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The membrane environment of endogenous cellular prion protein in primary rat cerebellar neurons
Nicoletta Loberto1, Simona Prioni, Arianna Bettiga
1Center of Excellence on Neurodegenerative Diseases, Department of Medical Chemistry, Biochemistry and Biotechnology, University of Milan, Segrate, Italy.
Abstract:
We studied the membrane environment of cellular prion protein in primary cultured rat cerebellar neurons differentiated in vitro. In these cells, about 45% of total cellular prion protein (corresponding to a 35-fold enrichment) is associated with a low-density, sphingolipid- and cholesterol-enriched membrane fraction, that can be separated by flotation on sucrose gradient. Biotinylation experiments indicated that almost all prion protein recovered in this fraction was exposed at the cell surface. Prion protein was efficiently separated from this fraction by a monoclonal antibody immuno-separation procedure. Under conditions designed to preserve lipid-mediated membrane organization, several proteins were found in the prion protein-enriched membrane domains (i.e. the non-receptor tyrosine kinases Lyn and Fyn and the neuronal glycosylphosphatidylinositol-anchored protein Thy-1). The prion protein-rich membrane domains contained, as well, about 50% of the sphingolipids, cholesterol and phosphatidylcholine present in the sphingolipid-enriched membrane fraction. All main sphingolipids, including sphingomyelin, neutral glycosphingolipids and gangliosides, were similarly enriched in the prion protein-rich membrane domains. Thus, prion protein plasma membrane environment in differentiated neurons resulted to be a complex entity, whose integrity requires a network of lipid-mediated non-covalent interactions.
Insights
Cellular prion protein resides in specialized membrane domains rich in lipids and cholesterol in neurons. These domains, crucial for protein function, involve complex lipid interactions for structural integrity.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Cellular prion protein (PrPC) is a cell surface glycoprotein implicated in neurodegenerative diseases.
- Understanding PrPC's membrane environment is key to elucidating its function and associated pathologies.
- Neuronal plasma membranes are complex, with specialized lipid domains influencing protein behavior.
Purpose of the Study:
- To investigate the specific membrane microenvironment of cellular prion protein (PrPC) in differentiated rat cerebellar neurons.
- To characterize the lipid and protein composition of PrPC-enriched membrane domains.
- To understand the role of lipid-protein interactions in maintaining the integrity of these domains.
Main Methods:
- Primary neuronal cell culture and differentiation.
- Sucrose gradient flotation to isolate low-density membrane fractions.
- Biotinylation assays to determine cell surface exposure.
- Monoclonal antibody immuno-separation for protein isolation.
- Biochemical analysis of lipid and protein content in isolated domains.
Main Results:
- Approximately 45% of total PrPC was found in a low-density membrane fraction enriched in sphingolipids and cholesterol.
- Biotinylation confirmed that PrPC in this fraction was predominantly cell surface-exposed.
- PrPC-enriched domains contained specific proteins like Lyn, Fyn, and Thy-1.
- These domains also concentrated significant amounts of sphingolipids (sphingomyelin, glycosphingolipids, gangliosides) and cholesterol.
Conclusions:
- PrPC in differentiated neurons is localized to complex, lipid-rich membrane microdomains.
- The integrity of these PrPC-associated domains relies on a network of lipid-mediated non-covalent interactions.
- These findings highlight the importance of the neuronal membrane's lipid architecture in regulating PrPC function.
