Differential Gene and Protein Expression of Conjunctival Bleb Hyperfibrosis in Early Failure of Glaucoma Surgery

The early failure of glaucoma surgery is mainly caused by over-fibrosis at the subconjunctival space, causing obliteration of the filtration bleb. Because fibrosis has a suspected basis of genetic predisposition, we have undertaken a prospective study to identify upregulated profibrotic genes in a population of glaucoma patients with signs of conjunctival fibrosis and early postoperative surgical failure. Clinical data of re-operated fibrosis patients, hyperfibrosis patients who re-operated more than once in a short time, and control patients with no fibrosis were recorded and analyzed at each follow-up visit. Conjunctival-Tenon surgical specimens were obtained intraoperatively to evaluate the local expression of a panel of genes potentially associated with fibrosis. In order to correlate gene expression signatures with protein levels, we quantified secreted proteins in primary cultures of fibroblasts from patients. Expression of VEGFA, CXCL8, MYC, and CDKN1A was induced in the conjunctiva of hyperfibrosis patients. VEGFA and IL8 protein levels were also increased in fibroblast supernatants. We propose that an increase in these proteins could be useful in detecting conjunctival fibrosis in glaucoma patients undergoing filtering surgery. Molecular markers could be crucial for early detection of patients at high risk of failure of filtration surgery, leading to more optimal and personalized treatments.

Sigma-1 Receptor Activation Is Protective against TGFβ2-Induced Extracellular Matrix Changes in Human Trabecular Meshwork Cells

The trabecular meshwork (TM) route is the principal outflow egress of the aqueous humor. Actin cytoskeletal remodeling in the TM and extracellular matrix (ECM) deposition increase TM stiffness, outflow resistance, and elevate intraocular pressure (IOP). These alterations are strongly linked to transforming growth factor-β2 (TGFβ2), a known profibrotic cytokine that is markedly elevated in the aqueous humor of glaucomatous eyes. Sigma-1 receptor (S1R) has been shown to have neuroprotective effects in the retina, but data are lacking about its role in the TM. In this study, we identified the presence of S1R in mouse TM tissue and investigated the effect of an S1R agonist fluvoxamine (FLU) on TGFβ2-induced human TM cells regarding cell proliferation; ECM-related functions, including F-actin reorganization; and the accumulation of ECM elements. TGFβ2 increased the proliferation, cytoskeletal remodeling, and protein levels of fibronectin, collagen type IV, and connective tissue growth factor, and decreased the level of matrix metalloproteinase-2. Most importantly, FLU reversed all these effects of TGFβ2, suggesting that S1R agonists could be potential candidates for preserving TM function and thus maintaining normal IOP.

Fast cycling of intermittent hypoxia in a physiomimetic 3D environment: A novel tool for the study of the parenchymal effects of sleep apnea

Background: Patients with obstructive sleep apnea (OSA) experience recurrent hypoxemic events with a frequency sometimes exceeding 60 events/h. These episodic events induce downstream transient hypoxia in the parenchymal tissue of all organs, thereby eliciting the pathological consequences of OSA. Whereas experimental models currently apply intermittent hypoxia to cells conventionally cultured in 2D plates, there is no well-characterized setting that will subject cells to well-controlled intermittent hypoxia in a 3D environment and enable the study of the effects of OSA on the cells of interest while preserving the underlying tissue environment. Aim: To design and characterize an experimental approach that exposes cells to high-frequency intermittent hypoxia mimicking OSA in 3D (hydrogels or tissue slices). Methods: Hydrogels made from lung extracellular matrix (L-ECM) or brain tissue slices (300-800-μm thickness) were placed on a well whose bottom consisted of a permeable silicone membrane. The chamber beneath the membrane was subjected to a square wave of hypoxic/normoxic air. The oxygen concentration at different depths within the hydrogel/tissue slice was measured with an oxygen microsensor. Results: 3D-seeded cells could be subjected to well-controlled and realistic intermittent hypoxia patterns mimicking 60 apneas/h when cultured in L-ECM hydrogels ≈500 μm-thick or ex-vivo in brain slices 300-500 μm-thick. Conclusion: This novel approach will facilitate the investigation of the effects of intermittent hypoxia simulating OSA in 3D-residing cells within the parenchyma of different tissues/organs.

Human CASPR2 antibodies reversibly alter memory and the CASPR2 protein complex

OBJECTIVE

The encephalitis associated with antibodies against contactin-associated protein-like 2 (CASPR2) is presumably antibody-mediated but the antibody effects and whether they cause behavioral alterations are not well-known. Here, we used a mouse model of patients' IgG transfer and super-resolution microscopy to demonstrate the antibody pathogenicity.

METHODS

IgG from patients with anti-CASPR2 encephalitis or healthy controls were infused into the cerebroventricular system of mice. The levels and colocalization of CASPR2 with transient axonal glycoprotein-1 (TAG1) were determined with Stimulated Emission Depletion (STED) microscopy (40-70μm lateral resolution). Hippocampal clusters of Kv1.1 voltage-gated potassium channels (VGKC) and GluA1-containing AMPA receptors were quantified with confocal microscopy. Behavioral alterations were assessed with standard behavioral paradigms. Cultured neurons were used to determine the levels of intracellular CASPR2 and TAG1 after exposure to patients' IgG.

RESULTS

Infusion of patients' IgG, but not control IgG, caused memory impairment along with hippocampal reduction of surface CASPR2 clusters and decreased CASPR2/TAG1 colocalization. In cultured neurons, patients' IgG led to an increase of intracellular CASPR2 without affecting TAG1, suggesting selective CASPR2 internalization. Additionally, mice infused with patients' IgG showed decreased levels of Kv1.1 and GluA1 (two CASPR2 regulated proteins). All these alterations and the memory deficit reverted to normal after removing patients' IgG.

INTERPRETATION

IgG from patients with anti-CASPR2 encephalitis cause reversible memory impairment, inhibit the interaction of CASPR2/TAG1, and decrease the levels of CASPR2 and related proteins (VGKC, AMPAR). These findings fulfill the postulates of antibody-mediated disease and provide a biological basis for antibody-removing treatment approaches. This article is protected by copyright. All rights reserved.

Neutrophils and neutrophil extracellular trap components: Emerging biomarkers and therapeutic targets for age-related eye diseases

Age-related eye diseases, including dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy, represent a major global health issue based on their increasing prevalence and disabling action. Unraveling the molecular mechanisms underlying these diseases will provide novel opportunities to reduce the burden of age-related eye diseases and improve eye health, contributing to sustainable development goals achievement. The impairment of neutrophil extracellular traps formation/degradation processes seems to be one of these mechanisms. These traps formed by a meshwork of DNA and neutrophil cytosolic granule proteins may exacerbate the inflammatory response promoting chronic inflammation, a pivotal cause of age-related diseases. In this review, we describe current findings that suggest the role of neutrophils and their traps in the pathogenesis of the above-mentioned age-related eye diseases. Furthermore, we discuss why these cells and their constituents could be biomarkers and therapeutic targets for dry eye, glaucoma, age-related macular degeneration, and diabetic retinopathy. We also examine the therapeutic potential of some neutrophil function modulators and provide several recommendations for future research in age-related eye diseases.

Hypothalamic pregnenolone mediates recognition memory in the context of metabolic disorders

Obesity and type 2 diabetes are associated with cognitive dysfunction. Because the hypothalamus is implicated in energy balance control and memory disorders, we hypothesized that specific neurons in this brain region are at the interface of metabolism and cognition. Acute obesogenic diet administration in mice impaired recognition memory due to defective production of the neurosteroid precursor pregnenolone in the hypothalamus. Genetic interference with pregnenolone synthesis by Star deletion in hypothalamic POMC, but not AgRP neurons, deteriorated recognition memory independently of metabolic disturbances. Our data suggest that pregnenolone's effects on cognitive function were mediated via an autocrine mechanism on POMC neurons, influencing hippocampal long-term potentiation. The relevance of central pregnenolone on cognition was also confirmed in metabolically unhealthy patients with obesity. Our data reveal an unsuspected role for POMC neuron-derived neurosteroids in cognition. These results provide the basis for a framework to investigate new facets of POMC neuron biology with implications for cognitive disorders.

Allosteric Modulation of NMDARs Reverses Patients' Autoantibody Effects in Mice

Background and Objectives

To demonstrate that an analog (SGE-301) of a brain-derived cholesterol metabolite, 24(S)-hydroxycholesterol, which is a selective positive allosteric modulator (PAM) of NMDA receptors (NMDARs), is able to reverse the memory and synaptic alterations caused by CSF from patients with anti-NMDAR encephalitis in an animal model of passive transfer of antibodies.

