Deletion of endothelial leptin receptors in mice promotes diet-induced obesity

Obesity promotes endothelial dysfunction. Endothelial cells not only respond, but possibly actively promote the development of obesity and metabolic dysfunction. Our aim was to characterize the role of endothelial leptin receptors (LepR) for endothelial and whole body metabolism and diet-induced obesity. Mice with tamoxifen-inducible, Tie2.Cre-ER^T2-mediated deletion of LepR in endothelial cells (End.LepR knockout, KO) were fed high-fat diet (HFD) for 16 weeks. Body weight gain, serum leptin levels, visceral adiposity and adipose tissue inflammation were more pronounced in obese End.LepR-KO mice, whereas fasting serum glucose and insulin levels or the extent of hepatic steatosis did not differ. Reduced brain endothelial transcytosis of exogenous leptin, increased food intake and total energy balance were observed in End.LepR-KO mice and accompanied by brain perivascular macrophage accumulation, whereas physical activity, energy expenditure and respiratory exchange rates did not differ. Metabolic flux analysis revealed no changes in the bioenergetic profile of endothelial cells from brain or visceral adipose tissue, but higher glycolysis and mitochondrial respiration rates in those isolated from lungs. Our findings support a role for endothelial LepRs in the transport of leptin into the brain and neuronal control of food intake, and also suggest organ-specific changes in endothelial cell, but not whole-body metabolism.

Boosting regulatory T cell function for the treatment of autoimmune diseases – That’s only half the battle!

Regulatory T cells (Treg) represent a subset of specialized T cells that are essential for the regulation of immune responses and maintenance of peripheral tolerance. Once activated, Treg exert powerful immunosuppressive properties, for example by inhibiting T cell-mediated immune responses against self-antigens, thereby protecting our body from autoimmunity. Autoimmune diseases such as multiple sclerosis, rheumatoid arthritis or systemic lupus erythematosus, exhibit an immunological imbalance mainly characterized by a reduced frequency and impaired function of Treg. In addition, there has been increasing evidence that – besides Treg dysfunction – immunoregulatory mechanisms fail to control autoreactive T cells due to a reduced responsiveness of T effector cells (Teff) for the suppressive properties of Treg, a process termed Treg resistance. In order to efficiently treat autoimmune diseases and thus fully induce immunological tolerance, a combined therapy aimed at both enhancing Treg function and restoring Teff responsiveness could most likely be beneficial. This review provides an overview of immunomodulating drugs that are currently used to treat various autoimmune diseases in the clinic and have been shown to increase Treg frequency as well as Teff sensitivity to Treg-mediated suppression. Furthermore, we discuss strategies on how to boost Treg activity and function, and their potential use in the treatment of autoimmunity. Finally, we present a humanized mouse model for the preclinical testing of Treg-activating substances in vivo.

Inflammatory Monocyte Counts Determine Venous Blood Clot Formation and Resolution

BACKGROUND

Monocytes are thought to be involved in venous thrombosis but the role of individual monocyte subpopulations on thrombus formation, clot inflammation, and degradation is an important unresolved issue. We investigate the role of inflammatory Ly6Chi monocytes in deep vein thrombosis and their potential therapeutic impact.

METHODS

Frequencies and compositions of blood monocytes were analyzed by flow cytometry in CCR2-/- (C-C chemokine receptor type 2) and wild-type mice of different ages and after treatment with the NR4A1 (nuclear receptor group 4 family A member 1, Nur77) agonist CnsB (cytosporone B). TF (tissue factor) sufficient and deficient Ly6Chi monocytes were adoptively transferred into aged CCR2-/- mice. Thrombus formation and size were followed by ultrasound over a 3-week period after surgical reduction of blood flow (stenosis) in the inferior vena cava.

