Involvement of inducible 6-phosphofructo-2-kinase in the anti-diabetic effect of peroxisome proliferator-activated receptor gamma activation in mice

Exercise timing influences multi-tissue metabolome and skeletal muscle proteome profiles in type 2 diabetic patients - A randomized crossover trial

AIMS/HYPOTHESIS

Metabolic effects of exercise may partly depend on the time-of-day when exercise is performed. We tested the hypothesis that exercise timing affects the adaptations in multi-tissue metabolome and skeletal muscle proteome profiles in men with type 2 diabetes.

METHODS

Men fitting the inclusion (type 2 diabetes, age 45-68 years and body mass index 23-33 kg/m²) and exclusion criteria (insulin treatment, smoking, concurrent systemic disease, and regular exercise training) were included in a randomized crossover trial (n = 15). Participants included in this metabolomics and proteomics analysis fully completed all exercise sessions (n = 8). The trial consisted of two weeks of high-intensity interval training (HIT) (three sessions/week) either in the morning (08:00, n = 5) or afternoon (16:45, n = 3), a two-week wash-out period, and an additional two weeks of HIT at the opposing time. Participants and researchers were not blinded to group allocation. Blood, skeletal muscle and subcutaneous adipose tissue were obtained before the first, and after each training period. Broad-spectrum, untargeted proteomic analysis was performed on skeletal muscle, and metabolomic analysis was performed on all biosamples. Differential content was assessed by linear regression and pathway set enrichment analyses were performed. Coordinated metabolic changes across tissues were identified by Spearman correlation analysis.

RESULTS

Metabolic and proteomic profiles remained stable after two weeks of HIT, and individual metabolites and proteins were not altered, irrespective of the time of day at which the training was performed. However, coordinated changes in relevant metabolic pathways and protein categories were identified. Morning and afternoon HIT similarly increased plasma diacylglycerols, skeletal muscle acyl-carnitines, and subcutaneous adipose tissue sphingomyelins and lysophospholipids. Acyl-carnitines were central to training-induced metabolic cross-talk across tissues. Plasma carbohydrates, via the penthose phosphate pathway, were increased and skeletal muscle lipids were decreased after morning compared to afternoon HIT. Skeletal muscle lipoproteins were higher, and mitochondrial complex III abundance was lower after morning compared to afternoon HIT.

CONCLUSIONS/INTERPRETATION

We provide a comprehensive analysis of a multi-tissue metabolomic and skeletal muscle proteomic responses to training at different times of the day in men with type 2 diabetes. Increased circulating lipids and changes in adipose tissue lipid composition were common between morning and afternoon HIT. However, afternoon HIT increased skeletal muscle lipids and mitochondrial content to a greater degree than morning training. Thus, there is a diurnal component in the metabolomic and proteomic response to exercise in men with type 2 diabetes. The clinical relevance of this response warrants further investigation.

Obesity elicits a unique metabolomic signature in human airway smooth muscle cells

Obesity can aggravate asthma by enhancing airway hyperresponsiveness (AHR) and attenuating response to treatment. However, the precise mechanisms linking obesity and asthma remain unknown. Human airway smooth muscle (HASM) cells exhibit amplified excitation-contraction (EC) coupling and force generation in obesity. Therefore, we posit that airway smooth muscle (ASM) cells obtained from obese donors manifest a metabolomic phenotype distinct from that of nonobese donor cells and that a differential metabolic phenotype, at least in part, drives enhanced ASM cell EC coupling. HASM cells derived from age-, sex-, and race-matched nonobese [body mass index (BMI) ≤ 24.9 kg·m-2] and obese (BMI ≥ 29.9 kg·m-2) lung donors were subjected to unbiased metabolomic screening. The unbiased metabolomic screening identified differentially altered metabolites linked to glycolysis and citric acid cycle in obese donor-derived cells compared with nonobese donor cells. The Seahorse assay measured the bioenergetic profile based on glycolysis, mitochondrial respiration, palmitate oxidation, and glutamine oxidation rates in HASM cells. Glycolytic rate and capacity were elevated in obese donor-derived HASM cells, whereas mitochondrial respiration, palmitate oxidation, and glutamine oxidation rates were comparable between obese and nonobese groups. PFKFB3 mRNA and protein expression levels were also elevated in obese donor-derived HASM cells. Furthermore, pharmacological inhibition of PFKFB3 attenuated agonist-induced myosin light chain (MLC) phosphorylation in HASM cells derived from obese and nonobese donors. Our findings identify elevated glycolysis as a signature metabolic phenotype of obesity and inhibition of glycolysis attenuates MLC phosphorylation in HASM cells. These findings identify novel therapeutic targets to mitigate AHR in obesity-associated asthma.

Recent Advances in Adipose Tissue Dysfunction and Its Role in the Pathogenesis of Non-Alcoholic Fatty Liver Disease

Obesity is a serious ongoing health problem that significantly increases the incidence of nonalcoholic fatty liver disease (NAFLD). During obesity, adipose tissue dysfunction is obvious and characterized by increased fat deposition (adiposity) and chronic low-grade inflammation. The latter has been implicated to critically promote the development and progression of NAFLD, whose advanced form non-alcoholic steatohepatitis (NASH) is considered one of the most common causes of terminal liver diseases. This review summarizes the current knowledge on obesity-related adipose dysfunction and its roles in the pathogenesis of hepatic steatosis and inflammation, as well as liver fibrosis. A better understanding of the crosstalk between adipose tissue and liver under obesity is essential for the development of new and improved preventive and/or therapeutic approaches for managing NAFLD.

Advances in Unhealthy Nutrition and Circadian Dysregulation in Pathophysiology of NAFLD

Unhealthy diets and lifestyle result in various metabolic conditions including metabolic syndrome and non-alcoholic fatty liver disease (NAFLD). Much evidence indicates that disruption of circadian rhythms contributes to the development and progression of excessive hepatic fat deposition and inflammation, as well as liver fibrosis, a key characteristic of non-steatohepatitis (NASH) or the advanced form of NAFLD. In this review, we emphasize the importance of nutrition as a critical factor in the regulation of circadian clock in the liver. We also focus on the roles of the rhythms of nutrient intake and the composition of diets in the regulation of circadian clocks in the context of controlling hepatic glucose and fat metabolism. We then summarize the effects of unhealthy nutrition and circadian dysregulation on the development of hepatic steatosis and inflammation. A better understanding of how the interplay among nutrition, circadian rhythms, and dysregulated metabolism result in hepatic steatosis and inflammation can help develop improved preventive and/or therapeutic strategies for managing NAFLD.

