Origin and fate of fetuin-containing neurons in the developing neocortex of the fetal sheep

Fetuin-A protein distribution in mature inflamed and ischemic brain tissue

Background

The liver-derived plasma protein fetuin-A is strongly expressed during fetal life, hence its name. Fetuin-A protein is normally present in most fetal organs and tissues, including brain tissue. Fetuin-A was neuroprotective in animal models of cerebral ischemia and lethal chronic inflammation, suggesting a role beyond the neonatal period. Little is known, however, on the presence of fetuin-A in mature human brain tissue under different physiological and pathological conditions.

Methods

We studied by immunohistochemistry (IHC) the distribution of fetuin-A protein in mature human brain autopsy tissues from patients without neurological disease, patients with inflammatory brain disorders, and patients with ischemic brain lesions. To identify fetuin-A-positive cells in these tissues we co-localized fetuin-A with GFAP (astrocytes) and CD68 (macrophages, activated microglia).

Results and discussion

Unlike previous reports, we detected fetuin-A protein also in mature human brain as would be expected from an abundant plasma protein also present in cerebrospinal fluid. Fetuin-A immunoreactivity was increased in ischemic white matter and decreased in inflamed cerebellar tissue. Fetuin-A immunostaining was predominantly associated with neurons and astrocytes. Unlike the developing brain, the adult brain lacked fetuin-A immunostaining in CD68-positive microglia. Our findings suggest a role for fetuin-A in tissue remodeling of neonatal brain, which becomes obsolete in the adult brain, but is re-activated in damaged brain tissue. To further assess the role of fetuin-A in the mature brain, animal models involving ischemia and inflammation need to be studied.

Biomarkers of therapeutic response in multiple sclerosis: current status

Multiple sclerosis (MS) is an autoimmune disease of unknown cause, in which chronic inflammation drives multifocal demyelination of axons in both white and gray matter in the CNS. The pathological course of the disease is heterogeneous and involves an early, predominantly inflammatory demyelinating disease phase of relapsing-remitting MS (RRMS), which, over a variable period of time, evolves into a progressively degenerative stage associated with axonal loss and scar formation, causing physical and cognitive disability. For patients with RRMS, there is a growing arsenal of disease-modifying agents (DMAs), with varying degrees of efficacy, as defined by reduced relapse rates, improved magnetic resonance imaging outcomes, and preservation of neurological function. Establishment of personalized treatment plans remains one of the biggest challenges in therapeutic decision-making in MS because the disease prognosis and individual therapeutic outcomes are extremely difficult to predict. Current research is aimed at discovery and validation of biomarkers that reliably measure disease progression and effective therapeutic intervention. Individual biomarker candidates with evident clinical utility are highlighted in this review and include neutralizing autoantibodies against DMAs, fetuin-A, osteopontin, isoprostanes, chemokine (C-X-C motif) ligand 13 (CXCL13), neurofilament light and heavy, and chitinase 3-like protein. In addition, application of more advanced screening technologies has opened up new categories of biomarkers that move beyond detection of individual soluble proteins, including gene expression and autoantibody arrays, microRNAs, and circulating microvesicles/exosomes. Development of clinically useful biomarkers in MS will not only shape the practice of personalized medicine but will also serve as surrogate markers to enable investigation of innovative treatments within clinical trials that are less costly, are of shorter duration, and have more certainty of outcomes.

Fetuin A concentration in the second trimester amniotic fluid of fetuses with trisomy 21 appears to be lower: phenotypic considerations

OBJECTIVE

We investigated whether the concentration of the glycoprotein fetuin A is altered in the second trimester amniotic fluid of trisomy 21 pregnancies compared with euploid pregnancies.

METHODS

25 pregnancies with an extra chromosome 21 were matched for maternal and gestational age with 25 pregnancies with normal karyotype. Levels of fetuin A in amniotic fluid were measured by a commercially available enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

The median concentration of fetuin A in amniotic fluid of trisomy 21 pregnancies (5.3 ng/ml) was statistically significantly lower (P value = 0.008) compared with that in euploid pregnancies (6.8 ng/mL).

