Elevated postprandial levels of triglyceride-rich lipoproteins (TRL) in the circulation are a risk factor for cardiovascular disease. Following a meal, chylomicrons produced by the intestine contribute prominently to circulating triglyceride (TG) levels, and production is primarily determined by the amount of fat ingested and absorbed. However, growing evidence suggests the intestine can actively regulate the rate of postprandial chylomicron production in part through transient TG storage and delayed export. Further, individuals with metabolic syndrome often exhibit hyperchylomicronemia. Thus, misregulation of intestinal TG storage and turnover likely contributes to disease risk. Intestinal enterocytes absorb and package dietary fatty acids into TG that is exported via chylomicrons or stored in cytoplasmic lipid droplets (LD). LDs are subcellular organelles composed of a core of TG and cholesterol esters surrounded by a monolayer of phospholipids and a variety of proteins, including perilipins. Intestinal LDs are dynamic storage compartments; they increase in number and size in the hours following a high-fat meal, but are nearly depleted 12-14 hours later in the absence of another meal. However, if a subsequent meal is consumed before the stored TG is depleted, it is rapidly exported in chylomicrons, suggesting that LD turnover is regulated. Despite the implications of intestinal LD regulation on postprandial serum TG levels, the mechanisms governing enterocyte LD regulation are poorly characterized. The overall goal of this proposal is to elucidate the cellular mechanisms regulating the maintenance and turnover of intestinal LDs following both an acute high-fat meal and in response to re- feeding. These studies will capitalize on the powerful transgenic and in vivo imaging opportunities afforded by the zebrafish model vertebrate system.
Aim 1 of this proposal will determine whether LDs in enterocytes undergo rapid lipolysis by neutral lipases in response to re-feeding or are degraded by autophagy-mediated lipolysis.
In Aim 2, the role of the LD-associated protein perilipin-2 in regulating intestinal LD storage and turnover will be explored. Human variants of perilipin-2 that are associated with favorable lipoprotein profiles will be evaluated to determine whether they alter intestinal LD dynamics.
Aim 3 will establish whether zebrafish detect fat as a taste sensation and if this results in neural activation that is sufficient to elicit LD breakdown and chylomicron release in the fish, as has been suggested by human studies. Understanding intestinal regulation of lipid storage and lipoprotein production is imperative for development of strategies for the prevention and treatment of hypertriglyceridemia. Collectively, the proposed experiments will elucidate the cellular mechanisms regulating the storage and turnover of lipid in the intestine, produce novel methods and tools to study LD dynamics in vivo, and establish whether the zebrafish is a valid model to address how the brain communicates fat taste detection to intestinal enterocytes.
Elevated levels of circulating fat in the blood are a known risk factor for cardiovascular disease. The intestine, which absorbs and re-packages dietary fat for delivery to the body, is the primary source of circulating fat following a meal. The goal of this proposal is to determine how the intestine regulates the temporary storage and export of dietary fat, which will aid in the prevention and treatment for cardiovascular disease
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