Methionine- and Choline-Deficient Diet-Induced Nonalcoholic Steatohepatitis Is Associated with Increased Intestinal Inflammation

Inflammation drives the development and progression of nonalcoholic steatohepatitis (NASH). The current study examined changes in intestinal inflammation during NASH. In male C57BL/6J mice, feeding a methionine- and choline-deficient diet (MCD) resulted in severe hepatic steatosis and inflammation relative to feeding a chow diet (CD). Also, MCD-fed mice exhibited characteristics of mucosal and submucosal inflammatory responses and increased CD68⁺ cells compared with mice fed a CD. Moreover, intestinal phosphorylation states of c-Jun N-terminal protein kinase p46 and mRNA levels of IL-1B, IL-6, tumor necrosis factor alpha, and monocyte chemoattractant protein-1 were significantly higher and intestinal mRNA levels of IL-4 and IL-13 significantly lower in MCD-fed mice compared with their respective levels in CD mice. Surprisingly, upon treatment with MCD-mimicking media, the proinflammatory responses in cultured intestinal epithelial cells (CMT-93 cells, a transformed epithelial cell line) did not differ significantly from those in intestinal epithelial cells treated with control media. In contrast, in RAW264.7 cells (transformed macrophages), MCD-mimicking media significantly increased the phosphorylation states of c-Jun N-terminal protein kinase p46 and mitogen-activated protein kinases p38 and mRNA levels of IL-1B, IL-6, IL-10, and tumor necrosis factor alpha under either basal or lipopolysaccharide-stimulated conditions. Collectively, these results suggest that increased intestinal inflammation is associated with NASH phenotype. In addition, elevated proinflammatory responses in macrophages likely contribute to, in large part, increased intestinal inflammation in NASH.

Effects of maternal gestational diet, with or without methionine, on muscle transcriptome of Bos indicus-influenced beef calves following a vaccine-induced immunological challenge

Maternal nutrition during gestation can cause epigenetic effects that translate to alterations in gene expression in offspring. This 2-year study employed RNA-sequencing technology to evaluate the pre- and post-vaccination muscle transcriptome of early-weaned Bos indicus-influenced beef calves born from dams offered different supplementation strategies from 57 ± 5 d prepartum until 17 ± 5 d postpartum. Seventy-two Brangus heifers (36 heifers/yr) were stratified by body weight and body condition score and assigned to bahiagrass pastures (3 heifers/pasture/yr). Treatments were randomly assigned to pastures and consisted of (i) no pre- or postpartum supplementation (NOSUP), (ii) pre- and postpartum supplementation of protein and energy using 7.2 kg of dry matter/heifer/wk of molasses + urea (MOL), or (iii) MOL fortified with 105 g/heifer/wk of methionine hydroxy analog (MOLMET). Calves were weaned on d 147 of the study. On d 154, 24 calves/yr (8 calves/treatment) were randomly selected and individually limit-fed a high-concentrate diet until d 201. Calves were vaccinated on d 160. Muscle biopsies were collected from the same calves (4 calves/treatment/day/yr) on d 154 (pre-vaccination) and 201 (post-vaccination) for gene expression analysis using RNA sequencing. Molasses maternal supplementation led to a downregulation of genes associated with muscle cell differentiation and development along with intracellular signaling pathways (e.g., Wnt and TGF-β signaling pathway) compared to no maternal supplementation. Maternal fortification with methionine altered functional gene-sets involved in amino acid transport and metabolism and the one-carbon cycle. In addition, muscle transcriptome was impacted by vaccination with a total of 2,396 differentially expressed genes (FDR ≤ 0.05) on d 201 vs. d 154. Genes involved in cell cycle progression, extracellular matrix, and collagen formation were upregulated after vaccination. This study demonstrated that maternal supplementation of energy and protein, with or without, methionine has long-term implications on the muscle transcriptome of offspring and potentially influence postnatal muscle development.

Different Effects of Leucine Supplementation and/or Exercise on Systemic Insulin Sensitivity in Mice

Objective

Obesity-related diseases such as diabetes, hypertension, dyslipidemia, and cardiovascular diseases have increased due to the obesity epidemic. Early intervention for obesity through lifestyle and nutrition plays an important role in preventing obesity-related diseases. Therefore, the purpose of this study is to explore the role of leucine and exercise in adiposity, systemic insulin resistance, and inflammation to provide theoretical and guiding basis for the early prevention and treatment of obesity.

Methods

C57BL/6J male mice were randomly divided into HFD or LFD-fed mice group. After 9 weeks, glucose tolerance test (GTT) was performed to detect their systemic insulin sensitivity. Starting from week 10, mice were divided into eight groups and treated with moderate exercise or/and 1.5% leucine. At week 13, systemic insulin sensitivity was detected by GTT. At week 14, mice were dissected to analyze adiposity and inflammation.

Results

In LFD mice, exercise significantly increased systemic insulin sensitivity by increasing GLUT4 expression in the muscle and decreasing adiposity through increasing AMPK phosphorylation in adipose tissue. In HFD mice, the simultaneous intervention of exercise and leucine increases systemic insulin sensitivity by reducing liver and adipose tissue inflammation via decreasing NF-κB p65 phosphorylation, and increasing the expression of adiponectin in adipose tissue.

Conclusion

There are different mechanisms underlying the effects of exercise and leucine on insulin resistance and inflammation in LFD-fed mice or HFD-fed mice.

Adipocyte inducible 6-phosphofructo-2-kinase suppresses adipose tissue inflammation and promotes macrophage anti-inflammatory activation

Obesity-associated inflammation in white adipose tissue (WAT) is a causal factor of systemic insulin resistance. To better understand how adipocytes regulate WAT inflammation, the present study generated chimeric mice in which inducible 6-phosphofructo-2-kinase was low, normal, or high in WAT while the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (Pfkfb3) was normal in hematopoietic cells, and analyzed changes in high-fat diet (HFD)-induced WAT inflammation and systemic insulin resistance in the mice. Indicated by proinflammatory signaling and cytokine expression, the severity of HFD-induced WAT inflammation in WT → Pfkfb3^+/- mice, whose Pfkfb3 was disrupted in WAT adipocytes but not hematopoietic cells, was comparable with that in WT → WT mice, whose Pfkfb3 was normal in all cells. In contrast, the severity of HFD-induced WAT inflammation in WT → Adi-Tg mice, whose Pfkfb3 was over-expressed in WAT adipocytes but not hematopoietic cells, remained much lower than that in WT → WT mice. Additionally, HFD-induced insulin resistance was correlated with the status of WAT inflammation and comparable between WT → Pfkfb3^+/- mice and WT → WT mice, but was significantly lower in WT → Adi-Tg mice than in WT → WT mice. In vitro, palmitoleate decreased macrophage phosphorylation states of Jnk p46 and Nfkb p65 and potentiated the effect of interleukin 4 on suppressing macrophage proinflammatory activation. Taken together, these results suggest that the Pfkfb3 in adipocytes functions to suppress WAT inflammation. Moreover, the role played by adipocyte Pfkfb3 is attributable to, at least in part, palmitoleate promotion of macrophage anti-inflammatory activation.

