Actin-ATP hydrolysis is a major energy drain for neurons

Mitochondrial dysfunction in bipolar disorder: Evidence, pathophysiology and translational implications

Bipolar disorder (BD) is a chronic psychiatric illness characterized by severe and biphasic changes in mood. Several pathophysiological mechanisms have been hypothesized to underpin the neurobiology of BD, including the presence of mitochondrial dysfunction. A confluence of evidence points to an underlying dysfunction of mitochondria, including decreases in mitochondrial respiration, high-energy phosphates and pH; changes in mitochondrial morphology; increases in mitochondrial DNA polymorphisms; and downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration. Mitochondria play a pivotal role in neuronal cell survival or death as regulators of both energy metabolism and cell survival and death pathways. Thus, in this review, we discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BD. The final part of this review discusses mitochondria as a potential target of therapeutic interventions in BD.

ATP and ADP actin states

This minireview is dedicated to the memory of Henryk Eisenberg and honors his major contributions to many areas of biophysics and to the analysis of macromolecular states and interactions in particular. This work reviews the ATP and ADP states of a ubiquitous protein, actins, and considers the present evidence for and against unique, nucleotide-dependent conformations of this protein. The effects of ATP and ADP on specific structural elements of actins, its loops and clefts, as revealed by mutational, crosslinking, spectroscopic, and EPR methods are discussed. It is concluded that the existing evidence points to dynamic equilibria of these structural elements among various conformational states in both ATP- and ADP-actins, with the nucleotides impacting the equilibria distributions.

Glucocorticoids alter neuronal differentiation of human neuroepithelial-like cells by inducing long-lasting changes in the reactive oxygen species balance

Prenatal exposure to excess glucocorticoid has been shown to have adverse effects on the developing nervous system that may lead to alterations of fetal and adult neurogenesis, resulting in behavioral changes. In addition, an imbalance of the redox state, with an increased susceptibility to oxidative stress, has been observed in rodent neural stem cells exposed to the synthetic glucocorticoid analog dexamethasone (Dex). In the present study, we used the induced pluripotent stem cells (IPSC)-derived lt-NES AF22 cell line, representative of the neuroepithelial stage in central nervous system development, to investigate the heritable effects of Dex on reactive oxygen species (ROS) balance and its impact on neuronal differentiation. By analysing gene expression in daughter cells that were never directly exposed to Dex, we could observe a downregulation of four key antioxidant enzymes, namely Catalase, superoxide dismutase 1, superoxide dismutase 2 and glutathione peroxidase7, along with an increased intracellular ROS concentration. The imbalance in the intracellular REDOX state was associated to a significant downregulation of major neuronal markers and a concomitant increase of glial cells. Interestingly, upon treatment with the antioxidant N-acetyl-cysteine (NAC), the misexpression of both neuronal and glial markers analyzed was recovered. These novel findings point to the increased ROS concentration playing a direct role in the heritable alterations of the differentiation potential induced by Dex exposure. Moreover, the data support the hypothesis that early insults may have detrimental long-lasting consequences on neurogenesis. Based on the positive effects exerted by NAC, it is conceivable that therapeutic strategies including antioxidants may be effective in the treatment of neuropsychiatric disorders that have been associated to increased ROS and impaired neurogenesis.

Actin dynamics and cofilin-actin rods in alzheimer disease

Cytoskeletal abnormalities and synaptic loss, typical of both familial and sporadic Alzheimer disease (AD), are induced by diverse stresses such as neuroinflammation, oxidative stress, and energetic stress, each of which may be initiated or enhanced by proinflammatory cytokines or amyloid-β (Aβ) peptides. Extracellular Aβ-containing plaques and intracellular phospho-tau-containing neurofibrillary tangles are postmortem pathologies required to confirm AD and have been the focus of most studies. However, AD brain, but not normal brain, also have increased levels of cytoplasmic rod-shaped bundles of filaments composed of ADF/cofilin-actin in a 1:1 complex (rods). Cofilin, the major ADF/cofilin isoform in mammalian neurons, severs actin filaments at low cofilin/actin ratios and stabilizes filaments at high cofilin/actin ratios. It binds cooperatively to ADP-actin subunits in F-actin. Cofilin is activated by dephosphorylation and may be oxidized in stressed neurons to form disulfide-linked dimers, required for bundling cofilin-actin filaments into stable rods. Rods form within neurites causing synaptic dysfunction by sequestering cofilin, disrupting normal actin dynamics, blocking transport, and exacerbating mitochondrial membrane potential loss. Aβ and proinflammatory cytokines induce rods through a cellular prion protein-dependent activation of NADPH oxidase and production of reactive oxygen species. Here we review recent advances in our understanding of cofilin biochemistry, rod formation, and the development of cognitive deficits. We will then discuss rod formation as a molecular pathway for synapse loss that may be common between all three prominent current AD hypotheses, thus making rods an attractive therapeutic target. © 2016 Wiley Periodicals, Inc.

Reelin and cofilin cooperate during the migration of cortical neurons: a quantitative morphological analysis

In reeler mutant mice, which are deficient in reelin (Reln), the lamination of the cerebral cortex is disrupted. Reelin signaling induces phosphorylation of LIM kinase 1, which phosphorylates the actin-depolymerizing protein cofilin in migrating neurons. Conditional cofilin mutants show neuronal migration defects. Thus, both reelin and cofilin are indispensable during cortical development. To analyze the effects of cofilin phosphorylation on neuronal migration we used in utero electroporation to transfect E14.5 wild-type cortical neurons with pCAG-EGFP plasmids encoding either a nonphosphorylatable form of cofilin 1 (cofilin(S3A)), a pseudophosphorylated form (cofilin(S3E)) or wild-type cofilin 1 (cofilin(WT)). Wild-type controls and reeler neurons were transfected with pCAG-EGFP. Real-time microscopy and histological analyses revealed that overexpression of cofilin(WT) and both phosphomutants induced migration defects and morphological abnormalities of cortical neurons. Of note, reeler neurons and cofilin(S3A)- and cofilin(S3E)-transfected neurons showed aberrant backward migration towards the ventricular zone. Overexpression of cofilin(S3E), the pseudophosphorylated form, partially rescued the migration defect of reeler neurons, as did overexpression of Limk1. Collectively, the results indicate that reelin and cofilin cooperate in controlling cytoskeletal dynamics during neuronal migration.

The Cellular and Molecular Basis of Translational Immunometabolism

The immune response requires major changes to metabolic processes, and indeed, energy metabolism and functional activation are fully integrated in immune cells to determine their ability to divide, differentiate, and carry out effector functions. Immune cell metabolism has therefore become an attractive target area for therapeutic purposes. A neglected aspect in the translation of immunometabolism is the critical connection between systemic and cellular metabolism. Here, we discuss the importance of understanding and manipulating the integration of systemic and immune cell metabolism through in-depth analysis of immune cell phenotype and function in human metabolic diseases and, in parallel, of the effects of conventional metabolic drugs on immune cell differentiation and function. We examine how the recent identification of selective metabolic programs operating in distinct immune cell subsets and functions has the potential to deliver tools for cell- and function-specific immunometabolic targeting.

