A new target for Parkinson's disease: Small molecule SERCA activator CDN1163 ameliorates dyskinesia in 6-OHDA-lesioned rats

Heat stress induces calcium dyshomeostasis to subsequent cognitive impairment through ERS-mediated apoptosis via SERCA/PERK/eIF2α pathway

Heat exposure is an environmental stressor that has been associated with cognitive impairment. However, the neural mechanisms that underlie this phenomenon have yet to be extensively investigated. The Morris water maze test was utilized to assess cognitive performance. RNA sequencing was employed to discover the primary regulators and pathological pathways involved in cognitive impairment caused by heat. Before heat exposure in vivo and in vitro, activation of the sarco/endoplasmic reticulum (SR/ER) calcium (Ca2+)-ATPase (SERCA) was achieved by CDN1163. Hematoxylin-Eosin, Nissl staining, calcium imaging, transmission electron microscopy, western blot, and immunofluorescence were utilized to visualize histological changes, intracellular calcium levels, endoplasmic reticulum stress (ERS) markers, apoptosis, and synaptic proteins alterations. Heat stress (HS) significantly induced cognitive decline and neuronal damage in mice. By the transcriptome sequencing between control (n = 5) and heat stress (n = 5) mice in hippocampal tissues, we identified a reduction in the expression of the atp2a gene encoding SERCA, accompanied by a corresponding decrease in its protein level. Consequently, this dysregulation resulted in an excessive accumulation of intracellular calcium ions. Furthermore, HS exposure also activated ERS and apoptosis, as evidenced by the upregulation of p-PERK, p-eIF2α, CHOP, and caspase-3. Consistently, a reduction in postsynaptic density protein 95 (PSD95) and synaptophysin (SYN) expressions indicated modifications in synaptic function. Notably, the impacts on neurons caused by HS were found to be mitigated by CDN1163 treatment both in vivo and in vitro. Additionally, SERCA-mediated ERS-induced apoptosis was attenuated by GSK2606414 treatment via inhibiting PERK-eIF2α-CHOP axis that not only curtailed the level of caspase-3 but also elevated the levels of PSD95 and SYN. These findings highlight the significant impact of heat stress on cognitive impairment, and further elucidate the underlying mechanism involving SERCA/PERK/eIF2α pathway.

Chronic pharmacological activation of SERCA with CDN1163 affects spatial cognitive flexibility but not attention and impulsivity in mice

Intracellular calcium (Ca2+) homeostasis is critical for many neural processes, including learning, memory and synaptic plasticity. The sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) is among the key regulators that preserve Ca2+ homeostasis in neurons. SERCAs comprise a set of ubiquitously expressed Ca2+ pumps that primarily function to sequester cytosolic Ca2+ into endoplasmic reticular stores. As SERCA has been implicated in the neurobiology of several neuropsychiatric and neurodegenerative diseases, pharmacological harnessing of its function is critical in understanding SERCA's role in brain physiology and pathophysiology. In the current study, we employed the Morris water maze and 5-choice serial reaction time task (5-CSRTT) to investigate the effects of chronic pharmacological activation of SERCA, using the small allosteric SERCA activator CDN1163, on spatial learning and memory, and executive functioning in naive C57BL/6J mice. Our data show that chronic pharmacological SERCA activation with CDN1163 (20 mg/kg) selectively impairs spatial cognitive flexibility and reversal learning in the Morris water maze while leaving executive functions such as attention and impulsivity intact. Present findings contribute to the growing field of the role of SERCA function in the brain and behavior and expand current knowledge on the use of the small allosteric activator CDN1163 as an investigational tool to study the role of SERCA in regulating neurobehavioral processes and as a potential therapeutic candidate for debilitating brain disorders.

