Differential roles for DNAJ isoforms in HTT-polyQ and FUS aggregation modulation revealed by chaperone screens

Area of Science:

• Neurobiology
• Molecular Biology
• Cellular Biology

Background:

• Protein aggregation is a key feature of neurodegenerative diseases like Huntington's disease (HD) and Amyotrophic Lateral Sclerosis (ALS).
• Cellular proteostasis, the maintenance of protein homeostasis, is crucial for neuronal health and is often disrupted in neurodegeneration.
• Chaperone proteins play vital roles in protein folding and quality control, but their specific roles in modulating different types of pathological aggregates are not fully understood.

Purpose of the Study:

• To investigate the differential effects of chaperone protein isoforms on Huntington's disease-related HTT-polyQ and ALS-related mutant FUS (mutFUS) aggregation.
• To explore the protective mechanisms of chaperone complexes, specifically DNAJB14 and DNAJB12, against pathological protein aggregation.
• To elucidate the role of naturally occurring short and full-length (FL) DNAJ isoforms in regulating proteostasis during neurodegeneration.

Main Methods:

• Cellular models expressing HTT-polyQ and mutFUS aggregates.
• Co-immunoprecipitation assays to identify chaperone complexes.
• Fluorescence microscopy to assess aggregate formation, mobility, and cellular proteostasis.
• Primary neuronal cultures to validate findings in a more physiologically relevant context.

Main Results:

• Huntington's disease-related HTT-polyQ aggregation triggers a proteotoxic stress response, whereas ALS-related mutFUS aggregation impairs proteostasis.
• Full-length DNAJB14 and DNAJB12 form a complex that protects against mutFUS aggregation in an HSP70-dependent manner.
• Short isoforms of DNAJB14 and DNAJB12 lack protective effects against mutFUS aggregation.
• DNAJB12-short alleviates HTT-polyQ aggregation, while DNAJB12-FL exacerbates it.
• DNAJB14-FL enhances mutFUS aggregate mobility and restores proteostasis in affected cells and neurons.

Conclusions:

• Cellular responses to pathological protein aggregation can be maladaptive.
• Naturally occurring DNAJ chaperone isoforms exhibit distinct regulatory functions depending on their length and the specific aggregation type.
• Targeting specific DNAJ isoforms offers a potential therapeutic strategy for neurodegenerative diseases characterized by protein aggregation.