In previous studies it has been observed that exogenously derived amyloid beta a
ID: 189967 • Letter: I
Question
In previous studies it has been observed that exogenously derived amyloid beta and prion protein aggregates co-localize with dextran, a marker for fluid-phase endocytosis (but the beta-amyloid and prion protein aggregates do not co-localize with cholera toxin subunit B, a marker of lipid rafts.
When cells were exposed to MTBR-AF488 Tau aggregates and dextran, it was observed that 24% of Tau aggregates co-localized with Dextran, but they did not co-localize with cholera toxin B. The authors said that this suggests that Tau aggregates enter cells via the endocytotic pathway involving the engulfment by the cell membrane, instead of simple penetration of the membrane
Why is lipid raft marker involved in this study? Why did the authors say that it was an endocytotic pathway instead of simple penetration of the membrane? What's the difference?
Explanation / Answer
Answer:
Lipid rifts are specialized domains in the plasma membrane of the cell that contains protein receptors and high concentration of sphingolipids, glycolipids and cholesterol. Lipid raft dependent processes are involved in regulating the passage of macromolecules through the membrane, trafficking and signaling.
Cholera Toxin B Subunit is a membrane bound subunit of the beta toxin and is used as a marker of lipid rifts (raft-associated protein). Cholera Toxin B subunit binds to gangaloside GM1 which is a lipid raft biomarker. Based on the study observation, Tau aggregates didnot co-localize with Cholera Toxin B subunit, this indicates that lipid rafts are not involved in the passage of Tau aggregates in the cell. Co-locatization of Tau aggregates with Dextran (which is a marker for fluid-phase endocytosis) indicates that the mechanism of Tau aggreates entry into cells is associated with endocytotic pathway.