Inhibition of TRF2 Accelerates Telomere Attrition and DNA Damage in NaÃ ̄ve CD4 T Cells During HCV Infection

T cells play a crucial role in viral clearance and vaccine responses; however, the mechanisms that regulate their homeostasis during viral infections remain unclear. In this study, we investigated the machineries of T-cell homeostasis and telomeric DNA damage using a human model of hepatitis C virus (HCV) infection. We found that naïve CD4 T cells in chronically HCV-infected patients (HCV T cells) were significantly reduced due to apoptosis compared with agematched healthy subjects (HSs). These HCV T cells were not only senescent, as demonstrated by overexpression of aging markers and particularly shortened telomeres; but also DNA damaged, as evidenced by increased dysfunctional telomere-induced foci (TIF). Mechanistically, the telomere shelterin protein, in particular telomeric repeat binding factor 2 (TRF2) that functions to protect telomeres from DNA damage, was significantly inhibited posttranscriptionally via the p53-dependent Siah-1a ubiquitination. Importantly, knockdown of TRF2 in healthy T cells resulted in increases in telomeric DNA damage and T-cell apoptosis, whereas overexpression of TRF2 in HCV T cells alleviated telomeric DNA damage and T-cell apoptosis. To the best of our knowledge, this is the first report revealing that inhibition of TRF2 promotes T-cell telomere attrition and telomeric DNA damage that accelerates T-cell senescent and apoptotic programs, which contribute to naïve T-cell loss during viral infection. Thus, restoring the impaired T-cell telomeric shelterin machinery may offer a new strategy to improve immunotherapy and vaccine response against human viral diseases. Introduction T cells play a pivotal role in controlling viral infection and vaccine responses; however, the mechanisms underlying T-cell dysfunction that lead to chronic infection and poor vaccine response remain unclear. Hepatitis C virus (HCV) is highly efficient at establishing chronic infection, thus becoming an excellent model to study the mechanisms of T-cell dysregulation and viral persistence. Recently, we and others have found that HCV infection can accelerate T-cell aging, as evidenced by overexpression of aging markers and attrition of telomeres, indicating excessive cell proliferative turnover or inadequate telomeric DNA maintenance. Telomeres are repeating hexameric DNA sequences that are found at chromosome ends in association with a complex of shelterin proteins. Telomere integrity is a key feature of linear chromosomes that preserve genome stability and function, whereas telomere erosion is a hallmark of cell senescence that drives cell dysfunction or apoptosis. Although telomere length is maintained in most cases by © The Author(s) 2018 OpenAccessThis article is licensedunder aCreativeCommonsAttribution 4.0 International License,whichpermits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changesweremade. The images or other third partymaterial in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to thematerial. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Correspondence: Zhi Q. Yao (yao@etsu.edu) Center of Excellence in Inflammation, Infectious Disease and Immunity, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA Division of Infectious, Inflammatory and Immunologic Diseases, Department of Internal Medicine, Quillen College of Medicine, ETSU, Johnson City, TN 37614, USA Full list of author information is available at the end of the article. Edited by H. -U. Simon Official journal of the Cell Death Differentiation Association 12 34 56 78 90 () :,; 12 34 56 78 90 () :,; 1 2 3 4 5 6 7 8 9 0 () :,; 12 34 56 78 90 () :,; the telomerase, shelterin is essential to protect telomeres against unwanted DNA damage response (DDR). Shelterin comprises six polypeptides (TRF1, TRF2, RAP1, TIN2, TPP1, and POT1), of which telomeric repeat binding factor 2 (TRF2) is a key factor that plays an essential role in maintaining telomere integrity. TRF2 also protects chromosome ends against replicative DNA damage, particularly those that occur due to topological stress. Notably, TRF2 expression is increased in a variety of human cancers; consistently, its downregulation reduces tumorigenicity. The role of TRF2 in reprogramming telomeric DNA damage and remodeling T-cell homeostasis during viral infection, however, is largely unknown. To identify factors that perturb T-cell homeostasis during viral infection, we have explored the role of TRF2 in protecting telomeric DNA damage and T-cell apoptosis with a model of HCV infection. We provide evidence revealing that TRF2 inhibition promotes telomere attrition and DNA damage during HCV infection, rendering HCV T cells more senescent and apoptotic, thus potentially contributing to the HCV persistence and vaccine non-responsiveness. Materials and methods