Methods

Four groups of mice received (days 1–14) patients' or controls' CSF via osmotic pumps connected to the cerebroventricular system and from day 11 were treated with daily subcutaneous injections of SGE-301 or vehicle (no drug). Visuospatial memory, locomotor activity (LA), synaptic NMDAR cluster density, hippocampal long-term potentiation (LTP), and paired-pulse facilitation (PPF) were assessed on days 10, 13, 18, and 26 using reported techniques.

Results

On day 10, mice infused with patients' CSF, but not controls' CSF, presented a significant visuospatial memory deficit, reduction of NMDAR clusters, and impairment of LTP, whereas LA and PPF were unaffected. These alterations persisted until day 18, the time of maximal deficits in this model. In contrast, mice that received patients' CSF but from day 11 were treated with SGE-301 showed memory recovery (day 13), and on day 18, all paradigms (memory, NMDAR clusters, and LTP) had reversed to values similar to those of controls. On day 26, no differences were observed among experimental groups.

Discussion

An oxysterol biology-based PAM of NMDARs is able to reverse the synaptic and memory deficits caused by CSF from patients with anti-NMDAR encephalitis. These findings suggest a novel adjuvant treatment approach that deserves future clinical evaluation.

Proton Sensing on the Ocular Surface: Implications in Eye Pain

Protons reaching the eyeball from exogenous acidic substances or released from damaged cells during inflammation, immune cells, after tissue injury or during chronic ophthalmic conditions, activate or modulate ion channels present in sensory nerve fibers that innervate the ocular anterior surface. Their identification as well as their role during disease is critical for the understanding of sensory ocular pathophysiology. They are likely to mediate some of the discomfort sensations accompanying several ophthalmic formulations and may represent novel targets for the development of new therapeutics for ocular pathologies. Among the ion channels expressed in trigeminal nociceptors innervating the anterior surface of the eye (cornea and conjunctiva) and annex ocular structures (eyelids), members of the TRP and ASIC families play a critical role in ocular acidic pain. Low pH (pH 6) activates TRPV1, a polymodal ion channel also activated by heat, capsaicin and hyperosmolar conditions. ASIC1, ASIC3 and heteromeric ASIC1/ASIC3 channels present in ocular nerve terminals are activated at pH 7.2–6.5, inducing pain by moderate acidifications of the ocular surface. These channels, together with TRPA1, are involved in acute ocular pain, as well as in painful sensations during allergic keratoconjunctivitis or other ophthalmic conditions, as blocking or reducing channel expression ameliorates ocular pain. TRPV1, TRPA1 and other ion channels are also present in corneal and conjunctival cells, promoting inflammation of the ocular surface after injury. In addition to the above-mentioned ion channels, members of the K_2P and P2X ion channel families are also expressed in trigeminal neurons, however, their role in ocular pain remains unclear to date. In this report, these and other ion channels and receptors involved in acid sensing during ocular pathologies and pain are reviewed.

Functional Interaction Between Caveolin 1 and LRRC8-Mediated Volume-Regulated Anion Channel

Volume-regulated anion channel (VRAC), constituted by leucine-rich repeat-containing 8 (LRRC8) heteromers, is crucial for volume homeostasis in vertebrate cells. This widely expressed channel has been associated with membrane potential modulation, proliferation, migration, apoptosis, and glutamate release. VRAC is activated by cell swelling and by low cytoplasmic ionic strength or intracellular guanosine 5′-O-(3-thiotriphosphate) (GTP-γS) in isotonic conditions. Despite the substantial number of studies that characterized the biophysical properties of VRAC, its mechanism of activation remains a mystery. Different evidence suggests a possible effect of caveolins in modulating VRAC activity: (1) Caveolin 1 (Cav1)-deficient cells display insignificant swelling-induced Cl^– currents mediated by VRAC, which can be restored by Cav1 expression; (2) Caveolin 3 (Cav3) knockout mice display reduced VRAC currents; and (3) Interaction between LRRC8A, the essential subunit for VRAC, and Cav3 has been found in transfected human embryonic kidney 293 (HEK 293) cells. In this study, we demonstrate a physical interaction between endogenous LRRC8A and Cav1 proteins, that is enhanced by hypotonic stimulation, suggesting that this will increase the availability of the channel to Cav1. In addition, LRRC8A targets plasma membrane regions outside caveolae of HEK 293 cells where it associates with non-caveolar Cav1. We propose that a rise in cell membrane tension by hypotonicity would flatten caveolae, as described previously, increasing the amount of Cav1 outside of caveolar structures interacting with VRAC. Besides, the expression of Cav1 in HEK Cav1- cells increases VRAC current density without changing the main biophysical properties of the channel. The present study provides further evidence on the relevance of Cav1 on the activation of endothelial VRAC through a functional molecular interaction.

Identification of the GlialCAM interactome: the G protein-coupled receptors GPRC5B and GPR37L1 modulate megalencephalic leukoencephalopathy proteins

Megalencephalic Leukoencephalopathy with subcortical Cysts (MLC) is a type of vacuolating leukodystrophy, which is mainly caused by mutations in MLC1 or GLIALCAM. The two MLC-causing genes encode for membrane proteins of yet unknown function that have been linked to the regulation of different chloride channels such as the ClC-2 and VRAC. To gain insight into the role of MLC proteins, we have determined the brain GlialCAM interacting proteome. The proteome includes different transporters and ion channels known to be involved in the regulation of brain homeostasis, proteins related to adhesion or signaling as several G protein-coupled receptors (GPCRs), including the orphan GPRC5B and the proposed prosaposin receptor GPR37L1. Focusing on these two GPCRs, we could validate that they interact directly with MLC proteins. The inactivation of Gpr37l1 in mice upregulated MLC proteins without altering their localization. Conversely, a reduction of GPRC5B levels in primary astrocytes downregulated MLC proteins, leading to an impaired activation of ClC-2 and VRAC. The interaction between the GPCRs and MLC1 was dynamically regulated upon changes in the osmolarity or potassium concentration. We propose that GlialCAM and MLC1 associate with different integral membrane proteins modulating their functions and acting as a recruitment site for various signaling components as the GPCRs identified here. We hypothesized that the GlialCAM/MLC1 complex is working as an adhesion molecule coupled to a tetraspanin-like molecule performing regulatory effects through direct binding or influencing signal transduction events.

Encephalitis with Autoantibodies against the Glutamate Kainate Receptors GluK2

OBJECTIVE

The objective of this study was to report the identification of antibodies against the glutamate kainate receptor subunit 2 (GluK2-abs) in patients with autoimmune encephalitis, and describe the clinical-immunological features and antibody effects.

METHODS

Two sera from 8 patients with similar rat brain immunostaining were used to precipitate the antigen from neuronal cultures. A cell-based assay (CBA) with GluK2-expressing HEK293 cells was used to assess 596 patients with different neurological disorders, and 23 healthy controls. GluK2-ab effects were determined by confocal microscopy in cultured neurons and electrophysiology in GluK2-expressing HEK293 cells.

RESULTS

Patients' antibodies precipitated GluK2. GluK2 antibody-specificity was confirmed by CBA, immunoprecipitation, GluK2-immunoabsorption, and GluK2 knockout brain immunohistochemistry. In 2 of 8 samples, antibodies reacted with additional GluK2 epitopes present in GluK1 or GluK3; in both, the reactivity was abrogated after GluK2 immuno-absorption. Six of 8 patients developed acute encephalitis and clinical or magnetic resonance imaging (MRI) features of predominant cerebellar involvement (4 presenting as cerebellitis, which in 2 patients caused obstructive hydrocephalus), and 2 patients had other syndromes (1 with cerebellar symptoms). One of the samples showed mild reactivity with non-kainate receptors (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors [AMPAR] and N-methyl-D-aspartate receptors [NMDAR]) leading to identify 6 additional cases with GluK2-abs among patients with anti-AMPAR (5/71) or anti-NMDAR encephalitis (1/73). GluK2-abs internalized GluK2 in HEK293 cells and neurons; these antibody-effects were reversible in neurons. A significant reduction of GluK2-mediated currents was observed in cells treated with patients' GluK2 serum following the time frame of antibody-mediated GluK2 internalization.

INTERPRETATION

GluK2-abs associate with an encephalitis with prominent clinicoradiological cerebellar involvement. The antibody effects are predominantly mediated by internalization of GluK2. ANN NEUROL 2021;90:107-123.

