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Mitochondria are small cellular constituents that generate cellular energy (ATP) by oxidative phosphorylation (OXPHOS). Dysfunction of these organelles is linked to a heterogeneous group of multisystemic disorders, including diabetes, cancer, ageing-related pathologies and rare mitochondrial diseases. With respect to the latter, mutations in subunit-encoding genes and assembly factors of the first OXPHOS complex (complex I) induce isolated complex I deficiency and Leigh syndrome. This syndrome is an early-onset, often fatal, encephalopathy with a variable clinical presentation and poor prognosis due to the lack of effective intervention strategies. Mutations in the nuclear DNA-encoded NDUFS4 gene, encoding the NADH:ubiquinone oxidoreductase subunit S4 (NDUFS4) of complex I, induce 'mitochondrial complex I deficiency, nuclear type 1' (MC1DN1) and Leigh syndrome in paediatric patients. A variety of (tissue-specific) Ndufs4 knockout mouse models were developed to study the Leigh syndrome pathomechanism and intervention testing. Here, we review and discuss the role of complex I and NDUFS4 mutations in human mitochondrial disease, and review how the analysis of Ndufs4 knockout mouse models has generated new insights into the MC1ND1/Leigh syndrome pathomechanism and its therapeutic targeting. The NDUFS4 gene encodes an accessory subunit of OXPHOS complex I and its mutation causes mitochondrial disease in children. Van de Wal et al. review how Ndufs4 knockout mouse models have provided new insights into the disease pathomechanism and potential intervention strategies for these disorders.

Passive motion can induce kinetosis (motion sickness, MS) in susceptible individuals. MS is an evolutionary conserved mechanism caused by mismatches between motion-related sensory information and past visual and motion memory, triggering a malaise accompanied by hypolocomotion, hypothermia, hypophagia and aversion to novel foods presented coincidentally. Vestibular nuclei (VN) are critical for the processing of movement input, and motion-induced activation of VN neurons recapitulates MS-related signs. However, the genetic identity of VN neurons mediating MS-related autonomic and aversive responses remains unknown. Here, we identify a glutamatergic vestibular circuitry necessary to elicit MS-related behavioral responses, defining a central role of cholecystokinin (CCK)- expressing glutamatergic VN neurons in vestibular-induced malaise. Moreover, we show that CCK VN inputs onto the parabrachial nucleus activate Calca-expressing neurons and are sufficient to establish hypothermia and aversion to novel food. Together, we provide novel insight into the neurobiological regulation of MS, unravelling key genetically defined neural substrates for kinetosis.

Funding: This work was supported by a Juan de la Cierva grant (IJC2018-036938-I). A.Q. received funds from the European Research Council (Starting grant NEUROMITO, ERC-2014-StG-638106), MINECO Proyectos I + D de Excelencia (SAF2014-57981P; SAF2017-88108-R), AGAUR (2017SGR- 323), and "la Caixa" Foundation (ID 100010434), under the agreement LCF/PR/HR20/52400018. This work was supported by a Juan de la Cierva grant (IJC2018?036938?I). A.Q. received funds from the European Research Council (Starting grant NEUROMITO, ERC?2014?StG?638106), MINECO Proyectos I + D de Excelencia (SAF2014?57981P; SAF2017?88108?R), AGAUR (2017SGR? 323), and ?la Caixa? Foundation (ID 100010434), under the agreement LCF/PR/HR20/52400018. Altres ajuts: NEUROMITO Altres ajuts: "la Caixa" Foundation Symbiosis between the mitochondrion and the ancestor of the eukaryotic cell allowed cellular complexity and supported life. Mitochondria have specialized in many key functions ensuring cell homeostasis and survival. Thus, proper communication between mitochondria and cell nucleus is paramount for cellular health. However, due to their archaebacterial origin, mitochondria possess a high immunogenic potential. Indeed, mitochondria have been identified as an intracellular source of molecules that can elicit cellular responses to pathogens. Compromised mitochondrial integrity leads to release of mitochondrial content into the cytosol, which triggers an unwanted cellular immune response. Mitochondrial nucleic acids (mtDNA and mtRNA) can interact with the same cytoplasmic sensors that are specialized in recognizing genetic material from pathogens. High-energy demanding cells, such as neurons, are highly affected by deficits in mitochondrial function. Notably, mitochondrial dysfunction, neurodegeneration, and chronic inflammation are concurrent events in many severe debilitating disorders. Interestingly in this context of pathology, increasing number of studies have detected immune-activating mtDNA and mtRNA that induce an aberrant production of pro-inflammatory cytokines and interferon effectors. Thus, this review provides new insights on mitochondria-driven inflammation as a potential therapeutic target for neurodegenerative and primary mitochondrial diseases.

