bims-brabim 2021-10-31 papers

bims-brabim

Biomed News

on Brain bioenergetics and metabolism

Issue of 2021–10–31
23 papers selected by
João Victor Cabral-Costa, University of São Paulo

Identification of long-lived proteins in the mitochondria reveals increased stability of the electron transport chain.
Synaptic dysfunction of Aldh1a1 neurons in the ventral tegmental area causes impulsive behaviors.
Neuron-specific ablation of eIF5A or deoxyhypusine synthase leads to impairments in growth, viability, neurodevelopment and cognitive functions in mice.
Selenomethionine Improves Mitochondrial Function by Upregulating Mitochondrial Selenoprotein in a Model of Alzheimer's Disease.
Rab7 reduces α-synuclein toxicity in rats and primary neurons.
Modulation of cGAS-STING Pathway by Nicotinamide Riboside in Alzheimer's Disease.
Disruption of Glucose Metabolism in Aged Octodon degus: A Sporadic Model of Alzheimer's Disease.
Irisin Rescues Blood-Brain Barrier Permeability following Traumatic Brain Injury and Contributes to the Neuroprotection of Exercise in Traumatic Brain Injury.
Mechanical stimulus-evoked signal transduction between keratinocytes and sensory neurons via extracellular ATP.
Circadian Regulation and Clock-Controlled Mechanisms of Glycerophospholipid Metabolism from Neuronal Cells and Tissues to Fibroblasts.
DCA Protects against Oxidation Injury Attributed to Cerebral Ischemia-Reperfusion by Regulating Glycolysis through PDK2-PDH-Nrf2 Axis.
Protective effects of medium chain triglyceride diet in a mouse model of Dravet syndrome.
Implications of Phosphoinositide 3-Kinase-Akt (PI3K-Akt) Pathway in the Pathogenesis of Alzheimer's Disease.
An assessment of the transport mechanism and intraneuronal stability of L-carnosine.
Poly (ADP-Ribose) Polymerase 1 Regulates Cajal-Retzius Cell Development and Neural Precursor Cell Adhesion.
Lysosomal targetomics of ghr KO mice shows chaperone-mediated autophagy degrades nucleocytosolic acetyl-coA enzymes.
Delivery Platforms for CRISPR/Cas9 Genome Editing of Glial Cells in the Central Nervous System.
Mitochondrial calcium exchange in physiology and disease.
Altered substrate metabolism in neurodegenerative disease: new insights from metabolic imaging.
An Overview of the Involvement of D-Serine in Cognitive Impairment in Normal Aging and Dementia.
Macroautophagy and normal aging of the nervous system: Lessons from animal models.
Metabolism in Huntington's disease: a major contributor to pathology.
Characterization of Astrocyte Morphology and Function Using a Fast and Reliable Tissue Clearing Technique.

Dev Cell. 2021 Oct 22. pii: S1534-5807(21)00809-1. [Epub ahead of print]

Identification of long-lived proteins in the mitochondria reveals increased stability of the electron transport chain.

Shefali Krishna, Rafael Arrojo E Drigo, Juliana S Capitanio, Ranjan Ramachandra, Mark Ellisman, Martin W Hetzer.

  In order to combat molecular damage, most cellular proteins undergo rapid turnover. We have previously identified large nuclear protein assemblies that can persist for years in post-mitotic tissues and are subject to age-related decline. Here, we report that mitochondria can be long lived in the mouse brain and reveal that specific mitochondrial proteins have half-lives longer than the average proteome. These mitochondrial long-lived proteins (mitoLLPs) are core components of the electron transport chain (ETC) and display increased longevity in respiratory supercomplexes. We find that COX7C, a mitoLLP that forms a stable contact site between complexes I and IV, is required for complex IV and supercomplex assembly. Remarkably, even upon depletion of COX7C transcripts, ETC function is maintained for days, effectively uncoupling mitochondrial function from ongoing transcription of its mitoLLPs. Our results suggest that modulating protein longevity within the ETC is critical for mitochondrial proteome maintenance and the robustness of mitochondrial function.

Keywords:  age mosaicism; aging; electron transport chain; heterogeneity; long-lived proteins; mitochondria; muscle; neurons; protein homeostasis; supercomplexes

DOI:  https://doi.org/10.1016/j.devcel.2021.10.008
Mol Neurodegener. 2021 Oct 26. 16(1): 73

Synaptic dysfunction of Aldh1a1 neurons in the ventral tegmental area causes impulsive behaviors.

Xinyan Li, Wenting Chen, Xian Huang, Wei Jing, Tongmei Zhang, Quntao Yu, Hongyan Yu, Hao Li, Qing Tian, Yumei Ding, Youming Lu.

   BACKGROUND: Aldh1a1 neurons are a subtype of gamma-aminobutyric acid (GABA) inhibitory neurons that use Aldh1a1 rather than glutamate decarboxylase (GAD) as an enzyme for synthesizing GABA transmitters. However, the behaviors and circuits of this newly identified subtype of inhibitory interneurons remain unknown.
METHODS: We generated a mutant mouse line in which cyclization recombination enzyme (CRE) was expressed under the control of the Aldh1a1 promotor (Aldh1a1-CRE mice). Using this mutant strain of mice together with the heterozygous male Alzheimer's disease (AD) related model mice (APPswe/PSEN1dE9, or AD mice) and a genetically modified retrograde and anterograde synaptic tracing strategy, we have studied a specific synaptic circuit of Aldh1a1 neurons with system-level function and disease progression in AD mice.
RESULTS: We demonstrate that Aldh1a1 neurons encode delay of gratification that measures self-control skills in decision making by projecting inhibitory synapses directly onto excitatory glutamate neurons in the intermediate lateral septum (EGNIS) and receiving synaptic inputs from layer 5b pyramidal neurons in the medial prefrontal cortex (L5PN). L5PN → Aldh1a1 synaptic transmission undergoes long-term potentiation (LTP). Pathway specific inhibition by either genetic silencing presynaptic terminals or antagonizing postsynaptic receptors impairs delay of gratification, resulting in the impulsive behaviors. Further studies show that reconstitution of Aldh1a1-deficient neurons with the expression of exogenous Aldh1a1 (eAldh1a1) restores Aldh1a1 → EGNIS synaptic transmission and rescues the impulsive behaviors in AD mice.
CONCLUSIONS: These results not only identify a specific function and circuit of Aldh1a1 neurons but also provide a cellular point of entry to an important but understudied synaptic mechanism for the induction of impulsive behaviors at an early stage of AD.

