Diet-induced type II diabetes in C57BL/6J mice

A multi-laboratory preclinical trial in rodents to assess treatment candidates for acute ischemic stroke

Human diseases may be modeled in animals to allow preclinical assessment of putative new clinical interventions. Recent, highly publicized failures of large clinical trials called into question the rigor, design, and value of preclinical assessment. We established the Stroke Preclinical Assessment Network (SPAN) to design and implement a randomized, controlled, blinded, multi-laboratory trial for the rigorous assessment of candidate stroke treatments combined with intravascular thrombectomy. Efficacy and futility boundaries in a multi-arm multi-stage statistical design aimed to exclude from further study highly effective or futile interventions after each of four sequential stages. Six independent research laboratories performed a standard focal cerebral ischemic insult in five animal models that included equal numbers of males and females: young mice, young rats, aging mice, mice with diet-induced obesity, and spontaneously hypertensive rats. The laboratories adhered to a common protocol and efficiently enrolled 2615 animals with full data completion and comprehensive animal tracking. SPAN successfully implemented treatment masking, randomization, prerandomization inclusion and exclusion criteria, and blinded assessment of outcomes. The SPAN design and infrastructure provide an effective approach that could be used in similar preclinical, multi-laboratory studies in other disease areas and should help improve reproducibility in translational science.

Comparison of three common inbred mouse strains reveals substantial differences in hippocampal GABAergic interneuron populations and in vitro network oscillations

A major challenge in neuroscience is to pinpoint neurobiological correlates of specific cognitive and neuropsychiatric traits. At the mesoscopic level, promising candidates for establishing such connections are brain oscillations that can be robustly recorded as local field potentials with varying frequencies in the hippocampus in vivo and in vitro. Inbred mouse strains show natural variation in hippocampal synaptic plasticity (e.g. long-term potentiation), a cellular correlate of learning and memory. However, their diversity in expression of different types of hippocampal network oscillations has not been fully explored. Here, we investigated hippocampal network oscillations in three widely used inbred mouse strains: C57BL/6J (B6J), C57BL/6NCrl (B6N) and 129S2/SvPasCrl (129) with the aim to identify common oscillatory characteristics in inbred mouse strains that show aberrant emotional/cognitive behaviour (B6N and 129) and compare them to "control" B6J strain. First, we detected higher gamma oscillation power in the hippocampal CA3 of both B6N and 129 strains. Second, higher incidence of hippocampal sharp wave-ripple (SPW-R) transients was evident in these strains. Third, we observed prominent differences in the densities of distinct interneuron types and CA3 associative network activity, which are indispensable for sustainment of mesoscopic network oscillations. Together, these results add further evidence to profound physiological differences among inbred mouse strains commonly used in neuroscience research.

Prenatal benzene exposure in mice alters offspring hypothalamic development predisposing to metabolic disease in later life

Maternal exposure to environmental contaminants during pregnancy poses a significant threat to a developing fetus, as these substances can easily cross the placenta and disrupt the neurodevelopment of offspring. Specifically, the hypothalamus is essential in the regulation of metabolism, notably during critical windows of development. An abnormal hormonal and inflammatory milieu during development can trigger persistent changes in the function of hypothalamic circuits, leading to long-lasting effects on the body's energy homeostasis and metabolism. We recently demonstrated that gestational exposure to clinically relevant levels of benzene induces severe metabolic dysregulation in the offspring. Given the central role of the hypothalamus in metabolic control, we hypothesized that prenatal exposure to benzene impacts hypothalamic development, contributing to the adverse metabolic effects in the offspring. C57BL/6JB dams were exposed to benzene at 50 ppm in the inhalation chambers exclusively during pregnancy (from E0.5 to E19). Transcriptomic analysis of the exposed offspring at postnatal day 21 (P21) revealed hypothalamic changes in genes related to metabolic regulation, inflammation, and neurodevelopment exclusively in males. Moreover, the hypothalamus of prenatally benzene-exposed male offspring displayed alterations in orexigenic and anorexigenic projections, impairments in leptin signaling, and increased microgliosis. Additional exposure to benzene during lactation did not promote further microgliosis or astrogliosis in the offspring, while the high-fat diet (HFD) challenge in adulthood exacerbated glucose metabolism and hypothalamic inflammation in benzene-exposed offspring of both sexes. These findings reveal the persistent adverse effects of prenatal benzene exposure on hypothalamic circuits and neuroinflammation, predisposing the offspring to long-lasting metabolic health conditions.

Small RNA Sequencing Analysis of STZ-Injured Pancreas Reveals Novel MicroRNA and Transfer RNA-Derived RNA with Biomarker Potential for Diabetes Mellitus

MicroRNAs (miRNAs) and transfer RNA-derived small RNAs (tsRNAs) play critical roles in the regulation of different biological processes, but their underlying mechanisms in diabetes mellitus (DM) are still largely unknown. This study aimed to gain a better understanding of the functions of miRNAs and tsRNAs in the pathogenesis of DM. A high-fat diet (HFD) and streptozocin (STZ)-induced DM rat model was established. Pancreatic tissues were obtained for subsequent studies. The miRNA and tsRNA expression profiles in the DM and control groups were obtained by RNA sequencing and validated with quantitative reverse transcription-PCR (qRT-PCR). Subsequently, bioinformatics methods were used to predict target genes and the biological functions of differentially expressed miRNAs and tsRNAs. We identified 17 miRNAs and 28 tsRNAs that were significantly differentiated between the DM and control group. Subsequently, target genes were predicted for these altered miRNAs and tsRNAs, including Nalcn, Lpin2 and E2f3. These target genes were significantly enriched in localization as well as intracellular and protein binding. In addition, the results of KEGG analysis showed that the target genes were significantly enriched in the Wnt signaling pathway, insulin pathway, MAPK signaling pathway and Hippo signaling pathway. This study revealed the expression profiles of miRNAs and tsRNAs in the pancreas of a DM rat model using small RNA-Seq and predicted the target genes and associated pathways using bioinformatics analysis. Our findings provide a novel aspect in understanding the mechanisms of DM and identify potential targets for the diagnosis and treatment of DM.

Dietary Docosahexaenoic Acid and Glucose Systemic Metabolic Changes in the Mouse

The endocannabinoid system (ECS) participates in regulating whole body energy balance. Overactivation of the ECS has been associated with the negative consequence of obesity and type 2 diabetes. Since activators of the ECS rely on lipid-derived ligands, an investigation was conducted to determine whether dietary PUFA could influence the ECS to affect glucose clearance by measuring metabolites of macronutrient metabolism. C57/blk6 mice were fed a control or DHA-enriched semi-purified diet for a period of 112 d. Plasma, skeletal muscle, and liver were collected after 56 d and 112 d of feeding the diets for metabolomics analysis. Key findings characterized a shift in glucose metabolism and greater catabolism of fatty acids in mice fed the DHA diet. Glucose use and promotion of fatty acids as substrate were found based on levels of metabolic pathway intermediates and altered metabolic changes related to pathway flux with DHA feeding. Greater levels of DHA-derived glycerol lipids were found subsequently leading to the decrease of arachidonate-derived endocannabinoids (eCB). Levels of 1- and 2-arachidonylglcerol eCB in muscle and liver were lower in the DHA diet group compared to controls. These findings demonstrate that DHA feeding in mice alters macronutrient metabolism and may restore ECS tone by lowering arachidonic acid derived eCB.

Strains of Faecalibacterium prausnitzii and its extracts reduce blood glucose levels, percent HbA1c, and improve glucose tolerance without causing hypoglycemic side effects in diabetic and prediabetic mice

INTRODUCTION

The commensal bacterium Faecalibacterium prausnitzii is a prominent member of the microbiome of animals and humans, and it plays an important role in several physiological processes. Numerous studies have correlated the reduction of F. prausnitzii abundance with many disease states, including irritable bowel syndrome, Crohn's disease, obesity, asthma, major depressive disorder, and metabolic diseases in humans. Studies have also correlated F. prausnitzii with diseases in humans involved in altered glucose metabolism, including diabetes.

