Apical splenic nerve electrical stimulation discloses an anti-inflammatory pathway relying on adrenergic and nicotinic receptors in myeloid cells.

The autonomic nervous system innervates all lymphoid tissues including the spleen therefore providing a link between the central nervous system and the immune system. The only known mechanism of neural inhibition of inflammation in the spleen relies on the production of norepinephrine by splenic catecholaminergic fibers which binds to ß2-adrenergic receptors (ß 2-ARs) of CD4+ T cells. These CD4+ T cells trigger the release of acetylcholine that inhibits the secretion of inflammatory cytokines by macrophages through α7 nicotinic acetylcholine receptor (α7nAchRs) signaling. While the vagal anti-inflammatory pathway has been extensively studied in rodents, it remains to be determined whether it coexists with other neural pathways. Here, we have found that three nerve branches project to the spleen in mice. While two of these nerves are associated with an artery and contain catecholaminergic fibers, the third is located at the apex of the spleen and contain both catecholaminergic and cholinergic fibers. We found that electrical stimulation of the apical nerve, but not the arterial nerves, inhibited inflammation independently of lymphocytes. In striking contrast to the anti-inflammatory pathway mechanism described so far, we also found that the inhibition of inflammation by apical nerve electrical stimulation relied on signaling by both ß 2-ARs and α7nAchRs in myeloid cells, with these two signaling pathways acting in parallel. Most importantly, apical splenic nerve electrical stimulation mitigated clinical symptoms in a mouse model of rheumatoid arthritis further providing the proof-of-concept that such an approach could be beneficial in patients with Immune-mediated inflammatory diseases.

Transfer of dysbiotic gut microbiota has beneficial effects on host liver metabolism.

Gut microbiota dysbiosis has been implicated in a variety of systemic disorders, notably metabolic diseases including obesity and impaired liver function, but the underlying mechanisms are uncertain. To investigate this question, we transferred caecal microbiota from either obese or lean mice to antibiotic-free, conventional wild-type mice. We found that transferring obese-mouse gut microbiota to mice on normal chow (NC) acutely reduces markers of hepatic gluconeogenesis with decreased hepatic PEPCK activity, compared to non-inoculated mice, a phenotypic trait blunted in conventional NOD2 KO mice. Furthermore, transferring of obese-mouse microbiota changes both the gut microbiota and the microbiome of recipient mice. We also found that transferring obese gut microbiota to NC-fed mice then fed with a high-fat diet (HFD) acutely impacts hepatic metabolism and prevents HFD-increased hepatic gluconeogenesis compared to non-inoculated mice. Moreover, the recipient mice exhibit reduced hepatic PEPCK and G6Pase activity, fed glycaemia and adiposity. Conversely, transfer of lean-mouse microbiota does not affect markers of hepatic gluconeogenesis. Our findings provide a new perspective on gut microbiota dysbiosis, potentially useful to better understand the aetiology of metabolic diseases.

Rab4b controls an early endosome sorting event by interacting with the γ-subunit of the clathrin adaptor complex 1.

The endocytic pathway is essential for cell homeostasis and numerous small Rab GTPases are involved in its control. The endocytic trafficking step controlled by Rab4b has not been elucidated, although recent data suggested it could be important for glucose homeostasis, synaptic homeostasis or adaptive immunity. Here, we show that Rab4b is required for early endosome sorting of transferrin receptors (TfRs) to the recycling endosomes, and we identified the AP1γ subunit of the clathrin adaptor AP-1 as a Rab4b effector and key component of the machinery of early endosome sorting. We show that internalised transferrin (Tf) does not reach Vamp3/Rab11 recycling endosomes in the absence of Rab4b, whereas it is rapidly recycled back to the plasma membrane. By contrast, overexpression of Rab4b leads to the accumulation of internalised Tf within AP-1- and clathrin-coated vesicles. These vesicles are poor in early and recycling endocytic markers except for TfR and require AP1γ for their formation. Furthermore, the targeted overexpression of the Rab4b-binding domain of AP1γ to early endosome upon its fusion with FYVE domains inhibited the interaction between Rab4b and endogenous AP1γ, and perturbed Tf traffic. We thus proposed that the interaction between early endocytic Rab4b and AP1γ could allow the budding of clathrin-coated vesicles for subsequent traffic to recycling endosomes. The data also uncover a novel type of endosomes, characterised by low abundance of either early or recycling endocytic markers, which could potentially be generated in cell types that naturally express high level of Rab4b.

Pancreatic nerve electrostimulation inhibits recent-onset autoimmune diabetes.

