Sudarshan Kriya Yoga Breathing and a Meditation Program for Burnout Among Physicians: A Randomized Clinical Trial

Importance

Physicians are exposed to high stress and strain that results in burnout, which affects them, their families, their patients, and the entire health care system; thus, there is an urgent need to develop methods to increase the resiliency of physicians. Sudarshan Kriya Yoga (SKY) is a comprehensive yoga breathing and meditation-based program that is a potential approach to mitigate physician burnout.

Objective

To determine whether SKY can reduce psychological distress and improve wellness in physicians.

Design, Setting, and Participants

This randomized clinical trial assessed the potential efficacy of SKY compared with a stress management education (SME) training as control. This study was conducted online from November 11, 2021, to March 14, 2022, and included physicians from Turkey, Germany, and Dubai. Both the SKY and the SME control groups received 1.5 hours of training for 3 consecutive days via a group video conference call. Participants were physicians willing to do some form of relaxation exercise everyday for 2 months. Exclusion criteria included presence of major illness and maintaining a regular mind-body program practice. Statistical analysis took place from March to November 2023.

Interventions

Participants were randomly assigned 1:1 into 2 groups-the SKY group or the SME (control) group-using a computer algorithm. After the 3-day instruction period, the participants in the SKY group practiced for approximately 30 minutes per day on their own and participated in a weekly 1-hour, group-based online follow-up practice. After the 3-day instruction period, participants in the SME group reviewed and applied the notes from stress management education training at their initiative and had a weekly 1-hour group-based online follow-up session.

Main Outcomes and Measures

The primary outcomes were stress and depression (measured by the 42-item Depression, Anxiety, and Stress Scale [DASS-42]) and insomnia measured by the Regensburg Insomnia Scale (RIS) with primary end point at 8 weeks. Secondary outcomes included anxiety (DASS-42); optimism (Life Orientation Test-Revised [LOT-R]); professional fulfillment, work exhaustion, interpersonal disengagement, and overall burnout (Professional Fulfillment Index [PFI]); and self-reported professional errors (Self-Reported Professional Error Questionnaire).

Results

This study included 129 participants (SME, 63 participants [48.9%]; SKY, 66 participants [51.1%]; 115 females [89.2%]; 14 males [10.8%]; mean [SD] age, 46.2 [9.0] years). Compared with the SME control group, participants in the SKY group had significantly decreased stress on the DASS-42 at posttraining (difference, -6.8 points; 95% CI, -9.6 to -4.1 points; P = .006) and at postintervention (difference, -6.0 points; 95% CI, -8.8 to -3.3 points; P = .03), significantly decreased depression at posttraining (difference, -5.7 points; 95% CI, -8.6 to -2.8 points; P < .001) and postintervention (difference, -5.4 points; 95% CI, -8.3 to -2.5 points; P < .001), and significantly decreased anxiety at postintervention. In addition, there was a significant decrease in insomnia from baseline to postintervention in the SKY group (difference, -0.3 points; 95% CI, -2.3 to 1.7 points; P = .01). The SKY group also showed significantly increased professional fulfillment as well as significant decreases in work exhaustion, interpersonal disengagement, and burnout. There was no effect on self-reported medical errors.

Conclusions and Relevance

In this randomized clinical trial, physicians who regularly practiced SKY throughout a 2-month period experienced improvements in wellness and decreased burnout. These data suggest that SKY may be an effective, practical, and safe strategy to increase wellness and mitigate burnout in physicians.

Trial Registration

ClinicalTrials.gov Identifier: NCT05956470.

TRAIL promotes the polarization of human macrophages toward a proinflammatory M1 phenotype and is associated with increased survival in cancer patients with high tumor macrophage content

Background

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can either induce cell death or activate survival pathways after binding to death receptors (DRs) DR4 or DR5. TRAIL is investigated as a therapeutic agent in clinical trials due to its selective toxicity to transformed cells. Macrophages can be polarized into pro-inflammatory/tumor-fighting M1 macrophages or anti-inflammatory/tumor-supportive M2 macrophages and an imbalance between M1 and M2 macrophages can promote diseases. Therefore, identifying modulators that regulate macrophage polarization is important to design effective macrophage-targeted immunotherapies. The impact of TRAIL on macrophage polarization is not known.