RESEARCH DESIGN AND METHODS

The aim of this study was to investigate the effects of compositions derived from three strains of F. prausnitzii (coined FPZ) on glucose metabolism in diet-induced obese male C57BL/6J prediabetic and type 2 diabetic mice. The primary endpoints of these studies were measuring changes in fasting blood glucose, glucose tolerance (as measured by a glucose tolerance test), and percent hemoglobin A1c (HbA1c) with longer term treatment. Two placebo-controlled trials were carried out using both live cell FPZ and killed cell FPZ and extracts. Two additional placebo-controlled trials were carried out in non-diabetic mice and mice that previously had type 2 diabetes (T2D).

RESULTS

Both trials in prediabetic and diabetic mice revealed that peroral administration of live FPZ or extracts from FPZ lowered fasting blood glucose levels and improved glucose tolerance compared with control mice. A trial administering longer FPZ treatment also resulted in lowered percent HbA1c compared with control mice. Additionally, trials in non-diabetic mice treated with FPZ demonstrated that FPZ treatment does not lead to hypoglycemia.

CONCLUSIONS

The trial results have shown that treatment with different formulations of FPZ result in lower blood glucose levels, lower percent HbA1c, and improved glucose response in mice compared with control prediabetic/diabetic mice. FPZ is a promising candidate as an orally administered probiotic or postbiotic to manage and improve pre-diabetes and T2D.

Precision pharmacological reversal of genotype-specific diet-induced metabolic syndrome in mice informed by transcriptional regulation

Diet-related metabolic syndrome is the largest contributor to adverse health in the United States. However, the study of gene-environment interactions and their epigenomic and transcriptomic integration is complicated by the lack of environmental and genetic control in humans that is possible in mouse models. Here we exposed three mouse strains, C57BL/6J (BL6), A/J, and NOD/ShiLtJ (NOD), to a high-fat high-carbohydrate diet, leading to varying degrees of metabolic syndrome. We then performed transcriptomic and genomic DNA methylation analyses and found overlapping but also highly divergent changes in gene expression and methylation upstream of the discordant metabolic phenotypes. Strain-specific pathway analysis of dietary effects reveals a dysregulation of cholesterol biosynthesis common to all three strains but distinct regulatory networks driving this dysregulation. This suggests a strategy for strain-specific targeted pharmacologic intervention of these upstream regulators informed by transcriptional regulation. As a pilot study, we administered the drug GW4064 to target one of these genotype-dependent networks, the Farnesoid X receptor pathway, and found that GW4064 exerts genotype-specific protection against dietary effects in BL6, as predicted by our transcriptomic analysis, as well as increased inflammatory-related gene expression changes in NOD. This pilot study demonstrates the potential efficacy of precision therapeutics for genotype-informed dietary metabolic intervention, and a mouse platform for guiding this approach.

Melanocortin 4 receptor signaling in Sim1 neurons permits sexual receptivity in female mice

Introduction

Female sexual dysfunction affects approximately 40% of women in the United States, yet few therapeutic options exist for these patients. The melanocortin system is a new treatment target for hypoactive sexual desire disorder (HSDD), but the neuronal pathways involved are unclear.

Methods

In this study, the sexual behavior of female MC4R knockout mice lacking melanocortin 4 receptors (MC4Rs) was examined. The mice were then bred to express MC4Rs exclusively on Sim1 neurons (tbMC4RSim1 mice) or on oxytocin neurons (tbMC4ROxt mice) to examine the effect on sexual responsiveness.

Results

MC4R knockout mice were found to approach males less and have reduced receptivity to copulation, as indicated by a low lordosis quotient. These changes were independent of body weight. Lordosis behavior was normalized in tbMC4RSim1 mice and improved in tbMC4ROxt mice. In contrast, approach behavior was unchanged in tbMC4RSim1 mice but greatly increased in tbMC4ROxt animals. The changes were independent of melanocortin-driven metabolic effects.

Discussion

These results implicate MC4R signaling in Oxt neurons in appetitive behaviors and MC4R signaling in Sim1 neurons in female sexual receptivity, while suggesting melanocortin-driven sexual function does not rely on metabolic neural circuits.

Vertical Sleeve Gastrectomy Offers Protection against Disturbed Flow-Induced Atherosclerosis in High-Fat Diet-Fed Mice

Bariatric surgery reduces body weight, enhances metabolic and diabetic control, and improves outcomes on obesity-related comorbidities. However, the mechanisms mediating this protection against cardiovascular diseases remain unclear. We investigated the effect of sleeve gastrectomy (SG) on vascular protection in response to shear stress-induced atherosclerosis using an overweighted and carotid artery ligation mouse model. Eight-week-old male wild-type mice (C57BL/6J) were fed a high-fat diet (HFD) for two weeks to induce weight gain and dysmetabolism. SG was performed in HFD-fed mice. Two weeks after the SG procedure, partial carotid-artery ligation was performed to promote disturbed flow-induced atherosclerosis. Compared with the control mice, HFD-fed wild-type mice exhibited increased body weight, total cholesterol level, hemoglobin A1c, and enhanced insulin resistance; SG significantly reversed these adverse effects. As expected, HFD-fed mice exhibited greater neointimal hyperplasia and atherosclerotic plaques than the control group, and the SG procedure attenuated HFD-promoted ligation-induced neointimal hyperplasia and arterial elastin fragmentation. Besides, HFD promoted ligation-induced macrophage infiltration, matrix metalloproteinase-9 expression, upregulation of inflammatory cytokines, and increased vascular endothelial growth factor secretion. SG significantly reduced the above-mentioned effects. Moreover, HFD restriction partially reversed the intimal hyperplasia caused by carotid artery ligation; however, this protective effect was significantly lower than that observed in SG-operated mice. Our study demonstrated that HFD deteriorates shear stress-induced atherosclerosis and SG mitigates vascular remodeling, and this protective effect was not comparable in HFD restriction group. These findings provide a rationale for using bariatric surgery to counter atherosclerosis in morbid obesity.

Mitotic CDK1 and 4E-BP1 II: A single phosphomimetic mutation in 4E-BP1 induces glucose intolerance in mice

OBJECTIVE

Cyclin-dependent kinase 1 (CDK1)/cyclin B1 phosphorylates many of the same substrates as mTORC1 (a key regulator of glucose metabolism), including the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). Only mitotic CDK1 phosphorylates 4E-BP1 at residue S82 in mice (S83 in humans), in addition to the common 4E-BP1 phospho-acceptor sites phosphorylated by both CDK1 and mTORC1. We examined glucose metabolism in mice having a single aspartate phosphomimetic amino acid knock in substitution at the 4E-BP1 serine 82 (4E-BP1S82D) mimicking constitutive CDK1 phosphorylation.

METHODS

Knock-in homozygous 4E-BP1S82D and 4E-BP1S82A C57Bl/6N mice were assessed for glucose tolerance testing (GTT) and metabolic cage analysis on regular and on high-fat chow diets. Gastrocnemius tissues from 4E-BP1S82D and WT mice were subject to Reverse Phase Protein Array analysis. Since the bone marrow is one of the few tissues typically having cycling cells that transit mitosis, reciprocal bone-marrow transplants were performed between male 4E-BP1S82D and WT mice, followed by metabolic assessment, to determine the role of actively cycling cells on glucose homeostasis.

RESULTS

Homozygous knock-in 4E-BP1S82D mice showed glucose intolerance that was markedly accentuated with a diabetogenic high-fat diet (p = 0.004). In contrast, homozygous mice with the unphosphorylatable alanine substitution (4E-BP1S82A) had normal glucose tolerance. Protein profiling of lean muscle tissues, largely arrested in G0, did not show protein expression or signaling changes that could account for these results. Reciprocal bone-marrow transplantation between 4E-BP1S82D and wild-type littermates revealed a trend for wild-type mice with 4E-BP1S82D marrow engraftment on high-fat diets to become hyperglycemic after glucose challenge.

CONCLUSIONS

4E-BP1S82D is a single amino acid substitution that induces glucose intolerance in mice. These findings indicate that glucose metabolism may be regulated by CDK1 4E-BP1 phosphorylation independent from mTOR and point towards an unexpected role for cycling cells that transit mitosis in diabetic glucose control.

Are the Properties of Bone Marrow-Derived Mesenchymal Stem Cells Influenced by Overweight and Obesity?

