The blockade of endothelin A receptor protects astrocytes against hypoxic injury: Common effects of BQ-123 and erythropoietin on the rejuvenation of the astrocyte population

Causative Effects of Genetically Determined High Maternal/Fetal Endothelin-1 on Preeclampsia-Like Conditions in Mice

Endothelin-1 (ET-1) is implicated in the pathophysiology of preeclampsia. An association between an EDN1 gene polymorphism with high ET-1 and preeclampsia was reported in humans, but their cause and effect relationships have not been defined. We examined the pregnancy effects in mice with a modified Edn1 allele that increases mRNA stability and thus ET-1 production. Heterozygous Edn1^H/+ females showed no obvious abnormalities before pregnancy, but when mated with wild-type (WT) males developed a full spectrum of preeclampsia-like phenotypes, including increased systolic blood pressure, proteinuria, glomerular endotheliosis, and intrauterine fetal growth restriction. At 7.5 days post-coitus, the embryos from Edn1^H/+ dams, regardless of their Edn1 genotype, lagged 12 hours in development compared with embryos from WT dams, had disoriented ectoplacental cones, and retained high E-cadherin expression. In contrast, WT females mated with Edn1^H/+ males, which also carried half of the fetuses with Edn1^H/+ genotype, showed a mild systolic blood pressure increase only. These WT dams had 2× higher plasma soluble fms-like tyrosine kinase-1 than WT dams mated with WT males. In human first trimester trophoblast cells, pharmacological doses of ET-1 increased the cellular sFlt1 transcripts and protein secretion via both type A and B ET-1 receptors. Our data demonstrate that high maternal ET-1 production causes preeclampsia-like phenotypes during pregnancy, affecting both initial stage of trophoblast differentiation/invasion and maternal peripheral vasculature during late gestation. High fetal ET-1 production, however, could cause increased soluble fms-like tyrosine kinase-1 in the maternal circulation and contribute to blood pressure elevation.

Neuroprotective, Neurogenic, and Amyloid Beta Reducing Effect of a Novel Alpha 2-Adrenoblocker, Mesedin, on Astroglia and Neuronal Progenitors upon Hypoxia and Glutamate Exposure

Locus coeruleus-noradrenergic system dysfunction is known to contribute to the progression of Alzheimer’s disease (AD). Besides a variety of reports showing the involvement of norepinephrine and its receptor systems in cognition, amyloid β (Aβ) metabolism, neuroinflammation, and neurogenesis, little is known about the contribution of the specific receptors to these actions. Here, we investigated the neurogenic and neuroprotective properties of a new α2 adrenoblocker, mesedin, in astroglial primary cultures (APC) from C57BL/6 and 3×Tg-AD mice. Our results demonstrate that mesedin rescues neuronal precursors and young neurons, and reduces the lactate dehydrogenase (LDH) release from astroglia under hypoxic and normoxic conditions. Mesedin also increased choline acetyltransferase, postsynaptic density marker 95 (PSD95), and Aβ-degrading enzyme neprilysin in the wild type APC, while in the 3×Tg-AD APC exposed to glutamate, it decreased the intracellular content of Aβ and enhanced the survival of synaptophysin-positive astroglia and neurons. These effects in APC can at least partially be attributed to the mesedin’s ability of increasing the expression of Interleukine(IL)-10, which is a potent anti-inflammatory, neuroprotective neurogenic, and Aβ metabolism enhancing factor. In summary, our data identify the neurogenic, neuroprotective, and anti-amyloidogenic action of mesedin in APC. Further in vivo studies are needed to estimate the therapeutic value of mesedin for AD.

Interplay between endothelin and erythropoietin in astroglia: the role in protection against hypoxia

We show that, under in vitro conditions, the vulnerability of astroglia to hypoxia is reflected by alterations in endothelin (ET)-1 release and capacity of erythropoietin (EPO) to regulate ET-1 levels. Exposure of cells to 24 h hypoxia did not induce changes in ET-1 release, while 48–72 h hypoxia resulted in increase of ET-1 release from astrocytes that could be abolished by EPO. The endothelin receptor type A (ETA) antagonist BQ123 increased extracellular levels of ET-1 in human fetal astroglial cell line (SV-FHAS). The survival and proliferation of rat primary astrocytes, neural precursors, and neurons upon hypoxic conditions were increased upon administration of BQ123. Hypoxic injury and aging affected the interaction between the EPO and ET systems. Under hypoxia EPO decreased ET-1 release from astrocytes, while ETA receptor blockade enhanced the expression of EPO mRNA and EPO receptor in culture-aged rat astroglia. The blockade of ETA receptor can increase the availability of ET-1 to the ETB receptor and can potentiate the neuroprotective effects of EPO. Thus, the new therapeutic use of combined administration of EPO and ETA receptor antagonists during hypoxia-associated neurodegenerative disorders of the central nervous system (CNS) can be suggested.

