The genetic landscape of type 2 diabetes in mice

Dietary Milk Phospholipids Increase Body Fat and Modulate Gut Permeability, Systemic Inflammation, and Lipid Metabolism in Mice

The study aimed at how dietary milk polar lipids affect gut permeability, systemic inflammation, and lipid metabolism during diet-induced obesity (DIO). C57BL/6J mice (n = 6x3) were fed diets with 34% fat as energy for 15 weeks: (1) modified AIN-93G diet (CO); (2) CO with milk gangliosides (GG); (3) CO with milk phospholipids (MPL). Gut permeability was assessed by FITC-dextran and sugar absorption tests. Intestinal tight junction proteins were evaluated by Western blot. Plasma cytokines were measured by immunoassay. Body composition was assessed by magnetic resonance imaging. Tissue lipid profiles were obtained by thin layer chromatography. Hepatic expression of genes associated with lipid metabolism was assessed by RT-qPCR. MPL increased the efficiency of converting food into body fat and facilitated body fat accumulation compared with CO. MPL and GG did not affect fasting glucose or HOMA-IR during DIO. MPL increased while GG decreased plasma TG compared with CO. MPL decreased phospholipids subclasses in the muscle while increased those in the liver compared with CO. GG and MPL had little effect on hepatic expression of genes associated with lipid metabolism. Compared with CO, MPL decreased polar lipids content in colon mucosa. Small intestinal permeability decreased while colon permeability increased and then recovered during the feeding period. High-fat feeding increased plasma endotoxin after DIO but did not affect plasma cytokines. MPL and GG did not affect plasma endotoxin, adipokines and inflammatory cytokines. After the establishment of obesity, MPL increased gut permeability to large molecules but decreased intestinal absorption of small molecules while GG tended to have the opposite effects. MPL and GG decreased mannitol and sucralose excretions, which peaked at d 45 in the CO group. MPL decreased occludin in jejunum mucosa compared with CO. GG and MPL did not affect zonula occludens-1 in gut mucosa. In conclusion, during DIO, milk GG decreased gut permeability, and had little effect on systemic inflammation and lipid metabolism; MPL facilitated body fat accumulation, decreased gut permeability, did not affect systemic inflammation.

Single-housing-induced islet epigenomic changes are related to polymorphisms in diabetic KK mice

A lack of social relationships is increasingly recognized as a type 2 diabetes (T2D) risk. To investigate the underlying mechanism, we used male KK mice, an inbred strain with spontaneous diabetes. Given the association between living alone and T2D risk in humans, we divided the non-diabetic mice into singly housed (KK-SH) and group-housed control mice. Around the onset of diabetes in KK-SH mice, we compared H3K27ac ChIP-Seq with RNA-Seq using pancreatic islets derived from each experimental group, revealing a positive correlation between single-housing-induced changes in H3K27ac and gene expression levels. In particular, single-housing-induced H3K27ac decreases revealed a significant association with islet cell functions and GWAS loci for T2D and related diseases, with significant enrichment of binding motifs for transcription factors representative of human diabetes. Although these H3K27ac regions were preferentially localized to a polymorphic genomic background, SNVs and indels did not cause sequence disruption of enriched transcription factor motifs in most of these elements. These results suggest alternative roles of genetic variants in environment-dependent epigenomic changes and provide insights into the complex mode of disease inheritance.

Obese mice have decreased uterine contractility and altered energy metabolism in the uterus at term gestation

Over 35% of reproductive-age women in the US are obese, putting them at increased risk for numerous obstetric complications due to abnormal labor. While the association between maternal obesity and abnormal labor has been well documented, the mechanisms responsible for this remain understudied. The uterine smooth muscle, myometrium, has high energy needs in order to fuel regular uterine contractions during parturition. However, the precise mechanisms by which the myometrium meets its energy demands has not been defined. Here, our objective was to define the effects of obesity on energy utilization in the myometrium during labor. We generated a mouse model of maternal diet-induced obesity (DIO) and found that these mice had a higher rate of dystocia than control chow-fed (CON) mice. Moreover, compared to CON mice, DIO mice at term, both before and during labor had lower in vivo spontaneous uterine contractility. Untargeted transcriptomic and metabolomic analyses suggest that DIO is associated with elevated long-chain fatty acid uptake and utilization in the uterus, but also an accumulation of medium-chain fatty acids. DIO uteri also had an increase in the abundance of long chain-specific β-oxidation enzymes, which may be responsible for the observed increase in long-chain fatty acid utilization. This altered energy substrate utilization may be a contributor to the observed contractile dysfunction.

Adipose tissue IL-18 production is independent of caspase-1 and caspase-11

BACKGROUND

Inflammation in adipose tissue, resulting from imbalanced caloric intake and energy expenditure, contributes to the metabolic dysregulation observed in obesity. The production of inflammatory cytokines, such as IL-1β and IL-18, plays a key role in this process. While IL-1β promotes insulin resistance and diabetes, IL-18 regulates energy expenditure and food intake. Previous studies have suggested that caspase-1, activated by the Nlrp3 inflammasome in response to lipid excess, mediates IL-1β production, whereas activated by the Nlrp1b inflammasome in response to energy excess, mediates IL-18 production. However, this has not been formally tested.

METHODS

Wild-type and caspase-1-deficient Balb/c mice, carrying the Nlrp1b1 allele, were fed with regular chow or a high-fat diet for twelve weeks. Food intake and mass gain were recorded weekly. At the end of the twelve weeks, glucose tolerance and insulin resistance were evaluated. Mature IL-18 protein levels and the inflammatory process in the adipose tissue were determined. Fasting lipid and cytokine levels were quantified in the sera of the different experimental groups.

RESULTS

We found that IL-18 production in adipose tissue is independent of caspase-1 activity, regardless of the metabolic state, while Nlrp3-mediated IL-1β production remains caspase-1 dependent. Additionally, caspase-1 null Balb/c mice did not develop metabolic abnormalities in response to energy excess from the high-fat diet.

CONCLUSION

Our findings suggest that IL-18 production in the adipose tissue is independent of Nlrp3 inflammasome and caspase-1 activation, regardless of caloric food intake. In contrast, Nlrp3-mediated IL-1β production is caspase-1 dependent. These results provide new insights into the mechanisms underlying cytokine production in the adipose tissue during both homeostatic conditions and metabolic stress, highlighting the distinct roles of caspase-1 and the Nlrp inflammasomes in regulating inflammatory responses.

Protective effect of SERCA2a-SUMOylation by SUMO-1 on diabetes-induced atherosclerosis and aortic vascular injury

Diabetes is a major risk factor for cardiovascular disease. However, the exact mechanism by which diabetes contributes to vascular damage is not fully understood. The aim of this study was to investigate the role of SUMO-1 mediated SERCA2a SUMOylation in the development of atherosclerotic vascular injury associated with diabetes mellitus. ApoE-/- mice were treated with streptozotocin (STZ) injection combined with high-fat feeding to simulate diabetic atherosclerosis and vascular injury. Human aortic vascular smooth muscle cells (HAVSMCs) were treated with high glucose (HG, 33.3 mM) and palmitic acid (PA, 200 µM) for 24 h to mimic a model of diabetes-induced vascular injury in vitro. Aortic vascular function, phenotypic conversion, migration, proliferation, intracellular Ca2+ concentration, the levels of small ubiquitin-like modifier type 1 (SUMO1), SERCA2a and SUMOylated SERCA2a were detected. Diabetes-induced atherosclerotic mice presented obvious atherosclerotic plaques and vascular injury, companied by significantly lower levels of SUMO1 and SERCA2a in aorta. HG and PA treatment in HAVSMCs reduced the expressions of SUMO1, SERCA2a and SUMOylated SERCA2a, facilitated the HAVSMCs phenotypic transformation, proliferation and migration, attenuated the Ca2+ transport, and increased the resting intracellular Ca2+ concentration. We also confirmed that SUMO1 directly bound to SERCA2a in HAVSMCs. Overexpression of SUMO1 restored the function and phenotypic contractile ability of HAVSMCs by upregulating SERCA2a SUMOylation, thereby alleviating HG and PA-induced vascular injury. These observations suggest an essential role of SUMO1 to protect diabetes-induced atherosclerosis and aortic vascular injury by the regulation of SERCA2a-SUMOylation and calcium homeostasis.

Reversal of biological age in multiple rat organs by young porcine plasma fraction

Young blood plasma is known to confer beneficial effects on various organs in mice and rats. However, it was not known whether plasma from young adult pigs rejuvenates old rat tissues at the epigenetic level; whether it alters the epigenetic clock, which is a highly accurate molecular biomarker of aging. To address this question, we developed and validated six different epigenetic clocks for rat tissues that are based on DNA methylation values derived from n = 613 tissue samples. As indicated by their respective names, the rat pan-tissue clock can be applied to DNA methylation profiles from all rat tissues, while the rat brain, liver, and blood clocks apply to the corresponding tissue types. We also developed two epigenetic clocks that apply to both human and rat tissues by adding n = 1366 human tissue samples to the training data. We employed these six rat clocks to investigate the rejuvenation effects of a porcine plasma fraction treatment in different rat tissues. The treatment more than halved the epigenetic ages of blood, heart, and liver tissue. A less pronounced, but statistically significant, rejuvenation effect could be observed in the hypothalamus. The treatment was accompanied by progressive improvement in the function of these organs as ascertained through numerous biochemical/physiological biomarkers, behavioral responses encompassing cognitive functions. An immunoglobulin G (IgG) N-glycosylation pattern shift from pro- to anti-inflammatory also indicated reversal of glycan aging. Overall, this study demonstrates that a young porcine plasma-derived treatment markedly reverses aging in rats according to epigenetic clocks, IgG glycans, and other biomarkers of aging.

