July 02, 2019
Cancer drugs for muscle diseases
Dysferlinopathies are a rare group of genetic diseases that cause muscle weakness and atrophy. All are associated with a mutation in the DYSF gene, which leaves myocytes (muscle cells) deficient in dysferlin, a protein responsible for membrane repair in muscle. In the new study, the laboratory of Hidetoshi Sakurai, who specializes in using iPS cells to study muscle diseases in a part of Takeda-CiRA Joint Program for iPS Cell Applications (T-CiRA) , prepared myocytes from the iPS cells of a dysferlinopathy patient and the patient's healthy sister. Using these myocytes, the researchers conducted a drug screening and found that nocodazole recovered the expression of dysferlin in myocytes made from the patient iPS cells.
The patient suffered from a missense mutation in the DYSF gene, in which amino acid 999 was changed from tryptophan to cysteine, causing the dysferlin protein to misfold. This mutated protein was still functional, but was excessively degraded by the cell, leading to lower dysferlin levels. Ideally, medicines would treat the misfolding or suppress the degradation, but current treatments focus on managing the symptoms.
For example, MG-132 is a proteasome inhibitor that increases normal and misfolded dysferlin. Based on that knowledge, the research team established a screening system to find drugs that increased dysferlin levels even if the protein was misfolded. Using this system, they found that the patient iPS cell-derived myocytes increased their dysferlin levels when treated with nocodazole but not with MG-132.
"Our data indicate that the main pathway of the degradation of dysferlin in iPS derived myocytes is provided by the autophagy system rather than the proteasome," observes Dr. Yuko Kokubu, who first-authored the study.
To test the functional significance of the increased dysferlin levels, the scientists intentionally damaged patient iPS cell-derived myocytes with a laser beam. Only the myocytes treated with nocodazole could recover.
The findings suggest that the targeted protein degradation system for drug treatment varies with the patient.
"Our screening system provides new insights on possible targets for increasing the level of misfolded dysferlin in dysferlinopathy," says Sakurai.
- Journal: STEM CELLS Translational Medicine
- Title: Phenotypic drug screening for dysferlinopathy using patient-derived induced pluripotent stem cells
- Authors: Yuko Kokubu1, Tomoko Nagino2, Katsunori Sasa2, Tatsuo Oikawa2, Katsuya Miyake3, Akiko Kume2, Mikiko Fukuda1, Hiromitsu Fuse2, Ryuichi Tozawa2, and Hidetoshi Sakurai1
- Author Affiliations:
- Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
- Regenerative Medicine Unit, Takeda Pharmaceutical Company, Ltd., Fujisawa, Kanagawa, Japan
- International University of Health and Welfare, Narita City, Chiba, Japan