CONCLUSION

Lower levels of fetuin A in trisomy 21 may indicate an association with altered metabolic pathways in this early stage that could potentially be associated with features of the syndrome, such as growth restriction or impaired osteogenesis.

Fetuin in the developing neocortex of the rat: distribution and origin

Immunocytochemical distribution of the fetal protein fetuin in the neocortex of developing rat brain and the presence of its mRNA, as detected by using reverse transcriptase-polymerase chain reaction analysis, was studied in fetuses at embryonic day 15 (E15) through E22, in neonates at postnatal day 0 (P0) through P20, and in adults. Quantitative estimates of fetuin in cerebrospinal fluid (CSF) and plasma were obtained over the same period. Exogenous (bovine) fetuin injected intraperitoneally into fetal and postnatal rats was used to study the uptake of fetuin into CSF and brain and its distribution compared with endogenous fetuin; bovine albumin was used as a control. Fetuin was identified immunocytochemically in the cortical plate and subplate cells of the developing neocortex. In the rat fetus, fetuin first was apparent at E17, mainly in cell processes, but a few subplate cells also were positive. By E18, there was strong staining in subplate neurons and in inner cells of the cortical plate. At E21, these inner cells of the cortical plate were beginning to differentiate into layer VI neurons, many of which were positive for fetuin. By P0-P1, more layer VI neurons and some layer V neurons had become positive for fetuin. Fetuin immunoreactivity generally was weaker at P1, and, by P2-P3, it had disappeared from all of the layers of the developing neocortex. Bovine fetuin (but not albumin), probably taken up through CSF over the neocortical dorsal surface, had a cytoplasmic distribution; endogenous rat fetuin was both cytoplasmic and membrane bound. Thus, much of this fetuin can be accounted for by uptake, although the presence of fetuin mRNA indicates that in situ synthesis may also contribute.

Fetuin in neurons of the retina and cerebellum during fetal and postnatal development of the rat

Although long known to be a liver-derived fetal plasma glycoprotein, fetuin has more recently been shown to be present in sub-populations of neurons in the developing nervous system of a number of mammalian species. We have extended these observations to examine the fetuin immunoreactivity (IR) in developing rat retina and cerebellum. Fetuin-IR was first seen in the retina on embryonic day (E)19 in a sub-population of cells in the retinal ganglion cell layer and a small proportion of cells in the neuroblastic layer. The proportion of cells in the ganglion layer exhibiting fetuin-IR increased until postnatal day (P)10 when all cells in this layer were strongly immunoreactive. From P14 onwards fetuin-IR was absent or very weak and restricted to a small proportion of ganglion cells. In the developing cerebellum, the outer and inner granule cell layers, the deep nuclei and cells in the sub-cortical white matter exhibited fetuin-IR from E19 to P10. There was little fetuin-IR in the cerebellum at ages P14 and older, and Purkinje cells did not exhibit fetuin-IR at any time. The results show that fetuin appears in many neurons in the retina and cerebellum that are differentiating during the period from E19 to P10. The concentration of fetuin in cerebrospinal fluid is at its highest in this same period which suggests that some sub-populations of neurons could obtain fetuin from extracellular fluid during this period; however, the lack of fetuin-IR in other neuronal populations suggests that fetuin uptake is not a general property of developing neurons.

