Guoliang Cui

Phosphoenolpyruvate Is a Metabolic Checkpoint of Anti-tumor T Cell Responses

Activated T cells engage aerobic glycolysis and anabolic metabolism for growth, proliferation, and effector functions. We propose that a glucose-poor tumor microenvironment limits aerobic glycolysis in tumor-infiltrating T cells, which suppresses tumoricidal effector functions. We discovered a new role for the glycolytic metabolite phosphoenolpyruvate (PEP) in sustaining T cell receptor-mediated Ca(2+)-NFAT signaling and effector functions by repressing sarco/ER Ca(2+)-ATPase (SERCA) activity. Tumor-specific CD4 and CD8 T cells could be metabolically reprogrammed by increasing PEP production through overexpression of phosphoenolpyruvate carboxykinase 1 (PCK1), which bolstered effector functions. Moreover, PCK1-overexpressing T cells restricted tumor growth and prolonged the survival of melanoma-bearing mice. This study uncovers new metabolic checkpoints for T cell activity and demonstrates that metabolic reprogramming of tumor-reactive T cells can enhance anti-tumor T cell responses, illuminating new forms of immunotherapy.

Liver X receptor (LXR) mediates negative regulation of mouse and human Th17 differentiation

Th17 cells are a subset of CD4+ T cells with an important role in clearing certain bacterial and fungal pathogens. However, they have also been implicated in autoimmune diseases such as multiple sclerosis. Exposure of naive CD4+ T cells to IL-6 and TGF-β leads to Th17 cell differentiation through a process in which many proteins have been implicated. We report here that ectopic expression of liver X receptor (LXR) inhibits Th17 polarization of mouse CD4+ T cells, while LXR deficiency promotes Th17 differentiation in vitro. LXR activation in mice ameliorated disease in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, whereas LXR deficiency exacerbated disease. Further analysis revealed that Srebp-1, which is encoded by an LXR target gene, mediated the suppression of Th17 differentiation by binding to the E-box element on the Il17 promoter, physically interacting with aryl hydrocarbon receptor (Ahr) and inhibiting Ahr-controlled Il17 transcription. The putative active site (PAS) domain of Ahr and the N-terminal acidic region of Srebp-1 were essential for this interaction. Additional analyses suggested that similar LXR-dependent mechanisms were operational during human Th17 differentiation in vitro. This study reports what we believe to be a novel signaling pathway underlying LXR-mediated regulation of Th17 cell differentiation and autoimmunity.

Berberine Differentially Modulates the Activities of ERK, p38 MAPK, and JNK to Suppress Th17 and Th1 T Cell Differentiation in Type 1 Diabetic Mice

Berberine, an alkaloid derivative from Berberis vulgaris L., has been used extensively in traditional Chinese medicine to treat diarrhea and diabetes, but the underlying mechanisms for treating diabetes are not fully understood. Recent studies suggested that berberine has many beneficial biological effects, including anti-inflammation. Because type 1 diabetes is caused by T cell-mediated destruction of β cells and severe islet inflammation, we hypothesized that berberine could ameliorate type 1 diabetes through its immune regulation properties. Here we reported that 2 weeks of oral administration of berberine prevented the progression of type 1 diabetes in half of the NOD mice and decreased Th17 and Th1 cytokine secretion. Berberine suppressed Th17 and Th1 differentiation by reducing the expression of lineage markers. We found that berberine inhibited Th17 differentiation by activating ERK1/2 and inhibited Th1 differentiation by inhibiting p38 MAPK and JNK activation. Berberine down-regulated the activity of STAT1 and STAT4 through the suppression of p38 MAPK and JNK activation, and it controlled the stability of STAT4 through the ubiquitin-proteasome pathway. Our findings indicate that berberine targets MAPK to suppress Th17 and Th1 differentiation in type 1 diabetic NOD mice. This study revealed a novel role of ERK in Th17 differentiation through down-regulation of STAT3 phosphorylation and RORγt expression.