Bone marrow-derived mesenchymal stem cells (BMSCs) are promising candidates for cell-based therapies. Growing evidence has indicated that overweight/obesity can change the bone marrow microenvironment, which affects some properties of BMSCs. As the overweight/obese population rapidly increases, they will inevitably become a potential source of BMSCs for clinical application, especially when receiving autologous BMSC transplantation. Given this situation, the quality control of these cells has become particularly important. Therefore, it is urgent to characterize BMSCs isolated from overweight/obese bone marrow environments. In this review, we summarize the evidence of the effects of overweight/obesity on the biological properties of BMSCs derived from humans and animals, including proliferation, clonogenicity, surface antigen expression, senescence, apoptosis, and trilineage differentiation, as well as the underlying mechanisms. Overall, the conclusions of existing studies are not consistent. Most studies demonstrate that overweight/obesity can influence one or more characteristics of BMSCs, while the involved mechanisms are still unclear. Moreover, insufficient evidence proves that weight loss or other interventions can rescue these qualities to baseline status. Thus, further research should address these issues and prioritize developing methods to improve functions of overweight- or obesity-derived BMSCs.

High-fat/high-sucrose diet worsens metabolic outcomes and widespread hypersensitivity following early-life stress exposure in female mice

Exposure to stress early in life has been associated with adult-onset comorbidities such as chronic pain, metabolic dysregulation, obesity, and inactivity. We have established an early-life stress model using neonatal maternal separation (NMS) in mice, which displays evidence of increased body weight and adiposity, widespread mechanical allodynia, and hypothalamic-pituitary-adrenal axis dysregulation in male mice. Early-life stress and consumption of a Western-style diet contribute to the development of obesity; however, relatively few preclinical studies have been performed in female rodents, which are known to be protected against diet-induced obesity and metabolic dysfunction. In this study, we gave naïve and NMS female mice access to a high-fat/high-sucrose (HFS) diet beginning at 4 wk of age. Robust increases in body weight and fat were observed in HFS-fed NMS mice during the first 10 wk on the diet, driven partly by increased food intake. Female NMS mice on an HFS diet showed widespread mechanical hypersensitivity compared with either naïve mice on an HFS diet or NMS mice on a control diet. HFS diet-fed NMS mice also had impaired glucose tolerance and fasting hyperinsulinemia. Strikingly, female NMS mice on an HFS diet showed evidence of hepatic steatosis with increased triglyceride levels and altered glucocorticoid receptor levels and phosphorylation state. They also exhibited increased energy expenditure as observed via indirect calorimetry and expression of proinflammatory markers in perigonadal adipose. Altogether, our data suggest that early-life stress exposure increased the susceptibility of female mice to develop diet-induced metabolic dysfunction and pain-like behaviors.

OBESE MICE WITH PNEUMONIA HAVE HYPERLEPTINEMIA AND INCREASED PULMONARY SIGNAL TRANSDUCER AND ACTIVATOR OF TRANSCRIPTION 3 ACTIVATION

ABSTRACT

Obesity is an ongoing epidemic that influences pathobiology in numerous disease states. Obesity is associated with increased plasma leptin levels, a hormone that activates the signal transducer and activator of transcription 3 (STAT3) pathway. Pneumonia is a significant cause of morbidity and mortality. During pneumonia, inflammatory pathways including STAT3 are activated. Outcomes in obese patients with pneumonia are mixed, with some studies showing obesity increases harm and others showing benefit. It is unclear whether obesity alters STAT3 activation during bacterial pneumonia and how this might impact outcomes from pneumonia. We used a murine model of obesity and pneumonia challenge with Pseudomonas aeruginosa in obese and nonobese mice to investigate the effect of obesity on STAT3 activation. We found obese mice with bacterial pneumonia had increased mortality compared with nonobese mice. Inflammatory markers, IL-6 and TNF-α, and lung neutrophil infiltration were elevated at 6 h after pneumonia in both nonobese and obese mice. Obese mice had greater lung injury compared with nonobese mice at 6 h after pneumonia. Leptin and insulin levels were higher in obese mice compared with nonobese mice, and obese mice with pneumonia had higher pulmonary STAT3 activation compared with nonobese mice.

SVEP1 is an endogenous ligand for the orphan receptor PEAR1

Sushi, von Willebrand factor type A, EGF and pentraxin domain containing 1 (SVEP1) is an extracellular matrix protein that causally promotes vascular disease and associates with platelet reactivity in humans. Here, using a human genomic and proteomic approach, we identify a high affinity, disease-relevant, and potentially targetable interaction between SVEP1 and the orphan receptor Platelet and Endothelial Aggregation Receptor 1 (PEAR1). This interaction promotes PEAR1 phosphorylation and disease associated AKT/mTOR signaling in vascular cells and platelets. Mice lacking SVEP1 have reduced platelet activation, and exogenous SVEP1 induces PEAR1-dependent activation of platelets. SVEP1 and PEAR1 causally and concordantly relate to platelet phenotypes and cardiovascular disease in humans, as determined by Mendelian Randomization. Targeting this receptor-ligand interaction may be a viable therapeutic strategy to treat or prevent cardiovascular and thrombotic disease.

MSR1 is not required for obesity-associated inflammation and insulin resistance in mice

Obesity induces a chronic inflammatory state associated with changes in adipose tissue macrophages (ATMs). Macrophage scavenger receptor 1 (MSR1) has been implicated in the regulation of adipose tissue inflammation and diabetes pathogenesis; however, reports have been mixed on the contribution of MSR1 in obesity and glucose intolerance. We observed increased MSR1 expression in VAT of obese diabetic individuals compared to non-diabetic and single nuclear RNA sequencing identified macrophage-specific expression of MSR1 in human adipose tissue. We examined male Msr1-/- (Msr1KO) and WT controls and observed protection from obesity and AT inflammation in non-littermate Msr1KO mice. We then evaluated obese littermate Msr1+/- (Msr1HET) and Msr1KO mice. Both Msr1KO mice and Msr1HET mice became obese and insulin resistant when compared to their normal chow diet counterparts, but there was no Msr1-dependent difference in body weight, glucose metabolism, or insulin resistance. Flow cytometry revealed no significant differences between genotypes in ATM subtypes or proliferation in male and female mice. We observed increased frequency of proliferating ATMs in obese female compared to male mice. Overall, we conclude that while MSR1 is a biomarker of diabetes status in human adipose tissue, in mice Msr1 is not required for obesity-associated insulin resistance or ATM accumulation.

Adipocyte-derived extracellular vesicles increase insulin secretion through transport of insulinotropic protein cargo

Adipocyte-derived extracellular vesicles (AdEVs) are membranous nanoparticles that convey communication from adipose tissue to other organs. Here, to delineate their role as messengers with glucoregulatory nature, we paired fluorescence AdEV-tracing and SILAC-labeling with (phospho)proteomics, and revealed that AdEVs transfer functional insulinotropic protein cargo into pancreatic β-cells. Upon transfer, AdEV proteins were subjects for phosphorylation, augmented insulinotropic GPCR/cAMP/PKA signaling by increasing total protein abundances and phosphosite dynamics, and ultimately enhanced 1st-phase glucose-stimulated insulin secretion (GSIS) in murine islets. Notably, insulinotropic effects were restricted to AdEVs isolated from obese and insulin resistant, but not lean mice, which was consistent with differential protein loads and AdEV luminal morphologies. Likewise, in vivo pre-treatment with AdEVs from obese but not lean mice amplified insulin secretion and glucose tolerance in mice. This data suggests that secreted AdEVs can inform pancreatic β-cells about insulin resistance in adipose tissue in order to amplify GSIS in times of increased insulin demand.

