Poster abstracts
Poster number 74 submitted by Rebecca Boland
Microglia depletion alters inflammatory gene expression following traumatic brain injury and sleep fragmentation
Rebecca Boland (Neuroscience Graduate Program), Samuel Houle (UT Health San Antonio ), Hailey M Donald (Neuroscience Graduate Program), Morgan Taylor, Christopher Cotter (Neuroscience Graduate Program), Olga Kokiko-Cochran (Department of Neuroscience, The Ohio State University)
Abstract:
Traumatic brain injury (TBI) affects over 2.8 million Americans yearly. TBI rarely occurs in isolation and recovery can be impeded by environmental stimuli. Sleep fragmentation (SF) after TBI increases microgliosis and neuroinflammation. Microglia mediate neuroinflammation post-injury, thus we predicted that depletion would disrupt the neuroimmune landscape at this subacute timepoint. C57BL6/J mice received TBI or sham injury followed by SF or control housing. Immediately after injury, half of the mice in each group received either vehicle chow or chow containing PLX5622, a CSF1R antagonist, which depletes microglia. Mice remained on the diet until tissue was collected for histology and RNA analysis 7 days post-injury. PLX treatment effectively depleted microglia in the cortex and the hippocampus. TBI significantly increased IBA-1 percent area and cell counts in the cortex, which was exaggerated by post-injury SF. RNA was then isolated from injured cortices for Nanostring nCounter glial profiling panel. TBI-SF increased expression of genes related to complement signaling (C3, C4a/b) and astrocyte reactivity (Gfap) compared to sham controls. Pathway analysis demonstrated that the complement cascade was uniquely activated in TBI-SF vehicle animals compared to all groups. Astrocytes are the primary producers of C3 in the brain, thus, we assessed GFAP and C3 as measures of astrocyte reactivity. TBI and PLX treatment increased GFAP percent area in the cortex. Although C3 percent area was increased by both injury and PLX, it was not exaggerated by post-injury SF. In direct PLX gene comparisons, there was a stronger effect within injury alone, with a suppressive effect in TBI-SF. Interestingly, in PLX to Vehicle gene comparisons, we observed widespread, bidirectional neuroinflammatory gene expression. Notably, Nlrp3, Mertk, and Fcgr4 were uniquely decreased by TBI-SF in the absence of microglia, providing potential candidate targets for future studies. Overall, microglia depletion resulted in increased astrocyte responses to injury but also elicited divergent neuroinflammatory transcriptional responses. These data provide deeper understanding of cellular changes that are vital for future therapeutic development to improve TBI survivors quality of life.
Keywords: microglia, TBI, sleep