Myocardial infarction elevates endoplasmic reticulum stress and protein aggregation in heart as well as brain

Cardiovascular diseases, including myocardial infarction (MI), constitute the leading cause of morbidity and mortality worldwide. Protein-aggregate deposition is a hallmark of aging and neurodegeneration. Our previous study reported that aggregation is strikingly elevated in hearts of hypertensive and aged mice; however, no prior study has addressed MI effects on aggregation in heart or brain. Here, we present novel data on heart and brain aggregation in mice following experimental MI, induced by left coronary artery (LCA) ligation. Infarcted and peri-infarcted heart tissue, and whole cerebra, were isolated from mice at sacrifice, 7 days following LCA ligation. Sham-MI mice (identical surgery without ligation) served as controls. We purified detergent-insoluble aggregates from these tissues, and quantified key protein constituents by high-resolution mass spectrometry (LC-MS/MS). Infarct heart tissue had 2.5- to 10-fold more aggregates than non-infarct or sham-MI heart tissue (each P = 0.001). Protein constituents from MI cerebral aggregates overlapped substantially with those from human Alzheimer's disease brain. Prior injection of mice with mesenchymal stem cell (MSC) exosomes, shown to limit infarct size after LCA ligation, reduced cardiac aggregation ~ 60%, and attenuated markers of endoplasmic reticulum (ER) stress in heart and brain (GRP78, ATF6, P-PERK) by 50-75%. MI also elevated aggregate constituents enriched in Alzheimer's disease (AD) aggregates, such as proteasomal subunits, heat-shock proteins, complement C3, clusterin/ApoJ, and other apolipoproteins. These data provide novel evidence that aggregation is elevated in mouse hearts and brains after myocardial ischemia, leading to cognitive impairment resembling AD, but can be attenuated by exosomes or drug (CDN1163) interventions that oppose ER stress.

CDN1163, an activator of sarco/endoplasmic reticulum Ca2+ ATPase, up-regulates mitochondrial functions and protects against lipotoxicity in pancreatic β-cells

BACKGROUND AND PURPOSE

High levels of Ca2+ in the endoplasmic reticulum (ER), established by the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA), are required for protein folding and cell signalling. Excessive ER Ca2+ release or decreased SERCA activity induces unfolded protein accumulation and ER stress in pancreatic β-cells, leading to defective insulin secretion and diabetes. Here we have investigated the consequences of enhancing ER Ca2+ uptake on β-cell survival and function.

EXPERIMENTAL APPROACH

The effects of SERCA activator, CDN1163, on Ca2+ homeostasis, protein expression, mitochondrial activities, insulin secretion, and lipotoxicity have been studied in mouse pancreatic β-cells and MIN6 cells.

KEY RESULTS

CDN1163, increased insulin synthesis and exocytosis from islets. CDN1163 also increased the sensitivity of the cytosolic Ca2+ oscillation response to glucose and potentiated it in dispersed and sorted β-cells. CDN1163 augmented the ER and mitochondrial Ca2+ content, the mitochondrial membrane potential, respiration, and ATP synthesis. CDN1163 up-regulated expression of inositol 1,4,5-trisphosphate receptors and antioxidant enzymes, and mitochondrial biogenesis, including peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α). Overexpression of SERCA2a or 2b replicated the effects of CDN1163, while knockdown of SERCA2 abolished the stimulatory actions of CDN1163. In palmitate-treated β-cells, CDN1163 prevented ER Ca2+ depletion, mitochondrial dysfunction, cytosolic and mitochondrial oxidative stress, defective insulin secretion, and apoptotic cell death.

CONCLUSIONS AND IMPLICATIONS

Activation of SERCA enhanced mitochondrial bioenergetics and antioxidant capability, suppressing the cytotoxic effects of palmitate. Our results suggest that targeting SERCA could be a novel therapeutic strategy to protect β-cells from lipotoxicity and the development of Type 2 diabetes.

