Type 2 Diabetes Impairs Insulin Receptor Substrate-2-Mediated Phosphatidylinositol 3-Kinase Activity in Primary Macrophages to Induce a State of Cytokine Resistance to IL-4 in Association with Overexpression of Suppressor of Cytokine Signaling-3

Exploring Visceral and Subcutaneous Adipose Tissue Secretomes in Human Obesity: Implications for Metabolic Disease

Adipose tissue secretions are depot-specific and vary based on anatomical location. Considerable attention has been focused on visceral (VAT) and subcutaneous (SAT) adipose tissue with regard to metabolic disease, yet our knowledge of the secretome from these depots is incomplete. We conducted a comprehensive analysis of VAT and SAT secretomes in the context of metabolic function. Conditioned media generated using SAT and VAT explants from individuals with obesity were analyzed using proteomics, mass spectrometry, and multiplex assays. Conditioned media were administered in vitro to rat hepatocytes and myotubes to assess the functional impact of adipose tissue signaling on insulin responsiveness. VAT secreted more cytokines (IL-12p70, IL-13, TNF-α, IL-6, and IL-8), adipokines (matrix metalloproteinase-1, PAI-1), and prostanoids (TBX2, PGE2) compared with SAT. Secretome proteomics revealed differences in immune/inflammatory response and extracellular matrix components. In vitro, VAT-conditioned media decreased hepatocyte and myotube insulin sensitivity, hepatocyte glucose handling, and increased basal activation of inflammatory signaling in myotubes compared with SAT. Depot-specific differences in adipose tissue secretome composition alter paracrine and endocrine signaling. The unique secretome of VAT has distinct and negative impact on hepatocyte and muscle insulin action.

Quantifying the inflammatory secretome of human intermuscular adipose tissue

Adipose tissue secretes an abundance of lipid and protein mediators, and this secretome is depot-specific, with local and systemic effects on metabolic regulation. Intermuscular adipose tissue (IMAT) accumulates within the skeletal muscle compartment in obesity, and is associated with insulin resistance and metabolic disease. While the human IMAT secretome decreases insulin sensitivity in vitro, its composition is entirely unknown. The current study was conducted to investigate the composition of the human IMAT secretome, compared to that of the subcutaneous (SAT) and visceral adipose tissue (VAT) depots. IMAT, SAT, and VAT explants from individuals with obesity were used to generate conditioned media. Proteomics analysis of conditioned media was performed using multiplex proximity extension assays, and eicosanoid analysis using liquid chromatography-tandem mass spectrometry. Compared to SAT and/or VAT, IMAT secreted significantly more cytokines (IL2, IL5, IL10, IL13, IL27, FGF23, IFNγ and CSF1) and chemokines (MCP1, IL8, CCL11, CCL20, CCL25 and CCL27). Adipokines hepatocyte growth factor and resistin were secreted significantly more by IMAT than SAT or VAT. IMAT secreted significantly more eicosanoids (PGE2, TXB2 , 5-HETE, and 12-HETE) compared to SAT and/or VAT. In the context of obesity, IMAT is a distinct adipose tissue with a highly immunogenic and inflammatory secretome, and given its proximity to skeletal muscle, may be critical to glucose regulation and insulin resistance.

Interleukin-4 Induces the Release of Opioid Peptides from M1 Macrophages in Pathological Pain

Interleukin-4 (IL-4) is an anti-inflammatory cytokine, which can be protective in inflammatory and neurologic disorders, and can alleviate pain. Classically, IL-4 diminishes pain by blocking the production of proinflammatory cytokines. Here, we uncovered that IL-4 induces acute antinociception by IL-4 receptor α (IL-4Rα)-dependent release of opioid peptides from M1 macrophages at injured nerves. As a model of pathologic pain, we used a chronic constriction injury (CCI) of the sciatic nerve in male mice. A single application of IL-4 at the injured nerves (14 d following CCI) attenuated mechanical hypersensitivity evaluated by von Frey filaments, which was reversed by co-injected antibody to IL-4Rα, antibodies to opioid peptides such as Met-enkephalin (ENK), β-endorphin and dynorphin A 1-17, and selective antagonists of δ-opioid, µ-opioid, and κ-opioid receptors. Injured nerves were predominately infiltrated by proinflammatory M1 macrophages and IL-4 did not change their numbers or the phenotype, assessed by flow cytometry and qRT-PCR, respectively. Macrophages isolated from damaged nerves by immunomagnetic separation (IMS) and stimulated with IL-4 dose dependently secreted all three opioid peptides measured by immunoassays. The IL-4-induced release of ENK was diminished by IL-4Rα antibody, intracellular Ca²⁺ chelator, and inhibitors of protein kinase A (PKA), phosphoinositide 3-kinase (PI3K), and ryanodine receptors. Together, we identified a new opioid mechanism underlying the IL-4-induced antinociception that involves PKA-mediated, PI3K-mediated, ryanodine receptor-mediated, and intracellular Ca²⁺-mediated release from M1 macrophages of opioid peptides, which activate peripheral opioid receptors in injured tissue.SIGNIFICANCE STATEMENT Interleukin-4 (IL-4) is an anti-inflammatory cytokine, which can ameliorate pain. The IL-4-mediated effects are considered to mostly result from the inhibition of the production of proinflammatory mediators (e.g., IL-1β, tumor necrosis factor, prostaglandin E2). Here, we found that IL-4 injected at the injured nerves attenuates pain by releasing opioid peptides from the infiltrating macrophages in mice. The opioids were secreted by IL-4 in the intracellular Ca²⁺-dependent manner and activated local peripheral opioid receptors. These actions represent a novel mode of IL-4 action, since its releasing properties have not been so far reported. Importantly, our findings suggest that the IL-4-opioid system should be targeted in the peripheral damaged tissue, since this can be devoid of central and systemic side effects.

