Extracellular matrix composition determines astrocyte responses to mechanical and inflammatory stimuli

A molecular brain atlas reveals cellular shifts during the repair phase of stroke

Ischemic stroke triggers a cascade of pathological events that affect multiple cell types and often lead to incomplete functional recovery. Despite advances in single-cell technologies, the molecular and cellular responses that contribute to long-term post-stroke impairment remain poorly understood. To gain better insight into the underlying mechanisms, we generated a single-cell transcriptomic atlas from distinct brain regions using a mouse model of permanent focal ischemia at one month post-injury. Our findings reveal cell- and region-specific changes within the stroke-injured and peri-infarct brain tissue. For instance, GABAergic and glutamatergic neurons exhibited upregulated genes in signaling pathways involved in axon guidance and synaptic plasticity, and downregulated pathways associated with aerobic metabolism. Using cell-cell communication analysis, we identified increased strength in predicted interactions within stroke tissue among both neural and non-neural cells via signaling pathways such as those involving collagen, protein tyrosine phosphatase receptor, neuronal growth regulator, laminin, and several cell adhesion molecules. Furthermore, we found a strong correlation between mouse transcriptome responses after stroke and those observed in human nonfatal brain stroke lesions. Common molecular features were linked to inflammatory responses, extracellular matrix organization, and angiogenesis. Our findings provide a detailed resource for advancing our molecular understanding of stroke pathology and for discovering therapeutic targets in the repair phase of stroke recovery.

Heterogeneity of brain extracellular matrix and astrocyte activation

From the blood brain barrier to the synaptic space, astrocytes provide structural, metabolic, ionic, and extracellular matrix (ECM) support across the brain. Astrocytes include a vast array of subtypes, their phenotypes and functions varying both regionally and temporally. Astrocytes' metabolic and regulatory functions poise them to be quick and sensitive responders to injury and disease in the brain as revealed by single cell sequencing. Far less is known about the influence of the local healthy and aging microenvironments on these astrocyte activation states. In this forward-looking review, we describe the known relationship between astrocytes and their local microenvironment, the remodeling of the microenvironment during disease and injury, and postulate how they may drive astrocyte activation. We suggest technology development to better understand the dynamic diversity of astrocyte activation states, and how basal and activation states depend on the ECM microenvironment. A deeper understanding of astrocyte response to stimuli in ECM-specific contexts (brain region, age, and sex of individual), paves the way to revolutionize how the field considers astrocyte-ECM interactions in brain injury and disease and opens routes to return astrocytes to a healthy quiescent state.

ADAR1 suppression causes interferon signaling and transposable element transcript accumulation in human astrocytes

Neuroinflammation is a central mechanism of brain aging and Alzheimer's disease (AD), but the exact causes of age- and AD-related neuroinflammation are incompletely understood. One potential modulator of neuroinflammation is the enzyme adenosine deaminase acting on RNA 1 (ADAR1), which regulates the accumulation of endogenous double-stranded RNA (dsRNA), a pro-inflammatory/innate immune activator. However, the role of ADAR1 and its transcriptomic targets in astrocytes, key mediators of neuroinflammation, have not been comprehensively investigated. Here, we knock down ADAR1 in primary human astrocytes via siRNA transfection and use transcriptomics (RNA-seq) to show that this results in: (1) increased expression of type I interferon and pro-inflammatory signaling pathways and (2) an accumulation of transposable element (TE) transcripts with the potential to form dsRNA. We also show that our findings may be clinically relevant, as ADAR1 gene expression declines with brain aging and AD in humans, and this is associated with a similar increase in TE transcripts. Together, our results suggest an important role for ADAR1 in preventing pro-inflammatory activation of astrocytes in response to endogenous dsRNA with aging and AD.

Interactions between astrocytes and extracellular matrix structures contribute to neuroinflammation-associated epilepsy pathology

Often considered the "housekeeping" cells of the brain, astrocytes have of late been rising to the forefront of neurodegenerative disorder research. Identified as crucial components of a healthy brain, it is undeniable that when astrocytes are dysfunctional, the entire brain is thrown into disarray. We offer epilepsy as a well-studied neurological disorder in which there is clear evidence of astrocyte contribution to diseases as evidenced across several different disease models, including mouse models of hippocampal sclerosis, trauma associated epilepsy, glioma-associated epilepsy, and beta-1 integrin knockout astrogliosis. In this review we suggest that astrocyte-driven neuroinflammation, which plays a large role in the pathology of epilepsy, is at least partially modulated by interactions with perineuronal nets (PNNs), highly structured formations of the extracellular matrix (ECM). These matrix structures affect synaptic placement, but also intrinsic neuronal properties such as membrane capacitance, as well as ion buffering in their immediate milieu all of which alters neuronal excitability. We propose that the interactions between PNNs and astrocytes contribute to the disease progression of epilepsy vis a vis neuroinflammation. Further investigation and alteration of these interactions to reduce the resultant neuroinflammation may serve as a potential therapeutic target that provides an alternative to the standard anti-seizure medications from which patients are so frequently unable to benefit.

Astrocyte-associated fibronectin promotes the proinflammatory phenotype of astrocytes through β1 integrin activation

Astrocytes are key players in neuroinflammation. In response to central nervous system (CNS) injury or disease, astrocytes undergo reactive astrogliosis, which is characterized by increased proliferation, migration, and glial fibrillary acidic protein (GFAP) expression. Activation of the transcription factor nuclear factor-κB (NF-κB) and upregulation of downstream proinflammatory mediators in reactive astrocytes induce a proinflammatory phenotype in astrocytes, thereby exacerbating neuroinflammation by establishing an inflammatory loop. In this study, we hypothesized that excessive fibronectin (FN) derived from reactive astrocytes would induce this proinflammatory phenotype in astrocytes in an autocrine manner. We exogenously treated astrocytes with monomer FN, which can be incorporated into the extracellular matrix (ECM), to mimic plasma FN extravasated through a compromised blood-brain barrier in neuroinflammation. We also induced de novo synthesis and accumulation of astrocyte-derived FN through tumor necrosis factor-α (TNF-α) stimulation. The excessive FN deposition resulting from both treatments initiated reactive astrogliosis and triggered NF-κB signaling in the cultured astrocytes. In addition, inhibition of FN accumulation in the ECM by the FN inhibitor pUR4 strongly attenuated the FN- and TNF-α-induced GFAP expression, NF-κB activation, and proinflammatory mediator production of astrocytes by interrupting FN-β1 integrin coupling and thus the inflammatory loop. In an in vivo experiment, intrathecal injection of pUR4 considerably ameliorated FN deposition, GFAP expression, and NF-κB activation in inflamed spinal cord, suggesting the therapeutic potential of pUR4 for attenuating neuroinflammation and promoting neuronal function restoration.

