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. 2015 Aug 11;5(2):174-84.
doi: 10.1016/j.stemcr.2015.07.002. Epub 2015 Jul 30.

Alpha-Synuclein Expression in the Oligodendrocyte Lineage: An In Vitro and In Vivo Study Using Rodent and Human Models

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Free PMC article

Alpha-Synuclein Expression in the Oligodendrocyte Lineage: An In Vitro and In Vivo Study Using Rodent and Human Models

Mehdi Djelloul et al. Stem Cell Reports. .
Free PMC article

Abstract

In this study, we sought evidence for alpha-synuclein (ASYN) expression in oligodendrocytes, as a possible endogenous source of ASYN to explain its presence in glial inclusions found in multiple system atrophy (MSA) and Parkinson's disease (PD). We identified ASYN in oligodendrocyte lineage progenitors isolated from the rodent brain, in oligodendrocytes generated from embryonic stem cells, and in induced pluripotent stem cells produced from fibroblasts of a healthy individual and patients diagnosed with MSA or PD, in cultures in vitro. Notably, we observed a significant decrease in ΑSYN during oligodendrocyte maturation. Additionally, we show the presence of transcripts in PDGFRΑ/CD140a(+) cells and SOX10(+) oligodendrocyte lineage nuclei isolated by FACS from rodent and human healthy and diseased brains, respectively. Our work identifies ASYN in oligodendrocyte lineage cells, and it offers additional in vitro cellular models that should provide significant insights of the functional implication of ASYN during oligodendrocyte development and disease.

