Energetic, oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky-Molodkina model)

Epileptiform Discharges Reduce Neuronal ATP Production by Inhibiting F0F1-ATP Synthase Activity via A Zinc-α2-Glycoprotein-Dependent Mechanism

Neuronal energy metabolism dysfunction, especially adenosine triphosphate (ATP) supply decrease, is observed in epilepsy and associated with epileptogenesis and prognosis. Zinc-α2-glycoprotein (ZAG) is known as an important modulator of energy metabolism and involved in neuronal glucose metabolism, fatty acid metabolism, and ketogenesis impairment in seizures, but its effect on neuronal ATP synthesis in seizures and the specific mechanism are unclear. In this study, we verified the localization of ZAG in primary cultured neuronal mitochondria by using double-labeling immunofluorescence, immune electron microscopy, and western blot. ZAG level in neuronal mitochondria was modulated by lentiviruses and detected by western blot. The F0F1-ATP synthase activity, ATP level, and acetyl-CoA level were measured. The binding between ZAG and F0F1-ATP synthase was determined by coimmunoprecipitation. We found that both ZAG and F0F1-ATP synthase existed in neuronal mitochondria, and there was mutual binding between them. Epileptiform discharge-induced decrease of mitochondrial ZAG level was reversed by ZAG overexpression. Epileptiform discharge or ZAG knockdown decreased F0F1-ATP synthase activity and ATP level in neurons, which were reversed by ZAG overexpression, while overexpression of ZAG along only increased F0F1-ATP synthase activity but not increased ATP level. Meanwhile, neither epileptiform discharges nor changes of ZAG level can alter the acetyl-CoA level. Moreover, epileptiform discharge did not alter F0F1-ATP synthase level. In conclusion, epileptiform discharge-induced ZAG decrease in neuronal mitochondria is correlated to F0F1-ATP synthase activity inhibition, which may possibly lead to ATP supply impairments. ZAG may be a potential therapeutic target for treating neuronal energy metabolism dysfunction in seizures with further researches.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Transcriptome of the Krushinsky-Molodkina Audiogenic Rat Strain and Identification of Possible Audiogenic Epilepsy-Associated Genes

Audiogenic epilepsy (AE), inherent to several rodent strains is widely studied as a model of generalized convulsive epilepsy. The molecular mechanisms that determine the manifestation of AE are not well understood. In the present work, we compared transcriptomes from the corpora quadrigemina in the midbrain zone, which are crucial for AE development, to identify genes associated with the AE phenotype. Three rat strains without sound exposure were compared: Krushinsky-Molodkina (KM) strain (100% AE-prone); Wistar outbred rat strain (non-AE prone) and “0” strain (partially AE-prone), selected from F2 KM × Wistar hybrids for their lack of AE. The findings showed that the KM strain gene expression profile exhibited a number of characteristics that differed from those of the Wistar and “0” strain profiles. In particular, the KM rats showed increased expression of a number of genes involved in the positive regulation of the MAPK signaling cascade and genes involved in the positive regulation of apoptotic processes. Another characteristic of the KM strain which differed from that of the Wistar and “0” rats was a multi-fold increase in the expression level of the Ttr gene and a significant decrease in the expression of the Msh3 gene. Decreased expression of a number of oxidative phosphorylation-related genes and a few other genes was also identified in the KM strain. Our data confirm the complex multigenic nature of AE inheritance in rodents. A comparison with data obtained from other independently selected AE-prone rodent strains suggests some common causes for the formation of the audiogenic phenotype.

Intranasal administration of mitochondria improves spatial memory in olfactory bulbectomized mice

Here, we found that functionally active mitochondria isolated from the brain of NMRI donor mice and administrated intranasally to recipient mice penetrated the brain structures in a dose-dependent manner. The injected mitochondria labeled with the MitoTracker Red localized in different brain regions, including the neocortex and hippocampus, which are responsible for memory and affected by degeneration in patients with Alzheimer's disease. In behavioral experiments, intranasal microinjections of brain mitochondria of native NMRI mice improved spatial memory in the olfactory bulbectomized (OBX) mice with Alzheimer's type degeneration. Control OBX mice demonstrated loss of spatial memory tested in the Morris water maze. Immunocytochemical analysis revealed that allogeneic mitochondria colocalized with the markers of astrocytes and neurons in hippocampal cell culture. The results suggest that a non-invasive route intranasal administration of mitochondria may be a promising approach to the treatment of neurodegenerative diseases characterized, like Alzheimer's disease, by mitochondrial dysfunction.

Energy Metabolism and Redox State in Brains of Wistar Audiogenic Rats, a Genetic Model of Epilepsy