A data-driven computational model enables integrative and mechanistic characterization of dynamic macrophage polarization

Macrophages are highly plastic immune cells that dynamically integrate microenvironmental signals to shape their own functional phenotypes, a process known as polarization. Here we develop a large-scale mechanistic computational model that for the first time enables a systems-level characterization, from quantitative, temporal, dose-dependent, and single-cell perspectives, of macrophage polarization driven by a complex multi-pathway signaling network. The model was extensively calibrated and validated against literature and focused on in-house experimental data. Using the model, we generated dynamic phenotype maps in response to numerous combinations of polarizing signals; we also probed into an in silico population of model-based macrophages to examine the impact of polarization continuum at the single-cell level. Additionally, we analyzed the model under an in vitro condition of peripheral arterial disease to evaluate strategies that can potentially induce therapeutic macrophage repolarization. Our model is a key step toward the future development of a network-centric, comprehensive "virtual macrophage" simulation platform.

Interleukin-4 Restores Insulin Sensitivity in Insulin-Resistant Osteoblasts by Increasing the Expression of Insulin Receptor Substrate 1

Obesity and latent inflammation can give rise to insulin resistance and type 2 diabetes. Here we established an insulin resistance model of osteoblasts to explore the restoration effect of anti-inflammatory interleukin-4 (IL-4) on insulin sensitivity and its mechanism. We found that IL-4 inhibited cell proliferation in a concentration- and time-dependent manner. Insulation resistance significantly reduced the phosphorylation levels of the insulin receptor substrate 1 (IRS1; Tyr612), Akt (Ser473), and AS160 (Ser318) proteins. The addition of IL-4 to the insulin resistance model led to a dose-dependent stimulation of the phosphorylation of IRS1, Akt, and AS160. IL-4 fully restored the activation of the insulin cascade in insulin-resistant cells at the concentration of 50 ng/ml. Additionally, IL-4 promoted the expression of IRS1 in a time-dependent manner. We conjecture that IL-4 restores insulin sensitivity in osteoblasts by upregulating the expression of IRS1. It was also found that IL-4 promoted the expression of osteoprotegerin depending on the time of exposure. This effect may play an important role in the regulation of the energy metabolism in the whole body.

Interleukin-4 Improves Metabolic Abnormalities in Leptin-Deficient and High-Fat Diet Mice

Obesity is a metabolic disorder that results from complex interactions between genetic predisposition and dietary factors. Interleukin-4 (IL-4), besides its role in immunity, has metabolic effects on insulin efficacy. We studied the effects of IL-4 on metabolic abnormalities in a mice model of obesity involving leptin deficiency and leptin resistance. Leptin-deficient 145E and leptin-resistant high-fat diet (HFD) mice showed lower levels of circulating IL-4. 145E and HFD mice showed a number of abnormalities: Obesity, hyperglycemia, hyperinsulinemia, insulin resistance, dyslipidemia, liver injury, and adiposity with concurrent inflammation, decreases in Akt, signal transducer and activator of transcription 3 (STAT3), and STAT6 phosphorylation in the hypothalamus, liver, and epididymal fat. Independent of leptin-deficient obesity and dietary obesity, a course of 8-week IL-4 supplementation improved obesity and impairment in Akt, STAT3, and STAT6 signaling. Amelioration of cytokine expression, despite variable extents, was closely linked with the actions of IL-4. Additionally, the browning of white adipocytes by IL-4 was found in epididymal white adipose tissues and 3T3-L1 preadipocytes. Chronic exercise, weight management, and probiotics are recommended to overweight patients and IL-4 signaling is associated with clinical improvement. Thus, IL-4 could be a metabolic regulator and antiobesity candidate for the treatment of obesity and its complications.

Attributes of alternatively activated (M2) macrophages

Macrophages are cells of innate immunity and are derived from circulating monocytes and embryonic yolk sac. They exhibit high plasticity and polarize functionally in response to stimulus triggering it into classically activated M1 macrophages and alternatively activated M2 macrophages. This review summarizes markers of M2 macrophages like transmembrane surface receptors and signaling cascades initiated on their activation; cytokine and chemokine repertoires along with their receptors; and genetic markers and their involvement in immunomodulation. The detailed discussion emphasizes the role of these markers in imparting functional benefits to this subset of macrophages which define their venture in various physiological and pathological conditions.