Animal Models of Type 2 Diabetes Complications: A Review

Diabetes mellitus is a multifactorial metabolic disease, of which type 2 diabetes (T2D) is one of the most common. The complications of diabetes are far more harmful than diabetes itself. Type 2 diabetes complications include diabetic nephropathy (DN), diabetic heart disease, diabetic foot ulcers (DFU), diabetic peripheral neuropathy (DPN), and diabetic retinopathy (DR) et al. Many animal models have been developed to study the pathogenesis of T2D and discover an effective strategy to treat its consequences. In this sense, it is crucial to choose the right animal model for the corresponding diabetic complication. This paper summarizes and classifies the animal modeling approaches to T2D complications and provides a comprehensive review of their advantages and disadvantages. It is hopeful that this paper will provide theoretical support for animal trials of diabetic complications.

Experimental diabetic animal models to study diabetes and diabetic complications

Diabetes is an endocrine illness involving numerous physiological systems. To understand the intricated pathophysiology and disease progression in diabetes, small animals are still the most relevant model systems, despite the availability and progression in numerous invitro and insilico research methods in recent years. In general, experimental diabetes is instigated mainly due to the effectiveness of animal models in illuminating disease etiology. Most diabetes trials are conducted on rodents, while some research is conducted on larger animals. This review will discuss the methodology and mechanisms in detail for preparing diabetic animal models, considering the following important points. The exact pathophysiology of the disease may or may not be replicated in animal models, the correct induction doses must be given and the combination of different approaches for the models is recommended to get desired results.•Animal models are essential to understand diabetes etiology and pathophysiology.•Diabetic models can be developed in both rodents and non-rodents.•Chemically induced and genetic models of diabetes are widely used to study diabetes and diabetic complications.

Endocrine, genetic, and microbiome nexus of obesity and potential role of postbiotics: a narrative review

Obesity is a public health crisis, presenting a huge burden on health care and the economic system in both developed and developing countries. According to the WHO's latest report on obesity, 39% of adults of age 18 and above are obese, with an increase of 18% compared to the last few decades. Metabolic energy imbalance due to contemporary lifestyle, changes in gut microbiota, hormonal imbalance, inherent genetics, and epigenetics is a major contributory factor to this crisis. Multiple studies have shown that probiotics and their metabolites (postbiotics) supplementation have an effect on obesity-related effects in vitro, in vivo, and in human clinical investigations. Postbiotics such as the SCFAs suppress obesity by regulating metabolic hormones such as GLP-1, and PPY thus reducing feed intake and suppressing appetite. Furthermore, muramyl di-peptides, bacteriocins, and LPS have been tested against obesity and yielded promising results in both human and mice studies. These insights provide an overview of targetable pharmacological sites and explore new opportunities for the safer use of postbiotics against obesity in the future.

Novel regulators of islet function identified from genetic variation in mouse islet Ca2+ oscillations

Insufficient insulin secretion to meet metabolic demand results in diabetes. The intracellular flux of Ca2+ into β-cells triggers insulin release. Since genetics strongly influences variation in islet secretory responses, we surveyed islet Ca2+ dynamics in eight genetically diverse mouse strains. We found high strain variation in response to four conditions: (1) 8 mM glucose; (2) 8 mM glucose plus amino acids; (3) 8 mM glucose, amino acids, plus 10 nM glucose-dependent insulinotropic polypeptide (GIP); and (4) 2 mM glucose. These stimuli interrogate β-cell function, α- to β-cell signaling, and incretin responses. We then correlated components of the Ca2+ waveforms to islet protein abundances in the same strains used for the Ca2+ measurements. To focus on proteins relevant to human islet function, we identified human orthologues of correlated mouse proteins that are proximal to glycemic-associated single-nucleotide polymorphisms in human genome-wide association studies. Several orthologues have previously been shown to regulate insulin secretion (e.g. ABCC8, PCSK1, and GCK), supporting our mouse-to-human integration as a discovery platform. By integrating these data, we nominate novel regulators of islet Ca2+ oscillations and insulin secretion with potential relevance for human islet function. We also provide a resource for identifying appropriate mouse strains in which to study these regulators.

Optimizing diabetic kidney disease animal models: Insights from a meta-analytic approach

Diabetic kidney disease (DKD) is a prevalent complication of diabetes, often leading to end-stage renal disease. Animal models have been widely used to study the pathogenesis of DKD and evaluate potential therapies. However, current animal models often fail to fully capture the pathological characteristics of renal injury observed in clinical patients with DKD. Additionally, modeling DKD is often a time-consuming, costly, and labor-intensive process. The current review aims to summarize modeling strategies in the establishment of DKD animal models by utilizing meta-analysis related methods and to aid in the optimization of these models for future research. A total of 1215 articles were retrieved with the keywords of "diabetic kidney disease" and "animal experiment" in the past 10 years. Following screening, 84 articles were selected for inclusion in the meta-analysis. Review manager 5.4.1 was employed to analyze the changes in blood glucose, glycosylated hemoglobin, total cholesterol, triglyceride, serum creatinine, blood urea nitrogen, and urinary albumin excretion rate in each model. Renal lesions shown in different models that were not suitable to be included in the meta-analysis were also extensively discussed. The above analysis suggested that combining various stimuli or introducing additional renal injuries to current models would be a promising avenue to overcome existing challenges and limitations. In conclusion, our review article provides an in-depth analysis of the limitations in current DKD animal models and proposes strategies for improving the accuracy and reliability of these models that will inspire future research efforts in the DKD research field.

Feeding High-Fat Diet Accelerates Development of Peripheral and Central Insulin Resistance and Inflammation and Worsens AD-like Pathology in APP/PS1 Mice

Alzheimer's disease (AD) is a progressive brain disorder characterized by extracellular amyloid-β (Aβ) plaques, intracellular neurofibrillary tangles formed by hyperphosphorylated Tau protein and neuroinflammation. Previous research has shown that obesity and type 2 diabetes mellitus, underlined by insulin resistance (IR), are risk factors for neurodegenerative disorders. In this study, obesity-induced peripheral and central IR and inflammation were studied in relation to AD-like pathology in the brains and periphery of APP/PS1 mice, a model of Aβ pathology, fed a high-fat diet (HFD). APP/PS1 mice and their wild-type controls fed either a standard diet or HFD were characterized at the ages of 3, 6 and 10 months by metabolic parameters related to obesity via mass spectroscopy, nuclear magnetic resonance, immunoblotting and immunohistochemistry to quantify how obesity affected AD pathology. The HFD induced substantial peripheral IR leading to central IR. APP/PS1-fed HFD mice had more pronounced IR, glucose intolerance and liver steatosis than their WT controls. The HFD worsened Aβ pathology in the hippocampi of APP/PS1 mice and significantly supported both peripheral and central inflammation. This study reveals a deleterious effect of obesity-related mild peripheral inflammation and prediabetes on the development of Aβ and Tau pathology and neuroinflammation in APP/PS1 mice.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

Metabolic labeling unveils alterations in the turnover of HDL-associated proteins during diabetes progression in mice

Several aspects of diabetes pathophysiology and complications result from hyperglycemia-induced alterations in the structure and function of plasma proteins. Furthermore, insulin has a significant influence on protein metabolism by affecting both the synthesis and degradation of proteins in various tissues. To understand the role of progressive hyperglycemia on plasma proteins, in this study, we measured the turnover rates of high-density lipoprotein (HDL)-associated proteins in control (chow diet), prediabetic [a high-fat diet (HFD) for 8 wk] or diabetic [HFD for 8 wk with low-dose streptozotocin (HFD + STZ) in weeks 5-8 of HFD] C57BL/6J mice using heavy water (2H2O)-based metabolic labeling approach. Compared with control mice, HFD and HFD + STZ mice showed elevations of fasting plasma glucose levels in the prediabetic and diabetic range, respectively. Furthermore, the HFD and HFD + STZ mice showed increased hepatic triglyceride (TG) levels, total plasma cholesterol, and plasma TGs. The kinetics of 40 proteins were quantified using the proteome dynamics method, which revealed an increase in the fractional synthesis rate (FSR) of HDL-associated proteins in the prediabetic mice compared with control mice, and a decrease in FSR in the diabetic mice. The pathway analysis revealed that proteins with altered turnover rates were involved in acute-phase response, lipid metabolism, and coagulation. In conclusion, prediabetes and diabetes have distinct effects on the turnover rates of HDL proteins. These findings suggest that an early dysregulation of the HDL proteome dynamics can provide mechanistic insights into the changes in protein levels in these conditions.NEW & NOTEWORTHY This study is the first to examine the role of gradual hyperglycemia during diabetes disease progression on HDL-associated protein dynamics in the prediabetes and diabetic mice. Our results show that the fractional synthesis rate of HDL-associated proteins increased in the prediabetic mice whereas it decreased in the diabetic mice compared with control mice. These kinetic changes can help to elucidate the mechanism of altered protein levels and HDL dysfunction during diabetes disease progression.

