Controlled cortical impact injury and craniotomy result in divergent alterations of pyruvate metabolizing enzymes in rat brain

Histological comparison of repeated mild weight drop and lateral fluid percussion injury models of traumatic brain injury (TBI) in female and male rats

Traumatic brain injury (TBI) heterogeneity has led to the development of several preclinical models, each modeling a distinct subset of outcomes. Selection of an injury model should be guided by the research question and the specific outcome measures of interest. Consequently, there is a need for conducting direct comparisons of different TBI models. Here, we used immunohistochemistry to directly compare the outcomes from two common models, lateral fluid percussion (LFP) and repeat mild weight drop (rmWD), on neuropathology in adult female and male Wistar rats. Specifically, we used immunohistochemistry to measure the effects of LFP and rmWD on cerebrovascular and tight junction disruption, inflammatory markers, mature neurons and perineuronal nets in the cortical site of injury, cortex adjacent to injury, dentate gyrus, and the CA2/3 area of the hippocampus. Animals were randomized into either LFP or rmWD groups. The LFP group received a craniotomy prior to LFP (or corresponding sham procedure) three days later, while rmWD animals underwent either weight drop or sham (isoflurane only) on each of those four days. After a recovery period of 7 days, animals were euthanized, and brains were harvested for analysis of RECA-1, claudin-5, GFAP, Iba-1, CD-68, NeuN, and wisteria floribunda lectin. Overall, our observations revealed that the most significant disruptions were evident in response to LFP, followed by craniotomy-only, while rmWD animals showed the least residual changes compared to isoflurane-only controls. These findings support consideration of rmWD as a mild, transient injury. LFP leads to longer-lasting disruptions that are more closely associated with a moderate TBI. We further show that both craniotomy and LFP produced greater disruptions in females relative to males at 7 days post-injury. These findings support the inclusion of a time-matched experimentally-naïve or anesthesia-only control group in preclinical TBI research to enhance the validity of data interpretation and conclusions.

Pyruvate Dehydrogenase Complex in Neonatal Hypoxic-Ischemic Brain Injury

The disruption of cerebral energy metabolism in relation to brain damage has been the subject of extensive research. However, the pyruvate dehydrogenase complex (PDHC), which is primarily characterized by poor cerebral energy metabolism following brain trauma, has received relatively little study in comparison to newborn hypoxic-ischemic brain injury. Mitochondrial PDHC, a multienzyme complex that functions as a crucial hub in energy metabolism and acts as a central metabolic node to mediate pyruvate oxidation after glycolysis and fuel the Krebs cycle to meet energy demands, has been reported to be one cause of energy metabolism dysfunction according to recent studies. Here we assess the potential mechanisms of neonatal hypoxic-ischemic brain injury-related brain dysfunction mediated by PDHC and further discuss the neuroprotective effects of therapeutic medicines that target PDHC activation. We also provide a summary of recent research on medicines that target PDHC in neonates with hypoxic-ischemic brain damage. Through an understanding of the mechanisms by which it is modulated and an investigation of the neuroprotective techniques available to activate brain PDHC and improve neonatal hypoxic-ischemic impairment, our review emphasizes the significance of PDHC impairment in neonatal hypoxic-ischemic brain injury.

Tau Phosphorylation Patterns in the Rat Cerebral Cortex After Traumatic Brain Injury and Sodium Selenate Effects: An Epibios4rx Project 2 Study

