Activity and localization of the secretory pathway Ca2+-ATPase isoform 1 (SPCA1) in different areas of the mouse brain during postnatal development

Upregulation of the secretory pathway Ca2+/Mn2+-ATPase isoform 1 in LPS-stimulated microglia and its involvement in Mn2+-induced Golgi fragmentation

Microglia play an important protective role in the healthy nervous tissue, being able to react to a variety of stimuli that induce different intracellular cascades for specific tasks. Ca2+ signaling can modulate these pathways, and we recently reported that microglial functions depend on the endoplasmic reticulum as a Ca2+ store, which involves the Ca2+ transporter SERCA2b. Here, we investigated whether microglial functions may also rely on the Golgi, another intracellular Ca2+ store that depends on the secretory pathway Ca2+/Mn2+-transport ATPase isoform 1 (SPCA1). We found upregulation of SPCA1 upon lipopolysaccharide stimulation of microglia BV2 cells and primary microglia, where alterations of the Golgi ribbon were also observed. Silencing and overexpression experiments revealed that SPCA1 affects cell morphology, Golgi apparatus integrity, and phagocytic functions. Since SPCA1 is also an efficient Mn2+ transporter and considering that Mn2+ excess causes manganism in the brain, we addressed the role of microglial SPCA1 in Mn2+ toxicity. Our results revealed a clear effect of Mn2+ excess on the viability and morphology of microglia. Subcellular analysis showed Golgi fragmentation and subsequent alteration of SPCA1 distribution from early stages of toxicity. Removal of Mn2+ by washing improved the culture viability, although it did not effectively reverse Golgi fragmentation. Interestingly, pretreatment with curcumin maintained microglia cultures viable, prevented Mn2+-induced Golgi fragmentation, and preserved SPCA Ca2+-dependent activity, suggesting curcumin as a potential protective agent against Mn2+-induced Golgi alterations in microglia.

Calcium flow at ER-TGN contact sites facilitates secretory cargo export

Ca2+ influx into the trans-Golgi Network (TGN) promotes secretory cargo sorting by the Ca2+-ATPase SPCA1 and the luminal Ca2+ binding protein Cab45. Cab45 oligomerizes upon local Ca2+ influx, and Cab45 oligomers sequester and separate soluble secretory cargo from the bulk flow of proteins in the TGN. However, how this Ca2+ flux into the lumen of the TGN is achieved remains mysterious, as the cytosol has a nanomolar steady-state Ca2+ concentration. The TGN forms membrane contact sites (MCS) with the Endoplasmic Reticulum (ER), allowing protein-mediated exchange of molecular species such as lipids. Here, we show that the TGN export of secretory proteins requires the integrity of ER-TGN MCS and inositol 3 phosphate receptor (IP3R)-dependent Ca2+ fluxes in the MCS, suggesting Ca2+ transfer between these organelles. Using an MCS-targeted Ca2+ FRET sensor module, we measure the Ca2+ flow in these sites in real time. These data show that ER-TGN MCS facilitates the Ca2+ transfer required for Ca2+-dependent cargo sorting and export from the TGN, thus solving a fundamental question in cell biology.

Distribution of intracellular Ca2+-ATPases in the mouse retina and their involvement in light-induced cone degeneration

Calcium signalling is involved in many processes in mammalian retina, from development to mature functions and neurodegeneration. Although proteins involved in Ca2+ entry in retinal cells have been well studied, less is known about Ca2+-clearance. Among the Ca2+ pumps, plasma membrane Ca2+-ATPases (PMCAs) have been identified as key proteins extruding Ca2+ across the plasma membrane with specific distribution in developing and adult retina. However, the two main isoforms of intracellular Ca2+-ATPases in the central nervous system, the sarco(endo)plasmic reticulum (ER) Ca2+-ATPase 2b (SERCA2b) and the secretory pathway Ca2+-ATPase 1 (SPCA1), which remove cytosolic Ca2+ into intracellular stores, have been less or not at all analysed, respectively. In this study, we described for the first time the SPCA1 localisation in adult mouse retina and we report differential distributions of SERCA2b and SPCA1 transporters within various classes of retinal neurons and distinct subcellular localisations. In addition, we studied the expression and localisation of both Ca2+ pumps in 661W cells, a cone photoreceptor-derived cell line. Since continuous exposure to high light intensity induces photodegeneration, we analysed the effect of LED light exposure on these cells and SERCA2b and SPCA1 distribution. We found that continuous mild LED-light exposure compromised cell survival and produced stress in the ER and Golgi, the Ca2+ stores where the two pumps are localised. These effects were reversed after halting light exposure and washing. This study demonstrates that Ca2+ signalling may be involved in light-induced photoreceptor cell damage and points to previously unrecognised functions of intracellular Ca2+-ATPases in retina physiology.

