Astrocytic TIMP-1 regulates production of Anastellin, an inhibitor of oligodendrocyte differentiation and FTY720 responses.

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. Astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout (Timp1KO) mice do not efficiently remyelinate following a demyelinating injury. Here, we performed an unbiased proteomic analysis and identified a fibronectin-derived peptide called Anastellin (Ana) that was unique to the Timp1KO astrocyte secretome. Ana was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Ana is known to act upon the sphingosine-1-phosphate receptor 1, and we determined that Ana also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro. Administration of FTY720 to wild-type C57BL/6 mice during MOG35-55-experimental autoimmune encephalomyelitis ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 (Timp1KO) had no effect. Analysis of Timp1 and fibronectin (FN1) transcripts from primary human astrocytes from healthy and multiple sclerosis (MS) donors revealed lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Last, analyses of proteomic databases of MS samples identified Ana peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high disease activity. A role for Ana in MS as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and innate remyelination potential in the MS brain.

Emerging Role of Astrocyte-Derived Extracellular Vesicles as Active Participants in CNS Neuroimmune Responses.

Astrocyte-derived extracellular vesicles (ADEVs) have garnered attention as a fundamental mechanism of intercellular communication in health and disease. In the context of neurological diseases, for which prodromal diagnosis would be advantageous, ADEVs are also being explored for their potential utility as biomarkers. In this review, we provide the current state of data supporting our understanding on the manifold roles of ADEVs in several common neurological disorders. We also discuss these findings from a unique emerging perspective that ADEVs represent a means by which the central nervous system may broadcast influence over other systems in the body to affect neuroinflammatory processes, with both dual potential to either propagate illness or restore health and homeostasis.

Anticoagulation for the treatment of septic cerebral venous sinus thrombosis in the setting of pediatric sinogenic and otogenic intracranial infections.

OBJECTIVE: Septic cerebral venous sinus thrombosis (CVST) is a recognized complication of pediatric sinogenic and otogenic intracranial infections. The optimal treatment paradigm remains controversial. Proponents of anticoagulation highlight its role in preventing thrombus propagation and promoting recanalization, while others cite the risk of hemorrhagic complications, especially after a neurosurgical procedure for an epidural abscess or subdural empyema. Here, the authors investigated the diagnosis, management, and outcomes of pediatric patients with sinogenic or otogenic intracranial infections and a septic CVST. METHODS: All patients 21 years of age or younger, who presented with an intracranial infection in the setting of sinusitis or otitis media and who underwent neurosurgical treatment at Connecticut Children's, Rady Children's Hospital-San Diego, or Ann and Robert H. Lurie Children's Hospital of Chicago from March 2015 to March 2023, were retrospectively reviewed. Demographic, clinical, and radiological data were systematically collated. RESULTS: Ninety-six patients were treated for sinusitis-related and/or otitis media-related intracranial infections during the study period, 15 (15.6%) of whom were diagnosed with a CVST. Of the 60 patients who presented prior to the COVID-19 pandemic, 6 (10.0%) were diagnosed with a septic CVST, whereas of the 36 who presented during the COVID-19 pandemic, 9 (25.0%) had a septic CVST (p = 0.050). The superior sagittal sinus was involved in 12 (80.0%) patients and the transverse and/or sigmoid sinuses in 4 (26.7%). Only 1 (6.7%) patient had a fully occlusive thrombus. Of the 15 patients with a septic CVST, 11 (73.3%) were initiated on anticoagulation at a median interval of 4 (IQR 3-5) days from the most recent neurosurgical procedure. Five (45.5%) patients who underwent anticoagulation demonstrated complete recanalization on follow-up imaging, and 4 (36.4%) had partial recanalization. Three (75.0%) patients who did not undergo anticoagulation demonstrated complete recanalization, and 1 (25.0%) had partial recanalization. None of the patients treated with anticoagulation experienced hemorrhagic complications. CONCLUSIONS: Septic CVST is frequently identified among pediatric patients undergoing neurosurgical intervention for sinogenic and/or otogenic intracranial infections and may have become more prevalent during the COVID-19 pandemic. Anticoagulation can be used safely in the acute postoperative period if administered cautiously, in a monitored setting, and with interval cross-sectional imaging. However, some patients exhibit excellent outcomes without anticoagulation, and further studies are needed to identify those who may benefit the most from anticoagulation.

CD8+ T cell depletion prevents neuropathology in a mouse model of globoid cell leukodystrophy.

