AMP kinase promotes Bcl6 expression in both mouse and human T cells

ZEB1 interferes with human periodontal ligament stem cell proliferation and differentiation

BACKGROUND

Periodontitis can eventually contribute to tooth loss. Zinc finger E-box binding homeobox 1 (ZEB1) is identified as overexpressed in the gingival tissue of mice with periodontitis. This study is designed to decipher the mechanism of ZEB1's involvement in periodontitis.

METHODS

Human periodontal mesenchymal stem cells (hPDLSCs) were exposed to LPS to mimic the inflammation in periodontitis. Following ZEB1 silencing, FX1 (an inhibitor of Bcl-6) treatment or ROCK1 overexpression, cell viability, and apoptosis were analyzed. Alkaline phosphatase (ALP) staining, Alizarin red staining, RT-qPCR, and western blot were performed to evaluate osteogenic differentiation and mineralization. hPDLSCs were processed for luciferase reporter assay and ChIP-PCR to confirm the association between ZEB1 and ROCK1.

RESULTS

The induction of ZEB1 silencing resulted in reduced cell apoptosis, enhanced osteogenic differentiation, and mineralization. Nevertheless, these effects were significantly blunted by FX1. ZEB1 was confirmed to bind to the promoter sites of ROCK1 and regulate the ROCK1/AMPK. Whereas ROCK1 overexpression reversed the effects of ZEB1 silencing on Bcl-6/STAT1, as well as cell proliferation and osteogenesis differentiation.

CONCLUSION

hPDLSCs displayed decreased proliferation and weakened osteogenesis differentiation in response to LPS. These impacts were mediated by ZEB1 regulating Bcl-6/STAT1 via AMPK/ROCK1.

Deficient leptin receptor signaling in T cells of human SLE

BACKGROUND

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease mainly mediated by IgG autoantibody. While follicular helper T (Tfh) cells are crucial for supporting IgG autoantibody generation in human SLE, underlying mechanisms for Tfh cell mal-differentiation remain unclear.

METHODS

In total, 129 SLE patients and 37 healthy donors were recruited for this study. Circulating leptin was determined by ELISA from patients with SLE and healthy individuals. CD4 T cells isolated from SLE patients and healthy donors were activated with anti-CD3/CD28 beads under cytokine-unbiased conditions in the presence or absence of recombinant leptin protein, followed by detection for Tfh cell differentiation by quantifying intracellular transcription factor Bcl-6 and cytokine IL-21. AMPK activation was assessed by analyzing phosphor-AMPK using phosflow cytometry and immunoblots. Leptin receptor expression was determined using flow cytometry and its overexpression was achieved by transfection with an expression vector. Humanized SLE chimeras were induced by injecting patients' immune cells into immune-deficient NSG mice and used for translational studies.

RESULTS

Circulating leptin was elevated in patients with SLE, inversely associated with disease activity. In healthy individuals, leptin efficiently inhibited Tfh cell differentiation through inducing AMPK activation. Meanwhile, leptin receptor deficiency was a feature of CD4 T cells in SLE patients, impairing the inhibitory effect of leptin on the differentiation of Tfh cells. As a result, we observed the coexistence of high circulating leptin and increased Tfh cell frequencies in SLE patients. Accordingly, overexpression of leptin receptor in SLE CD4 T cells abrogated Tfh cell mal-differentiation and IgG anti-dsDNA generation in humanized lupus chimeras.

CONCLUSION

Leptin receptor deficiency blocks the inhibitory effect of leptin on SLE Tfh cell differentiation, serving as a promising therapeutic target for lupus management.

