Academic literature on the topic 'Leptomeningeal niche'

Abstract For decades, the central nervous system was considered to be an immune privileged organ with limited access to systemic immunity. However, the leptomeninges, the cerebrospinal fluid (CSF)-filled anatomical structure that protects the brain and spinal cord, represent a relatively immune-rich environment. Despite the presence of immune cells, complications in the CSF, such as infectious meningitis and a neurological development of cancer known as leptomeningeal metastasis, are difficult to treat and are frequently fatal. We show that immune cells entering the CSF are held in an ‘idle’ state that limits their cytotoxic arsenal and antigen presentation machinery. To understand this underappreciated neuroanatomic niche, we used unique mouse models and rare patient samples to characterize its cellular composition and critical signaling events in health and disease at a single-cell resolution. Revealing the mediators of CSF immune response will allow us to re-evaluate current therapeutic protocols and employ rational combinations with immunotherapies, therefore turning the patient’s own immune system into an active weapon against pathogens and cancer.

Abstract Breast cancer (BC) patients diagnosed with leptomeningeal disease (LMD) have a median survival of less than six months. There has been limited therapeutic innovation in treating LMD due to our poor understanding of the molecular mechanisms governing breast cancer cell (BCC) invasion and survival within the leptomeninges (LM). Here we show that BCCs can invade the LM by migrating along the outer surface of emissary vessels that passage from the skull and vertebral bone marrow through cortical bone fenestrations, emerging as LM vasculature in the sub-arachnoid space. This process requires BCC integrin α6 engaging laminin on the vascular basement membrane of emissary vessels, mimicking an α6 integrin-dependent mechanism used by neural progenitors to migrate to the olfactory bulb. Once in the LM, BCCs co-localize with perivascular CSF1R+ meningeal macrophages which support BCC survival through the secretion of the protective neurotrophin, GDNF. Pharmacologic depletion of these meningeal macrophages causes a marked reduction of GDNF concurrent with a decrease in LMD progression, which is rescued by intraventricular delivery of recombinant GDNF. Together these data suggest that BCCs hijack neural migratory pathways and leptomeningeal macrophages to invade and survive in the LM niche. Finally, analysis of craniotomy samples from patients with breast cancer revealed a correlation between BCC integrin α6 expression and meningeal metastasis suggesting the potential of integrin α6 as a novel target to predict or treat LMD.

Abstract Breast cancer cell (BCC) metastasis to the leptomeninges (LM) is an increasingly common disease complication with a grim prognosis of weeks to months. There are currently few therapeutic options to prevent or treat leptomeningeal disease (LMD), in part due to our limited knowledge of the molecular pathways involved in tumor invasion and survival within this unique niche. Here we show that BCCs in mice can bypass the restrictive blood-brain barrier and invade the LM by migrating along the abluminal surface of emissary vessels that connect the vertebral/calvarial bone marrow and meninges. This is mediated by tumor cell integrin α6 engaging extracellular matrix laminin on the vascular basement membrane. Upon invasion of the LM, BCCs co-localize with CSF1R+ meningeal macrophages/microglia in the perivascular space. We demonstrate that ablation of these myeloid cells by CSF1R inhibition leads to prolonged disease-free survival due to decreased LMD burden. Importantly, we show that CSF1R+ cell depletion does not prevent tumor cell LM colonization, but instead limits disease expansion within the LM, highlighting the pro-tumor phenotype of these meningeal macrophages/microglia. Our data suggest that meningeal macrophages/microglia support BCC proliferation/survival by up-regulating glial cell line-derived neurotrophic factor (GDNF), a key neurotrophic factor released by macrophages/microglia in response to neuronal injury. In vitro, GDNF protects BCCs from cell death induced by glucose deprivation, suggesting that tumor cells may hijack a macrophage neuronal injury response program to thrive within the nutrient-poor LM niche. Unexpectedly, we found that integrin α6 deletion or antibody blockade eliminates the protective role of GDNF by modulating GDNF/NCAM receptor signaling in BCCs. Taken together, our data suggest that BCCs co-opt neuronal pathfinding mechanisms and resident macrophages/glia to efficiently invade and thrive within the LM niche. Integrin α6 appears to be a master regulator of this neuronal mimicry through its ability to promote abluminal vessel trafficking and mediate responsiveness to GDNF. Finally, a case-control study of bone-metastatic breast cancer patients reveals a significant correlation between integrin α6 expression and incidence of dural-based meningeal metastasis, suggesting the clinical relevance of this pathway and potential role of α6 integrin as a biomarker of LMD risk and therapeutic target. Citation Format: Andrew E. Whiteley, Trevor T. Price, Brennan G. Simon, Katie R. Xu, Dorothy A. Sipkins. Neuronal mimicry promotes breast cancer leptomeningeal metastasis from bone marrow [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3848.

