The crosstalk between FGF21 and GH leads to weakened GH receptor signaling and IGF1 expression and is associated with growth failure in very preterm infants.

Background: Fibroblast growth factor 21 (FGF21) is an essential metabolic regulator that adapts to changes in nutritional status. Severe childhood undernutrition induces elevated FGF21 levels, contributing to growth hormone (GH) resistance and subsequent linear growth attenuation potentially through a direct action on chondrocytes. Methods: In this study, we assessed expression of the components of both GH and FGF21 pathways in rare and unique human growth plates obtained from children. Moreover, we investigated the mechanistic interplay of FGF21 on GH receptor (GHR) signaling in a heterologous system. Results: Chronic FGF21 exposure increased GH-induced GHR turnover and SOCS2 expression, leading to the inhibition of STAT5 phosphorylation and IGF-1 expression. The clinical significance of FGF21 signaling through GH receptors was tested in nutritionally driven growth failure seen in very preterm (VPT) infants right after birth. VPT infants display an immediate linear growth failure after birth followed by growth catch-up. Consistent with the in vitro model data, we show that circulating FGF21 levels were elevated during deflection in linear growth compared to catch-up growth and were inversely correlated with the length velocity and circulating IGF1 levels. Conclusions: This study further supports a central role of FGF21 in GH resistance and linear growth failure and suggests a direct action on the growth plate.

The Androgen Metabolome of Preterm Infants Reflects Fetal Adrenal Gland Involution.

CONTEXT: The human adrenal cortex changes with fetal-neonatal transition from the fetal to the adult organ, accompanied by changes in the steroid metabolome. OBJECTIVE: As it is unclear how the observed developmental changes differ between preterm and full-term neonates, we investigated whether the involution of the fetal adrenals is following a fixed time course related to postmenstrual age or whether it is triggered by birth. Furthermore, the fetal and postnatal androgen metabolome of preterm infants was characterized in comparison to term babies. METHODS: This was a prospective, longitudinal, 2-center study collecting spot urines of preterm and term infants during the first 12 to 18 months of life. Steroid metabolites were measured from spot urines by gas chromatography-mass spectrometry. Data relating were modeled according to established pre- and postnatal pathways. RESULTS: Fetal adrenal involution occurs around term-equivalent age in preterm infants and is not triggered by premature birth. Testosterone levels are higher in preterm infants at birth and decline slower until term compared to full-term babies. Dihydrotestosterone levels and the activity of the classic androgen biosynthesis pathway are lower in premature infants as is 5α-reductase activity. No difference was found in the activity of the alternate backdoor pathway for androgen synthesis. CONCLUSION: Human adrenal involution follows a strict timing that is not affected by premature birth. By contrast, prematurity is associated with an altered androgen metabolome after birth. Whether this reflects altered androgen biosynthesis in utero remains to be investigated.

Carnitine Intake and Serum Levels Associate Positively with Postnatal Growth and Brain Size at Term in Very Preterm Infants.

Carnitine has an essential role in energy metabolism with possible neuroprotective effects. Very preterm (VPT, <32 gestation weeks) infants may be predisposed to carnitine deficiency during hospitalization. We studied the associations of carnitine intake and serum carnitine levels with growth and brain size at term equivalent age (TEA) in VPT infants. This prospective cohort study included 35 VTP infants admitted to Kuopio University Hospital, Finland. Daily nutrient intakes were registered at postnatal weeks (W) 1 and 5, and serum carnitine levels were determined at W1, W5, and TEA. The primary outcomes were weight, length, and head circumference Z-score change from birth to TEA, as well as brain size at TEA in magnetic resonance imaging. Carnitine intake at W1 and W5, obtained from enteral milk, correlated positively with serum carnitine levels. Both carnitine intake and serum levels at W1, W5, and TEA showed a positive correlation with weight, length, and head circumference Z-score change and with brain size at TEA. In linear models, independent positive associations of carnitine intake and serum carnitine levels with length and head circumference Z-score change and brain size at TEA were seen. In VPT infants, sufficient carnitine intake during hospitalization is necessary since it is associated with better postnatal growth and larger brain size at term age.

Elevated FGF21 leads to attenuated postnatal linear growth in preterm infants through GH resistance in chondrocytes.

CONTEXT: The hormone fibroblast growth factor 21 (FGF21) is a key metabolic regulator in the adaptation to fasting. In food-restricted mice, inhibition of skeletal growth is mediated by the antagonistic effect of FGF21 on GH action in the liver and growth plate. OBJECTIVE: The objective of the study was to assess the role of FGF21 in growth regulation in humans using postnatal growth failure of very preterm infants as a model. DESIGN: FGF21 levels were measured serially in very preterm infants, and their linear growth evaluated from birth to term-equivalent age. Primary chondrocytes obtained from pediatric donors were used to test whether FGF21 can directly interfere with GH signaling. RESULTS: A negative association (ß -.415, P < .005, linear regression model) of FGF21 levels with the change in SD score for length was found. In primary chondrocytes, FGF21 upregulated basal and GH-induced SOCS2 expression and inhibited GH-induced signal transducer and activator of transcription 5 (STAT5) phosphorylation as well as GH-induced COLII and ALP expression. Finally, FGF21 inhibited GH-induced IGF-1 expression and cell proliferation, indicating GH resistance. However, FGF21 did not affect IGF-1-induced cell proliferation. CONCLUSIONS: Elevated FGF21 serum levels during the first weeks of life are independently associated with postnatal growth failure in preterm infants. Furthermore, our data provide mechanistic insights into GH resistance secondary to prematurity and may offer an explanation for the growth failure commonly seen in chronic conditions of childhood.

Malignant giant cell tumor in the posterior fossa of a neonate.

Giant cell tumors (GCTs) of the bone are rare, usually benign but locally aggressive neoplasms that primarily occur in the epiphyses of long bones. They seldom develop in the cranium; when they do, they involve principally the sphenoid and temporal bones. These tumors usually affect young adults, and few reports in children have been published. Primary malignant GCTs of the skull are even more uncommon. The 3 published cases all involved adults over 40 years of age. Herein, the authors present a case of a highly aggressive primary malignant GCT of the posterior fossa in a 5-week old preterm infant. One month after the gross-total resection of the tumor found in the bone, the infant's condition rapidly deteriorated and she died. Magnetic resonance imaging and postmortem examination revealed a tumor larger than it had been before the operation, with expansion toward the brain. To the best of the authors' knowledge, this is the youngest patient reported with a primary malignant GCT of the skull, and actually the first case in a pediatric patient. In addition, the extremely high growth rate of the tumor in the postoperative period renders this case the most aggressive primary malignant GCT of the cranium described so far.