Diet Induced Obesity Alters Intestinal Cytoplasmic Lipid Droplet Morphology and Proteome in the Postprandial Response to Dietary Fat

Dietary fat absorption by the small intestine is an efficient, multistep process that regulates the uptake and delivery of essential nutrients and energy. Fatty acids taken up by enterocytes, the absorptive cells of the small intestine, are resynthesized into triacylglycerol (TAG) and either secreted in chylomicrons or temporarily stored in cytoplasmic lipid droplets (CLDs). Proteins that associate with CLDs are thought to regulate the dynamics of TAG storage and mobilization. It is currently unclear what effect diet induced obesity (DIO) has on the balance between dietary fat storage and secretion. Specifically, there is limited knowledge of how DIO affects the level and diversity of proteins that associate with CLDs and regulate CLD dynamics. In the current study, we characterize CLDs from lean and DIO mice through histological and proteomic analyses. We demonstrate that DIO mice have larger intestinal CLDs compared to lean mice in response to dietary fat. Additionally, we identified 375 proteins in the CLD fraction isolated from enterocytes of lean and DIO mice. We identified a subgroup of lipid related proteins that are either increased or unique to the DIO CLD proteome. These proteins are involved in steroid synthesis, TAG synthesis, and lipolysis. This analysis expands our knowledge of the effect of DIO on the process of dietary fat absorption in the small intestine (D’Aquila, 2016)

Cytoplasmic Lipid Droplets in Metabolic Disease

Metabolic diseases associated with conditions of the metabolic syndrome (MetS) are on the rise in the United States. MetS develops as a consequence of dysfunctional nutrient metabolism, leading to hypertriglyceridemia, insulin resistance, and obesity. These conditions contribute to the development of more serious diseases such as Type 2 diabetes, cardiovascular disease, non-alcoholic/metabolic associated fatty liver disease (NAFLD/MAFLD), and cancer. Therefore, it is important to understand the cellular and molecular factors contributing to metabolic dysfunction and disease progression. A common feature of metabolic disease and its contributing conditions is abnormal lipid metabolism, specifically the accumulation of neutral lipid in cellular cytoplasmic lipid droplets (CLDs). The objective of this dissertation is to examine the role of cytoplasmic lipid droplets in metabolic disease. First, we investigated CLDs in metastatic breast cancer. CLD accumulation in breast cancer cells is positively associated with cancer aggressiveness; however, the functional consequence of this phenomenon is unclear. The function of CLDs is often reflected by their associated proteins, which regulate both cellular and CLD metabolism. However, the proteome of CLDs in metastatic breast cancer cells has not been described. In this study, we characterized the proteome of CLDs in the human metastatic breast cancer cell line, MCF10CA1a, for the first time. We identified a novel CLD proteome with both similarities and differences to CLDs of other cell types. Overall, this study is the first to analyze the proteins associated with CLDs in metastatic breast cancer cells and in turn produced a hypothesis-generating list of potential proteins involved breast cancer metastasis that can be applied to future studies in order to define the role of CLDs and their proteins in breast cancer metabolism. Next, we investigated the characteristics and proteome of CLDs in enterocytes of the proximal, middle, and distal regions of the small intestine in the response to dietary fat. Enterocytes of all three regions of the small intestine are capable of packaging and secreting dietary fat on chylomicrons to contribute to blood triacylglycerol (TAG) levels, although to different extents. All regions can also store dietary fat in CLDs, however whether CLDs serve different roles or are differentially metabolized in each region is not clear. Further, obesity has been shown to influence the rate at which dietary fat is absorbed and stored in the middle region of the small intestine, however, whether obesity influences dietary fat storage in the other regions is not known. Therefore, we examined the effect of intestine region and obesity on the characteristics and proteome of CLDs in the proximal, middle, and distal regions of the small intestine in response to dietary fat to determine potential differences in lipid processing, storage, or CLD metabolism. We found dietary fat storage and CLD proteins varied in each region of the small intestine in lean and diet-induced obese mice, which may indicate differences in dietary fat processing or CLD metabolism in each intestine region. Overall, this study helped to characterize the dynamics of dietary fat absorption along the length of the small intestine and provides insight as to how the process of dietary fat absorption or enterocyte lipid metabolism may be altered in obesity