Adipose tissue inflammation and systemic insulin resistance in mice with diet-induced obesity is possibly associated with disruption of PFKFB3 in hematopoietic cells

Obesity-associated inflammation in white adipose tissue (WAT) is a causal factor of systemic insulin resistance; however, precisely how immune cells regulate WAT inflammation in relation to systemic insulin resistance remains to be elucidated. The present study examined a role for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in hematopoietic cells in regulating WAT inflammation and systemic insulin sensitivity. Male C57BL/6J mice were fed a high-fat diet (HFD) or low-fat diet (LFD) for 12 weeks and examined for WAT inducible 6-phosphofructo-2-kinase (iPFK2) content, while additional HFD-fed mice were treated with rosiglitazone and examined for PFKFB3 mRNAs in WAT stromal vascular cells (SVC). Also, chimeric mice in which PFKFB3 was disrupted only in hematopoietic cells and control chimeric mice were also fed an HFD and examined for HFD-induced WAT inflammation and systemic insulin resistance. In vitro, adipocytes were co-cultured with bone marrow-derived macrophages and examined for adipocyte proinflammatory responses and insulin signaling. Compared with their respective levels in controls, WAT iPFK2 amount in HFD-fed mice and WAT SVC PFKFB3 mRNAs in rosiglitazone-treated mice were significantly increased. When the inflammatory responses were analyzed, peritoneal macrophages from PFKFB3-disrputed mice revealed increased proinflammatory activation and decreased anti-inflammatory activation compared with control macrophages. At the whole animal level, hematopoietic cell-specific PFKFB3 disruption enhanced the effects of HFD feeding on promoting WAT inflammation, impairing WAT insulin signaling, and increasing systemic insulin resistance. In vitro, adipocytes co-cultured with PFKFB3-disrupted macrophages revealed increased proinflammatory responses and decreased insulin signaling compared with adipocytes co-cultured with control macrophages. These results suggest that PFKFB3 disruption in hematopoietic cells only exacerbates HFD-induced WAT inflammation and systemic insulin resistance.

The expression profile and role of non-coding RNAs in obesity

Latest years have experienced a dramatic upsurge in the knowledge about the function of non-coding transcripts in the determination of diverse human phenotypes including obesity. Several miRNAs and lncRNAs participate in the regulation of metabolic pathways leading to obesity. Several lncRNAs such as Mist, lincIRS2, lncRNA-p5549, H19, GAS5 and SNHG9 have been shown to be down-regulated in adipose tissues or other biological samples in the obese human or animal subjects. On the other hand, Meg3, Plnc1, Blnc1, AC092834.1, TINCR and PVT1 are among up-regulated lncRNAs in the obese subjects. Tens of miRNAs have differential expression between obese and non-obese subjects or between mature adipocytes and pre-adipocytes. Understanding the molecular mechanism of involvement of non-coding RNAs in the pathobiology of obesity would simplify design of therapeutic choices for protecting against obesity and its related comorbidities. We explain the available literature on the function of these transcripts in the pathobiology of obesity.

Indole Alleviates Diet-Induced Hepatic Steatosis and Inflammation in a Manner Involving Myeloid Cell 6-Phosphofructo-2-Kinase/Fructose-2,6-Biphosphatase 3

BACKGROUND AND AIMS

Indole is a microbiota metabolite that exerts anti-inflammatory responses. However, the relevance of indole to human non-alcoholic fatty liver disease (NAFLD) is not clear. It also remains largely unknown whether and how indole acts to protect against NAFLD. The present study sought to examine the association between the circulating levels of indole and liver fat content in human subjects and explore the mechanisms underlying indole actions in mice with diet-induced NAFLD.

APPROACH AND RESULTS

In a cohort of 137 subjects, the circulating levels of indole were reversely correlated with body mass index. In addition, the circulating levels of indole in obese subjects were significantly lower than those in lean subjects and were accompanied with increased liver fat content. At the whole-animal level, treatment of high-fat diet (HFD)-fed C57BL/6J mice with indole caused significant decreases in the severity of hepatic steatosis and inflammation. In cultured cells, indole treatment stimulated the expression of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a master regulatory gene of glycolysis, and suppressed macrophage proinflammatory activation in a PFKFB3-dependent manner. Moreover, myeloid cell-specific PFKFB3 disruption exacerbated the severity of HFD-induced hepatic steatosis and inflammation and blunted the effect of indole on alleviating diet-induced NAFLD phenotype.

CONCLUSIONS

Taken together, our results demonstrate that indole is relevant to human NAFLD and capable of alleviating diet-induced NAFLD phenotypes in mice in a myeloid cell PFKFB3-dependent manner. Therefore, indole mimetic and/or macrophage-specific PFKFB3 activation may be the viable preventive and/or therapeutic approaches for inflammation-associated diseases including NAFLD.

Adoptive transfer of Pfkfb3-disrupted hematopoietic cells to wild-type mice exacerbates diet-induced hepatic steatosis and inflammation

BACKGROUND AND OBJECTIVES

Hepatic steatosis and inflammation are key characteristics of non-alcoholic fatty liver disease (NAFLD). However, whether and how hepatic steatosis and liver inflammation are differentially regulated remains to be elucidated. Considering that disruption of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (Pfkfb3/iPfk2) dissociates fat deposition and inflammation, the present study examined a role for Pfkfb3/iPfk2 in hematopoietic cells in regulating hepatic steatosis and inflammation in mice.

METHODS

Pfkfb3-disrupted (Pfkfb3 ^+/-) mice and wild-type (WT) littermates were fed a high-fat diet (HFD) and examined for NAFLD phenotype. Also, bone marrow cells isolated from Pfkfb3 ^+/- mice and WT mice were differentiated into macrophages for analysis of macrophage activation status and for bone marrow transplantation (BMT) to generate chimeric (WT/BMT- Pfkfb3 ^+/-) mice in which Pfkfb3 was disrupted only in hematopoietic cells and control chimeric (WT/BMT-WT) mice. The latter were also fed an HFD and examined for NAFLD phenotype. In vitro, hepatocytes were co-cultured with bone marrow-derived macrophages and examined for hepatocyte fat deposition and proinflammatory responses.

RESULTS

After the feeding period, HFD-fed Pfkfb3 ^+/- mice displayed increased severity of liver inflammation in the absence of hepatic steatosis compared with HFD-fed WT mice. When inflammatory activation was analyzed, Pfkfb3 ^+/- macrophages revealed increased proinflammatory activation and decreased anti-proinflammatory activation. When NAFLD phenotype was analyzed in the chimeric mice, WT/BMT-Pfkfb3 ^+/- mice displayed increases in the severity of HFD-induced hepatic steatosis and inflammation compared with WT/BMT-WT mice. At the cellular level, hepatocytes co-cultured with Pfkfb3 ^+/- macrophages revealed increased fat deposition and proinflammatory responses compared with hepatocytes co-cultured with WT macrophages.

CONCLUSIONS

Pfkfb3 disruption only in hematopoietic cells exacerbates HFD-induced hepatic steatosis and inflammation whereas the Pfkfb3/iPfk2 in nonhematopoietic cells appeared to be needed for HFD feeding to induce hepatic steatosis. As such, the Pfkfb3/iPfk2 plays a unique role in regulating NAFLD pathophysiology.

The Construction and Analysis of the Aberrant lncRNA-miRNA-mRNA Network in Adipose Tissue from Type 2 Diabetes Individuals with Obesity

BACKGROUND

The prevalence of obesity and type 2 diabetes mellitus (T2DM) has become the most serious global public health issue. In recent years, there has been increasing attention to the role of long noncoding RNAs (lncRNAs) in the occurrence and development of obesity and T2DM. The aim of this work was to find new lncRNAs as potential predictive biomarkers or therapeutic targets for obesity and T2DM.

METHODS

In this study, we identified significant differentially expressed mRNAs (DEmRNAs) and differentially expressed lncRNAs (DElncRNAs) between adipose tissue of individuals with obesity and T2DM and normal adipose tissue (absolute log₂FC ≥ 1 and FDR < 0.05). Then, the lncRNA-miRNA interactions predicted by miRcode were further screened with a threshold of MIC > 0.2. Simultaneously, the mRNA-miRNA interactions were explored by miRWalk 2.0. Finally, a ceRNA network consisting of lncRNAs, miRNAs, and mRNAs was established by integrating lncRNA-miRNA interactions and mRNA-miRNA interactions.

