SIRT3 Haploinsufficiency Aggravates Loss of GABAergic Interneurons and Neuronal Network Hyperexcitability in an Alzheimer's Disease Model

Parvalbumin Interneuron Dysfunction in Neurological Disorders: Focus on Epilepsy and Alzheimer's Disease

Parvalbumin expressing (PV+) GABAergic interneurons are fast spiking neurons that provide powerful but relatively short-lived inhibition to principal excitatory cells in the brain. They play a vital role in feedforward and feedback synaptic inhibition, preventing run away excitation in neural networks. Hence, their dysfunction can lead to hyperexcitability and increased susceptibility to seizures. PV+ interneurons are also key players in generating gamma oscillations, which are synchronized neural oscillations associated with various cognitive functions. PV+ interneuron are particularly vulnerable to aging and their degeneration has been associated with cognitive decline and memory impairment in dementia and Alzheimer's disease (AD). Overall, dysfunction of PV+ interneurons disrupts the normal excitatory/inhibitory balance within specific neurocircuits in the brain and thus has been linked to a wide range of neurodevelopmental and neuropsychiatric disorders. This review focuses on the role of dysfunctional PV+ inhibitory interneurons in the generation of epileptic seizures and cognitive impairment and their potential as targets in the design of future therapeutic strategies to treat these disorders. Recent research using cutting-edge optogenetic and chemogenetic technologies has demonstrated that they can be selectively manipulated to control seizures and restore the balance of neural activity in the brains of animal models. This suggests that PV+ interneurons could be important targets in developing future treatments for patients with epilepsy and comorbid disorders, such as AD, where seizures and cognitive decline are directly linked to specific PV+ interneuron deficits.

Alzheimer's Disease-Related Epigenetic Changes: Novel Therapeutic Targets

Aging is a significant risk factor for Alzheimer's disease (AD), although the precise mechanism and molecular basis of AD are not yet fully understood. Epigenetic mechanisms, such as DNA methylation and hydroxymethylation, mitochondrial DNA methylation, histone modifications, and non-coding RNAs (ncRNAs), play a role in regulating gene expression related to neuron plasticity and integrity, which are closely associated with learning and memory development. This review describes the impact of dynamic and reversible epigenetic modifications and factors on memory and plasticity throughout life, emphasizing their potential as target for therapeutic intervention in AD. Additionally, we present insight from postmortem and animal studies on abnormal epigenetics regulation in AD, as well as current strategies aiming at targeting these factors in the context of AD therapy.

Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases

Ketone bodies (KBs), such as acetoacetate and β-hydroxybutyrate, serve as crucial alternative energy sources during glucose deficiency. KBs, generated through ketogenesis in the liver, are metabolized into acetyl-CoA in extrahepatic tissues, entering the tricarboxylic acid cycle and electron transport chain for ATP production. Reduced glucose metabolism and mitochondrial dysfunction correlate with increased neuronal death and brain damage during cerebral ischemia and neurodegeneration. Both KBs and the ketogenic diet (KD) demonstrate neuroprotective effects by orchestrating various cellular processes through metabolic and signaling functions. They enhance mitochondrial function, mitigate oxidative stress and apoptosis, and regulate epigenetic and post-translational modifications of histones and non-histone proteins. Additionally, KBs and KD contribute to reducing neuroinflammation and modulating autophagy, neurotransmission systems, and gut microbiome. This review aims to explore the current understanding of the molecular mechanisms underpinning the neuroprotective effects of KBs and KD against brain damage in cerebral ischemia and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease.

Association of Plasma Aβ42/Aβ40 Ratio and Late-Onset Epilepsy: Results From the Atherosclerosis Risk in Communities Study

BACKGROUND AND OBJECTIVES

The objective of this study was to determine the relationship between plasma β-amyloid (Aβ), specifically the ratio of 2 Aβ peptides (the Aβ42/Aβ40 ratio, which correlates with increased accumulation of Aβ in the CNS), and late-onset epilepsy (LOE).

METHODS

We used Medicare fee-for-service claims codes from 1991 to 2018 to identify cases of LOE among 1,424 Black and White men and women enrolled in the Atherosclerosis Risk in Communities (ARIC) study cohort. The Aβ42/Aβ40 ratio was calculated from plasma samples collected from ARIC participants in 1993-1995 (age 50-71 years) and 2011-2013 (age 67-90 years). We used survival analysis accounting for the competing risk of death to determine the relationship between late-life plasma Aβ42/Aβ40, and its change from midlife to late life, and the subsequent development of epilepsy. We adjusted for demographics, the apolipoprotein e4 genotype, and comorbidities, including stroke, dementia, and head injury. A low plasma ratio of 2 Aβ peptides, the Aβ42/Aβ40 ratio, correlates with low CSF Aβ42/Aβ40 and with increased accumulation of Aβ in the CNS.

RESULTS

Decrease in plasma Aβ42/Aβ40 ratio from midlife to late life, but not an isolated measurement of Aβ42/Aβ40, was associated with development of epilepsy in later life. For every 50% reduction in Aβ42/Aβ40, there was a 2-fold increase in risk of epilepsy (adjusted subhazard ratio 2.30, 95% CI 1.27-4.17).

DISCUSSION

A reduction in plasma Aβ42/Aβ40 is associated with an increased risk of subsequent epilepsy. Our observations provide a further validation of the link between Aβ, hyperexcitable states, and LOE.

Cell-Type-Specific Mitochondrial Quality Control in the Brain: A Plausible Mechanism of Neurodegeneration

Neurodegeneration is an age-dependent progressive phenomenon with no defined cause. Aging is the main risk factor for neurodegenerative diseases. During aging, activated microglia undergo phenotypic alterations that can lead to neuroinflammation, which is a well-accepted event in the pathogenesis of neurodegenerative diseases. Several common mechanisms are shared by genetically or pathologically distinct neurodegenerative diseases, such as excitotoxicity, mitochondrial deficits and oxidative stress, protein misfolding and translational dysfunction, autophagy and microglia activation. Progressive loss of the neuronal population due to increased oxidative stress leads to neurodegenerative diseases, mostly due to the accumulation of dysfunctional mitochondria. Mitochondrial dysfunction and excessive neuroinflammatory responses are both sufficient to induce pathology in age-dependent neurodegeneration. Therefore, mitochondrial quality control is a key determinant for the health and survival of neuronal cells in the brain. Research has been primarily focused to demonstrate the significance of neuronal mitochondrial health, despite the important contributions of non-neuronal cells that constitute a significant portion of the brain volume. Moreover, mitochondrial morphology and function are distinctly diverse in different tissues; however, little is known about their molecular diversity among cell types. Mitochondrial dynamics and quality in different cell types markedly decide the fate of overall brain health; therefore, it is not justifiable to overlook non-neuronal cells and their significant and active contribution in facilitating overall neuronal health. In this review article, we aim to discuss the mitochondrial quality control of different cell types in the brain and how important and remarkable the diversity and highly synchronized connecting property of non-neuronal cells are in keeping the neurons healthy to control neurodegeneration.

