Inhibition of Sarco-Endoplasmic Reticulum Ca2+ ATPase Extends the Lifespan in C. elegans Worms

Expanded polyQ aggregates interact with sarco-endoplasmic reticulum calcium ATPase and Drosophila inhibitor of apoptosis protein1 to regulate polyQ mediated neurodegeneration in Drosophila

Polyglutamine (polyQ) induced neurodegeneration is one of the leading causes of progressive neurodegenerative disorders characterized clinically by deteriorating movement defects, psychiatric disability, and dementia. Calcium [Ca2+] homeostasis, which is essential for the functioning of neuronal cells, is disrupted under these pathological conditions. In this paper, we simulated Huntington's disease phenotype in the neuronal cells of the Drosophila eye and identified [Ca2+] pump, sarco-endoplasmic reticulum calcium ATPase (SERCA), as one of the genetic modifiers of the neurodegenerative phenotype. This paper shows genetic and molecular interaction between polyglutamine (polyQ) aggregates, SERCA and DIAP1. We present evidence that polyQ aggregates interact with SERCA and alter its dynamics, resulting in a decrease in cytosolic [Ca2+] and an increase in ER [Ca2+], and thus toxicity. Downregulating SERCA lowers the enhanced calcium levels in the ER and rescues, morphological and functional defects caused due to expanded polyQ repeats. Cell proliferation markers such as Yorkie (Yki), Scalloped (Sd), and phosphatidylinositol 3 kinases/protein kinase B (PI3K/Akt), also respond to varying levels of calcium due to genetic manipulations, adding to the amelioration of degeneration. These results imply that neurodegeneration due to expanded polyQ repeats is sensitive to SERCA activity, and its manipulation can be an important step toward its therapeutic measures.

Pharmacological Regulation of Endoplasmic Reticulum Structure and Calcium Dynamics: Importance for Neurodegenerative Diseases

The endoplasmic reticulum (ER) is the largest organelle of the cell, composed of a continuous network of sheets and tubules, and is involved in protein, calcium (Ca2+), and lipid homeostasis. In neurons, the ER extends throughout the cell, both somal and axodendritic compartments, and is highly important for neuronal functions. A third of the proteome of a cell, secreted and membrane-bound proteins, are processed within the ER lumen and most of these proteins are vital for neuronal activity. The brain itself is high in lipid content, and many structural lipids are produced, in part, by the ER. Cholesterol and steroid synthesis are strictly regulated in the ER of the blood-brain barrier protected brain cells. The high Ca2+ level in the ER lumen and low cytosolic concentration is needed for Ca2+-based intracellular signaling, for synaptic signaling and Ca2+ waves, and for preparing proteins for correct folding in the presence of high Ca2+ concentrations to cope with the high concentrations of extracellular milieu. Particularly, ER Ca2+ is controlled in axodendritic areas for proper neurito- and synaptogenesis and synaptic plasticity and remodeling. In this review, we cover the physiologic functions of the neuronal ER and discuss it in context of common neurodegenerative diseases, focusing on pharmacological regulation of ER Ca2+ Furthermore, we postulate that heterogeneity of the ER, its protein folding capacity, and ensuring Ca2+ regulation are crucial factors for the aging and selective vulnerability of neurons in various neurodegenerative diseases. SIGNIFICANCE STATEMENT: Endoplasmic reticulum (ER) Ca2+ regulators are promising therapeutic targets for degenerative diseases for which efficacious drug therapies do not exist. The use of pharmacological probes targeting maintenance and restoration of ER Ca2+ can provide restoration of protein homeostasis (e.g., folding of complex plasma membrane signaling receptors) and slow down the degeneration process of neurons.

SERCA inhibition improves lifespan and healthspan in a chemical model of Parkinson disease in Caenorhabditis elegans