Sodium selenate (SS) activates protein phosphatase 2 (PP2A) and reduces phosphorylated tau (pTAU) and late post-traumatic seizures after lateral fluid percussion injury (LFPI). In EpiBioS4Rx Project 2, a multi-center international study for post-traumatic targets, biomarkers, and treatments, we tested the target relevance and modification by SS of pTAU forms and PP2A and in the LFPI model, at two sites: Einstein and Melbourne. In Experiment 1, adult male rats were assigned to LFPI and sham (both sites) and naïve controls (Einstein). Motor function was monitored by neuroscores. Brains were studied with immunohistochemistry (IHC), Western blots (WBs), or PP2A activity assay, from 2 days to 8 weeks post-operatively. In Experiment 2, LFPI rats received SS for 7 days (SS0.33: 0.33 mg/kg/day; SS1: 1 mg/kg/day, subcutaneously) or vehicle (Veh) post-LFPI and pTAU, PR55 expression, or PP2A activity were studied at 2 days and 1 week (on treatment), or 2 weeks (1 week off treatment). Plasma selenium and SS levels were measured. In Experiment 1 IHC, LFPI rats had higher cortical pTAU-Ser202/Thr205-immunoreactivity (AT8-ir) and pTAU-Ser199/202-ir at 2 days, and pTAU-Thr231-ir (AT180-ir) at 2 days, 2 weeks, and 8 weeks, ipsilaterally to LFPI, than controls. LFPI-2d rats also had higher AT8/total-TAU5-ir in cortical extracts ipsilateral to the lesion (WB). PP2A (PR55-ir) showed time- and region-dependent changes in IHC, but not in WB. PP2A activity was lower in LFPI-1wk than in sham rats. In Experiment 2, SS did not affect neuroscores or cellular AT8-ir, AT180-ir, or PR55-ir in IHC. In WB, total cortical AT8/total-TAU-ir was lower in SS0.33 and SS1 LFPI rats than in Veh rats (2 days, 1 week); total cortical PR55-ir (WB) and PP2A activity were higher in SS1 than Veh rats (2 days). SS dose dependently increased plasma selenium and SS levels. Concordant across-sites data confirm time and pTAU form-specific cortical increases ipsilateral to LFPI. The discordant SS effects may either suggest SS-induced reduction in the numbers of cells with increased pTAU-ir, need for longer treatment, or the involvement of other mechanisms of action.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

Effects of Pyruvate Administration on Mitochondrial Enzymes, Neurological Behaviors, and Neurodegeneration after Traumatic Brain Injury

Traumatic brain injury (TBI) is known to increase the susceptibility to various age-related neurodegenerative disorders such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Although the role of damaged mitochondrial electron transport chain (ETC) in the progression of AD and PD has been identified, its relationship with altered expression of neurodegenerative proteins has not been examined before. This study aimed to investigate 1) how TBI could affect mitochondrial ETC and neurodegeneration in rat brain regions related to behavioral alteration, and 2) if administration of the key mitochondrial substrate pyruvate can improve the outcome of mild TBI (mTBI). In a rat lateral fluid percussion injury model of mTBI, sodium pyruvate in sterile distilled water (1 g/kg body weight) was administered orally daily for 7 days. The protein expression of mitochondrial ETC enzymes, and neurodegeneration proteins in the hippocampus and cerebral cortex and was assessed on Day 7. The hippocampal and cortical expressions of ETC complex I, III, IV, V were significantly and variably impaired following mTBI. Pyruvate treatment altered ETC complex expression, reduced the nitrosyl stress and the MBP expression in the injured brain area, but increased the expression of the glial fibrillary acidic protein (GFAP) and Tau proteins. Pyruvate after mTBI augmented the Rotarod performance but decreased the horizontal and vertical open field locomotion activities and worsened neurobehavioural severity score, indicating a debilitating therapeutic effect on the acute phase of mTBI. These results suggest bidirectional neuroprotective and neurodegenerative modulating effects of pyruvate on TBI-induced alteration in mitochondrial activity and motor behavior. Pyruvate could potentially stimulate the proliferation of astrogliosis, and lactate acidosis, and caution should be exercised when used as a therapy in the acute phase of mTBI. More effective interventions targeted at multiple mechanisms are needed for the prevention and treatment of TBI-induced long-term neurodegeneration.