The vulnerability of the fetal sheep brain to hypoxemia at mid-gestation

Our aim was to test the hypothesis that a brief episode of hypoxemia near mid-gestation in fetal sheep will result in damage to the fetal brain with the extent and type of damage in any particular region being related to the developmental processes occurring at the time of the insult. Hypoxemia was induced, sufficient to reduce arterial O2 content by approximately 50%, by restricting utero-placental blood flow in 14 chronically catheterised fetuses for 6 h or 12 h at 84 days of gestation (term 145-8 days). Age-matched fetuses (n = 14; 4 operated and 10 unoperated) were used as controls. Fetuses were killed 7 days after being exposed to hypoxemia, and brains removed for histological analysis at the light and ultrastructural levels. Body weights of hypoxemic fetuses did not differ significantly from controls but brain weights were significantly reduced both in absolute terms and when expressed in relation to body weight (P < 0.05). Most fetuses exposed to hypoxemia sustained no gross brain damage. However, in one hypoxemic fetus from a multiple pregnancy there was extensive leucomalacia in the cortical white matter; mild focal damage was seen in another 8 hypoxemic fetuses. In the cerebral cortex (frontal lobe) the surface folding index was significantly reduced (P < 0.05) in hypoxemic fetuses compared to controls suggesting that gyral formation had been delayed. In these fetuses there were also degenerating neurons in the deeper cortical layers. In the hippocampus of hypoxemic fetuses there was a delay (P < 0.05), compared to controls, in the migration of cells from the germinal layer to the pyramidal layer in the CA1 region, and decreases (P < 0.05) in the density (area1) of neurons in the pyramidal layer and in the width of stratum oriens. In the cerebellum of hypoxemic fetuses there was a decrease (P < 0.05), compared to controls, in the density (area1) of mitotic bodies in the external granule cell layer. However, there were no significant differences in the number of pyknotic cells in this layer, in the density of Purkinje cells, in their somal area, or in the width of the external granule cell or molecular layers. There was an increase (P < 0.05) in the proportion of the brain parenchyma occupied by blood vessels in both the hippocampus and cortex of hypoxemic fetuses compared to controls. This study has shown that an hypoxemic insult near mid-gestation can result, one week later, in white matter damage and in neuronal death in the hippocampus and to a lesser extent in the cerebral cortex and cerebellum. It can also retard neuronal migration and the growth of neural processes in the hippocampus where development is well established at this age. Such brain damage could result in less than optimal neuronal connectivity and could affect function postnatally.

Fetuin expression in the dorsal root ganglia and trigeminal ganglia of perinatal rats

Fetuin, a fetal plasma glycoprotein, has been shown previously to be present in sub-populations of neurons in the developing central and peripheral nervous system. To gain a more complete description of the time course of the appearance of fetuin during neurogenesis we have examined fetuin immunoreactivity, and the presence of fetuin mRNA, in the developing rat trigeminal and dorsal root ganglia. Fetuin immunoreactivity and its mRNA were first seen at embryonic day 15 in the trigeminal ganglia, and at embryonic day 16 in dorsal root ganglia. In both trigeminal and dorsal root ganglion, fetuin appeared to be present up until around the time of birth, and then again between postnatal days 3 and 16. The results suggest that fetuin first appears at around the time that ganglion cell axons reach their central targets, which is also approximately when the cell-death period begins. The proportion of ganglion neurons that were fetuin immunoreactive at different ages was inversely related to the amount of cell death that is known to occur in these populations, thus it seems that fetuin is more likely to be associated not with dying cells, but with those that survive the cell-death period.

Albumin transfer across the choroid plexus of South American opossum (Monodelphis domestica)