Introduction: The high prevalence of neurodegenerative diseases in our population and the lack of effective treatments encourage the search for new therapeutic targets for these pathologies. We have recently described that submaximal inhibition of the Sarco-Endoplasmic Reticulum Ca²⁺ ATPase (SERCA), the main responsible for ER calcium storage, is able to increase lifespan in Caenorhabditis elegans worms by mechanisms involving mitochondrial metabolism and nutrient-sensitive pathways. Methods: We have studied here the effects of submaximal SERCA inhibition in a chemical model of Parkinson's disease (PD) induced in C. elegans worms by treatment with the mitochondrial complex I inhibitor rotenone. For specific SERCA inhibition, we treated worms with RNAi against sca-1, the sole orthologue of SERCA in C. elegans. Results and Discussion: Our results show that rotenone produces alterations in worms that include decreased lifespan, smaller size, reduced fertility, decreased motility, defecation and pumping rate, increased mitochondrial ROS production, reduced mitochondrial membrane potential and oxygen consumption rate, altered mitochondrial structure, and altered ethanol preference in behavioral studies. Most of these alterations were either fully or partially reversed in worms treated with sca-1 RNAi, suggesting that SERCA inhibition could be a novel pharmacological target in the prevention or treatment of neurodegeneration.

IKCa channels control breast cancer metabolism including AMPK-driven autophagy

Ca²⁺-activated K⁺ channels of intermediate conductance (IK) are frequently overexpressed in breast cancer (BC) cells, while IK channel depletion reduces BC cell proliferation and tumorigenesis. This raises the question, of whether and mechanistically how IK activity interferes with the metabolic activity and energy consumption rates, which are fundamental for rapidly growing cells. Using BC cells obtained from MMTV-PyMT tumor-bearing mice, we show that both, glycolysis and mitochondrial ATP-production are reduced in cells derived from IK-deficient breast tumors. Loss of IK altered the sub-/cellular K⁺- and Ca²⁺- homeostasis and mitochondrial membrane potential, ultimately resulting in reduced ATP-production and metabolic activity. Consequently, we find that BC cells lacking IK upregulate AMP-activated protein kinase activity to induce autophagy compensating the glycolytic and mitochondrial energy shortage. Our results emphasize that IK by modulating cellular Ca²⁺- and K⁺-dynamics contributes to the remodeling of metabolic pathways in cancer. Thus, targeting IK channel might disturb the metabolic activity of BC cells and reduce malignancy.

Natural Polyphenols as SERCA Activators: Role in the Endoplasmic Reticulum Stress-Related Diseases

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) is a key protein responsible for transporting Ca²⁺ ions from the cytosol into the lumen of the sarco/endoplasmic reticulum (SR/ER), thus maintaining Ca²⁺ homeostasis within cells. Accumulating evidence suggests that impaired SERCA function is associated with disruption of intracellular Ca²⁺ homeostasis and induction of ER stress, leading to different chronic pathological conditions. Therefore, appropriate strategies to control Ca²⁺ homeostasis via modulation of either SERCA pump activity/expression or relevant signaling pathways may represent a useful approach to combat pathological states associated with ER stress. Natural dietary polyphenolic compounds, such as resveratrol, gingerol, ellagic acid, luteolin, or green tea polyphenols, with a number of health-promoting properties, have been described either to increase SERCA activity/expression directly or to affect Ca²⁺ signaling pathways. In this review, potential Ca²⁺-mediated effects of the most studied polyphenols on SERCA pumps or related Ca²⁺ signaling pathways are summarized, and relevant mechanisms of their action on Ca²⁺ regulation with respect to various ER stress-related states are depicted. All data were collected using scientific search tools (i.e., Science Direct, PubMed, Scopus, and Google Scholar).

Interplay between SERCA, 4E-BP, and eIF4E in the Drosophila heart

Appropriate cardiac performance depends on a tightly controlled handling of Ca2+ in a broad range of species, from invertebrates to mammals. The role of the Ca2+ ATPase, SERCA, in Ca2+ handling is pivotal, and its activity is regulated, inter alia, by interacting with distinct proteins. Herein, we give evidence that 4E binding protein (4E-BP) is a novel regulator of SERCA activity in Drosophila melanogaster during cardiac function. Flies over-expressing 4E-BP showed improved cardiac performance in young individuals associated with incremented SERCA activity. Moreover, we demonstrate that SERCA interacts with translation initiation factors eIF4E-1, eIF4E-2 and eIF4E-4 in a yeast two-hybrid assay. The specific identification of eIF4E-4 in cardiac tissue leads us to propose that the interaction of elF4E-4 with SERCA may be the basis of the cardiac effects observed in 4E-BP over-expressing flies associated with incremented SERCA activity.