Toxicity to sensory neurons and Schwann cells in experimental linezolid-induced peripheral neuropathy

OBJECTIVES

Peripheral neuropathy is a common side effect of prolonged treatment with linezolid. This study aimed to explore injurious effects of linezolid on cells of the peripheral nervous system and to establish in vivo and in vitro models of linezolid-induced peripheral neuropathy.

METHODS

C57BL/6 mice were treated with linezolid or vehicle over a total period of 4 weeks. Animals were monitored by weight, nerve conduction studies and behavioural tests. Neuropathic changes were assessed by morphometry on sciatic nerves and epidermal nerve fibre density in skin sections. Rodent sensory neuron and Schwann cell cultures were exposed to linezolid in vitro and assessed for mitochondrial dysfunction.

RESULTS

Prolonged treatment with linezolid induced a mild, predominantly small sensory fibre neuropathy in vivo. Exposure of Schwann cells and sensory neurons to linezolid in vitro caused mitochondrial dysfunction primarily in neurons (and less prominently in Schwann cells). Sensory axonopathy could be partially prevented by co-administration of the Na(+)/Ca(2+) exchanger blocker KB-R7943.

CONCLUSIONS

Clinical and pathological features of linezolid-induced peripheral neuropathy can be replicated in in vivo and in vitro models. Mitochondrial dysfunction may contribute to the axonal damage to sensory neurons that occurs after linezolid exposure.

Spatiotemporal quantification of subcellular ATP levels in a single HeLa cell during changes in morphology

The quantitative relationship between change in cell shape and ATP consumption is an unsolved problem in cell biology. In this study, a simultaneous imaging and image processing analysis allowed us to observe and quantify these relationships under physiological conditions, for the first time. We focused on two marginal regions of cells: the microtubule-rich 'lamella' and the actin-rich 'peripheral structure'. Simultaneous imaging and correlation analysis revealed that microtubule dynamics cause lamellar shape change accompanying an increase in ATP level. Also, image processing and spatiotemporal quantification enabled to visualize a chronological change of the relationships between the protrusion length and ATP levels, and it suggested they are influencing each other. Furthermore, inhibition of microtubule dynamics diminished motility in the peripheral structure and the range of fluctuation of ATP level in the lamella. This work clearly demonstrates that cellular motility and morphology are regulated by ATP-related cooperative function between microtubule and actin dynamics.

Mitochondrial dysfunction in diabetic neuropathy: a series of unfortunate metabolic events

Diabetic neuropathy is a dying back neurodegenerative disease of the peripheral nervous system where mitochondrial dysfunction has been implicated as an etiological factor. Diabetes (type 1 or type 2) invokes an elevation of intracellular glucose concentration simultaneously with impaired growth factor support by insulin, and this dual alteration triggers a maladaptation in metabolism of adult sensory neurons. The energy sensing pathway comprising the AMP-activated protein kinase (AMPK)/sirtuin (SIRT)/peroxisome proliferator-activated receptor-γ coactivator α (PGC-1α) signaling axis is the target of these damaging changes in nutrient levels, e.g., induction of nutrient stress, and loss of insulin-dependent growth factor support and instigates an aberrant metabolic phenotype characterized by a suppression of mitochondrial oxidative phosphorylation and shift to anaerobic glycolysis. There is discussion of how this loss of mitochondrial function and transition to overreliance on glycolysis contributes to the diminishment of collateral sprouting and axon regeneration in diabetic neuropathy in the context of the highly energy-consuming nerve growth cone.

Mitochondrial Respiratory Disorders: A Perspective on their Metabolite Biomarkers and Implications for Clinical Diagnosis and Therapeutic Intervention

Mitochondrial respiratory disorders are incurable progressive degenerative diseases with multi-organ system manifestations. These orphan diseases are caused by mutations in the nuclear or mitochondrial genome affecting the oxidative phosphorylation (OXPHOS) system responsible for ATP synthesis. Currently, therapeutic treatments are not available to patients, resulting in significant disability and a poor prognosis. Patients exhibit a constellation of complex neurological and multisystem phenotypic symptoms. The hallmark of these diseases is their clinical heterogeneity and high variability among patients. Consequently, establishing an accurate diagnosis remains a challenging, invasive, and time-consuming process due to the limited sensitivity, specificity and reliability of the current serum biomarkers used in clinical settings. Recent mouse model-based research combined with patient studies led to the identification of fibroblast growth factor 21 (FGF-21) as a promising serum biomarker. With its high specificity and sensitivity, FGF-21 is a promising diagnostic tool for muscle-affecting mitochondrial respiratory disorders, which might be a useful first-line diagnostic tool instead of the invasive muscle biopsy currently performed in clinical settings. Discovering additional diagnostic biomarkers is critical for establishing an accurate diagnosis given the high clinical heterogeneity of these mitochondrial respiratory diseases. Ultimately, these novel biomarkers might be instrumental to monitor the progression of these diseases and the efficacy of novel therapeutic interventions.

Protein interaction patterns in different cellular environments are revealed by in-cell NMR

In-cell NMR allows obtaining atomic-level information on biological macromolecules in their physiological environment. Soluble proteins may interact with the cellular environment in different ways: either specifically, with their functional partners, or non-specifically, with other cellular components. Such behaviour often causes the disappearance of the NMR signals. Here we show that by introducing mutations on the human protein profilin 1, used here as a test case, the in-cell NMR signals can be recovered. In human cells both specific and non-specific interactions are present, while in bacterial cells only the effect of non-specific interactions is observed. By comparing the NMR signal recovery pattern in human and bacterial cells, the relative contribution of each type of interaction can be assessed. This strategy allows detecting solution in-cell NMR spectra of soluble proteins without altering their fold, thus extending the applicability of in-cell NMR to a wider range of proteins.

The proinflammatory cytokine, interleukin-17A, augments mitochondrial function and neurite outgrowth of cultured adult sensory neurons derived from normal and diabetic rats

BACKGROUND

Diabetic neuropathy comprises dying back of nerve endings that reflects impairment in axonal plasticity and regenerative nerve growth. Metabolic changes in diabetes can lead to a dysregulation of hormonal mediators, such as cytokines, that may constrain distal nerve fiber growth. Interleukin-17 (IL-17A), a proinflammatory and neurotropic cytokine produced by T-cells, was significantly reduced in sciatic nerve of streptozotocin (STZ)-diabetic rats. Thus we studied the effect of IL-17A on the phenotype of sensory neurons derived from age matched control or type 1 diabetic rats. The aims were to determine the ability of IL-17A to enhance neurite outgrowth in cultured sensory neurons, investigate the signaling pathways activated by IL-17A, study the role of mitochondria and mechanistically link to neurite outgrowth.

