Life in the lumen: The multivesicular endosome

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Late endosomes/endo-lysosomes contain lysobisphosphatidic acid (LBPA), a unique phospholipid not found elsewhere in vertebrate cells.
• LBPA is concentrated within the intralumenal vesicles (ILVs) and membrane systems inside these organelles.
• This phospholipid plays a critical role in endosomal cholesterol homeostasis.

Purpose of the Study:

• To review current knowledge on LBPA and LBPA-containing membranes.
• To outline LBPA's role in controlling endosomal cholesterol levels.
• To discuss the broader implications of intralumenal membranes in endo-lysosomal function and disease.

Main Methods:

• Literature review and synthesis of existing research on LBPA and intralumenal membranes.
• Discussion of mechanisms involved in intralumenal membrane biogenesis (e.g., ESCRTs).
• Analysis of the composition, fate, and functional roles of intralumenal membranes.

Main Results:

• LBPA is central to the structure and function of intralumenal vesicles within late endosomes.
• Intralumenal membranes are involved in cholesterol trafficking and can be disrupted in disorders like Niemann-Pick C.
• Mechanisms like ESCRTs drive the formation of these membranes, which have diverse compositions and fates.

Conclusions:

• LBPA and intralumenal membranes are crucial for endo-lysosomal dynamics, cholesterol regulation, and cellular defense.
• Pathogenic agents can exploit these structures, highlighting their importance in infection and intoxication.
• LBPA may function as a calcium chelator in the acidic environment of endo-lysosomes.