9-PAHPA long term intake in DIO and db/db mice ameliorates insulin sensitivity but has few effects on obesity and associated metabolic disorders

Branched fatty acid esters of hydroxy fatty acids are endogenous lipids reported to have antidiabetic and anti-inflammatory effects. Recently, we showed that 9-palmitic acid esters of hydroxypalmitic acid (9-PAHPA) and 9-oleic acid esters of hydroxypalmitic acid increased insulin sensitivity in mice when incorporated to a chow diet or to a high fat and high sucrose diet. However, preventive supplementation with 9-PAHPA and 9-oleic acid esters of hydroxypalmitic acid in high fat and high sucrose diet mice did not impair significant weight gain or the development of hyperglycemia. The aim of this work was therefore to study whether in two animal models of obesity, namely the classical diet-induced obesity (DIO) and the db/db mice, 9-PAHPA may have beneficial effects against obesity and liver and skeletal muscle metabolic dysfunction. In DIO mice, we observed that 9-PAHPA increased body weight and fat mass. In line with this observation, we found that 9-PAHPA supplementation decreased energy expenditure. In liver and in skeletal muscle, mitochondrial activities and oxidative stress parameters were not modified by 9-PAHPA supplementation. In db/db mice, 9-PAHPA had no effect on the dramatic weight gain and hyperglycemia. In addition, 9-PAHPA supplementation did not correct either the hepatomegaly and hepatic steatosis or the severe muscle atrophy recorded compared with db/+ animals. Likewise, supplementation with 9-PAHPA did not impact the different metabolic parameters analyzed, either in the liver or in the skeletal muscles. However, it decreased insulin resistance in DIO and db/db mice. In conclusion, our study indicated that a long-term intake of 9-PAHPA in DIO and db/db mice improved insulin sensitivity but had only few effects on obesity and associated metabolic disorders.

Probiotic induced synthesis of microbiota polyamine as a nutraceutical for metabolic syndrome and obesity-related type 2 diabetes

The gut microbiota regulates multiple facets of host metabolism and immunity through the production of signaling metabolites, such as polyamines which are small organic compounds that are essential to host cell growth and lymphocyte activation. Polyamines are most abundant in the intestinal lumen, where their synthesis by the gut microbiota is influenced by microbiome composition and host diet. Disruption of the host gut microbiome in metabolic syndrome and obesity-related type 2 diabetes (obesity/T2D) results in potential dysregulation of polyamine synthesis. A growing body of evidence suggests that restoration of the dysbiotic gut microbiota and polyamine synthesis is effective in ameliorating metabolic syndrome and strengthening the impaired immune responses of obesity/T2D. In this review, we discuss existing studies on gut microbiome determinants of polyamine synthesis, polyamine production in obesity/T2D, and evidence that demonstrates the potential of polyamines as a nutraceutical in obesity/T2D hosts.

Mouse Models of Obesity to Study the Tumor-Immune Microenvironment

Obesity is associated with chronic, low-grade systemic inflammation and leads to changes in the immune microenvironment of various tissues. As a result, obesity is associated with increased risk of cancer and a worse prognosis in patients. Given the prevalence of obesity worldwide, understanding the fundamental biology governing the relationship between obesity and cancer is critical. In this chapter, we describe preclinical models of obesity that can be combined with standard tumor models and techniques to study the tumor-immune microenvironment. We also discuss important considerations when planning experiments involving these models.

Effects of metformin and simvastatin treatment on ultrastructural features of liver macrophages in HFD mice

Type 2 diabetes is a major health burden to the society. Macrophages and liver inflammation emerged as important factors in its development. We investigated ultrastructural changes in the liver, with a special emphasis on macrophages in high fat diet (HFD) fed C57BL/6 J mice treated with metformin or simvastatin, two drugs that are used frequently in diabetes. Both metformin and simvastatin reduced the liver damage in HFD fed animals, manifested as the prevention of nonalcoholic steatohepatitis development and reduced activation and number of macrophages in the liver, as well as the percentage of these cells with lipid droplets in the cytoplasm compared to untreated HFD animals. In contrast with untreated HFD-fed animals, lipid droplets were not observed in lysosomes of macrophages in HFD animals treated with metformin and simvastatin. These findings provide new insight into the effects of metformin and simvastatin on the liver in this experimental model of type 2 diabetes and provide further rationale for implementation of statins in the therapeutic regimens in this disease.

IL-17/CXCL5 signaling within the oligovascular niche mediates human and mouse white matter injury

Cerebral small vessel disease and brain white matter injury are worsened by cardiovascular risk factors including obesity. Molecular pathways in cerebral endothelial cells activated by chronic cerebrovascular risk factors alter cell-cell signaling, blocking endogenous and post-ischemic white matter repair. Using cell-specific translating ribosome affinity purification (RiboTag) in white matter endothelia and oligodendrocyte progenitor cells (OPCs), we identify a coordinated interleukin-chemokine signaling cascade within the oligovascular niche of subcortical white matter that is triggered by diet-induced obesity (DIO). DIO induces interleukin-17B (IL-17B) signaling that acts on the cerebral endothelia through IL-17Rb to increase both circulating and local endothelial expression of CXCL5. In white matter endothelia, CXCL5 promotes the association of OPCs with the vasculature and triggers OPC gene expression programs regulating cell migration through chemokine signaling. Targeted blockade of IL-17B reduced vessel-associated OPCs by reducing endothelial CXCL5 expression. In multiple human cohorts, blood levels of CXCL5 function as a diagnostic and prognostic biomarker of vascular cognitive impairment.

ATP-Binding Cassette Protein ABCC10 Deficiency Prevents Diet-Induced Obesity but Not Atherosclerosis in Mice

Excess plasma lipid levels are a risk factor for various cardiometabolic disorders. Studies have shown that improving dyslipidemia lowers the progression of these disorders. In this study, we investigated the role of ATP-binding cassette transporter C10 (ABCC10) in regulating lipid metabolism. Our data indicate that deletion of the Abcc10 gene in male mice results in lower plasma and intestinal triglycerides by around 38% and 36%, respectively. Furthermore, deletion of ABCC10 ameliorates diet-induced obesity in mice and leads to a better response during insulin and glucose tolerance tests. Unexpectedly, ABCC10 deficiency does not affect triglyceride levels or atherosclerosis in ApoE-deficient mice. In addition, our studies demonstrate low oleate uptake by enterocytes (~25-30%) and less absorption (~37%) of triglycerides in the small intestine of ABCC10 knockout mice. Deletion of the Abcc10 gene also alters several lipid metabolism genes in the intestine, suggesting that ABCC10 regulates dietary fat absorption, which may contribute to diet-induced obesity in mice.

A Pathophysiological Intersection of Diabetes and Alzheimer's Disease

Diabetes is among the most prevalent diseases of the modern world and is strongly linked to an increased risk of numerous neurodegenerative disorders, although the exact pathophysiological mechanisms are not clear yet. Insulin resistance is a serious pathological condition, connecting type 2 diabetes, metabolic syndrome, and obesity. Recently, insulin resistance has been proven to be connected also to cognitive decline and dementias, including the most prevalent form, Alzheimer's disease. The relationship between diabetes and Alzheimer's disease regarding pathophysiology is so significant that it has been proposed that some presentations of the condition could be termed type 3 diabetes.

Maternal diabetes negatively impacts fetal health

Diabetes is a chronic metabolic disease affecting an increasing number of people. Although diabetes has negative health outcomes for diagnosed individuals, a population at particular risk are pregnant women, as diabetes impacts not only a pregnant woman's health but that of her child. In this review, we cover the current knowledge and unanswered questions on diabetes affecting an expectant mother, focusing on maternal and fetal outcomes.

The role of obesity and bariatric surgery-induced weight loss in breast cancer

Obesity is a complex metabolic condition considered a worldwide public health crisis, and a deeper mechanistic understanding of obesity-associated diseases is urgently needed. Obesity comorbidities include many associated cancers and are estimated to account for 20% of female cancer deaths in the USA. Breast cancer, in particular, is associated with obesity and is the focus of this review. The exact causal links between obesity and breast cancer remain unclear. Still, interactions have emerged between body mass index, tumor molecular subtype, genetic background, and environmental factors that strongly suggest obesity influences the risk and progression of certain breast cancers. Supportive preclinical research uses various diet-induced obesity models to demonstrate that weight loss, via dietary interventions or changes in energy expenditure, reduces the onset or progression of breast cancers. Ongoing and future studies are now aimed at elucidating the underpinning mechanisms behind weight-loss-driven observations to improve therapy and outcomes in patients with breast cancer and reduce risk. This review aims to summarize the rapidly emerging literature on obesity and weight loss strategies with a focused discussion of bariatric surgery in both clinical and preclinical studies detailing the complex interactions between metabolism, immune response, and immunotherapy in the setting of obesity and breast cancer.