RESULTS

IL-17A (10 ng/ml; p<0.05) significantly and dose-dependently increased total neurite outgrowth in cultures of adult dorsal root ganglia (DRG) sensory neurons derived from both control and streptozotocin (STZ)-diabetic rats. This enhancement was mediated by IL-17A-dependent activation of extracellular-regulated protein kinase (ERK) and phosphoinositide-3 kinase (PI-3K) signal transduction pathways. Pharmacological blockade of one of these activated pathways triggered complete inhibition of neurite outgrowth. IL-17A augmented mitochondrial bioenergetic function of sensory neurons derived from control or diabetic rats and this was also mediated via ERK or PI-3K. IL-17A-dependent elevation of bioenergetic function was associated with augmented expression of proteins of the mitochondrial electron transport system complexes.

CONCLUSIONS

IL-17A enhanced axonal plasticity through activation of ERK and PI-3K pathways and was associated with augmented mitochondrial bioenergetic function in sensory neurons.

Podocyte Purinergic P2X4 Channels Are Mechanotransducers That Mediate Cytoskeletal Disorganization

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X4) blocker 5-BDBD. Moreover, mechanical P2X4 channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X4 channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X4 channels as mechanotransducers in podocytes.

Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia

Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.

Two functionally distinct sources of actin monomers supply the leading edge of lamellipodia

Lamellipodia, the sheet-like protrusions of motile cells, consist of networks of actin filaments (F-actin) regulated by the ordered assembly from and disassembly into actin monomers (G-actin). Traditionally, G-actin is thought to exist as a homogeneous pool. Here, we show that there are two functionally and molecularly distinct sources of G-actin that supply lamellipodial actin networks. G-actin originating from the cytosolic pool requires the monomer-binding protein thymosin β4 (Tβ4) for optimal leading-edge localization, is targeted to formins, and is responsible for creating an elevated G/F-actin ratio that promotes membrane protrusion. The second source of G-actin comes from recycled lamellipodia F-actin. Recycling occurs independently of Tβ4 and appears to regulate lamellipodia homeostasis. Tβ4-bound G-actin specifically localizes to the leading edge because it does not interact with Arp2/3-mediated polymerization sites found throughout the lamellipodia. These findings demonstrate that actin networks can be constructed from multiple sources of monomers with discrete spatiotemporal functions.

Low-dose ionizing radiation rapidly affects mitochondrial and synaptic signaling pathways in murine hippocampus and cortex

The increased use of radiation-based medical imaging methods such as computer tomography is a matter of concern due to potential radiation-induced adverse effects. Efficient protection against such detrimental effects has not been possible due to inadequate understanding of radiation-induced alterations in signaling pathways. The aim of this study was to elucidate the molecular mechanisms behind learning and memory deficits after acute low and moderate doses of ionizing radiation. Female C57BL/6J mice were irradiated on postnatal day 10 (PND10) with gamma doses of 0.1 or 0.5 Gy. This was followed by evaluation of the cellular proteome, pathway-focused transcriptome, and neurological development/disease-focused miRNAome of hippocampus and cortex 24 h postirradiation. Our analysis showed that signaling pathways related to mitochondrial and synaptic functions were changed by acute irradiation. This may lead to reduced mitochondrial function paralleled by enhanced number of dendritic spines and neurite outgrowth due to elevated long-term potentiation, triggered by increased phosphorylated CREB. This was predominately observed in the cortex at 0.1 and 0.5 Gy and in the hippocampus only at 0.5 Gy. Moreover, a radiation-induced increase in the expression of several neural miRNAs associated with synaptic plasticity was found. The early changes in signaling pathways related to memory formation may be associated with the acute neurocognitive side effects in patients after brain radiotherapy but might also contribute to late radiation-induced cognitive injury.

Non-signalling energy use in the brain

Energy use limits the information processing power of the brain. However, apart from the ATP used to power electrical signalling, a significant fraction of the brain's energy consumption is not directly related to information processing. The brain spends just under half of its energy on non-signalling processes, but it remains poorly understood which tasks are so energetically costly for the brain. We review existing experimental data on subcellular processes that may contribute to this non-signalling energy use, and provide modelling estimates, to try to assess the magnitude of their ATP consumption and consider how their changes in pathology may compromise neuronal function. As a main result, surprisingly little consensus exists on the energetic cost of actin treadmilling, with estimates ranging from < 1% of the brain's global energy budget up to one-half of neuronal energy use. Microtubule treadmilling and protein synthesis have been estimated to account for very small fractions of the brain's energy budget, whereas there is stronger evidence that lipid synthesis and mitochondrial proton leak are energetically expensive. Substantial further research is necessary to close these gaps in knowledge about the brain's energy-expensive non-signalling tasks.

Prolyl hydroxylase regulates axonal rewiring and motor recovery after traumatic brain injury

Prolyl 4-hydroxylases (PHDs; PHD1, PHD2, and PHD3) are a component of cellular oxygen sensors that regulate the adaptive response depending on the oxygen concentration stabilized by hypoxia/stress-regulated genes transcription. In normoxic condition, PHD2 is required to stabilize hypoxia inducible factors. Silencing of PHD2 leads to the activation of intracellular signaling including RhoA and Rho-associated protein kinase (ROCK), which are key regulators of neurite growth. In this study, we determined that genetic or pharmacological inhibition of PHD2 in cultured cortical neurons prevents neurite elongation through a ROCK-dependent mechanism. We then explored the role of PHDs in axonal reorganization following a traumatic brain injury in adult mice. Unilateral destruction of motor cortex resulted in behavioral deficits due to disruption of the corticospinal tract (CST), a part of the descending motor pathway. In the spinal cord, sprouting of fibers from the intact side of the CST into the denervated side is thought to contribute to the recovery process following an injury. Intracortical infusion of PHD inhibitors into the intact side of the motor cortex abrogated spontaneous formation of CST collaterals and functional recovery after damage to the sensorimotor cortex. These findings suggest PHDs have an important role in the formation of compensatory axonal networks following an injury and may represent a new molecular target for the central nervous system disorders.

Intrinsic activity in cells and the brain

Motile cells such as bacteria, amoebae, and fibroblasts display a continual level of energy-consuming reactions involving the cytoskeleton and signal pathways, regardless of whether or not they are actually migrating. I draw parallels between these "silent signals" and the intrinsic activity of the human brain, especially that associated with the brain stem. In both cases, it can be argued that the organism continually rehearses possible future actions, so it can act quickly and accurately when suitable cues are received from the environment.

Calcium signalling in sensory neurones and peripheral glia in the context of diabetic neuropathies

Peripheral sensory nervous system is comprised of neurones with their axons and neuroglia that includes satellite glial cells in sensory ganglia, myelinating, non-myelinating and perisynaptic Schwann cells. Pathogenesis of peripheral diabetic polyneuropathies is associated with aberrant function of both neurones and glia. Deregulated Ca(2+) homoeostasis and aberrant Ca(2+) signalling in neuronal and glial elements contributes to many forms of neuropathology and is fundamental to neurodegenerative diseases. In diabetes both neurones and glia experience metabolic stress and mitochondrial dysfunction which lead to deregulation of Ca(2+) homeostasis and Ca(2+) signalling, which in their turn lead to pathological cellular reactions contributing to development of diabetic neuropathies. Molecular cascades responsible for Ca(2+) homeostasis and signalling, therefore, can be regarded as potential therapeutic targets.

