Intermediate filament protein partnership in astrocytes

The Cancer Chimera: Impact of Vimentin and Cytokeratin Co-Expression in Hybrid Epithelial/Mesenchymal Cancer Cells on Tumor Plasticity and Metastasis

The epithelial-mesenchymal transition (EMT) program is critical to metastatic cancer progression. EMT results in the expression of mesenchymal proteins and enhances migratory and invasive capabilities. In a small percentage of cells, EMT results in the expression of stemness-associated genes that provide a metastatic advantage. Although EMT had been viewed as a binary event, it has recently become clear that the program leads to a spectrum of phenotypes, including hybrid epithelial/mesenchymal (E/M) cells that have significantly greater metastatic capability than cells on the epithelial or mesenchymal ends of the spectrum. As hybrid E/M cells are rarely observed in physiological, non-diseased states in the adult human body, these cells are potential biomarkers and drug targets. Hybrid E/M cells are distinguished by the co-expression of epithelial and mesenchymal proteins, such as the intermediate filament proteins cytokeratin (CK; epithelial) and vimentin (VIM; mesenchymal). Although these intermediate filaments have been extensively used for pathological characterization and detection of aggressive carcinomas, little is known regarding the interactions between CK and VIM when co-expressed in hybrid E/M cells. This review describes the characteristics of hybrid E/M cells with a focus on the unique co-expression of VIM and CK. We will discuss the structures and functions of these two intermediate filament proteins and how they may interact when co-expressed in hybrid E/M cells. Additionally, we review what is known about cell-surface expression of these intermediate filament proteins and discuss their potential as predictive biomarkers and therapeutic targets.

Glial fibrillary acidic protein in Alzheimer's disease: a narrative review

Astrocytes are fundamental in neural functioning and homeostasis in the central nervous system. These cells respond to injuries and pathological conditions through astrogliosis, a reactive process associated with neurodegenerative diseases such as Alzheimer's disease. This process is thought to begin in the early stages of these conditions. Glial fibrillary acidic protein (GFAP), a type III intermediate filament protein predominantly expressed in astrocytes, has emerged as a key biomarker for monitoring this response. During astrogliosis, GFAP is released into biofluids, making it a candidate for non-invasive diagnosis and tracking of neurodegenerative diseases. Growing evidence positions GFAP as a biomarker for Alzheimer's disease with specificity and disease-correlation characteristics comparable to established clinical markers, such as Aβ peptides and phosphorylated tau protein. To improve diagnostic accuracy, particularly in the presence of confounders and comorbidities, incorporating a panel of biomarkers may be advantageous. This review will explore the potential of GFAP within such a panel, examining its role in early diagnosis, disease progression monitoring and its integration into clinical practice for Alzheimer's disease management.

Human neural stem cells derived from fetal human brain communicate with each other and rescue ischemic neuronal cells through tunneling nanotubes

Pre-clinical trials have demonstrated the neuroprotective effects of transplanted human neural stem cells (hNSCs) during the post-ischemic phase. However, the exact neuroprotective mechanism remains unclear. Tunneling nanotubes (TNTs) are long plasma membrane bridges that physically connect distant cells, enabling the intercellular transfer of mitochondria and contributing to post-ischemic repair processes. Whether hNSCs communicate through TNTs and their role in post-ischemic neuroprotection remains unknown. In this study, non-immortalized hNSC lines derived from fetal human brain tissues were examined to explore these possibilities and assess the post-ischemic neuroprotection potential of these hNSCs. Using Tau-STED super-resolution confocal microscopy, live cell time-lapse fluorescence microscopy, electron microscopy, and direct or non-contact homotypic co-cultures, we demonstrated that hNSCs generate nestin-positive TNTs in both 3D neurospheres and 2D cultures, through which they transfer functional mitochondria. Co-culturing hNSCs with differentiated SH-SY5Y (dSH-SY5Y) revealed heterotypic TNTs allowing mitochondrial transfer from hNSCs to dSH-SY5Y. To investigate the role of heterotypic TNTs in post-ischemic neuroprotection, dSH-SY5Y were subjected to oxygen-glucose deprivation (OGD) followed by reoxygenation (OGD/R) with or without hNSCs in direct or non-contact co-cultures. Compared to normoxia, OGD/R dSH-SY5Y became apoptotic with impaired electrical activity. When OGD/R dSH-SY5Y were co-cultured in direct contact with hNSCs, heterotypic TNTs enabled the transfer of functional mitochondria from hNSCs to OGD/R dSH-SY5Y, rescuing them from apoptosis and restoring the bioelectrical profile toward normoxic dSH-SY5Y. This complete neuroprotection did not occur in the non-contact co-culture. In summary, our data reveal the presence of a functional TNTs network containing nestin within hNSCs, demonstrate the involvement of TNTs in post-ischemic neuroprotection mediated by hNSCs, and highlight the strong efficacy of our hNSC lines in post-ischemic neuroprotection. Human neural stem cells (hNSCs) communicate with each other and rescue ischemic neurons through nestin-positive tunneling nanotubes (TNTs). A Functional mitochondria are exchanged via TNTs between hNSCs. B hNSCs transfer functional mitochondria to ischemic neurons through TNTs, rescuing neurons from ischemia/reperfusion ROS-dependent apoptosis.

Dissecting reactive astrocyte responses: lineage tracing and morphology-based clustering

Brain damage triggers diverse cellular and molecular events, with astrocytes playing a crucial role in activating local neuroprotective and reparative signaling within damaged neuronal circuits. Here, we investigated reactive astrocytes using a multidimensional approach to categorize their responses into different subtypes based on morphology. This approach utilized the StarTrack lineage tracer, single-cell imaging reconstruction and multivariate data analysis. Our findings identified three profiles of reactive astrocyte responses, categorized by their effects on cell size- and shape- related morphological parameters: "moderate", "strong," and "very strong". We also examined the heterogeneity of astrocyte reactivity, focusing on spatial and clonal distribution. Our research revealed a notable enrichment of protoplasmic and fibrous astrocytes within the "strong" and "very strong" response subtypes. Overall, our study contributes to a better understanding of astrocyte heterogeneity in response to an injury. By characterizing the diverse reactive responses among astrocyte subpopulations, we provide insights that could guide future research aimed at identifying novel therapeutic targets to mitigate brain damage and promote neural repair.

Glial fibrillary acidic protein is pathologically modified in Alexander disease

Here, we describe pathological events potentially involved in the disease pathogenesis of Alexander disease (AxD). This is a primary genetic disorder of astrocyte caused by dominant gain-of-function mutations in the gene coding for an intermediate filament protein glial fibrillary acidic protein (GFAP). Pathologically, this disease is characterized by the upregulation of GFAP and its accumulation as Rosenthal fibers. Although the genetic basis linking GFAP mutations with Alexander disease has been firmly established, the initiating events that promote GFAP accumulation and the role of Rosenthal fibers (RFs) in the disease process remain unknown. Here, we investigate the hypothesis that disease-associated mutations promote GFAP aggregation through aberrant posttranslational modifications. We found high molecular weight GFAP species in the RFs of AxD brains, indicating abnormal GFAP crosslinking as a prominent pathological feature of this disease. In vitro and cell-based studies demonstrate that cystine-generating mutations promote GFAP crosslinking by cysteine-dependent oxidation, resulting in defective GFAP assembly and decreased filament solubility. Moreover, we found GFAP was ubiquitinated in RFs of AxD patients and rodent models, supporting this modification as a critical factor linked to GFAP aggregation. Finally, we found that arginine could increase the solubility of aggregation-prone mutant GFAP by decreasing its ubiquitination and aggregation. Our study suggests a series of pathogenic events leading to AxD, involving interplay between GFAP aggregation and abnormal modifications by GFAP ubiquitination and oxidation. More important, our findings provide a basis for investigating new strategies to treat AxD by targeting abnormal GFAP modifications.

