Neuronal Knockout Research Articles

7788 Importance of Neuronal STAT3, but Not ERK2 or mTOR, for Pubertal Timing and Reproductive Activity in Mice

Abstract Disclosure: R.A. Lord: None. M.A. Inglis: None. G.M. Anderson: None. The adipose-derived hormone leptin is important for regulating reproduction. The canonical JAK2/STAT3 pathway is the best-characterised leptin receptor signalling pathway. Neural STAT3 deletion is known to cause obesity; however, its reproductive influence is less understood. This experiment investigated whether STAT3 knockout from brain neurons or AgRP neurons, a neuronal population necessary for normal pubertal timing and reproduction, would unveil the necessity of STAT3 in reproductive function. We also tested the role of ERK2 and mTOR, two alternative leptin signalling molecules.Transgenic mice with a neuronal knockout were created via the Cre-loxP system. CamKinaseIIα-Cre mice were crossed with STAT3, mTOR or ERK2 floxed mice. AgRP-Cre mice were crossed with STAT3 floxed mice for STAT3 knockout in AgRP neurons. All groups were compared to Cre-negative littermate controls (n=6-12/group). Puberty onset was assessed post-weaning by examining genitalia development. Reproductive cyclicity and organ weights were measured in adults. Metabolic effects were evaluated through body weight, abdominal fat and fasting glucose measurements. Brain tissue analysis evaluated cellular responses to leptin for STAT3, ERK2, and mTOR. Data presented as mean ± SEM.Mice with ERK2 KO or mTOR KO showed no reproductive or metabolic deficits compared to controls. In marked contrast, neuronal STAT3 KO mice showed significantly increased body weight by 5 weeks of age and a 6-fold increase in abdominal adiposity as adults (both p<0.001 using two-way ANOVA and Student’s t-test respectively) compared to controls. Males had a significant 5-day delay in age at preputial separation (KO: 32.1±2.09 d; Control: 26.8±0.45 d, p<0.01, Student’s t-test) while females had a significant 7-day delay in vaginal opening (KO: 33.0±1.85 d, Control: 26.6±0.37 d, p<0.05, Student’s t-test), a 9-day delay in first estrus (KO: 37.8±1.89 d; Control: 29.4±0.65 d, p<0.01, Student’s t-test) and pronounced acyclicity. Neuronal STAT3 KO mice also had a >2-fold elevation in fasting glucose levels (p<0.001, Student’s t-test) and regressed reproductive organs. Female mice with STAT3 knockout in AgRP neurons showed significantly increased body weight (by 3 weeks [p<0.001], two-way ANOVA) and a significant 3-day delay in first estrus (KO: 31.1±0.71 d, Control: 28.6±0.45 d, p<0.01, Student’s t-test). These data show that neuronal STAT3 is critical for correctly timed puberty and subsequent fertility in male and female mice, whereas mTOR and ERK2 are not essential. These results have prompted a re-evaluation of previous conclusions about the role of STAT3 from experiments using LepR-Cre mice. Additionally, AgRP neuronal requirements for STAT3 exactly recapitulate AgRP requirements for leptin receptors. A better grasp of leptin signalling pathways will improve our understanding of how infertility arises due to metabolic disease. Presentation: 6/3/2024

Coordinated stimulation of axon regenerative and neurodegenerative transcriptional programs by ATF4 following optic nerve injury.

Stress signaling is important for determining the fates of neurons following axonal insults. Previously we showed that the stress-responsive kinase PERK contributes to injury-induced neurodegeneration (Larhammar et al., 2017). Here we show that PERK acts primarily through Activating Transcription Factor-4 (ATF4) to stimulate not only pro-apoptotic but also pro-regenerative responses following optic nerve damage. Using conditional knockout mice, we find an extensive PERK/ATF4-dependent transcriptional response that includes canonical ATF4 target genes and modest contributions by C/EBP Homologous Protein (CHOP). Overlap with c-Jun-dependent transcription suggests interplay with a parallel stress pathway that orchestrates regenerative and apoptotic responses. Accordingly, neuronal knockout of ATF4 recapitulates the neuroprotection afforded by PERK deficiency, and PERK or ATF4 knockout impairs optic axon regeneration enabled by disrupting the tumor suppressor PTEN. These findings reveal an integral role for PERK/ATF4 in coordinating neurodegenerative and regenerative responses to CNS axon injury.