A Negative Feedback Loop in Ultraviolet A-Induced Senescence in Human Dermal Fibroblasts Formed by SPCA1 and MAPK

Secretory pathway calcium ATPase 1 (SPCA1) is a calcium pump localized specifically to the Golgi. Its effects on UVA-induced senescence have never been examined. In our study, expression of SPCA1 was increased in UVA-irradiated human dermal fibroblasts (HDFs) by activating mitogen-activated protein kinase (MAPK) and its downstream transcription factor, c-jun. Dual-luciferase reporter and chromatin immunoprecipitation assays revealed that c-jun regulated SPCA1 by binding to its promoter. Furthermore, downregulating SPCA1 with siRNA transfection aggravated UVA-induced senescence due to an elevation of intracellular calcium concentrations and a subsequent increase in reactive oxygen species (ROS) and MAPK activity. In contrast, overexpression of SPCA1 reduced calcium overload, consequently lowering the ROS level and suppressing MAPK activation. This alleviated the cellular senescence caused by UVA irradiation. These results indicated that SPCA1 might exert a protective effect on UVA-induced senescence in HDFs via forming a negative feedback loop. Specifically, activation of MAPK/c-jun triggered by UVA transcriptionally upregulated SPCA1. In turn, the increased SPCA1 lowered the intracellular Ca²⁺ level, probably through pumping Ca²⁺ into the Golgi, leading to a reduction of ROS, eventually decreasing MAPK activity and diminishing UVA-induced senescence.

An N-terminal Ca2+-binding motif regulates the secretory pathway Ca2+/Mn2+-transport ATPase SPCA1

The Ca²⁺/Mn²⁺ transport ATPases 1a and 2 (SPCA1a/2) are closely related to the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and are implicated in breast cancer and Hailey-Hailey skin disease. Here, we purified the human SPCA1a/2 isoforms from a yeast recombinant expression system and compared their biochemical properties after reconstitution. We observed that the purified SPCA1a displays a lower Ca²⁺ affinity and slightly lower Mn²⁺ affinity than SPCA2. Remarkably, the turnover rates of SPCA1a in the presence of Mn²⁺ and SPCA2 incubated with Ca²⁺ and Mn²⁺ were comparable, whereas the turnover rate of SPCA1a in Ca²⁺ was 2-fold higher. Moreover, we noted an unusual biphasic activation curve for the SPCA1a ATPase and autophosphorylation activity, not observed with SPCA2. We also found that the biphasic pattern and low apparent ion affinity of SPCA1a critically depends on ATP concentration. We further show that the specific properties of SPCA1a at least partially depend on an N-terminal EF-hand-like motif, which is present only in the SPCA1a isoform and absent in SPCA2. This motif binds Ca²⁺, and its mutation lowered the Ca²⁺ turnover rate relative to that of Mn²⁺, increased substrate affinity, and reduced the level of biphasic activation of SPCA1a. A biochemical analysis indicated that Ca²⁺ binding to the N-terminal EF-hand-like motif promotes the activity of SPCA1a by facilitating autophosphorylation. We propose that this regulation may be physiologically relevant in cells with a high Ca²⁺ load, such as mammary gland cells during lactation, or in cells with a low ATP content, such as keratinocytes.

