The ATP-sensitive K channel is seizure protective and required for effective dietary therapy in a model of mitochondrial encephalomyopathy

Thalamocortical circuits in generalized epilepsy: Pathophysiologic mechanisms and therapeutic targets

Generalized epilepsy affects 24 million people globally; at least 25% of cases remain medically refractory. The thalamus, with widespread connections throughout the brain, plays a critical role in generalized epilepsy. The intrinsic properties of thalamic neurons and the synaptic connections between populations of neurons in the nucleus reticularis thalami and thalamocortical relay nuclei help generate different firing patterns that influence brain states. In particular, transitions from tonic firing to highly synchronized burst firing mode in thalamic neurons can cause seizures that rapidly generalize and cause altered awareness and unconsciousness. Here, we review the most recent advances in our understanding of how thalamic activity is regulated and discuss the gaps in our understanding of the mechanisms of generalized epilepsy syndromes. Elucidating the role of the thalamus in generalized epilepsy syndromes may lead to new opportunities to better treat pharmaco-resistant generalized epilepsy by thalamic modulation and dietary therapy.

Ketone Body Rescued Seizure Behavior of LRP1 Deficiency in Drosophila by Modulating Glutamate Transport

LRP1, the low-density lipoprotein receptor 1, would be a novel candidate gene of epilepsy according to our bioinformatic results and the animal study. In this study, we explored the role of LRP1 in epilepsy and whether beta-hydroxybutyrate, the principal ketone body of the ketogenic diet, can treat epilepsy caused by LRP1 deficiency in drosophila. UAS/GAL4 system was used to establish different genotype models. Flies were given standard, high-sucrose, and ketone body food randomly. The bang-sensitive test was performed on flies and seizure-like behavior was assessed. In morphologic experiments, we found that LRP1 deficiency caused partial loss of the ellipsoidal body and partial destruction of the fan-shaped body. Whole-body and glia LRP1 defect flies had a higher seizure rate compared to the control group. Ketone body decreased the seizure rate in behavior test in all LRP1 defect flies, compared to standard and high sucrose diet. Overexpression of glutamate transporter gene Eaat1 could mimic the ketone body effect on LRP1 deficiency flies. This study demonstrated that LRP1 defect globally or in glial cells or neurons could induce epilepsy in drosophila. The ketone body efficaciously rescued epilepsy caused by LRP1 knockdown. The results support screening for LRP1 mutations as discriminating conduct for individuals who require clinical attention and further clarify the mechanism of the ketogenic diet in epilepsy, which could help epilepsy patients make a precise treatment case by case.

USE OF KETOGENIC DIET THERAPY IN EPILEPSY WITH MITOCHONDRIAL DYSFUNCTION: A SYSTEMATIC AND CRITICAL REVIEW

With the development of molecular techniques over time more than %60 of epilepsy has associated with mitochondrial (mt) dysfunction. Ketogenic diet (KD) has been used in the treatment of epilepsy since the 1920s. Aim. To evaluate the evidence behind KD in mt dysfunction in epilepsy. Methods. Databases PubMed, Google Scholar and MEDLINE were searched in an umbrella approach to 12 March 2021 in English. To identify relevant studies specific search strategies were devised for the following topics: (1) mitochondrial dysfunction (2) epilepsy (3) KD treatment. Results. From 1794 papers, 36 articles were included in analysis: 16 (%44.44) preclinical studies, 11 (%30.55) case reports, 9 (%25) clinical studies. In all the preclinic studies, KD regulated the number of mt profiles, transcripts of metabolic enzymes and encoding mt proteins, protected the mice against to seizures and had an anticonvulsant mechanism. Case reports and clinical trials have reported patients with good results in seizure control and mt functions, although not all of them give good results as well as preclinical. Conclusion. Healthcare institutions, researchers, neurologists, health promotion organizations, and dietitians should consider these results to improve KD programs and disease outcomes for mt dysfunction in epilepsy.

Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy

Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.

