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

The interplay between sodium/glucose cotransporter type 2 and mitochondrial ionic environment

Mitochondrial volume is maintained through the permeability of the inner mitochondrial membrane by a specific aquaporin and the osmotic balance between the mitochondrial matrix and cellular cytoplasm. Various electrolytes, such as calcium and hydrogen ions, potassium, and sodium, as well as other osmotic substances, affect the swelling of mitochondria. Intracellular glucose levels may also affect mitochondrial swelling, although the relationship between mitochondrial ion homeostasis and intracellular glucose is poorly understood. This article reviews what is currently known about how the Sodium-Glucose transporter (SGLT) may impact mitochondrial sodium (Na+) homeostasis. SGLTs regulate intracellular glucose and sodium levels and, therefore, interfere with mitochondrial ion homeostasis because mitochondrial Na+ is closely linked to cytoplasmic calcium and sodium dynamics. Recently, a large amount of data has been available on the effects of SGLT2 inhibitors on mitochondria in different cell types, including renal proximal tubule cells, endothelial cells, mesangial cells, podocytes, neuronal cells, and cardiac cells. The current evidence suggests that SGLT inhibitors (SGLTi) may affect mitochondrial dynamics regarding intracellular Sodium and hydrogen ions. Although the regulation of mitochondrial ion channels by SGLTs is still in its infancy, the evidence accumulated thus far of the effect of SGLTi on mitochondrial functions certainly will foster further research in this direction.

Control of Ca2+ and metabolic homeostasis by the Na+/Ca2+ exchangers (NCXs) in health and disease

Spatial and temporal control of calcium (Ca²⁺) levels is essential for the background rhythms and responses of living cells to environmental stimuli. Whatever other regulators a given cellular activity may have, localized and wider scale Ca²⁺ events (sparks, transients, and waves) are hierarchical determinants of fundamental processes such as cell contraction, excitability, growth, metabolism and survival. Different cell types express specific channels, pumps and exchangers to efficiently generate and adapt Ca²⁺ patterns to cell requirements. The Na⁺/Ca²⁺ exchangers (NCXs) in particular contribute to Ca²⁺ homeostasis by buffering intracellular Ca²⁺ loads according to the electrochemical gradients of substrate ions - i.e., Ca²⁺ and sodium (Na⁺) - and under a dynamic control of redundant regulatory processes. An interesting feature of NCX emerges from the strict relationship that connects transporter activity with cell metabolism: on the one hand NCX operates under constant control of ATP-dependent regulatory processes, on the other hand the ion fluxes generated through NCX provide mechanistic support for the Na⁺-driven uptake of glutamate and Ca²⁺ influx to fuel mitochondrial respiration. Proof of concept evidence highlights therapeutic potential of preserving a timed and balanced NCX activity in a growing rate of diseases (including excitability, neurodegenerative, and proliferative disorders) because of an improved ability of stressed cells to safely maintain ion gradients and mitochondrial bioenergetics. Here, we will summarize and review recent works that have focused on the pathophysiological roles of NCXs in balancing the two-way relationship between Ca²⁺ signals and metabolism.

Design of a Proteolytically Stable Sodium-Calcium Exchanger 1 Activator Peptide for In Vivo Studies

The cardiac sodium–calcium exchanger (NCX1) is important for normal Na⁺- and Ca²⁺-homeostasis and cardiomyocyte relaxation and contraction. It has been suggested that NCX1 activity is reduced by phosphorylated phospholemman (pSer68-PLM); however its direct interaction with PLM is debated. Disruption of the potentially inhibitory pSer68-PLM-NCX1 interaction might be a therapeutic strategy to increase NCX1 activity in cardiac disease. In the present study, we aimed to analyze the binding affinities and kinetics of the PLM-NCX1 and pSer68-PLM-NCX1 interactions by surface plasmon resonance (SPR) and to develop a proteolytically stable NCX1 activator peptide for future in vivo studies. The cytoplasmic parts of PLM (PLM_cyt) and pSer68-PLM (pSer68-PLM_cyt) were found to bind strongly to the intracellular loop of NCX1 (NCX1_cyt) with similar K_D values of 4.1 ± 1.0 nM and 4.3 ± 1.9 nM, but the PLM_cyt-NCX1_cyt interaction showed higher on/off rates. To develop a proteolytically stable NCX1 activator, we took advantage of a previously designed, high-affinity PLM binding peptide (OPT) that was derived from the PLM binding region in NCX1 and that reverses the inhibitory PLM (S68D)-NCX1 interaction in HEK293. We performed N- and C-terminal truncations of OPT and identified PYKEIEQLIELANYQV as the minimum sequence required for pSer68-PLM binding. To increase peptide stability in human serum, we replaced the proline with an N-methyl-proline (NOPT) after identification of N-terminus as substitution tolerant by two-dimensional peptide array analysis. Mass spectrometry analysis revealed that the half-life of NOPT was increased 17-fold from that of OPT. NOPT pulled down endogenous PLM from rat left ventricle lysate and exhibited direct pSer68-PLM binding in an ELISA-based assay and bound to pSer68-PLM_cyt with a K_D of 129 nM. Excess NOPT also reduced the PLM_cyt-NCX1_cyt interaction in an ELISA-based competition assay, but in line with that NCX1 and PLM form oligomers, NOPT was not able to outcompete the physical interaction between endogenous full length proteins. Importantly, cell-permeable NOPT-TAT increased NCX1 activity in cardiomyocytes isolated from both SHAM-operated and aorta banded heart failure (HF) mice, indicating that NOPT disrupted the inhibitory pSer68-PLM-NCX1 interaction. In conclusion, we have developed a proteolytically stable NCX1-derived PLM binding peptide that upregulates NCX1 activity in SHAM and HF cardiomyocytes.