Abstract Brain metastatic patients have multiple metastatic lesions or diagnostically challenging asymptomatic lesions, making surgery an inadequate therapeutic option. Given the challenges related to systemic delivery of a majority of therapeutic agents across the BBB, engineered cell based therapies offer an excellent platform to target metastatic tumors in the brain. We have established the use tumor cell surface receptor targeted allogeneic “off the shelf” gene engineered cellular therapies and developed two different approaches to treat brain metastases. In one approach, we have armed allogenic stem cells (SC) with oncolytic herpes virus (oHSV) variants and tested them in different mouse models of brain metastatic (BM) tumor derived from brain seeking metastatic melanoma tumor cells from patients. We show that intracarotid artery administration of SC-oHSV effectively tracks metastatic tumor lesions and significantly prolongs the survival of brain tumor bearing mice. We also show that a combination of SC-oHSV and PD-L1 blockade increases IFNγ-producing CD8+ tumor-infiltrating T lymphocytes and results in a profound extension of the median survival in syngeneic brain metastatic melanoma mouse models. In another approach, we have explored the versatility of cell mediated bi-functional EGFR and DR4/5-targeted treatment in basal like breast cancer (BLBC) mouse models featuring different patterns of brain metastasis. Most BLBC lines demonstrated a high sensitivity to EGFR and DR4/5 bi-targeting therapeutic protein, EVDRL [anti-EGFR VHH (EV) fused to DR ligand (DRL)]. Functional analyses using inhibitors and CRISPR-Cas9 knockouts revealed that the EV domain facilitated in augmenting DR4/5-DRL binding and enhancing DRL-induced apoptosis. EVDRL releasing allogeneic SCs alleviated tumor-burden and significantly increased survival in mouse models of residual-tumor after macrometastasis resection, perivascular niche micrometastasis, and leptomeningeal metastasis. These findings provide a clinically applicable therapeutic platform to target disseminated metastatic lesions in the brain and define a new paradigm for treatment of brain metastases.

Abstract A sixty-one year-old Hispanic female with Waldenstrom’s Macroglobulinemia diagnosed in 2011 and successfully treated with 6 monthly cycles of Cyclophosphamide, Rituximab and Dexamethasone (CDR) from 12/11 through 5/12 was then put on a two-year maintenance scheme with Rituximab every three months. In February, 2014 (six months before the end of the planned treatment), she came to the ER complaining with severe headache, aphasia and blurred vision. A stroke was initially ruled out and she received Paracetamol with partial improvement. Nonetheless, symptoms re-appeared accompanied with disorientation and agitation. Antipsychotic medication was given with no improvement. On PE she was disoriented with aphasia, paraparetic and neck stiffness suggestive of meningitis. Blood tests, a MRI and lumbar puncture were performed showing leptomeningeal hyperintensity with no signs of encephalitis (Figure 1). Figure 1 Leptomeningeal reinforcement as seen in MRI. Figure 1. Leptomeningeal reinforcement as seen in MRI. CSF analysis showed WBC 64 cells/µL, (95% MNC), glucose= 9.8 mg/dL and proteins= 110 g/dL. Gram dye was negative. A geneXpert for Tuberculosis was negative. CSF cytology showed an infiltration of lymphoid neoplastic cells confirmed by cytochemistry (Figures 2a and 2b). Figure 2a: CD 20+ and 2b: kappa + neoplastic cells in CSF Figure 2a:. CD 20+ and 2b: kappa + neoplastic cells in CSF Figure 3 Figure 3. With these results a Bing Neel syndrome was diagnosed and IT Methotrexate was given for a total of 6 doses resulting in a nice reduction of the neoplastic cells. However, she relapsed in April/2014 and IV Fludarabine was started. We are planning to add IT liposomal Cytarabine. Additionally, MYD 88 gene mutation was detected. DISCUSSION: There are only 33 reported cases of Bing-Neel syndrome in the medical literature for the last 80 years and this one has been confirmed with the newest tools such as: MRI, cytochemistry and gene mutation. CONCLUSION: Bing-Neel syndrome should be suspected in every patient with Waldenstrom’s Macroglobulinemia and CNS impairment. Disclosures No relevant conflicts of interest to declare.

