Sensory-Neuropathy-Causing Mutations in ATL3 Cause Aberrant ER Membrane Tethering

Area of Science:

• Cell Biology
• Neuroscience
• Molecular Biology

Background:

• The endoplasmic reticulum (ER) is a dynamic organelle crucial for cellular function.
• Mutations in atlastins (ATLs), essential ER fusion proteins, are linked to neurodegenerative diseases.
• The precise mechanisms by which ER membrane dynamics defects cause neurodegeneration remain unclear.

Purpose of the Study:

• To investigate the functional consequences of hereditary sensory and autonomic neuropathy (HSAN)-causing ATL3 mutations.
• To elucidate how ATL3 defects disrupt ER network organization and neuronal homeostasis.
• To understand the molecular defects underlying atlastin-related neuropathies.

Main Methods:

• Utilized electron microscopy (EM) volume reconstruction in transfected cells, neurons, and patient fibroblasts.
• Performed in vitro liposome tethering assays.
• Analyzed ATL3 variants' dimerization-dependent GTPase activity and fusion capabilities.

Main Results:

• HSAN-causing ATL3 mutants induce aberrant ER tethering, characterized by bundled, laterally attached ER tubules.
• In vitro experiments demonstrated excessive liposome tethering by ATL3 mutants.
• ATL3 variants maintained GTPase activity but failed to mediate membrane fusion, indicating a defect in an intermediate fusion step.

Conclusions:

• ATL3 mutations disrupt ER network organization through aberrant tethering, not just a loss of fusion.
• These findings provide insights into the pathogenesis of neuropathies associated with atlastin defects.
• The study highlights the critical role of ER membrane dynamics in maintaining neuronal homeostasis.