Long-term expression of metabolism-associated genes in the rat hippocampus following recurrent neonatal seizures and its regulation by melatonin

Food for Thought: Leptin and Hippocampal Synaptic Function

It is well documented that the endocrine hormone, leptin controls energy homeostasis by providing key signals to specific hypothalamic nuclei. However, our knowledge of leptin’s central actions has advanced considerably over the last 20 years, with the hippocampus now established as an important brain target for this hormone. Leptin receptors are highly localised to hippocampal synapses, and increasing evidence reveals that activation of synaptically located leptin receptors markedly impacts cognitive processes, and specifically hippocampal-dependent learning and memory. Here, we review the recent actions of leptin at hippocampal synapses and explore the consequences for brain health and disease.

Metal ion homeostasis with emphasis on zinc and copper: Potential crucial link to explain the non-classical antioxidative properties of vitamin D and melatonin

Metal ion homeostasis is an essential physiological mechanism necessary for achieving an adequate balance of these ions' concentrations in the different cellular compartments. This fact is of great importance because both an excess and a deficiency of cellular metal ion levels are usually equally harmful due to the exacerbated increase in oxidative stress that may occur in both cases. Metal ion homeostasis ensures an equilibrium among multiple functions associated with the body's antioxidative defense network controlled by metallic micronutrients such as zinc and copper, some of the central regulators of redox processes. These micronutrients significantly modulate the activity of some isoforms of superoxide dismutase (SOD) and other enzymes such as metallothioneins (MTs) and ceruloplasmin (CP), which are directly or indirectly involved in the regulation of redox homeostasis. Although it is well known that both melatonin (MEL) and vitamin D have important roles as natural antioxidants, often some of these effects are related to their actions on antioxidative processes dependent on metal ions. Thus, in addition to their classical antioxidative properties usually associated with mitochondrial effects, it is known that MEL and vitamin D modulate the expression and activity of Cu/Zn-dependent SOD isoforms, MTs and CP; function as copper chelators and regulate genomic and non-genomic mechanisms related to the zinc transport. This review summarizes the main findings related to the crucial participation of zinc and copper in physiological antioxidative status and their relationship with the non-classical antioxidant effects of MEL and vitamin D, suggesting a potential synergism among these four micronutrients.

Effects of Melatonin on Neurobehavior and Cognition in a Cerebral Palsy Model of plppr5-/- Mice

Cerebral palsy (CP), a group of clinical syndromes caused by non-progressive brain damage in the developing fetus or infant, is one of the most common causes of lifelong physical disability in children in most countries. At present, many researchers believe that perinatal cerebral hypoxic ischemic injury or inflammatory injury are the main causes of cerebral palsy. Previous studies including our works confirmed that melatonin has a protective effect against convulsive brain damage during development and that it affects the expression of various molecules involved in processes such as metabolism, plasticity and signaling in the brain. Integral membrane protein plppr5 is a new member of the plasticity-related protein family, which is specifically expressed in brain and spinal cord, and induces filopodia formation as well as neurite growth. It is highly expressed in the brain, especially in areas of high plasticity, such as the hippocampus. The signals are slightly lower in the cortex, the cerebellum, and in striatum. Noteworthy, during development plppr5 mRNA is expressed in the spinal cord, i.e., in neuron rich regions such as in medial motor nuclei, suggesting that plppr5 plays an important role in the regulation of neurons. However, the existing literature only states that plppr5 is involved in the occurrence and stability of dendritic spines, and research on its possible involvement in neonatal ischemic hypoxic encephalopathy has not been previously reported. We used plppr5 knockout (plppr5-/-) mice and their wild-type littermates to establish a model of hypoxicischemic brain injury (HI) to further explore the effects of melatonin on brain injury and the role of plppr5 in this treatment in an HI model, which mainly focuses on cognition, exercise, learning, and memory. All the tests were performed at 3-4 weeks after HI. As for melatonin treatment, which was performed 5 min after HI injury and followed by every 24h. In these experiments, we found that there was a significant interaction between genotype and treatment in novel object recognition tests, surface righting reflex tests and forelimb suspension reflex tests, which represent learning and memory, motor function and coordination, and the forelimb grip of the mice, respectively. However, a significant main effect of genotype and treatment on performance in all behavioral tests were observed. Specifically, wild-type mice with HI injury performed better than plppr5-/- mice, regardless of treatment with melatonin or vehicle. Moreover, treatment with melatonin could improve behavior in the tests for wild-type mice with HI injury, but not for plppr5-/- mice. This study showed that plppr5 knockout aggravated HI damage and partially weakened the neuroprotection of melatonin in some aspects (such as novel object recognition test and partial nerve reflexes), which deserves further study.

