Glycogen reserves in organs of human foetuses in the first half of pregnancy

Fetoplacental oxygen homeostasis in pregnancies with maternal diabetes mellitus and obesity

Despite improvements in clinical management, pregnancies complicated by pre-existing diabetes mellitus, gestational diabetes mellitus or obesity carry substantial risks for parent and offspring. Some of the endocrine and metabolic changes in parent and fetus in diabetes mellitus and obesity lead to fetal oxygen deficit, mostly due to insulin-induced accelerated fetal metabolism. The human fetus deals with reduced oxygenation through a wide range of adaptive responses that act at various levels in the placenta as well as the fetus. These responses ensure adequate oxygen delivery to the fetus, increase the oxygen transport capacity of fetal blood and redistribute oxygen-rich blood to vital organs such as the brain and heart. The liver has a central role in adapting to reduced oxygenation by increasing its oxygen extraction and stimulating erythropoietin synthesis to increase haematocrit. The type of adaptive response depends on the onset and duration of hypoxia and the severity of the metabolic disturbance. In pregnancies characterized by diabetes mellitus or obesity, these adaptive systems come under additional strain owing to the increased maternal supply of glucose and resultant fetal hyperinsulinaemia, both of which stimulate oxidative metabolism. In the rare situation that the adaptive responses are overwhelmed, stillbirth can ensue.

Beyond energy storage: roles of glycogen metabolism in health and disease

Beyond storing and supplying energy in the liver and muscles, glycogen also plays critical roles in cell differentiation, signaling, redox regulation, and stemness under various physiological and pathophysiological conditions. Such versatile functions have been revealed by various forms of glycogen storage diseases. Here, we outline the source of carbon flux in glycogen metabolism and discuss how glycogen metabolism guides CD8⁺ T-cell memory formation and maintenance. Likewise, we review how this affects macrophage polarization and inflammatory responses. Furthermore, we dissect how glycogen metabolism supports tumor development by promoting tumor-repopulating cell growth in hypoxic tumor microenvironments. This review highlights the essential role of the gluconeogenesis-glycogenesis-glycogenolysis-PPP metabolic chain in redox homeostasis, thus providing insights into potential therapeutic strategies against major chronic diseases including cancer.

Metabolic adaptation at birth

After birth, the neonate must make a transition from the assured continuous transplacental supply of glucose to a variable fat-based fuel economy. The normal infant born at term accomplishes this transition through a series of well-coordinated metabolic and hormonal adaptive changes. The patterns of adaptation in the preterm infant and the baby born after intrauterine growth restriction are, however, different to that of a full-term neonate, with the risk for former groups that there will be impaired counter-regulatory ketogenesis. There is much less precise linkage of neonatal insulin secretion to prevailing blood glucose concentrations. These patterns of metabolic adaptation are further influenced by feeding practices.

Histocytochemical and immunohistochemical studies related to the role of glycogen in human developing digestive organs

To elucidate the role of glycogen in the epithelium of developing digestive organs, we investigated the appearance of glycogen and glycogen phosphorylase (GP) in these organs. We studied 64 externally normal human embryos at Carnegie stages 13-23 (5.1-28.0 mm in crown-rump length, 4-8 weeks of gestation) by histocytochemical staining for glycogen and immunohistochemical staining with antibodies against two isoenzymes of GP: brain-type (BGP) and muscle-brain-type (MBGP) GP. At stage 13, glycogen appeared in the epithelium of the digestive tract and the parenchyma of the pancreas. As development advanced, glycogen granules increased in number and size in these tissues, and they became evenly distributed in the epithelium of the digestive tract as either single particles or aggregates, as deduced by electron microscopy at late embryonic stages. Immunoreactivity specific both for BGP and for MBGP was detected in the digestive tract and the pancreas from stage 13. As development advanced, both BGP- and MBGP-immunoreactive cells increased in number and in immunoreactivity, and the number of MBGP-immunoreactive cells became larger than that of BGP-immunoreactive cells. By contrast, in hepatic cells, which serve as a major storage site for glycogen in adults, glycogen was detected only from stage 20, in smaller amounts, without formation of aggregates, and no immunoreactivity specific for BGP or MBGP was apparent throughout the embryonic stages examined. Thus, in the epithelium of the digestive tract and the parenchyma of the pancreas, but not in hepatic cells, the appearance and localization of GP coincided almost exactly with that of glycogen. These observations suggest that glycogen in the epithelium of the digestive tract and the parenchyma of the pancreas has not only been synthesized but also degraded from an early embryonic period and may, thus, be related to active cellular metabolism that is specific for embryonic development, including proliferation of the epithelium and interactions between epithelium and mesenchyme.