Staminali neuronali adulte (NSC), sono state trovate nelle primcipali aree neurogeniche del cervello, per esempio ippocampo, regione subventricolare (SVZ), bulbi olfattivi, e in alcune regioni non neurogeniche come ad esempio il midollo spinale. Altre regioni del cervello possono ospitare nicchie di NSC e, in particolare, considerando il ruolo delle meningi nel corretto sviluppo della corteccia cerebrale, è nostro interesse esplorare la regione delle leptomeningi che si estende dall’aracnoide fino al primo strato della corteccia cerebrale. Lo scopo di questo progetto è caratterizzare le leptomeningi come potenziale nicchia di cellule staminali neuronali. La regione delle leptomeningi è stata caratterizzata mediante immunoistochimica, in ratti di diversa età, dall’embrione E20, a ratti in età postnatale P0, P15 e nell’adulto. Cellule positive per il marcatore di cellule staminali neuronali nestina, sono state individuate in leptomeninge. Queste cellule sono distribuite fuori dalla membrane basale (positive per il marker Laminina), come una popolazione distinta dagli astrociti (cellule GFAP positive) e dai precursori oligodendrocitari (cellule NG2 positive ), che risiedono nel tessuto circostante. Le cellule nestine positive sono state prelevate dale leptomeningi di ratti P0, P15 e adulti ed espanse in vitro. Le cellule così prelevate sono state espanse in aderenza come una popolazione omogena di cellule nestina positive. Se sottoposto a stimuli differentiativi neuranali, le cellule nestine positive sono in grado di differenziare principalmente in neuroni (positive per MAP2), ma anche in astrociti ed oligodendrociti (positive per O4). Come primo approcio di analisi funzionale delle cellule differenziate in vitro, è stata valutata la loro capacità di rispondere a stimuli depoarizzanti mediante calico imaging, dopo incubazione delle cellule con Fura2. I neuroni ottenuti dal differenziamento in vitro delle cellule nestine positive sono in grado di rispondere all’applicazione dell’agente depolarizzante KCl, suggerendo l’espressione di canali del calico voltaggio dipendenti, come i neuroni funzionali. Il potenziale differenziativo in vivo di queste cellule è stato valutato mediante infusione stereotassica in ippocampo di ratti adulti, di cellule nestine positive estratte dalle leptomeningi di ratti transgenici EGFP. L’ippocampo dei ratti iniettati sono stati analizzati mediante immunofluorescenza a due mesi dall’iniezione delle cellule EGFP. Circa metà delle cellule EGFP identificate in ippocampo esprimevano markers neuronali (DCX, MAP2, NeuN, Neurofilament-160, GAD67). Vista la persistenza di queste cellule nestina positive nelle meningi di ratto durante lo sviluppo fino all’età adulta, dato il loro potenziale proliferativo in vitro ed il loro potenziale differenziativo neuronale sia in vitro che in vivo, queste cellule sono state proposte come nuova entità con il nome di Leptomeningeal stem/progenitor cells (LeSC). Dall’anatomia delle meningi si evince che ricoprono l’intero sistema nervosa centrale, il che comprende anche il midollo spinale. Per questo motivo sono state analizzate anche le leptomeningi che ricoprono il midollo spinale. Come osservato in precedenza per il cervello, cellule positive per il marcatore delle cellule staminali neuronali nestina, sono state individuate in leptomeninge. Queste cellule sono distribuite fuori dalla membrane basale (positive per il marker Laminina), come una popolazione distinta dagli astrociti (cellule GFAP positive) e dai precursori oligodendrocitari (cellule NG2 positive ), che risiedono nel tessuto circostante. Un nuovo studio in collaborazione con la professoressa M. Schwartz group (Weizmann Institute, Rehovot, Israel) è in corso sul potenziale ruolo del sistema immunitario nel regolare le leptomeningi ed in particolare le LeSC (come suggerito da precedenti pubblicazioni del gruppo della prof. Schwartz). Risultati preliminary sul confronto ex vivo della proliferazione delle LeSC in topi SCID e wt, mostrano una significativa diminuzione dl numero di LeSC nestinepositive in topi SCID. Nonostante questa diminuzione di cellule nestine positive, il numero totale di cellule che risiedono in leptomeninge è comparabile in entrambi I topi SCID e wt. E’ in corso una più estensiva caratterizzazione delle leptomeningi dei topi SCID e wt per capire la natura delle cellule nestine negative che risiedono nelle leptomeningi dei topi SCID. L’importanza delle LeSC risiede nella posizione facilmente raggiungibile rispetto alle già note nicchie di staminali neuronali, ed inoltre nell’elevato potenziale differenziativo neuronale. Queste peculiarità apriranno nuovi studi nell’ambito della medicina rigenerativa
