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. 2011 Jan 7;8(1):59-71.
doi: 10.1016/j.stem.2010.11.028.

Proliferative neural stem cells have high endogenous ROS levels that regulate self-renewal and neurogenesis in a PI3K/Akt-dependant manner

Janel E Le Belle  1 , Nicolas M Orozco, Andres A Paucar, Jonathan P Saxe, Jack Mottahedeh, April D Pyle, Hong Wu, Harley I Kornblum
Affiliations

Proliferative neural stem cells have high endogenous ROS levels that regulate self-renewal and neurogenesis in a PI3K/Akt-dependant manner

Janel E Le Belle et al. Cell Stem Cell. .

Abstract

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 that may have significant implications for brain injury, disease, and repair.

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Figures

Figure 1
Figure 1. Stimulation of neurosphere cultures by reactive oxygen species promotes proliferation and self-renewal
(A) A diagram of NADPH oxidase (NOX) signaling in the PI3K/Akt/mTOR pathway. (B) Serial clonal density neurosphere formation, sphere diameters, and multipotency in response to exogenous H2O2 stimulation, (C) Clonal density neurosphere formation in mouse (ms) embryonic day 14 (E14) cortical cultures, adult subventricular zone (aSVZ) cultures, and human fetal (HF) cortical cultures as a percentage of control (untreated) conditions. (D) Cells sorted according to their relative endogenous ROS levels or unselected (US) cells from primary adult SVZ microdissections. (E) Secondary sorts of cells according to their relative endogenous ROS levels, (F) Human ES-derived monolayer cell proliferation following sorting into relative endogenous ROS levels. (See also supplemental figure 1A-C.)
Figure 2
Figure 2. Neural stem cells are associated with a high-ROS status and NOX is a significant endogenous source of cellular ROS regulating NSC function in low oxygen conditions
(A) Cells derived from adult SVZ were sorted for the highest (top 10%) endogenous ROS levels using DCFDA dye fluorescence (propidium iodide-negative population) or for unselected (US) propidium iodide-negative cells and then serially cultured at clonal density to determine relative stem cell numbers (B) The phenotypes of the high and low ROS cells immediately after sorting were evaluated by immunocytochemistry and flow cytometry. (C) The relative endogenous ROS levels were measured in the EGFR+GFAP+CD24- & ID1+GFAP+, cell populations (the stem cell containing fractions) compared to the GFAP negative populations (D) The relative endogenous ROS levels were measured in the EGFR+GFAP+CD24-, ID1+GFAP+, and Lex+ cells compared to the cells negative for those markers. (E) Relative expression of the NOX2 homologue in neurosphere cultures grown in normoxic, room-air oxygen levels (Norm) or in low-oxygen (4%) conditions (Hyp) normalized to 18S housekeeping expression. (F) Clonal neurosphere formation in room-air oxygen levels (Normoxia) or low oxygen (Hypoxia) in control media (C) or treated with hydrogen peroxide (H), or the NOX inhibitor Apocynin (A). See also Supplemental Figure 2A-B.
Figure 3
Figure 3. Reactive oxygen species are required for stimulation of normal neural stem cell self-renewal
(A) Clonal neurosphere formation by adult SVZ cells in low growth factor media (Low GF; 1/20th normal growth factor concentrations) is compared to normal growth factor concentrations (GF) or supplemented with hydrogen peroxide (H2O2). (B) The corresponding endogenous ROS levels detected by DCFDA dye and expressed in relative fluorescent units (RFU) in the same culture conditions described in (A). (C) Clonal neurosphere formation in response to NOX inhibition (DPI) and rescue with hydrogen peroxide (H) in cells from embryonic and adult brain. (D) Serial clonal neurosphere formation by NOX2 mutant (MUT) and wild-type (WT) cells with H2O2 rescue. (E) Multipotency of NOX2 MUT and WT neurospheres over serial clonal passages with H2O2 rescue. See also Supplemental Figure 3A-B.