NCX3 alleviates ethanol-induced apoptosis of SK-N-SH cells via the elimination of intracellular calcium ions

Long-term alcohol intake may cause nerve cell apoptosis and induce various encephalopathies. Previously, we have shown that the expression of Na⁺/Ca²⁺ exchanger 3 (NCX3) was associated with the intracellular calcium concentration ([Ca2+]i) and apoptosis, involved in the spatial memory impairment in male C57BL/6 mice with chronic ethanol (EtOH) exposure. However, the mechanism involved is unclear. Here, we investigated the expression of NCX3 and its protective effect on SK-N-SH cells (a nerve cell line) after EtOH exposure. [Ca²⁺]i was measured using Fluo-3 AM reagent. Cell viability and the apoptotic rate were assayed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) and flow cytometry, respectively. The expression of p-cAMP-responsive element binding protein1(p-CREB 1), NCX3 protein, and mRNA were observed using Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR), respectively. Cleaved-caspase-3, caspase-3, rabbit anti- poly (ADP-ribose) polymerase-1 (PARP-1) and calpain-1 proteins were used to assess the degree of apoptosis. Our results showed that EtOH increased [Ca²⁺]i and apoptosis of SK-N-SH cells in a concentration- and time-dependent manner. The expression of NCX3 protein and mRNA was up regulated obviously after SK-N-SH cells were treated with EtOH. The phosphorylation levels of Akt and CREB 1 were up regulated in cells treated with EtOH. The expression of NCX3 protein was reduced in the SK-N-SH cells treated with Akt phosphorylation inhibitor (LY294002). The [Ca²⁺]i and apoptosis rate of SK-N-SH cells increased 1.31-fold and 1.52-fold after silencing NCX3 compared with those treated with 200 mM EtOH alone for 2 d. In contrast, the [Ca²⁺]i and apoptosis rate of SK-N-SH cells decreased 0.26-fold and 0.35-fold after overexpression of NCX3 in the 2 d-200 mM EtOH treatment group. These results suggest that NCX3 plays a critical role in neuronal protection via the elimination of intracellular Ca²⁺, which may be a promising target for the prevention and treatment of encephalopathy after ethanol exposure.

Sodium Fluctuations in Astroglia and Their Potential Impact on Astrocyte Function

Astrocytes are the main cell type responsible for the regulation of brain homeostasis, including the maintenance of ion gradients and neurotransmitter clearance. These processes are tightly coupled to changes in the intracellular sodium (Na⁺) concentration. While activation of the sodium-potassium-ATPase (NKA) in response to an elevation of extracellular K⁺ may decrease intracellular Na⁺, the cotransport of transmitters, such as glutamate, together with Na⁺ results in an increase in astrocytic Na⁺. This increase in intracellular Na⁺ can modulate, for instance, metabolic downstream pathways. Thereby, astrocytes are capable to react on a fast time scale to surrounding neuronal activity via intracellular Na⁺ fluctuations and adjust energy production to the demand of their environment. Beside the well-documented conventional roles of Na⁺ signaling mainly mediated through changes in its electrochemical gradient, several recent studies have identified more atypical roles for Na⁺, including protein interactions leading to changes in their biochemical activity or Na⁺-dependent regulation of gene expression. In this review, we will address both the conventional as well as the atypical functions of astrocytic Na⁺ signaling, presenting the role of transporters and channels involved and their implications for physiological processes in the central nervous system (CNS). We will also discuss how these important functions are affected under pathological conditions, including stroke and migraine. We postulate that Na⁺ is an essential player not only in the maintenance of homeostatic processes but also as a messenger for the fast communication between neurons and astrocytes, adjusting the functional properties of various cellular interaction partners to the needs of the surrounding network.