Resveratrol Attenuates Chronic Unpredictable Mild Stress-Induced Alterations in the SIRT1/PGC1α/SIRT3 Pathway and Associated Mitochondrial Dysfunction in Mice

Environmental challenges, specifically chronic stress, have long been associated with neuropsychiatric disorders, including anxiety and depression. Sirtuin-1 (SIRT1) is a NAD+-dependent deacetylase that is widely distributed in the cortex and is involved in stress responses and neuropsychiatric disorders. Nevertheless, how chronic stress modulates the SIRT1 pathway and associated signaling remains unclear. In this study, we first explored the impact of chronic unpredictable mild stress (CUMS) on the SIRT1/PGC1α/SIRT3 pathway, on GABAergic mechanisms, and on mitophagy, autophagy and apoptosis in mice. We also asked whether activation of SIRT1 by resveratrol (RSV) can attenuate CUMS-induced molecular and behavioral alterations. Two-month-old C57/BL6J mice were subjected to three weeks of CUMS and one week of RSV treatment (30 mg/kg; i.p.) during the third week of CUMS. CUMS caused downregulation of the SIRT1/PGC1α/SIRT3 pathway leading to impaired mitochondrial morphology and function. CUMS also resulted in a reduction in numbers of parvalbumin-positive interneurons and increased oxidative stress leading to reduced expression of autophagy- and mitophagy-related proteins. Strikingly, activation of SIRT1 by RSV ameliorated expression of SIRT1/PGC1α/SIRT3, and also improved mitochondrial function, GABAergic mechanisms, mitophagy, autophagy and apoptosis. RSV also rescued CUMS-induced anxiety-like and depressive-like behavior in mice. Our results raise the compelling possibility that RSV treatment might be a viable therapeutic method of blocking stress-induced behavioral alterations.

A Compared Study of Eicosapentaenoic Acid and Docosahexaenoic Acid in Improving Seizure-Induced Cognitive Deficiency in a Pentylenetetrazol-Kindling Young Mice Model

Epilepsy is a chronic neurological disorder that is more prevalent in children, and recurrent unprovoked seizures can lead to cognitive impairment. Numerous studies have reported the benefits of docosahexaenoic acid (DHA) on neurodevelopment and cognitive ability, while comparatively less attention has been given to eicosapentaenoic acid (EPA). Additionally, little is known about the effects and mechanisms of DHA and EPA in relation to seizure-induced cognitive impairment in the young rodent model. Current research indicates that ferroptosis is involved in epilepsy and cognitive deficiency in children. Further investigation is warranted to determine whether EPA or DHA can mitigate seizure-induced cognitive deficits by inhibiting ferroptosis. Therefore, this study was conducted to compare the effects of DHA and EPA on seizure-induced cognitive deficiency and reveal the underlying mechanisms focused on ferroptosis in a pentylenetetrazol (PTZ)-kindling young mice model. Mice were fed a diet containing DHA-enriched ethyl esters or EPA-enriched ethyl esters for 21 days at the age of 3 weeks and treated with PTZ (35 mg/kg, i.p.) every other day 10 times. The findings indicated that both EPA and DHA exhibited ameliorative effects on seizure-induced cognitive impairment, with EPA demonstrating a superior efficacy. Further mechanism study revealed that supplementation of DHA and EPA significantly increased cerebral DHA and EPA levels, balanced neurotransmitters, and inhibited ferroptosis by modulating iron homeostasis and reducing lipid peroxide accumulation in the hippocampus through activating the Nrf2/Sirt3 signal pathway. Notably, EPA exhibited better an advantage in ameliorating iron dyshomeostasis compared to DHA, owing to its stronger upregulation of Sirt3. These results indicate that DHA and EPA can efficaciously alleviate seizure-induced cognitive deficiency by inhibiting ferroptosis in PTZ-kindled young mice.

Axonal energy metabolism, and the effects in aging and neurodegenerative diseases

Human studies consistently identify bioenergetic maladaptations in brains upon aging and neurodegenerative disorders of aging (NDAs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Glucose is the major brain fuel and glucose hypometabolism has been observed in brain regions vulnerable to aging and NDAs. Many neurodegenerative susceptible regions are in the topological central hub of the brain connectome, linked by densely interconnected long-range axons. Axons, key components of the connectome, have high metabolic needs to support neurotransmission and other essential activities. Long-range axons are particularly vulnerable to injury, neurotoxin exposure, protein stress, lysosomal dysfunction, etc. Axonopathy is often an early sign of neurodegeneration. Recent studies ascribe axonal maintenance failures to local bioenergetic dysregulation. With this review, we aim to stimulate research in exploring metabolically oriented neuroprotection strategies to enhance or normalize bioenergetics in NDA models. Here we start by summarizing evidence from human patients and animal models to reveal the correlation between glucose hypometabolism and connectomic disintegration upon aging/NDAs. To encourage mechanistic investigations on how axonal bioenergetic dysregulation occurs during aging/NDAs, we first review the current literature on axonal bioenergetics in distinct axonal subdomains: axon initial segments, myelinated axonal segments, and axonal arbors harboring pre-synaptic boutons. In each subdomain, we focus on the organization, activity-dependent regulation of the bioenergetic system, and external glial support. Second, we review the mechanisms regulating axonal nicotinamide adenine dinucleotide (NAD+) homeostasis, an essential molecule for energy metabolism processes, including NAD+ biosynthetic, recycling, and consuming pathways. Third, we highlight the innate metabolic vulnerability of the brain connectome and discuss its perturbation during aging and NDAs. As axonal bioenergetic deficits are developing into NDAs, especially in asymptomatic phase, they are likely exaggerated further by impaired NAD+ homeostasis, the high energetic cost of neural network hyperactivity, and glial pathology. Future research in interrogating the causal relationship between metabolic vulnerability, axonopathy, amyloid/tau pathology, and cognitive decline will provide fundamental knowledge for developing therapeutic interventions.

The mitochondrial unfolded protein response regulates hippocampal neural stem cell aging

Aging results in a decline in neural stem cells (NSCs), neurogenesis, and cognitive function, and evidence is emerging to demonstrate disrupted adult neurogenesis in the hippocampus of patients with several neurodegenerative disorders. Here, single-cell RNA sequencing of the dentate gyrus of young and old mice shows that the mitochondrial protein folding stress is prominent in activated NSCs/neural progenitors (NPCs) among the neurogenic niche, and it increases with aging accompanying dysregulated cell cycle and mitochondrial activity in activated NSCs/NPCs in the dentate gyrus. Increasing mitochondrial protein folding stress results in compromised NSC maintenance and reduced neurogenesis in the dentate gyrus, neural hyperactivity, and impaired cognitive function. Reducing mitochondrial protein folding stress in the dentate gyrus of old mice improves neurogenesis and cognitive function. These results establish the mitochondrial protein folding stress as a driver of NSC aging and suggest approaches to improve aging-associated cognitive decline.