The role of SERCA and sarcolipin in adaptive muscle remodeling

Sarcolipin (SLN) is a small integral membrane protein that regulates the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) pump. When bound to SERCA, SLN reduces the apparent Ca²⁺ affinity of SERCA and uncouples SERCA Ca²⁺ transport from its ATP consumption. As such, SLN plays a direct role in altering skeletal muscle relaxation and energy expenditure. Interestingly, the expression of SLN is dynamic during times of muscle adaptation, where large increases in SLN content are found in response to development, atrophy, overload and disease. Several groups have suggested that increases in SLN, especially in dystrophic muscle, are deleterious to muscle function and exacerbate already abhorrent intracellular Ca²⁺ levels. However, there is also significant evidence to show that increased SLN content is a beneficial adaptive mechanism which protects the SERCA pump and activates Ca²⁺ signaling and adaptive remodeling during times of cell stress. In this review, we first discuss the role for SLN in healthy muscle during both development and overload, where SLN has been shown to activate Ca²⁺ signaling to promote mitochondrial biogenesis, fibre type shifts and muscle hypertrophy. Then, with respect to muscle disease, we summarize the discrepancies in the literature as to whether SLN upregulation is adaptive or maladaptive in nature. This review is the first to offer the concept of SLN hormesis in muscle disease, wherein both too much and too little SLN are detrimental to muscle health. Finally, the underlying mechanisms which activate SLN upregulation are discussed, specifically acknowledging a potential positive feedback loop between SLN and Ca²⁺ signaling molecules.

Resveratrol Treatment in Human Parkin-Mutant Fibroblasts Modulates cAMP and Calcium Homeostasis Regulating the Expression of Mitochondria-Associated Membranes Resident Proteins

Parkin plays an important role in ensuring efficient mitochondrial function and calcium homeostasis. Parkin-mutant human fibroblasts, with defective oxidative phosphorylation activity, showed high basal cAMP level likely ascribed to increased activity/expression of soluble adenylyl cyclase and/or low expression/activity of the phosphodiesterase isoform 4 and to a higher Ca²⁺ level. Overall, these findings support the existence, in parkin-mutant fibroblasts, of an abnormal Ca²⁺ and cAMP homeostasis in mitochondria. In our previous studies resveratrol treatment of parkin-mutant fibroblasts induced a partial rescue of mitochondrial functions associated with stimulation of the AMPK/SIRT1/PGC-1α pathway. In this study we provide additional evidence of the potential beneficial effects of resveratrol inducing an increase in the pre-existing high Ca²⁺ level and remodulation of the cAMP homeostasis in parkin-mutant fibroblasts. Consistently, we report in these fibroblasts higher expression of proteins implicated in the tethering of ER and mitochondrial contact sites along with their renormalization after resveratrol treatment. On this basis we hypothesize that resveratrol-mediated enhancement of the Ca²⁺ level, fine-tuned by the ER-mitochondria Ca²⁺ crosstalk, might modulate the pAMPK/AMPK pathway in parkin-mutant fibroblasts.

The Mitochondrial Na+/Ca2+ Exchanger Inhibitor CGP37157 Preserves Muscle Structure and Function to Increase Lifespan and Healthspan in Caenorhabditis elegans

We have reported recently that the mitochondrial Na⁺/Ca²⁺ exchanger inhibitor CGP37157 extends lifespan in Caenorhabditis elegans by a mechanism involving mitochondria, the TOR pathway and the insulin/IGF1 pathway. Here we show that CGP37157 significantly improved the evolution with age of the sarcomeric regular structure, delaying development of sarcopenia in C. elegans body wall muscle and increasing the average and maximum speed of the worms. Similarly, CGP37157 favored the maintenance of a regular mitochondrial structure during aging. We have also investigated further the mechanism of the effect of CGP37157 by studying its effect in mutants of aak-1;aak-2/AMP-activated kinase, sir-2.1/sirtuin, rsks-1/S6 kinase and daf-16/FOXO. We found that this compound was still effective increasing lifespan in all these mutants, indicating that these pathways are not involved in the effect. We have then monitored pharynx cytosolic and mitochondrial Ca²⁺ signalling and our results suggest that CGP37157 is probably inhibiting not only the mitochondrial Na⁺/Ca²⁺ exchanger, but also Ca²⁺ entry through the plasma membrane. Finally, a transcriptomic study detected that CGP37157 induced changes in lipid metabolism enzymes and a four-fold increase in the expression of ncx-6, one of the C. elegans mitochondrial Na⁺/Ca²⁺ exchangers. In summary, CGP37157 increases both lifespan and healthspan by a mechanism involving changes in cytosolic and mitochondrial Ca²⁺ homeostasis. Thus, Ca²⁺ signalling could be a promising target to act on aging.