Keywords:  Aldh1a1 neurons; Alzheimer’s disease; Delay of gratification; Impulsive behaviors; Synaptic circuits

DOI:  https://doi.org/10.1186/s13024-021-00494-9
J Biol Chem. 2021 Oct 21. pii: S0021-9258(21)01139-X. [Epub ahead of print] 101333

Neuron-specific ablation of eIF5A or deoxyhypusine synthase leads to impairments in growth, viability, neurodevelopment and cognitive functions in mice.

Rajesh Kumar Kar, Ashleigh S Hanner, Matthew F Starost, Danielle Springer, Teresa L Mastracci, Raghavendra G Mirmira, Myung Hee Park.

  Eukaryotic initiation factor 5A (eIF5A) is an essential protein that requires a unique amino acid, hypusine, for its activity. Hypusine is formed exclusively in eIF5A post-translationally via two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Each of the genes encoding these proteins, Eif5a, Dhps, and Dohh, is required for mouse embryonic development. Variants in EIF5A or DHPS were recently identified as the genetic basis underlying certain rare neurodevelopmental disorders in humans. To investigate the roles of eIF5A and DHPS in brain development, we generated four conditional knockout mouse strains using the Emx1-Cre or Camk2a-Cre strains and examined the effects of temporal- and region-specific deletion of Eif5a or Dhps. The conditional deletion of Dhps or Eif5a by Emx1 promotor-driven Cre expression (E9.5, in the cortex and hippocampus) led to gross defects in forebrain development, reduced growth, and premature death. On the other hand, the conditional deletion of Dhps or Eif5a by Camk2a promoter-driven Cre expression (postnatal, mainly in the CA1 region of the hippocampus) did not lead to global developmental defects; rather, these knockout animals exhibited severe impairment in spatial learning, contextual learning, and memory when subjected to the Morris Water Maze and a contextual learning test. In both models, the Dhps knockout mice displayed more severe impairment than their Eif5a knockout counterparts. The observed defects in the brain, global development, or cognitive functions most likely result from translation errors due to a deficiency in active, hypusinated eIF5A. Our study underscores the important roles of eIF5A and DHPS in neurodevelopment.

Keywords:  cognitive function; deoxyhypusine synthase; eIF5A; hypusine; mouse genetics; neurodevelopment; neurodevelopmental disorder; post-translational modification; translation

DOI:  https://doi.org/10.1016/j.jbc.2021.101333
Front Aging Neurosci. 2021 ;13 750921

Selenomethionine Improves Mitochondrial Function by Upregulating Mitochondrial Selenoprotein in a Model of Alzheimer's Disease.

Chen Chen, Yao Chen, Zhong-Hao Zhang, Shi-Zheng Jia, Yu-Bin Chen, Shao-Ling Huang, Xin-Wen Xu, Guo-Li Song.

  Alzheimer's disease (AD), the most common neurodegenerative disease in elderly humans, is pathologically characterized by amyloid plaques and neurofibrillary tangles. Mitochondrial dysfunction that occurs in the early stages of AD, which includes dysfunction in mitochondrial generation and energy metabolism, is considered to be closely associated with AD pathology. Selenomethionine (Se-Met) has been reported to improve cognitive impairment and reduce amyloid plaques and neurofibrillary tangles in 3xTg-AD mice. Whether Se-Met can regulate mitochondrial dysfunction in an AD model during this process remains unknown.In this study, the N2a-APP695-Swedish (N2aSW) cell and 8-month-old 3xTg-AD mice were treated with Se-Met in vitro and in vivo. Our study showed that the numbers of mitochondria were increased after treatment with Se-Met. Se-Met treatment also significantly increased the levels of NRF1 and Mfn2, and decreased those of OPA1 and Drp1. In addition, the mitochondrial membrane potential was significantly increased, while the ROS levels and apoptosis rate were significantly decreased, in cells after treatment with Se-Met. The levels of ATP, complex IV, and Cyt c and the activity of complex V were all significantly increased. Furthermore, the expression level of SELENO O was increased after Se-Met treatment. Thus, Se-Met can maintain mitochondrial dynamic balance, promote mitochondrial fusion or division, restore mitochondrial membrane potential, promote mitochondrial energy metabolism, inhibit intracellular ROS generation, and reduce apoptosis. These effects are most likely mediated via upregulation of SELENO O. In summary, Se-Met improves mitochondrial function by upregulating mitochondrial selenoprotein in these AD models.

Keywords:  Alzheimer’s disease; mitochondria dysfunction and dementia; mitochondrial selenoprotein; selenomethionine; therapeutic effect and mechanism

DOI:  https://doi.org/10.3389/fnagi.2021.750921
Exp Neurol. 2021 Oct 22. pii: S0014-4886(21)00308-3. [Epub ahead of print] 113900

Rab7 reduces α-synuclein toxicity in rats and primary neurons.

Eva M Szegö, Chris Van den Haute, Lennart Höfs, Veerle Baekelandt, Anke Van der Perren, Björn Falkenburger.