Methods

Primary human monocyte-derived macrophages were pre-treated with either TRAIL or with DR4 or DR5-specific ligands and then polarized into M1, M2a, or M2c phenotypes in vitro. The expression of M1 and M2 markers in macrophage subtypes was analyzed by RNA sequencing, qPCR, ELISA, and flow cytometry. Furthermore, the cytotoxicity of the macrophages against U937 AML tumor targets was assessed by flow cytometry. TCGA datasets were also analyzed to correlate TRAIL with M1/M2 markers, and the overall survival of cancer patients.

Results

TRAIL increased the expression of M1 markers at both mRNA and protein levels while decreasing the expression of M2 markers at the mRNA level in human macrophages. TRAIL also shifted M2 macrophages towards an M1 phenotype. Our data showed that both DR4 and DR5 death receptors play a role in macrophage polarization. Furthermore, TRAIL enhanced the cytotoxicity of macrophages against the AML cancer cells in vitro. Finally, TRAIL expression was positively correlated with increased expression of M1 markers in the tumors from ovarian and sarcoma cancer patients and longer overall survival in cases with high, but not low, tumor macrophage content.

Conclusions

TRAIL promotes the polarization of human macrophages toward a proinflammatory M1 phenotype via both DR4 and DR5. Our study defines TRAIL as a new regulator of macrophage polarization and suggests that targeting DRs can enhance the anti-tumorigenic response of macrophages in the tumor microenvironment by increasing M1 polarization.

The Ca2+ concentration impacts the cytokine production of mouse and human lymphoid cells and the polarization of human macrophages in vitro

Various aspects of the in vitro culture conditions can impact the functional response of immune cells. For example, it was shown that a Ca2+ concentration of at least 1.5 mM during in vitro stimulation is needed for optimal cytokine production by conventional αβ T cells. Here we extend these findings by showing that also unconventional T cells (invariant Natural Killer T cells, mucosal-associated invariant T cells, γδ T cells), as well as B cells, show an increased cytokine response following in vitro stimulation in the presence of elevated Ca2+ concentrations. This effect appeared more pronounced with mouse than with human lymphoid cells and did not influence their survival. A similarly increased cytokine response due to elevated Ca2+ levels was observed with primary human monocytes. In contrast, primary human monocyte-derived macrophages, either unpolarized (M0) or polarized into M1 or M2 macrophages, displayed increased cell death in the presence of elevated Ca2+ concentrations. Furthermore, elevated Ca2+ concentrations promoted phenotypic M1 differentiation by increasing M1 markers on M1 and M2 macrophages and decreasing M2 markers on M2 macrophages. However, the cytokine production of macrophages, again in contrast to the lymphoid cells, was unaltered by the Ca2+ concentration. In summary, our data demonstrate that the Ca2+ concentration during in vitro cultures is an important variable to be considered for functional experiments and that elevated Ca2+ levels can boost cytokine production by both mouse and human lymphoid cells.

Effect of stimulation time on the expression of human macrophage polarization markers

Macrophages are highly plastic cells that can polarize into functionally distinct subsets in vivo and in vitro in response to environmental signals. The development of protocols to model macrophage polarization in vitro greatly contributes to our understanding of macrophage biology. Macrophages are divided into two main groups: Pro-inflammatory M1 macrophages (classically activated) and anti-inflammatory M2 macrophages (alternatively activated), based on several key surface markers and the production of inflammatory mediators. However, the expression of these common macrophage polarization markers is greatly affected by the stimulation time used. Unfortunately, there is no consensus yet regarding the optimal stimulation times for particular macrophage polarization markers in in vitro experiments. This situation is problematic, (i) as analysing a particular marker at a suboptimal time point can lead to false-negative results, and (ii) as it clearly impedes the comparison of different studies. Using human monocyte-derived macrophages (MDMs) in vitro, we analysed how the expression of the main polarization markers for M1 (CD64, CD86, CXCL9, CXCL10, HLA-DR, IDO1, IL1β, IL12, TNF), M2a (CD200R, CD206, CCL17, CCL22, IL-10, TGM2), and M2c (CD163, IL-10, TGFβ) macrophages changes over time at mRNA and protein levels. Our data establish the most appropriate stimulation time for the analysis of the expression of human macrophage polarization markers in vitro. Providing such a reference guide will likely facilitate the investigation of macrophage polarization and its reproducibility.