High-fat diet causes mechanical allodynia in the absence of injury or diabetic pathology

Understanding the interactions between diet, obesity, and diabetes is important to tease out mechanisms in painful pathology. Western diet is rich in fats, producing high amounts of circulating bioactive metabolites. However, no research has assessed how a high-fat diet (HFD) alone may sensitize an individual to non-painful stimuli in the absence of obesity or diabetic pathology. To investigate this, we tested the ability of a HFD to stimulate diet-induced hyperalgesic priming, or diet sensitization in male and female mice. Our results revealed that 8 weeks of HFD did not alter baseline pain sensitivity, but both male and female HFD-fed animals exhibited robust mechanical allodynia when exposed to a subthreshold dose of intraplantar Prostaglandin E₂ (PGE₂) compared to mice on chow diet. Furthermore, calcium imaging in isolated primary sensory neurons of both sexes revealed HFD induced an increased percentage of capsaicin-responsive neurons compared to their chow counterparts. Immunohistochemistry (IHC) showed a HFD-induced upregulation of ATF3, a neuronal marker of injury, in lumbar dorsal root ganglia (DRG). This suggests that a HFD induces allodynia in the absence of a pre-existing condition or injury via dietary components. With this new understanding of how a HFD can contribute to the onset of pain, we can understand the dissociation behind the comorbidities associated with obesity and diabetes to develop pharmacological interventions to treat them more efficiently.

Targeting Anti-Angiogenic VEGF165b-VEGFR1 Signaling Promotes Nitric Oxide Independent Therapeutic Angiogenesis in Preclinical Peripheral Artery Disease Models

Nitric oxide (NO) is the critical regulator of VEGFR2-induced angiogenesis. Neither VEGF-A over-expression nor L-Arginine (NO-precursor) supplementation has been effective in helping patients with Peripheral Artery Disease (PAD) in clinical trials. One incompletely studied reason may be due to the presence of the less characterized anti-angiogenic VEGF-A (VEGF165b) isoform. We have recently shown that VEGF165b inhibits ischemic angiogenesis by blocking VEGFR1, not VEGFR2 activation. Here we wanted to determine whether VEGF165b inhibition using a monoclonal isoform-specific antibody against VEGF165b vs. control, improved perfusion recovery in preclinical PAD models that have impaired VEGFR2-NO signaling, including (1) type-2 diabetic model, (2) endothelial Nitric oxide synthase-knock out mice, and (3) Myoglobin transgenic mice that have impaired NO bioavailability. In all PAD models, VEGF165b inhibition vs. control enhanced perfusion recovery, increased microvascular density in the ischemic limb, and activated VEGFR1-STAT3 signaling. In vitro, VEGF165b inhibition vs. control enhanced a VEGFR1-dependent endothelial survival/proliferation and angiogenic capacity. These data demonstrate that VEGF165b inhibition induces VEGFR1-STAT3 activation, which does not require increased NO to induce therapeutic angiogenesis in PAD. These results may have implications for advancing therapies for patients with PAD where the VEGFR2-eNOS-NO pathway is impaired.

Long Noncoding RNAs That Function in Nutrition: Lnc-ing Nutritional Cues to Metabolic Pathways

Long noncoding RNAs (lncRNAs) are sensitive to changing environments and play key roles in health and disease. Emerging evidence indicates that lncRNAs regulate gene expression to shape metabolic processes in response to changing nutritional cues. Here we review various lncRNAs sensitive to fasting, feeding, and high-fat diet in key metabolic tissues (liver, adipose, and muscle), highlighting regulatory mechanisms that trigger expression changes of lncRNAs themselves, and how these lncRNAs regulate gene expression of key metabolic genes in specific cell types or across tissues. Determining how lncRNAs respond to changes in nutrition is critical for our understanding of the complex downstream cascades following dietary changes and can shape how we treat metabolic disease. Furthermore, investigating sex biases that might influence lncRNA-regulated responses will likely reveal contributions toward the observed disparities between the sexes in metabolic diseases.

Wound Healing Impairment in Type 2 Diabetes Model of Leptin-Deficient Mice—A Mechanistic Systematic Review

Type II diabetes mellitus (T2DM) is one of the most prevalent diseases in the world, associated with diabetic foot ulcers and impaired wound healing. There is an ongoing need for interventions effective in treating these two problems. Pre-clinical studies in this field rely on adequate animal models. However, producing such a model is near-impossible given the complex and multifactorial pathogenesis of T2DM. A leptin-deficient murine model was developed in 1959 and relies on either dysfunctional leptin (ob/ob) or a leptin receptor (db/db). Though monogenic, this model has been used in hundreds of studies, including diabetic wound healing research. In this study, we systematically summarize data from over one hundred studies, which described the mechanisms underlying wound healing impairment in this model. We briefly review the wound healing dynamics, growth factors’ dysregulation, angiogenesis, inflammation, the function of leptin and insulin, the role of advanced glycation end-products, extracellular matrix abnormalities, stem cells’ dysregulation, and the role of non-coding RNAs. Some studies investigated novel chronic diabetes wound models, based on a leptin-deficient murine model, which was also described. We also discussed the interventions studied in vivo, which passed into human clinical trials. It is our hope that this review will help plan future research.

Exploring the link between Parkinson's disease and type 2 diabetes mellitus in Drosophila

Parkinson's disease (PD) is the second most common neurodegenerative disease. Diabetes mellitus (DM) is a metabolic disease characterized by high levels of glucose in blood. Recent epidemiological studies have highlighted the link between both diseases; it is even considered that DM might be a risk factor for PD. To further investigate the likely relation of these diseases, we have used a Drosophila PD model based on inactivation of the DJ-1β gene (ortholog of human DJ-1), and diet-induced Drosophila and mouse type 2 DM (T2DM) models, together with human neuron-like cells. T2DM models were obtained by feeding flies with a high sugar-containing medium, and mice with a high fat diet. Our results showed that both fly models exhibit common phenotypes such as alterations in carbohydrate homeostasis, mitochondrial dysfunction or motor defects, among others. In addition, we demonstrated that T2DM might be a risk factor of developing PD since our diet-induced fly and mouse T2DM models present DA neuron dysfunction, a hallmark of PD. We also confirmed that neurodegeneration is caused by increased glucose levels, which has detrimental effects in human neuron-like cells by triggering apoptosis and leading to cell death. Besides, the observed phenotypes were exacerbated in DJ-1β mutants cultured in the high sugar medium, indicating that DJ-1 might have a role in carbohydrate homeostasis. Finally, we have confirmed that metformin, an antidiabetic drug, is a potential candidate for PD treatment and that it could prevent PD onset in T2DM model flies. This result supports antidiabetic compounds as promising PD therapeutics.

Sirtuin 3 Deficiency Aggravates Kidney Disease in Response to High-Fat Diet through Lipotoxicity-Induced Mitochondrial Damage

Sirtuin 3 (SIRT3) is the primary mitochondrial deacetylase that controls the antioxidant pathway and energy metabolism. We previously found that renal Sirt3 expression and activity were reduced in mice with type 2 diabetic nephropathy associated with oxidative stress and mitochondrial abnormalities and that a specific SIRT3 activator improved renal damage. SIRT3 is modulated by diet, and to assess whether Sirt3 deficiency aggravates mitochondrial damage and accelerates kidney disease in response to nutrient overloads, wild-type (WT) and Sirt3^−/− mice were fed a high-fat-diet (HFD) or standard diet for 8 months. Sirt3^−/− mice on HFD exhibited earlier and more severe albuminuria compared to WT mice, accompanied by podocyte dysfunction and glomerular capillary rarefaction. Mesangial matrix expansion, tubular vacuolization and inflammation, associated with enhanced lipid accumulation, were more evident in Sirt3^−/− mice. After HFD, kidneys from Sirt3^−/− mice showed more oxidative stress than WT mice, mitochondria ultrastructural damage in tubular cells, and a reduction in mitochondrial mass and energy production. Our data demonstrate that Sirt3 deficiency renders mice more prone to developing oxidative stress and mitochondrial abnormalities in response to HFD, resulting in more severe kidney diseases, and this suggests that mitochondria protection may be a method to prevent HFD-induced renal injury.

