Sarco/endoplasmic Reticulum Ca2+-ATPase Research Articles

Identification of Mycobacterium tuberculosis CtpF as a target for designing new antituberculous compounds

The emergence of tuberculosis (TB) produced by multi-drug resistance (MDR) and extensively-drug resistance (XDR) Mycobacterium tuberculosis (Mtb), encourages the development of new antituberculous compounds, as well as the identification of novel drug targets. In this regard, plasma membrane P-type ATPases are interesting targets because they play a crucial role in ion homeostasis and mycobacterial survival. We focused on Mtb CtpF, a calcium P-type ATPase that responds to a broad number of intraphagosomal conditions, as a novel target. In this study, we evaluated the capacity of cyclopiazonic acid (CPA), a well-known inhibitor of the sarco-endoplasmic reticulum Ca2+-ATPase (SERCA), to inhibit the ATPase activity of CtpF and the Mtb growth demonstrating that CtpF is a druggable target. A homology modeling of CtpF was generated for molecular docking studies of CtpF with CPA and key pharmacophoric features were identified, which were used to perform a pharmacophore-based virtual screening of the ZINC database, and to identify CtpF inhibitor candidates. Molecular docking-based virtual screening and MM-BGSA calculations of candidates allowed identifying six compounds with the best binding energies. The compounds displayed in vitro minimum inhibitory concentrations (MIC) ranging from 50 to 100 μg/mL, growth inhibitions from 29.5 to 64.0% on Mtb, and inhibitions of Ca2+-dependent ATPase activity in Mtb membrane vesicles (IC50) ranging from 4.1 to 35.8 μM. The compound ZINC63908257 was the best candidate by displaying a MIC of 50 μg/mL and a Ca2+ P-type ATPase inhibition of 45% with IC50 = 4.4 μM. Overall, the results indicate that CtpF is a druggable target for designing new antituberculous compounds.

Abstract B113: Selective blockade of oncogenic NOTCH1 with the new SERCA inhibitor CAD204520 in T-cell acute lymphoblastic leukemia

Abstract Given its oncogenic role in human cancers, Notch1 signaling has garnered increased attention as a therapeutic target. Several Notch modulators, including γ-secretase inhibitors, have shown therapeutic efficacy in preclinical tumor models. However, despite this promise, few of these candidates have shown clinical benefit in patients, in part due to tissue-dependent on-target toxicities from the repression of both mutant and wild type Notch proteins. The discovery of the P-type ATPase Sarco/Endoplasmic Reticulum Ca2+-ATPase (SERCA) as a modulator of Notch transport and activity suggested a new approach to treat T-cell Acute Lymphoblastic Leukemia (T-ALL) an aggressive cancer dependent on aberrant Notch1 activation. In fact, thapsigargin mediated SERCA inhibitions had a stronger effect on the most common type of activating NOTCH1 mutants compared to wild type. However, the consequence of thapsigargin binding to SERCA is a rapid disruption of Ca2+ homeostasis that might cause cardiac toxicity in human, suggesting the need to identify inhibitors with better drug-like properties and reduced off-target toxicity. From a small molecule screening of 191,000 P-type ATPase modulators for inhibition of the yeast S. cerevisiae H+-ATPase Pma1, 407 hits were counter screened for their ability to target Na+/K+-ATPase and the Ca2+-ATPase proteins. CAD204520 displayed ~25 and ~79 fold greater selectivity toward human SERCA compared to Na+/K+and H+-ATPase and emerged as a candidate for the development of novel anti-NOTCH1 agents. We demonstrated that CAD204520 impairs the proliferation of a panel of lymphoid malignancies carrying activating mutations in the NOTCH1 heterodimerization domain (HD, such as T-ALL) and/or deletions in the degradation domain (PEST, such as mantle cell lymphoma (MCL)). Similar to thapsigargin, CAD204520 causes a defect in NOTCH1 trafficking that results in an accumulation of full-length NOTCH1 and in a depletion of the activated form: ICN1. Consequently, the NOTCH1 targets, MYC, DTX1, were repressed as measured by qRT-PCR. In contrast, no effect at protein level was observed in T-ALL wild type NOTCH1. To assess the in vivo efficacy of CAD204520 we established xenografts from the SKW-3/KE-37 T-ALL cell line and demonstrated that drug’s treatment reduced circulating and tissue infiltrating human leukemia cells without causing heart-related off-target effects. Consistently preclinical toxicity studies in rat cardiomyocytes showed that compared to thapsigargin, CAD204520 minimally alters cell cardiac mechanical performance (~25%) suggesting that the heart will likely tolerate CAD204520 modulation in vivo. In fact, in CD1 mice exposed to CAD204520 (30 mg/Kg, BID for 21 days) no adverse clinical symptoms were found. A tempting hypothesis to explain for the variation of Ca2+ dependent toxicities seen in our studies is that thapsigargin and CAD204520 inhibit SERCA in distinct pockets. Consistently, docking poses showed that CAD204520 binds SERCA in the trans-membrane helices M1, M3 and M4 while thapsigargin in the M3, M5 and M7 groove. Consequently, thapsigargin and CAD204520 co-treatment resulted in synergistic anti-proliferative effect in T-ALL. In conclusion, this study supports the development of tolerated SERCA inhibitors for Notch dependent cancers and extends its application to cases with mutations in the PEST degradation domain such as MCL or chronic lymphocytic leukemia. Citation Format: Marchesini Matteo, Andrea Gherli, Anne-Marie Lund Winter, Samuel Kitara, Anna Montanaro, Chiara Rompietti, Claudia Sorrentino, Donatella Stilli, Federica Rizzi, Luca Pagliaro, Kimberly Stegmaier, William Dalby-Brown, Giovanni Roti. Selective blockade of oncogenic NOTCH1 with the new SERCA inhibitor CAD204520 in T-cell acute lymphoblastic leukemia [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B113. doi:10.1158/1535-7163.TARG-19-B113

