DNMT1 mutations leading to neurodegeneration paradoxically reflect on mitochondrial metabolism

Area of Science:

• Neurogenetics
• Mitochondrial Biology
• Epigenetics

Background:

• Autosomal dominant cerebellar hypoplasia with pontocerebellar hypoplasia (ADCA-DN) and hereditary sensory and autonomic neuropathy type IE (HSN-IE) are rare neurodegenerative disorders.
• These syndromes are linked to dominant mutations in the replication foci targeting sequence (RFTS) of the DNA methyltransferase 1 (DNMT1) gene.
• Phenotypes resemble mitochondrial disorders, with initial observations of mitochondrial dysfunction in ADCA-DN.

Purpose of the Study:

• To investigate the role of mitochondrial dysfunction in ADCA-DN and HSN-IE.
• To explore the cellular and metabolic consequences of DNMT1 mutations.

Main Methods:

• Studied fibroblasts from ADCA-DN and HSN-IE patients with DNMT1 mutations.
• Assessed DNMT1 protein activity, localization, and mitochondrial DNA methylation.
• Analyzed mitochondrial biogenesis, oxidative phosphorylation (OXPHOS), ATP levels, and reactive oxygen species (ROS) production.
• Performed metabolomics profiling and investigated energy sensing pathways (AMPK, mTORC1).

Main Results:

• Mutant DNMT1 proteins showed impaired activity, leading to increased DNMT1 levels in fibroblasts.
• DNMT1 localized to the mitochondrial outer membrane, not within mitochondria, with reduced mitochondrial DNA methylation.
• Observed activated mitochondrial biogenesis and OXPHOS, increased H2O2, and decreased ATP content.
• Metabolomics revealed alterations in purine, arginine/urea cycle, and glutamate metabolism.
• Severe mutations activated AMPK and inhibited mTORC1, indicating energy shortage response.

Conclusions:

• DNMT1 RFTS mutations deregulate cellular metabolism, increasing purine catabolism and urea cycle activity, leading to reduced ATP levels.
• Paradoxical mitochondrial hyper-function and increased oxidative stress accompany reduced ATP, potentially driving neurodegeneration in non-dividing cells.