Helper T Cell (CD4+) Targeted Tacrolimus Delivery Mediates Precise Suppression of Allogeneic Humoral Immunity

Antibody-mediated rejection (ABMR) is a major cause of dysfunction and loss of transplanted kidney. The current treatments for ABMR involve nonspecific inhibition and clearance of T/B cells or plasma cells. However, the prognosis of patients following current treatment is poor. T follicular helper cells (Tfh) play an important role in allograft-specific antibodies secreting plasma cell (PC) development. Tfh cells are therefore considered to be important therapeutic targets for the treatment of antibody hypersecretion disorders, such as transplant rejection and autoimmune diseases. Tacrolimus (Tac), the primary immunosuppressant, prevents rejection by reducing T cell activation. However, its administration should be closely monitored to avoid serious side effects. In this study, we investigated whether Tac delivery to helper T (CD4+) cells using functionalized mesoporous nanoparticles can block Tfh cell differentiation after alloantigen exposure. Results showed that Tac delivery ameliorated humoral rejection injury in rodent kidney graft by suppressing Tfh cell development, PC, and donor-specific antibody (DSA) generation without causing severe side effects compared with delivery through the drug administration pathway. This study provides a promising therapeutic strategy for preventing humoral rejection in solid organ transplantation. The specific and controllable drug delivery avoids multiple disorder risks and side effects observed in currently used clinical approaches.

Biopolymeric composite hydrogel loaded with silver NPs and epigallocatechin gallate (EGCG) effectively manages ROS for rapid wound healing in type II diabetic wounds

Delayed wound healing in patients having type-II diabetes mellitus (T2DM) often results in a high rate of amputation. We report an innovative Guar Gum-based macroporous hydrogel (HG) infused with an antibacterial agent (Ag NPs), and antioxidant, epigallocatechin gallate (EGCG) to address rapid wound healing and interestingly could inhibit the associated pathophysical bone infection in a high-fat-diet-induced T2DM C57BL/6 mice model. The HG-Ag-EGCG elicits scar-free wound healing in subcutaneous wounds and histopathological evidence confirmed HG-Ag-EGCG hydrogel patch elicits better wound healing through enhanced cell proliferation, mature connecting tissue fiber formation, minimum void spaces formation, and better re-epithelialization when compared with a market available hydrogel patch material (Luofucon®). Supportive of the in vivo outcomes, in vitro experiments delineated better-wound closure due to improved management of ROS by the HG-Ag-EGCG. Additionally, a favorable non-toxicity outcome assessed through both in vitro and in vivo conditions confirmed its potential applicability in clinical wound care management.

Sex-specific changes in metabolism during the transition from chow to high-fat diet feeding are abolished in response to dieting in C57BL/6J mice

Background/Objective

Female mice are often excluded from diet-induced obesity studies as they are more resistant to the obesifying effects of a high-fat diet (HFD). However, the underlying mechanisms behind this sex disparity may actually have important implications for the development and management of obesity in humans. Therefore, we systematically investigated the immediate sex-specific effects of transitioning to a HFD in C57BL/6J mice as well as monitored whether these effects are altered after sustained HFD feeding and whether sex affects the response to a return to chow, representative of dieting.

Methods

Dual X-ray absorptiometry (DXA) analysis of body composition, indirect calorimetry measurements, and qPCR analysis of hypothalamic and brainstem regions were performed on male and female C57BL/6J mice.

Results

HFD had immediate and dramatic effects in males, increasing fat mass by 58% in the first 3 days. The resistance to the obesifying effect of HFD in females was linked both to an ability to maintain activity levels as well as to an immediate and significantly enhanced reduction in respiratory quotient (RQ), suggesting a greater ability to utilise fat in the diet as a source of fuel. Mechanistically, this sex disparity may be at least partially due to inherent sex differences in the catabolic (POMC/CART) versus anabolic (NPY/AgRP) neurological signalling pathways. Interestingly, the reintroduction of chow following HFD had immediate and consistent responses between the sexes with body composition and most metabolic parameters normalised within 3 days. However, both sexes displayed elevated hypothalamic Npy levels reminiscent of starvation. The difference in RQ seen between the sexes on HFD was immediately abolished suggesting similar abilities to burn fat reserves for fuel.

Conclusions

C57BL/6J mice have markedly different sex-specific behavioural and metabolic responses to the introduction as well as the sustained intake of a HFD, but consistent responses to a dieting situation.

Plcg2M28L Interacts With High Fat/High Sugar Diet to Accelerate Alzheimer's Disease-Relevant Phenotypes in Mice

Obesity is recognized as a significant risk factor for Alzheimer's disease (AD). Studies have supported the notion that obesity accelerates AD-related pathophysiology in mouse models of AD. The majority of studies, to date, have focused on the use of early-onset AD models. Here, we evaluate the impact of genetic risk factors on late-onset AD (LOAD) in mice fed with a high fat/high sugar diet (HFD). We focused on three mouse models created through the IU/JAX/PITT MODEL-AD Center. These included a combined risk model with APOE4 and a variant in triggering receptor expressed on myeloid cells 2 (Trem2R47H ). We have termed this model, LOAD1. Additional variants including the M28L variant in phospholipase C Gamma 2 (Plcg2M28L ) and the 677C > T variant in methylenetetrahydrofolate reductase (Mthfr 677C > T ) were engineered by CRISPR onto LOAD1 to generate LOAD1.Plcg2M28L and LOAD1.Mthfr 677C > T . At 2 months of age, animals were placed on an HFD that induces obesity or a control diet (CD), until 12 months of age. Throughout the study, blood was collected to assess the levels of cholesterol and glucose. Positron emission tomography/computed tomography (PET/CT) was completed prior to sacrifice to image for glucose utilization and brain perfusion. After the completion of the study, blood and brains were collected for analysis. As expected, animals fed a HFD, showed a significant increase in body weight compared to those fed a CD. Glucose increased as a function of HFD in females only with cholesterol increasing in both sexes. Interestingly, LOAD1.Plcg2M28L demonstrated an increase in microglia density and alterations in regional brain glucose and perfusion on HFD. These changes were not observed in LOAD1 or LOAD1.Mthfr 677C > T animals fed with HFD. Furthermore, LOAD1.Plcg2M28L but not LOAD1.Mthfr 677C > T or LOAD1 animals showed transcriptomics correlations with human AD modules. Our results show that HFD affects the brain in a genotype-specific manner. Further insight into this process may have significant implications for the development of lifestyle interventions for the treatment of AD.

Adipocyte-Specific Expression of PGC1α Promotes Adipocyte Browning and Alleviates Obesity-Induced Metabolic Dysfunction in an HO-1-Dependent Fashion

Recent studies suggest that PGC1-α plays a crucial role in mitochondrial and vascular function, yet the physiological significance of PGC1α and HO expression in adipose tissues in the context of obesity-linked vascular dysfunction remains unclear. We studied three groups of six-week-old C57BL/6J male mice: (1) mice fed a normal chow diet; (2) mice fed a high-fat diet (H.F.D.) for 28 weeks, and (3) mice fed a high-fat diet (H.F.D.) for 28 weeks, treated with adipose-specific overexpression of PGC-1α (transgenic-adipocyte-PGC-1α) at week 20, and continued on H.F.D. for weeks 20–28. R.N.A. arrays examined 88 genes involved in adipocyte proliferation and maturation. Blood pressure, tissue fibrosis, fasting glucose, and oxygen consumption were measured, as well as liver steatosis, and the expression levels of metabolic and mitochondrial markers. Obese mice exhibited a marked reduction of PGC1α and developed adipocyte hypertrophy, fibrosis, hepatic steatosis, and decreased mitochondrial respiration. Mice with adipose-specific overexpression of PGC1-α exhibited improvement in HO-1, mitochondrial biogenesis and respiration, with a decrease in fasting glucose, reduced blood pressure and fibrosis, and increased oxygen consumption. PGC-1α led to the upregulated expression of processes associated with the browning of fat tissue, including UCP1, FGF21, and pAMPK signaling, with a reduction in inflammatory adipokines, NOV/CCN3 expression, and TGFβ. These changes required HO-1 expression. The R.N.A. array analysis identified subgroups of genes positively correlated with contributions to the browning of adipose tissue, all dependent on HO-1. Our observations reveal a positive impact of adipose-PGC1-α on distal organ systems, with beneficial effects on HO-1 levels, reversing obesity-linked cardiometabolic disturbances.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Metabolic Profiling of Mice with Deletion of the Orphan G Protein-Coupled Receptor, GPR37L1

