Nicotinamide Riboside Supplementation Ameliorates Mitochondrial Dysfunction and Neuronal Loss in POLG Mutant Midbrain Organoids

Mitochondrial dysfunction is associated with many neurodegenerative disorders and is particularly prominent in conditions tied to POLG mutations. POLG encodes DNA polymerase gamma vital for mitochondrial DNA replication. Employing 3D human pluripotent stem cell-derived midbrain organoids (hMOs), harbouring POLG mutations, this study explores their differentiation, transcriptional alterations, and underlying pathways of neurodegeneration associated with POLG mutations. The generated hMOs displayed midbrain specificity and, at three months, a reduced diameter, suggesting growth challenges from POLG mutations. A reduced presence of dopaminergic neurons, particularly in DA2 and ventral midbrain classes, was evident. Intriguingly, post-treatment with 1 mM Nicotinamide Riboside (NR), an NAD+ precursor, the organoids demonstrated an increased count of DA and VMN neurons and an elevated gene expression, especially in processes crucial to mitochondrial and synaptic functions. Our findings spotlight NAD+ supplementation has potential therapeutic value in addressing POLG-associated neuronal and mitochondrial deficits. Moreover, the unique insights garnered from single-cell RNA sequencing, and enrichment analyses further emphasize the significance of mitochondrial disturbances and potential interventions for POLG-related neurodegenerative conditions. In summary, we underscore the transformative potential of NAD+ in managing neurodegenerative diseases associated with POLG mutations. It also establishes the utility of POLG mutant hMOs as a potent research model.