Long-term potentiation induced by temporary block of glycolysis in CA1 hippocampal neurons

This thesis focuses on the effects of temporary block of glycolysis by the competitive antimetabolite 2-deoxy-D-glucose (2-DG) on neuronal activity in the CA1 region of rat hippocampal slices. The overall aim was to investigate how synaptic transmission is suppressed when metabolism is greatly reduced by the replacement of glucose by 2-DG to provide some insight into the cellular mechanisms underlying these depressant effects. Experiments were carried out on hippocampal slices kept submerged and constantly superfused with oxygenated saline at 33--34°C. Block of glycolysis was induced by replacement of glucose by equimolar concentrations of 2-DG. Changes in synaptic efficacy and postsynaptic cell membrane properties were assessed in the initial slopes of EPSPs recorded by extra/intra or whole-cell patch recordings.The most striking observation of 2-DG induced glycolysis block is the consistent and sustained potentiation of CA1 synaptic transmission named as "2-DG LTP". Although in some respects 2-DG LTP is similar to conventional tetanic LTP, this novel type of LTP is unique in most of its features.Another finding is the reversible depression of synaptic function by 2-DG application. Adenosine receptor antagonists strongly delay or reduce this depression. In contrast, glyburide, a blocker of KATP channels, does not prevent the suppression of neuronal depression induced by 2-DG. In keeping with this only adenosine receptor blockers, but not glyburide, effectively attenuate 2-DG induced postsynaptic hyperpolarization.The evidence presented in this thesis indicates that, increased adenosine release as the result of 2-DG-induced energy deprivation, is a major cause of reversible loss of synaptic transmission and drop in membrane resistance. In addition, 2-DG LTP brings in a new concept that the regulation of glycolytic pathway plays an important role in modulation of neuronal synaptic plasticity that may contribute to learning and memory

Glycogen regulation and functional role in mouse white matter

CNS glycogen, contained predominantly in astrocytes, can be converted to a monocarboxylate and transported to axons as an energy source during aglycaemia. We analysed glycogen regulation and the role of glycogen in supporting neural activity in adult mouse optic nerve, a favourable white matter preparation. Axon function was quantified by measuring the compound action potential (CAP) area. During aglycaemia, axon function persisted for 20 min, then declined in conjunction with glycogen content. Lactate fully supported CAPs in the absence of glucose, but was unable to sustain glycogen content; thus, axon failure occurred rapidly when lactate was withdrawn. Glycogen content in the steady state was directly proportional to bath glucose concentration. Increasing [K+]o to 10 mm caused a rapid decrease in glycogen content. Latency to onset of CAP failure during aglycaemia was directly proportional to glycogen content and varied from about 2 to 30 min. Intense neural activity reduced glycogen content in the presence of 10 mm bath glucose and CAP area gradually declined. CAP area declined more rapidly during high frequency stimulation if monocarboxylate transport was inhibited. This suggested that astrocytic glycogen was broken down to a monocarboxylate(s) that was used by rapidly discharging axons. Likewise, depleting glycogen by brief periods of high frequency axon stimulation accelerated onset of CAP decline during aglycaemia. In summary, these experiments indicated that glycogen content was under dynamic control and that glycogen was used to support the energy needs of CNS axons during both physiological as well as pathological processes

Glutamate and ATP at the Interface Between Signaling and Metabolism in Astroglia:Examples from Pathology

Glutamate is the main excitatory transmitter in the brain, while ATP represents the most important energy currency in any living cell. Yet, these chemicals play an important role in both processes, enabling them with dual-acting functions in metabolic and intercellular signaling pathways. Glutamate can fuel ATP production, while ATP can act as a transmitter in intercellular signaling. We discuss the interface between glutamate and ATP in signaling and metabolism of astrocytes. Not only do glutamate and ATP cross each other’s paths in physiology of the brain, but they also do so in its pathology. We present the fabric of this process in (patho)physiology through the discussion of synthesis and metabolism of ATP and glutamate in astrocytes as well as by providing a general description of astroglial receptors for these molecules along with the downstream signaling pathways that may be activated. It is astroglial receptors for these dual-acting molecules that could hold a key for medical intervention in pathological conditions. We focus on two examples disclosing the role of activation of astroglial ATP and glutamate receptors in pathology of two kinds of brain tissue, gray matter and white matter, respectively. Interventions at the interface of metabolism and signaling show promise for translational medicine.</p

