NSun2 regulates aneurysm formation by promoting autotaxin expression and T cell recruitment.

Abdominal aortic aneurysm (AAA) is characterized by inflammatory cell infiltration and aggravated by hyperhomocysteinemia (HHcy). It is unknown whether the homocysteine (Hcy)-activated RNA methyltransferase NOP2/Sun domain family member 2 (NSun2) is associated with AAA. Here, we found that NSun2 deficiency significantly attenuated elastase-induced and HHcy-aggravated murine AAA with decreased T cell infiltration in the vessel walls. T cell labeling and adoptive transfer experiments confirmed that NSun2 deficiency inhibited the chemotaxis of vessels to T cells. RNA sequencing of endothelial cells showed that Hcy induced the accumulation of various metabolic enzymes of the phospholipid PC-LPC-LPA metabolic pathway, especially autotaxin (ATX). In the elastase-induced mouse model of AAA, ATX was specifically expressed in the endothelium and the plasma ATX concentration was upregulated and even higher in the HHcy group, which were decreased dramatically by NSun2 knockdown. In vitro Transwell experiments showed that ATX dose-dependently promoted T cell migration. HHcy may upregulate endothelial ATX expression and secretion and in turn recruit T cells into the vessel walls to induce vascular inflammation and consequently accelerate the pathogenesis of AAA. Mechanistically, secreted ATX interacted with T cells by binding to integrin α4, which subsequently activated downstream FAK/Src-RhoA signaling pathways and then induced T cell chemokinesis and adhesion. ATX overexpression in the vessel walls reversed the inhibited development of AAA in the NSun2-deficient mice. Therefore, NSun2 mediates the development of HHcy-aggravated AAA primarily by increasing endothelial ATX expression, secretion and T cell migration, which is a novel mechanism for HHcy-aggravated vascular inflammation and pathogenesis of AAA.

Shikonin attenuates hyperhomocysteinemia-induced CD4+ T cell inflammatory activation and atherosclerosis in ApoE-/- mice by metabolic suppression.

T cell metabolic activation plays a crucial role in inflammation of atherosclerosis. Shikonin (SKN), a natural naphthoquinone with anti-inflammatory activity, has shown to exert cardioprotective effects, but the effect of SKN on atherosclerosis is unclear. In addition, SKN was found to inhibit glycolysis via targeting pyruvate kinase muscle isozyme 2 (PKM2). In the present study, we investigated the effects of SKN on hyperhomocysteinemia (HHcy)-accelerated atherosclerosis and T cell inflammatory activation in ApoE-/- mice and the metabolic mechanisms in this process. Drinking water supplemented with Hcy (1.8 g/L) was administered to ApoE-/- mice for 2 weeks and the mice were injected with SKN (1.2 mg/kg, i.p.) or vehicle every 3 days. We showed that SKN treatment markedly attenuated HHcy-accelerated atherosclerosis in ApoE-/- mice and significantly decreased inflammatory activated CD4+ T cells and proinflammatory macrophages in plaques. In splenic CD4+ T cells isolated from HHcy-ApoE-/- mice, SKN treatment significantly inhibited HHcy-stimulated PKM2 activity, interferon-γ secretion and the capacity of these T cells to promote macrophage proinflammatory polarization. SKN treatment significantly inhibited HHcy-stimulated CD4+ T cell glycolysis and oxidative phosphorylation. Metabolic profiling analysis of CD4+ T cells revealed that Hcy administration significantly increased various glucose metabolites as well as lipids and acetyl-CoA carboxylase 1, which were reversed by SKN treatment. In conclusion, our results suggest that SKN is effective to ameliorate atherosclerosis in HHcy-ApoE-/- mice and this is at least partly associated with the inhibition of SKN on CD4+ T cell inflammatory activation via PKM2-dependent metabolic suppression.

T-cell-derived extracellular vesicles regulate B-cell IgG production via pyruvate kinase muscle isozyme 2.

