Retromer has a selective function in cargo sorting via endosome transport carriers

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Retromer is a protein complex involved in vesicular transport within the endolysosomal system.
• Lysosomes are crucial for cellular waste breakdown and autophagy.
• Proper lysosomal function depends on the correct trafficking of enzymes and receptors.

Purpose of the Study:

• To investigate the role of the retromer complex in maintaining lysosomal morphology and function.
• To determine the impact of retromer subunit Vps35 knockout on cellular processes like autophagy and proteolysis.
• To elucidate the specific mechanisms of retromer-mediated cargo trafficking, particularly for the cation-independent mannose 6-phosphate receptor (CI-M6PR).

Main Methods:

• Utilized knockout models to study the Vps35 subunit of retromer.
• Analyzed lysosomal structure and function using ultrastructural and biochemical assays.
• Investigated the trafficking pathways of CI-M6PR and its dependence on retromer and associated proteins (SNX3, GCC88, golgin-97, golgin-245, SNX27, SNX-BAR).

Main Results:

• Vps35 knockout led to altered lysosomal structure and impaired autophagy.
• Loss of Vps35 reduced lysosomal proteolytic capacity due to defective lysosomal hydrolase processing.
• Retromer-dependent CI-M6PR trafficking to endosomes is restricted to GCC88-tethered carriers and requires SNX3.
• This pathway is crucial for lysosomal hydrolase maturation and overall lysosomal function.

Conclusions:

• Retromer plays a vital role in maintaining lysosomal morphology and function.
• The retromer complex mediates the retrograde trafficking of CI-M6PR, essential for lysosomal hydrolase maturation.
• SNX3 is specifically required for this retromer-dependent trafficking pathway, highlighting its importance in endolysosomal homeostasis.