Astrocytic pyruvate dehydrogenase kinase-2 is involved in hypothalamic inflammation in mouse models of diabetes

Hypothalamic inflammation plays an important role in disrupting feeding behavior and energy homeostasis as well as in the pathogenesis of obesity and diabetes. Here, we show that pyruvate dehydrogenase kinase (PDK)-2 plays a role in hypothalamic inflammation and its sequelae in mouse models of diabetes. Cell type-specific genetic ablation and pharmacological inhibition of PDK2 in hypothalamic astrocytes suggest that hypothalamic astrocytes are involved in the diabetic phenotype. We also show that the PDK2-lactic acid axis plays a regulatory role in the observed metabolic imbalance and hypothalamic inflammation in mouse primary astrocyte and organotypic cultures, through the AMPK signaling pathway and neuropeptidergic circuitry governing feeding behavior. Our findings reveal that PDK2 ablation or inhibition in mouse astrocytes attenuates diabetes-induced hypothalamic inflammation and subsequent alterations in feeding behavior.

Hypothalamic inflammation is involved in the pathogenesis of diabetes. The underlying mechanisms are unclear. Here, the authors show that astrocytic PDK2 ablation or inhibition attenuates hypothalamic inflammation in mouse models of diabetes.

Pyruvate Dehydrogenase and Tricarboxylic Acid Cycle Enzymes Are Sensitive Targets of Traumatic Brain Injury Induced Metabolic Derangement

Using a closed-head impact acceleration model of mild or severe traumatic brain injury (mTBI or sTBI, respectively) in rats, we evaluated the effects of graded head impacts on the gene and protein expressions of pyruvate dehydrogenase (PDH), as well as major enzymes of mitochondrial tricarboxylic acid cycle (TCA). TBI was induced in anaesthetized rats by dropping 450 g from 1 (mTBI) or 2 m height (sTBI). After 6 h, 12 h, 24 h, 48 h, and 120 h gene expressions of enzymes and subunits of PDH. PDH kinases and phosphatases (PDK1-4 and PDP1-2, respectively), citrate synthase (CS), isocitrate dehydrogenase (IDH), oxoglutarate dehydrogenase (OGDH), succinate dehydrogenase (SDH), succinyl-CoA synthase (SUCLG), and malate dehydrogenase (MDH) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). In the same samples, the high performance liquid chromatographic (HPLC) determination of acetyl-coenzyme A (acetyl-CoA) and free coenzyme A (CoA-SH) was performed. Sham-operated animals (n = 6) were used as controls. After mTBI, the results indicated a general transient decrease, followed by significant increases, in PDH and TCA gene expressions. Conversely, permanent PDH and TCA downregulation occurred following sTBI. The inhibitory conditions of PDH (caused by PDP1-2 downregulations and PDK1-4 overexpression) and SDH appeared to operate only after sTBI. This produced almost no change in acetyl-CoA and free CoA-SH following mTBI and a remarkable depletion of both compounds after sTBI. These results again demonstrated temporary or steady mitochondrial malfunctioning, causing minimal or profound modifications to energy-related metabolites, following mTBI or sTBI, respectively. Additionally, PDH and SDH appeared to be highly sensitive to traumatic insults and are deeply involved in mitochondrial-related energy metabolism imbalance.

Craniectomy Effects on Resting State Functional Connectivity and Cognitive Performance in Immature Rats

Experimental models have been proven to be valuable tools to understand downstream cellular mechanisms of Traumatic Brain Injury (TBI). The models allow for reduction of confounding variables and tighter control of varying parameters. It has been recently reported that craniectomy induces pro-inflammatory responses, which therefore needs to be properly addressed given the fact that craniectomy is often considered a control procedure for experimental TBI models. The current study aims to determine whether a craniectomy induces alterations in Resting State Network (RSN) in a developmental rodent model. Functional Magnetic Resonance Imaging (fMRI) data-driven RSN show clusters of peak differences (left caudate putamen, somatosensory cortex, amygdala and piriform cortex) between craniectomy and control group, four days post-craniectomy. In addition, the Novel Object Recognition (NOR) task revealed impaired working memory in the craniectomy group. This evidence supports craniectomy-induced neurological changes which need to be carefully addressed, considering the frequent use of craniectomy as a control procedure for experimental models of TBI.

