Identification of a novel gene regulating amygdala-mediated fear extinction

Abstract

Recent years have seen advances in our understanding of the neural circuits associated with trauma-related disorders, and the development of relevant assays for these behaviors in rodents. Although inherited factors are known to influence individual differences in risk for these disorders, it has been difficult to identify specific genes that moderate circuit functions to affect trauma-related behaviors. Here, we exploited robust inbred mouse strain differences in Pavlovian fear extinction to uncover quantitative trait loci (QTL) associated with this trait. We found these strain differences to be resistant to developmental cross-fostering and associated with anatomical variation in basolateral amygdala (BLA) perineuronal nets, which are developmentally implicated in extinction. Next, by profiling extinction-driven BLA expression of QTL-linked genes, we nominated Ppid (peptidylprolyl isomerase D, a member of the tetratricopeptide repeat (TPR) protein family) as an extinction-related candidate gene. We then showed that Ppid was enriched in excitatory and inhibitory BLA neuronal populations, but at lower levels in the extinction-impaired mouse strain. Using a virus-based approach to directly regulate Ppid function, we demonstrated that downregulating BLA-Ppid impaired extinction, while upregulating BLA-Ppid facilitated extinction and altered in vivo neuronal extinction-encoding. Next, we showed that Ppid colocalized with the glucocorticoid receptor (GR) in BLA neurons and found that the extinction-facilitating effects of Ppid upregulation were blocked by a GR antagonist. Collectively, our results identify Ppid as a novel gene involved in regulating extinction via functional actions in the BLA, with possible implications for understanding genetic and pathophysiological mechanisms underlying risk for trauma-related disorders.

Environmental variables that ameliorate extinction learning deficits in the 129S1/SvlmJ mouse strain

“…24,25 In contrast, C57BL/6 mice have repeatedly been shown to exhibit robust fear extinction learning, as evidenced by a significant decrease in freezing behavior after exposure to an unpaired CS. 29 The extinction learning deficits in the 129S1 can be ameliorated by dietary zinc restriction, 30 deep brain stimulation of the nucleus accumbens, 23 pharmacological treatment with the α2-adrenoreceptor antagonist, yohimbine, the selective serotonin reuptake inhibitor, fluoxetine, or the dopamine precursor, L-dopa. For example, studies have shown that 129S1 mice have a downregulated hypothalamic-pituitary-adrenal axis 24 ; reduced neural activation in the infralimbic subregion of the medial prefrontal cortex, 27 a brain region critical for modulating extinction learning 28 ; enlarged dendritic arbors in basolateral amygdala (BLA) neurons 24 ; and a greater fraction of parvalbumin-positive inhibitory interneurons surrounded by perineuronal nets in the BLA.…”

“…29 The extinction learning deficits in the 129S1 can be ameliorated by dietary zinc restriction, 30 deep brain stimulation of the nucleus accumbens, 23 pharmacological treatment with the α2-adrenoreceptor antagonist, yohimbine, the selective serotonin reuptake inhibitor, fluoxetine, or the dopamine precursor, L-dopa. 29 These data suggest that certain therapeutic interventions can ameliorate the extinction learning deficits that may be genetically encoded in neural circuits of the 129S1 mice. 29 Of the genes identified, the expression of Ppid, a gene that is functionally coupled to the glucocorticoid receptor, was found to reduce extinction learning deficits in 129S1 mice when its expression was increased.…”

“…For example, studies have shown that 129S1 mice have a downregulated hypothalamic-pituitary-adrenal axis 24 ; reduced neural activation in the infralimbic subregion of the medial prefrontal cortex, 27 a brain region critical for modulating extinction learning 28 ; enlarged dendritic arbors in basolateral amygdala (BLA) neurons 24 ; and a greater fraction of parvalbumin-positive inhibitory interneurons surrounded by perineuronal nets in the BLA. 29 The extinction learning deficits in the 129S1 can be ameliorated by dietary zinc restriction, 30 deep brain stimulation of the nucleus accumbens, 23 pharmacological treatment with the α2-adrenoreceptor antagonist, yohimbine, the selective serotonin reuptake inhibitor, fluoxetine, or the dopamine precursor, L-dopa. 24,27,31 Interestingly, a recent study used linkage crosses between 129S1 and C57BL/6 mice combined with quantitative trait loci analysis to identify a panel of genes in the amygdala that show expression differences that correlate to the extinction learning deficits.…”

“…24,27,31 Interestingly, a recent study used linkage crosses between 129S1 and C57BL/6 mice combined with quantitative trait loci analysis to identify a panel of genes in the amygdala that show expression differences that correlate to the extinction learning deficits. 29 Of the genes identified, the expression of Ppid, a gene that is functionally coupled to the glucocorticoid receptor, was found to reduce extinction learning deficits in 129S1 mice when its expression was increased. 29 These data suggest that certain therapeutic interventions can ameliorate the extinction learning deficits that may be genetically encoded in neural circuits of the 129S1 mice.…”

“…29 Of the genes identified, the expression of Ppid, a gene that is functionally coupled to the glucocorticoid receptor, was found to reduce extinction learning deficits in 129S1 mice when its expression was increased. 29 These data suggest that certain therapeutic interventions can ameliorate the extinction learning deficits that may be genetically encoded in neural circuits of the 129S1 mice.…”