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.