In vitro skeletal muscle models for type 2 diabetes

Type 2 diabetes mellitus, a metabolic disorder characterized by abnormally elevated blood sugar, poses a growing social, economic, and medical burden worldwide. The skeletal muscle is the largest metabolic organ responsible for glucose homeostasis in the body, and its inability to properly uptake sugar often precedes type 2 diabetes. Although exercise is known to have preventative and therapeutic effects on type 2 diabetes, the underlying mechanism of these beneficial effects is largely unknown. Animal studies have been conducted to better understand the pathophysiology of type 2 diabetes and the positive effects of exercise on type 2 diabetes. However, the complexity of in vivo systems and the inability of animal models to fully capture human type 2 diabetes genetics and pathophysiology are two major limitations in these animal studies. Fortunately, in vitro models capable of recapitulating human genetics and physiology provide promising avenues to overcome these obstacles. This review summarizes current in vitro type 2 diabetes models with focuses on the skeletal muscle, interorgan crosstalk, and exercise. We discuss diabetes, its pathophysiology, common in vitro type 2 diabetes skeletal muscle models, interorgan crosstalk type 2 diabetes models, exercise benefits on type 2 diabetes, and in vitro type 2 diabetes models with exercise.

Investigating the Expression and Function of the Glucose Transporter GLUT6 in Obesity

Obesity-related insulin resistance is a highly prevalent and growing health concern, which places stress on the pancreatic islets of Langerhans by increasing insulin secretion to lower blood glucose levels. The glucose transporters GLUT1 and GLUT3 play a key role in glucose-stimulated insulin secretion in human islets, while GLUT2 is the key isoform in rodent islets. However, it is unclear whether other glucose transporters also contribute to insulin secretion by pancreatic islets. Herein, we show that SLC2A6 (GLUT6) is markedly upregulated in pancreatic islets from genetically obese leptin-mutant (ob/ob) and leptin receptor-mutant (db/db) mice, compared to lean controls. Furthermore, we observe that islet SLC2A6 expression positively correlates with body mass index in human patients with type 2 diabetes. To investigate whether GLUT6 plays a functional role in islets, we crossed GLUT6 knockout mice with C57BL/6 ob/ob mice. Pancreatic islets isolated from ob/ob mice lacking GLUT6 secreted more insulin in response to high-dose glucose, compared to ob/ob mice that were wild type for GLUT6. The loss of GLUT6 in ob/ob mice had no adverse impact on body mass, body composition, or glucose tolerance at a whole-body level. This study demonstrates that GLUT6 plays a role in pancreatic islet insulin secretion in vitro but is not a dominant glucose transporter that alters whole-body metabolic physiology in ob/ob mice.

Heterogeneity and altered β-cell identity in the TallyHo model of early-onset type 2 diabetes

A primary underlying defect makes β-cells "susceptible" to no longer compensate for the peripheral insulin resistance and to trigger the onset of type 2 diabetes (T2D). New evidence suggests that in T2D, β-cells are not destroyed but experience a loss of identity, reverting to a progenitor-like state and largely losing the ability to sense glucose and produce insulin. We assessed (using fluorescence microscopy and histomorphometry correlated with the glycaemic status) the main β-cell identity modifications as diabetes progresses in the TallyHo/JngJ (TH) male mice, a polygenic model of spontaneous T2D, akin to the human phenotype. We found that: 1) conversion to overt diabetes is paralleled by a progressive reduction of insulin-expressing cells and expansion of a glucagon-positive population, together with alteration of islet size and shape; 2) the β-cell population is highly heterogeneous in terms of insulin content and specific transcription factors like PDX1 and NKX6.1, that are gradually lost during diabetes progression; 3) GLUT2 expression is altered early and strongly reduced at late stages of diabetes; 4) an endocrine developmental program dependent on NGN3-expressing progenitors is revived when hyperglycaemia becomes severe; and 5) the re-expression of the EMT-associated factor vimentin occurs as diabetes worsens, representing a possible regenerative response to β-cell loss. Based on these results, we formulated additional hypotheses for the β-cell identity alteration in the TH model, together with several limitations of the study, that constitute future research directions.

Comparative genomic analyses of multiple backcross mouse populations suggest SGCG as a novel potential obesity-modifier gene

To nominate novel disease genes for obesity and type 2 diabetes (T2D), we recently generated two mouse backcross populations of the T2D-susceptible New Zealand Obese (NZO/HI) mouse strain and two genetically different, lean and T2D-resistant strains, 129P2/OlaHsd and C3HeB/FeJ. Comparative linkage analysis of our two female backcross populations identified seven novel body fat-associated quantitative trait loci (QTL). Only the locus Nbw14 (NZO body weight on chromosome 14) showed linkage to obesity-related traits in both backcross populations, indicating that the causal gene variant is likely specific for the NZO strain as NZO allele carriers in both crosses displayed elevated body weight and fat mass. To identify candidate genes for Nbw14, we used a combined approach of gene expression and haplotype analysis to filter for NZO-specific gene variants in gonadal white adipose tissue (gWAT), defined as the main QTL-target tissue. Only two genes, Arl11 and Sgcg, fulfilled our candidate criteria. In addition, expression QTL analysis revealed cis-signals for both genes within the Nbw14 locus. Moreover, retroviral overexpression of Sgcg in 3 T3-L1 adipocytes resulted in increased insulin-stimulated glucose uptake. In humans, mRNA levels of SGCG correlated with BMI and body fat mass exclusively in diabetic subjects, suggesting that SGCG may present a novel marker for metabolically unhealthy obesity. In conclusion, our comparative-cross analysis could substantially improve the mapping resolution of the obesity locus Nbw14. Future studies will shine light on the mechanism by which Sgcg may protect from the development of obesity.

Type 2 Diabetes Mellitus: Pathogenic Features and Experimental Models in Rodents

Type 2 diabetes mellitus (T2DM) is the most common endocrine disorder (90%) in the world; it has numerous clinical, immunological, and genetic differences from type 1 diabetes mellitus. The pathogenesis of T2DM is complex and not fully clear. To date, animal models remain the main tool by which to study the pathophysiology and therapy of T2DM. Rodents are considered the best choice among animal models, because they are characterized by a small size, short induction period, easy diabetes induction, and economic efficiency. This review summarizes data on experimental models of T2DM that are currently used, evaluates their advantages and disadvantages vis-a-vis research, and describes in detail the factors that should be taken into account when using these models. Selection of a suitable model for tackling a particular issue is not always trivial; it affects study results and their interpretation.

Ldlr-Deficient Mice with an Atherosclerosis-Resistant Background Develop Severe Hyperglycemia and Type 2 Diabetes on a Western-Type Diet

Apoe^-/- and Ldlr^-/- mice are two animal models extensively used for atherosclerosis research. We previously reported that Apoe^-/- mice on certain genetic backgrounds, including C3H/HeJ (C3H), develop type 2 diabetes when fed a Western diet. We sought to characterize diabetes-related traits in C3H-Ldlr^-/- mice through comparing with C3H-Apoe^-/- mice. On a chow diet, Ldlr^-/- mice had lower plasma total and non-HDL cholesterol levels but higher HDL levels than Apoe^-/- mice. Fasting plasma glucose was much lower in Ldlr^-/- than Apoe^-/- mice (male: 122.5 ± 5.9 vs. 229.4 ± 17.5 mg/dL; female: 144.1 ± 12.4 vs. 232.7 ± 6.4 mg/dL). When fed a Western diet, Ldlr^-/- and Apoe^-/- mice developed severe hypercholesterolemia and also hyperglycemia with fasting plasma glucose levels exceeding 250 mg/dL. Both knockouts had similar non-HDL cholesterol and triglyceride levels, and their fasting glucose levels were also similar. Male Ldlr^-/- mice exhibited greater glucose tolerance and insulin sensitivity compared to their Apoe^-/- counterpart. Female mice showed similar glucose tolerance and insulin sensitivity though Ldlr^-/- mice had higher non-fasting glucose levels. Male Ldlr^-/- and Apoe^-/- mice developed moderate obesity on the Western diet, but female mice did not. These results indicate that the Western diet and ensuing hyperlipidemia lead to the development of type 2 diabetes, irrespective of underlying genetic causes.