Epigenetic modifiers as game changers for healthy ageing

Epigenetic alterations during ageing are manifested with altered gene expression linking it to lifespan regulation, genetic instability, and diseases. Diet and epigenetic modifiers exert a profound effect on the lifespan of an organism by modulating the epigenetic marks. However, our understanding of the multifactorial nature of the epigenetic process during ageing and the onset of disease conditions as well as its reversal by epidrugs, diet, or environmental factors is still mystifying. This review covers the key findings in epigenetics related to ageing and age-related diseases. Further, it holds a discussion about the epigenetic clocks and their implications in various age-related disease conditions including cancer. Although, epigenetics is a reversible process how fast the epigenetic alterations can revert to normal is an intriguing question. Therefore, this paper touches on the possibility of utilizing nutrition and MSCs secretome to accelerate the epigenetic reversal and emphasizes the identification of new therapeutic epigenetic modifiers to counter epigenetic alteration during ageing.

Neuronal SIRT3 Deletion Predisposes to Female-Specific Alterations in Cellular Metabolism, Memory, and Network Excitability

Mitochondrial dysfunction is an early event in the pathogenesis of neurologic disorders and aging. Sirtuin 3 (SIRT3) regulates mitochondrial function in response to the cellular environment through the reversible deacetylation of proteins involved in metabolism and reactive oxygen species detoxification. As the primary mitochondrial deacetylase, germline, or peripheral tissue-specific deletion of SIRT3 produces mitochondrial hyperacetylation and the accelerated development of age-related diseases. Given the unique metabolic demands of neurons, the role of SIRT3 in the brain is only beginning to emerge. Using mass spectrometry-based acetylomics, high-resolution respirometry, video-EEG, and cognition testing, we report targeted deletion of SIRT3 from select neurons in the cortex and hippocampus produces altered neuronal excitability and metabolic dysfunction in female mice. Targeted deletion of SIRT3 from neuronal helix-loop-helix 1 (NEX)-expressing neurons resulted in mitochondrial hyperacetylation, female-specific superoxide dismutase-2 (SOD2) modification, increased steady-state superoxide levels, metabolic reprogramming, altered neuronal excitability, and working spatial memory deficits. Inducible neuronal deletion of SIRT3 likewise produced female-specific deficits in spatial working memory. Together, the data demonstrate that deletion of SIRT3 from forebrain neurons selectively predisposes female mice to deficits in mitochondrial and cognitive function.SIGNIFICANCE STATEMENT Mitochondrial SIRT3 is an enzyme shown to regulate energy metabolism and antioxidant function, by direct deacetylation of proteins. In this study, we show that neuronal SIRT3 deficiency renders female mice selectively vulnerable to impairment in redox and metabolic function, spatial memory, and neuronal excitability. The observed sex-specific effects on cognition and neuronal excitability in female SIRT3-deficient mice suggest that mitochondrial dysfunction may be one factor underlying comorbid neuronal diseases, such as Alzheimer's disease and epilepsy. Furthermore, the data suggest that SIRT3 dysfunction may predispose females to age-related metabolic and cognitive impairment.

Mitochondrial SIRT3 Deficiency Results in Neuronal Network Hyperexcitability, Accelerates Age-Related Aβ Pathology, and Renders Neurons Vulnerable to Aβ Toxicity

Aging is the major risk factor for Alzheimer's disease (AD). Mitochondrial dysfunction and neuronal network hyperexcitability are two age-related alterations implicated in AD pathogenesis. We found that levels of the mitochondrial protein deacetylase sirtuin-3 (SIRT3) are significantly reduced, and consequently mitochondria protein acetylation is increased in brain cells during aging. SIRT3-deficient mice exhibit robust mitochondrial protein hyperacetylation and reduced mitochondrial mass during aging. Moreover, SIRT3-deficient mice exhibit epileptiform and burst-firing electroencephalogram activity indicating neuronal network hyperexcitability. Both aging and SIRT3 deficiency result in increased sensitivity to kainic acid-induced seizures. Exposure of cultured cerebral cortical neurons to amyloid β-peptide (Aβ) results in a reduction in SIRT3 levels and SIRT3-deficient neurons exhibit heightened sensitivity to Aβ toxicity. Finally, SIRT3 haploinsufficiency in middle-aged App/Ps1 double mutant transgenic mice results in a significant increase in Aβ load compared with App/Ps1 double mutant mice with normal SIRT3 levels. Collectively, our findings suggest that SIRT3 plays an important role in protecting neurons against Aβ pathology and excitotoxicity.

Insights on benzodiazepines' potential in Alzheimer's disease

Alzheimer's disease (AD) is the most frequent type of dementia characterized by the deposition of amyloid beta (Aβ) plaque and tau-neurofibrillary tangles (TNTs) in the brain. AD is associated with the disturbances of various neurotransmitters including gamma-aminobutyric acid (GABA). Of note, GABA is reduced in AD, and restoration of GABA effect by benzodiazepines (BDZs) may improve AD outcomes. However, BDZs may adversely affect cognitive functions chiefly in elderly AD patients with sleep disorders. Besides, there is a controversy regarding the use of BDZs in AD. Consequently, the objective of the present review was to disclose the possible role of BDZs on the pathogenesis of AD that might be beneficial, neutral, or detrimental effects on AD. Prolonged use of intermediate-acting BDZ lorazepam exerts amnesic effects due to attenuation of synaptic plasticity and impairment of recognition memory. However, BDZs may have a protective effect against the development of AD by reducing tau phosphorylation, neuroinflammation, and progression of AD neuropathology. On the other side, other findings highlighted that extended use of BDZs was not associated with the development of AD. In conclusion, there are controversial points concerning the use of BDZs and the risk for the progression of AD. Thus, preclinical, and clinical studies are essential in this regard.

Sex-divergent effects on the NAD+-dependent deacetylase sirtuin signaling across the olfactory-entorhinal-amygdaloid axis in Alzheimer's and Parkinson's diseases

BACKGROUND

Smell impairment is one of the earliest features in Alzheimer's (AD) and Parkinson's diseases (PD). Due to sex differences exist in terms of smell and olfactory structures as well as in the prevalence and manifestation of both neurological syndromes, we have applied olfactory proteomics to favor the discovery of novel sex-biased physio-pathological mechanisms and potential therapeutic targets associated with olfactory dysfunction.

METHODS

SWATH-MS (sequential window acquisition of all theoretical fragment ion spectra mass spectrometry) and bioinformatic workflows were applied in 57 post-mortem olfactory tracts (OT) derived from controls with no known neurological history (n = 6F/11M), AD (n = 4F/13M) and PD (n = 7F/16M) subjects. Complementary molecular analyses by Western-blotting were performed in the olfactory bulb (OB), entorhinal cortex (EC) and amygdala areas.

RESULTS

327 and 151 OT differentially expressed proteins (DEPs) were observed in AD women and AD men, respectively (35 DEPs in common). With respect to PD, 198 DEPs were identified in PD women, whereas 95 DEPs were detected in PD men (20 DEPs in common). This proteome dyshomeostasis induced a disruption in OT protein interaction networks and widespread sex-dependent pathway perturbations in a disease-specific manner, among them Sirtuin (SIRT) signaling. SIRT1, SIRT2, SIRT3 and SIRT5 protein levels unveiled a tangled expression profile across the olfactory-entorhinal-amygdaloid axis, evidencing disease-, sex- and brain structure-dependent changes in olfactory protein acetylation.