Understanding the neurogenic causes of obesity may reveal novel drug targets to counter the obesity crisis and associated sequelae. Here, we investigate whether the deletion of GPR37L1, an astrocyte-specific orphan G protein-coupled receptor, affects whole-body energy homeostasis in mice. We subjected male Gpr37l1−/− mice and littermate wildtype (Gpr37l1+/+, C57BL/6J background) controls to either 12 weeks of high-fat diet (HFD) or chow feeding, or to 1 year of chow diet, with body composition quantified by EchoMRI, glucose handling by glucose tolerance test and metabolic rate by indirect calorimetry. Following an HFD, Gpr37l1−/− mice had similar glucose handling, body weight and fat mass compared with wildtype controls. Interestingly, we observed a significantly elevated respiratory exchange ratio in HFD- and chow-fed Gpr37l1−/− mice during daylight hours. After 1 year of chow feeding, we again saw no differences in glucose and insulin tolerance or body weight between genotypes, nor in energy expenditure or respiratory exchange ratio. However, there was significantly lower fat mass accumulation, and higher ambulatory activity in the Gpr37l1−/− mice during night hours. Overall, these results indicate that while GPR37L1 may play a minor role in whole-body metabolism, it is not a viable clinical target for the treatment of obesity.

Mitochondrial complex I subunit deficiency promotes pancreatic α-cell proliferation

OBJECTIVE

There is strong evidence that mitochondrial DNA mutations and mitochondrial dysfunction play a role in diabetes pathogenesis. The homozygous knock-in mtDNA mutator mouse is a model of premature aging due to the accumulation of mitochondrial DNA mutations. We used this mouse model to investigate the relationship between mitochondrial subunit expression and pancreatic islet cell composition.

METHODS

Quadruple immunofluorescence was used to quantify mitochondrial subunit expression (complex I and IV) and cell composition in pancreatic islets from mitochondrial DNA mutator mice (PolgAmut/mut) and control C57BL/6 mice at 12 and 44 weeks of age.

RESULTS

Mitochondrial complex I subunit expression was decreased in islets from 12 week PolgAmut/mut mice. This complex I deficiency persisted with age and was associated with decreased insulin staining intensity at 44 weeks. Complex I deficiency was greater in α-cells compared with β-cells in islets from 44 week PolgAmut/mut mice. Islet cell composition was normal in 12 week PolgAmut/mut mice, but the β: α cell ratio was decreased in islets from 44 week PolgAmut/mut mice. This was due to an increase in α-cell number linked to an increase in α-cell proliferation.

CONCLUSION

Complex I deficiency promotes α-cell proliferation and alters islet cell composition.

A Cardiac Amino-Terminal GRK2 Peptide Inhibits Maladaptive Adipocyte Hypertrophy and Insulin Resistance During Diet-Induced Obesity

Heart disease remains the leading cause of death, and mortality rates positively correlate with the presence of obesity and diabetes. Despite the correlation between cardiac and metabolic dysregulation, the mechanistic pathway(s) of interorgan crosstalk still remain undefined. This study reveals that cardiac-restricted expression of an amino-terminal peptide of GRK2 (βARKnt) preserves systemic and cardiac insulin responsiveness, and protects against adipocyte maladaptive hypertrophy in a diet-induced obesity model. These data suggest a cardiac-driven mechanism to ameliorate maladaptive cardiac remodeling and improve systemic metabolic homeostasis that may lead to new treatment modalities for cardioprotection in obesity and obesity-related metabolic syndromes.

Insights from a high-fat diet fed mouse model with a humanized liver

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disorder worldwide and is increasing at an alarming rate. NAFLD is strongly associated with obesity and insulin resistance. The use of animal models remains a vital aspect for investigating the molecular mechanisms contributing to metabolic dysregulation and facilitating novel drug target identification. However, some differences exist between mouse and human hepatocyte physiology. Recently, chimeric mice with human liver have been generated, representing a step forward in the development of animal models relevant to human disease. Here we explored the feasibility of using one of these models (cDNA-uPA/SCID) to recapitulate obesity, insulin resistance and NAFLD upon feeding a Western-style diet. Furthermore, given the importance of a proper control diet, we first evaluated whether there are differences between feeding a purified ingredient control diet that matches the composition of the high-fat diet and feeding a grain-based chow diet. We show that mice fed chow have a higher food intake and fed glucose levels than mice that received a low-fat purified ingredient diet, suggesting that the last one represents a better control diet. Upon feeding a high-fat or matched ingredient control diet for 12 weeks, cDNA-uPA/SCID chimeric mice developed extensive macrovesicular steatosis, a feature previously associated with reduced growth hormone action. However, mice were resistant to diet-induced obesity and remained glucose tolerant. Genetic background is fundamental for the development of obesity and insulin resistance. Our data suggests that using a background that favors the development of these traits, such as C57BL/6, may be necessary to establish a humanized mouse model of NAFLD exhibiting the metabolic dysfunction associated with obesity.

Overexpressed beta cell CART increases insulin secretion in mouse models of insulin resistance and diabetes

Impaired beta cell function and beta cell death are key features of type 2 diabetes (T2D). Cocaine- and amphetamine-regulated transcript (CART) is necessary for normal islet function in mice. CART increases glucose-stimulated insulin secretion in vivo in mice and in vitro in human islets and CART protects beta cells against glucotoxicity-induced cell death in vitro in rats. Furthermore, beta cell CART is upregulated in T2D patients and in diabetic rodent models as a consequence of hyperglycaemia. The aim of this study was to assess the impact of upregulated beta cell CART on islet hormone secretion and glucose homeostasis in a transgenic mouse model. To this end, mice with beta cell-specific overexpression of CART (CARTtg mice) were generated. CARTtg mice challenged by aging, high fat diet feeding or streptozotocin treatment were phenotyped with respect to in vivo and in vitro insulin and glucagon secretion, glucose homeostasis, and beta cell mass. In addition, the impact of adenoviral overexpression of CART on insulin secretion was studied in INS-1 832/13 cells. CARTtg mice had a normal metabolic phenotype under basal conditions. On the other hand, with age CARTtg mice displayed increased insulin secretion and improved glucose elimination, compared with age-matched WT mice. Furthermore, compared with WT controls, CARTtg mice had increased insulin secretion after feeding a high fat diet, as well as lower glucose levels and higher insulin secretion after streptozotocin treatment. Viral overexpression of CART in INS-1 832/13 cells resulted in increased glucose-stimulated insulin secretion. Together, these results imply that beta cell CART acts to increase insulin secretion when beta cell function is challenged. We propose that the increase in beta cell CART is part of a compensatory mechanisms trying to counteract the hyperglycaemia in T2D.

An improved model of type 2 diabetes with effects on glucose tolerance, neuropathy and retinopathy with and without obesity

RATIONALE

Type 2 diabetes (T2D) costs billions of dollars annually, is also associated with pain (diabetic neuropathy), as well as retinopathy, lower urinary tract/urinary bladder dysfunction, depression, and systemic inflammation, affecting quality of life for patients. To that end, animal models are utilized to explore potential treatments, but may not reflect the complexity of the condition.

OBJECTIVE

We aimed to test an improved model of T2D that more closely mimics the clinical mechanisms and symptoms in an outbred strain of mouse.

FINDINGS

Male and female CD-1 mice (n = 72) were fed one of four diets: regular chow (REG), our Standard American Diet (SAD), a revised SAD (SAD2), or the commonly-used high-fat diet (HFD). Overall, HFD- and SAD-fed mice had significant weight gain and increased fat mass. Following injury, the SAD- and SAD2-fed mice showed protracted recovery, but the HFD-fed mice did not. Similarly, SAD- and SAD2-fed mice showed impaired retinal function compared to REG-fed mice, but the HFD-fed mice did not.