RTP801 regulates motor cortex synaptic transmission and learning

BACKGROUND

RTP801/REDD1 is a stress-regulated protein whose upregulation is necessary and sufficient to trigger neuronal death in in vitro and in vivo models of Parkinson's and Huntington's diseases and is up regulated in compromised neurons in human postmortem brains of both neurodegenerative disorders. Indeed, in both Parkinson's and Huntington's disease mouse models, RTP801 knockdown alleviates motor-learning deficits.

RESULTS

We investigated the physiological role of RTP801 in neuronal plasticity and we found RTP801 in rat, mouse and human synapses. The absence of RTP801 enhanced excitatory synaptic transmission in both neuronal cultures and brain slices from RTP801 knock-out (KO) mice. Indeed, RTP801 KO mice showed improved motor learning, which correlated with lower spine density but increased basal filopodia and mushroom spines in the motor cortex layer V. This paralleled with higher levels of synaptosomal GluA1 and TrkB receptors in homogenates derived from KO mice motor cortex, proteins that are associated with synaptic strengthening.

CONCLUSIONS

Altogether, these results indicate that RTP801 has an important role modulating neuronal plasticity and motor learning. They will help to understand its role in neurodegenerative disorders where RTP801 levels are detrimentally upregulated.

Allosteric modulation of NMDA receptors prevents the antibody effects of patients with anti-NMDAR encephalitis

Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis is an immune-mediated disease characterized by a complex neuropsychiatric syndrome in association with an antibody-mediated decrease of NMDAR. About 85% of patients respond to immunotherapy (and removal of an associated tumour if it applies), but it often takes several months or more than 1 year for patients to recover. There are no complementary treatments, beyond immunotherapy, to accelerate this recovery. Previous studies showed that SGE-301, a synthetic analogue of 24(S)-hydroxycholesterol, which is a potent and selective positive allosteric modulator of NMDAR, reverted the memory deficit caused by phencyclidine (a non-competitive antagonist of NMDAR), and prevented the NMDAR dysfunction caused by patients’ NMDAR antibodies in cultured neurons. An advantage of SGE-301 is that it is optimized for systemic delivery such that plasma and brain exposures are sufficient to modulate NMDAR activity. Here, we used SGE-301 to confirm that in cultured neurons it prevented the antibody-mediated reduction of receptors, and then we applied it to a previously reported mouse model of passive cerebroventricular transfer of patient’s CSF antibodies. Four groups were established: mice receiving continuous (14-day) infusion of patients’ or controls’ CSF, treated with daily subcutaneous administration of SGE-301 or vehicle (no drug). The effects on memory were examined with the novel object location test at different time points, and the effects on synaptic levels of NMDAR (assessed with confocal microscopy) and plasticity (long-term potentiation) were examined in the hippocampus on Day 18, which in this model corresponds to the last day of maximal clinical and synaptic alterations. As expected, mice infused with patient’s CSF antibodies, but not those infused with controls’ CSF, and treated with vehicle developed severe memory deficit without locomotor alteration, accompanied by a decrease of NMDAR clusters and impairment of long-term potentiation. All antibody-mediated pathogenic effects (memory, synaptic NMDAR, long-term potentiation) were prevented in the animals treated with SGE-301, despite this compound not antagonizing antibody binding. Additional investigations on the potential mechanisms related to these SGE-301 effects showed that (i) in cultured neurons SGE-301 prolonged the decay time of NMDAR-dependent spontaneous excitatory postsynaptic currents suggesting a prolonged open time of the channel; and (ii) it significantly decreased, without fully preventing, the internalization of antibody-bound receptors suggesting that additional, yet unclear mechanisms, contribute in keeping unchanged the surface NMDAR density. Overall, these findings suggest that SGE-301, or similar NMDAR modulators, could potentially serve as complementary treatment for anti-NMDAR encephalitis and deserve future investigations.

AMPAR/TARP stoichiometry differentially modulates channel properties

AMPARs control fast synaptic communication between neurons and their function relies on auxiliary subunits, which importantly modulate channel properties. Although it has been suggested that AMPARs can bind to TARPs with variable stoichiometry, little is known about the effect that this stoichiometry exerts on certain AMPAR properties. Here we have found that AMPARs show a clear stoichiometry-dependent modulation by the prototypical TARP γ2 although the receptor still needs to be fully saturated with γ2 to show some typical TARP-induced characteristics (i.e. an increase in channel conductance). We also uncovered important differences in the stoichiometric modulation between calcium-permeable and calcium-impermeable AMPARs. Moreover, in heteromeric AMPARs, γ2 positioning in the complex is important to exert certain TARP-dependent features. Finally, by comparing data from recombinant receptors with endogenous AMPAR currents from mouse cerebellar granule cells, we have determined a likely presence of two γ2 molecules at somatic receptors in this cell type.

TRESK background K+ channel deletion selectively uncovers enhanced mechanical and cold sensitivity

KEY POINTS

TRESK background K⁺ channel is expressed in sensory neurons and acts as a brake to reduce neuronal activation. Deletion of the channel enhances the excitability of nociceptors. Skin nociceptive C-fibres show an enhanced activation by cold and mechanical stimulation in TRESK knockout animals. Channel deletion selectively enhances mechanical and cold sensitivity in mice, without altering sensitivity to heat. These results indicate that the channel regulates the excitability of specific neuronal subpopulations involved in mechanosensitivity and cold-sensing.

ABSTRACT

Background potassium-permeable ion channels play a critical role in tuning the excitability of nociceptors, yet the precise role played by different subsets of channels is not fully understood. Decreases in TRESK (TWIK-related spinal cord K⁺ channel) expression/function enhance excitability of sensory neurons, but its role in somatosensory perception and nociception is poorly understood. Here, we used a TRESK knockout (KO) mouse to address these questions. We show that TRESK regulates the sensitivity of sensory neurons in a modality-specific manner, contributing to mechanical and cold sensitivity but without any effect on heat sensitivity. Nociceptive neurons isolated from TRESK KO mice show a decreased threshold for activation and skin nociceptive C-fibres show an enhanced activation by cold and mechanical stimulation that was also observed in behavioural tests in vivo. TRESK is also involved in osmotic pain and in early phases of formalin-induced inflammatory pain, but not in the development of mechanical and heat hyperalgesia during chronic pain. In contrast, mice lacking TRESK present cold allodynia that is not further enhanced by oxaliplatin. In summary, genetic removal of TRESK uncovers enhanced mechanical and cold sensitivity, indicating that the channel regulates the excitability of specific neuronal subpopulations involved in mechanosensitivity and cold-sensing, acting as a brake to prevent activation by innocuous stimuli.

l-Serine dietary supplementation is associated with clinical improvement of loss-of-function GRIN2B-related pediatric encephalopathy

Autosomal dominant mutations in GRIN2B are associated with severe encephalopathy, but little is known about the pathophysiological outcomes and any potential therapeutic interventions. Genetic studies have described the association between de novo mutations of genes encoding the subunits of the N-methyl-d-aspartate receptor (NMDAR) and severe neurological conditions. Here, we evaluated a missense mutation in GRIN2B, causing a proline-to-threonine switch (P553T) in the GluN2B subunit of NMDAR, which was found in a 5-year-old patient with Rett-like syndrome with severe encephalopathy. Structural molecular modeling predicted a reduced pore size of the mutant GluN2B-containing NMDARs. Electrophysiological recordings in a HEK-293T cell line expressing the mutated subunit confirmed this prediction and showed an associated reduced glutamate affinity. Moreover, GluN2B(P553T)-expressing primary murine hippocampal neurons showed decreased spine density, concomitant with reduced NMDA-evoked currents and impaired NMDAR-dependent insertion of the AMPA receptor subunit GluA1 at stimulated synapses. Furthermore, the naturally occurring coagonist d-serine restored function to GluN2B(P553T)-containing NMDARs. l-Serine dietary supplementation of the patient was hence initiated, resulting in the increased abundance of d-serine in the plasma and brain. The patient has shown notable improvements in motor and cognitive performance and communication after 11 and 17 months of l-serine dietary supplementation. Our data suggest that l-serine supplementation might ameliorate GRIN2B-related severe encephalopathy and other neurological conditions caused by glutamatergic signaling deficiency.