Role of Homocysteine in the Ischemic Stroke and Development of Ischemic Tolerance

Homocysteine (Hcy) is a toxic, sulfur-containing intermediate of methionine metabolism. Hyperhomocysteinemia (hHcy), as a consequence of impaired Hcy metabolism or defects in crucial co-factors that participate in its recycling, is assumed as an independent human stroke risk factor. Neural cells are sensitive to prolonged hHcy treatment, because Hcy cannot be metabolized either by the transsulfuration pathway or by the folate/vitamin B12 independent remethylation pathway. Its detrimental effect after ischemia-induced damage includes accumulation of reactive oxygen species (ROS) and posttranslational modifications of proteins via homocysteinylation and thiolation. Ischemic preconditioning (IPC) is an adaptive response of the CNS to sub-lethal ischemia, which elevates tissues tolerance to subsequent ischemia. The main focus of this review is on the recent data on homocysteine metabolism and mechanisms of its neurotoxicity. In this context, the review documents an increased oxidative stress and functional modification of enzymes involved in redox balance in experimentally induced hyperhomocysteinemia. It also gives an interpretation whether hyperhomocysteinemia alone or in combination with IPC affects the ischemia-induced neurodegenerative changes as well as intracellular signaling. Studies document that hHcy alone significantly increased Fluoro-Jade C- and TUNEL-positive cell neurodegeneration in the rat hippocampus as well as in the cortex. IPC, even if combined with hHcy, could still preserve the neuronal tissue from the lethal ischemic effects. This review also describes the changes in the mitogen-activated protein kinase (MAPK) protein pathways following ischemic injury and IPC. These studies provide evidence for the interplay and tight integration between ERK and p38 MAPK signaling mechanisms in response to the hHcy and also in association of hHcy with ischemia/IPC challenge in the rat brain. Further investigations of the protective factors leading to ischemic tolerance and recognition of the co-morbid risk factors would result in development of new avenues for exploration of novel therapeutics against ischemia and stroke.

SPCA2 couples Ca2+ influx via Orai1 to Ca2+ uptake into the Golgi/secretory pathway

Dysregulation of the Golgi/Secretory Pathway Ca²⁺ transport ATPase SPCA2 is implicated in breast cancer. During lactation and in luminal breast cancer types, SPCA2 interacts with the plasma membrane Ca²⁺ channel Orai1, promoting constitutive Ca²⁺ influx, which is termed store independent Ca²⁺ entry (SICE). The mechanism of SPCA2/Orai1 interaction depends on the N- and C-termini of SPCA2. These extensions may play a dual role in activating not only Orai1, but also Ca²⁺ transport into the Golgi/secretory pathway, which we tested by investigating the impact of various SPCA2 N- and/or C-terminal truncations on SICE and Ca²⁺ transport activity of SPCA2. C-terminal truncations impair SICE and SPCA2 activity, but also affect targeting, whereas N-terminal truncations affect targeting and inactivate SPCA2, but remarkably, SICE activation remains unaffected. Importantly, overexpression of SPCA2 increases the Ca²⁺ content of non-ER stores, which depends on Orai1 and SPCA2 activity. Thus, Orai1-mediated Ca²⁺-influx and SPCA2-mediated Ca²⁺ uptake activity into the Golgi/secretory pathway might be coupled possibly in a microdomain. This channel/pump complex may efficiently transfer Ca²⁺ into the secretory pathway, which might play a role in SPCA2-expressing secretory cells, such as mammary gland during lactation.

Secretory pathway Ca(2+)-ATPase isoform 1 knockdown promotes Golgi apparatus stress injury in a mouse model of focal cerebral ischemia-reperfusion: In vivo and in vitro study

The present study was designed to investigate the potential role of secretory pathway Ca(2+)-ATPase isoform 1(SPCA1) in experimental focal cerebral ischemia-reperfusion injury. Cerebral ischemia-reperfusion was induced by transient middle cerebral artery occlusion (MCAO) for 2h s in Sprague-Dawley rats, and then the expression levels of SPAC1 mRNA and protein were determined. Results showed that SPCA1 level was transiently increased 1 day after reperfusion in peri-infarction area, while markedly increased in infarction core on 3day and 7 day after reperfusion. Then a SPCA1 lentivirus was used to achieve knockdown of SPCA1 gene: Ca(2+) transporting type 2C, member 1 (ATP2C1) gene. It has been observed that SPCA1 knockdown by lentivirus markedly increased cerebral infarction volume in vivo. Meanwhile, SPCA1 knockdown also facilitated per-oxidative production, including nitric oxide (NO) and 3-nitrotyrosine (3-NT) and decreased the expression of total superoxide dismutase (SOD) and manganese superoxide dismutase (MnSOD). Moreover, in vitro study showed that SPCA1 knockdown increased hydrogen peroxide (H2O2)-induced lactate dehydrogenase (LDH) leakage dose-dependently, and elevated caspase3 level in neuro-2a (N2a) cells. In addition, SPCA1 knockdown increased H2O2-induced production of nitric oxide and 3-NT dose-dependently, and reversed the increased activity of total SOD and MnSOD in neuro-2a cells. In conclusion, the present study indicated that SPCA1 could suppress over active Golgi apparatus (GA) stress thus attenuate cerebral ischemia-reperfusion injury.