Background: Microglia and macrophages adopt a pro-inflammatory phenotype after spinal cord injury (SCI), what is thought to contribute to secondary tissue degeneration. We previously reported that this is due, in part, to the low levels of anti-inflammatory cytokines, such as IL-4. Since IL-13 and IL-4 share receptors and both cytokines drive microglia and macrophages towards an anti-inflammatory phenotype in vitro, here we studied whether administration of IL-13 and IL-4 after SCI leads to beneficial effects. Methods: We injected mice with recombinant IL-13 or IL-4 at 48 h after SCI and assessed their effects on microglia and macrophage phenotype and functional outcomes. We also performed RNA sequencing analysis of macrophages and microglia sorted from the injured spinal cords of mice treated with IL-13 or IL-4 and evaluated the metabolic state of these cells by using Seahorse technology. Results: We observed that IL-13 induced the expression of anti-inflammatory markers in microglia and macrophages after SCI but, in contrast to IL-4, it failed to mediate functional recovery. We found that these two cytokines induced different gene signatures in microglia and macrophages after SCI and that IL-4, in contrast to IL-13, shifted microglia and macrophage metabolism from glycolytic to oxidative phosphorylation. These findings were further confirmed by measuring the metabolic profile of these cells. Importantly, we also revealed that macrophages stimulated with IL-4 or IL-13 are not deleterious to neurons, but they become cytotoxic when oxidative metabolism is blocked. This suggests that the metabolic shift, from glycolysis to oxidative phosphorylation, is required to minimize the cytotoxic responses of microglia and macrophages. Conclusions: These results reveal that the metabolic fitness of microglia and macrophages after SCI contributes to secondary damage and that strategies aimed at boosting oxidative phosphorylation might be a novel approach to minimize the deleterious actions of microglia and macrophages in neurotrauma. This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO, SAF2016-79774-R), Wings for Life International Foundation, Red de Terapia Celular (TERCEL) and, funds from ''la Caixa” Foundation under agreement LCF/TR/CI17/10020018 and LCF/PR/HA17/52170001 to RL-V, and by NIH Grant AI 15614 to CD and the Interleukin Foundation to CD

Kisspeptin-expressing neurons in the rostral periventricular region of the third ventricle (RP3V) play an essential role in female reproduction. However, adult male mice were reported to have very few Kisspeptin-expressing neurons in the RP3V compared to females. This led to the hypothesis that Kiss1RP3V neurons are responsible for the ability of females, but not males, to generate a surge of LH, triggering ovulation and steroid synthesis in the female. Using mouse genetics and cell type-specific gene expression analysis, we show that male mice harbor almost as many Kiss1RP3V neurons as the female and that gene expression in these neurons is very similar. Specific activation of male Kiss1RP3V neurons expressing viral-encoded hM3Dq caused a surge in serum testosterone levels. These results demonstrate that Kiss1RP3V neurons are present in the adult male and fully capable of regulating the hypothalamic/pituitary/gonadal axis. We suggest that these neurons may continue to play a role in reproductive behavior in adult male mice.

Mitochondrial diseases (MD), such as Leigh syndrome (LS), present with severe neurological and muscular phenotypes in patients, but have no known cure and limited treatment options. Based on their neuroprotective effects against other neurodegenerative diseases in vivo and their positive impact as an antioxidant against complex I deficiency in vitro, we investigated the potential protective effect of metallothioneins (MTs) in an Ndufs4 knockout mouse model (with a very similar phenotype to LS) crossed with an Mt1 overexpressing mouse model (TgMt1). Despite subtle reductions in the expression of neuroinflammatory markers GFAP and IBA1 in the vestibular nucleus and hippocampus, we found no improvement in survival, growth, locomotor activity, balance, or motor coordination in the Mt1 overexpressing Ndufs4-/- mice. Furthermore, at a cellular level, no differences were detected in the metabolomics profile or gene expression of selected one-carbon metabolism and oxidative stress genes, performed in the brain and quadriceps, nor in the ROS levels of macrophages derived from these mice. Considering these outcomes, we conclude that MT1, in general, does not protect against the impaired motor activity or improve survival in these complex I-deficient mice. The unexpected absence of increased oxidative stress and metabolic redox imbalance in this MD model may explain these observations. However, tissue-specific observations such as the mildly reduced inflammation in the hippocampus and vestibular nucleus, as well as differential MT1 expression in these tissues, may yet reveal a tissue- or cell-specific role for MTs in these mice.

Respiratory dysfunction is among the main cause of severe and fatal pathologies worldwide. The use of effective experimental models and methodologies for the study of the pulmonary pathophysiology is necessary to prevent, control and cure these diseases. Plethysmography, a technique for the assessment of lung function, has been widely applied in mice for the characterization of respiratory physiology. However, classical plethysmography methods present technical limitations such as the use of anesthesia and animal immobilization. Whole-body plethysmography (WBP) avoids these issues providing a non-invasive approach for the assessment of the respiratory function in conscious animals. WBP relies on the recording of pressure changes that are produced by the spontaneous breathing activity of an animal placed inside an airtight chamber. During normal respiration, pressure variation is directly proportional to the respiratory pattern of the animal allowing the measurement of the respiratory rate and tidal volume. These parameters are commonly used to evaluate pulmonary function in different physiological and disease models. In contrast to classical plethysmography methods, WBP technique allows reproducible serial measurements as it avoids animal restraint or the use of anesthesia. These key features rend WBP a suitable approach for longitudinal studies allowing the assessment of progressive respiratory alterations in physiological and pathological conditions. This protocol describes the procedures for the measurement of the breathing patterns in mice using the WBP method, the data analysis and results interpretation.

The cerebellum, a primary brain structure involved in the control of sensorimotor tasks, also contributes to higher cognitive functions including reward, emotion and social interaction. Although the regulation of these behaviors has been largely ascribed to the monoaminergic system in limbic regions, the contribution of cerebellar dopamine signaling in the modulation of these functions remains largely unknown. By combining cell-type-specific transcriptomics, histological analyses, three-dimensional imaging and patch-clamp recordings, we demonstrate that cerebellar dopamine D2 receptors (D2Rs) in mice are preferentially expressed in Purkinje cells (PCs) and regulate synaptic efficacy onto PCs. Moreover, we found that changes in D2R levels in PCs of male mice during adulthood alter sociability and preference for social novelty without affecting motor functions. Altogether, these findings demonstrate novel roles for D2R in PC function and causally link cerebellar D2R levels of expression to social behaviors.

