The study utilizes the yeast two-hybrid system to try and unravel the molecular link between the G protein-coupled receptors (GPCR) and the receptor tyrosine kinases (RTK). The fourth melanocortin receptor (MC4R) and the angiotensin receptor AT1 are both GPCRs while the insulin receptor (IR) and the epidermal growth factor receptor subtype-2 (ErbB2) belong to the RTK family. Alteration in the functioning of MC4R receptor can cause obesity. Development of insulin resistance and diabetes is a risk factor associated with obesity. Overexpression of the ErbB2 receptor is seen in a number of breast cancers. The interaction between the AT1 and ErbB2 receptors were studied based on previous studies that have shown an interaction between the epidermal and angiotensin receptors. Thus, Interactions between the MC4R and the IR, and that between the AT1 and ErbB2 receptors were studied for their possible roles in metabolic syndrome and cancer.

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In an attempt to replicate and extend previous research on the validity of food diary records, 18 obese and 16 previously obese individuals from the community were quizzed on food recording and kcalorie estimation in a controlled analogue of self-monitoring. Results of the experimental phase of the study replicate those of previous studies indicating that the food diaries of obese clients are invalid because of poor food descriptions, incorrect quantity estimates, and errors in converting kcalories. The results also indicate that subjects tend to overestimate quantities and kcalories of foods. However, the present study extended previous research by examining the differences between obese and previously obese individuals. It was thought that weight differences might be a function, to some degree, of the person's accuracy at food recording, quantity of portion and kcalorie estimation. The present results suggested no relationship between current weight and accuracy. The implications of this finding suggests that success at weight loss may not be significantly related to an individual's ability at food description, quantity of portion and ability in kcalorie estimation, as was suggested by previous studies. The results of this study strongly question the validity of self-reports in food consumption. Its implications in research and practice were examined. The assessment phase of the study obtained information via a questionnaire on 177 individuals involved in a weight control program. The areas in the questionnaire consisted of: (a) general information, (b) health, (c) environment, (d) emotional aspects of eating, (e) exercise. The findings support past research on obesity, and revealed some areas of interest for future research.

Given the current obesity epidemic, the prevalence of overweight and obese patients with critical illness is increasing rapidly, however how obesity shapes critical illness and immune response to infection is not entirely understood. We developed a clinically relevant murine model of obesity in the context of sepsis, and examined organ specific inflammatory responses. Male C57BL/6 mice were fed either a high fat Western Diet (WD) (Modified Breslow, 21% Butterfat and 0.15% cholesterol) or normal chow diet (NCD) for 6, 15 or 27 weeks. Sepsis was induced by cecal ligation and perforation (CLP), and six hours post-surgery, plasma and tissue samples were harvested and flash frozen in liquid nitrogen. Septic obese mice at 15 and 27 weeks had significantly (p<0.0001) lower levels of lung myeloperoxidase (26.3±3.8 U/mg tissue) compared to age matched ad libitum (44.1±2.8 U/mg tissue) and diet restricted (63.2±5.60 U/mg tissue) controls, indicative of less lung inflammation. Obese mice (4.23±0.10g) had significantly enlarged livers compared to controls (1.55±0.80g and 1.22±0.031g), with pronounced steatosis, and hepatocyte ballooning, independent of sepsis. These findings are in congruence with clinical observations that obese individuals are protected from sepsis-induced lung injury, however the mechanisms involved are not entirely clear. We also examined effects of housing conditions on susceptibility to developing metabolic syndrome, and inflammatory response in our obesity and sepsis model. For this study, animals were fed either WD or NCD for 15 weeks and were housed in static or ventilated cages. Unlike static cages, ventilated cages have HEPA filtered air supply system and exhaust air ventilation, protecting the animals from air borne particles and preserving the microbiological barrier. Therefore, ventilated cages provide a more sterile environment compared to static cages. After 15 weeks, fecal matter was collected from the cages and mice were subjected to sepsis using the CLP technique. Six hours post surgery, animals were sacrificed and tissues were harvested, snap frozen and stored at -80°C. The animals from the more sterile environment (ventilated cages) had significantly (p<0.0001) less weight gain and did not show signs of overt hyperglycemia, compared to mice housed in a less sterile environment (static cages). In addition, obese mice housed in static cages had less lung injury compared to controls during early sepsis, however this difference was not evident in mice from ventilated cages. There were also significant differences in the fecal microbe composition, where ventilated groups had greater Firmicutes (69% ± 0.06% for WD and 76% ± 0.03%) and less Bacteroidetes population (15% ± 0.04% for WD and 12% ± 0.02% for NCD) compared to static groups (Firmicutes: 42% ± 0.08% for WD and 24% ± 0.02% for NCD, Bacteroidetes: 37% ± 12% for WD and 53% ± 29% for NCD). This study highlighted the impact of environment on the susceptibility to developing metabolic syndrome, and the potential impact on the associated immune responses, in our mouse models of obesity and sepsis. Leptin is an important mediator of immune responses to infection, and the levels are elevated during diet induced obesity in both mice and humans. We found that mice treated with leptin one hour prior to surgery, had significantly less injury (32.62±1.6 U/mg tissue) compared to saline treated animals (46.58±3.48 U/mg tissue), as evident from lung myeloperoxidase levels and histopathology scores. In addition, proprotein convertase subtilisin/kexin type 9 (PCSK9) over expressing mice on a normal diet, had significantly greater lung injury (46.51±4.51 U/mg tissue myeloperoxidase levels) compared to knockouts (31.14±1.75 U/mg tissue), this difference was not observed in WD fed mice with differential PCKS9 expression. In conclusion, WD fed mice had significantly less lung inflammation but greater hepatic injury. Furthermore, both leptin and PCSK9 are important mediators of lung inflammation in early sepsis. / Thesis / Doctor of Science (PhD)