Differential protein expression of DARPP-32 versus Calcineurin in the prefrontal cortex and nucleus accumbens in schizophrenia and bipolar disorder

Yasuto Kunii,Junya Matsumoto,Hirooki Yabe,Akiyoshi Kakita,Hiroyasu Akatsu,Hiroyuki Nawa,Yoshio Hashizume,Mizuki Hino,Atsuko Nagaoka

doi:10.1038/s41598-019-51456-7

Abstract

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) integrates dopaminergic signaling into that of several other neurotransmitters. Calcineurin (CaN), located downstream of dopaminergic pathways, inactivates DARPP-32 by dephosphorylation. Despite several studies have examined their expression levels of gene and protein in postmortem patients’ brains, they rendered inconsistent results. In this study, protein expression levels of DARPP-32 and CaN were measured by enzyme-linked immunosorbent assay (ELISA) in the prefrontal cortex (PFC), and nucleus accumbens (NAc) of 49 postmortem samples from subjects with schizophrenia, bipolar disorder, and normal controls. We also examined the association between this expression and genetic variants of 8 dopaminergic system-associated molecules for 55 SNPs in the same postmortem samples. In the PFC of patients with schizophrenia, levels of DARPP-32 were significantly decreased, while those of CaN tended to increase. In the NAc, both of DARPP-32 and CaN showed no significant alternations in patients with schizophrenia or bipolar disorder. Further analysis of the correlation of DARPP-32 and CaN expressions, we found that positive correlations in controls and schizophrenia in PFC, and schizophrenia in NAc. In PFC, the expression ratio of DARPP-32/CaN were significantly lower in schizophrenia than controls. We also found that several of the aforementioned SNPs may predict protein expression, one of which was confirmed in a second independent sample set. This differential expression of DARPP-32 and CaN may reflect potential molecular mechanisms underlying the pathogenesis of schizophrenia and bipolar disorder, or differences between these two major psychiatric diseases.

Highlights

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32), known as phosphoprotein phosphatase-1 regulatory subunit 1B (PPP1R1B), is a key molecule that integrates dopaminergic signaling into that of several other neurotransmitters, such as a glutamate[1]
In the prefrontal cortex (PFC), we found that the expression levels of DARPP-32 evinced a significant decrease in patients with schizophrenia relative to controls (t (40.14) = 2.12, p = 0.040) (Fig. 1a) and that the expression of CaN tended to increase in patients with schizophrenia (t (40.72) = 1.97, p = 0.056) as compared with controls; the mean of CaN expression in 6 patients with bipolar disorder was higher than that of controls (Fig. 2a)
We examined the effects of 55 single nucleotide polymorphisms (SNPs) in 8 dopaminergic system associated molecules (ANKK1, DRD2, PPP1R1B, protein phosphatase 3 catalytic subunit alpha (PPP3CA), protein phosphatase 3 catalytic subunit beta (PPP3CB), protein phosphatase 3 catalytic subunit gamma (PPP3CC), PPP3R1, and PPP3R2) on the protein expression levels of DARPP-32 or CaN in a cohort of patients and controls (Table 1) as described in Materials and Methods

Summary

Introduction

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32), known as phosphoprotein phosphatase-1 regulatory subunit 1B (PPP1R1B), is a key molecule that integrates dopaminergic signaling into that of several other neurotransmitters, such as a glutamate[1]. Kleinman et al (2011) proposed “genetic neuropathology,” a novel strategy in which the expression of mRNA and proteins in postmortem brains is used as ultimate intermediate phenotypes They hypothesized that insights into the mechanisms of psychiatric diseases and identification of novel therapeutic targets will emerge from the association of genetic variations with relevant molecular phenotypes in postmortem brains[24]. In this study, we investigated the expression levels of DARPP-32 and CaN proteins in PFC and NAc, regions that receive dopaminergic input and are considered to be affected in schizophrenia. This analysis was performed in 49 postmortem samples from subjects with schizophrenia, bipolar disorder, and control subjects (Table 1) using enzyme-linked immunosorbent assay (ELISA). We analyzed the associations between this expression and genetic variants of dopaminergic signaling-associated molecules for 55 single nucleotide polymorphisms (SNPs) in a much larger set of postmortem samples to examine the potential involvement of genetic variants in the pathophysiology of schizophrenia and bipolar disorder

Methods

Results

Conclusion