Contribution of Oligodendrocytes, Microglia, and Astrocytes to Myelin Debris Uptake in an Explant Model of Inflammatory Demyelination in Rats

The internalization and degradation of myelin in glia contributes to the resolution of neuroinflammation and influences disease progression. The identification of a three-dimensional experimental model to study myelin processing under neuroinflammation will offer a novel approach for studying treatment strategies favoring inflammation resolution and neuroprotection. Here, by using a model of neuroinflammation in hippocampal explants, we show that myelin debris accumulated immediately after insult and declined at 3 days, a time point at which tentative repair processes were observed. Olig2+ oligodendrocytes upregulated the LRP1 receptor and progressively increased MBP immunoreactivity both at peri-membrane sites and within the cytosol. Oligodendrocyte NG2+ precursors increased in number and immunoreactivity one day after insult, and moderately internalized MBP particles. Three days after insult MBP was intensely coexpressed by microglia and, to a much lesser extent, by astrocytes. The engulfment of both MBP+ debris and whole MBP+ cells contributed to the greatest microglia response. In addition to improving our understanding of the spatial-temporal contribution of glial scarring to myelin uptake under neuroinflammation, our findings suggest that the exposure of hippocampal explants to LPS + IFN-γ-induced neuroinflammation may represent a valuable demyelination model for studying both the extrinsic and intrinsic myelin processing by glia under neuroinflammation.

Epidemiological and Immune Profile Analysis of Italian Subjects with Endometriosis and Multiple Sclerosis

OBJECTIVE

To report for the first time an Italian epidemiological analysis of the prevalence of multiple sclerosis (MS) in patients with endometriosis (EMS), through the study of the endometriosis population of our referral center; to analyze the clinical profile and perform a laboratory analysis to examine the immune profile and the possible correlation to other autoimmune diseases of the enrolled patients.

METHODS

We evaluated 1652 women registered with EMS in the University of Naples Federico II and retrospectively searched patients with a co-diagnosis of MS. Clinical features of both conditions were recorded. Serum autoantibody and immune profiles were analyzed.

RESULTS

9 out of 1652 patients presented a co-diagnosis of EMS and MS (9/1652 = 0.005%). Clinically, EMS and MS presented in mild forms. Hashimoto's thyroiditis was found in two patients (2/9). Even if not statistically significant, a trend of variation in CD4- CD8 T lymphocytes and of B cells were found.

CONCLUSION

Our findings suggest an increased risk of MS in women with EMS. However, large-scale prospective studies are needed.

Development of potent and selective FAAH inhibitors with improved drug-like properties as potential tools to treat neuroinflammatory conditions

The neuroprotective performance against neuroinflammation of the endocannabinoid system (ECS) can be remarkably improved by indirect stimulation mediated by the pharmacological inhibition of the key ECS catabolic enzyme fatty acid amide hydrolase (FAAH). Based on our previous works and aiming to discover new selective FAAH inhibitors , we herein reported a new series of carbamate-based FAAH inhibitors (4a-t) which showed improved drug disposition properties compared to the previously reported analogues 2a-b. The introduction of ionizable functions allowed us to obtain new FAAH inhibitors of nanomolar potency characterized by good water solubility and chemical stability at physiological pH. Interesting structure-activity relationships (SARs), deeply analyzed by molecular docking and molecular dynamic (MD) simulations, were obtained. All the newly developed inhibitors showed an excellent selectivity profile evaluated against monoacylglycerol lipase and cannabinoid receptors. The reversible mechanism of action was determined by a rapid dilution assay. Absence of toxicity was confirmed in mouse fibroblasts NIH3T3 (for compounds 4e, 4g, 4n-o, and 4s) and in human astrocytes cell line 1321N1 (for compounds 4e, 4n, and 4s). The absence of undesired cardiac effects was also confirmed for compound 4n. Selected analogues (compounds 4e, 4g, 4n, and 4s) were able to reduce oxidative stress in 1321N1 astrocytes and exhibited notable neuroprotective effects when tested in an ex vivo model of neuroinflammation.

Combined targeting of fatty acid amide hydrolase and melatonin receptors promotes neuroprotection and stimulates inflammation resolution in rats

BACKGROUND AND PURPOSE

Devising novel strategies to therapeutically favour inflammation resolution and provide neuroprotection is an unmet clinical need. Enhancing endocannabinoid tone by inhibiting the catabolic enzyme fatty acid amide hydrolase (FAAH), or stimulating melatonin receptors has therapeutic potential to treat neuropathological states in which neuroinflammation plays a central role.

EXPERIMENTAL APPROACH

A rodent hippocampal explant model of inflammatory injury was used to assess the effects of UCM1341, a dual-acting compound with FAAH inhibitory action and agonist activity at melatonin receptors, against neuroinflammatory damage. FAAH activity was measured by a radiometric assay, and N-acylethanolamine levels were assessed by HPLC-MS/MS methods. FAAH distribution, evolution of inflammation and the contribution of UCM1341 to the expression of proteins controlling macrophage behaviour were investigated by biochemical and confocal analyses.

KEY RESULTS

UCM1341 exhibited greater neuroprotection against neuroinflammatory degeneration, compared with the reference compounds URB597 (FAAH inhibitor) and melatonin. During neuroinflammation, UCM1341 augmented the levels of anandamide and N-oleoylethanolamine, but not N-palmitoylethanolamine, up-regulated PPAR-α levels, attenuated demyelination and prevented the release of TNF-α. UCM1341 modulated inflammatory responses by contributing to microglia/macrophage polarization, stimulating formation of lipid-laden macrophages and regulating expression of proteins controlling cholesterol metabolism and efflux. The neuroprotective effects of UCM1341 were prevented by PPARα, TRPV1 and melatonin receptor antagonists.

CONCLUSION AND IMPLICATIONS

UCM1341, by enhancing endocannabinoid and melatoninergic signalling, benefits neuroprotection and stimulates inflammation resolution pathways. Our findings provide an encouraging prospect of therapeutically targeting endocannabinoid and melatoninergic systems in inflammatory demyelinating states in the CNS.

The Neuroprotective Effects of mGlu1 Receptor Antagonists Are Mediated by an Enhancement of GABAergic Synaptic Transmission via a Presynaptic CB1 Receptor Mechanism

In this study, we investigated the cross-talk between mGlu1 and CB1 receptors in modulating GABA hippocampal output in whole-cell voltage clamp recordings in rat hippocampal acute slices, in organotypic hippocampal slices exposed to oxygen and glucose deprivation (OGD) and in gerbils subjected to global ischemia. CB1 receptor expression was studied using immunohistochemistry and the CA1 contents of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured by LC-MS/MS. Our results show that mGlu1 receptor antagonists enhance sIPSCs in CA1 pyramidal cells and the basal and ischemic hippocampal release of GABA in vivo in a manner that is mediated by CB1 receptor activation. In hippocampal slices exposed to OGD and in ischemic gerbils, mGlu1 receptor antagonists protected CA1 pyramidal cells against post-ischemic injury and this effect was reduced by CB1 receptor activation. OGD induced a transient increase in the hippocampal content of AEA and this effect is prevented by mGlu1 receptor antagonist. Finally, OGD induced a late disruption of CB1 receptors in the CA1 region and the effect was prevented when CA1 pyramidal cells were protected by mGlu1 antagonists. Altogether, these results suggest a cooperative interaction between mGlu1 receptors and the endocannabinoid system in the mechanisms that lead to post-ischemic neuronal death.