Meta-Inflammation and De Novo Lipogenesis Markers Are Involved in Metabolic Associated Fatty Liver Disease Progression in BTBR ob/ob Mice

Metabolic associated fatty liver disease (MAFLD) is a hepatic manifestation of metabolic syndrome and usually associated with obesity and diabetes. Our aim is to characterize the pathophysiological mechanism involved in MAFLD development in Black Tan and brachyuric (BTBR) insulin-resistant mice in combination with leptin deficiency (ob/ob). We studied liver morphology and biochemistry on our diabetic and obese mice model (BTBR ob/ob) as well as a diabetic non-obese control (BTBR + streptozotocin) and non-diabetic control mice (BTBR wild type) from 4–22 weeks. Lipid composition was assessed, and lipid related pathways were studied at transcriptional and protein level. Microvesicular steatosis was evident in BTBR ob/ob from week 6, progressing to macrovesicular in the following weeks. At 12th week, inflammatory clusters, activation of STAT3 and Nrf2 signaling pathways, and hepatocellular ballooning. At 22 weeks, the histopathological features previously observed were maintained and no signs of fibrosis were detected. Lipidomic analysis showed profiles associated with de novo lipogenesis (DNL). BTBR ob/ob mice develop MAFLD profile that resemble pathological features observed in humans, with overactivation of inflammatory response, oxidative stress and DNL signaling pathways. Therefore, BTBR ob/ob mouse is an excellent model for the study of the steatosis to steatohepatitis transition.

Aging-Related Behavioral, Adiposity, and Glucose Impairments and Their Association following Prenatal Alcohol Exposure in the C57BL/6J Mouse

People that experience prenatal alcohol exposure (PAE) may have behavioral and metabolic impairments, and it is unclear whether these remain stable or change with age. We assessed behavioral and metabolic endpoints across the lifespan in a mouse model of fetal alcohol spectrum disorder (FASD). Pregnant C57BL/6J mice received alcohol (ALC; 3 g/kg) or maltose-dextrin (control, CON) daily from embryonic day 8.5 to 17.5. Offspring were tested on accelerating rotarod, Y-maze, novel object recognition, and fear conditioning at 6 weeks and 10 and 17 months; females were also tested at 24 months. Body composition, fasting glucose, and glucose clearance were assessed at 18 months. Female but not male ALC mice had greater adiposity than age-matched CON from 7 months onward. At 18 months, male but not female ALC mice had reduced glucose clearance and ALC mice were more likely to have elevated fasting glucose. In the rotarod training session, ALC females performed worse than CON. In the Y-maze, significant exposure-age interactions affected ALC performance in both sexes versus age-match CON. For fear conditioning, all animals acquired the task and froze more at older ages. In both the context and cued tasks, there were exposure-age interactions and ALC animals frozen less than CON at 10 months. Correlation analysis revealed that fasting glucose and glucose clearance correlated with % of body fat in ALC but not in CON mice. Additionally, glucose intolerance and % body fat negatively correlated with performance in the rotarod, context learning, and novel object recognition tasks in ALC but not CON mice. All mice exhibit worsening of behavioral performance as they age, and PAE did not further exacerbate this. ALC but not CON mice displayed adiposity and glucose intolerance that correlate with their cognitive impairments, suggesting that these may be mechanistically related in PAE. Findings emphasize that FASD should be considered a whole-body disorder.

Genetic Connection between Hyperglycemia and Carotid Atherosclerosis in Hyperlipidemic Mice

Type 2 diabetes (T2D) is a major risk for atherosclerosis and its complications. Apoe-null (Apoe^−/−) mouse strains exhibit a wide range of variations in susceptibility to T2D and carotid atherosclerosis, with the latter being a major cause of ischemic stroke. To identify genetic connections between T2D and carotid atherosclerosis, 145 male F2 mice were generated from LP/J and BALB/cJ Apoe^−/− mice and fed 12 weeks of a Western diet. Atherosclerotic lesions in the carotid arteries, fasting, and non-fasting plasma glucose levels were measured, and genotyping was performed using miniMUGA arrays. Two significant QTL (quantitative trait loci) on chromosomes (Chr) 6 and 15 were identified for carotid lesions. The Chr15 QTL coincided precisely with QTL Bglu20 for fasting and non-fasting glucose levels. Carotid lesion sizes showed a trend toward correlation with fasting and non-fasting glucose levels in F2 mice. The Chr15 QTL for carotid lesions was suppressed after excluding the influence from fasting or non-fasting glucose. Likely candidate genes for the causal association were Tnfrsf11b, Deptor, and Gsdmc2. These results demonstrate a causative role for hyperglycemia in the development of carotid atherosclerosis in hyperlipidemic mice.

Increased Variation in Body Weight and Food Intake Is Related to Increased Dietary Fat but Not Increased Carbohydrate or Protein in Mice

A variety of inbred mouse strains have been used for research in metabolic disorders. Despite being inbred, they display large inter-individual variability for many traits like food intake and body weight. However, the relationship between dietary macronutrients and inter-individual variation in body weight and food intake of different mouse strains is still unclear. We investigated the association between macronutrient content of the diet and variations in food intake, body composition, and glucose tolerance by exposing five different mouse strains (C57BL/6, BALB/c, C3H, DBA/2, and FVB) to 24 different diets with variable protein, fat, and carbohydrate contents. We found only increasing dietary fat, but not protein or carbohydrate had a significant association (positive) with variation in both food intake and body weight. The highest variation in both body weight and food intake occurred with 50% dietary fat. However, there were no significant relationships between the variation in fat and lean mass with dietary protein, fat, or carbohydrate levels. In addition, none of the dietary macronutrients had significant impacts on the variation in glucose tolerance ability in C57BL/6 mice. In conclusion, the variations in food intake and body weight changes increased with the elevation of dietary fat levels.

Diabetic mice have retinal and choroidal blood flow deficits and electroretinogram deficits with impaired responses to hypercapnia

Purpose

The purpose of this study was to investigate neuronal and vascular functional deficits in the retina and their association in a diabetic mouse model. We measured electroretinography (ERG) responses and choroidal and retinal blood flow (ChBF, RBF) with magnetic resonance imaging (MRI) in healthy and diabetic mice under basal conditions and under hypercapnic challenge.

Methods

Ins2^Akita diabetic (Diab, n = 8) and age-matched, wild-type C57BL/6J mice (Ctrl, n = 8) were studied under room air and moderate hypercapnia (5% CO₂). Dark-adapted ERG a-wave, b-wave, and oscillatory potentials (OPs) were measured for a series of flashes. Regional ChBF and RBF under air and hypercapnia were measured using MRI in the same mice.

Results

Under room air, Diab mice had compromised ERG b-wave and OPs (e.g., b-wave amplitude was 422.2±10.7 μV in Diab vs. 600.1±13.9 μV in Ctrl, p < 0.001). Under hypercapnia, OPs and b-wave amplitudes were significantly reduced in Diab (OPs by 30.3±3.0% in Diab vs. -3.0±3.6% in Ctrl, b-wave by 17.9±1.4% in Diab vs. 1.3±0.5% in Ctrl). Both ChBF and RBF had significant differences in regional blood flow, with Diab mice having substantially lower blood flow in the nasal region (ChBF was 5.4±1.0 ml/g/min in Diab vs. 8.6±1.0 ml/g/min in Ctrl, RBF was 0.91±0.10 ml/g/min in Diab vs. 1.52±0.24 ml/g/min in Ctrl). Under hypercapnia, ChBF increased in both Ctrl and Diab without significant group difference (31±7% in Diab vs. 17±7% in Ctrl, p > 0.05), but an increase in RBF was not detected for either group.

Conclusions

Inner retinal neuronal function and both retinal and choroidal blood flow were impaired in Diab mice. Hypercapnia further compromised inner retinal neuronal function in diabetes, while the blood flow response was not affected, suggesting that the diabetic retina has difficulty adapting to metabolic challenges due to factors other than impaired blood flow regulation.

Regression of diabetic nephropathy by treatment with empagliflozin in BTBR ob/ob mice

BACKGROUND

The SGLT2 inhibitor empagliflozin lowers blood glucose via reduced tubular reabsorption of filtered glucose and is an important new therapy for diabetic nephropathy (DN). This study tested whether treatment with empagliflozin would ameliorate proteinuria and the pathologic alterations of DN including podocyte number and integrity in the leptin deficient BTBR ob/ob mouse model of DN.

METHODS

Study cohorts included wild type BTBR mice, untreated diabetic BTBR ob/ob mice, and mice treated with empagliflozin for six weeks after development of established DN at 18 weeks of age.

RESULTS

Hyperglycemia, proteinuria, serum creatinine, accumulation of mesangial matrix and the extent of mesangiolysis were reversed with empagliflozin treatment. Treatment with empagliflozin resulted in increased podocyte number and podocyte density, improvement in the degree of podocyte foot process effacement and parietal epithelial cell activation. SGLT2 inhibition reduced renal oxidative stress, measured by urinary excretion of markers of RNA/DNA damage and in situ demonstration of decreased carbonyl oxidation. There was no discernable difference in accumulations of advanced glycation endproducts by immunohistochemistry.

CONCLUSION

The structural improvements seen in BTBR ob/ob mice treated with empagliflozin provide insight into potential long term benefits for humans with DN, for whom there is no comparable biopsy information to identify structural changes effected by SGLT2 inhibition. The findings suggest SGLT2 inhibition may ameliorate diabetic nephropathy through glucose lowering-dependent and -independent mechanisms that lead to podocyte restoration and delay or reversal of the disease progress.