The Role of TRAIL/DRs in the Modulation of Immune Cells and Responses

Expression of TRAIL (tumor necrosis factor–related apoptosis–inducing ligand) by immune cells can lead to the induction of apoptosis in tumor cells. However, it becomes increasingly clear that the interaction of TRAIL and its death receptors (DRs) can also directly impact immune cells and influence immune responses. Here, we review what is known about the role of TRAIL/DRs in immune cells and immune responses in general and in the tumor microenvironment in particular.

The cholesterol transporter ABCG1 modulates macrophage polarization in human monocyte-derived macrophages

The ATP-binding Cassette Transporter G1 (ABCG1) promotes cholesterol efflux from cells and regulates intracellular cholesterol homeostasis. Recent studies have shown that in mice in the absence of ABCG1, macrophages shift from a tumor-promoting M2 phenotype to a tumor-fighting M1 phenotype within the tumor and suppress bladder cancer growth in vivo. Two important aspects of this effect are still unknown: (1) whether ABCG1-would also impact polarization of human macrophages, and (2) the underlying molecular mechanism of this effect. Here, we show that in human monocyte-derived macrophages the inhibition of ABCG1 by siRNA significantly increased the expression of the M1 markers IDO1, CXCL10, CD64 and TNF after LPS/IFNγ (M1) stimulation. In contrast, after IL-4 (M2) stimulation the expression of the M2 markers MRC1, TGM2 and CD163 was significantly reduced. These data indicate that ABCG1-deficiency promotes the polarization of macrophage to an M1 phenotype in human macrophages. To address the molecular mechanism, we analysed cell signalling in bone marrow-derived macrophages from Abcg1−/− mice. These macrophages displayed reduced levels of Akt activation after stimulation with LPS/IFNγ or IL4. In addition, while Abcg1−/− macrophages stimulated with LPS/IFNγ produced more TNF compared to WT macrophages, after treatment with an Akt activator the TNF-production of Abcg1−/− and WT macrophages was comparable. These data suggest that the M1 bias of Abcg1−/− macrophages is mediated through the Akt signalling pathway. In summary, these findings deepen our mechanistic understanding of the M1/M2 switch in macrophages and suggest that ABCG1 could be a potential new target to modulate macrophage polarization for cancer immunotherapy.

Improved Detection of Cytokines Produced by Invariant NKT Cells

Invariant Natural killer T (iNKT) cells rapidly produce copious amounts of multiple cytokines after in vivo activation, allowing for the direct detection of a number of cytokines directly ex vivo. However, for some cytokines this approach is suboptimal. Here, we report technical variations that allow the improved detection of IL-4, IL-10, IL-13 and IL-17A ex vivo. Furthermore, we describe an alternative approach for stimulation of iNKT cells in vitro that allows a significantly improved detection of cytokines produced by iNKT cells. Together, these protocols allow the detection of iNKT cell cytokines ex vivo and in vitro with increased sensitivity.

Patrolling monocytes control tumor metastasis to the lung

The immune system plays an important role in regulating tumor growth and metastasis. Classical monocytes promote tumorigenesis and cancer metastasis, but how nonclassical "patrolling" monocytes (PMo) interact with tumors is unknown. Here we show that PMo are enriched in the microvasculature of the lung and reduce tumor metastasis to lung in multiple mouse metastatic tumor models. Nr4a1-deficient mice, which specifically lack PMo, showed increased lung metastasis in vivo. Transfer of Nr4a1-proficient PMo into Nr4a1-deficient mice prevented tumor invasion in the lung. PMo established early interactions with metastasizing tumor cells, scavenged tumor material from the lung vasculature, and promoted natural killer cell recruitment and activation. Thus, PMo contribute to cancer immunosurveillance and may be targets for cancer immunotherapy.