Identification of miRNAs That Mediate Protective Functions of Anti-Cancer Drugs During White Matter Ischemic Injury

We have previously shown that two anti-cancer drugs, CX-4945 and MS-275, protect and preserve white matter (WM) architecture and improve functional recovery in a model of WM ischemic injury. While both compounds promote recovery, CX-4945 is a selective Casein kinase 2 (CK2) inhibitor and MS-275 is a selective Class I histone deacetylase (HDAC) inhibitor. Alterations in microRNAs (miRNAs) mediate some of the protective actions of these drugs. In this study, we aimed to (1) identify miRNAs expressed in mouse optic nerves (MONs); (2) determine which miRNAs are regulated by oxygen glucose deprivation (OGD); and (3) determine the effects of CX-4945 and MS-275 treatment on miRNA expression. RNA isolated from MONs from control and OGD-treated animals with and without CX-4945 or MS-275 treatment were quantified using NanoString nCounter ® miRNA expression profiling. Comparative analysis of experimental groups revealed that 12 miRNAs were expressed at high levels in MONs. OGD upregulated five miRNAs (miR-1959, miR-501-3p, miR-146b, miR-201, and miR-335-3p) and downregulated two miRNAs (miR-1937a and miR-1937b) compared to controls. OGD with CX-4945 upregulated miR-1937a and miR-1937b, and downregulated miR-501-3p, miR-200a, miR-1959, and miR-654-3p compared to OGD alone. OGD with MS-275 upregulated miR-2134, miR-2141, miR-2133, miR-34b-5p, miR-153, miR-487b, miR-376b, and downregulated miR-717, miR-190, miR-27a, miR-1959, miR-200a, miR-501-3p, and miR-200c compared to OGD alone. Interestingly, miR-501-3p and miR-1959 were the only miRNAs upregulated by OGD, and downregulated by OGD plus CX-4945 and MS-275. Therefore, we suggest that protective functions of CX-4945 or MS-275 against WM injury maybe mediated, in part, through miRNA expression

Proteolipid protein–deficient myelin promotes axonal mitochondrial dysfunction via altered metabolic coupling

Hereditary spastic paraplegia (HSP) is a neurological syndrome characterized by degeneration of central nervous system (CNS) axons. Mutated HSP proteins include myelin proteolipid protein (PLP) and axon-enriched proteins involved in mitochondrial function, smooth endoplasmic reticulum (SER) structure, and microtubule (MT) stability/function. We characterized axonal mitochondria, SER, and MTs in rodent optic nerves where PLP is replaced by the peripheral nerve myelin protein, P(0) (P(0)-CNS mice). Mitochondrial pathology and degeneration were prominent in juxtaparanodal axoplasm at 1 mo of age. In wild-type (WT) optic nerve axons, 25% of mitochondria–SER associations occurred on extensions of the mitochondrial outer membrane. Mitochondria–SER associations were reduced by 86% in 1-mo-old P(0)-CNS juxtaparanodal axoplasm. 1-mo-old P(0)-CNS optic nerves were more sensitive to oxygen-glucose deprivation and contained less adenosine triphosphate (ATP) than WT nerves. MT pathology and paranodal axonal ovoids were prominent at 6 mo. These data support juxtaparanodal mitochondrial degeneration, reduced mitochondria–SER associations, and reduced ATP production as causes of axonal ovoid formation and axonal degeneration

Proteolipid protein-deficient myelin promotes axonal mitochondrial dysfunction via altered metabolic coupling.