Misprogramming of glucose metabolism impairs recovery of hippocampal slices from neuronal GLT-1 knockout mice and contributes to excitotoxic injury through mitochondrial superoxide production.

We have previously reported a failure of recovery of synaptic function in the CA1 region of acute hippocampal slices from mice with a conditional neuronal knockout (KO) of GLT-1 (EAAT2, Slc1A2) driven by synapsin-Cre (synGLT-1 KO). The failure of recovery of synaptic function is due to excitotoxic injury. We hypothesized that changes in mitochondrial metabolism contribute to the heightened vulnerability to excitotoxicity in the synGLT-1 KO mice. We found impaired flux of carbon from 13C-glucose into the tricarboxylic acid cycle in synGLT-1 KO cortical and hippocampal slices compared with wild-type (WT) slices. In addition, we found downregulation of the neuronal glucose transporter GLUT3 in both genotypes. Flux of carbon from [1,2-13C]acetate, thought to be astrocyte-specific, was increased in the synGLT-KO hippocampal slices but not cortical slices. Glycogen stores, predominantly localized to astrocytes, are rapidly depleted in slices after cutting, and are replenished during exvivo incubation. In the synGLT-1 KO, replenishment of glycogen stores during exvivo incubation was compromised. These results suggest both neuronal and astrocytic metabolic perturbations in the synGLT-1 KO slices. Supplementing incubation medium during recovery with 20 mM D-glucose normalized glycogen replenishment but had no effect on recovery of synaptic function. In contrast, 20 mM non-metabolizable L-glucose substantially improved recovery of synaptic function, suggesting that D-glucose metabolism contributes to the excitotoxic injury in the synGLT-1 KO slices. L-lactate substitution for D-glucose did not promote recovery of synaptic function, implicating mitochondrial metabolism. Consistent with this hypothesis, phosphorylation of pyruvate dehydrogenase, which decreases enzyme activity, was increased in WT slices during the recovery period, but not in synGLT-1 KO slices. Since metabolism of glucose by the mitochondrial electron transport chain is associated with superoxide production, we tested the effect of drugs that scavenge and prevent superoxide production. The superoxide dismutase/catalase mimic EUK-134 conferred complete protection and full recovery of synaptic function. A site-specific inhibitor of complex III superoxide production, S3QEL-2, was also protective, but inhibitors of NADPH oxidase were not. In summary, we find that the failure of recovery of synaptic function in hippocampal slices from the synGLT-1 KO mouse, previously shown to be due to excitotoxic injury, is caused by production of superoxide by mitochondrial metabolism.

Prosapip1 in the dorsal hippocampus mediates synaptic protein composition, long-term potentiation, and spatial memory.

Prosapip1 is a brain-specific protein localized to the postsynaptic density, where it promotes dendritic spine maturation in primary hippocampal neurons. However, nothing is known about the role of Prosapip1 in vivo . To examine this, we utilized the Cre-loxP system to develop a Prosapip1 neuronal knockout mouse. We found that Prosapip1 controls the synaptic localization of its binding partner SPAR, along with PSD-95 and the GluN2B subunit of the NMDA receptor (NMDAR) in the dorsal hippocampus (dHP). We next sought to identify the potential contribution of Prosapip1 to the activity and function of the NMDAR and found that Prosapip1 plays an important role in NMDAR-mediated transmission and long-term potentiation (LTP) in the CA1 region of the dHP. As LTP is the cellular hallmark of learning and memory, we examined the consequences of neuronal knockout of Prosapip1 on dHP-dependent memory. We found that global or dHP-specific neuronal knockout of Prosapip1 caused a deficit in learning and memory whereas developmental, locomotor, and anxiety phenotypes were normal. Taken together, Prosapip1 in the dHP promotes the proper localization of synaptic proteins which, in turn, facilitates LTP driving recognition, social, and spatial learning and memory.

Selective neuronal knockout of STAT3 function inhibits epilepsy progression, improves cognition, and restores dysregulated gene networks in a temporal lobe epilepsy model.