Globoid cell leukodystrophy (GLD) or Krabbe's disease is a fatal genetic demyelinating disease of the central nervous system caused by loss-of-function mutations in the galactosylceramidase (galc) gene. While the metabolic basis for disease is known, the understanding of how this results in neuropathology is not well understood. Herein, we report that the rapid and protracted elevation of CD8+ cytotoxic T lymphocytes occurs coincident with clinical disease in a mouse model of GLD. Administration of a function-blocking antibody against CD8α effectively prevented disease onset, reduced morbidity and mortality, and prevented CNS demyelination in mice. These data indicate that subsequent to the genetic cause of disease, neuropathology is driven by pathogenic CD8+ T cells, thus offering novel therapeutic potential for treatment of GLD.

Changes in the epidemiology of pediatric sinogenic and otogenic intracranial infections during the COVID-19 pandemic: a single-institution study.

OBJECTIVE: Focal intracranial infections (epidural abscesses, subdural empyemas, and intraparenchymal abscesses) are uncommon complications of sinusitis and otitis media but can be associated with significant morbidity. Treatment typically requires neurosurgical and otolaryngological interventions in combination with antibiotic treatment. Historically, children have presented to the authors' pediatric referral center with sinusitis- or otitis media-related intracranial infections in low numbers. However, since the onset of the COVID-19 pandemic, the incidence of intracranial pyogenic complications has increased at this center. The objective of this study was to compare the epidemiology, severity, microbial causes, and management of pediatric sinusitis- and otitis-related intracranial infections in the periods before and during the COVID-19 pandemic. METHODS: All patients 21 years of age or younger who presented with an intracranial infection in the setting of sinusitis or otitis media and who underwent neurosurgical treatment at Connecticut Children's from January 2012 to December 2022 were retrospectively reviewed. Demographic, clinical, laboratory, and radiological data were systematically collated, and variables before and during COVID-19 were compared statistically. RESULTS: Overall, 18 patients were treated for sinusitis-related (n = 16) or otitis media-related (n = 2) intracranial infections during the study period. Ten patients (56%) presented from January 2012 to February 2020, none from March 2020 to June 2021, and 8 (44%) from July 2021 to December 2022. There were no significant demographic differences between the pre-COVID-19 and COVID-19 cohorts. The 10 patients in the pre-COVID-19 cohort underwent a total of 15 neurosurgical and 10 otolaryngological procedures, while the 8 patients in the COVID-19 cohort underwent a total of 12 neurosurgical and 10 otolaryngological procedures. Surgically obtained wound cultures yielded a variety of organisms; Streptococcus constellatus/S. anginosus/S. intermedius were more prevalent in the COVID-19 cohort (87.5% vs 0%, p < 0.001) as was Parvimonas micra (62.5% vs 0%, p = 0.007). CONCLUSIONS: At an institutional level, there has been an approximately threefold increase in cases of sinusitis- and otitis media-related intracranial infections during the COVID-19 pandemic. Multicenter studies are needed to confirm this observation and to investigate whether the mechanisms of infection are related directly to SARS-CoV-2, changes in the respiratory flora, or delayed care. The next steps will include expansion of this study to other pediatric centers throughout the United States and Canada.

Astrocytic TIMP-1 regulates production of Anastellin, a novel inhibitor of oligodendrocyte differentiation and FTY720 responses.

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. We have previously demonstrated that murine astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout ( Timp1 KO ) mice do not efficiently remyelinate following a demyelinating injury. To better understand the basis of this, we performed unbiased proteomic analyses and identified a fibronectin-derived peptide called anastellin that is unique to the murine Timp1 KO astrocyte secretome. Anastellin was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Anastellin is known to act upon the sphingosine-1-phosphate receptor 1 (S1PR1), and we determined that anastellin also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro . Further, administration of FTY720 to wild-type C57BL/6 mice during MOG 35-55 -EAE ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 in astrocytes ( Timp1 cKO ) had no effect. Analysis of human TIMP1 and fibronectin ( FN1 ) transcripts from healthy and multiple sclerosis (MS) patient brain samples revealed an inverse relationship where lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Lastly, we analyzed proteomic databases of MS samples and identified anastellin peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high versus low disease activity. The prospective role for anastellin generation in association with myelin lesions as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and the innate remyelination potential of the the MS brain. Significance Statement: Astrocytic production of TIMP-1 prevents the protein catabolism of fibronectin. In the absence of TIMP-1, fibronectin is further digested leading to a higher abundance of anastellin peptides that can bind to sphingosine-1-phosphate receptor 1. The binding of anastellin with the sphingosine-1-phosphate receptor 1 impairs the differentiation of oligodendrocytes progenitor cells into myelinating oligodendrocytes in vitro , and negates the astrocyte-mediated therapeutic effects of FTY720 in the EAE model of chronic CNS inflammation. These data indicate that TIMP-1 production by astrocytes is important in coordinating astrocytic functions during inflammation. In the absence of astrocyte produced TIMP-1, elevated expression of anastellin may represent a prospective biomarker for FTY720 therapeutic responsiveness.

Glia as antigen-presenting cells in the central nervous system.

