MicroRNA-186-5p controls GluA2 surface expression and synaptic scaling in hippocampal neurons.

Homeostatic synaptic scaling is a negative feedback response to fluctuations in synaptic strength induced by developmental or learning-related processes, which maintains neuronal activity stable. Although several components of the synaptic scaling apparatus have been characterized, the intrinsic regulatory mechanisms promoting scaling remain largely unknown. MicroRNAs may contribute to posttranscriptional control of mRNAs implicated in different stages of synaptic scaling, but their role in these mechanisms is still undervalued. Here, we report that chronic blockade of glutamate receptors of the AMPA and NMDA types in hippocampal neurons in culture induces changes in the neuronal mRNA and miRNA transcriptomes, leading to synaptic upscaling. Specifically, we show that synaptic activity blockade persistently down-regulates miR-186-5p. Moreover, we describe a conserved miR-186-5p-binding site within the 3'UTR of the mRNA encoding the AMPA receptor GluA2 subunit, and demonstrate that GluA2 is a direct target of miR-186-5p. Overexpression of miR-186 decreased GluA2 surface levels, increased synaptic expression of GluA2-lacking AMPA receptors, and blocked synaptic scaling, whereas inhibition of miR-186-5p increased GluA2 surface levels and the amplitude and frequency of AMPA receptor-mediated currents, and mimicked excitatory synaptic scaling induced by synaptic inactivity. Our findings elucidate an activity-dependent miRNA-mediated mechanism for regulation of AMPA receptor expression.

Disrupted AMPA Receptor Function upon Genetic- or Antibody-Mediated Loss of Autism-Associated CASPR2.

Neuropsychiatric disorders share susceptibility genes, suggesting a common origin. One such gene is CNTNAP2 encoding contactin-associated protein 2 (CASPR2), which harbours mutations associated to autism, schizophrenia, and intellectual disability. Antibodies targeting CASPR2 have also been recently described in patients with several neurological disorders, such as neuromyotonia, Morvan's syndrome, and limbic encephalitis. Despite the clear implication of CNTNAP2 and CASPR2 in neuropsychiatric disorders, the pathogenic mechanisms associated with alterations in CASPR2 function are unknown. Here, we show that Caspr2 is expressed in excitatory synapses in the cortex, and that silencing its expression in vitro or in vivo decreases the synaptic expression of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and the amplitude of AMPA receptor-mediated currents. Furthermore, Caspr2 loss of function blocks synaptic scaling in vitro and experience-dependent homoeostatic synaptic plasticity in the visual cortex. Patient CASPR2 antibodies decrease the dendritic levels of Caspr2 and synaptic AMPA receptor trafficking, and perturb excitatory transmission in the visual cortex. These results suggest that mutations in CNTNAP2 may contribute to alterations in AMPA receptor function and homoeostatic plasticity, and indicate that antibodies from anti-CASPR2 encephalitis patients affect cortical excitatory transmission.

Ghrelin triggers the synaptic incorporation of AMPA receptors in the hippocampus.

Ghrelin is a peptide mainly produced by the stomach and released into circulation, affecting energy balance and growth hormone release. These effects are guided largely by the expression of the ghrelin receptor growth hormone secretagogue type 1a (GHS-R1a) in the hypothalamus and pituitary. However, GHS-R1a is expressed in other brain regions, including the hippocampus, where its activation enhances memory retention. Herein we explore the molecular mechanism underlying the action of ghrelin on hippocampal-dependent memory. Our data show that GHS-R1a is localized in the vicinity of hippocampal excitatory synapses, and that its activation increases delivery of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic-type receptors (AMPARs) to synapses, producing functional modifications at excitatory synapses. Moreover, GHS-R1a activation enhances two different paradigms of long-term potentiation in the hippocampus, activates the phosphatidylinositol 3-kinase, and increases GluA1 AMPAR subunit and stargazin phosphorylation. We propose that GHS-R1a activation in the hippocampus enhances excitatory synaptic transmission and synaptic plasticity by regulating AMPAR trafficking. Our study provides insights into mechanisms that may mediate the cognition-enhancing effect of ghrelin, and suggests a possible link between the regulation of energy metabolism and learning.

Regulation of synapse composition by protein acetylation: the role of acetylated cortactin.