Temporal lobe epilepsy (TLE) is a progressive disorder mediated by pathological changes in molecular cascades and hippocampal neural circuit remodeling that results in spontaneous seizures and cognitive dysfunction. Targeting these cascades may provide disease-modifying treatments for TLE patients. Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) inhibitors have emerged as potential disease-modifying therapies; a more detailed understanding of JAK/STAT participation in epileptogenic responses is required, however, to increase the therapeutic efficacy and reduce adverse effects associated with global inhibition. We developed a mouse line in which tamoxifen treatment conditionally abolishes STAT3 signaling from forebrain excitatory neurons (nSTAT3KO). Seizure frequency (continuous in vivo electroencephalography) and memory (contextual fear conditioning and motor learning) were analyzed in wild-type and nSTAT3KO mice after intrahippocampal kainate (IHKA) injection as a model of TLE. Hippocampal RNA was obtained 24 h after IHKA and subjected to deep sequencing. Selective STAT3 KO in excitatory neurons reduced seizure progression and hippocampal memory deficits without reducing the extent of cell death or mossy fiber sprouting induced by IHKA injection. Gene expression was rescued in major networks associated with response to brain injury, neuronal plasticity, and learning and memory. We also provide the first evidence that neuronal STAT3 may directly influence brain inflammation. Inhibiting neuronal STAT3 signaling improved outcomes in an animal model of TLE, prevented progression of seizures and cognitive co-morbidities while rescuing pathogenic changes in gene expression of major networks associated with epileptogenesis. Specifically targeting neuronal STAT3 may be an effective disease-modifying strategy for TLE. This article is protected by copyright. All rights reserved.

Endocannabinoid control of neuroinflammation in traumatic brain injury by monoacylglycerol lipase in astrocytes.

Endocannabinoid control of neuroinflammation in traumatic brain injury by monoacylglycerol lipase in astrocytes.

Deletion of the clock gene Period2 (Per2) in glial cells alters mood-related behavior in mice

The circadian clock regulates many biochemical and physiological pathways, and lack of clock genes, such as Period (Per) 2, affects not only circadian activity rhythms, but can also modulate feeding and mood-related behaviors. However, it is not known how cell-type specific expression of Per2 contributes to these behaviors. In this study, we find that Per2 in glial cells is important for balancing mood-related behaviors, without affecting circadian activity parameters. Genetic and adeno-associated virus-mediated deletion of Per2 in glial cells of mice leads to reduced despair and anxiety. This is paralleled by an increase of the GABA transporter 2 (Gat2/Slc6a13) and Dopamine receptor D3 (Drd3) mRNA, and a reduction of glutamate levels in the nucleus accumbens (NAc). Interestingly, neuronal Per2 knock-out also reduces despair, but does not influence anxiety. The change in mood-related behavior is not a result of a defective molecular clock, as glial Bmal1 deletion has no effect on neither despair nor anxiety. Exclusive deletion of Per2 in glia of the NAc reduced despair, but had no influence on anxiety. Our data provide strong evidence for an important role of glial Per2 in regulating mood-related behavior.

MicroRNA-210 Regulates Dendritic Morphology and Behavioural Flexibility in Mice.

MicroRNAs are known to be critical regulators of neuronal plasticity. The highly conserved, hypoxia-regulated microRNA-210 (miR-210) has been shown to be associated with long-term memory in invertebrates and dysregulated in neurodevelopmental and neurodegenerative disease models. However, the role of miR-210 in mammalian neuronal function and cognitive behaviour remains unexplored. Here we generated Nestin-cre-driven miR-210 neuronal knockout mice to characterise miR-210 regulation and function using in vitro and in vivo methods. We identified miR-210 localisation throughout neuronal somas and dendritic processes and increased levels of mature miR-210 in response to neural activity in vitro. Loss of miR-210 in neurons resulted in higher oxidative phosphorylation and ROS production following hypoxia and increased dendritic arbour density in hippocampal cultures. Additionally, miR-210 knockout mice displayed altered behavioural flexibility in rodent touchscreen tests, particularly during early reversal learning suggesting processes underlying updating of information and feedback were impacted. Our findings support a conserved, activity-dependent role for miR-210 in neuroplasticity and cognitive function.

