The New Jersey Institute of Technology's
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Title:	Microglia induced neuroinflammation through the NLRP3 inflammasome following blast traumatic brain injury
Author:	Younger, Daniel
View Online:	njit-etd2020-098 (xi, 143 pages ~ 19.7 MB pdf)
Department:	Department of Biomedical Engineering
Degree:	Doctor of Philosophy
Program:	Biomedical Engineering
Document Type:	Dissertation
Advisory Committee:	Chandra, N. (Committee chair) Pfister, Bryan J. (Committee member) Haorah, James (Committee member) Kakulavarapu, Venkata R. (Committee member) Pang, Kevin (Committee member) Rameshwar, Pranela (Committee member)
Date:	2020-08
Keywords:	Blast Microglia Neuroinflammation NLRP3 TBI
Availability:	Unrestricted
Abstract:	The incidence of traumatic brain injury (TBI) among military personnel have been steadily increasing with modern conflicts. A recent RAND report estimated 320,000 service members, totaling 20% of deployed forces, suffer from TBI. However, of this population roughly 60% have not seen a medical professional specifically for TBI. Unlike the civilian population, the primary cause of TBI for active-duty military personnel is blast exposure. Blasts now account for over 70% of all US military casualties in operation Iraqi Freedom (OIF) and Operation enduring freedom (OEF) and are the major cause of TBI. Among many pathological mechanisms associated with blast TBI, disruption of Blood Brain Barrier (BBB) and subsequent leakage of blood-borne macromolecules into brain parenchyma is reported to be the earliest event, which could trigger sustained neuroinflammation in blast TBI (bTBI). Accordingly, several studies have implicated neuroinflammation in the pathology of blast induced TBI. However, the role of the central nervous system's innate immune response, specifically the involvement of resident microglia and the pathways through which microglia contribute to neuroinflammation, has not been thoroughly investigated. Hence, the temporal and spatial evolution of microglia activation and specific mechanisms operative during the course of microglial action are critically warranted in blast TBI. It is hypothesized that microglia contribute to chronic neuroinflammation in bTBI which plays a pivotal role in the neuropathological and neurobehavioral changes in bTBI. This study is divided into 3 aims: Aim 1 identifies temporal distribution of microglia's four active phenotypes and a morphological description of each phenotype in hippocampus and thalamus. Cell surface markers specific to all four active phenotypes were used to identify the microglia cells and a manual analysis done to describe their morphology. These studies were carried out at mild/moderate overpressure of 180 kPa and at six time points: 4 hours, 24 hours, 3 days, 7 days, 15 days, and 30 days. The rationale for choosing the hippocampus and thalamus is due to previous studies from this lab that reported that these regions were most vulnerable to BBB disruption and oxidative stress, and due to their critical involvement in neurocognitive and neurobehavioral outcomes. Aim 2 investigates the role of the NLRP3 inflammasome pathway and its involvement in the production of the pro-inflammatory cytokine IL-1β. Through a series of immunostains the cellular source of the inflammasome and its components are identified. Aim 3 investigates how the inhibition of NLRP3 inflammasome formation through the use of a specific inhibitor MCC950 will impact on the cognitive outcomes in rats following blast TBI. Results indicated that microglia become activated acutely (4h) and such activation persists up to 30 days after bTBI. Such microglial activation is more pronounced in the vicinity of vascular rupture (BBB disruption) compared to areas away from the site of BBB leakage. Further, levels of proinflammatory cytokine IL-1β shows a sustained increase in both hippocampus and thalamus and such raise in IL-0 is comparable to a parallel increase in NLRP3 inflammasome complex. Ultimately, inhibiting NLRP3 inflammasome by the administration of specific inhibitor MCC950 displays a significant improvement in motor function, anxiety/depression as well as improves short-term memory in animals exposed to blast injury. This project therefore addresses the key role of resident microglia in the evolution of chronic neuroinflammation via the activation of NLRP3 inflammasome and proinflammatory cytokine production, key events contributing to neurobehavioral deficits in bTBI. Therefore, targeting CNS innate immune system (microglia) response by NLRP3 inflammasome activation may have a therapeutic potential counteract neurobehavioral deficits in bTBI.