LGI1 antibodies alter Kv1.1 and AMPA receptors changing synaptic excitability, plasticity and memory

Leucine-rich glioma-inactivated 1 (LGI1) is a secreted neuronal protein that forms a trans-synaptic complex that includes the presynaptic disintegrin and metalloproteinase domain-containing protein 23 (ADAM23), which interacts with voltage-gated potassium channels Kv1.1, and the postsynaptic ADAM22, which interacts with AMPA receptors. Human autoantibodies against LGI1 associate with a form of autoimmune limbic encephalitis characterized by severe but treatable memory impairment and frequent faciobrachial dystonic seizures. Although there is evidence that this disease is immune-mediated, the underlying LGI1 antibody-mediated mechanisms are unknown. Here, we used patient-derived immunoglobulin G (IgG) antibodies to determine the main epitope regions of LGI1 and whether the antibodies disrupt the interaction of LGI1 with ADAM23 and ADAM22. In addition, we assessed the effects of patient-derived antibodies on Kv1.1, AMPA receptors, and memory in a mouse model based on cerebroventricular transfer of patient-derived IgG. We found that IgG from all patients (n = 25), but not from healthy participants (n = 20), prevented the binding of LGI1 to ADAM23 and ADAM22. Using full-length LGI1, LGI3, and LGI1 constructs containing the LRR1 domain (EPTP1-deleted) or EPTP1 domain (LRR3-EPTP1), IgG from all patients reacted with epitope regions contained in the LRR1 and EPTP1 domains. Confocal analysis of hippocampal slices of mice infused with pooled IgG from eight patients, but not pooled IgG from controls, showed a decrease of total and synaptic levels of Kv1.1 and AMPA receptors. The effects on Kv1.1 preceded those involving the AMPA receptors. In acute slice preparations of hippocampus, patch-clamp analysis from dentate gyrus granule cells and CA1 pyramidal neurons showed neuronal hyperexcitability with increased glutamatergic transmission, higher presynaptic release probability, and reduced synaptic failure rate upon minimal stimulation, all likely caused by the decreased expression of Kv1.1. Analysis of synaptic plasticity by recording field potentials in the CA1 region of the hippocampus showed a severe impairment of long-term potentiation. This defect in synaptic plasticity was independent from Kv1 blockade and was possibly mediated by ineffective recruitment of postsynaptic AMPA receptors. In parallel with these findings, mice infused with patient-derived IgG showed severe memory deficits in the novel object recognition test that progressively improved after stopping the infusion of patient-derived IgG. Different from genetic models of LGI1 deficiency, we did not observe aberrant dendritic sprouting or defective synaptic pruning as potential cause of the symptoms. Overall, these findings demonstrate that patient-derived IgG disrupt presynaptic and postsynaptic LGI1 signalling, causing neuronal hyperexcitability, decreased plasticity, and reversible memory deficits.

Mechanisms of CPT1C-Dependent AMPAR Trafficking Enhancement

In neurons, AMPA receptor (AMPAR) function depends essentially on their constituent components:the ion channel forming subunits and ion channel associated proteins. On the other hand, AMPAR trafficking is tightly regulated by a vast number of intracellular neuronal proteins that bind to AMPAR subunits. It has been recently shown that the interaction between the GluA1 subunit of AMPARs and carnitine palmitoyltransferase 1C (CPT1C), a novel protein partner of AMPARs, is important in modulating surface expression of these ionotropic glutamate receptors. Indeed, synaptic transmission in CPT1C knockout (KO) mice is diminished supporting a positive trafficking role for that protein. However, the molecular mechanisms of such modulation remain unknown although a putative role of CPT1C in depalmitoylating GluA1 has been hypothesized. Here, we explore that possibility and show that CPT1C effect on AMPARs is likely due to changes in the palmitoylation state of GluA1. Based on in silico analysis, Ser 252, His 470 and Asp 474 are predicted to be the catalytic triad responsible for CPT1C palmitoyl thioesterase (PTE) activity. When these residues are mutated or when PTE activity is inhibited, the CPT1C effect on AMPAR trafficking is abolished, validating the CPT1C catalytic triad as being responsible for PTE activity on AMPAR. Moreover, the histidine residue (His 470) of CPT1C is crucial for the increase in GluA1 surface expression in neurons and the H470A mutation impairs the depalmitoylating catalytic activity of CPT1C. Finally, we show that CPT1C effect seems to be specific for this CPT1 isoform and it takes place solely at endoplasmic reticulum (ER). This work adds another facet to the impressive degree of molecular mechanisms regulating AMPAR physiology.

Anionic Phospholipids Bind to and Modulate the Activity of Human TRESK Background K+ Channel

The background K⁺ channel TRESK regulates sensory neuron excitability, and changes in its function/expression contribute to neuronal hyperexcitability after injury/inflammation, making it an attractive therapeutic target for pain-related disorders. Factors that change lipid bilayer composition/properties (including volatile anesthetics, chloroform, chlorpromazine, shear stress, and cell swelling/shrinkage) modify TRESK current, but despite the importance of anionic phospholipids (e.g., PIP₂) in the regulation of many ion channels, it remains unknown if membrane lipids affect TRESK function. We describe that both human and rat TRESK contain potential anionic phospholipid binding sites (apbs) in the large cytoplasmic loop, but only the human channel is able to bind to multilamellar vesicles (MLVs), enriched with anionic phospholipids, suggesting an electrostatically mediated interaction. We mapped the apbs to a short stretch of 14 amino acids in the loop, located at the membrane-cytosol interface. Disruption of electrostatic lipid-TRESK interactions inhibited hTRESK currents, while subsequent application of Folch Fraction MLVs or a PIP₂ analog activated hTRESK, an effect that was absent in the rat ortholog. Strikingly, channel activation by anionic phospholipids was conferred to rTRESK by replacing the equivalent rat sequence with the human apbs. Finally, in the presence of a calcineurin inhibitor, stimulation of a G_q/11-linked GPCR reduced hTRESK current, revealing a likely inhibitory effect of membrane lipid hydrolysis on hTRESK activity. This novel regulation of hTRESK by anionic phospholipids is a characteristic of the human channel that is not present in rodent orthologs. This must be considered when extrapolating results from animal models and may open the door to the development of novel channel modulators as analgesics.

Rett-like Severe Encephalopathy Caused by a De Novo GRIN2B Mutation Is Attenuated by D-serine Dietary Supplement

BACKGROUND

N-Methyl-D-aspartate receptors (NMDARs) play pivotal roles in synaptic development, plasticity, neural survival, and cognition. Despite recent reports describing the genetic association between de novo mutations of NMDAR subunits and severe psychiatric diseases, little is known about their pathogenic mechanisms and potential therapeutic interventions. Here we report a case study of a 4-year-old Rett-like patient with severe encephalopathy carrying a missense de novo mutation in GRIN2B(p.P553T) coding for the GluN2B subunit of NMDAR.

METHODS

We generated a dynamic molecular model of mutant GluN2B-containing NMDARs. We expressed the mutation in cell lines and primary cultures, and we evaluated the putative morphological, electrophysiological, and synaptic plasticity alterations. Finally, we evaluated D-serine administration as a therapeutic strategy and translated it to the clinical practice.

RESULTS

Structural molecular modeling predicted a reduced pore size of mutant NMDARs. Electrophysiological recordings confirmed this prediction and also showed gating alterations, a reduced glutamate affinity associated with a strong decrease of NMDA-evoked currents. Moreover, GluN2B(P553T)-expressing neurons showed decreased spine density, concomitant with reduced NMDA-evoked currents and impaired NMDAR-dependent insertion of GluA1 at stimulated synapses. Notably, the naturally occurring coagonist D-serine was able to attenuate hypofunction of GluN2B(p.P553T)-containing NMDARs. Hence, D-serine dietary supplementation was initiated. Importantly, the patient has shown remarkable motor, cognitive, and communication improvements after 17 months of D-serine dietary supplementation.

CONCLUSIONS

Our data suggest that hypofunctional NMDARs containing GluN2B(p.P553T) can contribute to Rett-like encephalopathy and that their potentiation by D-serine treatment may underlie the associated clinical improvement.

Leukoencephalopathy-causing CLCN2 mutations are associated with impaired Cl- channel function and trafficking

KEY POINTS

Characterisation of most mutations found in CLCN2 in patients with CC2L leukodystrophy show that they cause a reduction in function of the chloride channel ClC-2. GlialCAM, a regulatory subunit of ClC-2 in glial cells and involved in the leukodystrophy megalencephalic leukoencephalopathy with subcortical cysts (MLC), increases the activity of a ClC-2 mutant by affecting ClC-2 gating and by stabilising the mutant at the plasma membrane. The stabilisation of ClC-2 at the plasma membrane by GlialCAM depends on its localisation at cell-cell junctions. The membrane protein MLC1, which is defective in MLC, also contributes to the stabilisation of ClC-2 at the plasma membrane, providing further support for the view that GlialCAM, MLC1 and ClC-2 form a protein complex in glial cells.

