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Impact of Mitochondrial A3243G Heteroplasmy on Mitochondrial Bioenergetics and Dynamics of Directly Reprogrammed
Dar-Shong Lin1,2, Yu-Wen Huang3, Che-Sheng Ho2,4
1Department of Pediatrics, Mackay Memorial Hospital, Taipei 10449, Taiwan.
Abstract:
The MELAS syndrome primarily affecting the CNS is mainly caused by the m.A3243G mutation. The heteroplasmy in different tissues affects the phenotypic spectrum, yet the impact of various levels of m.A3243G heteroplasmy on CNS remains elusive due to the lack of a proper neuronal model harboring m.A3243G mutation. We generated induced neurons (iNs) through the direct reprogramming of MELAS patients, with derived fibroblasts harboring high (>95%), intermediate (68%), and low (20%) m.A3243G mutation. iNs demonstrated neuronal morphology with neurite outgrowth, branching, and dendritic spines. The heteroplasmy and deficiency of respiratory chain complexes were retained in MELAS iNs. High heteroplasmy elicited the elevation in ROS levels and the disruption of mitochondrial membrane potential. Furthermore, high and intermediate heteroplasmy led to the impairment of mitochondrial bioenergetics and a change in mitochondrial dynamics toward the fission and fragmentation of mitochondria, with a reduction in mitochondrial networks. Moreover, iNs derived from aged individuals manifested with mitochondrial fission. These results help us in understanding the impact of various heteroplasmic levels on mitochondrial bioenergetics and mitochondrial dynamics in neurons as the underlying pathomechanism of neurological manifestations of MELAS syndrome. Furthermore, these findings provide targets for further pharmacological approaches of mitochondrial diseases and validate iNs as a reliable platform for studies in neuronal aspects of aging, neurodegenerative disorders, and mitochondrial diseases.
Insights
Researchers created patient-derived neurons to study MELAS syndrome, a mitochondrial disease. This model reveals how different mutation levels impact neuronal function, offering insights into neurological symptoms and potential treatments.
Area of Science:
- Mitochondrial biology
- Neuroscience
- Genetics
Background:
- MELAS syndrome, a CNS disorder, is primarily linked to the m.A3243G mutation.
- Tissue-specific heteroplasmy complicates understanding the mutation's impact on the central nervous system (CNS).
- A suitable neuronal model for studying m.A3243G heteroplasmy in neurons was lacking.
Purpose of the Study:
- To generate and characterize induced neurons (iNs) from MELAS patients with varying m.A3243G heteroplasmy levels.
- To investigate the impact of different heteroplasmy levels on neuronal mitochondrial function, bioenergetics, and dynamics.
- To establish iNs as a model for studying MELAS syndrome's neurological aspects.
Main Methods:
- Direct reprogramming of fibroblasts from MELAS patients with high (>95%), intermediate (68%), and low (20%) m.A3243G heteroplasmy into induced neurons (iNs).
- Assessment of neuronal morphology, heteroplasmy retention, respiratory chain complex deficiency, reactive oxygen species (ROS) levels, mitochondrial membrane potential, and mitochondrial dynamics.
- Comparison of iNs from MELAS patients with those derived from aged individuals.
Main Results:
- MELAS iNs retained patient-specific heteroplasmy and respiratory chain deficiencies.
- High heteroplasmy significantly increased ROS levels and disrupted mitochondrial membrane potential.
- Impaired mitochondrial bioenergetics and a shift towards mitochondrial fission/fragmentation were observed in high and intermediate heteroplasmy iNs.
- Neuronal aging also correlated with mitochondrial fission.
Conclusions:
- This study establishes patient-derived iNs as a robust model for investigating the pathomechanisms of MELAS syndrome's neurological manifestations.
- Varying levels of m.A3243G heteroplasmy differentially impact neuronal mitochondrial bioenergetics and dynamics.
- The findings provide insights into neurological disorders and suggest potential therapeutic targets for mitochondrial diseases.
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