Increased KV2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K+ Currents in Hippocampal Neurons of the Tg2576 Alzheimer's Disease Mouse

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Cortical and hippocampal hyperexcitability intervenes in the pathological derangement of brain activity leading to cognitive decline. As key regulators of neuronal excitability, the voltage-gated K⁺ channels (K_V) might play a crucial role in the AD pathophysiology. Among them, the K_V2.1 channel, the main α subunit mediating the delayed rectifier K⁺ currents (I_DR) and controlling the intrinsic excitability of pyramidal neurons, has been poorly examined in AD. In the present study, we investigated the K_V2.1 protein expression and activity in hippocampal neurons from the Tg2576 mouse, a widely used transgenic model of AD. To this aim we performed whole-cell patch-clamp recordings, Western blotting, and immunofluorescence analyses. Our Western blotting results reveal that K_V2.1 was overexpressed in the hippocampus of 3-month-old Tg2576 mice and in primary hippocampal neurons from Tg2576 mouse embryos compared with the WT counterparts. Electrophysiological experiments unveiled that the whole I_DR were reduced in the Tg2576 primary neurons compared with the WT neurons, and that this reduction was due to the loss of the K_V2.1 current component. Moreover, we found that the reduction of the K_V2.1-mediated currents was due to increased channel clustering, and that glutamate, a stimulus inducing K_V2.1 declustering, was able to restore the I_DR to levels comparable to those of the WT neurons. These findings add new information about the dysregulation of ionic homeostasis in the Tg2576 AD mouse model and identify K_V2.1 as a possible player in the AD-related alterations of neuronal excitability.

Na+/Ca2+ exchanger isoform 1 takes part to the Ca2+-related prosurvival pathway of SOD1 in primary motor neurons exposed to beta-methylamino-L-alanine

Background

The cycad neurotoxin beta-methylamino-l-alanine (L-BMAA), one of the environmental trigger factor for amyotrophic lateral sclerosis/Parkinson-dementia complex (ALS/PDC), may cause neurodegeneration by disrupting organellar Ca²⁺ homeostasis. Through the activation of Akt/ERK1/2 pathway, the Cu,Zn-superoxide dismutase (SOD1) and its non-metallated form, ApoSOD1, prevent endoplasmic reticulum (ER) stress-induced cell death in motor neurons exposed to L-BMAA. This occurs through the rapid increase of intracellular Ca²⁺ concentration ([Ca²⁺]_i) in part flowing from the extracellular compartment and in part released from ER. However, the molecular components of this mechanism remain uncharacterized.

Methods

By an integrated approach consisting on the use of siRNA strategy, Western blotting, confocal double- labeling immunofluorescence, patch-clamp electrophysiology, and Fura 2-/SBFI-single-cell imaging, we explored in rat motor neuron-enriched cultures the involvement of the plasma membrane proteins Na⁺/Ca²⁺ exchanger (NCX) and purinergic P₂X₇ receptor as well as that of the intracellular cADP-ribose (cADPR) pathway, in the neuroprotective mechanism of SOD1.

Results

We showed that SOD1-induced [Ca²⁺]_i rise was prevented neither by A430879, a P₂X₇ receptor specific antagonist or 8-bromo-cADPR, a cell permeant antagonist of cADP-ribose, but only by the pan inhibitor of NCX, CB-DMB. The same occurred for the ApoSOD1. Confocal double labeling immunofluorescence showed a huge expression of plasmalemmal NCX1 and intracellular NCX3 isoforms. Furthermore, we identified NCX1 reverse mode as the main mechanism responsible for the neuroprotective ER Ca²⁺ refilling elicited by SOD1 and ApoSOD1 through which they promoted translocation of active Akt in the nuclei of a subset of primary motor neurons. Finally, the activation of NCX1 by the specific agonist CN-PYB2 protected motor neurons from L-BMAA-induced cell death, mimicking the effect of SOD1.

Conclusion

Collectively, our data indicate that SOD1 and ApoSOD1 exert their neuroprotective effect by modulating ER Ca²⁺ content through the activation of NCX1 reverse mode and Akt nuclear translocation in a subset of primary motor neurons.

The Na+/Ca2+ Exchanger 3 Is Functionally Coupled With the NaV1.6 Voltage-Gated Channel and Promotes an Endoplasmic Reticulum Ca2+ Refilling in a Transgenic Model of Alzheimer's Disease

The remodelling of neuronal ionic homeostasis by altered channels and transporters is a critical feature of the Alzheimer's disease (AD) pathogenesis. Different reports converge on the concept that the Na⁺/Ca²⁺ exchanger (NCX), as one of the main regulators of Na⁺ and Ca²⁺ concentrations and signalling, could exert a neuroprotective role in AD. The activity of NCX has been found to be increased in AD brains, where it seemed to correlate with an increased neuronal survival. Moreover, the enhancement of the NCX3 currents (I_NCX) in primary neurons treated with the neurotoxic amyloid β 1-42 (Aβ_1-42) oligomers prevented the endoplasmic reticulum (ER) stress and neuronal death. The present study has been designed to investigate any possible modulation of the I_NCX, the functional interaction between NCX and the Na_V1.6 channel, and their impact on the Ca²⁺ homeostasis in a transgenic in vitro model of AD, the primary hippocampal neurons from the Tg2576 mouse, which overproduce the Aβ_1-42 peptide. Electrophysiological studies, carried in the presence of siRNA and the isoform-selective NCX inhibitor KB-R7943, showed that the activity of a specific NCX isoform, NCX3, was upregulated in its reverse, Ca²⁺ influx mode of operation in the Tg2576 neurons. The enhanced NCX activity contributed, in turn, to increase the ER Ca²⁺ content, without affecting the cytosolic Ca²⁺ concentrations of the Tg2576 neurons. Interestingly, our experiments have also uncovered a functional coupling between NCX3 and the voltage-gated Na_V1.6 channels. In particular, the increased Na_V1.6 currents appeared to be responsible for the upregulation of the reverse mode of NCX3, since both TTX and the Streptomyces griseolus antibiotic anisomycin, by reducing the Na_V1.6 currents, counteracted the increase of the I_NCX in the Tg2576 neurons. In agreement, our immunofluorescence analyses revealed that the NCX3/Na_V1.6 co-expression was increased in the Tg2576 hippocampal neurons in comparison with the WT neurons. Collectively, these findings indicate that NCX3 might intervene in the Ca²⁺ remodelling occurring in the Tg2576 primary neurons thus emerging as a molecular target with a neuroprotective potential, and provide a new outcome of the Na_V1.6 upregulation related to the modulation of the intracellular Ca²⁺ concentrations in AD neurons.

Rebound effects of NCX3 pharmacological inhibition: A novel strategy to accelerate myelin formation in oligodendrocytes

The Na+/Ca2+ exchanger NCX3 is an important regulator of sodium and calcium homeostasis in oligodendrocyte lineage. To date, no information is available on the effects resulting from prolonged exposure to NCX3 blockers and subsequent drug washout in oligodendroglia. Here, we investigated, by means of biochemical, morphological and functional analyses, the pharmacological effects of the NCX3 inhibitor, the 5-amino-N-butyl-2-(4-ethoxyphenoxy)-benzamide hydrochloride (BED), on NCXs expression and activity, as well as intracellular [Na+]i and [Ca2+]i levels, during treatment and following drug washout both in human MO3.13 oligodendrocytes and rat primary oligodendrocyte precursor cells (OPCs). BED exposure antagonized NCX activity, induced OPCs proliferation and [Na+]i accumulation. By contrast, 2 days of BED washout after 4 days of treatment significantly upregulated low molecular weight NCX3 proteins, reversed NCX activity, and increased intracellular [Ca2+]i. This BED-free effect was accompanied by an upregulation of NCX3 expression in oligodendrocyte processes and accelerated expression of myelin markers in rat primary oligodendrocytes. Collectively, our findings show that the pharmacological inhibition of the NCX3 exchanger with BED blocker maybe followed by a rebound increase in NCX3 expression and reversal activity that accelerate myelin sheet formation in oligodendrocytes. In addition, they indicate that a particular attention should be paid to the use of NCX inhibitors for possible rebound effects, and suggest that further studies will be necessary to investigate whether selective pharmacological modulation of NCX3 exchanger may be exploited to benefit demyelination and remyelination in demyelinating diseases.

Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function?

Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K⁺, Ca²⁺, Na⁺, and Cl^- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na⁺ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na⁺ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K⁺ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl^- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.

The Anemonia sulcata Toxin BDS-I Protects Astrocytes Exposed to Aβ1-42 Oligomers by Restoring [Ca2+]i Transients and ER Ca2+ Signaling

Intracellular calcium concentration ([Ca2+]i) transients in astrocytes represent a highly plastic signaling pathway underlying the communication between neurons and glial cells. However, how this important phenomenon may be compromised in Alzheimer's disease (AD) remains unexplored. Moreover, the involvement of several K+ channels, including KV3.4 underlying the fast-inactivating currents, has been demonstrated in several AD models. Here, the effect of KV3.4 modulation by the marine toxin blood depressing substance-I (BDS-I) extracted from Anemonia sulcata has been studied on [Ca2+]i transients in rat primary cortical astrocytes exposed to Aβ1-42 oligomers. We showed that: (1) primary cortical astrocytes expressing KV3.4 channels displayed [Ca2+]i transients depending on the occurrence of membrane potential spikes, (2) BDS-I restored, in a dose-dependent way, [Ca2+]i transients in astrocytes exposed to Aβ1-42 oligomers (5 µM/48 h) by inhibiting hyperfunctional KV3.4 channels, (3) BDS-I counteracted Ca2+ overload into the endoplasmic reticulum (ER) induced by Aβ1-42 oligomers, (4) BDS-I prevented the expression of the ER stress markers including active caspase 12 and GRP78/BiP in astrocytes treated with Aβ1-42 oligomers, and (5) BDS-I prevented Aβ1-42-induced reactive oxygen species (ROS) production and cell suffering measured as mitochondrial activity and lactate dehydrogenase (LDH) release. Collectively, we proposed that the marine toxin BDS-I, by inhibiting the hyperfunctional KV3.4 channels and restoring [Ca2+]i oscillation frequency, prevented Aβ1-42-induced ER stress and cell suffering in astrocytes.

HDAC4 and HDAC5 form a complex with DREAM that epigenetically down-regulates NCX3 gene and its pharmacological inhibition reduces neuronal stroke damage

The histone deacetylases (HDACs)-dependent mechanisms regulating gene transcription of the Na⁺/Ca⁺ exchanger isoform 3 (ncx3) after stroke are still unknown. Overexpression or knocking-down of HDAC4/HDAC5 down-regulates or increases, respectively, NCX3 mRNA and protein. Likewise, MC1568 (class IIa HDACs inhibitor), but not MS-275 (class I HDACs inhibitor) increased NCX3 promoter activity, gene and protein expression. Furthermore, HDAC4 and HDAC5 physically interacted with the transcription factor downstream regulatory element antagonist modulator (DREAM). As MC1568, DREAM knocking-down prevented HDAC4 and HDAC5 recruitment to the ncx3 promoter. Importantly, DREAM, HDAC4, and HDAC5 recruitment to the ncx3 gene was increased in the temporoparietal cortex of rats subjected to transient middle cerebral artery occlusion (tMCAO), with a consequent histone-deacetylation of ncx3 promoter. Conversely, the tMCAO-induced NCX3 reduction was prevented by intracerebroventricular injection of siDREAM, siHDAC4, and siHDAC5. Notably, MC1568 prevented oxygen glucose deprivation plus reoxygenation and tMCAO-induced neuronal damage, whereas its neuroprotective effect was abolished by ncx3 knockdown. Collectively, we found that: (1) DREAM/HDAC4/HDAC5 complex epigenetically down-regulates ncx3 gene transcription after stroke, and (2) pharmacological inhibition of class IIa HDACs reduces stroke-induced neurodetrimental effects.

In vivo imaging of CNS microglial activation/macrophage infiltration with combined [18F]DPA-714-PET and SPIO-MRI in a mouse model of relapsing remitting experimental autoimmune encephalomyelitis

Purpose

To evaluate the feasibility and sensitivity of multimodality PET/CT and MRI imaging for non-invasive characterization of brain microglial/macrophage activation occurring during the acute phase in a mouse model of relapsing remitting multiple sclerosis (RR-MS) using [¹⁸F]DPA-714, a selective radioligand for the 18-kDa translocator protein (TSPO), superparamagnetic iron oxide particles (SPIO), and ex vivo immunohistochemistry.

Methods

Experimental autoimmune encephalomyelitis (EAE) was induced in female SJL/J mice by immunization with PLP_139–151. Seven symptomatic EAE mice and five controls underwent both PET/CT and MRI studies between 11 and 14 days post-immunization. SPIO was injected i.v. in the same animals immediately after [¹⁸F]DPA-714 and MRI acquisition was performed after 24 h. Regional brain volumes were defined according to a mouse brain atlas on co-registered PET and SPIO-MRI images. [¹⁸F]DPA-714 standardized uptake value (SUV) ratios (SUVR), with unaffected neocortex as reference, and SPIO fractional volumes (SPIO-Vol) were generated. Both SUVR and SPIO-Vol values were correlated with the clinical score (CS) and among them. Five EAE and four control mice underwent immunohistochemical analysis with the aim of identifying activated microglia/macrophage and TSPO expressions.

Results

SUVR and SPIO-Vol values were significantly increased in EAE compared with controls in the hippocampus (p < 0.01; p < 0.02, respectively), thalamus (p < 0.02; p < 0.05, respectively), and cerebellum and brainstem (p < 0.02), while only SPIO-Vol was significantly increased in the caudate/putamen (p < 0.05). Both SUVR and SPIO-Vol values were positively significantly correlated with CS and among them in the same regions. TSPO/Iba1 and F4/80/Prussian blue staining immunohistochemistry suggests that increased activated microglia/macrophages underlay TSPO expression and SPIO uptake in symptomatic EAE mice.

Conclusions

These preliminary results suggest that both activated microglia and infiltrated macrophages are present in vulnerable brain regions during the acute phase of PLP-EAE and contribute to disease severity. Both [¹⁸F]DPA-714-PET and SPIO-MRI appear suitable modalities for preclinical study of neuroinflammation in MS mice models.

