Isozyme patterns in erythrocytes from human fetuses

The developmental transcriptome of the human heart

The human heart develops through complex mechanisms producing morphological and functional changes during gestation. We have recently demonstrated using diffusion tensor MRI that over the relatively short space of 40 days, between 100-140 days gestational age, the ventricular myocardium transforms from a disorganised tissue to the ordered structure characteristic of mature cardiac tissue. However, the genetic basis underpinning this maturation is unclear. Herein, we have used RNA-Seq to establish the developmentally-regulated transcriptome of gene expression in the developing human heart across three gestational ages in the first and second trimester. By comparing 9 weeks gestational age (WGA) with 12 WGA, we find 288 genes show significant differential expression. 305 genes were significantly altered comparing 12 and 16 WGA, and 806 genes differentially expressed between 9 and 16 WGA. Network analysis was used to identify genetic interactions, node properties and gene ontology categories. In summary, we present a comprehensive transcriptomic analysis of human heart development during early gestation, and identify differentially expressed genes during heart development between 9 and 16 weeks, overlapping the first and early second trimester.

Role of oxidative phosphorylation and ATP release in mediating birth-related pulmonary vasodilation in fetal lambs

We investigated the hypothesis that birth-related pulmonary vasodilation is mediated in part by an increase in oxidative phosphorylation and ATP release in response to oxygen exposure at birth. Studies were done in fetal lambs to evaluate the independent effects of oxygen, lung distension alone, or lung distension accompanied by oxygenation and shear stress on fetal pulmonary blood flow and resistance and plasma ATP levels in the pulmonary artery. The effect of each intervention was evaluated in lambs assigned to one of three groups: control or pretreatment with 2,4-dinitrophenol or antimycin-A, inhibitors of oxidative phosphorylation. Exposure to oxygen alone or with lung distension was associated with increases in plasma ATP levels and pulmonary blood flow and a decrease in pulmonary vascular resistance. Plasma ATP levels did not change during lung distension alone. 2,4-Dinitrophenol and antimycin-A attenuated the pulmonary vasodilator response to oxygen but did not attenuate the response to lung distension alone. An increase in oxidative phosphorylation and ATP release during oxygen exposure may contribute to birth-related pulmonary vasodilation in fetal lambs.

Metabolic gene expression in fetal and failing human heart

BACKGROUND

Previous studies suggest that the failing heart reactivates fetal genes and reverts to a fetal pattern of energy substrate metabolism. We tested this hypothesis by examining metabolic gene expression profiles in the fetal, nonfailing, and failing human heart.

METHODS AND RESULTS

Human left ventricular tissue (apex) was obtained from 9 fetal, 10 nonfailing, and 10 failing adult hearts. Using quantitative reverse transcription-polymerase chain reaction, we measured transcript levels of atrial natriuretic factor, myosin heavy chain-alpha and -beta, and 13 key regulators of energy substrate metabolism, of which 3 are considered "adult" isoforms (GLUT4, mGS, mCPT-I) and 3 are considered "fetal" isoforms (GLUT1, lGS, and lCPT-I), primarily through previous studies in rodent models. Compared with the nonfailing adult heart, steady-state mRNA levels of atrial natriuretic factor were increased in both the fetal and the failing heart. The 2 myosin heavy chain isoforms showed the highest expression level in the nonfailing heart. Transcript levels of most of the metabolic genes were higher in the nonfailing heart than the fetal heart. Adult isogenes predominated in all groups and always showed a greater induction than the fetal isogenes in the nonfailing heart compared with the fetal heart. In the failing heart, the expression of metabolic genes decreased to the same levels as in the fetal heart.

CONCLUSIONS

In the human heart, metabolic genes exist as constitutive and inducible forms. The failing adult heart reverts to a fetal metabolic gene profile by downregulating adult gene transcripts rather than by upregulating fetal genes.