Astrocyte 3D culture and bioprinting using peptide functionalized hyaluronan hydrogels

Astrocytes play an important role in the central nervous system, contributing to the development of and maintenance of synapses, recycling of neurotransmitters, and the integrity and function of the blood-brain barrier. Astrocytes are also linked to the pathophysiology of various neurodegenerative diseases. Astrocyte function and organization are tightly regulated by interactions mediated by the extracellular matrix (ECM). Engineered hydrogels can mimic key aspects of the ECM and can allow for systematic studies of ECM-related factors that govern astrocyte behaviour. In this study, we explore the interactions between neuroblastoma (SH-SY5Y) and glioblastoma (U87) cell lines and human fetal primary astrocytes (FPA) with a modular hyaluronan-based hydrogel system. Morphological analysis reveals that FPA have a higher degree of interactions with the hyaluronan-based gels compared to the cell lines. This interaction is enhanced by conjugation of cell-adhesion peptides (cRGD and IKVAV) to the hyaluronan backbone. These effects are retained and pronounced in 3D bioprinted structures. Bioprinted FPA using cRGD functionalized hyaluronan show extensive and defined protrusions and multiple connections between neighboring cells. Possibilities to tailor and optimize astrocyte-compatible ECM-mimicking hydrogels that can be processed by means of additive biofabrication can facilitate the development of advanced tissue and disease models of the central nervous system.

Distribution and inflammatory cell response to intracranial delivery of radioluminescent Y2(SiO4)O:Ce particles

Due to increasing advances in their manufacture and functionalization, nanoparticle-based systems have become a popular tool for in vivo drug delivery and biodetection. Recently, scintillating nanoparticles such as yttrium orthosilicate doped with cerium (Y2(SiO4)O:Ce) have come under study for their potential utility in optogenetic applications, as they emit photons upon low levels of stimulation from remote x-ray sources. The utility of such nanoparticles in vivo is hampered by rapid clearance from circulation by the mononuclear phagocytic system, which heavily restricts nanoparticle accumulation at target tissues. Local transcranial injection of nanoparticles may deliver scintillating nanoparticles to highly specific brain regions by circumventing the blood-brain barrier and avoiding phagocytic clearance. Few studies to date have examined the distribution and response to nanoparticles following localized delivery to cerebral cortex, a crucial step in understanding the therapeutic potential of nanoparticle-based biodetection in the brain. Following the synthesis and surface modification of these nanoparticles, two doses (1 and 3 mg/ml) were introduced into mouse secondary motor cortex (M2). This region was chosen as the site for RLP delivery, as it represents a common target for optogenetic manipulations of mouse behavior, and RLPs could eventually serve as an injectable x-ray inducible light delivery system. The spread of particles through the target tissue was assessed 24 hours, 72 hours, and 9 days post-injection. Y2(SiO4)O:Ce nanoparticles were found to be detectable in the brain for up to 9 days, initially diffusing through the tissue until 72 hours before achieving partial clearance by the final endpoint. Small transient increases in the presence of IBA-1+ microglia and GFAP+ astrocytic cell populations were detected near nanoparticle injection sites of both doses tested 24 hours after surgery. Taken together, these data provide evidence that Y2(SiO4)O:Ce nanoparticles coated with BSA can be injected directly into mouse cortex in vivo, where they persist for days and are broadly tolerated, such that they may be potentially utilized for remote x-ray activated stimulation and photon emission for optogenetic experiments in the near future.

Role of Vitronectin and Its Receptors in Neuronal Function and Neurodegenerative Diseases

Vitronectin (VTN), a multifunctional glycoprotein with various physiological functions, exists in plasma and the extracellular matrix. It is known to be involved in the cell attachment, spreading and migration through binding to the integrin receptor, mainly via the RGD sequence. VTN is also widely used in the maintenance and expansion of pluripotent stem cells, but its effects go beyond that. Recent evidence shows more functions of VTN in the nervous system as it participates in neural differentiation, neuronutrition and neurogenesis, as well as in regulating axon size, supporting and guiding neurite extension. Furthermore, VTN was proved to play a key role in protecting the brain as it can reduce the permeability of the blood-brain barrier by interacting with integrin receptors in vascular endothelial cells. Moreover, evidence suggests that VTN is associated with neurodegenerative diseases, such as Alzheimer's disease, but its function has not been fully understood. This review summarizes the functions of VTN and its receptors in neurons and describes the role of VTN in the blood-brain barrier and neurodegenerative diseases.

Organ-On-A-Chip Models of the Blood-Brain Barrier: Recent Advances and Future Prospects

The human brain and central nervous system (CNS) present unique challenges in drug development for neurological diseases. One major obstacle is the blood-brain barrier (BBB), which hampers the effective delivery of therapeutic molecules into the brain while protecting it from blood-born neurotoxic substances and maintaining CNS homeostasis. For BBB research, traditional in vitro models rely upon Petri dishes or Transwell systems. However, these static models lack essential microenvironmental factors such as shear stress and proper cell-cell interactions. To this end, organ-on-a-chip (OoC) technology has emerged as a new in vitro modeling approach to better recapitulate the highly dynamic in vivo human brain microenvironment so-called the neural vascular unit (NVU). Such BBB-on-a-chip models have made substantial progress over the last decade, and concurrently there has been increasing interest in modeling various neurological diseases such as Alzheimer's disease and Parkinson's disease using OoC technology. In addition, with recent advances in other scientific technologies, several new opportunities to improve the BBB-on-a-chip platform via multidisciplinary approaches are available. In this review, an overview of the NVU and OoC technology is provided, recent progress and applications of BBB-on-a-chip for personalized medicine and drug discovery are discussed, and current challenges and future directions are delineated.

3D Bioprinted Neural-Like Tissue as a Platform to Study Neurotropism of Mouse-Adapted SARS-CoV-2

The effects of neuroinvasion by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) become clinically relevant due to the numerous neurological symptoms observed in Corona Virus Disease 2019 (COVID-19) patients during infection and post-COVID syndrome or long COVID. This study reports the biofabrication of a 3D bioprinted neural-like tissue as a proof-of-concept platform for a more representative study of SARS-CoV-2 brain infection. Bioink is optimized regarding its biophysical properties and is mixed with murine neural cells to construct a 3D model of COVID-19 infection. Aiming to increase the specificity to murine cells, SARS-CoV-2 is mouse-adapted (MA-SARS-CoV-2) in vitro, in a protocol first reported here. MA-SARS-CoV-2 reveals mutations located at the Orf1a and Orf3a domains and is evolutionarily closer to the original Wuhan SARS-CoV-2 strain than SARS-CoV-2 used for adaptation. Remarkably, MA-SARS-CoV-2 shows high specificity to murine cells, which present distinct responses when cultured in 2D and 3D systems, regarding cell morphology, neuroinflammation, and virus titration. MA-SARS-CoV-2 represents a valuable tool in studies using animal models, and the 3D neural-like tissue serves as a powerful in vitro platform for modeling brain infection, contributing to the development of antivirals and new treatments for COVID-19.