The Wistar Audiogenic Rat (WAR) strain is a genetic model of epilepsy, specifically brainstem-dependent tonic-clonic seizures, triggered by acute auditory stimulation. Chronic audiogenic seizures (audiogenic kindling) mimic temporal lobe epilepsy, with significant participation of the hippocampus, amygdala, and cortex. The objective of the present study was to characterize the mitochondrial energy metabolism in hippocampus and cortex of WAR and verify its relationship with seizure severity. Hippocampus of WAR naïve (no seizures) presented higher oxygen consumption in respiratory states related to the maximum capacities of phosphorylation and electron transfer system, elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl and lactate contents, compared with their Wistar counterparts. Audiogenic kindling had no adding functional effect in WAR, but in Wistar, it induced the same alterations observed in the audiogenic strain. In the cortex, WAR naïve presented elevated mitochondrial density, lower GSH/GSSG and catalase activity, and higher protein carbonyl levels. Chronic acoustic stimulation in Wistar induced the same alterations in cortex and hippocampus. Mainly in the hippocampus, WAR naïve presented elevated mRNA expression of glucose, lactate and excitatory amino acids transporters, several glycolytic enzymes, lactate dehydrogenase, and Na⁺/K⁺ ATPase in neurons and in astrocytes. In vivo treatment with mitochondrial uncoupler 2,4-dinitrophenol (DNP) or N-acetylcysteine (NAC) in WAR had no effect on mitochondrial metabolism, but lowered oxidative stress. Unlike DNP, NAC downregulated all enzyme genes involved in glucose and lactate uptake, and metabolism in neurons and astrocytes. Additionally, it was able to reduce brainstem seizure severity in WAR. In conclusion, in WAR naïve animals, both cerebral cortex and hippocampus display elevated mitochondrial density and/or activity associated with oxidative damage, glucose and lactate metabolism pathways upregulation, and increased Na⁺/K⁺ ATPase mRNA expression. Only in vivo treatment with NAC was able to reduce seizure severity of kindled WARs, possibly via down regulation of glucose/lactate metabolism. Taken together, our results are a clear contribution to the field of mitochondrial metabolism associated to epileptic seizures.

A comparison of mitochondrial toxicity of mephedrone on three separate parts of brain including hippocampus, cortex and cerebellum

Mephedrone (4-methylmethcathinone) is a new and popular drug of abuse and also widely available on the internet and still legal in some parts of the world. The central nervous system is the target of mephedrone and recent evidence suggested that mephedrone could affect mitochondria in brain tissue. However, the underlying mechanisms of mephedrone toxicity in brain mitochondria have not yet been well understood. In this study, mitochondria from three separate parts of rat brain hippocampus, cortex, and cerebellum were obtained using differential centrifugation and were incubated with different concentrations of mephedrone (3, 6 and 12 μM). Then, the mitochondrial parameters toxicity were determined. The results showed that mephedrone (3, 6 and 12 μM) induced impairment in the activity of the mitochondrial complex II and IV. Also, mephedrone (3, 6 and 12 μM) increased mitochondrial reactive oxygen species (ROS) level, collapsed mitochondria membrane potential (MMP), induced swelling in the mitochondria and damaged the mitochondrial outer membrane (MOM) in the mitochondria obtained from hippocampus, cortex, and cerebellum, which in all cases is associated with the cytochrome c release. Furthermore, increased disturbance in oxidative phosphorylation was also shown by the decrease in ATP level in mephedrone-treated mitochondria indicating mitochondrial dysfunction in separate parts of the brain. This study suggests that mephedrone via increasing oxidative stress and impairment of the mitochondrial respiratory chain in the hippocampus, cortex, and cerebellum may play a key role in the neurotoxicity.

The highly efficient powerhouse in the Wistar audiogenic rat, an epileptic rat strain

The Wistar audiogenic rat (WAR) is an animal model of tonic-clonic epileptic seizures, developed after genetic selection by sister × brother inbreeding of Wistar rats susceptible to sound stimuli. Although metabolic changes have been described in this strain, nothing is known about its mitochondrial metabolism. Here, we addressed mitochondrial aspects of oxidative phosphorylation, oxidative stress, biogenesis, and dynamics in liver, skeletal muscle, and heart of male WARs and correlating them with physiological aspects of body metabolism. The results showed higher mitochondrial content, respiration rates in phosphorylation and noncoupled states, and H₂O₂ production in WARs. Liver presented higher content of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) and mammalian target of rapamycin, proteins related to mitochondrial biogenesis. In agreement, isolated liver mitochondria from WARs showed higher respiration rates in phosphorylation state and ADP-to-O ratio, as well as higher content of proteins related to electron transport chain ATP synthase, TCA cycle, and mitochondrial fusion and fission compared with their Wistar counterparts. Mitochondria with higher area and perimeter and more variable shapes were found in liver and soleus from WARs in addition to lower reduced-to-oxidized glutathione ratio. In vivo, WARs demonstrated lower body mass and energy expenditure but higher food and water intake and amino acid oxidation. When exposed to a running test, WARs reached higher speed and resisted for a longer time and distance than their Wistar controls. In conclusion, the WAR strain has mitochondrial changes in liver, skeletal muscle, and heart that improve its mitochondrial capacity of ATP production, making it an excellent rat model to study PGC1α overexpression and mitochondrial function in different physiological conditions or facing pathological challenges.

Study of Uridine Effect on the Development of Audiogenic Tonic Seizures in Krushinsky-Molodkina Strain Rats

The latency of tonic seizure in response to loud sound (in rats of the Krushinsky-Molodkina strain with audiogenic epilepsy) had been slightly (although statistically significantly) longer after chronic uridine injections (100 mg/kg, i.p., three times a day during 9 or 12 days). The recovery time from the tonic seizure was shorter after 12 days of injections in comparison to the 9-day injection period. At the same time, the intensity of tonic seizures provoked by loud sound did not change after chronic uridine injections. The lack of uridine anticonvulsive effect demonstrated in the audiogenic epilepsy model contradicts the anticonvulsant effects of uridine in experiments with other seizure models, in which the epileptic foci were localized in the forebrain structures.