Brown adipose tissue activity is higher in girls during the first year of life

A team led by Dr Lourdes Ibáñez and Dr Francesc Villarroya, IRSJD researchers, with the collaboration of researchers from Josep Trueta Hospital and the University of Leuven, publishes the first study that shows the very early appearance of differences in the activity of the brown adipose tissue between girls and boys. The study has been published in The Journal of Clinical Endocrinology and Metabolism.

Brown adipose tissue is composed mostly of adipocytes and its function, unlike white adipose tissue, is to produce heat to help maintain body temperature in low-temperature conditions. It is found around the neck, aorta, kidneys, and armpit area. And it is particularly abundant in newborns but with age it decreases.

Moreover, brown adipose tissue has recently been identified as an active site where bioactive molecules called brown adipokines are released. These molecules elicit local signaling and exert actions on distinct organs. In fact, many studies suggest the possibility of using brown adipokines as therapeutic candidates and potential biomarkers of brown adipose tissue activity.

Newly, in experimental studies, CXCL14 chemokine has been shown in mice to be one of the brown adipokines released by active brown adipose tissue. It exerts protective effects against metabolic alterations caused by obesogenic diets, that is, diets that promote overweight and obesity. But, not all studies agree on a positive role for CXCL14 on metabolism.

Nevertheless, it stills remain unclear which is the role of brown adipose tissue and its association with body adiposity or excess fat and the metabolic health in early infancy.

"Our goal is to assess for the first time the brown adipose tissue activity and the circulating levels of CXCL14 in a group of infants in the first year of life and determine their relationship with measures of adiposity and endocrine-metabolic parameters" explains Cristina Garcia, researcher from the Metabolic Endocrinology research group.

Brown adipose tissue activity significantly higher in girls

The study has analyzed a group of 43 babies from birth to 12 months to examine their levels of the adipokine CXCL14 and endocrine metabolic parameters, fat index and activity of brown adipose tissue via an infrared thermography (a technique that allows determining the remote temperature).

The results show that the posterior-cervical brown adipose tissue is more active in girls than in boys. In addition, only in girls, it has been seen that the more activity of this tissue, the less adiposity or excess fat there was. Finally, CXCL14 levels are also higher in girls at 12 months and are positively correlated with posterior-cervical adipose tissue activity.

"These results indicate that both the activity of brown adipose tissue and the levels of CXCL14 are sex-specific during the first year of life, being more active in girls" comments Dr Francesc Villarroya, head of the IRSJD research group in Adipose Tissue Molecular Biology and Gene Regulation and Associated Disorders and researcher at the Institute of Biomedicine of the University of Barcelona (IBUB).

"In addition, the results could mean that the cytokine CXCL14 could be a biomarker when evaluating the activity of brown adipose tissue since quantifying it is much easier and less invasive, especially in children" continues Dr Lourdes Ibáñez, head of IRSJD research group in Metabolic Endocrinology and pediatric endocrinologist at the Sant Joan de Déu Hospital.

These findings highlight the importance in considering sex differences in studies of brown adipose tissue activity, adiposity and biomarker analysis even in the early stages of development. Even so, subsequent analysis and follow-ups of the population studied are necessary to specifically determine these relationships.

Reference paper

Garcia-Beltran C, Cereijo R, Plou C, Gavaldà-Navarro A, Malpique R, Villarroya J, López-Bermejo A, de Zegher F, Ibáñez L, Villarroya F. Posterior Cervical Brown Fat and CXCL14 levels in the First Year of Life: Sex Differences and Association with Adiposity. J Clin Endocrinol Metab. 2021 Oct 22:dgab761. doi: 10.1210/clinem/dgab761. Epub ahead of print. PMID: 34677618.