Ultrastructural characterization of vitamin D receptors and metabolizing enzymes in the lipid droplets of the fatty liver in rat

Abstract

Vitamin D is a steroid hormone with numerous actions in the organism. There are strong evidences that relate vitamin D deficiency with liver lipid metabolism disturbances, but the mechanism of this action is still unknown. In our previous work we postulated the localization and accumulation of vitamin D receptor (VDR) in membrane of the lipid droplets (LDs) in hepatocytes. In this study, we applied the transmission electron microscopy (TEM) to confirm this hypothesis by using a long-term (6 months) high sucrose intake rat model that was previously found to be appropriate for research of the hepatic lipid accumulation. In addition to the VDR, we also found key vitamin D metabolizing enzymes, 1α-hydroxylase and CYP 24 associated with the membrane of the LDs. A light-microscopy data revealed significant increase in expression of VDR and CYP 24 in liver of high-sucrose treated rats, in comparison to controlones. According to the best of our knowledge, this is a first study confirming the presence of the VDR in the membrane of the LDs in general and also in particular in LDs of the hepatocytes that were accumulated as a consequence of the prolonged high sucrose intake. Moreover, we found association of main vitamin D metabolizing enzymes with LD membrane. These results provide a new insight in the possible relation of vitamin D signalling system with LD morphology and function and with the lipid metabolism in general.

Keywords: 1α-hydroxylase; CYP 24; Hepatic steatosis; Lipid droplets; VDR; Vitamin D.