ABSTRACT

Mutations in CLCN2 have been recently identified in patients suffering from a type of leukoencephalopathy involving intramyelinic oedema. Here, we characterised most of these mutations that reduce the function of the chloride channel ClC-2 and impair its plasma membrane (PM) expression. Detailed biochemical and electrophysiological analyses of the Ala500Val mutation revealed that defective gating and increased cellular and PM turnover contributed to defective A500V-ClC-2 functional expression. Co-expression of the adhesion molecule GlialCAM, which forms a tertiary complex with ClC-2 and megalencephalic leukoencephalopathy with subcortical cysts 1 (MLC1), rescued the functional expression of the mutant by modifying its gating properties. GlialCAM also restored the PM levels of the channel by impeding its turnover at the PM. This rescue required ClC-2 localisation to cell-cell junctions, since a GlialCAM mutant with compromised junctional localisation failed to rescue the impaired stability of mutant ClC-2 at the PM. Wild-type, but not mutant, ClC-2 was also stabilised by MLC1 overexpression. We suggest that leukodystrophy-causing CLCN2 mutations reduce the functional expression of ClC-2, which is partly counteracted by GlialCAM/MLC1-mediated increase in the gating and stability of the channel.

Interaction of cochlin and mechanosensitive channel TREK-1 in trabecular meshwork cells influences the regulation of intraocular pressure

In the eye, intraocular pressure (IOP) is tightly regulated and its persistent increase leads to ocular hypertension and glaucoma. We have previously shown that trabecular meshwork (TM) cells might detect aqueous humor fluid shear stress via interaction of the extracellular matrix (ECM) protein cochlin with the cell surface bound and stretch-activated channel TREK-1. We provide evidence here that interaction between both proteins are involved in IOP regulation. Silencing of TREK-1 in mice prevents the previously demonstrated cochlin-overexpression mediated increase in IOP. Biochemical and electrophysiological experiments demonstrate that high shear stress-induced multimeric cochlin produces a qualitatively different interaction with TREK-1 compared to monomeric cochlin. Physiological concentrations of multimeric but not monomeric cochlin reduce TREK-1 current. Results presented here indicate that the interaction of TREK-1 and cochlin play an important role for maintaining IOP homeostasis. [Corrected].

Sensory processing in Huntington's disease

OBJECTIVE

An intriguing electrophysiological feature of patients with Huntington's disease (HD) is the delayed latency and decreased amplitude of somatosensory long-latency evoked potentials (LLeps). We investigated whether such dysfunction was associated with delayed conscious perception of the sensory stimulus.

METHODS

Sixteen HD patients and 16 control subjects faced a computer screen showing the Libet's clock (Libet et al., 1983). In Rest trials, subjects had to memorize the position of the clock handle at perception of either electrical or thermal stimuli (AW). In React, additionally, they were asked to make a fist with their right hand, in a simple reaction time task (SRT). LLseps were recorded from Cz in both conditions.

RESULTS

LLeps negative peak latency (N2) and SRT were abnormally delayed in patients in all conditions. AW was only abnormally prolonged in the React condition but the time difference between AW and the negative peak of the LLeps was not different in the two groups. There was a significant negative correlation between SRT and AW or LLeps amplitude in patients but not in healthy subjects.

CONCLUSION

Our HD patients did not show abnormalities in conscious perception of sensory stimuli but their LLeps abnormalities were more marked when they had to react. This is compatible with failure to detect stimulus salience rather than with a cognitive defect.

SIGNIFICANCE

HD patients at early stages of the disease have preserved subjective perception of sensation but faulty sensorimotor integration.

Effects of the Post-Spinal Cord Injury Microenvironment on the Differentiation Capacity of Human Neural Stem Cells Derived from Induced Pluripotent Stem Cells

Spinal cord injury (SCI) causes loss of neural functions below the level of the lesion due to interruption of spinal pathways and secondary neurodegenerative processes. The transplant of neural stem cells (NSCs) is a promising approach for the repair of SCI. Reprogramming of adult somatic cells into induced pluripotent stem cells (iPSCs) is expected to provide an autologous source of iPSC-derived NSCs, avoiding the immune response as well as ethical issues. However, there is still limited information on the behavior and differentiation pattern of transplanted iPSC-derived NSCs within the damaged spinal cord. We transplanted iPSC-derived NSCs, obtained from adult human somatic cells, into rats at 0 or 7 days after SCI, and evaluated motor-evoked potentials and locomotion of the animals. We histologically analyzed engraftment, proliferation, and differentiation of the iPSC-derived NSCs and the spared tissue in the spinal cords at 7, 21, and 63 days posttransplant. Both transplanted groups showed a late decline in functional recovery compared to vehicle-injected groups. Histological analysis showed proliferation of transplanted cells within the tissue and that cells formed a mass. At the final time point, most grafted cells differentiated to neural and astroglial lineages, but not into oligodendrocytes, while some grafted cells remained undifferentiated and proliferative. The proinflammatory tissue microenviroment of the injured spinal cord induced proliferation of the grafted cells and, therefore, there are possible risks associated with iPSC-derived NSC transplantation. New approaches are needed to promote and guide cell differentiation, as well as reduce their tumorigenicity once the cells are transplanted at the lesion site.

Abnormal activity of corneal cold thermoreceptors underlies the unpleasant sensations in dry eye disease

Dry eye disease (DED) affects >10% of the population worldwide, and it provokes an unpleasant sensation of ocular dryness, whose underlying neural mechanisms remain unknown. Removal of the main lachrymal gland in guinea pigs caused long-term reduction of basal tearing accompanied by changes in the architecture and density of subbasal corneal nerves and epithelial terminals. After 4 weeks, ongoing impulse activity and responses to cooling of corneal cold thermoreceptor endings were enhanced. Menthol (200 μM) first excited and then inactivated this augmented spontaneous and cold-evoked activity. Comparatively, corneal polymodal nociceptors of tear-deficient eyes remained silent and exhibited only a mild sensitization to acidic stimulation, whereas mechanonociceptors were not affected. Dryness-induced changes in peripheral cold thermoreceptor responsiveness developed in parallel with a progressive excitability enhancement of corneal cold trigeminal ganglion neurons, primarily due to an increase of sodium currents and a decrease of potassium currents. In corneal polymodal nociceptor neurons, sodium currents were enhanced whereas potassium currents remain unaltered. In healthy humans, exposure of the eye surface to menthol vapors or to cold air currents evoked unpleasant sensations accompanied by increased blinking frequency that we attributed to cold thermoreceptor stimulation. Notably, stimulation with menthol reduced the ongoing background discomfort of patients with DED, conceivably due to use-dependent inactivation of cold thermoreceptors. Together, these data indicate that cold thermoreceptors contribute importantly to the detection and signaling of ocular surface wetness, and develop under chronic eye dryness conditions an injury-evoked neuropathic firing that seems to underlie the unpleasant sensations experienced by patients with DED.

Ion Channels in the Eye: Involvement in Ocular Pathologies

The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.

Modulation of TRESK background K+ channel by membrane stretch

The two-pore domain K⁺ channel TRESK is expressed in dorsal root ganglion and trigeminal sensory neurons where it is a major contributor to background K⁺ current. TRESK acts as a break to prevent excessive sensory neuron activation and decreases in its expression or function have been involved in neuronal hyperexcitability after injury/inflammation, migraine or altered sensory perception (tingling, cooling and pungent burning sensations). All these effects have implicated this channel in nociception and mechanotransduction. To determine the role of TRESK in sensory transduction, we studied its sensitivity to changes in membrane tension (stretch) in heterologous systems, F-11 cells and trigeminal neurons. Laminar shear stress increased TRESK currents by 22–30%. An increase in membrane tension induced by cell swelling (hypotonic medium) produced a reversible elevation of TRESK currents (39.9%). In contrast, cell shrinkage (hypertonic solution) produced the opposite effect. Membrane crenators or cup-formers produced equivalent effects. In trigeminal sensory neurons, TRESK channels were mechanically stimulated by negative pressure, which led to a 1.51-fold increase in channel open probability. TRESK-like currents in trigeminal neurons were additively inhibited by arachidonic acid, acidic pH and hypertonic stimulation, conditions usually found after tissue inflammation. Our results show that TRESK is modulated by changes in cell membrane tension and/or cell volume. Several key players released during inflammation or tissue injury could modulate sensory neuron activation through small changes in membrane tension.