Longevity-Promoting Pathways and Transcription Factors Respond to and Control Extracellular Matrix Dynamics During Aging and Disease

Aging is one of the largest risk factors for cancer, type 2 diabetes, osteoarthritis, cardiovascular diseases, and other age-related pathologies. Here, we give a detailed description of the interplay of chronic age-related pathologies with the remodeling of the extracellular matrix during disease development and progression. Longevity-promoting signaling pathways slow or prevent age-related diseases. In particular, we focus on the mTOR signaling pathway, sirtuins, and canonical longevity-promoting transcription factors, such as FOXO, NF-κB, and Nrf2. We extend our analysis using chromatin immunoprecipitation (ChIP) sequencing and transcriptomic data and report that many established and emerging longevity-promoting transcription factors, such as CREB1, FOXO1,3, GATA1,2,3,4, HIF1A, JUN, KLF4, MYC, NFE2L2/Nrf2, RELA/NF-κB, REST, STAT3,5A, and TP53/p53, directly regulate many extracellular matrix genes and remodelers. We propose that modulation of these pathways increases lifespan and protects from age-related diseases in part due to their effects on extracellular matrix remodeling. Therefore, to successfully treat age-related diseases, it is necessary to better understand the connection between extracellular matrix components and longevity pathways.

High-Throughput Analysis of Astrocyte Cultures Shows Prevention of Reactive Astrogliosis by the Multi-Nutrient Combination Fortasyn Connect

Astrocytes are specialized glial cells that tile the central nervous system (CNS) and perform numerous essential functions. Astrocytes react to various forms of CNS insults by altering their morphology and molecular profile, through a process known as reactive astrogliosis. Accordingly, astrocyte reactivity is apparent in many neurodegenerative diseases, among which one is Alzheimer’s disease (AD). Recent clinical trials on early-stage AD have demonstrated that Fortasyn Connect (FC), a multi-nutrient combination providing specific precursors and cofactors for phospholipid synthesis, helps to maintain neuronal functional connectivity and cognitive performance of patients. Several studies have shown that FC may act through its effects on neuronal survival and synaptogenesis, leading to reduced astrocyte reactivity, but whether FC can directly counteract astrocyte reactivity remains to be elucidated. Hence, we developed an in vitro model of reactive astrogliosis using the pro-inflammatory cytokines TNF-α and IFN-γ together with an automated high-throughput assay (AstroScan) to quantify molecular and morphological changes that accompany reactive astrogliosis. Next, we showed that FC is potent in preventing cytokine-induced reactive astrogliosis, a finding that might be of high relevance to understand the beneficial effects of FC-based interventions in the context of neurodegenerative diseases.

Brain Cancer Cell-Derived Matrices and Effects on Astrocyte Migration

Cell-derived matrices are useful tools for studying the extracellular matrix (ECM) of different cell types and testing the effects on cell migration or wound repair. These matrices typically are generated using extended culture with ascorbic acid to boost ECM production. Applying this technique to cancer cell cultures could advance the study of cancer ECM and its effects on recruitment and training of the tumor microenvironment, but ascorbic acid is potently cytotoxic to cancer cells. Macromolecular crowding (MMC) agents can also be added to increase matrix deposition based on the excluded volume principle. We report the use of MMC alone as an effective strategy to generate brain cancer cell-derived matrices for downstream analyses and cell migration studies. We cultured the mouse glioblastoma cell line GL261 for 1 week in the presence of three previously reported MMC agents (carrageenan, Ficoll 70/400, and hyaluronic acid). We measured the resulting deposition of collagens and sulfated glycosaminoglycans using quantitative assays, as well as other matrix components by immunostaining. Both carrageenan and Ficoll promoted significantly more accumulation of total collagen content, sulfated glycosaminoglycan content, and fibronectin staining. Only Ficoll, however, also demonstrated a significant increase in collagen I staining. The results were more variable in 3D spheroid culture. We focused on Ficoll MMC matrices, which were isolated using the small molecule Raptinal to induce cancer cell apoptosis and matrix decellularization. The cancer cell-derived matrix promoted significantly faster migration of human astrocytes in a scratch wound assay, which may be explained by focal adhesion morphology and an increase in cellular metabolic activity. Ultimately, these data show MMC culture is a useful technique to generate cancer cell-derived matrices and study the effects on stromal cell migration related to wound repair.

Astrocytic processes: from tripartite synapses to the active milieu

We define a new concept of 'active milieu' that unifies all components of nervous tissue (neuronal and glial compartments, extracellular space, extracellular matrix, and vasculature) into a dynamic information processing system. Within this framework, we focus on the role of astrocytic processes, classified into organelle-containing branches and organelle-free leaflets. We argue that astrocytic branches with emanating leaflets are homologous to dendritic shafts with spines. Within the active milieu, astrocytic processes are engaged in reciprocal interactions with neuronal compartments and communication with other cellular and non-cellular elements of the nervous tissue.

Modulation of Glial Function in Health, Aging, and Neurodegenerative Disease

In the central nervous system (CNS), glial cells, such as microglia and astrocytes, are normally associated with support roles including contributions to energy metabolism, synaptic plasticity, and ion homeostasis. In addition to providing support for neurons, microglia and astrocytes function as the resident immune cells in the brain. The glial function is impacted by multiple aspects including aging and local CNS changes caused by neurodegeneration. During aging, microglia and astrocytes display alterations in their homeostatic functions. For example, aged microglia and astrocytes exhibit impairments in the lysosome and mitochondrial function as well as in their regulation of synaptic plasticity. Recent evidence suggests that glia can also alter the pathology associated with many neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's disease (PD). Shifts in the microbiome can impact glial function as well. Disruptions in the microbiome can lead to aberrant microglial and astrocytic reactivity, which can contribute to an exacerbation of disease and neuronal dysfunction. In this review, we will discuss the normal physiological functions of microglia and astrocytes, summarize novel findings highlighting the role of glia in aging and neurodegenerative diseases, and examine the contribution of microglia and astrocytes to disease progression.