CONCLUSIONS

The SAD and SAD2 more closely model the problematic dietary intake and subsequent clinical symptoms associated with T2D.

POTENTIAL IMPACT OF STUDY

The adjusted SAD2 may be a better representation of a human-translatable diet than the SAD and HFD, and may allow for increased advances in the investigation of T2D-related symptoms.

Modulation of Gut Microbiota Metabolism in Obesity-Related Type 2 Diabetes Reduces Osteomyelitis Severity

Staphylococcus aureus is an opportunistic pathogen causing osteomyelitis through hematogenous seeding or contamination of implants and open wounds following orthopedic surgeries. The severity of S. aureus-mediated osteomyelitis is enhanced in obesity-related type 2 diabetes (obesity/T2D) due to chronic inflammation impairing both adaptive and innate immunity. Obesity-induced inflammation is linked to gut dysbiosis, with modification of the gut microbiota by high-fiber diets leading to a reduction in the symptoms and complications of obesity/T2D. However, our understanding of the mechanisms by which modifications of the gut microbiota alter host infection responses is limited. To address this gap, we monitored tibial S. aureus infections in obese/T2D mice treated with the inulin-like fructan fiber oligofructose. Treatment with oligofructose significantly decreased S. aureus colonization and lowered proinflammatory signaling postinfection in obese/T2D mice, as observed by decreased circulating inflammatory cytokines (tumor necrosis factor-α [TNF-α]) and chemokines (interferon-γ-induced protein 10 kDa [IP-10], keratinocyte-derived chemokine [KC], monokine induced by interferon-γ [MIG], monocyte chemoattractant protein-1 [MCP-1], and regulated upon activation, normal T cell expressed and presumably secreted [RANTES]), indicating partial reduction in inflammation. Oligofructose markedly shifted diversity in the gut microbiota of obese/T2D mice, with notable increases in the anti-inflammatory bacterium Bifidobacterium pseudolongum. Analysis of the cecum and plasma metabolome suggested that polyamine production was increased, specifically spermine and spermidine. Oral administration of these polyamines to obese/T2D mice resulted in reduced infection severity similar to oligofructose supplementation, suggesting that polyamines can mediate the beneficial effects of fiber on osteomyelitis severity. These results demonstrate the contribution of gut microbiota metabolites to the control of bacterial infections distal to the gut and polyamines as an adjunct therapeutic for osteomyelitis in obesity/T2D. IMPORTANCE Individuals with obesity-related type 2 diabetes (obesity/T2D) are at a five times increased risk for invasive Staphylococcus aureus osteomyelitis (bone infection) following orthopedic surgeries. With increasing antibiotic resistance and limited discoveries of novel antibiotics, it is imperative that we explore other avenues for therapeutics. In this study, we demonstrated that the dietary fiber oligofructose markedly reduced osteomyelitis severity and hyperinflammation following acute prosthetic joint infections in obese/T2D mice. Reduced infection severity was associated with changes in gut microbiota composition and metabolism, as indicated by increased production of natural polyamines in the gut and circulating plasma. This work identifies a novel role for the gut microbiome in mediating control of bacterial infections and polyamines as beneficial metabolites involved in improving the obesity/T2D host response to osteomyelitis. Understanding the impact of polyamines on host immunity and mechanisms behind decreasing susceptibility to severe implant-associated osteomyelitis is crucial to improving treatment strategies for this patient population.

Obesity modulates the immune macroenvironment associated with breast cancer development

Growing evidence demonstrates a strong correlation between obesity and an increased risk of breast cancer, although the mechanisms involved have not been completely elucidated. Some reports have described a crosstalk between adipocytes, cancer cells, and immune cells within the tumor microenvironment, however, it is currently unknown whether obesity can promote tumor growth by inducing systemic alterations of the immune cell homeostasis in peripheral lymphoid organs and adipose tissue. Here, we used the E0771 breast cancer cell line in a mouse model of diet-induced obesity to analyze the immune subpopulations present in the tumors, visceral adipose tissue (VAT), and spleen of lean and obese mice. Our results showed a significant reduction in the frequency of infiltrating CD8⁺ T cells and a decreased M1/M2 macrophage ratio, indicative of the compromised anti-tumoral immune response reported in obesity. Despite not finding differences in the percentage or numbers of intratumoral Tregs, phenotypic analysis showed that they were enriched in CD39⁺, PD-1⁺ and CCR8⁺ cells, compared to the draining lymph nodes, confirming the highly immunosuppressive profile of infiltrating Tregs reported in established tumors. Analysis of peripheral T lymphocytes showed that tumor development in obese mice was associated to a significant increase in the percentage of peripheral Tregs, which supports the systemic immunosuppressive effect caused by the tumor. Interestingly, evaluation of immune subpopulations in the VAT showed that the characteristic increase in the M1/M2 macrophage ratio reported in obesity, was completely reversed in tumor-bearing mice, resembling the M2-polarized profile found in the microenvironment of the growing tumor. Importantly, VAT Tregs, which are commonly decreased in obese mice, were significantly increased in the presence of breast tumors and displayed significantly higher levels of Foxp3, indicating a regulatory feedback mechanism triggered by tumor growth. Altogether, our results identify a complex reciprocal relationship between adipocytes, immune cells, and the tumor, which may modulate the immune macroenvironment that promotes breast cancer development in obesity.

Investigation of Behavior and Plasma Levels of Corticosterone in Restrictive- and Ad Libitum-Fed Diet-Induced Obese Mice

Diet-induced obesity (DIO) mice models are commonly used to investigate obesity-related health problems. Until now, only sparse data exist on the influence of DIO on behavior and stress hormones in mice. The present study investigates high-fat DIO with two different feeding regimes on behavioral parameters in mice. Various behavioral tests (open field, elevated plus maze, social interaction, hotplate) were performed with female BALB/c and male C57BL/6 mice after a feeding period of twelve weeks (restrictive vs. ad libitum and normal-fat diet vs. high-fat diet) to investigate levels of anxiety and aggression. BALB/c mice were DIO-resistant and therefore the prerequisite for the behavior analyses was not attained. C57BL/6 mice fed a high-fat diet had a significantly higher body weight and fat mass compared to C57BL/6 mice fed a control diet. Interestingly, the DIO C57BL/6 mice showed no changes in their aggression- or anxiety-related behavior but showed a significant change in the anxiety index. This was probably due to a lower activity level, as other ethological parameters did not show an altered anxiety-related behavior. In the ad libitum-fed DIO group, the highest corticosterone level was detected. Changes due to the feeding regime (restrictive vs. ad libitum) were not observed. These results provide a possible hint to a bias in the investigation of DIO-related health problems in laboratory animal experiments, which may be influenced by the lower activity level.

Glucose tolerance of iguanas is affected by high-sugar diets in the lab and supplemental feeding by ecotourists in the wild

There is great interspecific variation in the nutritional composition of natural diets, and the varied nutritional content is physiologically tolerated because of evolutionarily based balances between diet composition and processing ability. However, as a result of landscape change and human exposure, unnatural diets are becoming widespread among wildlife without the necessary time for evolutionary matching between the diet and its processing. We tested how a controlled, unnatural high glucose diet affects glucose tolerance using captive green iguanas, and we performed similar glucose tolerance tests on wild Northern Bahamian rock iguanas that are either frequently fed grapes by tourists or experience no such supplementation. We evaluated both short and longer-term blood glucose responses and corticosterone (CORT) concentrations as changes have been associated with altered diets. Experimental glucose supplementation in the laboratory and tourist feeding in the wild both significantly affected glucose metabolism. When iguanas received a glucose-rich diet, we found greater acute increases in blood glucose following a glucose challenge. Relative to unfed iguanas, tourist-fed iguanas had significantly lower baseline CORT, higher baseline blood glucose, and slower returns to baseline glucose levels following a glucose challenge. Therefore, unnatural consumption of high amounts of glucose alters glucose metabolism in laboratory iguanas with short-term glucose treatment and free-living iguanas exposed to long-term feeding by tourists. Based on these results and the increasing prevalence of anthropogenically altered wildlife diets, the consequences of dietary changes on glucose metabolism should be further investigated across species, as such changes in glucose metabolism have health consequences in humans (e.g. diabetes).