Defects in mitochondrial function lead to severe neuromuscular orphan pathologies known as mitochondrial disease. Among them, Leigh Syndrome is the most common pediatric presentation, characterized by symmetrical brain lesions, hypotonia, motor and respiratory deficits, and premature death. Mitochondrial diseases are characterized by a marked anatomical and cellular specificity. However, the molecular determinants for this susceptibility are currently unknown, hindering the efforts to find an effective treatment. Due to the complex crosstalk between mitochondria and their supporting cell, strategies to assess the underlying alterations in affected cell types in the context of mitochondrial dysfunction are critical. Here, we developed a novel virus-based tool, the AAV-mitoTag viral vector, to isolate mitochondria from genetically-defined cell types. Administration of the AAV-mitoTag in the vestibular neurons of a mouse model of Leigh Syndrome lacking the complex I subunitNdufs4allowed us to assess the proteome and acetylome of susceptible neurons in a well characterized model recapitulating the human disease. Our results show a marked reduction of complex-I N-module subunit abundance and an increase in the levels of the assembly factor NDUFA2. Transiently-associated non-mitochondrial proteins such as PKCδ, and the complement subcomponent C1Q were also increased inNdufs4-deficientmitochondria. Furthermore, lack ofNdufs4induced pyruvate dehydrogenase (PDH) subunit hyperacetylation, leading to decreased PDH activity. We provide novel insight on the pathways involved in mitochondrial disease, which could underlie potential therapeutic approaches for these pathologies.

Defects in mitochondrial function lead to severe neuromuscular orphan pathologies known as mitochondrial disease. Among them, Leigh Syndrome is the most common pediatric presentation, characterized by symmetrical brain lesions, hypotonia, motor and respiratory deficits, and premature death. Mitochondrial diseases are characterized by a marked anatomical and cellular specificity. However, the molecular determinants for this susceptibility are currently unknown, hindering the efforts to find an effective treatment. Due to the complex crosstalk between mitochondria and their supporting cell, strategies to assess the underlying alterations in affected cell types in the context of mitochondrial dysfunction are critical. Here, we developed a novel virus-based tool, the AAV-mitoTag viral vector, to isolate mitochondria from genetically defined cell types. Expression of the AAV-mitoTag in the glutamatergic vestibular neurons of a mouse model of Leigh Syndrome lacking the complex I subunit Ndufs4 allowed us to assess the proteome and acetylome of a subset of susceptible neurons in a well characterized model recapitulating the human disease. Our results show a marked reduction of complex I N-module subunit abundance and an increase in the levels of the assembly factor NDUFA2. Transiently associated non-mitochondrial proteins such as PKCδ, and the complement subcomponent C1Q were also increased in Ndufs4-deficient mitochondria. Furthermore, lack of Ndufs4 induced ATP synthase complex and pyruvate dehydrogenase (PDH) subunit hyperacetylation, leading to decreased PDH activity. We provide novel insight on the pathways involved in mitochondrial disease, which could underlie potential therapeutic approaches for these pathologies., This work was supported by a Marie Skłodowska-Curie COFUND action (H2020-MSCA-COFUND-2014-665919; AG), a Marie Skłodowska-Curie Individual Fellowship (H2020-MSCA-IF-2014-658352; ES), pre-doctoral fellowships (BES-2015-073041 to PP-D; 2018FI_B 00452 to AU), and a Ramón y Cajal fellowship (RyC-2012-11873; AQ). The Proteomics Laboratory CSIC/UAB is a member of Proteored, PRB3-ISCIII, and is supported by Grant PT17/0019/0008, funded by ISCIII and FEDER. ES received funds from MICIU Proyectos I+D+i “Retos Investigacion” (RTI2018-101838-J-I00). AQ received funds from the European Research Council (Starting grant NEUROMITO, ERC-2014-StG-638106), MINECO Proyectos I+D de Excelencia (SAF2014-57981P and SAF2017-88108-R), and AGAUR (2017SGR-323).

An important tenet of learning and memory is the notion of a molecular switch that promotes the formation of long-term memory1–4. The regulation of proteostasis is a critical and rate-limiting step in the consolidation of new memories5–10. One of the most effective and prevalent ways to enhance memory is by regulating the synthesis of proteins controlled by the translation initiation factor eIF211. Phosphorylation of the α-subunit of eIF2 (p-eIF2α), the central component of the integrated stress response (ISR), impairs long-term memory formation in rodents and birds11–13. By contrast, inhibiting the ISR by mutating the eIF2α phosphorylation site, genetically11 and pharmacologically inhibiting the ISR kinases14–17, or mimicking reduced p-eIF2α with the ISR inhibitor ISRIB11, enhances long-term memory in health and disease18. Here we used molecular genetics to dissect the neuronal circuits by which the ISR gates cognitive processing. We found that learning reduces eIF2α phosphorylation in hippocampal excitatory neurons and a subset of hippocampal inhibitory neurons (those that express somatostatin, but not parvalbumin). Moreover, ablation of p-eIF2α in either excitatory or somatostatin-expressing (but not parvalbumin-expressing) inhibitory neurons increased general mRNA translation, bolstered synaptic plasticity and enhanced long-term memory. Thus, eIF2α-dependent mRNA translation controls memory consolidation via autonomous mechanisms in excitatory and somatostatin-expressing inhibitory neurons. Stimulation of de novo protein synthesis in both excitatory and inhibitory, somatostatin-expressing neurons in the mouse hippocampus enhances memory consolidation.

