Nicotinamide riboside reduces glial inflammation and boosts mitochondrial function.

Astrocyte dysfunction plays a pivotal role in the pathogenesis of POLG-related mitochondrial diseases, yet the underlying mechanisms remain poorly understood. Here, we employed human iPSC-derived astrocytes, cortical organoids and astrocyte-neuron co-culture systems to model POLG mutations and investigate astrocyte-mediated neurotoxicity. Single-cell transcriptomic profiling revealed a marked expansion of A1 neurotoxic astrocytes, depletion of A2 neuroprotective astrocytes, and reduction of neuronal populations in POLG organoids. A1 astrocytes exhibited transcriptional signatures of mitochondrial dysfunction, inflammatory signaling (TGF-β, JAK-STAT), impaired neuro-supportive functions, and activation of senescence, autophagy, and proteostasis stress pathways. Co-cultured dopaminergic neurons displayed impaired morphology and widespread transcriptional downregulation of mitotic, cytoskeletal, and synaptic genes, along with activation of inflammatory and ion transport pathways. Treatment with the NAD⁺ precursor nicotinamide riboside (NR) attenuated astrocyte reactivity, reduced IL-6 and CXCL1 secretion, improved neuronal structure and synaptic marker expression, and increased mtDNA copy number and ATP production in POLG astrocytes. Our study identifies NAD⁺ augmentation as a promising strategy to mitigate astrocyte-driven pathology in mitochondrial encephalopathies.