Isoxanthohumol improves obesity and glucose metabolism via inhibiting intestinal lipid absorption with a bloom of Akkermansia muciniphila in mice.

OBJECTIVE: Polyphenols have health-promoting effects, such as improving insulin resistance. Isoxanthohumol (IX), a prenylated flavonoid found in beer hops, has been suggested to reduce obesity and insulin resistance; however, the mechanism remains unknown. METHODS: High-fat diet-fed mice were administered IX. We analyzed glucose metabolism, gene expression profiles and histology of liver, epididymal adipose tissue and colon. Lipase activity, fecal lipid profiles and plasma metabolomic analysis were assessed. Fecal 16s rRNA sequencing was obtained and selected bacterial species were used for in vitro studies. Fecal microbiota transplantation and monocolonization were conducted to antibiotic-treated or germ-free (GF) mice. RESULTS: The administration of IX lowered weight gain, decreased steatohepatitis and improved glucose metabolism. Mechanistically, IX inhibited pancreatic lipase activity and lipid absorption by decreasing the expression of the fatty acid transporter CD36 in the small intestine, which was confirmed by increased lipid excretion in feces. IX administration increased markers of intestinal barrier function, including thickening the mucin layer and increasing caludin-1, a tight-junction related protein in the colon. In contrast, the effects of IX were nullified by antibiotics. As revealed using 16S rRNA sequencing, the microbial community structure changed with a significant increase in the abundance of Akkermansia muciniphila in the IX-treated group. An anaerobic chamber study showed that IX selectively promoted the growth of A. muciniphila while exhibiting antimicrobial activity against some Bacteroides and Clostridium species. To further explore the direct effect of A. muciniphila on lipid and glucose metabolism, we monocolonized either A. muciniphila or Bacteroides thetaiotaomicron to GF mice. A. muciniphila monocolonization decreased CD36 expression in the jejunum and improved glucose metabolism, with decreased levels of multiple classes of fatty acids determined using plasma metabolomic analysis. CONCLUSIONS: Our study demonstrated that IX prevents obesity and enhances glucose metabolism by inhibiting dietary fat absorption. This mechanism is linked to suppressing pancreatic lipase activity and shifts in microbial composition, notably an increase in A. muciniphila. These highlight new treatment strategies for preventing metabolic syndrome by boosting the gut microbiota with food components.

The gut microbiome: a core regulator of metabolism.

The human body is inhabited by numerous bacteria, fungi, and viruses, and each part has a unique microbial community structure. The gastrointestinal tract harbors approximately 100 trillion strains comprising more than 1000 bacterial species that maintain symbiotic relationships with the host. The gut microbiota consists mainly of the phyla Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Of these, Firmicutes and Bacteroidetes constitute 70-90% of the total abundance. Gut microbiota utilize nutrients ingested by the host, interact with other bacterial species, and help maintain healthy homeostasis in the host. In recent years, it has become increasingly clear that a breakdown of the microbial structure and its functions, known as dysbiosis, is associated with the development of allergies, autoimmune diseases, cancers, and arteriosclerosis, among others. Metabolic diseases, such as obesity and diabetes, also have a causal relationship with dysbiosis. The present review provides a brief overview of the general roles of the gut microbiota and their relationship with metabolic disorders.

Depletion of CD206+ M2-like macrophages induces fibro-adipogenic progenitors activation and muscle regeneration.

Muscle regeneration requires the coordination of muscle stem cells, mesenchymal fibro-adipogenic progenitors (FAPs), and macrophages. How macrophages regulate the paracrine secretion of FAPs during the recovery process remains elusive. Herein, we systemically investigated the communication between CD206+ M2-like macrophages and FAPs during the recovery process using a transgenic mouse model. Depletion of CD206+ M2-like macrophages or deletion of CD206+ M2-like macrophages-specific TGF-ß1 gene induces myogenesis and muscle regeneration. We show that depletion of CD206+ M2-like macrophages activates FAPs and activated FAPs secrete follistatin, a promyogenic factor, thereby boosting the recovery process. Conversely, deletion of the FAP-specific follistatin gene results in impaired muscle stem cell function, enhanced fibrosis, and delayed muscle regeneration. Mechanistically, CD206+ M2-like macrophages inhibit the secretion of FAP-derived follistatin via TGF-ß signaling. Here we show that CD206+ M2-like macrophages constitute a microenvironment for FAPs and may regulate the myogenic potential of muscle stem/satellite cells.