Prostaglandin EP3 receptor signaling is required to prevent insulin hypersecretion and metabolic dysfunction in a non-obese mouse model of insulin resistance

When homozygous for the Leptin^Ob mutation (Ob), Black-and-Tan Brachyury (BTBR) mice become morbidly obese and severely insulin resistant, and by 10 wk of age, frankly diabetic. Previous work has shown prostaglandin EP3 receptor (EP3) expression and activity is upregulated in islets from BTBR-Ob mice as compared with lean controls, actively contributing to their β-cell dysfunction. In this work, we aimed to test the impact of β-cell-specific EP3 loss on the BTBR-Ob phenotype by crossing Ptger3 floxed mice with the rat insulin promoter (RIP)-Cre^Herr driver strain. Instead, germline recombination of the floxed allele in the founder mouse-an event whose prevalence we identified as directly associated with underlying insulin resistance of the background strain-generated a full-body knockout. Full-body EP3 loss provided no diabetes protection to BTBR-Ob mice but, unexpectedly, significantly worsened BTBR-lean insulin resistance and glucose tolerance. This in vivo phenotype was not associated with changes in β-cell fractional area or markers of β-cell replication ex vivo. Instead, EP3-null BTBR-lean islets had essentially uncontrolled insulin hypersecretion. The selective upregulation of constitutively active EP3 splice variants in islets from young, lean BTBR mice as compared with C57BL/6J, where no phenotype of EP3 loss has been observed, provides a potential explanation for the hypersecretion phenotype. In support of this, high islet EP3 expression in Balb/c females versus Balb/c males was fully consistent with their sexually dimorphic metabolic phenotype after loss of EP3-coupled Gα_z protein. Taken together, our findings provide a new dimension to the understanding of EP3 as a critical brake on insulin secretion.NEW & NOTEWORTHY Islet prostaglandin EP3 receptor (EP3) signaling is well known as upregulated in the pathophysiological conditions of type 2 diabetes, contributing to β-cell dysfunction. Unexpected findings in mouse models of non-obese insulin sensitivity and resistance provide a new dimension to our understanding of EP3 as a key modulator of insulin secretion. A previously unknown relationship between mouse insulin resistance and the penetrance of rat insulin promoter-driven germline floxed allele recombination is critical to consider when creating β-cell-specific knockouts.

Mito-Mendelian interactions alter in vivo glucose metabolism and insulin sensitivity in healthy mice

The regulation of euglycemia is essential for human health with both chronic hypoglycemia and hyperglycemia having detrimental effects. It is well documented that the incidence of type 2 diabetes increases with age and exhibits racial disparity. Interestingly, mitochondrial DNA (mtDNA) damage also accumulates with age and its sequence varies with geographic maternal origins (maternal race). From these two observations, we hypothesized that mtDNA background may contribute to glucose metabolism and insulin sensitivity. Pronuclear transfer was used to generate mitochondrial-nuclear eXchange (MNX) mice to directly test this hypothesis, by assessing physiologic parameters of glucose metabolism in nuclear isogenic C57BL/6J mice harboring either a C57BL/6J (C57ⁿ:C57^mt wild type-control) or C3H/HeN mtDNA (C57ⁿ:C3H^mt-MNX). All mice were fed normal chow diets. MNX mice were significantly leaner, had lower leptin levels, and were more insulin sensitive, with lower modified Homeostatic Model Assessment of Insulin Resistance (mHOMA-IR) values and enhanced insulin action when compared with their control counterparts. Further interrogation of muscle insulin signaling revealed higher phosphorylated Akt/total Akt ratios in MNX animals relative to control, consistent with greater insulin sensitivity. Overall, these results are consistent with the hypothesis that different mtDNA combinations on the same nuclear DNA (nDNA) background can significantly impact glucose metabolism and insulin sensitivity in healthy mice.NEW & NOTEWORTHY Different mitochondrial DNAs on the same nuclear genetic background can significantly impact body composition, glucose metabolism, and insulin sensitivity in healthy mice.

Correlation of Retinal Structure and Visual Function Assessments in Mouse Diabetes Models

Purpose

Diabetic retinopathy results in vision loss with changes to both retinal blood vessels and neural retina. Recent studies have revealed that animal models of diabetes demonstrate early loss of visual function. We explored the time course of retinal change in three different mouse models of diabetes in a longitudinal study using in vivo measures of retinal structure (optical coherence tomography [OCT]) and visual function (optomotor and pupillary responses).

Methods

OCT analysis of retinal microstructure, optokinetic response as a measure of visual acuity, and pupillary response to light stimulation were compared among the db/db, Ins2^Akita, and streptozotocin (STZ)-induced mouse models of diabetes at 1.5, 3, 6, and 9 months of diabetes.

Results

The db/db, Ins2^Akita, and STZ-induced models of diabetes all exhibited vision loss and retinal thinning as disease progressed. Both structural changes and functional measures were significantly correlated with the blood glucose levels. Despite this, vision loss and retinal thinning were not consistently correlated, except for the inner retinal layer thickness at 6 months of diabetes.

Conclusions

This longitudinal study compiled structural measures and functional outcome data for type 1 and 2 diabetes mouse models commonly used for diabetes studies and demonstrated an overall decline in retinal-related health in conjunction with weight change and blood glucose alterations. The relationship between the structural change and functional outcome could be correlative but is not necessarily causative, as retinal thinning was not sufficient to explain visual acuity decline.

Hyperlipidemia Influences the Accuracy of Glucometer-Measured Blood Glucose Concentrations in Genetically Diverse Mice

BACKGROUND

Glucometers are widely used in animal research due to simplicity and ease of utilization, but their accuracy in blood glucose assessment for hyperlipidemic mice is unknown.

METHODS

Here, we compared blood glucose levels measured by a glucometer with plasma glucose levels measured by a standard enzymatic assay for 325 genetically diverse F2 mice derived from LP and BALB/c (BALB) Apoe^-/- mice. Non-fasting glucose levels were measured before initiation of a Western diet and after 11 weeks on the diet.

RESULTS

On chow diet, lab-measured plasma glucose levels were 279.5 ± 42.6 mg/dl (mean ± SD), while blood glucose values measured by glucometer were 138.7 ± 16.6 mg/dl. The two measures had no correlation (R² = 0.006, p = 0.167). On the Western diet, plasma glucose levels rose to 351.1 ± 121.6 mg/dl, while glucometer-measured blood glucose fell to 128.7 ± 27.9 mg/dl. The two measures showed a moderate correlation (R² = 0.111, p = 3.1E-9). Lab-measured plasma glucose showed strong positive correlations with plasma triglyceride and non-high-density lipoprotein cholesterol levels, while glucometer-measured blood glucose showed an inverse correlation with non-high-density lipoprotein levels on the chow diet.

CONCLUSIONS

Our results indicate that hyperlipidemia affects the accuracy of glucometers in measuring blood glucose levels of mice.

INPP4B protects from metabolic syndrome and associated disorders

A high fat diet and obesity have been linked to the development of metabolic dysfunction and the promotion of multiple cancers. The causative cellular signals are multifactorial and not yet completely understood. In this report, we show that Inositol Polyphosphate-4-Phosphatase Type II B (INPP4B) signaling protects mice from diet-induced metabolic dysfunction. INPP4B suppresses AKT and PKC signaling in the liver thereby improving insulin sensitivity. INPP4B loss results in the proteolytic cleavage and activation of a key regulator in de novo lipogenesis and lipid storage, SREBP1. In mice fed with the high fat diet, SREBP1 increases expression and activity of PPARG and other lipogenic pathways, leading to obesity and non-alcoholic fatty liver disease (NAFLD). Inpp4b-/- male mice have reduced energy expenditure and respiratory exchange ratio leading to increased adiposity and insulin resistance. When treated with high fat diet, Inpp4b-/- males develop type II diabetes and inflammation of adipose tissue and prostate. In turn, inflammation drives the development of high-grade prostatic intraepithelial neoplasia (PIN). Thus, INPP4B plays a crucial role in maintenance of overall metabolic health and protects from prostate neoplasms associated with metabolic dysfunction.

Application of Animal Models in Diabetic Cardiomyopathy

Diabetic heart disease is a growing and important public health risk. Apart from the risk of coronary artery disease or hypertension, diabetes mellitus (DM) is a well-known risk factor for heart failure in the form of diabetic cardiomyopathy (DiaCM). Currently, DiaCM is defined as myocardial dysfunction in patients with DM in the absence of coronary artery disease and hypertension. The underlying pathomechanism of DiaCM is partially understood, but accumulating evidence suggests that metabolic derangements, oxidative stress, increased myocardial fibrosis and hypertrophy, inflammation, enhanced apoptosis, impaired intracellular calcium handling, activation of the renin-angiotensin-aldosterone system, mitochondrial dysfunction, and dysregulation of microRNAs, among other factors, are involved. Numerous animal models have been used to investigate the pathomechanisms of DiaCM. Despite some limitations, animal models for DiaCM have greatly advanced our understanding of pathomechanisms and have helped in the development of successful disease management strategies. In this review, we summarize the current pathomechanisms of DiaCM and provide animal models for DiaCM according to its pathomechanisms, which may contribute to broadening our understanding of the underlying mechanisms and facilitating the identification of possible new therapeutic targets.

