X-Linked IRAK1 Polymorphism is Associated with Sex-Related Differences in Polymorphonuclear Granulocyte and Monocyte Activation and Response Variabilities

INTERACTIONS BETWEEN BIOLOGICAL SEX AND THE X-LINKED VARIANT IRAK1 HAPLOTYPE IN MODULATING CLINICAL OUTCOME AND CELLULAR PHENOTYPES AFTER TRAUMA

ABSTRACT

Sex-related outcome differences in trauma remain controversial. The mechanisms causing sex-biased outcomes are likely to have hormonal and genetic components, in which X-linked genetic polymorphisms may play distinct roles because of X-linked inheritance, hemizygosity in males, and X chromosome mosaicism in females. The study aimed to elucidate the contribution of biological sex and the common X-linked IRAK1 haplotype to posttrauma clinical complications, inflammatory cytokine and chemokine production, and polymorphonuclear cell and monocyte activation. Postinjury clinical outcome was tested in 1507 trauma patients (1,110 males, 397 females) after stratification by sex or the variant IRAK1 haplotype. Males showed a three- to fivefold greater frequency of posttrauma sepsis, but similar mortality compared to females. Stratification by the variant IRAK1 haplotype revealed increased pneumonia and urinary tract infection in Wild type (WT) versus variant IRAK1 males, whereas increased respiratory failures in variant versus WT females. Cytokine/chemokine profiles were tested in whole blood from a subset of patients (n = 81) and healthy controls (n = 51), which indicated sex-related differences in ex vivo lipopolysaccharide responsiveness manifesting in a 1.5- to 2-fold increased production rate of tumor necrosis factor α, interleukin-1β (IL-1β), IL-10, Macrophage Inflammatory Protein-1 Alpha, and MIP1β in WT male compared to WT female trauma patients. Variant IRAK1 decreased IL-6, IL-8, and interferon gamma-induced protein 10 production in male trauma subjects compared to WT, whereas cytokine/chemokine responses were similar in variant IRAK1 and WT female trauma subjects. Trauma-induced and lipopolysaccharide-stimulated polymorphonuclear cell and monocyte activation determined by using a set of cluster of differentiation markers and flow cytometry were not influenced by sex or variant IRAK1. These findings suggest that variant IRAK1 is a potential contributor to sex-based outcome differences, but its immunomodulatory impacts are modulated by biological sex.

Sex-specific differences in cardiac function, inflammation and injury during early polymicrobial sepsis

BACKGROUND

Sex differences in sepsis are underexplored and incompletely understood. Cardiac function in early sepsis is pivotal in determining survival; hyperdynamic left ventricular ejection fraction is associated with higher mortality. Female sex may be cardioprotective, but variable experimental findings have not controlled for hypovolaemia. Sex-specific local cardiac versus peripheral inflammation in causing cardiovascular dysfunction also remain unclear. We therefore examined whether there are sex-specific differences in cardiac function in early sepsis, controlling for volaemic status and sex-specific differences in the peripheral inflammatory response initiated by tumour necrosis factor (TNFα).

METHODS

We used an experimental polymicrobial sepsis (faecal slurry) model titrated to minimise hypovolaemia as a confounding factor. We quantified cardiac function (transthoracic cardiac echocardiography) 1 week before, and 18 h after, sepsis. Cardiac injury (troponin I), inflammation and immune cell infiltration (flow cytometry) were quantified in naïve and septic female and male mice 18 h after sepsis. To evaluate the sex-specific influence of TNFα derived from peripheral leukocytes, we repeated the experiments in iRHOM2^-/- mice that are unable to shed TNFα exclusively from circulating leucocytes.

RESULTS

Serum troponin I increased to 1.39 ± 0.38 ng mL^-1 (from undetectable levels in controls) 18 h after onset of normovolaemic sepsis to a similar extent in both sexes. Stroke volume in male mice increased by 8 µL [(3-13); p = 0.004], compared to individualised pre-sepsis values. By contrast, stroke volume remained at baseline levels in females [mean difference: 4 µL (- 1 to 9)]. Messenger RNA levels of markers for cardiac injury/inflammation after sepsis (real-time polymerase-chain reaction) were elevated in male wild-type mice compared to female wild types (n = 10/sex), with higher cardiac mRNA levels of atrial natriuretic peptide, inflammation (TNFα) and oxidative stress (superoxide dismutase-1), although serum troponin I values were similarly elevated. Flow cytometry analysis of cardiac tissue showed doubling of CD4 + leukocyte infiltration in male mice. Sex-specific cardiac physiologic differences were similar in iRHOM2^-/- mice that are unable to shed TNFα exclusively from leucocytes.

CONCLUSIONS

In early normovolaemic polymicrobial sepsis, a relative hyperdynamic response develops in male mice. Myocardial stress/injury after early sepsis is limited in females, with less cardiac infiltration of CD4 + leukocytes but independent of shedding of TNFα from peripheral circulating leukocytes.

Directional X Chromosome Skewing of White Blood Cells from Subjects with Heterozygous Mosaicism for the Variant IRAK1 Haplotype

Random X chromosome (ChrX) inactivation and consequent cellular mosaicism for the active ChrXs in white blood cells (WBCs) is unique to females and may contribute to sex-biased modulation of the innate immune response. Polymorphic differences between the two parental ChrXs may result in ChrX skewing of circulating WBCs (ChrX inactivation-ratio (XCI) > 3) driven by differences in stem cell selection and activity in the bone marrow or WBC trafficking at the periphery. Independent of the mechanism, ChrX skewing may result in genotype-phenotype discrepancies. This study aimed to develop an allele-specific assay and test its applicability in clinical samples to determine the "direction" of ChrX skewing in the variant IRAK1 haplotype, a common X-linked polymorphism with major clinical impacts. Because alternative splice variants of IRAK1 are also produced in the region surrounding the critical single-nucleotide polymorphism (SNP, rs1059703), we also tested the abundance of alternative splice variant IRAK1 transcripts. The expression of splice variants IRAK1-B and IRAK1-C was about 30 and 50% of the full-length (IRAK1-A) in WBCs from healthy subjects (n = 53). IRAK1-A, B, and C showed about 30% lower expression level in males (n = 25) than females (n = 28). By contrast, the expression levels of IRAK1-A, B, and C were not affected by the variant IRAK1 haplotype in either sex. Allele-specific primers generated WT and variant-IRAK1 amplicons with high selectivity, and on average produced about half the expression levels of each transcript in heterozygous IRAK1-mosaic females. Because injury was shown to induce de novo ChrX skewing of WBCs, we tested the directional XCI ratio changes in WBC in a sample of trauma patients heterozygous for the variant IRAK1 haplotype (n = 18). Using the allele-specific assay in combination with the DNA methylation status at the polymorphic HUMARA locus, we found that at admission, about 60% the patients presented XCI ratios skewed toward WBCs with active ChrXs carrying the variant-IRAK1 similar to healthy controls. De novo, trauma-induced XCI ratio changes showed increased extravasation of the more abundant mosaic WBC subset without reversal in the direction of ChrX skewing during the injury course.