Nicotinamide Riboside Enhances Mitochondrial Bioenergetics and Dopaminergic Signaling Independent of Neuron Survival in a Double-Hit Parkinson’s Model

<title>Abstract</title> <p> Background: Parkinson’s disease (PD) is characterized by progressive degeneration of <italic>substantia nigra pars compacta</italic> (SNc) dopaminergic (DA) neurons and the development of motor and non-motor impairments. Mitochondrial dysfunction(definition), exacerbated by aging and environmental exposures, is a central contributor to PD pathogenesis. Nicotinamide riboside (NR), a dietary precursor of nicotinamide adenine dinucleotide (NAD⁺), enhances cellular bioenergetics and mitochondrial health, yet its translational potential for PD remains insufficiently defined. <h4>Methods:</h4> We used a “double-hit” PD mouse model combining A53T α-synuclein overexpression in SNc DA neurons with chronic dietary benomyl exposure. Mice received continuous NR supplementation in drinking water. Motor behavior was monitored longitudinally using open-field and rotarod assays. Striatal dopamine dynamics were quantified using genetically encoded fluorescent dopamine sensors to measure tonic and optogenetically evoked dopamine release. In vivo ATP/ADP ratios were measured in DA neurons and striatal spiny projection neurons (SPNs) using fiber photometry of the ratiometric sensor PercevalHR. <h4>Results:</h4> Chronic NR supplementation markedly improved motor performance in double-hit PD mice, despite failing to prevent SNc DA neuron degeneration. NR robustly increased both tonic and stimulus-evoked striatal dopamine release in control and PD mice. Additionally, NR elevated ATP/ADP ratios across multiple neuronal populations, indicating enhanced mitochondrial energetic capacity. <h4>Conclusions:</h4> NR supplementation enhances DA neurotransmission and mitochondrial bioenergetics in vivo, conferring functional benefits that occur independently of DA neuron survival. These findings identify metabolic augmentation via NR as a promising adjunctive strategy for mitigating PD-related functional deficits. </p>