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Glycoprotein 330/megalin (LRP-2) has low prevalence as mRNA and protein in brain microvessels and choroid plexus
J T Chun1, L Wang, G M Pasinetti
1Andrus Gerontology Center and Department of Biological Sciences, Children's Hospital of Los Angeles, Los Angeles, California 90033, USA.
Abstract:
Prior studies indicated that glycoprotein 330 (gp330)/megalin mediates transcytosis of apolipoprotein J (apoJ) with Alzheimer's amyloide-peptide (Abeta) across the vascular membranes of the central nervous system (CNS). Here we show the presence of gp330/megalin mRNA and gp330-like immunoepitopes in brain capillaries and choroid plexus and their absence from brain parenchyma. By polymerase chain reaction (PCR) we estimated 1.2 x 10(5) molecules (1 pg) of gp330/megalin mRNA/microg total brain capillary RNA, which is 3% of that in kidney RNA. However, gp330 mRNA was not detected by in situ hybridization in vascular CNS tissue, presumably because of low transcript prevalence. The ratio of gp330 protein:RNA was 17-fold higher in choroid plexus vs brain capillaries, which implies tissue specific regulation of the protein and mRNA prevalence. We conclude that gp330/megalin mRNA and protein are expressed in brain capillaries and choroid plexus in small amounts that are consistent with the observed activities of this endocytosing receptor in the regulation of apoJ and Abeta uptake by the CNS.
Insights
Glycoprotein 330 (gp330)/megalin is present in brain capillaries and choroid plexus, facilitating the transport of apolipoprotein J and Alzheimer's amyloid-beta peptide across CNS vascular membranes.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Prior studies suggest glycoprotein 330 (gp330)/megalin facilitates transcytosis of apolipoprotein J (apoJ) and Alzheimer's amyloid-beta peptide (Abeta) across central nervous system (CNS) vascular membranes.
- The specific expression and localization of gp330/megalin within the CNS vasculature remain incompletely understood.
Purpose of the Study:
- To investigate the presence and quantify the expression of gp330/megalin mRNA and protein in CNS vascular components.
- To determine the role of gp330/megalin in the uptake of apoJ and Abeta by the CNS.
Main Methods:
- Polymerase chain reaction (PCR) to quantify gp330/megalin mRNA in brain capillaries.
- Immunohistochemistry to detect gp330-like immunoepitopes in brain capillaries and choroid plexus.
- In situ hybridization to assess gp330 mRNA localization.
Main Results:
- gp330/megalin mRNA and protein were detected in brain capillaries and choroid plexus, but not in brain parenchyma.
- Quantification revealed approximately 1 pg of gp330/megalin mRNA per microgram of total brain capillary RNA.
- A significantly higher ratio of gp330 protein to mRNA was observed in the choroid plexus compared to brain capillaries, suggesting tissue-specific regulation.
Conclusions:
- gp330/megalin is expressed at low levels in CNS capillaries and choroid plexus.
- These findings support the role of gp330/megalin as an endocytosing receptor involved in regulating apoJ and Abeta uptake into the CNS.
- Tissue-specific regulation of gp330/megalin expression exists within the CNS vasculature.