Neuronal protein-tyrosine phosphatase 1B hinders sensory-motor functional recovery and causes affective disorders in two different focal ischemic stroke models.

Ischemic brain injury causes neuronal death and inflammation. Inflammation activates protein-tyrosine phosphatase 1B (PTP1B). Here, we tested the significance of PTP1B activation in glutamatergic projection neurons on functional recovery in two models of stroke: by photothrombosis, focal ischemic lesions were induced in the sensorimotor cortex (SM stroke) or in the peri-prefrontal cortex (peri-PFC stroke). Elevated PTP1B expression was detected at 4 days and up to 6 weeks after stroke. While ablation of PTP1B in neurons of neuronal knockout (NKO) mice had no effect on the volume or resorption of ischemic lesions, markedly different effects on functional recovery were observed. SM stroke caused severe sensory and motor deficits (adhesive removal test) in wild type and NKO mice at 4 days, but NKO mice showed drastically improved sensory and motor functional recovery at 8 days. In addition, peri-PFC stroke caused anxiety-like behaviors (elevated plus maze and open field tests), and depression-like behaviors (forced swimming and tail suspension tests) in wild type mice 9 and 28 days after stroke, respectively, with minimal effect on sensory and motor function. Peri-PFC stroke-induced affective disorders were associated with fewer active (FosB+) neurons in the PFC and nucleus accumbens but more FosB+ neurons in the basolateral amygdala, compared to sham-operated mice. In contrast, mice with neuronal ablation of PTP1B were protected from anxiety-like and depression-like behaviors and showed no change in FosB+ neurons after peri-PFC stroke. Taken together, our study identifies neuronal PTP1B as a key component that hinders sensory and motor functional recovery and also contributes to the development of anxiety-like and depression-like behaviors after stroke. Thus, PTP1B may represent a novel therapeutic target to improve stroke recovery. All procedures for animal use were approved by the Animal Care and Use Committee of the University of Ottawa Animal Care and Veterinary Service (protocol 1806) on July 27, 2018.

Cyclin-Dependent Kinase 5–Dependent BAG3 Degradation Modulates Synaptic Protein Turnover

BackgroundSynaptic protein dyshomeostasis and functional loss is an early invariant feature of Alzheimer’s disease (AD), yet the unifying etiological pathway remains largely unknown. Knowing that cyclin-dependent kinase 5 (CDK5) plays critical roles in synaptic formation and degeneration, its phosphorylation targets were reexamined in search of candidates with direct global impacts on synaptic protein dynamics, and the associated regulatory network was also analyzed. MethodsQuantitative phosphoproteomics and bioinformatics analyses were performed to identify top-ranked candidates. A series of biochemical assays was used to investigate the associated regulatory signaling networks. Histological, electrochemical, and behavioral assays were performed in conditional knockout, small hairpin RNA–mediated knockdown, and AD-related mice models to evaluate the relevance of CDK5 to synaptic homeostasis and functions. ResultsAmong candidates with known implications in synaptic modulations, BAG3 ranked the highest. CDK5-mediated phosphorylation on S297/S291 (mouse/human) destabilized BAG3. Loss of BAG3 unleashed the selective protein degradative function of the HSP70 machinery. In neurons, this resulted in enhanced degradation of a number of glutamatergic synaptic proteins. Conditional neuronal knockout of Bag3 in vivo led to impairment of learning and memory functions. In human AD and related mouse models, aberrant CDK5-mediated loss of BAG3 yielded similar effects on synaptic homeostasis. Detrimental effects of BAG3 loss on learning and memory functions were confirmed in these mice, and such effects were reversed by ectopic BAG3 reexpression. ConclusionsOur results highlight that the neuronal CDK5-BAG3-HSP70 signaling axis plays a critical role in modulating synaptic homeostasis. Dysregulation of the signaling pathway directly contributes to synaptic dysfunction and AD pathogenesis.

