Sex-Specific Alterations in Inflammatory MicroRNAs in Mouse Brain and Bone Marrow CD11b+ Cells Following Traumatic Brain Injury

Sex is a key biological variable in traumatic brain injury (TBI) and plays a significant role in neuroinflammatory responses. However, the molecular mechanisms contributing to this sexually dimorphic neuroinflammatory response remain elusive. Here we describe a significant and previously unreported tissue enrichment and sex-specific alteration of a set of inflammatory microRNAs (miRNAs) in CD11b+ cells of brain and bone marrow isolated from naïve mice as well as mice subjected to TBI. Our data from naïve mice demonstrated that expression levels of miR-146a-5p and miR-150-5p were relatively higher in brain CD11b+ cells, and that miR-155-5p and miR-223-3p were highly enriched in bone marrow CD11b+ cells. Furthermore, while miR-150-5p and miR-155-5p levels were higher in male brain CD11b+ cells, no significant sexual difference was observed for miR-146a-5p and miR-223-3p. However, TBI resulted in sex-specific differential responses of these miRNAs in brain CD11b+ cells. Specifically, miR-223-3p levels in brain CD11b+ cells were markedly elevated in both sexes in response to TBI at 3 and 24 h, with levels in females being significantly higher than males at 24 h. We then focused on analyzing several miR-223-3p targets and inflammation-related marker genes following injury. Corresponding to the greater elevation of miR-223-3p in females, the miR-223-3p targets, TRAF6 and FBXW7 were significantly reduced in females compared to males. Interestingly, anti-inflammatory genes ARG1 and IL4 were higher in females after TBI than in males. These observations suggest miR-223-3p and other inflammatory responsive miRNAs may play a key role in sex-specific neuroinflammatory response following TBI.