Extracellular matrix influences astrocytic extracellular vesicle function in wound repair

Astrocytic injury responses are known to be influenced by the extracellular matrix (ECM). Astrocytes are also recognized as a source of extracellular vesicles (EVs) that can impact the activity and function of other astrocytes and cell types. Whether the ECM influences the function of astrocytic EVs in the context of wound recovery has not been previously studied. We report EVs from astrocytes cultured on varied ECM substrates are sufficient to elicit distinct injury responses in naive astrocytes that recapitulate the effects of the ECM of origin. When compared with wound recovery on control substrates, EVs from ECM-exposed astrocytes elicited accelerated rates of wound recovery that varied based on each ECM. When EVs were collected from IL-1β treated and ECM-exposed astrocyte cultures, we found that IL-1β arrested wound recovery in naive astrocytes treated with EVs from astrocytes cultured on ECM but adding EVs from IL-1β treated Tenascin-c-cultured astrocytes increased wound recovery. To confirm that ECM was a primary influence on these astrocytic EV functions, we tested the contribution of β1-integrin, a major integrin receptor for the ECM molecules tested in this study. We found that the β1-integrin inhibitor Ha2/5, resulted in EVs that significantly attenuated the wound recovery of naive astrocytes. This provides new information on the importance of culture substrates on astrocytic responses, EV functions and injury responses that may impact the understanding of astroglial responses related to ECM compositional differences in diverse physiological states.

Alpha-pinene and dizocilpine (MK-801) attenuate kindling development and astrocytosis in an experimental mouse model of epilepsy

Understanding the molecular and cellular mechanisms involved during the onset of epilepsy is crucial for elucidating the overall mechanism of epileptogenesis and therapeutic strategies. Previous studies, using a pentylenetetrazole (PTZ)-induced kindling mouse model, showed that astrocyte activation and an increase in perineuronal nets (PNNs) and extracellular matrix (ECM) molecules occurred within the hippocampus. However, the mechanisms of initiation and suppression of these changes, remain unclear. Herein, we analyzed the attenuation of astrocyte activation caused by dizocilpine (MK-801) administration, as well as the anticonvulsant effect of α-pinene on seizures and production of ECM molecules. Our results showed that MK-801 significantly reduced kindling acquisition, while α-pinene treatment prevented an increase in seizures incidences. Both MK-801 and α-pinene administration attenuated astrocyte activation by PTZ and significantly attenuated the increase in ECM molecules. Our results indicate that astrocyte activation and an increase in ECM may contribute to epileptogenesis and suggest that MK-801 and α-pinene may prevent epileptic seizures by suppressing astrocyte activation and ECM molecule production.

Modeling the effects of hyaluronic acid degradation on the regulation of human astrocyte phenotype using multicomponent interpenetrating polymer networks (mIPNs)

Hyaluronic acid (HA) is a highly abundant component in the extracellular matrix (ECM) and a fundamental element to the architecture and the physiology of the central nervous system (CNS). Often, HA degradation occurs when an overreactive inflammatory response, derived from tissue trauma or neurodegenerative diseases such as Alzheimer's, causes the ECM in the CNS to be remodeled. Herein, we studied the effects of HA content as a key regulator of human astrocyte (HAf) reactivity using multicomponent interpenetrating polymer networks (mIPNs) comprised of Collagen I, HA and poly(ethylene glycol) diacrylate. The selected platform facilities the modulation of HA levels independently of matrix rigidity. Total astrocytic processes length, number of endpoints, the expression of the quiescent markers: Aldehyde Dehydrogenase 1 Family Member L1 (ALDH1L1) and Glutamate Aspartate Transporter (GLAST); the reactive markers: Glial Fibrillary Acidic Protein (GFAP) and S100 Calcium-Binding Protein β (S100β); and the inflammatory markers: Inducible Nitric Oxide Synthase (iNOS), Interleukin 1β (IL-1β) and Tumor Necrosis Factor Alpha (TNFα), were assessed. Cumulatively, our results demonstrated that the decrease in HA concentration elicited a reduction in the total length of astrocytic processes and an increase in the expression of HAf reactive and inflammatory markers.

Parp3 promotes astrocytic differentiation through a tight regulation of Nox4-induced ROS and mTorc2 activation

Parp3 is a member of the Poly(ADP-ribose) polymerase (Parp) family that has been characterized for its functions in strand break repair, chromosomal rearrangements, mitotic segregation and tumor aggressiveness. Yet its physiological implications remain unknown. Here we report a central function of Parp3 in the regulation of redox homeostasis in continuous neurogenesis in mice. We show that the absence of Parp3 provokes Nox4-induced oxidative stress and defective mTorc2 activation leading to inefficient differentiation of post-natal neural stem/progenitor cells to astrocytes. The accumulation of ROS contributes to the decreased activity of mTorc2 as a result of an oxidation-induced and Fbxw7-mediated ubiquitination and degradation of Rictor. In vivo, mTorc2 signaling is compromised in the striatum of naïve post-natal Parp3-deficient mice and 6 h after acute hypoxia-ischemia. These findings reveal a physiological function of Parp3 in the tight regulation of striatal oxidative stress and mTorc2 during astrocytic differentiation and in the acute phase of hypoxia-ischemia.

Loss of the Extracellular Matrix Molecule Tenascin-C Leads to Absence of Reactive Gliosis and Promotes Anti-inflammatory Cytokine Expression in an Autoimmune Glaucoma Mouse Model

Previous studies demonstrated that retinal damage correlates with a massive remodeling of extracellular matrix (ECM) molecules and reactive gliosis. However, the functional significance of the ECM in retinal neurodegeneration is still unknown. In the present study, we used an intraocular pressure (IOP) independent experimental autoimmune glaucoma (EAG) mouse model to examine the role of the ECM glycoprotein tenascin-C (Tnc). Wild type (WT ONA) and Tnc knockout (KO ONA) mice were immunized with an optic nerve antigen (ONA) homogenate and control groups (CO) obtained sodium chloride (WT CO, KO CO). IOP was measured weekly and electroretinographies were recorded at the end of the study. Ten weeks after immunization, we analyzed retinal ganglion cells (RGCs), glial cells, and the expression of different cytokines in retina and optic nerve tissue in all four groups. IOP and retinal function were comparable in all groups. Although RGC loss was less severe in KO ONA, WT as well as KO mice displayed a significant cell loss after immunization. Compared to KO ONA, less βIII-tubulin+ axons, and downregulated oligodendrocyte markers were noted in WT ONA optic nerves. In retina and optic nerve, we found an enhanced GFAP+ staining area of astrocytes in immunized WT. A significantly higher number of retinal Iba1+ microglia was found in WT ONA, while a lower number of Iba1+ cells was observed in KO ONA. Furthermore, an increased expression of the glial markers Gfap, Iba1, Nos2, and Cd68 was detected in retinal and optic nerve tissue of WT ONA, whereas comparable levels were observed in KO ONA. In addition, pro-inflammatory Tnfa expression was upregulated in WT ONA, but downregulated in KO ONA. Vice versa, a significantly increased anti-inflammatory Tgfb1 expression was measured in KO ONA animals. We conclude that Tnc plays an important role in glial and inflammatory response during retinal neurodegeneration. Our results provide evidence that Tnc is involved in glaucomatous damage by regulating retinal glial activation and cytokine release. Thus, this transgenic EAG mouse model for the first time offers the possibility to investigate IOP-independent glaucomatous damage in direct relation to ECM remodeling.