The contribution of the cells within the central nervous system (CNS) toward adaptive immune responses is emerging and incompletely understood. Recent findings indicate important functional interactions between T-cells and glial cells within the CNS that may contribute to disease and neuropathology through antigen presentation. Although glia are not classically considered antigen-presenting cell (APC) types, there is growing evidence indicating that glial antigen presentation plays an important role in several neurological diseases. This review discusses these findings which incriminate microglia, astrocytes, and oligodendrocyte lineage cells as CNS-resident APC types with implications for understanding disease.

The Cellular Senescence Factor Extracellular HMGB1 Directly Inhibits Oligodendrocyte Progenitor Cell Differentiation and Impairs CNS Remyelination.

HMGB1 is a highly conserved, ubiquitous protein in eukaryotic cells. HMGB1 is normally localized to the nucleus, where it acts as a chromatin associated non-histone binding protein. In contrast, extracellular HMGB1 is an alarmin released by stressed cells to act as a danger associated molecular pattern (DAMP). We have recently determined that progenitor cells from multiple sclerosis patients exhibit a cellular senescent phenotype and release extracellular HMGB1 which directly impaired the maturation of oligodendrocyte progenitor cells (OPCs) to myelinating oligodendrocytes (OLs). Herein, we report that administration of recombinant HMGB1 into the spinal cord at the time of lysolecithin administration resulted in arrest of OPC differentiation in vivo, and a profound impairment of remyelination. To define the receptor by which extracellular HMGB1 mediates its inhibitory influence on OPCs to impair OL differentiation, we tested selective inhibitors against the four primary receptors known to mediate the effects of HMGB1, the toll-like receptors (TLRs)-2, -4, -9 or the receptor for advanced glycation end-products (RAGE). We found that inhibition of neither TLR9 nor RAGE increased OL differentiation in the presence of HMGB1, while inhibition of TLR4 resulted in partial restoration of OL differentiation and inhibiting TLR2 fully restored differentiation of OLs in the presence of HMGB1. Analysis of transcriptomic data (RNAseq) from OPCs identified an overrepresentation of NFκB regulated genes in OPCs when in the presence of HMGB1. We found that application of HMGB1 to OPCs in culture resulted in a rapid and concentration dependent shift in NFκB nuclear translocation which was also attenuated with coincident TLR2 inhibition. These data provide new information on how extracellular HMGB1 directly affects the differentiation potential of OPCs. Recent and past evidence for elevated HMGB1 released from senescent progenitor cells within demyelinated lesions in the MS brain suggests that a greater understanding of how this molecule acts on OPCs may unfetter the endogenous remyelination potential in MS.

Lipidomic analysis identifies age-disease-related changes and potential new biomarkers in brain-derived extracellular vesicles from metachromatic leukodystrophy mice.

BACKGROUND: Recent findings show that extracellular vesicle constituents can exert short- and long-range biological effects on neighboring cells in the brain, opening an exciting avenue for investigation in the field of neurodegenerative diseases. Although it is well documented that extracellular vesicles contain many lipids and are enriched in sphingomyelin, cholesterol, phosphatidylserines and phosphatidylinositols, no reports have addressed the lipidomic profile of brain derived EVs in the context of Metachromatic Leukodystrophy, a lysosomal storage disease with established metabolic alterations in sulfatides. METHODS: In this study, we isolated and characterized the lipid content of brain-derived EVs using the arylsulfatase A knockout mouse as a model of the human condition. RESULTS: Our results suggest that biogenesis of brain-derived EVs is a tightly regulated process in terms of size and protein concentration during postnatal life. Our lipidomic analysis demonstrated that sulfatides and their precursors (ceramides) as well as other lipids including fatty acids are altered in an age-dependent manner in EVs isolated from the brain of the knockout mouse. CONCLUSIONS: In addition to the possible involvement of EVs in the pathology of Metachromatic Leukodystrophy, our study underlines that measuring lipid signatures in EVs may be useful as biomarkers of disease, with potential application to other genetic lipidoses.

Therapeutic opportunities for targeting cellular senescence in progressive multiple sclerosis.

Recent studies have implicated cellular senescence as a disease-related process linked to progressive forms of multiple sclerosis (MS). Herein, we present an overview of the current pharmacopeia of cellular senescence affecting compounds and evidence for their effects, if known, in murine and cellular models of MS. Consideration is also given to the utility of these compounds for the treatment of progressive MS, with an examination of past and current clinical trials that have tested these agents, often for other purposes, in the MS patient population. Lastly, we discuss the implications and potential utility for targeting cellular senescence as a strategy to fulfil the unmet need of treatment options for the progressive MS population.

Distinct profiles of cellular senescence-associated gene expression in the aged, diseased or injured central nervous system.