RESULTS

Upon comparing adipose tissue from individuals with obesity and T2DM and normal adipose tissues, 364 significant DEmRNAs, including 140 upregulated and 224 downregulated mRNAs, were identified in GSE104674; in addition, 231 significant DEmRNAs, including 146 upregulated and 85 downregulated mRNAs, were identified in GSE133099. GO and KEGG analyses have shown that downregulated DEmRNAs in GSE104674 and GSE133099 were associated with obesity- and T2DM-related biological pathways, such as lipid metabolism, AMPK signaling, and insulin resistance. Furthermore, 28 significant DElncRNAs, including 14 upregulated and 14 downregulated lncRNAs, were found. Based on the predicted lncRNA-miRNA and mRNA-miRNA relationships, we constructed a competitive endogenous RNA (ceRNA) network, including five lncRNAs, ten miRNAs, and 15 mRNAs. KEGG-GSEA analysis revealed that four lncRNAs (FLG-AS1, SNAI3-AS1, AC008147.0, and LINC02015) in the ceRNA network were related to the biological pathways of metabolic diseases.

CONCLUSIONS

Through ceRNA network analysis, our study identified four new lncRNAs that may be used as potential biomarkers and therapeutic targets of obesity and T2DM, thus laying a foundation for future clinical studies.

A locked immunometabolic switch underlies TREM2 R47H loss of function in human iPSC-derived microglia

Loss‐of‐function genetic variants of triggering receptor expressed on myeloid cells 2 (TREM2) are linked with an enhanced risk of developing dementias. Microglia, the resident immune cell of the brain, express TREM2, and microglial responses are implicated in dementia pathways. In a normal surveillance state, microglia use oxidative phosphorylation for their energy supply, but rely on the ability to undergo a metabolic switch to glycolysis to allow them to perform rapid plastic responses. We investigated the role of TREM2 on the microglial metabolic function in human patient iPSC‐derived microglia expressing loss of function variants in TREM2. We show that these TREM2 variant iPSC‐microglia, including the Alzheimer's disease R47H risk variant, exhibit significant metabolic deficits including a reduced mitochondrial respiratory capacity and an inability to perform a glycolytic immunometabolic switch. We determined that dysregulated PPARγ/p38MAPK signaling underlies the observed phenotypic deficits in TREM2 variants and that activation of these pathways can ameliorate the metabolic deficit in these cells and consequently rescue critical microglial cellular function such as β‐Amyloid phagocytosis. These findings have ramifications for microglial focussed‐treatments in AD.

Mice lacking adenosine 2A receptor reveal increased severity of MCD-induced NASH

Adenosine 2A receptor (A2AR) exerts a protective role in obesity-related non-alcoholic fatty liver disease. Here, we examined whether A2AR protects against non-alcoholic steatohepatitis (NASH). In C57BL/6J mice, feeding a methionine- and choline-deficient diet (MCD) resulted in significant weight loss, overt hepatic steatosis, and massive aggregation of macrophages in the liver compared with mice fed a chow diet. MCD feeding also significantly increased the numbers of A2AR-positive macrophages/Kupffer cells in liver sections although decreasing A2AR amount in liver lysates compared with chow diet feeding. Next, MCD-induced NASH phenotype was examined in A2AR-disrupted mice and control mice. Upon MCD feeding, A2AR-disruptd mice and control mice displayed comparable decreases in body weight and fat mass. However, MCD-fed A2AR-disrupted mice revealed greater liver weight and increased severity of hepatic steatosis compared with MCD-fed control mice. Moreover, A2AR-disupted mice displayed increased severity of MCD-induced liver inflammation, indicated by massive aggregation of macrophages and increased phosphorylation states of Jun-N terminal kinase (JNK) p46 and nuclear factor kappa B (NFκB) p65 and mRNA levels of tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6. In vitro, incubation with MCD-mimicking media increased lipopolysaccharide (LPS)-induced phosphorylation states of JNK p46 and/or NFκB p65 and cytokine mRNAs in control macrophages and RAW264.7 cells, but not primary hepatocytes. Additionally, MCD-mimicking media significantly increased lipopolysaccharide-induced phosphorylation states of p38 and NFκB p65 in A2AR-deficient macrophages, but insignificantly decreased lipopolysaccharide-induced phosphorylation states of JNK p46 and NFκB p65 in A2AR-deficient hepatocytes. Collectively, these results suggest that A2AR disruption exacerbates MCD-induced NASH, which is attributable to, in large part, increased inflammatory responses in macrophages.

PFKFB3 blockade inhibits hepatocellular carcinoma growth by impairing DNA repair through AKT

Overexpression of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a key molecule of glucose metabolism in cytoplasm, has been found in various tumors. Emerging evidence has suggested that PFKFB3 is also located in the nucleus and apparent in regulatory functions other than glycolysis. In this study, we found that PFKFB3 expression is associated with hepatocellular carcinoma (HCC) growth and located mainly in the nucleus of tumor cells. PFKFB3 overexpression was associated with large tumor size (p = 0.04) and poor survival of patients with HCC (p = 0.027). Knockdown of PFKFB3 inhibited HCC growth, not only by reducing glucose consumption but also by damaging the DNA repair function, leading to G2/M phase arrest and apoptosis. In animal studies, overexpression of PFKFB3 is associated with increased tumor growth. Mechanistically, PFKFB3 silencing decreased AKT phosphorylation and reduced the expression of ERCC1, which is an important DNA repair protein. Moreover, PFK15, a selective PFKFB3 inhibitor, significantly inhibited tumor growth in a xenograft model of human HCC. PFKFB3 is a potential novel target in the treatment of HCC.

Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism

Based on genetic models with mutation or deletion of core clock genes, circadian disruption has been implicated in the pathophysiology of metabolic disorders. Thus, we examined whether circadian desynchronization in response to shift work-type schedules is sufficient to compromise metabolic homeostasis and whether inflammatory mediators provide a key link in the mechanism by which alterations of circadian timekeeping contribute to diet-induced metabolic dysregulation. In high-fat diet (HFD)-fed mice, exposure to chronic shifts of the light-dark cycle (12 h advance every 5 d): 1) disrupts photoentrainment of circadian behavior and modulates the period of spleen and macrophage clock gene rhythms; 2) potentiates HFD-induced adipose tissue infiltration and activation of proinflammatory M1 macrophages; 3) amplifies macrophage proinflammatory cytokine expression in adipose tissue and bone marrow-derived macrophages; and 4) exacerbates diet-induced increases in body weight, insulin resistance, and glucose intolerance in the absence of changes in total daily food intake. Thus, complete disruption of circadian rhythmicity or clock gene function as transcription factors is not requisite to the link between circadian and metabolic phenotypes. These findings suggest that macrophage proinflammatory activation and inflammatory signaling are key processes in the physiologic cascade by which dysregulation of circadian rhythmicity exacerbates diet-induced systemic insulin resistance and glucose intolerance.-Kim, S.-M., Neuendorff, N., Alaniz, R. C., Sun, Y., Chapkin, R. S., Earnest, D. J. Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism.