Mechanism of the lifespan extension induced by submaximal SERCA inhibition in C. elegans

We have reported recently that submaximal inhibition of the Sarco Endoplasmic Reticulum Ca²⁺ ATPase (SERCA) produces an increase in the lifespan of C. elegans worms. We have explored here the mechanism of this increased survival by studying the effect of SERCA inhibition in several mutants of signaling pathways related to longevity. Our data show that the mechanism of the effect is unrelated with the insulin signaling pathway or the sirtuin activity, because SERCA inhibitors increased lifespan similarly in mutants of these pathways. However, the effect required functional mitochondria and both the AMP kinase and TOR pathways, as the SERCA inhibitors were ineffective in the corresponding mutants. The same effects were obtained after reducing SERCA expression with submaximal RNAi treatment. The SERCA inhibitors did not induce ER-stress at the concentrations used, and their effect was not modified by inactivation of the OP50 bacterial food. Altogether, our data suggest that the effect may be due to a reduced ER-mitochondria Ca²⁺ transfer acting via AMPK activation and mTOR inhibition to promote survival.

Caenorhabditis elegans as a possible model to screen anti-Alzheimer's therapeutics

Alzheimer's disease (AD) is regarded as one of the significant health burdens, as the prevalence is raising worldwide and gradually reaching to epidemic proportions. Consequently, a number of scientific investigations have been initiated to derive therapeutics to combat AD with a concurrent advancement in pharmacological methods and experimental models. Whilst, the available experimental pharmacological approaches both in vivo and in vitro led to the development of AD therapeutics, the precise manner by which experimental models mimic either one or more biomarkers of human pathology of AD is gaining scientific attentions. Caenorhabditis elegans (C. elegans) has been regarded as an emerging model for various reasons, including its high similarities with the biomarkers of human AD. Our review supports the versatile nature of C. elegans and collates that it is a well-suited model to elucidate various molecular mechanisms by which AD therapeutics elicit their pharmacological effects. It is apparent that C. elegans is capable of establishing the pathological processes that links the endoplasmic reticulum and mitochondria dysfunctions in AD, exploring novel molecular cascades of AD pathogenesis and underpinning causal and consequential changes in the associated proteins and genes. In summary, C. elegans is a unique and feasible model for the screening of anti-Alzheimer's therapeutics and has the potential for further scientific exploration.

Interrelation between ROS and Ca2+ in aging and age-related diseases

Calcium (Ca2+) and reactive oxygen species (ROS) are versatile signaling molecules coordinating physiological and pathophysiological processes. While channels and pumps shuttle Ca2+ ions between extracellular space, cytosol and cellular compartments, short-lived and highly reactive ROS are constantly generated by various production sites within the cell. Ca2+ controls membrane potential, modulates mitochondrial adenosine triphosphate (ATP) production and affects proteins like calcineurin (CaN) or calmodulin (CaM), which, in turn, have a wide area of action. Overwhelming Ca2+ levels within mitochondria efficiently induce and trigger cell death. In contrast, ROS comprise a diverse group of relatively unstable molecules with an odd number of electrons that abstract electrons from other molecules to gain stability. Depending on the type and produced amount, ROS act either as signaling molecules by affecting target proteins or as harmful oxidative stressors by damaging cellular components. Due to their wide range of actions, it is little wonder that Ca2+ and ROS signaling pathways overlap and impact one another. Growing evidence suggests a crucial implication of this mutual interplay on the development and enhancement of age-related disorders, including cardiovascular and neurodegenerative diseases as well as cancer.

Sarco/Endoplasmic Reticulum Calcium ATPase Inhibitors: Beyond Anticancer Perspective

The sarco/endoplasmic reticulum calcium ATPase (SERCA), which plays a key role in the maintenance of Ca²⁺ ion homeostasis, is an extensively studied enzyme, the inhibition of which has a considerable impact on cell life and death decision. To date, several SERCA inhibitors have been thoroughly studied and the most notable one, a derivative of the sesquiterpene lactone thapsigargin, is gradually approaching a clinical application. Meanwhile, new compounds with SERCA-inhibiting properties of natural, synthetic, or semisynthetic origin are being discovered and/or developed; some of these might also be suitable for the development of new drugs with improved performance. This review brings an up-to-date comprehensive overview of recently discovered compounds with the potential of SERCA inhibition, discusses their mechanism of action, and highlights their potential clinical applications, such as cancer treatment.