Hereditary spastic paraplegia (HSP) is a neurological syndrome characterized by degeneration of central nervous system (CNS) axons. Mutated HSP proteins include myelin proteolipid protein (PLP) and axon-enriched proteins involved in mitochondrial function, smooth endoplasmic reticulum (SER) structure, and microtubule (MT) stability/function. We characterized axonal mitochondria, SER, and MTs in rodent optic nerves where PLP is replaced by the peripheral nerve myelin protein, P0 (P0-CNS mice). Mitochondrial pathology and degeneration were prominent in juxtaparanodal axoplasm at 1 mo of age. In wild-type (WT) optic nerve axons, 25% of mitochondria-SER associations occurred on extensions of the mitochondrial outer membrane. Mitochondria-SER associations were reduced by 86% in 1-mo-old P0-CNS juxtaparanodal axoplasm. 1-mo-old P0-CNS optic nerves were more sensitive to oxygen-glucose deprivation and contained less adenosine triphosphate (ATP) than WT nerves. MT pathology and paranodal axonal ovoids were prominent at 6 mo. These data support juxtaparanodal mitochondrial degeneration, reduced mitochondria-SER associations, and reduced ATP production as causes of axonal ovoid formation and axonal degeneration

Abstract Number ‐ 25: Acute Ischemic Stroke Intervention With Penumbra RED Reperfusion Catheters: Updated Subset Analysis From INSIGHT Registry

Introduction The prospective INSIGHT Registry is a multicenter ‘multi‐omic’ analysis of thrombi associated with acute hemorrhagic or ischemic stroke. This updated interim analysis evaluated the performance of Penumbra RED catheters used during aspiration thrombectomy for acute ischemic stroke (AIS). Methods All AIS cases in which Penumbra RED aspiration catheters (RED 62, 68, or 72) were utilized as a frontline treatment were included in the analysis. Retrieved clot fragments were classified based on their gross appearance. Key time metrics and procedural data were also collected, including first‐pass / post‐procedure modified Treatment in Cerebral Ischemia (mTICI) score. Results Of 400 patients enrolled across 25 US centers, 161 underwent thrombectomy with Penumbra RED catheters over ten months (Jul 2021 through Apr 2022). The mean patient age was 70.7 years, and 50.9% were female. The middle cerebral artery first segment (M1) was the most common primary occlusion site (60.4%; 96/159). IV t‐PA was administered before the procedure in 13.7% (22/161) of patients. The median time from stroke onset / last known well to mTICI≥ 2b was 5.0 hrs. [IQR 3‐11], and the median time from a puncture to mTICI≥ 2b was 23.0 mins [IQR 15‐31]. Firm‐red clots represented 45.3% (67/148), while soft‐red clots were found in 37.8% (56/148) of retrieved clots. In turn, firm‐white and soft‐white clots were seen in 11.5% (17/148) and 5.4% (8/148) of cases, respectively. Rates of the first pass and final mTICI≥ 2b scores by clot type are shown in Table 1. Conclusions Aspiration thrombectomy with Penumbra RED catheters resulted in good revascularization rates for all clot types

Oligodendroglial NMDA Receptors Regulate Glucose Import and Axonal Energy Metabolism

Oligodendrocytes make myelin and support axons metabolically with lactate. However, it is unknown how glucose utilization and glycolysis are adapted to the different axonal energy demands. Spiking axons release glutamate and oligodendrocytes express NMDA receptors of unknown function. Here we show that the stimulation of oligodendroglial NMDA receptors mobilizes glucose transporter GLUT1, leading to its incorporation into the myelin compartment in vivo. When myelinated optic nerves from conditional NMDA receptor mutants are challenged with transient oxygen-glucose deprivation, they show a reduced functional recovery when returned to oxygen-glucose but are indistinguishable from wild-type when provided with oxygen-lactate. Moreover, the functional integrity of isolated optic nerves, which are electrically silent, is extended by preincubation with NMDA, mimicking axonal activity, and shortened by NMDA receptor blockers. This reveals a novel aspect of neuronal energy metabolism in which activity-dependent glutamate release enhances oligodendroglial glucose uptake and glycolytic support of fast spiking axons