Regulation of immune cell metabolism in health and disease: Special focus on T and B cell subsets

Metabolism is a dynamic process and keeps changing from time to time according to the demand of a particular cell to meet its bio-energetic requirement. Different immune cells rely on distinct metabolic programs which allow the cell to balance its requirements for energy, molecular biosynthesis, and effector activity. In the aspect of infection and cancer immunology, effector T and B cells get exhausted and help tumor cells to evade immunosurveillance. On the other hand, T cells become hyperresponsive in the scenario of autoimmune diseases. In this article, we have explored the uniqueness and distinct metabolic features of key CD4⁺ T and B helper cell subsets, CD4⁺ T, B regulatory cell subsets and CD8⁺ T cells regarding health and disease. Th1 cells rely on glycolysis and glutaminolysis; inhibition of these metabolic pathways promotes Th1 cells in Treg population. However, Th2 cells are also dependent on glycolysis but an abundance of lactate within TME shifts their metabolic dependency to fatty acid metabolism. Th17 cells depend on HIF-1α mediated glycolysis, ablation of HIF-1α reduces Th17 cells but enhance Treg population. In contrast to effector T cells which are largely dependent on glycolysis for their differentiation and function, Treg cells mainly rely on FAO for their function. Therefore, it is of utmost importance to understand the metabolic fates of immune cells and how it facilitates their differentiation and function for different disease models. Targeting metabolic pathways to restore the functionality of immune cells in diseased conditions can lead to potent therapeutic measures.

Metabolic regulation of follicular helper T cell differentiation in a mouse model of lupus

Follicular helper T (T_FH) cells are expanded in systemic lupus erythematosus (SLE), where they are required for production of high affinity autoantibodies. A better understanding of the mechanisms that regulate the differentiation of T_FH cells is critical. Naïve T cells from lupus-prone B6.NZM2410.Sle1.Sle2.Sle3 (TC) mice showed an intrinsic higher capacity to differentiate into T_FH cells. Metabolic reprogramming is a vital regulatory mechanism for T cell differentiation, but how metabolic pathways contribute to T_FH cell expansion in SLE remains elusive. Here we show that glycolysis, mTOR signaling, FAO, and the activity of complex V of the electron transport chain support T_FH lineage commitment. Blocking complex I uniquely decreased the expansion of T_FH cells from lupus-prone mice, and inhibition of some pathways had a greater effect in lupus-prone than control T_FH cells. However, blocking glutaminolysis, complex III and ADP/ATP translocase did not affect T_FH cell expansion. Together, our results identified novel intrinsic metabolic requirements for T_FH cell differentiation, and further defined the differential metabolic pathways that support the expansion of T_FH cells in lupus-prone mice. Together, our data indicates the crucial but distinct roles for metabolic pathways in T_FH cell differentiation and provide a comprehensive experimental basis for fully understanding the precise roles of distant metabolic signaling in regulating the T_FH cell differentiation.

Providing a Helping Hand: Metabolic Regulation of T Follicular Helper Cells and Their Association With Disease

T follicular helper (Tfh) cells provide support to B cells upon arrival in the germinal center, and thus are critical for the generation of a robust adaptive immune response. Tfh express specific transcription factors and cellular receptors including Bcl6, CXCR5, PD-1, and ICOS, which are critical for homing and overall function. Generally, the induction of an immune response is tightly regulated. However, deviation during this process can result in harmful autoimmunity or the inability to successfully clear pathogens. Recently, it has been shown that Tfh differentiation, activation, and proliferation may be linked with the cellular metabolic state. In this review we will highlight recent discoveries in Tfh differentiation and explore how these cells contribute to functional immunity in disease, including autoimmune-related disorders, cancer, and of particular emphasis, during infection.

Tox2 is required for the maintenance of GC TFH cells and the generation of memory TFH cells

Memory T follicular helper (TFH) cells play an essential role to induce secondary antibody response by providing help to memory and naïve B cells. Here, we show that the transcription factor Tox2 is vital for the maintenance of TFH cells in germinal centers (GCs) and the generation of memory TFH cells. High Tox2 expression was almost exclusive to GC TFH cells among human tonsillar and blood CD4+ T cell subsets. Tox2 overexpression maintained the expression of TFH-associated genes in T cell receptor–stimulated human GC TFH cells and inhibited their spontaneous conversion into TH1-like cells. Tox2-deficient mice displayed impaired secondary TFH cell expansion upon reimmunization with an antigen and upon secondary infection with a heterologous influenza virus. Collectively, our study shows that Tox2 is highly integrated into establishment of durable GC TFH cell responses and development of memory TFH cells in mice and humans.

