A team of researchers in Japan has developed a targeted mitochondrial DNA (mtDNA) editing tool that can precisely control heteroplasmy levels in human induced pluripotent stem cells (iPSCs). This tool offers a new platform for investigating mutation-associated mitochondrial disorders such as MELAS syndrome.
The study, published online ahead of print in Molecular Therapy Nucleic Acids, introduces an optimized system of platinum transcription activator-like effector nucleases (mpTALENs) engineered to selectively degrade either mutant or wild-type mtDNA carrying the m.3243A>G mutation. This pathogenic variant is commonly linked to MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes) as well as mitochondrial-related diabetes.
Heteroplasmy is the co-existence of mutated and wild-type mtDNA within a cell, which is a hallmark of mitochondrial disorders and a key challenge in both research and clinical settings. Fluctuating mutation loads across tissues complicate efforts to study disease progression and test therapeutic approaches. Until now, tools to systematically increase or decrease heteroplasmy in a controlled way have been lacking.
Naoki Yahata and colleagues addressed this gap by designing two complementary mpTALEN systems: one that selectively targets and degrades mutant mtDNA, and another that eliminates the wild-type variant. Using patient-derived iPSCs, they generated a panel of cell lines spanning a wide range of heteroplasmy, from 11% to 97%, while retaining pluripotency and differentiation capacity. “Our study is the first to demonstrate an increase in the proportion of pathogenic mutant mtDNA by programmable nuclease,” Yahata said.
Key modifications in the nuclease design included incorporation of non-conventional repeat-variable di-residues and obligate heterodimeric FokI domains. These refinements boosted sequence specificity and reduced off-target cleavage. To further stabilize cell lines with high mutant loads, the team used uridine supplementation to counteract potential metabolic stress.
“Our results demonstrate that our mpTALEN optimization process created a useful tool for altering heteroplasmy levels in m.3243A>G-iPSCs, improving their potential for studying mutation pathology,” Yahata added.
In addition to advancing basic research, the mpTALEN platform may be adaptable to other mtDNA mutations. “Our proposed method could be adapted for other mutant mtDNAs and may contribute to understanding their associated pathologies and developing new treatments,” Yahata concluded.
The work provides a scalable and precise approach to modeling mtDNA-linked diseases, helping to close a longstanding gap in the field.
Publication Details
Yahata, N., Goto, Y. I., & Hata, R. (2025). Optimization of mtDNA-targeted platinum TALENs for bi-directionally modifying heteroplasmy levels in patient-derived m. 3243A> G-iPSCs. Molecular Therapy Nucleic Acids, 36(2).
The study, published online ahead of print in Molecular Therapy Nucleic Acids, introduces an optimized system of platinum transcription activator-like effector nucleases (mpTALENs) engineered to selectively degrade either mutant or wild-type mtDNA carrying the m.3243A>G mutation. This pathogenic variant is commonly linked to MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes) as well as mitochondrial-related diabetes.
Heteroplasmy is the co-existence of mutated and wild-type mtDNA within a cell, which is a hallmark of mitochondrial disorders and a key challenge in both research and clinical settings. Fluctuating mutation loads across tissues complicate efforts to study disease progression and test therapeutic approaches. Until now, tools to systematically increase or decrease heteroplasmy in a controlled way have been lacking.
Naoki Yahata and colleagues addressed this gap by designing two complementary mpTALEN systems: one that selectively targets and degrades mutant mtDNA, and another that eliminates the wild-type variant. Using patient-derived iPSCs, they generated a panel of cell lines spanning a wide range of heteroplasmy, from 11% to 97%, while retaining pluripotency and differentiation capacity. “Our study is the first to demonstrate an increase in the proportion of pathogenic mutant mtDNA by programmable nuclease,” Yahata said.
Key modifications in the nuclease design included incorporation of non-conventional repeat-variable di-residues and obligate heterodimeric FokI domains. These refinements boosted sequence specificity and reduced off-target cleavage. To further stabilize cell lines with high mutant loads, the team used uridine supplementation to counteract potential metabolic stress.
“Our results demonstrate that our mpTALEN optimization process created a useful tool for altering heteroplasmy levels in m.3243A>G-iPSCs, improving their potential for studying mutation pathology,” Yahata added.
In addition to advancing basic research, the mpTALEN platform may be adaptable to other mtDNA mutations. “Our proposed method could be adapted for other mutant mtDNAs and may contribute to understanding their associated pathologies and developing new treatments,” Yahata concluded.
The work provides a scalable and precise approach to modeling mtDNA-linked diseases, helping to close a longstanding gap in the field.
Publication Details
Yahata, N., Goto, Y. I., & Hata, R. (2025). Optimization of mtDNA-targeted platinum TALENs for bi-directionally modifying heteroplasmy levels in patient-derived m. 3243A> G-iPSCs. Molecular Therapy Nucleic Acids, 36(2).