The Na+/Ca2+exchanger in Alzheimer's disease

As a pivotal player in regulating sodium (Na⁺) and calcium (Ca²⁺) homeostasis and signalling in excitable cells, the Na⁺/Ca²⁺ exchanger (NCX) is involved in many neurodegenerative disorders in which an imbalance of intracellular Ca²⁺ and/or Na⁺ concentrations occurs, including Alzheimer's disease (AD). Although NCX has been mainly implicated in neuroprotective mechanisms counteracting Ca²⁺ dysregulation, several studies highlighted its role in the neuronal responses to intracellular Na⁺ elevation occurring in several pathophysiological conditions. Since the alteration of Na⁺ and Ca²⁺ homeostasis significantly contributes to synaptic dysfunction and neuronal loss in AD, it is of crucial importance to analyze the contribution of NCX isoforms in the homeostatic responses at neuronal and synaptic levels. Some studies found that an increase of NCX activity in brains of AD patients was correlated with neuronal survival, while other research groups found that protein levels of two NCX subtypes, NCX2 and NCX3, were modulated in parietal cortex of late stage AD brains. In particular, NCX2 positive synaptic terminals were increased in AD cohort while the number of NCX3 positive terminals were reduced. In addition, NCX1, NCX2 and NCX3 isoforms were up-regulated in those synaptic terminals accumulating amyloid-beta (Aβ), the neurotoxic peptide responsible for AD neurodegeneration. More recently, the hyperfunction of a specific NCX subtype, NCX3, has been shown to delay endoplasmic reticulum stress and apoptotic neuronal death in hippocampal neurons exposed to Aβ insult. Despite some issues about the functional role of NCX in synaptic failure and neuronal loss require further studies, these findings highlight the putative neuroprotective role of NCX in AD and open new strategies to develop new druggable targets for AD therapy.

Nuclear localization of NCX: Role in Ca2+ handling and pathophysiological implications

Numerous lines of evidence indicate that nuclear calcium concentration ([Ca²⁺]_n) may be controlled independently from cytosolic events by a local machinery. In particular, the perinuclear space between the inner nuclear membrane (INM) and the outer nuclear membrane (ONM) of the nuclear envelope (NE) likely serves as an intracellular store for Ca²⁺ ions. Since ONM is contiguous with the endoplasmic reticulum (ER), the perinuclear space is adjacent to the lumen of ER thus allowing a direct exchange of ions and factors between the two organelles. Moreover, INM and ONM are fused at the nuclear pore complex (NPC), which provides the only direct passageway between the nucleoplasm and cytoplasm. However, due to the presence of ion channels, exchangers and transporters, it has been generally accepted that nuclear ion fluxes may occur across ONM and INM. Within the INM, the Na⁺/Ca²⁺ exchanger (NCX) isoform 1 seems to play an important role in handling Ca²⁺ through the different nuclear compartments. Particularly, nuclear NCX preferentially allows local Ca²⁺ flowing from nucleoplasm into NE lumen thanks to the Na⁺ gradient created by the juxtaposed Na⁺/K⁺-ATPase. Such transfer reduces abnormal elevation of [Ca²⁺]_n within the nucleoplasm thus modulating specific transductional pathways and providing a protective mechanism against cell death. Despite very few studies on this issue, here we discuss those making major contribution to the field, also addressing the pathophysiological implication of nuclear NCX malfunction.

D-Aspartate treatment attenuates myelin damage and stimulates myelin repair

Glutamate signaling may orchestrate oligodendrocyte precursor cell (OPC) development and myelin regeneration through the activation of glutamate receptors at OPC‐neuron synapses. D‐Aspartate is a D‐amino acid exerting modulatory actions at glutamatergic synapses. Chronic administration of D‐Aspartate has been proposed as therapeutic treatment in diseases related to myelin dysfunction and NMDA receptors hypofunction, including schizophrenia and cognitive deficits. Here, we show, by using an in vivo remyelination model, that administration of D‐Aspartate during remyelination improved motor coordination, accelerated myelin recovery, and significantly increased the number of small‐diameter myelinated axons. Chronically administered during demyelination, D‐Aspartate also attenuated myelin loss and inflammation. Interestingly, D‐Aspartate exposure stimulated OPC maturation and accelerated developmental myelination in organotypic cerebellar slices. D‐Aspartate promoting effects on OPC maturation involved the activation of glutamate transporters, AMPA and NMDA receptors, and the Na⁺/Ca²⁺ exchanger NCX3. While blocking NMDA or NCX3 significantly prevented D‐Aspartate‐induced [Ca²⁺]_i oscillations, blocking AMPA and glutamate transporters prevented both the initial and oscillatory [Ca²⁺]_i response as well as D‐Aspartate‐induced inward currents in OPC. Our findings reveal that D‐Aspartate treatment may represent a novel strategy for promoting myelin recovery.

Combined Surgical Ablation and Intravitreal Triamcinolone Acetonide for Retinal Angiomatous Proliferation

Purpose

Neovascular age-related macular degeneration (ARMD) with retinal angiomatous proliferation (RAP) has a poor natural history and the efficacy of any treatment has not yet been established. The authors describe a combined surgical treatment.

Methods

A 76-year-old woman presented with a best-corrected visual acuity (BCVA) of 20/600 in the right eye and macula with stage 3 RAP as identified by fluorescein angiography (FA), indocyanine green angiography (ICGA), and optical coherence tomography (OCT). After a standard three-port pars plana core vitrectomy (PPV), endodiathermy of the arteriolar and venous feeder vessels of each lesion was performed, intraretinal RAP feeder vessels were cut with manual vertical intraocular scissors, and 0.1 mL of triamcinolone acetonide (TAAC) was injected intravitreally At 1 and 4 weeks and at the sixth month, the patient underwent a complete eye examination, FA, ICGA, and OCT to assess outcomes and complications.

Results

Six months later, BCVA was stable at 20/300, intraocular pressure was 15 mmHg, anterior segment and vitreous cavity were clear without evidence of TAAC granules, and retina was attached. FA and ICGA showed a complete occlusion of the RAP and absence of leakage or ischemia and OCT demonstrated decreased macular thickness with resolution of both intraretinal edema and pigment epithelium detachment, and the restoration of the normal macular profile. At the end of follow-up, the authors did not observe any ocular or systemic complication.

Conclusions

Surgical approach to RAP stage 3 with intravitreal injection of 4 mg of TAAC was safe and anatomically effective.

Intravitreal Triamcinolone Acetonide in Refractory Pseudophakic Cystoid Macular Edema: Functional and Anatomic Results

PURPOSE

To evaluate safety and efficacy of intravitreal triamcinolone acetonide (TAAC) injections in the treatment of refractory pseudophakic cystoid macular edema (CME).

METHODS

Seven eyes of six patients (age range: 50-74) with pseudophakic CME resistant to standard treatment received intravitreal injections of 4 mg of TAAC with all vehicle. Mean preinjection duration of CME was 18.3 months. A mean of 2.1+/-1.2 (range 1 to 4) treatments were performed in four eyes (57.1 %) when visual acuity deteriorated towards baseline levels. Visual acuity assessment, optical coherence tomography (OCT), and fluorescein angiography (FFA) were performed pre- and postoperatively to evaluate results of TAAC injections. Intraocular pressure (IOP) and complications related to treatment were assessed.

RESULTS

After 11.1+/-3.9 months, mean best-corrected visual acuity (BCVA) increased (p =0.019) from 20/132 to a best value of 20/38. Mean macular thickness decreased from 517.29+/-146.98 mm to a best value of 263.71+/-83.13 mm (p=0.0018). Area of fluorescein leakage decreased (p<0.0001) from 11.84+/-0.93 mm2 at baseline to a minimal value of 3.86+/-0.98 mm2. The anatomic and functional improvement appeared after 1 month from the intravitreal injection and persisted through at least 3 months of follow-up. At the end of follow-up BCVA, macular thickness, and area of fluorescein leakage did not differ from baseline. Four eyes (57.1 %) developed IOP values higher than 21 mmHg, controlled by topical treatment. Two patients developed an endophthalmitis-like reaction.

