The Mitochondrial <scp>NAD</scp> Transporter <scp>SLC25A51</scp> in Adipocytes Regulates Adipose Tissue Mitochondrial Function and Systemic Metabolism During Aging

Nicotinamide adenine dinucleotide (NAD) is a classical coenzyme regulating cellular energy metabolism. Emerging evidence demonstrates the causal relationship between defective NAD metabolism and various age-associated diseases. The major purpose of the present study was to investigate the role of adipocyte mitochondrial NAD biology in age-associated metabolic diseases. To this end, we focused on solute carrier family 25 member 51 (SLC25A51), a recently identified mitochondrial NAD transporter. We found that aging was associated with decreased adipose tissue SLC25A51 expression in both humans and mice. We next generated and analyzed novel knockout and overexpression models, which we have named adipocyte-specific Slc25a51 knockout (ASKO) and Slc25a51 overexpressing (ASLO) mice. ASKO mice had a marked decrease in adipose tissue mitochondrial NAD levels and exhibited age-associated systemic metabolic complications, such as obesity, glucose intolerance, insulin resistance, hyperinsulinemia, metabolic inflexibility, dyslipidemia, and hepatosteatosis. Mechanistically, loss of Slc25a51 reduced mitochondrial respiratory function, fatty acid oxidation capacity, and adiponectin production in adipose tissue, likely contributing to the development of systemic metabolic complications. Conversely, ASLO mice were protected from obesity and insulin resistance caused by aging. In conclusion, our results provide novel mechanistic and therapeutic insights into understanding the critical role of adipocyte mitochondrial NAD transporter SLC25A51 in the pathophysiology of age-associated metabolic diseases, particularly obesity and insulin resistance.