CDN1163, a SERCA activator, causes intracellular Ca2+ leak, mitochondrial hyperpolarization and cell cycle arrest in mouse neuronal N2A cells

OBJECTIVE

Activity or expression of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) is diminished in some disease states such as cardiac failure and diabetes mellitus. A newly developed activator of SERCA, CDN1163, reportedly rescued or alleviated pathological conditions attributed to dysfunctional SERCA. We examined whether CDN1163 could relieve mouse neuronal N2A cell growth inhibition caused by cyclopiazonic acid (CPA, SERCA inhibitor). We also examined how CDN1163 affected cytosolic Ca2+, mitochondrial Ca2+ and mitochondrial membrane potential.

METHODS

Cell viability was measured by MTT assay and trypan blue exclusion test. Cytosolic Ca2+, mitochondrial Ca2+ and mitochondrial membrane potential were measured using fura 2, Rhod-2 and JC-1, respectively, as fluorescent probes.

RESULTS

CDN1163 (10 μM) itself suppressed cell proliferation, and did not alleviate CPA's inhibitory effect (and vice versa). Cell cycle was arrested at the G1 phase after CDN1163 treatment. CDN1163 treatment caused a slow yet persistent cytosolic [Ca2+] elevation partly due to Ca2+ release from an internal store other than the CPA-sensitive endoplasmic reticulum (ER). Treatment with CDN1163 for 3 h raised mitochondrial Ca2+ level and such increase was suppressed by MCU-i4 (an inhibitor of mitochondria Ca2+ uniporter, MCU), suggesting Ca2+ entered the mitochondrial matrix through MCU. Treatment of cells with CDN1163 up to 2 days resulted in mitochondrial hyperpolarization.

CONCLUSION

CDN1163 caused internal Ca2+ leak, cytosolic Ca2+ overload, mitochondrial Ca2+ elevation and hyperpolarization, cell cycle arrest and cell growth inhibition.

Targeting calcium regulators as therapy for heart failure: focus on the sarcoplasmic reticulum Ca-ATPase pump

Impaired myocardial Ca2+ cycling is a critical contributor to the development of heart failure (HF), causing changes in the contractile function and structure remodeling of the heart. Within cardiomyocytes, the regulation of sarcoplasmic reticulum (SR) Ca2+ storage and release is largely dependent on Ca2+ handling proteins, such as the SR Ca2+ ATPase (SERCA2a) pump. During the relaxation phase of the cardiac cycle (diastole), SERCA2a plays a critical role in transporting cytosolic Ca2+ back to the SR, which helps to restore both cytosolic Ca2+ levels to their resting state and SR Ca2+ content for the next contraction. However, decreased SERCA2a expression and/or pump activity are key features in HF. As a result, there is a growing interest in developing therapeutic approaches to target SERCA2a. This review provides an overview of the regulatory mechanisms of the SERCA2a pump and explores potential strategies for SERCA2a-targeted therapy, which are being investigated in both preclinical and clinical studies.

Calcium regulation by SERC-A before and during Alzheimer disease

There are many factors involved in the incidence of Alzheimer’s disease that, in combination, impede or hinder normal neuronal functions. Little is currently known about calcium regulation before and during the disease. Internal instability of calcium levels is associated with increased vascular risk, a prevalent condition in a high number of individuals already compromised by Alzheimer’s disease. This review provides a reevaluation of the molecular mechanism of the sarcoendoplasmic reticulum calcium ATPase (SERC-A) in the disease and discusses salient aspects of voltage-gated calcium channel function; in these way new alternatives could be open for its treatment. These regulation mechanisms are clinically relevant since the irregular functions of SERC+A has been implicated in pathologies of brain function.