Functional differentiation and regulation of follicular T helper cells in inflammation and autoimmunity

Follicular T helper (T_FH ) cells are specialized T cells that support B cells, which are essential for humoral immunity. T_FH cells express the transcription factor B-cell lymphoma 6 (Bcl-6), chemokine (C-X-C motif) receptor (CXCR) 5, the surface receptors programmed cell death protein 1 (PD-1) and inducible T-cell costimulator (ICOS), the cytokine IL-21 and other molecules. The activation, proliferation and differentiation of T_FH cells are closely related to dynamic changes in cellular metabolism. In this review, we summarize the progress made in understanding the development and functional differentiation of T_FH cells. Specifically, we focus on the regulatory mechanisms of T_FH cell functional differentiation, including regulatory signalling pathways and the metabolic regulatory mechanisms of T_FH cells. In addition, T_FH cells are closely related to immune-associated diseases, including infections, autoimmune diseases and cancers.

Inhibition of stearoyl-CoA desaturases suppresses follicular help T- and germinal center B- cell responses

Stearoyl-CoA desaturases (SCD) are endoplasmic reticulum (ER)-associated enzymes that catalyze the synthesis of the monounsaturated fatty acids (MUFAs). As such, SCD play important roles in maintaining the intracellular balance between saturated fatty acid (SFAs) and MUFAs. The roles of SCD in CD4⁺ T-helper cell responses are currently unexplored. Here, we have found that murine and human follicular helper T (T_FH ) cells express higher levels of SCD compared to non-T_FH cells. Further, the expression of SCD in T_FH cells is dependent on the T_FH lineage-specification transcription factor BCL6. We found that the inhibition of SCD impaired T_FH cell maintenance and shifted the balance between T_FH and follicular regulatory T (T_FR ) cells in the spleen. Consequently, SCD inhibition dampened germinal center B-cell responses following influenza immunization. Mechanistically, we found that SCD inhibition led to increased ER stress and enhanced T_FH cell apoptosis in vitro and in vivo. These results reveal a possible link between fatty acid metabolism and cellular and humoral responses induced by immunization or potentially, autoimmunity.

HIF1α-Dependent Metabolic Signals Control the Differentiation of Follicular Helper T Cells

Follicular helper T (T_FH) cells are critical for germinal center (GC) formation and are responsible for effective B cell-mediated immunity; metabolic signaling is an important regulatory mechanism for the differentiation of T_FH cells. However, the precise roles of hypoxia inducible factor (HIF) 1α-dependent glycolysis and oxidative phosphorylation (OXPHOS) metabolic signaling remain unclear in T_FH cell differentiation. Herein, we investigated the effects of glycolysis and OXPHOS on T_FH cell differentiation and GC responses using a pharmacological approach in mice under a steady immune status or an activated immune status, which can be caused by foreign antigen stimulation and viral infection. GC and T_FH cell responses are related to signals from glycolytic metabolism in mice of different ages. Foreign, specific antigen-induced GC, and T_FH cell responses and metabolic signals are essential upon PR8 infection. Glycolysis and succinate-mediated OXPHOS are required for the GC response and T_FH cell differentiation. Furthermore, HIF1α is responsible for glycolysis- and OXPHOS-induced alterations in the GC response and T_FH cell differentiation under steady or activated conditions in vivo. Blocking glycolysis and upregulating OXPHOS signaling significantly recovered T_FH cell differentiation upon PR8 infection and ameliorated inflammatory damage in mice. Thus, our data provide a comprehensive experimental basis for fully understanding the precise roles of HIF1α-mediated glycolysis and OXPHOS metabolic signaling in regulating the GC response and T_FH cell differentiation during stable physiological conditions or an antiviral immune response.