Selective Conditions Are Required for the Induction of Invariant NKT Cell Hyporesponsiveness by Antigenic Stimulation

Activation of invariant (i)NKT cells with the model Ag α-galactosylceramide induces rapid production of multiple cytokines, impacting a wide variety of different immune reactions. In contrast, following secondary activation with α-galactosylceramide, the behavior of iNKT cells is altered for months, with the production of most cytokines being strongly reduced. The requirements for the induction of this hyporesponsive state, however, remain poorly defined. In this study, we show that Th1-biasing iNKT cell Ags could induce iNKT cell hyporesponsiveness, as long as a minimum antigenic affinity was reached. In contrast, the Th2-biasing Ag OCH did not induce a hyporesponsive state, nor did cytokine-driven iNKT cell activation by LPS or infections. Furthermore, although dendritic cells and B cells have been reported to be essential for iNKT cell stimulation, neither dendritic cells nor B cells were required to induce iNKT cell hyporesponsiveness. Therefore, our data indicate that whereas some bone marrow-derived cells could induce iNKT cell hyporesponsiveness, selective conditions, dependent on the structure and potency of the Ag, were required to induce hyporesponsiveness.

The cholesterol transporter ABCG1 links cholesterol homeostasis and tumour immunity

ATP-binding Cassette Transporter G1 (ABCG1) promotes cholesterol efflux from cells and regulates intracellular cholesterol homeostasis. Here, we demonstrate a role of ABCG1 as a mediator of tumor immunity. Abcg1^−/− mice have dramatically suppressed subcutaneous MB49-bladder carcinoma and B16-melanoma growth and prolonged survival. We show that reduced tumor growth in Abcg1^−/− mice is myeloid cell-intrinsic and is associated with a phenotypic shift of the macrophages from a tumor-promoting M2 to a tumor-fighting M1 within the tumor. Abcg1^−/− macrophages exhibit an intrinsic bias toward M1 polarization with increased NF-κB activation and direct cytotoxicity for tumor cells in vitro. Overall, our study demonstrates that absence of ABCG1 inhibits tumor growth through modulation of macrophage function within the tumor and illustrates a link between cholesterol homeostasis and cancer.

Adenosine 5'-monophosphate-activated protein kinase regulates IL-10-mediated anti-inflammatory signaling pathways in macrophages

AMP-activated protein kinase (AMPK) is a conserved serine/threonine kinase with a critical function in the regulation of metabolic pathways in eukaryotic cells. Recently, AMPK has been shown to play an additional role as a regulator of inflammatory activity in leukocytes. Treatment of macrophages with chemical AMPK activators, or forced expression of a constitutively active form of AMPK, results in polarization to an anti-inflammatory phenotype. In addition, we reported previously that stimulation of macrophages with anti-inflammatory cytokines such as IL-10, IL-4, and TGF-β results in rapid activation of AMPK, suggesting that AMPK contributes to the suppressive function of these cytokines. In this study, we investigated the role of AMPK in IL-10-induced gene expression and anti-inflammatory function. IL-10-stimulated wild-type macrophages displayed rapid activation of PI3K and its downstream targets Akt and mammalian target of rapamycin complex (mTORC1), an effect that was not seen in macrophages generated from AMPKα1-deficient mice. AMPK activation was not impacted by treatment with either the PI3K inhibitor LY294002 or the JAK inhibitor CP-690550, suggesting that IL-10-mediated activation of AMPK is independent of PI3K and JAK activity. IL-10 induced phosphorylation of both Tyr(705) and Ser(727) residues of STAT3 in an AMPKα1-dependent manner, and these phosphorylation events were blocked by inhibition of Ca(2+)/calmodulin-dependent protein kinase kinase β, an upstream activator of AMPK, and by the mTORC1 inhibitor rapamycin, respectively. The impaired STAT3 phosphorylation in response to IL-10 observed in AMPKα1-deficient macrophages was accompanied by reduced suppressor of cytokine signaling 3 expression and an inadequacy of IL-10 to suppress LPS-induced proinflammatory cytokine production. Overall, our data demonstrate that AMPKα1 is required for IL-10 activation of the PI3K/Akt/mTORC1 and STAT3-mediated anti-inflammatory pathways regulating macrophage functional polarization.