A preliminary study of the relation between IL-4 and hypertension in type II diabetes mellitus

Clinical outcome of T2DM can be influenced by a polymorphism of different cytokines. The aim of this study was to evaluate the effect of genetic variation and gene expression of IL-4 in T2DM patients. This study was carried out on type II diabetic patients and healthy people served as controls. All subjects were submitted to estimation of IL-4 gene polymorphism using VNTR PCR method and gene expression by real-time PCR. There was a significant decrease of IL-4 gene expression and serum IL4 levels in subjects with B2B2 genotypes. A significant positive correlation was found between IL-4 gene expression and the HDL-c levels and negative correlation between serum IL4 levels and LDLc. Also, a negative correlation was found between serum IL4 and gene expression with both systolic and diastolic blood pressure levels in patients group. It can be concluded that IL-4 gene expression and serum IL4 reduction in patients with B2B2 genotypes has a relation to dyslipidemia and hypertension in the patient with type 2 diabetes mellitus.

Insulin Receptor Substrate 2 Controls Insulin-Mediated Vasoreactivity and Perivascular Adipose Tissue Function in Muscle

Introduction: Insulin signaling in adipose tissue has been shown to regulate insulin's effects in muscle. In muscle, perivascular adipose tissue (PVAT) and vascular insulin signaling regulate muscle perfusion. Insulin receptor substrate (IRS) 2 has been shown to control adipose tissue function and glucose metabolism, and here we tested the hypothesis that IRS2 mediates insulin's actions on the vessel wall as well as the vasoactive properties of PVAT.

Methods: We studied PVAT and muscle resistance arteries (RA) from littermate IRS2^+/+ and IRS2^−/− mice and vasoreactivity by pressure myography, vascular insulin signaling, adipokine expression, and release and PVAT morphology. As insulin induced constriction of IRS2^+/+ RA in our mouse model, we also exposed RA's of C57/Bl6 mice to PVAT from IRS2^+/+ and IRS2^−/− littermates to evaluate vasodilator properties of PVAT.

Results: IRS2^−/− RA exhibited normal vasomotor function, yet a decreased maximal diameter compared to IRS2^+/+ RA. IRS2^+/+ vessels unexpectedly constricted endothelin-dependently in response to insulin, and this effect was absent in IRS2^−/− RA due to reduced ERK1/2activation. For evaluation of PVAT function, we also used C57/Bl6 vessels with a neutral basal effect of insulin. In these experiments insulin (10.0 nM) increased diameter in the presence of IRS2^+/+ PVAT (17 ± 4.8, p = 0.014), yet induced a 10 ± 7.6% decrease in diameter in the presence of IRS2^−/− PVAT. Adipocytes in IRS2^−/− PVAT (1314 ± 161 μm²) were larger (p = 0.0013) than of IRS2^+/+ PVAT (915 ± 63 μm²). Adiponectin, IL-6, PAI-1 secretion were similar between IRS2^+/+ and IRS2^−/− PVAT, as were expression of pro-inflammatory genes (TNF-α, CCL2) and adipokines (adiponectin, leptin, endothelin-1). Insulin-induced AKT phosphorylation in RA was similar in the presence of IRS2^−/− and IRS2^+/+ PVAT.

Conclusion: In muscle, IRS2 regulates both insulin's vasoconstrictor effects, mediating ERK1/2-ET-1 activation, and its vasodilator effects, by mediating the vasodilator effect of PVAT. The regulatory role of IRS2 in PVAT is independent from adiponectin secretion.

Association of interleukin-6 polymorphisms with obesity or metabolic traits in young Mexican-Americans

Objective

The objective of the study is to investigate the association of interleukin-6 (IL6) promoter single-nucleotide polymorphisms rs1800797 (-597 G/A) and rs1800796 (-572 G/C) with obesity or metabolic syndrome in Mexican-Americans.

Methods

The rs1800797 and rs1800796 single-nucleotide polymorphisms were genotyped in Mexican-Americans (n = 437) from South Texas, and results were correlated with measures of obesity and metabolic syndrome including body mass index, waist circumference, blood pressure, cholesterol, triglycerides, glucose, liver enzymes, plasma IL6 and high-sensitive C-reactive protein (hs-CRP).

Results

Significant associations were found for the rs1800796 variant with increased waist circumference, insulin resistance, lower IL6 levels and higher hs-CRP levels. The rs1800797 variant showed no associations with metabolic traits but was associated with higher IL6 levels and lower hs-CRP levels.

Conclusions

Findings in this study support the anti-inflammatory, anti-obesity and glucose homeostatic roles of IL6 in Mexican-American youth.

