Summary The majority of research on reactive oxygen species (ROS) has focused on their cellular toxicities. Stem cells generally have been thought to maintain low levels of ROS as a protection against these processes. However, recent studies suggest that ROS can also play roles as second messengers, activating normal cellular processes. Here, we investigated ROS function in primary brain-derived neural progenitors. Somewhat surprisingly, we found that proliferative, self-renewing multipotent neural progenitors with the phenotypic characteristics of neural stem cells (NSC) maintained a high ROS status and were highly responsive to ROS stimulation. ROS-mediated enhancements in self-renewal and neurogenesis were dependent on PI3K/Akt signaling. Pharmacological or genetic manipulations that diminished cellular ROS levels also interfered with normal NSC and/or multipotent progenitor function both in vitro and in vivo. This study has identified a redox-mediated regulatory mechanism of NSC function which may have significant implications for brain injury, disease, and repair.

SummaryA period of mild brain overgrowth with an unknown etiology has been identified as one of the most common phenotypes in autism. Here, we test the hypothesis that maternal inflammation during critical periods of embryonic development can cause brain overgrowth and autism-associated behaviors as a result of altered neural stem cell function. Pregnant mice treated with low-dose lipopolysaccharide at embryonic day 9 had offspring with brain overgrowth, with a more pronounced effect in PTEN heterozygotes. Exposure to maternal inflammation also enhanced NADPH oxidase (NOX)-PI3K pathway signaling, stimulated the hyperproliferation of neural stem and progenitor cells, increased forebrain microglia, and produced abnormal autism-associated behaviors in affected pups. Our evidence supports the idea that a prenatal neuroinflammatory dysregulation in neural stem cell redox signaling can act in concert with underlying genetic susceptibilities to affect cellular responses to environmentally altered cellular levels of reactive oxygen species.

Summary Glioblastoma (GBM) metabolism has traditionally been characterized by a primary dependence on aerobic glycolysis, prompting the use of the ketogenic diet (KD) as a potential therapy. In this study we evaluated the effectiveness of the KD in GBM and assessed the role of fatty acid oxidation (FAO) in promoting GBM propagation. In vitro assays revealed FA utilization throughout the GBM metabolome and growth inhibition in nearly every cell line in a broad spectrum of patient-derived glioma cells treated with FAO inhibitors. In vivo assessments revealed that knockdown of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme for FAO, reduced the rate of tumor growth and increased survival. However, the unrestricted ketogenic diet did not reduce tumor growth and for some models significantly reduced survival. Altogether, these data highlight important roles for FA and ketone body metabolism that could serve to improve targeted therapies in GBM.

The use of stem cells in cell replacement therapy for neurodegenerative diseases has received a great deal of scientific and public interest in recent years. This is due to the remarkable pace at which paradigm-changing discoveries have been made regarding the neurogenic potential of embryonic, fetal, and adult cells. Over the last decade, clinical fetal tissue transplants have demonstrated that dopaminergic neurons can survive long term and provide functional clinical benefits for patients with Parkinson's disease. Pluripotent embryonic stem cells and multipotent neural stem cells may provide renewable sources that could replace these primary fetal grafts. Considerable advancement has been made in generating cultures with high numbers of neurons in general and of dopaminergic neurons using a varied array of techniques. However, much of this encouraging progress still remains to be tested on long-term expanded human cultures. Further problems include the low survival rate of these cells following transplantation and the tumorigenic tendencies of embryo-derived cells. However, pre-differentiation or genetic modification of stem cell cultures prior to transplantation may help lead to the generation of high numbers of cells of the desired phenotype following grafting. Boosting particular factors or substrates in the culture media may also protect grafted neurons from oxidative and metabolic stress, and provide epigenetic trophic support. Possible endogenous sources of cells for brain repair include the transdifferentiation of various types of adult cells into neurons. Despite the excitement generated by examples of this phenomenon, further work is needed in order to identify the precise instructive cues that generate neural cells from many other tissue types, and whether or not the new cells are functionally normal. Furthermore, issues such as cell homogeneity and fusion need to be addressed further before the true potential of transdifferentiation can be known. Endogenous stem cells also reside in the neurogenic zones of the adult brain (ventricle lining and hippocampus). Further elucidation of the mechanisms that stimulate cell division and migration are required in order to learn how to amplify the small amount of new cells generated by the adult brain and to direct these cells to areas of injury or degeneration. Finally, a more fundamental understanding of brain injury and disease is required in order to circumvent local brain environmental restrictions on endogenous cell differentiation and survival.

We have examined the effects of predifferentiation and energy substrate deprivation on long-term expanded human neural precursor cells (HNPCs). The pre-differentiation of HNPC cultures produced large numbers of neurons (>60%) and mature glial cells capable of generating glycogen stores that protected the neuronal population from experimental metabolic stress. When predifferentiated HNPCs were transplanted into intact adult rat hippocampus, fewer cells survived compared to undifferentiated HNPC transplants. This cell death was completely attenuated, however, when predifferentiated HNPC cultures were pretreated to boost glial energy stores and resulted in greatly increased neuronal survival in vivo. The transplanted cells primarily engrafted within the granular layer of the dentate gyrus, where a large proportion of the predifferentiated HNPCs co-expressed neuronal markers whereas most HNPCs outside of the neuronal layer did not, indicating that the predifferentiated cells remained capable of responding to local cues in the adult brain. Undifferentiated HNPCs migrated more widely in the brain after grafting than did the predifferentiated cells, which generally remained within the hippocampus.