Pentylenetetrazol kindling induces cortical astrocytosis and increased expression of extracellular matrix molecules in mice

Although epilepsy is one of the most common chronic neurological disorders with a prevalence of approximately 1.0 %, the underlying pathophysiology remains to be elucidated. Understanding the molecular and cellular mechanisms involved in the development of epilepsy is important for the development of appropriate therapeutic strategy. In this study, we investigated the effects of status epilepticus on astrocytes, microglia, and extracellular matrix (ECM) molecules in the somatosensory cortex and piriform cortex of mice. Activation of astrocytes was observed in many cortices except the retrosplenial granular cortex after pentylenetetrazol (PTZ)-induced kindling in mice. Activated astrocytes in the cortex were found in layers 1-3 but not in layers 4-6. In the somatosensory and piriform cortices, no change was observed in the number of parvalbumin (PV)-positive neurons and PV-positive neurons covered with perineuronal nets. However, the amount of ECM in the extracellular space increased. The expression of VGLUT1- and GAD67-positive synapses also increased. Thus, in the PTZ-kindling epilepsy mice model, an increase in the number of ECM molecules and activation of astrocytes were observed in the somatosensory cortex and piriform cortex. These results indicate that PTZ-induced seizures affect not only the hippocampus but also other cortical areas. Our study findings may help to develop new therapeutic approaches to prevent seizures or their sequelae.

Molecular changes in glaucomatous trabecular meshwork. Correlations with retinal ganglion cell death and novel strategies for neuroprotection

Glaucoma is a chronic neurodegenerative disease characterized by retinal ganglion cell loss. Although significant advances in ophthalmologic knowledge and practice have been made, some glaucoma mechanisms are not yet understood, therefore, up to now there is no effective treatment able to ensure healing. Indeed, either pharmacological or surgical approaches to this disease aim in lowering intraocular pressure, which is considered the only modifiable risk factor. However, it is well known that several factors and metabolites are equally (if not more) involved in glaucoma. Oxidative stress, for instance, plays a pivotal role in both glaucoma onset and progression because it is responsible for the trabecular meshwork cell damage and, consequently, for intraocular pressure increase as well as for glaucomatous damage cascade. This review at first shows accurately the molecular-derived dysfunctions in antioxidant system and in mitochondria homeostasis which due to both oxidative stress and aging, lead to a chronic inflammation state, the trabecular meshwork damage as well as the glaucoma neurodegeneration. Therefore, the main molecular events triggered by oxidative stress up to the proapoptotic signals that promote the ganglion cell death have been highlighted. The second part of this review, instead, describes some of neuroprotective agents such as polyphenols or polyunsaturated fatty acids as possible therapeutic source against the propagation of glaucomatous damage.

Immunomodulatory role of the extracellular matrix protein tenascin-C in neuroinflammation

The extracellular matrix (ECM) consists of a dynamic network of various macromolecules that are synthesized and released by surrounding cells into the intercellular space. Glycoproteins, proteoglycans and fibrillar proteins are main components of the ECM. In addition to general functions such as structure and stability, the ECM controls several cellular signaling pathways. In this context, ECM molecules have a profound influence on intracellular signaling as receptor-, adhesion- and adaptor-proteins. Due to its various functions, the ECM is essential in the healthy organism, but also under pathological conditions. ECM constituents are part of the glial scar, which is formed in several neurodegenerative diseases that are accompanied by the activation and infiltration of glia as well as immune cells. Remodeling of the ECM modulates the release of pro- and anti-inflammatory cytokines affecting the fate of immune, glial and neuronal cells. Tenascin-C is an ECM glycoprotein that is expressed during embryonic central nervous system (CNS) development. In adults it is present at lower levels but reappears under pathological conditions such as in brain tumors, following injury and in neurodegenerative disorders and is highly associated with glial reactivity as well as scar formation. As a key modulator of the immune response during neurodegeneration in the CNS, tenascin-C is highlighted in this mini-review.

Control of Astrocyte Quiescence and Activation in a Synthetic Brain Hydrogel

Bioengineers have designed numerous instructive brain extracellular matrix (ECM) environments with tailored and tunable protein compositions and biomechanical properties in vitro to study astrocyte reactivity during trauma and inflammation. However, a major limitation of both protein-based and synthetic model microenvironments is that astrocytes within fail to retain their characteristic stellate morphology and quiescent state without becoming activated under "normal" culture conditions. Here, a synthetic hydrogel is introduced, which for the first time demonstrates maintenance of astrocyte quiescence and activation on demand. With this synthetic brain hydrogel, the brain-specific integrin-binding and matrix metalloprotease-degradable domains of proteins are shown to control astrocyte star-shaped morphologies, and an ECM condition that maintains astrocyte quiescence with minimal activation can be achieved. In addition, activation can be induced in a dose-dependent manner via both defined cytokine cocktails and low molecular weight hyaluronic acid. This synthetic brain hydrogel is envisioned as a new tool to study the physiological role of astrocytes in health and disease.

Alteration of Extracellular Matrix Molecules and Perineuronal Nets in the Hippocampus of Pentylenetetrazol-Kindled Mice

The pathophysiological processes leading to epilepsy are poorly understood. Understanding the molecular and cellular mechanisms involved in the onset of epilepsy is crucial for drug development. Epileptogenicity is thought to be associated with changes in synaptic plasticity; however, whether extracellular matrix molecules—known regulators of synaptic plasticity—are altered during epileptogenesis is unknown. To test this, we used a pentylenetetrazole- (PTZ-) kindling model mouse to investigate changes to hippocampal parvalbumin- (PV-) positive neurons, extracellular matrix molecules, and perineuronal nets (PNNs) after the last kindled seizure. We found an increase in Wisteria floribunda agglutinin- (WFA-) and Cat-315-positive PNNs and a decrease in PV-positive neurons not surrounded by PNNs, in the hippocampus of PTZ-kindled mice compared to control mice. Furthermore, the expression of WFA- and Cat-315-positive molecules increased in the extracellular space of PTZ-kindled mice. In addition, consistent with previous studies, astrocytes were activated in PTZ-kindled mice. We propose that the increase in PNNs after kindling decreases neuroplasticity in the hippocampus and helps maintain the neural circuit for recurrent seizures. This study shows that possibility of changes in extracellular matrix molecules due to astrocyte activation is associated with epilepticus in PTZ-kindled mice.

