Abstract 621: Homocysteine Activates T Cells by Enhancing Endoplasmic Reticulum-mitochondria Coupling and Increasing Mitochondrial Respiration

Abstract

Hyperhomocysteinemia (HHcy) accelerates atherosclerosis by affecting the immuno-inflammatory response, increasing proliferation and stimulating cytokine secretion in T cells. However, whether homocysteine (Hcy) activation of T cells is associated with metabolic reprogramming is unclear. Here, we showed that Hcy (50 μM, 24 hr)-stimulated splenic T-cell proliferation in mice was accompanied by increased levels of mitochondrial reactive oxygen species (ROS) by 23.25±2.27%, calcium overload, increased mitochondrial mass by 24.29±7.97% and increased respiration. Inhibiting mitochondrial ROS levels and calcium signals or blocking mitochondrial respiration largely blunted Hcy-induced T-cell activation. Hcy also enhanced endoplasmic reticulum (ER) stress in T cells. Inhibiting ER stress with 4-phenylbutyric acid or mitochondrial respiration by rotenone blocked Hcy-induced T-cell proliferation and interferon-γ (IFN-γ) secretion. Mechanistically, Hcy treatment increased ER-mitochondria coupling as revealed by structured illumination microscopy and elevated expression of tethering proteins MFN2, Gpx7, and ERP44. Uncoupling ER and mitochondria by the microtubule inhibitor nocodazole attenuated Hcy-stimulated mitochondrial ROS production, calcium overload, mitochondrial membrane potential, IFN-γ secretion and T-cell proliferation; thus, juxtaposition of ER and mitochondria is required for Hcy-promoted mitochondrial function and T-cell activation. In conclusion, Hcy promotes T-cell proliferation and IFN-γ secretion by inducing metabolic reprogramming via regulating ER-mitochondrial coupling. Our results highlight the importance of metabolic regulation in T-cell activation and shed new light on understanding the pathogenesis of HHcy-accelerated atherosclerosis.