Intercellular communication between lymphocytes plays a fundamental role in numerous immune responses. Previously, we demonstrated that hyperhomocysteinemia (HHcy) induced T cell intracellular glycolytic-lipogenic reprogramming and IFN-γ secretion via pyruvate kinase muscle isozyme 2 (PKM2) to accelerate atherosclerosis. Usually, B cells partially obtain help from T cells in antibody responses. However, whether PKM2 activation in T cells regulates B cell antibody production is unknown. Extracellular vesicles (EVs) are important cellular communication vehicles. Here, we found that PKM2 activator TEPP46-stimulated T-cell-derived EVs promoted B-cell IgG secretion. Conversely, EVs secreted from PKM2-null T cells were internalized into B cells and markedly inhibited B-cell mitochondrial programming, activation, and IgG production. Mechanistically, lipidomics analyses showed that increased ceramides in PKM2-activated T-cell EVs were mainly responsible for enhanced B cell IgG secretion induced by these EVs. Finally, quantum dots (QDs) were packaged with PKM2-null T cell EVs and anti-CD19 antibody to exert B-cell targeting and inhibit IgG production, eventually ameliorating HHcy-accelerated atherosclerosis in vivo. Thus, PKM2-mediated EV ceramides in T cells may be an important cargo for T-cell-regulated B cell IgG production, and QD-CD19-PKM2-null T cell EVs hold high potential to treat B cell overactivation-related diseases.-Yang, J., Dang, G., Lü, S., Liu, H., Ma, X., Han, L., Deng, J., Miao, Y., Li, X., Shao, F., Jiang, C., Xu, Q., Wang, X., Feng, J. T-cell-derived extracellular vesicles regulate B-cell IgG production via pyruvate kinase muscle isozyme 2.

GSNOR modulates hyperhomocysteinemia-induced T cell activation and atherosclerosis by switching Akt S-nitrosylation to phosphorylation.

The adaptive immune system plays a critical role in hyperhomocysteinemia (HHcy)-accelerated atherosclerosis. Recent studies suggest that HHcy aggravates atherosclerosis with elevated oxidative stress and reduced S-nitrosylation level of redox-sensitive protein residues in the vasculature. However, whether and how S-nitrosylation contributes to T-cell-driven atherosclerosis remain unclear. In the present study, we report that HHcy reduced the level of protein S-nitrosylation in T cells by inducing S-nitrosoglutathione reductase (GSNOR), the key denitrosylase that catalyzes S-nitrosoglutathione (GSNO), which is the main restored form of nitric oxide in vivo. Consequently, secretion of inflammatory cytokines [interferon-γ (IFN-γ) and interleukin-2] and proliferation of T cells were increased. GSNOR knockout or GSNO stimulation rectified HHcy-induced inflammatory cytokine secretion and T-cell proliferation. Site-directed mutagenesis of Akt at Cys224 revealed that S-nitrosylation at this site was pivotal for the reduced phosphorylation at Akt Ser473, which led to impaired Akt signaling. Furthermore, on HHcy challenge, as compared with GSNOR+/+ApoE-/- littermate controls, GSNOR-/-ApoE-/- double knockout mice showed reduced T-cell activation with concurrent reduction of atherosclerosis. Adoptive transfer of GSNOR-/- T cells to ApoE-/- mice fed homocysteine (Hcy) decreased atherosclerosis, with fewer infiltrated T cells and macrophages in plaques. In patients with HHcy and coronary artery disease, the level of plasma Hcy was positively correlated with Gsnor expression in peripheral blood mononuclear cells and IFN-γ+ T cells but inversely correlated with the S-nitrosylation level in T cells. These data reveal that T cells are activated, in part via GSNOR-dependent Akt denitrosylation during HHcy-induced atherosclerosis. Thus, suppression of GSNOR in T cells may reduce the risk of atherosclerosis.

PKM2-dependent metabolic reprogramming in CD4+ T cells is crucial for hyperhomocysteinemia-accelerated atherosclerosis.