Protein acetylation affects synaptic plasticity and memory, but its effects on synapse composition have not been addressed. We found that protein acetylation promotes the dendritic clustering of the excitatory postsynaptic scaffold protein PSD95 in hippocampal neurons, without affecting the total levels of this protein. Cortactin, an F-actin-binding protein enriched in dendritic spines, is a substrate for acetylation and has a role in spine morphogenesis. Recent studies showed that cortactin acetylation changes its ability to bind F-actin and regulates cellular motility, but the function of cortactin acetylation in neuronal cells is so far unknown. We tested whether acetylation of cortactin influences its morphogenic function by overexpressing wild-type cortactin, or the mimetic mutants for acetylated or deacetylated cortactin, in hippocampal neurons, and found that cortactin acetylation has an impact on PSD95 clustering, independent from its function as actin dynamics regulator. Moreover, acetylated cortactin can rescue the reduction in PSD95 clustering mediated by knockdown of cortactin. We also found that acetylation of cortactin is correlated with decreased cortactin interaction with p140Cap and Shank1, and with lower cortactin phosphorylation at tyrosine 421. The neurotrophin BDNF promoted the acetylation of cortactin in hippocampal neurons, suggesting that BDNF may regulate excitatory synapses and PSD95 dendritic clustering at least in part by changing the acetylation level of cortactin. Our findings unravel an unsuspected role for cortactin acetylation in the regulation of PSD95 dendritic clustering, which may work in concert with cortactin's role in spine development.

Contactin-associated protein 1 (Caspr1) regulates the traffic and synaptic content of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors.

Glutamate receptors of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type mediate fast excitatory synaptic transmission in the CNS. Synaptic strength is modulated by AMPA receptor binding partners, which regulate receptor synaptic targeting and functional properties. We identify Contactin-associated protein 1 (Caspr1) as an AMPA receptor interactor. Caspr1 is present in synapses and interacts with AMPA receptors in brain synaptic fractions. Coexpression of Caspr1 with GluA1 increases the amplitude of glutamate-evoked currents. Caspr1 overexpression in hippocampal neurons increases the number and size of synaptic GluA1 clusters, whereas knockdown of Caspr1 decreases the intensity of synaptic GluA1 clusters. Hence, Caspr1 is a regulator of the trafficking of AMPA receptors to synapses.

Sinusitis and Late-Onset Asthma: A Red Flag of Eosinophilic Granulomatosis With Polyangiitis.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare systemic disease that develops with necrotizing granulomatous inflammation and is characterized by eosinophilia, asthma, and small vessel vasculitis. We report the case of a 74-year-old woman with a history of asthma, admitted to the Emergency Room with fever, headache, general malaise, weight loss and night sweats with one-month evolution, previously medicated with antibiotics without improvement. She presented with sinus palpation tenderness and lower leg bilateral sensitivity impairment. Laboratory tests showed neutrophilia and eosinophilia, normocytic anemia and elevated erythrocyte sedimentation rate and C-reactive protein. A computed tomography revealed sphenoid and maxillary sinusitis. Blood cultures and lumbar puncture were innocent. An extended autoimmune panel exposed a strong positive perinuclear anti-neutrophil cytoplasmic antibody - myeloperoxidase (pANCA-MPO). Sinus biopsy showed tissue infiltration by eosinophils, confirming EGPA. Corticosteroid (1 mg/kg/day) treatment was started with gradual improvement. Six months later there were no signs of active disease under prednisolone 10 mg and azathioprine 50 mg/day. This case highlights that refractory sinusitis in the presence of constitutional syndrome and peripheral eosinophilia should alert clinicians to the possibility of EGPA, particularly in patients with late-onset asthma.

Gallstone Ileus: A Rare Cause of Mechanical Bowel Obstruction.

A gallstone ileus is a rare cause of mechanical bowel obstruction, accounting for 1% to 4% of all cases. Twenty-five percent of the patients are 65 years of age or older and often present previous significant medical conditions. The authors report the case of an 87-year-old male patient, admitted with the diagnosis of community-acquired pneumonia, who later developed frequent episodes of biliary vomiting, intermittent constipation, and abdominal distension. Abdominal imaging (ultrasound and computed tomography (CT)) showed evidence of a localized inflammatory process in a small bowel loop but excluded vesicular lithiasis. After a failure in the medical approach with antibiotics, an exploratory laparotomy was performed, identifying the intestinal occlusion area, followed by an enterolithotomy at the specific area, and extraction of a 4 cm stone of acellular material. Posteriorly, the patient was treated for three weeks with a carbapenem and physical rehabilitation was promptly initiated with full recovery of his previous status. Gallstone ileus is a very challenging diagnosis and surgery is the treatment of choice. In elderly patients, it is important to promote prompt physical rehabilitation to prevent prolonged bed rest.

Cor Pulmonale Secondary to Severe Pulmonary Hypertension As the First Manifestation of Graves' Disease.