Adult neural stem cells (NSC), have been found in the main neurogenic regions of brain, i.e. hippocampus, sub ventricular zone (SVZ), olfactory bulb, and in some non-neurogenic regions, i.e. spinal cord. Other brain sites could host NSC niches and, in particular, considering the role of meninges in correct cortex development we were interested in exploring the region residing between arachnoide and the first layers of the cerebral cortex, called Leptomeninges. Aim of this project is characterized the leptomeningeal compartment as potential niche for neural stem cells with ex vivo and in vitro approaches. The leptomeningeal compartment has been characterized by immunohistochemistry at different rat ages, from embryo E20, postnatal day 0 (P0), P15 and adult. We found a(nestin) neuro-epithelial stem cells marker positive cells layer with decreasing thickness from embryo up to adult. Nestin positive cells were distributed outside the basal lamina (marked by laminin), and as a distinct population from astrocytes (stained with GFAP) and oligodendrocytes (stained with NG2). Nestin positive cells were dissected and expanded in vitro from P0, P15 and adult rats leptomeninges. We were able to culture them as homogeneus nestin positive cells population in adherent condition In neuronal differentiating conditions, nestin positive cells mainly differentiate into MAP2 positive cells but also GFAP and O4 (marker for mature oligodendrocyte) positive cells were detected in culture. As a first level of functional evaluation of differentiated cells, their ability to depolarize has been analyzed by calcium imaging assay after Fura-2 loading. In vitro differentiated neurones responded to fast applications of the depolarizing agent KCl suggesting the expression of voltage dependent calcium channels, similar to that of functional neurons. As following step, the in vivo neuronal differentiation potential was assessed by infusion of expanded EGFP LeSC in rat hippocampus. Engrafted LeSC were monitored by immunofluorescence up two months and during this period LeSC were able to survive after injection. About half of EGFP cells engrafted in hippocampus, expressed neuronal markers (DCX, MAP2, NeuN, Neurofilament-160, GAD67) and shown differentiated neuronal morphology. Because of the persistence of these cells up to adulthood, their proliferation capability in vitro, and their differentiation potential into neuronal cells in vitro and in vivo, we suggest to name them leptomeningeal stem/progenitor cells (LeSC) as a new population never described before. Since meninges cover whole brain, also Leptomeninges from rat spinal cord has been analyzed. Nestin positive cells were distributed as previously observed in the brain, outside the basal lamina, and as a distinct population from astrocytes and oligodendrocytes. Cells were dissected and kept in culture as neurosphere and resulted positive for nestin, MAP2, GFAP, O4, and Oct4. A new study In collaboration with professor M. Schwartz group (Weizmann Institute, Rehovot, Israel) is ongoing to understand the potential role of immune system in regulating leptomeninges and LeSC (as suggested by previous publications from Schwartz’s group). Preliminary results Comparison of LeSC proliferation and nestin expression by immunohistochemistry in SCID vs wt mice, revealed a significant decrease of nestin positive LeSC in SCID mice. However total cell number and proliferating cells in leptomeninges were not changed. Further characterizations are ongoing to understand the phenotype of proliferating nestin negative cells in meninges. The importance of Leptomeningeal stem cells reside in the easier reachable localization compared to the already known neural stem cell niches, and in their high neuronal differentiation potential. These characteristics will open novel studies in regenerative medicine.

