Genes known to escape X chromosome inactivation predict co-morbid chronic musculoskeletal pain and posttraumatic stress symptom development in women following trauma exposure

Abstract

Co-morbid chronic musculoskeletal pain (CMSP) and posttraumatic stress symptoms (PTSS) are frequent sequelae of motor vehicle collision, are associated with greater disability than either outcome alone, and are more prevalent in women than men. In the current study we assessed for evidence that gene transcripts originating from the X chromosome contribute to sex differences in vulnerability to CMSP and PTSS after motor vehicle collision. Nested samples were drawn from a longitudinal study of African American individuals, and CMSP (0-10 numeric rating scale) and PTSS (impact of events scale, revised) outcomes were assessed 6 months following motor vehicle collision. Blood RNA were sequenced (n = 101) and the relationship between X chromosome mRNA expression levels and co-morbid CMSP and PTSS outcomes was evaluated using logistic regression analyses. A disproportionate number of peritraumatic X chromosome mRNA predicting CMSP and PTSS in women were genes previously found to escape X chromosome inactivation (11/40, z = -2.9, p = .004). Secondary analyses assessing gene ontology relationships between these genes identified an enrichment in genes known to influence neuronal plasticity. Further, the relationship of expression of two critical regulators of X chromosome inactivation, X-inactive specific transcript (XIST) and Yin Yang 1 (YY1), was different in women developing CMSP and PTSS. Together, these data suggest that X chromosome genes that escape inactivation may contribute to sex differences in vulnerability to CMSP and PTSS after motor vehicle collision.

Keywords: XIST; RNA; anxiety; hyperalgesia; sex differences.

Figure 1.

Heatmap illustrating X chromosome genes that are differentially expressed in women who recover vs develop co-morbid CMSP and PTSS six months following motor vehicle collision (motor vehicle collision) (n=65). Each column represents a female participant from the study, with individuals who recovered on the left (light gray bar) and individuals who developed CMSP and PTSS on the right (dark gray bar). Each row represents an X chromosome mRNA (with the corresponding official gene symbol to the right) that significantly predicts CMSP and PTSS development following motor vehicle collision. Bolded mRNA represent genes that have been shown previously to escape X chromosome inactivation. The dendrogram on the left of the heatmap indicates the hierarchical clustering of X chromosome genes associated with CMSP and PTSS. CMSP = chronic musculoskeletal pain, PTSS = posttraumatic stress symptoms.

Figure 2.

In women, gene transcripts previously shown to escape X chromosome inactivation (X chromosome inactivation) are important predictors of co-morbid CMSP and PTSS. A) Escape genes are over-represented in the list of 40 X chromosome (X chromosome) genes that significantly predict co-morbid CMSP and PTSS in women following motor vehicle collision. The pie chart on the left represents the proportion of all X chromosome genes that have been shown to escape X chromosome inactivation (n=93, yellow wedge) out of the total number of non-PAR X chromosome genes (n=783); the pie chart on the right represents the proportion of genes that have been shown to escape X chromosome inactivation (n=11) out of the total number of X chromosome genes that predict CMSP and PTSS in women following motor vehicle collision. B) Schematic representation of the location of “EscapeSet” genes on the X chromosome. C) Results of competitive gene set analyses indicate that EscapeSet genes are more differentially expressed in women who develop co-morbid CMSP and PTSS vs recover following motor vehicle collision than ^aX chromosomeSet genes, ^bany other set of nine X chromosome genes, and ^cany other set of nine randomly selected genes from the full transcriptome. ^dDirection of expression of genes in women who developed co-morbid CMSP and PTSS relative to expression of the same genes in women who recover following motor vehicle collision (i.e. “Up” indicates the genes are higher expressed in women with co-morbid CMSP and PTSS). D) Network analysis results based on EscapeSet genes using Ingenuity design software (IPA, Qiagen).

Figure 3.

Relationship between RNA expression levels of key regulators of X Chromosome inactivation, XIST and YY1, and posttraumatic stress symptom (PTSS) severity scores in women following motor vehicle collision trauma. A) XIST RNA expression levels were examined in relation to PTSS severity scores in women who recovered following motor vehicle collision (top left, purple triangles, n=35), and in women who developed co-morbid CMSP and PTSS following motor vehicle collision (top right, teal circles, n=30). YY1 RNA expression levels were also analyzed in relation to PTSS severity scores in women who recovered following motor vehicle collision (bottom left, purple triangles, n=35), and in women who developed co-morbid CMSP and PTSS following motor vehicle collision (bottom right, teal circles, n=30). B) The relationship between XIST RNA expression levels and YY1 RNA expression levels in women who recovered following motor vehicle collision (left, green squares, n=35) and in women who developed co-morbid CMSP and PTSS following motor vehicle collision (right, yellow diamonds, n=30). RNA expression levels were measured via RNA sequencing of blood collected in the early aftermath of motor vehicle collision. Bivariate analyses were used to derive Spearman correlation coefficients and corresponding p values.