Cytoskeletal and signaling mechanisms of neurite formation

The formation of a neurite, the basis for axons and dendrites, begins with the concerted accumulation and organization of actin and microtubules. Whereas much is known about the proteins that play a role in these processes, because they perform similar functions in axon branching and filopodia formation, much remains to be discovered concerning the interaction of these individual cytoskeletal regulators during neurite formation. Here, we review the literature regarding various models of filopodial formation and the way in which proteins that control actin organization and polymerization induce neurite formation. Although several different regulators of actin polymerization are involved in neurite initiation, redundancy occurs between these regulators, as the effects of the loss of a single regulator can be mitigated by the addition of neurite-promoting substrates and proteins. Similar to actin dynamics, both microtubule stabilizing and destabilizing proteins play a role in neurite initiation. Furthermore, interactions between the actin and microtubule cytoskeleton are required for neurite formation. Several lines of evidence indicate that the interactions between these two components of the cytoskeleton are needed for force generation and for the localization of microtubules at sites of nascent neurites. The general theme that emerges is the existence of several central regulatory pathways on which extracellular cues converge to control and organize both actin and microtubules to induce the formation of neurites.

Ciliary neurotrophic factor reverses aberrant mitochondrial bioenergetics through the JAK/STAT pathway in cultured sensory neurons derived from streptozotocin-induced diabetic rodents

Mitochondrial dysfunction occurs in sensory neurons and contributes to diabetic neuropathy. Ciliary neurotrophic factor (CNTF) stimulates axon regeneration in type 1 diabetic rodents and prevents deficits in axonal caliber, nerve conduction, and thermal sensation. We tested the hypothesis that CNTF enhances sensory neuron function in diabetes through JAK/STAT (Janus kinase/signal transducers and activators of transcription) signaling to normalize impaired mitochondrial bioenergetics. The effect of CNTF on gene expression and neurite outgrowth of cultured adult dorsal root ganglia (DRG) sensory neurons derived from control and streptozotocin (STZ)-induced diabetic rodents was quantified. Polarization status and bioenergetics profile of mitochondria from cultured sensory neurons were determined. CNTF treatment prevented reduced STAT3 phosphorylation (Tyr 705) in DRG of STZ-diabetic mice and also enhanced STAT3 phosphorylation in rat DRG cultures. CNTF normalized polarization status of the mitochondrial inner membrane and corrected the aberrant oligomycin-induced mitochondrial hyperpolarization in axons of diabetic neurons. The mitochondrial bioenergetics profile demonstrated that spare respiratory capacity and respiratory control ratio were significantly depressed in sensory neurons cultured from STZ-diabetic rats and were corrected by acute CNTF treatment. The positive effects of CNTF on neuronal mitochondrial function were significantly inhibited by the specific JAK inhibitor, AG490. Neurite outgrowth of sensory neurons from age-matched control and STZ-induced diabetic rats was elevated by CNTF and blocked by AG490. We propose that CNTF's ability to enhance axon regeneration and protect from fiber degeneration in diabetes is associated with its targeting of mitochondrial function and improvement of cellular bioenergetics, in part, through JAK/STAT signaling.

Enhancement of mitochondrial ATP production by the Escherichia coli cytotoxic necrotizing factor 1

Mitochondria are dynamic organelles that constantly change shape and structure in response to different stimuli and metabolic demands of the cell. The Escherichia coli protein toxin cytotoxic necrotizing factor 1 (CNF1) has recently been reported to influence mitochondrial activity in a mouse model of Rett syndrome and to increase ATP content in the brain tissue of an Alzheimer's disease mouse model. In the present work, the ability of CNF1 to influence mitochondrial activity was investigated in IEC-6 normal intestinal crypt cells. In these cells, the toxin was able to induce an increase in cellular ATP content, probably due to an increment of the mitochondrial electron transport chain. In addition, the CNF1-induced Rho GTPase activity also caused changes in the mitochondrial architecture that mainly consisted in the formation of a complex network of elongated mitochondria. The involvement of the cAMP-dependent protein kinase A signaling pathway was postulated. Our results demonstrate that CNF1 positively affects mitochondria by bursting their energetic function and modifying their morphology.

Glucose controls morphodynamics of LPS-stimulated macrophages

Macrophages constantly undergo morphological changes when quiescently surveying the tissue milieu for signs of microbial infection or damage, or after activation when they are phagocytosing cellular debris or foreign material. These morphofunctional alterations require active actin cytoskeleton remodeling and metabolic adaptation. Here we analyzed RAW 264.7 and Maf-DKO macrophages as models to study whether there is a specific association between aspects of carbohydrate metabolism and actin-based processes in LPS-stimulated macrophages. We demonstrate that the capacity to undergo LPS-induced cell shape changes and to phagocytose complement-opsonized zymosan (COZ) particles does not depend on oxidative phosphorylation activity but is fueled by glycolysis. Different macrophage activities like spreading, formation of cell protrusions, as well as phagocytosis of COZ, were thereby strongly reliant on the presence of low levels of extracellular glucose. Since global ATP production was not affected by rewiring of glucose catabolism and inhibition of glycolysis by 2-deoxy-D-glucose and glucose deprivation had differential effects, our observations suggest a non-metabolic role for glucose in actin cytoskeletal remodeling in macrophages, e.g. via posttranslational modification of receptors or signaling molecules, or other effects on the machinery that drives actin cytoskeletal changes. Our findings impute a decisive role for the nutrient state of the tissue microenvironment in macrophage morphodynamics.

The role of the cofilin-actin rod stress response in neurodegenerative diseases uncovers potential new drug targets

The cofilin-actin rod stress response is an actin cytoskeletal dynamic arrest that occurs in cells under a variety of stress conditions. Upon stress, the rapidly activated cofilin saturates actin filaments causing them to bundle into rod structures in either the nucleus or cytoplasm, halting actin polymerization and thus freeing ATP. Importantly, these rods dissociate quickly following relief of the transient stress. The rods form inappropriately in neurons involved in the progression of Alzheimer disease (AD) and we have linked dysfunctional dynamics of the nuclear rod response to Huntington disease (HD). Cofilin levels are also perturbed in Parkinson disease (PD), and profilin, an actin binding protein with opposite action to cofilin, is mutated in Amyotrophic Lateral Sclerosis (ALS). The persistence of the rods post-stress suggests that critical molecular switches to turn this response both on and off are being affected in neurodegeneration. We have recently shown that the cofilin protein is regulated by highly conserved nuclear import and export signals and that these signals are required to be functional for an appropriate rod formation during stress. The ability of cofilin to form rods is required in a cell culture model for cells to be resistant to apoptosis under stress conditions, indicating that a normal cofilin-actin rod response is likely integral to proper cell health in higher order organisms. Here we hypothesize on the potential physiological function of nuclear cofilin-actin rods and why the dysregulation of this response could lead to the selective vulnerability of the most susceptible populations of cells in HD. We further suggest that learning more about this cytoskeletal cell stress response will open up new avenues for drug target discovery in neurodegenerative disorders.

