Dexamethasone effects on cerebral protein synthesis prior to and following hypoxia-ischemia in immature rat

Corticosteroids and perinatal hypoxic-ischemic brain injury

Perinatal hypoxic-ischemic (HI) brain injury is the major cause of neonatal mortality and severe long-term neurological morbidity. Yet, the effective therapeutic interventions currently available are extremely limited. Corticosteroids act on both mineralocorticoid (MR) and glucocorticoid (GR) receptors and modulate inflammation and apoptosis in the brain. Neuroinflammatory response to acute cerebral HI is a major contributor to the pathophysiology of perinatal brain injury. Here, we give an overview of current knowledge of corticosteroid-mediated modulations of inflammation and apoptosis in the neonatal brain, focusing on key regulatory cells of the innate and adaptive immune response. In addition, we provide new insights into targets of MR and GR in potential therapeutic strategies that could be beneficial for the treatment of infants with HI brain injury.

Maternal seizures can affect the brain developing of offspring

To elucidate the impact of maternal seizures in the developing rat brain, pregnant Wistar rats were subjected to the pilocarpine-induced seizures and pups from different litters were studied at different ages. In the first 24 h of life, blood glucose and blood gases were analyzed. (14)C-leucine [(14)C-Leu] incorporation was used to analyze protein synthesis at PN1, and Western Blot method was used to analyze protein levels of Bax, Bcl-2 and Poly(ADP-ribose) polymerase-1 (PARP-1) in the hippocampus (PN3-PN21). During the first 22 days of postnatal life, body weight gain, length, skull measures, tooth eruption, eye opening and righting reflex have been assessed. Pups from naive mothers were used as controls. Experimental pups showed a compensated metabolic acidosis and hyperglycemia. At PN1, the [(14)C-Leu] incorporation into different studied areas of experimental pups was lower than in the control pups. During development, the protein levels of Bax, Bcl-2 and PARP-1 in the hippocampus of experimental pups were altered when compared with control pups. A decreased level of pro- and anti-apoptotic proteins was verified in the early postnatal age (PN3), and an increased level of pro-apoptotic proteins concomitant with a reduced level of anti-apoptotic protein was observed at the later stages of the development (PN21). Experimental pups had a delay in postnatal growth and development beyond disturb in protein synthesis and some protein expression during development. These changes can be result from hormonal alterations linked to stress and/or hypoxic events caused by maternal epileptic seizures during pregnancy.

Neuroglobin is up-regulated in the cerebellum of pups exposed to maternal epileptic seizures

To evaluate a potential insult in the cerebellum of pups exposed to maternal epileptic seizures during intrauterine life, female rats were subjected to pilocarpine-induced epilepsy. Pups from different litters were sacrificed at 1, 3, 7 and 14 post-natal days (PN) and neuroglobin (Ngb) and gliosis were analyzed in the cerebellum by Western blotting (WB) and RT-PCR. (14)C-l-leucine-[(14)C-Leu] incorporation was used to analyze protein synthesis at PN1. Nitric Oxide (NO) and thiobarbituric acid-reactive substances (TBARS) levels were also measured. Pups from naive mothers were used as controls. The mRNA level of Ngb was increased in experimental animals at PN1 ((**)p ≤ 0.001) and PN3 ((**)p ≤ 0.001), at PN7 ((***)p ≤ 0.0001) and at PN14 ((**)p ≤ 0.001) compared to the respective controls. The protein level of Ngb increased significantly in the experimental pups at PN1 ((*)p ≤ 0.05) and at PN3 ((**)p ≤ 0.001), when compared to the control pups at PN1 and PN3. At PN7 and PN14 no difference was found. The mRNA level of GFAP increased significantly about two times at PN3 ((*)p ≤ 0.05) and PN7 ((*)p ≤ 0.05) in the experimental pups when compared to the respective controls, but was unchanged in the other studied ages. Data showed that experimental pups at PN1 exhibited reduced (about 2 times, (*)p ≤ 0.05) total protein synthesis in the cerebellum when compared to control. No differences were found in the NO and TBARS levels. Our data support the hypothesis that an up-regulation of Ngb could be a compensatory mechanism in response to the hypoxic-ischemic insults caused by seizures in pups during intrauterine life.

Hypoxia down-regulates glucocorticoid receptor alpha and attenuates the anti-inflammatory actions of dexamethasone in human alveolar epithelial A549 cells

AIMS

Glucocorticoids (GCs) are frequently used to treat various pulmonary diseases, which are typically accompanied by hypoxia. Whether hypoxia influences the effects of GCs on human airway cells remains unclear. The aim of the present study was to characterize changes in the expression levels of two isoforms of the glucocorticoid receptor (GR) and to evaluate the anti-inflammatory actions of GCs under hypoxic conditions in A549 cells.

MAIN METHODS

A549 cells were exposed to normoxic or hypoxic conditions for 24, 48 and 72 h. Morphological alterations of cells were captured using a differential interference contrast microscope (DIC), and cell cycle distribution was estimated by flow cytometry. Real-time quantitative polymerase chain reaction and western blot were used to determine the mRNA and protein expression levels of GRalpha and GRbeta. Radioimmunoassay (RIA) for interleukin (IL)-8 was used to assess the anti-inflammatory actions of GCs after cells were stimulated with lipopolysaccharide (LPS).

KEY FINDINGS

After cells were exposed to hypoxic conditions for 48 h, visible morphological alterations in the cells were observed. Cell cycle analysis showed that the number of cells in G1 phase increased significantly under hypoxia compared to the normoxic conditions. Hypoxia caused a time-dependent decrease in both mRNA and protein expression levels for GRalpha, but not GRbeta. Furthermore, when exposed to hypoxia for 48 h, the inhibitory effects of dexamethasone on LPS-stimulated IL-8 release were attenuated.