Targeting the differentiation of astrocytes by Bilobalide in the treatment of Parkinson's disease model

Background: The etiology of Parkinson's disease (PD), a chronic and progressive neurodegenerative disease, is multifactorial but not fully unknown. Until now, no drug has been proven to have neuroprotective or neuroregenerative effects in patients with PD. Objectives: To observe the therapeutic potential of Bilobalide (BB), a constituent of ginkgo biloba, in MPTP-induced PD model, and explore its possible mechanisms of action. Material and Methods: Mice were randomly divided into three groups: healthy group, MPTP group and MPTP + BB group. PD-related phenotypes were induced by intraperitoneal injection of MPTP into male C57BL/6 mice, and BB (40 mg/kg/day) was intraperitoneally given for 7 consecutive days at the end of modeling. The injection of saline was set up as the control in a similar manner. Results: BB induced M2 polarization of microglia, accompanied by inhibition of neuroinflammation in the brain. Simultaneously, BB promoted the expression of BDNF in astrocytes and neurons, and expression of GDNF in neurons. Most interestingly, BB enhanced the formation of GFAP+ astrocytes expressing nestin, Brn2 and Ki67, as well as the transformation of GFAP+ astrocytes expressing tyrosine hydroxylase around subventricular zone, providing experimental evidence that BB could promote the conversion of astrocytes into TH+ dopamine neurons in vivo and in vitro. Conclusions: These results suggest the natural product BB may utilize multiple pathways to modify degenerative process of TH+ neurons, revealing an exciting opportunity for novel neuroprotective therapeutics. However, its multi-target and important mechanisms need to be further explored.

Alexander disease: the road ahead

Alexander disease is a rare neurodegenerative disorder caused by mutations in the glial fibrillary acidic protein, a type III intermediate filament protein expressed in astrocytes. Both early (infantile or juvenile) and adult onsets of the disease are known and, in both cases, astrocytes present characteristic aggregates, named Rosenthal fibers. Mutations are spread along the glial fibrillary acidic protein sequence disrupting the typical filament network in a dominant manner. Although the presence of aggregates suggests a proteostasis problem of the mutant forms, this behavior is also observed when the expression of wild-type glial fibrillary acidic protein is increased. Additionally, several isoforms of glial fibrillary acidic protein have been described to date, while the impact of the mutations on their expression and proportion has not been exhaustively studied. Moreover, the posttranslational modification patterns and/or the protein-protein interaction networks of the glial fibrillary acidic protein mutants may be altered, leading to functional changes that may modify the morphology, positioning, and/or the function of several organelles, in turn, impairing astrocyte normal function and subsequently affecting neurons. In particular, mitochondrial function, redox balance and susceptibility to oxidative stress may contribute to the derangement of glial fibrillary acidic protein mutant-expressing astrocytes. To study the disease and to develop putative therapeutic strategies, several experimental models have been developed, a collection that is in constant growth. The fact that most cases of Alexander disease can be related to glial fibrillary acidic protein mutations, together with the availability of new and more relevant experimental models, holds promise for the design and assay of novel therapeutic strategies.

Intermediate filament proteins are reliable immunohistological biomarkers to help diagnose multiple tissue-specific diseases

Cytoskeletal networks are proteins that effectively maintain cell integrity and provide mechanical support to cells by actively transmitting mechanical signals. Intermediate filaments, which are from the cytoskeleton family and are 10 nanometres in diameter, are unlike actin and microtubules, which are highly dynamic cytoskeletal elements. Intermediate filaments are flexible at low strain, harden at high strain and resist breaking. For this reason, these filaments fulfil structural functions by providing mechanical support to the cells through their different strain-hardening properties. Intermediate filaments are suitable in that cells both cope with mechanical forces and modulate signal transmission. These filaments are composed of fibrous proteins that exhibit a central α-helical rod domain with a conserved substructure. Intermediate filament proteins are divided into six groups. Type I and type II include acidic and basic keratins, type III, vimentin, desmin, peripheralin and glial fibrillary acidic protein (GFAP), respectively. Type IV intermediate filament group includes neurofilament proteins and a fourth neurofilament subunit, α-internexin proteins. Type V consists of lamins located in the nucleus, and the type VI group consists of lens-specific intermediate filaments, CP49/phakinin and filen. Intermediate filament proteins show specific immunoreactivity in differentiating cells and mature cells of various types. Various carcinomas such as colorectal, urothelial and ovarian, diseases such as chronic pancreatitis, cirrhosis, hepatitis and cataract have been associated with intermediate filaments. Accordingly, this section reviews available immunohistochemical antibodies to intermediate filament proteins. Identification of intermediate filament proteins by methodological methods may contribute to the understanding of complex diseases.

Retinal gliosis and phenotypic diversity of intermediate filament induction and remodeling upon acoustic blast overpressure (ABO) exposure to the rat eye

Traumatic brain injury (TBI) caused by acoustic blast overpressure (ABO) is frequently associated with chronic visual deficits in military personnel and civilians. In this study, we characterized retinal gliotic response in adult male rats following a single ABO exposure directed to one side of the head. Expression of gliosis markers and intermediate filaments was assessed at 48 h and 1 wk post-ABO exposure, in comparison to age-matched non-exposed control retina. In response to a single ABO exposure, type III IF, glial fibrillary acidic protein (GFAP) was variably induced in a subpopulation of retinal Müller glia in ipsilateral eyes. ABO-exposed eyes exhibited radial Müller glial GFAP filament extension through the inner plexiform layer (IPL) and the inner nuclear layer (INL) through the retina in both the nasal quadrant and juxta-optic nerve head (jONH) eye regions at 1 wk post-ABO. We observed an ∼6-fold increase (p ≤ 0.05) in radial glial GFAP immunolabeling in the IPL in both eye regions, in comparison to regionally matched controls. Similarly, GFAP extension through the INL into the outer retina was elevated ∼3-fold, p ≤ 0.05 in the nasal retina, but exhibited wider variability in the jONH retina. In contrast, constitutive type III IF vimentin exhibited greater remodeling in retinal Müller glia through the jONH retina compared to the nasal retina in response to ABO. We observed areas of lateral vimentin remodeling through the Müller glial end-feet, and greater mid-outer retinal radial vimentin IF extension in a subpopulation of glia at 1 wk post-ABO. We also observed a significant increase in total retinal levels of the type III IF desmin in ABO-exposed retina vs. controls (∼1.6-fold, p ≤ 0.01). In addition, ABO-exposure elicited varied glial induction of developmentally regulated type VI family IFs (nestin and synemin) in subpopulations of Müller cells at 48 h and 1 wk post-ABO. We demonstrate that multiple glial phenotypes emerge in the rat retina following a single ABO exposure, rather than a global homogeneous retinal glial response, involving less well characterized IF protein forms which warrant further investigation in the context of ABO-induced retinal gliosis.

Cortical Astrocyte Progenitors and Astrocytes from Human Pluripotent Stem Cells

Astrocytes coordinate several homeostatic processes of the central nervous system and play essential roles for normal brain development and response to disease conditions. Protocols for the conversion of human induced pluripotent stem cells (hiPSCs) into mature astrocytes have opened to the generation of in vitro systems to explore astrocytes’ functions in living human cell contexts and patient-specific settings. In this study, we present an optimized monolayer procedure to commit hiPSC-derived cortical progenitors into enriched populations of cortical astrocyte progenitor cells (CX APCs) that can be further amplified and efficiently differentiated into mature astrocytes. Our optimized system provides a valid tool to explore the role of these cells in neurodevelopmental and neuropsychiatric diseases, opening it up to applications in drug development and biomarkers discovery/validation.

Mechanotherapy in oncology: Targeting nuclear mechanics and mechanotransduction

Mechanotherapy is proposed as a new option for cancer treatment. Increasing evidence suggests that characteristic differences are present in the nuclear mechanics and mechanotransduction of cancer cells compared with those of normal cells. Recent advances in understanding nuclear mechanics and mechanotransduction provide not only further insights into the process of malignant transformation but also useful references for developing new therapeutic approaches. Herein, we present an overview of the alterations of nuclear mechanics and mechanotransduction in cancer cells and highlight their implications in cancer mechanotherapy.

Redox-sensitive small GTPase H-Ras in murine astrocytes, an in vitro study

BACKGROUND

Although the protooncogenes small GTPases Ras are redox-sensitive proteins, how they are regulated by redox signaling in the central nervous system (CNS) is still poorly understood. Alteration in redox-sensitive targets by redox signaling may have myriad effects on Ras stability, activity and localization. Redox-mediated changes in astrocytic RAS may contribute to the control of redox homeostasis in the CNS that is connected to the pathogenesis of many diseases.

RESULTS AND METHODS

Here, we investigated the transient physiological induction, at both transcriptional and translational levels, of small GTPases Ras in response to redox stimulation. Cultured astrocytes were treated with hydrogen peroxide as in bolus addition and relative mRNA levels of murine hras and kras genes were detected by qRT-PCR. We found that de novo transcription of hras mRNA in reactive astrocytes is redox-sensitive and mimics the prototypical redox-sensitive gene iNOS. Protein abundance in combination with protein turnover measurements by cycloheximide-chase experiments revealed distinct translation efficiency, GTP-bound enrichment, and protein turnover rates between the two isoforms H-Ras and K-Ras.