Intranasal Delivery of Bone Marrow-Derived Mesenchymal Stem Cells, Macrophages, and Microglia to the Brain in Mouse Models of Alzheimer's and Parkinson's Disease

In view of the rapid preclinical development of cell-based therapies for neurodegenerative disorders, traumatic brain injury, and tumors, the safe and efficient delivery and targeting of therapeutic cells to the central nervous system is critical for maintaining therapeutic efficacy and safety in the respective disease models. Our previous data demonstrated therapeutically efficacious and targeted delivery of mesenchymal stem cells (MSCs) to the brain in the rat 6-hydroxydopamine model of Parkinson's disease (PD). The present study examined delivery of bone marrow-derived MSCs, macrophages, and microglia to the brain in a transgenic model of PD [(Thy1)-h[A30P] aS] and an APP/PS1 model of Alzheimer's disease (AD) via intranasal application (INA). INA of microglia in naive BL/6 mice led to targeted and effective delivery of cells to the brain. Quantitative PCR analysis of eGFP DNA showed that the brain contained the highest amount of eGFP-microglia (up to 2.1 × 104) after INA of 1 × 106 cells, while the total amount of cells detected in peripheral organs did not exceed 3.4 × 103. Seven days after INA, MSCs expressing eGFP were detected in the olfactory bulb (OB), cortex, amygdala, striatum, hippocampus, cerebellum, and brainstem of (Thy1)-h[A30P] aS transgenic mice, showing predominant distribution within the OB and brainstem. INA of eGFP-expressing macrophages in 13-month-old APP/PS1 mice led to delivery of cells to the OB, hippocampus, cortex, and cerebellum. Both MSCs and macrophages contained Iba-1-positive population of small microglia-like cells and Iba-1-negative large rounded cells showing either intracellular amyloid β (macrophages in APP/PS1 model) or α-synuclein [MSCs in (Thy1)-h[A30P] aS model] immunoreactivity. Here, we show, for the first time, intranasal delivery of cells to the brain of transgenic PD and AD mouse models. Additional work is needed to determine the optimal dosage (single treatment regimen or repeated administrations) to achieve functional improvement in these mouse models with intranasal microglia/macrophages and MSCs. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.

Age-dependent astroglial vulnerability to hypoxia and glutamate: the role for erythropoietin

Extracellular accumulation of toxic concentrations of glutamate (Glu) is a hallmark of many neurodegenerative diseases, often accompanied by hypoxia and impaired metabolism of this neuromediator. To address the question whether the multifunctional neuroprotective action of erythropoietin (EPO) extends to the regulation of extracellular Glu-level and is age-related, young and culture-aged rat astroglial primary cells (APC) were simultaneously treated with 1mM Glu and/or human recombinant EPO under normoxic and hypoxic conditions (NC and HC). EPO increased the Glu uptake by astrocytes under both NC and especially upon HC in culture-aged APC (by 60%). Moreover, treatment with EPO up-regulated the activity of glutamine synthetase (GS), the expression of glutamate-aspartate transporter (GLAST) and the level of EPO mRNA. EPO alleviated the Glu- and hypoxia-induced LDH release from astrocytes. These protective EPO effects were concentration-dependent and they were strongly intensified with age in culture. More than a 4-fold increase in apoptosis and a 2-fold decrease in GS enzyme activity was observed in APC transfected with EPO receptor (EPOR)-siRNA. Our in vivo data show decreased expression of EPO and a strong increase of EPOR in brain homogenates of APP/PS1 mice and their wild type controls during aging. Comparison of APP/PS1 and age-matched WT control mice revealed a stronger expression of EPOR but a weaker one of EPO in the Alzheimer's disease (AD) model mice. Here we show for the first time the direct correlation between the extent of differentiation (age) of astrocytes and the efficacy of EPO in balancing extracellular glutamate clearance and metabolism in an in-vitro model of hypoxia and Glu-induced astroglial injury. The clinical relevance of EPO and EPOR as markers of brain cells vulnerability during aging and neurodegeneration is evidenced by remarkable changes in their expression levels in a transgenic model of AD and their WT controls.

