Fig. 4.

Genes involved in the scaffolding, trafficking, and function of gap junction channels and cell–cell junctions are differentially expressed in the anterior cingulate cortex of depressed suicides. a RNA-sequencing results comparing samples from the anterior cingulate cortex of depressed suicides with a history of child abuse vs controls were screened to probe the differential expression of a literature-based list of genes related to GJ channel scaffolding and function. We found that among genes coding for major connexins, depressed suicides showed a downregulation specifically for the two oligodendrocyte-specific connexins Cx32 (GJB1) and Cx47 (GJC2). Major tight junction proteins (TJPs) such as occluding (OCLN), zona occludens-1 and -2 (TJP1/ZO-1 and TJP2/ZO-2), as well as claudin-11/OSP (CLDN11), an essential component of myelin interlamellar tight junctions were also found to be downregulated in depressed suicides. Genes coding for connexins-binding partners and regulators of GJ-mediated intercellular communication, such as caveolin-1 and -2 (CAV1 and CAV2) and alpha/beta catenins (CTNNA1 and CTNNB1) were also found to be downregulated. Of note, several genes coding for actin-binding proteins thought to bridge connexins to actin microfilament cytoskeleton, such as drebrin (developmentally regulated brain protein, DBN1) and spectrins were found to be collectively upregulated in depressed suicides compared with controls. Red and green bars indicate significant downregulation and upregulation, respectively, while gray bars indicate no significant change in gene expression. The drawing on the right depicts the suggested interactions between these different components of the GJ nexus and connexin-interacting proteins, adapted from Dbouk et al. [70]. Red and green indicate components found to be downregulated or upregulated, respectively, in the RNA-sequencing dataset. b Because the RNA-sequencing dataset was generated comparing samples from controls and depressed suicides with a history of child abuse (DS-CA), a subset of these differentially expressed genes was selected for validation with quantitative RT-PCR and adding a third group of depressed suicides with no history of child abuse (DS-nCA). Globally and consistent with the RNA-sequencing results, DS-CA subjects showed a downregulation of Cx32/GJB1, Cx47/GJC2, CAV1 and CAV2, OCLN, and an upregulation of DBN1 (Controls (N = 16–23) vs DS-CA (N = 19–25), *P < 0.05, **P < 0.01, ^#P < 0.1), although these results were not as statistically robust as observed in the RNA-sequencing dataset. Importantly these changes did not seem specific to a history of child abuse, as no significant difference was found between DS-CA and DS-nCA for any of these genes, while DS-nCA showed similar trends towards decreased expression of Cx32/GJB1, Cx47/GJC2, CAV2, and OCLN (Controls (N = 16–23) vs DS-nCA (N = 12–24), ^#P < 0.1). c Since changes in gene expression were not found to be specific to a history of child abuse, we combined both depressed suicides groups to increase our statistical power and perform backward stepwise linear regressions and tease out the contributions of confounding variables in differential gene expression (Tables S6–S13). Depressed Suicides showed significant downregulations of oligodendrocyte connexins Cx32/GJB1 and Cx47/GJC2, CAV1 and CAV2 as well as OCLN (Controls (N = 16–23) vs Depressed Suicides (N = 33–48), *P < 0.05, **P < 0.01). The upregulation of DBN1 observed in the RNA-seq dataset was however not validated, although a small trend towards increased expression was detectable (Controls (N = 23) vs Depressed Suicides (N = 36), P = 0.13). Data represent mean ± s.e.m. TJPs tight junction proteins, GJB6 gap junction protein beta 6 (Cx30), GJA1 gap junction protein alpha 1 (Cx43), GJB1 gap junction protein beta 1 (Cx32), GJC2 gap junction protein gamma 2 (Cx47), CAV1 Caveolin 1, CAV2 Caveolin 2, OCLN Occludin, DBN1 Drebrin