Dysfunctions of the mitochondrial energy-generating machinery cause a series of progressive, untreatable and usually fatal diseases collectively known as mitochondrial disease. High energy-requiring organs such as the brain are especially affected, leading to developmental delay, ataxia, respiratory failure, hypotonia, seizures and premature death. While neural affectation is a critical component of the pathology, only discrete neuronal populations are susceptible. However, their molecular identity and their contribution to the disease remain unknown. Mice lacking the mitochondrial Complex I subunit NDUFS4 (Ndufs4KO mice) recapitulate the classical signs of Leigh Syndrome (LS), the most common presentation of mitochondrial disease with predominant CNS affectation. Here, we identify the critical role of two genetically-defined neuronal populations driving the fatal phenotype in Ndufs4KO mice. Selective inactivation of Ndufs4 in Vglut2-expressing glutamatergic neurons causes brainstem inflammation, motor and respiratory deficits, and early death. On the other hand, Ndufs4 deletion in GABAergic neurons leads to basal ganglia inflammation without motor or respiratory involvement, but accompanied by severe refractory epileptic seizures preceding premature death. These results provide novel insight in the cell type-specific contribution to LS pathology and open new avenues to understand the underlying cellular mechanisms of mitochondrial disease.

Mitochondrial deficits in energy production cause untreatable and fatal pathologies known as mitochondrial disease (MD). Central nervous system affectation is critical in Leigh Syndrome (LS), a common MD presentation, leading to motor and respiratory deficits, seizures and premature death. However, only specific neuronal populations are affected. Furthermore, their molecular identity and their contribution to the disease remains unknown. Here, using a mouse model of LS lacking the mitochondrial complex I subunit Ndufs4, we dissect the critical role of genetically-defined neuronal populations in LS progression. Ndufs4 inactivation in Vglut2-expressing glutamatergic neurons leads to decreased neuronal firing, brainstem inflammation, motor and respiratory deficits, and early death. In contrast, Ndufs4 deletion in GABAergic neurons causes basal ganglia inflammation without motor or respiratory involvement, but accompanied by hypothermia and severe epileptic seizures preceding death. These results provide novel insight in the cell type-specific contribution to the pathology, dissecting the underlying cellular mechanisms of MD., eLife digest Mitochondria are often described as the power plants of cells because they generate most of the energy that a cell needs to survive. But one in every 5,000 children is born with a mutation that leads to faulty mitochondria, which generate less energy than their healthy counterparts. This is particularly problematic for tissues with high energy demands, such as the brain and muscles. Children with such mutations are said to have mitochondrial disease, and one of the most common and severe forms is Leigh syndrome. Children with Leigh syndrome suffer from epilepsy, and have difficulties with movement and breathing. There is no treatment for Leigh syndrome, and most of those affected will die in childhood. The brains of children with Leigh syndrome show a characteristic pattern of damage and inflammation, symmetrical across both hemispheres, with two areas of the brain affected the most. First, the brainstem, which connects the brain with the spinal cord and is responsible for many vital functions such as breathing, maintaining the heart rate or swallowing. Secondly, a group of neurons deep within the brain called the basal ganglia, which has a role in voluntary movement. But although all of a patient’s neurons carry the mutation responsible for their Leigh syndrome, not every neuron is harmed by it. Knowing which neurons are affected, and why, could help develop treatments. Bolea, Gella, Sanz et al. therefore introduced the same Leigh syndrome mutation into different groups of neurons in three groups of mice. The first group had the mutation in the neurons that activate other cells, called glutamatergic or 'go' neurons. The second group had the mutation in the neurons that inhibit other cells, known as GABAergic, or 'stop', neurons. The third had the mutation in cholinergic neurons, which carry information from the brain to the organs. Examining the mice revealed that having faulty mitochondria in GABAergic neurons from the basal ganglia and in glutamatergic neurons of the brainstem, but not in cholinergic neurons, leads to the symptoms of Leigh syndrome. The fault in the GABAergic neurons causes the epilepsy associated with the syndrome, while faulty mitochondria in the glutamatergic neurons give rise to the observed impairments in movement and breathing. This work could help researchers identify the cellular mechanisms that make neurons more or less resistant to the effects of faulty mitochondria. This in turn will provide a stepping stone to developing new treatments, which can then be tested on the mice developed for these experiments.

Ribosome tagging has become a very useful in vivo approach for analyzing gene expression and mRNA translation in specific cell types that are difficult and time consuming to isolate by conventional methods. The approach is based on selectively expressing a hemagglutinin A (HA)-tagged ribosomal protein in a target cell type and then using antibodies against HA to purify the polysomes and associated mRNAs from the target cell. The original approach makes use of a mouse line (RiboTag) harboring a modified allele of Rpl22 (Rpl22-HA) that is induced by the action of Cre recombinase. The Rpl22-HA gene can also be introduced into the animal by stereotaxic injection of an AAV-DIO-Rpl22-HA that is then activated in Cre-expressing cells. Both methods for tagging ribosomes facilitate the immunoprecipitation of ribosome-bound mRNAs and their analysis by qRT-PCR or RNA-Seq. This protocol will discuss the technical procedures and describe important considerations relevant to the analysis of the data. © 2019 by John Wiley & Sons, Inc.