Mitochondrial biogenesis: a therapeutic target for neurodevelopmental disorders and neurodegenerative diseases

In the developing and mature brain, mitochondria act as central hubs for distinct but interwined pathways, necessary for neural development, survival, activity, connectivity and plasticity. In neurons, mitochondria assume diverse functions, such as energy production in the form of ATP, calcium buffering and generation of reactive oxygen species. Mitochondrial dysfunction contributes to a range of neurodevelopmental and neurodegenerative diseases, making mitochondria a potential target for pharmacological-based therapies. Pathogenesis associated with these diseases is accompanied by an increase in mitochondrial mass, a quantitative increase to overcome a qualitative deficiency due to mutated mitochondrial proteins that are either nuclear- or mitochondrial-encoded. This compensatory biological response is maladaptive, as it fails to sufficiently augment the bioenergetically functional mitochondrial mass and correct for the ATP deficit. Since regulation of neuronal mitochondrial biogenesis has been scantily investigated, our current understanding on the network of transcriptional regulators, co-activators and signaling regulators mainly derives from other cellular systems. The purpose of this review is to present the current state of our knowledge and understanding of the transcriptional and signaling cascades controlling neuronal mitochondrial biogenesis and the various therapeutic approaches to enhance the functional mitochondrial mass in the context of neurodevelopmental disorders and adult-onset neurodegenerative diseases.

Energy-sensitive regulation of Na+/K+-ATPase by Janus kinase 2

Janus kinase 2 (JAK2) contributes to intracellular signaling of leptin and erythropoietin, hormones protecting cells during energy depletion. The present study explores whether JAK2 is activated by energy depletion and regulates Na(+)/K(+)-ATPase, the major energy-consuming pump. In Jurkat cells, JAK2 activity was determined by radioactive kinase assay, phosphorylated JAK2 detected by Western blotting, ATP levels measured by luciferase assay, as well as Na(+)/K(+)-ATPase α1-subunit transcript and protein abundance determined by real-time PCR and Western blotting, respectively. Ouabain-sensitive K(+)-induced currents (Ipump) were measured by whole cell patch clamp. Ipump was further determined by dual-electrode voltage clamp in Xenopus oocytes injected with cRNA-encoding JAK2, active (V617F)JAK2, or inactive (K882E)JAK2. As a result, in Jurkat T cells, JAK2 activity significantly increased following energy depletion by sodium azide (NaN3) or 2,4- dinitro phenol (DNP). DNP- and NaN3-induced decrease of cellular ATP was significantly augmented by JAK2 inhibitor AG490 and blunted by Na(+)/K(+)-ATPase inhibitor ouabain. DNP decreased and AG490 enhanced Ipump as well as Na(+)/K(+)-ATPase α1-subunit transcript and protein abundance. The α1-subunit transcript levels were also enhanced by signal transducer and activator of transcription-5 inhibitor CAS 285986-31-4. In Xenopus oocytes, Ipump was significantly decreased by expression of JAK2 and (V617F)JAK2 but not of (K882E)JAK2, effects again reversed by AG490. In (V617F)JAK2-expressing Xenopus oocytes, neither DNP nor NaN3 resulted in further decline of Ipump. In Xenopus oocytes, the effect of (V617F)JAK2 on Ipump was not prevented by inhibition of transcription with actinomycin. In conclusion, JAK2 is a novel energy-sensing kinase that curtails energy consumption by downregulating Na(+)/K(+)-ATPase expression and activity.

AMP-activated protein kinase mediates activity-dependent axon branching by recruiting mitochondria to axon

During development, axons are guided to their target areas and provide local branching. Spatiotemporal regulation of axon branching is crucial for the establishment of functional connections between appropriate pre- and postsynaptic neurons. Common understanding has been that neuronal activity contributes to the proper axon branching; however, intracellular mechanisms that underlie activity-dependent axon branching remain elusive. Here, we show, using primary cultures of the dentate granule cells, that neuronal depolarization-induced rebalance of mitochondrial motility between anterograde versus retrograde transport underlies the proper formation of axonal branches. We found that the depolarization-induced branch formation was blocked by the uncoupler p-trifluoromethoxyphenylhydrazone, which suggests that mitochondria-derived ATP mediates the observed phenomena. Real-time analysis of mitochondrial movement defined the molecular mechanisms by showing that the pharmacological activation of AMP-activated protein kinase (AMPK) after depolarization increased anterograde transport of mitochondria into axons. Simultaneous imaging of axonal morphology and mitochondrial distribution revealed that mitochondrial localization preceded the emergence of axonal branches. Moreover, the higher probability of mitochondrial localization was correlated with the longer lifetime of axon branches. We qualitatively confirmed that neuronal ATP levels decreased immediately after depolarization and found that the phosphorylated form of AMPK was increased. Thus, this study identifies a novel role for AMPK in the transport of axonal mitochondria that underlie the neuronal activity-dependent formation of axon branches.

Cofilin: a redox sensitive mediator of actin dynamics during T-cell activation and migration

Cofilin is an actin-binding protein that depolymerizes and/or severs actin filaments. This dual function of cofilin makes it one of the major regulators of actin dynamics important for T-cell activation and migration. The activity of cofilin is spatio-temporally regulated. Its main control mechanisms comprise a molecular toolbox of phospho-, phospholipid, and redox regulation. Phosphorylated cofilin is inactive and represents the dominant cofilin fraction in the cytoplasm of resting human T cells. A fraction of dephosphorylated cofilin is kept inactive at the plasma membrane by binding to phosphatidylinositol 4,5-bisphosphate. Costimulation via the T-cell receptor/CD3 complex (signal 1) together with accessory receptors (signal 2) or triggering through the chemokine SDF1α (stromal cell-derived factor 1α) induce Ras-dependent dephosphorylation of cofilin, which is important for immune synapse formation, T-cell activation, and T-cell migration. Recently, it became evident that cofilin is also highly sensitive for microenvironmental changes, particularly for alterations in the redox milieu. Cofilin is inactivated by oxidation, provoking T-cell hyporesponsiveness or necrotic-like programmed cell death. In contrast, in a reducing environment, even phosphatidylinositol 4,5-bisphosphate-bound cofilin becomes active, leading to actin dynamics in the vicinity of the plasma membrane. In addition to the well-established three signals for T-cell activation, this microenvironmental control of cofilin delivers a modulating signal for T-cell-dependent immune reactions. This fourth modulating signal highly impacts both initial T-cell activation and the effector phase of T-cell-mediated immune responses.

Root apex transition zone as oscillatory zone

Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone.