A role for PFKFB3/iPFK2 in metformin suppression of adipocyte inflammatory responses

Metformin improves obesity-associated metabolic dysregulation, but has controversial effects on adipose tissue inflammation. The objective of the study is to examine the direct effect of metformin on adipocyte inflammatory responses and elucidate the underlying mechanisms. Adipocytes were differentiated from 3T3-L1 cells and treated with metformin at various doses and for different time periods. The treated cells were examined for the proinflammatory responses, as well as the phosphorylation states of AMPK and the expression of PFKFB3/iPFK2. In addition, PFKFB3/iPFK2-knockdown adipocytes were treated with metformin and examined for changes in the proinflammatory responses. The following results were obtained from the study. Treatment of adipocytes with metformin decreased the effects of lipopolysaccharide on inducing the phosphorylation states of JNK p46 and on increasing the mRNA levels of IL-1β and TNFα. In addition, treatment with metformin increased the expression of PFKFB3/iPFK2, but failed to significantly alter the phosphorylation states of AMPK. In PFKFB3/iPFK2-knockdown adipocytes, treatment with metformin did not suppress the proinflammatory responses as did it in control adipocytes. In conclusion, metformin has a direct effect on suppressing adipocyte proinflammatory responses in an AMPK-independent manner. Also, metformin increases adipocyte expression of PFKFB3/iPFK2, which is involved in the anti-inflammatory effect of metformin.

The many ways tissue phagocytes respond to dying cells

Apoptosis is an important component of normal tissue physiology, and the prompt removal of apoptotic cells is equally essential to avoid the undesirable consequences of their accumulation and disintegration. Professional phagocytes are highly specialized for engulfing apoptotic cells. The recent ability to track cells that have undergone apoptosis in situ has revealed a division of labor among the tissue resident phagocytes that sample them. Macrophages are uniquely programmed to process internalized apoptotic cell-derived fatty acids, cholesterol and nucleotides, as a reflection of their dominant role in clearing the bulk of apoptotic cells. Dendritic cells carry apoptotic cells to lymph nodes where they signal the emergence and expansion of highly suppressive regulatory CD4 T cells. A broad suppression of inflammation is executed through distinct phagocyte-specific mechanisms. A clever induction of negative regulatory nodes is notable in dendritic cells serving to simultaneously shut down multiple pathways of inflammation. Several of the genes and pathways modulated in phagocytes in response to apoptotic cells have been linked to chronic inflammatory and autoimmune diseases such as atherosclerosis, inflammatory bowel disease and systemic lupus erythematosus. Our collective understanding of old and new phagocyte functions after apoptotic cell phagocytosis demonstrates the enormity of ways to mediate immune suppression and enforce tissue homeostasis.

Nutrition, microRNAs, and Human Health

MicroRNAs (miRs) hybridize with complementary sequences in mRNA and silence genes by destabilizing mRNA or preventing translation of mRNA. Over 60% of human protein-coding genes are regulated by miRs, and 1881 high-confidence miRs are encoded in the human genome. Evidence suggests that miRs not only are synthesized endogenously, but also might be obtained from dietary sources, and that food compounds alter the expression of endogenous miR genes. The main food matrices for studies of biological activity of dietary miRs include plant foods and cow milk. Encapsulation of miRs in exosomes and exosome-like particles confers protection against RNA degradation and creates a pathway for intestinal and vascular endothelial transport by endocytosis, as well as delivery to peripheral tissues. Evidence suggests that the amount of miRs absorbed from nutritionally relevant quantities of foods is sufficient to elicit biological effects, and that endogenous synthesis of miRs is insufficient to compensate for dietary miR depletion and rescue wild-type phenotypes. In addition, nutrition alters the expression of endogenous miR genes, thereby compounding the effects of nutrition-miR interactions in gene regulation and disease diagnosis in liquid biopsies. For example, food components and dietary preferences may modulate serum miR profiles that may influence biological processes. The complex crosstalk between nutrition, miRs, and gene targets poses a challenge to gene network analysis and studies of human disease. Novel pipelines and databases have been developed recently, including a dietary miR database for archiving reported miRs in 15 dietary resources. miRs derived from diet and endogenous synthesis have been implicated in physiologic and pathologic conditions, including those linked with nutrition and metabolism. In fact, several miRs are actively regulated in response to overnutrition and tissue inflammation, and are involved in facilitating the development of chronic inflammation by modulating tissue-infiltrated immune cell function.

Glucose and Palmitate Differentially Regulate PFKFB3/iPFK2 and Inflammatory Responses in Mouse Intestinal Epithelial Cells

The gene PFKFB3 encodes for inducible 6-phosphofructo-2-kinase, a glycolysis-regulatory enzyme that protects against diet-induced intestine inflammation. However, it is unclear how nutrient overload regulates PFKFB3 expression and inflammatory responses in intestinal epithelial cells (IECs). In the present study, primary IECs were isolated from small intestine of C57BL/6J mice fed a low-fat diet (LFD) or high-fat diet (HFD) for 12 weeks. Additionally, CMT-93 cells, a cell line for IECs, were cultured in low glucose (LG, 5.5 mmol/L) or high glucose (HG, 27.5 mmol/L) medium and treated with palmitate (50 μmol/L) or bovine serum albumin (BSA) for 24 hr. These cells were analyzed for PFKFB3 and inflammatory markers. Compared with LFD, HFD feeding decreased IEC PFKFB3 expression and increased IEC proinflammatory responses. In CMT-93 cells, HG significantly increased PFKFB3 expression and proinflammatory responses compared with LG. Interestingly, palmitate decreased PFKFB3 expression and increased proinflammatory responses compared with BSA, regardless of glucose concentrations. Furthermore, HG significantly increased PFKFB3 promoter transcription activity compared with LG. Upon PFKFB3 overexpression, proinflammatory responses in CMT-93 cells were decreased. Taken together, these results indicate that in IECs glucose stimulates PFKFB3 expression and palmitate contributes to increased proinflammatory responses. Therefore, PFKFB3 regulates IEC inflammatory status in response to macronutrients.

PFKFB3 Control of Cancer Growth by Responding to Circadian Clock Outputs

Circadian clock dysregulation promotes cancer growth. Here we show that PFKFB3, the gene that encodes for inducible 6-phosphofructo-2-kinase as an essential supporting enzyme of cancer cell survival through stimulating glycolysis, mediates circadian control of carcinogenesis. In patients with tongue cancers, PFKFB3 expression in both cancers and its surrounding tissues was increased significantly compared with that in the control, and was accompanied with dys-regulated expression of core circadian genes. In the in vitro systems, SCC9 tongue cancer cells displayed rhythmic expression of PFKFB3 and CLOCK that was distinct from control KC cells. Furthermore, PFKFB3 expression in SCC9 cells was stimulated by CLOCK through binding and enhancing the transcription activity of PFKFB3 promoter. Inhibition of PFKFB3 at zeitgeber time 7 (ZT7), but not at ZT19 caused significant decreases in lactate production and in cell proliferation. Consistently, PFKFB3 inhibition in mice at circadian time (CT) 7, but not CT19 significantly reduced the growth of implanted neoplasms. Taken together, these findings demonstrate PFKFB3 as a mediator of circadian control of cancer growth, thereby highlighting the importance of time-based PFKFB3 inhibition in cancer treatment.

