... Transcriptomic Evidence for Sex Differences in Stress- and Reward-Related Disorders...

... Stress-related disorders show a robust sex bias, which is reflected in transcriptional profiles (Valentino)....

... Non-genomic mechanisms, including environmental exposures, hormones, and societal pressures, may also drive sex differences in brain disorders (Lubin, Nestler, Seney)....

... Transcriptome analyses in post-mortem brain tissue have demonstrated highly distinct profiles and gene networks with little overlap between men and women with depression, and these findings have been replicated in mouse models (Issler, Seney)....

... Genomic and transcriptomic differences seen in posttraumatic stress disorder implicate different immune and interneuron pathways in males and females (Girgenti)....

... Sex-specific transcriptomic differences may translate into different therapeutic targets for men and women with chronic pain and other stress-related disorders (Price)....

... Stress-related disorders show a very robust sex bias, and thus provide a model for elucidating how sex differences at a molecular level translate to sex differences in expression and prevalence of a disease, ... Rita Valentino. For example, major depressive disorder (MDD), anxiety, posttraumatic stress disorder (PTSD), and chronic pain disorders are nearly twice as prevalent in females as in males. Even substance use disorders, which are more prevalent in males but have ... to stress in females, said Valentino. She added that females with substance use disorders demonstrate a higher propensity for stress-induced relapse and a higher incidence of comorbid stress-related psychiatric disorders....

... Valentino added that cognitive and affective features associated with depression, anxiety, PTSD, and pain disorders—negative affect, increased arousal, and reward deficit—are also linked to stress in that they have a common circuitry that ...

... at the University of Pittsburgh. She noted that compared with men, women are approximately twice as likely to have a single episode of depression and four times as likely to have recurrent depression. Women also have more symptoms, more severe symptoms, and higher subjective distress. In terms of ...

... The questions she and other scientists have set out to answer is whether these sex differences reflect the involvement of different biological pathways and/or sex-specific ... pathology, and whether a better understanding of...

... these pathways and pathology may inform the future development of sex-specific treatments....

... Seney suggested two different hypotheses regarding sex differences in the molecular pathology of depression. Men and women could have similar pathological changes moderated by sex-related factors such as gonadal hormones, or different pathologies altogether, she ... . To explore these hypotheses, her lab and others have investigated gene-expression changes in brain circuits involved in mood regulation. They have used large-scale transcriptomic studies ...

... across six different brain regions involved in mood regulation (Labonté et al., 2017). The results, she said, were striking: Across the cortical and subcortical brain regions they examined, they found that men and women with depression had distinct transcriptional profiles with very little overlap....

... (sets of genes whose expression is highly correlated across subjects). WGCNA enables investigators to identify gene networks with common functions and examine the commonalities and differences in expression modules between different populations (e.g., male versus female). This technique enabled ... and colleagues to identify sex-specific transcriptional networks in MDD. Within one female-specific module, they identified a candidate “hub” gene called DUSP6, which is highly connected to other genes in the network and differentially expressed in depressed women across all ...

..., of the small number of genes that were differentially expressed in both sexes, about 75 percent were changed in opposite directions in depressed men and women (Seney et al., 2018) (see Figure 2-1)....

... In total, Seney’s lab showed that in more than 1,000 genes, there was a significant interaction of sex and disease, meaning that these 1,000 genes were altered differently in depressed men and women. She noted that only about 1 percent of those genes were ...

... FIGURE 2-1 Distinct transcriptional changes in men and women with MDD....

... independent of hormone levels, she said. Her lab went on to show that differentially expressed genes were enriched for synapse structure, function, and organization (decreased expression in men versus increased expression in women) and immune function (increased expression or no change in men versus ...

... depression treatments. They further suggest the possibility that treatments effective in men may be ineffective or even deleterious in women, and vice versa, she said....

... depression, sex-specific genomic and transcriptomic differences are seen in PTSD, said Matthew Girgenti, research scientist in psychiatry at the Yale School of Medicine. PTSD also has a high degree of comorbidity with depression, he said. Characterized by an uncontrollable and persistent state of fear ...