CONCLUSIONS

Alteration in the OT proteostasis was more severe in AD than in PD. Moreover, protein expression changes were more abundant in women than men independent of the neurological syndrome. Mechanistically, the tangled SIRT profile observed across the olfactory pathway-associated brain regions in AD and PD indicates differential NAD (+)-dependent deacetylase mechanisms between women and men. All these data shed new light on differential olfactory mechanisms across AD and PD, pointing out that the evaluation of the feasibility of emerging sirtuin-based therapies against neurodegenerative diseases should be considered with caution, including further sex dimension analyses in vivo and in clinical studies.

Role of Oxidative Stress in Ocular Diseases: A Balancing Act

Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

A Promising Strategy to Treat Neurodegenerative Diseases by SIRT3 Activation

SIRT3, the primary mitochondrial deacetylase, regulates the functions of mitochondrial proteins including metabolic enzymes and respiratory chain components. Although SIRT3's functions in peripheral tissues are well established, the significance of its downregulation in neurodegenerative diseases is beginning to emerge. SIRT3 plays a key role in brain energy metabolism and provides substrate flexibility to neurons. It also facilitates metabolic coupling between fuel substrate-producing tissues and fuel-consuming tissues. SIRT3 mediates the health benefits of lifestyle-based modifications such as calorie restriction and exercise. SIRT3 deficiency is associated with metabolic syndrome (MetS), a precondition for diseases including obesity, diabetes, and cardiovascular disease. The pure form of Alzheimer's disease (AD) is rare, and it has been reported to coexist with these diseases in aging populations. SIRT3 downregulation leads to mitochondrial dysfunction, neuroinflammation, and inflammation, potentially triggering factors of AD pathogenesis. Recent studies have also suggested that SIRT3 may act through multiple pathways to reduce plaque formation in the AD brain. In this review, we give an overview of SIRT3's roles in brain physiology and pathology and discuss several activators of SIRT3 that can be considered potential therapeutic agents for the treatment of dementia.

Neurofilament light-associated connectivity in young-adult Huntington's disease is related to neuronal genes

Upregulation of functional network connectivity in the presence of structural degeneration is seen in the premanifest stages of Huntington's disease (preHD) 10-15 years from clinical diagnosis. However, whether widespread network connectivity changes are seen in gene carriers much further from onset has yet to be explored. We characterized functional network connectivity throughout the brain and related it to a measure of disease pathology burden (CSF neurofilament light, NfL) and measures of structural connectivity in asymptomatic gene carriers, on average 24 years from onset. We related these measurements to estimates of cortical and subcortical gene expression. We found no overall differences in functional (or structural) connectivity anywhere in the brain comparing control and preHD participants. However, increased functional connectivity, particularly between posterior cortical areas, correlated with increasing CSF NfL level in preHD participants. Using the Allen Human Brain Atlas and expression-weighted cell-type enrichment analysis, we demonstrated that this functional connectivity upregulation occurred in cortical regions associated with regional expression of genes specific to neuronal cells. This relationship was validated using single-nucleus RNAseq data from post-mortem Huntington's disease and control brains showing enrichment of neuronal-specific genes that are differentially expressed in Huntington's disease. Functional brain networks in asymptomatic preHD gene carriers very far from disease onset show evidence of upregulated connectivity correlating with increased disease burden. These changes occur among brain areas that show regional expression of genes specific to neuronal GABAergic and glutamatergic cells.

Fats, Friends or Foes: Investigating the Role of Short- and Medium-Chain Fatty Acids in Alzheimer's Disease

Characterising Alzheimer's disease (AD) as a metabolic disorder of the brain is gaining acceptance based on the pathophysiological commonalities between AD and major metabolic disorders. Therefore, metabolic interventions have been explored as a strategy for brain energetic rescue. Amongst these, medium-chain fatty acid (MCFA) supplementations have been reported to rescue the energetic failure in brain cells as well as the cognitive decline in patients. Short-chain fatty acids (SCFA) have also been implicated in AD pathology. Due to the increasing therapeutic interest in metabolic interventions and brain energetic rescue in neurodegenerative disorders, in this review, we first summarise the role of SCFAs and MCFAs in AD. We provide a comparison of the main findings regarding these lipid species in established AD animal models and recently developed human cell-based models of this devastating disorder.

Early death in a mouse model of Alzheimer's disease exacerbated by microglial loss of TAM receptor signaling

Recurrent seizure is a common comorbidity in early-stage Alzheimer's disease (AD) and may contribute to AD pathogenesis and cognitive decline. Similarly, many mouse models of Alzheimer's disease that overproduce amyloid beta are prone to epileptiform seizures that may result in early sudden death. We studied one such model, designated APP/PS1, and found that mutation of the TAM receptor tyrosine kinase (RTK) Mer or its ligand Gas6 greatly exacerbated early death. Lethality was tied to violent seizures that appeared to initiate in the dentate gyrus (DG) of the hippocampus, where Mer plays an essential role in the microglial phagocytosis of both apoptotic and newborn cells normally generated during adult neurogenesis. We found that newborn DG neurons and excitatory synapses between the DG and the cornu ammonis field 3 (CA3) field of the hippocampus were increased in TAM-deficient mice, and that premature death and adult neurogenesis in these mice were coincident. In contrast, the incidence of lethal seizures and the deposition of dense-core amyloid plaques were strongly anticorrelated. Together, these results argue that TAM-mediated phagocytosis sculpts synaptic connectivity in the hippocampus, and that seizure-inducing amyloid beta polymers are present prior to the formation of dense-core plaques.

Sirtuins functions in central nervous system cells under neurological disorders

The sirtuins (SIRTs), a class of NAD+ -dependent deacylases, contain seven SIRT family members in mammals, from SIRT1 to SIRT7. Extensive studies have revealed that SIRT proteins regulate virous cell functions. Central nervous system (CNS) decline resulted in progressive cognitive impairment, social and physical abilities dysfunction. Therefore, it is of vital importance to have a better understanding of potential target to promote homeostasis of CNS. SIRTs have merged as the underlying regulating factors of the process of neurological disorders. In this review, we profile multiple functions of SIRT proteins in different cells during brain function and under CNS injury.

Alterations of sleep oscillations in Alzheimer's disease: A potential role for GABAergic neurons in the cortex, hippocampus, and thalamus

Sleep abnormalities are widely reported in patients with Alzheimer's disease (AD) and are linked to cognitive impairments. Sleep abnormalities could be potential biomarkers to detect AD since they are often observed at the preclinical stage. Moreover, sleep could be a target for early intervention to prevent or slow AD progression. Thus, here we review changes in brain oscillations observed during sleep, their connection to AD pathophysiology and the role of specific brain circuits. Slow oscillations (0.1-1 Hz), sleep spindles (8-15 Hz) and their coupling during non-REM sleep are consistently reduced in studies of patients and in AD mouse models although the timing and magnitude of these alterations depends on the pathophysiological changes and the animal model studied. Changes in delta (1-4 Hz) activity are more variable. Animal studies suggest that hippocampal sharp-wave ripples (100-250 Hz) are also affected. Reductions in REM sleep amount and slower oscillations during REM are seen in patients but less consistently in animal models. Thus, changes in a variety of sleep oscillations could impact sleep-dependent memory consolidation or restorative functions of sleep. Recent mechanistic studies suggest that alterations in the activity of GABAergic neurons in the cortex, hippocampus and thalamic reticular nucleus mediate sleep oscillatory changes in AD and represent a potential target for intervention. Longitudinal studies of the timing of AD-related sleep abnormalities with respect to pathology and dysfunction of specific neural networks are needed to identify translationally relevant biomarkers and guide early intervention strategies to prevent or delay AD progression.