Maternal Hyperglycemia Induces Changes in Gene Expression and Morphology in Mouse Placentas

Background

Pregestational diabetes complicates one million pregnancies in the United States and is associated with placental dysfunction. Placental dysfunction can manifest as stillbirth, spontaneous abortions, fetal growth restriction, and preeclampsia in the mother. However, the underlying mechanisms of placental dysfunction are not well understood.

Objective

We hypothesize that maternal hyperglycemia disrupts cellular processes important for normal vascular development and function.

Study Design

Hyperglycemia, defined as a non-fasting glucose concentration of >250 mg/dL was induced in eight-week-old female CD1 mice by injecting a one-time intraperitoneal dose of 150mg/kg streptozotocin. Control mice received an equal volume of normal saline. Hyperglycemic and control females were mated with CD-1 males. At Embryonic Day 17.5, the pregnant mice were euthanized. Sixty-eight placentas were harvested from the six euglycemic dams and twenty-six placentas were harvested from three hyperglycemic dams. RNA was extracted from homogenized placental tissue (N=12/group; 2-4 placentas per litter of each group). Total RNA was prepared and sequenced. Differentially expressed genes that were >2-fold change was considered significant. Placentas (9-20/group) were fixed in paraffin wax and sectioned at 6 μm. Cross-sectional areas of placental zones were evaluated using slides stained for hematoxylin and eosin, glycogen, collagen, proliferation and apoptosis. Quantification of staining intensity and percent positive nuclei was done using Leica Image Hub Data software. Data were compared between the control and experimental group using t-tests. Values of p < 0.05 were considered to be statistically significant.

Results

The average maternal blood glucose concentrations for control and diabetic dams were 112+/-24 and 473+/-47 respectively (p<0.0001). A higher rate of resorptions was noted in the hyperglycemia exposed placentas compared to euglycemic exposed placentas (24% vs 7%; p=0.04). A total of 24 RNA libraries (12/group) were prepared. Placentas from hyperglycemic pregnancies exhibited 1374 differentially expressed genes (DEGs). The 10 most significantly differentially expressed genes are Filip 1, Prom 2, Fam 78a, Pde4d, Pou3f1, Kcnk5, Dusp4, Cxcr4, Slc6a4 and D430019H16Rik. Their corresponding biologic functions are related to chemotaxis, ossification, cellular and vascular development. Histologically, we found that hyperglycemia exposed placentas demonstrated increased proliferation, apoptosis, and glycogen content and decreased collagen deposition.

Conclusion

There was a higher rate of resorptions in the pregnancies of hyperglycemic dams. Pregestational diabetes resulted in significant changes in placental morphology, including increased glycogen content in the spongiotrophoblast, decreased collagen deposition, increased apoptosis and proliferation in the junction zone. Maternal diabetes causes widespread disruption in multiple cellular processes important for normal vascular development and sets the platform for placenta dysfunction.

Overexpression of p53 due to excess protein O-GlcNAcylation is associated with coronary microvascular disease in type 2 diabetes

AIMS

We previously reported that increased protein O-GlcNAcylation in diabetic mice led to vascular rarefaction in the heart. In this study, we aimed to investigate whether and how coronary endothelial cell (EC) apoptosis is enhanced by protein O-GlcNAcylation and thus induces coronary microvascular disease (CMD) and subsequent cardiac dysfunction in diabetes. We hypothesize that excessive protein O-GlcNAcylation increases p53 that leads to CMD and reduced cardiac contractility.

METHODS AND RESULTS

We conducted in vivo functional experiments in control mice, TALLYHO/Jng (TH) mice, a polygenic type 2 diabetic (T2D) model, and EC-specific O-GlcNAcase (OGA, an enzyme that catalyzes the removal of O-GlcNAc from proteins)-overexpressing TH mice, as well as in vitro experiments in isolated ECs from these mice. TH mice exhibited a significant increase in coronary EC apoptosis and reduction of coronary flow velocity reserve (CFVR), an assessment of coronary microvascular function, in comparison to wild-type mice. The decreased CFVR, due at least partially to EC apoptosis, was associated with decreased cardiac contractility in TH mice. Western blot experiments showed that p53 protein level was significantly higher in coronary ECs from TH mice and T2D patients than in control ECs. High glucose treatment also increased p53 protein level in control ECs. Furthermore, overexpression of OGA decreased protein O-GlcNAcylation and down-regulated p53 in coronary ECs, and conferred a protective effect on cardiac function in TH mice. Inhibition of p53 with pifithrin-α attenuated coronary EC apoptosis and restored CFVR and cardiac contractility in TH mice.

CONCLUSIONS

The data from this study indicate that inhibition of p53 or down-regulation of p53 by OGA overexpression attenuates coronary EC apoptosis and improves CFVR and cardiac function in diabetes. Lowering coronary endothelial p53 levels via OGA overexpression could be a potential therapeutic approach for CMD in diabetes.

Diet-induced rodent models of obesity-related metabolic disorders-A guide to a translational perspective

Diet is a critical element determining human health and diseases, and unbalanced food habits are major risk factors for the development of obesity and related metabolic disorders. Despite technological and pharmacological advances, as well as intensification of awareness campaigns, the prevalence of metabolic disorders worldwide is still increasing. Thus, novel therapeutic approaches with increased efficacy are urgently required, which often depends on cellular and molecular investigations using robust animal models. In the absence of perfect rodent models, those induced by excessive consumption of fat and sugars better replicate the key aspects that are the root causes of human metabolic diseases. However, the results obtained using these models cannot be directly compared, particularly because of the use of different dietary protocols, and animal species and strains, among other confounding factors. This review article revisits diet-induced models of obesity and related metabolic disorders, namely, metabolic syndrome, prediabetes, diabetes and nonalcoholic fatty liver disease. A critical analysis focused on the main pathophysiological features of rodent models, as opposed to the criteria defined for humans, is provided as a practical guide with a translational perspective for the establishment of animal models of obesity-related metabolic diseases.

No Association Between a Genetic Variant of FOXO3 and Risk of Type 2 Diabetes Mellitus in the Elderly Population of North India

Aging can be considered an evolutionary process that is modulated by various genetic and biochemical processes. Therefore the genetic variants may interplay a role in human longevity as well as age related illness. Forkhead Box O (FOXO) gene is one of the major defensive genes that are known for ameliorating lifespan. FOXO proteins act as nuclear transcription factors that facilitate the action of insulin or insulin-like growth factor (IGF-1) in various physiological processes. The rationale of our study is to find out association between genetic variant rs2253310 of FOXO3 and risk of Type 2 Diabetes Mellitus (T2DM) in elderly population. This case control study involved 172 age sex matched elderly subjects while patients were recruited as per IDF criteria. Clinical, biochemical, ELISA methods were employed for assesement of clinical samples while Taqman method was used for genotyping analysis. Our results revealed that there was no significant difference in genotypic and allelic frequencies for the tested SNP (p > 0.05) between elderly T2DM patients and controls. The SNP rs2253310 was not associated with risk of T2DM in any genetic model. Also no association was found among the studied group between FOXO3 variant and HOMA-IR, HOMA-B index and Fasting plasma glucose. Serum level of inflammatory markers like CRP and TNF-α was significantly higher in patients but its not associated with SNP rs2253310. Our study concluded that, this intronic longevity-associated variant rs2253310 in FOXO3 is not associated with type 2 diabetes in geriatric patients of northern India.

Impaired Glucose Tolerance and Reduced Plasma Insulin Precede Decreased AKT Phosphorylation and GLUT3 Translocation in the Hippocampus of Old 3xTg-AD Mice

Several studies have demonstrated that mouse models of Alzheimer's disease (AD) can exhibit impaired peripheral glucose tolerance. Further, in the APP/PS1 mouse model, this is observed prior to the appearance of AD-related neuropathology (e.g., amyloid-β plaques; Aβ) or cognitive impairment. In the current study, we examined whether impaired glucose tolerance also preceded AD-like changes in the triple transgenic model of AD (3xTg-AD). Glucose tolerance testing (GTT), insulin ELISAs, and insulin tolerance testing (ITT) were performed at ages prior to (1-3 months and 6-8 months old) and post-pathology (16-18 months old). Additionally, we examined for altered insulin signaling in the hippocampus. Western blots were used to evaluate the two-primary insulin signaling pathways: PI3K/AKT and MAPK/ERK. Since the PI3K/AKT pathway affects several downstream targets associated with metabolism (e.g., GSK3, glucose transporters), western blots were used to examine possible alterations in the expression, translocation, or activation of these targets. We found that 3xTg-AD mice display impaired glucose tolerance as early as 1 month of age, concomitant with a decrease in plasma insulin levels well prior to the detection of plaques (∼14 months old), aggregates of hyperphosphorylated tau (∼18 months old), and cognitive decline (≥18 months old). These alterations in peripheral metabolism were seen at all time points examined. In comparison, PI3K/AKT, but not MAPK/ERK, signaling was altered in the hippocampus only in 18-20-month-old 3xTg-AD mice, a time point at which there was a reduction in GLUT3 translocation to the plasma membrane. Taken together, our results provide further evidence that disruptions in energy metabolism may represent a foundational step in the development of AD.