Abdominal Obesity and Type 2 Diabetes Mellitus are Associated With Higher Seric Levels of IL 4 in Adults

Aims: Study of IL4 in relation to the anthropometric, biochemical and immunological parameters in patients with obesity and/or diabetes. Methods: The relationship between IL4 and clinical and biological parameters was studied in 76 patients divided into 4 groups: obese diabetics (OD), n = 25; obese without diabetes (O), n = 25; non obese diabetics (NOD), n = 11; controls (M), n = 15. IL4 was determined using the ELISA method. Statistical analysis was done using the MedCalc statistical software, version 16.1. Results: Serum IL4 was 0.38 ±0,40 pg / mL in the Control group, 0.366 (0,100-2,35) pg / ml in group O, 4.66±3.73 pg / ml in group OD, 0.30 (0.10-1.35) pg / ml in NOD. When IL4 levels were compared between the four groups, statistical significance was reached for the comparison between groups OD and M. Statistically significant correlations were detected between IL4 and age, waist circumference and hip circumference, blood glucose, glycated hemoglobin (HbA1c), VLDL, triglycerides and serum protein fraction β1. In univariate regression, the IL4 level predictors were age, height, BMI, abdominal circumference, hip circumference, beta 1% glucose, HbA1c, total lipids, total cholesterol, VLDL triglycerides, CRP. In multivariate regression, waist circumference and glycemia were significant predictors of levels of IL4 (p = 0.0001).

SOCS3 is a modulator of human macrophage phagocytosis

Suppressor of cytokine signaling (SOCS) proteins are recognized as key feedback inhibitors modulating the inflammatory activities of macrophages, but comparatively little is known about whether and how they affect phagocytosis. Here, we evaluated the role of SOCS3 in driving the inflammatory phenotype and phagocytic uptake of apoptotic cells by human macrophages and the signaling pathways that are necessary for efficient phagocytosis. In M1-activated human monocyte-derived macrophages, SOCS3 silencing, using short interfering RNA technology, resulted in a decreased expression of proinflammatory markers and an increased expression of M2 macrophage markers. Strikingly, we demonstrated for the first time that SOCS3 knockdown significantly enhances the phagocytic capacity of M1 macrophages for carboxylate-modified beads and apoptotic neutrophils. With the use of live-cell video microscopy, we showed that SOCS3 knockdown radically affects the temporal dynamics of particle engulfment, enabling more rapid uptake of a second target and delaying postengulfment processing, as evidenced by deferred acquisition of phagosome maturation markers. SOCS3 knockdown impacts on phagocytosis through increased PI3K and Ras-related C3 botulinum toxin substrate 1 (Rac1) activity, pathways essential for engulfment and clearance of apoptotic cells. Enhanced phagocytosis in SOCS3-silenced cells was reversed by pharmacological PI3K inhibition. Furthermore, we revealed that actin polymerization, downstream of PI3K/Rac1 activation, was significantly altered in SOCS3-silenced cells, providing a mechanism for their greater phagocytic activity. The findings support a new model, whereby SOCS3 not only plays an important role in driving macrophage inflammatory responses but modulates key signaling pathways organizing the actin cytoskeleton to regulate the efficiency of phagocytic processes.

Asparaginase treatment side-effects may be due to genes with homopolymeric Asn codons (Review-Hypothesis)

The present treatment of childhood T-cell leukemias involves the systemic administration of prokary-otic L-asparaginase (ASNase), which depletes plasma Asparagine (Asn) and inhibits protein synthesis. The mechanism of therapeutic action of ASNase is poorly understood, as are the etiologies of the side-effects incurred by treatment. Protein expression from genes bearing Asn homopolymeric coding regions (N-hCR) may be particularly susceptible to Asn level fluctuation. In mammals, N-hCR are rare, short and conserved. In humans, misfunctions of genes encoding N-hCR are associated with a cluster of disorders that mimic ASNase therapy side-effects which include impaired glycemic control, dislipidemia, pancreatitis, compromised vascular integrity, and neurological dysfunction. This paper proposes that dysregulation of Asn homeostasis, potentially even by ASNase produced by the microbiome, may contribute to several clinically important syndromes by altering expression of N-hCR bearing genes. By altering amino acid abundance and modulating ribosome translocation rates at codon repeats, the microbiomic environment may contribute to genome decoding and to shaping the proteome. We suggest that impaired translation at poly Asn codons elevates diabetes risk and severity.

Non-transcriptional regulation of NLRP3 inflammasome signaling by IL-4

Th2 cytokine IL-4 has been previously shown to suppress the production of proinflammatory cytokines in monocytes. However, the underlying molecular mechanism by which IL-4 signaling antagonizes proinflammatory responses is poorly characterized. In particular, whether IL-4 can modulate inflammasome signaling remains unknown. Here, we provide evidence that IL-4 suppresses NLRP3-dependent caspase-1 activation and the subsequent IL-1β secretion but does not inhibit absent in melanoma 2 (AIM2)- or NLRC4 (NOD-like receptor family, CARD domain-containing 4)-dependent caspase-1 activation in THP-1 and mouse bone marrow-derived macrophages. Upon lipopolysaccharide (LPS) or LPS/ATP stimulation, IL-4 markedly inhibited the assembly of NLRP3 inflammasome, including NLRP3-dependent ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) oligomerization, NLRP3-ASC interaction and NLRP3 speck-like oligomeric structure formation. The negative regulation of NLRP3 inflammasome by IL-4 was not due to the impaired mRNA or protein production of NLRP3 and proinflammatory cytokines. Supporting this observation, IL-4 attenuated NLRP3 inflammasome activation even in reconstituted NLRP3-expressing macrophages in which NLRP3 expression is not transcriptionally regulated by TLR-NF-κB signaling. Furthermore, the IL-4-mediated suppression of NLRP3 inflammasome was independent of STAT6-dependent transcription and mitochondrial reactive oxygen species (ROS). Instead, IL-4 inhibited subcellular redistribution of NLRP3 into mitochondria and microtubule polymerization upon NLRP3-activating stimulation. Our results collectively suggest that IL-4 could suppress NLRP3 inflammasome activation in a transcription-independent manner, thus providing an endogenous regulatory machinery to prevent excessive inflammasome activation.

