Background: Sex and age are emerging as influential variables that affect spinal cord injury (SCI) recovery. Despite a changing demographic towards older age at the time of SCI, the effects of sex or age on inflammation remain to be elucidated. This study determined the sex- and age-dependency of the innate immune response acutely after SCI. Methods: Male and female mice of ages 4- and 14-month-old received T9 contusion SCI and the proportion of microglia, monocyte-derived macrophages (MDM), and neutrophils surrounding the lesion were determined at 3- and 7-day post-injury (DPI) using flow cytometry. Cell counts of microglia and MDMs were obtained using immunohistochemistry to verify flow cytometry results at 3-DPI. Microglia and MDMs were separately isolated using fluorescence-activated cell sorting (FACS) at 3-day post-injury (DPI) to assess RNA expression of 27 genes associated with activation, redox, and debris metabolism/clearance. Results: Flow cytometry revealed that being female and older at the time of injury significantly increased MDMs relative to other phagocytes, specifically increasing the ratio of MDMs to microglia at 3-DPI. Cell counts using immunohistochemistry revealed that male mice have more total microglia within SCI lesions that can account for a lower MDM/microglia ratio. With NanoString analyses of 27 genes, only 1 was differentially expressed between sexes in MDMs; specifically, complement protein C1qa was increased in males. No genes were affected by age in MDMs. Only 2 genes were differentially regulated in microglia between sexes after controlling for false discovery rate, specifically CYBB (NOX2) as a reactive oxygen species (ROS)-associated marker as well as MRC1 (CD206), a gene associated with reparative phenotypes. Both genes were increased in female microglia. No microglial genes were differentially regulated between ages. Differences between microglia and MDMs were found in 26 of 27 genes analyzed, all expressed higher in MDMs with three exceptions. Specifically, C1qa, cPLA2, and CD86 were expressed higher in microglia. Conclusions: These findings indicate that inflammatory responses to SCI are sex-dependent at both the level of cellular recruitment and gene expression.
|Journal||Journal of Neuroinflammation|
|State||Published - Dec 2021|
Bibliographical noteFunding Information:
Additional appreciation is given to the University of Kentucky’s Flow Cytometry and Immune Monitoring Core Facility, Genomics Core Laboratory at the University of Kentucky, Jennifer Strange for FACS expertise, and Donna Wall for running the Nanostring. The UK Flow Cytometry & Immune Monitoring core facility is supported in part by the Office of the Vice President for Research, the Markey Cancer Center and an NCI Center Core Support Grant (P30 CA 177558) to the University of Kentucky Markey Cancer Center. NanoString analyses were supported by the OncoGenomics Shared Resource Facility (OG SRF) of the University of Kentucky Markey Cancer Center (P30CA177558). We would also like to thank Binoy Joseph for acquiring images and providing expertise using the Axioscan.
Funding support provided by the Craig H. Neilson Foundation under award #465079, the National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH) under Awards: R01NS091582 and F32NS111241, as well as, the National Institute on Alcohol Abuse and Alcoholism training grant T32AA027488 and National Cancer Institute grant P30CA177558.
© 2021, The Author(s).
- Acute inflammation
- Macrophage phenotype
- P2y12 receptor
- Sex as a biological variable
ASJC Scopus subject areas
- Neuroscience (all)
- Cellular and Molecular Neuroscience