High alpha-amylase activity in the syncytiotrophoblastic cells of first-trimester human placentas

The syncytiotrophoblastic brush border of the human placenta forms the maternal-fetal interface and is an important determinant of placental function. Electron micrographs of fresh brush border preparations isolated from first-trimester human placentas showed membrane vesicles, open-ended microvilli, and numerous glycogen particles. Analysis of the microvillar membranes for several plasma and intracellular membrane markers showed a high degree of purification, comparable to the results reported for the isolation of microvilli from full-term human placentas. The microvillar preparations from first-trimester placentas, however, also contained the enzymes necessary to synthesize and degrade glycogen. The degradation resulted in the accumulation of maltotriose and maltotetraose, apparently due to the action of a liver-type alpha-amylase. The occurrence of this enzyme and the enzymes for synthesizing glycogen in this brush border fraction is probably associated with the necessity for an extremely active glucose transport and liver-like storage system within the fetal tissue at this fetal-maternal membrane interface.

Accumulation of malto-oligosaccharides in the syncytiotrophoblastic cells of first-trimester human placentas

A cell-surface microvillar fraction that was isolated from the syncytiotrophoblastic cells of first-trimester human placentas was found to contain very high concentrations (890 +/- 32 microgram of hexose/mg of protein) of a class of low-molecular-weight oligosaccharides that were comprised entirely of glucose. T.l.c. and gel filtration showed that the saccharides contained from one to six glucose residues. The structures of the most prominent members of the series, a tetra- and a tri-saccharide, were determined. The anomeric configuration of the glucose residues was alpha, and methylation linkage analysis gave terminal and 4-linked hexose residues. These malto-oligosaccharides contained one reducing terminus per molecule, indicating that they were free and not bound to other structural elements of the cells. Within the placenta they appeared to be concentrated in the first-trimester trophoblastic cells, since crude membrane and particulate fractions isolated from either term trophoblastic cells or cultured placental fibroblasts did not contain detectable amounts of glucose oligomers. This series of oligosaccharides was similar to the products that are formed when glycogen is degraded by alpha-amylase in liver homogenates and may be indicative of a similar, highly active enzymic reaction closely associated with the brush border of the syncytiotrophoblastic cells of the first-trimester human placenta. Although the role of these oligosaccharides remains obscure they are probably involved in foetal metabolism.

Placental glycogen

The quantity and distribution of glycogen has been studied in 86 placentae from the last trimester of pregnancy and 8 of 8 to 16 weeks gestational age. In the first trimester glycogen concentrations were high, between 4-5 to 6-5 mg/g of blood-free tissue, but from about 12 weeks to term the concentrations were within a narrow range around 1-5 mg/g. The level did not deviate appreciably from normal in a range of clinical conditions: diabetes, intrauterine growth retardation, pre-eclampsia or acute fetal distress, and was unaffected by the length of labour and whether or not the mother had been given an infusion of dextrose. Nor was it affected by a wide range of glucose concentrations in the maternal and fetal plasma and in the placental tissue itself or by insulin concentrations in either circulation. After the first few weeks of pregnancy glycogen in the placenta was shown to be restricted to the vicinity of major fetal blood vessels. Here it may be presumed to act as an energy reserve for vasomotor activity. All the evidence suggests that any importance placental glycogen may have is likely to be local, in relation to the placental vessels; a more general role, as an emergency energy source for the fetus, seems unlikely.