CONCLUSION

Reports from recent years support a significant role of H-Ras in driving redox processes. Beyond its canonical functions, Ras may impact on the core astrocytic cellular machinery that operates during redox stimulation.

Low doses of imidacloprid induce neurotoxic effects in adult marsh frogs: GFAP, NfL, and angiostatin as biomarkers

Imidacloprid is one of the most widely used insecticides in the world. The neurotoxicity of imidacloprid in adult amphibians has not been studied thoroughly. We investigated the expression of glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL) and angiostatin in the amphibian brain to identify valid biomarkers of low dose imidacloprid exposure. For the experiment, 30 individuals of the marsh frog Pelophylax ridibundus were selected. The amphibians were divided into five groups. The duration of the experiment was 7 and 21 days. The exposure concentrations were 10 and 100 µg/L. The results of the study revealed a decrease in the expression of GFAP after 7 days in the exposure groups of 10 and 100 μg/L. An increase in the level of NfL was observed in the group exposed to 10 μg/L after 21 days of the experiment. The angiostatin level was increased after 7 days at 10 µg/L and after 21 days at 100 µg/L. The data obtained indicate that low concentrations of imidacloprid can cause neurotoxic effects in the brain of P. ridibundus. Such effects can have a significant impact on amphibian populations. According to the results of the study of the expression level of GFAP, NfL and angiostatin, it can be stated that imidacloprid has a neurotoxic effect on adult marsh frogs. The studied indicators can be promising biomarkers of environmental pollution by neonicotinoids.

Cortical Pathology in Vanishing White Matter

Vanishing white matter (VWM) is classified as a leukodystrophy with astrocytes as primary drivers in its pathogenesis. Magnetic resonance imaging has documented the progressive thinning of cortices in long-surviving patients. Routine histopathological analyses, however, have not yet pointed to cortical involvement in VWM. Here, we provide a comprehensive analysis of the VWM cortex. We employed high-resolution-mass-spectrometry-based proteomics and immunohistochemistry to gain insight into possible molecular disease mechanisms in the cortices of VWM patients. The proteome analysis revealed 268 differentially expressed proteins in the VWM cortices compared to the controls. A majority of these proteins formed a major protein interaction network. A subsequent gene ontology analysis identified enrichment for terms such as cellular metabolism, particularly mitochondrial activity. Importantly, some of the proteins with the most prominent changes in expression were found in astrocytes, indicating cortical astrocytic involvement. Indeed, we confirmed that VWM cortical astrocytes exhibit morphological changes and are less complex in structure than control cells. Our findings also suggest that these astrocytes are immature and not reactive. Taken together, we provide insights into cortical involvement in VWM, which has to be taken into account when developing therapeutic strategies.

Alexander disease GFAP R239C mutant shows increased susceptibility to lipoxidation and elicits mitochondrial dysfunction and oxidative stress

Alexander disease is a fatal neurological disorder caused by mutations in the intermediate filament protein Glial Fibrillary Acidic Protein (GFAP), which is key for astrocyte homeostasis. These mutations cause GFAP aggregation, astrocyte dysfunction and neurodegeneration. Remarkably, most of the known GFAP mutations imply a change by more nucleophilic amino acids, mainly cysteine or histidine, which are more susceptible to oxidation and lipoxidation. Therefore, we hypothesized that a higher susceptibility of Alexander disease GFAP mutants to oxidative or electrophilic damage, which frequently occurs during neurodegeneration, could contribute to disease pathogenesis. To address this point, we have expressed GFP-GFAP wild type or the harmful Alexander disease GFP-GFAP R239C mutant in astrocytic cells. Interestingly, GFAP R239C appears more oxidized than the wild type under control conditions, as indicated both by its lower cysteine residue accessibility and increased presence of disulfide-bonded oligomers. Moreover, GFP-GFAP R239C undergoes lipoxidation to a higher extent than GFAP wild type upon treatment with the electrophilic mediator 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). Importantly, GFAP R239C filament organization is altered in untreated cells and is earlier and more severely disrupted than GFAP wild type upon exposure to oxidants (diamide, H2O2) or electrophiles (4-hydroxynonenal, 15d-PGJ2), which exacerbate GFAP R239C aggregation. Furthermore, H2O2 causes reversible alterations in GFAP wild type, but irreversible damage in GFAP R239C expressing cells. Finally, we show that GFAP R239C expression induces a more oxidized cellular status, with decreased free thiol content and increased mitochondrial superoxide generation. In addition, mitochondria show decreased mass, increased colocalization with GFAP and altered morphology. Notably, a GFP-GFAP R239H mutant recapitulates R239C-elicited alterations whereas an R239G mutant induces a milder phenotype. Together, our results outline a deleterious cycle involving altered GFAP R239C organization, mitochondrial dysfunction, oxidative stress, and further GFAP R239C protein damage and network disruption, which could contribute to astrocyte derangement in Alexander disease.

Astroglial and oligodendroglial markers in the cuprizone animal model for de- and remyelination

Myelin loss with consecutive axon degeneration and impaired remyelination are the underlying causes of progressive disease in patients with multiple sclerosis. Astrocytes are suggested to play a major role in these processes. The unmasking of distinct astrocyte identities in health and disease would help to understand the pathophysiological mechanisms in which astrocytes are involved. However, the number of specific astrocyte markers is limited. Therefore, we performed immunohistochemical studies and analyzed various markers including GFAP, vimentin, S100B, ALDH1L1, and LCN2 during de- and remyelination using the toxic murine cuprizone animal model. Applying this animal model, we were able to confirm overlapping expression of vimentin and GFAP and highlighted the potential of ALDH1L1 as a pan-astrocytic marker, in agreement with previous data. Only a small population of GFAP-positive astrocytes in the corpus callosum highly up-regulated LCN2 at the peak of demyelination and S100B expression was found in a subset of oligodendroglia as well, thus S100B turned out to have a limited use as a particular astroglial marker. Additionally, numerous GFAP-positive astrocytes in the lateral corpus callosum did not express S100B, further strengthening findings of heterogeneity in the astrocytic population. In conclusion, our results acknowledged that GFAP, vimentin, LCN2, and ALDH1L1 serve as reliable marker to identify activated astrocytes during cuprizone-induced de- and remyelination. Moreover, there were clear regional and temporal differences in protein and mRNA expression levels and patterns of the studied markers, generally between gray and white matter structures.

Roles of vimentin in health and disease

More than 27 yr ago, the vimentin knockout (Vim-/- ) mouse was reported to develop and reproduce without an obvious phenotype, implying that this major cytoskeletal protein was nonessential. Subsequently, comprehensive and careful analyses have revealed numerous phenotypes in Vim-/- mice and their organs, tissues, and cells, frequently reflecting altered responses in the recovery of tissues following various insults or injuries. These findings have been supported by cell-based experiments demonstrating that vimentin intermediate filaments (IFs) play a critical role in regulating cell mechanics and are required to coordinate mechanosensing, transduction, signaling pathways, motility, and inflammatory responses. This review highlights the essential functions of vimentin IFs revealed from studies of Vim-/- mice and cells derived from them.

Molecular organization and mechanics of single vimentin filaments revealed by super-resolution imaging

Intermediate filaments (IFs) are involved in key cellular functions including polarization, migration, and protection against large deformations. These functions are related to their remarkable ability to extend without breaking, a capacity that should be determined by the molecular organization of subunits within filaments. However, this structure-mechanics relationship remains poorly understood at the molecular level. Here, using super-resolution microscopy (SRM), we show that vimentin filaments exhibit a ~49-nanometer axial repeat both in cells and in vitro. As unit-length filaments (ULFs) were measured at ~59 nanometers, this demonstrates a partial overlap of ULFs during filament assembly. Using an SRM-compatible stretching device, we also provide evidence that the extensibility of vimentin is due to the unfolding of its subunits and not to their sliding, thus establishing a direct link between the structural organization and its mechanical properties. Overall, our results pave the way for future studies of IF assembly, mechanical, and structural properties in cells.