Pulmonary hypertension (PH), especially if severe, carries a significant morbidity and mortality. Herein we describe a case of an 88-year-old woman with severe heart failure and several hospitalizations that year for the same reason, rapid re-admission after discharge and loss of walking ability. Transthoracic echocardiography (TTE) revealed severe pulmonary hypertension (PASP=69 mmHg) and right ventricular dysfunction without left structural or functional dysfunction. Pulmonary thromboembolism, relevant pulmonary pathology was excluded, and an extended autoimmune study was also negative. Thyroid disorders were investigated, a Graves' disease with thyrotoxicosis was diagnosed and promptly treated with thiamazole, also known as methimazole. There was a rapid improvement in the clinical and hemodynamic status of the patient, stabilization of the right heart failure (HF), resolution of the volume overload and a TTE showed improvement with moderate PH (PASP=55 mmHg). This case shows a reversible cause of PH and highlights how treatment of Graves' disease can reduce pulmonary artery pressure and contribute to symptomatic relief and better quality of life.

Primary Adrenal Lymphoma: When B Symptoms Appear Hand in Hand with Adrenal Masses.

Primary adrenal lymphoma (PAL) is a very rare type of non-Hodgkin's lymphoma (NHL). Herein, we report a case of NHL of both adrenal glands in a 69-year-old man. The patient was admitted because of a 1-month history of B symptoms and symptomatic hypotension. Biochemical analysis showed normocytic normochromic anaemia, hyponatraemia, hyperkalaemia, and elevated lactate dehydrogenase, C-reactive protein and D-dimers. A computed tomography scan revealed bilateral enlargement of the adrenal glands. There was no evidence of endocrine adrenal dysfunction. The mass in the right adrenal gland was biopsied and histopathology identified a diffuse large B-cell lymphoma of the activated B-cell subtype. A positron emission tomography 18F-fluorodeoxyglucose scan showed intensive hypermetabolic lesions involving both adrenal glands, as well as other locations, with higher uptake in the adrenal glands. Taken together, these findings suggested the diagnosis of PAL. The patient responded favourably to debulking therapy and is currently undergoing chemotherapy. LEARNING POINTS: Primary adrenal lymphoma is a rare condition presenting with unspecific symptoms; diagnosis requires histopathological confirmation.Adrenal function must be evaluated to rule out insufficiency.Positron emission tomography may reveal hitherto unsuspected extension of disease and should be performed where available.

Leptin regulates AMPA receptor trafficking via PTEN inhibition.

The hormone leptin can cross the blood-brain barrier and influences numerous brain functions (Harvey, 2007). Indeed, recent studies have demonstrated that leptin regulates activity-dependent synaptic plasticity in the CA1 region of the hippocampus (Shanley et al., 2001; Li et al., 2002; Durakoglugil et al., 2005; Moult et al., 2009). It is well documented that trafficking of AMPA receptors is pivotal for hippocampal synaptic plasticity (Collingridge et al., 2004), but there is limited knowledge of how hormonal systems like leptin influence this process. In this study we have examined how leptin influences AMPA receptor trafficking and in turn how this impacts on excitatory synaptic function. Here we show that leptin preferentially increases the cell surface expression of GluR1 and the synaptic density of GluR2-lacking AMPA receptors in adult hippocampal slices. The leptin-induced increase in surface GluR1 required NMDA receptor activation and was associated with an increase in cytoplasmic PtdIns(3,4,5)P(3) levels. In addition, leptin enhanced phosphorylation of the lipid phosphatase PTEN which inhibits PTEN function and elevates PtdIns(3,4,5)P(3) levels. Moreover, inhibition of PTEN mimicked and occluded the effects of leptin on GluR1 trafficking and excitatory synaptic strength. These data indicate that leptin, via a novel pathway involving PTEN inhibition, promotes GluR1 trafficking to hippocampal synapses. This process has important implications for the role of leptin in hippocampal synaptic function in health and disease.

Ligand-independent activity of the ghrelin receptor modulates AMPA receptor trafficking and supports memory formation.

The biological signals of hunger, satiety, and memory are interconnected. The role of the hormone ghrelin in regulating feeding and memory makes ghrelin receptors attractive targets for associated disorders. We investigated the effects of the high ligand-independent activity of the ghrelin receptor GHS-R1a on the physiology of excitatory synapses in the hippocampus. Blocking this activity produced a decrease in the synaptic content of AMPA receptors in hippocampal neurons and a reduction in GluA1 phosphorylation at Ser845 Reducing the ligand-independent activity of GHS-R1a increased the surface diffusion of AMPA receptors and impaired AMPA receptor-dependent synaptic delivery induced by chemical long-term potentiation. Accordingly, we found that blocking this GHS-R1a activity impaired spatial and recognition memory in mice. These observations support a role for the ligand-independent activity of GHS-R1a in regulating AMPA receptor trafficking under basal conditions and in the context of synaptic plasticity that underlies learning.

Proteomic analysis of an interactome for long-form AMPA receptor subunits.

