Interleukin-2 is a multifaceted cytokine with both immunostimulatory and immunosuppressive properties. Our laboratory recently demonstrated that the availability of IL-2 is regulated, in part, by association with perlecan, a heparan sulfate proteoglycan. Given the abundance of perlecan in blood vessels, we asked whether IL-2 is present in vessel walls. Our results indicate that IL-2 is associated with endothelial and smooth muscle cells within the human arterial wall. This IL-2 is released by heparanase, and promotes the proliferation of an IL-2 dependent cell line. Given the presence of IL-2 in human arteries, we asked whether the large vessels of IL-2 deficient mice were normal. The aortas of IL-2 deficient mice exhibited a loss of smooth muscle cells, suggesting that IL-2 may contribute to their survival. In their entirety, these results suggest a here-to-fore unrecognized role of IL-2 in vascular biology, and have significant implications for both the immune and cardiovascular systems.
Interleukin-2 (IL-2) is a multi-faceted cytokine, known for promoting proliferation, survival, and cell death depending on the cell type and state. For example, IL-2 facilitates cell death only in activated T cells when antigen and IL-2 are abundant. The availability of IL-2 clearly impacts this process. Our laboratory recently demonstrated that IL-2 is retained in blood vessels by heparan sulfate, and that biologically active IL-2 is released from vessel tissue by heparanase. We now demonstrate that heparanase digestion also releases a dimeric form of IL-2 that is highly cytotoxic to cells expressing the IL-2 receptor. These cells include “traditional” IL-2 receptor-bearing cells such as lymphocytes, as well as those less well known for IL-2 receptor expression, such as epithelial and smooth muscle cells. The morphologic changes and rapid cell death induced by dimeric IL-2 imply that cell death is mediated by disruption of membrane permeability and subsequent necrosis. These findings suggest that IL-2 has a direct and unexpectedly broad influence on cellular homeostatic mechanisms in both immune and non-immune systems.
Mice deficient in T regulatory cells (T regs) die from systemic inflammation. Breeding these mice with IL-2KO mice clears inflammation in lungs and skin, suggesting that IL-2 has pro-inflammatory functions beyond promoting survival of T regs. We recently identified a dimeric form of IL2 mammalian tissues that is cytotoxic to cells expressing IL-2 receptor (IL-2R), which provides an explanation for the above. Exposure of IL-2R+ cells to dimeric IL-2 results in rapid release of LDH. We hypothesized that dimer-mediated cell death is consistent with the characteristics of necrosis. To test this hypothesis, we exposed Jurkat cells to dimeric IL-2 and processed them for electron microscopy at 5 minutes. EM revealed swollen nuclear membranes and mitochondria consistent with early necrosis. Exposure of vascular smooth muscle cells (VSMC) to dimeric IL-2 induced 50% loss of cellular ATP at 5 minutes and nearly complete loss at 20 minutes. Using the mitochondrial membrane potential indicator JC-1 in VSMC, nearly all mitochondria lost their MMP by 10 minutes. These data indicate that dimeric IL-2 kills cells by necrosis. Our finding that dimeric IL-2 is cytotoxic to cells expressing IL-2R, lymphoid or non-lymphoid, has implications beyond the immune system. These studies combined with prior studies showing presence of matrix-bound IL-2 in arteries, suggests dimeric IL-2 may contribute to vascular inflammation in processes such as atherosclerosis.
Interleukin‐2 (IL‐2) is a cytokine critical to normal immune function. Our laboratory has shown that IL‐2 is retained in tissues by heparan sulfate (HS). While known as a monomer, a dimeric form of IL‐2 was previously identified in fish optic neurons, and this form was toxic to oligodendrocytes. Given this observation, we asked whether dimeric IL‐2 is found in mammalian tissues. Murine and human aorta and kidney were assessed by Western blot for the presence of IL‐2. Dimeric (30 kD) IL‐2 was identified in each tissue. Heparinase digestion of tissues liberated dimeric IL‐2, suggesting that the dimer is bound, at least in part, by HS. To ascertain whether dimeric IL‐2 is cytotoxic, we treated cultures of renal epithelial cells with increasing concentrations of dimeric IL‐2, isolated by electroelution. Signs of cytotoxicity were evident within 15 minutes of dimer addition. Commercial IL‐2, isolated identically to dimeric IL‐2, was not cytotoxic. Systemic administration to mice of 10 μg of dimeric IL‐2 induced vacuolization of renal epithelium, a morphology typically seen with ischemic injury. Finally, murine kidneys subjected to 60 minutes of ischemia, compared to sham controls, expressed greatly increased amounts of dimeric IL‐2 in tissue homogenates. These results suggest that dimeric IL‐2 may contribute to acute tubular necrosis and, in turn, renal dysfunction. This work was supported by institutional funds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.