Fast decline of hematopoiesis and uncoupling protein 2 content in human liver after birth: location of the protein in Kupffer cells

Ligand-activated PPARα-dependent DNA demethylation regulates the fatty acid β-oxidation genes in the postnatal liver

The metabolic function of the liver changes sequentially during early life in mammals to adapt to the marked changes in nutritional environment. Accordingly, hepatic fatty acid β-oxidation is activated after birth to produce energy from breast milk lipids. However, how it is induced during the neonatal period is poorly understood. Here we show DNA demethylation and increased mRNA expression of the fatty acid β-oxidation genes in the postnatal mouse liver. The DNA demethylation does not occur in the fetal mouse liver under the physiologic condition, suggesting that it is specific to the neonatal period. Analysis of mice deficient in the nuclear receptor peroxisome proliferator-activated receptor α (PPARα) and maternal administration of a PPARα ligand during the gestation and lactation periods reveal that the DNA demethylation is PPARα dependent. We also find that DNA methylation of the fatty acid β-oxidation genes are reduced in the adult human liver relative to the fetal liver. This study represents the first demonstration that the ligand-activated PPARα-dependent DNA demethylation regulates the hepatic fatty acid β-oxidation genes during the neonatal period, thereby highlighting the role of a lipid-sensing nuclear receptor in the gene- and life-stage-specific DNA demethylation of a particular metabolic pathway.

Fibroblast growth factor-21 is expressed in neonatal and pheochromocytoma-induced adult human brown adipose tissue

OBJECTIVE

In rodents, brown (BAT) and white (WAT) adipose tissues are targets and expression sites for fibroblast growth factor-21 (FGF21). In contrast, human WAT expresses negligible levels of FGF21. We examined FGF21 expression in human BAT samples, including the induced BAT found in adult patients with pheochromocytoma, and interscapular and visceral BAT from newborns.

METHODS

The expression of FGF21 and uncoupling protein-1 (UCP1, a brown adipocyte marker), was determined by quantitative real-time-PCR and immunoblotting. The transcript levels of marker genes for developmentally-programmed BAT (zinc-finger-protein of the cerebellum-1, ZIC1) and inducible-BAT (cluster of differentiation-137, CD137) were also determined.

RESULTS

FGF21 and UCP1 are significantly expressed in visceral adipose tissue from pheochromocytoma patients, but not in visceral fat from healthy individuals. In neonates, FGF21 and UCP1 are both expressed in visceral and interscapular fat, and their expression levels show a significant positive correlation. Marker gene expression profiles suggest that inducible BAT is present in visceral fat from pheochromocytoma patients and neonates, whereas developmentally-programmed BAT is present in neonatal interscapular fat.

CONCLUSIONS

Human BAT, but not WAT, expresses FGF21. The expression of FGF21 is especially high in inducible, also called beige/brite, neonatal BAT, but it is also found in the interscapular, developmentally-programmed, BAT of neonates.

Mitochondrial uncoupling protein 2 gene transcript levels are elevated in maturating erythroid cells

Mitochondrial uncoupling protein 2 (UCP2) is abundant in developing monocyte/macrophage cells and may affect hematopoiesis by reducing formation of reactive oxygen species. The aims of this study were to further characterize the involvement of UCP2 in hematopoiesis. In situ hybridization in mouse embryos identified UCP2-positive cells in liver and inside primitive blood vessels from 10.5 days of prenatal development. High UCP2 transcript levels were detected in reticulocytes and other maturating erythroid cells in peripheral blood of mice exposed to hypoxia, and in umbilical cord blood of human neonates and peripheral blood of adults. Our results suggest involvement of UCP2 in erythropoiesis.

Expression of uncoupling protein 3 and GLUT4 gene in skeletal muscle of preterm newborns: possible control by AMP-activated protein kinase

We seek to understand the mechanism for the delayed postnatal switch between glycolytic and oxidative metabolism in preterm newborns. Our previous study [Brauner et al. (Pediatr Res 53: 691-697, 2003)] suggested impaired postnatal recruitment of the gene for mitochondrial uncoupling protein 3 (UCP3) by nutritional lipids in skeletal muscle of neonates delivered before approximately 26 wk of gestation. UCP3 is linked to lipid oxidation and may be involved in the defective development of energy metabolism in skeletal muscles of very preterm newborns. In extension of our previous study, autopsy samples of musculus quadriceps femoris from 40 mostly preterm neonates and 5 fetuses were used for quantification of transcripts for UCP3, GLUT4, and their transcriptional regulator, AMP-activated protein kinase (AMPK). The new analysis confirmed the defect in the recruitment of the UCP3 gene expression by lipids in very preterm neonates. It also suggested involvement of AMPK in the control of expression of both metabolic genes, UCP3 and GLUT4, in the skeletal muscle of the newborns. Experiments on adult C57BL/6J mice confirmed the relationships between the transcripts and supported the involvement of AMPK in the control of UCP3 gene expression.