Metabolic and Inflammatory Adaptation of Reactive Astrocytes: Role of PPARs

Astrocyte-mediated inflammation is associated with degenerative pathologies such as Alzheimer's and Parkinson's diseases and multiple sclerosis. The acute inflammation and morphological and metabolic changes that astrocytes develop after the insult are known as reactive astroglia or astrogliosis that is an important response to protect and repair the lesion. Astrocytes optimize their metabolism to produce lactate, glutamate, and ketone bodies in order to provide energy to the neurons that are deprived of nutrients upon insult. Firstly, we review the basis of inflammation and morphological changes of the different cell population implicated in reactive gliosis. Next, we discuss the more active metabolic pathways in healthy astrocytes and explain the metabolic response of astrocytes to the insult in different pathologies and which metabolic alterations generate complications in these diseases. We emphasize the role of peroxisome proliferator-activated receptors isotypes in the inflammatory and metabolic adaptation of astrogliosis developed in ischemia or neurodegenerative diseases. Based on results reported in astrocytes and other cells, we resume and hypothesize the effect of peroxisome proliferator-activated receptor (PPAR) activation with ligands on different metabolic pathways in order to supply energy to the neurons. The activation of selective PPAR isotype activity may serve as an input to better understand the role played by these receptors on the metabolic and inflammatory compensation of astrogliosis and might represent an opportunity to develop new therapeutic strategies against traumatic brain injuries and neurodegenerative diseases.

Berberine Ameliorates Hepatic Steatosis and Suppresses Liver and Adipose Tissue Inflammation in Mice with Diet-induced Obesity

Increasing evidence demonstrates that berberine (BBR) is beneficial for obesity-associated non-alcoholic fatty liver disease (NAFLD). However, it remains to be elucidated how BBR improves aspects of NAFLD. Here we revealed an AMP-activated protein kinase (AMPK)-independent mechanism for BBR to suppress obesity-associated inflammation and improve hepatic steatosis. In C57BL/6J mice fed a high-fat diet (HFD), treatment with BBR decreased inflammation in both the liver and adipose tissue as indicated by reduction of the phosphorylation state of JNK1 and the mRNA levels of proinflammatory cytokines. BBR treatment also decreased hepatic steatosis, as well as the expression of acetyl-CoA carboxylase and fatty acid synthase. Interestingly, treatment with BBR did not significantly alter the phosphorylation state of AMPK in both the liver and adipose tissue of HFD-fed mice. Consistently, BBR treatment significantly decreased the phosphorylation state of JNK1 in both hepatoma H4IIE cells and mouse primary hepatocytes in both dose-dependent and time-dependent manners, which was independent of AMPK phosphorylation. BBR treatment also caused a decrease in palmitate-induced fat deposition in primary mouse hepatocytes. Taken together, these results suggest that BBR actions on improving aspects of NAFLD are largely attributable to BBR suppression of inflammation, which is independent of AMPK.

Obesity: An overview of possible role(s) of gut hormones, lipid sensing and gut microbiota

Obesity is one of the major challenges for public health in 21st century, with 1.9 billion people being considered as overweight and 600 million as obese. There are certain diseases such as type 2 diabetes, hypertension, cardiovascular disease, and several forms of cancer which were found to be associated with obesity. Therefore, understanding the key molecular mechanisms involved in the pathogenesis of obesity could be beneficial for the development of a therapeutic approach. Hormones such as ghrelin, glucagon like peptide 1 (GLP-1) peptide YY (PYY), pancreatic polypeptide (PP), cholecystokinin (CCK) secreted by an endocrine organ gut, have an intense impact on energy balance and maintenance of homeostasis by inducing satiety and meal termination. Glucose and energy homeostasis are also affected by lipid sensing in which different organs respond in different ways. However, there is one common mechanism i.e. formation of esterified lipids (long chain fatty acyl CoAs) and the activation of protein kinase C δ (PKC δ) involved in all these organs. The possible role of gut microbiota and obesity has been addressed by several researchers in recent years, indicating the possible therapeutic approach toward the management of obesity by the introduction of an external living system such as a probiotic. The proposed mechanism behind this activity is attributed by metabolites produced by gut microbial organisms. Thus, this review summarizes the role of various physiological factors such as gut hormone and lipid sensing involved in various tissues and organ and most important by the role of gut microbiota in weight management.

High-Fat Diet-Induced Retinal Dysfunction

PURPOSE

The purpose of this study was to investigate the impact of obesity-induced prediabetes/early diabetes on the retina to provide new evidence on the pathogenesis of type 2 diabetes-associated diabetic retinopathy (DR).

METHODS

A high-fat diet (HFD)-induced obesity mouse model (male C57BL/6J) was used in this study. At the end of the 12-week HFD feeding regimen, mice were evaluated for glucose and insulin tolerance, and retinal light responses were recorded by electroretinogram (ERG). Western immunoblot and immunohistochemical staining were used to determine changes in elements regulating calcium homeostasis between HFD and control retinas, as well as unstained human retinal sections from DR patients and age-appropriate controls.

RESULTS

Compared to the control, the scotopic and photopic ERGs from HFD mice were decreased. There were significant decreases in molecules related to cell signaling, calcium homeostasis, and glucose metabolism from HFD retinas, including phosphorylated protein kinase B (pAKT), glucose transporter 4, L-type voltage-gated calcium channel (L-VGCC), and plasma membrane calcium ATPase (PMCA). Similar changes for pAKT, PMCA, and L-VGCC were also observed in human retinal sections from DR patients.

CONCLUSIONS

Obesity-induced hyperglycemic and prediabetic/early diabetic conditions caused detrimental impacts on retinal light sensitivities and health. The decrease of the ERG components in early diabetes reflects the decreased neuronal activity of retinal light responses, which may be caused by a decrease in neuronal calcium signaling. Since PI3K-AKT is important in regulating calcium homeostasis and neural survival, maintaining proper PI3K-AKT signaling in early diabetes or at the prediabetic stage might be a new strategy for DR prevention.

Myeloid cell-specific disruption of Period1 and Period2 exacerbates diet-induced inflammation and insulin resistance

The circadian clockworks gate macrophage inflammatory responses. Given the association between clock dysregulation and metabolic disorders, we conducted experiments to determine the extent to which over-nutrition modulates macrophage clock function and whether macrophage circadian dysregulation is a key factor linking over-nutrition to macrophage proinflammatory activation, adipose tissue inflammation, and systemic insulin resistance. Our results demonstrate that 1) macrophages from high fat diet-fed mice are marked by dysregulation of the molecular clockworks in conjunction with increased proinflammatory activation, 2) global disruption of the clock genes Period1 (Per1) and Per2 recapitulates this amplified macrophage proinflammatory activation, 3) adoptive transfer of Per1/2-disrupted bone marrow cells into wild-type mice potentiates high fat diet-induced adipose and liver tissue inflammation and systemic insulin resistance, and 4) Per1/2-disrupted macrophages similarly exacerbate inflammatory responses and decrease insulin sensitivity in co-cultured adipocytes in vitro. Furthermore, PPARγ levels are decreased in Per1/2-disrupted macrophages and PPARγ2 overexpression ameliorates Per1/2 disruption-associated macrophage proinflammatory activation, suggesting that this transcription factor may link the molecular clockworks to signaling pathways regulating macrophage polarization. Thus, macrophage circadian clock dysregulation is a key process in the physiological cascade by which diet-induced obesity triggers macrophage proinflammatory activation, adipose tissue inflammation, and insulin resistance.

