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Localization of StarD5 cholesterol binding protein.
Daniel Rodriguez-Agudo1, Shunlin Ren, Phillip B Hylemon
1Department of Medicine, Veterans Affairs Medical Center and Virginia Commonwealth University, Richmond, VA, USA.
Journal of Lipid Research
|March 15, 2006
Summary
Human StarD5 protein, a cholesterol transporter, is found in immune cells like macrophages in the liver, not hepatocytes. This suggests a role in lipid transport and potentially in inflammatory diseases like atherosclerosis.
Area of Science:
- Cell Biology
- Lipid Metabolism
- Immunology
Background:
- Human StarD5 is a START domain protein involved in lipid transfer.
- Previous studies indicated StarD5 binds cholesterol and 25-hydroxycholesterol and is cytosolic in liver.
- Overexpression in rat hepatocytes suggested StarD5 is a cytosolic sterol transporter.
Purpose of the Study:
- To determine the precise localization of StarD5 in human liver tissue.
- To identify specific cell types expressing StarD5 in the liver.
- To investigate the cellular localization of StarD5 in macrophages.
Main Methods:
- Western blot analysis of human liver and various cell types.
- Immunohistochemistry on human liver tissue.
- Immunocytochemistry and cell fractionation of THP-1 macrophages.
Main Results:
- StarD5 is present in human liver but absent in human hepatocytes.
- Immunohistochemistry revealed StarD5 in sinusoidal lining cells, co-localizing with CD68 (Kupffer cell marker).
- StarD5 was detected in monocytes, macrophages, mast cells, basophils, and promyelocytic cells, but not in hepatocytes, endothelial cells, or brain tissue.
- In THP-1 macrophages, StarD5 localized to the cytosol and associated with the Golgi apparatus.
Conclusions:
- Human StarD5 is primarily expressed in immune cells within the liver, particularly Kupffer cells.
- The localization of StarD5 in macrophages suggests a role in cellular sterol transport within these cells.
- These findings offer new insights into the function of StarD5 in lipid metabolism and its potential involvement in lipid-mediated inflammatory diseases such as atherosclerosis.