A systems biology approach identifies inflammatory abnormalities between mouse strains prior to development of metabolic disease

Childhood Obesity, Hypothalamic Inflammation, and the Onset of Puberty: A Narrative Review

The onset of puberty, which is under the control of the hypothalamic-pituitary-gonadal (HPG) axis, is influenced by various factors, including obesity, which has been associated with the earlier onset of puberty. Obesity-induced hypothalamic inflammation may cause premature activation of gonadotropin-releasing hormone (GnRH) neurons, resulting in the development of precocious or early puberty. Mechanisms involving phoenixin action and hypothalamic microglial cells are implicated. Furthermore, obesity induces structural and cellular brain alterations, disrupting metabolic regulation. Imaging studies reveal neuroinflammatory changes in obese individuals, impacting pubertal timing. Magnetic resonance spectroscopy enables the assessment of the brain's neurochemical composition by measuring key metabolites, highlighting potential pathways involved in neurological changes associated with obesity. In this article, we present evidence indicating a potential association among obesity, hypothalamic inflammation, and precocious puberty.

Immune-mediated myogenesis and acetylcholine receptor clustering promote a slow disease progression in ALS mouse models

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a heterogeneous disease in terms of onset and progression rate. This may account for therapeutic clinical trial failure. Transgenic SOD1G93A mice on C57 or 129Sv background have a slow and fast disease progression rate, mimicking the variability observed in patients. Based on evidence inferring the active influence of skeletal muscle on ALS pathogenesis, we explored whether dysregulation in hindlimb skeletal muscle reflects the phenotypic difference between the two mouse models.

METHODS

Ex vivo immunohistochemical, biochemical, and biomolecular methodologies, together with in vivo electrophysiology and in vitro approaches on primary cells, were used to afford a comparative and longitudinal analysis of gastrocnemius medialis between fast- and slow-progressing ALS mice.

RESULTS

We reported that slow-progressing mice counteracted muscle denervation atrophy by increasing acetylcholine receptor clustering, enhancing evoked currents, and preserving compound muscle action potential. This matched with prompt and sustained myogenesis, likely triggered by an early inflammatory response switching the infiltrated macrophages towards a M2 pro-regenerative phenotype. Conversely, upon denervation, fast-progressing mice failed to promptly activate a compensatory muscle response, exhibiting a rapidly progressive deterioration of muscle force.

CONCLUSIONS

Our findings further pinpoint the pivotal role of skeletal muscle in ALS, providing new insights into underestimated disease mechanisms occurring at the periphery and providing useful (diagnostic, prognostic, and mechanistic) information to facilitate the translation of cost-effective therapeutic strategies from the laboratory to the clinic.

Brain sex-dependent alterations after prolonged high fat diet exposure in mice

We examined effects of exposing female and male mice for 33 weeks to 45% or 60% high fat diet (HFD). Males fed with either diet were more vulnerable than females, displaying higher and faster increase in body weight and more elevated cholesterol and liver enzymes levels. Higher glucose metabolism was revealed by PET in the olfactory bulbs of both sexes. However, males also displayed altered anterior cortex and cerebellum metabolism, accompanied by a more prominent brain inflammation relative to females. Although both sexes displayed reduced transcripts of neuronal and synaptic genes in anterior cortex, only males had decreased protein levels of AMPA and NMDA receptors. Oppositely, to anterior cortex, cerebellum of HFD-exposed mice displayed hypometabolism and transcriptional up-regulation of neuronal and synaptic genes. These results indicate that male brain is more susceptible to metabolic changes induced by HFD and that the anterior cortex versus cerebellum display inverse susceptibility to HFD.

AMP-activated protein kinase activation in skeletal muscle modulates exercise-induced uncoupled protein 1 expression in brown adipocyte in mouse model

Abstract

Aerobic exercise is an effective intervention in preventing obesity and is also an important factor associated with thermogenesis. There is an increasing interest in the factors and mechanisms induced by aerobic exercise that can influence the metabolism and thermogenic activity in an individual. Recent studies suggest that exercise induced circulating factors (known as ‘exerkines’), which are able to modulate activation of brown adipose tissue (BAT) and browning of white adipose tissue. However, the underlying molecular mechanisms associated with the effect of exercise‐induced peripheral factors on BAT activation remain poorly understood. Furthermore, the role of exercise training in BAT activation is still debatable. Hence, the purpose of our study is to assess whether exercise training affects the expression of uncoupled protein 1 (UCP1) in brown adipocytes via release of different blood factors. Four weeks of exercise training significantly decreased the body weight gain and fat mass gain. Furthermore, trained mice exhibit higher levels of energy expenditure and UCP1 expression than untrained mice. Surprisingly, treatment with serum from exercise‐trained mice increased the expression of UCP1 in differentiated brown adipocytes. To gain a better understanding of these mechanisms, we analysed the conditioned media obtained after treating the C2C12 myotubes with an AMP‐activated protein kinase (AMPK) activator (AICAR; 5‐aminoimidazole‐4‐carboxamide ribonucleotide), which leads to an increased expression of UCP1 when added to brown adipocytes. Our observations suggest the possibility of aerobic exercise‐induced BAT activation via activation of AMPK in skeletal muscles.

Key points

Exercise promotes thermogenesis by activating uncoupling protein 1 (UCP1), which leads to a decrease in the body weight gain and body fat content. However, little is known about the role of exerkines in modulating UCP1 expression and subsequent brown adipose tissue (BAT) activation.

Four weeks of voluntary wheel‐running exercise reduces body weight and fat content.

Exercise induces the increase in AMP‐activated protein kinase (AMPK) and slow‐type muscle fibre marker genes in skeletal muscles and promotes UCP1 expression in white and brown adipose tissues.

Incubation of brown adipocytes with serum isolated from exercise‐trained mice significantly increased their UCP1 gene and protein levels; moreover, conditioned media of AMPK‐activator‐treated C2C12 myotubes induces increased UCP1 expression in brown adipocytes.

These results show that aerobic exercise‐induced skeletal muscle AMPK has a significant effect on UCP1 expression in BAT.

Ipragliflozin, an SGLT2 Inhibitor, Ameliorates High-Fat Diet-Induced Metabolic Changes by Upregulating Energy Expenditure through Activation of the AMPK/ SIRT1 Pathway

BACKGROUND

Sodium-glucose co-transporter 2 (SGLT2) inhibitors are a new class of antidiabetic drugs that exhibit multiple extraglycemic effects. However, there are conflicting results regarding the effects of SGLT2 inhibition on energy expenditure and thermogenesis. Therefore, we investigated the effect of ipragliflozin (a selective SGLT2 inhibitor) on energy metabolism.

METHODS

Six-week-old male 129S6/Sv mice with a high propensity for adipose tissue browning were randomly assigned to three groups: normal chow control, 60% high-fat diet (HFD)-fed control, and 60% HFD-fed ipragliflozin-treated groups. The administration of diet and medication was continued for 16 weeks.

RESULTS

The HFD-fed mice became obese and developed hepatic steatosis and adipose tissue hypertrophy, but their random glucose levels were within the normal ranges; these features are similar to the metabolic features of a prediabetic condition. Ipragliflozin treatment markedly attenuated HFD-induced hepatic steatosis and reduced the size of hypertrophied adipocytes to that of smaller adipocytes. In the ipragliflozin treatment group, uncoupling protein 1 (Ucp1) and other thermogenesis-related genes were significantly upregulated in the visceral and subcutaneous adipose tissue, and fatty acid oxidation was increased in the brown adipose tissue. These effects were associated with a significant reduction in the insulin-to-glucagon ratio and the activation of the AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) pathway in the liver and adipose tissue.

CONCLUSION

SGLT2 inhibition by ipragliflozin showed beneficial metabolic effects in 129S6/Sv mice with HFD-induced obesity that mimics prediabetic conditions. Our data suggest that SGLT2 inhibitors, through their upregulation of energy expenditure, may have therapeutic potential in prediabetic obesity.

Mouse background genetics in biomedical research: The devil's in the details

BACKGROUND

Genetically modified mice are used widely to explore mechanisms in most biomedical fields-including transfusion. Concluding that a gene modification is responsible for a phenotypic change assumes no other differences between the gene-modified and wild-type mice besides the targetted gene.