Accelerated Metabolite Levels of Aerobic Glycolysis and the Pentose Phosphate Pathway Are Required for Efficient Replication of Infectious Spleen and Kidney Necrosis Virus in Chinese Perch Brain Cells

Glucose is a main carbon and energy source for virus proliferation and is usually involved in the glycolysis, pentose phosphate pathway (PPP), and tricarboxylic acid cycle (TCA cycle) pathways. In this study, we investigated the roles of glucose-related metabolic pathways during the replication of infectious spleen and kidney necrosis virus (ISKNV), which has caused serious economic losses in the cultured Chinese perch (Siniperca chuatsi) industry. We found that ISKNV infection enhanced the metabolic pathways of the PPP and the TCA cycle at the early stage of the ISKNV infection cycle and enhanced the glycolysis pathway at the late stage of the ISKNV infection cycle though the comprehensive analysis of transcriptomics, proteomics, and metabolomics. The advanced results proved that ISKNV replication induced upregulation of aerobic glycolysis at the late stage of ISKNV infection cycle and aerobic glycolysis were required for ISKNV multiplication. In addition, the PPP, providing nucleotide biosynthesis, was also required for ISKNV multiplication. However, the TCA cycle involving glucose was not important and necessary for ISKNV multiplication. The results reported here provide new insights into viral pathogenesis mechanism of metabolic shift, as well as antiviral treatment strategies.

The Effects of Sodium Dichloroacetate on Mitochondrial Dysfunction and Neuronal Death Following Hypoglycemia-Induced Injury

Our previous studies demonstrated that some degree of neuronal death is caused by hypoglycemia, but a subsequent and more severe wave of neuronal cell death occurs due to glucose reperfusion, which results from the rapid restoration of low blood glucose levels. Mitochondrial dysfunction caused by hypoglycemia leads to increased levels of pyruvate dehydrogenase kinase (PDK) and suppresses the formation of ATP by inhibiting pyruvate dehydrogenase (PDH) activation, which can convert pyruvate into acetyl-coenzyme A (acetyl-CoA). Sodium dichloroacetate (DCA) is a PDK inhibitor and activates PDH, the gatekeeper of glucose oxidation. However, no studies about the effect of DCA on hypoglycemia have been published. In the present study, we hypothesized that DCA treatment could reduce neuronal death through improvement of glycolysis and prevention of reactive oxygen species production after hypoglycemia. To test this, we used an animal model of insulin-induced hypoglycemia and injected DCA (100 mg/kg, i.v., two days) following hypoglycemic insult. Histological evaluation was performed one week after hypoglycemia. DCA treatment reduced hypoglycemia-induced oxidative stress, microglial activation, blood–brain barrier disruption, and neuronal death compared to the vehicle-treated hypoglycemia group. Therefore, our findings suggest that DCA may have the therapeutic potential to reduce hippocampal neuronal death after hypoglycemia.

Divergent Induction of Branched-Chain Aminotransferases and Phosphorylation of Branched Chain Keto-Acid Dehydrogenase Is a Potential Mechanism Coupling Branched-Chain Keto-Acid-Mediated-Astrocyte Activation to Branched-Chain Amino Acid Depletion-Mediated Cognitive Deficit after Traumatic Brain Injury

Deficient branched-chain amino acids (BCAAs) are implicated in cognitive dysfunction after traumatic brain injury (TBI). The mechanism remains unknown. BCAAs are catabolized by neuron-specific cytosolic and astrocyte-specific mitochondrial branched-chain aminotransferases (BCATc, BCATm) to generate glutamate and branched-chain keto-acids (BCKAs) that are metabolized by the mitochondrial branched-chain keto-acid dehydrogenase (BCKD) whose activity is regulated by its phosphorylation state. BCKD phosphorylation by BCKD kinase (BCKDK) inactivates BCKD and cause neurocognitive dysfunction, whereas dephosphorylation by specific phosphatase restores BCKD activity. Real-time polymerase chain reaction showed rapidly and significantly decreased BCATc messenger RNA (mRNA) levels, but significantly increased BCATm mRNA level post-CCI (controlled cortical impact). BCKD and BCKDK mRNA decreased significantly immediately after CCI-induced TBI (CCI) in the rat. Phosphorylated BCKD proteins (pBCKD) increased significantly in the ipsilateral-CCI hemisphere. Immunohistochemistry revealed significantly increased pBCKD proteins in ipsilateral astrocytes post-CCI. BCKD protein expression is higher in primarily cultured cortical neurons than in astrocytes, whereas pBCKD protein level is higher in astrocytes than in cortical neurons. Transforming growth factor beta treatment (10 μg/mL for 48 h) significantly increased pBCKD protein expression in astrocytes, whereas glutamate treatment (25 μM for 24 h) significantly decreased pBCKD protein in neurons. Because increased pBCKD would lead to increased BCKA accumulation, BCKA-mediated astrocyte activation, cell death, and cognitive dysfunction as found in maple syrup urine disease; thus, TBI may potentially induce cognitive deficit through diverting BCAA from glutamate production in neurons to BCKA production in astrocytes through the pBCKD-dependent mechanism.