Manganese Is Essential for Neuronal Health

The understanding of manganese (Mn) biology, in particular its cellular regulation and role in neurological disease, is an area of expanding interest. Mn is an essential micronutrient that is required for the activity of a diverse set of enzymatic proteins (e.g., arginase and glutamine synthase). Although necessary for life, Mn is toxic in excess. Thus, maintaining appropriate levels of intracellular Mn is critical. Unlike other essential metals, cell-level homeostatic mechanisms of Mn have not been identified. In this review, we discuss common forms of Mn exposure, absorption, and transport via regulated uptake/exchange at the gut and blood-brain barrier and via biliary excretion. We present the current understanding of cellular uptake and efflux as well as subcellular storage and transport of Mn. In addition, we highlight the Mn-dependent and Mn-responsive pathways implicated in the growing evidence of its role in Parkinson's disease and Huntington's disease. We conclude with suggestions for future focuses of Mn health-related research.

Ischemic conditioning-induced endogenous brain protection: Applications pre-, per- or post-stroke

In the area of brain injury and neurodegenerative diseases, a plethora of experimental and clinical evidence strongly indicates the promise of therapeutically exploiting the endogenous adaptive system at various levels like triggers, mediators and the end-effectors to stimulate and mobilize intrinsic protective capacities against brain injuries. It is believed that ischemic pre-conditioning and post-conditioning are actually the strongest known interventions to stimulate the innate neuroprotective mechanism to prevent or reverse neurodegenerative diseases including stroke and traumatic brain injury. Recently, studies showed the effectiveness of ischemic per-conditioning in some organs. Therefore the term ischemic conditioning, including all interventions applied pre-, per- and post-ischemia, which spans therapeutic windows in 3 time periods, has recently been broadly accepted by scientific communities. In addition, it is extensively acknowledged that ischemia-mediated protection not only affects the neurons but also all the components of the neurovascular network (consisting of neurons, glial cells, vascular endothelial cells, pericytes, smooth muscle cells, and venule/veins). The concept of cerebroprotection has been widely used in place of neuroprotection. Intensive studies on the cellular signaling pathways involved in ischemic conditioning have improved the mechanistic understanding of tolerance to cerebral ischemia. This has added impetus to exploration for potential pharmacologic mimetics, which could possibly induce and maximize inherent protective capacities. However, most of these studies were performed in rodents, and the efficacy of these mimetics remains to be evaluated in human patients. Several classical signaling pathways involving apoptosis, inflammation, or oxidation have been elaborated in the past decades. Newly characterized mechanisms are emerging with the advances in biotechnology and conceptual renewal. In this review we are going to focus on those recently reported methodological and mechanistic discoveries in the realm of ischemic conditioning. Due to the varied time differences of ischemic conditioning in different animal models and clinical trials, it is important to define optimal timing to achieve the best conditioning induced neuroprotection. This brings not only an opportunity in the treatment of stroke, but challenges as well, as data is just becoming available and the procedures are not yet optimized. The purpose of this review is to shed light on exploiting these ischemic conditioning modalities to protect the cerebrovascular system against diverse injuries and neurodegenerative disorders.

Mechanisms involved in the ischemic tolerance in brain: effect of the homocysteine

Hyperhomocysteinemia (hHCy) is recognized as a co-morbid risk factor of human stroke. It also aggravates the ischemia-induced injury by increased production of reactive oxygen species, and by the homocysteinylation and thiolation of functional proteins. Ischemic preconditioning represents adaptation of the CNS to sub-lethal ischemia, resulting in increased brain tolerance to subsequent ischemia. We present here an overview of recent data on the homocysteine (Hcy) metabolism and on the genetic and metabolic causes of hHCy-related neuropathologies in humans. In this context, the review documents for an increased oxidative stress and for the functional modifications of enzymes involved in the redox balance in experimentally induced hHCy. Hcy metabolism leads also to the redox imbalance and increased oxidative stress resulting in elevated lipoperoxidation and protein oxidation, the products known to be included in the neuronal degeneration. Additionally, we examine the effect of the experimental hHCy in combination with ischemic insult, and/or with the preischemic challenge on the extent of neuronal degeneration as well as the intracellular signaling and the regulation of DNA methylation. The review also highlights that identification of the effects of co-morbid factors in the mechanisms of ischemic tolerance mechanisms would lead to improved therapeutics, especially the brain tissue.