Regulation of glial inflammatory mediators synthesis: possible role of endothelins

Endothelins are well known as modulators of inflammation in the periphery, but little is known about their possible role in brain inflammation. Stimulation of astrocyte prostaglandin, an inflammatory mediator, synthesis was shown so far only by endothelin 3 (ET-3). By contrast, several studies showed no change or slight decrease of basal nitric oxide synthesis after treatment of astrocytes with endothelin 1 (ET-1) and ET-3. However, a significant increase in astrocytic and microglial nitric oxide synthase (NOS) was observed after exposure to ET-1 and ET-3 in a model of forebrain ischaemia. Here we demonstrate that all three endothelins (ET-1, ET-2, ET-3) significantly enhanced the synthesis of prostaglandin E(2) and nitric oxide in glial cells. Each of the selective antagonists for ETA and ETB receptors (BQ123 and BQ788 respectively), significantly inhibited endothelins-induced production of both nitric oxide and prostaglandin E(2). These results suggest a regulatory mechanism of endothelins, interacting with both endothelin receptors, on glial inflammation. Therefore, inhibition of endothelin receptors may have a therapeutic potential in pathological conditions of the brain, when an uncontrolled inflammatory response is involved.

Angiotensin Receptor Type 1 Blockade in Astroglia Decreases Hypoxia-Induced Cell Damage and TNF Alpha Release

The present study investigated the role of angiotensin receptors (AT-R) in the survival and inflammatory response of astroglia upon hypoxic injury. Exposure of rat astroglial primary cultures (APC) to hypoxic conditions (HC) led to decreased viability of the cells and to a 3.5-fold increase in TNF-alpha release. AT-R type1 (AT1-R) antagonist losartan and its metabolite EXP3174 decrease the LDH release (by 36 +/- 9%; 45 +/- 6%) from APC under HC. Losartan diminished TNF-alpha release (by 40 +/- 15%) and the number of TUNEL-cells by 204 +/- 38% under HC, alone and together with angiotensin II (ATII), while EXP3174 was dependent on ATII for its effect on TNF-alpha. The AT2-R antagonist, PD123.319, did not influence the release of LDH and TNF-alpha under normoxic (NC) and HC. These data suggest that AT1-R may decrease the susceptibility of astrocytes to hypoxic injury and their propensity to release TNF-alpha. AT1-R antagonists may therefore be of therapeutic value during hypoxia-associated neurodegeneration.

Astrocyte dysfunction in neurological disorders: a molecular perspective

Recent work on glial cell physiology has revealed that glial cells, and astrocytes in particular, are much more actively involved in brain information processing than previously thought. This finding has stimulated the view that the active brain should no longer be regarded solely as a network of neuronal contacts, but instead as a circuit of integrated, interactive neurons and glial cells. Consequently, glial cells could also have as yet unexpected roles in the diseased brain. An improved understanding of astrocyte biology and heterogeneity and the involvement of these cells in pathogenesis offers the potential for developing novel strategies to treat neurological disorders.

Similar protective effects of BQ-123 and erythropoietin on survival of neural cells and generation of neurons upon hypoxic injury

Our recent study [Danielyan et al., 2005. Eur. J. Cell Biol. 84, 567-579] showed an additive protective effect of endothelin (ET) receptor A (ETA-R) blockade and erythropoietin (EPO) on the survival and rejuvenation of rat astroglial cells exposed to hypoxia. Whether the effects observed with rodent astroglial cells can be reproduced in human astrocytes and whether these effects of ETA-R blockade and EPO on astrocytes are associated with neuronal survival remained open. Therefore, in the present study, the effects of the ETA-R antagonist BQ-123 and EPO on the maintenance of the neuronal population and survival of the human fetal astroglial cell line (SV-FHAS) under normoxic and hypoxic conditions (NC and HC, respectively) were investigated. Rat brain primary cultures exposed to BQ-123 and/or EPO revealed an increase in the number of beta-III tubulin-positive neurons under NC. The hypoxia-caused loss of neurons was abolished by administration of BQ-123 or EPO. Simultaneous application of EPO and BQ-123 led to an additive protective effect on the generation of neurons under NC only. By contrast, BQ-788, the selective ETB-R antagonist, diminished the neuronal population both in NC and HC. Both under NC and HC the number of non-differentiated nestin+/GFAP- neural cells increased upon application of EPO or BQ-123. SV-FHAS responded to BQ-123 or EPO by a decrease in LDH activity in the culture medium under NC (35%) and HC (26% LDH decrease). Concomitant effects of EPO and BQ-123 were illustrated in an additional increase in the survival of human astrocytes (33% under NC and 17% under HC). These data hint at a neuroprotective therapeutic potency of ETA-R blockade, which either alone or in combination with EPO may improve the survival of astroglial and neuronal cells upon hypoxic injury.