Intestinal αβ T Cells Differentiate and Rearrange Antigen Receptor Genes In Situ in the Human Infant

Intestinal Ag exposure during neonatal life influences appropriate adult immune responses. To define the mechanisms shaping the T cell repertoire during this period, we examined T cell differentiation and receptor diversity in the intestine of human infants. Developmental phenotypes of intraepithelial and lamina propria intestinal T cells from infants aged 1 day to 2 years were assessed ex vivo by flow cytometry and in situ by triple-fluorescent immunohistochemistry. Gene recombination-specific enzymes were assessed by PCR. TCR beta-chain V region gene diversity was determined by sequencing. Several different early lineage T cell populations were present neonatally: CD3(+)4(-)8(-) T cells were present at birth and numbers decreased during the neonatal period; CD3(+)4(+)8(+) T cells were present in low numbers throughout infancy; and CD3(+)4(+)8(-) or CD3(+)4(-)8(+) T cells increased with age. Very early lineage T cells, CD3(-)2(-)7(+) and CD3(-)2(+)7(+), were present neonatally, but were essentially absent at 1 year. Most lamina propria T cells differentiated rapidly after birth, but maturation of intraepithelial T cells took place over 1 year. Intestinal samples from infants less than 6 mo old contained transcripts of T early alpha and TdT, and 15 of 19 infant samples contained mRNA for RAG-1, some coexpressing RAG-2. TCR beta-chain repertoires were polyclonal in infants. Immature T cells, pre-T cells, and genes involved in T cell recombination were found in the intestine during infancy. T cell differentiation occurs within the neonatal human intestine, and the TCR repertoire of these developing immature T cells is likely to be influenced by luminal Ags. Thus, mucosal T cell responsiveness to environmental Ag is shaped in situ during early life.

Induction of uncoupling protein 3 gene expression in skeletal muscle of preterm newborns

Prematurity is associated with delayed postnatal activation of mitochondrial oxidative phosphorylation and impaired switch from glycolytic to oxidative metabolism. Fatty acids (FA), which represent a major energy substrate in mature muscle cells, are engaged in the postnatal activation of genes of energy metabolism and lipid oxidation. To understand the mechanism activating mitochondria in human newborns, expression of the genes for mitochondrial uncoupling proteins (UCP) was characterized in autopsy samples of skeletal (n = 28) and cardiac (n = 13) muscles of preterm neonates, who mostly died during the first postnatal month, and two aborted fetuses. Transcripts levels for UCP2, UCP3, and also for genes engaged in the transport of FA between cytoplasm and mitochondria were measured using real-time reverse transcriptase PCR. In accordance with studies in mice, our results document postnatal induction of UCP3 gene expression in skeletal muscle, involvement of nutritional FA in the induction, and a role of UCP3 in mitochondrial FA oxidation. They suggest impaired postnatal activation of UCP3 gene in neonates delivered before approximately 26 wk of gestation. Mean levels of the UCP3 transcript in skeletal muscle were by two orders of magnitude higher than in the heart. In contrast to UCP3, the UCP2 gene was active in fetuses, and its expression was not affected by nutrition. Our results support a role of UCP3 in postnatal activation of lipid oxidation in skeletal muscle and suggest the involvement of UCP3 in the delayed activation of mitochondrial energy conversion in very immature preterm neonates.

Brown fat UCP1 is specifically expressed in uterine longitudinal smooth muscle cells

Until now, uncoupling protein 1 (UCP1) was considered as unique to brown adipocytes. It supports a highly regulated uncoupling of oxidative phosphorylation that is associated with diet as well as with non-shivering thermogenesis. Here we report that UCP1 is not specific to brown adipocytes and can be expressed in longitudinal smooth muscle layers. In the uterus, this conclusion was drawn from different convergent data. A specific antibody against mouse UCP1 revealed, in mitochondrial fractions, a protein with the same molecular weight as brown fat UCP1. Sensitive and specific reverse transcriptase-polymerase chain reaction detected a mRNA whose sequence was totally homologous to that of brown fat UCP1 mRNA. Antibody against UCP1 as well as a UCP1 antisense probe specifically stained uterine longitudinal smooth muscles. UCP1 was also expressed in longitudinal smooth muscle of digestive and male reproductive tracts but was never expressed in other types of smooth muscle, including those of arterial vessels. In uterine tract, UCP1 content was increased after cold exposure or beta-adrenergic agonist treatment. It was also up-regulated during the postovulatory period after sexual cycle synchronization. Its content transiently increased during gestation and decreased markedly after birth. These regulations strongly argue about a role for UCP1 in thermogenesis as well as in relaxation of longitudinal smooth muscle layers.