Interaction of a Sarcolipin Pentamer and Monomer with the Sarcoplasmic Reticulum Calcium Pump, SERCA

The sequential rise and fall of cytosolic calcium underlies the contraction-relaxation cycle of muscle cells. Whereas contraction is initiated by the release of calcium from the sarcoplasmic reticulum, muscle relaxation involves the active transport of calcium back into the sarcoplasmic reticulum. This reuptake of calcium is catalyzed by the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA), which plays a lead role in muscle contractility. The activity of SERCA is regulated by small membrane protein subunits, the most well-known being phospholamban (PLN) and sarcolipin (SLN). SLN physically interacts with SERCA and differentially regulates contractility in skeletal and atrial muscle. SLN has also been implicated in skeletal muscle thermogenesis. Despite these important roles, the structural mechanisms by which SLN modulates SERCA-dependent contractility and thermogenesis remain unclear. Here, we functionally characterized wild-type SLN and a pair of mutants, Asn4-Ala and Thr5-Ala, which yielded gain-of-function behavior comparable to what has been found for PLN. Next, we analyzed two-dimensional crystals of SERCA in the presence of wild-type SLN by electron cryomicroscopy. The fundamental units of the crystals are antiparallel dimer ribbons of SERCA, known for decades as an assembly of calcium-free SERCA molecules induced by the addition of decavanadate. A projection map of the SERCA-SLN complex was determined to a resolution of 8.5 Å, which allowed the direct visualization of an SLN pentamer. The SLN pentamer was found to interact with transmembrane segment M3 of SERCA, although the interaction appeared to be indirect and mediated by an additional density consistent with an SLN monomer. This SERCA-SLN complex correlated with the ability of SLN to decrease the maximal activity of SERCA, which is distinct from the ability of PLN to increase the maximal activity of SLN. Protein-protein docking and molecular dynamics simulations provided models for the SLN pentamer and the novel interaction between SERCA and an SLN monomer.

Targeting the Activating Mutations of NOTCH1 in T-Cell Lymphoblastic Leukemia with a New SERCA Inhibitor CAD204520

Given its oncogenic role in human cancers, Notch1 signaling has garnered increased attention as a therapeutic target. Several Notch modulators, including γ-secretase inhibitors, have shown therapeutic efficacy in preclinical tumor models. However, despite this promise, few of these candidates have shown clinical benefit in patients, in part due to tissue-dependent on-target toxicities from the repression of both mutant and wild type Notch proteins. The discovery of the P-type ATPase Sarco/Endoplasmic Reticulum Ca2+-ATPase (SERCA) as a modulator of oncogenic NOTCH1 suggested a new approach to treat T-cell Acute Lymphoblastic Leukemia (T-ALL). In fact, thapsigargin mediated SERCA inhibition had a stronger effect on the most common type of activating NOTCH1 mutants compared to wild type. However, the consequence of thapsigargin binding to SERCA is a rapid increase in cytosolic Ca2+ and a depletion of Ca2+ stored in the endoplasmic reticulum (ER). This shift of Ca2+ efflux might cause cardiac toxicity in human, suggesting the need to identify inhibitors with better drug-like properties and reduced off-target toxicity. From a small molecule screening of 191,000 P-type ATPase modulators CAD204520 displayed ~25 and ~79-fold greater selectivity toward human SERCA compared to Na+/K+ and H+-ATPase respectively and emerged as a candidate for the development of novel anti-NOTCH1 agents. In a series of in vitro studies, we showed that CAD204520 impairs the proliferation of a panel of lymphoid malignancies carrying activating mutations in the NOTCH1 heterodimerization domain (HD, such as T-ALL) and/or deletions in the degradation domain (PEST, such as mantle cell lymphoma (MCL)). Importantly, T-ALL lymphoblasts from patients carrying NOTCH1 mutations were more sensitive to CAD204520 suppression compared with normal lymphocytes or ALL wild type NOTCH1. Similar to thapsigargin, CAD204520 causes a defect in NOTCH1 trafficking that results in an accumulation of full-length NOTCH1 and in a depletion of the activated form: ICN1. Consequently, the NOTCH1 targets, MYC and DTX1, were repressed as measured by qRT-PCR. In contrast, we observed no effect at protein level in T-ALL wild type NOTCH1 suggesting that clinically relevant NOTCH1 mutations including PEST deletions are more sensitive to CAD204250 treatment than wild type proteins. The next question is whether CAD204520 activity has limitations in vivo due to Ca2+ shifts. Thus we analysed cardiac mechanics in isolated rat cardiomyocytes and showed that compared to thapsigargin, CAD204520 minimally alters myocardial performance (~25%) suggesting that the heart will likely tolerate CAD204520 modulation in vivo. This effect may be caused to differences between Ca2+ mediated ER stress upon thapsigargin or CAD204520 treatment. To test this hypothesis, we treated T-ALL cell lines at equimolar doses of CAD204520 and thapsigargin. We showed that, despite a similar effect on NOTCH1 protein levels, CAD204520 does not induce the unfolded protein response (UPR) pathway as measured by the phosphorylation of eIF2α or the induction of the ER chaperone BIP. This result suggests that CAD204520 retains ATPase activity, responsible for Notch inhibition, decoupled from the Ca2+ transport activity responsible for the off-target effects. A tempting hypothesis to explain these differences is that thapsigargin and CAD204520 inhibit SERCA in distinct pockets. Consistently, docking poses showed that CAD204520 binds SERCA in the trans-membrane helices M1, M3 and M4 while thapsigargin in the M3, M5 and M7 groove. Consequently, thapsigargin and CAD204520 co-treatment resulted in synergistic anti-proliferative effect in T-ALL. To test CAD204520 in vivo we studied its effect in CD1 mice and established a maximum tolerated dose. Mice exposed to CAD204520 for 21 days at 30 mg/Kg BID showed no decrease in body weight and, importantly no effect on cardiac hemodynamic. Finally, to assess the in vivo efficacy of CAD204520 we xenografted SKW-3/KE-37 T-ALL cell line in L-2Rγ null mice and demonstrated that drug's treatment reduced circulating and tissue infiltrating human leukemia T-ALL cells without causing heart-related off target effects. In conclusion, this study supports the development of tolerated SERCA inhibitors for Notch dependent cancers and extends its application to cases with mutations in the PEST degradation domain such as MCL or chronic lymphocytic leukemia. Disclosures Lund Winter: CaDo Biotechnology IvS: Employment. Stegmaier:Novartis: Research Funding; Rigel Pharmaceuticals: Consultancy. Dalby-Brown:CaDo Biotechnology IvS: Employment.