STUDY DESIGN AND METHODS

To test the hypothesis that the N-terminus of Band3, which regulates metabolism, affects RBC storage biology, RBCs from mice with a modified N-terminus of Band3 were stored under simulated blood bank conditions. All strains of mice were generated with the same initial embryonic stem cells from 129 mice and each strain was backcrossed with C57BL/6 (B6) mice. Both 24-h recoveries post-transfusion and metabolomics were determined for stored RBCs. Genetic profiles of mice were assessed by a high-resolution SNP array.

RESULTS

RBCs from mice with a mutated Band3 N-terminus had increased lipid oxidation and worse 24-h recoveries, "demonstrating" that Band3 regulates oxidative injury during RBC storage. However, SNP analysis demonstrated variable inheritance of 129 genetic elements between strains. Controlled interbreeding experiments demonstrated that the changes in lipid oxidation and some of the decreased 24-hr recovery were caused by inheritance of a region of chromosome 1 of 129 origin, and not due to the modification of Band 3. SNP genotyping of a panel of commonly used commercially available KO mice showed considerable 129 contamination, despite wild-type B6 mice being listed as the correct control.

DISCUSSION

Thousands of articles published each year use gene-modified mice, yet genetic background issues are rarely considered. Assessment of such issues are not, but should become, routine norms of murine experimentation.

Obesity induced by high-fat diet is associated with critical changes in biological and molecular functions of mesenchymal stromal cells present in visceral adipose tissue

The mesenchymal stromal cells (MSCs) residing within the stromal component of visceral adipose tissue appear to be greatly affected by obesity, with impairment of their functions and presence of senescence. To gain further insight into these phenomena, we analyzed the changes in total proteome content and secretome of mouse MSCs after a high-fat diet (HFD) treatment compared to a normal diet (ND). In healthy conditions, MSCs are endowed with functions mainly devoted to vesicle trafficking. These cells have an immunoregulatory role, affecting leukocyte activation and migration, acute inflammation phase response, chemokine signaling, and platelet activities. They also present a robust response to stress. We identified four signaling pathways (TGF-β, VEGFR2, HMGB1, and Leptin) that appear to govern the cells' functions. In the obese mice, MSCs showed a change in their functions. The immunoregulation shifted toward pro-inflammatory tasks with the activation of interleukin-1 pathway and of Granzyme A signaling. Moreover, the methionine degradation pathway and the processing of capped intronless pre-mRNAs may be related to the inflammation process. The signaling pathways we identified in ND MSCs were replaced by MET, WNT, and FGFR2 signal transduction, which may play a role in promoting inflammation, cancer, and aging.

Lisofylline mitigates cardiac inflammation in a mouse model of obesity through improving insulin secretion and activating cardiac AMPK signaling pathway

Obesity has emerged as a leading cause of death in the last few decades, mainly due to associated cardiovascular diseases. Obesity, inflammation, and insulin resistance are strongly interlinked. Lisofylline (LSF), an anti-inflammatory agent, demonstrated protection against type 1 diabetes, as well as reduced obesity-induced insulin resistance and adipose tissue inflammation. However, its role in mitigating cardiac inflammation associated with obesity is not well studied. Mice were divided into 4 groups; the first group was fed regular chow diet, the second was fed regular chow diet and treated with LSF, the third was fed high fat diet (HFD), and the fourth was fed HFD and treated with LSF. Cardiac inflammation was interrogated via expression levels of TNF α, interleukins 6 and 10, phosphorylated STAT4 and lipoxygenases 12 and 12/15. Apoptosis and expression of the survival gene, AMPK, were also evaluated. We observed that LSF alleviated obesity-induced cardiac injury indirectly by improving both pancreatic β-cell function and insulin sensitivity, as well as, directly via upregulation of cardiac AMPK expression and downregulation of cardiac inflammation and apoptosis. LSF may represent an effective therapy targeting obesity-induced metabolic and cardiovascular complications.

Spinal Cord Metabolic Signatures in Models of Fast- and Slow-Progressing SOD1G93A Amyotrophic Lateral Sclerosis

The rate of disease progression in amyotrophic lateral sclerosis (ALS) is highly variable, even between patients with the same genetic mutations. Metabolic alterations may affect disease course variability in ALS patients, but challenges in identifying the preclinical and early phases of the disease limit our understanding of molecular mechanisms underlying differences in the rate of disease progression. We examined effects of SOD1^G93A on thoracic and lumbar spinal cord metabolites in two mouse ALS models with different rates of disease progression: the transgenic SOD1^G93A-C57BL/6JOlaHsd (C57-G93A, slow progression) and transgenic SOD1^G93A-129SvHsd (129S-G93A, fast progression) strains. Samples from three timepoints (presymptomatic, disease onset, and late stage disease) were analyzed using Gas Chromatography-Mass Spectrometry metabolomics. Tissue metabolome differences in the lumbar spinal cord were driven primarily by mouse genetic background, although larger responses were observed in metabolic trajectories after the onset of symptoms. The significantly affected lumbar spinal cord metabolites were involved in energy and lipid metabolism. In the thoracic spinal cord, metabolic differences related to genetic background, background-SOD1 genotype interactions, and longitudinal SOD1^G93A effects. The largest responses in thoracic spinal cord metabolic trajectories related to SOD1^G93A effects before onset of visible symptoms. More metabolites were significantly affected in the thoracic segment, which were involved in energy homeostasis, neurotransmitter synthesis and utilization, and the oxidative stress response. We find evidence that initial metabolic alterations in SOD1^G93A mice confer disadvantages for maintaining neuronal viability under ALS-related stressors, with slow-progressing C57-G93A mice potentially having more favorable spinal cord bioenergetic profiles than 129S-G93A. These genetic background-associated metabolic differences together with the different early metabolic responses underscore the need to better characterize the impact of germline genetic variation on cellular responses to ALS gene mutations both before and after the onset of symptoms in order to understand their impact on disease development.

Extracellular miRNAs: From Biomarkers to Mediators of Physiology and Disease

miRNAs can be found in serum and other body fluids and serve as biomarkers for disease. More importantly, secreted miRNAs, especially those in extracellular vesicles (EVs) such as exosomes, may mediate paracrine and endocrine communication between different tissues and thus modulate gene expression and the function of distal cells. When impaired, these processes can lead to tissue dysfunction, aging, and disease. Adipose tissue is an especially important contributor to the pool of circulating exosomal miRNAs. As a result, alterations in adipose tissue mass or function, which occur in many metabolic conditions, can lead to changes in circulating miRNAs, which then function systemically. Here we review the findings that led to these conclusions and discuss how this sets the stage for new lines of investigation in which extracellular miRNAs are recognized as important mediators of intercellular communication and potential candidates for therapy of disease.

Macrophage LRP1 Promotes Diet-Induced Hepatic Inflammation and Metabolic Dysfunction by Modulating Wnt Signaling

Hepatic inflammation is associated with the development of insulin resistance, which can perpetuate the disease state and may increase the risk of metabolic syndrome and diabetes. Despite recent advances, mechanisms linking hepatic inflammation and insulin resistance are still unclear. The low-density lipoprotein receptor-related protein 1 (LRP1) is a large endocytic and signaling receptor that is highly expressed in macrophages, adipocytes, hepatocytes, and vascular smooth muscle cells. To investigate the potential role of macrophage LRP1 in hepatic inflammation and insulin resistance, we conducted experiments using macrophage-specific LRP1-deficient mice (macLRP1-/- ) generated on a low-density lipoprotein receptor knockout (LDLR-/- ) background and fed a Western diet. LDLR-/-; macLRP1-/- mice gained less body weight and had improved glucose tolerance compared to LDLR-/- mice. Livers from LDLR-/-; macLRP1-/- mice displayed lower levels of gene expression for several inflammatory cytokines, including Ccl3, Ccl4, Ccl8, Ccr1, Ccr2, Cxcl9, and Tnf, and reduced phosphorylation of GSK3α and p38 MAPK proteins. Furthermore, LRP1-deficient peritoneal macrophages displayed altered cholesterol metabolism. Finally, circulating levels of sFRP-5, a potent anti-inflammatory adipokine that functions as a decoy receptor for Wnt5a, were elevated in LDLR-/-; macLRP1-/- mice. Surface plasmon resonance experiments revealed that sFRP-5 is a novel high affinity ligand for LRP1, revealing that LRP1 regulates levels of this inhibitor of Wnt5a-mediated signaling. Collectively, our results suggest that LRP1 expression in macrophages promotes hepatic inflammation and the development of glucose intolerance and insulin resistance by modulating Wnt signaling.