Vagus nerve stimulation can ameliorate autoimmune diseases such as rheumatoid arthritis by modulation of the immune system. Its efficacy for the treatment of type 1 diabetes has not been explored, in part because the nerves projecting to the pancreatic lymph nodes (pLNs) in mice are unmapped. Here, we map the nerve projecting to the pancreas and pLNs in mice and use a minimally invasive surgical procedure to implant micro-cuff electrodes onto the nerve. Pancreatic nerve electrical stimulation (PNES) resulted in ß-adrenergic receptor-mediated-accumulation of B and T cells in pLNs and reduced production of pro-inflammatory cytokines following lipopolysaccharide stimulation. Autoreactive T cells showed reduced proliferation in pLNs of mice receiving PNES as compared to sham controls. In a spontaneous mouse model of autoimmune diabetes, PNES inhibited disease progression in diabetic mice.

Rab4b Deficiency in T Cells Promotes Adipose Treg/Th17 Imbalance, Adipose Tissue Dysfunction, and Insulin Resistance.

Obesity modifies T cell populations in adipose tissue, thereby contributing to adipose tissue inflammation and insulin resistance. Here, we show that Rab4b, a small GTPase governing endocytic trafficking, is pivotal in T cells for the development of these pathological events. Rab4b expression is decreased in adipose T cells from mice and patients with obesity. The specific depletion of Rab4b in T cells causes adipocyte hypertrophy and insulin resistance in chow-fed mice and worsens insulin resistance in obese mice. This phenotype is driven by an increase in adipose Th17 and a decrease in adipose Treg due to a cell-autonomous skew of differentiation toward Th17. The Th17/Treg imbalance initiates adipose tissue inflammation and reduces adipogenesis, leading to lipid deposition in liver and muscles. Therefore, we propose that the obesity-induced loss of Rab4b in adipose T cells may contribute to maladaptive white adipose tissue remodeling and insulin resistance by altering adipose T cell fate.

DNA Damage and the Activation of the p53 Pathway Mediate Alterations in Metabolic and Secretory Functions of Adipocytes.

Activation of the p53 pathway in adipose tissue contributes to insulin resistance associated with obesity. However, the mechanisms of p53 activation and the effect on adipocyte functions are still elusive. Here we found a higher level of DNA oxidation and a reduction in telomere length in adipose tissue of mice fed a high-fat diet and an increase in DNA damage and activation of the p53 pathway in adipocytes. Interestingly, hallmarks of chronic DNA damage are visible at the onset of obesity. Furthermore, injection of lean mice with doxorubicin, a DNA damage-inducing drug, increased the expression of chemokines in adipose tissue and promoted its infiltration by proinflammatory macrophages and neutrophils together with adipocyte insulin resistance. In vitro, DNA damage in adipocytes increased the expression of chemokines and triggered the production of chemotactic factors for macrophages and neutrophils. Insulin signaling and effect on glucose uptake and Glut4 translocation were decreased, and lipolysis was increased. These events were prevented by p53 inhibition, whereas its activation by nutlin-3 reproduced the DNA damage-induced adverse effects. This study reveals that DNA damage in obese adipocytes could trigger p53-dependent signals involved in alteration of adipocyte metabolism and secretory function leading to adipose tissue inflammation, adipocyte dysfunction, and insulin resistance.

The Tpl2 Kinase Regulates the COX-2/Prostaglandin E2 Axis in Adipocytes in Inflammatory Conditions.

Bioactive lipid mediators such as prostaglandin E2 (PGE2) have emerged as potent regulator of obese adipocyte inflammation and functions. PGE2 is produced by cyclooxygenases (COXs) from arachidonic acid, but inflammatory signaling pathways controlling COX-2 expression and PGE2 production in adipocytes remain ill-defined. Here, we demonstrated that the MAP kinase kinase kinase tumor progression locus 2 (Tpl2) controls COX-2 expression and PGE2 secretion in adipocytes in response to different inflammatory mediators. We found that pharmacological- or small interfering RNA-mediated Tpl2 inhibition in 3T3-L1 adipocytes decreased by 50% COX-2 induction in response to IL-1ß, TNF-α, or a mix of the 2 cytokines. PGE2 secretion induced by the cytokine mix was also markedly blunted. At the molecular level, nuclear factor κB was required for Tpl2-induced COX-2 expression in response to IL-1ß but was inhibitory for the TNF-α or cytokine mix response. In a coculture between adipocytes and macrophages, COX-2 was mainly increased in adipocytes and pharmacological inhibition of Tpl2 or its silencing in adipocytes markedly reduced COX-2 expression and PGE2 secretion. Further, Tpl2 inhibition in adipocytes reduces by 60% COX-2 expression induced by a conditioned medium from lipopolysaccharide (LPS)-treated macrophages. Importantly, LPS was less efficient to induce COX-2 mRNA in adipose tissue explants of Tpl2 null mice compared with wild-type and Tpl2 null mice displayed low COX-2 mRNA induction in adipose tissue in response to LPS injection. Collectively, these data established that activation of Tpl2 by inflammatory stimuli in adipocytes and adipose tissue contributes to increase COX-2 expression and production of PGE2 that could participate in the modulation of adipose tissue inflammation during obesity.

