Decreased Cyclic AMP Levels in Dendritic Cells: Effects on Cell Signaling and Role in Allergic Inflammation
Dendritic cells (DCs) are crucial targets for modulating allergic disease due to their role in initiating helper T cell activation and differentiation. CD11cGnas (Gnas) mice have a DC-specific deletion of the G subunit of the heterotrimeric () GPT binding protein Gs, which activates adenylyl cyclase to produce cyclic AMP (cAMP). Isolated Gnas DCs have aberrant cAMP signaling, induce type II helper T cell (Th2) differentiation, and mediate the development of allergic asthma in vivo.
The studies presented in this dissertation investigate the mechanism by which cells respond to atypical cAMP signaling, and in particular decreased levels of cAMP, and how in DCs this mediates Th2 inflammation which contributes to the development of allergic disease.
In Chapter One, I review current knowledge of DCs, asthma, the cAMP pathway, and the role of both DCs and cAMP in the pathophysiology of asthma.
In Chapter Two, I present a transcriptomic analysis of RNA-Sequencing of WT and Gnas DCs to identify pathways with altered expression in Gnas DCs. Gnas DCs have an increase in microtubule-associated genes. Increased tubulin expression appears to be mediated by decreased Protein Kinase A (PKA) activation, indicating that decreased cAMP levels is responsible for the increased microtubule expression in Gnas DCs. I theorize that changes in microtubule function contribute to Gnas DCs’ increased Th2 induction.
In Chapter Three, I demonstrate that Gnas DCs have decreased basal cAMP levels and investigate how cells compensate for chronically reduced cAMP concentrations. Gnas DCs have decreased gene expression of PKA RII, multiple GPCRs, and the phosphodiesterases PDE4B and PDE4D in response to lower cAMP levels. Experiments show that PDE4B is a regulator of cAMP levels in DCs and its expression rises and falls via PKA in an attempt to return the cell to cAMP homeostasis. Furthermore, the high expression of PDE4B makes it a novel target to raise cAMP levels in DCs and reduce Th2 differentiation.
Together, these data indicate that raising cyclic AMP levels in DCs is an effective approach to reduce Th2 inflammation and identifies PDE4B as a novel target in DCs to decrease Th2 inflammation for the treatment of allergic disease.