Artesunate Inhibits Graft-Versus-Host Disease in Mice Via a Mechanism of Inducing Mitochondrial Calcium Overloading in Activated T Cells

Despite pharmacological prophylaxis using calcineurin (CN) inhibitors (i.e., cyclosporin A and Tacrolimus), graft-versus-host disease (GVHD) remains a major barrier to the success of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Upon antigen stimulation, activated T cell receptor (TCR) signaling triggers rapid Ca2+ influx. This induces both CN-mediated NFAT activation, and increase of mitochondrial Ca2+ content, a major driver of metabolic activity. However, mitochondrial Ca2+ overload triggers opening of the mitochondrial permeability transition pore and cell death. We hypothesize that pharmacologically increasing mitochondrial Ca2+ load may decrease T cell survival capability, thereby reducing the GVH reaction. If this can be accomplished, it may lead to new strategies for inhibition of GVHD, which is conceptually different from the use of CN inhibitors. To test this hypothesis, we employed a high throughput drug screening system with the proliferation and cytotoxicity of TCR-activated human T cells as the readout, and screened the NPL-800 library (https://www.timtec.net) composed of 800 pure natural compounds. With a stringent criterion in consideration of dose-dependent effect, 26 compounds stood out for reducing the count of activated human T cells with a reduction rate of at least 30% at both 1.0uM and 10.0uM. Positive hits included inhibitors of DNA synthesis, the Na-K-ATPase and mitochondrial metabolism. We were particularly interested in artesunate (ART), which is a derivative of artemisinin that has been used for treating malaria in patients. While artemisinin acts by inhibiting sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) in P. falciparum malaria, which causes passive endoplasmic reticulum (ER) Ca2+ depletion and the subsequent cytosolic Ca2+ influx, ART did not inhibit SERCA in T cells. Ex vivo culture assays showed that ART dose-dependently reduced the survival of TCR-activated murine T cells. This inhibitory effect of ART was abrogated by inhibiting Ca2+ influx using BTP2, a potent inhibitor of store-operated Ca2+ channels. Furthermore, treatment of murine CD8 T cells with ART induced significant increases in mitochondrial Ca2+ loading upon TCR activation. These data suggest that inhibition of T cell survival by ART was dependent on TCR activation-induced Ca2+ influx and associated with enhanced mitochondrial Ca2+ uptake. We examined the impact of ART on GVHD in Balb/c mice receiving C57BL/6 (B6) mouse T cell-depleted bone marrow (TCD-BM) and CD4+ T cells. Intraperitoneal injection of ART (10 mg/kg, every other day) from day 1 to day 28 after transplantation reduced clinical signs of GVHD in these recipients and significantly improved their overall survival. Similar inhibition effects of ART on GVHD were observed in miHA-mismatched B6 anti-Balb/b and haplo-identical B6 anti-BDF1 mouse models of GVHD. Further investigations showed that in vivo administration of ART caused significant decreases in the number of host-reactive donor T cells in the spleen and liver of Balb/c mice 7 days after transfer of B6 TCD-BM plus CD4+ T cells. ART treatment did not affect the capacity of donor T cells to produce effector cytokines (e.g., IFN-g and TNF-α) in individual cells. Importantly, in vivo administration of ART preserved anti-leukemia activity of donor T cells and did not impair the reconstitution of hematopoiesis and lymphocytes. Collectively, our findings indicate that pharmacologically increasing mitochondrial Ca2+ loading may have significant implications in the development of novel strategies to prevent GVHD and other T cell-mediated inflammatory disorders in a broad context. Since ART therapy has been clinically approved, this work could be immediately translated into patients. Disclosures No relevant conflicts of interest to declare.

