Neonatal hypoxia-ischemia in rat elicits a region-specific neurotrophic response in SVZ microglia.

BACKGROUND: Recent findings describe microglia as modulators of neurogenesis in the subventricular zone (SVZ). SVZ microglia in the adult rat are thought to adopt a neurotrophic phenotype after ischemic stroke. Early postnatal microglia are endogenously activated and may therefore exhibit an increased sensitivity to neonatal hypoxia-ischemia (HI). The goal of this study was to investigate the impact of cortico-striatal HI on the microglial phenotype, function, and gene expression in the early postnatal SVZ. METHODS: Postnatal day (P)7 rats underwent sham or right-hemispheric HI surgery. Microglia in the SVZ, the uninjured cortex, and corpus callosum were immunohistochemically analyzed at P10, P20, and P40. The transcriptome of microdissected SVZ and cortical microglia was analyzed at P10 and P20, and the effect of P10 SVZ microglia on neurosphere generation in vitro was studied. RESULTS: The microglial response to HI was region-specific. In the SVZ, a microglial accumulation, prolonged activation and phagocytosis was noted that was not observed in the cortex and corpus callosum. The transcriptome of SVZ microglia and cortical microglia were distinct, and after HI, SVZ microglia concurrently upregulated pro- and anti-inflammatory as well as neurotrophic genes. In vitro, microglia isolated from the SVZ supported neurosphere generation in a concentration-dependent manner. CONCLUSIONS: Microglia are an inherent cellular component of the early postnatal SVZ and undergo developmental changes that are affected on many aspects by neonatal HI injury. Our results demonstrate that early postnatal SVZ microglia are sensitive to HI injury and display a long-lasting region-specific response including neurotrophic features.

Neonatal hypoxia-ischemia in rat increases doublecortin concentration in the cerebrospinal fluid.

Doublecortin (DCX) is a microtubule-associated protein widely used as an indicator of neurogenesis in immunohistochemical analyses of the postmortem adult brain. A recent study reported that DCX can be quantified in the cerebrospinal fluid (CSF) from healthy rats between postnatal day 0 (P0) and P30. However, it is currently unclear whether the concentration of DCX in the CSF (CSF-DCX) may represent a measure of endogenous neurogenesis. To address this question, this study examined the impact of a neonatal hypoxic-ischemic (HI) brain injury, known to induce neurogenesis, on CSF-DCX. HI was elicited at P7 in Sprague-Dawley rat neonates, and CSF was collected serially from the cisterna magna at P5 and P10, or at P10 and P15. A sandwich immunoassay was used to measure CSF-DCX. Brains from P10 neonates were analyzed immunohistochemically for neurogenesis and cell death markers. Mean CSF-DCX was significantly higher in HI- than in sham-exposed animals, at both P10 and P15. In the HI group at P10, CSF-DCX and stroke severity correlated positively. DCX immunoreactivity was increased in the ipsilateral neurogenic niches from the P10 HI brains in comparison with that of shams. The number of proliferative DCX-positive cells was higher in the ipsilateral hippocampal subgranular zone (SGZ) than in the HI contralateral or sham SGZ. Thus, neonatal HI brain injury disrupts the developmental time-course of DCX levels in the CSF. Our data suggest that the increased concentration of DCX in the CSF after neonatal HI is the result of both cellular injury and increased neurogenesis.

Maternal immune activation and abnormal brain development across CNS disorders.

Epidemiological studies have shown a clear association between maternal infection and schizophrenia or autism in the progeny. Animal models have revealed maternal immune activation (mIA) to be a profound risk factor for neurochemical and behavioural abnormalities in the offspring. Microglial priming has been proposed as a major consequence of mIA, and represents a critical link in a causal chain that leads to the wide spectrum of neuronal dysfunctions and behavioural phenotypes observed in the juvenile, adult or aged offspring. Such diversity of phenotypic outcomes in the mIA model are mirrored by recent clinical evidence suggesting that infectious exposure during pregnancy is also associated with epilepsy and, to a lesser extent, cerebral palsy in children. Preclinical research also suggests that mIA might precipitate the development of Alzheimer and Parkinson diseases. Here, we summarize and critically review the emerging evidence that mIA is a shared environmental risk factor across CNS disorders that varies as a function of interactions between genetic and additional environmental factors. We also review ongoing clinical trials targeting immune pathways affected by mIA that may play a part in disease manifestation. In addition, future directions and outstanding questions are discussed, including potential symptomatic, disease-modifying and preventive treatment strategies.