CONCLUSIONS

Intravitreal TAAC was relatively safe and effective in resistant cases of pseudophakic CME with a temporary beneficial effect on visual acuity and macular edema.

Macular Hole following Conventional Repair of Bullous Retinal Detachment Using Air Injection (D-ACE Procedure)

PURPOSE

Sequential drainage of subretinal fluid (D), injection of air (A), cryotherapy (C), and application of local explants (E) (D-ACE) sequence was introduced in order to overcome the problems encountered in managing superior bullous detachments from multiple large equatorial breaks. The authors recently observed the occurrence of a full-thickness macular hole in one patient developing the day after he underwent a D-ACE procedure.

METHODS

A 61-year-old man presented a bullous retinal detachment in the right eye extending from the 9:30 to the 2 o'clock position, and posteriorly to the vascular arcades two retinal tears were noted, at the equator at 11 o'clock, and anterior to the equator at 12 o'clock. The patient underwent a D-ACE procedure. Subretinal fluid was drained above the lateral rectus muscle at the equator. One and a half milliliters of air were injected 3.5 mm from the limbus midway between the superior and the medial rectus insertions. Cryotherapy was applied to the retinal breaks. A 240 encircling band was used in conjunction with a 276 tyre segment at the level of the tears.

RESULTS

One day after surgery, the retina was flat, but a full-thickness macular hole could be seen with a surrounding cuff of subretinal fluid.

CONCLUSIONS

The mechanisms proposed to explain the occurrence of full-thickness macular holes after D-ACE may involve the concurrence of scleral elongation and vitreofoveal traction by means of previous partial posterior vitreous detachment with persistent posterior attachments at the fovea.

The expression and activity of KV3.4 channel subunits are precociously upregulated in astrocytes exposed to Aβ oligomers and in astrocytes of Alzheimer's disease Tg2576 mice

Astrocyte dysfunction emerges early in Alzheimer's disease (AD) and may contribute to its pathology and progression. Recently, the voltage gated potassium channel K_V3.4 subunit, which underlies the fast-inactivating K⁺ currents, has been recognized to be relevant for AD pathogenesis and is emerging as a new target candidate for AD. In the present study, we investigated both in in vitro and in vivo models of AD the expression and functional activity of K_V3.4 potassium channel subunits in astrocytes. In primary astrocytes our biochemical, immunohistochemical, and electrophysiological studies demonstrated a time-dependent upregulation of K_V3.4 expression and functional activity after exposure to amyloid-β (Aβ) oligomers. Consistently, astrocytic K_V3.4 expression was upregulated in the cerebral cortex, hippocampus, and cerebellum of 6-month-old Tg2576 mice. Further, confocal triple labeling studies revealed that in 6-month-old Tg2576 mice, K_V3.4 was intensely coexpressed with Aβ in nonplaque associated astrocytes. Interestingly, in the cortical and hippocampal regions of 12-month-old Tg2576 mice, plaque-associated astrocytes much more intensely expressed K_V3.4 subunits, but not Aβ. More important, we evidenced that the selective knockdown of K_V3.4 expression significantly downregulated both glial fibrillary acidic protein levels and Aβ trimers in the brain of 6-month-old Tg2576 mice. Collectively, our results demonstrate that the expression and function of K_V3.4 channel subunits are precociously upregulated in cultured astrocytes exposed to Aβ oligomers and in reactive astrocytes of AD Tg2576 mice.

Tracking the evolution of epialleles during neural differentiation and brain development: D-Aspartate oxidase as a model gene

We performed ultra-deep methylation analysis at single molecule level of the promoter region of developmentally regulated D-Aspartate oxidase (Ddo), as a model gene, during brain development and embryonic stem cell neural differentiation. Single molecule methylation analysis enabled us to establish the effective epiallele composition within mixed or pure brain cell populations. In this framework, an epiallele is defined as a specific combination of methylated CpG within Ddo locus and can represent the epigenetic haplotype revealing a cell-to-cell methylation heterogeneity. Using this approach, we found a high degree of polymorphism of methylated alleles (epipolymorphism) evolving in a remarkably conserved fashion during brain development. The different sets of epialleles mark stage, brain areas, and cell type and unravel the possible role of specific CpGs in favoring or inhibiting local methylation. Undifferentiated embryonic stem cells showed non-organized distribution of epialleles that apparently originated by stochastic methylation events on individual CpGs. Upon neural differentiation, despite detecting no changes in average methylation, we observed that the epiallele distribution was profoundly different, gradually shifting toward organized patterns specific to the glial or neuronal cell types. Our findings provide a deep view of gene methylation heterogeneity in brain cell populations promising to furnish innovative ways to unravel mechanisms underlying methylation patterns generation and alteration in brain diseases.

Neuronal NCX1 overexpression induces stroke resistance while knockout induces vulnerability via Akt

Three different Na⁺/Ca²⁺ exchanger (NCX) isoforms, NCX1, NCX2, and NCX3, are expressed in brain where they play a relevant role in maintaining Na⁺ and Ca²⁺ homeostasis. Although the neuroprotective roles of NCX2 and NCX3 in stroke have been elucidated, the relevance of NCX1 is still unknown because of embryonic lethality of its knocking-out, heart dysfunctions when it is overexpressed, and the lack of selectivity in currently available drugs. To overcome these limitations we generated two conditional genetically modified mice that upon tamoxifen administration showed a selective decrease or increase of NCX1 in cortical and hippocampal neurons. Interestingly, in cortex and hippocampus NCX1 overexpression increased, where NCX1 knock-out reduced, both exchanger activity and Akt1 phosphorylation, a neuronal survival signaling. More important, mice overexpressing NCX1 showed a reduced ischemic volume and an amelioration of focal and general deficits when subjected to transient middle cerebral artery occlusion. Conversely, NCX1-knock-out mice displayed a worsening of brain damage, focal and neurological deficits with a decrease in Akt phosphorylation. These results support the idea that NCX1 overexpression/activation may represent a feasible therapeutic opportunity in stroke intervention.

Glial Na(+) -dependent ion transporters in pathophysiological conditions

Sodium dynamics are essential for regulating functional processes in glial cells. Indeed, glial Na(+) signaling influences and regulates important glial activities, and plays a role in neuron-glia interaction under physiological conditions or in response to injury of the central nervous system (CNS). Emerging studies indicate that Na(+) pumps and Na(+) -dependent ion transporters in astrocytes, microglia, and oligodendrocytes regulate Na(+) homeostasis and play a fundamental role in modulating glial activities in neurological diseases. In this review, we first briefly introduced the emerging roles of each glial cell type in the pathophysiology of cerebral ischemia, Alzheimer's disease, epilepsy, Parkinson's disease, Amyotrophic Lateral Sclerosis, and myelin diseases. Then, we discussed the current knowledge on the main roles played by the different glial Na(+) -dependent ion transporters, including Na(+) /K(+) ATPase, Na(+) /Ca(2+) exchangers, Na(+) /H(+) exchangers, Na(+) -K(+) -Cl(-) cotransporters, and Na(+) - HCO3- cotransporter in the pathophysiology of the diverse CNS diseases. We highlighted their contributions in cell survival, synaptic pathology, gliotransmission, pH homeostasis, and their role in glial activation, migration, gliosis, inflammation, and tissue repair processes. Therefore, this review summarizes the foundation work for targeting Na(+) -dependent ion transporters in glia as a novel strategy to control important glial activities associated with Na(+) dynamics in different neurological disorders. GLIA 2016;64:1677-1697.