Overlapping ATP2C1 and ASTE1 genes in human genome: implications for SPCA1 expression?

The ATP2C1 gene encodes for the secretory pathway calcium (Ca²⁺)-ATPase pump (SPCA1), which localizes along the secretory pathway, mainly in the trans-Golgi. The loss of one ATP2C1 allele causes Hailey-Hailey disease in humans but not mice. Examining differences in genomic organization between mouse and human we speculate that the overlap between ATP2C1 and ASTE1 genes only in humans could explain this different response to ATP2C1 dysregulation. We propose that ASTE1, overlapping with ATP2C1 in humans, affects alternative splicing, and potentially protein expression of the latter. If dysregulated, the composition of the SPCA1 isoform pool could diverge from the physiological status, affecting cytosolic Ca²⁺-signaling, and in turn perturbing cell division, leading to cell death or to neoplastic transformation.

Nuclear Na+/K+-ATPase plays an active role in nucleoplasmic Ca2+ homeostasis

Na(+)/K(+)-ATPase, an integral membrane protein, has been studied for over a half century with respect to its transporter function in the plasma membrane, where it expels three Na(+) ions from the cell in exchange for two K(+) ions. In this study, we demonstrate a functioning Na(+)/K(+)-ATPase within HEK293 cell nuclei. This subcellular localization was confirmed by western blotting, ouabain-sensitive ATPase activity of the nuclear membrane fraction, immunocytochemistry and delivery of fluorescently tagged Na(+)/K(+)-ATPase α- and β-subunits. In addition, we observed an overlap between nuclear Na(+)/K(+)-ATPase and Na/Ca-exchanger (NCX) when nuclei were immunostained with commercially available Na(+)/K(+)-ATPase and NCX antibodies, suggesting a concerted physiological coupling between these transporters. In keeping with this, we observed an ATP-dependent, strophanthidin-sensitive Na(+) flux into the nuclear envelope (NE) lumen loaded with the Na-sensitive dye, CoroNa-Green. Analogous experiments using Fluo-5N, a low affinity Ca(2+) indicator, demonstrated a similar ATP-dependent and strophanthidin-sensitive Ca(2+) flux into the NE lumen. Our results reveal an intracellular physiological role for the coordinated efforts of the Na(+)/K(+)-ATPase and NCX to actively remove Ca(2+) from the nucleoplasm into the NE lumen (i.e. the nucleoplasmic reticulum).

High levels of Mn²⁺ inhibit secretory pathway Ca²⁺/Mn²⁺-ATPase (SPCA) activity and cause Golgi fragmentation in neurons and glia

Excess Mn(2+) in humans causes a neurological disorder known as manganism, which shares symptoms with Parkinson's disease. However, the cellular mechanisms underlying Mn(2+) -neurotoxicity and the involvement of Mn(2+) -transporters in cellular homeostasis and repair are poorly understood and require further investigation. In this work, we have analyzed the effect of Mn(2+) on neurons and glia from mice in primary cultures. Mn(2+) overload compromised survival of both cell types, specifically affecting cellular integrity and Golgi organization, where the secretory pathway Ca(2+) /Mn(2+) -ATPase is localized. This ATP-driven Mn(2+) transporter might take part in Mn(2+) accumulation/detoxification at low loads of Mn(2+) , but its ATPase activity is inhibited at high concentration of Mn(2+) . Glial cells appear to be significantly more resistant to this toxicity than neurons and their presence in cocultures provided some protection to neurons against degeneration induced by Mn(2+) . Interestingly, the Mn(2+) toxicity was partially reversed upon Mn(2+) removal by wash out or by the addition of EDTA as a chelating agent, in particular in glial cells. These studies provide data on Mn(2+) neurotoxicity and may contribute to explore new therapeutic approaches for reducing Mn(2+) poisoning.