Mitochondria and immunity in chronic fatigue syndrome

It is widely accepted that the pathophysiology and treatment of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) could be considerably improved. The heterogeneity of ME/CFS and the confusion over its classification have undoubtedly contributed to this, although this would seem a consequence of the complexity of the array of ME/CFS presentations and high levels of diverse comorbidities. This article reviews the biological underpinnings of ME/CFS presentations, including the interacting roles of the gut microbiome/permeability, endogenous opioidergic system, immune cell mitochondria, autonomic nervous system, microRNA-155, viral infection/re-awakening and leptin as well as melatonin and the circadian rhythm. This details not only relevant pathophysiological processes and treatment options, but also highlights future research directions. Due to the complexity of interacting systems in ME/CFS pathophysiology, clarification as to its biological underpinnings is likely to considerably contribute to the understanding and treatment of other complex and poorly managed conditions, including fibromyalgia, depression, migraine, and dementia. The gut and immune cell mitochondria are proposed to be two important hubs that interact with the circadian rhythm in driving ME/CFS pathophysiology.

TMT-Based Proteomic Analysis of Plasma from Children with Rolandic Epilepsy

Rolandic epilepsy is one of the most common epileptic syndromes in childhood. We used TMT-based proteomics and bioinformatics analysis to identify the differentially expressed proteins in plasma of children with Rolandic epilepsy. Our aim was to provide a molecular basis for exploring possible mechanisms underlying the pathogenesis of epilepsy. Subjects were divided into two groups (five in each): patients with Rolandic epilepsy as cases and patients with migraine as controls. Total proteins were extracted and quantitatively labeled with TMT, then analyzed using liquid chromatography mass spectrometry. Bioinformatics analysis was used to identify the hub genes. A total of 752 proteins were identified, of which 670 contained quantitative proteins. 217 differentially expressed proteins were identified, 46 of which were only upregulated in more than two groups and 111 of which were only downregulated in more than two groups. Bioinformatics analysis revealed top 10 hub genes in the up- and downregulated groups, respectively. Our study demonstrates that some differentially expressed proteins are associated with epilepsy. Activation of acute-phase or innate immune response and complement and fibrinogen systems and repression of glycolysis, lipoprotein metabolism, and antioxidant activity may play a role in the development of epilepsy.

Protective effects of leptin against cerebral ischemia/reperfusion injury

In recent years, the use of thrombolytic therapy for treating ischemia/reperfusion injury has resulted in damage to the self-regulatory mechanisms of the brain. This is due to the increased production of free radicals, excitatory amino acids and pro-inflammatory cytokines causing secondary damage to the brain. Simple thrombolytic therapy has not been the best approach for treating ischemia/reperfusion injury. Excessive perfusion leads to failure of the body's self-regulatory functions, which in turn increases the area of cerebral edema and aggravates cerebral ischemia. Previous studies have evaluated the satiety hormone leptin as a link between energy expenditure and obesity. Of note, leptin, which is involved in brain development, synaptic transmission and angiogenesis following ischemia/reperfusion injury, has been considered an important factor for treating ischemia/reperfusion injury. The present review outlines the discovery of leptin and discusses its association with cerebral ischemia/reperfusion.

Reduction of Mitophagy-Related Oxidative Stress and Preservation of Mitochondria Function Using Melatonin Therapy in an HT22 Hippocampal Neuronal Cell Model of Glutamate-Induced Excitotoxicity

Recent evidence indicates that autophagy-mediated mitochondrial homeostasis is crucial for oxidative stress-related brain damage and repair. The highest concentration of melatonin is in the mitochondria of cells, and melatonin exhibits well-known antioxidant properties. We investigated the impact and mechanism involved in mitochondrial function and the mitochondrial oxidative stress/autophagy regulator parameters of glutamate cytotoxicity in mouse HT22 hippocampal neurons. We tested the hypothesis that melatonin confers neuroprotective effects via protecting against mitochondrial impairment and mitophagy. Cells were divided into four groups: the control group, melatonin alone group, glutamate injury group, and melatonin pretreatment group. We found that glutamate induced significant changes in mitochondrial function/oxidative stress-related parameters. Leptin administration preserved mitochondrial function, and this effect was associated with increased superoxide dismutase, glutathione (GSH), and mitochondrial membrane potential and decreased GSSG (oxidized glutathione) and mitochondrial reactive oxygen species. Melatonin significantly reduced the fluorescence intensity of mitophagy via the Beclin-1/Bcl-2 pathway, which involves Beclin-1 and Bcl-2 proteins. The mitophagy inhibitor CsA corrected these glutamate-induce changes, as measured by the fluorescence intensity of Mitophagy-Tracker Red CMXROS, mitochondrial ROS, and mitochondrial membrane potential changes. These findings indicate that melatonin exerts neuroprotective effects against glutamate-induced excitotoxicity by reducing mitophagy-related oxidative stress and maintaining mitochondrial function.

