Hongna Pan

Subchronic alpha-linolenic acid treatment enhances brain plasticity and exerts an antidepressant effect: a versatile potential therapy for stroke.

Omega-3 polyunsaturated fatty acids are known to have therapeutic potential in several neurological and psychiatric disorders. However, the molecular mechanisms of action underlying these effects are not well elucidated. We previously showed that alpha-linolenic acid (ALA) reduced ischemic brain damage after a single treatment. To follow-up this finding, we investigated whether subchronic ALA treatment promoted neuronal plasticity. Three sequential injections with a neuroprotective dose of ALA increased neurogenesis and expression of key proteins involved in synaptic functions, namely, synaptophysin-1, VAMP-2, and SNAP-25, as well as proteins supporting glutamatergic neurotransmission, namely, V-GLUT1 and V-GLUT2. These effects were correlated with an increase in brain-derived neurotrophic factor (BDNF) protein levels, both in vitro using neural stem cells and hippocampal cultures and in vivo, after subchronic ALA treatment. Given that BDNF has antidepressant activity, this led us to test whether subchronic ALA treatment could produce antidepressant-like behavior. ALA-treated mice had significantly reduced measures of depressive-like behavior compared with vehicle-treated animals, suggesting another aspect of ALA treatment that could stimulate functional stroke recovery by potentially combining acute neuroprotection with long-term repair/compensatory plasticity. Indeed, three sequential injections of ALA enhanced protection, either as a pretreatment, wherein it reduced post-ischemic infarct volume 24 h after a 1-hour occlusion of the middle cerebral artery or as post-treatment therapy, wherein it augmented animal survival rates by threefold 10 days after ischemia.

BHLHB2 Controls Bdnf Promoter 4 Activity and Neuronal Excitability

Brain-derived neurotrophic factor (BDNF), via activation of TrkB receptors, mediates vital physiological functions in the brain, ranging from neuronal survival to synaptic plasticity, and has been implicated in the pathophysiology of neurodegenerative disorders. Although transcriptional regulation of the BDNF gene (Bdnf) has been extensively studied, much remains to be understood. We discovered a sequence within Bdnf promoter 4 that binds the basic helix-loop-helix protein BHLHB2 and is a target for BHLHB2-mediated transcriptional repression. NMDA receptor activation de-repressed promoter 4-mediated transcription and correlated with reduced occupancy of the promoter by BHLHB2 in cultured hippocampal neurons. Bhlhb2 gene −/− mice showed increased hippocampal exon 4-specific Bdnf mRNA levels compared with +/+ littermates under basal and activity-dependent conditions. Bhlhb2 knock-out mice also showed increased status epilepticus susceptibility, suggesting that BHLHB2 alters neuronal excitability. Together, these results support a role for BHLHB2 as a new modulator of Bdnf transcription and neuronal excitability.

Preconditioning and neurotrophins: a model for brain adaptation to seizures, ischemia and other stressful stimuli.

Summary.The amino acid glutamate, the major excitatory neurotransmitter in the central nervous system, activates receptors coupled to calcium influx. Excessive activation of glutamate receptors in conditions such as severe epileptic seizures or stroke can kill neurons in a process called excitotoxicity. However, subtoxic levels of activation of the N-methyl-D-aspartate (NMDA) type of glutamate receptor elicit adaptive responses in neurons that enhance their ability to withstand more severe stress. A variety of stimuli induce adaptive responses to protect neurons. For example, sublethal ischemic episodes or a mild epileptic insult can protect neurons in a process referred to as tolerance. The molecular mechanisms that protect neurons by these different stressful stimuli are largely unknown but they share common features such as the transcription factor, nuclear factor kappa B (NF-κB), which is activated by ischemic and epileptic preconditioning as well as exposure to subtoxic NMDA concentrations. In this article, we describe stress-induced neuroprotective mechanisms highlighting the role of brain-derived neurotrophic factor (BDNF), a protein that plays a crucial role in neuronal survival and maintenance, neurogenesis and learning and memory.

Dynamic chromatin remodeling events in hippocampal neurons are associated with NMDA receptor-mediated activation of Bdnf gene promoter 1.