  During the pathogenesis of Parkinson's disease (PD), aggregation of alpha-synuclein (αSyn) induces a vicious cycle of cellular impairments that lead to neurodegeneration. Consequently, removing toxic αSyn aggregates constitutes a plausible strategy against PD. In this work, we tested whether stimulating the autolysosomal degradation of αSyn aggregates through the Ras-related in brain 7 (Rab7) pathway can reverse αSyn-induced cellular impairment and prevent neurodegeneration in vivo. The disease-related A53T mutant of αSyn was expressed in primary neurons and in dopaminergic neurons of the rat brain simultaneously with wild type (WT) Rab7 or the T22N mutant as negative control. The cellular integrity was quantified by morphological and biochemical analyses. In primary neurons, WT Rab7 rescued the αSyn-induced loss of neurons and neurites. Furthermore, Rab7 decreased the amount of reactive oxygen species and the amount of Triton X-100 insoluble αSyn. In rat brain, WT Rab7 reduced αSyn-induced loss of dopaminergic axon terminals in the striatum and the loss of dopaminergic dendrites in the substantia nigra pars reticulata. Further, WT Rab7 lowered αSyn pathology as quantified by phosphorylated αSyn staining. Finally, WT Rab7 attenuated αSyn-induced DNA damage in primary neurons and rat brain. In brief, Rab7 reduced αSyn-induced pathology, ameliorated αSyn-induced neuronal degeneration, oxidative stress and DNA damage. These findings indicate that Rab7 is able to disrupt the vicious cycle of cellular impairment, αSyn pathology and neurodegeneration present in PD. Stimulation of Rab7 and the autolysosomal degradation pathway could therefore constitute a beneficial strategy for PD.

Keywords:  Autophagy; DNA damage; Neuroprotection; Oxidative stress; Parkinson's disease; Protein aggregation; Rab7; alpha-Synuclein

DOI:  https://doi.org/10.1016/j.expneurol.2021.113900
Rejuvenation Res. 2021 Oct;24(5): 397-402

Modulation of cGAS-STING Pathway by Nicotinamide Riboside in Alzheimer's Disease.

James W Larrick, Andrew R Mendelsohn.

  Numerous studies demonstrate a global decrease in nicotinamide adenine dinucleotide (NAD+) with aging. This decline is associated with the development of several of the hallmarks of aging such as reduced mitophagy and neuroinflammation, processes thought to play a significant role in the progression of Alzheimer's disease (AD). Augmentation of NAD+ by oral administration of a precursor, nicotinamide riboside (NR), reduces senescence of affected cells, attenuates DNA damage and neuroinflammation in the transgenic APP/PS1 murine model of AD. Inflammation mediated by microglial cells plays an important role in progression of AD and other neurodegenerative diseases. The cytoplasmic DNA sensor, cyclic GMP-AMP synthase (cGAS) and downstream stimulator of interferon genes (STING), generates an interferon signature characteristic of senescence and inflammaging in the brain of AD mice. Elevated cGAS-STING observed in the AD mouse brains and human AD fibroblasts was normalized by NR. This intervention also increased mitophagy with improved cognition and behavior in the APP/PS1 mice. These studies suggest that modulation of the cGAS-STING pathway may benefit AD patients and possibly other disorders characterized by compromised mitophagy and excessive neuroinflammation.

Keywords:  Alzheimer's disease; NAD; cGAS/STING; inflammation; nicotinamide riboside

DOI:  https://doi.org/10.1089/rej.2021.0062
Front Integr Neurosci. 2021 ;15 733007

Disruption of Glucose Metabolism in Aged Octodon degus: A Sporadic Model of Alzheimer's Disease.

Pedro Cisternas, Camila Gherardelli, Paulina Salazar, Nibaldo C Inestrosa.

  Alzheimer's disease is a progressive neurodegenerative disorder and the most common cause of dementia. Although transgenic Alzheimer's disease (AD) animal models have greatly contributed to our understanding of the disease, therapies tested in these animals have resulted in a high rate of failure in preclinical trials for AD. A promising model is Octodon degus (degu), a Chilean rodent that spontaneously develops AD-like neuropathology. Previous studies have reported that, during aging, degus exhibit a progressive decline in cognitive function, reduced neuroinflammation, and concomitant increases in the number and size of amyloid β (Aβ) plaques in several brain regions. Importantly, in humans and several AD models, a correlation has been shown between brain dysfunction and neuronal glucose utilization impairment, a critical aspect considering the high-energy demand of the brain. However, whether degus develop alterations in glucose metabolism remains unknown. In the present work, we measured several markers of glucose metabolism, namely, glucose uptake, ATP production, and glycolysis and pentose phosphate pathway (PPP) flux, in hippocampal slices from degus of different ages. We found a significant decrease in hippocampal glucose metabolism in aged degus, caused mainly by a drop in glucose uptake, which in turn, reduced ATP synthesis. Moreover, we observed a negative correlation between age and PPP flux. Together, our data further support the use of degus as a model for studying the neuropathology involved in sporadic AD-like pathology and as a potentially valuable tool in the search for effective treatments against the disease.

Keywords:  Alzheimer's disease; Octodon degus; aging; glucose; metabolism

DOI:  https://doi.org/10.3389/fnint.2021.733007
Oxid Med Cell Longev. 2021 ;2021 1118981

Irisin Rescues Blood-Brain Barrier Permeability following Traumatic Brain Injury and Contributes to the Neuroprotection of Exercise in Traumatic Brain Injury.

Peipei Guo, Zhao Jin, Jin Wang, Aming Sang, Huisheng Wu.