Myeloid expression of adenosine A2A receptor suppresses T and NK cell responses in the solid tumor microenvironment

High concentrations of adenosine in tumor microenvironments inhibit antitumor cytotoxic lymphocyte responses. Although T cells express inhibitory adenosine A2A receptors (A2AR) that suppress their activation and inhibit immune killing of tumors, a role for myeloid cell A2ARs in suppressing the immune response to tumors has yet to be investigated. In this study, we show that the growth of transplanted syngeneic B16F10 melanoma or Lewis lung carcinoma cells is slowed in Adora2a(f/f)-LysMCre(+/-) mice, which selectively lack myeloid A2ARs. Reduced melanoma growth is associated with significant increases in MHCII and IL12 expression in tumor-associated macrophages and with >90% reductions in IL10 expression in tumor-associated macrophages, dendritic cells (DC), and Ly6C(+) or Ly6G(+) myeloid-derived suppressor cells (MDSC). Myeloid deletion of A2ARs significantly increases CD44 expression on tumor-associated T cells and natural killer (NK) cells. Depletion of CD8(+) T cells or NK cells in tumor-bearing mice indicates that both cell types initially contribute to slowing melanoma growth in mice lacking myeloid A2A receptors, but tumor suppression mediated by CD8(+) T cells is more persistent. Myeloid-selective A2AR deletion significantly reduces lung metastasis of melanomas that express luciferase (for in vivo tracking) and ovalbumin (as a model antigen). Reduced metastasis is associated with increased numbers and activation of NK cells and antigen-specific CD8(+) T cells in lung infiltrates. Overall, the findings indicate that myeloid cell A2ARs have direct myelosuppressive effects that indirectly contribute to the suppression of T cells and NK cells in primary and metastatic tumor microenvironments. The results indicate that tumor-associated myeloid cells, including macrophages, DCs, and MDSCs all express immunosuppressive A2ARs that are potential targets of adenosine receptor blockers to enhance immune killing of tumors.

IL-10-producing NKT10 cells are a distinct regulatory invariant NKT cell subset

Invariant natural killer T (iNKT) cells rapidly produce copious amounts of multiple cytokines after activation, thereby impacting a wide variety of different immune reactions. However, strong activation of iNKT cells with α-galactosylceramide (αGalCer) reportedly induces a hyporeactive state that resembles anergy. In contrast, we determined here that iNKT cells from mice pretreated with αGalCer retain cytotoxic activity and maintain the ability to respond to TCR-dependent as well as TCR-independent cytokine-mediated stimulation. Additionally, αGalCer-pretreated iNKT cells acquired characteristics of regulatory cells, including production and secretion of the immunomodulatory cytokine IL-10. Through the production of IL-10, αGalCer-pretreated iNKT cells impaired antitumor responses and reduced disease in experimental autoimmune encephalomyelitis, a mouse model of autoimmune disease. Furthermore, a subset of iNKT cells with a similar inhibitory phenotype and function were present in mice not exposed to αGalCer and were enriched in mouse adipose tissue and detectable in human PBMCs. These data demonstrate that IL-10-producing iNKT cells with regulatory potential (NKT10 cells) represent a distinct iNKT cell subset.

Extracellular adenosine regulates naive T cell development and peripheral maintenance

Adenosine receptor signaling inhibits TCR-induced activation of PI3K–Akt to reduce IL-7Rα expression on T cells, thereby regulating development and maintenance of naive T cells in the periphery.

Adenosine produced as a byproduct of metabolic activity is present in all tissues and produces dose-dependent suppression of TCR signaling. Naive T cell maintenance depends on inhibition of TCR signals by environmental sensors, which are yet to be fully defined. We produced mice with a floxed adenosine A_2A receptor (A_2AR) gene, Adora2a, and show that either global A_2AR deletion or cre-mediated T cell deletion elicits a decline in the number of naive but not memory T cells. A_2AR signaling maintains naive T cells in a quiescent state by inhibiting TCR-induced activation of the phosphatidylinositide 3-kinase (PI3K)–AKT pathway, thereby reducing IL-7Rα down-regulation and naive T cell apoptosis. Patterns of IL-7Rα expression on T cells in chimeric mice reconstituted with Adora2a^+/+ and Adora2a^−/− bone marrow cells suggest that decreased IL-7Rα in naive T cells is a cell-intrinsic consequence of Adora2a deletion. In addition, A_2AR expression increases in early thymic T cell development and contributes to progression of double-negative thymic precursors to single-positive thymocytes with increased IL-7Rα expression. Therefore, A_2AR signaling regulates T cell development and maintenance to sustain normal numbers of naive T cells in the periphery.