Loss of Endothelial Laminin α5 Exacerbates Hemorrhagic Brain Injury

Endothelial cells make laminin-411 and laminin-511. Although laminin-411 is well studied, the role of laminin-511 remains largely unknown due to the embryonic lethality of lama5-/- mutants. In this study, we generated endothelium-specific lama5 conditional knockout (α5-TKO) mice and investigated the biological functions of endothelial lama5 in blood-brain barrier (BBB) maintenance under homeostatic conditions and the pathogenesis of intracerebral hemorrhage (ICH). First, the BBB integrity of α5-TKO mice was measured under homeostatic conditions. Next, ICH was induced in α5-TKO mice and their littermate controls using the collagenase model. Various parameters, including injury volume, neuronal death, neurological score, brain edema, BBB integrity, inflammatory cell infiltration, and gliosis, were examined at various time points after injury. Under homeostatic conditions, comparable levels of IgG or exogenous tracers were detected in α5-TKO and control mice. Additionally, no differences in tight junction expression, pericyte coverage, and astrocyte polarity were found in these mice. After ICH, α5-TKO mice displayed enlarged injury volume, increased neuronal death, elevated BBB permeability, exacerbated infiltration of inflammatory cells (leukocytes, neutrophils, and mononuclear cells), aggravated gliosis, unchanged brain edema, and worse neurological function, compared to the controls. These findings suggest that endothelial lama5 is dispensable for BBB maintenance under homeostatic conditions but plays a beneficial role in ICH.

Astrocyte culture models: Molecular and function characterization of primary culture, immortalized astrocytes and C6 glioma cells

The understanding of the physiology of astrocytes and their role in brain function progresses continuously. Primary astrocyte culture is an alternative method to study these cells in an isolated system: in their physiologic and pathologic states. Cell lines are often used as an astrocyte model, since they are easier and faster to manipulate and cost less. However, there are a few studies evaluating the different features of these cells which may put into question the validity of using them as astrocyte models. The aim of this study was to compare primary cultures (PC) with two cell lines - immortalized astrocytes and C6 cells, in terms of protein characterization, morphology and metabolic functional activity. Our results showed, under the same culture condition, that immortalized astrocytes and C6 are positive for differentiated astrocytic markers (eg. GFAP, S100B, AQP4 and ALDH1L1), although expressing them in less quantities then primary astrocyte cultures. Glutamate metabolism and cell communication are reduced in proliferative cells. However, glucose uptake is elevated in C6 lineage cells in comparison with primary astrocytes, probably due to their tumorigenic origin and high proliferation rate. Immortalized astrocytes presented a lower growth rate than C6 cells, and a similar basal morphology as primary astrocytes. However, they did not prove to be as good reproductive models of some of the classic astrocytic functions, such as S100B secretion and GFAP content, especially while under stimulation. In contrast, C6 cells presented similar results in comparison to primary astrocytes in response to stimuli. Here we provide a functional comparison of three astrocytic models, in an attempt to select the most suitable model for the study of astrocytes, optimizing the research in this area of knowledge.

Sijunzi decoction may decrease apoptosis via stabilization of the extracellular matrix following cerebral ischaemia-reperfusion in rats

Neurons undergo degeneration, apoptosis and death due to ischaemic stroke. The present study investigated the effect of Sijunzi decoction (SJZD), a type of traditional Chinese medicine known as invigorating spleen therapy, on anoikis (a type of apoptosis) in rat brains following cerebral ischaemia-reperfusion. Rats were randomly divided into sham, model, nimodipine and SJZD low/medium/high dose groups. A middle cerebral artery occlusion model was established. Neurobehavioural scores were evaluated after administration for 14 days using a five-grade scale. Blood-brain barrier permeability and apoptotic rate were detected using Evans blue (EB) extravasation and TUNEL staining, respectively. Tissue inhibitor of metalloproteinase 1 (TIMP-1), matrix metalloproteinase 9 (MMP-9) and collagen IV (COL IV) were determined using immunohistochemistry. Neurobehavioural scores decreased remarkably in all SJZD and nimodipine groups compared to the model group (P<0.05). Compared with the sham group, EB extravasation was higher in the model group (P<0.01). The amount of EB extravasation decreased in the SJZD high dose and nimodipine groups compared to the model group (P<0.01), and extravasation in the SJZD high dose group was lower than the SJZD low and medium dose groups (P<0.01). TIMP-1 and MMP-9 expression and apoptotic rate increased, but COL IV decreased significantly in the hippocampus of the model group compared to the sham group (P<0.01). TIMP-1 and COL IV expression increased significantly and MMP-9 and apoptotic rate decreased remarkably in all SJZD and nimodipine groups compared to the model group (P<0.01). TIMP-1 and COL IV expression decreased, but MMP-9 expression and apoptotic rate increased in the SJZD low and medium dose groups compared to the SJZD high dose group (P<0.01). SJZD rescued neurons and improved neurobehavioural function in rats following cerebral ischaemia-reperfusion, especially when used at a high dose. The mechanism may be related to protection of the extracellular matrix followed by anti-apoptotic effects.

Effects and Mechanism of Action of Neonatal Versus Adult Astrocytes on Neural Stem Cell Proliferation After Traumatic Brain Injury

Due to the limited capacity of brain tissue to self-regenerate after traumatic brain injury (TBI), the mobilization of endogenous neural stem cells (NSCs) is a popular research topic. In the clinic, the neurogenic abilities of adults versus neonates vary greatly, which is likely related to functional differences in NSCs. Recent studies have demonstrated that the molecules secreted from astrocytes play important roles in NSC fate determination. In this study, conditioned media (CM) derived from neonatal or adult rat astrocytes, which were unstimulated or stimulated by lipopolysaccharide (LPS), were prepared to treat NSCs. Our results revealed that neonatal rat astrocytes can significantly promote the proliferation of NSCs, compared with adult rat astrocytes, regardless of whether or not they were stimulated by LPS. Furthermore, we used mass spectrometry to detect the constituents of the CM from each group. We analyzed and screened for a protein, Tenascin-C (TNC), which was highly expressed in the neonatal group but poorly expressed in the adult group. We found that TNC can bind to the NSC surface epidermal growth factor receptor and promote proliferation through the PI3K-AKT pathway in vitro. Additionally, we confirmed in vivo that TNC can promote damage repair in a rat model of TBI, through enhancing the proliferation of endogenous NSCs. We believe that these findings provide a mechanistic understanding of why neonates show better neuroregenerative abilities than adults. This also provides a potential future therapeutic target, TNC, for injury repair after TBI. Stem Cells 2019;37:1344-1356.

