Altered gene expression in early postnatal monoamine oxidase A knockout mice

Abstract

We reported previously that monoamine oxidase (MAO) A knockout (KO) mice show increased serotonin (5-hydroxytryptamine, 5-HT) levels and autistic-like behaviors characterized by repetitive behaviors, and anti-social behaviors. We showed that administration of the serotonin synthesis inhibitor para-chlorophenylalanine (pCPA) from post-natal day 1 (P1) through 7 (P7) in MAO A KO mice reduced the serotonin level to normal and reverses the repetitive behavior. These results suggested that the altered gene expression at P1 and P7 may be important for the autistic-like behaviors seen in MAO A KO mice and was studied here. In this study, Affymetrix mRNA array data for P1 and P7 MAO A KO mice were analyzed using Partek Genomics Suite and Ingenuity Pathways Analysis to identify genes differentially expressed versus wild-type and assess their functions and relationships. The number of significant differentially expressed genes (DEGs) varied with age: P1 (664) and P7 (3307) [false discovery rate (FDR) <0.05, fold-change (FC) >1.5 for autism-linked genes and >2.0 for functionally categorized genes]. Eight autism-linked genes were differentially expressed in P1 (upregulated: NLGN3, SLC6A2; down-regulated: HTR2C, MET, ADSL, MECP2, ALDH5A1, GRIN3B) while four autism-linked genes were differentially expressed at P7 (upregulated: HTR2B; downregulated: GRIN2D, GRIN2B, CHRNA4). Many other genes involved in neurodevelopment, apoptosis, neurotransmission, and cognitive function were differentially expressed at P7 in MAO A KO mice. This result suggests that modulation of these genes by the increased serotonin may lead to neurodevelopmental alteration in MAO A KO mice and results in autistic-like behaviors.

Keywords: Autism; Brain; Development; Monoamine oxidase; Serotonin.

Figure 1. Number of genes differentially expressed in monoamine oxidase A (MAO A) knockout (KO) mice at P1 and P7 are different

Venn diagram of differentially expressed genes (DEGs) at P1 versus P7 from whole brain cDNA microarray. DEGs are defined as MAO KO vs wild-type (Wt) [false discovery rate (FDR) < 0.05, fold-change (FC) >1.5 for autism-linked genes and >2.0 for functionally categorized genes].

Figure 2. Altered expression of autism-linked genes in monoamine oxidase A (MAO A) knockout (KO) mice at P1 and P7

Ingenuity Pathways Analysis (IPA) annotation database was used to identify autism-linked differentially expressed genes (DEGs) [false discovery rate (FDR) < 0.05; fold-change (FC) >1.5]. Fold change of each gene is displayed at P1 and P7 as well as a gene description and autism association. Up-regulated genes are shown in red and down-regulated genes are shown in blue.

Figure 3. Top differentially expressed genes in 4 functional categories in monoamine oxidase A (MAO A) knockout (KO) mice at P7

The 20 genes with the largest fold change between MAO A KO vs wild-type (Wt) at P7 in each category are displayed. The altered genes in these functional categories: neurodevelopment, apoptosis, neurotransmission, and cognitive function, may explain the autistic-like behavior in the MAO A KO mice. Differentially expressed genes (DEGs) are defined as MAO KO vs Wt [false discovery rate (FDR) < 0.05; fold-change (FC) >2.0 for functionally categorized genes].

Figure 4. Molecular functions of differentially expressed genes in monoamine oxidase A (MAO A) knockout (KO) mice at P1 and P7 according to PANTHER (Protein Analysis Through Evolutionary Relationships) database

Although the MAO A KO mice had different numbers of differentially expressed genes (DEGs) at P1 and P7, the percentage of genes with each molecular function was largely the same at P1 and P7. The top molecular functions were binding (P1–33%, P7–31%) and catalytic activity (P1–26%, P7–30%). Transcription regulator activity was a significant portion of total genes at P1 (13%) and P7 (7%). DEGs are defined as MAO KO vs wild-type (Wt) [false discovery rate (FDR) < 0.05; fold-change (FC) >1.5 for autism-linked genes and >2.0 for functionally categorized genes].

Figure 5. IPA functional analysis of differentially expressed genes in monoamine oxidase A (MAO A) knockout (KO) mouse brain at P7 based on z-score and p-value

Z-score algorithm predicts the biological functions that are expected to be increased or decreased according to the gene expression changes in the data and literature annotations for each gene in the category. A z-score >2 or < −2 predicts that a function is increased or decreased in MAO A KO vs wild-type (Wt). The corresponding p-values for the biological functions listed are shown schematically in a graph (with a logarithmic scale) embedded in the figure. Differentially expressed genes (DEGs) are defined as MAO KO vs Wt [false discovery rate (FDR) < 0.05; fold-change (FC) >1.5 for autism-linked genes and >2.0 for functionally categorized genes].