Graduation Date

Fall 12-15-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pharmacology and Experimental Neuroscience

First Advisor

R. Lee Mosley PhD

Abstract

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder. Pathologically, loss of nigrostriatal neurons and dopamine released by these neurons are responsible for PD motor symptoms. During PD, activation of resident microglia and infiltrating lymphocytes leads to progressive neuroinflammation and reduction in the number and function of regulatory immune cells. Neuroinflammation contributes to progressive neurodegeneration and declining motor function. Reducing neuroinflammation is the target for novel PD therapeutics. Our goal is to increase the number and function of regulatory T cells (Tregs) in PD patients to decrease neuroinflammation and reduce PD symptoms. One potential therapy is granulocyte-macrophage colony stimulating factor (GM-CSF) which induces Tregs, decreases neuroinflammation, and protects dopaminergic neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD.

In a Phase 1 trial, recombinant human GM-CSF (sargramostim) was well-tolerated in PD patients, increased Treg frequency and function, and improved motor function. Expression of helper T cell-related genes in CD4+CD25- cells in blood was determined by PCR array. Sargramostim increased expression of both pro- and anti-inflammatory cytokine genes supporting the notion that sargramostim alters the immune response by increasing the expression of immune mediators, including anti-inflammatory genes.

As T cells do not express GM-CSF receptors and to explore myeloid-mediated Treg induction, GM-CSF-induced bone marrow-derived dendritic cells were further cultured with GM-CSF and/or stimulated with nitrated α-synuclein. Continued culture with GM-CSF yielded little change in dendritic cells as determined by surface co-stimulatory molecule expression, and proinflammatory cytokine expression and release; however, their ability to induce Tregs was diminished. In contrast, stimulation with nitrated α-synuclein, regardless of continued culture in GM-CSF, increases proinflammatory gene expression by dendritic cells, but showed variable effects on Treg induction. In the MPTP model, adoptive transfer of GM-CSF-induced tolerogenic dendritic cells protect dopaminergic neurons in the substantia nigra, decrease neuroinflammation, and increase splenic Tregs in a fashion similar to direct administration of GM-CSF.

In conclusion, GM-CSF induces Tregs in part by acting on dendritic cells to change their response to stimulation. The data suggest that GM-CSF may not suppress neuroinflammation directly, but rather alters the immune response with increased expression of anti-inflammatory mediators and induction of Tregs. Moreover, the introduction of nitrated α-synuclein and possibly other misfolded proteins diminishes homeostasis and Treg induction.

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