The P-type ATPase CtpF is a plasma membrane transporter mediating calcium efflux in Mycobacterium tuberculosis cells

Among the 12 P-type ATPases encoded by the genome of Mycobacterium tuberculosis(Mtb), CtpF responds to the greatest number of stress conditions, including oxidative stress, hypoxia, and infection. CtpF is the mycobacterial homolog of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) of higher eukaryotes. Its expression is regulated by the global regulator of latency, DosR. However, the role that CtpF plays in the mycobacterial plasma membrane remains unknown. In this study, different functional analyses showed that CtpF is associated with calcium pumping from mycobacterial cells. Specifically, Mtb CtpF expression in Mycobacterium smegmatis cells prevents Ca2+ accumulation compared with wild type (WT) cells. In addition, plasma membrane vesicles from recombinant membranes, in which the direction of ion transport is inverted, accumulate more Ca2+ compared with vesicles obtained from the WT strain. This findings support the hypothesis that CtpF contributes to calcium efflux from mycobacterial cells. Accordingly, Mtb cells defective in ctpF (MtbΔctpF) accumulate more Ca2+ compared with WT cells, while the Ca2+-dependent ATPase activity is significantly lower in the mutant cells. Interestingly, the deletion of ctpF in Mtb impairs the tolerance of the bacteria to oxidative and nitrosative stress. Overall, our results indicate that CtpF is associated with calcium pumping from mycobacterial cells and the response to oxidative stress.

Endoplasmic reticulum stress induced apoptosis and caspase activation is mediated through mitochondria during megakaryocyte differentiation

Megakaryocytopoiesis involves the process of the development of hematopoietic stem cells into megakaryocytes (MKs), which are the specialized cells responsible for the production of blood platelets. Platelets are one of the crucial factors for hemostasis and thrombosis. In terminally differentiated MKs, many molecular process such as caspase activation and a massive cytoskeletal rearrangement drive the formation of cytoplasmic extensions called proplatelets. These cytoplasmic extensions packed with granules and organelles are then released from the bone marrow into the blood circulation as platelets. Classically, caspase activation is associated with apoptosis and recent reports suggest their involvement in cell differentiation and maturation. There is no clear evidence about the stimulus for caspase activation during megakaryocyte development. In the current study, we attempted to understand the importance of endoplasmic reticulum stress in the caspase activation during megakaryocyte maturation. We used human megakaryoblstic cell line (Dami cells) as an experimental model. We used PMA (Phorbol 12-myristate 13 acetate) to induce megakaryocytic differentiation to understand the involvement of ER stress and caspase activation during MK maturation. Further, we used Thapsigargin, a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) as a positive control to induce ER stress. We observed larger and adherent cells with the increased expression of megakaryocytic markers (CD41 and CD61) and UPR markers in PMA or Thapsigargin treated cells as compared to control. Also, Thapsigargin treatment induced increased caspase activity and PARP cleavage. The increased expression of megakaryocyte maturation markers alongside with ER stress and caspase activation suggests the importance of ER stress in caspase activation during MK maturation.

SERCA stimulation: A potential approach in therapeutics.

sarco-endoplasmic reticulum Ca-ATPase (SERCA) is the major transporter present in sarco-endoplasmic reticulum (SR/ER), transporting calcium back into SR/ER from cytosol. The calcium-sequestering activity of SERCA facilitates relaxation in both cardiac and skeletal tissue. ER stress is one of the etiological factors in various diseases such as neurodegenerative diseases and diabetes. Disrupted calcium handling can cause ER stress. In the cardiac tissue, impairment of systolic and diastolic function can cause various cardiovascular diseases. SERCA ensures the proper calcium handling in cells and may act as a therapeutic target for the disease associated with dysregulation of calcium ions. This review examines the principle of calcium ion handling through SERCA and its role in various diseases.