To determine the epigenetic events associated with NMDA receptor‐mediated activation of brain‐derived neurotrophic factor gene (Bdnf) promoter 1 by hippocampal neurons in culture, we screened 12 loci across 4.5 kb of genomic DNA 5′ of the transcription start site (TSS) of rat Bdnf for specific changes in histone modification and transcription factor binding following NMDA receptor stimulation. Chromatin immunoprecipitation (ChIP) assays showed that NMDA receptor stimulation produced a durable, time‐dependent decrease in histone H3 at lysine 9 dimethylation (H3K9me2), within 3 h after NMDA treatment across multiple loci. Concomitant increases in H3K4me2 and H3K9/14 acetylation (H3AcK9/14) were associated with transcriptional activation, but occurred at fewer sites within the promoter. The decrease in H3K9me2 was associated with release of HDAC1, MBD1, MeCP2, and REST from specific locations within promoter 1, although with different kinetics. In addition, occupancy of sites proximal to and distal to the TSS by the transcription factors NF‐κB, CREB‐binding protein (CBP), and cAMP‐response element‐binding protein were correlated with increased occupancy of RNA polymerase II at two loci proximal to the TSS following NMDA receptor stimulation. These temporal changes in promoter occupancy could occur thousands of base pairs 5′ of the TSS, suggesting a mechanism that produces waves of Bdnf transcription.

Alpha-linolenic acid is a potent neuroprotective agent against soman-induced neuropathology

Nerve agents are deadly threats to military and civilian populations around the world. Nerve agents cause toxicity to peripheral and central sites through the irreversible inhibition of acetylcholinesterase, the enzyme that metabolizes acetylcholine. Excessive acetylcholine accumulation in synapses results in status epilepticus in the central nervous system. Prolonged status epilepticus leads to brain damage, neurological dysfunction and poor outcome. Anticonvulsants are effective but must be given rapidly following exposure. Because these agents cause mass casualties, effective neuroprotective agents are needed to reduce brain damage and improve cognitive outcome. α-Linolenic acid is an omega-3 fatty acid that is found in vegetable products and has no known side effects. α-Linolenic acid is neuroprotective against kainic acid-induced brain damage in vivo, but its neuroprotective efficacy against nerve agents is unknown. α-Linolenic acid also exerts anti-depressant and anti-inflammatory activities and enhances synaptic plasticity in vivo. These properties make this polyunsaturated fatty acid (PUFA) a potential candidate against nerve agent-induced neuropathology. Here we show that α-linolenic acid is neuroprotective against soman-induced neuropathology in either a pretreatment or post-treatment paradigm. We also show that subcutaneous injection of α-linolenic acid shows greater neuroprotective efficacy compared with intravenous injection in a brain region-specific manner.

Brain Adaptation to Stressful Stimuli: A New Perspective on Potential Therapeutic Approaches Based on BDNF and NMDA Receptors

A variety of sublethal or stressful stimuli induce a phenomenon in the brain known as tolerance, an adaptive response that protects the brain against the same stress, or against a different stress (cross-tolerance). Understanding the molecular mechanisms of brain preconditioning holds promise in developing innovative therapies to prevent and treat neurodegenerative disorders, particularly ischemic stroke. Many of the detailed steps involved in tolerance and cross-tolerance are unknown. It is also likely that different stressors differentially regulate sets of genes, transcription factors, and signal transduction pathways that depend upon the molecules that are released in response to the stressor, activation of particular receptors, and the surrounding milieu. The focus of this review is to highlight a few examples of stimuli that induce tolerance: 1) cortical spreading depression; 2) 3-nitropropionic acid; and 3) 2-deoxy-D-glucose. We will summarize by discussing one pathway where intracellular mediators may converge to upregulate intrinsic neuronal survival pathways to promote survival by resisting damage. This mechanism, activation of N-methyl-D-aspartate receptors and its integral relationship with brain-derived neurotrophic factor, may be a critical and general mechanism developed in brain to respond to stressful stimuli.

Repeated systemic administration of the nutraceutical alpha-linolenic acid exerts neuroprotective efficacy, an antidepressant effect and improves cognitive performance when given after soman exposure

Exposure to nerve agents results in severe seizures or status epilepticus caused by the inhibition of acetylcholinesterase, a critical enzyme that breaks down acetylcholine to terminate neurotransmission. Prolonged seizures cause brain damage and can lead to long-term consequences. Current countermeasures are only modestly effective against the brain damage supporting interest in the evaluation of new and efficacious therapies. The nutraceutical alpha-linolenic acid (LIN) is an essential omega-3 polyunsaturated fatty acid that has a wide safety margin. Previous work showed that a single intravenous injection of alpha-linolenic acid (500 nmol/kg) administered before or after soman significantly protected against soman-induced brain damage when analyzed 24h after exposure. Here, we show that administration of three intravenous injections of alpha-linolenic acid over a 7 day period after soman significantly improved motor performance on the rotarod, enhanced memory retention, exerted an anti-depressant-like activity and increased animal survival. This dosing schedule significantly reduced soman-induced neuronal degeneration in four major vulnerable brain regions up to 21 days. Taken together, alpha-linolenic acid reduces the profound behavioral deficits induced by soman possibly by decreasing neuronal cell death, and increases animal survival.

