Locomotor hyperactivity in 14-3-3ζ KO mice is associated with dopamine transporter dysfunction

Abstract

Dopamine (DA) neurotransmission requires a complex series of enzymatic reactions that are tightly linked to catecholamine exocytosis and receptor interactions on pre- and postsynaptic neurons. Regulation of dopaminergic signalling is primarily achieved through reuptake of extracellular DA by the DA transporter (DAT) on presynaptic neurons. Aberrant regulation of DA signalling, and in particular hyperactivation, has been proposed as a key insult in the presentation of schizophrenia and related neuropsychiatric disorders. We recently identified 14-3-3ζ as an essential component of neurodevelopment and a central risk factor in the schizophrenia protein interaction network. Our analysis of 14-3-3ζ-deficient mice now shows that baseline hyperactivity of knockout (KO) mice is rescued by the antipsychotic drug clozapine. 14-3-3ζ KO mice displayed enhanced locomotor hyperactivity induced by the DA releaser amphetamine. Consistent with 14-3-3ζ having a role in DA signalling, we found increased levels of DA in the striatum of 14-3-3ζ KO mice. Although 14-3-3ζ is proposed to modulate activity of the rate-limiting DA biosynthesis enzyme, tyrosine hydroxylase (TH), we were unable to identify any differences in total TH levels, TH localization or TH activation in 14-3-3ζ KO mice. Rather, our analysis identified significantly reduced levels of DAT in the absence of notable differences in RNA or protein levels of DA receptors D1–D5. Providing insight into the mechanisms by which 14-3-3ζ controls DAT stability, we found a physical association between 14-3-3ζ and DAT by co-immunoprecipitation. Taken together, our results identify a novel role for 14-3-3ζ in DA neurotransmission and provide support to the hyperdopaminergic basis of pathologies associated with schizophrenia and related disorders.

In-vivo administration of clozapine affects behaviour but does not reverse dendritic spine deficits in the 14-3-3ζ KO mouse model of schizophrenia-like disorders

“…We found that 14-3-3ζ KO mice display several schizophrenia-like behavioural deficits such as hyperactivity and disrupted sensorimotor gating, impaired novel object recognition, impaired learning in a water crossmaze escape task, and lower levels of anxiety in the elevated plus maze (Cheah et al, 2012). As previously reported, we found that clozapine ameliorated hyperactivity in 14-3-3ζ KO mice (Ramshaw et al, 2013). Anatomically, we have identified neuronal migration defects, disrupted mossy fibre circuits, and aberrant synaptic terminals in the hippocampi of 14-3-3ζ KO mice (Cheah et al, 2012).…”

“…Previous studies in 14-3-3ζ -depleted mice have reported a beneficial effect of clozapine on isolated behavioural paradigms such as hyperactivity (Ramshaw et al, 2013;Foote et al, 2015) and prepulse inhibition (Foote et al, 2015). The incorporation of a more comprehensive test battery in our study shows that clozapine effects are not clear-cut in this model.…”

“…Anatomically, we have identified neuronal migration defects, disrupted mossy fibre circuits, and aberrant synaptic terminals in the hippocampi of 14-3-3ζ KO mice (Cheah et al, 2012). Molecular investigations suggest that 14-3-3ζ forms a central hub within the schizophrenia protein interaction network through interactions with schizophrenia risk genes including disrupted-in-schizophrenia 1 (DISC1), Ndel1, Lis1 and tyrosine hydroxylase (Toyo-oka et al, 2003;Cheah et al, 2012;Toma et al, 2014), and that 14-3-3ζ plays an essential role in dopamine neurotransmission by controlling the abundance of the dopamine transporter DAT (Ramshaw et al, 2013).…”

Inhibition of 14-3-3 Proteins Leads to Schizophrenia-Related Behavioral Phenotypes and Synaptic Defects in Mice

“…Compared with WT, the 14-3-3 FKO mice had a higher DA level in the striatum (Figure 2A), but not in the cortex (Figure 2B). While 14-3-3 proteins have been implicated in regulating DA synthesis and transport (46), transgene expression in the 14-3-3 FKO mice was not detected within the dopaminergic neurons of the Ventral Tegmental Area (VTA) and the Substantia Nigra pars compacta (SNc) (Figure 2C), or their processes in the striatum (Figure 2D). Thus, the elevated striatal DA level of the 14-3-3 FKO mice is unlikely a direct consequence of 14-3-3 inhibition in DA producing neurons and their terminals.…”

“…Recently, similar findings were reported for the 14-3-3ζ knockout mice, including increased striatal DA content and antipsychotic drug effectiveness on locomotor hyperactivity (55). Additionally, the 14-3-3ζ mice were shown to have a reduced level of the DA transporter (DAT), suggesting a direct role for 14-3-3ζ in regulating DA neurotransmission (46). However, in the 14-3-3 FKO mice, transgene expression was not detected in the dopaminergic neurons.…”