The molecular process of cellular senescence, which is known to contribute to aging, has been implicated in several diseases of the central nervous system (CNS). The purpose of this study was to generate an unbiased survey of cellular senescence gene expression with whole brain tissues using a standardized, curated set of 88 genes associated with cellular senescence. We performed a comparative analysis of aged brains with two CNS disease models; the 5xFAD mouse model of Alzheimer's disease, and cuprizone-induced CNS demyelination. Each experimental group could be distinguished from the others by expression of unique subsets of cellular senescence genes, with minimal overlap between each group. Gene ontology analyses identified unique processes within cellular senescence among each group. To examine how these changes translate to the human condition, we interrogated gene expression data from publicly available databases of human aging and AD cases which also corroborated our finding that cellular senescence gene expression changes in AD differ significantly from healthy aging, although the changes in human did not always correlate with the murine models. These data provide important insight on the common and unique global changes in expression of cellular senescence genes in the CNS accompanying aging, injury or disease. Future studies may define, using more refined cellular assays, the specific cellular phenotype differences, and how disparate drivers of unique disease pathologies all seemingly culminate in a common activation of cellular senescence.

Astrocyte-Derived Extracellular Vesicles (ADEVs): Deciphering their Influences in Aging.

Astrocytes are an abundant and dynamic glial cell exclusive to the central nervous system (CNS). In the context of injury, inflammation, and/or diseases of the nervous system, astrocyte responses, termed reactive astrogliosis, are a recognized pathological feature across a range of conditions and diseases. However, the impact of reactive astrogliosis is not uniform and varies by context and duration (time). In recent years, extracellular communication between glial cells via extracellular vesicles (EVs) has garnered interest as a process connected with reactive astrogliosis. In this review, we relate recent findings on astrocyte-derived extracellular vesicles (ADEVs) with a focus on factors that can influence the effects of ADEVs and identified age related changes in the function of ADEVs. Additionally, we will discuss the current limitations of existing experimental approaches and identify questions that highlight areas for growth in this field, which will continue to enhance our understanding of ADEVs in age-associated processes.

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-1ß treated and ECM-exposed astrocyte cultures, we found that IL-1ß arrested wound recovery in naive astrocytes treated with EVs from astrocytes cultured on ECM but adding EVs from IL-1ß 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 ß1-integrin, a major integrin receptor for the ECM molecules tested in this study. We found that the ß1-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.

Mesenchyme-specific loss of Dot1L histone methyltransferase leads to skeletal dysplasia phenotype in mice.

Chromatin modifying enzymes play essential roles in skeletal development and bone maintenance, and deregulation of epigenetic mechanisms can lead to skeletal growth and malformation disorders. Here, we report a novel skeletal dysplasia phenotype in mice with conditional loss of Disruptor of telomeric silencing 1-like (Dot1L) histone methyltransferase in limb mesenchymal progenitors and downstream descendants. Phenotypic characterizations of mice with Dot1L inactivation by Prrx1-Cre (Dot1L-cKOPrrx1) revealed limb shortening, abnormal bone morphologies, and forelimb dislocations. Our in vivo and in vitro data support a crucial role for Dot1L in regulating growth plate chondrocyte proliferation and differentiation, extracellular matrix production, and secondary ossification center formation. Micro-computed tomography analysis of femurs revealed that partial loss of Dot1L expression is sufficient to impair trabecular bone formation and microarchitecture in young mice. Moreover, RNAseq analysis of Dot1L deficient chondrocytes implicated Dot1L in the regulation of key genes and pathways necessary to promote cell cycle regulation and skeletal growth. Collectively, our data show that early expression of Dot1L in limb mesenchyme provides essential regulatory control of endochondral bone morphology, growth, and stability.

Astrocyte Support for Oligodendrocyte Differentiation can be Conveyed via Extracellular Vesicles but Diminishes with Age.

The aging brain is associated with significant changes in physiology that alter the tissue microenvironment of the central nervous system (CNS). In the aged CNS, increased demyelination has been associated with astrocyte hypertrophy and aging has been implicated as a basis for these pathological changes. Aging tissues accumulate chronic cellular stress, which can lead to the development of a pro-inflammatory phenotype that can be associated with cellular senescence. Herein, we provide evidence that astrocytes aged in culture develop a spontaneous pro-inflammatory and senescence-like phenotype. We found that extracellular vesicles (EVs) from young astrocyte were sufficient to convey support for oligodendrocyte differentiation while this support was lost by EVs from aged astrocytes. Importantly, the negative influence of culture age on astrocytes, and their cognate EVs, could be countered by treatment with rapamycin. Comparative proteomic analysis of EVs from young and aged astrocytes revealed peptide repertoires unique to each age. Taken together, these findings provide new information on the contribution of EVs as potent mediators by which astrocytes can extert changing influence in either the disease or aged brain.