKO mouse lens exhibited striking defects including loss of E-cadherin- and ZO-1-based cell-cell junctions, disruption of paxillin and β1-integrin-based cell adhesive interactions along with abnormalities in cell shape and apical-basal polarity of epithelium. These epithelial changes were accompanied by increased levels of α-smooth muscle actin, vimentin and N-cadherin, and expression of transcriptional suppressors of E-cadherin (Snai1, Slug and Zeb2), and a mesenchymal metabolic protein (Dihydropyrimidine dehydrogenase). Additionally, while lens differentiation was not overtly affected, increased apoptosis and dysregulated cell cycle progression were noted in epithelium and fibers in Rap1 cKO mice. Collectively these observations uncover a requirement for Rap1 in maintenance of lens epithelial phenotype and morphogenesis.

Vimentin Phosphorylation Underlies Myofibroblast Sensitivity to Withaferin A In Vitro and during Corneal Fibrosis

Vimentin is a newly recognized target for corneal fibrosis. Using primary rabbit corneal fibroblasts and myofibroblasts we show that myofibroblasts, unlike fibroblasts, display impaired cell spreading and cell polarization, which is associated with increased levels of soluble serine-38 phosphorylated vimentin (pSer38Vim). This pSer38Vim isoform is inefficiently incorporated into growing vimentin intermediate filaments (IFs) of myofibroblasts during cell spreading, and as a result, myofibroblasts maintain higher soluble pSer38Vim levels compared to fibroblasts. Moreover, the soluble vimentin-targeting small molecule and fibrotic inhibitor withaferin A (WFA) causes a potent blockade of cell spreading selectively in myofibroblasts by targeting soluble pSer38Vim for hyperphosphorylation. WFA treatment does not induce vimentin hyperphosphorylation in fibroblasts. This hyperphosphorylated pSer38Vim species in WFA-treated myofibroblasts becomes complexed with adaptor protein filamin A (FlnA), and these complexes appear as short squiggles when displaced from focal adhesions. The extracellular-signal regulated kinase (ERK) is also phosphorylated (pERK) in response to WFA, but surprisingly, pERK does not enter the nucleus but remains bound to pSer38Vim in cytoplasmic complexes. Using a model of corneal alkali injury, we show that fibrotic corneas of wild type mice possess high levels of pERK, whereas injured corneas of vimentin-deficient (Vim KO) mice that heal with reduced fibrosis have highly reduced pERK expression. Finally, WFA treatment causes a decrease in pERK and pSer38Vim expression in healing corneas of wild type mice. Taken together, these findings identify a hereto-unappreciated role for pSer38Vim as an important determinant of myofibroblast sensitivity to WFA.

Establishment of a Clinically Relevant Ex Vivo Mock Cataract Surgery Model for Investigating Epithelial Wound Repair in a Native Microenvironment

The major impediment to understanding how an epithelial tissue executes wound repair is the limited availability of models in which it is possible to follow and manipulate the wound response ex vivo in an environment that closely mimics that of epithelial tissue injury in vivo. This issue was addressed by creating a clinically relevant epithelial ex vivo injury-repair model based on cataract surgery. In this culture model, the response of the lens epithelium to wounding can be followed live in the cells' native microenvironment, and the molecular mediators of wound repair easily manipulated during the repair process. To prepare the cultures, lenses are removed from the eye and a small incision is made in the anterior of the lens from which the inner mass of lens fiber cells is removed. This procedure creates a circular wound on the posterior lens capsule, the thick basement membrane that surrounds the lens. This wound area where the fiber cells were attached is located just adjacent to a continuous monolayer of lens epithelial cells that remains linked to the lens capsule during the surgical procedure. The wounded epithelium, the cell type from which fiber cells are derived during development, responds to the injury of fiber cell removal by moving collectively across the wound area, led by a population of vimentin-rich repair cells whose mesenchymal progenitors are endogenous to the lens. These properties are typical of a normal epithelial wound healing response. In this model, as in vivo, wound repair is dependent on signals supplied by the endogenous environment that is uniquely maintained in this ex vivo culture system, providing an ideal opportunity for discovery of the mechanisms that regulate repair of an epithelium following wounding.

Lens Biology and Biochemistry

The primary function of the lens resides in its transparency and ability to focus light on the retina. These require both that the lens cells contain high concentrations of densely packed lens crystallins to maintain a refractive index constant over distances approximating the wavelength of the light to be transmitted, and a specific arrangement of anterior epithelial cells and arcuate fiber cells lacking organelles in the nucleus to avoid blocking transmission of light. Because cells in the lens nucleus have shed their organelles, lens crystallins have to last for the lifetime of the organism, and are specifically adapted to this function. The lens crystallins comprise two major families: the βγ-crystallins are among the most stable proteins known and the α-crystallins, which have a chaperone-like function. Other proteins and metabolic activities of the lens are primarily organized to protect the crystallins from damage over time and to maintain homeostasis of the lens cells. Membrane protein channels maintain osmotic and ionic balance across the lens, while the lens cytoskeleton provides for the specific shape of the lens cells, especially the fiber cells of the nucleus. Perhaps most importantly, a large part of the metabolic activity in the lens is directed toward maintaining a reduced state, which shelters the lens crystallins and other cellular components from damage from UV light and oxidative stress. Finally, the energy requirements of the lens are met largely by glycolysis and the pentose phosphate pathway, perhaps in response to the avascular nature of the lens. Together, all these systems cooperate to maintain lens transparency over time.

