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Kidney Week

Abstract: PO0204

The Fibrogenic Response to Renal Injury Is Epigenetically Regulated Through the Activation of Bivalent Genes

Session Information

  • AKI Mechanisms - 2
    October 22, 2020 | Location: On-Demand
    Abstract Time: 10:00 AM - 12:00 PM

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Nguyen, Elizabeth D., Seattle Children's Hospital Department of Pediatric Nephrology, Seattle, Washington, United States
  • Okamura, Daryl M., Seattle Children's Hospital Department of Pediatric Nephrology, Seattle, Washington, United States
  • Houghtaling, Scott Robert, Seattle Children's Research Institute, Seattle, Washington, United States
  • Collins, Sarah J., Seattle Children's Research Institute, Seattle, Washington, United States
  • Timms, Andrew E., Seattle Children's Research Institute, Seattle, Washington, United States
  • Beier, David R., Seattle Children's Research Institute, Seattle, Washington, United States
  • Majesky, Mark W., Seattle Children's Research Institute, Seattle, Washington, United States
Background

Bivalent genes are regions of epigenetically modified nucleosomes that carry both H3K4me3 and H3K27me3 simultaneously and exist in a poised transcriptional state, ready for activation or repression depending on stimuli. While important in directing gene expression during development, the role of bivalency has not been fully characterized in renal injury. In this work, we demonstrate that activated bivalent genes are associated with upregulation of genes that drive the response to unilateral ureteric obstruction (UUO) in the mouse.

Methods

CUT&RUN ChIP-Seq analysis using antibodies to H3K4me3 and H3K27me3 was carried out on normal kidneys and kidneys of mice 5 days after UUO. Enriched peaks were identified using SEACR, and HOMER was used to perform peak annotation. To determine fold change gene expression, RNA was collected and analyzed from samples 5 days after they were subjected to sham or UUO surgery.

Results

Through peak annotation of CUT&RUN results, 1546 bivalently marked genes were identified in the normal kidney. With the onset of UUO, 62% of these bivalent genes (951/1546, activated bivalent genes) are activated by the loss of the repressive H3K27me3 mark and the persistence of the activating H3K4me3 mark, indicating these genes are available for transcription. Upon correlation of activated bivalent genes with RNA Seq data after UUO only 13% were significantly upregulated (fold change >1.5, FDR <0.05). Functional analysis of these activated bivalent genes identified enriched pathways associated with kidney injury including apoptotic signaling, regulation of fibroblast proliferation and inflammation. Significantly increased expression of genes involved in these pathways were noted after UUO, including Nfkb2 (7 fold), Rhob (6 fold), Cdkn1 (5 fold) and Tgfbr2 (2.5 fold). The activated bivalent gene with the most significant increase in gene expression (20 fold in UUO compared to sham) was Atf3, a transcription factor which plays a protective role in kidney injury by attenuating the inflammatory response.

Conclusion

We provide evidence to suggest that the response to renal injury via inflammatory, apoptotic and fibrogenic pathways is orchestrated through the epigenetic regulation of bivalent genes that are poised for response in the normal kidney.

Funding

  • NIDDK Support