RESULTS

Reduced numbers of peripheral monocytes in aged (>30 w) CCR2-/- mice are accompanied by reduced thrombus formation after inferior vena cava ligation. Reducing the number of inflammatory Ly6Chi monocytes in wild-type mice by CsnB treatment before ligation, similarly suspends clotting, while later treatment (d1 or d4) reduces thrombus growth and accelerates resolution. We describe how changes in inflammatory monocyte numbers affect the gradual differentiation of monocytes in thrombi and show that only tissue factor-competent Ly6Chi monocytes restore thrombosis in aged CCR2-/- mice.

CONCLUSIONS

We conclude that the number of inflammatory Ly6Chi monocytes controls deep vein thrombosis formation, growth, and resolution and can be therapeutically manipulated with a NR4A1 agonist at all disease stages.

Therapeutic melanoma inhibition by local micelle-mediated cyclic nucleotide repression

The acidic tumor microenvironment in melanoma drives immune evasion by up-regulating cyclic adenosine monophosphate (cAMP) in tumor-infiltrating monocytes. Here we show that the release of non-toxic concentrations of an adenylate cyclase (AC) inhibitor from poly(sarcosine)-block-poly(L-glutamic acid γ-benzyl ester) (polypept(o)id) copolymer micelles restores antitumor immunity. In combination with selective, non-therapeutic regulatory T cell depletion, AC inhibitor micelles achieve a complete remission of established B16-F10-OVA tumors. Single-cell sequencing of melanoma-infiltrating immune cells shows that AC inhibitor micelles reduce the number of anti-inflammatory myeloid cells and checkpoint receptor expression on T cells. AC inhibitor micelles thus represent an immunotherapeutic measure to counteract melanoma immune escape.

The acidic tumour microenvironment in melanoma drives immune evasion by cAMP in tumor-infiltrating monocytes. Here, the authors show that the release of an adenylate cyclase inhibitor from micelles restores antitumor immunity and, when combined with regulatory T cell depletion, leads to remission of established B16-F10-OVA tumors.

Specialized regulatory T cells control venous blood clot resolution through SPARC

The cells and mechanisms involved in blood clot resorption are only partially known. We show that regulatory T cells (Tregs) accumulate in venous blood clots and regulate thrombolysis by controlling the recruitment, differentiation and matrix metalloproteinase (MMP) activity of monocytes. We describe a clot Treg population that forms the matricellular acid- and cysteine-rich protein SPARC (secreted protein acidic and rich in cysteine) and show that SPARC enhances monocyte MMP activity and that SPARC+ Tregs are crucial for blood clot resorption. By comparing different treatment times, we define a therapeutic window of Treg expansion that accelerates clot resorption.

Innate Effector-Memory T-Cell Activation Regulates Post-Thrombotic Vein Wall Inflammation and Thrombus Resolution

RATIONALE

Immune cells play an important role during the generation and resolution of thrombosis. T cells are powerful regulators of immune and nonimmune cell function, however, their role in sterile inflammation in venous thrombosis has not been systematically examined.

OBJECTIVE

This study investigated the recruitment, activation, and inflammatory activity of T cells in deep vein thrombosis and its consequences for venous thrombus resolution.

METHODS AND RESULTS

CD4⁺ and CD8⁺ T cells infiltrate the thrombus and vein wall rapidly on deep vein thrombosis induction and remain in the tissue throughout the thrombus resolution. In the vein wall, recruited T cells largely consist of effector-memory T (T_EM) cells. Using T-cell receptor transgenic reporter mice, we demonstrate that deep vein thrombosis-recruited T_EM receive an immediate antigen-independent activation and produce IFN-γ (interferon) in situ. Mapping inflammatory conditions in the thrombotic vein, we identify a set of deep vein thrombosis upregulated cytokines and chemokines that synergize to induce antigen-independent IFN-γ production in CD4⁺ and CD8⁺ T_EM cells. Reducing the number of T_EM cells through a depletion recovery procedure, we show that intravenous T_EM activation determines neutrophil and monocyte recruitment and delays thrombus neovascularization and resolution. Examining T-cell recruitment in human venous stasis, we show that superficial varicose veins preferentially contain activated memory T cells.

CONCLUSIONS

T_EM orchestrate the inflammatory response in venous thrombosis affecting thrombus resolution.