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theses

Activation of brain microglia can be both beneficial and detrimental during the pathogenesis of neuroinflammation. Healthy microglia will propagate short-term inflammation as a means of protecting the central nervous system (CNS) from ensuing injury. However, when this process becomes dysregulated, chronic neuroinflammation results, which further propagates injury to the neuro-environment. Consequently, chronic neuroinflammation results in neuronal death and loss of synapses, which will eventually culminate in neurodegeneration. The principal aim of this dissertation research was to determine whether adaptive changes in the expression of microglial efflux transporters during a neuro-inflammatory state could be attenuated by activation of the antioxidant Nrf2 pathway. The primary function of efflux transporters is to remove both endogenous and exogenous substrates from the cell. This efflux can prevent the accumulation of toxic substrates and ensure proper cell-cell communication. Our laboratory has previously demonstrated that increasing concentrations of the bacterial endotoxin, lipopolysaccharide (LPS), in immortalized mouse BV-2 microglial cells decreases the expression and function of the multidrug resistance proteins 1a and 1b (Mdr1a/1b) and the breast cancer resistance protein (Bcrp) transporter while increasing the expression of several multidrug resistance-associated protein (Mrp) efflux transporters. These findings were confirmed in the present study using the same model of microglial activation. Further, studies were conducted to assess the ability of a Nrf2 activator, dimethyl fumarate (DMF, Tecfidera), to mitigate the down-regulation of efflux transporters in mouse microglial cells. Dose- and time-course studies for LPS and DMF were performed in BV-2 cells. Activation of the Nrf2 pathway was assessed by quantifying Nrf2 binding to a prototypical antioxidant response element and the expression of the Nrf2 target genes, NAD(P)H quinone oxidoreductase 1 (Nqo1) and heme oxygenase-1 (Ho-1). Microglial cells were co-treated with both LPS and DMF for 12 and 24 hr and profiled for expression of cytokines, Nrf2 targets and efflux transporters using qPCR and western blotting. In general, the treatment of BV-2 cells with LPS decreased the expression of Mdr1a, Mdr1b, and Bcrp. LPS treatment also up-regulated the levels of Mrp1 and Mrp5 mRNAs. Co-treatment of DMF with LPS prevented mRNA changes in cytokines and efflux transporters and, for Bcrp, restored protein expression to that observed in vehicle-treated BV-2 cells. Together, this research establishes a connection between neuroinflammation, Nrf2 activation, and efflux transporter expression that may be exploited pharmacologically to restore microglial functions.

ETD_8516

M.S.

Includes bibliographical references

by Rachel Nicole Ritzau

doi:10.7282/T3X63R34

ETD graduate

The author owns the copyright to this work.