A TPCN1 gene–deficient mouse strain is used to show that two convergent working NAADP-dependent pathways with nonoverlapping activation and self-inactivation profiles for distinct NAADP concentrations drive acrosomal exocytosis, by which TPC1 is central for the pathway activated by low-micromolar NAADP concentrations.

Macrophages are essential for innate immunity and inflammatory responses and differentiate into various functional phenotypes. Tribbles homolog 1 (), a member of the mammalian Tribbles homolog pseudokinase family, has been implicated in regulation of cell differentiation, proliferation, and metabolism, but its role in macrophage biology has not been fully elucidated. Here, we investigated the consequences of deficiency on macrophage functions and M1/M2 polarization. Bone marrow-derived macrophages (BMDMs) fromdeficient () mice exhibited elevated phagocytic capacity, correlating with up-regulation of several scavenger receptors. Concomitantly, uptake of modified low-density lipoprotein was increased in BMDMs. macrophages also exhibited diminished migration in the presence of the chemokine MCP-1, associated with reduced expression of the MCP-1 receptor Furthermore, deficiency attenuated the response of BMDMs to both M1 and M2 stimuli; induction of the M1-marker genes ,, and upon LPS/IFNγ stimulation and of the M2-marker genes, , and upon IL-4 stimulation was reduced. Functionally, deficiency decreased secretion of proinflammatory cytokines (IL-6, TNFα, IL-1β, and CXCL1) and reduced nitric oxide and reactive oxygen species production in M1-polarized macrophages. Supporting the attenuated M2 phenotype, IL-4-stimulated macrophages secreted less IL-10 and TGFβ. Mechanistically, BMDMs displayed lower levels of Janus kinase 1 (JAK1), resulting in reduced activation of LPS/IFNγ-mediated STAT1 signaling. Likewise, decreased levels of JAK1 along with lower activation of STAT6 and STAT3 were observed in M2-polarized BMDMs. Our findings suggest that extensively controls macrophage M1/M2 polarization via the JAK/STAT signaling pathway.

IL-4 receptor signaling is supposed to play a major role in anti-inflammatory polarization and proliferation of adipose tissue macrophages. In this study, we examined the metabolic and inflammatory phenotype of C57BL/6J mice (IIl4ra) with LysM-dependent knockout (IIl4raΔmyel) of the IL-4 receptor α-chain (IL-4Rα), the mandatory signaling component of IL-4 and IL-13, on chow and high-fat diet. Lean IIl4raΔmyel mice showed decreased insulin sensitivity, no divergent adipose tissue macrophage polarization, but an increased percentage of CD8+ T cells in visceral adipose tissue. After 20 wk of a high-fat diet, IIl4raΔmyel mice exhibited higher glucose tolerance, no changes in the lymphocyte compartment and fewer M1 macrophages in visceral adipose tissue. In vivo adipose tissue macrophage proliferation measured by BrdU incorporation was unaffected by Il4ra knockout. Interestingly, we show that IL-4Rα signaling directly augmented Itgax (Cd11c) gene expression in bone marrow–derived macrophages and increased the amount of CD11c+ macrophages in adipose tissue explants. Myeloid cell–specific knockout of Il4ra deteriorated insulin sensitivity in lean mice but improved parameters of glucose homeostasis and partially protected from adipose tissue inflammation in obese mice. Hence, IL-4Rα signaling probably plays a minor role in maintaining the macrophage M2 population and proliferation rates in vivo. Moreover, our data indicate that IL-4 signaling plays a proinflammatory role in adipose tissue inflammation by directly upregulating CD11c on adipose tissue macrophages.

