Metformin rescues muscle function in BAG3 myofibrillar myopathy models.

Abstract

Dominant de novo mutations in the co-chaperone BAG3 cause a severe form of myofibrillar myopathy, exhibiting progressive muscle weakness, muscle structural failure, and protein aggregation. To elucidate the mechanism of disease in, and identify therapies for, BAG3 myofibrillar myopathy, we generated two zebrafish models, one conditionally expressing BAG3P209L and one with a nonsense mutation in bag3. While transgenic BAG3P209L-expressing fish display protein aggregation, modeling the early phase of the disease, bag3-/- fish exhibit exercise dependent fiber disintegration, and reduced swimming activity, consistent with later stages of the disease. Detailed characterization of the bag3-/- fish, revealed an impairment in macroautophagic/autophagic activity, a defect we confirmed in BAG3 patient samples. Taken together, our data highlights that while BAG3P209L expression is sufficient to promote protein aggregation, it is the loss of BAG3 due to its sequestration within aggregates, which results in impaired autophagic activity, and subsequent muscle weakness. We therefore screened autophagy-promoting compounds for their effectiveness at removing protein aggregates, identifying nine including metformin. Further evaluation demonstrated metformin is not only able to bring about the removal of protein aggregates in zebrafish and human myoblasts but is also able to rescue the fiber disintegration and swimming deficit observed in the bag3-/- fish. Therefore, repurposing metformin provides a promising therapy for BAG3 myopathy.Abbreviations:ACTN: actinin, alpha; BAG3: BAG cochaperone 3; CRYAB: crystallin alpha B; DES: desmin; DMSO: dimethyl sulfoxide; DNAJB6: DnaJ heat shock protein family (Hsp40) member B6; dpf: days post fertilization; eGFP: enhanced green fluorescent protein; FDA: Food and Drug Administration; FHL1: four and a half LIM domains 1; FLNC: filamin C; hpf: hours post-fertilization; HSPB8: heat shock protein family B [small] member 8; LDB3/ZASP: LIM domain binding 3; MYOT: myotilin; TTN: titin; WT: wild-type.

• Authors: Avnika A Ruparelia, Emily A McKaige, Caitlin Williams, Keith E Schulze, Margit Fuchs, Viola Oorschot, Emmanuelle Lacene, Mirella Meregalli, Clara Lee, Rita J Serrano, Emily C Baxter, Keyne Monro, Yvan Torrente, Georg Ramm, Tanya Stojkovic, Josée N Lavoie, Robert J Bryson-Richardson
• Journal: Autophagy (Autophagy) Vol. 17 Issue 9 Pg. 2494-2510 (09 2021) ISSN: 1554-8635 [Electronic] United States
• PMID: 33030392 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Adaptor Proteins, Signal Transducing
• Apoptosis Regulatory Proteins
• BAG3 protein, human
• BAG3 protein, zebrafish
• DNAJB6 protein, human
• FHL1 protein, human
• HSP40 Heat-Shock Proteins
• Intracellular Signaling Peptides and Proteins
• LIM Domain Proteins
• Molecular Chaperones
• Muscle Proteins
• Nerve Tissue Proteins
• Zebrafish Proteins
• Metformin

Topics

• Adaptor Proteins, Signal Transducing (metabolism)
• Animals
• Apoptosis Regulatory Proteins (metabolism)
• Autophagy
• HSP40 Heat-Shock Proteins (genetics, metabolism)
• Humans
• Intracellular Signaling Peptides and Proteins
• LIM Domain Proteins
• Metformin (pharmacology)
• Molecular Chaperones (metabolism)
• Muscle Proteins
• Muscles (metabolism)
• Mutation
• Myopathies, Structural, Congenital (genetics)
• Nerve Tissue Proteins (metabolism)
• Zebrafish (metabolism)
• Zebrafish Proteins