Functional Reconstitution of Membrane Proteins Derived From Eukaryotic Cell-Free Systems

Cell-free protein synthesis (CFPS) based on eukaryotic Sf21 lysate is gaining interest among researchers due to its ability to handle the synthesis of complex human membrane proteins (MPs). Additionally Sf21 cell-free systems contain endogenous microsomal vesicles originally derived from the endoplasmic reticulum (ER). After CFPS, MPs will be translocated into the microsomal vesicles membranes present in the lysates. Thus microsomal membranes offer a natural environment for de novo synthesized MPs. Despite the advantage of synthesizing complex MPs with post translational modifications directly into the microsomal membranes without any additional solubilization supplements, batch based Sf21 cell-free synthesis suffers from low yields. The bottleneck for MPs in particular after the synthesis and incorporation into the microsomal membranes is to analyze their functionality. Apart from low yields of the synthesized MPs with batch based cell-free synthesis, the challenges arise in the form of cytoskeleton elements and peripheral endogenous proteins surrounding the microsomes which may impede the functional analysis of the synthesized proteins. So careful sample processing after the synthesis is particularly important for developing the appropriate functional assays. Here we demonstrate how MPs (native and batch synthesized) from ER derived microsomes can be processed for functional analysis by electrophysiology and radioactive uptake assay methods. Treatment of the microsomal membranes either with a sucrose washing step in the case of human serotonin transporter (hSERT) and sarco/endoplasmic reticulum Ca2+/ATPase (SERCA) pump or with mild detergents followed by the preparation of proteoliposomes in the case of the human voltage dependent anionic channel (hVDAC1) helps to analyze the functional properties of MPs.

SERCA2a tyrosine nitration coincides with impairments in maximal SERCA activity in left ventricles from tafazzin‐deficient mice

The sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA) is imperative for normal cardiac function regulating both muscle relaxation and contractility. SERCA2a is the predominant isoform in cardiac muscles and is inhibited by phospholamban (PLN). Under conditions of oxidative stress, SERCA2a may also be impaired by tyrosine nitration. Tafazzin (Taz) is a mitochondrial‐specific transacylase that regulates mature cardiolipin (CL) formation, and its absence leads to mitochondrial dysfunction and excessive production of reactive oxygen/nitrogen species (ROS/RNS). In the present study, we examined SERCA function, SERCA2a tyrosine nitration, and PLN expression/phosphorylation in left ventricles (LV) obtained from young (3‐5 months) and old (10‐12 months) wild‐type (WT) and Taz knockdown (TazKD) male mice. These mice are a mouse model for Barth syndrome, which is characterized by mitochondrial dysfunction, excessive ROS/RNS production, and dilated cardiomyopathy (DCM). Here, we show that maximal SERCA activity was impaired in both young and old TazKD LV, a result that correlated with elevated SERCA2a tyrosine nitration. In addition PLN protein was decreased, and its phosphorylation was increased in TazKD LV compared with control, which suggests that PLN may not contribute to the impairments in SERCA function. These changes in expression and phosphorylation of PLN may be an adaptive response aimed to improve SERCA function in TazKD mice. Nonetheless, we demonstrate for the first time that SERCA function is impaired in LVs obtained from young and old TazKD mice likely due to elevated ROS/RNS production. Future studies should determine whether improving SERCA function can improve cardiac contractility and pathology in TazKD mice.

ER responses play a key role in Swiss-Cheese/Neuropathy Target Esterase-associated neurodegeneration

Swiss Cheese (SWS) is the Drosophila orthologue of Neuropathy Target Esterase (NTE), a phospholipase that when mutated has been shown to cause a spectrum of disorders in humans that range from intellectual disabilities to ataxia. Loss of SWS in Drosophila also causes locomotion deficits, age-dependent neurodegeneration, and an increase in lysophosphatidylcholine (LPC) and phosphatidylcholine (PC). SWS is localized to the Endoplasmic Reticulum (ER), and recently, it has been shown that perturbing the membrane lipid composition of the ER can lead to the activation of ER stress responses through the inhibition of the Sarco/Endoplasmic Reticulum Ca2+ ATPase (SERCA). To investigate whether ER stress induction occurs in NTE-associated disorders, we used the fly sws null mutant as a model. sws flies showed an activated ER stress response as determined by elevated levels of the chaperone GRP78 and by increased splicing of XBP, an ER transcription factor that activates transcriptional ER stress responses. To address whether ER stress plays a role in the degenerative and behavioral phenotypes detected in sws1, we overexpressed XBP1, or treated the flies with tauroursodeoxycholic acid (TUDCA), a chemical known to attenuate ER stress-mediated cell death. Both manipulations suppressed the locomotor deficits and neurodegeneration of sws1. In addition, sws1 flies showed reduced SERCA levels and expressing additional SERCA also suppressed the sws1-related phenotypes. This suggests that the disruption in lipid compositions and its effect on SERCA are inducing ER stress, aimed to ameliorate the deleterious effects of sws1. This includes the effects on lipid composition because XBP1 and SERCA expression also reduced the LPC levels in sws1. Promoting cytoprotective ER stress pathways may therefore provide a therapeutic approach to alleviate the neurodegeneration and motor symptoms seen in NTE-associated disorders.

Parkinson\u2019s disease-associated LRRK2-G2019S mutant acts through regulation of SERCA activity to control ER stress in astrocytes

Accumulating evidence indicates that endoplasmic reticulum (ER) stress is a common feature of Parkinson’s disease (PD) and further suggests that several PD-related genes are responsible for ER dysfunction. However, the underlying mechanisms are largely unknown. Here, we defined the mechanism by which LRRK2-G2019S (LRRK2-GS), a pathogenic mutation in the PD-associated gene LRRK2, accelerates ER stress and cell death. Treatment of cells with α-synuclein increased the expression of ER stress proteins and subsequent cell death in LRRK2-GS astrocytes. Intriguingly, we found that LRRK2-GS localizes to the ER membrane, where it interacts with sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and suppress its activity by preventing displacement of phospholamban (PLN). LRRK2-GS–mediated SERCA malfunction leads to ER Ca2+ depletion, which induces the formation of mitochondria-ER contacts and subsequent Ca2+ overload in mitochondria, ultimately resulting in mitochondrial dysfunction. Collectively, our data suggest that, in astrocytes, LRRK2-GS impairs ER Ca2+ homeostasis, which determines cell survival, and as a result, could contribute to the development of PD.

