Atherosclerosis Impairs Naive CD4 T-Cell Responses via Disruption of Glycolysis

Objective

CD4 T cells are important regulators of atherosclerotic progression. The metabolic profile of CD4 T cells controls their signaling and function, but how atherosclerosis affects T-cell metabolism is unknown. Here, we sought to determine the impact of atherosclerosis on CD4 T-cell metabolism and the contribution of such metabolic alterations to atheroprogression.

Approach and Results

Using PCR arrays, we profiled the expression of metabolism genes in CD4 T cells from atherosclerotic apolipoprotein-E knockout mice fed a Western diet. These cells exhibited dysregulated expression of genes critically involved in glycolysis and fatty acid degradation, compared with those from animals fed a standard laboratory diet. We examined how T-cell metabolism was changed in either Western diet–fed apolipoprotein-E knockout mice or samples from patients with cardiovascular disease by measuring glucose uptake, activation, and proliferation in CD4 T cells. We found that naive CD4 T cells from Western diet–fed apolipoprotein-E knockout mice failed to uptake glucose and displayed impaired proliferation and activation, compared with CD4 T cells from standard laboratory diet–fed animals. Similarly, we observed that naive CD4 T-cell frequencies were reduced in the circulation of human subjects with high cardiovascular disease compared with low cardiovascular disease. Naive T cells from high cardiovascular disease subjects also showed reduced proliferative capacity.

Conclusions

These results highlight the dysfunction that occurs in CD4 T-cell metabolism and immune responses during atherosclerosis. Targeting metabolic pathways within naive CD4 T cells could thus yield novel therapeutic approaches for improving CD4 T-cell responses against atheroprogression.

Naive CD8+ T Cells Expressing CD95 Increase Human Cardiovascular Disease Severity

OBJECTIVE

Cardiovascular disease (CVD) remains a significant global health concern with a high degree of mortality. While CD4⁺ T cells have been extensively studied in CVD, the importance of CD8⁺ T cells in this disease, despite their abundance and increased activation in human atherosclerotic plaques, remains largely unknown. Thus, the objective of this study was to compare peripheral T-cell signatures between humans with a high (severe) risk of CVD (including myocardial infarction or stroke) and those with a low risk of CVD. Approach and Results: Using mass cytometry, we uncovered a naive CD8⁺ T (T_N) cell population expressing CD95 (termed CD95⁺CD8⁺ stem cell memory T [CD8 T_SCM] cells) that was enriched in patients with high compared with low CVD. This T-cell subset enrichment within individuals with high CVD was a relative increase and resulted from the loss of CD95^lo cells within the T_N compartment. We found that CD8 T_SCM cells positively correlated with CVD risk in humans, while CD8⁺ T_N cells were inversely correlated. Atherosclerotic apolipoprotein E-deficient (ApoE^-/-) mice also displayed respective 7- and 2-fold increases in CD8⁺ T_SCM frequencies within the peripheral blood and aorta-draining paraaortic lymph nodes compared with C57BL/6J mice. CD8⁺ T_SCM cells were 1.7-fold increased in aortas from western diet fed ApoE^-/- mice compared with normal laboratory diet-fed ApoE^-/- mice. Importantly, transfer of T_SCM cells into immune-deficient Rag.Ldlr recipient mice that lacked T cells increased atherosclerosis, illustrating the importance of these cells in atherogenesis.

CONCLUSIONS

CD8⁺ T_SCM cells are increased in humans with high CVD. As these T_SCM cells promote atherosclerosis, targeting them may attenuate atherosclerotic plaque progression.

Pathogenic Autoimmunity in Atherosclerosis Evolves From Initially Protective Apolipoprotein B100-Reactive CD4+ T-Regulatory Cells

BACKGROUND

Throughout the inflammatory response that accompanies atherosclerosis, autoreactive CD4⁺ T-helper cells accumulate in the atherosclerotic plaque. Apolipoprotein B₁₀₀ (apoB), the core protein of low-density lipoprotein, is an autoantigen that drives the generation of pathogenic T-helper type 1 (T_H1) cells with proinflammatory cytokine secretion. Clinical data suggest the existence of apoB-specific CD4⁺ T cells with an atheroprotective, regulatory T cell (T_reg) phenotype in healthy individuals. Yet, the function of apoB-reactive T_regs and their relationship with pathogenic T_H1 cells remain unknown.