α-Linolenic Acid, A Nutraceutical with Pleiotropic Properties That Targets Endogenous Neuroprotective Pathways to Protect against Organophosphate Nerve Agent-Induced Neuropathology

α-Linolenic acid (ALA) is a nutraceutical found in vegetable products such as flax and walnuts. The pleiotropic properties of ALA target endogenous neuroprotective and neurorestorative pathways in brain and involve the transcription factor nuclear factor kappa B (NF-κB), brain-derived neurotrophic factor (BDNF), a major neuroprotective protein in brain, and downstream signaling pathways likely mediated via activation of TrkB, the cognate receptor of BDNF. In this review, we discuss possible mechanisms of ALA efficacy against the highly toxic OP nerve agent soman. Organophosphate (OP) nerve agents are highly toxic chemical warfare agents and a threat to military and civilian populations. Once considered only for battlefield use, these agents are now used by terrorists to inflict mass casualties. OP nerve agents inhibit the critical enzyme acetylcholinesterase (AChE) that rapidly leads to a cholinergic crisis involving multiple organs. Status epilepticus results from the excessive accumulation of synaptic acetylcholine which in turn leads to the overactivation of muscarinic receptors; prolonged seizures cause the neuropathology and long-term consequences in survivors. Current countermeasures mitigate symptoms and signs as well as reduce brain damage, but must be given within minutes after exposure to OP nerve agents supporting interest in newer and more effective therapies. The pleiotropic properties of ALA result in a coordinated molecular and cellular program to restore neuronal networks and improve cognitive function in soman-exposed animals. Collectively, ALA should be brought to the clinic to treat the long-term consequences of nerve agents in survivors. ALA may be an effective therapy for other acute and chronic neurodegenerative disorders.

Alpha-Linolenic Acid-Induced Increase in Neurogenesis is a Key Factor in the Improvement in the Passive Avoidance Task After Soman Exposure

AbstractExposure to organophosphorous (OP) nerve agents such as soman inhibits the critical enzyme acetylcholinesterase (AChE) leading to excessive acetylcholine accumulation in synapses, resulting in cholinergic crisis, status epilepticus and brain damage in survivors. The hippocampus is profoundly damaged after soman exposure leading to long-term memory deficits. We have previously shown that treatment with three sequential doses of alpha-linolenic acid, an essential omega-3 polyunsaturated fatty acid, increases brain plasticity in naïve animals. However, the effects of this dosing schedule administered after a brain insult and the underlying molecular mechanisms in the hippocampus are unknown. We now show that injection of three sequential doses of alpha-linolenic acid after soman exposure increases the endogenous expression of mature BDNF, activates Akt and the mammalian target of rapamycin complex 1 (mTORC1), increases neurogenesis in the subgranular zone of the dentate gyrus, increases retention latency in the passive avoidance task and increases animal survival. In sharp contrast, while soman exposure also increases mature BDNF, this increase did not activate downstream signaling pathways or neurogenesis. Administration of the inhibitor of mTORC1, rapamycin, blocked the alpha-linolenic acid-induced neurogenesis and the enhanced retention latency but did not affect animal survival. Our results suggest that alpha-linolenic acid induces a long-lasting neurorestorative effect that involves activation of mTORC1 possibly via a BDNF-TrkB-mediated mechanism.

(-)-Phenserine attenuates soman-induced neuropathology.

Organophosphorus (OP) nerve agents are deadly chemical weapons that pose an alarming threat to military and civilian populations. The irreversible inhibition of the critical cholinergic degradative enzyme acetylcholinesterase (AChE) by OP nerve agents leads to cholinergic crisis. Resulting excessive synaptic acetylcholine levels leads to status epilepticus that, in turn, results in brain damage. Current countermeasures are only modestly effective in protecting against OP-induced brain damage, supporting interest for evaluation of new ones. (-)-Phenserine is a reversible AChE inhibitor possessing neuroprotective and amyloid precursor protein lowering actions that reached Phase III clinical trials for Alzheimers Disease where it exhibited a wide safety margin. This compound preferentially enters the CNS and has potential to impede soman binding to the active site of AChE to, thereby, serve in a protective capacity. Herein, we demonstrate that (-)-phenserine protects neurons against soman-induced neuronal cell death in rats when administered either as a pretreatment or post-treatment paradigm, improves motoric movement in soman-exposed animals and reduces mortality when given as a pretreatment. Gene expression analysis, undertaken to elucidate mechanism, showed that (-)-phenserine pretreatment increased select neuroprotective genes and reversed a Homer1expression elevation induced by soman exposure. These studies suggest that (-)-phenserine warrants further evaluation as an OP nerve agent protective strategy.