Endothelial PFKFB3 plays a critical role in angiogenesis

OBJECTIVE

Vascular cells, particularly endothelial cells, adopt aerobic glycolysis to generate energy to support cellular functions. The effect of endothelial glycolysis on angiogenesis remains unclear. 6-Phosphofructo-2-kinase/fructose-2, 6-bisphosphatase, isoform 3 (PFKFB3) is a critical enzyme for endothelial glycolysis. By blocking or deleting PFKFB3 in endothelial cells, we investigated the influence of endothelial glycolysis on angiogenesis both in vitro and in vivo.

APPROACH AND RESULTS

Under hypoxic conditions or after treatment with angiogenic factors, endothelial PFKFB3 was upregulated both in vitro and in vivo. The knockdown or overexpression of PFKFB3 suppressed or accelerated endothelial proliferation and migration in vitro, respectively. Neonatal mice from a model of oxygen-induced retinopathy showed suppressed neovascular growth in the retina when endothelial PFKFB3 was genetically deleted or when the mice were treated with a PFKFB3 inhibitor. In addition, tumors implanted in mice deficient in endothelial PFKFB3 grew more slowly and were provided with less blood flow. A lower level of phosphorylated protein kinase B was observed in PFKFB3-knockdown endothelial cells, which was accompanied by a decrease in intracellular lactate. The addition of lactate to PFKFB3-knockdown cells rescued the suppression of endothelial proliferation and migration.

CONCLUSIONS

The blockade or deletion of endothelial PFKFB3 decreases angiogenesis both in vitro and in vivo. Thus, PFKFB3 is a promising target for the reduction of endothelial glycolysis and its related pathological angiogenesis.

Metformin ameliorates hepatic steatosis and inflammation without altering adipose phenotype in diet-induced obesity

Non-alcoholic fatty liver disease (NAFLD) is closely associated with obesity and insulin resistance. To better understand the pathophysiology of obesity-associated NAFLD, the present study examined the involvement of liver and adipose tissues in metformin actions on reducing hepatic steatosis and inflammation during obesity. C57BL/6J mice were fed a high-fat diet (HFD) for 12 weeks to induce obesity-associated NAFLD and treated with metformin (150 mg/kg/d) orally for the last four weeks of HFD feeding. Compared with HFD-fed control mice, metformin-treated mice showed improvement in both glucose tolerance and insulin sensitivity. Also, metformin treatment caused a significant decrease in liver weight, but not adiposity. As indicated by histological changes, metformin treatment decreased hepatic steatosis, but not the size of adipocytes. In addition, metformin treatment caused an increase in the phosphorylation of liver AMP-activated protein kinase (AMPK), which was accompanied by an increase in the phosphorylation of liver acetyl-CoA carboxylase and decreases in the phosphorylation of liver c-Jun N-terminal kinase 1 (JNK1) and in the mRNA levels of lipogenic enzymes and proinflammatory cytokines. However, metformin treatment did not significantly alter adipose tissue AMPK phosphorylation and inflammatory responses. In cultured hepatocytes, metformin treatment increased AMPK phosphorylation and decreased fat deposition and inflammatory responses. Additionally, in bone marrow-derived macrophages, metformin treatment partially blunted the effects of lipopolysaccharide on inducing the phosphorylation of JNK1 and nuclear factor kappa B (NF-κB) p65 and on increasing the mRNA levels of proinflammatory cytokines. Taken together, these results suggest that metformin protects against obesity-associated NAFLD largely through direct effects on decreasing hepatocyte fat deposition and on inhibiting inflammatory responses in both hepatocytes and macrophages.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

Gly482Ser mutation impairs the effects of peroxisome proliferator-activated receptor γ coactivator-1α on decreasing fat deposition and stimulating phosphoenolpyruvate carboxykinase expression in hepatocytes

Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a transcriptional coactivator of nuclear receptor peroxisome proliferator-activated receptor γ that critically regulates glucose and fat metabolism. Although clinical evidence suggests that Gly482Ser polymorphism of PGC-1α is associated with an increased incidence of nonalcoholic fatty liver disease, a direct role for Gly482Ser mutation in altering PGC-1α actions on hepatocyte fat deposition remains to be explored. We hypothesized that Gly482Ser mutation impairs the abilities of PGC-1α in ameliorating overnutrition-induced hepatocyte fat deposition and in stimulating hepatocyte expression of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; encoded by a key PGC-1α target gene). In the present study, treatment of cultured hepatocytes with palmitate induced fat deposition, serving as a cell model of hepatic steatosis. Upon overexpression of wild-type PGC-1α, H4IIE cells exhibited a significant decrease in palmitate-induced hepatocyte fat deposition compared with control cells and/or cells upon overexpression of mutant PGC-1α (Gly482Ser). Overexpression of wild-type PGC-1α, but not mutant PGC-1α, also caused a significant increase in hepatocyte expression of carnitine palmitoyl transferase 1a, a rate-determining enzyme that transfers long-chain fatty acids into mitochondria for oxidation. In addition, overexpression of mutant PGC-1α did not stimulate PEPCK-C expression as overexpression of wild-type PGC-1α did, likely due to a decrease in the ability of mutant PGC-1α in increasing PEPCK promoter transcription activity. Together, these results suggest that Gly482Ser mutation impairs the abilities of PGC-1α in decreasing fat deposition and in stimulating PEPCK-C expression in cultured hepatocytes.

A role for inducible 6-phosphofructo-2-kinase in the control of neuronal glycolysis

Increased glycolysis is the result of the sensing of glucose by hypothalamic neurons. The biochemical mechanisms underlying the control of hypothalamic glycolysis, however, remain to be elucidated. Here we showed that PFKFB3, the gene that encodes for inducible 6-phosphofructo-2-kinase (iPFK2), was expressed at high abundance in both mouse hypothalami and clonal hypothalamic neurons. In response to re-feeding, PFKFB3 mRNA levels were increased by 10-fold in mouse hypothalami. In the hypothalamus, re-feeding also decreased the phosphorylation of AMP-activated protein kinase (AMPK) (Thr172) and the mRNA levels of agouti-related protein (AgRP), and increased the mRNA levels of cocaine-amphetamine-related transcript (CART). Similar results were observed in N-43/5 clonal hypothalamic neurons upon treatment with glucose and/or insulin. In addition, knockdown of PFKFB3/iPFK2 in N-43/5 neurons caused a decrease in rates of glycolysis, which was accompanied by increased AMPK phosphorylation, increased AgRP mRNA levels and decreased CART mRNA levels. In contrast, overexpression of PFKFB3/iPFK2 in N-43/5 neurons caused an increase in glycolysis, which was accompanied by decreased AMPK phosphorylation and decreased AgRP mRNA levels and increased CART mRNA levels. Together, these results suggest that PFKFB3/iPFK2 responds to re-feeding, which in turn stimulates hypothalamic glycolysis and decreases hypothalamic AMPK phosphorylation and alters neuropeptide expression in a pattern that is associated with suppression of food intake.