Reactive Astrocytes Prevent Maladaptive Plasticity after Ischemic Stroke

Restoration of functional connectivity is a major contributor to functional recovery after stroke. We investigated the role of reactive astrocytes in functional connectivity and recovery after photothrombotic stroke in mice with attenuated reactive gliosis (GFAP^-/-Vim^-/-). Infarct volume and longitudinal functional connectivity changes were determined by in vivo T2-weighted magnetic resonance imaging (MRI) and resting-state functional MRI. Sensorimotor function was assessed with behavioral tests, and glial and neural plasticity responses were quantified in the peri-infarct region. Four weeks after stroke, GFAP^-/-Vim^-/- mice showed impaired recovery of sensorimotor function and aberrant restoration of global neuronal connectivity. These mice also exhibited maladaptive plasticity responses, shown by higher number of lost and newly formed functional connections between primary and secondary targets of cortical stroke regions and increased peri-infarct expression of the axonal plasticity marker Gap43. We conclude that reactive astrocytes modulate recovery-promoting plasticity responses after ischemic stroke.

Targeting Complement C3a Receptor to Improve Outcome After Ischemic Brain Injury

Ischemic stroke is a major cause of disability. No efficient therapy is currently available, except for the removal of the occluding blood clot during the first hours after symptom onset. Loss of function after stroke is due to cell death in the infarcted tissue, cell dysfunction in the peri-infarct region, as well as dysfunction and neurodegeneration in remote brain areas. Plasticity responses in spared brain regions are a major contributor to functional recovery, while secondary neurodegeneration in remote regions is associated with depression and impedes the long-term outcome after stroke. Hypoxic-ischemic encephalopathy due to birth asphyxia is the leading cause of neurological disability resulting from birth complications. Despite major progress in neonatal care, approximately 50% of survivors develop complications such as mental retardation, cerebral palsy or epilepsy. The C3a receptor (C3aR) is expressed by many cell types including neurons and glia. While there is a body of evidence for its deleterious effects in the acute phase after ischemic injury to the adult brain, C3aR signaling contributes to better outcome in the post-acute and chronic phase after ischemic stroke in adults and in the ischemic immature brain. Here we discuss recent insights into the novel roles of C3aR signaling in the ischemic brain with focus on the therapeutic opportunities of modulating C3aR activity to improve the outcome after ischemic stroke and birth asphyxia.

RNAi-mediated suppression of vimentin or glial fibrillary acidic protein prevents the establishment of Müller glial cell hypertrophy in progressive retinal degeneration

Gliosis is a complex process comprising upregulation of intermediate filament (IF) proteins, particularly glial fibrillary acidic protein (GFAP) and vimentin, changes in glial cell morphology (hypertrophy) and increased deposition of inhibitory extracellular matrix molecules. Gliosis is common to numerous pathologies and can have deleterious effects on tissue function and regeneration. The role of IFs in gliosis is controversial, but a key hypothesized function is the stabilization of glial cell hypertrophy. Here, we developed RNAi approaches to examine the role of GFAP and vimentin in vivo in a murine model of inherited retinal degeneration, the Rhodopsin knockout (Rho-/- ) mouse. Specifically, we sought to examine the role of these IFs in the establishment of Müller glial hypertrophy during progressive degeneration, as opposed to (more commonly assessed) acute injury. Prevention of Gfap upregulation had a significant effect on the morphology of reactive Müller glia cells in vivo and, more strikingly, the reduction of Vimentin expression almost completely prevented these cells from undergoing degeneration-associated hypertrophy. Moreover, and in contrast to studies in knockout mice, simultaneous suppression of both GFAP and vimentin expression led to severe changes in the cytoarchitecture of the retina, in both diseased and wild-type eyes. These data demonstrate a crucial role for Vimentin, as well as GFAP, in the establishment of glial hypertrophy and support the further exploration of RNAi-mediated knockdown of vimentin as a potential therapeutic approach for modulating scar formation in the degenerating retina.

Therapeutically viable generation of neurons with antisense oligonucleotide suppression of PTB

Methods to enhance adult neurogenesis by reprogramming glial cells into neurons enable production of new neurons in the adult nervous system. Development of therapeutically viable approaches to induce new neurons is now required to bring this concept to clinical application. Here, we successfully generate new neurons in the cortex and dentate gyrus of the aged adult mouse brain by transiently suppressing polypyrimidine tract binding protein 1 using an antisense oligonucleotide delivered by a single injection into cerebral spinal fluid. Radial glial-like cells and other GFAP-expressing cells convert into new neurons that, over a 2-month period, acquire mature neuronal character in a process mimicking normal neuronal maturation. The new neurons functionally integrate into endogenous circuits and modify mouse behavior. Thus, generation of new neurons in the dentate gyrus of the aging brain can be achieved with a therapeutically feasible approach, thereby opening prospects for production of neurons to replace those lost to neurodegenerative disease.

Elevated GFAP isoform expression promotes protein aggregation and compromises astrocyte function

Alexander disease (AxD) caused by mutations in the coding region of GFAP is a neurodegenerative disease characterized by astrocyte dysfunction, GFAP aggregation, and Rosenthal fiber accumulation. Although how GFAP mutations cause disease is not fully understood, Rosenthal fibers could be induced by forced overexpression of human GFAP and this could be lethal in mice implicate that an increase in GFAP levels is central to AxD pathogenesis. Our recent studies demonstrated that intronic GFAP mutations cause disease by altering GFAP splicing, suggesting that an increase in GFAP isoform expression could lead to protein aggregation and astrocyte dysfunction that typify AxD. Here we test this hypothesis by establishing primary astrocyte cultures from transgenic mice overexpressing human GFAP. We found that GFAP-δ and GFAP-κ were disproportionately increased in transgenic astrocytes and both were enriched in Rosenthal fibers of human AxD brains. In vitro assembly studies showed that while the major isoform GFAP-α self-assembled into typical 10-nm filaments, minor isoforms including GFAP-δ, -κ, and -λ were assembly-compromised and aggregation prone. Lentiviral transduction showed that expression of these minor GFAP isoforms decreased filament solubility and increased GFAP stability, leading to the formation of Rosenthal fibers-like aggregates that also disrupted the endogenous intermediate filament networks. The aggregate-bearing astrocytes lost their normal morphology and glutamate buffering capacity, which had a toxic effect on neighboring neurons. In conclusion, our findings provide evidence that links elevated GFAP isoform expression with GFAP aggregation and impaired glutamate transport, and suggest a potential non-cell-autonomous mechanism underlying neurodegeneration through astrocyte dysfunction.

The Complement System: A Powerful Modulator and Effector of Astrocyte Function in the Healthy and Diseased Central Nervous System

The complement system, an effector arm of the innate immune system that plays a critical role in tissue inflammation, the elimination of pathogens and the clearance of dead cells and cell debris, has emerged as a regulator of many processes in the central nervous system, including neural cell genesis and migration, control of synapse number and function, and modulation of glial cell responses. Complement dysfunction has also been put forward as a major contributor to neurological disease. Astrocytes are neuroectoderm-derived glial cells that maintain water and ionic homeostasis, and control cerebral blood flow and multiple aspects of neuronal functioning. By virtue of their expression of soluble as well as membrane-bound complement proteins and receptors, astrocytes are able to both send and receive complement-related signals. Here we review the current understanding of the multiple functions of the complement system in the central nervous system as they pertain to the modulation of astrocyte activity, and how astrocytes use the complement system to affect their environment in the healthy brain and in the context of neurological disease.

Lineage tracing reveals the origin of Nestin-positive cells are heterogeneous and rarely from ependymal cells after spinal cord injury

Nestin is expressed extensively in neural stem/progenitor cells during neural development, but its expression is mainly restricted to the ependymal cells in the adult spinal cord. After spinal cord injury (SCI), Nestin expression is reactivated and Nestin-positive (Nestin⁺) cells aggregate at the injury site. However, the derivation of Nestin⁺ cells is not clearly defined. Here, we found that Nestin expression was substantially increased in the lesion edge and lesion core after SCI. Using a tamoxifen inducible CreER(T2)-loxP system, we verified that ependymal cells contribute few Nestin⁺ cells either to the lesion core or the lesion edge after SCI. In the lesion edge, GFAP⁺ astrocytes were the main cell type that expressed Nestin; they then formed an astrocyte scar. In the lesion core, Nestin⁺ cells expressed αSMA or Desmin, indicating that they might be derived from pericytes. Our results reveal that Nestin⁺ cells in the lesion core and edge came from various cell types and rarely from ependymal cells after complete transected SCI, which may provide new insights into SCI repair.