Obesity is frequently associated with a chronic low‐grade inflammation in the adipose tissue (AT) and impaired glucose homeostasis. Adipose tissue macrophages (ATMs) have been shown to accumulate in the inflamed AT either by means of recruitment from the blood or local proliferation. ATM proliferation and activation can be stimulated by TH2 cytokines, such as IL‐4 and IL‐13, suggesting involvement of CD4‐positive T cells in ATM proliferation and activation. Furthermore, several studies have associated T cells to alterations in glucose metabolism. Therefore, we sought to examine a direct impact of CD4‐positive T cells on ATM activation, ATM proliferation and glucose homeostasis using an in vivo depletion model. Surprisingly, CD4 depletion did not affect ATM activation, ATM proliferation, or insulin sensitivity. However, CD4 depletion led to a significant improvement of glucose tolerance. In line with this, we found moderate disturbances in pancreatic endocrine function following CD4 depletion. Hence, our data suggest that the effect on glucose metabolism observed after CD4 depletion might be mediated by organs other than AT and independent of AT inflammation.

White adipose tissue (WAT) fibrosis, characterized by an excess of extracellular (ECM) matrix components, is strongly associated with WAT inflammation and dysfunction due to obesity. Interleukin (IL)-13 and IL-4 were recently identified as critical mediators in the pathogenesis of fibrotic diseases. However, their role in WAT fibrosis is still ill-defined. We therefore established an ex vivo WAT organotypic culture system and demonstrated an upregulation of fibrosis-related genes and an increase of α-smooth muscle actin (αSMA) and fibronectin abundance upon dose-dependent stimulation with IL-13/IL-4. These fibrotic effects were lost in WAT lacking il4ra, which encodes for the underlying receptor controlling this process. Adipose tissue macrophages were found to play a key role in mediating IL-13/IL-4 effects in WAT fibrosis as their depletion through clodronate dramatically decreased the fibrotic phenotype. IL-4-induced WAT fibrosis was partly confirmed in mice injected intraperitoneally with IL-4. Furthermore, gene correlation analyses of human WAT samples revealed a strong positive correlation of fibrosis markers with IL-13/IL-4 receptors, whereas IL13 and IL4 correlations failed to confirm this association. In conclusion, IL-13 and IL-4 can induce WAT fibrosis ex vivo and partly in vivo, but their role in human WAT remains to be further elucidated.

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BACKGROUND: Genetic variants at the TRIB1 gene locus are strongly associated with plasma lipid traits and the risk of coronary artery disease in humans. Here, we analyzed the consequences of Trib1 deficiency on lipid metabolism and atherosclerotic lesion formation in atherosclerosis-susceptible Ldlr −/ − . METHODS: Trib1 −/− mice were crossed onto the Ldlr −/− background to generate double-knockout mice ( Trib1 −/− Ldlr −/− ) and fed a semisynthetic, modified AIN76 diet (0.02% cholesterol and 4.3% fat) until 20 weeks of age. RESULTS: Trib1 −/− Ldlr −/− mice had profoundly larger (5.8-fold) and more advanced atherosclerotic lesions at the aortic root as compared with Trib1 +/+ Ldlr −/− controls. Further, we observed significantly elevated plasma total cholesterol and triglyceride levels in Trib1 −/− Ldlr −/− mice, resulting from higher VLDL (very-low-density lipoprotein) secretion. Lipidomics analysis revealed that loss of Trib1 altered hepatic lipid composition, including the accumulation of cholesterol and proinflammatory ceramide species, which was accompanied by signs of hepatic inflammation and injury. Concomitantly, we detected higher plasma levels of IL (interleukin)-6 and LCN2 (lipocalin 2), suggesting increased systemic inflammation in Trib1 −/− Ldlr −/− mice. Hepatic transcriptome analysis demonstrated significant upregulation of key genes controlling lipid metabolism and inflammation in Trib1 −/− Ldlr −/− mice. Further experiments suggested that these effects may be mediated through pathways involving a C/EPB-PPARγ axis and JNK signaling. CONCLUSIONS: We provide experimental evidence that Trib1 deficiency promotes atherosclerotic lesion formation in a complex manner that includes the modulation of lipid metabolism and inflammation.

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