The ketogenic diet as a therapeutic intervention strategy in mitochondrial disease

Classical mitochondrial disease (MD) represents a group of complex metabolic syndromes primarily linked to dysfunction of the mitochondrial ATP-generating oxidative phosphorylation (OXPHOS) system. To date, effective therapies for these diseases are lacking. Here we discuss the ketogenic diet (KD), being a high-fat, moderate protein, and low carbohydrate diet, as a potential intervention strategy. We concisely review the impact of the KD on bioenergetics, ROS/redox metabolism, mitochondrial dynamics and mitophagy. Next, the consequences of the KD in (models of) MD, as well as KD adverse effects, are described. It is concluded that the current experimental evidence suggests that the KD can positively impact on mitochondrial bioenergetics, mitochondrial ROS/redox metabolism and mitochondrial dynamics. However, more information is required on the bioenergetic consequences and mechanistic mode-of-action aspects of the KD at the cellular level and in MD patients.

Analysis of KATP Channels Opening Probability of Hippocampus Cells Treated with Kainic Acid

Background

Kainic acid (KA)-induced seizures may be a valuable tool in the assessment of anti-epileptic drug efficacy in complex partial seizures. This study investigated the effects of KA on ATP-sensitive K⁺ (K_ATP) channels opening probability (NPo), which plays a crucial role in neuronal activities.

Methods

For the optimisation and validation protocol, β-cells were plated onto 35 mm plastic petri dishes and maintained in RPMI-1640 media supplemented with 10 mM glucose, 10% FCS and 25 mM of N-2-hydroxyethylpiperazine-N-ethanesulfonic acid (HEPES). The treatment effects of 10 mM glucose and 30 μM fluoxetine on K_ATP channels NPo of β-cells were assessed via cell-attached patch-clamp recordings. For hippocampus cell experiments, hippocampi were harvested from day 17 of maternal Lister-hooded rat foetus, and then transferred to a Ca²⁺ and Mg²⁺-free HEPES-buffered Hank's salt solution (HHSS). The dissociated cells were cultured and plated onto a 25 mm round cover glasses coated with poly-d-lysine (0.1 mg/mL) in a petri dish. The K_ATP channels NPo of hippocampus cells when perfused with 1 mM and 10 mM of KA were determined.

Results

NPo of β-cells showed significant decreasing patterns (P < 0.001) when treated with 10 mM glucose 0.048 (0.027) as well as 30 μM fluoxetine 0.190 (0.141) as compared to basal counterpart. In hippocampus cell experiment, a significant increase (P < 0.001) in mean NPo 2.148 (0.175) of neurons when applied with 1 mM of KA as compared to basal was observed.

Conclusion

The two concentrations of KA used in the study exerted contrasting effects toward the mean of NPo. It is hypothesised that KA at lower concentration (1 mM) opens more K_ATP channels, leading to hyperpolarisation of the neurons, which may prevent neuronal hyper excitability. No effect was shown in 10 mM KA treatment, suggesting that only lower than 10 mM KA produced significant changes in K_ATP channels. This implies further validation of KA concentration to be used in the future.

Energy sensors in drug addiction: A potential therapeutic target

Addiction is defined as the repeated exposure and compulsive seek of psychotropic drugs that, despite the harmful effects, generate relapse after the abstinence period. The psychophysiological processes associated with drug addiction (acquisition/expression, withdrawal, and relapse) imply important alterations in neurotransmission and changes in presynaptic and postsynaptic plasticity and cellular structure (neuroadaptations) in neurons of the reward circuits (dopaminergic neuronal activity) and other corticolimbic regions. These neuroadaptation mechanisms imply important changes in neuronal energy balance and protein synthesis machinery. Scientific literature links drug-induced stimulation of dopaminergic and glutamatergic pathways along with presence of neurotrophic factors with alterations in synaptic plasticity and membrane excitability driven by metabolic sensors. Here, we provide current knowledge of the role of molecular targets that constitute true metabolic/energy sensors such as AMPK, mTOR, ERK, or K_ATP in the development of the different phases of addiction standing out the main brain regions (ventral tegmental area, nucleus accumbens, hippocampus, and amygdala) constituting the hubs in the development of addiction. Because the available treatments show very limited effectiveness, evaluating the drug efficacy of AMPK and mTOR specific modulators opens up the possibility of testing novel pharmacotherapies for an individualized approach in drug abuse.