Traumatic brain injury (TBI) has a high incidence, mortality, and morbidity all over the world. One important reason for its poor clinical prognosis is brain edema caused by blood-brain barrier (BBB) dysfunction after TBI. The mechanism may be related to the disorder of mitochondrial morphology and function of neurons in damaged brain tissue, the decrease of uncoupling protein 2 (UCP2) activity, and the increase of inflammatory reaction and oxidative stress. In this study, we aimed to investigate the effects of exogenous irisin on BBB dysfunction after TBI and its role in the neuroprotective effects of endurance exercise (EE) in mice. The concentrations of irisin in cerebrospinal fluid (CSF) and plasma of patients with mild to severe TBI were measured by ELISA. Then, male C57BL/6J mice and UCP2 knockout mice with C57BL/6J background were used to establish the TBI model. The BBB structure and permeability were examined by transmission electron microscopy and Evans blue extravasation, respectively. The protein expressions of irisin, occludin, claudin-5, zonula occludens-1 (ZO-1), nuclear factor E2-related factor 2(Nrf2), quinine oxidoreductase (NQO-1), hemeoxygenase-1 (HO-1), cytochrome C (Cyt-C), cytochrome C oxidase (COX IV), BCL2-associated X protein (Bax), cleaved caspase-3, and UCP2 were detected by western blot. The production of reactive oxygen species (ROS) was evaluated by the dihydroethidium (DHE) staining. The levels of inflammatory factors were detected by ELISA. In this study, we found that the CSF irisin levels were positively correlated with the severity of disease in patients with TBI and both EE and exogenous irisin could reduce BBB damage in a mouse model of TBI. In addition, we used UCP2-/- mice and further found that irisin could improve the dysfunction of BBB after TBI by promoting the expression of UCP2 on the mitochondrial membrane of neurons, reducing the damage of mitochondrial structure and function, thus alleviating the inflammatory response and oxidative stress. In conclusion, the results of this study suggested that irisin might alleviate brain edema after TBI by promoting the expression of UCP2 on the mitochondrial membrane of neurons and contribute to the neuroprotection of EE against TBI.

DOI: https://doi.org/10.1155/2021/1118981
Biochem Biophys Res Commun. 2021 Oct 21. pii: S0006-291X(21)01454-6. [Epub ahead of print]582 131-136

Mechanical stimulus-evoked signal transduction between keratinocytes and sensory neurons via extracellular ATP.

Yutaka Shindo, Keigo Fujita, Mari Tanaka, Hiroki Fujio, Kohji Hotta, Kotaro Oka.

  The skin is exposed to various external stimuli. Keratinocytes, which are the main cell type in the epidermis, interact with peripheral sensory neurons and modulate neuronal activity. Recent studies have revealed that keratinocytes play crucial roles in nociception, and that ATP is one of the main mediators of signal transduction from keratinocytes to sensory neurons. However, no quantitative cellular level analyses of ATP-mediated information flow from keratinocytes to sensory dorsal root ganglion (DRG) neurons have been conducted. In this study, we performed simultaneous imaging of cell surface ATP and intracellular Ca2+ signals using both iATPSnFR, a genetically encoded ATP probe localized to the outside of the cell membrane, and the Ca2+ probe, Fura-red. Upon mechanical stimulation of the keratinocyte with a glass needle, an increase in Ca2+ and ATP release were observed around the stimulated area, and these phenomena were positively correlated. In cultured DRG neurons and keratinocytes neighboring the stimulated keratinocyte, increased intracellular Ca2+ concentration and levels of cell surface ATP on the side closer to the stimulated cell were detected. The ratio of Ca2+ response to input ATP signal was significantly larger in DRG neurons than in keratinocytes. We found that DRG neurons were more sensitive to ATP than keratinocytes, and therefore, only DRG neurons responded to ATP at 1 μM or lower concentrations when in co-culture with keratinocytes. Moreover, signals caused by moderate mechanical stimulation of keratinocytes were transmitted predominantly to DRG neurons. These findings would be important in the further determination of the detailed mechanism of nociception in the epidermis.

Keywords:  ATP release; Ca(2+) imaging; DRG neurons; Epidermis; Mechanical stimulus; iATPSnFR

DOI:  https://doi.org/10.1016/j.bbrc.2021.10.046
Mol Neurobiol. 2021 Oct 26.

Circadian Regulation and Clock-Controlled Mechanisms of Glycerophospholipid Metabolism from Neuronal Cells and Tissues to Fibroblasts.

Mario E Guido, Natalia M Monjes, Paula M Wagner, Gabriela A Salvador.

  Along evolution, living organisms developed a precise timekeeping system, circadian clocks, to adapt life to the 24-h light/dark cycle and temporally regulate physiology and behavior. The transcriptional molecular circadian clock and metabolic/redox oscillator conforming these clocks are present in organs, tissues, and even in individual cells, where they exert circadian control over cellular metabolism. Disruption of the molecular clock may cause metabolic disorders and higher cancer risk. The synthesis and degradation of glycerophospholipids (GPLs) is one of the most highly regulated metabolisms across the 24-h cycle in terms of total lipid content and enzyme expression and activity in the nervous system and individual cells. Lipids play a plethora of roles (membrane biogenesis, energy sourcing, signaling, and the regulation of protein-chromatin interaction, among others), making control of their metabolism a vital checkpoint in the cellular organization of physiology. An increasing body of evidence clearly demonstrates an orchestrated and sequential series of events occurring in GPL metabolism across the 24-h day in diverse retinal cell layers, immortalized fibroblasts, and glioma cells. Moreover, the clock gene Per1 and other circadian-related genes are tightly involved in the regulation of GPL synthesis in quiescent cells. However, under proliferation, the metabolic oscillator continues to control GPL metabolism of brain cancer cells even after molecular circadian clock disruption, reflecting the crucial role of the temporal metabolism organization in cell preservation. The aim of this review is to examine the control exerted by circadian clocks over GPL metabolism, their synthesizing enzyme expression and activities in normal and tumorous cells of the nervous system and in immortalized fibroblasts.

Keywords:  Acyltransferases; Choline kinase; Circadian rhythms; Clock genes; Fibroblasts; Lipin1; Metabolic oscillator; Molecular clock; Nuclear receptors; Phosphatidylcholine; Phospholipid metabolism; Retina; Tumor cells

DOI:  https://doi.org/10.1007/s12035-021-02595-4
Oxid Med Cell Longev. 2021 ;2021 5173035

DCA Protects against Oxidation Injury Attributed to Cerebral Ischemia-Reperfusion by Regulating Glycolysis through PDK2-PDH-Nrf2 Axis.

Xiaoyong Zhao, Shan Li, Yunchang Mo, Ruru Li, Shaoyi Huang, Anqi Zhang, Xuqing Ni, Qinxue Dai, Junlu Wang.