Inflammation mediated by activated T cells plays an important role in the initiation and progression of hyperhomocysteinemia (HHcy)-accelerated atherosclerosis in ApoE-/- mice. Homocysteine (Hcy) activates T cells to secrete proinflammatory cytokines, especially interferon (IFN)-γ; however, the precise mechanisms remain unclear. Metabolic reprogramming is critical for T cell inflammatory activation and effector functions. Our previous study demonstrated that Hcy regulates T cell mitochondrial reprogramming by enhancing endoplasmic reticulum (ER)-mitochondria coupling. In this study, we further explored the important role of glycolysis-mediated metabolic reprogramming in Hcy-activated CD4+ T cells. Mechanistically, Hcy-activated CD4+ T cell increased the protein expression and activity of pyruvate kinase muscle isozyme 2 (PKM2), the final rate-limiting enzyme in glycolysis, via the phosphatidylinositol 3-kinase/AKT/mechanistic target of rapamycin signaling pathway. Knockdown of PKM2 by small interfering RNA reduced Hcy-induced CD4+ T cell IFN-γ secretion. Furthermore, we generated T cell-specific PKM2 knockout mice by crossing LckCre transgenic mice with PKM2fl/fl mice and observed that Hcy-induced glycolysis and oxidative phosphorylation were both diminished in PKM2-deficient CD4+ T cells with reduced glucose and lipid metabolites, and subsequently reduced IFN-γ secretion. T cell-depleted apolipoprotein E-deficient (ApoE-/-) mice adoptively transferred with PKM2-deficient CD4+ T cells, compared to mice transferred with control cells, showed significantly decreased HHcy-accelerated early atherosclerotic lesion formation. In conclusion, this work indicates that the PKM2-dependent glycolytic-lipogenic axis, a novel mechanism of metabolic regulation, is crucial for HHcy-induced CD4+ T cell activation to accelerate early atherosclerosis in ApoE-/- mice. KEY MESSAGES: Metabolic reprogramming is crucial for Hcy-induced CD4+ T cell inflammatory activation. Hcy activates the glycolytic-lipogenic pathway in CD4+ T cells via PKM2. Targeting PKM2 attenuated HHcy-accelerated early atherosclerosis in ApoE-/- mice in vivo.

Homocysteine Activates B Cells via Regulating PKM2-Dependent Metabolic Reprogramming.

The overactivation of immune cells plays an important role in the pathogenesis of hyperhomocysteinemia (HHcy)-accelerated atherosclerosis. Homocysteine (Hcy) activates B cell proliferation and Ab secretion; however, the underlying mechanisms for these effects remain largely unknown. Metabolic reprogramming is critical for lymphocyte activation and effector function. In this study, we showed that Hcy-activated B cells displayed an increase in both oxidative phosphorylation and glycolysis, with a tendency to shift toward the latter, as well as an accumulation of intermediates in the pentose phosphate pathway, to provide energy and biosynthetic substrates for cell growth and function. Mechanistically, Hcy increased both the protein expression and glycolytic enzyme activity of the pyruvate kinase muscle isozyme 2 (PKM2) in B cells, whereas the PKM2 inhibitor shikonin restored Hcy-induced metabolic changes, as well as B cell proliferation and Ab secretion both in vivo and in vitro, indicating that PKM2 plays a critical role in metabolic reprogramming in Hcy-activated B cells. Further investigation revealed that the Akt-mechanistic target of rapamycin signaling pathway was involved in this process, as the mechanistic target of rapamycin inhibitor rapamycin inhibited Hcy-induced changes in PKM2 enzyme activity and B cell activation. Notably, shikonin treatment effectively attenuated HHcy-accelerated atherosclerotic lesion formation in apolipoprotein E-deficient mice. In conclusion, our results demonstrate that PKM2 is required to support metabolic reprogramming for Hcy-induced B cell activation and function, and it might serve as a critical regulator in HHcy-accelerated initiation of atherosclerosis.

Homocysteine activates T cells by enhancing endoplasmic reticulum-mitochondria coupling and increasing mitochondrial respiration.

Hyperhomocysteinemia (HHcy) accelerates atherosclerosis by increasing proliferation and stimulating cytokine secretion in T cells. However, whether homocysteine (Hcy)-mediated T cell activation is associated with metabolic reprogramming is unclear. Here, our in vivo and in vitro studies showed that Hcy-stimulated splenic T-cell activation in mice was accompanied by increased levels of mitochondrial reactive oxygen species (ROS) and calcium, mitochondrial mass and respiration. Inhibiting mitochondrial ROS production and calcium signals or blocking mitochondrial respiration largely blunted Hcy-induced T-cell interferon γ (IFN-γ) secretion and proliferation. Hcy also enhanced endoplasmic reticulum (ER) stress in T cells, and inhibition of ER stress with 4-phenylbutyric acid blocked Hcy-induced T-cell activation. Mechanistically, Hcy increased ER-mitochondria coupling, and uncoupling ER-mitochondria by the microtubule inhibitor nocodazole attenuated Hcy-stimulated mitochondrial reprogramming, IFN-γ secretion and proliferation in T cells, suggesting that juxtaposition of ER and mitochondria is required for Hcy-promoted mitochondrial function and T-cell activation. In conclusion, Hcy promotes T-cell activation by increasing ER-mitochondria coupling and regulating metabolic reprogramming.