Functional Proteomics Related to Energy Metabolism of Synaptosomes from Different Neuronal Systems of Rat Hippocampus during Aging

Effects of Chronic Hypertension on the Energy Metabolism of Cerebral Cortex Mitochondria in Normotensive and in Spontaneously Hypertensive Rats During Aging

In this study the subcellular modifications undergone by cerebral cortex mitochondrial metabolism in chronic hypertension during aging were evaluated. The catalytic properties of regulatory energy-linked enzymes of Tricarboxylic Acid Cycle (TCA), Electron Transport Chain (ETC) and glutamate metabolism were assayed on non-synaptic mitochondria (FM, located in post-synaptic compartment) and on intra-synaptic mitochondria of pre-synaptic compartment, furtherly divided in "light" (LM) and "heavy" (HM) mitochondria, purified form cerebral cortex of normotensive Wistar Kyoto Rats (WKY) versus Spontaneously Hypertensive Rats (SHR) at 6, 12 and 18 months. During physiological aging, the metabolic machinery was differently expressed in pre- and post-synaptic compartments: LM and above all HM were more affected by aging, displaying lower ETC activities. In SHR at 6 months, FM and LM showed an uncoupling between TCA and ETC, likely as initial adaptive response to hypertension. During pathological aging, HM were particularly affected at 12 months in SHR, as if the adaptive modifications in FM and LM at 6 months granted a mitochondrial functional balance, while at 18 months all the neuronal mitochondria displayed decreased metabolic fluxes versus WKY. This study describes the effects of chronic hypertension on cerebral mitochondrial energy metabolism during aging through functional proteomics of enzymes at subcellular levels, i.e. in neuronal soma and synapses. In addition, this represents the starting point to envisage an experimental physiopathological model which could be useful also for pharmacological studies, to assess drug actions during the development of age-related pathologies that could coexist and/or are provoked by chronic hypertension.

Semaglutide ameliorates cognition and glucose metabolism dysfunction in the 3xTg mouse model of Alzheimer's disease via the GLP-1R/SIRT1/GLUT4 pathway

Disorders of brain glucose metabolism is known to affect brain activity in neurodegenerative diseases including Alzheimer's disease (AD). Furthermore, recent evidence has shown an association between AD and type 2 diabetes. Numerous reports have found that glucagon-like peptide-1 (GLP-1) receptor agonists improve the cognitive behavior and pathological features in AD patients and animals, which may be related to the improvement of glucose metabolism in the brain. However, the mechanism by which GLP-1 agonists improve the brain glucose metabolism in AD patients remains unclear. In this study, we found that SIRT1 is closely related to expression of GLP-1R in hippocampus of 3xTg mice. Therefore, we used semaglutide, a novel GLP-1R agonist currently undergoing two phase 3 clinical trials in AD patients, to observe the effect of SIRT1 after semaglutide treatment in 3XTg mice and HT22 cells, and to explore the mechanism of SIRT1 in the glucose metabolism disorders of AD. The mice were injected with semaglutide on alternate days for 30 days, followed by behavioral experiments including open field test, new object recognition test, and Y-maze. The content of glucose in the brain was also measured by using 18FDG-PET-CT scans. We measured the expression of Aβ and tau in the hippocampus, observed the expression of GLUT4 which is downstream of SIRT1, and tested the Glucose oxidase assay (GOD-POD) and Hexokinase (HK) in HT22 cells. Here, we found in the 3xTg mouse model of AD and in cultured HT22 mouse neurons that SIRT1 signaling is involved in the impairment of glucose metabolism in AD. Semaglutide can increased the expression levels of SIRT1 and GLUT4 in the hippocampus of 3xTg mice, accompanied by an improvement in learning and memory, decreased in Aβ plaques and neurofibrillary tangles. In addition, we further demonstrated that semaglutide improved glucose metabolism in the brain of 3xTg mice in vitro, semaglutide promoted glycolysis and improved glycolytic disorders, and increased the membrane translocation of GLUT4 in cultured HT22 cells. These effects were blocked by the SIRT1 inhibitor (EX527). These findings indicate that semaglutide can regulate the expression of GLUT4 to mediate glucose transport through SIRT1, thereby improving glucose metabolism dysfunction in AD mice and cells. The present study suggests that SIRT1/GLUT4 signaling pathway may be an important mechanism for GLP-1R to promote glucose metabolism in the brain, providing a reliable strategy for effective therapy of AD.