Cellule staminali con potenzialità differenziativa neurale sono cararatterizzate dall’espressione di nestina e risiedono in specifiche aree dell’encefalo, quali l’ippocampo, la zona sottoventricolare (SVZ) e il bulbo olfattivo. Questo lavoro si basa sul’ipotesi che altre strutture encefaliche possano contenere nicchie di cellule staminali neurali. Noi ci siamo focalizzati nell’esplorare la porzione comprendente i primi strati corticali e le leptomeningi, poichè in questa regione, interazioni spazio-temporali tra le cellule assicurano la corretta corticogenesi. Il nostro lavoro ha identificato la presenza di una popolazione di cellule nestina-positive nelle leptomeningi di ratto durante lo sviluppo fino all’età adulta. Queste cellule nestina-positive possono essere estratte ed espanse in vitro sia come neurosfere, mostrando elevata similitudine con le neurosfere ottenute da staminali neurali di SVZ, che come coltura omogenea di cellule con caratteristiche di staminalità. La popolazione di cellule staminali espansa in vitro può essere indotta a differenziare con elevata efficienza in cellule eccitabili con fenotipo e morfologia neuronale. Trapiantate in un encefalo di ratto adulto, queste cellule sopravvivono e differenziano in neuroni, mostrando quindi che il potenziale differenziativo neurale è mantenuto anche in vivo. In conclusione, questi dati evidenziano l’esistenza di una popolazione di cellule immature con potenziale differenziativo neuronale residenti nelle leptomeningi per tutta la durata della vita. Considerando che le leptomeningi ricoprono l’intero sistema nervoso centrale, questi risultati potrebbero avere ripercussioni importanti nell’ambito della medicina rigenerativa applicata alle patologie neurologiche e per studi concernenti lo sviluppo corticale.
Stem cells capable of generating neural differentiated cells are recognized by the expression of nestin and reside in specific regions of the brain, namely hippocampus, subventricular zone (SVZ), and olfactory bulb. Our work hypotesis is based on the assumption that other brain sites could host NSC niches. We were interested in exploring the region between leptomeninges and the first layers of the cerebral cortex. In this region, spatial-temporal interactions amongst environmental cells ensure the correct cortex development. In this work, we show that nestin-positive cells are present in rat leptomeninges during development up to adulthood. The newly identified nestin-positive cells can be extracted and expanded in vitro both as neurospheres, displaying high similarity with SVZ-derived neural stem cells, and as homogeneous cell population with stem cell features. In vitro expanded stem cell population can differentiate with high efficiency into excitable cells with neuronal phenotype and morphology. Once injected into adult brain, these cells survive and differentiate into neurons, thus showing that their neuronal differentiation potential is operational also in vivo. In conclusion, our data provide evidence that a specific population of immature cells endowed of neuronal differentiation potential is resident in the leptomeninges throughout the life. As leptomemniges cover the entire central nervous system, these findings could have relevant implications for studies on cortical development and for regenerative medicine applied to neurological disorders.