1. Blood-cerebrospinal fluid (CSF) transfer of various exogenous albumins has been investigated in developing Monodelphis domestica (South American grey short-tailed opossum) and compared with the steady-state CSF: plasma ratios for endogenous (Monodelphis) albumin. Ratios for Monodelphis albumin and human albumin were similar and were the highest at postnatal day 5 (P5) (48.2 +/- 4.4 and 40.6 +/- 4.5%, respectively). The ratio for bovine albumin was similar to the steady-state ratio for Monodelphis albumin at P7-8 but became consistently lower than the Monodelphis albumin ratio at all other ages until P32-36 when all albumins tested attained a similar low ratio. The CSF:plasma ratio of chemically modified (succinylated) bovine albumin was always significantly lower than that of other albumins, except at the oldest age examined (P32-36). 2. Immunocytochemistry showed that within the brain, albumin was confined to the lumen and endothelial cells of blood vessels. In the choroid plexus only a small proportion (0.2-1.7% of the total cell number) of epithelial cells was positive for albumin, both endogenous and exogenous, at all ages studied (except the 3rd ventricle where cells were only positive from P8). The CSF was strongly positive for all albumins. The peak proportion of positive cells and of albumin concentrations in CSF occurred at P8. These findings suggest that the primary route for penetration of albumin into CSF is directly across the choroid plexus rather than via the brain. 3. Double-labelling immunocytochemistry revealed that the same epithelial cells contained both endogenous (Monodelphis) and exogenous (human) albumin. In contrast, for succinylated albumin, at P7 only about 35% (lateral ventricle) and 50% (4th ventricle) of Monodelphis albumin-positive cells were also positive for succinylated albumin, but by P30 this proportion increased to 90% at both sites. 4. Thus the developing choroid plexus distinguishes between different albumins. Chemical modification of albumin (succinylation) disrupts this mechanism. It is proposed that in older animals (P32-36) all of the albumin in the CSF is derived from plasma by diffusion (as in adult animals). At earlier stages of development, a proportion of the albumin in CSF also appears to be transferred from the plasma by diffusion with an additional component transferred by a mechanism that can distinguish between different species of albumin. The main route of entry of albumin to CSF seems likely to be via the choroid plexus epithelial cells.

Expression and distribution of fetuin in the developing sheep fetus

Tissue distribution and developmental expression of fetuin were studied in the sheep fetus from embryonic day (E) 30 to adult (gestational period is 150 days). The presence of fetuin was demonstrated immunocytochemically using anti-fetuin antibodies; in situ hybridisation using short anti-sense oligonucleotide probes labelled with digoxigenin was used to study the ability of the developing tissue to synthesise fetuin, and reverse transcription-polymerase chain reaction (RT-PCR) was used to estimate the level of fetuin mRNA in selected tissues. Tissue distribution of fetuin was widespread in the younger fetuses (E30 to E40). The most prominent presence due to in situ synthesis was demonstrated in the liver, central nervous system (CNS) including anterior horn cells, dorsal root ganglia and in skeletal muscle cells. Other developing tissues and organs that showed evidence of fetuin synthesis and presence of the protein included mesenchyme, kidney, adrenal, developing bone, gut, lung and heart. In the immature liver (E30-40) there was a strong signal for fetuin mRNA in hepatocytes and also in numerous haemopoietic cells; the proportion of these latter cells that was positive for fetuin mRNA increased between E30 and E40. Only some hepatocytes and a proportion of the haemopoietic stem cells were immunoreactive for fetuin itself at E30-40; immunoreactive hepatocytes were more frequently observed in the more mature outer regions of the developing liver. Lung and gut contained scattered fetuin-positive epithelial cells, especially at E30; a weak fetuin mRNA signal could be detected above background in many of these cells up to E40, but not at E60-E115 or in the adult. Particularly at E30 to E40, mesenchymal tissue both within organs such as the gut and lung and around forming bone and skeletal muscle contained cells that were positive for fetuin mRNA. Mesenchyme at these ages was also very strongly stained for fetuin protein, much of which may reflect fetuin in tissue extracellular spaces and be derived from the high concentration in plasma. By E80 fetuin mRNA was mainly present in the liver and the CNS; staining of the muscle tissue was becoming less pronounced. However in developing bone tissue, staining of chondrocytes for fetuin mRNA was still prominent in older (E80) fetuses; there was also fetuin protein staining of chondrocytes at the growing surfaces of bones and in bone marrow at this age. In the adult, weak immunocytochemical staining for fetuin itself was present in hepatocytes, but the mRNA signal was barely above the threshold limit of detection.(ABSTRACT TRUNCATED AT 400 WORDS)

GRASP: a novel heparin-binding serum glycoprotein that mediates oligodendrocyte-substratum adhesion

