Macrophage alternative activation confers protection against lipotoxicity-induced cell death.

OBJECTIVE: Alternative activation (M2) of adipose tissue resident macrophage (ATM) inhibits obesity-induced metabolic inflammation. The underlying mechanisms remain unclear. Recent studies have shown that dysregulated lipid homeostasis caused by increased lipolysis in white adipose tissue (WAT) in the obese state is a trigger of inflammatory responses. We investigated the role of M2 macrophages in lipotoxicity-induced inflammation. METHODS: We used microarray experiments to profile macrophage gene expression regulated by two M2 inducers, interleukin-4 (Il-4), and peroxisome proliferator-activated receptor delta/gamma (Pparδ/Pparγ) agonists. Functional validation studies were performed in bone marrow-derived macrophages and mice deprived of the signal transducer and activator of transcription 6 gene (Stat6; downstream effector of Il-4) or Pparδ/Pparγ genes (downstream effectors of Stat6). Palmitic acid (PA) and ß-adrenergic agonist were employed to induce macrophage lipid loading in vitro and in vivo, respectively. RESULTS: Profiling of genes regulated by Il-4 or Pparδ/Pparγ agonists reveals that alternative activation promotes the cell survival program, while inhibiting that of inflammation-related cell death. Deletion of Stat6 or Pparδ/Pparγ increases the susceptibility of macrophages to PA-induced cell death. NLR family pyrin domain containing 3 (Nlrp3) inflammasome activation by PA in the presence of lipopolysaccharide is also increased in Stat6-/- macrophages and to a lesser extent, in Pparδ/γ-/- macrophages. In concert, ß-adrenergic agonist-induced lipolysis results in higher levels of cell death and inflammatory markers in ATMs derived from myeloid-specific Pparδ/γ-/- or Stat6-/- mice. CONCLUSIONS: Our data suggest that ATM cell death is closely linked to metabolic inflammation. Within WAT where concentrations of free fatty acids fluctuate, M2 polarization regulated by the Stat6-Ppar axis enhances ATM's tolerance to lipid-mediated stress, thereby maintaining the homeostatic state.

Effects of iron supplementation in mice with hypoferremia induced by obesity.

Iron is an important micronutrient, but it can also act as a dangerous element by interfering with glucose homeostasis and inflammation, two features that are already disturbed in obese subjects. In this work, we study the effects of systemic iron supplementation on metabolic and inflammatory responses in mice with hypoferremia induced by obesity to better characterize whether iron worsens the parameters that are already altered after 24 weeks of a high-fat diet (HFD). Mice were maintained on a control diet or a HFD for 24 weeks and received iron-III polymaltose (50 mg/kg/every 2 days) during the last two weeks. Glucose homeostasis (basal glucose and insulin test tolerance) and systemic and visceral adipose tissue (VAT) inflammation were assessed. Iron levels were measured in serum. The Prussian blue reaction was used in isolated macrophages to detect iron deposition. Iron supplementation resulted in an increased number of VAT macrophages that were positive for Prussian blue staining as well as increased serum iron levels. Systemic hepcidin, leptin, resistin, and monocyte chemoattractant protein-1 (MCP-1) levels were not altered by iron supplementation. Local adipose tissue inflammation was also not made worse by iron supplementation because the levels of hepcidin, MCP-1, leptin, and interleukin (IL)-6 were not altered. In contrast, iron supplementation resulted in an increased production of IL-10 by adipose tissue and VAT macrophages. Leukocytosis and VAT plasminogen activator inhibitor-1 (PAI-1) level were reduced, but insulin resistance was not altered after iron supplementation. In conclusion, systemic iron supplementation in mice with hypoferremia induced by obesity did not worsen inflammatory marker or adipose tissue inflammation or the metabolic status established by obesity. Iron deposition was observed in adipose tissue, mainly in macrophages, suggesting that these cells have mechanisms that promote iron incorporation without increasing the production of inflammatory mediators.

Beneficial effects of Brazilian propolis on type 2 diabetes in ob/ob mice: Possible involvement of immune cells in mesenteric adipose tissue.

The anti-diabetic effects of Brazilian propolis were examined using ob/ob mice. Although repeated injection of an ethanol extract of Brazilian propolis (100 mg/kg, ip, twice a week for 12 weeks) did not affect body weight gain and food intake of ob/ob mice, blood glucose and plasma cholesterol levels were significantly attenuated. Moreover, the propolis extract partially restored glucose tolerance and insulin resistance, indicating anti-diabetic properties of the extract. The propolis-treated mice exhibited lower weight gain in mesenteric adipose tissue, while weight gains in inguinal and epididymal adipose tissues were not modulated. Flow cytometric and microscopic analyses suggested that the extract promoted accumulation of eosinophils into mesenteric and epididymal adipose tissues. Alternatively, the ratio of M1-like macrophages to M2-like macrophages in mesenteric adipose tissue was reduced by the propolis injection, coincident with the decrement of the number of interleukin-12A(+) cells. Levels of M1 macrophage markers, such as Itgax and Il12b transcripts, were decreased in the vascular stromal fraction of mesenteric adipose tissue, whereas those of pan-macrophage markers Emr1 and Cd68 were not influenced. Microarray and subsequent gene ontology term analyses suggested that propolis attenuated immune activation in mesenteric adipose tissues. Taken together, this indicates that Brazilian propolis improves diabetes in ob/ob mice, presumably through modification of immune cells in mesenteric adipose tissues.