Effects of bone marrow mesenchymal stem cells (BM-MSCs) on rat pial microvascular remodeling after transient middle cerebral artery occlusion

Previous studies have shown that the pial microcirculation remodeling improves neurological outcome after middle cerebral artery occlusion (MCAO), accompanied by higher expression of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS), modulating in vivo angiogenesis. This study was aimed to assess the effects of bone marrow mesenchymal stem cells (BM-MSCs) infused after MCAO on rat pial microcirculation. Animals were subjected to 2 h MCAO followed by BM-MSCs infusion into internal carotid artery. Pial microcirculation was observed at different reperfusion times by fluorescence microscopy. Geometric characteristics of arteriolar networks, permeability increase, leukocyte adhesion, perfused capillary density, VEGF, and endothelial nitric oxide synthase (e-NOS) expression were evaluated. Green fluorescent protein (GFP)-BM-MSCs were used to evaluate their distribution and cell phenotype development during reperfusion. BM-MSCs stimulated a geometric rearrangement of pial networks with formation of new anastomotic vessels sprouting from preexistent arterioles in the penumbra at 7-14-28 days of reperfusion. At the same time VEGF and eNOS expression increased. GFP-BM-MSCs appear to be involved in endothelial and smooth muscle cell programming in the infarcted area. In conclusion, transient MCAO induced pial vascular remodeling characterized by arteriolar anastomotic arcades (originated from preexistent arterioles in penumbra area) able to overlap the ischemic core supplying blood to the neuronal tissue. BM-MSCs appear to accelerate angiogenic processes facilitating new vessel formation; this mechanism was promoted by an increase in VEGF and eNOS expression.

Pharmacological characterization of the newly synthesized 5-amino-N-butyl-2-(4-ethoxyphenoxy)-benzamide hydrochloride (BED) as a potent NCX3 inhibitor that worsens anoxic injury in cortical neurons, organotypic hippocampal cultures, and ischemic brain

The Na(+)/Ca(2+) exchanger (NCX), a 10-transmembrane domain protein mainly involved in the regulation of intracellular Ca(2+) homeostasis, plays a crucial role in cerebral ischemia. In the present paper, we characterized the effect of the newly synthesized compound 5-amino-N-butyl-2-(4-ethoxyphenoxy)-benzamide hydrochloride (BED) on the activity of the three NCX isoforms and on the evolution of cerebral ischemia. BED inhibited NCX isoform 3 (NCX3) activity (IC50 = 1.9 nM) recorded with the help of single-cell microflorimetry, (45)Ca(2+) radiotracer fluxes, and patch-clamp in whole-cell configuration. Furthermore, this drug displayed negligible effect on NCX2, the other isoform expressed within the CNS, and it failed to modulate the ubiquitously expressed NCX1 isoform. Concerning the molecular site of action, the use of chimera strategy and deletion mutagenesis showed that α1 and α2 repeats of NCX3 represented relevant molecular determinants for BED inhibitory action, whereas the intracellular regulatory f-loop was not involved. At 10 nM, BED worsened the damage induced by oxygen/glucose deprivation (OGD) followed by reoxygenation in cortical neurons through a dysregulation of [Ca(2+)]i. Furthermore, at the same concentration, BED significantly enhanced cell death in CA3 subregion of hippocampal organotypic slices exposed to OGD and aggravated infarct injury after transient middle cerebral artery occlusion in mice. These results showed that the newly synthesized 5-amino-N-butyl-2-(4-ethoxyphenoxy)-benzamide hydrochloride is one of the most potent inhibitor of NCX3 so far identified, representing an useful tool to dissect the role played by NCX3 in the control of Ca(2+) homeostasis under physiological and pathological conditions.

High levels of GPR30 protein in human testicular carcinoma in situ and seminomas correlate with low levels of estrogen receptor-beta and indicate a switch in estrogen responsiveness

The G protein-coupled estrogen receptor (GPR30) is suggested to be involved in non-nuclear estrogen signalling and is expressed in a variety of hormone dependent cancer entities. It is well established that oestrogens are involved in pathological germ cell proliferation including testicular germ cell tumours. This study was performed to further elucidate the role of this receptor and the possible correlation with the estrogen receptor β in human testicular carcinoma in situ (CIS), seminomas and in GC1 and TCam-2 germ cell lines; in addition, a Tissue Micro-Array was built using the most representative areas from 25 cases of human testicular seminomas and 20 cases of CIS. The expression of ERβ and GPR30 were observed by using Western blot analysis in combination with immunocytochemistry and immunofluorescence analyses. Here, we show that down regulation of ERβ associates with GPR30 over-expression both in human testicular CIS and seminomas. In addition, we show that 17β-oestradiol induces the ERK1/2 activation and increases c-Fos expression through GPR30 associated with ERβ down-regulation in TCam-2 cell line. The present results suggest that exposure to oestrogens or oestrogen-mimics, in some as of yet undefined manner, diminishes the ERβ-mediated growth restraint in CIS and in human testicular seminoma, probably due to ERβ down-regulation associated to GPR30 increased expression indicating that GPR30 could be a potential therapeutic target to design specific inhibitors.

Involvement of the Na+/Ca2+ exchanger isoform 1 (NCX1) in neuronal growth factor (NGF)-induced neuronal differentiation through Ca2+-dependent Akt phosphorylation

NGF induces neuronal differentiation by modulating [Ca(2+)]i. However, the role of the three isoforms of the main Ca(2+)-extruding system, the Na(+)/Ca(2+) exchanger (NCX), in NGF-induced differentiation remains unexplored. We investigated whether NCX1, NCX2, and NCX3 isoforms could play a relevant role in neuronal differentiation through the modulation of [Ca(2+)]i and the Akt pathway. NGF caused progressive neurite elongation; a significant increase of the well known marker of growth cones, GAP-43; and an enhancement of endoplasmic reticulum (ER) Ca(2+) content and of Akt phosphorylation through an early activation of ERK1/2. Interestingly, during NGF-induced differentiation, the NCX1 protein level increased, NCX3 decreased, and NCX2 remained unaffected. At the same time, NCX total activity increased. Moreover, NCX1 colocalized and coimmunoprecipitated with GAP-43, and NCX1 silencing prevented NGF-induced effects on GAP-43 expression, Akt phosphorylation, and neurite outgrowth. On the other hand, the overexpression of its neuronal splicing isoform, NCX1.4, even in the absence of NGF, induced an increase in Akt phosphorylation and GAP-43 protein expression. Interestingly, tetrodotoxin-sensitive Na(+) currents and 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10-trioxa-7,13-diazacyclopentadecane-7,13-diylbis(5-methoxy-6,12-benzofurandiyl)]bis-, tetrakis[(acetyloxy)methyl] ester-detected [Na(+)]i significantly increased in cells overexpressing NCX1.4 as well as ER Ca(2+) content. This latter effect was prevented by tetrodotoxin. Furthermore, either the [Ca(2+)]i chelator(1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) (BAPTA-AM) or the PI3K inhibitor LY 294002 prevented Akt phosphorylation and GAP-43 protein expression rise in NCX1.4 overexpressing cells. Moreover, in primary cortical neurons, NCX1 silencing prevented Akt phosphorylation, GAP-43 and MAP2 overexpression, and neurite elongation. Collectively, these data show that NCX1 participates in neuronal differentiation through the modulation of ER Ca(2+) content and PI3K signaling.