Identification of protein quality control regulators using a Drosophila model of TPI deficiency

Triosephosphate isomerase (TPI) deficiency (Df) is a rare recessive metabolic disorder that manifests as hemolytic anemia, locomotor impairment, and progressive neurodegeneration. Research suggests that TPI Df mutations, including the "common" TPI^E105Dmutation, result in reduced TPI protein stability that appears to underlie disease pathogenesis. Drosophila with the recessive TPI^sugarkill allele (a.k.a. sgk or M81T) exhibit progressive locomotor impairment, neuromuscular impairment and reduced longevity, modeling the human disorder. TPI^sugarkill produces a functional protein that is degraded by the proteasome. Molecular chaperones, such as Hsp70 and Hsp90, have been shown to contribute to the regulation of TPI^sugarkill degradation. In addition, stabilizing the mutant protein through chaperone modulation results in improved TPI deficiency phenotypes. To identify additional regulators of TPI^sugarkill degradation, we performed a genome-wide RNAi screen that targeted known and predicted quality control proteins in the cell to identify novel factors that modulate TPI^sugarkill turnover. Of the 430 proteins screened, 25 regulators of TPI^sugarkill were identified. Interestingly, 10 proteins identified were novel, previously undescribed Drosophila proteins. Proteins involved in co-translational protein quality control and ribosome function were also isolated in the screen, suggesting that TPI^sugarkill may undergo co-translational selection for polyubiquitination and proteasomal degradation as a nascent polypeptide. The proteins identified in this study may reveal novel pathways for the degradation of a functional, cytosolic protein by the ubiquitin proteasome system and define therapeutic pathways for TPI Df and other biomedically important diseases.

Dietary Supplementation With the Ketogenic Diet Metabolite Beta-Hydroxybutyrate Ameliorates Post-TBI Aggression in Young-Adult Male Drosophila

Traumatic brain injury (TBI), caused by repeated concussive head trauma can induce chronic traumatic encephalopathy (CTE), a neurodegenerative disease featuring behavioral symptoms ranging from cognitive deficits to elevated aggression. In a Drosophila model, we used a high-impact trauma device (Katzenberger et al., 2013, 2015) to induce TBI-like symptoms and to study post-TBI behavioral outcomes. Following TBI, aggression in banged male flies was significantly elevated as compared with that in unbanged flies. These increases in aggressive behavior were not the result of basal motility changes, as measured by a negative geotaxis assay. In addition, the increase in post-TBI aggression appeared to be specific to concussive trauma: neither cold exposure nor electric shock-two alternate types of trauma-significantly elevated aggressive behavior in male-male pairs. Various forms of dietary therapy, especially the high-fat, low-carbohydrate ketogenic diet (KD), have recently been explored for a wide variety of neuropathies. We thus hypothesized that putatively neuroprotective dietary interventions might be able to suppress post-traumatic elevations in aggressive behavior in animals subjected to head-trauma-inducing strikes, or "bangs". We supplemented a normal high-carbohydrate Drosophila diet with the KD metabolite beta-hydroxybutyrate (β-HB)-a ketone body (KB). Banged flies raised on a KB-supplemented diet exhibited a marked reduction in aggression, whereas aggression in unbanged flies was equivalent whether dieted with KB supplements or not. Pharmacological blockade of the ATP-sensitive potassium (KATP) channel abrogated KB effects reducing post-TBI aggression while pharmacological activation mimicked them, suggesting a mechanism by which KBs act in this model. KBs did not significantly extend lifespan in banged flies, but markedly extended lifespan in unbanged flies. We have thus developed a functional model for the study of post-TBI elevations of aggression. Further, we conclude that dietary interventions may be a fruitful avenue for further exploration of treatments for TBI- and CTE-related cognitive-behavioral symptoms.

Ketogenic and anaplerotic dietary modifications ameliorate seizure activity in Drosophila models of mitochondrial encephalomyopathy and glycolytic enzymopathy