Brain Bioenergetics in Chronic Hypertension: Risk Factor for Acute Ischemic Stroke

Chronic hypertension is one of the key modifiable risk factors for acute ischemic stroke, also contributing to determine greater neurological deficits and worse functional outcome when an acute cerebrovascular event would occur. A tight relationship exists between cerebrovascular autoregulation, neuronal activity and brain bioenergetics. In chronic hypertension, progressive adaptations of these processes occur as an attempt to cope with the demanding necessity of brain functions, creating a new steady-state homeostatic condition. However, these adaptive modifications are insufficient to grant an adequate response to possible pathological perturbations of the established fragile hemodynamic and metabolic homeostasis. In this narrative review, we will discuss the main mechanisms by which alterations in brain bioenergetics and mitochondrial function in chronic hypertension could lead to increased risk of acute ischemic stroke, stressing the interconnections between hemodynamic factors (i.e. cerebral autoregulation and neurovascular coupling) and metabolic processes. Both experimental and clinical pieces of evidence will be discussed. Moreover, the potential role of mitochondrial dysfunction in determining, or at least sustaining, the pathogenesis and progression of chronic neurogenic hypertension will be considered. In the perspective of novel therapeutic strategies aiming at improving brain bioenergetics, we propose some determinant factors to consider in future studies focused on the cause-effect relationships between chronic hypertension and brain bioenergetic abnormalities (and vice versa), so to help translational research in this so-far unfilled gap.

Hyperglycemia in acute ischemic stroke: physiopathological and therapeutic complexity

Diabetes mellitus and associated chronic hyperglycemia enhance the risk of acute ischemic stroke and lead to worsened clinical outcome and increased mortality. However, post-stroke hyperglycemia is also present in a number of non-diabetic patients after acute ischemic stroke, presumably as a stress response. The aim of this review is to summarize the main effects of hyperglycemia when associated to ischemic injury in acute stroke patients, highlighting the clinical and neurological outcomes in these conditions and after the administration of the currently approved pharmacological treatment, i.e. insulin. The disappointing results of the clinical trials on insulin (including the hypoglycemic events) demand a change of strategy based on more focused therapies. Starting from the comprehensive evaluation of the physiopathological alterations occurring in the ischemic brain during hyperglycemic conditions, the effects of various classes of glucose-lowering drugs are reviewed, such as glucose-like peptide-1 receptor agonists, DPP-4 inhibitors and sodium glucose cotransporter 2 inhibitors, in the perspective of overcoming the up-to-date limitations and of evaluating the effectiveness of new potential therapeutic strategies.

Glutamate metabolism in cerebral mitochondria after ischemia and post-ischemic recovery during aging: relationships with brain energy metabolism

