Date of Award

2021

Embargo Period

6-29-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Neuroscience

College

College of Graduate Studies

First Advisor

Stephen Tomlinson

Second Advisor

Silvia Guglietta

Third Advisor

Christopher Cowan

Fourth Advisor

Heather Boger

Fifth Advisor

Ramin Eskandari

Sixth Advisor

Carl Atkinson

Abstract

Activation of the complement system propagates neuroinflammation and brain damage early and chronically after traumatic brain injury (TBI). However, the complement system is complex and comprises more than 50 components, many of which remain to be investigated in the normal and injured brain. In order to start delineating the various roles of complement components, we here used high-throughput NanoString and mass cytometric analyses to comprehensively characterize the complement transcriptome and the immune cellular expression of complement receptors in the brain after TBI, and in relation to other neuroinflammatory pathways. We also assessed the effect of complement inhibition with CR2-Crry on the neuroinflammatory transcriptome and immune cellular profile of TBI brains. The analyses were performed at days 3, 7, and 28 post injury in male C57BL/6 mice following a controlled cortical impact injury (and 1- and 2 years post injury for complement transcriptome). The transcriptomic analysis showed dysregulation of 40+ complement genes within 4 weeks after TBI that was partially sustained through 2 years post injury. The mass cytometric analysis showed increased abundance of 13 immune cell types, most of which had increased expression of C5aR1 acutely after TBI and of CD11c at day 28 after TBI. This analysis also showed chronic emergence of a distinct CXCR1+CD11c+ microglial subpopulation. Moreover, complement inhibition was neuroprotective and was associated with significant reversal of neuroinflammatory transcriptomic changes, including markers of neurotoxic astrogliosis and neuronal and synaptic loss, and with decreased immune cell infiltration after TBI. Reasoning that C5aR1 promoted immune cell infiltration, we also showed that targeted C5aR1 inhibition significantly decreased immune cell numbers but failed to alter behavioral outcomes. Overall, our findings demonstrate that complement gene dysregulation occurs extensively after severe open-head TBI and persists chronically, hence expanding the set of potential complement therapeutic targets (e.g., CD11c) and extending their window of treatment. Moreover, the resistance of some immune and synaptic genes to CR2-Crry treatment suggests adjuvant anti-inflammatory and neurotropic therapy may confer additional neuroprotection. Future therapeutic studies will focus on developing therapeutic tools for specific targeting of the dysregulated complement effectors and receptors and for assessing the benefits of non-complement adjuvant therapy.

Rights

All rights reserved. Copyright is held by the author.

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