# TET2 has endothelial-specific roles in interferon responses that are dysregulated by hyperglycemia in vitro and in vivo

## TL;DR

TET2 in endothelial cells regulates interferon responses, and its loss or dysfunction due to hyperglycemia may contribute to vascular issues and increased infection risk in diabetes.

## Contribution

Identifies endothelial-specific roles of TET2 in interferon signaling and its dysregulation by hyperglycemia.

## Key findings

- TET2 loss in endothelium disrupts interferon signaling and resembles transcriptional changes in diabetic endothelium.
- TET2 regulates IFITM1 and ISG15 independently of DNA demethylation, but controls CXCL9 and CXCL10 via demethylation.
- Interferon signaling and glycosaminoglycan metabolism are major pathways affected by TET2 loss.

## Abstract

Dysregulated DNA methylation in the endothelium is associated with the development of cardiovascular disease. Ten-eleven translocation 2 (TET2), a DNA demethylase, plays a regulatory role in endothelial function. Loss of endothelial-expressed TET2 correlates with atherosclerosis progression in vivo and alters vasoactive signaling in vitro. Hyperglycemia acts to downregulate TET2 stability and activity in endothelial cells, but the relevance of this to endothelial dysfunction in diabetes remains unclear. Here, we explore the transcriptional and functional consequences of endothelial-specific TET2 loss in vivo and assess the role of DNA methylation in TET2-dependent transcriptional regulation. Ex vivo aortic responses to acetylcholine and phenylephrine were equivalent between wild-type and endothelial-specific TET2 knockout (TET2KO) mice. RNA sequencing of endothelial-enriched lung cells from TET2KO mice revealed significant dysregulation of interferon signaling. In cultured endothelial cells, qPCR, hydroxymethylated-DNA immunoprecipitation sequencing, and nanopore sequencing showed that IFITM1 and ISG15—classical interferon-responsive genes—were negatively regulated by TET2 independent of DNA demethylation. Conversely, the IFNγ-inducible chemokines CXCL9 and CXCL10 were positively regulated by TET2 in a mechanism involving catalytic demethylation, as evidenced by increased 5hmC and decreased 5 mC at an enhancer region. Strikingly, approximately 70% of transcriptional changes observed in TET2KO endothelium were mirrored in diabetic mouse endothelium. Pathway analysis highlighted dysregulation of interferon signaling and altered glycosaminoglycan metabolism as the most significant biological consequences. In summary, endothelial TET2 loss leads to transcriptional dysregulation of interferon-regulated genes, partly through altered DNA methylation. This may have relevance to the susceptibility of diabetics to recurrent viral infections and endothelial dysfunction.