Perioperative C-peptide index is associated with the status of diabetes management after pancreatectomy.

AIMS/INTRODUCTION: This study aimed to identify the clinical factors affecting postoperative residual pancreatic ß-cell function, as assessed by the C-peptide index (CPI), and to investigate the association between perioperative CPI and the status of diabetes management after pancreatectomy. MATERIALS AND METHODS: The associations between perioperative CPI and clinical background, including surgical procedures of pancreatectomy, were analyzed in 47 patients who underwent pancreatectomy, and were assessed for pre-and postoperative CPI. The association between perioperative CPI and glycemic control after pancreatectomy was investigated. RESULTS: The low postoperative CPI group (CPI <0.7) had longer duration of diabetes (17.5 ± 14.5 vs 5.5 ± 11.0 years, P = 0.004), a higher percentage of sulfonylurea users (41.7 vs 8.7%, P = 0.003) and a greater number of drug categories used for diabetes treatment (1.9 ± 1.1 vs 0.8 ± 0.8, P <0.001) than did the high postoperative CPI group. Postoperative CPI was higher (1.4 ± 1.2 vs 0.7 ± 0.6, P = 0.039) in patients with low glycosylated hemoglobin (<7.0%) at 6 months after pancreatectomy; preoperative (2.0 ± 1.5 vs 0.7 ± 0.5, P = 0.012) and postoperative CPI (2.5 ± 1.4 vs 1.4 ± 1.1, P = 0.020) were higher in non-insulin users than in insulin users at 6 months after surgery. CONCLUSIONS: The duration of diabetes and preoperative diabetes treatment were associated with residual pancreatic ß-cell function after pancreatectomy. Furthermore, perioperative ß-cell function as assessed by CPI was associated with diabetes management status after pancreatectomy.

Astaxanthin, a Marine Carotenoid, Maintains the Tolerance and Integrity of Adipose Tissue and Contributes to Its Healthy Functions.

Recently, obesity-induced insulin resistance, type 2 diabetes, and cardiovascular disease have become major social problems. We have previously shown that Astaxanthin (AX), which is a natural antioxidant, significantly ameliorates obesity-induced glucose intolerance and insulin resistance. It is well known that AX is a strong lipophilic antioxidant and has been shown to be beneficial for acute inflammation. However, the actual effects of AX on chronic inflammation in adipose tissue (AT) remain unclear. To observe the effects of AX on AT functions in obese mice, we fed six-week-old male C57BL/6J on high-fat-diet (HFD) supplemented with or without 0.02% of AX for 24 weeks. We determined the effect of AX at 10 and 24 weeks of HFD with or without AX on various parameters including insulin sensitivity, glucose tolerance, inflammation, and mitochondrial function in AT. We found that AX significantly reduced oxidative stress and macrophage infiltration into AT, as well as maintaining healthy AT function. Furthermore, AX prevented pathological AT remodeling probably caused by hypoxia in AT. Collectively, AX treatment exerted anti-inflammatory effects via its antioxidant activity in AT, maintained the vascular structure of AT and preserved the stem cells and progenitor's niche, and enhanced anti-inflammatory hypoxia induction factor-2α-dominant hypoxic response. Through these mechanisms of action, it prevented the pathological remodeling of AT and maintained its integrity.

Generation and characterization of a Meflin-CreERT2 transgenic line for lineage tracing in white adipose tissue.

Meflin (Islr) expression has gained attention as a marker for mesenchymal stem cells, but its function remains largely unexplored. Here, we report the generation of Meflin-CreERT2 mice with CreERT2 inserted under the Meflin gene promoter to label Meflin-expressing cells genetically, thereby enabling their lineages to be traced. We found that in adult mice, Meflin-expressing lineage cells were present in adipose tissue stroma and had differentiated into mature adipocytes. These cells constituted Crown-like structures in the adipose tissue of mice after high-fat diet loading. Cold stimulation led to the differentiation of Meflin-expressing lineage cells into beige adipocytes. Thus, the Meflin-CreERT2 mouse line is a useful new tool for visualizing and tracking the lineage of Meflin-expressing cells.