GFAP hyperpalmitoylation exacerbates astrogliosis and neurodegenerative pathology in PPT1-deficient mice

This study reports that the intermediate filament protein GFAP is modified with protein palmitoylation. Increased GFAP expression and palmitoylation is involved in astrocyte proliferation and astrogliosis. We demonstrate that GFAP palmitoylation is regulated by PPT1, a palmitoylprotein thioesterase linked to a childhood neurodegenerative disorder, infantile neuronal ceroid lipofuscinosis. A palmitoylation-defective mutant of GFAP attenuates astrogliosis and the concurrent pathology in a loss-of-function PPT1 mouse. We conclude that accumulation of palmitoylated GFAP contributes to the pathogenesis of astrogliosis and neurodegeneration, suggesting that targeting the modified cysteine in GFAP may be a potential therapeutic strategy for the treatment of infantile neuronal ceroid lipofuscinosis and other neurodegenerative disorders.

The homeostasis of protein palmitoylation and depalmitoylation is essential for proper physiological functions in various tissues, in particular the central nervous system (CNS). The dysfunction of PPT1 (PPT1-KI, infantile neuronal ceroid lipofuscinosis [INCL] mouse model), which catalyze the depalmitoylation process, results in serious neurodegeneration accompanied by severe astrogliosis in the brain. Endeavoring to determine critical factors that might account for the pathogenesis in CNS by palm-proteomics, glial fibrillary acidic protein (GFAP) was spotted, indicating that GFAP is probably palmitoylated. Questions concerning if GFAP is indeed palmitoylated in vivo and how palmitoylation of GFAP might participate in neural pathology remain unexplored and are waiting to be investigated. Here we show that GFAP is readily palmitoylated in vitro and in vivo; specifically, cysteine-291 is the unique palmitoylated residue in GFAP. Interestingly, it was found that palmitoylated GFAP promotes astrocyte proliferation in vitro. Furthermore, we showed that PPT1 depalmitoylates GFAP, and the level of palmitoylated GFAP is overwhelmingly up-regulated in PPT1-knockin mice, which lead us to speculate that the elevated level of palmitoylated GFAP might accelerate astrocyte proliferation in vivo and ultimately led to astrogliosis in INCL. Indeed, blocking palmitoylation by mutating cysteine-291 into alanine in GFAP attenuate astrogliosis, and remarkably, the concurrent neurodegenerative pathology in PPT1-knockin mice. Together, these findings demonstrate that hyperpalmitoylated GFAP plays critical roles in regulating the pathogenesis of astrogliosis and neurodegeneration in the CNS, and most importantly, pinpointing that cysteine-291 in GFAP might be a valuable pharmaceutical target for treating INCL and other potential neurodegenerative diseases.

Establishment of Long-Term Primary Cortical Neuronal Cultures From Neonatal Opossum Monodelphis domestica

Primary dissociated neuronal cultures have become a standard model for studying central nervous system (CNS) development. Such cultures are predominantly prepared from the hippocampus or cortex of rodents (mice and rats), while other mammals are less used. Here, we describe the establishment and extensive characterization of the primary dissociated neuronal cultures derived from the cortex of the gray South American short-tailed opossums, Monodelphis domestica. Opossums are unique in their ability to fully regenerate their CNS after an injury during their early postnatal development. Thus, we used cortex of postnatal day (P) 3-5 opossum to establish long-surviving and nearly pure neuronal cultures, as well as mixed cultures composed of radial glia cells (RGCs) in which their neurogenic and gliogenic potential was confirmed. Both types of cultures can survive for more than 1 month in vitro. We also prepared neuronal cultures from the P16-18 opossum cortex, which were composed of astrocytes and microglia, in addition to neurons. The long-surviving opossum primary dissociated neuronal cultures represent a novel mammalian in vitro platform particularly useful to study CNS development and regeneration.

Ethyl Pyruvate-Derived Transdifferentiation of Astrocytes to Oligodendrogenesis in Cuprizone-Induced Demyelinating Model

Astrocytes redifferentiate into oligodendrogenesis, raising the possibility that astrocytes may be a potential target in the treatment of adult demyelinated lesion. Upon the basis of the improvement of behavior abnormality and demyelination by ethyl pyruvate (EP) treatment, we further explored whether EP affects the function of astrocytes, especially the transdifferentiation of astrocytes into oligodendrogenesis. The results showed that EP treatment increased the accumulation of astrocytes in myelin sheath and promoted the phagocytosis of myelin debris by astrocytes in vivo and in vitro. At the same time, EP treatment induced astrocytes to upregulate the expression of CNTF and BDNF in the corpus callosum and striatum as well as cultured astrocytes, accompanied by increased expression of nestin, Sox2, and β-catenin and decreased expression of Notch1 by astrocytes. As a result, EP treatment effectively promoted the generation of NG2+ and PDGF-Ra+ oligodendrocyte precursor cells (OPCs) that, in part, express astrocyte marker GFAP. Further confirmation was performed by intracerebral injection of primary astrocytes labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE). As expected, NG2+ OPCs expressing CFSE and Sox2 were elevated in the corpus callosum of mice treated with EP following transplantation, revealing that EP can convert astrocytes into myelinating cells. Our results indicate the possibility that EP lead to effective myelin repair in patients suffering from myelination deficit.Graphical Abstract The diagram of EP action for promoting myelin regeneration in CPZ model. EP promoted migration and enrichment of astrocytes to demyelinated tissue and induced astrocytes to express neurotrophic CNTF and BDNF as well as translation factor nestin, Sox2, and β-catenin, which should contribute to astrocytes to differentiate of oligodendrogenesis. At the same time, EP promoted astrocytes to phagocytized myelin debris for removing the harmful substances of myelin regeneration.

Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation

Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.

Fatty Acid Binding Protein 7 is Involved in the Proliferation of Reactive Astrocytes, but not in Cell Migration and Polarity

Reactive gliosis is a defense mechanism to minimize and repair the initial damage after CNS injuries that is characterized by increases in astrocytic reactivity and proliferation, with enhanced expression of glial fibrillary acidic protein (GFAP) and cellular hypertrophy. Fatty acid binding protein 7 (FABP7) is abundantly expressed in several types of glial cells, such as astrocytes and oligodendrocyte precursor cells, during brain development and FABP7-positive astrocytes have been shown to be significantly increased in the mouse cortex after a stab injury. However, the functional significance of FABP7 in gliosis remains unclear. In the present study, we examined the mechanism of FABP7-mediated regulation of gliosis using an in vitro scratch-injury model using primary cultured astrocytes. Western blotting showed that FABP7 expression was increased significantly in scratch wounded astrocytes at the edge of the injury compared with intact astrocytes. Through monitoring the occupancy of the injured area, FAB7-KO astrocytes showed a slower proliferation rate compared with WT astrocytes after 48 hr, which was confirmed by BrdU immunostaining. There were no differences in cell migration and polarity of reactive astrocytes between FABP-KO and WT. Conclusively, our data suggest that FABP7 is important in the proliferation of reactive astrocytes in the context of CNS injury.

Type III intermediate filaments as targets and effectors of electrophiles and oxidants

Intermediate filaments (IFs) play key roles in cell mechanics, signaling and homeostasis. Their assembly and dynamics are finely regulated by posttranslational modifications. The type III IFs, vimentin, desmin, peripherin and glial fibrillary acidic protein (GFAP), are targets for diverse modifications by oxidants and electrophiles, for which their conserved cysteine residue emerges as a hot spot. Pathophysiological examples of these modifications include lipoxidation in cell senescence and rheumatoid arthritis, disulfide formation in cataracts and nitrosation in endothelial shear stress, although some oxidative modifications can also be detected under basal conditions. We previously proposed that cysteine residues of vimentin and GFAP act as sensors for oxidative and electrophilic stress, and as hinges influencing filament assembly. Accumulating evidence indicates that the structurally diverse cysteine modifications, either per se or in combination with other posttranslational modifications, elicit specific functional outcomes inducing distinct assemblies or network rearrangements, including filament stabilization, bundling or fragmentation. Cysteine-deficient mutants are protected from these alterations but show compromised cellular performance in network assembly and expansion, organelle positioning and aggresome formation, revealing the importance of this residue. Therefore, the high susceptibility to modification of the conserved cysteine of type III IFs and its cornerstone position in filament architecture sustains their role in redox sensing and integration of cellular responses. This has deep pathophysiological implications and supports the potential of this residue as a drug target.

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Type III intermediate filaments can be modified by many oxidants and electrophiles.

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Oxidative modifications of type III IFs occur in normal and pathological conditions.

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The conserved cysteine residue acts as a hub for redox/electrophilic modifications.

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Cysteine modifications elicit structure-dependent type III IF rearrangements.

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Type III intermediate filaments act as sensors for oxidative and electrophilic stress.