ABCG1 as a novel link between cholesterol homeostasis and tumor immunity (P2031)

ATP-binding Cassette Transporter G1 (ABCG1) promotes cholesterol efflux from cells for intracellular cholesterol homeostasis. ABCG1 has been shown to regulate macrophage and lymphocyte immune responses. In this study, we demonstrate a role of ABCG1 as a novel modulator of tumor immunity. MB49 bladder carcinoma or B16 melanoma cells were injected into Abcg1-/- or B6 mice subcutaneously. Both groups of mice were fed with either high-fat diet or chow diet starting a week before injection of tumor cells. Abcg1-/- mice on high-fat diet had dramatically reduced (80 %) tumor growth compared to B6 mice. Abcg1-/- mice on high-fat diet also showed diminished tumor metastasis and prolonged survival. Furthermore, we showed that reduced tumor size in Abcg1-/- mice on high-fat diet was associated with an increase in the frequency of NK cells and T cells and decrease in the frequency of macrophages and Tregs in tumor. Selective inhibition of ABCG1 in myeloid cells, but not in T cells, reduced tumor growth in vivo, demonstrating that impaired tumor growth in the absence of ABCG1 is mediated through myeloid cell-intrinsic factors. Moreover, ABCG1 deficiency caused an increase in apoptosis of macrophages and a shift of macrophages to an M1 phenotype in the tumor under high-fat diet conditions. Overall, our study shows that absence of ABCG1 inhibits tumor growth through regulation of macrophage function within the tumor and provides a link between diet, cholesterol homeostasis, and cancer.

Stunned invariant NKT cells are not anergic, but acquire IL-10-dependent regulatory characteristics (P1052)

Invariant NKT (iNKT) cells are a unique subset of T lymphocytes that after activation produce copious amounts of cytokines, impacting a dazzling variety of different immune reactions. However, it has been reported that strong activation of iNKT cells with the synthetic model antigen α-galactosylceramide (αGalCer) induces a hypo-reactivity that was proposed to be related to anergy. In contrast, here we report, that αGalCer pretreated iNKT cells, referred to here as ‘induced stunned’ iNKT (isNKT) cells, retain their cytotoxic activity and their response to TCR-independent, cytokine-mediated stimulation. Additionally, isNKT cells acquire characteristics of regulatory cells, marked by the expression of PD-1, Neuropilin-1, CD152 and the ability to produce IL-10. Through the production of IL-10, isNKT cells were able to modulate the tumor load of mice challenged with B16 melanoma and to ameliorate the outcome of Experimental Autoimmune Encephalomyelitis (EAE). Furthermore, a subset of iNKT cells with a stunned phenotype and function were present even in untreated mice, and were enriched in adipose tissue, indicating that natural stunned iNKT cells are present in vivo under steady state conditions. Preliminary data suggest that such stunned iNKT cells can also be found in human PBMCs. These data demonstrate that stunned iNKT cells are not anergic but rather acquire a novel functional state with regulatory potential and that they likely represent a novel, distinct iNKT cell subset.

ATP-binding cassette transporter G1 intrinsically regulates invariant NKT cell development

ATP-binding cassette transporter G1 (ABCG1) plays a role in the intracellular transport of cholesterol. Invariant NKT (iNKT) cells are a subpopulation of T lymphocytes that recognize glycolipid Ags. In this study, we demonstrate that ABCG1 regulates iNKT cell development and functions in a cell-intrinsic manner. Abcg1(-/-) mice displayed reduced frequencies of iNKT cells in thymus and periphery. Thymic iNKT cells deficient in ABCG1 had reduced membrane lipid raft content, and showed impaired proliferation and defective maturation during the early stages of development. Moreover, we found that Abcg1(-/-) mice possess a higher frequency of Vβ7(+) iNKT cells, suggesting alterations in iNKT cell thymic selection. Furthermore, in response to CD3ε/CD28 stimulation, Abcg1(-/-) thymic iNKT cells showed reduced production of IL-4 but increased production of IFN-γ. Our results demonstrate that changes in intracellular cholesterol homeostasis by ABCG1 profoundly impact iNKT cell development and function.