Cerebral ischemic stroke (IS) is still a difficult problem to be solved; energy metabolism failure is one of the main factors causing mitochondrion dysfunction and oxidation stress damage within the pathogenesis of cerebral ischemia, which produces considerable reactive oxygen species (ROS) and opens the blood-brain barrier. Dichloroacetic acid (DCA) can inhibit pyruvate dehydrogenase kinase (PDK). Moreover, DCA has been indicated with the capability of increasing mitochondrial pyruvate uptake and promoting oxidation of glucose in the course of glycolysis, thereby improving the activity of pyruvate dehydrogenase (PDH). As a result, pyruvate flow is promoted into the tricarboxylic acid cycle to expedite ATP production. DCA has a protective effect on IS and brain ischemia/reperfusion (I/R) injury, but the specific mechanism remains unclear. This study adopted a transient middle cerebral artery occlusion (MCAO) mouse model for simulating IS and I/R injury in mice. We investigated the mechanism by which DCA regulates glycolysis and protects the oxidative damage induced by I/R injury through the PDK2-PDH-Nrf2 axis. As indicated from the results of this study, DCA may improve glycolysis, reduce oxidative stress and neuronal death, damage the blood-brain barrier, and promote the recovery of oxidative metabolism through inhibiting PDK2 and activating PDH. Additionally, DCA noticeably elevated the neurological score and reduced the infarct volume, brain water content, and necrotic neurons. Moreover, as suggested from the results, DCA elevated the content of Nrf2 as well as HO-1, i.e., the downstream antioxidant proteins pertaining to Nrf2, while decreasing the damage of BBB and the degradation of tight junction proteins. To simulate the condition of hypoxia and ischemia in vitro, HBMEC cells received exposure to transient oxygen and glucose deprivation (OGD). The DCA treatment is capable of reducing the oxidative stress and blood-brain barrier of HBMEC cells after in vitro hypoxia and reperfusion (H/R). Furthermore, this study evidenced that HBMEC cells could exhibit higher susceptibility to H/R-induced oxidative stress after ML385 application, the specific inhibitor of Nrf2. Besides, the protection mediated by DCA disappeared after ML385 application. To sum up, as revealed from the mentioned results, DCA could exert the neuroprotective effect on oxidative stress and blood-brain barrier after brain I/R injury via PDK2-PDH-Nrf2 pathway activation. Accordingly, the PDK2-PDH-Nrf2 pathway may play a key role and provide a new pharmacology target in cerebral IS and I/R protection by DCA.

DOI: https://doi.org/10.1155/2021/5173035
Epilepsia. 2021 Oct 28.

Protective effects of medium chain triglyceride diet in a mouse model of Dravet syndrome.

Nikola Jancovski, Tomas Baldwin, Michael Orford, Melody Li, Gabriel Davis Jones, Lisseth Estefania Burbano, Tricia Rutherford, Christopher Reid, Simon Heales, Simon Eaton, Steven Petrou.

   OBJECTIVE: Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy with early childhood onset. Patients with DS do not respond well to antiepileptic drugs and have only a few treatment options available. Here, we evaluated the effect of medium chain triglyceride (MCT) diet therapy in a mouse model of DS.
METHODS: Scn1aR1407X/+ DS mice were given diets supplemented with MCTs with varying ratios of decanoic (C10) and octanoic (C8) acid or a control diet for 4 weeks. Video monitoring was performed to evaluate spontaneous convulsive seizure frequency. Susceptibility to hyperthermia-induced seizures was also examined. Medium chain fatty acids, and mitochondrial and antioxidant markers were assessed in brain homogenate.
RESULTS: Dietary intervention with MCTs significantly prolonged survival and reduced convulsive seizure frequency during the critical period of highest seizure occurrence in the Scn1aR1407X/+ DS mice. Moreover, MCT diet therapy showed protective effects against hyperthermia-induced seizures. We demonstrated that coadministration of C10/C8 was effective at reducing both seizures and mortality, whereas C10 alone only reduced mortality, suggesting that the ratio of C10 to C8 in the MCT is an important factor for efficacy. When C10 and C8 are supplemented at an 80:20 ratio in the diet, C10 accumulates in the brain in high enough concentrations to enhance brain energy metabolism by both stimulating mitochondrial enrichment and increasing its antioxidant status.
SIGNIFICANCE: The results from this study indicate that MCT diet therapy may provide therapeutic benefits in DS. Future clinical studies would elucidate whether these positive effects are mirrored in human patients.

Keywords:  Dravet syndrome; MCT; decanoic acid; epilepsy; octanoic acid; seizure reduction

DOI:  https://doi.org/10.1111/epi.17101
Mol Neurobiol. 2021 Oct 26.

Implications of Phosphoinositide 3-Kinase-Akt (PI3K-Akt) Pathway in the Pathogenesis of Alzheimer's Disease.

Manish Kumar, Nitin Bansal.

  Alzheimer's disease (AD) is the foremost type of dementia that afflicts considerable morbidity and mortality in aged population. Several transcription molecules, pathways, and molecular mechanisms such as oxidative stress, inflammation, autophagy, and immune system interact in a multifaceted way that disrupt physiological processes (cell growth, differentiation, survival, lipid and energy metabolism, endocytosis) leading to apoptosis, tauopathy, β-amyloidopathy, neuron, and synapse loss, which play an important role in AD pathophysiology. Despite of stupendous advancements in pathogenic mechanisms, treatment of AD is still a nightmare in the field of medicine. There is compelling urgency to find not only symptomatic but effective disease-modifying therapies. Recently, phosphoinositide 3-kinase (PI3K) and Akt are identified as a pathway triggered by diverse stimuli, including insulin, growth factors, cytokines, and cellular stress, that link amyloid-β, neurofibrillary tangles, and brain atrophy. The present review aims to explore and analyze the role of PI3K-Akt pathway in AD and agents which may modulate Akt and have therapeutic prospects in AD. The literature was researched using keywords "PI3K-Akt" and "Alzheimer's disease" from PubMed, Web of Science, Bentham, Science Direct, Springer Nature, Scopus, and Google Scholar databases including books. Articles published from 1992 to 2021 were prioritized and analyzed for their strengths and limitations, and most appropriate ones were selected for the purpose of review. PI3K-Akt pathway regulates various biological processes such as cell proliferation, motility, growth, survival, and metabolic functions, and inhibits many neurotoxic mechanisms. Furthermore, experimental data indicate that PI3K-Akt signaling might be an important therapeutic target in treatment of AD.

