Selenotranscriptomic Analyses Identify Signature Selenoproteins in Brain Regions in a Mouse Model of Parkinson's Disease

Abstract

Genes of selenoproteome have been increasingly implicated in various aspects of neurobiology and neurological disorders, but remain largely elusive in Parkinson's disease (PD). In this study, we investigated the selenotranscriptome (24 selenoproteins in total) in five brain regions (cerebellum, substantia nigra, cortex, pons and hippocampus) by real time qPCR in a two-phase manner using a mouse model of chronic PD. A wide range of changes in selenotranscriptome was observed in a manner depending on selenoproteins and brain regions. While Selv mRNA was not detectable and Dio1& 3 mRNA levels were not affected, 1, 11 and 9 selenoproteins displayed patterns of increase only, decrease only, and mixed response, respectively, in these brain regions of PD mice. In particular, the mRNA expression of Gpx1-4 showed only a decreased trend in the PD mouse brains. In substantia nigra, levels of 17 selenoprotein mRNAs were significantly decreased whereas no selenoprotein was up-regulated in the PD mice. In contrast, the majority of selenotranscriptome did not change and a few selenoprotein mRNAs that respond displayed a mixed pattern of up- and down-regulation in cerebellum, cortex, hippocampus, and/or pons of the PD mice. Gpx4, Sep15, Selm, Sepw1, and Sepp1 mRNAs were most abundant across all these five brain regions. Our results showed differential responses of selenoproteins in various brain regions of the PD mouse model, providing critical selenotranscriptomic profiling for future functional investigation of individual selenoprotein in PD etiology.

Fig 1. The mRNA expression of tyrosine hydroxylase (Th) in substantia nigra.

*, p < 0.05, compared to control.

Fig 2. Two-phase mapping of selenotranscriptome in the cerebellum, substantia nigra, cortex, pons and hippocampus of control and PD mice.

The selenotranscriptome is categorized as iodothyronine deiodinases (A), glutathione peroxidases (B), thioredoxin reductases (C), thioredoxin-like endoplasmic reticulum proteins (D), the Rdx family members (E), SelK and SelS (F), and others (G). The black and white bars indicate those with repeatability in the discovery and replication phases. *, p < 0.05, compared to control. ^#, ^##, and ^### indicates a trend of difference with percentage of change at 10–15%, 15–20%, and > 20% respectively. The left and right bars for each of the sub-brain regions denote control and PD mice, respectively.

Fig 3. The changes of selenotranscriptome in the five brain regions of PD mice.

(A) Volcano plots showing up-regulated (X axis > 0) or down-regulated (X axis < 0) selenoprotein mRNAs. Labeled are genes with significant difference (p < 0.05; above the X axis) or with a trend of difference (changes > 10%; underlined). d2, Dio2; g1, Gpx1; g2, Gpx2; g3, Gpx3; g4, Gpx4; t1, Txnrd1; t2, Txnrd2; t3, Txnrd3; 15, Sep15; m, Selm; h, Selh; t, Selt; w, Sepw1; k, Selk; s, Sels; i, Seli; p, Sepp1; o, Selo; r, MsrB1; n, Sepn1; s2, Sephs2. (B) A heat map displaying the extent of changes. The color scale ranges from saturated red (0.327) to white (-0.034) to saturated blue (-0.435). Red and blue colors represent increased and decreased expression, respectively. (C) A brain diagram illustrating the responses in each brain region. Saturated red and blue colors represent increased and decreased expression (p < 0.05), respectively. Pale colors represent a trend of difference (> 10%). Each of the brain regions is labeled symmetrically.

Fig 4. Relative abundance of selenotranscriptome in the brain regions of control mice.

The individual mRNA expression level was calculated and normalized with their respective β-actin expression in the brain region. The relative abundance of selenoprotein mRNA expression was divided into the four groups: barely detectable (values < 0.1), low expression (0.1–0.5), medium expression (0.5–1), and high expression (> 1).

Fig 5. Gpx1 and Gpx4 protein expression in the substantia nigra, cortex and hippocampus of control and PD mice determined by immunohistochemistry.

Representative images were presented following visual inspections of the brain slices from three control and PD mice, respectively. Bar size, 20 μM. TH, tyrosine hydroxylase. Arrows indicate examples of positive staining in brown. Blue color indicates nuclei.