Adipose depot-specific effects of ileal interposition surgery in UCD-T2D rats: unexpected implications for obesity and diabetes

Ileal interposition (IT) surgery delays the onset of diabetes in a rat model of type-2 diabetes (UCD-T2DM). Here, to gain a deeper understanding of the molecular events underlying the effects of IT surgery, we examined the changes in the proteome of four white adipose depots (retroperitoneal, mesenteric, inguinal, and epididymal) and plasma-free fatty acid profile in pre-diabetic rats 1.5 months following IT or sham surgery. The IT-mediated changes were exerted mainly in mesenteric fat and spanned from delayed adipocyte maturation to a neuroendocrine remodeling. Conversely, inguinal, retroperitoneal, and epididymal depots showed opposite trends consistent with increased adipocyte maturation and adipogenesis development prior to overt signs of diabetes, probably orchestrated by peroxisome proliferator-activated receptor gamma signaling and higher plasma n-6/n-3 free fatty acid ratios. The resulting scenario suggests a targeted use of surgical strategies that seek to delay or improve diabetes in order to manipulate adipose depot-specific responses to maximize the duration and beneficial effects of the surgery.

Genetics of metabolic syndrome: potential clues from wild-derived inbred mouse strains

The metabolic syndrome (MetS) is a complex constellation of metabolic abnormalities including obesity, abnormal glucose metabolism, dyslipidemia, and elevated blood pressure that together substantially increase risk for cardiovascular disease and Type 2 diabetes. Both genetic and environmental factors contribute to the development of MetS, but this process is still far from understood. Human studies have revealed only part of the underlying basis. Studies in mice offer many strengths that can complement human studies to help elucidate the etiology and pathophysiology of MetS. Here we review the ways mice can contribute to MetS research. In particular, we focus on the information that can be obtained from studies of the inbred strains, with specific focus on the phenotypes of the wild-derived inbred strains. These are newly derived inbred strains that were created from wild-caught mice. They contain substantial genetic variation that is not present in the classical inbred strains, have phenotypes of relevance for MetS, and various mouse strain resources have been created to facilitate the mining of this new genetic variation. Thus studies using wild-derived inbred strains hold great promise for increasing our understanding of MetS.

Fat-specific Dicer deficiency accelerates aging and mitigates several effects of dietary restriction in mice

Aging increases the risk of type 2 diabetes, and this can be prevented by dietary restriction (DR). We have previously shown that DR inhibits the downregulation of miRNAs and their processing enzymes - mainly Dicer - that occurs with aging in mouse white adipose tissue (WAT). Here we used fat-specific Dicer knockout mice (AdicerKO) to understand the contributions of adipose tissue Dicer to the metabolic effects of aging and DR. Metabolomic data uncovered a clear distinction between the serum metabolite profiles of Lox control and AdicerKO mice, with a notable elevation of branched-chain amino acids (BCAA) in AdicerKO. These profiles were associated with reduced oxidative metabolism and increased lactate in WAT of AdicerKO mice and were accompanied by structural and functional changes in mitochondria, particularly under DR. AdicerKO mice displayed increased mTORC1 activation in WAT and skeletal muscle, where Dicer expression is not affected. This was accompanied by accelerated age-associated insulin resistance and premature mortality. Moreover, DR-induced insulin sensitivity was abrogated in AdicerKO mice. This was reverted by rapamycin injection, demonstrating that insulin resistance in AdicerKO mice is caused by mTORC1 hyperactivation. Our study evidences a DR-modulated role for WAT Dicer in controlling metabolism and insulin resistance.

Dual specificity phosphatase 6 deficiency is associated with impaired systemic glucose tolerance and reversible weight retardation in mice

Here, we aimed to investigate the potential role of DUSP6, a dual specificity phosphatase, that specifically inactivates extracellular signal-regulated kinase (ERK), for the regulation of body weight and glucose homeostasis. We further assessed whether metabolic challenges affect Dusp6 expression in selected brain areas or white adipose tissue. Hypothalamic Dusp6 mRNA levels remained unchanged in chow-fed lean vs. high fat diet (HFD) fed obese C57Bl/6J mice, and in C57Bl/6J mice undergoing prolonged fasting or refeeding with fat free diet (FFD) or HFD. Similarly, Dusp6 expression levels were unchanged in selected brain regions of Lep^ob mice treated with 1 mg/kg of leptin for 6 days, compared to pair-fed or saline-treated Lep^ob controls. Dusp6 expression levels remained unaltered in vitro in primary adipocytes undergoing differentiation, but were increased in eWAT of HFD-fed obese C57Bl/6J mice, compared to chow-fed lean controls. Global chow-fed DUSP6 KO mice displayed reduced body weight and lean mass and slightly increased fat mass at a young age, which is indicative for early-age weight retardation. Subsequent exposure to HFD led to a significant increase in lean mass and body weight in DUSP6 deficient mice, compared to WT controls. Nevertheless, after 26 weeks of high-fat diet exposure, we observed comparable body weight, fat and lean mass in DUSP6 WT and KO mice, suggesting overall normal susceptibility to develop obesity. In line with the increased weight gain to compensate for early-age weight retardation, HFD-fed DUSP6 KO displayed increased expression levels of anabolic genes involved in lipid and cholesterol metabolism in the epididymal white adipose tissue (eWAT), compared to WT controls. Glucose tolerance was perturbed in both chow-fed lean or HFD-fed obese DUSP6 KO, compared to their respective WT controls. Overall, our data indicate that DUSP6 deficiency has limited impact on the regulation of energy metabolism, but impairs systemic glucose tolerance. Our data are in conflict to earlier reports that propose protection from diet-induced obesity and glucose intolerance in DUSP6 deficient mice. Reasons for the discrepancies remain elusive, but may entail differential genetic backgrounds, environmental factors such as the type and source of HFD, or alterations in the gut microbiome between facilities.

Molecular and genetic inflammation networks in major human diseases

It has been well-recognized that inflammation alongside tissue repair and damage maintaining tissue homeostasis determines the initiation and progression of complex diseases. Albeit with the accomplishment of having captured the most critical inflammation-involved molecules, genetic susceptibilities, epigenetic factors, and environmental factors, our schemata on the role of inflammation in complex diseases remain largely patchy, in part due to the success of reductionism in terms of research methodology per se. Omics data alongside the advances in data integration technologies have enabled reconstruction of molecular and genetic inflammation networks which shed light on the underlying pathophysiology of complex diseases or clinical conditions. Given the proven beneficial role of anti-inflammation in coronary heart disease as well as other complex diseases and immunotherapy as a revolutionary transition in oncology, it becomes timely to review our current understanding of the molecular and genetic inflammation networks underlying major human diseases. In this review, we first briefly discuss the complexity of infectious diseases and then highlight recently uncovered molecular and genetic inflammation networks in other major human diseases including obesity, type II diabetes, coronary heart disease, late onset Alzheimer's disease, Parkinson's disease, and sporadic cancer. The commonality and specificity of these molecular networks are addressed in the context of genetics based on genome-wide association study (GWAS). The double-sword role of inflammation, such as how the aberrant type 1 and/or type 2 immunity leads to chronic and severe clinical conditions, remains open in terms of the inflammasome and the core inflammatome network features. Increasingly available large Omics and clinical data in tandem with systems biology approaches have offered an exciting yet challenging opportunity toward reconstruction of more comprehensive and dynamic molecular and genetic inflammation networks, which hold great promise in transiting network snapshots to video-style multi-scale interplays of disease mechanisms, in turn leading to effective clinical intervention.

Sodium Iodate Produces a Strain-Dependent Retinal Oxidative Stress Response Measured In Vivo Using QUEST MRI

Purpose

We identify noninvasive biomarkers that measure the severity of oxidative stress within retina layers in sodium iodate (SI)-atrophy vulnerable (C57BL/6 [B6]) and SI-atrophy resistant (129S6/SvEvTac [S6]) mice.

Methods

At 24 hours after administering systemic SI to B6 and S6 mice we measured: (1) superoxide production in whole retina ex vivo, (2) excessive free radical production in vivo based on layer-specific 1/T1 values before and after α-lipoic acid (ALA) administration while the animal was inside the magnet (QUEnch-assiSTed MRI [QUEST MRI]), and (3) visual performance (optokinetic tracking) ± antioxidants; control mice were similarly assessed. Retinal layer spacing and thickness in vivo also were evaluated (optical coherence tomography, MRI).

