Cholinergic neurons degenerate when exposed to conditioned medium of primary rat brain capillary endothelial cells: counteraction by NGF, MK-801 and inflammation

Dysregulation of neurotrophin expression in prefrontal cortex and nucleus basalis magnocellularis during and after adolescent intermittent ethanol exposure

A preclinical model of human adolescent binge drinking, adolescent intermittent ethanol exposure (AIE) recreates the heavy binge withdrawal consummatory patterns of adolescents and has identified the loss of basal forebrain cholinergic neurons as a pathological hallmark of this model. Cholinergic neurons of the nucleus basalis magnocellularis (NbM) that innervate the prefrontal cortex (PFC) are particularly vulnerable to alcohol related neurodegeneration. Target derived neurotrophins (nerve growth factor [NGF] and brain-derived neurotrophic factor [BDNF]) regulate cholinergic phenotype expression and survival. Evidence from other disease models implicates the role of immature neurotrophin, or proneurotrophins, activity at neurotrophic receptors in promoting cholinergic degeneration; however, it has yet to be explored in adolescent binge drinking. We sought to characterize the pro- and mature neurotrophin expression, alongside their cognate receptors and cholinergic markers in an AIE model. Male and female Sprague Dawley rats underwent 5 g/kg 20% EtOH or water gavage on two-day-on, two-day-off cycles from post-natal day 25-57. Rats were sacrificed 2 h, 24 h, or 3 weeks following the last gavage, and tissue were collected for protein measurement. Western blot analyses revealed that ethanol intoxication reduced the expression of BDNF and vesicular acetylcholine transporter (vAChT) in the PFC, while NGF was lower in the NbM of AIE treated animals. During acute alcohol withdrawal, proNGF in the PFC was increased while proBDNF decreased, and in the NbM proBDNF increased while NGF decreased. During AIE abstinence, the expression of neurotrophins, their receptors, and vAChT did not differ from controls in the PFC. In contrast, in the NbM the expression of both NGF and choline acetyltransferase (ChAT) were reduced long-term following AIE. Taken together these findings suggest that AIE alters the expression of proneurotrophins and neurotrophins during intoxication and withdrawal that favor prodegenerative mechanisms by increasing the expression of proNGF and proBDNF, while also reducing NGF and BDNF.

Endothelial dysfunction in neurodegenerative disease: Is endothelial inflammation an overlooked druggable target?

Neurological diseases with a neurodegenerative component have been associated with alterations in the cerebrovasculature. At the anatomical level, these are centred around changes in cerebral blood flow and vessel organisation. At the molecular level, there is extensive expression of cellular adhesion molecules and increased release of pro-inflammatory mediators. Together, these has been found to negatively impact blood-brain barrier integrity. Systemic inflammation has been found to accelerate and exacerbate endothelial dysfunction, neuroinflammation and degeneration. Here, we review the role of cerebrovasculature dysfunction in neurodegenerative disease and discuss the potential contribution of intermittent pro-inflammatory systemic disease in causing endothelial pathology, highlighting a possible mechanism that may allow broad-spectrum therapeutic targeting in the future.

NGF Prevents Loss of TrkA/VEGFR2 Cells, and VEGF Isoform Dysregulation in the Retina of Adult Diabetic Rats