Keywords:  Acetylcholine; Amyloid; Inflammation; Neurofibrillary tangles; Neuroprotection; Oxidative stress

DOI:  https://doi.org/10.1007/s12035-021-02611-7
Amino Acids. 2021 Oct 25.

An assessment of the transport mechanism and intraneuronal stability of L-carnosine.

Alexander V Lopachev, Denis A Abaimov, Ivan S Filimonov, Kseniya N Kulichenkova, Tatiana N Fedorova.

  L-Carnosine (β-alanyl-L-histidine) is a well-known antioxidant and neuroprotector in various models on animals and cell cultures. However, while there is a plethora of data demonstrating its efficiency as a neuroprotector, there is a distinct lack of data regarding the mechanism of its take up by neurons. According to literature, cultures of rat astrocytes, SKPT cells and rat choroid plexus epithelial cells take up carnosine via the H+-coupled PEPT2 membrane transporter. We've assessed the effectiveness and mechanism of carnosine transport, and its stability in primary rat cortical culture neurons. We demonstrated that neurons take up carnosine via active transport with Km = 119 μM and a maximum velocity of 0.289 nmol/mg (prot)/min. Passive transport speed constituted 0.21∙10-4 nmol/mg (prot)/min (with 119 μM concentration in the medium)-significantly less than active transport speed. However, carnosine concentrations over 12.5 mM led to passive transport speed becoming greater than active transport speed. Using PEPT2 inhibitor zofenopril, we demonstrated that PEPT2-dependent transport is one of the main modes of carnosine take up by neurons. Our experiments demonstrated that incubation with carnosine does not affect PEPT2 amount present in culture. At the same time, after removing carnosine from the medium, its elimination speed by culture cells reached 0.035 nmol/mg (prot)/min, which led to a decrease in carnosine quantity to control levels in culture within 1 h. Thus, carnosine is taken up by neurons with an effectiveness comparable to that of other PEPT2 substrates, but its elimination rate suggests that for effective use as a neuroprotector it's necessary to either maintain a high concentration in brain tissue, or increase the effectiveness of glial cell synthesis of endogenous carnosine and its shuttling into neurons, or use more stable chemical modifications of carnosine.

Keywords:  Carnosine; Neuron; PEPT2; Take up; Transport efficiency; Transport kinetics

DOI:  https://doi.org/10.1007/s00726-021-03094-5
Front Cell Dev Biol. 2021 ;9 693595

Poly (ADP-Ribose) Polymerase 1 Regulates Cajal-Retzius Cell Development and Neural Precursor Cell Adhesion.

Megan M Nelson, J Damon Hoff, Mya L Zeese, Gabriel Corfas.

  Poly (ADP-ribose) polymerase 1 (PARP1) is a ubiquitously expressed enzyme that regulates DNA damage repair, cell death, inflammation, and transcription. PARP1 functions by adding ADP-ribose polymers (PAR) to proteins including itself, using NAD+ as a donor. This post-translational modification known as PARylation results in changes in the activity of PARP1 and its substrate proteins and has been linked to the pathogenesis of various neurological diseases. PARP1 KO mice display schizophrenia-like behaviors, have impaired memory formation, and have defects in neuronal proliferation and survival, while mutations in genes that affect PARylation have been associated with intellectual disability, psychosis, neurodegeneration, and stroke in humans. Yet, the roles of PARP1 in brain development have not been extensively studied. We now find that loss of PARP1 leads to defects in brain development and increased neuronal density at birth. We further demonstrate that PARP1 loss increases the expression levels of genes associated with neuronal migration and adhesion in the E15.5 cerebral cortex, including Reln. This correlates with an increased number of Cajal-Retzius (CR) cells in vivo and in cultures of embryonic neural progenitor cells (NPCs) derived from the PARP1 KO cortex. Furthermore, PARP1 loss leads to increased NPC adhesion to N-cadherin, like that induced by experimental exposure to Reelin. Taken together, these results uncover a novel role for PARP1 in brain development, i.e., regulation of CR cells, neuronal density, and cell adhesion.

Keywords:  N-cadherin; PARP1; Reelin; cortical development; neuronal adhesion

DOI:  https://doi.org/10.3389/fcell.2021.693595
Autophagy. 2021 Oct 27.

Lysosomal targetomics of ghr KO mice shows chaperone-mediated autophagy degrades nucleocytosolic acetyl-coA enzymes.

S Joseph Endicott, Alexander C Monovich, Eric L Huang, Evelynn I Henry, Dennis N Boynton, Logan J Beckmann, Michael J MacCoss, Richard A Miller.

  Mice deficient for GHR (growth hormone receptor; ghr KO) have a dramatic lifespan extension, and elevated levels of hepatic chaperone-mediated autophagy (CMA). Using quantitative proteomics to identify protein changes in purified liver lysosomes and whole liver lysates, we provide evidence that elevated CMA in ghr KO mice downregulates proteins involved in ribosomal structure, translation initiation and elongation, and nucleocytosolic acetyl-coA production. Following up on these initial proteomics findings, we used a cell culture approach to show that CMA is necessary and sufficient to regulate the abundance of ACLY and ACSS2, the two enzymes that produce nucleocytosolic (but not mitochondrial) acetyl-coA. Inhibition of CMA in NIH3T3 cells has been shown to lead to aberrant accumulation of lipid droplets. We show that this lipid droplet phenotype is rescued by knocking down ACLY or ACSS2, suggesting that CMA regulates lipid droplet formation by controlling ACLY and ACSS2. This evidence leads to a model of how constitutive activation of CMA can shape specific metabolic pathways in long-lived endocrine mutant mice.

Keywords:  aging; autophagy; growth hormone; metabolism; proteomics

DOI:  https://doi.org/10.1080/15548627.2021.1990670
Front Genome Ed. 2021 ;3 644319

Delivery Platforms for CRISPR/Cas9 Genome Editing of Glial Cells in the Central Nervous System.

