Toll-like receptor 3 expression in glia and neurons alters in response to white matter injury in preterm infants.

Toll-like receptors (TLRs) are members of the pattern recognition receptor family that detect components of foreign pathogens or endogenous molecules released in response to injury. Recent studies demonstrate that TLRs also have a functional role in regulating neuronal proliferation in the developing brain. This study investigated cellular expression of TLR3 using immunohistochemistry on human brain tissue. The tissue sections analysed contained anterior and lateral periventricular white matter from the frontal and parietal lobes in post-mortem neonatal cases with a postmenstrual age range of 23.6-31.4 weeks. In addition to preterm brains without overt pathology (control), preterm pathology cases with evidence of white matter injuries (WMI) were also examined. In order to identify TLR-positive cells, we utilized standard double-labelling immunofluorescence co-labelling techniques and confocal microscopy to compare co-expression of TLR3 with a neuronal marker (NeuN) or with glial markers (GFAP for astrocytes, Iba-1 for microglia and Olig2 for oligodendrocytes). We observed an increase in the neuronal (28 vs. 17%) and astroglial (38 vs. 21%) populations in the WMI group compared to controls in the anterior regions of the periventricular white matter in the frontal lobe. The increase in neurons and astrocytes in the WMI cases was associated with an increase in TLR3 immunoreactivity. This expression was significantly increased in the astroglia. The morphology of the TLR3 signal in the control cases was globular and restricted to the perinuclear region of the neurons and astrocytes, whilst in the cases of WMI, both neuronal, axonal and astroglial TLR3 expression was more diffuse (i.e., a different intracellular distribution) and could be detected along the extensions of the processes. This study demonstrates for the first time that neurons and glial cells in human neonatal periventricular white matter express TLR3 during development. The patterns of TLR3 expression were altered in the presence of WMI, which might influence normal developmental processes within the immature brain. Identifying changes in TLR3 expression during fetal development may be key to understanding the reduced volumes of grey matter and impaired cortical development seen in preterm infants.

Chronic fetal hypoxia increases activin A concentrations in the late-pregnant sheep.

OBJECTIVE: To determine whether activin A concentrations are altered in chronic fetal hypoxemia and intrauterine fetal growth restriction (IUGR). DESIGN: In vivo animal experimental model. SETTING: Department of Physiology, Monash University. POPULATION: Chronically catherised fetal sheep in late pregnancy. METHODS: Chronic fetal hypoxia and IUGR were experimentally induced by single umbilical artery ligation (SUAL) in catheterised fetal sheep. Maternal and fetal blood samples and amniotic fluid (AF) samples were collected during surgery and thereafter on alternate days, until the time of delivery for analyte measurement. Fetal blood gas parameters were measured daily. MAIN OUTCOME MEASURES: Plasma and AF was used to analyse activin A, prostaglandin E2 (PGE2) and cortisol and fetal blood gas analysis was undertaken in whole blood. RESULTS: SUAL produced asymmetric IUGR and non-acidaemic chronic fetal hypoxia and resulted in preterm labour (129 [3] days). AF activin A concentrations were 10-fold higher in the SUAL group than in controls whereas levels in the fetal and maternal circulations were similar between groups. CONCLUSIONS: SUAL-induced IUGR and fetal hypoxaemia increases AF activin A. This may be an important adaptive or protective response to IUGR.

Effect of graded hypoxia on activin A, prostaglandin E2 and cortisol levels in the late-pregnant sheep.

The aim of the present study was to determine whether activin A concentrations are dependent on feto-placental oxygen availability and to investigate the temporal relationship of activin A with prostaglandin (PG) E(2) and cortisol. Nine fetal sheep (six hypoxic and three control) were instrumented and catheterised at 0.8 gestation. Reduced uterine blood flow was used to achieve three levels of hypoxia (mild = fetal SaO(2) 40-50%; moderate = fetal SaO(2) 30-40%; severe = fetal SaO(2) 20-30%), for 4 h on 3 consecutive days. Activin A, PGE(2) and cortisol levels were determined in maternal and fetal blood and amniotic fluid. Moderate and severe hypoxia produced a significant (P < 0.05) increase in fetal plasma activin A concentrations. The amniotic fluid activin A concentrations were 15-fold higher than those in the fetal circulation, but were unchanged by hypoxia. The fetal PGE(2) response reflected the degree of hypoxia over the 3 days, with moderate and severe hypoxia producing a significant (P < 0.05) increase in PGE(2) concentrations. Fetal plasma cortisol concentrations were increased ( P < 0.05) during all levels of hypoxia. Fetal arterial activin A was increased in response to moderate and severe hypoxia, but levels were not maintained over the hypoxic period. The increases in activin A and cortisol concentrations preceded the increase in PGE(2).