Results

SI-treated B6 mice retina had a significantly higher superoxide production than SI-treated S6 mice. ALA-injected SI-treated B6 mice had reduced 1/T1 in more retinal layers in vivo than in SI-treated S6 mice. Uninjected and saline-injected SI-treated B6 mice had similar transretinal 1/T1 profiles. Notably, the inner segment layer 1/T1 of SI-treated B6 mice was responsive to ALA but was unresponsive in SI-treated S6 mice. In both SI-treated strains, antioxidants improved contrast sensitivity to similar extents; antioxidants did not change acuity in either group. Retinal thicknesses were normal in both SI-treated strains at 24 hours after treatment.

Conclusions

QUEST MRI uniquely measured severity of excessive free radical production within retinal layers of the same subject. Identifying the mechanisms underlying genetic vulnerabilities to oxidative stress is expected to help in understanding the pathogenesis of retinal degeneration.

High-fat feeding rather than obesity drives taxonomical and functional changes in the gut microbiota in mice

BACKGROUND

It is well known that the microbiota of high-fat (HF) diet-induced obese mice differs from that of lean mice, but to what extent, this difference reflects the obese state or the diet is unclear. To dissociate changes in the gut microbiota associated with high HF feeding from those associated with obesity, we took advantage of the different susceptibility of C57BL/6JBomTac (BL6) and 129S6/SvEvTac (Sv129) mice to diet-induced obesity and of their different responses to inhibition of cyclooxygenase (COX) activity, where inhibition of COX activity in BL6 mice prevents HF diet-induced obesity, but in Sv129 mice accentuates obesity.

RESULTS

Using HiSeq-based whole genome sequencing, we identified taxonomic and functional differences in the gut microbiota of the two mouse strains fed regular low-fat or HF diets with or without supplementation with the COX-inhibitor, indomethacin. HF feeding rather than obesity development led to distinct changes in the gut microbiota. We observed a robust increase in alpha diversity, gene count, abundance of genera known to be butyrate producers, and abundance of genes involved in butyrate production in Sv129 mice compared to BL6 mice fed either a LF or a HF diet. Conversely, the abundance of genes involved in propionate metabolism, associated with increased energy harvest, was higher in BL6 mice than Sv129 mice.

CONCLUSIONS

The changes in the composition of the gut microbiota were predominantly driven by high-fat feeding rather than reflecting the obese state of the mice. Differences in the abundance of butyrate and propionate producing bacteria in the gut may at least in part contribute to the observed differences in obesity propensity in Sv129 and BL6 mice.

Cumulus cell mitochondrial activity in relation to body mass index in women undergoing assisted reproductive therapy

Most studies have considered the negative influence of obesity on fertility in both genders. In the present study, we assessed mitochondrial activity expressed as the mitochondrial potential index (MPI) in cumulus cells from obese women and women with a normal body mass index (BMI) during assisted reproductive therapy. The results revealed a significant reduction of MPI with increased body mass. The lower MPI levels in cumulus cells from obese women may reflect mitochondrial dysfunction caused by oxidative stress, which can affect the cumulus-oocyte complex and have an impact on oocyte development.

Key Role of STAT4 Deficiency in the Hematopoietic Compartment in Insulin Resistance and Adipose Tissue Inflammation

Visceral adipose tissue (AT) inflammation is linked to the complications of obesity, including insulin resistance (IR) and type 2 diabetes. Recent data from our lab showed that germline deficiency in STAT4 reduces inflammation and improves IR in obese mice. The objective of this study was to determine the contribution of selective STAT4 deficiency in subsets of hematopoietic cells to IR and AT inflammation. To determine the contribution of hematopoietic lineage, we sublethally irradiated Stat4^-/-C57Bl6 mice and reconstituted them with bone marrow cells (BMC) from Stat4^+/+C57Bl6 congenic donors. We also established the contribution of selective STAT4 deficiency in CD4+ or CD8+ T cells using adoptive transfer in Rag1-/- mice. All mice received a HFD for 15 weeks (n = 7-12 mice/group). BMC that expressed STAT4 induced increases in glucose intolerance and IR compared to STAT4-deficient cells. Also, AT inflammation was increased and the numbers of CD8+ cells infiltrating AT were higher in mice with STAT4 expressing BMC. Studies in Rag1-/- mice further confirmed the prominent role of CD8+ cells expressing STAT4 in insulin resistance and AT and islet inflammation. Collectively our results show specific and dominant contribution of STAT4 in the hematopoietic compartment to metabolic health and inflammation in diet-induced obesity.

FFAR4 (GPR120) Signaling Is Not Required for Anti-Inflammatory and Insulin-Sensitizing Effects of Omega-3 Fatty Acids

Free fatty acid receptor-4 (FFAR4), also known as GPR120, has been reported to mediate the beneficial effects of omega-3 polyunsaturated fatty acids (ω3-PUFAs) by inducing an anti-inflammatory immune response. Thus, activation of FFAR4 has been reported to ameliorate chronic low-grade inflammation and insulin resistance accompanying obesity. However, conflicting reports on the role of FFAR4 in mediating the effects of ω3-PUFAs are emerging, suggesting that FFAR4 may not be the sole effector. Hence analyses of the importance of this receptor in relation to other signaling pathways and prominent effects of ω3-PUFAs remain to be elucidated. In the present study, we used Ffar4 knockouts (KO) and heterozygous (HET) mice fed either low fat, low sucrose reference diet; high fat, high sucrose ω3-PUFA; or high fat, high sucrose ω6-PUFA diet for 36 weeks. We demonstrate that both KO and HET mice fed ω3-PUFAs were protected against obesity, hepatic triacylglycerol accumulation, and whole-body insulin resistance. Moreover, ω3-PUFA fed mice had increased circulating protein levels of the anti-inflammatory adipokine, adiponectin, decreased fasting insulin levels, and decreased mRNA expression of several proinflammatory molecules within visceral adipose tissue. In conclusion, we find that FFAR4 signaling is not required for the reported anti-inflammatory and insulin-sensitizing effects mediated by ω3-PUFAs.

Antibiotic effects on gut microbiota and metabolism are host dependent

Interactions of diet, gut microbiota, and host genetics play important roles in the development of obesity and insulin resistance. Here, we have investigated the molecular links between gut microbiota, insulin resistance, and glucose metabolism in 3 inbred mouse strains with differing susceptibilities to metabolic syndrome using diet and antibiotic treatment. Antibiotic treatment altered intestinal microbiota, decreased tissue inflammation, improved insulin signaling in basal and stimulated states, and improved glucose metabolism in obesity- and diabetes-prone C57BL/6J mice on a high-fat diet (HFD). Many of these changes were reproduced by the transfer of gut microbiota from antibiotic-treated donors to germ-free or germ-depleted mice. These physiological changes closely correlated with changes in serum bile acids and levels of the antiinflammatory bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) and were partially recapitulated by treatment with a TGR5 agonist. In contrast, antibiotic treatment of HFD-fed, obesity-resistant 129S1 and obesity-prone 129S6 mice did not improve metabolism, despite changes in microbiota and bile acids. These mice also failed to show a reduction in inflammatory gene expression in response to the TGR5 agonist. Thus, changes in bile acid and inflammatory signaling, insulin resistance, and glucose metabolism driven by an HFD can be modified by antibiotic-induced changes in gut microbiota; however, these effects depend on important interactions with the host's genetic background and inflammatory potential.

Interactions between host genetics and gut microbiome in diabetes and metabolic syndrome

BACKGROUND

Diabetes, obesity, and the metabolic syndrome are multifactorial diseases dependent on a complex interaction of host genetics, diet, and other environmental factors. Increasing evidence places gut microbiota as important modulators of the crosstalk between diet and development of obesity and metabolic dysfunction. In addition, host genetics can have important impact on the composition and function of gut microbiota. Indeed, depending on the genetic background of the host, diet and other environmental factors may produce different changes in gut microbiota, have different impacts on host metabolism, and create different interactions between the microbiome and the host.

SCOPE OF REVIEW

In this review, we highlight how appropriate animal models can help dissect the complex interaction of host genetics with the gut microbiome and how diet can lead to different degrees of weight gain, levels of insulin resistance, and metabolic outcomes, such as diabetes, in different individuals. We also discuss the challenges of identifying specific disease-associated microbiota and the limitations of simple metrics, such as phylogenetic diversity or the ratio of Firmicutes to Bacteroidetes.

MAJOR CONCLUSIONS

Understanding these complex interactions will help in the development of novel treatments for microbiome-related metabolic diseases. This article is part of a special issue on microbiota.

