Abstract 613: Disturbed Flow-induced Telomeric Repeat Binding Factor 2 (terf2)-interacting Protein (terf2ip) K240 Sumoylation is Critical for Endothelial Senescence but Not Inflammation

Abstract

Upregulation of both inflammation and senescence (Sen) of endothelial cells (ECs) in the disturbed flow area within the aortic arch is well established, but the exact mechanisms and the relationship between inflammation and senescence remain unclear. TERF2IP is involved in regulation of DNA double strand break (DSB) repair of telomeres (TLs) as a component of the shelterin complex and in IκB kinase (IKK)-NF-kB signaling in the cytosol. TERF2IP and TERF2 form a stable heterodimer to protect the duplex region of TLs. Recent studies showed that TERF2IP or TERF2 deficiency caused TL shortening in mice. We studied how TERF2IP SUMOylation is regulated in ECs and what role it may play in EC inflammation and Sen. We found that disturbed flow (d-flow) activated p90RSK and increased TERF2IP S205 phosphorylation and subsequently K240 SUMOylation. Overexpression of dominant negative p90RSK inhibited d-flow-induced TERF2IP S205 phosphorylation and K240 SUMOylation, and also inhibited EC inflammation and Sen provoked by d-flow. TERF2IP S205 phosphorylation induced TERF2IP nuclear export, which then caused EC inflammation and Sen. In contrast, TERF2IP K240 SUMOylation had no effect on TERF2IP nuclear export, and the TERF2IP K240R SUMOylation site mutant failed to inhibit d-flow-induced NF-kB activation. Interestingly, this point mutation inhibited d-flow-induced Sen with reduced d-flow-induced TL shortening, 8-OHdG level, and apoptosis. Overexpression of a de-SUMOylation enzyme SENP2 and SENP2 T368 mutant significantly inhibited d-flow-induced TERF2IP SUMOylation, suggesting that SENP2 regulates nuclear TERF2IP SUMOylation. Lastly, EC Sen increased when SENP2 was specifically knocked out in ECs in mice, suggesting that TERF2IP K240 SUMOylation may play a role in d-flow-induced EC Sen. These data suggest that TERF2IP post-translational modifications play roles in regulating EC inflammation and Sen, which are differentially regulated by S205 phosphorylation and K240 SUMOylation. TERF2IP K240R knock-in mice will be used to determine the role of TERF2IP K240 SUMOylation in d-flow-induced atherogenesis. We suggest that TERF2IP SUMOylation promotes TL dysfunction, but it does not interfere with TERF2IP-mediated IKK-NF-kB activation in the cytosol.