Pyruvate dehydrogenase complex in cerebral ischemia-reperfusion injury

Pyruvate dehydrogenase (PDH) complex is a mitochondrial matrix enzyme that serves a critical role in the conversion of anaerobic to aerobic cerebral energy. The regulatory complexity of PDH, coupled with its significant influence in brain metabolism, underscores its susceptibility to, and significance in, ischemia-reperfusion injury. Here, we evaluate proposed mechanisms of PDH-mediated neurodysfunction in stroke, including oxidative stress, altered regulatory enzymatic control, and loss of PDH activity. We also describe the neuroprotective influence of antioxidants, dichloroacetate, acetyl-L-carnitine, and combined therapy with ethanol and normobaric oxygen, explained in relation to PDH modulation. Our review highlights the significance of PDH impairment in stroke injury through an understanding of the mechanisms by which it is modulated, as well as an exploration of neuroprotective strategies available to limit its impairment.

Metabolic reprogramming by the pyruvate dehydrogenase kinase-lactic acid axis: Linking metabolism and diverse neuropathophysiologies

Emerging evidence indicates that there is a complex interplay between metabolism and chronic disorders in the nervous system. In particular, the pyruvate dehydrogenase (PDH) kinase (PDK)-lactic acid axis is a critical link that connects metabolic reprogramming and the pathophysiology of neurological disorders. PDKs, via regulation of PDH complex activity, orchestrate the conversion of pyruvate either aerobically to acetyl-CoA, or anaerobically to lactate. The kinases are also involved in neurometabolic dysregulation under pathological conditions. Lactate, an energy substrate for neurons, is also a recently acknowledged signaling molecule involved in neuronal plasticity, neuron-glia interactions, neuroimmune communication, and nociception. More recently, the PDK-lactic acid axis has been recognized to modulate neuronal and glial phenotypes and activities, contributing to the pathophysiologies of diverse neurological disorders. This review covers the recent advances that implicate the PDK-lactic acid axis as a novel linker of metabolism and diverse neuropathophysiologies. We finally explore the possibilities of employing the PDK-lactic acid axis and its downstream mediators as putative future therapeutic strategies aimed at prevention or treatment of neurological disorders.

Divergent Temporal Expression of Hyaluronan Metabolizing Enzymes and Receptors with Craniotomy vs. Controlled-Cortical Impact Injury in Rat Brain: A Pilot Study

Traumatic brain injury (TBI) triggers many secondary changes in tissue biology, which ultimately determine the extent of injury and clinical outcome. Hyaluronan [hyaluronic acid (HA)] is a protective cementing gel present in the intercellular spaces whose degradation has been reported as a causative factor in tissue damage. Yet little is known about the expression and activities of genes involved in HA catabolism after TBI. Young adult male Sprague-Dawley rats were assigned to three groups: naïve control, craniotomy, and controlled-cortical impact-induced TBI (CCI-TBI). Four animals per group were sacrificed at 4 h, 1, 3, and 7 days post-CCI. The mRNA expression of hyaluronan synthases (HAS1-3), hyaluronidases (enzymes for HA degradation, HYAL 1–4, and PH20), and CD44 and RHAMM (membrane receptors for HA signaling and removal) were determined using real-time PCR. Compared to the naïve controls, expression of HAS1 and HAS2 mRNA, but not HAS3 mRNA increased significantly following craniotomy alone and following CCI with differential kinetics. Expression of HAS2 mRNA increased significantly in the ipsilateral brain at 1 and 3 days post-CCI. HYAL1 mRNA expression also increased significantly in the craniotomy group and in the contralateral CCI at 1 and 3 days post-CCI. CD44 mRNA expression increased significantly in the ipsilateral CCI at 4 h, 1, 3, and 7 days post-CCI (up to 25-fold increase). These data suggest a dynamic regulation and role for HA metabolism in secondary responses to TBI.