Cortical excitability and plasticity in Alzheimer's disease and mild cognitive impairment: A systematic review and meta-analysis of transcranial magnetic stimulation studies

BACKGROUND

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique. When stimulation is applied over the primary motor cortex and coupled with electromyography measures, TMS can probe functions of cortical excitability and plasticity in vivo. The purpose of this meta-analysis is to evaluate the utility of TMS-derived measures for differentiating patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) from cognitively normal older adults (CN).

METHODS

Databases searched included PubMed, Embase, APA PsycInfo, Medline, and CINAHL Plus from inception to July 2021.

RESULTS

Sixty-one studies with a total of 2728 participants (1454 patients with AD, 163 patients with MCI, and 1111 CN) were included. Patients with AD showed significantly higher cortical excitability, lower cortical inhibition, and impaired cortical plasticity compared to the CN cohorts. Patients with MCI exhibited increased cortical excitability and reduced plasticity compared to the CN cohort. Additionally, lower cognitive performance was significantly associated with higher cortical excitability and lower inhibition. No seizure events due to TMS were reported, and the mild adverse response rate is approximately 3/1000 (i.e., 9/2728).

CONCLUSIONS

Findings of our meta-analysis demonstrate the potential of using TMS-derived cortical excitability and plasticity measures as diagnostic biomarkers and therapeutic targets for AD and MCI.

Amyloid beta induces Fmr1 ‐dependent translational suppression and hyposynchrony of neural activity via phosphorylation of eIF2α and eEF2

Alzheimer's disease (AD) is the most common cause of dementia, with the accumulation of amyloid beta peptide (Aβ) being one of the main causes of the disease. Fragile X mental retardation protein (FMRP), encoded by fragile X mental retardation 1 (Fmr1), is an RNA‐binding protein that represses translation of its bound mRNAs or exerts other indirect mechanisms that result in translational suppression. Because the accumulation of Aβ has been shown to cause translational suppression resulting from the elevated cellular stress response, in this study we asked whether and how Fmr1 is involved in Aβ‐induced translational regulation. Our data first showed that the application of synthetic Aβ peptide induces the expression of Fmr1 in cultured primary neurons. We followed by showing that Fmr1 is required for Aβ‐induced translational suppression, hyposynchrony of neuronal firing activity, and loss of excitatory synapses. Mechanistically, we revealed that Fmr1 functions to repress the expression of phosphatases including protein phosphatase 2A (PP2A) and protein phosphatase 1 (PP1), leading to elevated phosphorylation of eukaryotic initiation factor 2‐α (eIF2α) and eukaryotic elongation factor 2 (eEF2), and subsequent translational suppression. Finally, our data suggest that such translational suppression is critical to Aβ‐induced hyposynchrony of firing activity, but not the loss of synapses. Altogether, our study uncovers a novel mechanism by which Aβ triggers translational suppression and we reveal the participation of Fmr1 in altered neural plasticity associated with Aβ pathology. Our study may also provide information for a better understanding of Aβ‐induced cellular stress responses in AD.

Restoration and targeting of aberrant neurotransmitters in Parkinson's disease therapeutics

Neurotransmitters are considered as a fundamental regulator in the process of neuronal growth, differentiation and survival. Parkinson's Disease (PD) occurs due to extensive damage of dopamine-producing neurons; this causes dopamine deficits in the midbrain, followed by the alternation of various other neurotransmitters (glutamate, GABA, serotonin, etc.). It has been observed that fluctuation of neurotransmission in the basal ganglia exhibits a great impact on the pathophysiology of PD. Dopamine replacement therapy, such as the use of L-DOPA, can increase the dopamine level, but it majorly ameliorates the motor symptoms and is also associated with long-term complications (for e.g., LID). While the non-dopaminergic system can efficiently target non-motor symptoms, for instance, the noradrenergic system regulates the synthesis of BDNF via the MAPK pathway, which is important in learning and memory. Herein, we briefly discuss the role of different neurotransmitters, implementation of neurotransmitter receptors in PD. We also illustrate the recent advances of neurotransmitter-based drugs, which are currently under in vivo and clinical studies. Reinstating normal neurotransmitter levels has been believed to be advantageous in the treatment of PD. Thus, there is an increasing demand for drugs that can specifically target the neurotransmission system and reinstate the normal levels of neurotransmitters, which might prevent or delay neurodegeneration in PD.

Sirtuins at the Crossroads between Mitochondrial Quality Control and Neurodegenerative Diseases: Structure, Regulation, Modifications, and Modulators

Sirtuins (SIRT1-SIRT7), a family of nicotinamide adenine dinucleotide (NAD⁺)-dependent enzymes, are key regulators of life span and metabolism. In addition to acting as deacetylates, some sirtuins have the properties of deacylase, decrotonylase, adenosine diphosphate (ADP)-ribosyltransferase, lipoamidase, desuccinylase, demalonylase, deglutarylase, and demyristolyase. Mitochondrial dysfunction occurs early on and acts causally in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Sirtuins are implicated in the regulation of mitochondrial quality control, which is highly associated with the pathogenesis of neurodegenerative diseases. There is growing evidence indicating that sirtuins are promising and well-documented molecular targets for the treatment of mitochondrial dysfunction and neurodegenerative disorders by regulating mitochondrial quality control, including mitochondrial biogenesis, mitophagy, mitochondrial fission/fusion dynamics, and mitochondrial unfolded protein responses (mtUPR). Therefore, elucidation of the molecular etiology of sirtuin-mediated mitochondrial quality control points to new prospects for the treatment of neurodegenerative diseases. However, the mechanisms underlying sirtuin-mediated mitochondrial quality control remain obscure. In this review, we update and summarize the current understanding of the structure, function, and regulation of sirtuins with an emphasis on the cumulative and putative effects of sirtuins on mitochondrial biology and neurodegenerative diseases, particularly their roles in mitochondrial quality control. In addition, we outline the potential therapeutic applications for neurodegenerative diseases of targeting sirtuin-mediated mitochondrial quality control through exercise training, calorie restriction, and sirtuin modulators in neurodegenerative diseases.

SIRT5 Represses Neurotrophic Pathways and Aβ Production in Alzheimer's Disease by Targeting Autophagy

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in elderly individuals and characterized by impaired cognition and accumulation of β-amyloid (Aβ). Activating autophagy to clear Aβ is a plausible approach for AD treatment. The levels of Aβ and autophagy signaling factors in APP695/PS1-dE9 transgenic (APP/PS1) mice were detected by immuno histological analysis, real-time PCR, and the western blotting assay. The progression of AD was determined by Aβ levels, activated neurons (MAP2+), and microglia (Iba-1⁺). The learning ability was measured using a Morris water maze. Reactive oxygen species (ROS) production, malondialdehyde (MDA) levels, and mitochondrial superoxide dismutase (SOD) activity were checked to determine oxidative stress. AD mice exhibited impaired autophagy and a decreased level of SIRT5. SIRT5 overexpression promoted autophagy, manifested by elevated Becn1 and ratio of LC3b-II/I, as well as suppressed oxidative stress. The SIRT5-ameliorated neuron damage was correlated with suppressed activation of microglia and astrocytes. Elevated SIRT5 expression decreased the inflammation in AD brains and neurons. Inhibition of autophagy abolished the protective role of SIRT5 in neurons during AD. Our findings suggested that SIRT5 overexpression could ameliorate the progression of AD both in vitro and in vivo through activating autophagy. We presented ectopic expression of SIRT5 as a promising therapeutic approach for AD.