Extracellular signal-related kinase 2/specificity protein 1/specificity protein 3/repressor element-1 silencing transcription factor pathway is involved in Aroclor 1254-induced toxicity in SH-SY5Y neuronal cells

Polychlorinated biphenyls (PCBs) cause a wide spectrum of toxic effects in the brain through undefined mechanisms. Exposure to the PCB mixture Aroclor-1254 (A1254) increases the repressor element-1 silencing transcription factor (REST) expression, leading to neuronal death. This study sought to understand the sequence of some molecular mechanisms to determine whether A1254 could increase REST expression and the cytoprotective effect of the phorbol ester tetradecanoylphorbol acetate (TPA) on A1254-induced toxicity in SH-SY5Y cells. As shown by Western blot analysis, A1254 (10 µg/ml) downregulates extracellular signal-related kinase 2 (ERK2) phosphorylation in a time-dependent manner, thereby triggering the binding of specificity protein 1 (Sp1) and Sp3 to the REST gene promoter as revealed by chromatin immunoprecipitation analysis. This chain of events results in an increase in REST mRNA and cell death, as assessed by quantitative real-time polymerase chain reaction and dimethylthiazolyl-2-5-diphenyltetrazolium-bromide assay, respectively. Accordingly, TPA prevented both the A1254-induced decrease in ERK2 phosphorylation and the A1254-induced increase in Sp1, Sp3, and REST protein expression. After 48 hr, TPA prevented A1254-induced cell death. ERK2 overexpression counteracted the A1254-induced increase in Sp1 and Sp3 protein expression and prevented A1254-induced Sp1 and Sp3 binding to the REST gene promoter, thus counteracting the increase in REST mRNA expression induced by the toxicant. In neuroblastoma SH-SY5Y cells, ERK2/Sp1/SP3/REST is a new pathway underlying the neurotoxic effect of PCB. The ERK2/Sp1/Sp3/REST pathway, which underlies A1254-induced neuronal death, might represent a new drug signaling cascade in PCB-induced neuronal toxicity.

Critical role of large-conductance calcium- and voltage-activated potassium channels in leptin-induced neuroprotection of N-methyl-d-aspartate-exposed cortical neurons

In the present study, the neuroprotective effects of the adipokine leptin, and the molecular mechanism involved, have been studied in rat and mice cortical neurons exposed to N-methyl-d-aspartate (NMDA) in vitro. In rat cortical neurons, leptin elicited neuroprotective effects against NMDA-induced cell death, which were concentration-dependent (10-100 ng/ml) and largest when the adipokine was preincubated for 2h before the neurotoxic stimulus. In both rat and mouse cortical neurons, leptin-induced neuroprotection was fully antagonized by paxilline (Pax, 0.01-1 μM) and iberiotoxin (Ibtx, 1-100 nM), with EC50s of 38 ± 10 nM and 5 ± 2 nM for Pax and Ibtx, respectively, close to those reported for Pax- and Ibtx-induced Ca(2+)- and voltage-activated K(+) channels (Slo1 BK channels) blockade; the BK channel opener NS1619 (1-30 μM) induced a concentration-dependent protection against NMDA-induced excitotoxicity. Moreover, cortical neurons from mice lacking one or both alleles coding for Slo1 BK channel pore-forming subunits were insensitive to leptin-induced neuroprotection. Finally, leptin exposure dose-dependently (10-100 ng/ml) increased intracellular Ca(2+) levels in rat cortical neurons. In conclusion, our results suggest that Slo1 BK channel activation following increases in intracellular Ca(2+) levels is a critical step for leptin-induced neuroprotection in NMDA-exposed cortical neurons in vitro, thus highlighting leptin-based intervention via BK channel activation as a potential strategy to counteract neurodegenerative diseases.

NCX3 regulates mitochondrial Ca(2+) handling through the AKAP121-anchored signaling complex and prevents hypoxia-induced neuronal death

The mitochondrial influx and efflux of Ca(2+) play a relevant role in cytosolic and mitochondrial Ca(2+) homeostasis, and contribute to the regulation of mitochondrial functions in neurons. The mitochondrial Na(+)/Ca(2+) exchanger, which was first postulated in 1974, has been primarily investigated only from a functional point of view, and its identity and localization in the mitochondria have been a matter of debate over the past three decades. Recently, a Li(+)-dependent Na(+)/Ca(2+) exchanger extruding Ca(2+) from the matrix has been found in the inner mitochondrial membrane of neuronal cells. However, evidence has been provided that the outer membrane is impermeable to Ca(2+) efflux into the cytoplasm. In this study, we demonstrate for the first time that the nuclear-encoded NCX3 isoform (1) is located on the outer mitochondrial membrane (OMM) of neurons; (2) colocalizes and immunoprecipitates with AKAP121 (also known as AKAP1), a member of the protein kinase A anchoring proteins (AKAPs) present on the outer membrane; (3) extrudes Ca(2+) from mitochondria through AKAP121 interaction in a PKA-mediated manner, both under normoxia and hypoxia; and (4) improves cell survival when it works in the Ca(2+) efflux mode at the level of the OMM. Collectively, these results suggest that, in neurons, NCX3 regulates mitochondrial Ca(2+) handling from the OMM through an AKAP121-anchored signaling complex, thus promoting cell survival during hypoxia.

The isolectin IB4 binds RET receptor tyrosine kinase in microglia

Ret receptor tyrosine kinase is the signaling component of the receptor complex for the family ligands of the glial cell line-derived neurotrophic factor (GDNF). Ret is involved in the development of enteric nervous system, of sympathetic, parasympathetic, motor and sensory neurons, and it is necessary for the post-natal maintenance of dopaminergic neurons. Ret expression has been as well demonstrated on microglia and several evidence indicate that GDNF regulates not only neuronal survival and maturation but also certain functions of microglia in the brain. Here, we demonstrated that the plant lectin Griffonia (Bandeiraea) simplicifolia lectin I, isolectin B4 (IB4), commonly used as a microglial marker in the brain, binds to the glycosylated extracellular domain of Ret on the surface of living NIH3T3 fibroblasts cells stably transfected with Ret as well as in adult rat brain as revealed by immunoblotting. Furthermore, confocal immunofluorescence analysis demonstrated a clear overlap in staining between pRet and IB4 in primary microglia cultures as well as in adult rat sections obtained from control or post-ischemic brain after permanent middle artery occlusion (pMCAO). Interestingly, IB4 staining identified activated or ameboid Ret-expressing microglia under ischemic conditions. Collectively, our data indicate Ret receptor as one of the IB4-reactive glycoconjugate accounting for the IB4 stain in microglia under physiological and ischemic conditions.

Transcriptional regulation of ncx1 gene in the brain

The ubiquitous sodium-calcium exchanger isoform 1 (NCX1) is a -bidirectional transporter that plays a relevant role under physiological and pathophysiological conditions including brain ischemia by regulating intraneuronal Ca(2+) and Na(+) homeostasis. Although changes in ncx1 protein and transcript expression have been detected during stroke, its transcriptional regulation is still largely unexplored. Here, we reviewed our recent findings on several transcription factors including cAMP response element-binding protein (CREB), nuclear factor kappa B (NF-κB), and hypoxia-inducible factor-1 (HIF-1) in the control of the ncx1 gene expression in neuronal cells.