Impact of repeated stress on traumatic brain injury-induced mitochondrial electron transport chain expression and behavioral responses in rats

A significant proportion of the military personnel returning from Iraq and Afghanistan conflicts have suffered from both mild traumatic brain injury (mTBI) and post-traumatic stress disorder. The mechanisms are unknown. We used a rat model of repeated stress and mTBI to examine brain activity and behavioral function. Adult male Sprague-Dawley rats were divided into four groups: Naïve; 3 days repeated tail-shock stress; lateral fluid percussion mTBI; and repeated stress followed by mTBI (S-mTBI). Open field activity, sensorimotor responses, and acoustic startle responses (ASRs) were measured at various time points after mTBI. The protein expression of mitochondrial electron transport chain (ETC) complex subunits (CI-V) and pyruvate dehydrogenase (PDHE1α1) were determined in four brain regions at day 7-post mTBI. Compared to Naïves, repeated stress decreased horizontal activity; repeated stress and mTBI both decreased vertical activity; and the mTBI and S-mTBI groups were impaired in sensorimotor and ASRs. Repeated stress significantly increased CI, CII, and CIII protein levels in the prefrontal cortex (PFC), but decreased PDHE1α1 protein in the PFC and cerebellum, and decreased CIV protein in the hippocampus. The mTBI treatment decreased CV protein levels in the ipsilateral hippocampus. The S-mTBI treatment resulted in increased CII, CIII, CIV, and CV protein levels in the PFC, increased CI level in the cerebellum, and increased CIII and CV levels in the cerebral cortex, but decreased CI, CII, CIV, and PDHE1α1 protein levels in the hippocampus. Thus, repeated stress or mTBI alone differentially altered ETC expression in heterogeneous brain regions. Repeated stress followed by mTBI had synergistic effects on brain ETC expression, and resulted in more severe behavioral deficits. These results suggest that repeated stress could have contributed to the high incidence of long-term neurologic and neuropsychiatric morbidity in military personnel with or without mTBI.

Acute mitochondrial dysfunction after blast exposure: potential role of mitochondrial glutamate oxaloacetate transaminase

Use of improvised explosive devices has significantly increased the incidence of traumatic brain injury (TBI) and associated neuropsychiatric deficits in the recent wars in Iraq and Afghanistan. Acute deleterious effects of single and repeated blast exposure can lead to long-term neurobiological effects and neuropsychiatric deficits. Using in vitro and in vivo shock tube models of blast-induced TBI, we studied changes in mitochondrial energy metabolism after blast exposure. Single and repeated blast exposures in vitro resulted in significant decreases in neuronal adenosine triphosphate (ATP) levels at 6 h post-blast that returned towards normal levels by 24 h. Similar changes in ATP also were observed in the cerebral cortices of mice subjected to single and repeated blast exposures. In neurons, mitochondrial glutamate oxaloacetate transaminase (GOT2) plays a critical role in metabolism and energy production. Proteomic analysis of brain cortices showed a significant decrease in GOT2 levels 6 h after repeated blast exposures, which was further confirmed by Western blotting. Western blot analysis of GOT2 and pyruvate dehydrogenase in the cortex showed direct correlation only between GOT2 and ATP levels. Activity of GOT2 in the isolated cortical mitochondria also showed significant decrease at 6 h supporting the results of proteomic and Western blot analyses. Knowing the significant role of GOT2 in the neuronal mitochondrial energy metabolism, it is quite likely that the down regulation of GOT2 after blast exposure is playing a significant role in mitochondrial dysfunction after blast exposure.