Astaxanthin stimulates mitochondrial biogenesis in insulin resistant muscle via activation of AMPK pathway.

BACKGROUND: Skeletal muscle is mainly responsible for insulin-stimulated glucose disposal. Dysfunction in skeletal muscle metabolism especially during obesity contributes to the insulin resistance. Astaxanthin (AX), a natural antioxidant, has been shown to ameliorate hepatic insulin resistance in obese mice. However, its effects in skeletal muscle are poorly understood. The current study aimed to investigate the molecular target of AX in ameliorating skeletal muscle insulin resistance. METHODS: We fed 6-week-old male C57BL/6J mice with normal chow (NC) or NC supplemented with AX (NC+AX) and high-fat-diet (HFD) or HFD supplemented with AX for 24 weeks. We determined the effect of AX on various parameters including insulin sensitivity, glucose uptake, inflammation, kinase signaling, gene expression, and mitochondrial function in muscle. We also determined energy metabolism in intact C2C12 cells treated with AX using the Seahorse XFe96 Extracellular Flux Analyzer and assessed the effect of AX on mitochondrial oxidative phosphorylation and mitochondrial biogenesis. RESULTS: AX-treated HFD mice showed improved metabolic status with significant reduction in blood glucose, serum total triglycerides, and cholesterol (p< 0.05). AX-treated HFD mice also showed improved glucose metabolism by enhancing glucose incorporation into peripheral target tissues, such as the skeletal muscle, rather than by suppressing gluconeogenesis in the liver as shown by hyperinsulinemic-euglycemic clamp study. AX activated AMPK in the skeletal muscle of the HFD mice and upregulated the expressions of transcriptional factors and coactivator, thereby inducing mitochondrial remodeling, including increased mitochondrial oxidative phosphorylation component and free fatty acid metabolism. We also assessed the effects of AX on mitochondrial biogenesis in the siRNA-mediated AMPK-depleted C2C12 cells and showed that the effect of AX was lost in the genetically AMPK-depleted C2C12 cells. Collectively, AX treatment (i) significantly ameliorated insulin resistance and glucose intolerance through regulation of AMPK activation in the muscle, (ii) stimulated mitochondrial biogenesis in the muscle, (iii) enhanced exercise tolerance and exercise-induced fatty acid metabolism, and (iv) exerted antiinflammatory effects via its antioxidant activity in adipose tissue. CONCLUSIONS: We concluded that AX treatment stimulated mitochondrial biogenesis and significantly ameliorated insulin resistance through activation of AMPK pathway in the skeletal muscle.

Macrophage-specific hypoxia-inducible factor-1α deletion suppresses the development of liver tumors in high-fat diet-fed obese and diabetic mice.

AIMS/INTRODUCTION: Chronic inflammation of the liver is often observed with obesity or type 2 diabetes. In these pathological conditions, the immunological cells, such as macrophages, play important roles in the development or growth of liver cancer. Recently, it was reported that hypoxia-inducible factor-1α (HIF-1α) is a key molecule for the acquisition of inflammatory M1 polarity of macrophages. In the present study, we examined the effects of altered macrophage polarity on obesity- and diabetes-associated liver cancer using macrophage-specific HIF-1α knockout (KO) mice. MATERIALS AND METHODS: To induce liver cancer in the mice, diethylnitrosamine, a chemical carcinogen, was used. Both KO mice and wild-type littermates were fed either a high-fat diet (HFD) or normal chow. They were mainly analyzed 6 months after HFD feeding. RESULTS: Development of liver cancer after HFD feeding was 45% less in KO mice than in wild-type littermates mice. Phosphorylation of extracellular signal-regulated kinase 2 was also lower in the liver of KO mice. Those effects of HIF-1α deletion in macrophages were not observed in normal chow-fed mice. Furthermore, the size of liver tumors did not differ between KO and wild-type littermates mice, even those on a HFD. These results suggest that the activation of macrophage HIF-1α by HFD is involved not in the growth, but in the development of liver cancer with the enhanced oncogenic extracellular signal-regulated kinase 2 signaling in hepatocytes. CONCLUSIONS: The activation of macrophage HIF-1α might play important roles in the development of liver cancer associated with diet-induced obesity and diabetes.