Intermediate Filaments Play a Pivotal Role in Regulating Cell Architecture and Function

Intermediate filaments (IFs) are composed of one or more members of a large family of cytoskeletal proteins, whose expression is cell- and tissue type-specific. Their importance in regulating the physiological properties of cells is becoming widely recognized in functions ranging from cell motility to signal transduction. IF proteins assemble into nanoscale biopolymers with unique strain-hardening properties that are related to their roles in regulating the mechanical integrity of cells. Furthermore, mutations in the genes encoding IF proteins cause a wide range of human diseases. Due to the number of different types of IF proteins, we have limited this short review to cover structure and function topics mainly related to the simpler homopolymeric IF networks composed of vimentin, and specifically for diseases, the related muscle-specific desmin IF networks.

Intermediate filaments in cell migration and invasion: the unusual suspects

Cell migration is a multistep process which relies on the coordination of cytoskeletal structures in space and time. While the roles of actin and microtubules have been investigated in great details, the lack of inhibitors and visualizing tools and the large number of proteins forming intermediate filaments (IFs) have delayed the characterization of IF functions during migration. However, a large body of evidence has progressively pointed to changes in IF composition as an important parameter in the regulation of cell migratory properties both during development and tumor invasion. More recent in-depth analyses show that IFs are dynamically reorganized to participate, together with microfilaments and microtubules, to the key steps leading to cell migration.

Hexavalent chromium induces expression of mesenchymal and stem cell markers in renal epithelial cells

Cr(VI) causes severe kidney damage. The patient's renal function could gradually recover by spontaneous kidney regeneration. The molecular effect of Cr(VI) on recovery of kidney cells, however, has not been clearly elucidated. Here we show that Cr(VI) induces expression of mesenchymal and stem cell markers, cell markers, such as paxillin, vimentin, α-SMA, nanog, and CD133 of HK-2 cells. Moreover, Cr(VI) activates epithelial-to-mesenchymal transition (EMT). By revealing that levels of dihydrodiol dehydrogenase were promptly reduced following Cr(VI) challenge, our data suggested that DDH could be involved in a Cr(VI)-related oxidation to generate massive reactive oxygen species and H2 O2 , and to create intracellular hypoxia, which then increased levels of SUMO-1 activating enzyme subunit 2, and sumoylation of eukaryotic elongation factor-2, to mediate the subsequent molecular and cellular responses, e.g., expression of mesenchymal and stem cell markers. Pretreatment with vitamin C reduced Cr(VI)-related cellular effects. However, no evident effect was observed when vitamin C was added following Cr(VI) challenge.

Wound healing potential of scaffolds prepared from porcine jejunum and urinary bladder by a non-detergent/enzymatic method

Scaffolds prepared using extracellular matrices of mammalian organs/tissues, when used as grafts, have wound healing potential. This paper evaluated the physical properties and in vivo wound healing potential of jejunum-derived scaffold (JDS) and urinary bladder-derived scaffold (UDS) of porcine origin prepared by a non-detergent/enzymatic method. The former had higher flexural rigidity and suture retention strength compared to the latter, but both of them had the essential flexural rigidity and suture retention strength required for skin grafts. Full thickness skin-wounds on rabbit dorsum were treated with these scaffolds and the wound healing ability was compared by studying histomorphology parameters such as re-epithelialisation, collagen deposition, angiogenesis, proliferation of cells, mesenchymal cell infiltration and myofibroblast response. The extent of these reactions was assessed using histomorphometry. The results indicated that both grafts initiated healing faster than those wounds without any graft, as evidenced by the extent of cell proliferation and mesenchymal cell infiltration. The myofibroblast response persisted longer in the non-graft assisted wound healing reaction compared to the healing in the graft assisted wounds. Moreover, the JDS induced higher cell proliferation and greater angiogenesis than UDS probably indicating better healing by the former. The results suggested that JDS and UDS prepared by non-detergent/enzymatic method have potential clinical applications.

Intermediate filaments and the regulation of focal adhesion

Focal adhesions are localized actin filament-anchoring signalling centres at the cell-extracellular matrix interface. The currently emerging view is that they fulfil an all-embracing coordinating function for the entire cytoskeleton. This review highlights the tight relationship between focal adhesions and the intermediate filament cytoskeleton. We summarize the accumulating evidence for direct binding of intermediate filaments to focal adhesion components and their mutual cross-talk through signalling molecules. Examples are presented to emphasize the high degree of complexity of these interactions equipping cells with a precisely controlled machinery for context-dependent adjustment of their biomechanical properties.