Pyruvate Dehydrogenase Kinases in the Nervous System: Their Principal Functions in Neuronal-glial Metabolic Interaction and Neuro-metabolic Disorders

Metabolism is involved directly or indirectly in all processes conducted in living cells. The brain, popularly viewed as a neuronal-glial complex, gets most of its energy from the oxygen-dependent metabolism of glucose, and the mitochondrial pyruvate dehydrogenase complex (PDC) plays a key regulatory role during the oxidation of glucose. Pyruvate dehydrogenase kinase (also called PDC kinase or PDK) is a kinase that regulates glucose metabolism by switching off PDC. Four isoforms of PDKs with tissue specific activities have been identified. The metabolisms of neurons and glial cells, especially, those of astroglial cells, are interrelated, and these cells function in an integrated fashion. The energetic coupling between neuronal and astroglial cells is essential to meet the energy requirements of the brain in an efficient way. Accumulating evidence suggests that alterations in the PDKs and/or neuron-astroglia metabolic interactions are associated with the development of several neurological disorders. Here, the authors review the results of recent research efforts that have shed light on the functions of PDKs in the nervous system, particularly on neuron-glia metabolic interactions and neuro-metabolic disorders.

Altered neurochemical profile after traumatic brain injury: (1)H-MRS biomarkers of pathological mechanisms

Specific neurochemicals measured with proton magnetic resonance spectroscopy ((1)H-MRS) may serve as biomarkers of pathological mechanism in the brain. We used high field in vivo (1)H-MRS to measure a detailed neurochemical profile after experimental traumatic brain injury (TBI) in rats. We characterized neurochemical changes in the contused cortex and the normal-appearing perilesional hippocampus over a time course from 1 hour to 2 weeks after injury. We found significant changes in 19 out of 20 neurochemicals in the cortex, and 9 out of 20 neurochemicals in the hippocampus. These changes provide evidence of altered cellular metabolic status after TBI, with specific compounds proposed to reflect edema, excitotoxicity, neuronal and glial integrity, mitochondrial status and bioenergetics, oxidative stress, inflammation, and cell membrane disruption. Our results support the utility of (1)H-MRS for monitoring cellular mechanisms of TBI pathology in animal models, and the potential of this approach for preclinical evaluation of novel therapies.

Pyruvate dehydrogenase phosphatase1 mRNA expression is divergently and dynamically regulated between rat cerebral cortex, hippocampus and thalamus after traumatic brain injury: a potential biomarker of TBI-induced hyper- and hypo-glycaemia and neuronal vulnerability

Cerebral pyruvate depletion and lactate acidosis are common metabolic characteristics of patients with traumatic brain injury (TBI) and are associated with poor prognosis. Pyruvate dehydrogenase (PDH) is the rate-limiting enzyme coupling glycolysis to mitochondrial tricarboxylic acid (TCA) cycle. Brain PDH activity is regulated by its phosphorylation status and other effectors. Phosphorylation of PDH E1α1 subunit by PDH kinase inhibits PDH activity while dephosphorylation of phosphorylated PDHE1α1 by PDH phosphatase (PDP1) restores PDH activity. In situ hybridization showed that PDP1 mRNA is highly expressed in the cerebral cortex, hippocampus and thalamus of rat. Controlled cortical impact (CCI) induced a significant increase in PDP1 mRNA expression in ipsilateral cerebral cortex at 4 h (P<0.05) and 24 h post CCI (P<0.01) that returned to basal level 72 h post CCI. PDP1 mRNA level increased transiently in ipsilateral hippocampal dentate gyrus and CA1-3 subfields 4 h post CCI (P<0.01) but decreased significantly 24 h and 72 h (P<0.01) post CCI, coinciding with a marked increase in neuronal apoptosis in ipsilateral hippocampus 24 h post CCI. PDP1 mRNA expression in thalamus and other subcortical regions decreased persistently post CCI. Contralateral CCI and craniotomy showed similar effects on PDP1 mRNA expression as ipsilateral CCI. Because GFAP mRNA expression was induced in brain regions where PDP1 expression was altered, further study should determine the potential relationship between astrocyte activation, PDP1 alteration, and pyruvate metabolism following TBI.