SummaryReactive oxygen species (ROS) and mitochondrial defects in neurons are implicated in neurodegenerative disease. Here, we find that a key consequence of ROS and neuronal mitochondrial dysfunction is the accumulation of lipid droplets (LD) in glia. In Drosophila, ROS triggers c-Jun-N-terminal Kinase (JNK) and Sterol Regulatory Element Binding Protein (SREBP) activity in neurons leading to LD accumulation in glia prior to or at the onset of neurodegeneration. The accumulated lipids are peroxidated in the presence of ROS. Reducing LD accumulation in glia and lipid peroxidation via targeted lipase overexpression and/or lowering ROS significantly delays the onset of neurodegeneration. Furthermore, a similar pathway leads to glial LD accumulation in Ndufs4 mutant mice with neuronal mitochondrial defects, suggesting that LD accumulation following mitochondrial dysfunction is an evolutionarily conserved phenomenon, and represents an early, transient indicator and promoter of neurodegenerative disease.

Aim: Interleukin-6 (IL-6) is a major cytokine controlling body weight and metabolism, but because many types of cells can synthesize and respond to IL-6 considerable uncertainty still exists about the mechanisms underlying IL-6 effects. Therefore, the aim of this study was to analyse the effects of tissue-specific deletion of IL-6 using a fatty acid binding protein (aP2) promoter-Cre inducible system (aP2-Cre-ERT2). Methods: Tissue-specific IL-6 KO mice (aP2-IL-6 KO mice) were produced upon tamoxifen administration and were fed a high-fat diet (HFD, 58.4% kcal from fat) or a control diet (18%) for 14 weeks. Results: aP2-IL-6 KO female mice on a HFD gained less weight and adiposity than littermate wild-type mice, but these effects were not observed in males. Hypothalamic factors such as NPY and AgRP showed a pattern of expression consistent with this sex-specific phenotype. PGC-1α expression was increased in several tissues in aP2-IL-6 KO female mice, which is compatible with increased energy expenditure. Serum leptin, insulin, glucose, cholesterol and triglycerides levels were increased by HFD, and in females IL-6 deficiency reversed this effect in the case of insulin and cholesterol. HFD induced impaired responses to insulin and glucose tolerance tests, but no significant differences between genotypes were observed. Conclusion: The present results demonstrate that deletion of IL-6 driven by aP2-Cre regulates body weight, body fat and metabolism in a sex-specific fashion. © 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

The striatum is anatomically and behaviorally implicated in behaviors that promote efficient foraging. To investigate this function, we studied instrumental choice behavior in mice lacking GPR88, a striatum-enriched orphan G-protein-coupled receptor that modulates striatal medium spiny neuron excitability. Our results reveal that hungry mice lacking GPR88 (KO mice) were slow to acquire food-reinforced lever press but could lever press similar to controls on a progressive ratio schedule. Both WT and KO mice discriminated between reward and no-reward levers; however, KO mice failed to discriminate based on relative quantity-reward (1 vs 3 food pellets) or effort (3 vs 9 lever presses). We also demonstrate preference for the high-reward (3 pellet) lever was selectively reestablished when GPR88 expression was restored to the striatum. We propose that GPR88 expression within the striatum is integral to efficient action-selection during foraging. SIGNIFICANCE STATEMENT Evolutionary pressure driving energy homeostasis favored detection and comparison of caloric value. In wild and laboratory settings, neural systems involved in energy homeostasis bias foraging to maximize energy efficiency. This is observed when foraging behaviors are guided by superior nutritional density or minimized caloric expenditure. The striatum is anatomically and functionally well placed to perform the sensory and motor integration necessary for efficient action selection during foraging. However, few studies have examined this behavioral phenomenon or elucidated underlying molecular mechanisms. Both humans and mice with nonfunctional GPR88 have been shown to present striatal dysfunctions and impaired learning. We demonstrate that GPR88 expression is necessary to efficiently integrate effort and energy density information guiding instrumental choice.

Gene delivery vectors derived from adeno-associated virus (AAV) have great potential as therapeutic agents. rAAV1 and rAAV6, efficiently target striated muscle, but the mechanisms that determine their tropism remain unclear. It is known that AAV6, but not AAV1, interacts with heparin-sulfate proteoglycans (HSPG). HSPGs are not primary receptors for AAV6, but heparin interactions may affect tissue tropism and transduction. To investigate these possibilities, we generated rAAV1 and rAAV6 capsids that do or do not bind heparin. We evaluated the transduction profile of these vectors in vivo across multiple routes of administration, and found that heparin binding capability influences tissue transduction in striated muscle and neuronal tissues. Heparin-binding capsids transduce striated muscle more efficiently than non-binding capsids, via both intramuscular and intravenous injection. However, rAAV6 achieved greater muscle transduction than the heparin-binding rAAV1 variant, suggesting that there are additional factors that influence differences in transduction efficiency between AAV1 and AAV6. Interestingly, the opposite trend was found when vectors were delivered via intracranial injection. Non-binding vectors achieved robust and widespread gene expression, whereas transduction via heparin-binding serotypes was substantially reduced. These data indicate that heparin-binding capability is an important determinant of transduction that should be considered in the design of rAAV-mediated gene therapies.

Leigh syndrome (LS) is a subacute necrotizing encephalomyelopathy with gliosis in several brain regions that usually results in infantile death. Loss of murine Ndufs4, which encodes NADH dehydrogenase (ubiquinone) iron-sulfur protein 4, results in compromised activity of mitochondrial complex I as well as progressive neurodegenerative and behavioral changes that resemble LS. Here, we report the development of breathing abnormalities in a murine model of LS. Magnetic resonance imaging revealed hyperintense bilateral lesions in the dorsal brain stem vestibular nucleus (VN) and cerebellum of severely affected mice. The mutant mice manifested a progressive increase in apnea and had aberrant responses to hypoxia. Electrophysiological recordings within the ventral brain stem pre-Bötzinger respiratory complex were also abnormal. Selective inactivation of Ndufs4 in the VN, one of the principle sites of gliosis, also led to breathing abnormalities and premature death. Conversely, Ndufs4 restoration in the VN corrected breathing deficits and prolonged the life span of knockout mice. These data demonstrate that mitochondrial dysfunction within the VN results in aberrant regulation of respiration and contributes to the lethality of Ndufs4-knockout mice.