Among the factors involved in diabetic retinopathy (DR), nerve growth factor (NGF) and vascular endothelial growth factor A (VEGFA) have been shown to affect both neuronal survival and vascular function, suggesting that their crosstalk might influence DR outcomes. To address this question, the administration of eye drops containing NGF (ed-NGF) to adult Sprague Dawley rats receiving streptozotocin (STZ) intraperitoneal injection was used as an experimental paradigm to investigate NGF modulation of VEGFA and its receptor VEGFR2 expression. We show that ed-NGF treatment prevents the histological and vascular alterations in STZ retina, VEGFR2 expression decreased in GCL and INL, and preserved the co-expression of VEGFR2 and NGF-tropomyosin-related kinase A (TrkA) receptor in retinal ganglion cells (RGCs). The WB analysis confirmed the NGF effect on VEGFR2 expression and activation, and showed a recovery of VEGF isoform dysregulation by suppressing STZ-induced VEGFA₁₂₁ expression. Reduction in inflammatory and pro-apoptotic intracellular signals were also found in STZ+NGF retina. These findings suggest that ed-NGF administration might favor neuroretina protection, and in turn counteract the vascular impairment by regulating VEGFR2 and/or VEGFA isoform expression during the early stages of the disease. The possibility that an increase in the NGF availability might contribute to the switch from the proangiogenic/apoptotic to the neuroprotective action of VEGF is discussed.

Effects of acidosis on brain capillary endothelial cells and cholinergic neurons: relevance to vascular dementia and Alzheimer's disease

Alzheimer's disease is a progressive brain disorder which is neuropathologically characterized by an increased number of beta-amyloid plaques, tau pathology and synapse loss. Recent research suggests that vascular pathology may be also important for the development and progression of Alzheimer's disease. It is still unknown whether there is a relation between damage of brain capillary endothelial cells (BCEC) and subsequent cholinergic cell death. The aim of this study was to examine the effects of acidosis on cell death of BCEC and cholinergic neurons in an organotypic brain slice model. We show that BCEC were heavily damaged in medium at pH<6.6. Cholinergic neurons incubated in medium pH 6.0 degenerated within 2-3 days and were not rescued by nerve growth factor (NGF). Lactate did not affect the survival of BCEC or cholinergic neurons. Both BCEC and cholinergic cells were not affected at pH 7.4, 7.0 or 6.6. It is concluded that both endothelial cells and cholinergic neurons have a high capacity to compensate for pH changes. At a certain pH, however, the vascular and neuronal cells show the same vulnerability, indicating that a low pH is deleterious for the cerebral microenvironment. Future studies are necessary to explore whether temporary pH changes could be responsible for cerebrovascular damage and cholinergic cell death. Acidosis may play an important role in the development of vascular dementia and Alzheimer's disease.

Vascular and neuronal protection induced by the ocular administration of nerve growth factor in diabetic-induced rat encephalopathy

BACKGROUND

Based on our previous findings on the efficacy of ocular applied nerve growth factor as eye drops (oNGF) to act in brain and counteract neuronal damage, we hypothesized that oNGF treatment might revert neuronal atrophy occurring in diabetic brain also by controlling neurotrophin system changes. The major NGF brain target areas, such as the septum and the hippocampus, were used as an experimental paradigma to test this hypothesis.

METHODS

Bilateral oNGF treatment was performed twice a day for 2 weeks in full-blown streptozotocin-treated adult male rats. The forebrain distribution of cholinergic and endothelial cell markers and NGF receptors were studied by confocal microscopy. The septo-hippocampal content of NGF mature and precursor form and NGF receptors expression were also analyzed by Elisa and Western blot.

RESULTS

oNGF treatment recovers the morphological alterations and the neuronal atrophy in septum and normalized the expression of mature and pro-NGF, as well as NGF receptors in the septum and hippocampus of diabetic rats. In addition, oNGF stimulated brain vascularization and up-regulated the TRKA receptor in vessel endothelium.

CONCLUSIONS

Our findings confirm that reduced availability of mature NGF and NGF signaling impairment favors vascular and neuronal alterations in diabetic septo-hippocampal areas and corroborate the ability of oNGF to act as a neuroprotective agent in brain.

Inflammatory status of transmigrating primary rat monocytes in a novel perfusion model simulating blood flow

It remains unclear whether monocyte infiltration plays a protective or detrimental role in neurodegenerative disease. The present study characterizes the inflammatory status of primary monocytes in a novel in vitro perfusion model. Monocytes under perfusion do not undergo elevated cell death. However, perfusion does lead to altered morphology, which can be counteracted by anti-inflammatory drugs. Functional studies indicate that cytokine levels are significantly reduced in perfusion compared to stationary conditions and enhanced with brain slices or capillary endothelial cells. Understanding monocyte properties could lead to refined treatment and new ways to interfere with inflammation in diseased brains.

