Numerical density of oligodendrocytes and oligodendrocyte clusters in the anterior putamen in major psychiatric disorders

There is increasing evidence to support the notion that oligodendrocyte and myelin abnormalities may contribute to the functional dysconnectivity found in the major psychiatric disorders. The putamen, which is an important hub in the cortico-striato-thalamo-cortical loop, has been implicated in a broad spectrum of psychiatric illnesses and is a central target of their treatments. Previously we reported a reduction in the numerical density of oligodendrocytes and oligodendrocyte clusters in the prefrontal and parietal cortex in schizophrenia. Oligodendrocyte clusters contain oligodendrocyte progenitors and are involved in functionally dependent myelination. We measured the numerical density (Nv) of oligodendrocytes and oligodendrocyte clusters in the putamen in schizophrenia, bipolar disorder (BPD) and major depressive disorder (MDD) as compared to healthy controls (15 cases per group). Optical disector was used to estimate the Nv of oligodendrocytes and oligodendrocyte clusters. A significant reduction in both the Nv of oligodendrocytes (- 34%; p < 0.01) and the Nv of oligodendrocyte clusters (- 41%; p < 0.05) was found in the schizophrenia group as compared to the control group. Sexual dimorphism for both measurements was found only within the control group. The Nv of oligodendrocytes was significantly lower in male schizophrenia cases as compared to the male control cases. However, the Nv of oligodendrocyte clusters was significantly lower in all male clinical cases as compared to the male control group. The data suggest that lowered density of oligodendrocytes and oligodendrocyte clusters may contribute to the altered functional connectivity in the putamen in subjects with schizophrenia.

Prefrontal cortex alterations in glia gene expression in schizophrenia with and without suicide

BACKGROUND

Patients with schizophrenia (SCZ) run a lifelong risk of suicide. Alterations in glia activities in the prefrontal cortex (PFC) have been reported in relation to suicide in patients with SCZ. While immune processes in the CNS have been related to the susceptibility and course of SCZ, there are hardly any direct comparisons between individuals with SCZ, both those who died of natural causes and those that committed suicide, and healthy controls.

MATERIALS AND METHODS

We compared mRNA expression using real time qPCR of 16 glia-related genes in the dorsal lateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) between 35 patients with SCZ (7 suicide completers and 28 patients who died of natural causes) and 34 well-matched controls without psychiatric or neurological diseases.

RESULTS

We found an increased expression of the astrocytic gene aldehyde dehydrogenase-1 family member L1 (ALDH1L1) mRNA, a marker involved in dopaminergic activity, in SCZ versus controls. Excluding individuals with SCZ that committed suicide resulted in an elevated expression in the DLPFC of both ALDH1L1 and glutamine synthetase (GS) genes in patients with SCZ, compared to suicide completers and non-psychiatric controls. Regarding microglia genes: in the ACC, homeostatic markers such as chemokine (C-X3-C motif) ligand 1 (CX3CR1) mRNA expression was increased in SCZ without suicide as compared to suicide completers, while no change was found when compared to controls. Another, purinergic receptor 12 (P2RY12) mRNA was exclusively elevated in the ACC of suicide completers, compared to either other group. Triggering receptor expressed on myeloid cells 2 (TREM2) expression, which maintains microglial metabolism, was reduced in non-suicide patients with SCZ, compared to suicide victims and control subjects.

CONCLUSIONS

Differential changes are found in astrocyte and microglia genes in the PFC subregions in relation to SCZ and suicide, indicating possible disturbances of glia homeostasis in these conditions.

Reduced density of oligodendrocytes and oligodendrocyte clusters in the caudate nucleus in major psychiatric illnesses

Functional dysconnectivity in schizophrenia and affective disorders may be associated with myelin and oligodendrocyte abnormalities. Altered network integration involving the caudate nucleus (CN) and metabolic abnormalities in fronto-striatal-thalamic white matter tracts have been reported in schizophrenia and impaired patterns of cortico-caudate functional connectivity have been found in both bipolar disorder (BPD) and schizophrenia compared to healthy controls. Postmortem studies have found ultrastructural dystrophy and degeneration of oligodendrocytes and dysmyelination in the CN in schizophrenia and BPD. We aimed to test the hypothesis that oligodendrocyte density may be reduced in the CN in major psychiatric disorders and may thereby form the cellular basis for the functional dysconnectivity observed in these disorders. Optical disector was used to estimate the numerical density (Nv) of oligodendrocytes and oligodendrocyte clusters (OLC) in the CN of cases with schizophrenia, BPD and major depressive disorder (MDD) and in normal controls (15 cases per group). A significant reduction in the Nv of oligodendrocytes was found in schizophrenia and BPD as compared to the control group (p < 0.05), and the Nv of OLC was significantly lowered in schizophrenia and BPD compared to controls (p < 0.05). There were no significant differences between MDD and control groups. The Nv of OLC was significantly decreased in the left hemisphere in schizophrenia as compared to the left hemisphere of the control group (-52%, p < 0.01). The data indicates that a decreased density of oligodendrocytes and OLC could contribute to the altered functional connectivity of the CN in subjects with severe mental illnesses.

Perineuronal oligodendrocytes in health and disease: the journey so far

Perineuronal oligodendrocytes (pn-Ols) are located in the cerebral gray matter in close proximity to neuronal perikarya and less frequently near dendrites and neurites. Although their morphology is indistinguishable from that of other oligodendrocytes, it is not known if pn-Ols have a similar or different cell signature from that of typical myelinating oligodendroglial cells. In this review, we discussed the potential roles of these cells in myelination under normal and pathophysiologic conditions as functional and nutritional supporters of neurons, as restrainers of neuronal firing, and as possible players in glutamate-glutamine homeostasis. We also highlighted the occurrences in which perineuronal oligodendroglia are altered, such as in experimental demyelination, multiple sclerosis, cerebral ischemia, epilepsy, Alzheimer’s disease, schizophrenia, major depression, and bipolar disorder.