The Ca2+ pumps of the endoplasmic reticulum and Golgi apparatus

The various splice variants of the three SERCA- and the two SPCA-pump genes in higher vertebrates encode P-type ATPases of the P(2A) group found respectively in the membranes of the endoplasmic reticulum and the secretory pathway. Of these, SERCA2b and SPCA1a represent the housekeeping isoforms. The SERCA2b form is characterized by a luminal carboxy terminus imposing a higher affinity for cytosolic Ca(2+) compared to the other SERCAs. This is mediated by intramembrane and luminal interactions of this extension with the pump. Other known affinity modulators like phospholamban and sarcolipin decrease the affinity for Ca(2+). The number of proteins reported to interact with SERCA is rapidly growing. Here, we limit the discussion to those for which the interaction site with the ATPase is specified: HAX-1, calumenin, histidine-rich Ca(2+)-binding protein, and indirectly calreticulin, calnexin, and ERp57. The role of the phylogenetically older and structurally simpler SPCAs as transporters of Ca(2+), but also of Mn(2+), is also addressed.

Plasma membrane Ca2+-ATPases in the nervous system during development and ageing

Calcium signaling is used by neurons to control a variety of functions, including cellular differentiation, synaptic maturation, neurotransmitter release, intracellular signaling and cell death. This review focuses on one of the most important Ca²⁺ regulators in the cell, the plasma membrane Ca²⁺-ATPase (PMCA), which has a high affinity for Ca²⁺ and is widely expressed in brain. The ontogeny of PMCA isoforms, linked to specific requirements of Ca²⁺ during development of different brain areas, is addressed, as well as their function in the adult tissue. This is based on the high diversity of variants in the PMCA family in brain, which show particular kinetic differences possibly related to specific localizations and functions of the cell. Conversely, alterations in the activity of PMCAs could lead to changes in Ca²⁺ homeostasis and, consequently, to neural dysfunction. The involvement of PMCA isoforms in certain neuropathologies and in brain ageing is also discussed.

The E646D-ATP13A4 mutation associated with autism reveals a defect in calcium regulation

ATP13A4 is a member of the subfamily of P5-type ATPases. P5-type ATPases are the least studied of the P-type ATPase subfamilies with no ion specificities assigned to them. In order to elucidate ATP13A4 function, we studied the protein's subcellular localization and tested whether it is involved in calcium regulation. The intracellular calcium concentration was measured in COS-7 cells over-expressing mouse ATP13A4 using ratiometric calcium imaging with fura-2 AM as a calcium indicator. The results of this study show that ATP13A4 is localized to the endoplasmic reticulum (ER). Furthermore, we demonstrate that over-expression of ATP13A4 in COS-7 cells caused a significant increase in the intracellular calcium level. Interestingly, over-expression of the sequence variant containing a substitution of aspartic acid for a glutamic acid (E646D), previously found in patients with autism spectrum disorder (ASD), did not increase the free cellular calcium likely due to the mutation. In this study, we also describe the expression of ATP13A4 during mouse embryonic development. Quantitative real-time PCR revealed that ATP13A4 was highly expressed at embryonic days 15-17, when neurogenesis takes place. The present study is the first to provide further insights into the biological role of a P5-type ATPase. Our results demonstrate that ATP13A4 may be involved in calcium regulation and that its expression is developmentally regulated. Overall, this study provides support for the hypothesis that ATP13A4 may play a vital role in the developing nervous system and its impairment can contribute to the symptoms seen in ASD.

Silencing the SPCA1 (secretory pathway Ca2+-ATPase isoform 1) impairs Ca2+ homeostasis in the Golgi and disturbs neural polarity