Partial depletion of CD206-positive M2-like macrophages induces proliferation of beige progenitors and enhances browning after cold stimulation.

Beige adipocytes are an inducible form of thermogenic adipocytes that become interspersed within white adipose tissue (WAT) depots in response to cold exposure. Previous studies have shown that type 2 cytokines and M2 macrophages induce cold-induced browning in inguinal WAT (ingWAT) by producing catecholamines. Exactly how the conditional and partial depletion of CD206+ M2-like macrophages regulates the cold-induced browning of ingWAT, however, remains unknown. We examined the role of CD206+ M2-like macrophages in the cold-induced browning of WAT using genetically engineered CD206DTR mice, in which CD206+ M2-like macrophages were conditionally depleted. The partial depletion of CD206+ M2-like enhanced UCP1 expression in ingWAT, as shown by immunostaining, and also upregulated the expression of Ucp1 and other browning-related marker genes in ingWAT after cold exposure. A flow cytometry analysis showed that the partial depletion of CD206+ M2-like macrophages caused an increase in the number of beige progenitors in ingWAT in response to cold. Thus, we concluded that CD206+ M2-like macrophages inhibit the proliferation of beige progenitors and that the partial depletion of CD206+ M2-like macrophages releases this inhibition, thereby enhancing browning and insulin sensitivity.

CD206+ M2-like macrophages regulate systemic glucose metabolism by inhibiting proliferation of adipocyte progenitors.

Adipose tissue resident macrophages have important roles in the maintenance of tissue homeostasis and regulate insulin sensitivity for example by secreting pro-inflammatory or anti-inflammatory cytokines. Here, we show that M2-like macrophages in adipose tissue regulate systemic glucose homeostasis by inhibiting adipocyte progenitor proliferation via the CD206/TGFß signaling pathway. We show that adipose tissue CD206+ cells are primarily M2-like macrophages, and ablation of CD206+ M2-like macrophages improves systemic insulin sensitivity, which was associated with an increased number of smaller adipocytes. Mice genetically engineered to have reduced numbers of CD206+ M2-like macrophages show a down-regulation of TGFß signaling in adipose tissue, together with up-regulated proliferation and differentiation of adipocyte progenitors. Our findings indicate that CD206+ M2-like macrophages in adipose tissues create a microenvironment that inhibits growth and differentiation of adipocyte progenitors and, thereby, control adiposity and systemic insulin sensitivity.Adipose tissue contains macrophages that can influence both local and systemic metabolism via the secretion of cytokines. Here, Nawaz et al. report that M2-like macrophages, present in adipose tissue, create a microenvironment that inhibits proliferation of adipocyte progenitors due to the secretion of TGF-ß1.

Regulation of Glucose Uptake and Enteroendocrine Function by the Intestinal Epithelial Insulin Receptor.

Insulin receptors (IRs) and IGF-I receptors (IGF-IR) are major regulators of metabolism and cell growth throughout the body; however, their roles in the intestine remain controversial. Here we show that genetic ablation of the IR or IGF-IR in intestinal epithelial cells of mice does not impair intestinal growth or development or the composition of the gut microbiome. However, the loss of IRs alters intestinal epithelial gene expression, especially in pathways related to glucose uptake and metabolism. More importantly, the loss of IRs reduces intestinal glucose uptake. As a result, mice lacking the IR in intestinal epithelium retain normal glucose tolerance during aging compared with controls, which show an age-dependent decline in glucose tolerance. Loss of the IR also results in a reduction of glucose-dependent insulinotropic polypeptide (GIP) expression from enteroendocrine K-cells and decreased GIP release in vivo after glucose ingestion but has no effect on glucagon-like peptide 1 expression or secretion. Thus, the IR in the intestinal epithelium plays important roles in intestinal gene expression, glucose uptake, and GIP production, which may contribute to pathophysiological changes in individuals with diabetes, metabolic syndrome, and other insulin-resistant states.

HIF-1α in Myeloid Cells Promotes Adipose Tissue Remodeling Toward Insulin Resistance.