Glutamate is involved in cerebral ischemic injury, but its role has not been completely clarified and studies are required to understand how to minimize its detrimental effects, contemporarily boosting the positive ones. In fact, glutamate is not only a neurotransmitter, but primarily a key metabolite for brain bioenergetics. Thus, we investigated the relationships between glutamate and brain energy metabolism in an in vivo model of complete cerebral ischemia of 15 min and during post-ischemic recovery after 1, 24, 48, 72, and 96 h in 1-year-old adult and 2-year-old aged rats. The maximum rates (V_max ) of glutamate dehydrogenase (GlDH), glutamate-oxaloacetate transaminase, and glutamate-pyruvate transaminase were assayed in somatic mitochondria (FM) and in intra-synaptic 'Light' mitochondria and intra-synaptic 'Heavy' mitochondria ones purified from cerebral cortex, distinguishing post- and pre-synaptic compartments. During ischemia, none of the enzymes were modified in adult animals. In aged ones, glutamate-oxaloacetate transaminase was increased in FM and GlDH in intra-synaptic 'Heavy' mitochondria, stimulating glutamate catabolism. During post-ischemic recovery, FM did not show modifications at both ages while, in intra-synaptic mitochondria of adult animals, glutamate catabolism was increased after 1 h of recirculation and decreased after 48 and 72 h, whereas it remained decreased up to 96 h in aged rats. These results, with those previously published about Krebs' cycle and Electron Transport Chain (Villa et al., [2013] Neurochem. Int. 63, 765-781), demonstrate that: (i) V_max of energy-linked enzymes are different in the various cerebral mitochondria, which (ii) respond differently to ischemia and post-ischemic recovery, also (iii) with respect to aging.

Revealing the Inhibitory Effect of Ginseng on Mitochondrial Respiration through Synaptosomal Proteomics

Ginseng, the active ingredients of which are ginsenosides, is the most popular herbal medicine and has potential merit in the treatment of cerebral disorders. To better understand the function of Ginseng in the cerebral system, we examined changes in the protein expression profiles of synaptosomes extracted from the cerebral cortical and hippocampal tissues of rats administered a high or low dose of Ginseng for 2 weeks. More than 5000 proteins belonging to synaptosomes were simultaneously identified and quantitated by an approach combining tandem mass tags with 2D liquid chromatography-mass spectrometry (LC-MS). Regarding differentially expressed proteins, downregulated proteins were much more highly induced than upregulators in the cerebral cortical and hippocampal synaptosomes, regardless of the dose of Ginseng. Bioinformatic analysis indicated the majority of the altered proteins to be located in the mitochondria, directly or indirectly affecting mitochondrial oxidative respiration. Further functional experiments using the substrate-uncoupler inhibitor titration approach confirmed that three representative ginsenosides were able to inhibit oxidative phosphorylation in mitochondria. Our results demonstrate that Ginseng can regulate the function of mitochondria and alter the energy metabolism of cells, which may be useful for the treatment of central nervous disorders.

Delayed bradykinin postconditioning modulates intrinsic neuroprotective enzyme expression in the rat CA1 region after cerebral ischemia: a proteomic study

Pyramidal cells in the CA1 brain region exhibit an ischemic tolerance after delayed postconditioning; therefore, this approach seems to be a promising neuroprotective procedure in cerebral postischemic injury improvement. However, little is known about the effect of postconditioning on protein expression patterns in the brain, especially in the affected hippocampal neurons after global cerebral ischemia. This study is focused on the examination of the ischemia-vulnerable CA1 neuronal layer and on the acquisition of protection from delayed neuronal death after ischemia. Ischemic-reperfusion injury was induced in Wistar rats and bradykinin was applied 2 days after the ischemic insult in an attempt to overcome delayed cell death. Analysis of complex peptide CA1 samples was performed by automated two dimensional liquid chromatography (2D-LC) fractionation coupled to tandem matrix assisted laser desorption/ionization time-of-flight (MALDI TOF/TOF) mass spectrometry instrumentation. We devoted our attention to differences in protein expression mapping in ischemic injured CA1 neurons in comparison with equally affected neurons, but with bradykinin application. Proteomic analysis identified several proteins occurring only after postconditioning and control, which could have a potentially neuroprotective influence on ischemic injured neurons. Among them, the prominent position occupies a regulator of glutamate level aspartate transaminase AATC, a scavenger of glutamate in brain neuroprotection after ischemia-reperfusion. We identified this enzyme in controls and after postconditioning, but AATC presence was not detected in the ischemic injured CA1 region. This finding was confirmed by two-dimensional differential electrophoresis followed by MALDI-TOF/TOF MS identification. Results suggest that bradykinin as delayed postconditioning may be associated with modulation of protein expression after ischemic injury and thus this procedure can be involved in neuroprotective metabolic pathways.