Maintenance of Macrophage Redox Status by ChREBP Limits Inflammation and Apoptosis and Protects against Advanced Atherosclerotic Lesion Formation.

Enhanced glucose utilization can be visualized in atherosclerotic lesions and may reflect a high glycolytic rate in lesional macrophages, but its causative role in plaque progression remains unclear. We observe that the activity of the carbohydrate-responsive element binding protein ChREBP is rapidly downregulated upon TLR4 activation in macrophages. ChREBP inactivation refocuses cellular metabolism to a high redox state favoring enhanced inflammatory responses after TLR4 activation and increased cell death after TLR4 activation or oxidized LDL loading. Targeted deletion of ChREBP in bone marrow cells resulted in accelerated atherosclerosis progression in Ldlr(-/-) mice with increased monocytosis, lesional macrophage accumulation, and plaque necrosis. Thus, ChREBP-dependent macrophage metabolic reprogramming hinders plaque progression and establishes a causative role for leukocyte glucose metabolism in atherosclerosis.

[Implication of MAP kinases in obesity-induced inflammation and insulin resistance]. / Implication des MAP kinases dans l'inflammation et l'insulino-résistance associées à l'obésité

Insulin resistance is often associated with obesity and is a major risk factor for development of type 2 diabetes as well as cardiovascular and hepatic diseases. Insulin resistance may also increase the incidence or the aggressiveness of some cancers. Insulin resistance occurs owing to defects in insulin signaling in target tissues of this hormone. During the last ten years, it became evident that the chronic low-grade inflammatory state that develops during obesity plays an important role in insulin resistance development. Indeed, inflammatory cytokines activate several signaling pathways that impinge on the insulin signaling pathway. Among them, this review will focus on the implication of the MAP kinases JNK and ERK1/2 signaling in the development of insulin signaling alterations and will discuss the possibility to target these pathways in order to fight insulin resistance.

Implication of the Tpl2 kinase in inflammatory changes and insulin resistance induced by the interaction between adipocytes and macrophages.

Adipose tissue inflammation is associated with the development of insulin resistance. In obese adipose tissue, lipopolysaccharides (LPSs) and saturated fatty acids trigger inflammatory factors that mediate a paracrine loop between adipocytes and macrophages. However, the inflammatory signaling proteins underlying this cross talk remain to be identified. The mitogen-activated protein kinase kinase kinase tumor progression locus 2 (Tpl2) is activated by inflammatory stimuli, including LPS, and its expression is up-regulated in obese adipose tissue, but its role in the interaction between adipocytes and macrophages remains ill-defined. To assess the implication of Tpl2 in the cross talk between these 2 cell types, we used coculture system and conditioned medium (CM) from macrophages. Pharmacological inhibition of Tpl2 in the coculture markedly reduced lipolysis and cytokine production and prevented the decrease in adipocyte insulin signaling. Tpl2 knockdown in cocultured adipocytes reduced lipolysis but had a weak effect on cytokine production and did not prevent the alteration of insulin signaling. By contrast, Tpl2 silencing in cocultured macrophages resulted in a marked inhibition of cytokine production and prevented the alteration of adipocyte insulin signaling. Further, when Tpl2 was inhibited in LPS-activated macrophages, the produced CM did not alter adipocyte insulin signaling and did not induce an inflammatory response in adipocytes. By contrast, Tpl2 silencing in adipocytes did not prevent the deleterious effects of a CM from LPS-activated macrophages. Together, these data establish that Tpl2, mainly in macrophages, is involved in the cross talk between adipocytes and macrophages that promotes inflammatory changes and alteration of insulin signaling in adipocytes.

Implication of inflammatory signaling pathways in obesity-induced insulin resistance.

Obesity is characterized by the development of a low-grade chronic inflammatory state in different metabolic tissues including adipose tissue and liver. This inflammation develops in response to an excess of nutrient flux and is now recognized as an important link between obesity and insulin resistance. Several dietary factors like saturated fatty acids and glucose as well as changes in gut microbiota have been proposed as triggers of this metabolic inflammation through the activation of pattern-recognition receptors (PRRs), including Toll-like receptors (TLR), inflammasome, and nucleotide oligomerization domain (NOD). The consequences are the production of pro-inflammatory cytokines and the recruitment of immune cells such as macrophages and T lymphocytes in metabolic tissues. Inflammatory cytokines activate several kinases like IKKß, mTOR/S6 kinase, and MAP kinases as well as SOCS proteins that interfere with insulin signaling and action in adipocytes and hepatocytes. In this review, we summarize recent studies demonstrating that PRRs and stress kinases are important integrators of metabolic and inflammatory stress signals in metabolic tissues leading to peripheral and central insulin resistance and metabolic dysfunction. We discuss recent data obtained with genetically modified mice and pharmacological approaches suggesting that these inflammatory pathways are potential novel pharmacological targets for the management of obesity-associated insulin resistance.