Adipose tissue hypoxia is an important feature of pathological adipose tissue expansion. Hypoxia-inducible factor-1α (HIF-1α) in adipocytes reportedly induces oxidative stress and fibrosis, rather than neoangiogenesis via vascular endothelial growth factor (VEGF)-A. We previously reported that macrophages in crown-like structures (CLSs) are both hypoxic and inflammatory. In the current study, we examined how macrophage HIF-1α is involved in high-fat diet (HFD)-induced inflammation, neovascularization, hypoxia, and insulin resistance using mice with myeloid cell-specific HIF-1α deletion that were fed an HFD. Myeloid cell-specific HIF-1α gene deletion protected against HFD-induced inflammation, CLS formation, poor vasculature development in the adipose tissue, and systemic insulin resistance. Despite a reduced expression of Vegfa in epididymal white adipose tissue (eWAT), the preadipocytes and endothelial cells of HIF-1α-deficient mice expressed higher levels of angiogenic factors, including Vegfa, Angpt1, Fgf1, and Fgf10 in accordance with preferable eWAT remodeling. Our in vitro study revealed that lipopolysaccharide-treated bone marrow-derived macrophages directly inhibited the expression of angiogenic factors in 3T3-L1 preadipocytes. Thus, macrophage HIF-1α is involved not only in the formation of CLSs, further enhancing the inflammatory responses, but also in the inhibition of neoangiogenesis in preadipocytes. We concluded that these two pathways contribute to the obesity-related physiology of pathological adipose tissue expansion, thus causing systemic insulin resistance.

Lipodystrophy Due to Adipose Tissue-Specific Insulin Receptor Knockout Results in Progressive NAFLD.

Ectopic lipid accumulation in the liver is an almost universal feature of human and rodent models of generalized lipodystrophy and is also a common feature of type 2 diabetes, obesity, and metabolic syndrome. Here we explore the progression of fatty liver disease using a mouse model of lipodystrophy created by a fat-specific knockout of the insulin receptor (F-IRKO) or both IR and insulin-like growth factor 1 receptor (F-IR/IGFRKO). These mice develop severe lipodystrophy, diabetes, hyperlipidemia, and fatty liver disease within the first weeks of life. By 12 weeks of age, liver demonstrated increased reactive oxygen species, lipid peroxidation, histological evidence of balloon degeneration, and elevated serum alanine aminotransferase and aspartate aminotransferase levels. In these lipodystrophic mice, stored liver lipids can be used for energy production, as indicated by a marked decrease in liver weight with fasting and increased liver fibroblast growth factor 21 expression and intact ketogenesis. By 52 weeks of age, liver accounted for 25% of body weight and showed continued balloon degeneration in addition to inflammation, fibrosis, and highly dysplastic liver nodules. Progression of liver disease was associated with improvement in blood glucose levels, with evidence of altered expression of gluconeogenic and glycolytic enzymes. However, these mice were able to mobilize stored glycogen in response to glucagon. Feeding F-IRKO and F-IR/IGFRKO mice a high-fat diet for 12 weeks accelerated the liver injury and normalization of blood glucose levels. Thus, severe fatty liver disease develops early in lipodystrophic mice and progresses to advanced nonalcoholic steatohepatitis with highly dysplastic liver nodules. The liver injury is propagated by lipotoxicity and is associated with improved blood glucose levels.

In vivo depletion of CD206+ M2 macrophages exaggerates lung injury in endotoxemic mice.

Although phenotypically polarized macrophages are now generally classified into two major subtypes termed proinflammatory M1 and anti-inflammatory M2 macrophages, a contributory role of lung M2 macrophages in the pathophysiological features of acute lung injury is not fully understood. Herein, we show in an endotoxemic murine model that M2 macrophages serve as key anti-inflammatory cells that play a regulatory role in the severity of lung injury. To study whether M2 macrophages can modify inflammation, we depleted M2 macrophages from lungs of CD206-diphtheria toxin (DT) receptor transgenic (Tg) mice during challenge with lipopolysaccharide. The i.p. administration of DT depleted CD206-positive cells in bronchoalveolar lavage fluid. The use of M2 macrophage markers Ym1 and arginase-1 identified pulmonary CD206-positive cells as M2 macrophages. A striking increase in neutrophils in bronchoalveolar lavage fluid cell contents was found in DT-treated CD206-DT receptor Tg mice. In CD206-DT receptor Tg mice given DT, endotoxin challenge exaggerated lung inflammation, including up-regulation of proinflammatory cytokines and increased histological lung damage, but the endotoxemia-induced increase in NF-κB activity was significantly reduced, suggesting that M2 phenotype-dependent counteraction of inflammatory insult cannot be attributed to the inhibition of the NF-κB pathway. Our results indicate a critical role of CD206-positive pulmonary macrophages in triggering inflammatory cascade during endotoxemic lung inflammation.