GlialCAM, a protein defective in a leukodystrophy, serves as a ClC-2 Cl(-) channel auxiliary subunit

Ion fluxes mediated by glial cells are required for several physiological processes such as fluid homeostasis or the maintenance of low extracellular potassium during high neuronal activity. In mice, the disruption of the Cl⁻ channel ClC-2 causes fluid accumulation leading to myelin vacuolation. A similar vacuolation phenotype is detected in humans affected with megalencephalic leukoencephalopathy with subcortical cysts (MLC), a leukodystrophy which is caused by mutations in MLC1 or GLIALCAM. We here identify GlialCAM as a ClC-2 binding partner. GlialCAM and ClC-2 colocalize in Bergmann glia, in astrocyte-astrocyte junctions at astrocytic endfeet around blood vessels, and in myelinated fiber tracts. GlialCAM targets ClC-2 to cell junctions, increases ClC-2 mediated currents, and changes its functional properties. Disease-causing GLIALCAM mutations abolish the targeting of the channel to cell junctions. This work describes the first auxiliary subunit of ClC-2 and suggests that ClC-2 may play a role in the pathology of MLC disease.

Video Abstract

TRESK channel contribution to nociceptive sensory neurons excitability: modulation by nerve injury

Background

Neuronal hyperexcitability is a crucial phenomenon underlying spontaneous and evoked pain. In invertebrate nociceptors, the S-type leak K⁺ channel (analogous to TREK-1 in mammals) plays a critical role of in determining neuronal excitability following nerve injury. Few data are available on the role of leak K_2P channels after peripheral axotomy in mammals.

Results

Here we describe that rat sciatic nerve axotomy induces hyperexcitability of L4-L5 DRG sensory neurons and decreases TRESK (K2P18.1) expression, a channel with a major contribution to total leak current in DRGs. While the expression of other channels from the same family did not significantly change, injury markers ATF3 and Cacna2d1 were highly upregulated. Similarly, acute sensory neuron dissociation (in vitro axotomy) produced marked hyperexcitability and similar total background currents compared with neurons injured in vivo. In addition, the sanshool derivative IBA, which blocked TRESK currents in transfected HEK293 cells and DRGs, increased intracellular calcium in 49% of DRG neurons in culture. Most IBA-responding neurons (71%) also responded to the TRPV1 agonist capsaicin, indicating that they were nociceptors. Additional evidence of a biological role of TRESK channels was provided by behavioral evidence of pain (flinching and licking), in vivo electrophysiological evidence of C-nociceptor activation following IBA injection in the rat hindpaw, and increased sensitivity to painful pressure after TRESK knockdown in vivo.

Conclusions

In summary, our results clearly support an important role of TRESK channels in determining neuronal excitability in specific DRG neurons subpopulations, and show that axonal injury down-regulates TRESK channels, therefore contributing to neuronal hyperexcitability.

Acid-sensing ion channels (ASICs): pharmacology and implication in pain

Tissue acidosis is a common feature of many painful conditions. Protons are indeed among the first factors released by injured tissues, inducing a local pH fall that depolarizes peripheral free terminals of nociceptors and leads to pain. ASICs are excitatory cation channels directly gated by extracellular protons that are expressed in the nervous system. In sensory neurons, they act as "chemo-electrical" transducers and are involved in somatic and visceral nociception. Two highly specific inhibitory peptides isolated from animal venoms have considerably helped in the understanding of the physiological roles of these channels in pain. At the peripheral level, ASIC3 is important for inflammatory pain. Its expression and its activity are potentiated by several pain mediators present in the "inflammatory soup" that sensitize nociceptors. ASICs have also been involved in some aspects of mechanosensation and mechanonociception, notably in the gastrointestinal tract, but the underlying mechanisms remain to be determined. At the central level, ASIC1a is largely expressed in spinal cord neurons where it has been proposed to participate in the processing of noxious stimuli and in central sensitization. Blocking ASIC1a in the spinal cord also produces a potent analgesia in a broad range of pain conditions through activation of the opiate system. Targeting ASIC channels at different levels of the nervous system could therefore be an interesting strategy for the relief of pain.

Effects of platelet-derived growth factor on aqueous humor dynamics

PURPOSE

It is well known that the small GTPase RhoA modulates actin cytoskeleton and cellular contractility in the trabecular meshwork (TM). Several substances known to contract the TM reduce outflow facility, whereas cellular relaxation is commonly associated with the opposite effect. Inhibitors of the RhoA pathway are under development as antiglaucoma drugs. Here the authors investigate the role of platelet-derived growth factor (PDGF), a known activator of the Rac1 pathway, in cell cytoskeleton, outflow facility, and intraocular pressure (IOP).

METHODS

Effects of PDGF on actin cytoskeleton, Rac1, and AKT activation were tested in preconfluent and confluent bovine TM cells in culture. Rac1 and AKT/P-AKT activation were assessed by Western blot analysis. Trabecular outflow facility was measured in bovine perfused anterior segments. Changes in IOP were measured for up to 6 hours after topical application in the cornea of rabbit eyes by means of a contact tonometer.

RESULTS

In TM cells, PDGF (10 ng/mL) activated Rac1 through AKT and induced actin cytoskeleton rearrangement with lamellipodia formation. In this sense, lamellipodia formation in TM cells was prevented by NSC23766, a Rac1 inhibitor, and LY294002, a PI3K inhibitor. In perfused anterior segments, PDGF (100 ng/mL) increased trabecular outflow facility by 26%. In vivo, when topically applied to rabbit corneas, PDGF induced a 20% decrease in IOP (100 ng/mL). This reduction was concentration dependent and presented an EC(50) value of 2.7 nM.

CONCLUSIONS

PDGF, by activating the Rac1 pathway, induces cytoskeletal changes in TM cells that enhance outflow facility. Decreased IOP after PDGF application is likely caused by the facilitation of aqueous humor outflow. Rac1 pathway activation appears to be a positive modulator of outflow facility and an interesting target for decreasing IOP after ocular hypertension.

Activation of store-operated Ca(2+) channels in trabecular meshwork cells

PURPOSE

In nonexcitable cells, G(q)-coupled membrane receptor activation induces a biphasic increase in intracellular calcium ([Ca(2+)](i)) expressed as an initial IP(3)-dependent release from intracellular stores followed by a sustained Ca(2+) influx from the extracellular space that involves store-operated Ca(2+) channels (SOCs). In trabecular meshwork (TM) cells, contractile agonists such as bradykinin (BK) and endothelin-1 (ET-1) induce this type of Ca(2+) signaling. Given that trabecular outflow is modified by tissue contractility, the authors characterized SOCs and studied their participation in TM cell contractility.

METHODS

[Ca(2+)](i) was measured in cultured bovine TM cells loaded with Fura-2. Ca(2+) currents were recorded using the patch clamp technique. Cell contractility measurements were assessed by traction microscopy.

RESULTS

BK and ET-1 activate a store-operated Ca(2+) entry that was greatly reduced in the absence of extracellular Ca(2+) or by preincubation with SOC blocker 2-APB or SKF96365. Store-operated Ca(2+) currents were also activated by intracellular dialysis with IP(3) + EGTA or after stimulation with thapsigargin. Electrophysiological characterization supports the presence of Ca(2+) release-activated Ca(2+) channels (CRACs) and nonselective cation channels, of which TRPC1 and TRPC4 channels may be candidate TRPs detected in TM cells. Extracellular Ca(2+) entry through SOCs is not required for TM cell contraction in response to BK or ET-1, but it modulates this process.

CONCLUSIONS

Extracellular Ca(2+) entry in TM cells in response to agonist stimulation and store-depletion is mediated by the activation of SOCs, which do not contribute to cell contraction but which may activate regulatory mechanisms to prevent excessive contraction. CRAC and TRPC channels involved represent interesting modulators of TM function to improve aqueous humor outflow.