Leptin-regulated autophagy plays a role in long-term neurobehavioral injury after neonatal seizures and the regulation of zinc/cPLA2 and CaMK II signaling in cerebral cortex

Metabolic disorders play an important role in the pathogenesis of many neurological diseases. Recent evidence suggests that leptin levels in peripheral blood and brain are lower in patients with epilepsy. Leptin is an energy-regulating hormone that plays a neuroprotective role in neurodegenerative diseases and brain trauma. However, little is known about the effects and molecular mechanisms of leptin treatment on long-term neurobehavioral impairment caused by developmental seizures. The present study evaluated whether chronic leptin treatment protected against neurobehavioral impairments induced by recurrent seizures in newborns treated with flurothyl. We also examined the effect of leptin on the expression of zinc/cPLA2-related autophagy signaling molecules and CaMKII in the cerebral cortex. Twenty Sprague-Dawley rats (6 days after birth, P6) were randomly divided into two groups, a neonatal seizure group and control group. Rats were subdivided on P13 into control, control + leptin (leptin, 2 mg/kg/day, continuous 10 days), seizure (RS), and seizure + leptin group (RS + leptin, 2 mg/kg/day for 10 consecutive days). Neurological behavioral parameters (negative geotaxis reaction reflex, righting reflex, cliff avoidance reflex, forelimb suspension reflex and open field test) were observed from P23 to P30. mRNA and protein levels in the cerebral cortex were detected using real-time RT-PCR and Western blotting, respectively. Flurothyl-induced seizures (RS group) produced long-term abnormal neurobehavior, which was improved with leptin treatment. Chronic leptin treatment restored several expression parameters affected by neonatal seizures, including seizure-induced up-regulated zinc transporter ZnT1/ZIP7, lipid membrane injury-related cPLA2, autophagy marker beclin-1/bcl2, LC3II/LC3I, and its execution molecule cathepsin-E, and down-regulated memory marker CaMK II alpha. Our results suggest that the early use of leptin after neonatal recurrent seizures may exert neuroprotective effects and antagonize the long-term neurobehavioral impairment caused by seizures. Autophagy-mediated Zn/cPLA2 and CaMK II signaling in the cerebral cortex may be involved in the neuroprotective effect of leptin. Our results provide new clues for anti-epileptogenetic treatment.

HMGB1 regulates P-glycoprotein expression in status epilepticus rat brains via the RAGE/NF-κB signaling pathway

Overexpression of P-glycoprotein (P-gp) in the brain is an important mechanism involved in drug-resistant epilepsy (DRE). High-mobility group box 1 (HMGB1), an inflammatory cytokine, significantly increases following seizures and may be involved in upregulation of P-gp. However, the underlying mechanisms remain elusive. The aim of the present study was to evaluate the role of HMGB1 and its downstream signaling components, receptor for advanced glycation end-product (RAGE) and nuclear factor-κB (NF-κB), on P-gp expression in rat brains during status epilepticus (SE). Small interfering RNA (siRNA) was administered to rats prior to induction of SE by pilocarpine, to block transcription of the genes encoding HMGB1 and RAGE, respectively. An inhibitor of NF-κB, pyrrolidinedithiocarbamic acid (PDTC), was utilized to inhibit activation of NF-κB. The expression levels of HMGB1, RAGE, phosphorylated-NF-κB p65 (p-p65) and P-gp were detected by western blotting. The relative mRNA expression levels of the genes encoding these proteins were measured using reverse transcription-quantitative polymerase chain reaction and the cellular localization of the proteins was determined by immunofluorescence. Pre-treatment with HMGB1 siRNA reduced the expression levels of RAGE, p-p65 and P-gp. PDTC reduced the expression levels of P-gp. These findings suggested that overexpression of P-gp during seizures may be regulated by HMGB1 via the RAGE/NF-κB signaling pathway, and may be a novel target for treating DRE.