Impact of divergent effects of astaxanthin on insulin signaling in L6 cells.

Because oxidative stress promotes insulin resistance in obesity and type 2 diabetes, it is crucial to find effective antioxidant for the purpose of decreasing this threat. In this study, we explored the effect of astaxanthin, a carotenoid antioxidant, on insulin signaling and investigated whether astaxanthin improves cytokine- and free fatty acid-induced insulin resistance in vitro. We examined the effect of astaxanthin on insulin-stimulated glucose transporter 4 (GLUT4) translocation, glucose uptake, and insulin signaling in cultured rat L6 muscle cells using plasma membrane lawn assay, 2-deoxyglucose uptake, and Western blot analysis. Next, we examined the effect of astaxanthin on TNFα- and palmitate-induced insulin resistance. The amount of reactive oxygen species generated by TNFα or palmitate with or without astaxanthin was evaluated by dichlorofluorescein staining. We also compared the effect of astaxanthin on insulin signaling with that of other antioxidants, α-lipoic acid and α-tocopherol. We observed astaxanthin enhanced insulin-stimulated GLUT4 translocation and glucose uptake, which was associated with an increase in insulin receptor substrate-1 tyrosine and Akt phosphorylation and a decrease in c-Jun N-terminal kinase (JNK) and insulin receptor substrate-1 serine 307 phosphorylation. Furthermore, astaxanthin restored TNFα- and palmitate-induced decreases in insulin-stimulated GLUT4 translocation or glucose uptake with a concomitant decrease in reactive oxygen species generation. α-Lipoic acid enhanced Akt phosphorylation and decreased ERK and JNK phosphorylation, whereas α-tocopherol enhanced ERK and JNK phosphorylation but had little effect on Akt phosphorylation. Collectively these findings indicate astaxanthin is a very effective antioxidant for ameliorating insulin resistance by protecting cells from oxidative stress generated by various stimuli including TNFα and palmitate.

PACAP attenuates NMDA-induced retinal damage in association with modulation of the microglia/macrophage status into an acquired deactivation subtype.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been known as a neuroprotectant agent in several retinal injury models. However, a detailed mechanism of this effect is still not well understood. In this study, we examined the retinoprotective effects and associated underlying mechanisms of action of PACAP in the mouse N-methyl-D-aspartic acid (NMDA)-induced retinal injury model, focusing on the relationship between PACAP and retinal microglia/macrophage (MG/MΦ) status. Adult male C57BL/6 mice received an intravitreal injection of NMDA to induce retinal injury. Three days after NMDA injection, the number of MG/MΦ increased significantly in the retinas. The concomitant intravitreal injection of PACAP suppressed NMDA-induced cell loss in the ganglion cell layer (GCL) and significantly increased the number of MG/MΦ. These outcomes associated with PACAP were attenuated by cotreatment with PACAP6-38, while the beneficial effects of PACAP were not seen in interleukin-10 (IL-10) knockout mice. PACAP significantly elevated the messenger RNA levels of anti-inflammatory cytokines such as transforming growth factor beta 1 and IL-10 in the injured retina, with the immunoreactivities seen to overlap with markers of MG/MΦ. These results suggest that PACAP enhances the proliferation and/or infiltration of retinal MG/MΦ and modulates their status into an acquired deactivation subtype to favor conditions for neuroprotection.

Loss of Pdk1-Foxo1 signaling in myeloid cells predisposes to adipose tissue inflammation and insulin resistance.