Profilin induces lamellipodia by growth factor-independent mechanism

Profilin has been implicated in cell motility and in a variety of cellular processes, such as membrane extension, endocytosis, and formation of focal complexes. In vivo, profilin replenish the pool of ATP-actin monomers by increasing the rate of nucleotide exchange of ADP-actin for ATP-actin, promoting the incorporation of new actin monomers at the barbed end of actin filaments. For this report, we generated a membrane-permeable version of profilin I (PTD4-PfnI) for the alteration of intracellular profilin levels taking advantage of the protein transduction technique. We show that profilin I induces lamellipodia formation independently of growth factor presence in primary bovine trabecular meshwork (BTM) cells. The effects are time- and concentration-dependent and specific to the profilin I isoform. Profilin II, the neuronal isoform, failed to extend lamellipodia in the same degree as profilin I. H133S, a mutation in the polyproline binding domain, showed a reduced ability to induce lamellipodia. H199E, mutation in the actin binding domain failed to induce membrane spreading and inhibit fetal bovine serum (FBS) -induced lamellipodia extension. Incubation with a synthetic polyproline domain peptide (GP5)3, fused to a transduction domain, abolished lamellipodia induction by profilin or FBS. Time-lapse microscopy confirmed the effects of profilin on lamellipodia extension with a higher spreading velocity than FBS. PTD4-Pfn I was found in the inner lamellipodia domain, at the membrane leading edge where it colocalizes with endogenous profilin. While FBS-induced lamellipodia formation activates Rac1, PTD4-Pfn I stimulation did not induce Rac1 activation. We propose a role of profilin I favoring lamellipodia formation by a mechanism downstream of growth factor.

Hypotensive effect of profilin on rabbit intraocular pressure

Ocular hypertension is a negative process that occurs within the eye and is the main risk factor to develop glaucoma, a progressive loss of vision due to degeneration of retinal ganglion cells. The protein transduction technique allows a cargo to cross biological membranes. Using this technique we have previously shown that a membrane permeable version of profilin I (PTD4-profilin) increased aqueous humour outflow facility. Here we have investigated if a topical application of PTD4-profilin was able to modify intraocular pressure in rabbits. 10 microM PTD4-profilin (10 microL), reduced intraocular pressure by 20% compared to the control vehicle, this value being in the range of other commercial drugs, which produced intraocular pressure reductions between 18 and 35%. The mean-time effect for PTD4-profilin was 6.8 h and was also in the same range as commercial products that provided values between 4.3 and 5.5 h. According to the results presented here we propose PTD4-profilin as a new approach for the treatment of ocular hypertension and PTD4 as a new strategy to facilitate the penetration of molecules into the eye.

Norepinephrine induces calcium spikes and proinflammatory actions in human hepatic stellate cells

Catecholamines participate in the pathogenesis of portal hypertension and liver fibrosis through alpha1-adrenoceptors. However, the underlying cellular and molecular mechanisms are largely unknown. Here, we investigated the effects of norepinephrine (NE) on human hepatic stellate cells (HSC), which exert vasoactive, inflammatory, and fibrogenic actions in the injured liver. Adrenoceptor expression was assessed in human HSC by RT-PCR and immunocytochemistry. Intracellular Ca2+ concentration ([Ca2+]i) was studied in fura-2-loaded cells. Cell contraction was studied by assessing wrinkle formation and myosin light chain II (MLC II) phosphorylation. Cell proliferation and collagen-alpha1(I) expression were assessed by [3H]thymidine incorporation and quantitative PCR, respectively. NF-kappaB activation was assessed by luciferase reporter gene and p65 nuclear translocation. Chemokine secretion was assessed by ELISA. Normal human livers expressed alpha(1A)-adrenoceptors, which were markedly upregulated in livers with advanced fibrosis. Activated human HSC expressed alpha(1A)-adrenoceptors. NE induced multiple rapid [Ca2+]i oscillations (Ca2+ spikes). Prazosin (alpha1-blocker) completely prevented NE-induced Ca2+ spikes, whereas propranolol (nonspecific beta-blocker) partially attenuated this effect. NE caused phosphorylation of MLC II and cell contraction. In contrast, NE did not affect cell proliferation or collagen-alpha1(I) expression. Importantly, NE stimulated the secretion of inflammatory chemokines (RANTES and interleukin-8) in a dose-dependent manner. Prazosin blocked NE-induced chemokine secretion. NE stimulated NF-kappaB activation. BAY 11-7082, a specific NF-kappaB inhibitor, blocked NE-induced chemokine secretion. We conclude that NE stimulates NF-kappaB and induces cell contraction and proinflammatory effects in human HSC. Catecholamines may participate in the pathogenesis of portal hypertension and liver fibrosis by targeting HSC.

Identification and functional characterization of ClC-2 chloride channels in trabecular meshwork cells

In the eye, trabecular meshwork (TM) cell volume may be an important determinant of aqueous humor outflow. Among their functions, ClC-2 chloride channels are thought to be involved in regulation of cellular volume and intracellular [Cl(-)]. We characterized the properties and modulation of an inwardly rectifying chloride current activated in these cells. Patch-clamp recordings revealed inwardly rectifying chloride currents activated by membrane hyperpolarization in primary cultures of both bovine (BTM) and human (HTM) TM cells. Electrophysiological properties and anion permeability sequence (Cl(-)>Br(-)>I(-)>F(-)) were in agreement with previous data for ClC-2 in other cells. The currents were blocked by Cd(2+) and enhanced by extracellular acidification, 8Br-cAMP and cell swelling, while extracellular alkalinization decreased them. RT-PCR experiments using total RNA revealed the molecular expression of ClC-2 channels. Previously we reported the involvement of swelling-activated chloride channels (Cl(swell)) and Ca(2+)-activated K(+) channels (BK(Ca)) in cell volume and outflow facility regulation. However, in the present analysis, cell volume experiments in calcein-loaded cells and outflow facility studies performed in bovine anterior segments revealed that ClC-2 channels do not make a significant contribution to the recovery of cellular volume or to the regulation of the outflow facility. Nevertheless, ClC-2 modulation by different stimuli may contribute to intracellular [Cl(-)] regulation and other cellular functions yet to be determined in the TM.

Use of transduction proteins to target trabecular meshwork cells: outflow modulation by profilin I

PURPOSE

Fusion proteins containing a protein transduction domain (PTD4) are able to cross biological membranes. We tested the applicability of the protein transduction method for study of the aqueous humor trabecular outflow pathway by targeting the actin cytoskeleton, which is known to be involved in outflow facility regulation.

METHODS

Expression vectors useful for generating fusion proteins with the PTD4 domain and the actin-binding protein Profilin I were constructed. The transductional and functional properties of these proteins were tested in bovine trabecular meshwork cells in culture. The effects of PTD4-Profilin I on outflow facility were evaluated in perfused bovine anterior segments. PTD4-beta-galactosidase was used to visually check correct delivery of fusion proteins to trabecular meshwork cells.

RESULTS

The fusion proteins generated were characterized by western blot. Immunocytochemistry experiments showed intracellular staining for PTD4-Profilin I in trabecular meshwork cells in culture. The fusion protein was found in the cytoplasm associated with actin filaments and in the leading edge of the cellular membrane. In contrast, control Profilin I, without the PTD4 domain, was unable to cross the cell membrane. In perfused anterior segments, 2 microM PTD4-Profilin I increased trabecular outflow facility in a reversible manner, while Profilin I had no significant effect. Anterior segments perfused with PTD4-beta-galactosidase showed positive staining in the trabecular meshwork tissue.

CONCLUSIONS

Protein transduction technology is a valuable tool for targeting trabecular meshwork tissue, not only for performing physiological studies, but also as a potential drug-delivery method. Profilin I action on the actin cytoskeleton further reinforces the importance of this structure in outflow facility regulation.

Evidence That Long-Term Hyperexcitability of the Sensory Neuron Soma Induced by Nerve Injury inAplysiaIs Adaptive

Peripheral axotomy induces long-term hyperexcitability (LTH) of centrally located sensory neuron (SN) somata in diverse species. In mammals this LTH can promote spontaneous activity of pain-related SNs, and such activity may contribute to neuropathic pain and hyperalgesia. However, few axotomized SN somata begin to fire spontaneously in any species, and why so many SNs display soma LTH after axotomy remains a mystery. Is soma LTH a side effect of injury with pathological but no adaptive consequences, or was this response selected during evolution for particular functions? A hypothesis for one function of soma LTH in nociceptive SNs in Aplysia californica is proposed: after peripheral injury that produces partial axotomy of some SNs, compensation for sensory deficits and protective sensitization are achieved by facilitating afterdischarge near the soma, which amplifies sensory input from injured peripheral fields. Four predictions of this hypothesis were confirmed in SNs that innervate the tail. First, LTH of SN somata was induced by a relatively natural axotomizing event—a small cut across part of the tail in the absence of anesthesia. Second, soma LTH was selectively expressed in SNs having axons in cut or crushed nerves rather than nearby, uninjured nerves. Third, after several weeks soma LTH began to reverse when functional recovery of the interrupted afferent pathway was shown by reestablishment of a centrally mediated siphon reflex. Fourth, axotomized SNs developed central afterdischarge that amplified sensory discharge coming from the periphery, and the afterdepolarization underlying this afterdischarge was enhanced by previous axotomy.