METHODS

To interrogate the function of autoreactive CD4⁺ T cells in atherosclerosis, we used a novel tetramer of major histocompatibility complex II to track T cells reactive to the mouse self-peptide apo B_978-993 (apoB⁺) at the single-cell level.

RESULTS

We found that apoB⁺ T cells build an oligoclonal population in lymph nodes of healthy mice that exhibit a T_reg-like transcriptome, although only 21% of all apoB⁺ T cells expressed the T_reg transcription factor FoxP3 (Forkhead Box P3) protein as detected by flow cytometry. In single-cell RNA sequencing, apoB⁺ T cells formed several clusters with mixed T_H signatures that suggested overlapping multilineage phenotypes with pro- and anti-inflammatory transcripts of T_H1, T helper cell type 2 (T_H2), and T helper cell type 17 (T_H17), and of follicular-helper T cells. ApoB⁺ T cells were increased in mice and humans with atherosclerosis and progressively converted into pathogenic T_H1/T_H17-like cells with proinflammatory properties and only a residual T_reg transcriptome. Plaque T cells that expanded during progression of atherosclerosis consistently showed a mixed T_H1/T_H17 phenotype in single-cell RNA sequencing. In addition, we observed a loss of FoxP3 in a fraction of apoB⁺ T_regs in lineage tracing of hyperlipidemic Apoe^-/- mice. In adoptive transfer experiments, converting apoB⁺ T_regs failed to protect from atherosclerosis.

CONCLUSIONS

Our results demonstrate an unexpected mixed phenotype of apoB-reactive autoimmune T cells in atherosclerosis and suggest an initially protective autoimmune response against apoB with a progressive derangement in clinical disease. These findings identify apoB autoreactive T_regs as a novel cellular target in atherosclerosis.

Neuropilin-1 Expression on CD4 T Cells Is Atherogenic and Facilitates T Cell Migration to the Aorta in Atherosclerosis

Neuropilin 1 (Nrp1) is a type I transmembrane protein that plays important roles in axonal guidance, neuronal development, and angiogenesis. Nrp1 also helps migrate thymus-derived regulatory T cells to vascular endothelial growth factor (VEGF)-producing tumors. However, little is known about the role of Nrp1 on CD4 T cells in atherosclerosis. In ApoE^-/- mice fed a Western diet for 15 wk, we found a 2-fold increase in Nrp1⁺Foxp3^- CD4 T cells in their spleens, periaortic lymph nodes, and aortas, compared with chow-fed mice. Nrp1⁺Foxp3^- CD4 T cells had higher proliferation potential, expressed higher levels of the memory marker CD44, and produced more IFN-γ when compared with Nrp1^- CD4 T cells. Treatment of CD4 T cells with oxLDL increased Nrp1 expression. Furthermore, atherosclerosis-susceptible mice selectively deficient for Nrp1 expression on T cells developed less atherosclerosis than their Nrp1-sufficient counterparts. Mechanistically, we found that CD4 T cells that express Nrp1 have an increased capacity to migrate to the aorta and periaortic lymph nodes compared to Nrp1^- T cells, suggesting that the expression of Nrp1 facilitates the recruitment of CD4 T cells into the aorta where they can be pathogenic. Thus, we have identified a novel role of Nrp1 on CD4 T cells in atherosclerosis. These results suggest that manipulation of Nrp1 expression on T cells can affect the outcome of atherosclerosis and lower disease incidence.

Publisher Correction: Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

In this Letter, affiliation number 1 was originally missing from the HTML; the affiliations were missing for author Ming-Yow Hung in the HTML; and the Fig. 4 legend erroneously referred to panels a-h, instead of a-g. These errors have been corrected online.

