Transmembrane protein 108 involves in adult neurogenesis in the hippocampal dentate gyrus

Abstract

Background: Transmembrane protein 108 (Tmem108) is a risk gene of psychiatric diseases including schizophrenia, bipolar disorder and major depression disorder. However, the pathophysiological mechanisms of Tmem108 are largely unknown.

Results: Here we investigated the pathophysiological function of Tmem108 in the hippocampal dentate gyrus by using Tmem108 mutant mice. Tmem108 highly expressed in the dentate gyrus and CA3 of the hippocampus. Dentate gyrus is a brain region where adult neurogenesis occurs, and aberrant adult neurogenesis in dentate gyrus has been implicated in major depression disorder. Indeed, Tmem108 mutant mice had lower immobility than wild type mice in tail suspension test and forced swimming test. BrdU and anti-Ki67 antibody staining indicated that adult neurogenesis of the hippocampal dentate gyrus region decreased in Tmem108 mutant mice. qPCR results showed that expression of Axin2, DISC1 and β-Catenin, three dentate gyrus adult neurogenesis related genes in Wnt/β-Catenin signaling pathway, decreased in Tmem108 mutant mice. Furthermore, Tmem108 enhanced free β-Catenin level in dual luciferase assay.

Conclusions: Thus, our data suggest that Tmem108 increases adult neurogenesis and plays a complexity role in psychiatric disorders.

Keywords: Adult neurogenesis; Bipolar disorder; Dentate gyrus; Major depression disorder; Transmembrane protein 108.

Fig. 1

High Tmem108 expression area in mice brain. A Tmem108 relative expression in different tissues in adult wild type mice (Gapdh expression as internal control, Tmem108 expression in heart was defined as one, wild type mice n = 3). B Tmem108 mutant mice targeting strategy; the initiation code of Tmem108 localizes in the exon 3, and LacZ gene is inserted into the downstream of Tmem108 promotor. C LacZ staining of Tmem108 mutant mouse (Tmem108 +/−) hippocampus; PMCo: posteromedial cortical amygdaloid nucleus, PTN: Parafascicular thalamic nucleus. D Tmem108 levels in hippocampus were evaluated by Western blotting assay; D (a) Representative image of Western blotting assays, D (b) Statistics of Tmem108 expression from Western blotting assay; 1: wild type mice n = 3; 2: Tmem108 knockout mice homozygous (Tmem108 −/−) n = 3; 3: Tmem108 knockout mice heterozygous (Tmem108 +/−) n = 3

Fig. 2

Tmem108 mutant mice had lower immobility. a Tmem108 mutant mice locomotor activity was not different from wild type mice in open field test (total travel distance was no difference). b Tmem108 mutant mice did not have anxious behavior in open field test (duration in the center was no difference, wild type mice, n = 12, Tmem108 −/− mice, n = 10). c Tmem108 mutant mice had lower immobility in tail suspension test (TST, wild type mice n = 12, Tmem108 −/− mice n = 15). d Tmem108 mutant mice had lower immobility in forced swimming test (FST, wild type mice n = 17, Tmem108 −/− mice n = 10) (^#p > 0.05, *p < 0.05)

Fig. 3

Loss of Tmem108 decreased DG adult neurogenesis. Representative images of BrdU assay, the low panel was from the rectangular area of the upper panel in a (wild type mice n = 5) or c (Tmem108 −/− mice n = 5); 2-month mice were injected ip with 300 mg/kg BrdU 24 h before sacrifice; incorporated BrdU was detected in sections by IHC using an anti-BrdU antibody (green), nuclei were counterstained with DAPI (blue). Quantification of BrdU positive cell number per mm DG inner edge (b) and per square mm DG region (d). Representative images of anti-Ki67 staining (red) from 2-month mice, the low panel was from the rectangular area of upper panel in e (wild type mice n = 4) or g (Tmem108 −/− mice n = 4); nuclei were counterstained with DAPI (blue). Quantification of Ki67 positive cell number per mm DG inner edge (f) and per square mm DG region (h) (**p < 0.01, ***p < 0.001)

Fig. 4

Tmem108 affected Wnt/β-Catenin signaling pathway. a Expression profiling of Wnt signaling pathway by qPCR. Wnt signaling pathway was disturbed in hippocampus of Tmem108 mutant mice; Gapdh mRNA expression was used as an internal control, mRNA expression relative to Gapdh in wild type was defined as one (wild type mice, n = 5, Tmem108 −/− mice, n = 4, ^#p > 0.05, *p < 0.05). b In HEK293 cell culture, Tmem108 increased free β-Catenin level in Dual luciferase assay. Relative TOP-Flash Firefly Luciferase (TFL1)/Renilla Luciferase (RL1) = Raw TFL1/Raw RL1; Relative FOP-Flash Firefly Luciferase (FFL2)/Renilla Luciferase (RL2) = Raw FFL2/Raw RL2; and final relative Firefly Luciferase (FL)/Renilla Luciferase (RL) = (Raw TFL1/Raw RL1)/(Raw FFL2/Raw RL2). Fold changes of FL/RL at p3×Flag-cmv-24-treated condition is normalized as 1, and fold changes of FL/RL at pFlag-cmv1-Wnt3a-treated or pFlag-cmv1-Tmem108-treated condition is normalized to FL/RL at p3×Flag-cmv-24-treated condition