Posterior cervical brown fat and CXCL14 levels in the first year of life: sex differences and association with adiposity

Context: Brown adipose tissue (BAT) is particularly abundant in
neonates but its association with measures of adiposity and metabolic
health in early infancy is poorly delineated. Besides sustaining
non-shivering thermogenesis, BAT secretes brown adipokines that act on
systemic metabolism. The chemokine CXCL14 has been identified as a brown
adipokine in experimental studies. Objective: To
determine the relationships among BAT activity, adiposity and
circulating CXCL14 levels in the first year of life in girls and boys.
Design, setting and participants: Indices of fat accretion,
circulating endocrine-metabolic parameters and serum CXCL14 levels were
assessed longitudinally in a cohort of infants at birth and at 4 and 12
months. BAT activity was estimated using infrared thermography only at age
12 months. Main outcome measures: Weight and length Z-scores,
total and abdominal fat content (by DXA), BAT activity at the
posterior-cervical and supraclavicular regions, serum levels of glucose,
insulin, insulin-like growth factor-I, high-molecular-weight adiponectin
and CXCL14; CXCL14 transcript levels in neonatal BAT and liver.
Results: Posterior-cervical BAT was more active in girls than in
boys (p=0.02). BAT activity was negatively associated with adiposity
parameters only in girls. CXCL14 levels were higher in girls than in boys
at age 12 months and correlated positively with the area of active
posterior-cervical BAT in girls. Neonatal BAT showed high CXCL14 gene
expression levels. Conclusions: BAT activity and the levels of
CXCL14 -a potential surrogate of BAT activity- are sex-specific
in the first year of life. BAT activity associates negatively
with indices of adiposity only in girls.