The Diversity of Intermediate Filaments in Astrocytes

Despite the remarkable complexity of the individual neuron and of neuronal circuits, it has been clear for quite a while that, in order to understand the functioning of the brain, the contribution of other cell types in the brain have to be accounted for. Among glial cells, astrocytes have multiple roles in orchestrating neuronal functions. Their communication with neurons by exchanging signaling molecules and removing molecules from extracellular space takes place at several levels and is governed by different cellular processes, supported by multiple cellular structures, including the cytoskeleton. Intermediate filaments in astrocytes are emerging as important integrators of cellular processes. Astrocytes express five types of intermediate filaments: glial fibrillary acidic protein (GFAP); vimentin; nestin; synemin; lamins. Variability, interactions with different cellular structures and the particular roles of individual intermediate filaments in astrocytes have been studied extensively in the case of GFAP and vimentin, but far less attention has been given to nestin, synemin and lamins. Similarly, the interplay between different types of cytoskeleton and the interaction between the cytoskeleton and membranous structures, which is mediated by cytolinker proteins, are understudied in astrocytes. The present review summarizes the basic properties of astrocytic intermediate filaments and of other cytoskeletal macromolecules, such as cytolinker proteins, and describes the current knowledge of their roles in normal physiological and pathological conditions.

Nestin affects fusion pore dynamics in mouse astrocytes

AIM

Astrocytes play a homeostatic role in the central nervous system and influence numerous aspects of neurophysiology via intracellular trafficking of vesicles. Intermediate filaments (IFs), also known as nanofilaments, regulate a number of cellular processes including organelle trafficking and adult hippocampal neurogenesis. We have recently demonstrated that the IF protein nestin, a marker of neural stem cells and immature and reactive astrocytes, is also expressed in some astrocytes in the unchallenged hippocampus and regulates neurogenesis through Notch signalling from astrocytes to neural stem cells, possibly via altered trafficking of vesicles containing the Notch ligand Jagged-1.

METHODS

We thus investigated whether nestin affects vesicle dynamics in astrocytes by examining single vesicle interactions with the plasmalemma and vesicle trafficking with high-resolution cell-attached membrane capacitance measurements and confocal microscopy. We used cell cultures of astrocytes from nestin-deficient (Nes^-/- ) and wild-type (wt) mice, and fluorescent dextran and Fluo-2 to examine vesicle mobility and intracellular Ca²⁺ concentration respectively.

RESULTS

Nes^-/- astrocytes exhibited altered sizes of vesicles undergoing full fission and transient fusion, altered vesicle fusion pore geometry and kinetics, decreased spontaneous vesicle mobility and altered ATP-evoked mobility. Purinergic stimulation evoked Ca²⁺ signalling that was slightly attenuated in Nes^-/- astrocytes, which exhibited more oscillatory Ca²⁺ responses than wt astrocytes.

CONCLUSION

These results demonstrate at the single vesicle level that nestin regulates vesicle interactions with the plasmalemma and vesicle trafficking, indicating its potential role in astrocyte vesicle-based communication.

The role of GFAP and vimentin in learning and memory

Intermediate filaments (also termed nanofilaments) are involved in many cellular functions and play important roles in cellular responses to stress. The upregulation of glial fibrillary acidic protein (GFAP) and vimentin (Vim), intermediate filament proteins of astrocytes, is the hallmark of astrocyte activation and reactive gliosis in response to injury, ischemia or neurodegeneration. Reactive gliosis is essential for the protective role of astrocytes at acute stages of neurotrauma or ischemic stroke. However, GFAP and Vim were also linked to neural plasticity and regenerative responses in healthy and injured brain. Mice deficient for GFAP and vimentin (GFAP-/-Vim-/-) exhibit increased post-traumatic synaptic plasticity and increased basal and post-traumatic hippocampal neurogenesis. Here we assessed the locomotor and exploratory behavior of GFAP-/-Vim-/- mice, their learning, memory and memory extinction, by using the open field, object recognition and Morris water maze tests, trace fear conditioning, and by recording reversal learning in IntelliCages. While the locomotion, exploratory behavior and learning of GFAP-/-Vim-/- mice, as assessed by object recognition, the Morris water maze, and trace fear conditioning tests, were comparable to wildtype mice, GFAP-/-Vim-/- mice showed more pronounced memory extinction when tested in IntelliCages, a finding compatible with the scenario of an increased rate of reorganization of the hippocampal circuitry.

Vimentin is required for normal accumulation of body fat

Intermediate filaments (nanofilaments) have many functions, especially in response to cellular stress. Mice lacking vimentin (Vim-/-) display phenotypes reflecting reduced levels of cell activation and ability to counteract stress, for example, decreased reactivity of astrocytes after neurotrauma, decreased migration of astrocytes and fibroblasts, attenuated inflammation and fibrosis in lung injury, delayed wound healing, impaired vascular adaptation to nephrectomy, impaired transendothelial migration of lymphocytes and attenuated atherosclerosis. To address the role of vimentin in fat accumulation, we assessed the body weight and fat by dual-energy X-ray absorptiometry (DEXA) in Vim-/- and matched wildtype (WT) mice. While the weight of 1.5-month-old Vim-/- and WT mice was comparable, Vim-/- mice showed decreased body weight at 3.5, 5.5 and 8.5 months (males by 19-22%, females by 18-29%). At 8.5 months, Vim-/- males and females had less body fat compared to WT mice (a decrease by 24%, p < 0.05, and 33%, p < 0.0001, respectively). The body mass index in 8.5 months old Vim-/- mice was lower in males (6.8 vs. 7.8, p < 0.005) and females (6.0 vs. 7.7, p < 0.0001) despite the slightly lower body length of Vim-/- mice. Increased mortality was observed in adult Vim-/- males. We conclude that vimentin is required for the normal accumulation of body fat.

Three-dimensional differentiation of human pluripotent stem cell-derived neural precursor cells using tailored porous polymer scaffolds

This study investigates the utility of a tailored poly(ethylene glycol) diacrylate-crosslinked porous polymeric tissue engineering scaffold, with mechanical properties specifically optimised to be comparable to that of mammalian brain tissue for 3D human neural cell culture. Results obtained here demonstrate the attachment, proliferation and terminal differentiation of both human induced pluripotent stem cell- and embryonic stem cell-derived neural precursor cells (hPSC-NPCs) throughout the interconnected porous network within laminin-coated scaffolds. Phenotypic data and functional analyses are presented demonstrating that this material supports terminal in vitro neural differentiation of hPSC-NPCs to a mixed population of viable neuronal and glial cells for periods of up to 49 days. This is evidenced by the upregulation of TUBB3, MAP2, SYP and GFAP gene expression, as well as the presence of the proteins βIII-TUBULIN, NEUN, MAP2 and GFAP. Functional maturity of neural cells following 49 days 3D differentiation culture was tested via measurement of intracellular calcium. These analyses revealed spontaneously active, synchronous and rhythmic calcium flux, as well as response to the neurotransmitter glutamate. This tailored construct has potential application as an improved in vitro human neurogenesis model with utility in platform drug discovery programs. STATEMENT OF SIGNIFICANCE: The interconnected porosity of polyHIPE scaffolds exhibits the ability to support three-dimensional neural cell network formation due to limited resistance to cellular migration and re-organisation. The previously developed scaffold material displays mechanical properties similar to that of the mammalian brain. This research also employs the utility of pluripotent stem cell-derived neural cells which are of greater clinical relevance than primary neural cell lines. This scaffold material has future potential in better mimicking three-dimensional neural networks found in the human brain and may result in improved in vitro models for disease modelling and drug screening applications.

Effects of miR-219/miR-338 on microglia and astrocyte behaviors and astrocyte-oligodendrocyte precursor cell interactions

MiR-219 and miR-338 (miR-219/miR-338) are oligodendrocyte-specific microRNAs. The overexpression of these miRs in oligodendrocyte precursor cells promotes their differentiation and maturation into oligodendrocytes, which may enhance axonal remyelination after nerve injuries in the central nervous system (CNS). As such, the delivery of miR-219/miR-338 to the CNS to promote oligodendrocyte precursor cell differentiation, maturation and myelination could be a promising approach for nerve repair. However, nerve injuries in the CNS also involve other cell types, such as microglia and astrocytes. Herein, we investigated the effects of miR-219/miR-338 treatment on microglia and astrocytes in vitro and in vivo. We found that miR-219/miR-338 diminished microglial expression of pro-inflammatory cytokines and suppressed astrocyte activation. In addition, we showed that miR-219/miR-338 enhanced oligodendrocyte precursor cell differentiation and maturation in a scratch assay paradigm that re-created a nerve injury condition in vitro. Collectively, our results suggest miR-219/miR-338 as a promising treatment for axonal remyelination in the CNS following nerve injuries. All experimental procedures were approved by the Institutional Animal Care and Use Committee (IACUC), Nanyang Technological University (approval No. A0309 and A0333) on April 27, 2016 and October 8, 2016.