Acute activation of SERCA with CDN1163 attenuates IgE-mediated mast cell activation through selective impairment of ROS and p38 signaling

Mast cells are granulocytic immune sentinels present in vascularized tissues that drive chronic inflammatory mechanisms characteristic of allergic pathologies. IgE-mediated mast cell activation leads to a rapid mobilization of Ca²⁺ from intracellular stores, which is essential for the release of preformed mediators via degranulation and de novo synthesized proinflammatory cytokines and chemokines. Given its potent signaling capacity, the dynamics of Ca²⁺ localization are highly regulated by various pumps and channels controlling cytosolic Ca²⁺ concentrations. Among these is sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA), which functions to maintain low cytosolic Ca²⁺ concentrations by actively transporting cytosolic Ca²⁺ ions into the endoplasmic reticulum. In this study, we characterized the role of SERCA in allergen-activated mast cells using IgE-sensitized bone marrow-derived mast cells (BMMCs) treated with the SERCA activating compound, CDN1163, and simultaneously stimulated with allergen through FcεRI under stem cell factor (SCF) potentiation. Acute treatment with CDN1163 was found to attenuate early phase mast cell degranulation along with reactive oxygen species (ROS) production. Additionally, treatment with CDN1163 significantly reduced secretion of IL-6, IL-13, and CCL3, suggesting a role for SERCA in the late phase mast cell response. The protective effects of SERCA activation via CDN1163 treatment on the early and late phase mast cell response may be driven by the selective suppression of p38 MAPK signaling. Together, these findings implicate SERCA as an important regulator of the mast cell response to allergen and suggest SERCA activity may offer therapeutic potential targeting allergic pathologies, warranting further investigation.

New N-aryl-N-alkyl-thiophene-2-carboxamide compound enhances intracellular Ca2+ dynamics by increasing SERCA2a Ca2+ pumping

The type 2a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a) plays a central role in the intracellular Ca2+ homeostasis of cardiac myocytes, pumping Ca2+ from the cytoplasm into the sarcoplasmic reticulum (SR) lumen to maintain relaxation (diastole) and prepare for contraction (systole). Diminished SERCA2a function has been reported in several pathological conditions, including heart failure. Therefore, development of new drugs that improve SERCA2a Ca2+ transport is of great clinical significance. In this study, we characterized the effect of a recently identified N-aryl-N-alkyl-thiophene-2-carboxamide (or compound 1) on SERCA2a Ca2+-ATPase and Ca2+ transport activities in cardiac SR vesicles, and on Ca2+ regulation in a HEK293 cell expression system and in mouse ventricular myocytes. We found that compound 1 enhances SERCA2a Ca2+-ATPase and Ca2+ transport in SR vesicles. Fluorescence lifetime measurements of fluorescence resonance energy transfer between SERCA2a and phospholamban indicated that compound 1 interacts with the SERCA-phospholamban complex. Measurement of endoplasmic reticulum Ca2+ dynamics in HEK293 cells expressing human SERCA2a showed that compound 1 increases endoplasmic reticulum Ca2+ load by enhancing SERCA2a-mediated Ca2+ transport. Analysis of cytosolic Ca2+ dynamics in mouse ventricular myocytes revealed that compound 1 increases the action potential-induced Ca2+ transients and SR Ca2+ load, with negligible effects on L-type Ca2+ channels and Na+/Ca2+ exchanger. However, during adrenergic receptor activation, compound 1 did not further increase Ca2+ transients and SR Ca2+ load, but it decreased the propensity toward Ca2+ waves. Suggestive of concurrent desirable effects of compound 1 on RyR2, [3H]-ryanodine binding to cardiac SR vesicles shows a small decrease in nM Ca2+ and a small increase in μM Ca2+. Accordingly, compound 1 slightly decreased Ca2+ sparks in permeabilized myocytes. Thus, this novel compound shows promising characteristics to improve intracellular Ca2+ dynamics in cardiomyocytes that exhibit reduced SERCA2a Ca2+ uptake, as found in failing hearts.

