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. 2015 Dec 8;5(6):988-995.
doi: 10.1016/j.stemcr.2015.10.014. Epub 2015 Nov 19.

Metformin Acts on Two Different Molecular Pathways to Enhance Adult Neural Precursor Proliferation/Self-Renewal and Differentiation

Michael Fatt  1 , Karolynn Hsu  2 , Ling He  3 , Fredric Wondisford  4 , Freda D Miller  5 , David R Kaplan  6 , Jing Wang  7
Affiliations

Metformin Acts on Two Different Molecular Pathways to Enhance Adult Neural Precursor Proliferation/Self-Renewal and Differentiation

Michael Fatt et al. Stem Cell Reports. .

Abstract

The recruitment of endogenous adult neural stem cells for brain repair is a promising regenerative therapeutic strategy. This strategy involves stimulation of multiple stages of adult neural stem cell development, including proliferation, self-renewal, and differentiation. Currently, there is a lack of a single therapeutic approach that can act on these multiple stages of adult neural stem cell development to enhance neural regeneration. Here we show that metformin, an FDA-approved diabetes drug, promotes proliferation, self-renewal, and differentiation of adult neural precursors (NPCs). Specifically, we show that metformin enhances adult NPC proliferation and self-renewal dependent upon the p53 family member and transcription factor TAp73, while it promotes neuronal differentiation of these cells by activating the AMPK-aPKC-CBP pathway. Thus, metformin represents an optimal candidate neuro-regenerative agent that is capable of not only expanding the adult NPC population but also subsequently driving them toward neuronal differentiation by activating two distinct molecular pathways.