Follicular regulatory T cells inhibit the development of granzyme B-expressing follicular helper T cells

T follicular regulatory (TFR) cells are found in the germinal center (GC) response and help shape the antibody (Ab) response. However, the precise role of TFR cells in the GC is controversial. Here, we addressed TFR cell function using mice with impaired TFR cell development (Bcl6-flox/Foxp3-cre, or Bcl6FC mice), mice with augmented TFR cell development (Blimp1-flox/Foxp3-cre, or Blimp1FC mice), and two different methods of immunization. Unexpectedly, GC B cell levels positively correlated with TFR cell levels. Using a gene profiling approach, we found that TFH cells from TFR-deficient mice showed strong upregulation of granzyme B (Gzmb) and other effector CD8+ T cell genes, many of which were Stat4 dependent. The upregulation of cytotoxic genes was the highest in TFH cells from TFR-deficient mice where Blimp1 was also deleted in Foxp3+ regulatory T cells (Bcl6-flox/Prdm1-flox/Foxp3-cre [DKO] mice). Granzyme B- and Eomesodermin-expressing TFH cells correlated with a higher rate of apoptotic GC B cells. Klrg1+ TFH cells from DKO mice expressed higher levels of Gzmb. Our data show that TFR cells repress the development of abnormal cytotoxic TFH cells, and the presence of cytotoxic TFH cells correlates with a lower GC and Ab response. Our data show what we believe is a novel mechanism of action for TFR cells helping the GC response.

DUSP6 mediates T cell receptor-engaged glycolysis and restrains TFH cell differentiation

Activated T cells undergo metabolic reprogramming and effector-cell differentiation but the factors involved are unclear. Utilizing mice lacking DUSP6 (DUSP6^-/-), we show that this phosphatase regulates T cell receptor (TCR) signaling to influence follicular helper T (T_FH) cell differentiation and T cell metabolism. In vitro, DUSP6^-/- CD4⁺ T_FH cells produced elevated IL-21. In vivo, T_FH cells were increased in DUSP6^-/- mice and in transgenic OTII-DUSP6^-/- mice at steady state. After immunization, DUSP6^-/- and OTII-DUSP6^-/- mice generated more T_FH cells and produced more antigen-specific IgG2 than controls. Activated DUSP6^-/- T cells showed enhanced JNK and p38 phosphorylation but impaired glycolysis. JNK or p38 inhibitors significantly reduced IL-21 production but did not restore glycolysis. TCR-stimulated DUSP6^-/- T cells could not induce phosphofructokinase activity and relied on glucose-independent fueling of mitochondrial respiration. Upon CD28 costimulation, activated DUSP6^-/- T cells did not undergo the metabolic commitment to glycolysis pathway to maintain viability. Unexpectedly, inhibition of fatty acid oxidation drastically lowered IL-21 production in DUSP6^-/- T_FH cells. Our findings suggest that DUSP6 connects TCR signaling to activation-induced metabolic commitment toward glycolysis and restrains T_FH cell differentiation via inhibiting IL-21 production.

Bcl6 promotes follicular helper T-cell differentiation and PD-1 expression in a Blimp1-independent manner in mice

The transcription factors Bcl6 and Blimp1 have opposing roles in the development of the follicular helper T (T_FH ) cells: Bcl6 promotes and Blimp1 inhibits T_FH -cell differentiation. Similarly, Bcl6 activates, while Blimp1 represses, expression of the T_FH -cell marker PD-1. However, Bcl6 and Blimp1 repress each other's expression, complicating the interpretation of the regulatory network. Here we sought to clarify the extent to which Bcl6 and Blimp1 independently control T_FH -cell differentiation by generating mice with T-cell specific deletion of both Bcl6 and Blimp1 (double conditional KO [dcKO] mice). Our data indicate that Blimp1 does not control T_FH -cell differentiation independently of Bcl6. However, a population of T follicular regulatory (T_FR ) cells developed independently of Bcl6 in dcKO mice. We have also analyzed regulation of IL-10 and PD-1, two genes controlled by both Bcl6 and Blimp1, and observed that Bcl6 regulates both genes independently of Blimp1. We found that Bcl6 positively regulates PD-1 expression by inhibiting the ability of T-bet/Tbx21 to repress Pdcd1 transcription. Our data provide a novel mechanism for positive control of gene expression by Bcl6, and illuminate how Bcl6 and Blimp1 control T_FH -cell differentiation.