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

A critical role for suppressor of cytokine signalling 3 in promoting M1 macrophage activation and function in vitro and in vivo

Macrophages respond to their microenvironment and develop polarized functions critical for orchestrating appropriate inflammatory responses. Classical (M1) activation eliminates pathogens while alternative (M2) activation promotes regulation and repair. M1 macrophage activation is strongly associated with suppressor of cytokine signalling 3 (SOCS3) expression in vitro, but the functional consequences of this are unclear and the role of SOCS3 in M1-macrophage polarization in vivo remains controversial. To address these questions, we defined the characteristics and function of SOCS3-expressing macrophages in vivo and identified potential mechanisms of SOCS3 action. Macrophages infiltrating inflamed glomeruli in a model of acute nephritis show significant up-regulation of SOCS3 that co-localizes with the M1-activation marker, inducible nitric oxide synthase. Numbers of SOCS3(hi) -expressing, but not SOCS1(hi) -expressing, macrophages correlate strongly with the severity of renal injury, supporting their inflammatory role in vivo. Adoptive transfer of SOCS3-short interfering RNA-silenced macrophages into a peritonitis model demonstrated the importance of SOCS3 in driving production of pro-inflammatory IL-6 and nitric oxide, while curtailing expression of anti-inflammatory IL-10 and SOCS1. SOCS3-induced pro-inflammatory effects were due, at least in part, to its role in controlling activation and nuclear accumulation of nuclear factor-κB and activity of phosphatidylinositol 3-kinase. We show for the first time that SOCS3 also directs the functions of human monocyte-derived macrophages, including efficient M1-induced cytokine production (IL-1β, IL-6, IL-23, IL-12), attenuated signal transducer and activator of transcription 3 activity and ability of antigen-loaded macrophages to drive T-cell responses. Hence, M1-associated SOCS3 was a positive regulator of pro-inflammatory responses in our rodent models and up-regulated SOCS3 is essential for effective M1-macrophage activation and function in human macrophages.

Urine miRNAs: potential biomarkers for monitoring progression of early stages of diabetic nephropathy

With a steep increase in the incidence of type 1 and 2 diabetes globally, diabetic nephropathy (DN) has now become the leading cause of renal failure in the world. There are no suitable biomarkers for the diagnosis of early stages of DN. In recent years, tremendous efforts are being made worldwide to delineate the role of micro RNAs in the pathogenesis of DN. Circulating miRNAs in serum, plasma, urine and other body fluids, which reflect a response to various pathophysiological stresses, are being investigated in the context of diabetic nephropathy. Delineation of the changes in miRNA levels in patients with DN may lead to a better understanding of the progression of the disease. We present here an exhaustive survey of the miRNA literature, highlighting various studies performed over the last decade. The aim is to assess if changes in various miRNAs could correlate with the progression of diabetic nephropathy. Based on the survey, we found that miRNA-377, miRNA-192, miRNA-216/217 and miRNA-144 are increased in body fluids of patients with DN, while miRNA-21 and miRNA-375 are decreased. Overall, there are a very few miRNAs that are kidney specific, and although significant differences were observed in the urinary excretion of certain miRNAs, they were not correlative to their levels in the blood or plasma. Thus, it is completely plausible that urine-specific miRNAs could serve as novel biomarkers for the diagnosis of early stages of diabetic nephropathy.

Altered polarization, morphology, and impaired innate immunity germane to resident peritoneal macrophages in mice with long-term type 2 diabetes

Type 2 diabetes (T2D) is associated with perturbed innate immunity. Macrophages, bridging innate immunity and metabolic disturbances, play important roles in controlling immune homeostasis. However, the effect of long-term diabetic milieu (DM) on the functions and phenotypes of macrophages is still not clear. In this study, we used resident peritoneal macrophages (RPMs) from 5-month-old db/db mice to investigate the changes of macrophages. It was found that RPMs in db/db mice significantly reduced phagocytosis and adhesion capacity. After standardization with body weight, the number of F4/80⁺ RPMs markedly reduced in db/db mice, and, furthermore, the macrophages skewed to M2-polarizated macrophages. The results of morphology found that the RPMs shape of db/db mice was nearly round, but the RPMs shape of control mice was spindle-shaped and irregular. In this study, we found the cell numbers, morphology, and innate immunity functions of RPMs in 5-month-old type 2 diabetic mice (db/db mice) obtained by abdominal cavity lavage were significantly altered. Importantly, we also found the remarkably increased M2-RPMs in diabetic mice for the first time.

