Radiation induces senescence in lymphatic endothelial cells (LECs) and murine tail lymphedema tissue, contributing to lymphedema progression.

Cancer-related lymphedema (CRL) is an incurable disease characterized by progressive swelling of extremities. One of the risk factors in developing CRL is cancer treatments, including surgery and radiation. This leads to damage to the lymphatic system, causing accumulation of interstitial fluid, infiltration of inflammatory cells and cytokine release, tissue remodeling, accumulation of subcutaneous fat, and fibrosis. Radiation therapy (RT) inhibits lymphatic proliferation and survival by downregulating vascular endothelial growth factor receptor 3 (VEGFR-3) in lymphatic endothelial cells (LECs). How radiation affects CRL progression remains unclear. In this study, we found that RT reduced LEC growth and increased senescence in LECs as determined by increased senescence-associated β-galactosidase (SA-βgal) activity and increased protein expression of senescence markers p53, p21, and p16. Using the mouse tail lymphedema model, we found that tail swelling was increased after RT in both sham control and lymphatic ablation mice. After 30 days, tail swelling was maintained in RT treated mice with lymphatic ablation, whereas RT treated sham controls showed reduced swelling. This corresponded to an increase in senescent cells and apoptosis after RT in lymphatic-ablated mice compared to sham controls. We also found increased levels of senescence-related cytokines and chemokines in lymphedema patients' plasma samples who had RT compared to surgery alone or non-lymphedema controls. Finally, we found that RT increased anti-apoptotic protein BCL-2 in human LECs and lymphatic ablated mouse tissue. Treatment with the senolytic agent venetoclax (VCX), a BCL-2 inhibitor, selectively killed RT-induced senescent LECs and reduced swelling in the RT-induced tail lymphedema model. This suggests that RT contributes to CRL, at least in part, by inducing cellular senescence.