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Figures

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Graphical abstract
Figure 1
Figure 1
Metformin Enhances the Self-Renewal and Neuronal Differentiation of Adult Neural Precursors (A–C) Primary neurospheres cultured from the adult SVZ were grown in the presence or absence of 500 nM metformin (Met) and quantified 6 days later, as pictured in (A). Scale bar, 200 μm. (B) Quantification of primary neurosphere (NS) number following metformin or PBS exposure. ∗∗∗p ≤ 0.001 (n = 5 for each group). (C) Quantification of the neurosphere diameter following metformin or PBS exposure, as in (A). ∗∗∗p ≤ 0.001 (pooled data from five independent experiments). (D and E) Primary neurospheres were passaged either once (secondary) or twice (tertiary) into untreated media, and the number (D) and diameter (E) of spheres was quantified 4 days later. ∗∗∗p ≤ 0.001 (n = 4 for each group). (F) Quantitative analysis of number of secondary neurospheres in the absence and presence of metformin (1 μM). ∗p < 0.05 (pooled data from four independent experiments). (G) Immunofluorescence images of βIII-tubulin (βIII tub)-positive neurons generated from SVZ adult neurospheres in the absence and presence of metformin. Arrows denote βIII-tubulin-positive cells. Scale bar, 50 μm. (H) Quantitative analysis of the percentage of βIII-tubulin-positive (β III tubulin+ive) neurons generated in the absence and presence of metformin (200 nM), as shown in (G). ∗∗∗p < 0.001 (pooled data from four independent experiments). (I–L) In (I) and (K), fluorescence photomicrographs are shown of coronal SVZ (I) and SGZ (K) sections from 3-month-old WT mice that received PBS or metformin daily by injection (i.p., 200 mg/kg) for 7 days, followed by a single BrdU (100 mg/kg) injection 24 hr before. Sections were stained for BrdU (green) and counterstained with Hoechst 33258 (blue). Scale bar, 100 μm. (J and L) Quantitative analysis of total number of BrdU-positive (BrdU+ve) precursor cells within the SVZ (J) and SGZ (L) regions, determined from sections as shown in (I) and (K). ∗∗∗p < 0.001 (pooled data from three independent experiments). Arrows denote BrdU-positive cells. Error bars indicate SEM. See also Figure S1.
Figure 2
Figure 2
TAp73 Is Required for Metformin-Induced Self-Renewal and Proliferation of Adult Neural Precursors (A and B) Primary neurospheres (NSs) were cultured from the SVZ of adult mice (3 months old) in the presence or absence of metformin (Met) and treated with the pan-PKC inhibitor, chelerythrine. (B) Quantification of primary neurospheres following 6 days in culture was done based on representative micrographs shown in (A). Scale bar, 200 μm. ∗∗p ≤ 0.01 (pooled data from four independent experiments). (C) The SVZ of 3-month-old WT and CBPS436A-KI mice was dissected and cultured, and primary neurosphere formation was quantified 6 days later in the presence and absence of metformin. ∗∗p ≤ 0.01. (pooled data from three independent experiments). (D) Metformin- or PBS-treated primary neurospheres (as in A) from both genotypes were passaged into untreated media, and the number of secondary neurospheres was quantified 4 days later. ∗∗p ≤ 0.01. (pooled data from three independent experiments). (E) qRT-PCR for TAp73 mRNA performed on RNA extracted from primary neurospheres grown in the presence or absence of metformin. ∗∗p ≤ 0.01 (n = 4 for each group). (F–H) Primary neurospheres were cultured from the SVZ of 3-month-old TAp73+/+ and TAp73−/− mice in either the presence or absence of 500 nM metformin. Scale bar, 200 μm. (G) Quantification of primary neurospheres from both genotypes following metformin exposure was done based on representative micrographs shown in (F). ∗∗p ≤ 0.01 (pooled data from four independent experiments). (H) Primary neurospheres cultured with or without metformin (as in A) from both genotypes were passaged into untreated media, and secondary neurospheres were counted 4 days later. ∗∗p ≤ 0.01 (pooled data from four independent experiments). (I) Confocal micrographs of representative coronal sections through the lateral ventricles of metformin- or PBS-injected TAp73+/+ and TAp73−/− mice, stained for BrdU (green) 24 hr after BrdU injection. Sections are counterstained for Hoechst 33258 (blue). Scale bar, 100 μm. (J and K) Quantification of the total number of BrdU-positive (BrdU+ve) cells in the SVZ (J) and SGZ (K) of metformin- or PBS-treated mice of both genotypes, as pictured in (I). ∗∗∗p ≤ 0.001; ∗∗p ≤ 0.01 (pooled data from three independent experiments). Error bars indicate SEM.
Figure 3
Figure 3
Metformin Enhances Neuronal Differentiation of Adult Neural Precursors by Activating the aPKC-CBP Pathway (A) Quantification of primary neurosphere (NS) number cultured from 3-month-old CBPS436A-KI and p300G422S-KI (KI) mice (pooled data from four independent experiments). (B) Quantification of the secondary neurosphere number from CBPS436A-KI and p300G422S-KI mice in the absence and presence of metformin (Met). ∗∗p < 0.01; ∗∗∗p < 0.001 (pooled data from four independent experiments). (C) Immunofluorescence images of βIII-tubulin-positive neurons generated from SVZ WT and CBPS436A-KI neurospheres in the absence and presence of metformin. Arrows denote βIII-tubulin-positive cells. Scale bar, 20 μm. (D and E) Quantitative analysis of the percentage of βIII-tubulin-positive (β III tubulin+ve) neurons generated from CBPS436A-KI neurospheres (D) and p300G422S-KI neurospheres (E), determined as shown in (C). (pooled data from four independent experiments). (F and G) Quantitative analysis of the percentage of βIII-tubulin (βIII tub)-positive neurons generated from SVZ WT and CBPS436A-KI (F) and p300G422S (G) neurospheres in the absence and presence of metformin (200 nM). ∗∗∗p < 0.001; ∗∗p < 0.01 (pooled data from four independent experiments). (H) Quantitative analysis of the percentage of βIII-tubulin-positive neurons generated from SVZ WT, CBPS436A-KI, and p300G422S-KI neurospheres in the absence and presence of AICAR (500 nM). ∗p < 0.05 (pooled data from four independent experiments). (I) Immunofluorescence images of GFP-positive, βIII-tubulin-positive neurons generated from SVZ WT neurospheres transfected with CA-AMPKα1. Arrows denote GFP-positive, βIII-tubulin-positive cells. Scale bar, 20 μm. (J) Quantification of the percentage of transfected, βIII-tubulin-positive neurons generated from SVZ WT and CBPS436A-KI neurospheres. EV, empty vector, CA-AMPKα1, constitutively active AMPK α1 subunit. ∗∗p < 0.01 (pooled data from four independent experiments). Error bars indicate SEM.
Figure 4
Figure 4
Model Describing Two Distinct Molecular Pathways Mediating Metformin-Induced Proliferation/Self-Renewal and Neuronal Differentiation TF, transcription factors; Ac, acetylation.
See this image and copyright information in PMC

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