Lipopolysaccharide-induced interleukin (IL)-4 receptor-α expression and corresponding sensitivity to the M2 promoting effects of IL-4 are impaired in microglia of aged mice

In several models of aging, microglia become more inflammatory and reactive to immune challenges. For example, peripheral LPS injection causes exaggerated microglial activation associated with prolonged sickness and depressive-like behavior in aged BALB/c mice. Therefore, the purpose of this study was to determine the extent to which age-related amplified microglial activation was associated with reduced sensitivity to the anti-inflammatory and M2 promoting cytokines interleukin (IL)-10 and IL-4. In initial studies with adult mice, LPS induced a time-dependent increase in M1 and M2 mRNA profiles in microglia. Furthermore, peripheral LPS injection markedly increased surface expression of IL-4 receptor-alpha (IL-4Rα), but not IL-10 receptor-1 (IL-10R1) on microglia. In BV-2 cells, IL-4, but not IL-10, re-directed LPS-activated microglia towards an M2 phenotype. Based on these findings, comparisons of M1 and M2 activation profiles, induction of IL-4Rα, and sensitivity to IL-4 were determined in microglia from adult (3-4 mo) and aged (18-22 mo) mice. In aged microglia, LPS promoted an exaggerated and prolonged M1 and M2 profile compared to adults. Moreover, IL-4Rα protein was not increased on aged microglia following LPS injection. To determine the consequence of impaired IL-4Rα upregulation, adult and aged mice were injected with LPS and activated microglia were then isolated and treated ex vivo with IL-4. While ex vivo IL-4 induced an M2 profile in activated microglia from adult mice, activated microglia from aged mice retained a prominent M1 profile. These data indicate that activated microglia from aged mice are less sensitive to the anti-inflammatory and M2-promoting effects of IL-4.

Role and function of macrophages in the metabolic syndrome

Macrophages are key innate immune effector cells best known for their role as professional phagocytes, which also include neutrophils and dendritic cells. Recent evidence indicates that macrophages are also key players in metabolic homoeostasis. Macrophages can be found in many tissues, where they respond to metabolic cues and produce pro- and/or anti-inflammatory mediators to modulate metabolite programmes. Certain metabolites, such as fatty acids, ceramides and cholesterol crystals, elicit inflammatory responses through pathogen-sensing signalling pathways, implicating a maladaptation of macrophages and the innate immune system to elevated metabolic stress associated with overnutrition in modern societies. The outcome of this maladaptation is a feedforward inflammatory response leading to a state of unresolved inflammation and a collection of metabolic pathologies, including insulin resistance, fatty liver, atherosclerosis and dyslipidaemia. The present review summarizes what is known about the contributions of macrophages to metabolic diseases and the signalling pathways that are involved in metabolic stress-induced macrophage activation. Understanding the role of macrophages in these processes will help us to develop therapies against detrimental effects of the metabolic syndrome.

IRS-2 deficiency in macrophages promotes their accumulation in the vascular wall

The aim of this study was to investigate the role of insulin receptor substrate-2 (IRS-2) mediated signal in macrophages on the accumulation of macrophages in the vascular wall. Mice transplanted with IRS-2(-/-) bone marrow, a model of myeloid cell restricted defect of IRS-2, showed accumulation of monocyte chemoattractant protein-1-expressing macrophages in the vascular wall. Experiments using cultured peritoneal macrophages showed that IRS-2-mediated signal pathway stimulated by physiological concentrations of insulin, not by IL-4, contributed to the suppression of monocyte chemoattractant protein-1 expression induced by lipopolysaccharide. Our data indicated that IRS-2 deficiency in macrophages enhanced their accumulation in the vascular wall accompanied by increased expression of proinflammatory mediators in macrophages. These results suggest a role for insulin resistance in macrophages in early atherosclerogenesis.

Suppressor of cytokine signaling (SOCS)1 is a key determinant of differential macrophage activation and function

Macrophages become activated by their environment and develop polarized functions: classically activated (M1) macrophages eliminate pathogens but can cause tissue injury, whereas alternatively activated (M2) macrophages promote healing and repair. Mechanisms directing polarized activation, especially in vivo, are not understood completely, and here, we examined the role of SOCS proteins. M2 macrophages activated in vitro or elicited by implanting mice i.p. with the parasitic nematode Brugia malayi display a selective and IL-4-dependent up-regulation of SOCS1 but not SOCS3. Using siRNA-targeted knockdown in BMDM, we reveal that the enhanced SOCS1 is crucial for IL-4-induced M2 characteristics, including a high arginase I:iNOS activity ratio, suppression of T cell proliferation, attenuated responses to IFN-γ/LPS, and curtailed SOCS3 expression. Importantly, SOCS1 was essential in sustaining the enhanced PI3K activity that drives M2 activation, defining a new regulatory mechanism by which SOCS1 controls M2 polarization. By contrast, for M1 macrophages, SOCS1 was not only an important regulator of proinflammatory mediators (IL-6, IL-12, MHC class II, NO), but critically, for M1, we show that SOCS1 also restricted IL-10 secretion and arginase I activity, which otherwise would limit the efficiency of M1 macrophage proinflammatory responses. Together, our results uncover SOCS1, not only as a feedback inhibitor of inflammation but also as a critical molecular switch that tunes key signaling pathways to effectively program different sides of the macrophage balance.

