AMBMP activates WNT pathway and alleviates stress-induced behaviors in maternal separation and chronic stress models

Abstract

Depressive disorders are both prevalent and debilitating, and a proportion of patients have treatment resistance to classic antidepressants. Recent evidence has implicated the intracellular WNT signaling pathway as having a key role in the pathogenesis of major depressive disorder. In the present study, we investigated the role of β-catenin and transcription factor-4 (TCF4) in the depression-like and anxiety-like behaviors exhibited by mice exposed to maternal separation, or chronic mild stress. Both rodent models of childhood and adulthood stress showed depression and anxiety-like behaviors. During the last three weeks of medication, we applied AMBMP (2-Amino-4-[3,4- (methylenedioxy)benzylamino]-6-(3-methoxyphenyl)pyrimidine) to the maternal separation and chronic stress model for the first time. The drug alleviated the depression-like index in saccharin preference test (SPT) and forced swim test (FST), and anxiety-like index in open field test (OFT) and elevated-plus maze (EPM), and reversed the disruption of β-catenin and TCF4 in stressed mice by upregulating the WNT pathway specifically. Therefore, the WNT pathway may be involved in the mediation of patient recovery and could be a target for novel antidepressants.

Introduction

Depressive disorder is the most common psychiatric disorder, and as such represents a large economic burden to the health care system involved in its treatment (Bandelow and Michaelis, 2015). Depression affects nearly 6.9% of the population in China at any one time during their life time (Huang et al., 2019) and about 30–40% of patients with major depressive disorder are resistant to multiple antidepressants (Popova et al., 2019), suggesting a need for new targeted therapies.

Depressive disorder is a heterogeneous disease triggered by biological, psychological, genetic and social factors. Stress, particularly chronic stress, is a contributing factor to depression in humans (Hill et al., 2012). Animal studies are crucial tools for the study of specific symptoms of human mental disorders (Sapolsky, 1996). One classical animal stress model is chronic mild stress (CMS), resulting in a state of anhedonia or learned helplessness (Willner, 2005), the central feature of depressive disorder. In addition, the maternal separation (MS) model focuses on inhibiting parent/offspring interactions, as the quality of the childhood environment can induce epigenetic changes in the various responses to stress (Heim et al., 2008), shaping the immature brain and having long-lasting effects on behavior (Anda et al., 2010; Kundakovic and Champagne, 2015). Research on rodent stress models has been increasing recently, however, it remains to be fully established how chronic stress affects the regulation of intracellular molecular mechanisms and their association with depression.

Current pharmacological treatments for major depressive disorders aim to modulate monoamines and their therapeutic efficacy is produced by enhanced serotonin or norepinephrine neurotransmission. This then mediates the development of synaptic plasticity in neurons and regulations on intracellular signaling cascades (Kraus et al., 2017). The WNT pathway is essential for both correct embryo development and tissue homeostasis in adult mammals (Nusse and Clevers, 2017). The activation of the classical WNT pathway leads to the phosphorylation of glycogen synthase kinase 3β (GSK3β) and the stabilization of β-catenin resulting in its subsequent entry into the nucleus, activating transcription factors and promoting gene expression (Gao and Chen, 2010; Logan and Nusse, 2004). β-catenin is one of the key factors involved in the WNT pathway and plays a key role in the mechanism of antidepressant action. For example, in a transgenic mouse model overexpressing β-catenin, mice exhibited the same behavioral changes as seen with antidepressant treatment, such as a decreased immobility time in the forced swim test (FST) (Gould et al., 2007). The T-cell factor transcription factor (TCF) family are downstream of the WNT pathway and can recruit β-catenin to target genes for activation (Cadigan and Waterman, 2012). As one of the nuclear factors within the TCF family, TCF4 has not been detected in rodent stress models associated with depression, although some clinical studies have found a link between the TCF4 gene and potential predisposition to depressive disorder (Mossakowska-Wojcik et al., 2018). As a WNT agonist, 2-Amino-4-[3,4- (methylenedioxy)benzylamino]-6-(3-methoxyphenyl)pyrimidine (AMBMP) is a new experimental reagent for the activation of the WNT signaling pathway, which are virtually no studies looking at the use of AMBMP as psychopharmacological treatments.

There is growing evidence demonstrating that the WNT signaling pathway may mediate recovery from depression or anxiety, but the precise role of this signaling cascade needs further investigation. In the present study, we focused on the regulation and function of the WNT pathway and observed behavioral results and expression changes in β-catenin and TCF4 in the hippocampus when AMBMP was applied.