Oxidized phospholipids are proinflammatory and proatherogenic in hypercholesterolaemic mice

Oxidized phospholipids (OxPL) are ubiquitous, are formed in many inflammatory tissues, including atherosclerotic lesions, and frequently mediate proinflammatory changes ¹ . Because OxPL are mostly the products of non-enzymatic lipid peroxidation, mechanisms to specifically neutralize them are unavailable and their roles in vivo are largely unknown. We previously cloned the IgM natural antibody E06, which binds to the phosphocholine headgroup of OxPL, and blocks the uptake of oxidized low-density lipoprotein (OxLDL) by macrophages and inhibits the proinflammatory properties of OxPL^2-4. Here, to determine the role of OxPL in vivo in the context of atherogenesis, we generated transgenic mice in the Ldlr^-/- background that expressed a single-chain variable fragment of E06 (E06-scFv) using the Apoe promoter. E06-scFv was secreted into the plasma from the liver and macrophages, and achieved sufficient plasma levels to inhibit in vivo macrophage uptake of OxLDL and to prevent OxPL-induced inflammatory signalling. Compared to Ldlr^-/- mice, Ldlr ^-/- E06-scFv mice had 57-28% less atherosclerosis after 4, 7 and even 12 months of 1% high-cholesterol diet. Echocardiographic and histologic evaluation of the aortic valves demonstrated that E06-scFv ameliorated the development of aortic valve gradients and decreased aortic valve calcification. Both cholesterol accumulation and in vivo uptake of OxLDL were decreased in peritoneal macrophages, and both peritoneal and aortic macrophages had a decreased inflammatory phenotype. Serum amyloid A was decreased by 32%, indicating decreased systemic inflammation, and hepatic steatosis and inflammation were also decreased. Finally, the E06-scFv prolonged life as measured over 15 months. Because the E06-scFv lacks the functional effects of an intact antibody other than the ability to bind OxPL and inhibit OxLDL uptake in macrophages, these data support a major proatherogenic role of OxLDL and demonstrate that OxPL are proinflammatory and proatherogenic, which E06 counteracts in vivo. These studies suggest that therapies inactivating OxPL may be beneficial for reducing generalized inflammation, including the progression of atherosclerosis, aortic stenosis and hepatic steatosis.

Apolipoprotein AI prevents regulatory to follicular helper T cell switching during atherosclerosis

Regulatory T (Treg) cells contribute to the anti-inflammatory response during atherogenesis. Here we show that during atherogenesis Treg cells lose Foxp3 expression and their immunosuppressive function, leading to the conversion of a fraction of these cells into T follicular helper (Tfh) cells. We show that Tfh cells are pro-atherogenic and that their depletion reduces atherosclerosis. Mechanistically, the conversion of Treg cells to Tfh cells correlates with reduced expression of IL-2Rα and pSTAT5 levels and increased expression of IL-6Rα. In vitro, incubation of naive T cells with oxLDL prevents their differentiation into Treg cells. Furthermore, injection of lipid-free Apolipoprotein AI (ApoAI) into ApoE^−/− mice reduces intracellular cholesterol levels in Treg cells and prevents their conversion into Tfh cells. Together our results suggest that ApoAI, the main protein in high-density lipoprotein particles, modulates the cellular fate of Treg cells and thus influences the immune response during atherosclerosis.

Regulatory T (Treg) cells contribute to the anti-inflammatory response during atherogenesis. Here Gaddis et al. show that Apolipoprotein AI prevents the conversion of Treg cells into pro-atherogenic T follicular helper cells, and thus regulates the immune response during atherogenesis.

Loss of ABCG1 influences regulatory T cell differentiation and atherosclerosis

ATP-binding cassette transporter G1 (ABCG1) promotes cholesterol accumulation and alters T cell homeostasis, which may contribute to progression of atherosclerosis. Here, we investigated how the selective loss of ABCG1 in T cells impacts atherosclerosis in LDL receptor-deficient (LDLR-deficient) mice, a model of the disease. In LDLR-deficient mice fed a high-cholesterol diet, T cell-specific ABCG1 deficiency protected against atherosclerotic lesions. Furthermore, T cell-specific ABCG1 deficiency led to a 30% increase in Treg percentages in aorta and aorta-draining lymph nodes (LNs) of these mice compared with animals with only LDLR deficiency. When Abcg1 was selectively deleted in Tregs of LDLR-deficient mice, we observed a 30% increase in Treg percentages in aorta and aorta-draining LNs and reduced atherosclerosis. In the absence of ABCG1, intracellular cholesterol accumulation led to downregulation of the mTOR pathway, which increased the differentiation of naive CD4 T cells into Tregs. The increase in Tregs resulted in reduced T cell activation and increased IL-10 production by T cells. Last, we found that higher ABCG1 expression in Tregs was associated with a higher frequency of these cells in human blood samples. Our study indicates that ABCG1 regulates T cell differentiation into Tregs, highlighting a pathway by which cholesterol accumulation can influence T cell homeostasis in atherosclerosis.