Endoplasmic reticulum (ER) stress has recently been proposed as one of the factors contributing to apoptotic cell death in Parkinson's disease (PD). Although MAO-B inhibitors have been suggested to exert neuroprotective effects in several experimental models of PD, their effectiveness against ER stress has not been fully determined. Therefore, we have studied the potential usefulness of PF9601N, a non-amphetamine-like MAO-B inhibitor, in preventing cell death in a cell culture model of ER stress. Exposure of human dopaminergic cell line SH-SY5Y to the ER stressor brefeldin A led to Golgi disassembly, activation of the unfolded protein response (UPR), and subsequent expression of the proapoptotic mediator GADD153/CHOP. In this context, PF9601N pretreatment prevented brefeldin A-induced UPR responses, thus blocking the expression of GADD153/CHOP and resulting apoptotic features. In summary, our data suggests that PF9601N is able to block the responses elicited by ER stress, thus preventing apoptotic cell death in brefeldin A-treated cells.

Cryolesion of the frontoparietal cortex in mice is a well-described brain injury paradigm that results in increased astrogliosis surrounding the lesion site and is accompanied by a prominent increase in the MAO-B levels in astrocytes. Whether these increased MAO-B levels contribute to cellular damage or modulate reactive astrocytosis remains unclear. MAO-B activity may contribute to cellular damage, since its metabolism products are highly toxic to the cells. Additionally, it has been suggested that MAO-B inhibition may regulate astrocytic reaction. In this study, we have determined the relative contribution of MAO-B activity to the outcome following freeze injury. Freeze injury induced a prominent increase of several inflammatory markers, including ICAM, Mac-1, EB22, and GFAP. Inhibition of MAO-B activity using the selective inhibitor PF9601N did not reduce this cryolesion-induced inflammatory response. Additional data revealed that the expression of several cryolesion-induced cell death genes, such as Fas, Rip, p53, and ICE, was not reduced in PF9601N-treated mice, evidencing that MAO-B activity did not contribute to cryolesion-induced cell death. Definitive functional analysis of the mice using the ladder beam task revealed that MAO-B inhibition did not improve the cryolesion-induced motor impairment. These data strongly suggest that, although MAO-B is highly expressed in the area surrounding the lesion site, its activity does not contribute to the cellular damage or play any role in regulating astrocytic reactivity.

PF9601N [N-(2-propynyl) 2-(5-benzyloxyindol) methylamine] is a non-amphetamine type MAO-B inhibitor that has shown neuroprotective properties in vivo using different experimental models of Parkinson's disease. The mechanisms underlying its neuroprotective effects are poorly understood, but appear to be independent of MAO-B inhibition. We have studied its neuroprotective properties using the human SH-SY5Y dopaminergic cell line exposed to 1-methyl-4-phenylpyridinium (MPP(+)), a cellular model of Parkinson's disease. PF9601N pre-treatment significantly reduced MPP(+)-induced cell death and decreased the activation of one of the main executioner caspases, caspase-3. MPP(+) induced stabilization of transcription factor p53, which led to increased levels of this transcription factor, its nuclear translocation and transactivation of p53 response elements. PF9601N prevented this increase, thus reducing its transcriptional activity. Additional results showed that p53 may mediate its pro-apoptotic actions through caspase-2 under our experimental conditions. PUMA-alpha may also contribute to the p53-induced cell death. Since PF9601N significantly reduced MPP(+)-induced caspase-2 activity and PUMA-alpha levels, this reduction may lead to increased cell survival. Thus, PF9601N is a novel molecule with an apparently novel mechanism of action which has a promising potential as a therapeutic agent in the treatment of neurodegenerative diseases.

In the face of starvation, animals will engage in high-risk behaviors that would normally be considered maladaptive. Starving rodents, for example, will forage in areas that are more susceptible to predators and will also modulate aggressive behavior within a territory of limited or depleted nutrients. The neural basis of these adaptive behaviors likely involves circuits that link innate feeding, aggression and fear. Hypothalamic agouti-related peptide (AgRP)-expressing neurons are critically important for driving feeding and project axons to brain regions implicated in aggression and fear. Using circuit-mapping techniques in mice, we define a disynaptic network originating from a subset of AgRP neurons that project to the medial nucleus of the amygdala and then to the principal bed nucleus of the stria terminalis, which suppresses territorial aggression and reduces contextual fear. We propose that AgRP neurons serve as a master switch capable of coordinating behavioral decisions relative to internal state and environmental cues.

Traumatic brain injury is one of the leading causes of incapacity and death among young people. Injury to the brain elicits a potent inflammatory response, comprising recruitment of inflammatory cells, reactive astrogliosis and activation of brain macrophages. Under the influence of presumably several cytokines and growth factors, a cascade of events is activated that result ultimately in increased oxidative stress and tissue damage, but also in activation of counterregulatory factors and tissue regeneration. The complexity of this response is being unraveled by high-throughput methodologies such as microarrays. The combination of these modern techniques with the comparison of normal and genetically modified mice boosts the significance of the results obtained. With this approach, we have demonstrated that a cytokine such as interleukin-6 is one of the key players in the response of the brain to injury.

