MicroRNA Regulation in GW/P Body Cell Biology, Lipopolysaccharide Signaling, and Rheumatoid Arthritis

Date of Award

2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Institution Granting Degree

University of Florida

Cedarville University School or Department

Science and Mathematics

First Advisor

Edward K.L. Chan

Keywords

Health and environmental sciences, Lipopolysaccharide, Rheumatoid arthritis, GW/P bodies, Innate immunity, Autoimmune diseases, Inflammatory cytokines

Abstract

MicroRNA (miRNA) are a recently discovered class of small RNA molecules that negatively regulate gene expression by targeting specific messenger RNAs (mRNAs). Once bound to the 3' untranslated region of their target mRNA, miRNA cause the translational repression or degradation of that message. Due to the novelty of miRNA research, the cell biology of miRNA-mediated regulation is not yet well understood, but it is known that miRNA and miRNA-effector proteins such as argonaute-2, GW182, and Rck/p54 all localize to cytoplasmic foci known as GW or P bodies (GWB). To better understand the cell biology of miRNA function, we first examined the relationship between GWB and miRNA. We found that in the absence of mature miRNA, GWB formation was abolished, indicating that miRNA are required for the formation of GWB and may be useful indicators of miRNA activity in cells. Next, we examined the effect of immune stimulation on GWB formation and found that the number and size of GWB increased in response to lipopolysaccharide (LPS) treatment in human monocytes. Furthermore, we found that the expression of three miRNA, miR-146a, miR-155, and miR-132, was concurrently increased in LPS-stimulated cells, and that miR-146a regulated LPS-induced cytokine production. These findings further establish GWB as biomarkers for miRNA activity and demonstrate a role for miRNA regulation in LPS-induced cytokine production. Finally, we investigated miRNA expression in rheumatoid arthritis (RA) patients compared to healthy controls. Interestingly, the expression of miR-146a, miR-155, miR-132 and miR-16 was significantly increased in the RA patients; however, we found that the increased miR-146a in RA patients did not negatively regulate its target genes. These findings suggest a possible role for defective miRNA regulation in RA pathogenesis, and implicate miRNA expression as a potential marker for RA diagnosis, treatment efficacy, or therapeutic target.

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