Neuronal Deletion of the Mammalian Indy Homolog (Slc13a5) Increases Energy Expenditure in Mice

INDY (I’m Not Dead Yet) is a transporter of TCA cycle intermediates, mediating cellular citrate uptake and is highly expressed in liver and brain. Reduced expression of Indy in lower organisms extended lifespan, reduced whole body fat content and increased mitochondrial biogenesis. In mammals, whole body deletion of the mammalian Indy homolog (mIndy, Slc13a5) increased energy expenditure and protected mice from diet and aging induced obesity and insulin resistance. Here, we address the role of neuronal mIndy in energy homeostasis. We generated a neuronal mIndy knockout (NINKO) mouse model by crossing mIndy-floxed to NestinCre mice. Deletion of mIndy in neurons led to an increase in energy expenditure compared to NestinCre mice after 8 weeks of high fat diet (HFD) feeding (average 24h EE: NestinCre: 11.5±0.5 kcal/h/kg lean mass (lm); NINKO: 13.6±0.6 kcal/h/kg lm; p<0.001). The respiratory exchange ratio decreased from 0.78±0.01 in NestinCre mice to 0.77±0.01 in NINKO mice during the light phase (p<0.001), indicating augmented lipid oxidation in NINKO mice. Body temperature increased in NINKO compared to NestinCre mice (NestinCre: 37.0±0.1°C, NINKO: 37.3±0.1°C at 6pm; p<0.05). Fat mass was reduced and lean mass increased significantly in NINKO mice (NestinCre: 60±1% lm, 31±1% fat mass; NINKO: 63±1% lm, 27±1% fat mass after 8 weeks of HFD feeding; p<0.05). Hyperinsulinemic-euglycemic clamp studies showed improved insulin sensitivity in NINKO mice (steady state GINF NestinCre: 26±2 mg/kg/min; NINKO: 34.6±2 mg/kg/min; p<0.05). Together, these data suggest that neuronal mIndy is a critical regulator of energy and glucose homeostasis in mammals. Further studies will address the mechanisms involved in the effect. Disclosure A. Kurzbach: None. D.M. Willmes: None. T. Schumann: None. C. Henke: None. N. El-Agroudy: None. A. Kleinridders: None. A.L. Birkenfeld: None.

Neuronal O-GlcNAc transferase regulates appetite, body weight, and peripheral insulin resistance.

The ogt gene encodes O-linked N-acetylglucosamine transferase (O-GlcNAc transferase [OGT]) that catalyzes the transfer of β-N-acetylglucosamine (GlcNAc) from the uridine-diphosphate-GlcNAc to the hydroxyl group of serine or threonine residues of nucleocytoplasmic proteins. This process is a common protein posttranslational modification, called protein O-GlcNAcylation, which is a known intracellular sensor of glucose metabolism and plays an important role in regulating cellular signaling, transcription, and metabolism. However, little is known about the function of OGT in the brain. Here, we report that the CaMKIIα promoter-dependent neuronal knockout (KO) of OGT in adult mice led to short-term overeating, body weight gain, and peripheral insulin resistance. These phenotype changes were accompanied by marked elevation of serum insulin and leptin levels and neuronal cell death, including the loss of leptin receptor-expressing neurons, in the hypothalamus. The neuronal OGT KO exacerbated obesity and insulin resistance induced by high-fat diet. Surprisingly, the peripheral insulin resistance induced by neuronal OGT KO was reversed at its own 2-3months after OGT KO, and the mice even showed increased insulin sensitivity several months later. These findings reveal an important role of neuronal OGT in the regulation of feeding behavior, body weight, and peripheral insulin sensitivity.

Astrocyte-Specific Deletion of Peroxisome-Proliferator Activated Receptor-γ Impairs Glucose Metabolism and Estrous Cycling in Female Mice.

Mice lacking peroxisome-proliferator activated receptor-γ (PPARγ) in neurons do not become leptin resistant when placed on a high-fat diet (HFD). In male mice, this results in decreased food intake and increased energy expenditure, causing reduced body weight, but this difference in body weight is not observed in female mice. In addition, estrous cycles are disturbed and the ovaries present with hemorrhagic follicles. We observed that PPARγ was more highly expressed in astrocytes than neurons, so we created an inducible, conditional knockout of PPARγ in astrocytes (AKO). The AKO mice had impaired glucose tolerance and hepatic steatosis that did not worsen with HFD. Expression of gluconeogenic genes was elevated in the mouse livers, as was expression of several genes involved in lipogenesis, lipid transport, and storage. The AKO mice also had a reproductive phenotype with fewer estrous cycles, elevated plasma testosterone levels, reduced corpora lutea formation, and alterations in hypothalamic and ovarian gene expression. Thus, the phenotypes of the AKO mice were very different from those seen in the neuronal knockout mice, suggesting distinct roles for PPARγ in these two cell types.

