Involvement of protein S, a vitamin K- dependent protein, in the phagocytosis and anti-tumor effects of brain stem cells

Des cellules souches neurales (CSN) persistent dans le cerveau de mammifères adultes, y compris l'Homme. Les CSN participent à l'homéostasie tissulaire en générant de nouveaux neurones, permettant le remplacement de certains neurones morts. Cependant, la production de nouvelles cellules se fait en excès et plus de la moitié des cellules nouvellement générées meurent. Les cellules mortes ainsi que leurs débris doivent être éliminés par phagocytose. Dans une première partie de ma thèse, nous avons montré pour la première fois, que les CSN sont capables de phagocytose et que cette activité des CSN est régulée par la protéine S (ProS), une protéine vitamine-K dépendante, et son récepteur MerTK. Une rupture de l'homéostasie tissulaire conduit à des pathologies dont les cancers. Les interactions entre les CSN et des tumeurs cérébrales, les gliomes, sont duelles et étroites : des CSN dont la prolifération est dérégulée seraient à l'origine des tumeurs, mais, à l'inverse, les CSN saines peuvent migrer vers les gliomes et inhiber leur croissance. Dans une deuxième partie de ma thèse, nous avons confirmé l'effet anti-tumoral des CSN et nous avons établi que la ProS sécrétée par les gliomes attire les CSN vers la tumeur d'une part, et d'autre part, que les CSN diminuent la croissance tumorale par la sécrétion de leur ProS. Nous démontrons de plus, que ce processus s'accompagne d'une mort cellulaire des gliomes dont les débris sont phagocytés par les CSN. Mon travail de thèse a permis d'identifier de nouveaux mécanismes impliqués dans le maintien de l'homéostasie tissulaire par les CSN en conditions physiopathologiques.Neural stem cells (NSC) persist in the brain of adult mammals, including humans. NSC contribute to tissue homeostasis maintenance through the genesis of new neurons that replace part of the cells that are maybe lost. However, the production of new cells is in excess and half of the newly generated cells die. Dead cells and their debris must be removed by phagocytosis. NSC express protein S (ProS) and its receptors, which are involved in phagocytosis. During the first part of my PhD thesis, we established for the first time, using in vitro and in vivo experiments, that NSC possess a phagocytic activity which is regulated by protein S (ProS), a vitamin K-dependent protein, and its receptor MerTK. Tissue homeostasis disruption leads to diseases such as cancers. Interactions between the NSC and brain tumors such as gliomas are dual and complex: glioma may arise from transformed NSC, but, conversely, normal NSC migrate towards glioma and inhibit their growth. Our study confirms the anti-tumoral effect of NSC and demonstrates, for the first time that ProS secreted by gliomas acts on Tyro-3 to attract NSC and that NSC secrete ProS which reduces tumor growth of ProS. In addition, we show that this process results in the death of glioma cells that are then phagocytosed by NSC. Our highlights identified novel mechanisms by which NSC contribute to tissue homeostasis in pathophysiological conditions

The vitamin K-dependent factor, protein S, regulates brain neural stem cell migration and phagocytic activities towards glioma cells

International audienceMalignant gliomas are the most common primary brain tumors. Due to both their invasive nature and resistance to multimodal treatments, these tumors have a very high percentage of recurrence leading in most cases to a rapid fatal outcome. Recent data demonstrated that neural stem/progenitor cells possess an inherent ability to migrate towards glioma cells, track them in the brain and reduce their growth. However, mechanisms involved in these processes have not been explored in-depth. In the present report, we investigated interactions between glioma cells and neural stem/progenitor cells derived from the subventricular zone, the major brain stem cell niche. Our data show that neural stem/pro-genitor cells are attracted by cultured glioma-derived factors. Using multiple approaches, we demonstrate for the first time that the vitamin K-dependent factor protein S produced by glioma cells is involved in tumor tropism through a mechanism involving the tyrosine kinase receptor Tyro3 that, in turn, is expressed by neural stem/ progenitor cells. Neural stem/progenitor cells decrease the growth of both glioma cell cultures and clonogenic population. Cultured neural stem/progenitor cells also engulf, by phagocytosis, apoptotic glioma cell-derived fragments and this mechanism depends on the exposure of phosphatidylserine eat-me signal and is stimulated by protein S. The disclosure of a role of protein S/Tyro3 axis in neural stem/progenitor cell tumor-tropism and the demonstration of a phagocytic activity of neural stem/progenitor cells towards dead glioma cells that is regulated by protein S open up new perspectives for both stem cell biology and brain physiopathology

Evidence for a subventricular zone neural stem cell phagocytic activity stimulated by the vitamin K-dependent factor protein S.