SIGNIFICANCE

These results indicate that hypoxia impairs the anti-inflammatory actions of GCs in A549 cells, which could be attributed to down-regulation of GRalpha expression under hypoxic conditions.

Recruitment of the p160 coactivators by the glucocorticoid receptor: dependence on the promoter context and cell type but not hypoxic conditions

In the nervous system, glucocorticoids exert beneficial or noxious effects, depending on their concentration and time-exposure. They act via the glucocorticoid receptor (GR) which recruits the p160 coactivators (SRC-1, SRC-2 and SRC-3). It was often shown that the three SRCs are interchangeable. The aim of the present study was to evaluate if the GR-SRCs interactions are dependent on several parameters like the target promoter structure, cell type or exogenous stressful parameters like hypoxia. We investigated the GR-SRCs interactions in two glial cells: astrocytes for the central nervous system and Schwann cells for the peripheral nervous system. We have shown by performing functional studies (overexpression and siRNA knock-down) that the recruitment of the three p160 by the GR is promoter-dependent and cell-specific. Moreover, we have shown that hypoxia (5% of oxygen) enhanced GR transactivation in both glial cells. Although hypoxia enhanced GR transactivation, it did not alter the interactions between the GR and the three p160s. Finally, we have shown that the potentiation of GR transactivation by hypoxia is due to an increase of the GR transcripts in Schwann cells but not in astrocytes. Altogether, these results reveal that the p160s are not interchangeable and that their recruitment by the GR is a multiparametric event.

Down-regulation of Phospholipase D2 mRNA in Neonatal Rat Brainstem and Cerebellum after Hypoxia-Ischemia

Phospholipase D (PLD) and phosphatidylcholine (PC) were implicated in apoptosis and cancer. However, direct evidence on the role of PLD in the cause of apoptosis remains obscure. It was recently reported that apoptosis and necrosis could be induced in the cerebellum and brainstem after focal cerebral hypoxic-ischemic (HI) injury. It was found that apoptosis could be enhanced by farnesol inhibition of PLD signal transduction. Whereas it was shown that highly invasive cancer cell line depends on PLD activity for survival when deprived of serum growth factors. Based on these reports, it is postulated that apoptosis in the cerebellum and brainstem induced after focal cerebral HI treatment may be caused by faulty PLD expression. This is consistent with a report that PLD1 activity and mRNA levels were down-regulated during apoptosis. To test this hypothesis, Northern blotting was used to examine PLD2 mRNA expression after focal cerebral HI. The results show that both PLD2 mRNA 10.8 and 3.9 kb transcripts were significantly decreased by as much as 37% in the brainstem and cerebellum areas 3 h after HI compared to the control, concur with previous report of decreasing PLD activity after ischemia. These PLD2 transcripts, however, were not significantly different from the control 3 days after HI, indicating that the decrease in PLD2 transcription after HI maybe a transient phenomenon. This is the first report to show that the loss of membrane integrity resulting from deprivation of energy and growth factors after HI could cause decrease in PLD2 transcription that promotes apoptosis. The hypothetic role of PLD2 and the mechanism leading to apoptosis remains to be further elucidated.

Differential effects of testosterone on protein synthesis activity in male and female quail brain

In Japanese quail, testosterone (T) increases the Nissl staining density in the medial preoptic nucleus (POM) in relation to the differential activation by T of copulatory behavior. The effect of T on protein synthesis was quantified here in 97 discrete brain regions by the in vivo autoradiographic (14)C-leucine (Leu) incorporation method in adult gonadectomized male and female quail that had been treated for 4 weeks with T or left without hormone. T activated male sexual behaviors in males but not females. Overall Leu incorporation was increased by T in five brain regions, many of which contain sex steroid receptors such as the POM, archistriatum and lateral hypothalamus. T decreased Leu incorporation in the medial septum. Leu incorporation was higher in males than females in two nuclei but higher in females in three nuclei including the hypothalamic ventromedial nucleus. Significant interactions between effects of T and sex were seen in 13 nuclei: in most nuclei (n=12), T increased Leu incorporation in males but decreased it in females. The POM boundaries were defined by a denser Leu incorporation than the surrounding area and incorporation was increased by T more in males (25%) than in females (6%). These results confirm that protein synthesis in brain areas relevant to the control of sexual behavior can be affected by the sex of the subjects or their endocrine condition and that T can have differential effects in the two sexes. These anabolic changes should reflect the sexually differentiated neurochemical mechanisms mediating behavioral activation.

Role of sodium channel inhibition in neuroprotection: effect of vinpocetine

Vinpocetine (ethyl apovincaminate) discovered during the late 1960s has successfully been used in the treatment of central nervous system disorders of cerebrovascular origin for decades. The increase in the regional cerebral blood flow in response to vinpocetine administration is well established and strengthened by new diagnostical techniques (transcranial Doppler, near infrared spectroscopy, positron emission tomography). The latest in vitro studies have revealed the effect of the compound on Ca(2+)/calmodulin dependent cyclic guanosine monophosphate-phosphodiesterase 1, voltage-operated Ca(2+) channels, glutamate receptors and voltage dependent Na(+)-channels; the latest being especially relevant to the neuroprotective action of vinpocetine. The good brain penetration profile and heterogenous brain distribution pattern (mainly in the thalamus, basal ganglia and visual cortex) of labelled vinpocetin were demonstrated by positron emission tomography in primates and man. Multicentric, randomized, placebo-controlled clinical studies proved the efficacy of orally administered vinpocetin in patients with organic psychosyndrome. Recently positron emission tomography studies have proved that vinpocetine is able to redistribute regional cerebral blood flow and enhance glucose supply of brain tissue in ischemic post-stroke patients.