Drosophila Hsp67Bc hot-spot variants alter muscle structure and function

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Small heat-shock proteins (sHSPs) prevent protein aggregation and are vital for cellular processes like development and aging.
• Hsp67Bc in Drosophila is the closest functional ortholog to human HSPB8, playing roles in muscle Z-disk and neuromuscular junction (NMJ) maintenance.
• Pathogenic variants of human HSPB8 are linked to neurodegenerative diseases.

Purpose of the Study:

• To investigate the functional consequences of muscle-specific overexpression of Drosophila Hsp67Bc variants (R126E and R126N) that mimic pathogenic human HSPB8 mutations.
• To assess the impact of these variants on muscle structure, performance, and neuromuscular junction integrity.

Main Methods:

• Muscle-targeted overexpression of Hsp67BcR126E and Hsp67BcR126N variants in Drosophila.
• Assessment of larval motility and muscle performance.
• Analysis of neuromuscular junction structure, including synaptic bouton count.
• Evaluation of mitochondrial respiratory function.

Main Results:

• Hsp67BcR126E overexpression significantly affected larval motility, potentially due to impaired mitochondrial respiration and/or NMJ abnormalities (reduced synaptic boutons).
• Hsp67BcR126N variant exhibited aggregate-prone behavior with significant protein accumulation and large aggregate formation.
• The Hsp67BcR126N variant had a comparatively lesser impact on overall muscle structure and performance than the Hsp67BcR126E variant.

Conclusions:

• Muscle-specific expression of Drosophila Hsp67Bc variants mimicking human HSPB8 mutations leads to distinct cellular and functional deficits.
• The Hsp67BcR126E variant highlights a role in maintaining mitochondrial function and NMJ integrity, with its disruption impacting motility.
• The Hsp67BcR126N variant demonstrates the consequences of aggregate formation, with a milder effect on muscle performance, suggesting different pathogenic mechanisms for HSPB8 variants.