Cell-intrinsic adenosine A2A receptor signaling is required for T cell homeostasis and control of tumor growth (47.1)

Adenosine generated as a result of normal metabolic activity is elevated in response to tissue stress, damage, or hypoxia. By stimulating adenosine A2A receptors (A2ARs) adenosine links metabolic activity to regulation of normal physiological functions such as sleep, blood flow, and inflammation. Although stimulation of A2ARs on activated T cells and APCs acutely suppresses inflammation and immune killing of tumor cells, global A2AR deletion has variable effects on the growth rate of syngeneic tumors, suggesting that A2AR signaling has opposing effects on immune function. Here we show that A2ARs are required for homeostatic maintenance of naïve T cells. In global A2AR-deficient mice naïve T cells undergo apoptosis, which drastically lower their number in blood and in peripheral lymph nodes. Lymphoid deletion of A2ARs, adoptive co-transfer and mixed bone-marrow reconstitution experiments showed that cell intrinsic A2AR signaling is required for T cell homeostasis. A2AR signaling is also required for interleukin 7 to optimally facilitate T cell survival ex vivo. In mice injected with syngeneic melanoma cells, lymphoid-specific A2AR deletion decreases T cell numbers in the periphery and in the tumor, reduces the proportion of tumor infiltrating T cells with an activated/memory phenotype, and markedly accelerates tumor growth. The results indicate that homeostatic adenosine production and A2AR signaling are required in naïve T cell maintenance and immune defense against tumors.

Adenosine A2B receptor blockade slows growth of bladder and breast tumors

The accumulation of high levels of adenosine in tumors activates A(2A) and A(2B) receptors on immune cells and inhibits their ability to suppress tumor growth. Deletion of adenosine A(2A) receptors (A(2A)ARs) has been reported to activate antitumor T cells, stimulate dendritic cell (DC) function, and inhibit angiogenesis. In this study, we evaluated the effects of intermittent intratumor injection of a nonselective adenosine receptor antagonist, aminophylline (AMO; theophylline ethylenediamine) and, for the first time to our knowledge, a selective A(2B)AR antagonist, ATL801. AMO and ATL801 slowed the growth of MB49 bladder and 4T1 breast tumors in syngeneic mice and reduced by 85% metastasizes of breast cancer cells from mammary fat to lung. Based on experiments with A(2A)AR(-/-) or adenosine A(2B) receptor(-/-) mice, the effect of AMO injection was unexpectedly attributed to A(2B)AR and not to A(2A)AR blockade. AMO and ATL801 significantly increased tumor levels of IFN-γ and the IFN-inducible chemokine CXCL10, which is a ligand for CXCR3. This was associated with an increase in activated tumor-infiltrating CXCR3(+) T cells and a decrease in endothelial cell precursors within tumors. Tumor growth inhibition by AMO or ATL801 was eliminated in CXCR3(-/-) mice and RAG1(-/-) mice that lack mature T cells. In RAG1(-/-) mice, A(2B)AR deletion enhanced CD86 expression on CD11b(-) DCs. Bone marrow chimera experiments demonstrated that CXCR3 and A(2B)AR expression on bone marrow cells is required for the antitumor effects of AMO. The data suggest that blockade of A(2B)ARs enhances DC activation and CXCR3-dependent antitumor responses.

Aminophylline inhibits breast and bladder tumor growth in mice due to CXCR3-dependent adenosine A2B receptor blockade (165.32)

