HUWE1 targets mitochondria via RMC1 to promote neurodevelopment

Area of Science:

• Biochemistry
• Neuroscience
• Genetics

Background:

• HUWE1, a HECT-type E3 ubiquitin ligase, is crucial for protein homeostasis, genome stability, and neurodevelopment.
• Variants in HUWE1 are associated with X-linked intellectual disability (XLID), but mechanisms for noncatalytic variants remain unclear.

Purpose of the Study:

• To investigate the role of noncatalytic HUWE1 variants in neurodevelopment and identify underlying disease mechanisms.
• To elucidate the signaling axis regulating HUWE1 localization and function in neural development.

Main Methods:

• Utilized zebrafish models expressing XLID-associated noncatalytic HUWE1 variants (M375I, G660R, H669Q).
• Performed global ubiquitin profiling to assess substrate ubiquitination.
• Investigated protein-protein interactions and subcellular localization using biochemical and imaging techniques.
• Assessed therapeutic potential of Urolithin A in zebrafish models.

Main Results:

• Noncatalytic HUWE1 variants caused neurodevelopmental deficits in zebrafish, including impaired brain growth and motor neuron defects.
• Disease-associated HUWE1 variants selectively impaired ubiquitination of mitochondrial proteins, not nuclear substrates.
• Identified an AMBRA1-RMC1-HUWE1 signaling axis where AMBRA1 scaffolds RMC1 to recruit HUWE1 to mitochondria.
• Disruption of this axis by disease variants prevented mitochondrial targeting and substrate ubiquitination.
• Urolithin A treatment rescued neurodevelopmental phenotypes in HUWE1-deficient zebrafish.

Conclusions:

• Defined a novel AMBRA1-organized mitochondrial recruitment pathway involving RMC1 and HUWE1.
• Explained the disease mechanisms of noncatalytic HUWE1 variants in XLID through impaired mitochondrial ubiquitination.
• Proposed mitochondrial quality control enhancement as a potential therapeutic strategy for XLID.