New Insights on the Mechanisms of Disease Course Variability in ALS from Mutant SOD1 Mouse Models

Amyotrophic Lateral Sclerosis (ALS) is a heterogeneous disease in terms of progression rate and survival. This is probably one of the reasons for the failure of many clinical trials and the lack of effective therapies. Similar variability is also seen in SOD1(G93A) mouse models based on their genetic background. For example, when the SOD1(G93A) transgene is expressed in C57BL6 background the phenotype is mild with slower disease progression than in the 129Sv mice expressing the same amount of transgene but showing faster progression and shorter lifespan. This review summarizes and discusses data obtained from the analysis of these two mouse models under different aspects such as the motor phenotype, neuropathological alterations in the central nervous system (CNS) and peripheral nervous system (PNS) and the motor neuron autonomous and non-cell autonomous mechanisms with the aim of finding elements to explain the different rates of disease progression. We also discuss the identification of promising prognostic biomarkers by comparative analysis of the two ALS mouse models. This analysis might possibly suggest new strategies for effective therapeutic intervention in ALS to slow significantly or even block the course of the disease.

Thrombospondin-4 ablation reduces macrophage recruitment in adipose tissue and neointima and suppresses injury-induced restenosis in mice

OBJECTIVE

Thrombospondin-4 (Thbs4) is a member of the extracellular calcium-binding protein family and is linked to cell adhesion and migration. Given the involvement of Thbs4 in vascular inflammation, we hypothesized that Thbs4 plays a role in restenosis.

METHODS AND RESULTS

Here we show evidence that Thbs4 is upregulated in wire-injured mouse arteries and correlated with CD68 expression. Macrophage infiltration is reduced in both adipose tissue (AT) and neointima of Thbs4/ApoE double knockout (DKO) mice after injury. Moreover, Thbs4 deficiency prevents restenosis in ApoE KO mice fed a Western-type diet (WTD). Lethally irradiated DKO mice that receive bone marrow from ApoE KO or DKO mice have reduced neointima development. While considering related mechanisms, we note decreased chemokine production in both AT and neointima of DKO mice. In addition, vascular smooth muscle cells (VSMCs) derived from DKO mice display suppressed proliferation and migration in comparison with controls. Thioglycollate (TG)-induced macrophages from DKO mice show retarded adhesion to VSMCs. Recombinant Thbs4 promoted macrophage adhesion to VSMCs, and enhanced VSMC proliferation and migration.

CONCLUSION

Collectively, these data highlight the significance of Thbs4 in regulating macrophage accumulation and treating restenosis.

Hypothalamic inflammation in the control of metabolic function

Diet-induced obesity leads to devastating and common chronic diseases, fueling ongoing interest in determining new mechanisms underlying both obesity and its consequences. It is now well known that chronic overnutrition produces a unique form of inflammation in peripheral insulin target tissues, and efforts to limit this inflammation have met with some success in preserving insulin sensitivity in obese individuals. Recently, the activation of inflammatory pathways by dietary excess has also been observed among cells located in the mediobasal hypothalamus, a brain area that exerts central control over peripheral glucose, fat, and energy metabolism. Here we review progress in the field of diet-induced hypothalamic inflammation, drawing key distinctions between metabolic inflammation in the hypothalamus and that occurring in peripheral tissues. We focus on specific stimuli of the inflammatory response, the roles of individual hypothalamic cell types, and the links between hypothalamic inflammation and metabolic function under normal and pathophysiological circumstances. Finally, we explore the concept of controlling hypothalamic inflammation to mitigate metabolic disease.

Interactions between Gut Microbiota, Host Genetics and Diet Modulate the Predisposition to Obesity and Metabolic Syndrome

Obesity, diabetes, and metabolic syndrome result from complex interactions between genetic and environmental factors, including the gut microbiota. To dissect these interactions, we utilized three commonly used inbred strains of mice-obesity/diabetes-prone C57Bl/6J mice, obesity/diabetes-resistant 129S1/SvImJ from Jackson Laboratory, and obesity-prone but diabetes-resistant 129S6/SvEvTac from Taconic-plus three derivative lines generated by breeding these strains in a new, common environment. Analysis of metabolic parameters and gut microbiota in all strains and their environmentally normalized derivatives revealed strong interactions between microbiota, diet, breeding site, and metabolic phenotype. Strain-dependent and strain-independent correlations were found between specific microbiota and phenotypes, some of which could be transferred to germ-free recipient animals by fecal transplantation. Environmental reprogramming of microbiota resulted in 129S6/SvEvTac becoming obesity resistant. Thus, development of obesity/metabolic syndrome is the result of interactions between gut microbiota, host genetics, and diet. In permissive genetic backgrounds, environmental reprograming of microbiota can ameliorate development of metabolic syndrome.

Type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is an expanding global health problem, closely linked to the epidemic of obesity. Individuals with T2DM are at high risk for both microvascular complications (including retinopathy, nephropathy and neuropathy) and macrovascular complications (such as cardiovascular comorbidities), owing to hyperglycaemia and individual components of the insulin resistance (metabolic) syndrome. Environmental factors (for example, obesity, an unhealthy diet and physical inactivity) and genetic factors contribute to the multiple pathophysiological disturbances that are responsible for impaired glucose homeostasis in T2DM. Insulin resistance and impaired insulin secretion remain the core defects in T2DM, but at least six other pathophysiological abnormalities contribute to the dysregulation of glucose metabolism. The multiple pathogenetic disturbances present in T2DM dictate that multiple antidiabetic agents, used in combination, will be required to maintain normoglycaemia. The treatment must not only be effective and safe but also improve the quality of life. Several novel medications are in development, but the greatest need is for agents that enhance insulin sensitivity, halt the progressive pancreatic β-cell failure that is characteristic of T2DM and prevent or reverse the microvascular complications. For an illustrated summary of this Primer, visit: http://go.nature.com/V2eGfN.

RGC32 deficiency protects against high-fat diet-induced obesity and insulin resistance in mice

Obesity is an important independent risk factor for type 2 diabetes, cardiovascular diseases and many other chronic diseases. Adipose tissue inflammation is a critical link between obesity and insulin resistance and type 2 diabetes and a contributor to disease susceptibility and progression. The objective of this study was to determine the role of response gene to complement 32 (RGC32) in the development of obesity and insulin resistance. WT and RGC32 knockout (Rgc32(-/-) (Rgcc)) mice were fed normal chow or high-fat diet (HFD) for 12 weeks. Metabolic, biochemical, and histologic analyses were performed. 3T3-L1 preadipocytes were used to study the role of RGC32 in adipocytes in vitro. Rgc32(-/-) mice fed with HFD exhibited a lean phenotype with reduced epididymal fat weight compared with WT controls. Blood biochemical analysis and insulin tolerance test showed that RGC32 deficiency improved HFD-induced dyslipidemia and insulin resistance. Although it had no effect on adipocyte differentiation, RGC32 deficiency ameliorated adipose tissue and systemic inflammation. Moreover, Rgc32(-/-) induced browning of adipose tissues and increased energy expenditure. Our data indicated that RGC32 plays an important role in diet-induced obesity and insulin resistance, and thus it may serve as a potential novel drug target for developing therapeutics to treat obesity and metabolic disorders.

Altered miRNA processing disrupts brown/white adipocyte determination and associates with lipodystrophy

miRNAs are important regulators of biological processes in many tissues, including the differentiation and function of brown and white adipocytes. The endoribonuclease dicer is a major component of the miRNA-processing pathway, and in adipose tissue, levels of dicer have been shown to decrease with age, increase with caloric restriction, and influence stress resistance. Here, we demonstrated that mice with a fat-specific KO of dicer develop a form of lipodystrophy that is characterized by loss of intra-abdominal and subcutaneous white fat, severe insulin resistance, and enlargement and "whitening" of interscapular brown fat. Additionally, KO of dicer in cultured brown preadipocytes promoted a white adipocyte-like phenotype and reduced expression of several miRNAs. Brown preadipocyte whitening was partially reversed by expression of miR-365, a miRNA known to promote brown fat differentiation; however, introduction of other miRNAs, including miR-346 and miR-362, also contributed to reversal of the loss of the dicer phenotype. Interestingly, fat samples from patients with HIV-related lipodystrophy exhibited a substantial downregulation of dicer mRNA expression. Together, these findings indicate the importance of miRNA processing in white and brown adipose tissue determination and provide a potential link between this process and HIV-related lipodystrophy.