IL-7-Induced Glycerol Transport and TAG Synthesis Promotes Memory CD8+ T Cell Longevity

Memory T cells are critical for long-term immunity against reinfection and require interleukin-7 (IL-7), but the mechanisms by which IL-7 controls memory T cell survival, particularly metabolic fitness, remain elusive. We discover that IL-7 induces expression of the glycerol channel aquaporin 9 (AQP9) in virus-specific memory CD8+ T cells, but not naive cells, and that AQP9 is vitally required for their long-term survival. AQP9 deficiency impairs glycerol import into memory CD8+ T cells for fatty acid esterification and triglyceride (TAG) synthesis and storage. These defects can be rescued by ectopic expression of TAG synthases, which restores lipid stores and memory T cell survival. Finally, we find that TAG synthesis is a central component of IL-7-mediated survival of human and mouse memory CD8+T cells. This study uncovers the metabolic mechanisms by which IL-7 tailors the metabolism of memory T cells to promote their longevity and fast response to rechallenge.

Induction of CD4+CD25+Foxp3+ regulatory T cell response by glatiramer acetate in type 1 diabetes

Glatiramer acetate (GA) is an immunomodulatory peptide drug used to treat multiple sclerosis. Its treatment effect has been expanded to other autoimmune conditions such as uveoretinitis, inflammatory bowel disease, graft rejection and hepatic fibrosis. Here, we report that GA was effective in altering the clinical course of diabetes in cyclophosphamide (CY)-potentiated non-obese diabetic (CY-NOD) mice. Treatment with GA significantly reduced the diabetic rate in the mice and ameliorated insulitis, which coincided with increased CD4+CD25+Foxp3+ T cell response in treated mice. GA treatment led to increased expression of transcription factor Foxp3 and elevated production of interleukin-4 (IL-4) both in vivo and in vitro. It was evident that the effect of GA on up-regulation of Foxp3 was mediated partially through IL-4. IL-4 was found to maintain Foxp3 expression and regulatory function of CD4+CD25+ regulatory T cells (Tregs). This study provides new evidence that GA has treatment potential for type 1 diabetes through the induction of Tregs and that increased IL-4 production is partially responsible for the enhanced Tregs function in GA treatment.

Rhein Protects against Obesity and Related Metabolic Disorders through Liver X Receptor-Mediated Uncoupling Protein 1 Upregulation in Brown Adipose Tissue

Liver X receptors (LXRs) play important roles in regulating cholesterol homeostasis, and lipid and energy metabolism. Therefore, LXR ligands could be used for the management of metabolic disorders. We evaluated rhein, a natural compound from Rheum palmatum L., as an antagonist for LXRs and investigated its anti-obesity mechanism in high-fat diet-fed mice. Surface plasmon resonance assays were performed to examine the direct binding of rhein to LXRs. LXR target gene expression was assessed in 3T3-L1 adipocytes and HepG2 hepatic cells in vitro. C57BL/6J mice fed a high-fat diet were orally administered with rhein for 4 weeks, and then the expression levels of LXR-related genes were analyzed. Rhein bound directly to LXRs. The expression levels of LXR target genes were suppressed by rhein in 3T3-L1 and HepG2 cells. In white adipose tissue, muscle and liver, rhein reprogrammed the expression of LXR target genes related to adipogenesis and cholesterol metabolism. Rhein activated uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT) in wild-type mice, but did not affect UCP1 expression in LXR knockout mice. In HIB-1B brown adipocytes, rhein activated the UCP1 gene by antagonizing the repressive effect of LXR on UCP1 expression. This study suggests that rhein may protect against obesity and related metabolic disorders through LXR antagonism and regulation of UCP1 expression in BAT.

Endothelial APLNR regulates tissue fatty acid uptake and is essential for apelin’s glucose-lowering effects

