P465L-PPARγ mutation confers partial resistance to the hypolipidaemic action of fibrates

Familial partial lipodystrophic syndrome 3 (FPLD3) is associated with mutations in the transcription factor PPAR. One of these mutations, the P467L, confers a dominant negative effect. We and others have previously investigated the pathophysiology associated to this mutation using a humanised mouse model that recapitulated most of the clinical symptoms observed in human patients under different experimental conditions. One of the key clinical manifestations observed both in humans and mouse models is the ectopic accumulation of fat in the liver. Here, we dissect the molecular mechanisms that contribute to the excessive accumulation of lipids in the liver and characterise the negative effect of this PPAR mutation on the activity of PPAR in vivo when activated by fibrates. P465L mice have increased levels of insulin and free fatty acids (FFA), exhibit decreased levels of Very Low Density Lipoproteins (VLDL) when fed high fat diet (HFD) and partial impaired response to the hypolipidemic action of WY14643. This indicates that the deleterious effects of P465L-PPAR mutation may be augmented by their collateral negative effect on PPAR function.Wellcome Trust, MRC MDU (MC_UU_12012/2), FP7-MITIN (Integration of the System Models of Mitochondrial Function and Insulin Signaling and its Application in the Study of Complex Diseases) (Grant Agreement 223450) and H2020 EPoS (Elucidating Pathways of Steatohepatitis) (Grant Agreement 634413). Disease Model Core, Biochemistry Assay Lab and the Histology Core are funded by MRC_MC_UU_12012/5 and a Wellcome Trust Strategic Award [100574/Z/12/Z

Obesogenic and diabetic effects of CD44 in mice are sexually dimorphic and dependent on genetic background

IntroductionCD44 is a candidate gene for obesity and diabetes development and may be a critical mediator of a systemic inflammation associated with obesity and diabetes.MethodsWe investigated the relationship of CD44 with obesity in CD44-deficient mice challenged with a high-fat diet.ResultsIn mice fed a diet high in fat, cholesterol, and sucrose for 12 weeks fat mass accumulation was reduced in CD44-deficient mice bred onto both a C57BL/6J and the naturally TLR deficient C3H/HeJ background. Reduced fat mass could not be attributed to lower food intake or an increase in energy expenditure as measured by indirect calorimetry. However, we observed a 40-60% lower mRNA expression of the inflammation markers, F4/80, CD11b, TNF-α, and CD14, in adipose tissue of CD44-deficient mice on the C57BL/6J background but not the C3H/HeJ background, perhaps indicating that alternative factors may be affecting adiposity in this model. Measures of hepatic steatosis and insulin sensitivity were improved in CD44-deficient mice on a C57BL/6J but not in the C3H/HeJ mice. These results were highly sexually dimorphic as there were no detectable effects of CD44 inactivation in female mice on a C57BL/6 J or C3H/HeJ background.ConclusionCD44 was associated with adiposity, liver fat, and glucose in male mice. However, the effects of CD44 on obesity may be independent of TLR4 signaling

Altered macronutrient composition and genetics influence the complex transcriptional network associated with adiposity in the Collaborative Cross

BackgroundObesity is a serious disease with a complex etiology characterized by overaccumulation of adiposity resulting in detrimental health outcomes. Given the liver's critical role in the biological processes that attenuate adiposity accumulation, elucidating the influence of genetics and dietary patterns on hepatic gene expression is fundamental for improving methods of obesity prevention and treatment. To determine how genetics and diet impact obesity development, mice from 22 strains of the genetically diverse recombinant inbred Collaborative Cross (CC) mouse panel were challenged to either a high-protein or high-fat high-sucrose diet, followed by extensive phenotyping and analysis of hepatic gene expression.ResultsOver 1000 genes differentially expressed by perturbed dietary macronutrient composition were enriched for biological processes related to metabolic pathways. Additionally, over 9000 genes were differentially expressed by strain and enriched for biological process involved in cell adhesion and signaling. Weighted gene co-expression network analysis identified multiple gene clusters (modules) associated with body fat % whose average expression levels were influenced by both dietary macronutrient composition and genetics. Each module was enriched for distinct types of biological functions.ConclusionsGenetic background affected hepatic gene expression in the CC overall, but diet macronutrient differences also altered expression of a specific subset of genes. Changes in macronutrient composition altered gene expression related to metabolic processes, while genetic background heavily influenced a broad range of cellular functions and processes irrespective of adiposity. Understanding the individual role of macronutrient composition, genetics, and their interaction is critical to developing therapeutic strategies and policy recommendations for precision nutrition

Genetic Background Shapes Phenotypic Response to Diet for Adiposity in the Collaborative Cross

Defined as chronic excessive accumulation of adiposity, obesity results from long-term imbalance between energy intake and expenditure. The mechanisms behind how caloric imbalance occurs are complex and influenced by numerous biological and environmental factors, especially genetics, and diet. Population-based diet recommendations have had limited success partly due to the wide variation in physiological responses across individuals when they consume the same diet. Thus, it is necessary to broaden our understanding of how individual genetics and diet interact relative to the development of obesity for improving weight loss treatment. To determine how consumption of diets with different macronutrient composition alter adiposity and other obesity-related traits in a genetically diverse population, we analyzed body composition, metabolic rate, clinical blood chemistries, and circulating metabolites in 22 strains of mice from the Collaborative Cross (CC), a highly diverse recombinant inbred mouse population, before and after 8 weeks of feeding either a high protein or high fat high sucrose diet. At both baseline and post-diet, adiposity and other obesity-related traits exhibited a broad range of phenotypic variation based on CC strain; diet-induced changes in adiposity and other traits also depended largely on CC strain. In addition to estimating heritability at baseline, we also quantified the effect size of diet for each trait, which varied by trait and experimental diet. Our findings identified CC strains prone to developing obesity, demonstrate the genotypic and phenotypic diversity of the CC for studying complex traits, and highlight the importance of accounting for genetic differences when making dietary recommendations

Dissecting the Genetic Architecture of Cystatin C in Diversity Outbred Mice

Plasma concentration of Cystatin C (CysC) level is a biomarker of glomerular filtration rate in the kidney. We use a Systems Genetics approach to investigate the genetic determinants of plasma CysC concentration. To do so we perform Quantitative Trait Loci (QTL) and expression QTL (eQTL) analysis of 120 Diversity Outbred (DO) female mice, 56 weeks of age. We performed network analysis of kidney gene expression to determine if the gene modules with common functions are associated with kidney biomarkers of chronic kidney diseases. Our data demonstrates that plasma concentrations and kidney mRNA levels of CysC are associated with genetic variation and are transcriptionally coregulated by immune genes. Specifically, Type-I interferon signaling genes are coexpressed with Cst3 mRNA levels and associated with CysC concentrations in plasma. Our findings demonstrate the complex control of CysC by genetic polymorphisms and inflammatory pathways