Genetic Up-Regulation or Pharmacological Activation of the Na+/Ca2+ Exchanger 1 (NCX1) Enhances Hippocampal-Dependent Contextual and Spatial Learning and Memory

The Na⁺/Ca²⁺ exchanger 1 (NCX1) participates in the maintenance of neuronal Na⁺ and Ca²⁺ homeostasis, and it is highly expressed at synapse level of some brain areas involved in learning and memory processes, including the hippocampus, cortex, and amygdala. Furthermore, NCX1 increases Akt1 phosphorylation and enhances glutamate-mediated Ca²⁺ influx during depolarization in hippocampal and cortical neurons, two processes involved in learning and memory mechanisms. We investigated whether the modulation of NCX1 expression/activity might influence learning and memory processes. To this aim, we used a knock-in mouse overexpressing NCX1 in hippocampal, cortical, and amygdala neurons (ncx1.4^over) and a newly synthesized selective NCX1 stimulating compound, named CN-PYB2. Both ncx1.4^over and CN-PYB2-treated mice showed an amelioration in spatial learning performance in Barnes maze task, and in context-dependent memory consolidation after trace fear conditioning. On the other hand, these mice showed no improvement in novel object recognition task which is mainly dependent on non-spatial memory and displayed an increase in the active phosphorylated CaMKIIα levels in the hippocampus. Interestingly, both of these mice showed an increased level of context-dependent anxiety.Altogether, these results demonstrate that neuronal NCX1 participates in spatial-dependent hippocampal learning and memory processes.

Ionic Homeostasis Maintenance in ALS: Focus on New Therapeutic Targets

Amyotrophic lateral sclerosis (ALS) is one of the most threatening neurodegenerative disease since it causes muscular paralysis for the loss of Motor Neurons in the spinal cord, brainstem and motor cortex. Up until now, no effective pharmacological treatment is available. Two forms of ALS have been described so far: 90% of the cases presents the sporadic form (sALS) whereas the remaining 10% of the cases displays the familiar form (fALS). Approximately 20% of fALS is associated with inherited mutations in the Cu, Zn-superoxide dismutase 1 (SOD1) gene. In the last decade, ionic homeostasis dysregulation has been proposed as the main trigger of the pathological cascade that brings to motor-neurons loss. In the light of these premises, the present review will analyze the involvement in ALS pathophysiology of the most well studied metal ions, i.e., calcium, sodium, iron, copper and zinc, with particular focus to the role of ionic channels and transporters able to contribute in the regulation of ionic homeostasis, in order to propose new putative molecular targets for future therapeutic strategies to ameliorate the progression of this devastating neurodegenerative disease.

NCX-DB: a unified resource for integrative analysis of the sodium calcium exchanger super-family

Na⁺/Ca²⁺ exchangers are low-affinity high-capacity transporters that mediate Ca²⁺ extrusion by coupling Ca²⁺ efflux to the influx of Na⁺ ions. The Na⁺/Ca²⁺ exchangers form a super-family comprised of three branches each differing in ion-substrate selectivity: Na⁺/Ca²⁺ exchangers (NCX), Na⁺/Ca²⁺/K⁺ exchangers, and Ca²⁺/cation exchangers. Their primary function is to maintain Ca²⁺ homeostasis and play a particularly important role in excitable cells that experience transient Ca²⁺ fluxes. Research into the role and activity of Na⁺/Ca²⁺ exchangers has focused extensively on the cardio-vascular system, however, growing evidence suggests that Na⁺/Ca²⁺ exchangers play a key role in neuronal processes such as memory formation, learning, oligodendrocyte differentiation, neuroprotection during brain ischemia and axon guidance. They have also been implicated in pathologies such as Alzheimer’s disease, Parkinson’s disease, Multiple Sclerosis and Epilepsy, however, a clear understanding of their mechanism during disease is lacking. To date, there has never been a central resource or database for Na⁺/Ca²⁺ exchangers. With clear disease relevance and ever-increasing research on Na⁺/Ca²⁺ exchangers from both model and non-model species, a database that unifies the data on Na⁺/Ca²⁺ exchangers is needed for future research. NCX-DB is a publicly available database with a web interface that enables users to explore various Na⁺/Ca²⁺ exchangers, perform cross-species sequence comparison, identify new exchangers, and stay-up to date with recent literature. NCX-DB is available on the web via an interactive user interface with an intuitive design, which is applicable for the identification and comparison of Na⁺/Ca²⁺ exchanger proteins across diverse species.

