Abnormal social behavior and altered gene expression in mice lacking NDRG2

Highlights

• NDRG2 expression increased during postnatal brain development.

• NDRG2 deficiency altered gene expression in the brain, including Bmp4 and Per2.

• NDRG2 knockout mice showed abnormal social behavior.

Abstract

N-myc downstream-regulated gene 2 (NDRG2), a member of the NDRG family, has multiple functions in cell proliferation, differentiation, and stress responses, and is predominantly expressed by astrocytes in the central nervous system. Previous studies including ours demonstrated that NDRG2 is involved in various central nervous system pathologies. However, the significance of NDRG2 in neurodevelopment is not fully understood. Here, we investigated the expression profile of NDRG2 during postnatal brain development, the role of NDRG2 in social behavior, and transcriptome changes in the brain of NDRG2-deficient mice. NDRG2 expression in the brain increased over time from postnatal day 1 to adulthood. Deletion of NDRG2 resulted in abnormal social behavior, as indicated by reduced exploratory activity toward a novel mouse in a three-chamber social interaction test. Microarray analysis identified genes differentially expressed in the NDRG2-deficient brain, and upregulated gene expression of Bmp4 and Per2 was confirmed by quantitative PCR analysis. Expression of both these genes and the encoded proteins increased over time during postnatal brain development, similar to NDRG2. Gene expression of Bmp4 and Per2 was upregulated in cultured astrocytes isolated from NDRG2-deficient mice. These results suggest that NDRG2 contributes to brain development required for proper social behavior by modulating gene expression in astrocytes.

Introduction

N-myc downstream-regulated gene 2 (NDRG2) is a member of the NDRG family, which comprises four proteins called NDRG1–4 and is a cytoplasmic phosphoprotein with multiple functions in cell proliferation, differentiation, and stress responses [1]. NDRG2 also functions as a tumor suppressor and is highly expressed in the heart, liver, skeletal muscle, and central nervous system (CNS) [2,3]. Multiple lines of evidence including ours indicate that NDRG2 is involved in CNS pathologies, such as brain tumors, cerebral ischemia, and neurodegenerative disorders. This is based on investigation of NDRG2 expression in animal disease models or patients and phenotypic analysis of loss-of-function mice in the context of stress responses [[4], [5], [6], [7]]. However, the physiological role of NDRG2 in the brain is poorly understood. NDRG2 expression increases during mouse embryonic development from E12.5 [3,8]. In adulthood, NDRG2 is widely expressed throughout the brain and is predominantly expressed by astrocytes in the CNS [9].

Increasing evidence has recently shown that glial cells, including astrocytes, play an important role in brain development such as neural circuit formation by controlling synapse formation and pruning [10]. Dysregulation of brain development can cause functional impairments of the brain known as neurodevelopmental disorders, such as intellectual disability, autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and schizophrenia [11]. Neurodevelopmental disorders are characterized by deficits in behavior, social communication, and cognition. During human brain development, NDRG2 is upregulated from the prenatal period to early childhood [12,13]. A recent study showed that NDRG2-deficient mice display ADHD-like phenotypes and that children with a single-nucleotide polymorphism of NDRG2 have a higher risk of developing ADHD, suggesting that NDRG2 dysfunction is involved in ADHD [14]. ADHD has high rates of comorbidity with other neurodevelopmental disorders, such as ASD, which have behavioral and biological overlap due to shared genetic risk [15]. Thus, NDRG2 may be involved in other neurodevelopmental disorders in addition to ADHD. However, it remains unknown whether NDRG2 functions in social behavior, which is frequently impaired in neurodevelopmental disorders such as ASD. Here, we examined the expression profile of NDRG2 during postnatal brain development, investigated the role of NDRG2 in social interaction using loss-of-function mice, and used a transcriptome profiling approach to elucidate the possible mechanisms associated with functional abnormalities in the NDRG2-deficient brain.