Glutamate receptors of the AMPA-type mediate fast excitatory synaptic transmission in the central nervous system and play key roles in synaptic plasticity. The binding of these receptors to a variety of proteins is known to regulate their targeting to the synapse and consequently to modulate synaptic strength, as well as to modify receptor characteristics. In this study, a proteomic screening was conducted in order to identify new binding partners for GluR4 AMPA receptor subunit. Immunoprecipitation of GluR4 and associated proteins was performed using rat cerebellum lysates and an heterologous systems overexpressing GluR4 AMPA receptor subunit. Isolated immuno-complexes were resolved by 1-D SDS-PAGE, and analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS). This approach led to the identification of several interactors, most of which are novel AMPA receptor partners, namely, cytoskeleton proteins, motor proteins, RNA processing proteins which are part of neuronal RNA granules, and kinases, among others. This study unravels new constituents of the macromolecular complex of long-form calcium-permeable AMPA receptors.

The Role of Ghrelin in Regulating Synaptic Function and Plasticity of Feeding-Associated Circuits.

Synaptic plasticity of the neuronal circuits associated with feeding behavior is regulated by peripheral signals as a response to changes in the energy status of the body. These signals include glucose, free fatty acids, leptin and ghrelin and are released into circulation, being able to reach the brain. Ghrelin, a small peptide released from the stomach, is an orexigenic hormone produced in peripheral organs, and its action regulates food intake, body weight and glucose homeostasis. Behavioral studies show that ghrelin is implicated in the regulation of both hedonic and homeostatic feeding and of cognition. Ghrelin-induced synaptic plasticity has been described in neuronal circuits associated with these behaviors. In this review, we discuss the neuromodulatory mechanisms induced by ghrelin in regulating synaptic plasticity in three main neuronal circuits previously associated with feeding behaviors, namely hypothalamic (homeostatic feeding), ventral tegmental (hedonic and motivational feeding) and hippocampal (cognitive) circuits. Given the central role of ghrelin in regulating feeding behaviors, and the altered ghrelin levels associated with metabolic disorders such as obesity and anorexia, it is of paramount relevance to understand the effects of ghrelin on synaptic plasticity of neuronal circuits associated with feeding behaviors.

A single exposure to morphine induces long-lasting hyporeactivity of rat caudate putamen dopaminergic nerve terminals.

The long-lasting effects of exposure to drugs of abuse on the brain is a central theme in drug addiction research. This study was designed to evaluate whether enduring neurochemical adaptations within caudate putamen can be evoked by a single injection of a high dose of morphine. Rats were pretreated once with 10 mg/kg morphine. Seven days later the effect of another injection of 10 mg/kg morphine on total levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanilic acid (HVA) in caudate putamen was assessed in half the pretreated animals. An irreversible mu-opioid receptor antagonist, cloccinamox (C-CAM; 0.1 mg/kg), significantly antagonized the elevation of the HVA/DA ratio, but not the elevation of the DOPAC/DA ratio induced by morphine in the caudate putamen from drug-naive animals. Pretreatment with morphine blunted changes in the HVA/DA ratio induced by another morphine challenge, but it had no effect on the DOPAC/DA ratio within the caudate putamen. Therefore, a single dose of 10 mg/kg morphine hampered nigrostriatal DA release and extraneuronal metabolism, mu-opioid receptor mediated, on another 10 mg/kg morphine challenge. This confirms that the first exposure to morphine does not go without long-lasting neurochemical adaptations.

Binding analysis between L-histidine immobilized and oligonucleotides by SPR and NMR.

Saturation transfer difference (STD) NMR technique and surface plasmon resonance (SPR) are used to study amino acid affinity supports-nucleotides interactions with L-histidine amino acid immobilized on a surface as model support. We have immobilized L-histidine ligand on a carboxymethyldextran-modified gold surface intended for surface plasmon resonance and we analyze the binding profiles of synthetic polynucleotides (1-6 base, sugar and backbone) by determining the equilibrium dissociation constant (KD). The SPR binding profile (square-shaped) is identical for all the complexes and the highest binding affinity can be found for polyA6 followed by polyG6. As expected, the 5'-mononucleotides have the lowest affinity. To further study the structural aspects of the interaction we investigate the polynucleotide binding preferences to L-histidine chromatography support by STD-NMR spectroscopy. These results revealed that an increase in the number of bases and backbone to 6 units leads to more contacts with the support, where the main driving force for the interaction with polynucleotides are through the base, except for polyC6, which is mainly through sugar-phosphate backbone. Therefore, the combination of SPR measurements with STD-NMR technique allowed to establish fine details of the molecular recognition process involved in amino acid affinity supports-nucleotides complexes.