Role of Inflammation in Diet-Induced Obesity: A Dissertation

Obesity results from expansion of white adipose tissue. The inability of white adipose tissue to adequately store lipids leads to ectopic deposition of lipids in non-adipose tissue that can lead to systemic insulin resistance. It is well known that insulin resistance correlates with inflammation of adipose tissue in obese animals and humans. Decreasing inflammation in the adipose tissue has been proven as a therapeutic strategy for improvement of insulin sensitivity in vivo. Numerous factors secreted by immune cells, including macrophages, have been suggested as regulating adipose tissue insulin sensitivity In the first part of my thesis, I describe the role of one such factor, CD40 in adipose tissue inflammation. The CD40-CD40L dyad acts as co-stimulation in the interaction of antigen-presenting cells, such as macrophages and dendritic cells, with effector cells, such as T cells, in adaptive immunity. We found that CD40 knockout mice were smaller but surprisingly more insulin resistant and glucose intolerant compared to wild-type mice when fed a high fat diet. Consistent with their metabolic phenotype, knockout mice displayed increased adipose tissue inflammation with infiltration of immune cells including macrophages and T cells. Consistent with increased inflammation, CD40 knockout adipose tissue displayed decreased lipid storage. Deficiency of CD40 also led to increased lipid deposition in liver, which may be due to increased lipid release into circulation from the adipose tissue as well as increased lipid synthesis in the liver. CD40 knockout mice had increased hepatic insulin resistance and increased gluconeogensis