Fat Cell NAD Transporter SLC25A51 Drives Metabolic Aging and Obesity
A newly identified mitochondrial NAD transporter in fat cells controls whether you develop obesity and insulin resistance as you age.
Summary
Scientists have identified a protein called SLC25A51 that shuttles NAD — a critical energy molecule — into the mitochondria of fat cells. This transporter naturally declines with age in both humans and mice. When researchers deleted it from fat cells, mice developed obesity, insulin resistance, fatty liver, and other hallmarks of metabolic aging. When they boosted its expression, mice were protected from age-related obesity and insulin resistance. The mechanism involves reduced mitochondrial energy burning, impaired fat oxidation, and lower adiponectin — a hormone that keeps metabolism healthy. This research positions SLC25A51 as a potential therapeutic target for age-related metabolic disease and adds important nuance to the growing field of NAD biology in aging.
Detailed Summary
NAD (nicotinamide adenine dinucleotide) is one of the most studied molecules in longevity science, but most research has focused on its cytoplasmic roles. This study shifts attention to a critical but underexplored question: how does NAD get into mitochondria, and what happens when that process fails with age?
Researchers from Keio University and collaborating Japanese institutions investigated SLC25A51, a recently discovered mitochondrial NAD transporter, specifically within adipocytes (fat cells). They first confirmed that SLC25A51 expression declines with aging in both human and mouse adipose tissue — a finding that links the transporter directly to the biology of aging.
To test causality, the team created two novel mouse models: one lacking SLC25A51 specifically in fat cells (ASKO) and one overexpressing it (ASLO). ASKO mice showed dramatically reduced mitochondrial NAD levels in adipose tissue and developed a striking cluster of metabolic problems — obesity, glucose intolerance, insulin resistance, hyperinsulinemia, dyslipidemia, and hepatosteatosis — mirroring the metabolic syndrome seen in aging humans. Mechanistically, loss of the transporter impaired mitochondrial respiration, reduced fatty acid oxidation, and suppressed adiponectin secretion.
Conversely, ASLO mice with elevated SLC25A51 were protected against obesity and insulin resistance induced by aging, providing strong evidence that maintaining mitochondrial NAD transport in fat tissue is metabolically protective.
These findings have significant implications for NAD-boosting strategies. Current interventions like NMN and NR raise cytoplasmic NAD, but mitochondrial delivery may require the SLC25A51 transporter to be functional. If the transporter is downregulated with age, supplementation strategies may be partially bypassing the most critical compartment. Future therapies targeting SLC25A51 expression or activity in adipose tissue could represent a more precise approach to combating metabolic aging.
Key Findings
- SLC25A51 expression in adipose tissue declines with aging in both humans and mice.
- Fat-cell-specific SLC25A51 deletion causes obesity, insulin resistance, and fatty liver in mice.
- Loss of SLC25A51 impairs mitochondrial respiration and fatty acid oxidation in adipose tissue.
- Overexpressing SLC25A51 in fat cells protects aging mice from obesity and insulin resistance.
- Reduced adiponectin production may link mitochondrial NAD decline to systemic metabolic disease.
Methodology
The study used adipocyte-specific knockout (ASKO) and overexpression (ASLO) mouse models to isolate the role of SLC25A51 in fat cell mitochondria. Human and mouse adipose tissue samples were analyzed to confirm age-associated expression changes. Metabolic phenotyping included glucose tolerance tests, insulin sensitivity assays, lipid panels, and mitochondrial function assays.
Study Limitations
This summary is based on the abstract only, as the full text is not open access; mechanistic details and statistical data could not be fully evaluated. The primary evidence comes from mouse models, and translation to human therapeutic interventions requires further validation. The study does not directly test whether NAD precursor supplementation (NMN/NR) can compensate for SLC25A51 deficiency.
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