RNA sequencing reveals MMP2 and TGFB1 downregulation in LRRK2 G2019S Parkinson's iPSC-derived astrocytes

Non-neuronal cell types such as astrocytes can contribute to Parkinson's disease (PD) pathology. The G2019S mutation in leucine-rich repeat kinase 2 (LRRK2) is one of the most common known causes of familial PD. To characterize its effect on astrocytes, we developed a protocol to produce midbrain-patterned astrocytes from human induced pluripotent stem cells (iPSCs) derived from PD LRRK2 G2019S patients and healthy controls. RNA sequencing analysis revealed the downregulation of genes involved in the extracellular matrix in PD cases. In particular, transforming growth factor beta 1 (TGFB1), which has been shown to inhibit microglial inflammatory response in a rat model of PD, and matrix metallopeptidase 2 (MMP2), which has been shown to degrade α-synuclein aggregates, were found to be down-regulated in LRRK2 G2019S astrocytes. Our findings suggest that midbrain astrocytes carrying the LRRK2 G2019S mutation may have reduced neuroprotective capacity and may contribute to the development of PD pathology.

Astrocyte Mechano-Activation by High-Rate Overpressure Involves Alterations in Structural and Junctional Proteins

Primary blast neurotrauma represents a unique injury paradigm characterized by high-rate overpressure effects on brain tissue. One major hallmark of blast neurotrauma is glial reactivity, notably prolonged astrocyte activation. This cellular response has been mainly defined in primary blast neurotrauma by increased intermediate filament expression. Because the intermediate filament networks physically interface with transmembrane proteins for junctional support, it was hypothesized that cell junction regulation is altered in the reactive phenotype as well. This would have implications for downstream transcriptional regulation via signal transduction pathways like nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Therefore, a custom high-rate overpressure simulator was built for in vitro testing using mechanical conditions based on intracranial pressure measurements in a rat model of blast neurotrauma. Primary rat astrocytes were exposed to isolated high-rate mechanical stimulation to study cell junction dynamics in relation to their mechano-activation. First, a time course for "classical" features of reactivity was devised by evaluation of glial fibrillary acidic protein (GFAP) and proliferating cell nuclear antigen (PCNA) expression. This was followed by gene and protein expression for both gap junction (connexins) and anchoring junction proteins (integrins and cadherins). Signal transduction analysis was carried out by nuclear localization of two molecules, NF-κB p65 and mitogen-activated protein kinase (MAPK) p38. Results indicated significant increases in connexin-43 expression and PCNA first at 24 h post-overpressure (p < 0.05), followed by structural reactivity (via increased GFAP, p < 0.05) corresponding to increased anchoring junction dynamics at 48 h post-overpressure (p < 0.05). Moreover, increased phosphorylation of focal adhesion kinase (FAK) was observed in addition to increased nuclear localization of both p65 and p38 (p < 0.05) during the period of structural reactivity. To evaluate the transcriptional activity of p65 in the nucleus, electrophoretic mobility shift assay was conducted for a binding site on the promoter region for intracellular adhesion molecule-1 (ICAM-1), an antagonist of tight junctions. A significant increase in the interaction of nuclear proteins with the NF-κB site on the ICAM-1 corresponded to increased gene and protein expression of ICAM-1 (p < 0.05). Altogether, these results indicate multiple targets and corresponding signaling pathways which involve cell junction dynamics in the mechano-activation of astrocytes following high-rate overpressure.

In vivo migration of endogenous brain progenitor cells guided by an injectable peptide amphiphile biomaterial

Biomaterials hold great promise in helping the adult brain regenerate and rebuild after trauma. Peptide amphiphiles (PAs) are highly versatile biomaterials, gelling and forming macromolecular structures when exposed to physiological levels of electrolytes. We are here reporting on the first ever in vivo use of self-assembling PA carrying a Tenascin-C signal (E₂ Ten-C PA) for the redirection of endogenous neuroblasts in the rodent brain. The PA forms highly aligned nanofibers, displaying the migratory sequence of Tenascin-C glycoprotein as epitope. In this in vivo work, we have formed in situ a gel of aligned PA nanofibers presenting a migratory Tenascin-C signal sequence in the ventral horn of the rostral migratory stream, creating a track reaching the neocortex. Seven days posttransplant, doublecortin positive cells were observed migrating inside and alongside the injected biomaterial, reaching the cortex. We observed a 24-fold increase in number of redirected neuroblasts for the E₂ Ten-C PA-injected animals compared to control. We also found injecting the E₂ Ten-C PA to cause minimal neuroinflammatory response. Analysing GFAP⁺ astrocytes and Iba1⁺ microglia activation, the PA does not elicit a stronger neuroinflammatory response than would be expected from a small needle stab wound. Redirecting endogenous neuroblasts and increasing the number of cells reaching a site of injury using PAs may open up new avenues for utilizing the pool of neuroblasts and neural stem cells within the adult brain for regenerating damaged brain tissue and replacing neurons lost to injury.

Brain-region specific responses of astrocytes to an in vitro injury and neurotrophins

Astrocytes are a heterogeneous population of glial cells that react to brain insults through a process referred to as astrogliosis. Reactive astrocytes are characterized by an increase in proliferation, size, migration to the injured zone and release of a plethora of chemical mediators such as NGF and BDNF. The aim of this study was to determine whether there are brain region-associated responses of astrocytes to an injury and to the neurotrophins NGF and BDNF. We used the scratch injury model to study the closure of a wound inflicted on a monolayer of astrocytes obtained from cortex, hippocampus or striatum. Our results indicate that the response of astrocytes to a mechanical lesion differ according to brain regions. Astrocytes from the striatum proliferate and repopulate the injury site more rapidly than astrocytes from cortex or hippocampus. We found that the scratch injury induced the upregulation of neurotrophin receptor p75NTR and TrkB.t in astrocytes from all brain regions studied. When astrocytes from all regions were treated with NGF, the neurotrophin induced migration of the astrocytes (assessed in Boyden chambers) and induced wound closure but did not affect proliferation. In contrast, BDNF induced wound closure but only in astrocytes from striatum. Our overall findings show the heterogeneity in astrocyte functions based on their brain region of origin, and how this functional diversity may determine their responses to an injury and to neurotrophins.

Tissue transglutaminase in astrocytes is enhanced by inflammatory mediators and is involved in the formation of fibronectin fibril-like structures

Background

During multiple sclerosis (MS) lesion formation, inflammatory mediators are produced by microglial cells and invading leukocytes. Subsequently, hypertrophic astrocytes fill the lesion and produce extracellular matrix (ECM) proteins that together form the astroglial scar. This is beneficial because it seals off the site of central nervous system (CNS) damage. However, astroglial scarring also forms an obstacle that inhibits remyelination of brain lesions. This is possibly an important cause for incomplete remyelination of the CNS in early stage MS patients and for failure of remyelination when the disease progresses. Tissue transglutaminase (TG2), a Ca²⁺-dependent enzyme that can cross-link proteins, appears in astrocytes in inflammatory MS lesions and may contribute to the rearrangement of ECM protein deposition and aggregation.