Hepatic Monoacylglycerol O-acyltransferase 1 as a Promising Therapeutic Target for Steatosis, Obesity, and Type 2 Diabetes

Over the past decade, considerable advances have been made in the discovery of gene targets in metabolic diseases. However, in vivo studies based on molecular biological technologies such as the generation of knockout mice and the construction of short hairpin RNA vectors require considerable effort and time, which is a major limitation for in vivo functional analysis. Here, we introduce a liver-specific nonviral small interfering RNA (siRNA) delivery system into rapid and efficient characterization of hepatic gene targets in metabolic disease mice. The comparative transcriptome analysis in liver between KKAy diabetic and normal control mice demonstrated that the expression of monoacylglycerol O-acyltransferase 1 (Mogat1), an enzyme involved in triglyceride synthesis and storage, was highly elevated during the disease progression. The upregulation of Mogat1 expression in liver was also found in other genetic (db/db) and diet-induced obese mice. The silencing of hepatic Mogat1 via a liver-specific siRNA delivery system resulted in a dramatic improvement in blood glucose levels and hepatic steatosis as well as overweight with no apparent overall toxicities, indicating that hepatic Mogat1 is a promising therapeutic target for metabolic diseases. The integrated approach with transcriptomics and nonviral siRNA delivery system provides a blueprint for rapid drug discovery and development.

Network analysis: a new approach to study endocrine disorders

Systems biology is the study of the interactions that occur between the components of individual cells - including genes, proteins, transcription factors, small molecules, and metabolites, and their relationships to complex physiological and pathological processes. The application of systems biology to medicine promises rapid advances in both our understanding of disease and the development of novel treatment options. Network biology has emerged as the primary tool for studying systems biology as it utilises the mathematical analysis of the relationships between connected objects in a biological system and allows the integration of varied 'omic' datasets (including genomics, metabolomics, proteomics, etc.). Analysis of network biology generates interactome models to infer and assess function; to understand mechanisms, and to prioritise candidates for further investigation. This review provides an overview of network methods used to support this research and an insight into current applications of network analysis applied to endocrinology. A wide spectrum of endocrine disorders are included ranging from congenital hyperinsulinism in infancy, through childhood developmental and growth disorders, to the development of metabolic diseases in early and late adulthood, such as obesity and obesity-related pathologies. In addition to providing a deeper understanding of diseases processes, network biology is also central to the development of personalised treatment strategies which will integrate pharmacogenomics with systems biology of the individual.

Carboxyl-ester lipase maturity-onset diabetes of the young is associated with development of pancreatic cysts and upregulated MAPK signaling in secretin-stimulated duodenal fluid

Carboxyl-ester lipase (CEL) maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes and pancreatic exocrine dysfunction due to mutations in the CEL gene encoding CEL. The pathogenic mechanism for diabetes development is unknown. Since CEL is expressed mainly in pancreatic acinar cells, we asked whether we could find structural pancreatic changes in CEL-MODY subjects during the course of diabetes development. Furthermore, we hypothesized that the diseased pancreas releases proteins that are detectable in pancreatic fluid and potentially reflect activation or inactivation of disease-specific pathways. We therefore investigated nondiabetic and diabetic CEL-mutation carriers by pancreatic imaging studies and secretin-stimulated duodenal juice sampling. The secretin-stimulated duodenal juice was studied using cytokine assays, mass spectrometry (MS) proteomics, and multiplexed MS-based measurement of kinase activities. We identified multiple pancreatic cysts in all eight diabetic mutation carriers but not in any of the four nondiabetic mutation carriers or the six healthy controls. Furthermore, we identified upregulated mitogen-activated protein kinase (MAPK) target proteins and MAPK-driven cytokines and increased MAPK activity in the secretin-stimulated duodenal juice. These findings show that subjects with CEL-MODY develop multiple pancreatic cysts by the time they develop diabetes and that upregulated MAPK signaling in the pancreatic secretome may reflect the pathophysiological development of pancreatic cysts and diabetes.

STAT4 deficiency reduces obesity-induced insulin resistance and adipose tissue inflammation

Signal transducer and activator of transcription (STAT) 4 is one of the seven members of the STAT family. STAT4 has a prominent role in mediating interleukin-12-induced T-helper cell type 1 lineage differentiation. T cells are key players in the maintenance of adipose tissue (AT) inflammation. The role of STAT4 in obesity and AT inflammation is unknown. We sought to determine the role of STAT4 in AT inflammation in obesity-induced insulin resistance. We studied STAT4-null mice on the C57Bl6/J background. We have found that STAT4(-/-)C57Bl6/J mice develop high-fat diet-induced obesity (DIO) similar to wild-type controls, but that they have significantly improved insulin sensitivity and better glucose tolerance. Using flow cytometry and real-time PCR, we show that STAT4(-/-) mice with DIO produce significantly reduced numbers of inflammatory cytokines and chemokines in adipocytes, have reduced numbers of CD8(+) cells, and display increased alternative (M2) macrophage polarization. CD8(+) cells, but not CD4(+) cells, from STAT4(-/-) mice displayed reduced in vitro migration. Also, we found that adipocyte inflammation is reduced and insulin signaling is improved in STAT4(-/-) mice with DIO. We have identified STAT4 as a key contributor to insulin resistance and AT inflammation in DIO. Targeting STAT4 activation could be a novel approach to reducing AT inflammation and insulin resistance in obesity.

Structure and dynamics of molecular networks: a novel paradigm of drug discovery: a comprehensive review

Despite considerable progress in genome- and proteome-based high-throughput screening methods and in rational drug design, the increase in approved drugs in the past decade did not match the increase of drug development costs. Network description and analysis not only give a systems-level understanding of drug action and disease complexity, but can also help to improve the efficiency of drug design. We give a comprehensive assessment of the analytical tools of network topology and dynamics. The state-of-the-art use of chemical similarity, protein structure, protein-protein interaction, signaling, genetic interaction and metabolic networks in the discovery of drug targets is summarized. We propose that network targeting follows two basic strategies. The "central hit strategy" selectively targets central nodes/edges of the flexible networks of infectious agents or cancer cells to kill them. The "network influence strategy" works against other diseases, where an efficient reconfiguration of rigid networks needs to be achieved by targeting the neighbors of central nodes/edges. It is shown how network techniques can help in the identification of single-target, edgetic, multi-target and allo-network drug target candidates. We review the recent boom in network methods helping hit identification, lead selection optimizing drug efficacy, as well as minimizing side-effects and drug toxicity. Successful network-based drug development strategies are shown through the examples of infections, cancer, metabolic diseases, neurodegenerative diseases and aging. Summarizing >1200 references we suggest an optimized protocol of network-aided drug development, and provide a list of systems-level hallmarks of drug quality. Finally, we highlight network-related drug development trends helping to achieve these hallmarks by a cohesive, global approach.

Neuropeptide Y is produced by adipose tissue macrophages and regulates obesity-induced inflammation

Neuropeptide Y (NPY) is induced in peripheral tissues such as adipose tissue with obesity. The mechanism and function of NPY induction in fat are unclear. Given the evidence that NPY can modulate inflammation, we examined the hypothesis that NPY regulates the function of adipose tissue macrophages (ATMs) in response to dietary obesity in mice. NPY was induced by dietary obesity in the stromal vascular cells of visceral fat depots from mice. Surprisingly, the induction of Npy was limited to purified ATMs from obese mice. Significant basal production of NPY was observed in cultured bone marrow derived macrophage and dendritic cells (DCs) and was increased with LPS stimulation. In vitro, addition of NPY to myeloid cells had minimal effects on their activation profiles. NPY receptor inhibition promoted DC maturation and the production of IL-6 and TNFα suggesting an anti-inflammatory function for NPY signaling in DCs. Consistent with this, NPY injection into lean mice decreased the quantity of M1-like CD11c⁺ ATMs and suppressed Ly6c^hi monocytes. BM chimeras generated from Npy^−/− donors demonstrated that hematopoietic NPY contributes to the obesity-induced induction of Npy in fat. In addition, loss of Npy expression from hematopoietic cells led to an increase in CD11c⁺ ATMs in visceral fat with high fat diet feeding. Overall, our studies suggest that NPY is produced by a range of myeloid cells and that obesity activates the production of NPY in adipose tissue macrophages with autocrine and paracrine effects.