Obese Neuronal PPARγ Knockout Mice Are Leptin Sensitive but Show Impaired Glucose Tolerance and Fertility.

The peroxisome-proliferator activated receptor γ (PPARγ) is expressed in the hypothalamus in areas involved in energy homeostasis and glucose metabolism. In this study, we created a deletion of PPARγ brain-knockout (BKO) in mature neurons in female mice to investigate its involvement in metabolism and reproduction. We observed that there was no difference in age at puberty onset between female BKOs and littermate controls, but the BKOs gave smaller litters when mated and fewer oocytes when ovulated. The female BKO mice had regular cycles but showed an increase in the number of cycles with prolonged estrus. The mice also had increased luteinizing hormone (LH) levels during the LH surge and histological examination showed hemorrhagic corpora lutea. The mice were challenged with a 60% high-fat diet (HFD). Metabolically, the female BKO mice showed normal body weight, glucose and insulin tolerance, and leptin levels but were protected from obesity-induced leptin resistance. The neuronal knockout also prevented the reduction in estrous cycles due to the HFD. Examination of ovarian histology showed a decrease in the number of primary and secondary follicles in both genotypes due to the HFD, but the BKO ovaries showed an increase in the number of hemorrhagic follicles. In summary, our results show that neuronal PPARγ is required for optimal female fertility but is also involved in the adverse effects of diet-induced obesity by creating leptin resistance potentially through induction of the repressor Socs3.

Neuronal seipin knockout facilitates Aβ-induced neuroinflammation and neurotoxicity via reduction of PPARγ in hippocampus of mouse

BackgroundA characteristic phenotype of congenital generalized lipodystrophy 2 (CGL2) that is caused by loss-of-function of seipin gene is mental retardation. Seipin is highly expressed in hippocampal pyramidal cells and astrocytes. Neuronal knockout of seipin in mice (seipin-KO mice) reduces the hippocampal peroxisome proliferator-activated receptor gamma (PPARγ) level without the loss of pyramidal cells. The down-regulation of PPARγ has gained increasing attention in neuroinflammation of Alzheimer’s disease (AD). Thus, the present study focused on exploring the influence of seipin depletion on β-amyloid (Aβ)-induced neuroinflammation and Aβ neurotoxicity.MethodsAdult male seipin-KO mice were treated with a single intracerebroventricular (i.c.v.) injection of Aβ25–35 (1.2 nmol/mouse) or Aβ1–42 (0.1 nmol/mouse), generally a non-neurotoxic dose in wild-type (WT) mice. Spatial cognitive behaviors were assessed by Morris water maze and Y-maze tests, and hippocampal CA1 pyramidal cells and inflammatory responses were examined.ResultsThe Aβ25–35/1–42 injection in the seipin-KO mice caused approximately 30–35 % death of pyramidal cells and production of Hoechst-positive cells with the impairment of spatial memory. In comparison with the WT mice, the number of astrocytes and microglia in the seipin-KO mice had no significant difference, whereas the levels of IL-6 and TNF-α were slightly increased. Similarly, the Aβ25–35/1–42 injection in the seipin-KO mice rather than the WT mice could stimulate the activation of astrocytes or microglia and further elevated the levels of IL-6 and TNF-α. Treatment of the seipin-KO mice with the PPARγ agonist rosiglitazone (rosi) could prevent Aβ25–35/1–42-induced neuroinflammation and neurotoxicity, which was blocked by the PPARγ antagonist GW9962. In the seipin-KO mice, the level of glycogen synthase kinase-3β (GSK3β) phosphorylation at Tyr216 was elevated, while at Ser9, it was reduced compared to the WT mice, which were corrected by the rosi treatment but were unaffected by the Aβ25–35 injection.ConclusionsSeipin deficiency in astrocytes increases GSK3β activity and levels of IL-6 and TNF-α through reducing PPARγ, which can facilitate Aβ25–35/1–42-induced neuroinflammation to cause the death of neuronal cells and cognitive deficits.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0598-3) contains supplementary material, which is available to authorized users.

