Hepatocyte Conditioned Media Promotes Endothelial Fatty Acid Uptake

The overconsumption of fatty acids (FAs) can lead to a variety of metabolic diseases, such as non-alcoholic fatty liver disease (NAFLD). This is because the liver is an important organ for fat metabolism. Therefore, examining how FAs enter the liver can potentially lead to the discovery of drug targets for NAFLD. FAs traveling in the blood must cross the blood vessel wall, composed of endothelial cells (ECs), to get into the liver. Previous research has shown that when exposed to insulin, other cells such as adipocytes can stimulate the neighboring endothelium to transport more FAs. We hypothesize that hepatocytes should perform similarly: when exposed to insulin or other hormones, hepatocytes stimulate endothelial cells to take up more FAs. To test this hypothesis, we first treated hepatocytes with metabolic hormones. Once the cells have been exposed to a hormone for a certain time, they condition the media by secreting certain factors. This conditioned media is collected and put onto ECs. We then give the ECs a fluorescent fatty acid analog called Bodipy-C12, and measure the intracellular fluorescence with a microplate reader. We also perform western blots to confirm that hormone is behaving properly within the cells with regards to intracellular signaling. These experiments have provided evidence that hepatocytes do secrete some factor that causes endothelial FA uptake. My results indicate that treating hepatocytes with insulin does not stimulate FA uptake in endothelial cells, even when hepatocytes are starved by removing glucose. In addition, glucagon also does not initiate this process. Both hormones were tested with different concentrations and different exposure times on hepatocytes. My next steps are to repeat this experiment with thyroid hormone as well as treat the conditioned media in various ways (e.g., boiling) to determine the nature of the active factor that stimulates EC fat uptake. This research investigates the complex interactions between the liver and the blood vessel wall, and as such will provide more information as to how metabolic disorders like NAFLD progress and how they can be treated.