Cell-substratum adhesion plays a crucial part in the cascade of events that control growth or turn on and consummate a differentiation program. We are investigating the molecular basis of oligodendrocyte (OLG) cytodifferentiation, employing pure cultures of OLGs isolated from postmyelination brains. We have shown that such OLGs will regenerate in vitro and reenact the ontogenic development of myelin, but to do so they need a signal. Adherence to a polylysine surface in the presence of 20% horse serum generates such a signal. Among the events that are turned on upon OLG adhesion is the phosphorylation of myelin basic protein; no such phosphorylation takes place in the non-adhered cell. We postulated that horse serum provides an adhesion molecule. Laminin, fibronectin, collagen and native vitronectin failed to replace horse serum. Hence, we set out to fractionate horse serum by screening with an adhesion assay. We report here the identification, purification and partial characterization of a novel, heparin-binding horse serum glycoprotein that we have termed Glycine-Rich Adhesion Serum Protein--GRASP--to stress the fact that this protein has a high content of glycine and functions, in vitro, as an adhesion molecule for OLGs. There is 61% similarity at the N-terminus between GRASP and histidine-rich glycoprotein precursor (HRGP), an alpha 2-glycoprotein from human plasma. However, our data suggest that GRASP is not the horse serum homolog of HRGP. First, the two Gps are functionally distinct: HRGP does not promote the adhesion of OLGs. Second, the amino acid compositions differ significantly, e.g., GRASP is not histidine- but rather glycine-rich. Third, the region of sequence similarity between GRASP and HRGP is conserved throughout the cystatin superfamily. Fourth, anti-Gp55 polyclonal Abs recognize a similar set of polypeptides--save for slight differences in M(r)-in human serum as in horse serum, indicating that HRGP and GRASP are two distinct but related proteins and are both present in human and horse sera. GRASP is a dimer trimer of seemingly identical subunits of M(r) approximately 55,000 ; the native protein has an M(r) x 10(-3) approximately 120-140, of which 24-27% is contributed by carbohydrate. Using GRASP as a substratum allows the growth of OLGs in serum-free medium. GRASP is as good an effector of myelin basic protein phosphorylation as 20% horse serum. We conjecture that the mechanism of GRASP function features: 1) exposure of a cryptic sequence--after a change in conformation induced upon binding to polylysine--with affinity for an OLG signal-transducing receptor; and 2) interaction of its heparin-binding domain with OLG surface heparin sulfate proteoglycans and/or the aforementioned receptor.

Brain growth and neocortical development in the opossum

General brain growth and differentiation of the neocortex have been studied in the marsupial, Didelphis virginiana from the 10.5 day embryo through adulthood. Didelphis is born after a short gestation period of about 12.5 days, at a time when the telencephalic wall consists only of two layers and is considered to be at an embryonic stage of development. The cortical plate does not appear until late in the first postnatal week, thus neocortical development is totally a postnatal phenomenon in Didelphis as has been shown in other marsupial species examined to date. The general pattern of development and the establishment of the six-layered adult neocortex in Didelphis is similar to that described in eutherian mammals. Signs of cortical lamination can be seen as early as postnatal day 35 and the cytoarchitecture of a typical mammalian neocortex is well defined by postnatal day 60 in Didelphis prior to the onset of weaning.

Neuropathology of the near-term and midgestation ovine fetal brain after sustained in utero hypoxemia

OBJECTIVE

The neuropathologic mechanisms of the ovine fetal brain in response to several hours of sustained hypoxemia with variable degrees of metabolic acidemia was investigated in both the preterm and near-term ovine fetus.

STUDY DESIGN

Three groups of fetuses were studied in each of the near-term and midgestation groups: a hypoxic group, a control group, and an uninstrumented control group. Histopathologic studies were performed after a 40-hour recovery period after experimentation.

RESULTS

Pathologic findings consisted of predominately white matter damage with some adjacent cortical necrosis but no selective neuronal injury. In the near-term group the hypoxia group fetuses demonstrated significantly higher white matter injury scores than did control group fetuses (p < 0.05). Periventricular white matter injury was the predominant pattern seen in the midgestation group.

CONCLUSIONS

In spite of normalization of biophysical and biochemical parameters after hypoxemia both midgestation and near-term fetuses sustained pathologic changes. Presence or extent of injury did not correlate with the degree of hypoxemia or metabolic acidosis achieved.