Astrocytic energetics during excitatory neurotransmission: What are contributions of glutamate oxidation and glycolysis?

Astrocytic energetics of excitatory neurotransmission is controversial due to discrepant findings in different experimental systems in vitro and in vivo. The energy requirements of glutamate uptake are believed by some researchers to be satisfied by glycolysis coupled with shuttling of lactate to neurons for oxidation. However, astrocytes increase glycogenolysis and oxidative metabolism during sensory stimulation in vivo, indicating that other sources of energy are used by astrocytes during brain activation. Furthermore, glutamate uptake into cultured astrocytes stimulates glutamate oxidation and oxygen consumption, and glutamate maintains respiration as well as glucose. The neurotransmitter pool of glutamate is associated with the faster component of total glutamate turnover in vivo, and use of neurotransmitter glutamate to fuel its own uptake by oxidation-competent perisynaptic processes has two advantages, substrate is supplied concomitant with demand, and glutamate spares glucose for use by neurons and astrocytes. Some, but not all, perisynaptic processes of astrocytes in adult rodent brain contain mitochondria, and oxidation of only a small fraction of the neurotransmitter glutamate taken up into these structures would be sufficient to supply the ATP required for sodium extrusion and conversion of glutamate to glutamine. Glycolysis would, however, be required in perisynaptic processes lacking oxidative capacity. Three lines of evidence indicate that critical cornerstones of the astrocyte-to-neuron lactate shuttle model are not established and normal brain does not need lactate as supplemental fuel: (i) rapid onset of hemodynamic responses to activation delivers oxygen and glucose in excess of demand, (ii) total glucose utilization greatly exceeds glucose oxidation in awake rodents during activation, indicating that the lactate generated is released, not locally oxidized, and (iii) glutamate-induced glycolysis is not a robust phenotype of all astrocyte cultures. Various metabolic pathways, including glutamate oxidation and glycolysis with lactate release, contribute to cellular energy demands of excitatory neurotransmission.

Emergent complexity of the cytoskeleton: from single filaments to tissue

Despite their overwhelming complexity, living cells display a high degree of internal mechanical and functional organization which can largely be attributed to the intracellular biopolymer scaffold, the cytoskeleton. Being a very complex system far from thermodynamic equilibrium, the cytoskeleton's ability to organize is at the same time challenging and fascinating. The extensive amounts of frequently interacting cellular building blocks and their inherent multifunctionality permits highly adaptive behavior and obstructs a purely reductionist approach. Nevertheless (and despite the field's relative novelty), the physics approach has already proved to be extremely successful in revealing very fundamental concepts of cytoskeleton organization and behavior. This review aims at introducing the physics of the cytoskeleton ranging from single biopolymer filaments to multicellular organisms. Throughout this wide range of phenomena, the focus is set on the intertwined nature of the different physical scales (levels of complexity) that give rise to numerous emergent properties by means of self-organization or self-assembly.

Normalization of NF-κB activity in dorsal root ganglia neurons cultured from diabetic rats reverses neuropathy-linked markers of cellular pathology

AIMS/HYPOTHESIS

Dorsal root ganglia (DRG) sensory neurons cultured from 3 to 5 month streptozotocin (STZ)-induced diabetic rats exhibit structural and biochemical changes seen in peripheral nerve fibers in vivo, including axonal swellings, oxidative damage, reduced axonal sprouting, and decreased NF-κB activity. NF-κB is a transcription factor required by DRG neurons for survival and plasticity, and regulates transcription of antioxidant proteins (e.g. MnSOD). We hypothesized that the diabetes-induced decrease in NF-κB activity in DRG contributes to pathological phenomena observed in cultured DRG neurons from diabetic rats.

METHODS

NF-κB localization was assessed in intact DRG and neuron cultures using immunostaining. NF-κB activity was manipulated in sensory neuron cultures derived from age-matched normal or 3-5 month STZ-diabetic rats using pharmacological means and lentiviral expression of shRNA. The impact of diabetes and altered NF-κB activity on neuronal phenotype involved analysis of neurite outgrowth, neurite morphology, oxidative stress (lipid peroxidation) and expression of MnSOD.

RESULTS

STZ-induced diabetes caused a significant decrease in nuclear localization of NF-κB subunits p50 and c-rel, but no change in p65 in intact DRG. Inhibition of NF-κB in normal neuron cultures significantly increased axonal swellings and oxidative stress, and reduced both neurite outgrowth and expression of MnSOD. These phenomena mimicked markers of pathology in cultured DRG neurons from diabetic rats. Enhancement of NF-κB activity in cultured diabetic DRG neurons ameliorated the sub-optimal neurite outgrowth and MnSOD levels triggered by diabetes. Exogenous insulin enhanced nuclear localization of p50 and c-rel but not p65 in diabetic neuronal cultures.

CONCLUSION/INTERPRETATION

The diabetes-induced decrease of nuclear localization of NF-κB subunits p50 and c-rel in DRG contributes to development of in vitro markers of peripheral neuropathy, possibly through impaired mitochondrial ROS scavenging by deficient MnSOD.

Controlling the cortical actin motor

Actin is the essential force-generating component of the microfilament system, which powers numerous motile processes in eukaryotic cells and undergoes dynamic remodeling in response to different internal and external signaling. The ability of actin to polymerize into asymmetric filaments is the inherent property behind the site-directed force-generating capacity that operates during various intracellular movements and in surface protrusions. Not surprisingly, a broad variety of signaling pathways and components are involved in controlling and coordinating the activities of the actin microfilament system in a myriad of different interactions. The characterization of these processes has stimulated cell biologists for decades and has, as a consequence, resulted in a huge body of data. The purpose here is to present a cellular perspective on recent advances in our understanding of the microfilament system with respect to actin polymerization, filament structure and specific folding requirements.

Ciliary neurotrophic factor activates NF-κB to enhance mitochondrial bioenergetics and prevent neuropathy in sensory neurons of streptozotocin-induced diabetic rodents

Diabetes causes mitochondrial dysfunction in sensory neurons that may contribute to peripheral neuropathy. Ciliary neurotrophic factor (CNTF) promotes sensory neuron survival and axon regeneration and prevents axonal dwindling, nerve conduction deficits and thermal hypoalgesia in diabetic rats. In this study, we tested the hypothesis that CNTF protects sensory neuron function during diabetes through normalization of impaired mitochondrial bioenergetics. In addition, we investigated whether the NF-κB signal transduction pathway was mobilized by CNTF. Neurite outgrowth of sensory neurons derived from streptozotocin (STZ)-induced diabetic rats was reduced compared to neurons from control rats and exposure to CNTF for 24 h enhanced neurite outgrowth. CNTF also activated NF-κB, as assessed by Western blotting for the NF-κB p50 subunit and reporter assays for NF-κB promoter activity. Conversely, blockade of NF-κB signaling using SN50 peptide inhibited CNTF-mediated neurite outgrowth. Studies in mice with STZ-induced diabetes demonstrated that systemic therapy with CNTF prevented functional indices of peripheral neuropathy along with deficiencies in dorsal root ganglion (DRG) NF-κB p50 expression and DNA binding activity. DRG neurons derived from STZ-diabetic mice also exhibited deficiencies in maximal oxygen consumption rate and associated spare respiratory capacity that were corrected by exposure to CNTF for 24 h in an NF-κB-dependent manner. We propose that the ability of CNTF to enhance axon regeneration and protect peripheral nerve from structural and functional indices of diabetic peripheral neuropathy is associated with targeting of mitochondrial function, in part via NF-κB activation, and improvement of cellular bioenergetics.