Seizures are a feature not only of the many forms of epilepsy, but also of global metabolic diseases such as mitochondrial encephalomyopathy (ME) and glycolytic enzymopathy (GE). Modern anti-epileptic drugs (AEDs) are successful in many cases, but some patients are refractory to existing AEDs, which has led to a surge in interest in clinically managed dietary therapy such as the ketogenic diet (KD). This high-fat, low-carbohydrate diet causes a cellular switch from glycolysis to fatty acid oxidation and ketone body generation, with a wide array of downstream effects at the genetic, protein, and metabolite level that may mediate seizure protection. We have recently shown that a Drosophila model of human ME (ATP6¹) responds robustly to the KD; here, we have investigated the mechanistic importance of the major metabolic consequences of the KD in the context of this bioenergetics disease: ketogenesis, reduction of glycolysis, and anaplerosis. We have found that reduction of glycolysis does not confer seizure protection, but that dietary supplementation with ketone bodies or the anaplerotic lipid triheptanoin, which directly replenishes the citric acid cycle, can mimic the success of the ketogenic diet even in the presence of standard carbohydrate levels. We have also shown that the proper functioning of the citric acid cycle is crucial to the success of the KD in the context of ME. Furthermore, our data reveal that multiple seizure models, in addition to ATP6¹, are treatable with the ketogenic diet. Importantly, one of these mutants is TPI^sugarkill, which models human glycolytic enzymopathy, an incurable metabolic disorder with severe neurological consequences. Overall, these studies reveal widespread success of the KD in Drosophila, further cementing its status as an excellent model for studies of KD treatment and mechanism, and reveal key insights into the therapeutic potential of dietary therapy against neuronal hyperexcitability in epilepsy and metabolic disease.

Sleep and circadian defects in a Drosophila model of mitochondrial encephalomyopathy

Mitochondrial encephalomyopathies (ME) are complex, incurable diseases characterized by severe bioenergetic distress that can affect the function of all major organ systems but is especially taxing to neuromuscular tissues. Animal models of MEs are rare, but the Drosophila ATP6¹ mutant is a stable, well-characterized genetic line that accurately models progressive human mitochondrial diseases such as Maternally-Inherited Leigh Syndrome (MILS), Neuropathy, Ataxia, and Retinitis Pigmentosa (NARP), and Familial Bilateral Striatal Necrosis (FBSN). While it is established that this model exhibits important hallmarks of ME, including excess cellular and mitochondrial reactive oxygen species, shortened lifespan, muscle degeneration, and stress-induced seizures, it is unknown whether it exhibits defects in sleep or circadian function. This is a clinically relevant question, as many neurological and neurodegenerative diseases are characterized by such disturbances, which can exacerbate other symptoms and worsen quality of life. Since Drosophila is highly amenable to sleep and circadian studies, we asked whether we could detect disease phenotypes in the circadian behaviors of ATP6¹. Indeed, we found that day-time and night-time activity and sleep are altered through disease progression, and that circadian patterns are disrupted at both the behavioral and neuronal levels. These results establish ATP6¹ as an important model of sleep and circadian disruption in ME that can be studied mechanistically at the molecular, cellular, and behavioral level to uncover underlying pathophysiology and test novel therapies.

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A Drosophila model of mitochondrial disease (ATP6¹) displays altered sleep patterns.

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ATP6¹ sleep quantity and consolidation are reduced in advanced disease.

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ATP6¹ is behaviorally arrhythmic under conditions of constant darkness.

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Selected neurons of the circadian circuit display altered daily firing rates in ATP6¹.

Protein coding mitochondrial-targeted RNAs rescue mitochondrial disease in vivo

Mitochondrial encephalomyopathies (MEs) result from mutations in mitochondrial genes critical to oxidative phosphorylation. Severe and untreatable ME results from mutations affecting each endogenous mitochondrial encoded gene, including all 13 established protein coding genes. Effective techniques to manipulate mitochondrial genome are limited and targeted mitochondrial protein expression is currently unavailable. Here we report the development of a mitochondrial-targeted RNA expression (mtTRES) vector capable of protein expression within mitochondria (mtTRES^Pro). We demonstrate that mtTRES^Pro expressed RNAs are targeted to mitochondria and are capable of being translated using EGFP encoded constructs in vivo. We additionally test mtTRES^Pro constructs encoding wild type ATP6 for their ability to rescue an established ATP6¹Drosophila model of ME. Genetic rescue is examined including tests with co-expression of mitochondrial targeted translational inhibitors TLI-NCL::ATP6 RNAs that function to reduce expression of the endogenous mutant protein. The data demonstrate allotopic RNA expression of mitochondrial targeted wild type ATP6 coding RNAs are sufficient to partially rescue a severe and established animal model of ME but only when combined with a method to inhibit mutant protein expression, which likely competes for incorporation into complex V.