Improvement of Contused Spinal Cord in Rats by Cholinergic-like Neuron Therapy

Background

Disability in spinal cord injury is an important medical problem, and cell transplantation is considered as an option for the treatment.

Objectives

The purpose of this study is to use bone marrow stromal cells (BMSCs) derived cholinergic neuron-like cells (CNL) in order to ameliorate the contusion model of spinal cord injury in rats.

Materials and Methods

The CNLs were produced by pre inducing BMSCs with β-mercaptoethanol (BME) followed by inducing with nerve growth factor (NGF). The cells were immunoreactive to neurofilament 200, NeuN, synaptophysin, synapsin, microtubule associated protein-2 and choline acetyl transferase (ChAT). The CNL were transplanted in contused rats (CR), which were sacrificed after 12 weeks.

Results

The results showed that BBB test showed an improvement in the CR, while the quantitative analysis showed that the improvement rate was higher in the rats treated with CNL than those treated with BMSCs only or the untreated animals, similar results were noticed in the improvement index. Immunohistochemical analysis of the tissue section prepared from the CR showed that the transplanted cells were engrafted and integrated in the traumatized spinal cord. The morphometric analysis showed that the volume density of the cavity in the CNL treated rats was significantly lower than that of the untreated ones, while the spinal tissue regeneration index was significantly higher.

Conclusions

The conclusion of the study is that CNL can improve the injured spinal cord.

Ethanol transiently suppresses choline-acetyltransferase in basal nucleus of Meynert slices

The cholinergic system plays a major role in learning and cognition and cholinergic neurons appear to be particularly vulnerable to ethanol (EtOH) exposure. There are conflicting results if EtOH directly damages cholinergic neurons. Thus, the aims of the present study were (1) to investigate the effect of different EtOH concentrations on cholinergic neurons in organotypic brain slices of the nucleus basalis of Meynert (nbM) and (2) to study if the most potent cholinotrophic substance nerve growth factor (NGF) or inhibitors of mitogen activated kinase (MAPK) p38- and nitric-oxide synthase (NOS)-pathways may counteract any EtOH effect. Two-week old organotypic rat brain slices of the nbM were exposed to 1–100 mM EtOH for 7 days with or without drugs and the number of choline-acetyltransferase (ChAT)-positive neurons was counted. Our data show that EtOH significantly reduced the number of ChAT-positive neurons with the most potent effect at a concentration of 50 mM EtOH (54 ± 5 neurons per slice, p < 0.001), compared to control slices (120 ± 13 neurons per slice). Inhibition of MAPK p38 (SB 203580, 10 μM) and NOS (L-thiocitrulline, 10 μM) counteracted the EtOH-induced decline of cholinergic neurons and NGF protected cholinergic neurons against the EtOH-induced effect. Withdrawal of EtOH resulted in a reversal of cholinergic neurons to nearly controls. In conclusion, EtOH caused a transient decline of cholinergic neurons, possibly involving MAPK p38- and NOS-pathways suggesting that EtOH does not induce direct cell death, but causes a transient downregulation of the cholinergic key enzyme, possibly reflecting a form of EtOH-associated plasticity.

Neurovascular pathways to neurodegeneration in Alzheimer's disease and other disorders

The neurovascular unit (NVU) comprises brain endothelial cells, pericytes or vascular smooth muscle cells, glia and neurons. The NVU controls blood-brain barrier (BBB) permeability and cerebral blood flow, and maintains the chemical composition of the neuronal 'milieu', which is required for proper functioning of neuronal circuits. Recent evidence indicates that BBB dysfunction is associated with the accumulation of several vasculotoxic and neurotoxic molecules within brain parenchyma, a reduction in cerebral blood flow, and hypoxia. Together, these vascular-derived insults might initiate and/or contribute to neuronal degeneration. This article examines mechanisms of BBB dysfunction in neurodegenerative disorders, notably Alzheimer's disease, and highlights therapeutic opportunities relating to these neurovascular deficits.