Inverse regulation of inflammation and mitochondrial function in adipose tissue defines extreme insulin sensitivity in morbidly obese patients

Obesity is associated with insulin resistance, a major risk factor for type 2 diabetes and cardiovascular disease. However, not all obese individuals are insulin resistant, which confounds our understanding of the mechanistic link between these conditions. We conducted transcriptome analyses on 835 obese subjects with mean BMI of 48.8, on which we have previously reported genetic associations of gene expression. Here, we selected ~320 nondiabetic (HbA(1c) <7.0) subjects and further stratified the cohort into insulin-resistant versus insulin-sensitive subgroups based on homeostasis model assessment-insulin resistance. An unsupervised informatics analysis revealed that immune response and inflammation-related genes were significantly downregulated in the omental adipose tissue of obese individuals with extreme insulin sensitivity and, to a much lesser extent, in subcutaneous adipose tissue. In contrast, genes related to β-oxidation and the citric acid cycle were relatively overexpressed in adipose of insulin-sensitive patients. These observations were verified by querying an independent cohort of our published dataset of 37 subjects whose subcutaneous adipose tissue was sampled before and after treatment with thiazolidinediones. Whereas the immune response and inflammation pathway genes were downregulated by thiazolidinedione treatment, β-oxidation and citric acid cycle genes were upregulated. This work highlights the critical role that omental adipose inflammatory pathways might play in the pathophysiology of insulin resistance, independent of body weight.

Liver-derived systemic factors drive β cell hyperplasia in insulin-resistant states

Integrative organ crosstalk regulates key aspects of energy homeostasis, and its dysregulation may underlie metabolic disorders such as obesity and diabetes. To test the hypothesis that crosstalk between the liver and pancreatic islets modulates β cell growth in response to insulin resistance, we used the liver-specific insulin receptor knockout (LIRKO) mouse, a unique model that exhibits dramatic islet hyperplasia. Using complementary in vivo parabiosis and transplantation assays, as well as in vitro islet culture approaches, we demonstrate that humoral, nonneural, non-cell-autonomous factor(s) induces β cell proliferation in LIRKO mice. Furthermore, we report that a hepatocyte-derived factor(s) stimulates mouse and human β cell proliferation in ex vivo assays, independent of ambient glucose and insulin levels. These data implicate the liver as a critical source of β cell growth factor(s) in insulin-resistant states.

Systems biology of adipose tissue metabolism: regulation of growth, signaling and inflammation

Adipose tissue (AT) depots actively regulate whole body energy homeostasis by orchestrating complex communications with other physiological systems as well as within the tissue. Adipocytes readily respond to hormonal and nutritional inputs to store excess nutrients as intracellular lipids or mobilize the stored fat for utilization. Co-ordinated regulation of metabolic pathways balancing uptake, esterification, and hydrolysis of lipids is accomplished through positive and negative feedback interactions of regulatory hubs comprising several pleiotropic protein kinases and nuclear receptors. Metabolic regulation in adipocytes encompasses biogenesis and remodeling of uniquely large lipid droplets (LDs). The regulatory hubs also function as energy and nutrient sensors, and integrate metabolic regulation with intercellular signaling. Over-nutrition causes hypertrophic expansion of adipocytes, which, through incompletely understood mechanisms, initiates a cascade of metabolic and signaling events leading to tissue remodeling and immune cell recruitment. Macrophage activation and polarization toward a pro-inflammatory phenotype drives a self-reinforcing cycle of pro-inflammatory signals in the AT, establishing an inflammatory state. Sustained inflammation accelerates lipolysis and elevates free fatty acids in circulation, which robustly correlates with development of obesity-related diseases. The adipose regulatory network coupling metabolism, growth, and signaling of multiple cell types is exceedingly complex. While components of the regulatory network have been individually studied in exquisite detail, systems approaches have rarely been utilized to comprehensively assess the relative engagements of the components. Thus, need and opportunity exist to develop quantitative models of metabolic and signaling networks to achieve a more complete understanding of AT biology in both health and disease.

Systems Biology Approaches and Applications in Obesity, Diabetes, and Cardiovascular Diseases

The metabolically connected triad of obesity, diabetes, and cardiovascular diseases is a major public health threat, and is expected to worsen due to the global shift toward energy-rich and sedentary living. Despite decades of intense research, a large part of the molecular pathogenesis behind complex metabolic diseases remains unknown. Recent advances in genetics, epigenomics, transcriptomics, proteomics and metabolomics enable us to obtain large-scale snapshots of the etiological processes in multiple disease-related cells, tissues and organs. These datasets provide us with an opportunity to go beyond conventional reductionist approaches and to pinpoint the specific perturbations in critical biological processes. In this review, we summarize systems biology methodologies such as functional genomics, causality inference, data-driven biological network construction, and higher-level integrative analyses that can produce novel mechanistic insights, identify disease biomarkers, and uncover potential therapeutic targets from a combination of omics datasets. Importantly, we also demonstrate the power of these approaches by application examples in obesity, diabetes, and cardiovascular diseases.

Adipose tissue-specific deletion of 12/15-lipoxygenase protects mice from the consequences of a high-fat diet

Type 2 diabetes is associated with obesity, insulin resistance, and inflammation in adipose tissue. 12/15-Lipoxygenase (12/15-LO) generates proinflammatory lipid mediators, which induce inflammation in adipose tissue. Therefore we investigated the role of 12/15-LO activity in mouse white adipose tissue in promoting obesity-induced local and systemic inflammatory consequences. We generated a mouse model for fat-specific deletion of 12/15-LO, aP2-Cre; 12/15-LO^loxP/loxP, which we call ad-12/15-LO mice, and placed wild-type controls and ad-12/15-LO mice on a high-fat diet for 16 weeks and examined obesity-induced inflammation and insulin resistance. High-fat diet-fed ad-12/15-LO exhibited improved fasting glucose levels and glucose metabolism, and epididymal adipose tissue from these mice exhibited reduced inflammation and macrophage infiltration compared to wild-type mice. Furthermore, fat-specific deletion of 12/15-LO led to decreased peripheral pancreatic islet inflammation with enlarged pancreatic islets when mice were fed the high-fat diet compared to wild-type mice. These results suggest an interesting crosstalk between 12/15-LO expression in adipose tissue and inflammation in pancreatic islets. Therefore, deletion of 12/15-LO in adipose tissue can offer local and systemic protection from obesity-induced consequences, and blocking 12/15-LO activity in adipose tissue may be a novel therapeutic target in the treatment of type 2 diabetes.

The Ups and Downs of Insulin Resistance and Type 2 Diabetes: Lessons from Genomic Analyses in Humans

We are in the midst of a worldwide epidemic of type 2 diabetes (T2D) and obesity. Understanding the mechanisms underlying these diseases is critical if we are to halt their progression and ultimately prevent their development. The advent and widespread implementation of microarray technology has allowed analysis of small samples of human skeletal muscle, adipose, liver, pancreas and blood. While patterns differ in each tissue, several dominant themes have emerged from these studies, including altered expression of genes indicating increased inflammation and altered lipid and mitochondrial oxidative metabolism and insulin signaling in patients with T2D, and in some cases, in those at risk for disease. Unraveling which changes in gene expression are primary, and which are secondary to an insulin resistant or diabetes metabolic milieu remains a scientific challenge but we are one step closer.

Kinin B1 receptor in adipocytes regulates glucose tolerance and predisposition to obesity

BACKGROUND

Kinins participate in the pathophysiology of obesity and type 2 diabetes by mechanisms which are not fully understood. Kinin B(1) receptor knockout mice (B(1) (-/-)) are leaner and exhibit improved insulin sensitivity.

METHODOLOGY/PRINCIPAL FINDINGS

Here we show that kinin B(1) receptors in adipocytes play a role in controlling whole body insulin action and glucose homeostasis. Adipocytes isolated from mouse white adipose tissue (WAT) constitutively express kinin B(1) receptors. In these cells, treatment with the B(1) receptor agonist des-Arg(9)-bradykinin improved insulin signaling, GLUT4 translocation, and glucose uptake. Adipocytes from B(1) (-/-) mice showed reduced GLUT4 expression and impaired glucose uptake at both basal and insulin-stimulated states. To investigate the consequences of these phenomena to whole body metabolism, we generated mice where the expression of the kinin B(1) receptor was limited to cells of the adipose tissue (aP2-B(1)/B(1) (-/-)). Similarly to B(1) (-/-) mice, aP2-B(1)/B(1) (-/-) mice were leaner than wild type controls. However, exclusive expression of the kinin B(1) receptor in adipose tissue completely rescued the improved systemic insulin sensitivity phenotype of B(1) (-/-) mice. Adipose tissue gene expression analysis also revealed that genes involved in insulin signaling were significantly affected by the presence of the kinin B(1) receptor in adipose tissue. In agreement, GLUT4 expression and glucose uptake were increased in fat tissue of aP2-B(1)/B(1) (-/-) when compared to B(1) (-/-) mice. When subjected to high fat diet, aP2-B(1)/B(1) (-/-) mice gained more weight than B(1) (-/-) littermates, becoming as obese as the wild types.