Genomic and functional characterization of stellate cells isolated from human cirrhotic livers

BACKGROUND/AIMS

Hepatic stellate cells (HSCs) are believed to participate in liver fibrogenesis and portal hypertension. Knowledge on human HSCs is based on studies using HSCs isolated from normal livers. We investigated the phenotypic, genomic and functional characteristics of HSCs from human cirrhotic livers.

METHODS

HSC were obtained from normal and cirrhotic human livers. Cells were characterized by immunocytochemistry and gene microarray analysis. Cell proliferation, Ca(2+) changes and cell contraction were assessed by 3H-thymidine incorporation and by using an epifluorescence microscope.

RESULTS

HSCs freshly isolated from human cirrhotic livers showed phenotypical features of myofibroblasts. These features were absent in HSCs freshly isolated from normal human livers and become prominent after prolonged culture. HSCs from cirrhotic human livers markedly express genes involved in fibrogensis, inflammation and apoptosis. HSCs from normal livers after prolonged culture preferntially expressed genes related to fibrogenesis and contractility. Agonists induced proliferation, Ca(2+) increase and cell contraction in HSCs isolated from human cirrhotic livers. Response to agonists was more marked in culture-activated HSCs and was not observed in HSCs freshly isolated from normal livers.

CONCLUSIONS

HSCs from human cirrhotic livers show fibrogenic and contractile features. However, the current model of HSCs activated in culture does not exactly reproduce the activated phenotype found in cirrhotic human livers.

Effects of dinucleoside polyphosphates on trabecular meshwork cells and aqueous humor outflow facility

The most important risk factor for the development of glaucoma is elevated intraocular pressure (IOP). Hypotensive drugs decrease IOP, preventing optic nerve damage and further vision loss. The balance between aqueous humor (AH) production and drainage determines IOP, and problems in AH outflow pathways are associated with open-angle glaucoma development. Previous studies have shown the presence of diadenosine tetraphosphate (Ap(4)A) and pentaphosphate (Ap(5)A) in the AH. Topic application of Ap(4)A to the cornea decreased IOP, whereas Ap(5)A increased it. Because dinucleoside polyphosphates stimulate P2Y purinergic receptors, we studied their presence in trabecular meshwork (TM) cells. Additionally, the effects of diadenosine polyphosphates (Ap(n)As; n = 3-5) and Up(4)U (P(1),P(4)-(diuridine 5')-tetraphosphate; INS365) in outflow facility were tested. P2Y(1), P2Y(2), and P2Y(4) receptors were detected in TM cells by Western blot and immunocytochemistry. In TM cells, Ap(3)A, Ap(4)A, and Ap(5)A induced discrete intracellular calcium concentration ([Ca(2+)](i)) mobilizations compared with higher and more sustained [Ca(2+)](i) mobilizations after Up(4)U application. In bovine ocular anterior segments perfused at constant pressure, 1 microM Ap(3)A or Ap(4)A increased outflow facility, whereas Up(4)U or Ap(5)A did not modify it. 2-MeSADP, a selective P2Y(1) agonist, induced outflow facility increases similar to those obtained after Ap(3)A and Ap(4)A, and these were prevented by addition of the selective P2Y(1) receptor antagonist MRS-2179 (2'-deoxy-N(6)-methyladenosine-3',5'-diphosphate). Our results demonstrate that the hypotensive effect of Ap(4)A and other dinucleotides is mediated, at least in part, by increasing trabecular outflow facility through activation of P2Y(1) receptors. The latter would seem to be an interesting target in the development of antiglaucomatous drugs to selectively increase AH outflow.

Differential expression of the human chloride channel genes in the trabecular meshwork under stress conditions

Among other channels, voltage-gated chloride channels (ClC) regulate cell volume, membrane potential and cellular transport. Because changes in trabecular meshwork (TM) cell volume influence outflow facility and because the relative abundance of a gene's transcript is an indication of the relevance of the gene's function, we investigated the presence and relative expression of seven members of the CLCN gene family in the human TM. To elucidate the role of ClC-2 and ClC-3 in cell swelling, we studied changes in their mRNA levels after hypotonic shock. In addition, to examine the potential involvement of these two channels in conditions associated with glaucoma, we determined their transcripts levels in response to elevated intraocular pressure (IOP) and dexamethasone (DEX). For our evaluations, we used non-transformed human TM cells and perfused human anterior segments from post-mortem donors. For hypotonic shock, cells were exposed to 260 mOsm kg(-1) medium for 15 and 30 min. For DEX, cells were treated with 0.1 microm DEX for 1, 4 and 10 days. For elevated IOP, one eye of each pair of perfused human anterior segments was subjected to DeltaP 38+/-4 mm Hg for 1 hr, 4 and 7 days while the contralateral remained at baseline pressure as a control. ClCs transcripts were determined by relative quantitative RT-PCR. Our results showed that all transcripts but ClC-1 were detected in HTM cells. ClC-2 and ClC-3 were the most abundant and comprised about twice the amount of ClC-6 and ClC-7 and four times that of ClC-4 and ClC-5. Hypotonic conditions consistently up regulated CLCN2 and slightly up regulated CLCN3. After short periods of elevated pressure, ClC-2 and ClC-3 transcripts were increased but ClC-2 induction was significantly higher than that of ClC-3. In contrast, after long pressure insults (7 days), ClC-3 mRNA was significantly increased while CLCN2 was not changed. DEX treatment markedly down regulated CLCN3 and little, if any, reduced ClC-2. The extent of response of the CLCN2 and CLCN3 to these conditions was markedly affected by individual traits but at all times maintained the relative expression pattern of both genes. CLCN2 gene expression was predominantly influenced by cell volume regulation while that of CLCN3 was preferentially affected by conditions associated with TM pathology.

Modulation of aqueous humor outflow by ionic mechanisms involved in trabecular meshwork cell volume regulation

PURPOSE

Trabecular meshwork (TM) cell shape, volume, contractility and their interactions with extracellular matrix determine outflow facility. Because cell volume seems essential to TM function, this study was conducted to investigate further the ionic channels and receptors involved in regulatory volume decrease and their roles in modulating outflow facility.

METHODS

Primary cultures of bovine TM cells were used. K(+) and Cl(-) currents were studied with whole-cell patch clamping. Swelling was induced by hypotonic shock. [Ca(2+)](i) was measured in TM cells loaded with fura-2. Bovine anterior segments were perfused at constant pressure to measure outflow facility.

RESULTS

Hypotonic media activated both the high-conductance Ca(2+)-activated K(+) channel (BK(Ca)) and swelling-activated Cl(-) channel (Cl(swell)) currents and induced release of adenosine 5'-triphosphate (ATP) from TM cells. ATP activated P2Y(2) receptors with the following profile: ATP = uridine 5'-triphosphate (UTP) > adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma S) > adenosine 5'-diphosphate (ADP) = uridine 5'-diphosphate (UDP), and increased BK(Ca) current. Hypotonic medium initially decreased outflow facility in perfused anterior segments, which recovered with time to baseline levels. Addition of tamoxifen or iberiotoxin (Cl(swell) and BK(Ca) blockers, respectively) lengthened the recovery phase, which implies that these channels participate in cell volume regulation. In contrast, an activator of BK(Ca)s (NS1619) produced the opposite effect.

CONCLUSIONS

Cell swelling activates a regulatory volume decrease mechanism that implies activation of K(+) and Cl(-) currents and participation of P2Y(2) receptors. Because previous studies have shown that intracellular volume of TM cells is an important determinant of outflow facility, it seems feasible that cell volume regulation would be part of the homeostatic mechanisms of the TM, to regulate the outflow pathway.

Understanding trabecular meshwork physiology: a key to the control of intraocular pressure?

The trabecular meshwork is a tissue located in the anterior chamber angle of the eye, and it is a crucial determinant of intraocular pressure values because of its resistance to the evacuation of aqueous humor from the eye. Here we bring together classical and recent discoveries on the function of the trabecular meshwork, keys to understanding eye pathophysiology.