... also heritable genetic components (Blacker et al., 2019). Moreover, genome-wide association studies (GWASs) with large diverse cohorts of PTSD cases and controls indicate that the heritability of PTSD is much higher in females than in males and nearly as high as schizophrenia in terms of heritability ( ... et al., 2019). According to Girgenti, this means that about 10 percent of women will develop PTSD during their lifetime and are nearly twice as likely as men to develop PTSD after a traumatic event....

... The neurobiology of PTSD has focused on regions of the brain that have been implicated in animal studies of fear—the prefrontal cortex, amygdala, and hippocampus (Nees et al., 2018). Girgenti’s lab has conducted a large multi-omics project in post-mortem brain tissue, looking at four areas of the ... cortex—the orbital frontal cortex, anterior cingulate, subgenual, and dorsolateral prefrontal cortex. These studies have shown that gene expression changes overwhelmingly occur in the orbital frontal cortex and ... prefrontal cortex, with genes involved in synaptic organization tending to be up-regulated, and genes related to glia and gliogenesis tending to be down-regulated, Girgenti said (Girgenti et al., 2021). He noted that this same phenomenon is seen in other neuropsychiatric ...

... Girgenti and colleagues examined the impact of multiple covariates on differential gene expression and found, to their surprise, that the overwhelming amount of differential variance was caused by sex. In females, substantial gene expression changes ... seen in three brain regions, while in males, differential gene expression occurred only in one region, and there was very little overlap between male and female brains in terms of their gene expression profiles....

... with female PTSD is enriched for markers of endothelial cells, while gene modules associated with male PTSD are enriched for markers of microglia and endothelial cells. Girgenti concluded that there is an overwhelming immune response resulting from the top sex-specific genes in both males and ... , but that the genes and pathways differ between the sexes. Digging deeper, they conducted transcriptome-wide association studies (TWASs), which, in combination with GWAS, ... the identification of one of the most highly significant female-specific, PTSD-associated modules (coral2) and the key driver of this module—a gene involved in interneuron synapse forma-...

... 1 To learn more, see https://www.ptsd.va.gov (accessed November 27, 2020)....

..., said Girgenti. Using bulk sequencing RNA data combined with single-cell data, they demonstrated a significant increase in excitatory neurons and a decrease in astrocytes in females, and an increase in oligodendrocyte precursor cells and endothelial cells in males....

... Girgenti and colleagues have also used their transcriptomic data to conduct drug repositioning analyses, a technique that predicts which drugs on the market might ... disorder. This analysis suggested that another gene they linked to PTSD—PLEKHM1—has a shared biological effect with several classes of drugs and thus might be a druggable target....

... Addiction manifests differently in men and women and provides opportunities to better understand basic mechanisms of disrupted sex-specific behavior, said Deena Walker, assistant professor of behavioral neuroscience at Oregon Health & Science ... at a greater rate than women, but women progress to dependence more quickly, report greater craving during withdrawal, are more likely to relapse, and show greater consumption during relapse, putting them at greater risk for overdose, she said (Bobzean et al., 2014). Robust sex differences are also ... underlie the qualitative difference in risk seen in twin studies or differ in their quantitative effects, said Rohan Palmer, a behavioral geneticist and assistant professor of psychology at Emory University. There is still room for improvement in this area, he said, in part because females account for ...

..., said Walker. For example, she said neuropharmacological studies indicate that amphetamines induce less release of striatal dopamine in women and that women report less euphoric effects of amphetamines. Adolescent experience and adolescent stress also contribute to sex differences in motivation ... stress paradigm in mice demonstrated that social isolation drives a big sex difference in behavior: In comparison to group-housed animals where males and females showed an equal preference for cocaine, socially isolated males showed a greater...

... preference for cocaine while socially isolated females showed a decreased preference (Walker et al., 2020).2...

... Walker and colleagues examined transcriptional differences in animals displaying sex-specific behavioral responses to cocaine using the social isolation stress ... . As was shown earlier in depression and PTSD, in group-housed animals there was little overlap between males and females in terms of the transcriptional response to cocaine. However, there was a gain in the transcriptional response among the socially isolated ... animals but not in females, again with little overlap between males and females....