Neurovascular dysfunction, inflammation and endothelial activation: implications for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is an age-related disorder characterized by progressive cognitive decline and dementia. Alzheimer's disease is an increasingly prevalent disease with 5.3 million people in the United States currently affected. This number is a 10 percent increase from previous estimates and is projected to sharply increase to 8 million by 2030; it is the sixth-leading cause of death. In the United States the direct and indirect costs of Alzheimer's and other dementias to Medicare, Medicaid and businesses amount to more than $172 billion each year. Despite intense research efforts, effective disease-modifying therapies for this devastating disease remain elusive. At present, the few agents that are FDA-approved for the treatment of AD have demonstrated only modest effects in modifying clinical symptoms for relatively short periods and none has shown a clear effect on disease progression. New therapeutic approaches are desperately needed. Although the idea that vascular defects are present in AD and may be important in disease pathogenesis was suggested over 25 years ago, little work has focused on an active role for cerebrovascular mechanisms in the pathogenesis of AD. Nevertheless, increasing literature supports a vascular-neuronal axis in AD as shared risk factors for both AD and atherosclerotic cardiovascular disease implicate vascular mechanisms in the development and/or progression of AD. Also, chronic inflammation is closely associated with cardiovascular disease, as well as a broad spectrum of neurodegenerative diseases of aging including AD. In this review we summarize data regarding, cardiovascular risk factors and vascular abnormalities, neuro- and vascular-inflammation, and brain endothelial dysfunction in AD. We conclude that the endothelial interface, a highly synthetic bioreactor that produces a large number of soluble factors, is functionally altered in AD and contributes to a noxious CNS milieu by releasing inflammatory and neurotoxic species.

Homocysteine enhances transmigration of rat monocytes through a brain capillary endothelial cell monolayer via ICAM-1

Increased homocysteine (Hcy) levels contribute to a variety of cardiovascular and cerebrovascular diseases including stroke and Alzheimer's disease. Recent data has shown that elevated levels of Hcy can lead to the blood-brain barrier (BBB) dysfunction and activation. However, the mechanism for Hcy-mediated dysfunction remains unclear. The aim of this study is to characterize the effects of moderate Hcy administration in rat brain capillary endothelial cells (BCECs), which serve as a simple model to study blood-brain barrier (BBB) functions. This present study shows that addition of 20 microM Hcy for 6 days did not significantly affect BCEC survival, as measured by acridine orange staining, propidium iodide staining, and nitrite content. However, addition of 20 microM Hcy for 6 days did elevate lactate dehydrogenase (LDH) activity released into the supernatant of BCECs, as well as significantly enhance the transmigration of monocytes across the BCEC in a time-dependent manner. In addition, TNFalpha levels in BCEC were also elevated by Hcy, whereas inflammatory markers MIP3alpha and RANTES were significantly reduced. Finally, this study also shows that intercellular adhesion molecule-1 (ICAM-1) expression is significantly enhanced by 20 microM Hcy treatment compared to control conditions. These results suggest that moderate levels of homocysteine can affect proinflammatory patterns expressed by BCECs ultimately leading to BBB activation and dysfunction through enhanced monocyte transmigration and ICAM-1 expression.

S100b counteracts neurodegeneration of rat cholinergic neurons in brain slices after oxygen-glucose deprivation

Alzheimer's disease is a severe chronic neurodegenerative disorder characterized by beta-amyloid plaques, tau pathology, cerebrovascular damage, inflammation, reactive gliosis, and cell death of cholinergic neurons. The aim of the present study is to test whether the glia-derived molecule S100b can counteract neurodegeneration of cholinergic neurons after oxygen-glucose deprivation (OGD) in organotypic brain slices of basal nucleus of Meynert. Our data showed that 3 days of OGD induced a marked decrease of cholinergic neurons (60% of control), which could be counteracted by 50 μg/mL recombinant S100b. The effect was dose and time dependent. Application of nerve growth factor or fibroblast growth factor-2 was less protective. C-fos-like immunoreactivity was enhanced 3 hours after OGD indicating metabolic stress. We conclude that S100b is a potent neuroprotective factor for cholinergic neurons during ischemic events.