Acute and long-term NCX activation reduces brain injury and restores behavioral functions in mice subjected to neonatal brain ischemia

Hypoxic-ischemic encephalopathy (HI) accounts for the majority of developmental, motor and cognitive deficits in children, leading to life-long neurological impairments. Since the plasmamembrane sodium/calcium exchanger (NCX) plays a fundamental role in maintaining ionic homeostasis during adult brain ischemia, in the present work we aimed to demonstrate (1)the involvement of NCX in the pathophysiology of neonatal HI and (2)a possible NCX-based pharmacological intervention. HI was induced in neonatal mice at postnatal day 7(P7) by unilateral cut of the right common carotid artery, followed by 60 min exposure to 8%O₂. Expression profiles of NCX isoforms from embryos stage to adulthood was evaluated in the hippocampus of hypoxic-ischemic and control mice. To assess the effect of NCX pharmacological stimulation, brain infarct volume was evaluated in brain sections, obtained at several time intervals after systemic administration of the newly synthesized NCX activator neurounina. Moreover, the long term effect of NCX activation was evaluated in adult mice (P60) subjected to neonatal HI and daily treated with neurounina for three weeks. Hypoxic-ischemic insult induced a reduction of NCX1 and NCX3 expression starting from day 7 until day 60. Notably, 8 weeks after HI induction in P7 mice, NCX pharmacological stimulation not only reduced infarct volume but improved also motor behaviour, spatial and visual memory. The present study highlights the significant role of NCX in the evolution of neonatal brain injury and in the learning and memory processes that are impaired in mice injured in the neonatal period.

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.

Development of a high-affinity peptide that prevents phospholemman (PLM) inhibition of the sodium/calcium exchanger 1 (NCX1)

NCX1 (Na⁺/Ca²⁺ exchanger 1) is an important regulator of intracellular Ca²⁺ and a potential therapeutic target for brain ischaemia and for diastolic heart failure with preserved ejection fraction. PLM (phospholemman), a substrate for protein kinases A and C, has been suggested to regulate NCX1 activity. However, although several studies have demonstrated that binding of phosphorylated PLM (pSer⁶⁸-PLM) leads to NCX1 inhibition, other studies have failed to demonstrate a functional interaction of these proteins. In the present study, we aimed to analyse the biological function of the pSer⁶⁸-PLM–NCX1 interaction by developing high-affinity blocking peptides. PLM was observed to co-fractionate and co-immunoprecipitate with NCX1 in rat left ventricle, and in co-transfected HEK (human embryonic kidney)-293 cells. For the first time, the NCX1–PLM interaction was also demonstrated in the brain. PLM binding sites on NCX1 were mapped to two regions by peptide array assays, containing the previously reported PASKT and QKHPD motifs. Conversely, the two NCX1 regions bound identical sequences in the cytoplasmic domain of PLM, suggesting that NCX1-PASKT and NCX1-QKHPD might bind to each PLM monomer. Using two-dimensional peptide arrays of the native NCX1 sequence KHPDKEIEQLIELANYQVLS revealed that double substitution of tyrosine for positions 1 and 4 (K1Y and D4Y) enhanced pSer⁶⁸-PLM binding 8-fold. The optimized peptide blocked binding of NCX1-PASKT and NCX1-QKHPD to PLM and reversed PLM(S68D) inhibition of NCX1 activity (both forward and reverse mode) in HEK-293 cells. Altogether our data indicate that PLM interacts directly with NCX1 and inhibits NCX1 activity when phosphorylated at Ser⁶⁸.

