O11.2. ELEVATION OF MACROPHAGE-RELATED TRANSCRIPTS IN THE MIDBRAIN IN SCHIZOPHRENIA
Authors: Purves-Tyson Tertia , Cai Helen , Boerrigter Danny , Rothmond Debora , Shannon Weickert Cynthia 
Published: May 2020

Background

Neuroinflammation and dopamine dysregulation contribute to psychosis and cognitive deficits in schizophrenia. Approximately 50% of people with schizophrenia have elevated gene expression of proinflammatory cytokines in the postmortem midbrain, the location of the dopamine neurons. Infiltration of macrophages into the cortex was identified in a subset of high inflammatory schizophrenia cases. It is not known whether molecular measures of macrophages and cell adhesion molecules are increased in the midbrain in schizophrenia. We hypothesised that gene expression of macrophage markers CD163 (cluster of differentiation 163; perivascular macrophages), Fn1 (fibronectin 1; expressed by peripheral macrophages, not brain microglia), CD64 (pro-inflammatory macrophage), MRC1 (anti-inflammatory macrophage) and intracellular cell adhesion molecule 1 (ICAM1; enabling recruitment of peripheral macrophages into the brain), will be elevated in the midbrain of schizophrenia cases compared to controls.

Methods

Gene expression was examined by qRT-PCR in the midbrain from 28 schizophrenia cases (13 high inflammation, 15 low inflammation) and 29 healthy controls (low inflammation). ANCOVA, with age, PMI and RIN as covariates when correlations detected, were used to detect differences between diagnostic or diagnostic/inflammatory groups. For schizophrenia cases, antipsychotic doses were converted to chlorpromazine (CPZ) equivalents. Correlations were used to determine relationships between illness duration, antipsychotics and gene expression. CD163+ cells were identified in fresh frozen midbrain (14µm) from schizophrenia and control cases by immunohistochemistry to qualitatively assess their location relative to dopamine neurons.

Results

We found abundant macrophages (CD163+ cells) in and around blood vessels and in the schizophrenia midbrain parenchyma in close proximity to dopamine neurons. CD163, Fn1 and ICAM mRNAs were increased 237.6%, 39.67% and 137.7% respectively, in schizophrenia cases compared to control cases [all F(1,50 &gt;5.045, p&lt;0.05]. The pro-inflammatory macrophage marker (CD64 mRNA) was increased by 39% (F1,51=11.10, p=0.002), while the anti-inflammatory macrophage marker (MRC1 mRNA) was unchanged (F(1,52=2.97. p=0.09) in schizophrenia midbrain compared to control. CD163 and Fn1 mRNAs were not correlated in controls (R=0.319, p=0.112, n=24) but were correlated in schizophrenia cases (R=0.455, p=0.019, n=24). CD163 and ICAM mRNAs were positively correlated in controls (R=0.42, p=0.031, n=24) and schizophrenia cases (R=0.84, p&lt;0.0001, n=24), and the correlation was stronger in schizophrenia cases (p=0.014). CD163 and ICAM mRNAs were positively correlated with CPZ (Rho&gt;0.5, p&lt;0.02, n=21) but not illness duration (Rho=0.024, p&gt;0.05, n=28). Fn1 mRNA did not correlate with illness duration or antipsychotics.

Discussion

Increased ICAM1 may lead to increased transmigration of monocytes into the midbrain parenchyma. The increase in CD64 and the positive relationship between Fn1, expressed by peripheral monocytes/macrophages but not brain microglia, and CD163 expression in schizophrenia cases provides support that there is an increase in pro-inflammatory bone marrow-derived immune cells in the psychotic midbrain. These peripheral immune cells may be a source of increased cytokines identified in the midbrain schizophrenia cases and thus may contribute to dopamine neuron pathophysiology. Although the role of antipsychotics in increased macrophage marker expression in the midbrain is suggested, increased antipsychotics in patients displaying higher expression of inflammatory transcripts may indicate a more symptomatic patient requiring higher treatment doses.