Date of Completion

3-31-2017

Embargo Period

3-31-2019

Keywords

Phosphodiesterase-8, CD4+ T cells, Integrins, Autoimmunity, T cell motility, Inflammation

Major Advisor

Dr. Stefan Brocke

Associate Advisor

Dr. Robert Clark

Associate Advisor

Dr. Paul Epstein

Field of Study

Biomedical Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The levels of cAMP are regulated by phosphodiesterases (PDE), which are targets for the treatment of inflammatory disorders. The overarching goal of this study was to harness recent successful developments in PDE research for the treatment of experimental autoimmune encephalomyelitis (EAE) and ultimately human autoimmune diseases. We report here that PDE8A exerts its control of T cell function through the Raf-1 kinase signaling pathway. The highly PDE8-selective enzymatic inhibitor PF-04957325 significantly suppresses rolling and adhesion of in vivo MOG35-55 activated inflammatory CD4+ T effector (Teff) cells while interacting with inflamed brain endothelial cells under shear flow conditions. Recently, PDE8A was shown to associate with Raf-1 creating a compartment of low cAMP around Raf-1 thereby protecting it from protein kinase A (PKA) mediated inhibitory phosphorylation. Disruption of the PDE8A-Raf-1 complex by disruptor peptide (DP) significantly reduces adhesion of Teff cells to endothelial cells. We further observed that disrupting PDE8A-Raf-1 through DP specifically reduces adhesion, spreading and locomotion of Teff cells while interacting with the vascular adhesion molecule ICAM-1. Our investigation of the effect of PDE8 inhibitor on chronic and relapsing-remitting (EAE) in vivo indicates suppression of clinical and histopathological signs of disease. PDE8 inhibitor affects accumulation of CD4+ T cells into the spinal cord. In addition, there is a reduction in pro-inflammatory cytokines TNF-α and IL-17 production in the spinal cord after PDE8 inhibition in vivo. Collectively, our studies demonstrate that PDE8A inhibition by enzymatic inhibitors or PDE8A-Raf-1 kinase signaling complex disruptors significantly decreases Teff cell adhesion and migration on endothelial cells, and represents a novel approach to treat autoimmune inflammation in vivo.

Available for download on Sunday, March 31, 2019

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