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Identification of cytokine induced changes to the pancreatic islet epigenome

University of British Columbia

The initial onset of type 1 diabetes, as well as islet graft rejection, is characterized by the autoimmune assault on the β-cells of the pancreatic islets of Langerhans. Resident and infiltrating immune cells secrete a cocktail of cytokines, such as IFNγ, Il-1β, and TNFα, which in turn, signal the β-cells to produce and secrete various chemokines and cytokines that lead to the recruitment of additional immune cells, eventually leading to β-cell failure and death. During these processes the expression of many genes becomes altered within β-cells, and we hypothesized that alterations to the chromatin states of β-cell cis-regulatory regions underlies these gene expression changes. The chromatin state of a given cis-regulatory region can be identified by the pattern of post-translational histone modifications on adjacent nucleosomes. For this study we focused on 4 histone modifications: Histone 3 Lysine 4 monomethylation (H3K4me1) and trimethylation (H3K4me3), Histone 3 Lysine 9 trimethylation (H3K9me3) and Histone 3 Lysine 27 trimethylation (H3K27me3); with a particular focus on H3K4me1 that is associated with active or poised enhancers and promoters. Our ChIP-Seq analysis revealed that, upon IFNγ, Il-1β, and TNFα exposure, many genomic regions in β-cells acquire de novo H3K4me1, despite being initially marked by the repressive histone modification H3K27me3. Many chemokine and cytokine genes were associated with these de novo enhancer regions, and the expression of many of these chemokine and cytokine genes is induced in islets exposed to IFNγ, Il-1β, and TNFα. We identified the Trithorax group (TrxG) complexes as likely candidates involved in the generation of these de novo enhancers, as they can contain proteins with H3K4 methyltransferase and H3K27me3 demethylase activity. To confirm the involvement of these complexes we attempted to block their activity by using an adenovirus expressing shRNAs targeting the core TrxG complex subunit Wdr5, and by using a small molecule selective inhibitor (GSK-J4) of the H3K27me demethylases Utx and Jmjd3. Both approaches resulted in blunting of the IFNγ, Il-1β, and TNFα induced expression of proinflammatory cytokines, with GSK-J4 having a more pronounced effect.

Text

2015-08-25

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54633

Cell and Developmental Biology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/