Adipocyte-derived exosomes in macrophage regulation

Project Summary Obesity is a common condition that is associated with poor health outcomes, and a significant portion of these pathologies are mediated by dysfunction and dysregulation of adipose tissue at a cellular and molecular level. Adipose tissue contains a unique population of macrophages (adipose tissue macrophages, or ATMs). These ATMs accumulate in obesity and mediate a number of key processes and pathologies in adipose tissue, including lipid handling, inflammation, and insulin resistance. Multiple populations of ATMs exist: a tissue- resident, anti-inflammatory population is descended from yolk sac embryonic hematopoietic progenitors and is present at all times; a pro-inflammatory population is derived from circulating monocyte precursors in adults and is recruited under conditions of metabolic stress such as obesity. Exosomes are small, secreted, endosome-derived, membrane-bound extracellular vesicles. Adipocytes constitutively release lipid-containing exosomes (adipocyte-derived exosomes, or AdExos), and the rate of their secretion is increased during states of increased ATM accumulation, including obesity and acute fasting. AdExos can also act as macrophage chemoattractants and drive reprogramming of bone marrow-derived macrophages toward an ATM-like transcriptional and phenotypic identity. However, many questions regarding the full scope and effects of AdExos remain unaddressed. We hypothesize that AdExos regulate the accumulation and differentiation of macrophages in adipose tissue via pathways canonically known to regulate ATMs. Given that AdExo production is increased in conditions during which monocyte recruitment and ATM recruitment occurs, and that AdExos both act directly as macrophage chemoattractants and drive production of monocyte chemoattractant factors in adipose tissue, we believe that AdExos regulate monocyte recruitment to adipose tissue. Aim 1 seeks to establish this role in an in vivo setting by monitoring the effect of direct AdExo injection on chemoattraction and accumulation of monocytes. Previous work has examined the effect of AdExos on the identity of bone marrow-derived macrophages, but not more relevant precursors such as yolk sac hematopoietic progenitors and peripheral monocytes. Aim 2 seeks to test the relationship between progenitor cell identity and the effect of AdExo exposure on cell fate. While we have established that AdExos may play a role in both ATM recruitment and ATM identity, we do not know the mechanisms that govern these actions. Aim 3 seeks to test whether pathways known to canonically regulate ATM differentiation and identity, like the CCR2 axis and PPARG, respectively, are also responsible for the AdExo-mediated regulation of these processes in ATMs.