Crosstalk between Estrogen Withdrawal and NFκB Signaling following Penetrating Brain Injury.

OBJECTIVES: Characterized by neuroinflammation, traumatic brain injury (TBI) induces neuropathological changes and cognitive deficits. Estrogens are neuroprotective by increasing cell survival and this increase is mediated by a decrease in neuroinflammation. To further explore the relationship between estrogens, brain injury, and neuroinflammation, we examined the expression of the IKK/NFκB complex. The IKK/NFκB complex is a pleiotropic regulator of many cellular signaling pathways linked to inflammation, as well as three major cytokines (IL-1β, IL-6, and TNF-α). We hypothesized that NFκB expression would be upregulated following injury and that this increase would be exacerbated when circulating estrogens were decreased with fadrozole (aromatase inhibitor).

METHODS: Using adult zebra finches, we first determined the expression of major components of the NFκB complex (NFκB, IκB-α, and IκB-β) following injury using qPCR. Next, male and female finches were collected at 2 time points (2 or 24 h after injury) and brain tissue was analyzed to determine whether NFκB expression was differentially expressed in males and females at either time point. Finally, we examined how the expression of NFκB changed when estrogen levels were decreased immediately after injury.

RESULTS: Our study documented an increase in the expression of the major components of the NFκB complex (NFκB, IκB-α, and IκB-β) following injury. Decreasing estrogen levels resulted in a surprising decrease in the NFκB complex studied here.

DISCUSSION: These data further expand the model of how estrogens and other steroid hormones interact with the inflammatory pathways following injury and may prove beneficial when developing therapies for treatment of TBI.