... Sexually dimorphic baseline behaviors such as marble burying—males bury more marbles than females—were lost under the stress of social isolation, and these behaviors are also reflected in the transcriptome, said Walker. This observation suggested that the transcriptome might provide information ... how behaviors are programmed. To assess changes in global transcriptional structure and potentially identify targets that regulate sex differences in reward, Walker and colleagues used an updated co-expression analytical technique called ... , they could induce a large increase in male-specific cocaine conditioned place preference (CPP), which provides an indirect measure of drug reward, and a decrease in female-specific CPP, thus demonstrating that the medial amygdala is crucial for regulating the sex-specific response to cocaine at both ... circuit and the molecular level....

... associated with psychiatric disease, said Theodore (Ted) Price, Eugene McDermott Professor and chair of the Department of Neuroscience in the School of Behavioral and Brain Sciences at The University of Texas at Dallas. Yet, while women and men perceive pain similarly, the underlying mechanisms ...

... 2 Made available in preprint format. To learn more, see https://www.biorxiv.org/content/10.1101/2020.02.18.955187v1.full (accessed January 6, 2021)....

... lag in understanding mechanisms in females because of the historical bias resulting from using only male rodents in studies....

... in the pathophysiology of migraine. In addition, new migraine treatments target CGRP or its receptor. Using an inflammatory pain model, Price and colleagues have shown in female mice that a CGRP-sequestering antibody prevented both the development of mechanical hypersensitivity and the ... no such effect, he said. Several anti-CGRP monoclonal antibodies have recently been approved for the treatment of migraine, said Price, although this and other research suggests that for preventing chronic pain, these drugs may be less effective in men than in women (Moehring and Sadler, 2019)....

... Transcriptomic studies by Price and others have identified many differences in the peripheral immune system that appear to contribute to the transition from acute to chronic pain, known ... translating ribosome affinity purification (TRAP), she demonstrated striking sex differences, said Price. Among these is an enzyme called prostaglandin-H2 D-isomerase (PTDGS), which synthesizes the pain mediator prostaglandin D2. Price and colleagues showed that PTDGS and prostaglandin D2 levels ... PTDGS inhibitors exhibited a robust, dose-dependent pain response, while female mice showed no significant effect, suggesting that baseline prostaglandin D2 levels are protective against pain (Tavares-Ferreira et al., 2020). Price commented that although prostaglandins have long been known to play an ...

... The Price lab has also been studying pain mechanisms in clinical samples in collaboration with colleagues at the MD Anderson Cancer Center. In well-phenotyped patients with cancer that has infiltrated their vertebrae, doctors at MD Anderson surgically remove DRGs. ... and colleagues then conduct histochemical, electrophysiological, and RNA sequencing studies on DRG neurons from pain and non-pain dermatomes (areas of skin supplied by specific nerves from the DRG). After showing that only the neurons from the pain dermatomes showed ...

... versus females (North et al., 2019). Price suggested that these transcriptomic differences may translate into different therapeutic targets for males and females with neuropathic pain....

... Neuropathic pain in males and females also differs at a cellular level, said Price. In males, macrophages are the primary cell type that infiltrates and proliferates in the DRG, ... in females there is a mix of phenotypically different macrophages, B cells, and possibly T cells, he said. While these different immune cells release different cytokines, the pathways in males and females seem to converge by ... nociceptors both spontaneously active and hyperexcitable. This convergence results from the fact that nociceptors express a “dizzying array of receptors,” he said. This could explain why ...

... ADDITIONAL FACTORS CONTRIBUTING TO SEX DIFFERENCES IN STRESS- AND REWARD-RELATED DISORDERS...

... in brain disorders because they appear to play an important role in regulating higher brain functions, said Orna Issler, an instructor at Icahn School of Medicine at Mount Sinai. In depression, at least one-third of the genes that are differentially expressed are lncRNAs, with very little overlap ...

... Exposure to gonadal hormones, may also drive sex differences, said Marianne Seney. Lubin noted that hormone levels change over the life span and may also help to explain the impact of age on disorders....

... To conclude the discussion, Eric Nestler mentioned that there are also societal and other non-biological drivers of sex differences. For example, Issler noted that psychosocial factors lead to differences between how boys and girls ... with stress. Nestler added that the stress on parents coping with child care issues during the COVID-19 pandemic also falls disproportionately on women....