The lysosomal disease caused by mutant VPS33A

Area of Science:

• Genetics
• Cell Biology
• Biochemistry

Background:

• A rare lysosomal disorder affecting the Yakut ethnic group presents with renal and platelet dysfunction.
• The disease is linked to mutations in the VPS33A gene, crucial for endocytic pathway function.
• VPS33A is a component of the CORVET and HOPS tethering complexes involved in vesicle trafficking.

Purpose of the Study:

• To investigate the molecular mechanisms underlying a rare lysosomal disease caused by VPS33A mutations.
• To identify potential therapeutic strategies for this fatal orphan disease.

Main Methods:

• Analysis of patient-derived fibroblasts for morphological and trafficking defects.
• Urine glycosaminoglycan analysis and lipidomic screening.
• Structural analysis of VPS33A and assessment of mutant protein stability.
• Treatment of cells with proteasome inhibitors and glucosylceramide synthesis inhibitors.

Main Results:

• Patient fibroblasts exhibit vacuolation, disordered endosomal/lysosomal compartments, and abnormal lactosylceramide trafficking.
• Elevated β-D-galactosylsphingosine and excess urinary glycosaminoglycans were observed.
• A specific VPS33A missense mutation destabilizes the protein, reducing its abundance and affecting HOPS/CORVET complex integrity.
• Proteasome inhibitors partially rescued the trafficking defect, suggesting a mechanism of protein degradation.

Conclusions:

• The disease is likely caused by reduced intracellular levels of functional VPS33A protein.
• Therapeutic interventions targeting proteasomal degradation or glucosylceramide synthesis may offer treatment avenues.