Intensified vmPFC surveillance over PTSS under perturbed microRNA-608/AChE interaction

Abstract

Trauma causes variable risk of posttraumatic stress symptoms (PTSS) owing to yet-unknown genome-neuronal interactions. Here, we report co-intensified amygdala and ventromedial prefrontal cortex (vmPFC) emotional responses that may overcome PTSS in individuals with the single-nucleotide polymorphism (SNP) rs17228616 in the acetylcholinesterase (AChE) gene. We have recently shown that in individuals with the minor rs17228616 allele, this SNP interrupts AChE suppression by microRNA (miRNA)-608, leading to cortical elevation of brain AChE and reduced cortisol and the miRNA-608 target GABAergic modulator CDC42, all stress-associated. To examine whether this SNP has effects on PTSS and threat-related brain circuits, we exposed 76 healthy Israel Defense Forces soldiers who experienced chronic military stress to a functional magnetic resonance imaging task of emotional and neutral visual stimuli. Minor allele individuals predictably reacted to emotional stimuli by hyperactivated amygdala, a hallmark of PTSS and a predisposing factor of posttraumatic stress disorder (PTSD). Despite this, minor allele individuals showed no difference in PTSS levels. Mediation analyses indicated that the potentiated amygdala reactivity in minor allele soldiers promoted enhanced vmPFC recruitment that was associated with their limited PTSS. Furthermore, we found interrelated expression levels of several miRNA-608 targets including CD44, CDC42 and interleukin 6 in human amygdala samples (N=7). Our findings suggest that miRNA-608/AChE interaction is involved in the threat circuitry and PTSS and support a model where greater vmPFC regulatory activity compensates for amygdala hyperactivation in minor allele individuals to neutralize their PTSS susceptibility.

Figure 1

rs17228616 single-nucleotide polymorphism impairs hsa-miR-608/AChE interaction. (a) Schematic illustration of the AChE transcript, exon numbers and the rs17228616 location, with the C to A (C2098A) major to minor allele substitution interrupting hsa-miR-608 binding. (b) Increased activation within the amygdala region of interest (ROI; −28, 0, −21) for the minor allele (AA, AC, n=13) relative to the major allele (CC, n=63) group. (c) Limited elevation in posttraumatic stress symptoms (PTSS, z-score) in the minor allele (AA, AC, n=13) relative to major allele (CC, n=58) group. (d) Increased activation within the ventromedial prefrontal cortex (vmPFC) ROI (0, 50, −12) for the minor allele (AA, AC, n=13) relative to the major allele (CC, n=63) group. The data are represented as mean±s.e. Bar charts in a and c show the mean of beta values across all voxels in the ROIs for emotional versus neutral stimuli. *P<0.05. AChE, acetylcholinesterase.

Figure 2

Models of the relationship between rs17228616 genotype, brain activity and posttraumatic stress symptom (PTSS). (a) The illustrated mediation model depicts a significant indirect path of the effect of genotype on ventromedial prefrontal cortex (vmPFC) activity via amygdala activation. Specifically, A-allele carriers exhibited greater amygdala reactivity to emotional stimuli, which in turn was associated with increased vmPFC activity. (b) The illustrated mediation model depicts a significant indirect effect of genotype on PTSS via vmPFC activation. Specifically, A-allele carriers exhibited greater vmPFC response to emotional stimuli, which in turn was associated with lower levels of PTSS symptoms. The β-values are shown next to the arrows indicating each link in the analysis. *P<0.05. 95% CI, 95% confidence interval.

Figure 3

Interrelated expression of miR-608 and its targets in the amygdala. (a) Human amygdala (marked red) served to extract RNA. hsa-miR-608, as well as six of its verified and predicted targets, including acetylcholinesterase (AChE) and CDC42 and the normalizing beta-actin gene are all expressed in the human amygdala (quantitative PCR (qPCR) cycle <34 for targets, qPCR cycle <36 for miRNA-608). Shown are Cq values as measured by qPCR. (b) Several pairs of verified and predicted targets of hsa-miR-608 show positively correlated expression patterns, normalized to beta-actin and RIN (RNA integrity number) values (P<0.05, false discovery rate corrected). Color code shows correlation matrix intensity. IL-6, interleukin 6; miRNA, micro RNA.

Figure 4

Schematic presentation of how the rs17228616 single-nucleotide polymorphism (SNP) in the acetylcholinesterase (AChE) gene may affect the vulnerability to stress. This SNP interrupts miRNA-608/AChE interaction, leading to (1) elevated brain AChE activity and thus reduced cholinergic signaling, (2) reduction in the GABAergic modulator CDC42, limiting the inhibitory GABAergic signaling and (3) reduced IL-6 levels, effecting inflammatory pathways. Together, these signaling pathway impairments may enhance amygdala reactivity to emotional stimuli of minor allele individuals due to insufficient suppression of stress-related increases in cholinergic signaling and reduced inhibitory GABAergic signaling. As a coping mechanism under trauma load, these individuals over-recruit the ventromedial prefrontal cortex to downregulate the amygdala, and thus develop limited posttraumatic stress syndrome. Broken arrows represent reduced inhibitory input. The effects of this SNP, of stress exposure and of SNP-exposure interactions are represented by black, purple and striped black/purple arrows, respectively. IL-6, interleukin 6; miRNA, micro RNA.