We thank Ms. Jennifer Bethard, Medical University of South Carolina for the mass spectrometric analysis of the 2D gel spots. We would like to thank Professor John Baynes, USC for helpful discussion. We thank Dr. Boris Kantor, USC Viral Vector Core for production of the lentiviral vectors. This work was supported by grants from the National Institutes of Health (R03 HD077187, R01 NS092938, R37 DK19971 and P20 GM109091), the American Diabetes Association (1-11-JF-13), and a University of South Carolina Research Foundation ASPIRE-I award. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Elevated fumarate concentrations as a result of Krebs cycle inhibition lead to increases in protein succination, an irreversible post-Translational modification that occurs when fumarate reacts with cysteine residues to generate S-(2-succino)cysteine (2SC). Metabolic events that reduce NADH re-oxidation can block Krebs cycle activity; therefore we hypothesized that oxidative phosphorylation deficiencies, such as those observed in some mitochondrial diseases, would also lead to increased protein succination. Using the Ndufs4 knockout (Ndufs4 KO) mouse, a model of Leigh syndrome, we demonstrate for the first time that protein succination is increased in the brainstem (BS), particularly in the vestibular nucleus. Importantly, the brainstem is the most affected region exhibiting neurodegeneration and astrocyte and microglial proliferation, and these mice typically die of respiratory failure attributed to vestibular nucleus pathology. In contrast, no increases in protein succination were observed in the skeletal muscle, corresponding with the lack of muscle pathology observed in this model. 2D SDS-PAGE followed by immunoblotting for succinated proteins and MS/MS analysis of BS proteins allowed us to identify the voltagedependent anion channels 1 and 2 as specific targets of succination in the Ndufs4 knockout. Using targeted mass spectrometry, Cys77 and Cys48 were identified as endogenous sites of succination in voltage-dependent anion channels 2. Given the important role of voltage-dependent anion channels isoforms in the exchange of ADP/ATP between the cytosol and the mitochondria, and the already decreased capacity for ATP synthesis in the Ndufs4 KO mice, we propose that the increased protein succination observed in the BS of these animals would further decrease the already compromised mitochondrial function. These data suggest that fumarate is a novel biochemical link that may contribute to the progression of the neuropathology in this mitochondrial disease model.

Hypothalamic neuronal populations are central regulators of energy homeostasis and reproductive function. However, the ontogeny of these critical hypothalamic neuronal populations is largely unknown. We developed a novel approach to examine the developmental pathways that link specific subtypes of neurons by combining embryonic and adult ribosome-tagging strategies in mice. This new method shows thatPomc-expressing precursors not only differentiate into discrete neuronal populations that mediate energy balance (POMC and AgRP neurons), but also into neurons critical for puberty onset and the regulation of reproductive function (Kiss1 neurons). These results demonstrate a developmental link between nutrient-sensing and reproductive neuropeptide synthesizing neuronal populations and suggest a potential pathway that could link maternal nutrition to reproductive development in the offspring.

In recent years it has become increasingly clear that the metallothionein (MT) family of proteins is important in neurobiology. MT-I and MT-II are normally dramatically up-regulated by neuroinflammation. Results for MT-III are less clear. MTs could also be relevant in human neuropathology. In Alzheimer disease (AD), a major neurodegenerative disease, clear signs of inflammation and oxidative stress were detected associated with amyloid plaques. Furthermore, the number of cells expressing apoptotic markers was also significantly increased in these plaques. As expected, MT-I and MT-II immunostaining was dramatically increased in cells surrounding the plaques, consistent with astrocytosis and microgliosis, as well as the increased oxidative stress elicited by the amyloid deposits. MT-III, In contrast, remained essentially unaltered, which agrees with some but not all studies, of AD. In situ hybridization results in a transgenic mouse model of AD amyloid deposits, the Tg2576 mouse, which expresses human Aβ precursor protein harboring the Swedish K670N/M671L mutations, are in accordance with results in human brains. Overall, these and other studies strongly suggest specific roles for MT-I, MT-II, and MT-III in brain physiology.

Traumatic injury to the brain is one of the leading causes of injury-related death or disability. Brain response to injury is orchestrated by cytokines, such as interleukin (IL)-6, but the full repertoire of responses involved is not well known. We here report the results obtained with microarrays in wild-type and IL-6 knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8 and 16 days post-lesion. Overall gene expression was analyzed by using Affymetrix genechips/oligonucleotide arrays with approximately 12,400 probe sets corresponding to approximately 10,000 different murine genes (MG_U74Av2). A robust, conventional statistical method (two-way anova) was employed to select the genes significantly affected. An orderly pattern of gene responses was clearly detected, with genes being up- or down-regulated at specific timings consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma. IL-6 deficiency showed a dramatic effect in the expression of many genes, especially in the 1 day post-lesion timing, which presumably underlies the poor capacity of IL-6 knockout mice to cope with brain damage. The results highlight the importance of IL-6 controlling the response of the brain to injury as well as the suitability of microarrays for identifying specific targets worthy of further study.