An Adenosine-Mediated Glial-Neuronal Circuit for Homeostatic Sleep.

The work presented here provides evidence for an adenosine-mediated regulation of sleep in response to waking (i.e., homeostatic sleep need), requiring activation of neuronal adenosine A1 receptors and controlled by glial adenosine kinase. Adenosine kinase acts as a highly sensitive and important metabolic sensor of the glial ATP/ADP and AMP ratio directly controlling intracellular adenosine concentration. Glial equilibrative adenosine transporters reflect the intracellular concentration to the extracellular milieu to activate neuronal adenosine receptors. Thus, adenosine mediates a glial-neuronal circuit linking glial metabolic state to neural-expressed sleep homeostasis. This indicates a metabolically related function(s) for this glial-neuronal circuit in the buildup and resolution of our need to sleep and suggests potential therapeutic targets more directly related to sleep function.

Abstract 033: Neuronal Knock-out of AT1 Receptor Attenuates the Development of Doca-salt-induced Hypertension

We previously reported that neurogenic hypertension is associated with an increase in A Disintegrin And Metalloprotease 17 (ADAM17) activity and a reduction of Angiotensin Converting Enzyme 2 (ACE2) activity in the hypothalamus. In addition, we showed that silencing ADAM17 or blocking Angiotensin (Ang)-II type 1 receptors (AT1R) in the central nervous system (CNS) prevented DOCA-salt hypertension, confirming the pivotal role of AT1R and ADAM17 in neurogenic hypertension. However, the interaction between AT1R, ADAM17, and ACE2 is still unclear. Since ADAM17 is known to be expressed in multiple cell types and can be activated by various receptors, we tested the hypothesis that neuronal AT1R are necessary for ADAM17-mediated ACE2 shedding in neurogenic hypertension. Male neuronal AT1R knockout (AT1R floxed crossed with Nefh-cre recombinase mice, 12-16 week-old, n=5) and littermate mice (n=8) were implanted with telemetry probes for continuous recording of blood pressure (BP) and heart rate (HR). Following DOCA-salt treatment, both strains developed hypertension, however mean arterial pressure (MAP; 123.9 ±6.4 vs. 138.4 ±4.3 mmHg) and HR (483.9 ±24.1 vs. 520.3 ±22.5 bmp) were significantly lower in neuronal AT1R knockout mice after 2 weeks of treatment, compared to controls. Western blot and enzyme activity assays from the hypothalamus of these DOCA-salt-treated mice revealed that the expression of pro-ADAM17 (inactive form) was significantly increased (+17.0 ±5.3%, P<0.05), while the activity of ADAM17 was decreased (-37.4 ±10.5%) in neuronal AT1R knockout animals. Concomitant to the down-regulation of ADAM17, both the expression and activity of ACE2 were found to be significantly (P<0.05) up-regulated in the hypothalamus of neuronal AT1R knockout mice, by +20.7 ±8.5% and +32.3 ±10.1%, respectively. These results suggest that activation of neuronal AT1R is responsible for ADAM17-mediated ACE2 shedding and the maintenance of neurogenic hypertension.

Hyperactivity of newborn Pten knock-out neurons results from increased excitatory synaptic drive.

Developing neurons must regulate morphology, intrinsic excitability, and synaptogenesis to form neural circuits. When these processes go awry, disorders, including autism spectrum disorder (ASD) or epilepsy, may result. The phosphatase Pten is mutated in some patients having ASD and seizures, suggesting that its mutation disrupts neurological function in part through increasing neuronal activity. Supporting this idea, neuronal knock-out of Pten in mice can cause macrocephaly, behavioral changes similar to ASD, and seizures. However, the mechanisms through which excitability is enhanced following Pten depletion are unclear. Previous studies have separately shown that Pten-depleted neurons can drive seizures, receive elevated excitatory synaptic input, and have abnormal dendrites. We therefore tested the hypothesis that developing Pten-depleted neurons are hyperactive due to increased excitatory synaptogenesis using electrophysiology, calcium imaging, morphological analyses, and modeling. This was accomplished by coinjecting retroviruses to either "birthdate" or birthdate and knock-out Pten in granule neurons of the murine neonatal dentate gyrus. We found that Pten knock-out neurons, despite a rapid onset of hypertrophy, were more active in vivo. Pten knock-out neurons fired at more hyperpolarized membrane potentials, displayed greater peak spike rates, and were more sensitive to depolarizing synaptic input. The increased sensitivity of Pten knock-out neurons was due, in part, to a higher density of synapses located more proximal to the soma. We determined that increased synaptic drive was sufficient to drive hypertrophic Pten knock-out neurons beyond their altered action potential threshold. Thus, our work contributes a developmental mechanism for the increased activity of Pten-depleted neurons.

