Determining Sex-Based Differences in Inflammatory Response in an Experimental Traumatic Brain Injury Model

Abstract

IntroductionTraumatic brain injury is a leading cause of injury-related death and morbidity. Multiple clinical and pre-clinical studies have reported various results regarding sex-based differences in TBI. Our accepted rodent model of traumatic brain injury was used to identify sex-based differences in the pathological features of TBI.MethodsMale and female Sprague-Dawley rats were subjected to either controlled-cortical impact (CCI) or sham injury; brain tissue was harvested at different time intervals depending on the specific study. Blood-brain barrier (BBB) analysis was performed using infrared imaging to measure fluorescence dye extravasation. Microglia and splenocytes were characterized with traditional flow cytometry; microglia markers such as CD45, P2Y12, CD32, and CD163 were analyzed with t-distributed stochastic neighbor embedding (t-SNE). Flow cytometry was used to study tissue cytokine levels, and supplemented with ELISAs of TNF-⍺, IL-17, and IL-1β of the ipsilateral hemisphere tissue.ResultsCCI groups of both sexes recorded a higher BBB permeability at 72 hours post-injury than their respective sham groups. There was significant difference in the integrated density value of BBB permeability between the male CCI group and the female CCI group (female CCI mean = 3.08 x 108 ± 2.83 x 107, male CCI mean = 2.20 x 108 ± 4.05 x 106, p = 0.0210), but otherwise no differences were observed. Traditional flow cytometry did not distinguish any sex-based difference in regards to splenocyte cell population after CCI. t-SNE did not reveal any significant difference between the male and female injury groups in the activation of microglia. Cytokine analysis after injury by flow cytometry and ELISA was limited in differences at the time point of 6 hours post-injury.ConclusionIn our rodent model of traumatic brain injury, sex-based differences in pathology and neuroinflammation at specified time points are limited, and only noted in one specific analysis of BBB permeability.

Central role for neurally dysregulated IL-17A in dynamic networks of systemic and local inflammation in combat casualties

“…Additionally, our study cohorts were predominantly male. While a recent study in rodents found no sex-based differences in various pathological features of TBI including splenocyte cell proliferation, activation of microglia, and inflammatory cytokine production at 6 h post-injury 58 , future multi-center studies in diverse cohorts of TBI patients remain necessary to confirm this equivalence. We also note that, in addition to TBI, psychiatric and neurological factors (e.g., PTSD) can have an impact on the systemic stress response and need to be considered in future studies.…”

Multi-Mechanistic Approaches to the Treatment of Traumatic Brain Injury: A Review

“…The pathophysiologic mechanisms underlying primary and secondary injury following TBI are likely more similar than different males and females, however, some differences are known to exist between males and females in TBI. In preclinical models of TBI, female animals have demonstrated decreased neuroinflammation, including reductions in reactive microglia and infiltrating peripheral immune cells [ 136 , 137 ], decreased BBB disruption [ 138 ], and decreased oxidative stress [ 139 ]. While the mechanistic differences in TBI pathophysiology are complex and still under investigation, the effect of female sex steroids, including estrogen and progesterone, has been suggested as a key underlying driver for these observed differences [ 140 ].…”

The Role of Apoptosis and Autophagy in the Hypothalamic-Pituitary-Adrenal (HPA) Axis after Traumatic Brain Injury (TBI)

“…The male rats were randomly divided into three groups, and each group included 14 rats. TBI was generated in rats by using the CCI model [ 21 , 39 , 40 ]. The details were as follows: (1) control group, no operated group (only opened 10 mm median linear incision was then sutured under anesthesia); (2) acute TBI, rats were sacrificed at 24 h after TBI; (3) chronic TBI, rats were sacrificed 30 days after TBI.…”

“…The CCI techniques, parameters, and postoperative care have all been thoroughly reported previously [ 21 , 39 , 40 ]. Rats were sedated with isoflurane (2.0–2.5 percent in 100% O 2 , 2.0 mL/min flow rate) and put in a stereotaxic frame with the head in a horizontal plane about the interaural line.…”