Subcortical oligodendrocyte- and astrocyte-associated gene expression in subjects with schizophrenia, major depression and bipolar disorder

Abstract 

Deficits in the expression of oligodendrocyte and myelin genes have been described in numerous cortical regions in schizophrenia and affective disorders; however, relatively little attention has been paid to subcortical structures. Here we employed quantitative real time PCR to examine the mRNA expression of 17 genes that are expressed by oligodendrocyte precursors (OLPs) and their derivatives, including astrocytes. Four subcortical regions were examined (the anteroventral (AV) and mediodorsal thalamic nuclei (MDN), internal capsule (IC) and putamen (Put)) in postmortem material from subjects (age 25–68 at time of death) with no known psychiatric history (NCs) as well as in subjects with schizophrenia (SZ), major depressive disorder (MDD), and bipolar disorder (BPD). In all regions examined, genes expressed after the terminal differentiation of oligodendrocytes tended to have lower levels of mRNA expression in subjects with SZ compared to NCs. These differences were statistically significant across regions for four genes (CNP, GALC, MAG and MOG) and approached significance for TF. No genes were under expressed in MDD. Only TF was under expressed in BPD and only in the IC. In contrast, two astrocyte-associated genes (GFAP and ALDH1L1) had higher mean expression levels across regions in all psychiatric groups relative to NCs. These differences reached statistical significance for SZ and MDD relative to NCs. There were no age by diagnosis interactions. The majority of age regressions had negative slopes for the expression of oligodendrocyte-associated genes. GFAP but not ALDH1L1 expression was significantly and positively correlated with age in the MDN, AV and Put. Across subject groups the expression of both astrocyte genes was highly correlated with cumulative neuroleptic exposure in all regions except the Put. Significant positive correlations were also observed in some regions between cumulative neuroleptic exposure and the expression of genes associated with mature oligodendrocytes as well as with bipotential OLPs. Multiple negative correlations were observed between the mRNA expression of astrocyte genes and genes expressed by terminally differentiated oligodendrocytes. These data are discussed in the context of myelin turnover and potential effects of psychiatric illness as well as medications on the developmental fate of OLPs.

Keywords: Oligodendrocyte, Myelin, Schizophrenia, Bipolar disorder, Major depression, Thalamus, Mediodorsal nucleus, Anterior nucleus, Internal capsule, Putamen