Figures

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Figure 1
Figure 1
Localization of ASYN in Mouse Primary Neurons and Pre-oligodendrocyte Progenitors (A) Experimental approach used for generating rodent postnatal primary forebrain cultures is shown. (B) Rodent postnatal primary forebrain cultures aged 25 DIV contain B-III-TUB+ neurons expressing Snca. The scale bar represents 50 μm. (C) Rodent postnatal primary forebrain cultures contain O4+ oligodendrocytes expressing ASYN. Nuclei are counterstained with DAPI. (Right) Higher magnification of the region of interest is shown. The scale bar represents 50 μm. (D) Quantification of neurons (B-III-TUB+), oligodendrocytes (O4+), astrocytes (GFAP+), and microglia (IBA1+ and GAL-3+) co-expressing ASYN (white bars). Black bars represent quantification for each cell type. Values are indicated as the number of cells per field of view. Mean ± SEM; n = 3 independent cultures. (E) Quantitative real-time PCR analysis shows the abundance (>10-fold) of Snca transcripts in FACS-purified O4+ oligodendrocyte samples compared to whole primary culture sample. Oligodendrocyte enrichment is assessed by the quantification of oligodendrocyte-specific marker transcripts and the absence of astrocytic Gfap transcripts (see Supplemental Experimental Procedures). Mean ± SEM; n = 3–4 independent experiments; t test, p < 0.05, ∗∗p < 0.01. (F) The set of primers we designed to assess mouse Snca expression by quantitative real-time PCR recognizes a unique product of 271 bp and was tested on two independent cultures. (G) Quantitative real-time PCR analysis shows significant enrichment in Cyclin-D1 transcripts in purified O4+ oligodendrocyte sample compared to whole primary culture sample. Mean ± SEM; n = 3 independent experiments; t test, p < 0.05. (H) Identification of KI67+/O4+/ASYN+ oligodendrocyte in rodent postnatal primary forebrain culture. Nuclei are counterstained with DAPI. Insets show higher magnification of the region indicated with straight lines. The scale bar represents 50 μm.
Figure 2
Figure 2
ASYN Expression Decreases during Oligodendrocyte Maturation (A) Absence of ASYN in RIP+ and MBP+ oligodendrocytes detected by confocal microscopy. White arrows pinpoint oligodendrocyte cell bodies. The scale bar represents 50 μm. (B) Rodent postnatal primary forebrain cultures contain O4+ immature oligodendrocytes (≈70% of total oligodendrocyte markers) and CNPASE+, GAL-C+, and MBP+ (<20% for all three markers) mature oligodendrocytes. Mean ± SEM; n = 2–3 independent experiments. There is decreased co-expression between ASYN and CNPASE, GAL-C, or MBP compared to O4+ oligodendrocytes. Mean ± SEM; n = 2–3 independent experiments. (C) Rodent postnatal primary forebrain cultures contain PDGFRA+ oligodendrocyte progenitors expressing ASYN. Nuclei are counterstained with DAPI. White arrowhead pinpoints an O4/ASYN+/PDGFRA+ oligodendrocyte progenitor. The scale bar represents 50 μm. (D) Quantitative real-time PCR analysis shows the abundance (>10-fold) of Snca transcripts in FACS-purified PDGFRA+ oligodendrocyte progenitor samples compared to PDGFRA+ oligodendrocyte progenitor-depleted samples. Enrichment in oligodendrocyte progenitors is assessed by the quantification of Pdgfra transcripts and the absence of astrocytic Gfap and mature oligodendrocytic Mbp transcripts. Mean ± SEM; n = 2–3 independent experiments. (E) Experimental approach used for assessing ASYN expression during rodent oligodendrocyte development. The mESCs were derived from a blastocyste aged E3.5 and subsequently differentiated into oligodendrocytes for a period of 4–5 weeks in vitro. (F) Quantitative real-time PCR shows the loss of Oct4 and upregulation of Nkx2.2, Pdgfra, Cnpase and Mbp, and Snca during the differentiation of mESCs into oligodendrocytes. For each marker, values are presented as a percentage of the highest value. Mean ± SEM; n = 2 independent experiments. (G) Western blotting confirms the downregulation of OCT4 and expression of the oligodendroglial markers and ASYN during the differentiation of mESCs into oligodendrocytes. Blot is representative of two independent experiments. (H) ICC on mESC-differentiated cultures aged 36 DIV confirms the presence and absence of ASYN in PDGFRA+ and CNPASE+, and MBP+ oligodendrocytes, respectively. Quantifications are based on two differentiations. Images are representative of four independent differentiations. Scale bars represent 50 μm.
Figure 3
Figure 3
ASYN in iPSC-Derived O4+ Oligodendrocytes (A) Experimental approach used for generating and assessing ASYN expression during human iPSC-derived oligodendrocyte development. Healthy individual, MSA-C, MSA-P, and PD patient’s skin fibroblasts were reprogrammed by means of viral overexpression of stemness factors hKLF4, hC-MYC, hOCT4, and hSOX2. Following characterization, human iPSCs were subsequently differentiated into oligodendrocytes over a period of 110 DIV. (B) Western blotting confirms the expression of the oligodendroglial marker SOX10 and ASYN during the differentiation of human iPSCs into oligodendrocytes. Blot is representative of two independent experiments. Quantitative real-time PCR shows the upregulation of SNCA in iPSCs during oligodendrocyte differentiation. (C) Perinuclear localization of ASYN in immature O4+ oligodendrocytes aged 65 DIV revealed by ICC. Images are representative of two to three independent differentiations. Scale bars represent 50 μm. (D) Presence of ASYN in O4+, CNPASE+, and MBP+ oligodendrocytes aged 110 DIV revealed by ICC. (Middle, bottom left inset) O4+/MBP/ASYN and O4+/MBP+/ASYN+ oligodendrocytes are shown. Scale bars represent 50 μm. (E) Quantification of O4+ oligodendrocytes by flow cytometry for eight PSC lines differentiated side by side. The early emergence of O4+ oligodendrocytes from line 4 was observed in separate rounds of differentiation. (F) Quantification of O4+ oligodendrocytes co-expressing ASYN over time is shown. (G) Quantitative real-time PCR shows SNCA transcripts in 3S iPSC-derived O4+ oligodendrocyte samples, purified by FACS.
Figure 4
Figure 4
ASYN in Oligodendrocytes In Vivo (A) Schematic representation shows the experimental approach used for assessing ASYN in the mouse embryonic brain. (B) Quantification of PDGFRA/CD140a+ oligodendrocyte progenitors and O4+ oligodendrocytes from the rodent brain at embryonic and postnatal stages, measured by FACS, is shown. (C) Loading of quantitative real-time PCR product confirms the presence of Snca transcripts in E18 PDGFRA/CD140a+ oligodendrocyte progenitors, freshly isolated by FACS, from the mouse embryonic brain. (D) Detection of ASYN in homogenous cultures from mouse embryonic PDGFRA/CD140a+ oligodendrocyte progenitors isolated by FACS at E17.5. ASYN is maintained in homogenous cultures of PDGFRA/CD140a+ oligodendrocyte progenitors maturing into O4+ oligodendrocytes. The scale bar represents 50 μm. (E) Schematic representation shows the experimental approach used for assessing ASYN expression in oligodendrocyte lineage nuclei isolated from the brain of healthy and MSA patients. (F) FACS plots represent the gating strategy employed for isolating SOX10+ oligodendrocyte lineage nuclei from the samples. (G) The decrease in the percentage of NEUN+ nuclei of the total population of all nuclei, in the pons region of MSA patients (n = 3) compared to control (n = 3), was measured by FACS. Mean ± SEM; t test, p < 0.05. (H) Quantitative real-time PCR shows SNCA transcripts in SOX10+ oligodendrocyte lineage nuclei samples purified by FACS from patients T172 and T4640. (I) Loading of quantitative real-time PCR product confirms the presence of SNCA transcripts. The set of primers used to assess human SNCA expression by quantitative real-time PCR recognizes a unique product of 163 bp (from Asi et al., 2014). (J) A summary of our findings is shown.

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