Evidence of decreased gap junction coupling between astrocytes and oligodendrocytes in the anterior cingulate cortex of depressed suicides

Glial dysfunction is a major feature in the pathophysiology of mood disorders. While altered astrocyte (AS) and oligodendrocyte-lineage (OL) cell functions have been associated with depression, the crosstalk between these two major glial cell types has never been assessed in that context. AS are potent regulators of OL cells and myelination, in part through gap junction-mediated intercellular communication made possible by the heterotypic coupling of AS-specific (Cx30 and Cx43) and OL-specific (Cx32 and Cx47) connexins, allowing cytosolic transport and metabolic support to OL cells. Because changes in the expression of AS-specific connexins have been previously reported in the brain of depressed individuals, this study aimed at addressing the integrity of AS-OL coupling in the anterior cingulate cortex (ACC) of depressed suicides. Using immunofluorescence and confocal imaging, we characterized the distribution of the AS-specific Cx30 in the ACC, and mapped its expression onto oligodendrocyte somas and myelinated axons as well as brain vasculature in post-mortem brain samples from depressed suicides (N=48) and matched controls (N=23). The differential gene expression of key components of the gap junction nexus was also screened through RNA-sequencing dataset previously generated by our group, and validated by quantitative real-time PCR. Our results indicate that Cx30 expression mapping to OL cells is selectively decreased in depressed suicides, an effect that was associated with decreased expression of OL-specific connexins Cx32 and Cx47, as well as the downregulation of major connexin-interacting proteins essential for the scaffolding, trafficking and function of gap junction channels. These results provide a first evidence of impaired gap junction mediated communication between astrocytes and oligodendrocytes in the ACC of individuals with mood disorders. These changes in glial coupling are likely to have significant impact on brain function, and may contribute to the altered OL function previously reported in this brain region.