Neural cell differentiation involves a complex regulatory signal transduction network in which Ca(2+) ions and the secretory pathway play pivotal roles. The secretory pathway Ca(2+)-ATPase isoform 1 (SPCA1) is found in the Golgi apparatus where it is actively involved in the transport of Ca(2+) or Mn(2+) from the cytosol to the Golgi lumen. Its expression during brain development in different types of neurons has been documented recently, which raises the possibility that SPCA1 contributes to neuronal differentiation. In the present study, we investigated the potential impact of SPCA1 on neuronal polarization both in a cell line and in primary neuronal culture. In N2a neuroblastoma cells, SPCA1 was immunocytochemically localized in the juxtanuclear Golgi. Knockdown of SPCA1 by RNA interference markedly delayed the differentiation in these cells. The cells retarded in differentiation showed increased numbers of neurites of reduced length compared with control cells. Ca(2+) imaging assays showed that the lack of SPCA1 impaired Golgi Ca(2+) homeostasis and resulted in disturbed trafficking of different classes of proteins including normally Golgi-localized cameleon GT-YC3.3, bearing a Golgi-specific galactosyltransferase N terminus, and a normally plasma membrane-targeted, glycosyl phosphatidyl inositol-anchored cyan fluorescent protein construct. Also in hippocampal primary neurons, which showed a differential distribution of SPCA1 expression in Golgi stacks depending on differentiation stage, partial silencing of SPCA1 resulted in delayed differentiation, whereas total suppression drastically affected the cell survival. The disturbed overall cellular Ca(2+) homeostasis and/or the altered targeting of organellar proteins under conditions of SPCA1 knockdown highlight the importance of SPCA1 function for normal neural differentiation.

Ontogeny of ATP hydrolysis and isoform expression of the plasma membrane Ca(2+)-ATPase in mouse brain

Background

Plasma membrane Ca²⁺-ATPases (PMCAs) are high affinity Ca²⁺ transporters actively involved in intracellular Ca²⁺ homeostasis. Considering the critical role of Ca²⁺ signalling in neuronal development and plasticity, we have analyzed PMCA-mediated Ca²⁺-ATPase activity and PMCA-isoform content in membranes from mouse cortex, hippocampus and cerebellum during postnatal development.

Results

PMCA activity was detected from birth, with a faster evolution in cortex than in hippocampus and cerebellum. Western blots revealed the presence of the four isoforms in all regions, with similar increase in their expression patterns as those seen for the activity profile. Immunohistochemistry assays in cortex and hippocampus showed co-expression of all isoforms in the neuropil associated with synapses and in the plasma membrane of pyramidal cells soma, while cerebellum showed a more isoform-specific distribution pattern in Purkinje cells.

Conclusion

These results show an upregulation of PMCA activity and PMCA isoforms expression during brain development in mouse, with specific localizations mainly in cerebellum. Overall, our findings support a close relationship between the ontogeny of PMCA isoforms and specific requirements of Ca²⁺ during development of different brain areas.

Alterations induced by ischemic preconditioning on secretory pathways Ca2+-ATPase (SPCA) gene expression and oxidative damage after global cerebral ischemia/reperfusion in rats

Ischemic preconditioning (IPC) represents the phenomenon of CNC adaptation, which results in increased tolerance of CNS to lethal ischemia. Brain ischemia/reperfusion (IRI) initiates a catastrophic cascade in which many subcellular organelles play an important role. The Golgi apparatus, which is a part of secretory pathways (SP), represents the Ca(2+) store and regulates secretion of proteins for growth/reorganization of neuronal circuit by secretory Ca(2+)ATPases (SPCA1). The purpose of this study is to evaluate the effect of IRI and preconditioning on SPCA1 gene expression and oxidative damage after 4-vessel occlusion for 15 min and after being exposed to different reperfusion periods. Rats were preconditioned by 5 min of sub-lethal ischemia and 2 days later, 15 min of lethal ischemia was induced. Our experiments conclusively showed IRI-induced depression of SPCA activity and lipo- and protein oxidation in rat hippocampal membranes. IRI also activates the induction of SPCA1 gene expression in later reperfusion periods. IPC partially suppresses lipo- and protein oxidation in hippocampal membranes and leads to partiall rovery of the ischemic-induced depression of SPCA activity. In addition, IPC initiates earlier cellular response to the injury by the significant elevation of mRNA expression to 142% comparing to 1 h of corresponding reperfusion and to 11% comparing to 24 h of corresponding reperfusion, respectively. Similar patterns were observed on the translational level by Western blot analysis. Our results indicate the specific SPCA1 expression pattern in ischemic hippocampus. It also shows that the SPCA expression and the post-translational changes induced by ischemia are modulated by the IPC. This might serve to understand the molecular mechanisms involved in the structural integrity and function of the SP after ischemic challenge. It also suggests that there is a correlation of SPCA function with the role of SP in the response to pre-ischemic challenge.