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Published on: May 4, 2016
Selective mitophagy activation and protein aggregate accumulation in MTMR5/SBF1-deficient fibroblasts
Paola Zanfardino1, Alessandro Amati1, Stefano Doccini2
1Department of Translational Biomedicine and Neuroscience (DiBraiN), University of Bari Aldo Moro, Bari, Italy.
Aims:
Charcot-Marie-Tooth disease type 4B3 (CMT4B3) is a rare autosomal recessive neuropathy caused by biallelic MTMR5/SBF1 variants, which encode a catalytically inactive myotubularin involved in phosphoinositide metabolism and autophagy regulation. This study investigates the impact of MTMR5/SBF1 dysfunction on autophagy and mitophagy in patient-derived fibroblasts and examines the relationship between protein aggregates and autophagic machinery.
Materials And Methods:
Fibroblasts from a CMT4B3 patient with compound heterozygous MTMR5/SBF1 mutations were compared with a healthy control. Autophagic flux was analyzed via LC3B and SQSTM1; mitophagy was assessed through PINK1 and PRKN recruitment and by quantifying mitophagosomes and autolysosomes under mitochondrial stress. Protein aggregates were visualized using Proteostat and tested for colocalisation with autophagic structures.
Key Findings:
CMT4B3 fibroblasts showed normal basal macroautophagy but failed to increase autophagy in response to mitochondrial stress or protein aggregates. Conversely, mitophagy was strongly activated via the PINK1-PRKN pathway.
Significance:
These results reveal an uncoupling between mitophagy and macroautophagy, indicating that MTMR5/SBF1 mutations modify autophagic selectivity. Our findings provide new mechanistic insights into the pathogenesis of CMT4B3 and highlight the value of patient-derived fibroblasts for studying selective autophagy defects.
Insights
Mutations in MTMR5/SBF1 cause Charcot-Marie-Tooth disease type 4B3 (CMT4B3). CMT4B3 fibroblasts show selective autophagy defects, with impaired macroautophagy but enhanced mitophagy, revealing insights into disease mechanisms.
Area of Science:
- Neuroscience
- Cell Biology
- Genetics
Background:
- Charcot-Marie-Tooth disease type 4B3 (CMT4B3) is a rare, inherited neuropathy.
- It stems from mutations in MTMR5/SBF1, affecting phosphoinositide metabolism and autophagy.
- Understanding MTMR5/SBF1's role in autophagy is crucial for CMT4B3 pathogenesis.
Purpose of the Study:
- Investigate the impact of MTMR5/SBF1 dysfunction on autophagy and mitophagy.
- Examine the interplay between protein aggregates and autophagic machinery in CMT4B3.
- Utilize patient-derived fibroblasts to study selective autophagy defects.
Main Methods:
- Compared fibroblasts from a CMT4B3 patient with a healthy control.
- Assessed autophagic flux using LC3B and SQSTM1.
- Evaluated mitophagy via PINK1/PRKN recruitment and mitophagosome/autolysosome quantification.
- Visualized protein aggregates and their colocalization with autophagic structures.
Main Results:
- CMT4B3 fibroblasts exhibited normal basal macroautophagy.
- Autophagy induction failed in response to mitochondrial stress or protein aggregates.
- Mitophagy was significantly upregulated through the PINK1-PRKN pathway.
Conclusions:
- MTMR5/SBF1 mutations cause an uncoupling between mitophagy and macroautophagy.
- This suggests altered autophagic selectivity in CMT4B3.
- Findings offer mechanistic insights into CMT4B3 pathogenesis and highlight patient fibroblasts for studying selective autophagy.
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