Astrocytes as new targets to improve cognitive functions

Astrocytes are now viewed as key elements of brain wiring as well as neuronal communication. Indeed, they not only bridge the gap between metabolic supplies by blood vessels and neurons, but also allow fine control of neurotransmission by providing appropriate signaling molecules and insulation through a tight enwrapping of synapses. Recognition that astroglia is essential to neuronal communication is nevertheless fairly recent and the large body of evidence dissecting such role has focused on the synaptic level by identifying neuro- and gliotransmitters uptaken and released at synaptic or extrasynaptic sites. Yet, more integrated research deciphering the impact of astroglial functions on neuronal network activity have led to the reasonable assumption that the role of astrocytes in supervising synaptic activity translates in influencing neuronal processing and cognitive functions. Several investigations using recent genetic tools now support this notion by showing that inactivating or boosting astroglial function directly affects cognitive abilities. Accordingly, brain diseases resulting in impaired cognitive functions have seen their physiopathological mechanisms revisited in light of this primary protagonist of brain processing. We here provide a review of the current knowledge on the role of astrocytes in cognition and in several brain diseases including neurodegenerative disorders, psychiatric illnesses, as well as other conditions such as epilepsy. Potential astroglial therapeutic targets are also discussed.

The role of Na+/Ca2+ exchanger subtypes in neuronal ischemic injury

The Na(+)/Ca(2+) exchanger (NCX) plays an important role in the maintenance of Na(+) and Ca(2+) homeostasis in most cells including neurons under physiological and pathological conditions. It exists in three subtypes (NCX1-3) with different tissue distributions but all of them are present in the brain. NCX transports Na(+) and Ca(2+) in either Ca(2+)-efflux (forward) or Ca(2+)-influx (reverse) mode, depending on membrane potential and transmembrane ion gradients. During neuronal ischemia, Na(+) and Ca(2+) ionic disturbances favor NCX to work in reverse mode, giving rise to increased intracellular Ca(2+) levels, while it may regain its forward mode activity on reperfusion. The exact significance of NCX in neuronal ischemic and reperfusion states remains unclear. The differential role of NCX subtypes in ischemic neuronal injury has been extensively investigated using various pharmacological tools as well as genetic models. This review discusses the mode of action of NCX in ischemic and reperfusion states, the differential roles played by NCX subtypes in these states as well as the role of NCX in pre- and postconditioning. NCX subtypes carry variable roles in ischemic injury. Furthermore, the mode of action of each subtype varies in ischemia and reperfusion states. Thus, therapeutic targeting of NCX in stroke should be based on appropriate timing of the administration of NCX subtype-specific strategies.

A new cell-penetrating peptide that blocks the autoinhibitory XIP domain of NCX1 and enhances antiporter activity

The plasma membrane Na(+)/Ca(2+) exchanger (NCX) is a high-capacity ionic transporter that exchanges 3Na(+) ions for 1Ca(2+) ion. The first 20 amino acids of the f-loop, named exchanger inhibitory peptide (XIP(NCX1)), represent an autoinhibitory region involved in the Na(+)-dependent inactivation of the exchanger. Previous research has shown that an exogenous peptide having the same amino acid sequence as the XIP(NCX1) region exerts an inhibitory effect on NCX activity. In this study, we identified another regulatory peptide, named P1, which corresponds to the 562-688aa region of the exchanger. Patch-clamp analysis revealed that P1 increased the activity of the exchanger, whereas the XIP inhibited it. Furthermore, P1 colocalized with NCX1 thus suggesting a direct binding interaction. In addition, site-directed mutagenesis experiments revealed that the binding and the stimulatory effect of P1 requires a functional XIP(NCX1) domain on NCX1 thereby suggesting that P1 increases the exchanger activity by counteracting the action of this autoinhibitory sequence. Taken together, these results open a new strategy for developing peptidomimetic compounds that, by mimicking the functional pharmacophore of P1, might increase NCX1 activity and thus exert a therapeutic action in those diseases in which an increase in NCX1 activity might be helpful.

Involvement of the sodium-calcium exchanger 3 (NCX3) in ziram-induced calcium dysregulation and toxicity

Ziram is a dimethyldithiocarbamate fungicide which can cause intraneuronal calcium (Ca(2+)) dysregulation and subsequently neuronal death. The signaling mechanisms underlying ziram-induced Ca(2+) dyshomeostasis and neurotoxicity are not fully understood. NCX3 is the third isoform of the sodium-calcium exchanger (NCX) family and plays an important role in regulating Ca(2+) homeostasis in excitable cells. We previously generated a mouse model deficient for the sodium-calcium exchanger 3 and showed that NCX3 is protective against ischemic damage. In the present study, we aim to examine whether NCX3 exerts a similar role against toxicological injury caused by the pesticide ziram. Our data show baby hamster kidney (BHK) cells stably transfected with NCX3 (BHK-NCX3) are more susceptible to ziram toxicity than cells transfected with the empty vector (BHK-WT). Increased toxicity in BHK-NCX3 was associated with a rapid rise in cytosolic Ca(2+) concentration [Ca(2+)]i induced by ziram. Profound mitochondrial dysfunction and ATP depletion were also observed in BHK-NCX3 cells following treatment with ziram. Lastly, primary dopaminergic neurons lacking NCX3 (NCX3(-/-)) were less sensitive to ziram neurotoxicity than wildtype control dopaminergic neurons. These results demonstrate that NCX3 genetic deletion protects against ziram-induced neurotoxicity and suggest NCX3 and its downstream molecular pathways as key factors involved in ziram toxicity. Our study identifies new molecular events through which pesticides (e.g. ziram) can lead to pathological features of degenerative diseases such as Parkinson's disease and indicates new targets to slow down neuronal degeneration.

