Role of Perivascular and Visceral Adipose Tissues in Murine Models of Obesity and Atherosclerosis: A Dissertation

Expansion of visceral adipose tissue correlates with the metabolic syndrome and increased cardiovascular risk. Hypertrophied visceral fat becomes inflamed, causing increased lipolysis, decreased triglyceride storage, and lipotoxicity in skeletal muscle and liver resulting in insulin resistance. Perivascular adipose tissue is a normal component of the adventitia of arteries in humans and animals. Whether or not perivascular adipose also becomes inflamed in obesity is an important question, as this may be an additional, direct mechanism by which obesity causes vascular inflammation and disease. Thus, for the first part of my thesis, we asked the question: does perivascular adipose in mice become inflamed with high fat feeding? In contrast to visceral adipose, macrophage gene expression was not increased in perivascular adipose in response to high fat diet, and this correlated with reduced F480 antigen positive cells as seen by immunohistochemistry and flow cytometry. Interestingly, perivascular adipose surrounding the thoracic aorta was similar to brown adipose tissue, a highly thermogenic fat depot, as shown by histology and DNA microarrays. Moreover, inter-scapular brown adipose was also resistant to diet induced inflammation in comparison to visceral adipose. These findings suggest that brown adipose in the perivascular niche may serve to protect the vasculature from diet induced inflammation, or from cold exposure, or both; whether or not brown perivascular adipose tissue exists in humans has yet to be determined.