Intestine to adipose tissue interorgan communication in homeostasis and obesity - PROJECT SUMMARY Secreted proteins coordinate organ functions during homeostasis. The secreted proteome represents a poorly- characterized interorgan communication network, which is central in the etiology of various metabolic disor- ders. For example, obesity affects 40% of the US population, and the metabolic complications of obesity may result from dysfunctional interorgan communication. Despite this, the composition and activity of interorgan communication networks and their impact on obesity remain poorly defined. White adipose tissue (WAT) plays a central role in energy sensing and storage, and coordination of activities across organs to regulate systemic metabolism. In turn, energy storage in WAT is affected by the intestine in response to dietary and internal met- abolic inputs. Obesity disrupts this normal interorgan network and impacts metabolism of visceral and subcu- taneous WAT depots. We therefore anticipate that defining proteins secreted from intestine to the WAT depots will discover novel factors that regulate obesity. However, it has historically been difficult to identify such se- creted proteins due to their low abundance and lack of information on their organ(s) of origin. To address this, we established in mice a conditional BirA*G3 engineered biotin ligase system that generally labels secreted proteins within the endoplasmic reticulum of one organ, allowing identification of proteins that traffic to distal organs using affinity enrichment and quantitative mass spectrometry. This transgenic system can be ex- pressed in specific organs (e.g., intestine) to identify key secreted factors that communicate to distal organs, and provide clues to the labeled secreted factors’ underlying biology based on the organ-of-origin, the destination, and their levels in homeostatic or disease states. Using this approach in mice, we identified hun- dreds of proteins trafficking from intestinal epithelium to subcutaneous WAT, visceral WAT, brown adipose tis- sue, pancreas, and skeletal muscles in response to food intake, including the known low-abundance hormones GLP1/2, SST, FGF15, BMP8b, REG3, and CCK. We identified PLEXIN-B2 as a novel intestine-secreted pro- tein specifically targeting subcutaneous WAT. PLEXIN-B2 is produced during fasting and in diet-induced obesi- ty, and acts through SEMA4A receptor and SCRIB signaling to reduce adipocyte lipolysis and to promote adi- pogenesis. Our primary goal is to define the obesity-associated imbalances in intestine-secreted proteins, such as PLEXIN-B2, that directly impact the depot-specific differences in adipogenesis, lipolysis, lipogenesis and mitochondrial biogenesis, and contribute to systemic glucose and lipid metabolism, fibrosis, and inflammation. We will first use the BirA*G3 approach to establish the interorgan circuitry of intestine-to-visceral and subcuta- neous WAT communication during the development of obesity (Aim 1). Next, we will determine the impact of intestine-secreted proteins on WAT depots and metabolic maladaptation in obesity (Aim 2). Finally, we will de- fine the regulation of WAT depot function, metabolic homeostasis, and development of obesity by PLEXIN-B2 (Aim 3). In sum, we will discover mechanisms by which the intestine modulates WAT depot metabolic activities
