The Mitochondrial Brown Adipose Tissue Maintenance Factor Nipsnap1 Interfaces Directly With the β-Oxidation Protein Machinery in Rodents.

BACKGROUND: The activation of brown adipose tissue (BAT) is associated with improved metabolic health in humans. We previously identified the mitochondrial protein Nipsnap1 as a novel regulatory factor that integrates with lipid metabolism and is critical to sustain the long-term activation of BAT, but the precise mechanism and function of Nipsnap1 are unknown. OBJECTIVES: The study aims to define the function of the regulatory factor Nipsnap1 in lipid metabolism by identifying its specific protein-protein interactions and regulatory role in fatty acid β-oxidation. METHODS: We used adeno-associated viral (AAV) vectors to overexpress Nipsnap1 in the thermogenic adipose tissue of male C57BL/6J mice and assessed whole-body energy metabolism using metabolic cages. Mitochondrial respiration in primary brown adipocytes was measured by Seahorse assay after AAV-Nipsnap1 infection. To further investigate molecular mechanisms, an immunoprecipitation assay was performed to identify Nipsnap1-interacting proteins. RESULTS: We showed that adipose-specific overexpression of Nipsnap1 in mice elicits a 20% increase in energy expenditure through the utilization of lipids as an energy substrate as evidenced by the shift of the respiratory exchange ratio to 0.7 (P < 0.001). Additionally, we showed that Nipsnap1 overexpression in primary adipocytes increases lipid β-oxidation by 39% to increase cellular energy expenditure (P < 0.05). Moreover, we mapped the first protein-protein network of Nipsnap1 in brown adipocytes and showed that Nipsnap1 interacts with proteins such as solute carrier family 25 member 20 and enoyl-coenzyme A (CoA) hydratase and 3-hydroxyacyl CoA dehydrogenase that regulate both mitochondrial and peroxisomal fatty acid β-oxidation, respectively. CONCLUSIONS: This study elucidates a mechanistic function of Nipsnap1 in thermogenic fat where Nipsnap1 facilitates a functional connection between peroxisomal and mitochondrial β-oxidation pathways. By enhancing lipid utilization as energy substrates, Nipsnap1 plays a pivotal role in sustaining thermogenic fat activation to increase energy expenditure. These findings underscore the potential of Nipsnap1 as a therapeutic target for metabolic health.