Impact of streptozotocin-induced diabetes on functional responses of dendritic cells and macrophages towards Burkholderia pseudomallei

Diabetes mellitus is a documented risk factor for melioidosis, a tropical infection caused by Burkholderia pseudomallei. The increased susceptibility of diabetic individuals to infections with other pathogens has been associated with immune dysregulation. However, the impact of diabetes on the functional responses of dendritic cells (DC) and macrophages during B. pseudomallei infection has not been investigated. This study compared the responses of macrophages and DC towards B. pseudomallei using bone marrow-derived DC (BMDC) and peritoneal elicited macrophages (PEM) isolated from streptozotocin-induced diabetic C57BL/6 mice exhibiting hyperglycaemia for 9 days (acute) or 70 days (chronic) and age-matched nondiabetic C57BL/6 mice. Following coincubation of BMDC and PEM with a highly virulent B. pseudomallei isolate, maturation, bacterial internalization plus intracellular survival and cytokine gene expression profiles were assessed. No significant differences in functional responses of BMDC or PEM isolated from acute diabetic and nondiabetic mice were observed. However, significant differences in BMDC and PEM function were observed when chronic diabetic and nondiabetic mice were compared. This study demonstrates that diabetic mice with extended periods of uncontrolled hyperglycaemia have impaired DC and macrophage function towards B. pseudomallei, which may contribute to the high susceptibility observed in clinical practice.

β-cell specific overexpression of suppressor of cytokine signalling-3 does not protect against multiple low dose streptozotocin induced type 1 diabetes in mice

We investigated the impact of β-cell specific overexpression of suppressor of cytokine signalling-3 (SOCS-3) on the development of multiple low dose streptozotocin (MLDSTZ) induced Type 1 diabetes and the possible mechanisms involved. MLDSTZ treatment was administered to RIP-SOCS-3 transgenic and wild-type (wt) mice and progression of hyperglycemia monitored. Isolated islets from both strains were exposed to human IL-1β (25U/ml) or a combination of human IL-1β (25U/ml) and murine IFN-γ (1000U/ml) for 24h or 48h and we investigated the expression of IL-1 receptor antagonist (IL-1Ra) mRNA in islet cells and secretion of IL-1Ra into culture medium. MLDSTZ treatment caused gradual hyperglycemia both in the wt mice and in the transgenic mice with the latter tending to be more sensitive. In vitro experiments on wt and transgenic islets did not reveal any differences in sensitivity to damaging effects of STZ. Exposure of wt islets to IL-1β or IL-1β+IFN-γ seemed to lead to a failing IL-1Ra response from SOCS-3 transgenic islets. It could be that an increased expression of a possible protective molecule against β-cell destruction may lead to a dampered response of another putative protective molecule. This may have counteracted a protective effect against MLDSTZ in SOCS-3 transgenic mice.

Alternative activation of tumor-associated macrophages by IL-4: priming for protumoral functions

Although macrophages were originally recognized as major immune effector cells, it is now appreciated that they also play many important roles in the maintenance of tissue homeostasis, and are involved in a variety of pathological conditions including cancer. Several studies have demonstrated the contributions of tumor-associated macrophages (TAMs) to tumor initiation, progression, and metastasis. However, the detailed mechanisms underlying how TAMs differ molecularly from their normal counterparts and how the conversion to TAMs occurs have only just begun to be understood. TAMs have been proposed to exhibit phenotypes of 'alternatively activated' macrophages, though there has been limited evidence directly linking the phenotypes of TAMs to the alternative activation of macrophages. This review will focus on IL-4, the prototypic cytokine that induces the alternative activation of macrophages, and review current knowledge regarding the contributions of IL-4 to the phenotypes of TAMs and its effects on tumorigenesis.

Sickness behavior induced by endotoxin can be mitigated by the dietary soluble fiber, pectin, through up-regulation of IL-4 and Th2 polarization