Abstract 20: Apolipoprotein A-I Influences Regulatory T Cell Development and Proliferation in Homeostasis and Atherogenesis

Apolipoprotein A-I (ApoAI) is the major protein component of HDL. HDL ApoAI is involved in the efflux of cholesterol from cells to maintain cellular cholesterol homeostasis. ApoAI also has anti-inflammatory properties. We previously showed that injecting mice fed an atherogenic diet with ApoAI decreased the number of activated CD4 lymphocytes. Since T regulatory lymphocytes (Treg) play a major role in inhibiting the immune response during atherosclerosis development, we wanted to determine if ApoAI influences Treg development, hypothesizing that ApoAI enhances Treg development. To test this hypothesis, we compared the numbers of Treg in ApoAI-/- mice to B6 mice, and found a 50% decrease in the numbers of Treg in the periaortic LNs (PaLN) of ApoAI-/- mice. BrdU labeling studies showed that ApoAI-/- Treg had a significant 30% reduction in proliferation, suggesting that in the absence of ApoAI and normal cholesterol homeostasis, Tregs have defective proliferation. Functionally, we discovered that ApoAI-/- Treg were significantly less suppressive than B6 Treg in reducing CD4 effector T cell proliferation, suggesting that ApoAI plays a role in both the development and function of Tregs. To determine if the addition of exogenous lipid-free ApoAI could rescue and promote Treg differentiation in ApoAI-/- mice, ApoAI-/- naïve T cells were incubated in vitro with TGFβ and exogenous ApoAI. Addition of ApoAI significantly increased development of naïve ApoA1-/- lymphocytes into Treg. To verify these results in vivo, we fed a novel Treg lineage tracker mouse (LT), Foxp3-YFP-Cre-Rosa26-RFP-ApoE-/- mice a western diet for 15 weeks and administered subcutaneous injections of ApoAI for the last 9 weeks of diet. These mice allow us to identify current functional Tregs and any exTregs that have lost active Treg function in vivo. We found that LT mice treated with ApoAI had a 37% decrease in exTregs and a concomitant 33% increase in current functional Tregs in the aorta. This was accompanied by decreased IFNγ and IL-17 production in PaLN, further confirming our in vitro findings that ApoAI promotes Treg development and function. In conclusion, we have identified a novel role for ApoAI by enhancing Treg development, emphasizing the immune properties of ApoAI for atheroprotection.

Abstract 544: Nrp-1+Foxp3-CD4 T Cells Are a Novel Subset of T Lymphocytes that Are Induced in Aorta During Development of Atherosclerosis