Suppression of Ca2+ oscillations by SERCA inhibition in human alveolar type 2 A549 cells: rescue by ochratoxin A but not CDN1163

AIMS

Lung type 2 alveolar cells, by secreting surfactant to lower surface tension, contribute to enhance lung compliance. Stretching, as a result of lung expansion, triggers type 1 alveolar cell to release ATP, which in turn stimulates Ca²⁺-dependent surfactant secretion by neighboring type 2 cells. In this report, we studied ATP-triggered Ca²⁺ signaling in human alveolar type 2 A549 cells.

MAIN METHODS

Ca²⁺ signaling was examined using microfluorimetric measurement with fura-2 as fluorescent dye.

KEY FINDINGS

Ca²⁺ oscillations triggered by ATP relied on inositol 1,4,5-trisphosphate-induced Ca²⁺ release and store-operated Ca²⁺ entry. Pathological conditions such as influenza virus infection and diabetes reportedly inhibit sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA). We found that a very mild inhibition of SERCA by cyclopiazonic acid (CPA) sufficed to decrease Ca²⁺ oscillation frequency and the percentage of cells exhibiting Ca²⁺ oscillations. Ochratoxin A (OTA), an activator of SERCA, could prevent the suppressive effects by CPA. Inhibition of SERCA by hydrogen peroxide also suppressed Ca²⁺ oscillations. Interestingly, hydrogen peroxide-induced inhibition was prevented by OTA but aggravated by CDN1163, an allosteric activator of SERCA. CDN1163 also had an untoward effect of releasing intracellular Ca²⁺.

SIGNIFICANCE

Different modes of activation of SERCA may determine the outcome of rescue of Ca²⁺ oscillations in case of SERCA inhibition in alveolar type 2 cells.

Impaired Calcium Signaling and Neuropsychiatric Disorders in Darier Disease: An Exploratory Review

Darier (Darier-White) disease (DD) is an autosomal dominant skin disorder caused by pathogenic mutations in the ATP2A2 gene which encodes a calcium ATPase in the sarco-endoplasmic reticulum (SERCA2). Defects in the SERCA2 protein leads to an impairment of cellular calcium homeostasis, which in turn, triggers cell death pathways. There is a high prevalence of neuropsychiatric disorders in patients affected by this condition, namely intellectual disability, bipolar disorder, schizophrenia, and suicidality. Though these associations have been well-documented over the years, little has been discussed or investigated regarding the pathophysiological mechanisms. The goal of this article is to review the literature related to the most commonly associated neuropsychiatric disorders found in patients with DD, highlight the pathophysiological mechanisms underlying each condition, and examine potential interventions that may be of interest for future development. A literature search was performed using PubMed to access and review relevant articles published in the last 40 years. Keywords searched included Darier disease neuropsychiatric, Darier disease pathophysiology, SERCA2 central nervous system, SERCA 2 skin, ATP2A2 central nervous system, ATP2A2 skin, sphingosine-1-phosphate signaling skin, sphingosine-1-phosphate signaling central nervous system, P2X7 receptor skin, and P2X7 receptor central nervous system. Our search resulted in 2,692 articles, of which 61 articles were ultimately included in this review.

Restoration of Sarco/Endoplasmic Reticulum Ca2+-ATPase Activity Functions as a Pivotal Therapeutic Target of Anti-Glutamate-Induced Excitotoxicity to Attenuate Endoplasmic Reticulum Ca2+ Depletion