Vasco Meneghini, Marco Peviani, Marco Luciani, Giada Zambonini, Angela Gritti.

  Glial cells (astrocytes, oligodendrocytes, and microglia) are emerging as key players in several physiological and pathological processes of the central nervous system (CNS). Astrocytes and oligodendrocytes are not only supportive cells that release trophic factors or regulate energy metabolism, but they also actively modulate critical neuronal processes and functions in the tripartite synapse. Microglia are defined as CNS-resident cells that provide immune surveillance; however, they also actively contribute to shaping the neuronal microenvironment by scavenging cell debris or regulating synaptogenesis and pruning. Given the many interconnected processes coordinated by glial cells, it is not surprising that both acute and chronic CNS insults not only cause neuronal damage but also trigger complex multifaceted responses, including neuroinflammation, which can critically contribute to the disease progression and worsening of symptoms in several neurodegenerative diseases. Overall, this makes glial cells excellent candidates for targeted therapies to treat CNS disorders. In recent years, the application of gene editing technologies has redefined therapeutic strategies to treat genetic and age-related neurological diseases. In this review, we discuss the advantages and limitations of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based gene editing in the treatment of neurodegenerative disorders, focusing on the development of viral- and nanoparticle-based delivery methods for in vivo glial cell targeting.

Keywords:  CRISPR/Cas9 system; adeno-associated viral vectors; astrocytes; editing; lentiviral vectors; microglia; nanoparticles; oligodendrocytes

DOI:  https://doi.org/10.3389/fgeed.2021.644319
Physiol Rev. 2021 10 26.

Mitochondrial calcium exchange in physiology and disease.

Joanne F Garbincius, John W Elrod.

  The uptake of calcium into and extrusion of calcium from the mitochondrial matrix is a fundamental biological process that has critical effects on cellular metabolism, signaling, and survival. Disruption of mitochondrial calcium (mCa2+) cycling is implicated in numerous acquired diseases such as heart failure, stroke, neurodegeneration, diabetes, and cancer, and is genetically linked to several inherited neuromuscular disorders. Understanding the mechanisms responsible for mCa2+ exchange therefore holds great promise for the treatment of these diseases. The past decade has seen the genetic identification of many of the key proteins that mediate mitochondrial calcium uptake and efflux. Here, we present an overview of the phenomenon of mCa2+ transport, and a comprehensive examination of the molecular machinery that mediates calcium flux across the inner mitochondrial membrane: the mitochondrial uniporter complex (consisting of MCU, EMRE, MICU1, MICU2, MICU3, MCUB, and MCUR1), NCLX, LETM1, the mitochondrial ryanodine receptor, and the mitochondrial permeability transition pore. We then consider the physiological implications of mCa2+ flux and evaluate how alterations in mCa2+ homeostasis contribute to human disease. This review concludes by highlighting opportunities and challenges for therapeutic intervention in pathologies characterized by aberrant mCa2+ handling and by summarizing critical unanswered questions regarding the biology of mCa2+ flux.

Keywords:  calcium; energetics; metabolism; mitochondria; oxidative phosphorylation

DOI:  https://doi.org/10.1152/physrev.00041.2020
J Neuroinflammation. 2021 Oct 28. 18(1): 248

Altered substrate metabolism in neurodegenerative disease: new insights from metabolic imaging.

Nicholas R W Cleland, Saif I Al-Juboori, Evgenia Dobrinskikh, Kimberley D Bruce.

  Neurodegenerative diseases (NDs), such as Alzheimer's disease (AD), Parkinson's disease (PD) and multiple sclerosis (MS), are relatively common and devastating neurological disorders. For example, there are 6 million individuals living with AD in the United States, a number that is projected to grow to 14 million by the year 2030. Importantly, AD, PD and MS are all characterized by the lack of a true disease-modifying therapy that is able to reverse or halt disease progression. In addition, the existing standard of care for most NDs only addresses the symptoms of the disease. Therefore, alternative strategies that target mechanisms underlying the neuropathogenesis of disease are much needed. Recent studies have indicated that metabolic alterations in neurons and glia are commonly observed in AD, PD and MS and lead to changes in cell function that can either precede or protect against disease onset and progression. Specifically, single-cell RNAseq studies have shown that AD progression is tightly linked to the metabolic phenotype of microglia, the key immune effector cells of the brain. However, these analyses involve removing cells from their native environment and performing measurements in vitro, influencing metabolic status. Therefore, technical approaches that can accurately assess cell-specific metabolism in situ have the potential to be transformative to our understanding of the mechanisms driving AD. Here, we review our current understanding of metabolism in both neurons and glia during homeostasis and disease. We also evaluate recent advances in metabolic imaging, and discuss how emerging modalities, such as fluorescence lifetime imaging microscopy (FLIM) have the potential to determine how metabolic perturbations may drive the progression of NDs. Finally, we propose that the temporal, regional, and cell-specific characterization of brain metabolism afforded by FLIM will be a critical first step in the rational design of metabolism-focused interventions that delay or even prevent NDs.

Keywords:  Brain metabolism; Glia; Metabolic imaging; Neurodegenerative disease; Neurons

DOI:  https://doi.org/10.1186/s12974-021-02305-w
Front Psychiatry. 2021 ;12 754032

An Overview of the Involvement of D-Serine in Cognitive Impairment in Normal Aging and Dementia.

Magdalena Orzylowski, Esther Fujiwara, Darrell D Mousseau, Glen B Baker.