Primitive erythropoiesis is regulated by miR-126 via nonhematopoietic Vcam-1+ cells.

Primitive erythropoiesis defines the onset of hematopoiesis in the yolk sac of the early embryo and is initiated by the emergence of progenitors assayed as colony-forming cells (EryP-CFCs). EryP-CFCs are detected for only a narrow window during embryonic development, suggesting that both their initiation and termination are tightly controlled. Using the embryonic stem differentiation system to model primitive erythropoiesis, we found that miR-126 regulates the termination of EryP-CFC development. Analyses of miR-126 null embryos revealed that this miR also regulates EryP-CFCs in vivo. We identified vascular cell adhesion molecule-1 (Vcam-1) expressed by a mesenchymal cell population as a relevant target of miR-126. Interaction of EryP-CFCs with Vcam-1 accelerated their maturation to ßh1-globin(+) and Ter119(+) cells through a Src family kinase. These findings uncover a cell nonautonomous regulatory pathway for primitive erythropoiesis that may provide insight into the mechanism(s) controlling the developmental switch from primitive to definitive hematopoiesis.

Human pluripotent stem cells differentiated in fully defined medium generate hematopoietic CD34- and CD34+ progenitors with distinct characteristics.

BACKGROUND: Differentiation of pluripotent stem cells in vitro provides a powerful means to investigate early developmental fates, including hematopoiesis. In particular, the use of a fully defined medium (FDM) would avoid biases induced by unidentified factors contained in serum, and would also allow key molecular mediators involved in such a process to be identified. Our goal was to induce in vitro, the differentiation of human embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC) into morphologically and phenotypically mature leukocytes and erythrocytes, in the complete absence of serum and feeder cells. METHODOLOGY/PRINCIPAL FINDINGS: ESC and iPSC were sequentially induced in liquid cultures for 4 days with bone morphogenic protein-4, and for 4 days with FLT3-ligand, stem cell factor, thrombopoietin and vascular endothelium growth factor. Cell differentiation status was investigated by both mRNA expression and FACS expression profiles. Cells were further sorted and assayed for their hematopoietic properties in colony-forming unit (CFU) assays. In liquid cultures, cells progressively down-modulated Oct-4 expression while a sizeable cell fraction expressed CD34 de novo. SCL/Tal1 and Runx1 transcripts were exclusively detected in CD34(+) cells. In clonal assays, both ESC and iPSC-derived cells generated CFU, albeit with a 150-fold lower efficacy than cord blood (CB) CD34(+) cells. ESC-derived CD34(+) cells generated myeloid and fully hemoglobinized erythroid cells whereas CD34(-) cells almost exclusively generated small erythroid colonies. Both ESC and iPSC-derived erythroid cells expressed embryonic and fetal globins but were unable to synthesize adult ß-globin in contrast with CB cells, suggesting that they had differentiated from primitive rather than from definitive hematopoietic progenitors. CONCLUSIONS/SIGNIFICANCE: Short-term, animal protein-free culture conditions are sufficient to sustain the differentiation of human ESC and iPSC into primitive hematopoietic progenitors, which, in turn, produce more mature blood cell types. However, additional factors have yet to be identified to allow their differentiation into definitive erythroid cultures.

Fetal bovine serum enables cardiac differentiation of human embryonic stem cells.

