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Extrahepatic expression of apolipoprotein A-II in mouse tissues: possible contribution to mouse senile amyloidosis
1Department of Aging Angiology, Shinshu University School of Medicine, Matsumoto, Japan.
Abstract:
Apolipoprotein A-II (apoA-II), an apolipoprotein in serum high-density lipoprotein, is a precursor of mouse senile amyloid fibrils. The liver has been considered to be the primary site of synthesis. However, we performed nonradioactive in situ hybridization analysis in tissue sections from young and old amyloidogenic (R1.P1-Apoa2C) and amyloid-resistant (SAMR1) mice and revealed that other tissues in addition to the liver synthesize apoA-II. We found a strong hybridization signal in the basal cells of the squamous epithelium and the chief cells of the fundic gland in the stomach, the crypt cells and a small portion of the absorptive epithelial cells in the small intestine, the basal cells of the tongue mucosa, and the basal cells of the epidermis and hair follicles in the skin in both mouse strains. Expression of apoA-II mRNA in those tissues was also examined by RT-PCR analysis. Immunolocalization of apoA-II protein also indicated the cellular localization of apoA-II. ApoA-II transcription was not observed in the heart. Amyloid deposition was observed around the cells expressing apoA-II mRNA in the old R1.P1-Apoa2C mice. These results demonstrate that the apoA-II mRNA is transcribed and translated in various extrahepatic tissues and suggest a possible contribution of apoA-II synthesized in these tissues to amyloid deposition.
Insights
Apolipoprotein A-II (apoA-II) is synthesized in various tissues beyond the liver, including the stomach, intestines, tongue, and skin. This extrahepatic apoA-II production may contribute to amyloid deposition in aging mice.
Area of Science:
- Biochemistry
- Molecular Biology
- Pathology
Background:
- Apolipoprotein A-II (apoA-II) is a component of high-density lipoprotein and a known precursor of amyloid fibrils.
- The liver has been traditionally identified as the primary site of apoA-II synthesis.
Purpose of the Study:
- To investigate extrahepatic sites of apoA-II synthesis.
- To determine if apoA-II expression in non-hepatic tissues correlates with amyloid deposition.
Main Methods:
- Nonradioactive in situ hybridization was used to detect apoA-II mRNA in tissue sections of young and old amyloidogenic and amyloid-resistant mice.
- Reverse transcription polymerase chain reaction (RT-PCR) was employed to confirm apoA-II mRNA expression.
- Immunolocalization studies identified apoA-II protein presence and cellular localization.
Main Results:
- ApoA-II mRNA was detected in various extrahepatic tissues, including the stomach, small intestine, tongue, skin (epidermis and hair follicles), and their associated basal/epithelial cells.
- Significant hybridization signals were observed in the basal cells of the tongue mucosa and epidermis, and chief cells of the stomach's fundic gland.
- ApoA-II transcription was notably absent in the heart.
- Amyloid deposition was observed surrounding apoA-II-expressing cells in aged amyloidogenic mice.
Conclusions:
- Apolipoprotein A-II is synthesized in multiple extrahepatic tissues, challenging the notion of the liver as the sole production site.
- The presence of apoA-II mRNA and protein in various tissues suggests a broader role in physiological processes.
- Extrahepatic apoA-II synthesis may play a significant role in the pathogenesis of amyloid deposition, particularly in aging and disease states.