Chronic inflammation in adipose tissue contributes to obesity-related insulin resistance. The 3-phosphoinositide-dependent protein kinase 1 (Pdk1)/forkhead transcription factor (Foxo1) pathway is important in regulating glucose and energy homeostasis, but little is known about this pathway in adipose tissue macrophages (ATMs). To investigate this, we generated transgenic mice that carried macrophage/granulocyte-specific mutations, including a Pdk1 knockout (LysMPdk1(-/-)), a Pdk1 knockout with transactivation-defective Foxo1 (Δ256LysMPdk1(-/-)), a constitutively active nuclear (CN) Foxo1 (CNFoxo1(LysM)), or a transactivation-defective Foxo1 (Δ256Foxo1(LysM)). We analyzed glucose metabolism and gene expression in ATM populations isolated with fluorescence-activated cell sorting. The LysMPdk1(-/-) mice exhibited elevated M1 macrophages in adipose tissue and insulin resistance. Overexpression of transactivation-defective Foxo1 rescued these phenotypes. CNFoxo1(LysM) promoted transcription of the C-C motif chemokine receptor 2 (Ccr2) in ATMs and increased M1 macrophages in adipose tissue. On a high-fat diet, CNFoxo1(LysM) mice exhibited insulin resistance. Pdk1 deletion or Foxo1 activation in bone marrow-derived macrophages abolished insulin and interleukin-4 induction of genes involved in alternative macrophage activation. Thus, Pdk1 regulated macrophage infiltration by inhibiting Foxo1-induced Ccr2 expression. This shows that the macrophage Pdk1/Foxo1 pathway is important in regulating insulin sensitivity in vivo.

The radioprotective 105/MD-1 complex contributes to diet-induced obesity and adipose tissue inflammation.

Recent accumulating evidence suggests that innate immunity is associated with obesity-induced chronic inflammation and metabolic disorders. Here, we show that a Toll-like receptor (TLR) protein, radioprotective 105 (RP105)/myeloid differentiation protein (MD)-1 complex, contributes to high-fat diet (HFD)-induced obesity, adipose tissue inflammation, and insulin resistance. An HFD dramatically increased RP105 mRNA and protein expression in stromal vascular fraction of epididymal white adipose tissue (eWAT) in wild-type (WT) mice. RP105 mRNA expression also was significantly increased in the visceral adipose tissue of obese human subjects relative to nonobese subjects. The RP105/MD-1 complex was expressed by most adipose tissue macrophages (ATMs). An HFD increased RP105/MD-1 expression on the M1 subset of ATMs that accumulate in eWAT. Macrophages also acquired this characteristic in coculture with 3T3-L1 adipocytes. RP105 knockout (KO) and MD-1 KO mice had less HFD-induced adipose tissue inflammation, hepatic steatosis, and insulin resistance compared with wild-type (WT) and TLR4 KO mice. Finally, the saturated fatty acids, palmitic and stearic acids, are endogenous ligands for TLR4, but they did not activate RP105/MD-1. Thus, the RP105/MD-1 complex is a major mediator of adipose tissue inflammation independent of TLR4 signaling and may represent a novel therapeutic target for obesity-associated metabolic disorders.

Telmisartan improves insulin resistance and modulates adipose tissue macrophage polarization in high-fat-fed mice.

Diet-induced obesity is reported to induce a phenotypic switch in adipose tissue macrophages from an antiinflammatory M2 state to a proinflammatory M1 state. Telmisartan, an angiotensin II type 1 receptor blocker and a peroxisome proliferator-activated receptor-γ agonist, reportedly has more beneficial effects on insulin sensitivity than other angiotensin II type 1 receptor blockers. In this study, we studied the effects of telmisartan on the adipose tissue macrophage phenotype in high-fat-fed mice. Telmisartan was administered for 5 wk to high-fat-fed C57BL/6 mice. Insulin sensitivity, macrophage infiltration, and the gene expressions of M1 and M2 markers in visceral adipose tissues were then examined. An insulin- or a glucose-tolerance test showed that telmisartan treatment improved insulin resistance, decreasing the body weight gain, visceral fat weight, and adipocyte size without affecting the amount of energy intake. Telmisartan reduced the mRNA expression of CD11c and TNF-α, M1 macrophage markers, and significantly increased the expressions of M2 markers, such as CD163, CD209, and macrophage galactose N-acetyl-galactosamine specific lectin (Mgl2), in a quantitative RT-PCR analysis. A flow cytometry analysis showed that telmisartan decreased the number of M1 macrophages in visceral adipose tissues. In conclusion, telmisartan improves insulin sensitivity and modulates adipose tissue macrophage polarization to an antiinflammatory M2 state in high-fat-fed mice.