Analysis of the Na+/Ca2+ exchanger gene family within the phylum Nematoda

Na⁺/Ca²⁺ exchangers are low affinity, high capacity transporters that rapidly transport calcium at the plasma membrane, mitochondrion, endoplasmic (and sarcoplasmic) reticulum, and the nucleus. Na⁺/Ca²⁺ exchangers are widely expressed in diverse cell types where they contribute homeostatic balance to calcium levels. In animals, Na⁺/Ca²⁺ exchangers are divided into three groups based upon stoichiometry: Na⁺/Ca²⁺ exchangers (NCX), Na⁺/Ca²⁺/K⁺ exchangers (NCKX), and Ca²⁺/Cation exchangers (CCX). In mammals there are three NCX genes, five NCKX genes and one CCX (NCLX) gene. The genome of the nematode Caenorhabditis elegans contains ten Na⁺/Ca²⁺ exchanger genes: three NCX; five CCX; and two NCKX genes. Here we set out to characterize structural and taxonomic specializations within the family of Na⁺/Ca²⁺ exchangers across the phylum Nematoda. In this analysis we identify Na⁺/Ca²⁺ exchanger genes from twelve species of nematodes and reconstruct their phylogenetic and evolutionary relationships. The most notable feature of the resulting phylogenies was the heterogeneous evolution observed within exchanger subtypes. Specifically, in the case of the CCX exchangers we did not detect members of this class in three Clade III nematodes. Within the Caenorhabditis and Pristionchus lineages we identify between three and five CCX representatives, whereas in other Clade V and also Clade IV nematode taxa we only observed a single CCX gene in each species, and in the Clade III nematode taxa that we sampled we identify NCX and NCKX encoding genes but no evidence of CCX representatives using our mining approach. We also provided re-annotation for predicted CCX gene structures from Heterorhabditis bacteriophora and Caenorhabditis japonica by RT-PCR and sequencing. Together, these findings reveal a complex picture of Na⁺/Ca²⁺ transporters in nematodes that suggest an incongruent evolutionary history of proteins that provide central control of calcium dynamics.

Does Na⁺/Ca²⁺ exchanger, NCX, represent a new druggable target in stroke intervention?

Stroke causes a rapid cell death in the core of the injured region and triggers mechanisms in surrounding penumbra area that leads to changes in concentrations of several ions like intracellular Ca²⁺, Na⁺, H⁺, K⁺, and radicals such as reactive oxygen species and reactive nitrogen species. When a dysregulation of homeostasis of these messengers occurs, it can trigger cell death. In particular, it is widely accepted that a critical factor in determining neuronal death during cerebral ischemia is progressive dysregulation of Ca²⁺, Na⁺, K⁺, and H⁺ homeostasis that activate several death pathways, including oxidative and nitrosative stress, mitochondrial dysfunction, protease activation, and apoptosis. In the last decade, several seminal experimental works are markedly changing the scenario of research of principal players of an ischemic event. Indeed, some plasma membrane channels and transporters, involved in the control of Ca²⁺, Na⁺, K⁺, and H⁺ ion influx or efflux and, therefore, responsible for maintaining the homeostasis of these four cations, might function as crucial players in initiation of brain ischemic process. Indeed, these proteins, by regulating ionic homeostasis, may provide the molecular basis underlying glutamate-independent Ca²⁺ and Na⁺ overload mechanisms in neuronal ischemic cell death and, most importantly, may represent more suitable molecular targets for therapeutic intervention. Recently, a great deal of interest has been devoted to clarify the role of the plasma membrane protein known as Na⁺/Ca²⁺ exchanger, a transporter able to control Na⁺ and Ca²⁺ homeostasis. In this review, the pathophysiological role of NCX and its implication as a potential target in stroke intervention will be examined.