Project 2: Summary During obesity, the increased accumulation of macrophages in VAT and other metabolic organs (liver, skeletal muscle) propagates chronic inflammation, which is associated with systemic insulin resistance, the development of type 2 diabetes, and its associated co-morbidities such as atherosclerosis. While the mechanisms regulating macrophage recruitment have been well studied, the signals directing macrophage persistence and failure to resolve inflammation in metabolic tissues are poorly understood. Identifying the mechanisms contributing to non-resolving macrophage inflammation and crucial pathways amenable for intervention is a key objective of this application. Emerging data suggest that neuronal guidance cues typically expressed during development, such as netrin-1, have additional roles outside the central nervous system in the induction and inhibition of cell migration. Our proposal investigates the concept that netrin-1 is expressed by adipose tissue macrophages and regulates immune cell trafficking, survival and accumulation in obese VAT, thereby leading to metabolic dysfunction and insulin resistance. We will use novel mouse models of tissue-specific or conditional deletion/gain-of-function of netrin-1 and its receptor Unc5b to determine how this guidance cue/receptor pair alters macrophage migration into and out of VAT, macrophage survival and inflammatory polarization. In addition, using nanoparticle technology, we will test how targeting netrin-1 and Unc5b alters metabolic inflammation and dysfunction. Furthermore, we will work with other projects to determine the role of factors that accumulate in hyperglycemia and insulin resistance in the induction of netrin- 1 in macrophages from obese VAT and atherosclerotic plaques in order to glean common and tissue-specific mechanisms promoting macrophage dysfunction. These studies will provide insight into the signals that promote macrophage accumulation during obesity and the potential of netrin-1 and its receptor as therapeutic targets in obesity and type 2 diabetes, and potentially other chronic inflammatory disorders.