Three-plane description of astroglial populations of OVLT subdivisions in rat: Tanycyte connections to distant parts of third ventricle

This study demonstrates glial and gliovascular markers of organon vasculosum laminae terminalis (OVLT) in three planes. The distribution of glial markers displayed similarities to the subfornical organ. There was an inner part with vimentin- and nestin-immunopositive glia whereas GFAP and the water-channel aquaporin 4 were found at the periphery. This separation indicates different functions of the two regions. The presence of nestin may indicate stem cell-capabilities whereas aquaporin 4 has been reported to promote the osmoreceptor function. Glutamine synthetase immunoreactivity was sparse like in the area postrema and subfornical organ. The laminin and β-dystroglycan immunolabelings altered along the vessels such as in the subfornical organ indicating altering gliovascular relations. The different subdivisions of OVLT received glial processes of different origins. The posterior periventricular zone contained short vimentin-immunopositive processes from the ependyma of the adjacent surface of the third ventricle. The lateral periventricular zone received forceps-like process systems from the anterolateral part of the third ventricle. Most interestingly, the "dorsal cap" received a mixed group of long GFAP- and vimentin-immunopositive processes from a distant part of the third ventricle. The processes may have two functions: a guidance for newly produced cells like radial glia in immature brain and/or a connection between distant parts of the third ventricle and OVLT.

High potassium exposure reveals the altered ability of astrocytes to regulate their volume in the aged hippocampus of GFAP/EGFP mice

In this study, we focused on age-related changes in astrocyte functioning, predominantly on the ability of astrocytes to regulate their volume in response to a pathological stimulus, namely extracellular 50 mM K⁺ concentration. The aim of our project was to identify changes in the expression and function of transport proteins in the astrocytic membrane and properties of the extracellular space, triggered by aging. We used three-dimensional confocal morphometry, gene expression profiling, immunohistochemical analysis, and diffusion measurement in the hippocampal slices from 3-, 9-, 12-, and 18-month-old mice, in which astrocytes are visualized by enhanced green fluorescent protein under the control of the promoter for human glial fibrillary acidic protein. Combining a pharmacological approach and the quantification of astrocyte volume changes evoked by hyperkalemia, we found that marked diversity in the extent of astrocyte swelling in the hippocampus during aging is due to the gradually declining participation of Na⁺-K⁺-Cl^- transporters, glutamate transporters (glutamate aspartate transporter and glutamate transporter 1), and volume-regulated anion channels. Interestingly, there was a redistribution of Na⁺-K⁺-Cl^- cotransporter and glutamate transporters from astrocytic soma to processes. In addition, immunohistochemical analysis confirmed an age-dependent decrease in the content of Na⁺-K⁺-Cl^- cotransporter in astrocytes. The overall extracellular volume changes revealed a similar age-dependent diversity during hyperkalemia as observed in astrocytes. In addition, the recovery of the extracellular space was markedly impaired in aged animals.

Vimentin Phosphorylation Is Required for Normal Cell Division of Immature Astrocytes

Vimentin (VIM) is an intermediate filament (nanofilament) protein expressed in multiple cell types, including astrocytes. Mice with VIM mutations of serine sites phosphorylated during mitosis (VIM^SA/SA) show cytokinetic failure in fibroblasts and lens epithelial cells, chromosomal instability, facilitated cell senescence, and increased neuronal differentiation of neural progenitor cells. Here we report that in vitro immature VIM^SA/SA astrocytes exhibit cytokinetic failure and contain vimentin accumulations that co-localize with mitochondria. This phenotype is transient and disappears with VIM^SA/SA astrocyte maturation and expression of glial fibrillary acidic protein (GFAP); it is also alleviated by the inhibition of cell proliferation. To test the hypothesis that GFAP compensates for the effect of VIM^SA/SA in astrocytes, we crossed the VIM^SA/SA and GFAP^−/− mice. Surprisingly, the fraction of VIM^SA/SA immature astrocytes with abundant vimentin accumulations was reduced when on GFAP^−/− background. This indicates that the disappearance of vimentin accumulations and cytokinetic failure in mature astrocyte cultures are independent of GFAP expression. Both VIM^SA/SA and VIM^SA/SAGFAP^−/− astrocytes showed normal mitochondrial membrane potential and vulnerability to H₂O₂, oxygen/glucose deprivation, and chemical ischemia. Thus, mutation of mitotic phosphorylation sites in vimentin triggers formation of vimentin accumulations and cytokinetic failure in immature astrocytes without altering their vulnerability to oxidative stress.

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.

Nestin Regulates Neurogenesis in Mice Through Notch Signaling From Astrocytes to Neural Stem Cells

The intermediate filament (nanofilament) protein nestin is a marker of neural stem cells, but its role in neurogenesis, including adult neurogenesis, remains unclear. Here, we investigated the role of nestin in neurogenesis in adult nestin-deficient (Nes–/–) mice. We found that the proliferation of Nes–/– neural stem cells was not altered, but neurogenesis in the hippocampal dentate gyrus of Nes–/– mice was increased. Surprisingly, the proneurogenic effect of nestin deficiency was mediated by its function in the astrocyte niche. Through its role in Notch signaling from astrocytes to neural stem cells, nestin negatively regulates neuronal differentiation and survival; however, its expression in neural stem cells is not required for normal neurogenesis. In behavioral studies, nestin deficiency in mice did not affect associative learning but was associated with impaired long-term memory.

Vimentin on the move: new developments in cell migration

The vimentin gene ( VIM) encodes one of the 71 human intermediate filament (IF) proteins, which are the building blocks of highly ordered, dynamic, and cell type-specific fiber networks. Vimentin is a multi-functional 466 amino acid protein with a high degree of evolutionary conservation among vertebrates. Vim ^−/− mice, though viable, exhibit systemic defects related to development and wound repair, which may have implications for understanding human disease pathogenesis. Vimentin IFs are required for the plasticity of mesenchymal cells under normal physiological conditions and for the migration of cancer cells that have undergone epithelial–mesenchymal transition. Although it was observed years ago that vimentin promotes cell migration, the molecular mechanisms were not completely understood. Recent advances in microscopic techniques, combined with computational image analysis, have helped illuminate vimentin dynamics and function in migrating cells on a precise scale. This review includes a brief historical account of early studies that unveiled vimentin as a unique component of the cell cytoskeleton followed by an overview of the physiological vimentin functions documented in studies on Vim ^−/− mice. The primary focus of the discussion is on novel mechanisms related to how vimentin coordinates cell migration. The current hypothesis is that vimentin promotes cell migration by integrating mechanical input from the environment and modulating the dynamics of microtubules and the actomyosin network. These new findings undoubtedly will open up multiple avenues to study the broader function of vimentin and other IF proteins in cell biology and will lead to critical insights into the relevance of different vimentin levels for the invasive behaviors of metastatic cancer cells.

Spheroids Spontaneously Generated In Vitro from Sheep Ovarian Cortical Cells Contain Integrating Cells That Exhibit Hallmarks of Neural Stem/Progenitor Cells

Cell spheroids are inducible or spontaneously generated cell aggregates produced in vitro that can provide a valuable model for developmental biology, stem cell biology, and cancer therapy research. This investigation aimed to define the cellular identity of spheroids spontaneously generated in vitro from sheep ovarian cortical cells cultured under specific serum-free conditions. Spheroids were characterized during 21 days of culture by morphometric evaluation, detection of alkaline phosphatase (AP) activity, gene expression analyses of stemness transcription factors and several lineage markers, immunolocalization analyses, as well as assessment of self-renewal and differentiation potential. Cell aggregation, evidenced from day 3 of culture onward, resulted in efficient generation of 65-75 spheroids for every 500,000 cells seeded. The spheroids reached maximum diameter (187 ± 15.9 μm) during the second week of culture and exhibited AP activity. Sox2, Oct4, and Nanog were expressed throughout the culture period, with upregulation of Sox2. Neural lineage specification genes (eg, nestin, vimentin, Pax6, and p75NTR) were expressed from day 10 onward at levels above that of Oct4, Nanog and those for endoderm [alpha-fetoprotein (AFP)], and mesoderm (brachyury) specification. Neural stem cell (NSC)/neural progenitor cell (NPC) markers, nestin, Pax6, p75NTR, and vimentin, were extensively localized in cells on day 10, 15 (44.75% ± 5.84%; 93.54% ± 1.35%; 78.90% ± 4.80%; 73.82% ± 3.40%, respectively), and 21 (49.98% ± 5.30%; 91.84% ± 1.9%; 76.74% ± 11.0%; 95.80% ± 3.60%, respectively). Spheroid cell self-renewal was evidenced by cell proliferation and the generation of new spheroids during two consecutive expansion periods. Culture of spheroid cells under differentiation conditions gave rise to cells showing immunolocalization of the neuron-specific antigen NeuN and the astroglial antigen GFAP (glial fibrillary acidic protein). Our results indicate that spheroids spontaneously generated in this culture system were comprised of cells with molecular characteristics of NSC/NPC that can self-renew and differentiate into neurons and glia, supporting the identity of spheroids as neurospheres.