Characteristics of hexokinase, pyruvate kinase, and glucose-6-phosphate dehydrogenase during adult and neonatal reticulocyte maturation

Erythrocytes from adults and newborn infants (at term and premature) were separated by Percoll density gradient centrifugation into four fractions of increasing density. Glycolytic enzymes, especially the age-dependent ones, hexokinase (EC 2.7.1.1, HK), pyruvate kinase (EC 2.7.1.40, PK), and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6PD) were studied during reticulocyte maturation and further red cell senescence. Analysis of the fraction with lowest density showed an almost linear and steep decline of HK, PK, and G6PD activity with a decreasing number of reticulocytes. In the next three fractions of increasing density, the activity decline was far less. These data are therefore illustrative for a biphasic activity decay pattern of HK, PK, and G6PD during both adult and neonatal red cell aging. The strong decline in HK activity could not be ascribed to the disappearance of a particulate (mitochondrial) bound fraction of the enzyme during reticulocyte maturation. All hexokinase activity in human reticulocytes was found to be cytosolic in contrast with rabbit reticulocytes in which 70% of HK activity was particulate.

Fetal haemoglobin synthesis following fetal liver transplantation in man

Transplantation of haematopoietic tissue from the fetus to the adult is of considerable clinical and theoretical interest. In particular it could help to understand whether the haemoglobin switch is under the influence of environmental factors or inherently programmed in the haemopoietic cell population. In the present study we have monitored haemoglobin synthesis following fetal liver transplantation (FLT) in a patient with acute leukaemia after intensive chemoradiotherapy. 28 days following FLT, the haemoglobin synthesis showed a predominantly fetal haemoglobin pattern, as determined by globin chain synthesis of bone marrow cells and by the peroxidase anti-peroxidase (PAP) method applied to bone marrow sections treated with anti-fetal haemoglobin antibodies. These findings demonstrate that, in man, fetal haemopoietic cells, transplanted into an adult environment, do not immediately switch to the production of adult haemoglobin.

Alterations in phosphofructokinase isoenzymes during early human development. Establishment of adult organ-specific patterns

Human 6-phosphofructokinase (EC 2.7.1.11) exists in tetrameric isoenzymic forms composed of muscle (M), liver (L) and platelet (P) subunits, which are under separate genetic control. In the adult, the proportion of these subunits in different organs reflects the relative activity of glycolysis versus gluconeogenesis. To elucidate the developmental basis for the observed distribution, we investigated the isoenzymic transitions of phosphofructokinase in human foetuses (12-40 weeks' gestation) by using high-resolution chromatography and monoclonal antibodies. We studied skeletal muscle, heart, liver and brain because these organs show very different glycolytic fluxes and isoenzymic patterns in adult individuals. Our results demonstrate that there is no unique 'foetal' form of phosphofructokinase in humans, but all three loci are variably expressed in all foetal organs during early gestation. As development proceeds, muscle and liver isoenzyme patterns show dramatic changes, with disappearance of P and L subunits in muscle and transient reappearance of M and P subunits in liver; in contrast, phosphofructokinase isoenzymes change little in brain and heart. Most changes occur at mid-gestation and near term, and adult isoenzyme patterns are expressed at birth, indicating that organ differentiation is complete. These studies show that phosphofructokinase undergoes changes of isoenzyme patterns similar to, but not identical with, those of other multilocus isoenzyme systems of glycolysis. The observed changes probably reflect changing patterns of gene expression, with repression of some loci and activation of others.

Characteristics of enzymes of erythrocytes from newborn infants and adults: activity, thermostability, and electrophoretic profile as a function of cell age

THe level of enzyme activity, the enzyme thermostability profile, and the isozyme electrophoretic pattern were determined in young and old erythrocytes from newborn infants and adults and in samples from adult individuals with increased reticulocyte counts. Cord blood samples had higher levels of enzymatic activity for 12 of the 14 enzymes measured, adenylate kinase and phosphoglucomutase being the exceptions. The largest differences in activity between newborns and adults were for glutamic oxaloacetic transaminase, hexokinase, glucose 6-phosphate dehydrogenase, and glutathione reductase, while glutamic oxaloacetic transaminase and pyruvate kinase showed the largest differences between young and old cells. The levels of activity of glutathione reductase, adenylate kinase, phosphoglucomutase, lactate dehydrogenase, phosphoglycerokinase, and glucose phosphate isomerase in cord blood samples suggest the regulation of expression of these enzymes is different in fetal erythrocytes than in erythrocytes from an adult. Differences in the thermostability profile of enzymes from cells from different sources and/or of different ages were noted for 5 of 9 enzymes. No unique electrophoretically identifiable fetal isozymes were observed, although differences in isozyme distribution and staining intensity associated with cell source and/or cell age were noted for many of the 23 enzymes examined. Many of these differences in enzyme characteristics have the potential to be confused with genetic alterations in enzyme structure and function.