Il nostro gruppo ha dimostrato per la prima volta che una nuova nicchia di cellule precursori/staminali con potenziale di differenziamento neuronale risiede nelle meningi cerebrali di ratti in età postnatale. Grazie alla loro locazione superficiale, le meningi possono rappresentare una un nuovo ed accessibile tessuto ospitante cellule neuronali precursori/staminali nel Sistema Nervoso Centrale (SNC). Questo rappresenta un importante aspetto che può aprire nuove prospettive per la possibile estrazione e collezione di Cellule Staminali Neuronali (CSN) per la medicina rigenerativa e il trapianto autologo. Inoltre, ogni vaso nel SNC è circondato dallo Spazio Perivascolare (spazio di Virchow-Robin) formato da estroflessioni delle meningi e riempito da liquido cerebrospinale. Ciò suggerisce che le cellule precursori/staminali possono essere ampiamente distribuite anche nel parenchima del SNC. Per questo, noi ipotizziamo che le cellule neuronali precursori/staminali residenti nelle meningi possono contribuire alla omeostasi del SNC in situazioni normali e di malattia. La verifica di questa ipotesi può offrire nuove prospettive per la generazione di nuovi approcci farmacologici per il trattamento di malattie neurodegenerative. Basandosi sugli ottimi potenziali e sulla rilevanza delle nostre precedenti scoperte, durante il mio PhD, ho indirizzato i miei studi nelle seguenti principali domande: Come si distribuiscono le cellule meningee precursori/staminali nel cervello e nel midollo spinale di adulto? La nicchia meningea di cellule precursori/staminali è modificata da condizioni patologiche? Il piano sperimentale di questi due anni di PhD è stato focalizzato nello studio delle cellule meningee precursori/staminali e nella nicchia staminale meningea di organismi modello (ratti e topi). Al fine di analizzare la nicchia meningea a livello cellulare e molecolare, abbiamo usato la combinazione di diverse tecniche come la microscopia confocale ad immunofluorescenza, la real time PCR, il western blot e la coltura di cellule in vitro. Per descrivere le caratteristiche cellulari e molecolari della nicchia staminale meningea, abbiamo analizzato l’espressione e la distribuzione di markers per le cellule progenitrici/staminali (nestina, dcx, cxcr4), per la proliferazione (ki67), l’auto-rinnovamento (oct4, BrdU) e per la matrice extracellulare (laminina, fibronectina). Abbiamo trovato che cellule precursori/staminali con capacità di auto-rinnovamento sono presenti nelle meningi del cervello adulto. Inoltre, abbiamo dimostrato che la presenza di una popolazione di cellule immature nestina positive è una caratteristica conservata tra le speci, compresa quella umana. Il complesso equilibrio presente nel CNS adulto include anche la partecipazione di nicchie NSC funzionali. per studiare l'influenza del SNC in condizioni di malattia nella nicchia staminale meningea, abbiamo analizzato le meningi del cervello di topi affetti da una severa immunodeficienza (SCID) e le meningi del midollo spinale di ratti lesionati (SCI). La nicchia staminale meningea nei topi SCID era profondamente cambiata. Il numero di cellule precursori/staminali era statisticamente diminuita e ciò era associato ad un drammatico aumento delle componenti della matrice cellulare ed extracellulare (fibroblasti, fibronectina e collagene). Oltre a questo, le cellule precorsori/staminali delle meningi di topi SCID hanno dimostrato una velocità proliferativa diminuita in vitro. Questi risultati indicano che la mancanza del sistema immunitario adattativo porta ad una diminuzione delle proprietà staminali della nicchia staminale meningea. Nei ratti SCI abbiamo invece trovato che la nicchia di cellule precursori/staminali aumenta in spessore, e queste cellule aumentano la loro capacità proliferativa e il loro numero. Inoltre, la lesione induce un globale aumento della staminalità legata al profilo di espressione genica. Questa osservazione suggerisce che la SCI induce nelle meningi del midollo spinale un'amplificazione delle proprietà di staminalità della nicchia. In conclusione, i principali risultati di questo lavoro sono: 1) Una popolazione di cellule Precursori/staminali è presente nelle meningi adulte ed è conservata tra le specie. 2) La nicchia meningea, compresa la popolazione di cellule nestina positive del cervello di topo adulto risulta perturbata in modelli di immunodeficienza; 3) La nicchia meningea del midollo spinale di ratto adulto è attivata da un trauma di natura contusiva: le cellule precursori/staminali proliferano ed aumentano in numero. Tutti assieme questi risultati suggeriscono un nuovo ruolo delle meningi come una potenziale nicchia di cellule precorsori/staminali endogene che possono essere modificate in condizione di malattia. Sarà necessaria un ulteriore valutazioni dei meccanismi molecolari coinvolti in condizioni fisiopatologiche delle cellule precursori/staminali delle meningi. Altri risultati potranno aprire interessanti prospettive nella ricerca di nuovi trattamenti farmacologici e nella medicina rigenerativa applicata alle malattie del SNC.