  Dementia, of which Alzheimer's disease (AD) is the most common form, is characterized by progressive cognitive deterioration, including profound memory loss, which affects functioning in many aspects of life. Although cognitive deterioration is relatively common in aging and aging is a risk factor for AD, the condition is not necessarily a part of the aging process. The N-methyl-D-aspartate glutamate receptor (NMDAR) and its co-agonist D-serine are currently of great interest as potential important contributors to cognitive function in normal aging and dementia. D-Serine is necessary for activation of the NMDAR and in maintenance of long-term potentiation (LTP) and is involved in brain development, neuronal connectivity, synaptic plasticity and regulation of learning and memory. In this paper, we review evidence, from both preclinical and human studies, on the involvement of D-serine (and the enzymes involved in its metabolism) in regulation of cognition. Potential mechanisms of action of D-serine are discussed in the context of normal aging and in dementia, as is the potential for using D-serine as a potential biomarker and/or therapeutic agent in dementia. Although there is some controversy in the literature, it has been proposed that in normal aging there is decreased expression of serine racemase and decreased levels of D-serine and down-regulation of NMDARs, resulting in impaired synaptic plasticity and deficits in learning and memory. In contrast, in AD there appears to be activation of serine racemase, increased levels of D-serine and overstimulation of NMDARs, resulting in cytotoxicity, synaptic deficits, and dementia.

Keywords:  Alzheimer's disease; D-serine; NMDA receptor; aging; cognition; dementia; glutamate; long-term potentiation

DOI:  https://doi.org/10.3389/fpsyt.2021.754032
Cell Stress. 2021 Oct;5(10): 146-166

Macroautophagy and normal aging of the nervous system: Lessons from animal models.

Emmanouela Kallergi, Vassiliki Nikoletopoulou.

  Aging represents a cumulative form of cellular stress, which is thought to challenge many aspects of proteostasis. The non-dividing, long-lived neurons are particularly vulnerable to stress, and, not surprisingly, even normal aging is highly associated with a decline in brain function in humans, as well as in other animals. Macroautophagy is a fundamental arm of the proteostasis network, safeguarding proper protein turnover during different cellular states and against diverse cellular stressors. An intricate interplay between macroautophagy and aging is beginning to unravel, with the emergence of new tools, including those for monitoring autophagy in cultured neurons and in the nervous system of different organisms in vivo. Here, we review recent findings on the impact of aging on neuronal integrity and on neuronal macroautophagy, as they emerge from studies in invertebrate and mammalian models.

Keywords:  aging; macroautophagy; nervous system; proteostasis

DOI:  https://doi.org/10.15698/cst2021.10.257
Metab Brain Dis. 2021 Oct 27.

Metabolism in Huntington's disease: a major contributor to pathology.

Akanksha Singh, Namita Agrawal.

  Huntington's disease (HD) is a progressively debilitating neurodegenerative disease exhibiting autosomal-dominant inheritance. It is caused by an unstable expansion in the CAG repeat tract of HD gene, which transforms the disease-specific Huntingtin protein (HTT) to a mutant form (mHTT). The profound neuronal death in cortico-striatal circuits led to its identification and characterisation as a neurodegenerative disease. However, equally disturbing are the concomitant whole-body manifestations affecting nearly every organ of the diseased individuals, at varying extents. Altered central and peripheral metabolism of energy, proteins, nucleic acids, lipids and carbohydrates encompass the gross pathology of the disease. Intense fluctuation of body weight, glucose homeostasis and organ-specific subcellular abnormalities are being increasingly recognised in HD. Many of these metabolic abnormalities exist years before the neuropathological manifestations such as chorea, cognitive decline and behavioural abnormalities develop, and prove to be reliable predictors of the disease progression. In this review, we provide a consolidated overview of the central and peripheral metabolic abnormalities associated with HD, as evidenced from clinical and experimental studies. Additionally, we have discussed the potential of metabolic biomolecules to translate into efficient biomarkers for the disease onset as well as progression. Finally, we provide a brief outlook on the efficacy of existing therapies targeting metabolic remediation. While it is clear that components of altered metabolic pathways can mark many aspects of the disease, it is only conceivable that combinatorial therapies aiming for neuronal protection in consort with metabolic upliftment will prove to be more efficient than the existing symptomatic treatment options.

Keywords:  Biomarker potential; Huntington’s disease; Metabolic dysfunction; Neurodegeneration; Peripheral tissues; Therapeutics

DOI:  https://doi.org/10.1007/s11011-021-00844-y
Curr Protoc. 2021 Oct;1(10): e279

Characterization of Astrocyte Morphology and Function Using a Fast and Reliable Tissue Clearing Technique.

Surya P Aryal, Khaga R Neupane, Abdullah A Masud, Christopher I Richards.

  Astrocytic processes interact with synapses throughout the brain modulating neurotransmitter signaling and synaptic communication. During conditions such as exposure to drugs of abuse and neurological diseases, astrocytes respond by altering their morphological and functional properties. Reactive astrocyte phenotypes exhibit a bushy morphology with altered soma volume and an increased number of processes compared to resting astrocytes. The reactive astrocytic phenotype also overexpresses proteins one of which can be glial fibrillary acidic protein (GFAP). Fluorescence microscopy on thin tissue sections (<20 µm) requires reconstruction, often through multiple sections, to delineate the full astrocytic morphology. In contrast, tissue clearing methods have been developed that enable imaging of larger sections including the whole brain, providing an opportunity to see in-depth changes in single cell structure. In this article, a detailed protocol for studying astrocyte morphology using tissue clearing and subsequent imaging of whole brains as well as region-specific slices is provided. This method is ideal for understanding the effect of different physiological conditions on astrocyte morphology. A standard biochemistry laboratory has the resources to accomplish tissue clearing using this protocol and most universities have the required imaging facilities. Protocols to study brains from both genetically modified mice that contain an astrocyte-specific marker and from wild-type mice using antibody labeling steps after tissue clearing are provided. We also describe general protocols to conduct fluorescence imaging of astrocytes in cleared tissue to characterize their morphology. This protocol could be useful for researchers working in the rapidly growing field of astrocyte biology. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Brain perfusion, fixation, and tissue clearing Alternate Protocol: Clearing brain tissue with passive clarity Basic Protocol 2: Antibody labeling and refractive index matching Basic Protocol 3: Fluorescence imaging and characterization of astrocyte morphology.

Keywords:  astrocyte; brain; fluorescence; microscopy; tissue clearing

DOI:  https://doi.org/10.1002/cpz1.279