Inhibition of FABP4 rescues defective apelin signaling, decreases fatty acid accumulation, and promotes insulin sensitivity. An apelin a day keeps the doctor away Apelin is an atheroprotective protein, which promotes insulin sensitivity and metabolic health, but the details of its signaling are not well understood. Hwangbo et al. discovered that the apelin receptor is predominantly localized in endothelial cells of metabolic organs, such as muscle and adipose tissues, and that it functions, in part, by inhibiting fatty acid binding protein 4 (FABP4) activity. The authors also found that inhibition of FABP4 can reverse the metabolic disease phenotype associated with defective apelin signaling and thus improve fatty acid uptake, glucose utilization, and insulin sensitivity. Treatment of type 2 diabetes mellitus continues to pose an important clinical challenge, with most existing therapies lacking demonstrable ability to improve cardiovascular outcomes. The atheroprotective peptide apelin (APLN) enhances glucose utilization and improves insulin sensitivity. However, the mechanism of these effects remains poorly defined. We demonstrate that the expression of APLNR (APJ/AGTRL1), the only known receptor for apelin, is predominantly restricted to the endothelial cells (ECs) of multiple adult metabolic organs, including skeletal muscle and adipose tissue. Conditional endothelial-specific deletion of Aplnr (AplnrECKO) resulted in markedly impaired glucose utilization and abrogation of apelin-induced glucose lowering. Furthermore, we identified inactivation of Forkhead box protein O1 (FOXO1) and inhibition of endothelial expression of fatty acid (FA) binding protein 4 (FABP4) as key downstream signaling targets of apelin/APLNR signaling. Both the Apln−/− and AplnrECKO mice demonstrated increased endothelial FABP4 expression and excess tissue FA accumulation, whereas concurrent endothelial Foxo1 deletion or pharmacologic FABP4 inhibition rescued the excess FA accumulation phenotype of the Apln−/− mice. The impaired glucose utilization in the AplnrECKO mice was associated with excess FA accumulation in the skeletal muscle. Treatment of these mice with an FABP4 inhibitor abrogated these metabolic phenotypes. These findings provide mechanistic insights that could greatly expand the therapeutic repertoire for type 2 diabetes and related metabolic disorders.

Early TCR Signaling Sweetens Effector Function through PDHK1

T cells rapidly engage glycolysis upon activation. The signaling pathways through which T cell receptor (TCR) activation initiates glycolysis have been a mystery. A long-awaited answer has been provided by Menk et al., who show that pyruvate dehydrogenase kinase 1 (PDHK1) is in the center of signaling events linking TCR activation to glycolysis.

Abstract B063: Unsaturated fatty acids cause CD8+ T cell exhaustion in melanoma

Remarkable progress in cancer immunotherapy has revealed the power of harnessing immunity to combat cancer. However, the immunosuppressive nature of the tumor microenvironment remains a fundamental challenge to improving immune-based anti-cancer therapies. We aim to develop new immunotherapies by studying the nutrient utilization of immune cells in the tumors. Using an inducible Braf/Pten melanoma model, we found that tumors contain higher amounts of available free fatty acids (FFAs) and lower amounts of glucose than the blood. Exposure to high concentration of FFAs induced an exhaustion-like phenotype of CD8+ T cells. Furthermore, mice deficient of FFA transporter CD36 developed smaller tumors compared to wild-type control mice. Tumor-infiltrating Cd36-/- CD8+ T cells expressed lower level of inhibitory receptors, such as PD-1 and LAG-3. This study highlights an important role of lipid metabolism in regulating T cell exhaustion in the tumor microenvironment and reveals CD36 as a potential drug candidate for immunotherapy. Citation Format: Guoliang Cui, Susan Kaech. Unsaturated fatty acids cause CD8+ T cell exhaustion in melanoma. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B063.

Abstract IA03: Anti-tumor T cells: You are what you eat

Activated T cells engage aerobic glycolysis and anabolic metabolism for growth, proliferation, and effector functions. In contrast, resting memory CD8 T cells depend less on high rates of glycolysis and more on fatty acid oxidation to persist, self-renew and respond to secondary infection. This talk will discuss the concept of metabolic checkpoints for immune cells in tumors, referring to the idea that the nutrients utilized by different types of T cells can affect both their energetic demands and their functionality. In particular, the metabolic state of exhausted T cells found in tumors is only recently starting to be studied. Our data in mouse models of cancer suggest that a glucose-poor, fatty acid-rich tumor microenvironment limits aerobic glycolysis, but promotes fatty acid uptake in tumor-infiltrating T cells, which suppresses tumoricidal effector functions and increases PD-1 expression. This talk will discuss recent analyses of the signaling pathways that respond to these nutrient alterations in T cells in tumors and how this may relate to new modalities of treatment in combination with checkpoint blockade. Citation Format: Guoliang Cui, Ping-Chih Ho, Robert Amezquita, Susan M. Kaech. Anti-tumor T cells: You are what you eat. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr IA03.