SIRT3 Regulates Neuronal Excitability of Alzheimer's Disease Models in an Oxidative Stress-Dependent Manner

Mitochondrial deacetylase Sirtuin-3 (SIRT3) has been shown to regulate metabolic and antioxidant functions. Previous studies have reported that SIRT3 mediates change of neuronal excitability. However, the underlying mechanism is unclear. Here, we show that SIRT3 deficiency results in neural hyperactivity, decreased survival rate, and increased oxidative stress of culture neurons, while a superoxide dismutase 2 mimetic reduces oxidative stress and suppresses the neuronal hyperactivity. In culture neurons treated with Aβ, SIRT3 activator reduces level of reactive oxygen species (ROS) and hyperactivity of neurons while increasing level of ROS restores the neuronal hyperactivity. Utilizing two photon in vivo brain imaging, we show that inhibition of SIRT3 results in elevated neuronal excitatory in an animal model of Alzheimer's disease of early stage, whereas suppression of the ROS level reverses it. These findings demonstrate an oxidative stress-dependent role of SIRT3 in regulation of neuronal excitability in Alzheimer's disease.

Metabolic and Signaling Roles of Ketone Bodies in Health and Disease

Ketone bodies play significant roles in organismal energy homeostasis, serving as oxidative fuels, modulators of redox potential, lipogenic precursors, and signals, primarily during states of low carbohydrate availability. Efforts to enhance wellness and ameliorate disease via nutritional, chronobiological, and pharmacological interventions have markedly intensified interest in ketone body metabolism. The two ketone body redox partners, acetoacetate and D-β-hydroxybutyrate, serve distinct metabolic and signaling roles in biological systems. We discuss the pleiotropic roles played by both of these ketones in health and disease. While enthusiasm is warranted, prudent procession through therapeutic applications of ketogenic and ketone therapies is also advised, as a range of metabolic and signaling consequences continue to emerge. Organ-specific and cell-type-specific effects of ketone bodies are important to consider as prospective therapeutic and wellness applications increase.

Curcumin Alleviates Aβ42-Induced Neuronal Metabolic Dysfunction via the Thrb/SIRT3 Axis and Improves Cognition in APPTG Mice

Curcumin has been reported to have a therapeutic effect on Alzheimer's disease (AD), but the specific mechanism remains to be elucidated. In the present research, we aimed to investigate the effect and molecular mechanism of curcumin on AD. Mouse primary hippocampal neuron cells were treated with various concentrations of beta-amyloid 42 (Aβ₄₂) and the results found that Aβ₄₂ inhibited cell viability in a dose-dependent manner. Compared with 50 ng/mL Aβ₄₂, 500 ng/mL Aβ₄₂ could further promote cell apoptosis, reduce the ratio of Nicotinamide adenine dinucleotide (NAD(+))/Nicotinamide adenine diphosphate hydride (NADH) and Adenosine 5'-triphosphate (ATP) level, and inhibit Sirtuins 3 (SIRT3) deacetylation activity and protein expression of Thyroid hormone receptor beta (Thrb) and SIRT3. Hence, 500 ng/mL Aβ₄₂ was used to establish a cell model of AD. Curcumin significantly reversed the inhibitory effects of Aβ₄₂ on cell viability, SIRT3 deacetylation activity, the ratio of NAD⁺/NADH, ATP level and the protein expression of Thrb and SIRT3, and the promotive effect on apoptosis. ChIPBase was used to predict the binding region of Thrb and SIRT3. Dual luciferase reporter gene and Chromatin immune precipitation (ChIP) assays were employed to verify the relationship between Thrb and promoter of SIRT3 mRNA. Overexpression of Thrb recovered Aβ₄₂ induced metabolic dysfunction, while Thrb silence aggravated Aβ₄₂ induced metabolic dysfunction. Moreover, Thrb silence or 3-TYP (a selective inhibitor of SIRT3) treatment abolished the amelioration of curcumin on Aβ₄₂ induced metabolic dysfunction. Additionally, curcumin attenuated memory deficits in Amyloid precursor protein transgenic (APP_TG) mice. Collectively, curcumin alleviated Aβ₄₂-induced neuronal metabolic dysfunction through increasing Thrb expression and SIRT3 activity and improved cognition in APP_TG mice.

Dysregulated clock gene expression and abnormal diurnal regulation of hippocampal inhibitory transmission and spatial memory in amyloid precursor protein transgenic mice

Patients with Alzheimer's disease (AD) often have fragmentation of sleep/wake cycles and disrupted 24-h (circadian) activity. Despite this, little work has investigated the potential underlying day/night disruptions in cognition and neuronal physiology in the hippocampus. The molecular clock, an intrinsic transcription-translation feedback loop that regulates circadian behavior, may also regulate hippocampal neurophysiological activity. We hypothesized that disrupted diurnal variation in clock gene expression in the hippocampus corresponds with loss of normal day/night differences in membrane excitability, synaptic physiology, and cognition. We previously reported disrupted circadian locomotor rhythms and neurophysiological output of the suprachiasmatic nucleus (the primary circadian clock) in Tg-SwDI mice with human amyloid-beta precursor protein mutations. Here, we report that Tg-SwDI mice failed to show day/night differences in a spatial working memory task, unlike wild-type controls that exhibited enhanced spatial working memory at night. Moreover, Tg-SwDI mice had lower levels of Per2, one of the core components of the molecular clock, at both mRNA and protein levels when compared to age-matched controls. Interestingly, we discovered neurophysiological impairments in area CA1 of the Tg-SwDI hippocampus. In controls, spontaneous inhibitory post-synaptic currents (sIPSCs) in pyramidal cells showed greater amplitude and lower inter-event interval during the day than the night. However, the normal day/night differences in sIPSCs were absent (amplitude) or reversed (inter-event interval) in pyramidal cells from Tg-SwDI mice. In control mice, current injection into CA1 pyramidal cells produced more firing during the night than during the day, but no day/night difference in excitability was observed in Tg-SwDI mice. The normal day/night difference in excitability in controls was blocked by GABA receptor inhibition. Together, these results demonstrate that the normal diurnal regulation of inhibitory transmission in the hippocampus is diminished in a mouse model of AD, leading to decreased daytime inhibition onto hippocampal CA1 pyramidal cells. Uncovering disrupted day/night differences in circadian gene regulation, hippocampal physiology, and memory in AD mouse models may provide insight into possible chronotherapeutic strategies to ameliorate Alzheimer's disease symptoms or delay pathological onset.