Neuroprotective and reparative effects of endoplasmic reticulum luminal proteins – mesencephalic astrocyte-derived neurotrophic factor and cerebral dopamine neurotrophic factor

Cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) are proteins that have received increasing attention in the last decades. Although they are called neurotrophic factors they are drastically different from neurotrophic factors in their expression and physiological actions. They are located in the lumen of the endoplasmic reticulum (ER) and their basal secretion from neurons is very low. However their secretion is stimulated upon ER calcium depletion by chemical probes such as thapsigargin, a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitor. Exogenous MANF and CDNF possess therapeutic properties in several neurological disease models, including Parkinson’s disease and stroke. Endogenous MANF expression has been shown to be neuroprotective, as well as administration of either CDNF or MANF into the extracellular space. In this review, we focus on their therapeutic effects, regulation of expression and secretion, comparison of their mechanisms of action, and their application to the brain parenchyma as recombinant proteins.

Exercise, but not statins improve endothelial function in obese rats

IntroductionStatins and exercise training (ET) improve endothelial function. The mechanisms by which statins in combination with ET alter vascular function are largely unknown. We investigated how statins influence the effects of ET on vascular function in obese rats.MethodsEight‐week‐old male Wistar rats (n = 46) received a high‐fat diet for 20 weeks. The rats were randomized after into four groups after eight weeks: sedentary (SED; n =11), exercise (EX; n=11), statin (STAT; n=13) and exercise with statin (EX/STAT; n=11). Simvastatin (10mg/d/kg) was administered in drinking water. The rats exercised for 12 weeks, 5 days/week for 1 h/day at 18 m/min. Endothelium‐dependent (acetylcholine [Ach]) and – independent (sodium‐nitroprusside [SNP]) vascular function was assessed in the abdominal aorta using in vitro myography. Gene expression and protein abundance of nitric‐oxide soluble guanylate cyclase (NO‐sGC) signaling was assessed using q‐PCR and Western blot.ResultsStatin treatment significantly reduced cholesterol levels and did not influence exercise duration or intensity. ET independent of statins improved endothelium dependent vasodilation in EX and EX/STAT compared to SED and STAT, respectively. In untreated rats ET did not alter SNP vasodilation. However, in statin treated animals, ET improved SNP vasodilation. ET and statins increased NO protein abundance by 40% and 80%, respectively, compared to SED. However, in treated rats ET reduced NO to 40% above SED. Protein phosphatase 1 regulatory subunit 14A (CPI17), an inhibitor protein of smooth muscle myosin phosphatase showed a significant statin and exercise interaction at gene expression level (p < .0001). In untreated rats, ET upregulated CPI17 gene expression by 50% (p < .05). In treated rats a downregulation of 35% (p < .05) was observed. The results were similar on the protein level. The myosin phosphatase target subunit 1 (MYPT1) which drives the cGMP independent smooth muscle myosin phosphatase calcium desensitization was increased due to statin treatment (40%) and not affected by ET. Statin reduced sGCα protein content by more than 80%. Protein kinase cGMP‐dependent 1 (PRKG1), which phosphorylates multiple targets implicated in modulating cellular calcium was significantly increased (50%; p < .05) in non‐treated but decreased in treated rats. Protein abundance of the sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA), which drives the uptake of calcium into the sarcoplasmic reticulum was reduced by statins (50%) and not rescued by ET.ConclusionET independent of statin treatment improved endothelium‐dependent vasodilation. Interestingly, in untreated animals these improvements were most likely driven by NO, while in animals receiving statins, ET altered vascular smooth muscle calcium handling and desensitization. Overall our results suggests that individuals receiving statins should exercise to maintain vascular health.Support or Funding InformationDZHK (German Centre for Cardiovascular Research)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Novel approach for quantification of endoplasmic reticulum Ca2+ transport.