The classification of microglial activation phenotypes on neurodegeneration and regeneration in Alzheimer's disease brain

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline of cognitive function. There is no therapy that can halt or reverse its progression. Contemporary research suggests that age-dependent neuroinflammatory changes may play a significant role in the decreased neurogenesis and cognitive impairments in AD. The innate immune response is characterized by pro-inflammatory (M1) activation of macrophages and subsequent production of specific cytokines, chemokines, and reactive intermediates, followed by resolution and alternative activation for anti-inflammatory signaling (M2a) and wound healing (M2c). We propose that microglial activation phenotypes are analogous to those of macrophages and that their activation plays a significant role in regulating neurogenesis in the brain. Microglia undergo a switch from an M2- to an M1-skewed activation phenotype during aging. This review will assess the neuroimmunological studies that led to characterization of the different microglial activation states in AD mouse models. It will also discuss the roles of microglial activation on neurogenesis in AD and propose anti-inflammatory molecules as exciting therapeutic targets for research. Molecules such as interleukin-4 and CD200 have proven to be important anti-inflammatory mediators in the regulation of neuroinflammation in the brain, which will be discussed in detail for their therapeutic potential.

The neurogenic basic helix-loop-helix transcription factor NeuroD6 enhances mitochondrial biogenesis and bioenergetics to confer tolerance of neuronal PC12-NeuroD6 cells to the mitochondrial stressor rotenone

The fundamental question of how and which neuronal specific transcription factors tailor mitochondrial biogenesis and bioenergetics to the need of developing neuronal cells has remained largely unexplored. In this study, we report that the neurogenic basic helix-loop-helix transcription factor NeuroD6 possesses mitochondrial biogenic properties by amplifying the mitochondrial DNA content and TFAM expression levels, a key regulator for mitochondrial biogenesis. NeuroD6-mediated increase in mitochondrial biogenesis in the neuronal progenitor-like PC12-NEUROD6 cells is concomitant with enhanced mitochondrial bioenergetic functions, including increased expression levels of specific subunits of respiratory complexes of the electron transport chain, elevated mitochondrial membrane potential and ATP levels produced by oxidative phosphorylation. Thus, NeuroD6 augments the bioenergetic capacity of PC12-NEUROD6 cells to generate an energetic reserve, which confers tolerance to the mitochondrial stressor, rotenone. We found that NeuroD6 induces an adaptive bioenergetic response throughout rotenone treatment involving maintenance of the mitochondrial membrane potential and ATP levels in conjunction with preservation of the actin network. In conclusion, our results support the concept that NeuroD6 plays an integrative role in regulating and coordinating the onset of neuronal differentiation with acquisition of adequate mitochondrial mass and energetic capacity to ensure energy demanding events, such as cytoskeletal remodeling, plasmalemmal expansion, and growth cone formation.

Impaired adenosine monophosphate-activated protein kinase signalling in dorsal root ganglia neurons is linked to mitochondrial dysfunction and peripheral neuropathy in diabetes

Mitochondrial dysfunction occurs in sensory neurons and may contribute to distal axonopathy in animal models of diabetic neuropathy. The adenosine monophosphate-activated protein kinase and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signalling axis senses the metabolic demands of cells and regulates mitochondrial function. Studies in muscle, liver and cardiac tissues have shown that the activity of adenosine monophosphate-activated protein kinase and PGC-1α is decreased under hyperglycaemia. In this study, we tested the hypothesis that deficits in adenosine monophosphate-activated protein kinase/PGC-1α signalling in sensory neurons underlie impaired axonal plasticity, suboptimal mitochondrial function and development of neuropathy in rodent models of type 1 and type 2 diabetes. Phosphorylation and expression of adenosine monophosphate-activated protein kinase/PGC-1α and mitochondrial respiratory chain complex proteins were downregulated in dorsal root ganglia of both streptozotocin-diabetic rats and db/db mice. Adenoviral-mediated manipulation of endogenous adenosine monophosphate-activated protein kinase activity using mutant proteins modulated neurotrophin-directed neurite outgrowth in cultures of sensory neurons derived from adult rats. Addition of resveratrol to cultures of sensory neurons derived from rats after 3-5 months of streptozotocin-induced diabetes, significantly elevated adenosine monophosphate-activated protein kinase levels, enhanced neurite outgrowth and normalized mitochondrial inner membrane polarization in axons. The bioenergetics profile (maximal oxygen consumption rate, coupling efficiency, respiratory control ratio and spare respiratory capacity) was aberrant in cultured sensory neurons from streptozotocin-diabetic rats and was corrected by resveratrol treatment. Finally, resveratrol treatment for the last 2 months of a 5-month period of diabetes reversed thermal hypoalgesia and attenuated foot skin intraepidermal nerve fibre loss and reduced myelinated fibre mean axonal calibre in streptozotocin-diabetic rats. These data suggest that the development of distal axonopathy in diabetic neuropathy is linked to nutrient excess and mitochondrial dysfunction via defective signalling of the adenosine monophosphate-activated protein kinase/PGC-1α pathway.

Proteomic analysis of a drosophila IBMPFD model reveals potential pathogenic mechanisms

IBMPFD, Inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia, is a hereditary degenerative disorder due to single missense mutations in VCP (Valosin-Containing Protein). The mechanisms of how mutations of VCP lead to IBMPFD remain mysterious. Here we utilize two-dimensional difference gel electrophoresis (2D-DIGE) combined with mass spectrometry to study the IBMPFD disorder at the protein level. With this set-up, we are able to employ comparative proteomics to analyze IBMPFD disease using Drosophila melanogaster as our disease model organism. Head proteome of transgenic D. melanogaster expressing wild type VCP is compared, respectively, with the head proteome of transgenic mutant type VCPs that correspond to human IBMPFD disease alleles (TER94(A229E), TER94(R188Q), and TER94(R152H)). Of all the proteins identified, a significant fraction of proteins altered in TER94(A229E) and TER94(R188Q) mutants belong to the same functional categories, i.e. apoptosis and metabolism. Among these, Drosophila transferrin is observed to be significantly up-regulated in mutant flies expressing TER94(A229E). A knock-down experiment suggests that fly transferrin might be a potential modifier in IBMPFD disease. The molecular analysis of IBMPFD disease may benefit from the proteomics approach which combines the advantages of high throughput analysis and the focus on protein levels.