Beneficial effect on podocyte number in experimental diabetic nephropathy resulting from combined atrasentan and RAAS inhibition therapy

Podocyte loss and proteinuria are both key features of human diabetic nephropathy (DN). The leptin-deficient BTBR mouse strain with the ob/ob mutation develops progressive weight gain, type 2 diabetes, and diabetic nephropathy that has many features of advanced human DN, including increased mesangial matrix, mesangiolysis, podocyte loss, and proteinuria. Selective antagonism of the endothelin-1 type A receptor (ET_AR) by atrasentan treatment in combination with renin-angiotensin-aldosterone system inhibition with losartan has been shown to have the therapeutic benefit of lowering proteinuria in patients with DN, but the underlying mechanism for this benefit is not well understood. Using a similar therapeutic approach in diabetic BTBR ob/ob mice, this treatment regimen significantly increased glomerular podocyte number compared with diabetic BTBR ob/ob controls and suggested that parietal epithelial cells were a source for podocyte restoration. Atrasentan treatment alone also increased podocyte number but to a lesser degree. Mice treated with atrasentan demonstrated a reduction in proteinuria, matching the functional improvement reported in humans. This is a first demonstration that treatment with the highly selective ET_AR antagonist atrasentan can lead to restoration of the diminished podocyte number characteristic of DN in humans and thereby underlies the reduction in proteinuria in patients with diabetes undergoing similar treatment. The benefit of ET_AR antagonism in DN extended to a decrease in mesangial matrix as measured by a reduction in accumulations of collagen type IV in both the atrasentan and atrasentan + losartan-treated groups compared with untreated controls.

Rodent models of obesity

Obese or overweight people exceed one-third of the global population and obesity along with diabetes mellitus consist basic components of metabolic syndrome, both of which are known cardio-cerebrovascular risk factors with detrimental consequences. These data signify the pandemic character of obesity and the necessity for effective treatments. Substantial advances have been accomplished in preclinical research of obesity by using animal models, which mimic the human disease. In particular, rodent models have been widely used for many decades with success for the elucidation of the pathophysiology of obesity, since they share physiological and genetic components with humans and appear advantageous in their husbandry. The most representative rodents include the laboratory mouse and rat. Within this review, we attempted to consolidate the most widely used mice and rat models of obesity and highlight their strengths as well as weaknesses in a critical way. Our aim was to bridge the gap between laboratory facilities and patient's bed and help the researcher find the appropriate animal model for his/her obesity research. This tactful selection of the appropriate model of obesity may offer more translational derived results. In this regard, we included, the main diet induced models, the chemical/mechanical ones, as well as a selection of monogenic or polygenic models.

Hepatic gene expression variations in response to high-fat diet-induced impaired glucose tolerance using RNAseq analysis in collaborative cross mouse population

Hepatic gene expression is known to differ between healthy and type 2 diabetes conditions. Identifying these variations will provide better knowledge to the development of gene-targeted therapies. The aim of this study is to assess diet-induced hepatic gene expression of susceptible versus resistant CC lines to T2D development. Next-generation RNA-sequencing was performed for 84 livers of diabetic and non-diabetic mice of 41 different CC lines (both sexes) following 12 weeks on high-fat diet (42% fat). Data analysis revealed significant variations of hepatic gene expression in diabetic versus non-diabetic mice with significant sex effect, where 601 genes were differentially expressed (DE) in overall population (males and females), 718 genes in female mice, and 599 genes in male mice. Top prioritized DE candidate genes were Lepr, Ins2, Mb, Ckm, Mrap2, and Ckmt2 for the overall population; for females-only group were Hdc, Serpina12, Socs1, Socs2, and Mb, while for males-only group were Serpine1, Mb, Ren1, Slc4a1, and Atp2a1. Data analysis for sex differences revealed 193 DE genes in health (Top: Lepr, Cav1, Socs2, Abcg2, and Col5a3), and 389 genes DE between diabetic females versus males (Top: Lepr, Clps, Ins2, Cav1, and Mrap2). Furthermore, integrating gene expression results with previously published QTL, we identified significant variants mapped at chromosomes at positions 36-49 Mb, 62-71 Mb, and 79-99 Mb, on chromosomes 9, 11, and 12, respectively. Our findings emphasize the complexity of T2D development and that significantly controlled by host complex genetic factors. As well, we demonstrate the significant sex differences between males and females during health and increasing to extent levels during disease/diabetes. Altogether, opening the venue for further studies targets the discovery of effective sex-specific and personalized preventions and therapies.

Nlrp1b1 negatively modulates obesity-induced inflammation by promoting IL-18 production

Obesity-induced inflammation, triggered by lipid-mediated activation of the Nlrp3 inflammasome, results in glucose metabolism alterations and type 2 diabetes. This knowledge has been generated using animals deficient for any of the different components of this inflammasome (Caspase-1, Asc or Nlrp3) in the C57BL/6 background. Unlike C57BL/6 mice, which carry allele 2 of the Nlrp1b gene (Nlrp1b2), Balb/c mice that carry allele 1 (Nlrp1b1) are less prone to develop alterations in the glucose metabolism when fed with a high fat diet. However, the molecular bases for these metabolic differences are unknown. Here we show that the Nlrp1b1 allele down regulates the adipose tissue inflammatory response attenuating glucose intolerance and insulin resistance in obese C57BL/mice. Our results indicate that the positive effects of the Nlrp1b1 inflammasome on glucose tolerance and insulin sensitivity involve IL-18-mediated effects on lipolysis, pointing out that differential expression of allelic variants of genes coding for inflammasome components might control susceptibility or resistance to develop diabetes in obese individuals.

Sugar-Lowering Drugs for Type 2 Diabetes Mellitus and Metabolic Syndrome-Strategies for In Vivo Administration: Part-II

Diabetes is a complex disease characterized by hyperglycemia, together with polyuria, polydipsia, and polyphagia. While Type 1 diabetes mellitus (T1DM) results from genetic, environmental, or immune dysfunction factors leading to pancreatic β-cell destruction depriving the organism from endogenous insulin, Type 2 diabetes mellitus (T2DM) is characterized by peripheral insulin resistance. Depending on the type of diabetes mellitus and drug mechanism to study, the animal model should be carefully selected among the wide variety of the currently available ones. This review discusses the most common animal models currently employed to study T1DM and T2DM. Moreover, an overview on the administration routes that could be used is also discussed.

Adenovirus 36 improves glycemic control and markers of Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder worldwide. While the causes of AD are unclear, several risk factors have been identified, including impaired glycemic control, which significantly increases the risk of cognitive decline and AD. In vitro and in vivo studies show that human adenovirus 36 (Ad36) improves glycemic control by increasing cellular glucose uptake in cells, experimental animal models and in humans who are naturally exposed to the virus. This study, tested improvement in glycemic control by Ad36 and delay in onset of cognitive decline in APPswe transgenic mice (Tg2576 line), a model of genetic predisposition to impaired glycemic control and AD. Three-month old APPswe mice were divided into Ad36 infected (Ad36) or mock infected (control) groups and baseline glycemic control measured by glucose tolerance test (GTT) prior to infection. Changes in glycemic control were determined 10- and 24-week post infection. Serum insulin was also measured during GTT. Cognition was determined by Y-maze test, while motor coordination and skill acquisition by rotarod test. Glycemic control as determined by GTT showed less deterioration in Ad36 infected mice over time, accompanied by a significant attenuation of cognitive decline. Analysis of brain tissue lysate showed significantly reduced levels of amyloid beta 42 in Ad36 mice relative to control mice. Golgi-Cox staining analysis also revealed reduced dendritic spines and synaptic gene expression in control mice compared to Ad36 infected mice. This proof of concept study shows that in a mouse model of AD, Ad36 improves glycemic control and ameliorates cognitive decline.

Leptin and the endocrine control of energy balance

The discovery of leptin changed the view of adipose tissue from that of a passive vessel that stores fat to that of a dynamic endocrine organ that actively regulates behaviour and metabolism. Secreted by adipose tissue, leptin functions as an afferent signal in a negative feedback loop, acting primarily on neurons in the hypothalamus and regulating feeding and many other functions. The leptin endocrine system serves a critical evolutionary function by maintaining the relative constancy of adipose tissue mass, thereby protecting individuals from the risks associated with being too thin (starvation and infertility) or too obese (predation). In this Review, the biology of leptin is summarized, and a conceptual framework is established for studying the pathogenesis of obesity, which, analogously to diabetes, can result from either leptin hyposecretion or leptin resistance. Herein, these two states are distinguished with the terms 'type 1 obesity' and 'type 2 obesity': type 1 obesity describes a subset of obese individuals with low endogenous plasma leptin levels who respond to leptin therapy, whereas type 2 obesity describes most obese individuals, who are leptin resistant but might respond to leptin therapy in combination with other drugs, such as leptin sensitizers.