The activation of adenosine A2A or A2B receptors on immune cells inhibits their ability to suppress tumor growth. In this study, we evaluated the anti-tumor effects of aminophyllilne (AMO) a nonselective antagonist of A2A and A2B receptors that is used clinically to treat asthma. Intra-tumor injection of AMO inhibited the growth of syngeneic MB49 bladder cells subcutaneously injected into C57BL/6 mice and the growth and lung metastasis of luminescent syngeneic 4T1 breast tumor cells inoculated into the mammary fat pats of Balb/c mice. Although AMO inhibited the growth of MB49 in A2AR-/- mice it failed to do so in Rag1-/-, A2BR-/- or CXCR3-/- mice. The selective deletion of the A2BR or CXCR3 from bone marrow cells also blocked tumor suppression by AMO. Transcript levels of interferon-γ and CXCL10, and activation of CD4+ and CD8+ T cells, were increased in tumors treated with AMO, while numbers of CD34+/CD45- endothelial cell precursors were decreased. We conclude that: 1) the anti-tumor effects of non-selective adenosine receptor blockade by AMO are primarily mediated by the A2BR; 2) CXCR3 receptors are required for anti-tumor effects of AMO and influence both T cell trafficking and chemokine-mediated angiogenesis; and 3) AMO may be useful for proof-of-principle studies to determine the efficacy of adenosine receptor antagonists as tumor suppressors alone or in conjunction with tumor vaccines.

MyD88-dependent SHIP1 regulates proinflammatory signaling pathways in dendritic cells after monophosphoryl lipid A stimulation of TLR4

We previously showed that monophosphoryl lipid A (MLA) activates TLR4 in dendritic cells (DCs) in a Toll/IL-1R domain-containing adaptor inducing IFN-β (TRIF)-biased manner: MLA produced from Salmonella minnesota Re595 induced signaling events and expression of gene products that were primarily TRIF dependent, whereas MyD88-dependent signaling was impaired. Moreover, when tested in TRIF-intact/MyD88-deficient DCs, synthetic MLA of the Escherichia coli chemotype (sMLA) showed the same activity as its diphosphoryl, inflammatory counterpart (synthetic diphosphoryl lipid A), indicating that TRIF-mediated signaling is fully induced by sMLA. Unexpectedly, we found that the transcript level of one proinflammatory cytokine was increased in sMLA-treated cells by MyD88 deficiency to the higher level induced by synthetic diphosphoryl lipid A, which suggested MyD88 may paradoxically help restrain proinflammatory signaling by TRIF-biased sMLA. In this article, we demonstrate that sMLA induces MyD88 recruitment to TLR4 and activates the anti-inflammatory lipid phosphatase SHIP1 in an MyD88-dependent manner. At the same time, MyD88-dependent signaling activity at the level of IL-1R-associated kinase 1 is markedly reduced. Increased SHIP1 activity is associated with reductions in sMLA-induced IκB kinase α/β and IFN regulatory factor 3 activation and with restrained expression of their downstream targets, endothelin-1 and IFN-β, respectively. Results of this study identify a pattern that is desirable in the context of vaccine adjuvant design: TRIF-biased sMLA can stimulate partial MyD88 activity, with MyD88-dependent SHIP1 helping to reduce proinflammatory signaling in DCs.

Adenosine 5'-monophosphate-activated protein kinase promotes macrophage polarization to an anti-inflammatory functional phenotype

Herein, we demonstrate a role of AMP-activated protein kinase (AMPK) as a potent counterregulator of inflammatory signaling pathways in macrophages. Stimulation of macrophages with anti-inflammatory cytokines (i.e., IL-10 and TGFbeta) resulted in the rapid phosphorylation/activation of AMPK, whereas stimulation of macrophages with a proinflammatory stimulus (LPS) resulted in AMPK dephosphorylation/inactivation. Inhibition of AMPKalpha expression by RNA interference dramatically increased the mRNA levels of LPS-induced TNF-alpha, IL-6, and cyclooxygenase-2. Likewise, expression of a dominant negative AMPKalpha1 in macrophages enhanced TNF-alpha and IL-6 protein synthesis in response to LPS stimulation, while diminishing the production of IL-10. In contrast, transfection of macrophages with a constitutively active form of AMPKalpha1 resulted in decreased LPS-induced TNF-alpha and IL-6 production, and heightened production of IL-10. In addition, we found that AMPK negatively regulated LPS-induced IkappaB-alpha degradation and positively regulated Akt activation, accompanied by inhibition of glycogen synthase kinase beta and activation of CREB. Thus, AMPK directs signaling pathways in macrophages in a manner that suppresses proinflammatory responses and promotes macrophage polarization to an anti-inflammatory functional phenotype.