The type 2a sarco-/endoplasmic reticulum Ca2+-ATPase (SERCA2a) plays a key role in Ca2+ regulation in the heart. However, available techniques to study SERCA function are either cell destructive or lack sensitivity. The goal of this study was to develop an approach to selectively measure SERCA2a function in the cellular environment. The genetically encoded Ca2+ sensor R-CEPIA1er was used to measure the concentration of Ca2+ in the lumen of the endoplasmic reticulum (ER) ([Ca2+]ER) in HEK293 cells expressing human SERCA2a. Coexpression of the ER Ca2+ release channel ryanodine receptor (RyR2) created a Ca2+ release/reuptake system that mimicked aspects of cardiac myocyte Ca2+ handling. SERCA2a function was quantified from the rate of [Ca2+]ER refilling after ER Ca2+ depletion; then, ER Ca2+ leak was measured after SERCA inhibition. ER Ca2+ uptake and leak were analyzed as a function of [Ca2+]ER to determine maximum ER Ca2+ uptake rate and maximum ER Ca2+ load. The sensitivity of this assay was validated by analyzing effects of SERCA inhibitors, [ATP]/[ADP], oxidative stress, phospholamban, and a loss-of-function SERCA2a mutation. In addition, the feasibility of using R-CEPIA1er to study SERCA2a in a native system was evaluated by using in vivo gene delivery to express R-CEPIA1er in mouse hearts. After ventricular myocyte isolation, the same methodology used in HEK293 cells was applied to study endogenous SERCA2a. In conclusion, this new approach can be used as a sensitive screening tool to study the effect of different drugs, posttranslational modifications, and mutations on SERCA function. NEW & NOTEWORTHY The aim of this study was to develop a sensitive approach to selectively measure sarco-/endoplasmic reticulum Ca2+-ATPase (SERCA) function in the cellular environment. The newly developed Ca2+ sensor R-CEPIA1er was used to successfully analyze Ca2+ uptake mediated by recombinant and native cardiac SERCA. These results demonstrate that this new approach can be used as a powerful tool to study new mechanisms of Ca2+ pump regulation.

Thermodynamics of Cation Binding to the Sarcoendoplasmic Reticulum Calcium ATPase Pump and Impacts on Enzyme Function.

Sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) is a transmembrane pump that plays an important role in transporting calcium into the sarcoplasmic reticulum (SR). While calcium (Ca2+) binds SERCA with micromolar affinity, magnesium (Mg2+) and potassium (K+) also compete with Ca2+ binding. However, the molecular bases for these competing ions' influence on the SERCA function and the selectivity of the pump for Ca2+ are not well-established. We therefore used in silico methods to resolve molecular determinants of cation binding in the canonical site I and II Ca2+ binding sites via (1) triplicate molecular dynamics (MD) simulations of Mg2+, Ca2+, and K+-bound SERCA, (2) mean spherical approximation (MSA) theory to score the affinity and selectivity of cation binding to the MD-resolved structures, and (3) state models of SERCA turnover informed from MSA-derived affinity data. Our key findings are that (a) coordination at sites I and II is optimized for Ca2+ and to a lesser extent for Mg2+ and K+, as determined by MD-derived cation-amino acid oxygen and bound water configurations, (b) the impaired coordination and high desolvation cost for Mg2+ precludes favorable Mg2+ binding relative to Ca2+, while K+ has limited capacity to bind site I, and (c) Mg2+ most likely acts as inhibitor and K+ as intermediate in SERCA's reaction cycle, based on a best-fit state model of SERCA turnover. These findings provide a quantitative basis for SERCA function that leverages molecular-scale thermodynamic data and rationalizes enzyme activity across broad ranges of K+, Ca2+, and Mg2+ concentrations.

Familial Alzheimer’s disease-linked presenilin mutants and intracellular Ca2+ handling: A single-organelle, FRET-based analysis

An imbalance in Ca2+ homeostasis represents an early event in the pathogenesis of Alzheimer’s disease (AD). Presenilin-1 and -2 (PS1 and PS2) mutations, the major cause of familial AD (FAD), have been extensively associated with alterations in different Ca2+ signaling pathways, in particular those handled by storage compartments. However, FAD-PSs effect on organelles Ca2+ content is still debated and the mechanism of action of mutant proteins is unclear.To fulfil the need of a direct investigation of intracellular stores Ca2+ dynamics, we here present a detailed and quantitative single-cell analysis of FAD-PSs effects on organelle Ca2+ handling using specifically targeted, FRET (Fluorescence/Förster Resonance Energy Transfer)-based Ca2+ indicators. In SH-SY5Y human neuroblastoma cells and in patient-derived fibroblasts expressing different FAD-PSs mutations, we directly measured Ca2+ concentration within the main intracellular Ca2+ stores, e.g., Endoplasmic Reticulum (ER) and Golgi Apparatus (GA) medial- and trans-compartment. We unambiguously demonstrate that the expression of FAD-PS2 mutants, but not FAD-PS1, in either SH-SY5Y cells or FAD patient-derived fibroblasts, is able to alter Ca2+ handling of ER and medial-GA, but not trans-GA, reducing, compared to control cells, the Ca2+ content within these organelles by partially blocking SERCA (Sarco/Endoplasmic Reticulum Ca2+-ATPase) activity. Moreover, by using a cytosolic Ca2+ probe, we show that the expression of both FAD-PS1 and -PS2 reduces the Ca2+ influx activated by stores depletion (Store-Operated Ca2+ Entry; SOCE), by decreasing the expression levels of one of the key molecules, STIM1 (STromal Interaction Molecule 1), controlling this pathway.Our data indicate that FAD-linked PSs mutants differentially modulate the Ca2+ content of intracellular stores yet leading to a complex dysregulation of Ca2+ homeostasis, which represents a common disease phenotype of AD.