Progress on mitochondrial silence information regulator family in epilepsy

SIRT3, SIRT4 and SIRT5 are located in mitochondria and also known as mitochondrial sirtuins. They play important roles in regulating many cellular functions including cell survival, cell cycle or apoptosis, DNA repair and metabolism. Mitochondrial sirtuins are involved in the protection of mitochondrial integrity and energy metabolism under stress regulating the expression of neurotransmitter receptors, neurotrophins, extracellular matrix proteins and various transcription factors, thus involved in epileptogenesis triggered by both genetic or acquired factors. Here we review research progress on the actions of mitochondrial sirtuin in epilepsy; and discuss the challenges and perspectives of mitochondrial sirtuin as a potential therapeutic target for epilepsy.

Piceatannol alleviate ROS-mediated PC-12 cells damage and mitochondrial dysfunction through SIRT3/FOXO3a signaling pathway

Oxidative stress-associated mitochondrial dysfunction has been identified as a major mechanism in multiple neurodegenerative diseases. This study aims to investigate the cytoprotective effects of piceatannol on ROS-mediated PC-12 cells damage and related mitochondrial dysfunction. Piceatannol treatment could significantly attenuate PC-12 cells oxidative damage and ROS-mediated cells apoptosis. Moreover, pretreatment with piceatannol effectively decreased mitochondrial membrane depolarization, cleaved-caspase 3, and increased Bcl-2 and Bcl-2/Bax compared with control H₂ O₂ group. Meanwhile, piceatannol treatment improved mitochondrial respiration function which led to an enhancement in the maximal respiration and spare respiratory capacity. Further mechanisms analysis showed that the protein expression of SIRT3 and its downstream protein FOXO3a were significantly increased after piceatannol addition in a dose-dependent manner. Whereas the cytoprotective role of piceatannol was markedly abolished by the SIRT3 inhibitor 3-TYP, suggesting that SIRT3/FOXO3a signaling pathway played a vital role in mediating the neuronal cytoprotective effects of piceatannol. PRACTICAL APPLICATIONS: The results of our study provide a novel insight that piceatannol could be potentially used as a promising bioactive component against oxidative damage and neurocyte apoptosis. The findings may provide theoretical basis for brain health of piceatannol consumption in some extent.

Glucose metabolic crosstalk and regulation in brain function and diseases

Brain glucose metabolism, including glycolysis, the pentose phosphate pathway, and glycogen turnover, produces ATP for energetic support and provides the precursors for the synthesis of biological macromolecules. Although glucose metabolism in neurons and astrocytes has been extensively studied, the glucose metabolism of microglia and oligodendrocytes, and their interactions with neurons and astrocytes, remain critical to understand brain function. Brain regions with heterogeneous cell composition and cell-type-specific profiles of glucose metabolism suggest that metabolic networks within the brain are complex. Signal transduction proteins including those in the Wnt, GSK-3β, PI3K-AKT, and AMPK pathways are involved in regulating these networks. Additionally, glycolytic enzymes and metabolites, such as hexokinase 2, acetyl-CoA, and enolase 2, are implicated in the modulation of cellular function, microglial activation, glycation, and acetylation of biomolecules. Given these extensive networks, glucose metabolism dysfunction in the whole brain or specific cell types is strongly associated with neurologic pathology including ischemic brain injury and neurodegenerative disorders. This review characterizes the glucose metabolism networks of the brain based on molecular signaling and cellular and regional interactions, and elucidates glucose metabolism-based mechanisms of neurological diseases and therapeutic approaches that may ameliorate metabolic abnormalities in those diseases.

Enhancing myelin renewal reverses cognitive dysfunction in a murine model of Alzheimer's disease

Severe cognitive decline is a hallmark of Alzheimer's disease (AD). In addition to gray matter loss, significant white matter pathology has been identified in AD patients. Here, we characterized the dynamics of myelin generation and loss in the APP/PS1 mouse model of AD. Unexpectedly, we observed a dramatic increase in the rate of new myelin formation in APP/PS1 mice, reminiscent of the robust oligodendroglial response to demyelination. Despite this increase, overall levels of myelination are decreased in the cortex and hippocampus of APP/PS1 mice and postmortem AD tissue. Genetically or pharmacologically enhancing myelin renewal, by oligodendroglial deletion of the muscarinic M1 receptor or systemic administration of the pro-myelinating drug clemastine, improved the performance of APP/PS1 mice in memory-related tasks and increased hippocampal sharp wave ripples. Taken together, these results demonstrate the potential of enhancing myelination as a therapeutic strategy to alleviate AD-related cognitive impairment.

Recommendations for Preclinical Testing of Treatments Against Alzheimer's Disease-Related Epileptiform Spikes in Transgenic Rodent Models

Recent evidence suggests that about 30%of patients with mild to moderate Alzheimer's disease (AD) without a known diagnosis of epilepsy may display epileptiform spikes during electroencephalographic (EEG) recordings. These abnormal discharges occur predominantly during sleep and may be associated with accelerated disease progression. Subclinical spikes may represent a relevant target for clinical drug interventions, and there is a clear unmet need for preclinical testing of novel disease modifying agents in suitable animal models. Transgenic rodent models of AD pathology exhibit various forms of epileptiform EEG activity related to the abnormal levels of amyloid species in the brain. Among them, large-amplitude cortical and hippocampal EEG spikes in mouse and rat AD models may be reminiscent of the subclinical epileptiform EEG spikes recorded in some AD patients. This article reports the recommendations of a multidisciplinary panel of experts on optimal EEG markers and experimental designs to measure and report epileptiform activities and their response to symptomatic and disease-modifying drugs in transgenic AD model rodents. These recommendations may harmonize future preclinical EEG studies in the drug discovery research and may increase the comparability of experimental outcomes and their translational clinical value.

Role of histone deacetylase Sirt3 in the development and regression of atherosclerosis

Atherosclerosis (AS) is the most common cause of death in cardiovascular diseases and poses severe challenges to human life and safety. Epigenetics plays a vital role in every single link of AS. Whereas, how epigenetics regulates its development and regression is still unknown. Sirt3, a recognized histone deacetylase, having been reported to be involved in other acylation processes in recent years, is broadening its role in epigenetic modifications. Sirt3 is an important factor in the normal physiology of blood vessels through deacetylation of mitochondrial proteins and participates in various metabolic activities. Besides, medical research targeting Sirt3 is in full swing as well. This review combining histone deacetylase Sirt3 with AS, aims to clarify the latest progress in the significant role of Sirt3 in the development and regression of AS and to provide a novel prospect for a new regulatory factor and potential intervention target for AS.

Murine neonatal ketogenesis preserves mitochondrial energetics by preventing protein hyperacetylation

Ketone bodies are generated in the liver and allow for the maintenance of systemic caloric and energy homeostasis during fasting and caloric restriction. It has previously been demonstrated that neonatal ketogenesis is activated independently of starvation. However, the role of ketogenesis during the perinatal period remains unclear. Here, we show that neonatal ketogenesis plays a protective role in mitochondrial function. We generated a mouse model of insufficient ketogenesis by disrupting the rate-limiting hydroxymethylglutaryl-CoA synthase 2 enzyme gene (Hmgcs2). Hmgcs2 knockout (KO) neonates develop microvesicular steatosis within a few days of birth. Electron microscopic analysis and metabolite profiling indicate a restricted energy production capacity and accumulation of acetyl-CoA in Hmgcs2 KO mice. Furthermore, acetylome analysis of Hmgcs2 KO cells revealed enhanced acetylation of mitochondrial proteins. These findings suggest that neonatal ketogenesis protects the energy-producing capacity of mitochondria by preventing the hyperacetylation of mitochondrial proteins.

