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Apolipoprotein J expression at fluid-tissue interfaces: potential role in barrier cytoprotection
B J Aronow1, S D Lund, T L Brown
1Department of Pathology & Laboratory Medicine, College of Medicine, University of Cincinnati, OH.
Summary
Apolipoprotein J (apoJ) is found in specialized secretory cells across human and mouse tissues. This expression pattern suggests apoJ protects barrier cells from the extracellular environment.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Apolipoprotein J (apoJ) is a secreted glycoprotein with proposed roles in cell death, reproduction, immunity, and lipid transport.
- Its ubiquitous expression and conservation suggest critical physiological functions.
- Understanding apoJ's cellular synthesis is key to elucidating its diverse roles.
Purpose of the Study:
- To identify the specific cell types that synthesize apolipoprotein J (apoJ) in mammalian tissues.
- To correlate apoJ expression patterns with its proposed functions.
- To provide a comprehensive map of apoJ synthesis for future research.
Main Methods:
- In situ hybridization was employed to screen apoJ expression in adult and fetal mouse tissues.
- Human tissues were also analyzed using in situ hybridization to identify homologous expression patterns.
- Expression levels were assessed in a wide array of specialized cell types.
Main Results:
- Apolipoprotein J (apoJ) was highly expressed in numerous specialized secretory cell types in both mouse and human tissues.
- These cells are often located at the cellular interfaces of fluid compartments, acting as barriers.
- Examples include epithelial cells of the digestive, urinary, and reproductive tracts, as well as choroid plexus, ependyma, and synovial lining cells.
Conclusions:
- The expression pattern of apolipoprotein J (apoJ) strongly indicates a protective role for secretory, mucosal, and barrier cells.
- Localized apoJ synthesis likely defends these cells against potentially harmful surface-active extracellular components.
- This study provides a foundational understanding of apoJ's tissue distribution and suggests its involvement in maintaining cellular integrity at various interfaces.