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Non-alcoholic fatty liver disease (NAFLD) is an asymptomatic increasingly common disorder that affects liver metabolism and is often the precursor for liver pathologies such as fibrosis, cirrhosis and hepato-cellular carcinoma. The liver sinusoidal endothelial cells act as a liver sieve by allowing macromolecules and chylomicrons to traverse through their fenestrations (sieve plates) to hepatocytes. Since liver sinusoidal endothelial cells (LSEC) regulate serum derived macromolecular exposure to hepatocytes, we asked what role LSEC could play in the pathogenesis of NAFLD. To investigate the early events of NAFLD we used a rat model (Sprague-Dawley) in which animals were maintained on standard and high fat diets (HFD) for a period of 8 weeks. The lipid accumulation in the livers, isolated hepatocytes and LSEC were visualized by Oil Red O, BODIPY (boron-dipyrromethene) stains and CARS (Coherent Anti-stokes Raman Scattering) imaging. There was evidence of increased size of lipid droplets in the hepatocytes of HFD rats in contrast to their LSEC, which showed minimal to no lipid accumulation. The lipid content of the liver tissues was analyzed by thin layer chromatography, which revealed the accumulation of triglycerides and cholesteryl esters in the livers of HFD rats compared to the control rats. In vitro endocytosis of 125I-HA (hyaluronic acid) experiments carried out on LSECs isolated from the rat livers showed that the 125I-HA uptake is significantly higher in control rats compared to HFD rats. We also observed that serum HA levels and alkaline phosphatase (ALP) levels were increased in HFD rats, in contrast to alanine transaminase (ALT), triglycerides and cholesterol, which remained the same. Purified RNA from the isolated LSECs was subjected to microarray analysis demonstrating altered gene expression patterns between rats on two different diets. The kidneys, gut, and spleens were also harvested to study the interplay of the organs in the disease. We have been able to demonstrate that decreased endocytic ability of LSECs precedes fibrosis of liver in NAFLD.
Adviser: Edward N. Harris