NO donors induce vascular relaxation by different cellular mechanisms in hypertensive and normotensive rats

PurposeThis study investigated the intracellular mechanisms involved in the vasodilatation induced by the classic NO donor SNP and the non-classic NO donor cis-[Ru(bpy)2(py)(NO2)](PF6) (or RuBPY) in mesenteric resistance arteries obtained from renal hypertensive (2K-1C) and normotensive (2K) rats. MethodsOn the basis of fluorimetric assays in cultured vascular smooth muscle cells (VSMCs) isolated from 2K-1C and 2K rats, we measured NO release from SNP and RuBPY, cytosolic Ca2+ concentration ([Ca2+]c), and reactive oxygen species (ROS) with the selective probes DAF-2DA, Fluo-3AM and the more selective probe for peroxynitrite (7-CBA), respectively. We determined isometric tension in mesenteric arteries to assess SNP- and RuBPY-induced relaxation. ResultsSNP and RuBPY released NO in comparable amounts in cultured aortic VSMCs from hypertensive 2K-1C and normotensive 2K rats. The NO0 scavenger hydroxocobalamin blunted NO release. Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) inhibition with thapsigargin reduced [Ca2+]c in normotensive 2K rat VSMCs only. ROS amounts were greater in hypertensive 2K-1C than in normotensive 2K rat VSMCs, but neither SNP nor RuBPY altered ROS concentrations in any of the groups. SNP and RuBPY induced similar relaxation in hypertensive 2K-1C and normotensive 2K rat mesenteric resistance arteries. The SNP and RuBPY-induced relaxation involves sGC and PKG activation. On the other hand, SNP but not RuBPY activates K+ channels. Interestingly, SERCA inhibition reduces SNP induced relaxation only in normotensive 2K rat mesenteric arteries whereas RuBPY-induced relaxation does not involve SERCA activation in both normotensive and hypertensive arteries. ConclusionOur results indicate that SNP and RuBPY-induced mesenteric resistance artery relaxation involves NO/sGC/cGMP/PKG pathway activation. K+ channels and SERCA activation is required to SNP but not for RuBPY-induced relaxation. Moreover, SERCA seems to be impaired in hypertensive 2K-1C rat mesenteric resistance arteries although it does not impact SNP- or RuBPY-induced relaxation.

Role of the PRC2-Six1-miR-25 signaling axis in heart failure

The reduced expression of cardiac sarco-endoplasmic reticulum Ca2+ ATPase (SERCA2a) is a hallmark of heart failure. We previously showed that miR-25 is a crucial transcriptional regulator of SERCA2a in the heart. However, the precise mechanism of cardiac miR-25 regulation is largely unknown. Literatures suggested that miR-25 is regulated by the transcriptional co-factor, sine oculis homeobox homolog 1 (Six1), which in turn is epigenetically regulated by polycomb repressive complex 2 (PRC 2) in cardiac progenitor cells. Therefore, we aimed to investigate whether Six1 and PRC2 are indeed involved in the regulation of the miR-25 level in the setting of heart failure. Six1 was up-regulated in the failing hearts of humans and mice. Overexpression of Six1 led to adverse cardiac remodeling, whereas knock-down of Six1 attenuated pressure overload-induced cardiac dysfunction. The adverse effects of Six1 were ameliorated by knock-down of miR-25. The epigenetic repression on the Six1 promoter by PRC2 was significantly reduced in failing hearts. Epigenetic repression of Six1 is relieved through a reduction of PRC2 activity in heart failure. Six1 up-regulates miR-25, which is followed by reduction of cardiac SERCA2a expression. Collectively, these data showed that the PRC2-Six1-miR-25 signaling axis is involved in heart failure. Our finding introduces new insight into potential treatments of heart failure.

Relaxant effect of atorvastatin on isolated rat gastric fundus strips: implications for Ca2+-signalling mechanisms.

Statins are determined to have various pleiotropic effects apart from their lipid-lowering properties. Herein, we investigated the direct effects of atorvastatin on gastric smooth muscle tone. Atorvastatin effectively relaxed isolated rat gastric fundus strips precontracted with acetylcholine, potassium chloride, and serotonin. Incubation of the strips with nitric oxide synthase inhibitor, l-NOARG (10-4 M, 20 min), l-type voltage-operated Ca2+ channel (VOCC) blocker, nifedipine (10-6 M, 30 min), KATP channel blocker, glibenclamide (10-5 M, 30 min), or precursor of cholesterol, mevalonate (10-2 M, 45 min) did not change the relaxations to atorvastatin. However, pretreatment of fundus strips with atorvastatin (3×10-5-3×10-4 M, 30 min) inhibited the contractions to calcium chloride (10-4-10-1 M), acetylcholine (10-4 M), and caffeine (20 mM) in the calcium-free medium. Moreover, atorvastatin reduced the contractions induced by sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor, cyclopiazonic acid (10-7-3×10-5 M). The current study demonstrated that atorvastatin produces an acute relaxant effect on gastric fundus strips, which appears to be mediated by several Ca2+-signalling mechanisms such as the blockade of l-type VOCC-independent Ca2+ entry, decrease in smooth muscle Ca2+ sensitivity, inhibition of IP3- and ryanodine-sensitive intracellular stores to mediate Ca2+ release, as well as the activation of SERCA. This acute relaxing effect seems unlikely to be related with nitric oxide, KATP channels, and the mevalonate pathway.