New roles of NCX in glial cells: activation of microglia in ischemia and differentiation of oligodendrocytes

The initiation of microglial responses to the ischemic injury involves modifications of calcium homeostasis. Changes in [Ca(2+)](i) levels have also been shown to influence the developmental processes that accompany the transition of human oligodendrocyte precursor cells (OPCs) into mature myelinating oligodendrocytes and are required for the initiation of myelination and remyelination processes.We investigated the regional and temporal changes of NCX1 protein in microglial cells of the peri-infarct and core regions after permanent middle cerebral artery occlusion (pMCAO). Interestingly, 3 and 7 days after pMCAO, NCX1 signal strongly increased in the round-shaped microglia invading the infarct core. Cultured microglial cells from the core displayed increased NCX1 expression as compared with contralateral cells and showed enhanced NCX activity in the reverse mode of operation. Similarly, NCX activity and NCX1 protein expression were significantly enhanced in BV2 microglia exposed to oxygen and glucose deprivation, whereas NCX2 and NCX3 were downregulated. Interestingly, in NCX1-silenced cells, [Ca(2+)](i) increase induced by hypoxia was completely prevented. The upregulation of NCX1 expression and activity observed in microglia after pMCAO suggests a relevant role of NCX1 in modulating microglia functions in the postischemic brain.Next, we explored whether calcium signals mediated by NCX1, NCX2, or NCX3 play a role in oligodendrocyte maturation. Functional studies, as well as mRNA and protein expression analyses, revealed that NCX1 and NCX3, but not NCX2, were divergently modulated during OPC differentiation into oligodendrocyte. In fact, while NCX1 was downregulated, NCX3 was strongly upregulated during the oligodendrocyte development. Whereas the knocking down of the NCX3 isoform in OPCs prevented the upregulation of the myelin protein markers CNPase and MBP, its overexpression induced their upregulation. Furthermore, NCX3 knockout mice exhibited not only a reduced size of spinal cord but also a marked hypomyelination, as revealed by the decrease in MBP expression and by the accompanying increase in OPCs number. Our findings indicate that calcium signaling mediated by NCX3 plays a crucial role in oligodendrocyte maturation and myelin formation.

Genetically modified mice as a strategy to unravel the role played by the Na(+)/Ca (2+) exchanger in brain ischemia and in spatial learning and memory deficits

Because no isoform-specific blocker of NCX has ever been synthesized, a more selective strategy to identify the role of each antiporter isoform in the brain was represented by the generation of knockout and knockin mice for the different isoforms of the antiporter.Experiments performed in NCX2 and NCX3 knockout mice provided evidence that these two isoforms participate in spatial learning and memory consolidation, although in an opposite manner. These new data from ncx2-/- and ncx3-/- mice may open new experimental avenues for the development of effective therapeutic compounds that, by selectively inhibiting or activating these molecular targets, could treat patients affected by cognitive impairment including Alzheimer's, Parkinson's, Huntington's diseases, and infarct dementia.More importantly, knockout and knockin mice also provided new relevant information on the role played by NCX in maintaining the intracellular Na(+) and Ca(2+) homeostasis and in protecting neurons during brain ischemia. In particular, both ncx2-/- and ncx3-/- mice showed an increased neuronal vulnerability after the ischemic insult induced by transient middle cerebral artery occlusion.As the ubiquitous deletion of NCX1 brings about to an early death of embryos because of a lack of heartbeat, this strategy could not be successfully pursued. However, information on the role of NCX1 in normal and ischemic brain could be obtained by developing conditional knockout mice lacking NCX1 in the brain. Preliminarily results obtained in these conditional mice suggest that also NCX1 protects neurons from ischemic cell death.Overall, the use of genetic-modified mice for NCX1, NCX2, and NCX3 represents a fruitful strategy to characterize the physiological role exerted by NCX in CNS and to identify the isoforms of the antiporter as potential molecular targets for therapeutic intervention in cerebral ischemia.

NCX1 is a new rest target gene: role in cerebral ischemia

The Na(+)-Ca(2+) exchanger 1 (NCX1), a bidirectional transporter that mediates the electrogenic exchange of one calcium ion for three sodium ions across the plasma membrane, is known to be involved in brain ischemia. Since the RE1-silencing transcription factor (REST) is a key modulator of neuronal gene expression in several neurological conditions, we studied the possible involvement of REST in regulating NCX1 gene expression and activity in stroke. We found that: (1) REST binds in a sequence specific manner and represses through H4 deacetylation, ncx1 gene in neuronal cells by recruting CoREST, but not mSin3A. (2) In neurons and in SH-SY5Y cells REST silencing by siRNA and site-direct mutagenesis of REST consensus sequence on NCX1 brain promoter determined an increase in NCX1 promoter activity. (3) By contrast, REST overexpression caused a reduction in NCX1 protein expression and activity. (4) Interestingly, in rats subjected to transient middle cerebral artery occlusion (tMCAO) and in organotypic hippocampal slices or SH-SY5Y cells exposed to oxygen and glucose deprivation (OGD) plus reoxygenation (RX), the increase in REST was associated with a decrease in NCX1. However, this reduction was reverted by REST silencing. (5) REST knocking down, along with the deriving NCX1 overexpression in the deep V and VIb cortical layers caused a marked reduction in infarct volume after tMCAO. Double silencing of REST and NCX1 completely abolished neuroprotection induced by siREST administration. Collectively, these results demonstrate that REST, by regulating NCX1 expression, may represent a potential druggable target for the treatment of brain ischemia.

Activation of stress kinases in the brain of mucopolysaccharidosis IIIB mice

The accumulation of heparan sulfate (HS) in lysosomes is the primary consequence of the enzyme defect (α-N-acetylglucosaminidase) in mucopolysaccharidosis type IIIB. This accumulation triggers a cascade of pathological events that progressively leads to CNS pathology. Here we examined the activation of the three major stress kinases in the neuronal tissue of a murine model of the disease. ERK1/2 was significantly higher in the cortex of 1–2-month-old affected animals compared with wild-type (Wt) littermates. Similarly, ERK1/2 was stimulated in neurons cultured from MPS IIIB mice. SAPK/JNK was also found to be activated in the cortex of 1–2-month-old affected animals compared with Wt subjects, and the same was found for cultured neurons. In contrast, the active form of p38MAPK was lower in the cortex of 1-month-old MPS IIIB mice compared with Wt animals, but no significant difference was found between the two p38MAPK analyzed in normal and affected neurons cultured in vitro. These data indicate the possible involvement of MAPK dysregulation in the early stage of MPS IIIB brain disease. © 2011 Wiley-Liss, Inc.

GPR30 is overexpressed in post-puberal testicular germ cell tumors

GPR30 is a 7-transmembrane G protein-coupled estrogen receptor that functions alongside traditional estrogen receptors to regulate cellular responses to 17β-estradiol and environmental estrogens. In this study, we have evaluated by immunohistochemical analysis GPR30 expression in post-puberal testicular germ cell tumours (30 seminomas, 5 teratomas, 12 embryonal carcinomas, and 20 intratubular germ cell tumors). The GPR30 protein expression was detected at high level in all intratubular germ cell tumours, seminomas, and embryonal carcinomas, whereas in teratomas the expression was low. The immunohistochemical data were further confirmed by Western blot analysis. GPR30 protein expression has also been analyzed in GC1 and TCam-2 cell lines, respectively derived from immortalized type B murine spermatogonia and human seminoma. Our results indicate that GPR30 could be a potential therapeutic target; the design of a specific GPR30 inhibitors could be a useful molecular target to block neoplastic germ cells with a high proliferative rate for the treatment of TGCTs.