Early‐Life Thymectomy Results in T‐Cell Aging and Arterial Dysfunction in Middle‐Aged Mice
Authors: Buckley David J. , Sharma Sunita , Sabnani Manoj , Fadel Paul J. , Trott Daniel W. 
Published: May 2022

Previously we have found that T cells contribute to age‐related large artery stiffness and impairments in endothelium dependent dilation. The thymus is an immunological organ that is responsible for the generation of new naïve T cells. A hallmark of T cell aging is a phenotypic shift from a naïve to a memory phenotype. In this study, we sought to determine 1) whether early life thymectomy at 3wks of age would induce an aged (memory) T cell phenotype and 2) that these alterations in T cell phenotype will result in arterial dysfunction in otherwise middle‐aged mice. This study was approved by the institutional animal care and use committee at the University of Texas Arlington. Male C57BL6 mice underwent thymectomy (thymex; n=7‐17) at 3wks of age or left with their thymus intact (control; n=7‐17). At 9 months of age, doppler pulse wave velocity was used to assess large artery stiffness and following euthanasia, splenic, aortic, and mesenteric T cell phenotype was assessed using flow‐cytometry and T cell proliferation was assessed in vitro. To assess endothelium‐dependent dilation, second order mesenteric arteries were gently cleared of adipose and connective tissue and cannulated on the stage of a pressure myograph. Group differences were assessed by independent samples t‐test or repeated measures ANOVA and Bonferroni post‐hoc test. Data are presented as mean±SEM. Pulse wave velocity indicated that the thymex mice had significantly higher aortic stiffness (304.1±12.2 cm/s) compared to controls (270.2±13.8 cm/s; p=0.05). Flow cytometry results (expressed as thymex vs control) demonstrate that the spleen (CD4:79.4±5, 55.4±7.6 %memory; p=0.01; CD8: 72.2±2.4, 44.8±6.7 %memory; p=0.0008), aorta (CD4: 63.4±5.2, 34.6±6.5 %memory; p=0.001; CD8: 64.5±4, 30.6±2.4 %memory; p=<0.0001), and mesentery (CD4: 68.3±5.6,44.2±6.5 %memory; p=0.006; CD8: 47.1±6.1, 31.6±5.7 %memory; p=0.04) all exhibited a greater proportion (relative to all immune cells) of memory CD4+ (helper T) and CD8+ (cytotoxic T) T cells in the thymex animals compared to controls which is consistent with chronological aging. The after 96 hours in culture cell proliferation was blunted in both the CD4+ (45142±7214.4 cells) and CD8+ (50285.7±7870.7 cells) cells from the thymex mice compared to the control mice (CD4: 75428.6±3652.5 cells; p=0.0023; CD8: 81142.9±2756.9 cells; p=0.0025), which is also consistent with an aged T cell phenotype. Finally, the thymex mice exhibited significantly blunted endothelium dependent dilation in response to 10‐4 ­­M acetylcholine (46.1±6.99 % dilation) compared to controls (71.5±5%; p=0.005). Assessing dilation in the presence of L‐NAME revealed a significant blunting of nitric oxide bioavailability in arteries from thymex mice (33.91±8.2% NO dependent dilation) compared to controls (55.7±8.5%; p=0.05). In conclusion, these results indicate that early‐life thymectomy results in T cell aging as well as arterial dysfunction in otherwise middle‐aged mice. These observations suggest that aged T cells alone can drive age‐related dysfunction independent of the age of the arteries.