Partial inhibition of mitochondrial complex I ameliorates Alzheimer's disease pathology and cognition in APP/PS1 female mice

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder without a cure. Here we show that mitochondrial respiratory chain complex I is an important small molecule druggable target in AD. Partial inhibition of complex I triggers the AMP-activated protein kinase-dependent signaling network leading to neuroprotection in symptomatic APP/PS1 female mice, a translational model of AD. Treatment of symptomatic APP/PS1 mice with complex I inhibitor improved energy homeostasis, synaptic activity, long-term potentiation, dendritic spine maturation, cognitive function and proteostasis, and reduced oxidative stress and inflammation in brain and periphery, ultimately blocking the ongoing neurodegeneration. Therapeutic efficacy in vivo was monitored using translational biomarkers FDG-PET, 31P NMR, and metabolomics. Cross-validation of the mouse and the human transcriptomic data from the NIH Accelerating Medicines Partnership-AD database demonstrated that pathways improved by the treatment in APP/PS1 mice, including the immune system response and neurotransmission, represent mechanisms essential for therapeutic efficacy in AD patients.

Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.

Metabolic regulation of aging and age-related disease

Inquiry into relationships between energy metabolism and brain function requires a uniquely interdisciplinary mindset, and implementation of anti-aging lifestyle strategies based on this work also involves consistent mental and physical discipline. Dr. Mark P. Mattson embodies both of these qualities, based on the breadth and depth of his work on neurobiological responses to energetic stress, and on his own diligent practice of regular exercise and caloric restriction. Dr. Mattson created a neurotrophic niche in his own laboratory, allowing trainees to grow their skills, form new connections, and eventually migrate, forming their own labs while remaining part of the extended lab family. In this historical review, we highlight Dr. Mattson's many contributions to understanding neurobiological responses to physical exercise and dietary restriction, with an emphasis on the mechanisms that may underlie neuroprotection in ageing and age-related disease. On the occasion of Dr. Mattson's retirement from the National Institute on Aging, we highlight his foundational work on metabolism and neuroplasticity by reviewing the context for these findings and considering their impact on future research on the neuroscience of aging.

Dementia in late-onset epilepsy: The Atherosclerosis Risk in Communities study

OBJECTIVE

To determine the risk of dementia after the development of late-onset epilepsy.

METHODS

We used data from the Atherosclerosis Risk in Communities (ARIC) cohort study, which started in 1987 to 1989 with 15,792 mostly Black and White men and women from 4 US communities. We identified late-onset epilepsy (LOE; seizures starting at age 67 or later) from linked Medicare claims data. We used a Cox proportional hazards regression model to evaluate associations between LOE and dementia through 2017 as ascertained from neuropsychological testing, interviews, and hospital discharge surveillance, and we used multinomial logistic regression to assess the risk of dementia and mild cognitive impairment in the subset with full neuropsychological assessments available. We adjusted for demographics and vascular and Alzheimer disease risk factors.

RESULTS

Of 9,033 ARIC participants with sufficient Medicare coverage data (4,980 [55.1%] female, 1993 [22.1%] Black), 671 met the definition of LOE. Two hundred seventy-nine (41.6%) participants with and 1,408 (16.8%) without LOE developed dementia (p < 0.001). After a diagnosis of LOE, the adjusted hazard ratio for developing subsequent dementia was 3.05 (95% confidence interval 2.65-3.51). The median time to dementia ascertainment after the onset of LOE was 3.66 years (quartile 1-3, 1.28-8.28 years).

INTERPRETATION

The risk of incident dementia is substantially elevated in individuals with LOE. Further work is needed to explore causes for the increased risk of dementia in this growing population.

Brain energy rescue: an emerging therapeutic concept for neurodegenerative disorders of ageing

The brain requires a continuous supply of energy in the form of ATP, most of which is produced from glucose by oxidative phosphorylation in mitochondria, complemented by aerobic glycolysis in the cytoplasm. When glucose levels are limited, ketone bodies generated in the liver and lactate derived from exercising skeletal muscle can also become important energy substrates for the brain. In neurodegenerative disorders of ageing, brain glucose metabolism deteriorates in a progressive, region-specific and disease-specific manner - a problem that is best characterized in Alzheimer disease, where it begins presymptomatically. This Review discusses the status and prospects of therapeutic strategies for countering neurodegenerative disorders of ageing by improving, preserving or rescuing brain energetics. The approaches described include restoring oxidative phosphorylation and glycolysis, increasing insulin sensitivity, correcting mitochondrial dysfunction, ketone-based interventions, acting via hormones that modulate cerebral energetics, RNA therapeutics and complementary multimodal lifestyle changes.

Hormesis: A potential strategic approach to the treatment of neurodegenerative disease

This review describes neuroprotective effects mediated by pre- and post-conditioning-induced processes that act via the quantitative features of the hormetic dose response. These lead to the development of acquired resilience that can protect neuronal systems from endogenous and exogenous stresses and insult. Particular attention is directed to issues of dose optimization, inter-individual variation, and potential ways to further study and employ hormetic-based preconditioning approaches in medical and public health efforts to treat and prevent neurodegenerative disease.

Ketotherapeutics for neurodegenerative diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are, respectively, the most prevalent and fastest growing neurodegenerative diseases worldwide. The former is primarily characterized by memory loss and the latter by the motor symptoms of tremor and bradykinesia. Both AD and PD are progressive diseases that share several key underlying mitochondrial, inflammatory, and other metabolic pathologies. This review will detail how these pathologies intersect with ketone body metabolism and signaling, and how ketone bodies, particularly d-β-hydroxybutyrate (βHB), may serve as a potential adjunctive nutritional therapy for two of the world's most devastating conditions.

Seizing the Alzheimer's Brain: A Role for Sirtuin 3 in Hyperexcitability

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GABAergic Inhibitory Interneuron Deficits in Alzheimer's Disease: Implications for Treatment

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized clinically by severe cognitive deficits and pathologically by amyloid plaques, neuronal loss, and neurofibrillary tangles. Abnormal amyloid β-protein (Aβ) deposition in the brain is often thought of as a major initiating factor in AD neuropathology. However, gamma-aminobutyric acid (GABA) inhibitory interneurons are resistant to Aβ deposition, and Aβ decreases synaptic glutamatergic transmission to decrease neural network activity. Furthermore, there is now evidence suggesting that neural network activity is aberrantly increased in AD patients and animal models due to functional deficits in and decreased activity of GABA inhibitory interneurons, contributing to cognitive deficits. Here we describe the roles played by excitatory neurons and GABA inhibitory interneurons in Aβ-induced cognitive deficits and how altered GABA interneurons regulate AD neuropathology. We also comprehensively review recent studies on how GABA interneurons and GABA receptors can be exploited for therapeutic benefit. GABA interneurons are an emerging therapeutic target in AD, with further clinical trials urgently warranted.