article dans une revue avec comité de lectureInternational audienceNeural stem cells, whose major reservoir in the adult mammalian brain is the subventricular zone (SVZ), ensure neuropoiesis, a process during which many generated cells die. Removal of dead cells and debris by phagocytes is necessary for tissue homeostasis. Using confocal and electron microscopy, we demonstrate that cultured SVZ cells phagocytose both 1 and 2 µm latex beads and apoptotic cell-derived fragments. We determine by flow cytometry that phagocytic cells represent more than 10% of SVZ cultured cells. Phenotyping of SVZ cells using nestin, GFAP, Sox2, or LeX/SSEA and quantification of aldehyde dehydrogenase (ALDH) activity, reveals that cells with neural stem-cell features phagocytose and represent more than 30% of SVZ phagocytic cells. In vivo, nestin-, Sox2-, and ALDH-expressing neural stem-like cells engulfed latex beads or apoptotic cell-derived fragments that were injected into mice lateral brain ventricles. We show also that SVZ cell phagocytic activity is an active process, which depends both on cytoskeleton dynamic and on recognition of phosphatidylserine eat-me signal, and is stimulated by the vitamin K-dependent factor protein S (ProS). ProS neutralizing antibodies inhibit SVZ cell phagocytic activity and exposure of SVZ cells to apoptotic cell-derived fragments induces a transient Mer tyrosine kinase receptor (MerTK) phosphorylation. Conversely, MerTK blocking antibodies impair both basal and ProS-stimulated SVZ cell phagocytic activity. By revealing that neural stem-like cells act within the SVZ neurogenic niche as phagocytes and that the ProS/MerTK path represents an endogenous regulatory mechanism for SVZ cell phagocytic activity, the present report opens-up new perspectives for both stem cell biology and brain physiopathology

Loss of Cxcr5 alters neuroblast proliferation and migration in the aged brain

Neurogenesis, the production of new neurons from neural stem cells, dramatically decreases during aging concomitantly with increased inflammation both systemically and in the brain. However, the precise role of inflammation and whether local or systemic factors drive the neurogenic decline during aging is poorly understood. Here, we identify CXCR5/5/CXCL13 signaling as a novel regulator of neurogenesis in the aged brain. The chemokine Cxcl13 was found to be upregulated in the brain during aging. Loss of its receptor, Cxcr5, led to increased proliferation and decreased numbers of neuroblasts in the aged subventricular zone (SVZ), together with accumulation of neuroblasts in the rostral migratory stream and olfactory bulb (OB), without increasing the amount of new mature neurons in the OB. The effect on proliferation and migration was specific to neuroblasts and likely mediated through increased levels of systemic IL-6 and local Cxcl12 expression in the SVZ. Our study raises the possibility of a new mechanism by which interplay between systemic and local alterations in inflammation regulates neurogenesis during aging

FOXO3 targets are reprogrammed as Huntington's disease neural cells and striatal neurons face senescence with p16INK4a increase.

Neurodegenerative diseases (ND) have been linked to the critical process in aging-cellular senescence. However, the temporal dynamics of cellular senescence in ND conditions is unresolved. Here, we show senescence features develop in human Huntington's disease (HD) neural stem cells (NSCs) and medium spiny neurons (MSNs), including the increase of p16INK4a , a key inducer of cellular senescence. We found that HD NSCs reprogram the transcriptional targets of FOXO3, a major cell survival factor able to repress cell senescence, antagonizing p16INK4a expression via the FOXO3 repression of the transcriptional modulator ETS2. Additionally, p16INK4a promotes cellular senescence features in human HD NSCs and MSNs. These findings suggest that cellular senescence may develop during neuronal differentiation in HD and that the FOXO3-ETS2-p16INK4a axis may be part of molecular responses aimed at mitigating this phenomenon. Our studies identify neuronal differentiation with accelerated aging of neural progenitors and neurons as an alteration that could be linked to NDs

FOXO3 targets are reprogrammed as Huntington's disease neural cells and striatal neurons face senescence with p16 INK4a increase

International audienceNeurodegenerative diseases (ND) have been linked to the critical process in aging-cellular senescence. However, the temporal dynamics of cellular senescence in ND conditions is unresolved. Here, we show senescence features develop in human Huntington's disease (HD) neural stem cells (NSCs) and medium spiny neurons (MSNs), including the increase of p16INK4a , a key inducer of cellular senescence. We found that HD NSCs reprogram the transcriptional targets of FOXO3, a major cell survival factor able to repress cell senescence, antagonizing p16INK4a expression via the FOXO3 repression of the transcriptional modulator ETS2. Additionally, p16INK4a promotes cellular senescence features in human HD NSCs and MSNs. These findings suggest that cellular senescence may develop during neuronal differentiation in HD and that the FOXO3-ETS2-p16INK4a axis may be part of molecular responses aimed at mitigating this phenomenon. Our studies identify neuronal differentiation with accelerated aging of neural progenitors and neurons as an alteration that could be linked to NDs

Rapid and efficient induction of functional astrocytes from human pluripotent stem cells

The derivation of astrocytes from human pluripotent stem cells is currently slow and inefficient. We demonstrate that overexpression of the transcription factors SOX9 and NFIB in human pluripotent stem cells rapidly and efficiently yields homogeneous populations of induced astrocytes. In our study these cells exhibited molecular and functional properties resembling those of adult human astrocytes and were deemed suitable for disease modeling. Our method provides new possibilities for the study of human astrocytes in health and disease