Actin reorganization as the molecular basis for the regulation of apoptosis in gastrointestinal epithelial cells

The gastrointestinal (GI) epithelium is a rapidly renewing tissue in which apoptosis represents part of the overall homeostatic process. Regulation of apoptosis in the GI epithelium is complex with a precise relationship between cell position and apoptosis. Apoptosis occurs spontaneously and in response to radiation and cytotoxic drugs at the base of the crypts. By contrast, the villus epithelial cells are extremely resistant to apoptosis. The molecular mechanism underlying this loss of function of villus epithelial cells to undergo apoptosis shortly after their exit from the crypt is unknown. In this study we demonstrate for the first time, that deletion of two homologous actin-binding proteins, villin and gelsolin renders villus epithelial cells extremely sensitive to apoptosis. Ultrastructural analysis of the villin-gelsolin(-/-) double-knockout mice shows an abnormal accumulation of damaged mitochondria demonstrating that villin and gelsolin function on an early step in the apoptotic signaling at the level of the mitochondria. A characterization of functional and ligand-binding mutants demonstrate that regulated changes in actin dynamics determined by the actin severing activities of villin and gelsolin are required to maintain cellular homeostasis. Our study provides a molecular basis for the regulation of apoptosis in the GI epithelium and identifies cell biological mechanisms that couple changes in actin dynamics to apoptotic cell death.

The role of aberrant mitochondrial bioenergetics in diabetic neuropathy

Diabetic neuropathy is a neurological complication of diabetes that causes significant morbidity and, because of the obesity-driven rise in incidence of type 2 diabetes, is becoming a major international health problem. Mitochondrial phenotype is abnormal in sensory neurons in diabetes and may contribute to the etiology of diabetic neuropathy where a distal dying-back neurodegenerative process is a key component contributing to fiber loss. This review summarizes the major features of mitochondrial dysfunction in neurons and Schwann cells in human diabetic patients and in experimental animal models (primarily exhibiting type 1 diabetes). This article attempts to relate these findings to the development of critical neuropathological hallmarks of the disease. Recent work reveals that hyperglycemia in diabetes triggers nutrient excess in neurons that, in turn, mediates a phenotypic change in mitochondrial biology through alteration of the AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signaling axis. This vital energy sensing metabolic pathway modulates mitochondrial function, biogenesis and regeneration. The bioenergetic phenotype of mitochondria in diabetic neurons is aberrant due to deleterious alterations in expression and activity of respiratory chain components as a direct consequence of abnormal AMPK/PGC-1α signaling. Utilization of innovative respirometry equipment to analyze mitochondrial function of cultured adult sensory neurons from diabetic rodents shows that the outcome for cellular bioenergetics is a reduced adaptability to fluctuations in ATP demand. The diabetes-induced maladaptive process is hypothesized to result in exhaustion of the ATP supply in the distal nerve compartment and induction of nerve fiber dissolution. The role of mitochondrial dysfunction in the etiology of diabetic neuropathy is compared with other types of neuropathy with a distal dying-back pathology such as Friedreich ataxia, Charcot-Marie-Tooth disease type 2 and human immunodeficiency virus-associated distal-symmetric neuropathy.

Emerging roles of the neuronal nucleolus

Although, the nucleolus has been observed for almost 200 years in neurons, studies that directly address the neuronal roles of this subnuclear structure have appeared only recently. The aim of this review is to discuss recent progress and identify some critical questions that remain to be answered. As expected for the cellular center of ribosome biogenesis, the nucleolus is essential for the growth of developing neurons, including neurite morphogenesis and long-term maintenance of mature neurons. In addition, the nucleolus contributes to neuronal stress responses, including the regulation of apoptosis. Hence, disrupted neurodevelopment or neurodegeneration are among the likely consequences of nucleolar dysfunction. Conversely, the presence of active nucleoli may determine the potential for neurorepair.

Identification of agents that reduce renal hypoxia-reoxygenation injury using cell-based screening: purine nucleosides are alternative energy sources in LLC-PK1 cells during hypoxia

Acute tubular necrosis is a clinical problem that lacks specific therapy and is characterized by high mortality rate. The ischemic renal injury affects the proximal tubule cells causing dysfunction and cell death after severe hypoperfusion. We utilized a cell-based screening approach in a hypoxia-reoxygenation model of tubular injury to search for cytoprotective action using a library of pharmacologically active compounds. Oxygen-glucose deprivation (OGD) induced ATP depletion, suppressed aerobic and anaerobic metabolism, increased the permeability of the monolayer, caused poly(ADP-ribose) polymerase cleavage and caspase-dependent cell death. The only compound that proved cytoprotective either applied prior to the hypoxia induction or during the reoxygenation was adenosine. The protective effect of adenosine required the coordinated actions of adenosine deaminase and adenosine kinase, but did not requisite the purine receptors. Adenosine and inosine better preserved the cellular ATP content during ischemia than equimolar amount of glucose, and accelerated the restoration of the cellular ATP pool following the OGD. Our results suggest that radical changes occur in the cellular metabolism to respond to the energy demand during and following hypoxia, which include the use of nucleosides as an essential energy source. Thus purine nucleoside supplementation holds promise in the treatment of acute renal failure.

Inflammation, mitochondria, and the inhibition of adult neurogenesis

The process of neurogenesis continues throughout life, with thousands of new neurons generated every day in the mammalian brain. Impairment of hippocampal neurogenesis has been suggested to be involved in neurodegenerative conditions, including the cognitive decline associated with aging, Alzheimer's disease, Parkinson's disease, and ionizing radiation. These neurodegenerative conditions are all characterized by proinflammatory changes and increased numbers of activated microglia. Activated microglia produce a variety of proinflammatory factors, including interleukin-6, tumor necrosis factor-α, reactive oxygen species, and nitric oxide, all of which are antineurogenic. These same factors have also been shown to suppress mitochondrial function, but the role of mitochondria in neurogenesis remains barely investigated. This brief review summarizes the findings of several studies that support a role for mitochondrial impairment as part of the mechanism of the reduction of neurogenesis associated with inflammation.

Neuronal differentiation involves a shift from glucose oxidation to fermentation

Energy metabolism in the adult brain consumes large quantities of glucose, but little is known to date regarding how glucose metabolism changes during neuronal differentiation, a process that is highly demanding energetically. We studied changes in glucose metabolism during neuronal differentiation of P19 mouse embryonal carcinoma cells, E14Tg2A embryonic stem cells as well as during brain development of BLC57 mice. In all these models, we find that neurogenesis is accompanied by a shift from oxidative to fermentative glucose metabolism. This shift is accompanied by both a decrease in mitochondrial enzymatic activities and mitochondrial uncoupling. In keeping with this finding, we also observe that differentiation does not require oxidative metabolism, as indicated by experiments demonstrating that the process is preserved in cells treated with the ATP synthase inhibitor oligomycin. Overall, we provide evidence that neuronal differentiation involves a shift from oxidative to fermentative metabolism, and that oxidative phosphorylation is not essential for this process.