PDGFR-β-Positive Perivascular Adventitial Cells Expressing Nestin Contribute to Fibrotic Scar Formation in the Striatum of 3-NP Intoxicated Rats

Perivascular cells expressing platelet-derived growth factor receptor beta (PDGFR-β) have recently been implicated in fibrotic scar formation after acute brain injury, but their precise identity and detailed morphological characteristics remain elusive. This study sought to characterize and define the cellular phenotype of vascular-associated cells expressing PDGFR-β in the striatum of rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). In the control striatum, PDGFR-β-positive cells were invariably localized on the abluminal side of smooth muscle cells of larger caliber vessels, and demonstrated morphological features typical of perivascular fibroblasts. PDGFR-β expression increased and expanded to almost all vessels, including microvessels in the lesion core, at 7 days after 3-NP injection. The cells expressing PDGFR-β had ultrastructural features of fibroblasts undergoing active collagen synthesis: large euchromatic nuclei with a prominent nucleolus, well-developed rough endoplasmic reticulum (rER) with dilated cisterns and extracellular collagen fibrils. By 14 days, PDGFR-β-positive cells had somata located at a distance from the vasculature, and their highly ramified, slender processes overlapped with those from other cells, thus forming a plexus of processes in the extravascular space of the lesion core. In addition, their ultrastructural morphology and spatial correlation with activated microglia/macrophages were elaborated by three-dimensional reconstruction. Using a correlative light- and electron-microscopy technique, we found that the intermediate filament proteins nestin and vimentin were induced in PDGFRβ-positive fibroblasts in the lesion core. Collectively, our data suggest that perivascular PDGFR-β-positive fibroblasts are distinct from other vascular cell types, including pericytes and contribute to fibrotic scar formation in the lesion core after acute brain injury. Nestin and vimentin play critical roles in the structural dynamics of these reactive fibroblasts.

A systems-approach reveals human nestin is an endothelial-enriched, angiogenesis-independent intermediate filament protein

The intermediate filament protein nestin is expressed during embryonic development, but considered largely restricted to areas of regeneration in the adult. Here, we perform a body-wide transcriptome and protein-profiling analysis to reveal that nestin is constitutively, and highly-selectively, expressed in adult human endothelial cells (EC), independent of proliferative status. Correspondingly, we demonstrate that it is not a marker for tumour EC in multiple malignancy types. Imaging of EC from different vascular beds reveals nestin subcellular distribution is shear-modulated. siRNA inhibition of nestin increases EC proliferation, and nestin expression is reduced in atherosclerotic plaque neovessels. eQTL analysis reveals an association between SNPs linked to cardiovascular disease and reduced aortic EC nestin mRNA expression. Our study challenges the dogma that nestin is a marker of proliferation, and provides insight into its regulation and function in EC. Furthermore, our systems-based approach can be applied to investigate body-wide expression profiles of any candidate protein.

Astrocyte activation and reactive gliosis-A new target in stroke?

Stroke is an acute insult to the central nervous system (CNS) that triggers a sequence of responses in the acute, subacute as well as later stages, with prominent involvement of astrocytes. Astrocyte activation and reactive gliosis in the acute stage of stroke limit the tissue damage and contribute to the restoration of homeostasis. Astrocytes also control many aspects of neural plasticity that is the basis for functional recovery. Here, we discuss the concept of intermediate filaments (nanofilaments) and the complement system as two handles on the astrocyte responses to injury that both present attractive opportunities for novel treatment strategies modulating astrocyte functions and reactive gliosis.

Effect of autophagy on allodynia, hyperalgesia and astrocyte activation in a rat model of neuropathic pain

Primary damage or dysfunction of the nervous system may cause or initiate neuropathic pain. However, it has been difficult to establish an effective treatment for neuropathic pain, as the mechanisms responsible for its pathology remain largely unknown. Autophagy is closely associated with the pathological process of neurodegenerative diseases, neuropathic injury and cancer, among others. The aim of the present study was to examine the changes in the autophagy-lysosomal pathway and discuss the effects of autophagy on allodynia, hyperalgesia and astrocyte activation in neuropathic pain. A neuropathic pain model was induced by chronic constriction injury (CCI) in rats. Inducers and inhibitors of autophagy and lysosomes were used to assess autophagy, allodynia, hyperalgesia and astrocyte activity. Neuropathic pain was found to induce an increase in the levels of the autophagy-related proteins, LC3II and Beclin 1 and, and in those of the lysosomal proteins, lysosomal-associated membrane protein type 2 (LAMP2) and Ras-related protein Rab-7a (RAB7), whereas p62 levels were found to decrease from day 1 to 14 following CCI. The autophagy inducer, rapamycin, further increased the LC3II, Beclin 1, lysosomal-associated membrane protein 2 (LAMP2) and Ras-related protein Rab-7a (RAB7) expression levels, and decreased the p62 expression levels, which were accompanied by alleviation of allodynia, hyperalgesia and astrocyte activation in the rats subjected to CCI; the autophagy inhibitor, 3-methyladenine, reversed these effects. The use of the lysosomal inhibitors, bafilomycin and chloroquine, resulted in the accumulation of LC3II and Beclin 1, a decrease in the levels of LAMP2 and RAB7, and the exacerbation of allodynia, hyperalgesia and astrocyte activation in rats with neuropathic pain. On the whole, the findings of this study indicate that neuropathic pain activates autophagy, which alleviates mechanical and thermal hyperalgesia and suppresses astrocyte activity. Therefore, neuropathic pain induced by CCI in rats appears to be mediated via the autophagy-lysosomal pathway.

Expression of Oligodendrocyte Precursor Cell Markers in Canine Oligodendrogliomas

Oligodendroglioma is a common brain tumor in dogs, particularly brachycephalic breeds. Oligodendrocyte precursor cells (OPCs) are suspected to be a possible origin of oligodendroglioma, although it has not been well elucidated. In the present study, 27 cases of canine brain oligodendrogliomas were histologically and immunohistochemically examined. The most commonly affected breed was the French Bulldog ( n = 19 of 27, 70%). Seizure was the most predominant clinical sign ( n = 17 of 25, 68%). The tumors were located mainly in the cerebrum, particularly in the frontal lobe ( n = 10 of 27, 37%). All cases were diagnosed as anaplastic oligodendroglioma (AO) and had common histologic features characterized by the proliferation of round to polygonal cells with pronounced atypia and conspicuous mitotic activity (average, 10.7 mitoses per 10 high-power fields). Honeycomb pattern ( n = 5 of 27, 19%), myxoid matrix ( n = 10, 37%), cyst formation ( n = 6, 22%), necrosis ( n = 19, 70%), pseudopalisading ( n = 5, 18.5%), glomeruloid vessels ( n = 16, 59%), and microcalcification ( n = 5, 19%) were other histopathologic features of the present tumors. Immunohistochemically, the tumor cells were positive for Olig2 in all cases and for other markers of OPCs in most cases, including SOX10 ( n = 24 of 27, 89%), platelet-derived growth factor receptor α ( n = 24, 89%), and NG2 ( n = 23, 85%). The present AO also consisted of heterogeneous cell populations that were positive for nestin ( n = 13 of 27, 48%), glial fibrillary acidic protein ( n = 5, 19%), doublecortin ( n = 22, 82%), and βIII-tubulin ( n = 15, 56%). Moreover, cultured AO cells obtained from 1 case retained expression of OPC markers and exhibited multipotent characteristics in a serum culture condition. Overall, the findings suggest that transformed multipotent OPCs may be a potential origin of canine AO.