CD1 is involved in diet-induced hypothalamic inflammation in obesity

Obesity-associated hypothalamic inflammation plays an important role in the development of defective neuronal control of whole body energy balance. Because dietary fats are the main triggers of hypothalamic inflammation, we hypothesized that CD1, a lipid-presenting protein, may be involved in the hypothalamic inflammatory response in obesity. Here, we show that early after the introduction of a high-fat diet, CD1 expressing cells gradually appear in the mediobasal hypothalamus. The inhibition of hypothalamic CD1 reduces diet-induced hypothalamic inflammation and rescues the obese and glucose-intolerance phenotype of mice fed a high-fat diet. Conversely, the chemical activation of hypothalamic CD1 further increases diet-induced obesity and hypothalamic inflammation. A bioinformatics analysis revealed that hypothalamic CD1 correlates with transcripts encoding for proteins known to be involved in diet-induced hypothalamic abnormalities in obesity. Thus, CD1 is involved in at least part of the hypothalamic inflammatory response in diet-induced obesity and its modulation affects the body mass phenotype of mice.

A collective diabetes cross in combination with a computational framework to dissect the genetics of human obesity and Type 2 diabetes

To explore the genetic determinants of obesity and Type 2 diabetes (T2D), the German Center for Diabetes Research (DZD) conducted crossbreedings of the obese and diabetes-prone New Zealand Obese mouse strain with four different lean strains (B6, DBA, C3H, 129P2) that vary in their susceptibility to develop T2D. Genome-wide linkage analyses localized more than 290 quantitative trait loci (QTL) for obesity, 190 QTL for diabetes-related traits and 100 QTL for plasma metabolites in the outcross populations. A computational framework was developed that allowed to refine critical regions and to nominate a small number of candidate genes by integrating reciprocal haplotype mapping and transcriptome data. The efficiency of the complex procedure was demonstrated for one obesity QTL. The genomic interval of 35 Mb with 502 annotated candidate genes was narrowed down to six candidates. Accordingly, congenic mice retained the obesity phenotype owing to an interval that contains three of the six candidate genes. Among these the phospholipase PLA2G4A exhibited an elevated expression in adipose tissue of obese human subjects and is therefore a critical regulator of the obesity locus. Together, our broad and complex approach demonstrates that combined- and comparative-cross analysis exhibits improved mapping resolution and represents a valid tool for the identification of disease genes.

In Vivo Rodent Models of Type 2 Diabetes and Their Usefulness for Evaluating Flavonoid Bioactivity

About 40% of the world’s population is overweight or obese and exist at risk of developing type 2 diabetes mellitus (T2D). Obesity is a leading pathogenic factor for developing insulin resistance (IR). It is well established that IR and a progressive decline in functional β-cell mass are hallmarks of developing T2D. In order to mitigate the global prevalence of T2D, we must carefully select the appropriate animal models to explore the cellular and molecular mechanisms of T2D, and to optimize novel therapeutics for their safe use in humans. Flavonoids, a group of polyphenols, have drawn great interest for their various health benefits, and have been identified in naturally occurring anti-diabetic compounds. Results from many clinical and animal studies demonstrate that dietary intake of flavonoids might prove helpful in preventing T2D. In this review, we discuss the currently available rodent animal models of T2D and analyze the advantages, the limitations of each T2D model, and highlight the potential anti-diabetic effects of flavonoids as well as the mechanisms of their actions.

Genome-wide profiling of histone H3K27 acetylation featured fatty acid signalling in pancreatic beta cells in diet-induced obesity in mice

AIMS/HYPOTHESIS

Epigenetic regulation of gene expression has been implicated in the pathogenesis of obesity and type 2 diabetes. However, detailed information, such as key transcription factors in pancreatic beta cells that mediate environmental effects, is not yet available.

METHODS

To analyse genome-wide cis-regulatory profiles and transcriptome of pancreatic islets derived from a diet-induced obesity (DIO) mouse model, we conducted chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-Seq) of histone H3 lysine 27 acetylation (histone H3K27ac) and high-throughput RNA sequencing. Transcription factor-binding motifs enriched in differential H3K27ac regions were examined by de novo motif analysis. For the predicted transcription factors, loss of function experiments were performed by transfecting specific siRNA in INS-1, a rat beta cell line, with and without palmitate treatment. Epigenomic and transcriptional changes of possible target genes were evaluated by ChIP and quantitative RT-PCR.

RESULTS

After long-term feeding with a high-fat diet, C57BL/6J mice were obese and mildly glucose intolerant. Among 39,350 islet cis-regulatory regions, 13,369 and 4610 elements showed increase and decrease in ChIP-Seq signals, respectively, significantly associated with global change in gene expression. Remarkably, increased H3K27ac showed a distinctive genomic localisation, mainly in the proximal-promoter regions, revealing enriched elements for nuclear respiratory factor 1 (NRF1), GA repeat binding protein α (GABPA) and myocyte enhancer factor 2A (MEF2A) by de novo motif analysis, whereas decreased H3K27ac was enriched for v-maf musculoaponeurotic fibrosarcoma oncogene family protein K (MAFK), a known negative regulator of beta cells. By siRNA-mediated knockdown of NRF1, GABPA or MEF2A we found that INS-1 cells exhibited downregulation of fatty acid β-oxidation genes in parallel with decrease in the associated H3K27ac. Furthermore, in line with the epigenome in DIO mice, palmitate treatment caused increase in H3K27ac and induction of β-oxidation genes; these responses were blunted when NRF1, GABPA or MEF2A were suppressed.

CONCLUSIONS/INTERPRETATION

These results suggest novel roles for DNA-binding proteins and fatty acid signalling in obesity-induced epigenomic regulation of beta cell function.

DATA AVAILABILITY

The next-generation sequencing data in the present study were deposited at ArrayExpress. RNA-Seq: Dataset name: ERR2538129 (Control), ERR2538130 (Diet-induced obesity) Repository name and number: E-MTAB-6718 - RNA-Seq of pancreatic islets derived from mice fed a long-term high-fat diet against chow-fed controls. ChIP-Seq: Dataset name: ERR2538131 (Control), ERR2538132 (Diet-induced obesity) Repository name and number: E-MTAB-6719 - H3K27ac ChIP-Seq of pancreatic islets derived from mice fed a long-term high-fat diet (HFD) against chow-fed controls.

Two Novel Candidate Genes for Insulin Secretion Identified by Comparative Genomics of Multiple Backcross Mouse Populations

To identify novel disease genes for type 2 diabetes (T2D) we generated two backcross populations of obese and diabetes-susceptible New Zealand Obese (NZO/HI) mice with the two lean mouse strains 129P2/OlaHsd and C3HeB/FeJ. Subsequent whole-genome linkage scans revealed 30 novel quantitative trait loci (QTL) for T2D-associated traits. The strongest association with blood glucose [12 cM, logarithm of the odds (LOD) 13.3] and plasma insulin (17 cM, LOD 4.8) was detected on proximal chromosome 7 (designated Nbg7p, NZO blood glucose on proximal chromosome 7) exclusively in the NZOxC3H crossbreeding, suggesting that the causal gene is contributed by the C3H genome. Introgression of the critical C3H fragment into the genetic NZO background by generating recombinant congenic strains and metabolic phenotyping validated the phenotype. For the detection of candidate genes in the critical region (30-46 Mb), we used a combined approach of haplotype and gene expression analysis to search for C3H-specific gene variants in the pancreatic islets, which appeared to be the most likely target tissue for the QTL. Two genes, Atp4a and Pop4, fulfilled the criteria from our candidate gene approaches. The knockdown of both genes in MIN6 cells led to decreased glucose-stimulated insulin secretion, indicating a regulatory role of both genes in insulin secretion, thereby possibly contributing to the phenotype linked to Nbg7p In conclusion, our combined- and comparative-cross analysis approach has successfully led to the identification of two novel diabetes susceptibility candidate genes, and thus has been proven to be a valuable tool for the discovery of novel disease genes.

Fatal gastric distension in a gold thioglucose mouse model of obesity

This case report addresses the problem of underreporting negative results and adverse side effects in animal testing. We present our findings regarding a hyperphagic mouse model associated with unforeseen high mortality. The results outline the necessity of reporting detailed information in the literature to avoid duplication. Obese mouse models are essential in the study of obesity, metabolic syndrome and diabetes mellitus. An experimental model of obesity can be induced by the administration of gold thioglucose (GTG). After transcending the blood-brain barrier, the GTG molecule interacts with regions of the ventromedial hypothalamus, thereby primarily targeting glucose-sensitive neurons. When these neurons are impaired, mice become insensitive to the satiety effects of glucose and develop hyperphagia. In a pilot study for optimising dosage and body weight development, C57BL/6 mice were treated with GTG (0.5 mg/g body weight) or saline, respectively. Animals were provided a physiological amount of standard diet (5 g per animal) for the first 24 hours after treatment to prevent gastric dilatation. Within 24 hours after GTG injection, all GTG-treated animals died of gastric overload and subsequent circulatory shock. Animals developed severe attacks of hyperphagia, and as the amount of provided chow was restricted, mice exhibited unforeseen pica and ingested bedding material. These observations strongly suggest that restricted feeding is contraindicated concerning GTG application. Presumably, the impulse of excessive food intake was a strong driving force. Therefore, the actual degree of suffering in the GTG-induced model of hyperphagia should be revised from moderate to severe.