A role for prolyl hydroxylase domain proteins in hippocampal synaptic plasticity

Hypoxia-inducible factors (HIFs) are key transcriptional regulators that play a major role in oxygen homeostasis. HIF activity is tightly regulated by oxygen-dependent hydroxylases, which additionally require iron and 2-oxoglutarate as cofactors. Inhibition of these enzymes has become a novel target to modulate the hypoxic response for therapeutic benefit. Inhibition of prolyl-4-hydroxylase domains (PHDs) have been shown to delay neuronal cell death and protect against ischemic injury in the hippocampus. In this study we have examined the effects of prolyl hydroxylase inhibition on synaptic transmission and plasticity in the hippocampus. Field excitatory postsynaptic potentials (fEPSPs) and excitatory postsynaptic currents (EPSCs) were elicited by stimulation of the Schaffer collateral pathway in the CA1 region of the hippocampus. Treatment of rat hippocampal slices with low concentrations (10 µM) of the iron chelator deferosoxamine (DFO) or the 2-oxoglutarate analogue dimethyloxalyl glycine (DMOG) had no effect on fEPSP. In contrast, application of 1 mM DMOG resulted in a significant decrease in fEPSP slope. Antagonism of the NMDA receptor attenuated the effects of DMOG on baseline synaptic signalling. In rat hippocampal slices pretreated with DMOG and DFO the induction of long-term potentiation (LTP) by tetanic stimulation was strongly impaired. Similarly, neuronal knockout of the single PHD family member PHD2 prevented murine hippocampal LTP. Preconditioning of PHD2 deficient hippocampi with either DMOG, DFO, or the PHD specific inhibitor JNJ-42041935, did not further decrease LTP suggesting that DMOG and DFO influences synaptic plasticity primarily by inhibiting PHDs rather than unspecific effects. These findings provide striking evidence for a modulatory role of PHD proteins on synaptic plasticity in the hippocampus.

Conditional neural knockout of the adenosine A2A receptor and pharmacological A2A antagonism reduce pilocarpine-induced tremulous jaw movements: Studies with a mouse model of parkinsonian tremor

Tremulous jaw movements are rapid vertical deflections of the lower jaw that resemble chewing but are not directed at any particular stimulus. In rats, tremulous jaw movements can be induced by a number of conditions that parallel those seen in human parkinsonism, including dopamine depletion, dopamine antagonism, and cholinomimetic drugs. Moreover, tremulous jaw movements in rats can be attenuated using antiparkinsonian agents such as L-DOPA, dopamine agonists, muscarinic antagonists, and adenosine A2A antagonists. In the present studies, a mouse model of tremulous jaw movements was established to investigate the effects of adenosine A2A antagonism, and a conditional neuronal knockout of adenosine A2A receptors, on cholinomimetic-induced tremulous jaw movements. The muscarinic agonist pilocarpine significantly induced tremulous jaw movements in a dose-dependent manner (0.25–1.0mg/kg IP). These movements occurred largely in the 3–7.5Hz local frequency range. Administration of the adenosine A2A antagonist MSX-3 (2.5–10.0mg/kg IP) significantly attenuated pilocarpine-induced tremulous jaw movements. Furthermore, adenosine A2A receptor knockout mice showed a significant reduction in pilocarpine-induced tremulous jaw movements compared to littermate controls. These results demonstrate the feasibility of using the tremulous jaw movement model in mice, and indicate that adenosine A2A receptor antagonism and deletion are capable of reducing cholinomimetic-induced tremulous jaw movements in mice. Future studies should investigate the effects of additional genetic manipulations using the mouse tremulous jaw movement model.