CONCLUSIONS/SIGNIFICANCE

Thus, kinin B(1) receptor participates in the modulation of insulin action in adipocytes, contributing to systemic insulin sensitivity and predisposition to obesity.

Identification of adipose tissue dendritic cells correlated with obesity-associated insulin-resistance and inducing Th17 responses in mice and patients

T-cell regulation in adipose tissue provides a link between inflammation and insulin resistance. Because of alterations in adipose tissue T-cell composition in obesity, we aimed to identify the antigen-presenting cells in adipose tissue of obese mice and patients with insulin resistance. Dendritic cells (DCs) and T cells were studied in mice and in two cohorts of obese patients. In lean mice, only CD11c(+) DCs were detected in adipose tissue. Adoptive transfer of naive CD4(+) T cells in Rag1(-/-) mice led to a predominant Th1 response in adipose tissue. In contrast, during obesity DCs (human CD11c(+)CD1c(+) and mouse CD11c(high)F4/80(low)) accumulated in adipose tissue. CD11c(high)F4/80(low) DCs from obese mice induced Th17 differentiation. In patients, the presence of CD11c(+)CD1c(+) DCs correlated with the BMI and with an elevation in Th17 cells. In addition, these DCs led to ex vivo Th17 differentiation. CD1c gene expression further correlated with homeostatic model assessment-insulin resistance in the subcutaneous adipose tissue of obese patients. We show for the first time the presence and accumulation of specific DCs in adipose tissue in mouse and human obesity. These DCs were functional and could be important regulators of adipose tissue inflammation by regulating the switch toward Th17 cell responses in obesity-associated insulin resistance.

Early onset inflammation in pre-insulin-resistant diet-induced obese rats does not affect the vasoreactivity of isolated small mesenteric arteries

BACKGROUND

Obesity is an increasing burden affecting developed and emerging societies since it is associated with an increased risk of diabetes and consequent cardiovascular complications. Increasing evidence points towards a pivotal role of inflammation in the etiology of vascular dysfunction. Our study aimed to investigate signs of inflammation and their relation to vascular dysfunction in rats receiving a high fat diet.

METHODS

Diet-induced obese (DIO) rats were used as a model since these rats exhibit a human pre-diabetic pathology. Oral glucose and insulin tolerance tests were conducted on DIO rats and their controls prior to the development of insulin resistance. Furthermore, the plasma contents of selected cytokines [macrophage chemoattractant protein (MCP-1), interleukin-6 (IL-6), and interleukin-1 (IL-1)] and the concentration of adiponectin were measured. Using wire myography, we tested the vascular function of isolated small mesenteric arteries.

RESULTS

DIO animals had significantly (p < 0.05) increased body weight (721.2 ± 6.3 g) compared to age- and sex-matched controls (643.4 ± 14.6 g), as well as a significant increase (p < 0.01) in body fat percentage (29.7 ± 1.7% and 22.7 ± 0.97%, respectively). No significant difference in fasting plasma insulin levels could be detected between the two groups (chow-fed group 141.5 ± 15.1 pmol/l; high fat-fed group 125.9 ± 18.8 pmol/l). However, the levels of MCP-1 (89.7 ± 4.2 pg/ml vs. 60.8 ± 7.7 pg/ml) and IL-6 (61.6 ± 3.1 pg/ml vs. 41.6 ± 7.4 pg/ml) were significantly elevated in DIO animals (p < 0.05) as compared to controls. Adiponectin levels were also significantly increased (p < 0.01) in DIO rats (10.8 ± 0.7 ng/ml) versus controls (6.9 ± 0.5 ng/ml). No difference in vascular or endothelial function was evident as determined by responses to acetylcholine, sodium nitroprusside, endothelin-1, and calcitonin gene-related peptide.

CONCLUSION

In DIO rats, which have not yet developed hyperinsulinaemia or glucose intolerance, the levels of inflammatory mediators MCP-1 and Il-6 are significantly increased without concomitant vascular dysfunction. The results show that inflammation and obesity are tightly associated, and that inflammation is manifested prior to significant insulin resistance and vascular dysfunction.

Intrinsic differences in adipocyte precursor cells from different white fat depots

Obesity and body fat distribution are important risk factors for the development of type 2 diabetes and metabolic syndrome. Evidence has accumulated that this risk is related to intrinsic differences in behavior of adipocytes in different fat depots. In the current study, we demonstrate that adipocyte precursor cells (APCs) isolated from visceral and subcutaneous white adipose depots of mice have distinct patterns of gene expression, differentiation potential, and response to environmental and genetic influences. APCs derived from subcutaneous fat differentiate well in the presence of classical induction cocktail, whereas those from visceral fat differentiate poorly but can be induced to differentiate by addition of bone morphogenetic protein (BMP)-2 or BMP-4. This difference correlates with major differences in gene expression signature between subcutaneous and visceral APCs. The number of APCs is higher in obesity-prone C57BL/6 mice than obesity-resistant 129 mice, and the number in both depots is increased by up to 270% by exposure of mice to high-fat diet. Thus, APCs from visceral and subcutaneous depots are dynamic populations, which have intrinsic differences in gene expression, differentiation properties, and responses to environmental/genetic factors. Regulation of these populations may provide a new target for the treatment and prevention of obesity and its metabolic complications.

12/15-Lipoxygenase signaling in the endoplasmic reticulum stress response

Central obesity is associated with chronic inflammation, insulin resistance, β-cell dysfunction, and endoplasmic reticulum (ER) stress. The 12/15-lipoxygenase enzyme (12/15-LO) promotes inflammation and insulin resistance in adipose and peripheral tissues. Given that obesity is associated with ER stress and 12/15-LO is expressed in adipose tissue, we determined whether 12/15-LO could mediate ER stress signals. Addition of 12/15-LO lipid products 12(S)-HETE and 12(S)-HPETE to differentiated 3T3-L1 adipocytes induced expression and activation of ER stress markers, including BiP, XBP-1, p-PERK, and p-IRE1α. The ER stress inducer, tunicamycin, upregulated ER stress markers in adipocytes with concomitant 12/15-LO activation. Addition of a 12/15-LO inhibitor, CDC, to tunicamycin-treated adipocytes attenuated the ER stress response. Furthermore, 12/15-LO-deficient adipocytes exhibited significantly decreased tunicamycin-induced ER stress. 12/15-LO action involves upregulation of interleukin-12 (IL-12) expression. Tunicamycin significantly upregulated IL-12p40 expression in adipocytes, and IL-12 addition increased ER stress gene expression; conversely, LSF, an IL-12 signaling inhibitor, and an IL-12p40-neutralizing antibody attenuated tunicamycin-induced ER stress. Isolated adipocytes and liver from 12/15-LO-deficient mice fed a high-fat diet revealed a decrease in spliced XBP-1 expression compared with wild-type C57BL/6 mice on a high-fat diet. Furthermore, pancreatic islets from 12/15-LO-deficient mice showed reduced high-fat diet-induced ER stress genes compared with wild-type mice. These data suggest that 12/15-LO activity participates in ER stress in adipocytes, pancreatic islets, and liver. Therefore, reduction of 12/15-LO activity or expression could provide a new therapeutic target to reduce ER stress and downstream inflammation linked to obesity.

Obesity is associated with hypothalamic injury in rodents and humans

Rodent models of obesity induced by consuming high-fat diet (HFD) are characterized by inflammation both in peripheral tissues and in hypothalamic areas critical for energy homeostasis. Here we report that unlike inflammation in peripheral tissues, which develops as a consequence of obesity, hypothalamic inflammatory signaling was evident in both rats and mice within 1 to 3 days of HFD onset, prior to substantial weight gain. Furthermore, both reactive gliosis and markers suggestive of neuron injury were evident in the hypothalamic arcuate nucleus of rats and mice within the first week of HFD feeding. Although these responses temporarily subsided, suggesting that neuroprotective mechanisms may initially limit the damage, with continued HFD feeding, inflammation and gliosis returned permanently to the mediobasal hypothalamus. Consistent with these data in rodents, we found evidence of increased gliosis in the mediobasal hypothalamus of obese humans, as assessed by MRI. These findings collectively suggest that, in both humans and rodent models, obesity is associated with neuronal injury in a brain area crucial for body weight control.