Our group have demonstrated for the first time that a new niche for stem/precursor cells with neural differentiation potential resides in brain meninges (arachnoid and pia mater) of postnatal rats. Meningeal stem/progenitor cells express the neural stem progenitor marker nestin and can be extracted and expanded in vitro as neurospheres. Moreover, they can be induced to differentiate into neurons both in vitro and in vivo (Bifari et al., 2009). Thanks to their superficial location, meninges might represent a new easy accessible tissue hosting neural stem/progenitor cell in the Central Nervous system (CNS). This represents an important aspect that may open new perspective for the possible collection of Neural Stem Cells (NSCs) for regenerative medicine and autologous transplantation. Moreover, every parenchymal vessels inside the CNS are surrounded by a perivascular space (Virchow–Robin space) formed by the extroflexions of meninges filled with cerebrospinal fluid suggesting that meningeal stem/progenitor cells might be widely distributed also in CNS parenchyma. Thus, we hypothesized that meningeal stem/progenitor cells may contribute to CNS homeostasis in health and disease. Verifying this hypothesis could offer new insights for the generation of novel pharmacological approaches to treat neurodegenerative diseases. Based on the great potential and the relevance of our previous finding, during my PhD period, I addressed the following main questions: How is the distribution of the meningeal stem/progenitor cell niche in adult brain and spinal cord? Is the meningeal stem/progenitor cell niche modified by pathological conditions? The experimental plan of these two years of PhD has been focused on the study of the meningeal stem/progenitor cells and the meningeal stem cell niche in healthy and disease animal models (rat and mice). To analyze the meningeal niche at the cellular and molecular levels, we used the combinations of different technical approaches such as immunofluorescence confocal microcopy, real time PCR, western blot and in vitro cell culture. To describe the molecular and cellular features of the meningeal stem/progenitor cells and the organization of the meningeal stem cell niche in adult animals, we analyzed the expression and 4 distribution of markers of stem/progenitor cells (nestin/dcx/cxcr4), proliferation (ki67), self renewal (oct4, BrdU) and extracellular matrix components (laminin, fibronectin, condroitin sulphate, collagen 1a). We found that stem/progenitor cells with self-renewal and proliferative properties are present in adult brain and spinal cord meninges. Moreover, we have shown that the presence of immature nestin/positive cells population is a conserved feature across species including human. The complex dynamic equilibrium present in healthy adult CNS also involves the participation of functional NSC niches. In CNS, various pathogenic events acting by different mechanisms may cause neural cell loss and chronic inflammation. Several agents and mediators sustaining these mechanisms also act on niche homeostasis and it is therefore expected that these conditions may have a deep impact on NSC biology and NSC niche properties. To investigate the influence of CNS disease conditions on the meningeal stem cell niche, we have analyzed meninges of severe combined immunodeficient (SCID) mice and spinal cord injured (SCI) rats. Meningeal stem cell niche in SCID mice was deeply changed. The number of the stem/progenitor cells was statistically significantly decreased associated with a dramatically increase in the cellular and extracellular matrix components related to fibrosis (i.e. fibroblasts, fibronectin and collagene). Furthermore, stem/progenitor cells of meninges have shown a lower proliferation rate in vitro. These data indicate that the lack of the adaptive immune system decreases the stemness properties of the meningeal stem cell niche. In SCI mice model we found that meningeal stem/progenitor cell niche is activated. Following the contusion the meningeal niche increase in thickens, stem/progenitor cells largely increase their proliferation and number. Moreover, we found that SCI induced a global increase in the stemness related gene expression profile. This observation suggests that SCI induces in spinal cord meninges an amplification of the stemness properties of the niche. In conclusion the main results of this work are: I) A stem/precursor cell population, is present in adult meninges and is conserved across species; II) The meningeal niche, including the immature nestin positive cell population, of adult mice brain result perturbed in immunodeficient animal model; 5 III) Meningeal niche is activated by contusive spinal cord injury: meningeal stem/precursor cells proliferate and increase in number. All together our data suggest a novel role for meninges as a potential niche harboring endogenous stem/precursor cells that can be functionally modulated in disease conditions. Depending on specific disease-related stimuli, the meningeal stem cell niche can react both by increasing or decreasing its stem cell properties. This differential response to specific conditions, suggests a potential role and contribution of the meningeal stem/progenitor cells in the physiopathological events occurring in CNS diseases. Further evaluation of the molecular mechanisms involved in the meningeal stem/progenitor cells contribution to the physiopathology of different diseases, will open new prospective for the research on pharmacological treatments and regenerative medicine applied to CNS disease.