Monocytes deliver bioactive nerve growth factor through a brain capillary endothelial cell-monolayer in vitro and counteract degeneration of cholinergic neurons

Alzheimer's disease is an age-dependent brain disorder, characterized by progressive memory deficits and cognitive decline and loss of cholinergic neurons. Nerve growth factor (NGF) is the most potent protein to protect cholinergic neurons against degeneration. However, problems of delivery to the brain limit the therapeutical use of NGF. The aim of the present study was to test, if primary rat monocytes can be loaded with recombinant NGF and pass an in vitro monolayer of brain capillary endothelial cells (BCEC), release NGF, and support the cholinergic neurons in an organotypic brain slice model. Monocytes were isolated from rat blood by negative magnetic selection, loaded with recombinant NGF using Bioporter. The monocytes adhered and migrated through an in vitro rat BCEC-monolayer. NGF released at the basolateral side counteracted degeneration of cholinergic basal nucleus of Meynert neurons. In conclusion, our present study shows a proof-of-principle, that primary monocytes secreting NGF might be useful tools to deliver NGF into the brain, however, further in vivo studies are necessary.

Isotype-specific inhibitors of the glycolytic key regulator pyruvate kinase subtype M2 moderately decelerate tumor cell proliferation

Tumor cells express the glycolytic regulator pyruvate kinase subtype M2 (M2-PK), which can occur in a tetrameric form with high affinity to its substrate phosphoenolpyruvate (PEP) and a dimeric form with a low PEP affinity. The transition between both conformations contributes to the control of glycolysis and is important for tumor cell proliferation and survival. Here we targeted M2-PK by synthetic peptide aptamers, which specifically bind to M2-PK and shift the isoenzyme into its low affinity dimeric conformation. The aptamer-induced dimerization and inactivation of M2-PK led to a significant decrease in the PK mass-action ratio as well as ATP:ADP ratio in the target cells. Furthermore, the expression of M2-PK-binding peptide aptamers moderately reduced the growth of immortalized NIH3T3 cell populations by decelerating cell proliferation, but without affecting apoptotic cell death. Moreover, the M2-PK-binding peptide aptamers also reduced the proliferation rate of human U-2 OS osteosarcoma cells. In the present study, we developed the first specific inhibitors of the pyruvate kinase isoenzyme type M2 and present evidence that these inhibitors moderately decelerate tumor cell proliferation.

Primary rat monocytes migrate through a BCEC-monolayer and express microglia-markers at the basolateral side

Monocytes are pluripotent cells of the immune system, circulate in the blood and cross the blood-brain barrier continuously through life. The aim of this study was to explore if primary rat monocytes can adhere and transmigrate at a monolayer of brain capillary endothelial cells (BCEC) and if the monocytes undergo differentiation toward a microglial phenotype at the basolateral side. Monocytes and as a control primary microglia were immunohistochemically stained with markers for CD68 (clone ED-1), CD11b (clone OX-42) or CD11c (clone 8A2). The primary rat monocytes (100,000 cells added) adhered at the BCEC-monolayer (approx. 1200 cells/well) within 30 min and migrated to the basolateral side within 18 h (approx. 40,000 cells/well). The transmigrated monocytes partly differentiated and expressed microglia-markers at the basolateral side. Tumor necrosis factor-alpha as well as conditioned medium derived from BCEC stimulated the differentiation of monocytes in culture. In conclusion, monocytes adhere and migrate through a BCEC-monolayer and express microglia-markers at the basolateral side.