Paracardial fat and vitamin A: a mechanism for regulating exercise performance.

Different fat depots have different physiologic functions. In a provocative study published in this issue of the JCI, Petrosino et al. investigate the role of paracardial fat in whole-body metabolism and exercise physiology. Petrosino et al. show that paracardial fat samples from older mice or mice fed a Western diet had decreased levels of alcohol dehydrogenase 1 (ADH1). Paracardial fat samples from humans with obesity also had decreased levels of ADH1 mRNA, supporting the translational relevance. Additional experiments with Adh1-KO mice and surgical fat transplantation experiments provide additional mechanistic insight. Paracardial fat may regulate exercise performance by altering circulating metabolites and/or endocrine effects. ADH1 appears to regulate the mitochondrial content of paracardial fat, a mechanism mediated by retinaldehyde. When ADH1 is active, the paracardial fat has characteristics of brown fat, which is beneficial for exercise performance. Further research is warranted to determine the translational potential of these findings, such as whether removing paracardial fat at the time of open-heart surgery might improve recovery time by increasing exercise capacity.