Adipocyte PU.1 knockout promotes insulin sensitivity in HFD-fed obese mice.

Insulin resistance is a key feature of obesity and type 2 diabetes. PU.1 is a master transcription factor predominantly expressed in macrophages but after HFD feeding PU.1 expression is also significantly increased in adipocytes. We generated adipocyte specific PU.1 knockout mice using adiponectin cre to investigate the role of PU.1 in adipocyte biology, insulin and glucose homeostasis. In HFD-fed obese mice systemic glucose tolerance and insulin sensitivity were improved in PU.1 AKO mice and clamp studies indicated improvements in both adipose and liver insulin sensitivity. At the level of adipose tissue, macrophage infiltration and inflammation was decreased and glucose uptake was increased in PU.1 AKO mice compared with controls. While PU.1 deletion in adipocytes did not affect the gene expression of PPARg itself, we observed increased expression of PPARg target genes in eWAT from HFD fed PU.1 AKO mice compared with controls. Furthermore, we observed decreased phosphorylation at serine 273 in PU.1 AKO mice compared with fl/fl controls, indicating that PPARg is more active when PU.1 expression is reduced in adipocytes. Therefore, in obesity the increased expression of PU.1 in adipocytes modifies the adipocyte PPARg cistrome resulting in impaired glucose tolerance and insulin sensitivity

Regulation of Energy Balance by Dietary Protein

The protein leverage hypothesis posits that protein restriction triggers a compensatory hyperphagia to facilitate the acquirement of the animal's protein needs whereas protein excess elicit hypophagia as the animal's protein requirement is met at a lesser calorie intake. However, the effects of dietary protein on energy expenditure and the underlying mechanisms are not well-established. Moreover, the domestic cat has potential to more closely model human obesity and diabetes; however, the role of dietary protein in the secretion of metabolic hormones has not been well-studied in cats. In this thesis, the effects of protein-restricted diets, tryptophan or histidine-restricted diets, and diets with excess protein on energy intake, energy expenditure, body weight and composition, gut hormones, glucose clearance, key protein and glucose metabolism markers and thermogenesis were determined in rodent models of diet-induced obesity. In addition, the tissue distribution of the transcripts for proglucagon, glucose-dependent insulinotropic peptide, peptide YY and their cognate receptors in feline peripheral tissues and the effects of the consumption of high-protein diets on the concentrations of circulating metabolites and metabolic hormones were determined in lean, overweight and diabetic cats. Using diet-induced obese rats and a clinical population of domestic cats, this work provided important insights on the mechanisms by which dietary protein regulates energy balance. First, moderately restricting dietary protein transiently promoted hyperphagia yet robustly increased energy expenditure. Second, tryptophan restriction partially recapitulates the age-dependent effects of moderate protein restriction on energy intake and expenditure. Third, the protein source has a significant contribution on the hypophagic and thermogenic effects of high-protein diets, with the increased PYY signaling and reduced diet preference mediating this reduction in energy intake, but not thermogenesis. Finally, although there were inherent differences in plasma concentrations of metabolic hormones between lean, overweight and diabetic cats, protein consumption alone did not alter weight or the secretion of these hormones. Collectively, dietary protein greatly influences energy balance in rodent models of human obesity, but has minimal impact in domestic cats

Susceptibility of male wild type mouse strains to antipsychotic-induced weight gain

While both men and women gain weight as a side effect of antipsychotic (AP) treatment, studies in mice have found only female mice are susceptible to weight gain. Therefore, to we set out to identify a strain of male mice that gain significant weight in response to APs which could better model AP-induced weight gain observed in humans. These studies determined that male Balb/c mice developed late onset olanzapine-induced weight gain. Patients often take APs for many years and thus understanding AP-mediated changes in food intake, energy expenditure and body weight regulation is particularly important

Self-Administration of Drugs in Mouse Models of Feeding and Obesity.

Preclinical studies in mice often rely on invasive protocols, such as injections or oral gavage, to deliver drugs. These stressful routes of administration have significant effects on important metabolic parameters including food intake and body weight. Although an attractive option to circumvent this is to compound the drug in rodent food or dissolve it in water, these approaches also have limitations as they are affected by drug stability at room temperature for extended periods of time, the drug's solubility in water, and that the dosing is highly dependent on timing of food or water intake. The constant availability of the drug also limits translational relevance on how drugs are administered to patients. To overcome these limitations, drugs can be mixed with highly palatable food, such as peanut butter, allowing mice to self-administer compounds. Mice reliably and reproducibly consume the drug/peanut butter pellet in a short time frame. This approach facilitates a delivery approach with minimal stress compared with an injection or gavage. This protocol demonstrates the approach of drug preparation, animal acclimatization to placebo delivery, and drug delivery. The implications of this approach are discussed in studies related to timing of drug administration and the circadian rhythm