Figure 4
Figure 4. ROS augment trophic factor signaling and are dependent on the PI3K/Akt signaling pathway for their effects
(A) Clonal neurosphere formation following stimulation of adult SVZ cells by BDNF (B), BDNF plus the NOX inhibitor DPI (B+D), and BDNF plus the anti-oxidant N-acetyl-cysteine (B+N) all expressed as a percentage of control (untreated) cells. (B) Endogenous superoxide production in BDNF (B) and BDNF plus DPI (B+D) treated adult SVZ cultures. (C) Oxidized and reduced PTEN are visualized on a redox-sensitive western blot. (D) Clonal density neurosphere formation in response to stimulation by hydrogen peroxide (H2O2) and glucose oxidase (Gox) was determined in PTEN-deficient (KO), PTEN heterozygous (HET), and wild-type (WT) cells. (E) Phospho-Akt activation in exogenous ROS-stimulated cells, NOX-inhibited cells, ROShi and ROSlo cells, BDNF-stimulated, low growth factor and low growth factor supplemented with exogenous H2O2. (F) Phospho-S6 activation detected by immunocytochemistry and flow cytometry in ROShi, ROSlo, NOX2 mutant & wild-type, and LY294002-treated cells (G) IC50 calculations for LY294002 (Pi3K inhibitor) and U0126 (ERK inhibitor). See also Supplemental Figure 4A-C.
Figure 5
Figure 5. ROS stimulation during mitogenic expansion enhances neurogenesis in a PI3K-dependent manner
(A) TuJ1 positive neurons produced in hydrogen peroxide (H), glucose oxidase (G), Apocynin (A), DPI (D), or LY294002 (LY; H+LY=HL; G+LY=GL) supplemented conditions during mitogenic expansion. (B) Picomicrographs of TuJ1 staining (green) and Hoechst (blue) counterstain in differentiated neurospheres under the conditions described above taken at 10× magnification. (C) Neuron numbers (as a percentage of total Hoechst cells) produced by differentiated neurospheres from NOX2 mutant (MUT) and wild-type (WT) cultures (D) Picomicrographs of TUJ1 (red) and Hoechst (blue) expression in differentiated cultures from NOX2 mutants and wild-type cultures.
Figure 6
Figure 6. In vivo inhibition of NADPH oxidase by Apocynin decreases SVZ proliferation, endogenous ROS levels, and NSC self-renewal
(A) Picomicrographs of hydroethidine (HEt) fluorescence in the subventricular zone of Apocynin and vehicle treated mice. The lateral ventricle (LV) is indicated. (B) Relative expression of the NOX2 (gp91phox) homologue of NADPH oxidase in the adult SVZ compared to neighboring cortex. (C) Hydroethidine fluorescence (ROS levels) in the SVZ and the surrounding cortical (CTX) or striatal (STR) tissue. (D) Hydroethidine fluorescence intensity (ROS) levels within the SVZ following a 3-week daily apocynin (Apo) or vehicle (control) treatment. (E) Cell proliferation (Ki67) in the SVZ of apocynin- and vehicle-treated animals. (F) Serial clonal density neurosphere formation by cells derived from the SVZ of mice which received apocynin or vehicle treatment in vivo.
Figure 7
Figure 7. In vivo SVZ proliferation and neurogenesis are significantly impacted by changes in cellular ROS
(A) SVZ proliferation (Ki67+) and Olfactory bulb (OB) neurogenesis (BrdU+/NeuN+) was stereologically quantitated in mutant and wildtype mice. (B) Picomicrographs of Ki67 and BrdU labeling in the adult SVZ at 20× magnification (C) Area measurements of the granule cell layer (GCL) of the olfactory bulb in mutant (MUT) and wild-type (WT) mice. (D) Pictomicrograph of olfactory bulb (NeuN-red, BrdU-green, and Hoechst-blue). (E) Cell phenotypes in NOX2 mutant SVZ compared to wild-type cells. (F) SVZ proliferation (Ki67+ cells) was quantitated in wild-type mice treated with the NOX inhibitor apocynin (APO), the neuroinflammatory mediator lipopolysaccharide (LPS), or both. Results are expressed as a percentage of control (vehicle) treated. (G) Picomicrographs of of Ki67 immunostaining the SVZ of the mice described in (F). See also Supplemental Figure 5A.
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