We examined metallothionein (MT)-induced neuroprotection during kainic acid (KA)-induced excitotoxicity by studying transgenic mice with MT-I overexpression (TgMT mice). KA induces epileptic seizures and hippocampal excitotoxicity, followed by inflammation and delayed brain damage. We show for the first time that even though TgMT mice were more susceptible to KA, the cerebral MT-I overexpression decreases the hippocampal inflammation and delayed neuronal degeneration and cell death as measured 3 days after KA administration. Hence, the proinflammatory responses of microglia/macrophages and lymphocytes and their expression of interleukin (IL)-1, IL-6, IL-12, tumor necrosis factor-alpha and matrix metalloproteinases (MMP-3, MMP-9) were significantly reduced in hippocampi of TgMT mice relative to wild-type mice. Also by 3 days after KA, the TgMT mice showed significantly less delayed damage, such as oxidative stress (formation of nitrotyrosine, malondialdehyde, and 8-oxoguanine), neurodegeneration (neuronal accumulation of abnormal proteins), and apoptotic cell death (judged by TUNEL and activated caspase-3). This reduced bystander damage in TgMT mice could be due to antiinflammatory and antioxidant actions of MT-I but also to direct MT-I effects on the neurons, in that significant extracellular MT presence was detected. Furthermore, MT-I overexpression stimulated astroglia and increased immunostaining of antiinflammatory IL-10, growth factors, and neurotrophins (basic fibroblastic growth factor, transforming growth factor-beta, nerve growth factor, brain-derived neurotrophic factor, glial-derived neurotrophic factor) in hippocampus. Accordingly, MT-I has different functions that likely contribute to the increased neuron survival and improved CNS condition of TgMT mice. The data presented here add new insight into MT-induced neuroprotection and indicate that MT-I therapy could be used against neurological disorders.

6-aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray matter astrocytes mainly in the brainstem. We have examined the role of interleukin-6 (IL-6) in this degenerative process by using transgenic mice with astrocyte-targeted IL-6 expression (GFAP-IL6 mice). This study demonstrates that transgenic IL-6 expression significantly increases the 6-AN-induced inflammatory response of reactive astrocytes, microglia/macrophages, and lymphocytes in the brainstem. Also, IL-6 induced significant increases in proinflammatory cytokines IL-1, IL-12, and tumor necrosis factor-alpha as well as growth factors basic fibroblast growth factor (bFGF), transforming growth factor-beta, neurotrophin-3, angiopoietin, vascular endothelial growth factor, and the receptor for bFGF. In accordance, angiogenesis was increased in GFAP-IL6 mice relative to controls after 6-AN. Moreover, oxidative stress and apoptotic cell death were significantly reduced by transgenic IL-6 expression. IL-6 is also a major inducer in the CNS of metallothionein I and II (MT-I+II), which were significantly increased in the GFAP-IL6 mice. MT-I+II are antioxidants and neuroregenerative factors in the CNS, so increased MT-I+II levels in GFAP-IL6 mice could contribute to the reduction of oxidative stress and cell death in these mice.

Metallothioneins (MTs) are multipurpose proteins with clear antioxidant, anti-inflammatory and metal homeostasis properties. The roles of brain MT-1 and MT-2 are similar to those described in the periphery, and are inducible by metals, inflammatory and stress stimuli. MT-3, originally named growth inhibitory factor, exists mainly in the central nervous system, is hardly ever inducible and its functional role and regulation are poorly understood and controversial. In the present study we examined how absence of MT-3 affects phenotypic characteristics and its effects on MT1/2 expression in basal situation and after induction. Hyperactive behavior was found only in young male Mt-3 KO mice and disappeared in the older ones. Absence of MT-3 was associated with a significant increase of MT-1/2 protein levels in several brain areas but decreased MT-1 mRNA levels, which might be related to lower corticosterone levels. The response to stress or inflammation on corticosterone plasma levels was similar in wild type and Mt-3 KO mice, suggesting that the relevant MT-3 role as MT-1/2 regulator in basal conditions is lost when other important regulatory factors such as glucocorticoids or cytokines appear.

More from mTOR Leigh syndrome is a rare, untreatable, inherited neurodegenerative disease in children that is caused by functional disruption of mitochondria, the cell's energy-producing organelles. Johnson et al. (p. 1524 , published online 14 November; see Perspective by Vafai and Mootha ) show that rapamycin, a drug used clinically as an immunosuppressant and for treatment of certain cancers, delayed the onset and progression of neurological symptoms in a mouse model of Leigh syndrome and significantly extended survival of the animals. Rapamycin inhibits the so-called “mTOR” signaling pathway, which is currently under intense study because it plays a contributory role in many common diseases.

Interleukin-6 (IL-6) is a major cytokine controlling not only the immune system but also basic physiological variables such as body weight and metabolism. While central IL-6 is clearly implicated in the latter, the putative role of peripheral IL-6 controlling body weight remains unclear. We herewith report results obtained in muscle-specific IL-6 KO (mIL-6 KO) mice. mIL-6 KO male mice fed a high-fat diet (HFD, 58.4% kcal from fat) or a control diet (18%) gained less weight and body fat than littermate floxed male mice, while the opposite pattern was observed in female mice. Food intake was not affected by muscle IL-6 deficiency, but male and female mIL-6 KO mice were more and less active, respectively, in the hole-board test. Moreover, female mIL-6 KO mice did not control adequately their body temperature upon exposure to 4°C, suggesting a role of muscle IL-6 in energy expenditure. At least part of this regulatory role of muscle IL-6 may be mediated by the hypothalamus, as IL-6 deficiency regulated the expression of critical hypothalamic neuropeptides (NPY, AgRP, POMC, CRH and preproOX). Leptin and insulin changes cannot explain the phenotype of these mice. In summary, the present results demonstrate that muscle IL-6 controls body weight and body fat in a sex-specific fashion, influencing the expression of the main neuropeptides involved in energy homeostasis.