Neuropilin 1 (Nrp-1) is a type I transmembrane protein that plays an important role in axonal guidance and neuronal development as well as vascular sprouting and angiogenesis through the interaction with Semaphorin-3A and vascular endothelial growth factor (VEGF), respectively. Recently, Nrp-1 was found on a subset of thymus-derived regulatory T cells (Treg) that migrated into VEGF producing tumors. Moreover, Nrp-1+ CD4 T cells were protective in a murine experimental model of autoimmune encephalomyelitis, suggesting that these cells may have a participating role in other inflammatory diseases. Since atherosclerosis is a chronic inflammatory disease where T cells, macrophages, and other immune cells orchestrate disease progression, we hypothesized that Nrp-1+ CD4 T cells are induced in the aorta during atherosclerosis development and play a role during disease progression. We fed ApoE-/- mice a western diet for 15 weeks and found a 2-fold increase in Nrp-1+Foxp3- CD4 T cells in the spleens, peri-aortic lymph nodes and aortas of western diet fed mice compared to chow-fed mice. In addition, these Nrp-1+Foxp3- CD4 T cells expressed higher levels of the memory marker CD44 and produced more IFNγ when compared to Nrp-1- CD4 T cells, suggesting that these cells are more activated. Treatment of CD4 T cells with oxidized LDL (OxLDL), but not minimally modified LDL (mmLDL), oxidized cholesterol ester (OxCE) or oxidized phospholipids (POVPC), caused upregulation of Nrp-1 on CD4 T cells. Using a transwell migration assay, we found that Nrp1+ CD4 T cells had a 2-fold higher migration index towards VEGF165, a splice variant of VEGF, than did Nrp1- CD4 T cells; thus this migration was dependent on Nrp-1 expression. Similarly, CD4 T cells from ApoE-/- mice fed a western diet, which expressed more Nrp-1, had a higher migration index towards VEGF165 compared to cells from chow controls. In conclusion, we have identified a novel subset of Nrp-1+CD4+ T lymphocytes that is increased during atherosclerosis development, and is induced by OxLDL. Our data suggest that Nrp-1 may play a role in the migration of CD4 T cells to the aorta during atherosclerosis development.

Role of TLR2-dependent IL-10 production in the inhibition of the initial IFN-γ T cell response to Porphyromonas gingivalis

P.g., a Gram-negative bacterium, is one of the main etiological agents of the chronic inflammatory disease, periodontitis. Disease progression is thought to occur as a result of an inadequate immune response, which although happens locally, can also occur distally as a result of the dissemination of P.g. into the circulation. As IL-10 and TLR2 are pivotal molecules in the immune response that P.g. elicits, we hypothesized that TLR2-mediated IL-10 production, following the initial systemic exposure to P.g., inhibits the IFN-γ T cell response. To address this hypothesis, mice were primed with P.g., and the types of cells producing IL-10 and the capacity of T cells to produce IFN-γ following blocking or neutralization of IL-10 were assessed. Our results showed that upon initial encounter with P.g., splenic T cells and CD11b(+) cells produce IL-10, which when neutralized, resulted in a substantial increase in IFN-γ production by T cells. Furthermore, IL-10 production was dependent on TLR2/1 signaling, partly in response to the major surface protein, FimA of P.g. In addition, P.g. stimulation resulted in the up-regulation of PD-1 and its ligand PD-L1 on CD4 T cells and CD11b(+) cells, respectively. Up-regulation of PD-1 was partially dependent on IL-10 but independent of TLR2 or FimA. These results highlight the role of IL-10 in inhibiting T cell responses to the initial systemic P.g. exposure and suggest multiple inhibitory mechanisms potentially used by P.g. to evade the host's immune response, thus allowing its persistence in the host.

TLR4 signaling via MyD88 and TRIF differentially shape the CD4+ T cell response to Porphyromonas gingivalis hemagglutinin B

Recombinant hemagglutinin B (rHagB), a virulence factor of the periodontal pathogen Porphyromonas gingivalis, has been shown to induce protective immunity against bacterial infection. Furthermore, we have demonstrated that rHagB is a TLR4 agonist for dendritic cells. However, it is not known how rHagB dendritic cell stimulation affects the activation and differentiation of T cells. Therefore, we undertook the present study to examine the role of TLR4 signaling in shaping the CD4(+) T cell response following immunization of mice with rHagB. Immunization with this Ag resulted in the induction of specific CD4(+) T cells and Ab responses. In TLR4(-/-) and MyD88(-/-) but not Toll/IL-1R domain-containing adapter inducing IFN-β-deficient (TRIF(Lps2)) mice, there was an increase in the Th2 CD4(+) T cell subset, a decrease in the Th1 subset, and higher serum IgG(1)/IgG(2) levels of HagB-specific Abs compared with those in wild-type mice. These finding were accompanied by increased GATA-3 and Foxp3 expression and a decrease in the activation of CD4(+) T cells isolated from TLR4(-/-) and MyD88(-/-) mice. Interestingly, TLR4(-/-) CD4(+) T cells showed an increase in IL-2/STAT5 signaling. Whereas TRIF deficiency had minimal effects on the CD4(+) T cell response, it resulted in increased IFN-γ and IL-17 production by memory CD4(+) T cells. To our knowledge, these results demonstrate for the first time that TLR4 signaling, via the downstream MyD88 and TRIF molecules, exerts a differential regulation on the CD4(+) T cell response to HagB Ag. The gained insight from the present work will aid in designing better therapeutic strategies against P. gingivalis infection.