During development, cardiac commitment within the mesoderm requires endoderm-secreted factors. Differentiation of embryonic stem cells into the three germ layers in vitro recapitulates developmental processes and can be influenced by supplements added to culture medium. Hence, we investigated the effect of fetal bovine serum (FBS) and KnockOut serum replacement (SR) on germ layers specification and cardiac differentiation of H1 human embryonic stem cells (hESC) within embryoid bodies (EB). At the time of EB formation, FBS triggered an increased apoptosis. As assessed by quantitative PCR on 4-, 10-, and 20-day-old EB, FBS promoted a faster down-regulation of pluripotency marker Oct4 and an increased expression of endodermal (Sox17, alpha-fetoprotein, AFP) and mesodermal genes (Brachyury, CSX). While neuronal and hematopoietic differentiation occurred in both supplements, spontaneously beating cardiomyocytes were only observed in FBS. Action potential (AP) morphology of hESC-derived cardiomyocytes indicated that ventricular cells were present only after 2 months of culture. However, quantification of myosin light chain 2 ventricular (mlc2v)-positive areas revealed that mlc2v-expressing cardiomyocytes could be detected already after 2 weeks of differentiation, but not in all beating clusters. In conclusion, FBS enabled cardiac differentiation of hESC, likely in an endodermal-dependent pathway. Among cardiac cells, ventricular cardiomyocytes differentiated over time, but not as the predominant cardiac cell subtype.

Human adaptive immune system Rag2-/-gamma(c)-/- mice.

Although many biologic principles are conserved in mice and humans, species-specific differences exist, for example, in susceptibility and response to pathogens, that often do not allow direct implementation of findings in experimental mice to humans. Research in humans, however, for ethical and practical reasons, is largely restricted to in vitro assays that lack components and the complexity of a living organism. To nevertheless study the human hematopoietic and immune system in vivo, xenotransplantation assays have been developed that substitute human components to small animals. Here, we summarize our recent findings that transplantation of human cord blood CD34(+) cells to newborn Rag2(-/-)gamma(c)(-/-) mice leads to de novo development of major functional components of the human adaptive immune system. These human adaptive immune system Rag2(-/-)gamma(c)(-/-) (huAIS-RG) mice can now be used as a technically straightforward preclinical model to evaluate in vivo human adaptive immune system development as well as immune responses, for example, to vaccines or live infectious pathogens.

Clonal type I interferon-producing and dendritic cell precursors are contained in both human lymphoid and myeloid progenitor populations.

Because of different cytokine responsiveness, surface receptor, and transcription factor expression, human CD11c(-) natural type I interferon-producing cells (IPCs) and CD11c(+) dendritic cells were thought to derive through lymphoid and myeloid hematopoietic developmental pathways, respectively. To directly test this hypothesis, we used an in vitro assay allowing simultaneous IPC, dendritic cell, and B cell development and we tested lymphoid and myeloid committed hematopoietic progenitor cells for their developmental capacity. Lymphoid and common myeloid and granulocyte/macrophage progenitors were capable of developing into both functional IPCs, expressing gene transcripts thought to be associated with lymphoid lineage development, and into dendritic cells. However, clonal progenitors for both populations were about fivefold more frequent within myeloid committed progenitor cells. Thus, in humans as in mice, natural IPC and dendritic cell development robustly segregates with myeloid differentiation. This would fit with natural interferon type I-producing cell and dendritic cell activity in innate immunity, the evolutionary older arm of the cellular immune system.

Development of a human adaptive immune system in cord blood cell-transplanted mice.

Because ethical restrictions limit in vivo studies of the human hemato-lymphoid system, substitute human to small animal xenotransplantation models have been employed. Existing models, however, sustain only limited development and maintenance of human lymphoid cells and rarely produce immune responses. Here we show that intrahepatic injection of CD34+ human cord blood cells into conditioned newborn Rag2-/-gammac-/- mice leads to de novo development of B, T, and dendritic cells; formation of structured primary and secondary lymphoid organs; and production of functional immune responses. This provides a valuable model to study development and function of the human adaptive immune system in vivo.