The Role of Ca2+ Signaling in Aging and Neurodegeneration: Insights from Caenorhabditis elegans Models

Ca²⁺ is a ubiquitous second messenger that plays an essential role in physiological processes such as muscle contraction, neuronal secretion, and cell proliferation or differentiation. There is ample evidence that the dysregulation of Ca²⁺ signaling is one of the key events in the development of neurodegenerative processes, an idea called the "calcium hypothesis" of neurodegeneration. Caenorhabditis elegans (C. elegans) is a very good model for the study of aging and neurodegeneration. In fact, many of the signaling pathways involved in longevity were first discovered in this nematode, and many models of neurodegenerative diseases have also been developed therein, either through mutations in the worm genome or by expressing human proteins involved in neurodegeneration (β-amyloid, α-synuclein, polyglutamine, or others) in defined worm tissues. The worm is completely transparent throughout its whole life, which makes it possible to carry out Ca²⁺ dynamics studies in vivo at any time, by expressing Ca²⁺ fluorescent probes in defined worm tissues, and even in specific organelles such as mitochondria. This review will summarize the evidence obtained using this model organism to understand the role of Ca²⁺ signaling in aging and neurodegeneration.

The exploration of effect of terfenadine on Ca2+ signaling in renal tubular cells

Terfenadine, an antihistamine used for the treatment of allergic conditions, affected Ca²⁺-related physiological responses in various models. However, the effect of terfenadine on cytosolic free Ca²⁺ levels ([Ca²⁺]_i) and its related physiology in renal tubular cells is unknown. This study examined whether terfenadine altered Ca²⁺ signaling and caused cytotoxicity in Madin-Darby canine kidney (MDCK) renal tubular cells. The Ca²⁺-sensitive fluorescent dye fura-2 was used to measure [Ca²⁺]_i. Cell viability was measured by the fluorescent reagent 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay. Terfenadine at concentrations of 100-1000 μM induced [Ca²⁺]_i rises concentration dependently. The response was reduced by approximately 35% by removing extracellular Ca²⁺. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) partly inhibited terfenadine-evoked [Ca²⁺]_i rises. Conversely, treatment with terfenadine abolished BHQ-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with U73122 inhibited 95% of terfenadine-induced Ca²⁺ release. Terfenadine-induced Ca²⁺ entry was supported by Mn²⁺-caused quenching of fura-2 fluorescence. Terfenadine-induced Ca²⁺ entry was partly inhibited by an activator of protein kinase C (PKC), phorbol 12-myristate 13 acetate (PMA) and by three modulators of store-operated Ca²⁺ channels (nifedipine, econazole, and SKF96365). Terfenadine at 200-300 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in MDCK cells, terfenadine induced [Ca²⁺]_i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Furthermore, terfenadine caused cell death that was not triggered by preceding [Ca²⁺]_i rises.

Effects of ammonia nitrogen on gill mitochondria in clam Ruditapes philippinarum

Ammonia nitrogen exposure has been found to significantly increase the early apoptosis rates of gill cells, affect the contents of ATP and disturb expressions of calcium-related genes in clam Ruditapes philippinarum. Mitochondria are the centers for energy production, initiation of apoptosis and calcium signal regulation. It is hypothesized that gill mitochondrion is a target organelle for the ammonia nitrogen. Thus, ATP metabolism together with ATP-consuming functions would be interfered by ammonia exposure. In the present study, mitochondrial transmembrane potential (MTP), ATPase activities, gill functions in clearance and respiration, and histological changes were detected to characterize the effects of ammonia to the gill mitochondria in clam R. philippinarum. Results indicated that ammonia exposure led to significant decreases in MTP, Ca²⁺-ATPase activity and clearance rates. However, different concentrations of ammonia nitrogen induced different variations on H⁺, K⁺-ATPase activity and respiration rates. Histological observation revealed that subacute exposure of ammonia damaged the microstructure of gill tissues. Therefore, ammonia exposure dramatically damaged the normal structure and function of mitochondria, resulting in irreversible damage in energy formation and supply. In addition, it affected Ca²⁺ and K⁺ metabolism and inhibited food intake and respiration in clam R. philippinarum.