Requirement of TLR4 and CD14 in dendritic cell activation by Hemagglutinin B from Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that is one of the causative agents of chronic adult periodontal disease. Among the potential virulence factors of P. gingivalis are the hemagglutinins. Recombinant Hemagglutinin B (rHagB) from P. gingivalis has been shown to activate the immune system by inducing specific antibodies that protect against experimental periodontal bone loss following P. gingivalis infection. Since different microbial products can stimulate dendritic cells (DC) through Toll-like receptors (TLRs), subsequently leading to T cell activation and antibody production, we wanted to investigate the immunostimulatory effect of rHagB on DC and the role of TLR signaling in this process. Using an endotoxin free rHagB preparation, our results show that stimulation of murine bone marrow-derived DC with rHagB leads to upregulation of the costimulatory molecules CD86 and CD40, activation of p38 and ERK MAP kinases, transcription factors NF-kappaB, CREB and IRF-3 and the production of IL-6, TNF-alpha, IL-12p40 and to a lesser extent IL-10 and IFN-beta. This activation process was absolutely dependent on TLR4 and CD14. While upregulation of CD86 was independent of the adaptor molecule MyD88, CD40 upregulation and optimal cytokine (IL-6, TNF-alpha, IL-12p40, IL-10 and IFN-beta) production required both MyD88 and TRIF molecules. These results are of importance since they are the first to provide insights into the interaction of rHagB with DC and TLRs. The information from this study will aid in the design of effective vaccines strategies against chronic adult periodontal disease.

Rapid recruitment of virus-specific CD8 T cells restructures immunodominance during protective secondary responses

In this study we investigate the attributes of virus-specific memory CD8 T cells which most effectively control secondary infections. By rechallenging mice that had cleared primary lymphocytic choriomeningitis virus infections, we revealed that the secondary response is remarkably swift. Within 6 h following secondary infection, the production of gamma interferon becomes detectable directly ex vivo. During this protective phase of the secondary response, a very early elaboration of effector activities is preferentially exhibited by T cells specific for the viral NP396 epitope. This wave of activation contains the infection primarily before the initiation of the proliferative phase of the secondary response. Marked expansion is observed, but its magnitude differs depending on the epitope specificity of the responding cells; between 42 and 48 h following infection, approximately 70% of NP396-specific memory cells are in the S phase of the cell cycle, as assessed by bromodeoxyuridine incorporation studies. Epitope-dependent differences during the proliferative phase of the secondary response were confirmed by adoptive transfer studies with CFSE-labeled T cells. Although NP396-specific T cells typically dominate secondary responses, the broader multiepitope-specific population of antiviral T cells is beneficial for controlling a variant virus with an escape mutation in this epitope. These findings indicate that the induction and maintenance of a focused response contribute to the clearance of secondary infections; however, a more diverse pool of antiviral T cells facilitates long-term immunity to mutable pathogens.

Cutting edge: emergence of CD127high functionally competent memory T cells is compromised by high viral loads and inadequate T cell help

In this report we have inspected whether difficulties in controlling viral infections negatively impacts the generation of CD127(high) memory T cells. Using both MHC class I and II tetramers we reveal that CD127(low) T cells are not necessarily rapidly deleted but can persist in a pseudoeffector state in which they display the hallmarks of activated effector cells but are functionally inferior. CD127(high) cells can, however, emerge if the infection is contained. We also show that in the absence of CD4 T cell help significant populations of CD127(high) CD8 T cells fail to emerge. Analyses of cytokine-producing activities by both mouse and human CD8 T cells further document that the extended maintenance of T cells in a CD127(low) state has functional consequences which manifest as an impairment of IL-2 production.