Methods

The effect of different inflammatory mediators on TG2 and fibronectin, an ECM protein, protein levels was examined in primary rat microglia and astrocytes by western blotting. Also, TG2 activity was analyzed in primary rat astrocytes by a TG activity assay. To determine the role of TG2 in the deposition and cross-linking of fibronectin, a TG2 inhibitor and TG2 knockdown astrocytes were used.

Results

Our data show that under inflammatory conditions in vitro, TG2 production is enhanced in astrocytes and microglia. We observed that in particular, astrocytes produce fibronectin that can be cross-linked and aggregated by exogenous TG2. Moreover, inflammatory stimulus-induced endogenously produced TG2 is involved in the appearance of morphological fibril-like fibronectin deposits but does not lead to cross-linked fibronectin aggregates.

Conclusions

Our in vitro observations suggest that during MS lesion formation, when inflammatory mediators are produced, astrocyte-derived TG2 may contribute to ECM rearrangement, and subsequent astroglial scarring.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1031-2) contains supplementary material, which is available to authorized users.

Hyperbaric oxygen attenuates neuropathic pain and reverses inflammatory signaling likely via the Kindlin-1/Wnt-10a signaling pathway in the chronic pain injury model in rats

BACKGROUND

Hyperbaric oxygen (HBO) therapy is proven to attenuate neuropathic pain in rodents. The goal of the present study was to determine the potential involvement of the Kindlin-1/Wnt-10a signaling pathway during astrocyte activation and inflammation in a rodent model of neuropathic pain.

METHODS

Rats were assigned into sham operation, chronic constriction injury (CCI), and CCI + HBO treatment groups. Neuropathic pain developed in rats following CCI of the sciatic nerve. Rats in the CCI + HBO group received HBO treatment for five consecutive days beginning on postoperative day 1. The mechanical withdrawal threshold (MWT) and the thermal withdrawal latency (TWL) tests were performed to determine mechanical and heat hypersensitivity of animals, respectively. Kindlin-1, Wnt-10a and β-catenin protein expression was examined by immunohistochemistry and Western blot analysis. Expression of tumor necrosis factor (TNF)-α was also determined by ELISA.

RESULTS

Our findings demonstrated that HBO treatment significantly suppressed mechanical and thermal hypersensitivity in the CCI neuropathic pain model in rats. HBO therapy significantly reversed the up-regulation of Kindlin-1 in dorsal root ganglia (DRG), spinal cord, and hippocampus of CCI rats. CCI-induced astrocyte activation and increased levels of TNF-α were efficiently reversed by HBO (P < 0.05 vs. CCI). HBO also reversed Wnt-10a up-regulation induced by CCI in the DRG, spinal cord, and hippocampus (P < 0.05 vs. CCI).

CONCLUSIONS

Our findings demonstrate that HBO attenuated CCI-induced rat neuropathic pain and inflammatory responses, possibly through regulation of the Kindlin-1/Wnt-10a signaling pathway.

Conditioned Medium of Human Adipose Mesenchymal Stem Cells Increases Wound Closure and Protects Human Astrocytes Following Scratch Assay In Vitro

Astrocytes perform essential functions in the preservation of neural tissue. For this reason, these cells can respond with changes in gene expression, hypertrophy, and proliferation upon a traumatic brain injury event (TBI). Different therapeutic strategies may be focused on preserving astrocyte functions and favor a non-generalized and non-sustained protective response over time post-injury. A recent strategy has been the use of the conditioned medium of human adipose mesenchymal stem cells (CM-hMSCA) as a therapeutic strategy for the treatment of various neuropathologies. However, although there is a lot of information about its effect on neuronal protection, studies on astrocytes are scarce and its specific action in glial cells is not well explored. In the present study, the effects of CM-hMSCA on human astrocytes subjected to scratch assay were assessed. Our findings indicated that CM-hMSCA improved cell viability, reduced nuclear fragmentation, and preserved mitochondrial membrane potential. These effects were accompanied by morphological changes and an increased polarity index thus reflecting the ability of astrocytes to migrate to the wound stimulated by CM-hMSCA. In conclusion, CM-hMSCA may be considered as a promising therapeutic strategy for the protection of astrocyte function in brain pathologies.

Nerve Guidance by a Decellularized Fibroblast Extracellular Matrix

Spinal cord and peripheral nerve injuries require the regeneration of nerve fibers across the lesion site for successful recovery. Providing guidance cues and soluble factors to promote neurite outgrowth and cell survival can enhance repair. The extracellular matrix (ECM) plays a key role in tissue repair by controlling cell adhesion, motility, and growth. In this study, we explored the ability of a mesenchymal ECM to support neurite outgrowth from neurons in the superior cervical ganglia (SCG). Length and morphology of neurites extended on a decellularized fibroblast ECM were compared to those on substrates coated with laminin, a major ECM protein in neural tissue, or fibronectin, the main component of a mesenchymal ECM. Average radial neurite extension was equivalent on laminin and on the decellularized ECM, but contrasted with the shorter, curved neurites observed on the fibronectin substrate. Differences between neurites on fibronectin and on other substrates were confirmed by fast Fourier transform analyses. To control the direction of neurite outgrowth, we developed an ECM with linearly aligned fibril organization by orienting the fibroblasts that deposit the matrix on a polymeric surface micropatterned with a striped chemical interface. Neurites projected from SCGs appeared to reorient in the direction of the pattern. These results highlight the ability of a mesenchymal ECM to enhance neurite extension and to control the directional outgrowth of neurites. This micropatterned decellularized ECM architecture has potential as a regenerative microenvironment for nerve repair.

TIMP-1 couples RhoK activation to IL-1β-induced astrocyte responses

Interleukin-1β (IL-1β) is a pleotropic cytokine known to influence the central nervous system (CNS) responses to injury or infection. IL-1β also directly induces astrocytic expression of tissue inhibitor of metalloproteinases (TIMP)-1, a potent trophic factor and regulator of matrix metalloproteinase activity. In this study, we examined the functional relationship between IL-1β and TIMP-1 and determined that the behavior of astrocytes in response to IL-1β is determined by TIMP-1 expression. Using primary astrocytes from C57Bl/6 mice, we found astrocytes from wildtype (Wt) mice exhibited a robust wound healing response to a scratch wound that was arrested in response to IL-1β. In contrast, TIMP-1 knockout (TIMP-1KO) astrocytes, exhibited minimal response to the scratch wound but an accelerated response following IL-1β-treatment. We also determined that the scratch wound effect in Wt cultures was attenuated by inhibition of Rho kinase but amplified in the TIMP-1KO cultures. We propose that the specific induction of TIMP-1 from astrocytes in response to IL-1β reflects a previously unrecognized physiological relationship where the directionality of astrocytic behavior is determined by the actions of TIMP‑1. These findings may provide additional insight into glial responses in the context of neuropathology where expression of TIMP-1 may vary and astrocytic responses may be impacted by the inflammatory milieu of the CNS.