An immunohistochemical study of the fetal sheep neocortex and cerebellum with antibodies against nervous system-specific proteins

The topographical distribution of glial fibrillary acidic protein (GFAP), vimentin, neuron-specific enolase (NSE) and neurofilament (NF) proteins in the developing neocortex and cerebellum of sheep fetuses of different gestational ages (60-149 days) was described. For comparison, brain tissues from a lamb and two adult sheep were included in this study. In the walls of the developing cerebral hemispheres GFAP- and vimentin-immunoreactive radial glial fibres were demonstrated. From 80 days of gestation onwards a continuous decrease of radial fibres occurred which was accompanied by an increase of GFAP-positive mature astrocytes. In Bergmann glial fibres of the cerebellum, which are the equivalent of radial fibres in the telencephalon, both GFAP and vimentin were detectable in fetuses and adult sheep. With polyclonal antibodies against NSE and NF proteins (NF-M, NF-H) prominent staining of neuronal fibre tracts was seen in fetuses of all gestational ages studied. In the neocortex, staining for NF-L did not occur before day 80 of gestation. With monoclonal antibodies against phosphorylated NF-H (clone SMI 31), however, reaction of neocortical fibre tracts was first seen at 85 days of gestation, and cytoplasmic staining of single neocortical neurons was first found in a 149-day-old fetus. Several fixatives and proteolytic pretreatment were examined for their effects on preservation and re-establishment of marker protein expression, respectively. GFAP and vimentin in radial glial fibres were not demonstrable without pretrypsinization of tissue sections. The most intensive staining of NF proteins with polyclonal antisera was seen in brains fixed in Bouin's fluid.

Neuraminic acid specific lectins as markers of early cortical plate neurons

Early cortical plate and subplate cells in the developing neocortex of many animal species and humans contain one specific plasma protein, fetuin. Fetuin is heavily glycosylated and it is possible that due to the large amount of sugars, this molecule may play a part in cellular recognition during brain development. Cellular and extracellular carbohydrates in the developing brain of the sheep were studied histochemically using a battery of fluorescein-labelled lectins. Two neuraminic acid specific lectins, Sambucus nigra and Maackia amurensis, labelled consistently the fetuin-positive cells as demonstrated by double labelling with lectins and antifetuin antibodies. Brain sections from other species, known to contain fetuin-positive cells (fetal cow, postnatal tammar wallaby) showed a similar lectin staining pattern to that of the sheep fetus. Additionally, sections from species thought to contain fetuin in their developing brains that failed to cross-react with available antifetuin antibodies (postnatal Monodelphis, fetal cat) also demonstrated lectin-positive staining in the same neuronal cell population. Thus, neuraminic acid is a common and well conserved terminal carbohydrate in cortical plate and subplate neurons of the developing brain. Neuraminic-specific lectins are useful markers for these neurons in addition to the more traditional use of immunocytochemical methods in studies of formation of the neocortex.

Synthesis of the foetal protein fetuin by early developing neurons in the immature neocortex

The presence of the foetal protein fetuin has previously been demonstrated by immunocytochemistry to be specifically confined to the primordial plexiform layer, the early cortical plate and subplate zone cells in the developing neocortex of a number of species. In order to investigate its origin there, we have applied in situ hybridization in paraffin sections of Bouin's fixed foetal sheep brain, using a short anti-sense oligonucleotide probe. The distribution of fetuin mRNA has been compared with that of the protein by using anti-fetuin antibodies and immunocytochemistry. This allowed us to confirm that fetuin is synthesised initially in cells of the primordial plexiform layer and subsequently cortical plate and subplate cells. On the other hand, cells in the ventricular zone that are fetuin (protein) positive do not contain detectable fetuin mRNA. The time course of fetuin mRNA expression in the developing neocortex follows closely the previously described pattern of fetuin (protein) distribution in the sheep brain, apart from its absence from the ventricular zone where its origin is probably by uptake from cerebrospinal fluid.