Peripheral activation of the immune system by infectious agents triggers the brain-cytokine system causing sickness behaviors which profoundly impact well-being. Dietary fiber is a beneficial foodstuff that, from a gastrointestinal tract perspective, exists in both insoluble and soluble forms. We show that a diet rich in soluble fiber protects mice from endotoxin-induced sickness behavior by polarizing mice Th2 when compared to a diet containing only insoluble fiber. Mice fed soluble fiber became less sick and recovered faster from endotoxin-induced sickness behaviors than mice fed insoluble fiber. In response to intraperitoneal endotoxin, mice fed soluble fiber had up-regulated IL-1RA and reduced IL-1beta and TNF-alpha in the brain as compared to mice fed insoluble fiber. Importantly, mice fed soluble fiber had a basal increase in IL-4 in the ileum and spleen which was absent in MyD88 knockout mice. Con-A stimulated splenocytes from mice fed soluble fiber showed increased IL-4 and IL-5 and decreased IL-2, IL-12 and IFN-gamma when compared to mice fed insoluble fiber. Likewise, endotoxin-stimulated macrophages from mice fed soluble fiber demonstrated decreased IL-1beta, TNF-alpha, IFN-gamma, IL-12 and nitrate and increased IL-1RA, arginase 1 and Ym1 when compared to mice fed insoluble fiber. Finally, the behavioral protection afforded by feeding mice soluble fiber was reduced in IL-4 knockout mice, as was the impact of soluble fiber on Con-A stimulated splenocytes and endotoxin activated macrophages. These data show that a diet rich in soluble fiber protects against endotoxin-induced sickness behavior by polarizing mice Th2 and promoting alternative activation of macrophages.

Psychoneuroimmune implications of type 2 diabetes: redux

A sizable body of knowledge has arisen demonstrating that type 2 diabetes (T2D) is associated with alterations in the innate immune system. The resulting proinflammatory-leaning imbalance is implicated in the development of secondary disease complications and comorbidities, such as delayed wound healing, accelerated progress of atherosclerosis, and retinopathy, in people who have T2D. New experimental data and the results of recently published health-related quality-of-life surveys indicate that individuals who have T2D experience diminished feelings of happiness, well being, and satisfaction with life. These emotional and psychological consequences of T2D point to altered neuroimmunity as a previously unappreciated complication of T2D. This article discusses recent data detailing the impact of T2D on a person's PNI response.

Macropinocytosis is decreased in diabetic mouse macrophages and is regulated by AMPK

BACKGROUND

Macrophages (MPhis) utilize macropinocytosis to integrate immune and metabolic signals in order to initiate an effective immune response. Diabetes is characterized by metabolic abnormalities and altered immune function. Here we examine the influence of diabetes on macropinocytosis in primary mouse macrophages and in an in vitro diabetes model.

RESULTS

The data demonstrate that peritoneal MPhis from diabetic (db/db) mice had reduced macropinocytosis when compared to MPhis from non-diabetic (db/+) mice. Additionally, MPhis cultured in hyperglycemic conditions were less adept at macropinocytosis than those cultured in low glucose. Notably, AMP-activated protein kinase (AMPK) activity was decreased in MPhis cultured in hyperglycemic conditions. Activation of AMPK with leptin or 5-aminoimidazole-4-carboxamide-1-beta-riboside (AICAR) increased macropinocytosis and inhibition of AMPK with compound C decreased macropinocytosis.

CONCLUSION

Taken together, these findings indicate that MPhis from diabetic mice have decreased macropinocytosis. This decrease appears dependent on reduced AMPK activity. These results demonstrate a previously unrealized role for AMPK in MPhis and suggest that increasing AMPK activity in diabetic MPhis could improve innate immunity and decrease susceptibility to infection.

Unique expression of suppressor of cytokine signaling 3 is essential for classical macrophage activation in rodents in vitro and in vivo

On infiltrating inflamed tissue, macrophages respond to the local microenvironment and develop one of two broad phenotypes: classically activated (M1) macrophages that cause tissue injury and alternatively activated macrophages that promote repair. Understanding how this polarization occurs in vivo is far from complete, and in this study, using a Th1-mediated macrophage-dependent model of acute glomerulonephritis, nephrotoxic nephritis, we examine the role of suppressor of cytokine signaling (SOCS)1 and SOCS3. Macrophages in normal kidneys did not express detectable SOCS proteins but those infiltrating inflamed glomeruli were rapidly polarized to express either SOCS1 (27 +/- 6%) or SOCS3 (54 +/- 12%) but rarely both (10 +/- 3%). Rat bone marrow-derived macrophages incubated with IFN-gamma or LPS expressed SOCS1 and SOCS3, whereas IL-4 stimulated macrophages expressed SOCS1 exclusively. By contrast, incubation with IFN-gamma and LPS together suppressed SOCS1 while uniquely polarizing macrophages to SOCS3 expressing cells. Macrophages in which SOCS3 was knocked down by short interfering RNA responded to IFN-gamma and LPS very differently: they had enhanced STAT3 activity; induction of macrophage mannose receptor, arginase and SOCS1; restoration of IL-4 responsiveness that is inhibited in M1 macrophages; and decreased synthesis of inflammatory mediators (NO and IL-6) and costimulatory molecule CD86, demonstrating that SOCS3 is essential for M1 activation. Without it, macrophages develop characteristic alternatively activated markers when exposed to classical activating stimuli. Lastly, increased glomerular IL-4 in nephrotoxic nephritis inhibits infiltrating macrophages from expressing SOCS3 and was associated with attenuated glomerular injury. Consequently, we propose that SOCS3 is essential for development of M1 macrophages in vitro and in vivo.