Disruption of inducible 6-phosphofructo-2-kinase impairs the suppressive effect of PPARγ activation on diet-induced intestine inflammatory response

PFKFB3 is a target gene of peroxisome proliferator-activated receptor gamma (PPARγ) and encodes for inducible 6-phosphofructo-2-kinase (iPFK2). As a key regulatory enzyme that stimulates glycolysis, PFKFB3/iPFK2 links adipocyte metabolic and inflammatory responses. Additionally, PFKFB3/iPFK2 is involved in the effect of active PPARγ on suppressing overnutrition-induced adipose tissue inflammatory response, which accounts for the insulin-sensitizing and antidiabetic effects of PPARγ activation. Using PFKFB3/iPFK2-disrupted mice, the present study investigated the role of PFKFB3/iPFK2 in regulating overnutrition-associated intestine inflammatory response and in mediating the effects of PPARγ activation. In wild-type mice, intestine PFKFB3/iPFK2 was increased in response to high-fat diet (HFD) feeding compared with that in mice fed a low-fat diet. However, intestine PFKFB3/iPFK2 was decreased in PFKFB3/iPFK2-disrupted mice and did not respond to HFD feeding. Furthermore, on an HFD, PFKFB3/iPFK2-disrupted mice displayed a significant increase in major intestine proinflammatory indicators such as toll-like receptor 4 expression, c-Jun N-terminal kinase 1 and nuclear factor kappa B phosphorylation, and proinflammatory cytokine expression compared with wild-type littermates. Upon treatment with rosiglitazone, an agonist of PPARγ, intestine proinflammatory indicators were markedly decreased in wild-type mice, but to a much lesser degree in PFKFB3/iPFK2-disrupted mice. Overall, the status of HFD-induced intestine inflammatory response in all treated mice correlated inversely with systemic insulin sensitivity, indicated by the homeostasis model assessment of insulin resistance data. Together, these results suggest that PFKFB3/iPFK2 is critically involved in the effect of PPARγ activation on suppressing diet-induced intestine inflammatory response.

Palmitoleate induces hepatic steatosis but suppresses liver inflammatory response in mice

The interaction between fat deposition and inflammation during obesity contributes to the development of non-alcoholic fatty liver disease (NAFLD). The present study examined the effects of palmitoleate, a monounsaturated fatty acid (16∶1n7), on liver metabolic and inflammatory responses, and investigated the mechanisms by which palmitoleate increases hepatocyte fatty acid synthase (FAS) expression. Male wild-type C57BL/6J mice were supplemented with palmitoleate and subjected to the assays to analyze hepatic steatosis and liver inflammatory response. Additionally, mouse primary hepatocytes were treated with palmitoleate and used to analyze fat deposition, the inflammatory response, and sterol regulatory element-binding protein 1c (SREBP1c) activation. Compared with controls, palmitoleate supplementation increased the circulating levels of palmitoleate and improved systemic insulin sensitivity. Locally, hepatic fat deposition and SREBP1c and FAS expression were significantly increased in palmitoleate-supplemented mice. These pro-lipogenic events were accompanied by improvement of liver insulin signaling. In addition, palmitoleate supplementation reduced the numbers of macrophages/Kupffer cells in livers of the treated mice. Consistently, supplementation of palmitoleate decreased the phosphorylation of nuclear factor kappa B (NF-κB, p65) and the expression of proinflammatory cytokines. These results were recapitulated in primary mouse hepatocytes. In terms of regulating FAS expression, treatment of palmitoleate increased the transcription activity of SREBP1c and enhanced the binding of SREBP1c to FAS promoter. Palmitoleate also decreased the phosphorylation of NF-κB p65 and the expression of proinflammatory cytokines in cultured macrophages. Together, these results suggest that palmitoleate acts through dissociating liver inflammatory response from hepatic steatosis to play a unique role in NAFLD.

A novel regulator of macrophage activation: miR-223 in obesity-associated adipose tissue inflammation

BACKGROUND

Macrophage activation plays a crucial role in regulating adipose tissue inflammation and is a major contributor to the pathogenesis of obesity-associated cardiovascular diseases. On various types of stimuli, macrophages respond with either classic (M1) or alternative (M2) activation. M1- and M2-mediated signaling pathways and corresponding cytokine production profiles are not completely understood. The discovery of microRNAs provides a new opportunity to understand this complicated but crucial network for macrophage activation and adipose tissue function.

METHODS AND RESULTS

We have examined the activity of microRNA-223 (miR-223) and its role in controlling macrophage functions in adipose tissue inflammation and systemic insulin resistance. miR-223(-/-) mice on a high-fat diet exhibited an increased severity of systemic insulin resistance compared with wild-type mice that was accompanied by a marked increase in adipose tissue inflammation. The specific regulatory effects of miR-223 in myeloid cell-mediated regulation of adipose tissue inflammation and insulin resistance were then confirmed by transplantation analysis. Moreover, using bone marrow-derived macrophages, we demonstrated that miR-223 is a novel regulator of macrophage polarization, which suppresses classic proinflammatory pathways and enhances the alternative antiinflammatory responses. In addition, we identified Pknox1 as a genuine miR-223 target gene and an essential regulator for macrophage polarization.

CONCLUSION

For the first time, this study demonstrates that miR-223 acts to inhibit Pknox1, suppressing proinflammatory activation of macrophages; thus, it is a crucial regulator of macrophage polarization and protects against diet-induced adipose tissue inflammatory response and systemic insulin resistance.

Targeted overexpression of inducible 6-phosphofructo-2-kinase in adipose tissue increases fat deposition but protects against diet-induced insulin resistance and inflammatory responses

Increasing evidence demonstrates the dissociation of fat deposition, the inflammatory response, and insulin resistance in the development of obesity-related metabolic diseases. As a regulatory enzyme of glycolysis, inducible 6-phosphofructo-2-kinase (iPFK2, encoded by PFKFB3) protects against diet-induced adipose tissue inflammatory response and systemic insulin resistance independently of adiposity. Using aP2-PFKFB3 transgenic (Tg) mice, we explored the ability of targeted adipocyte PFKFB3/iPFK2 overexpression to modulate diet-induced inflammatory responses and insulin resistance arising from fat deposition in both adipose and liver tissues. Compared with wild-type littermates (controls) on a high fat diet (HFD), Tg mice exhibited increased adiposity, decreased adipose inflammatory response, and improved insulin sensitivity. In a parallel pattern, HFD-fed Tg mice showed increased hepatic steatosis, decreased liver inflammatory response, and improved liver insulin sensitivity compared with controls. In both adipose and liver tissues, increased fat deposition was associated with lipid profile alterations characterized by an increase in palmitoleate. Additionally, plasma lipid profiles also displayed an increase in palmitoleate in HFD-Tg mice compared with controls. In cultured 3T3-L1 adipocytes, overexpression of PFKFB3/iPFK2 recapitulated metabolic and inflammatory changes observed in adipose tissue of Tg mice. Upon treatment with conditioned medium from iPFK2-overexpressing adipocytes, mouse primary hepatocytes displayed metabolic and inflammatory responses that were similar to those observed in livers of Tg mice. Together, these data demonstrate a unique role for PFKFB3/iPFK2 in adipocytes with regard to diet-induced inflammatory responses in both adipose and liver tissues.