Glutamate-induced excitotoxicity is a pathological basis of many acute/chronic neurodegenerative diseases. Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2b) is a membrane-embedded P-type ATPase pump that manages the translocation of calcium ions (Ca²⁺) from cytosol into the lumen of the endoplasmic reticulum (ER) calcium stores. It participates in a wide range of biological functions in the central nervous system (CNS). However, the role of SERCA2b in glutamate-induced excitotoxicity and its mechanism must be elucidated. Herein, we demonstrate that SERCA2b mutants exacerbate the excitotoxicity of hypo-glutamate stimulation on HT22 cells. In this study, SERCA2b mutants accelerated Ca²⁺ depletion through loss-of-function (reduced pumping capacity) or gain-of-function (acquired leakage), resulting in ER stress. In addition, the occurrence of ER Ca²⁺ depletion increased mitochondria-associated membrane formation, which led to mitochondrial Ca²⁺ overload and dysfunction. Moreover, the enhancement of SERCA2b pumping capacity or inhibition of Ca²⁺ leakage attenuated Ca²⁺ depletion and impeded excitotoxicity in response to hypo-glutamate stimulation. In conclusion, SERCA2b mutants exacerbate ER Ca²⁺-depletion-mediated excitotoxicity in glutamate-sensitive HT22 cells. The mechanism of disruption is mainly related to the heterogeneity of SERCA2b mutation sites. Stabilization of SRECA2b function is a critical therapeutic approach against glutamate-induced excitotoxicity. These data will expand understanding of organelle regulatory networks and facilitate the discovery and creation of drugs against excitatory/inhibitory imbalance in the CNS.

Sarco/Endoplasmic Reticulum Ca2+ ATPase 2 Activator Ameliorates Endothelial Dysfunction; Insulin Resistance in Diabetic Mice

Background: Sarco/endoplasmic reticulum Ca2+-ATPase2 (SERCA2) is impaired in various organs in animal models of diabetes. The purpose of this study was to test the effects of an allosteric SERCA2 activator (CDN1163) on glucose intolerance, hepatosteatosis, skeletal muscle function, and endothelial dysfunction in diabetic (db/db) mice. Methods: Either CDN1163 or vehicle was injected intraperitoneally into 16-week-old male control and db/db mice for 5 consecutive days. Results: SERCA2 protein expression was decreased in the aorta of db/db mice. In isometric tension measurements of aortic rings from db/db mice treated with CDN1163, acetylcholine (ACh)-induced relaxation was improved. In vivo intraperitoneal administrations of CDN 1163 also increased ACh-induced relaxation. Moreover, CDN1163 significantly decreased blood glucose in db/db mice at 60 and 120 min during a glucose tolerance test; it also decreased serum insulin levels, hepatosteatosis, and oxygen consumption in skeletal muscle during the early period of exercise in db/db mice. Conclusions: CDN1163 directly improved aortic endothelial dysfunction in db/db mice. Moreover, CDN1163 improved hepatosteatosis, skeletal muscle function, and insulin resistance in db/db mice. The activation of SERCA2 might be a strategy for the all the tissue expressed SERCA2a improvement of endothelial dysfunction and the target for the organs related to insulin resistance.

Microproteins in skeletal muscle: hidden keys in muscle physiology

Recent advances in the transcriptomics, translatomics, and proteomics have led us to the exciting new world of functional endogenous microproteins. These microproteins have a small size and are derived from small open reading frames (smORFs) of RNAs previously annotated as non-coding (e.g. lncRNAs and circRNAs) as well as from untranslated regions and canonical mRNAs. The presence of these microproteins reveals a much larger translatable portion of the genome, shifting previously defined dogmas and paradigms. These findings affect our view of organisms as a whole, including skeletal muscle tissue. Emerging evidence demonstrates that several smORF-derived microproteins play crucial roles during muscle development (myogenesis), maintenance, and regeneration, as well as lipid and glucose metabolism and skeletal muscle bioenergetics. These microproteins are also involved in processes including physical activity capacity, cellular stress, and muscular-related diseases (i.e. myopathy, cachexia, atrophy, and muscle wasting). Given the role of these small proteins as important key regulators of several skeletal muscle processes, there are rich prospects for the discovery of new microproteins and possible therapies using synthetic microproteins.

The small molecule SERCA activator CDN1163 increases energy metabolism in human skeletal muscle cells

Background and objective

A number of studies have highlighted muscle-specific mechanisms of thermogenesis involving futile cycling of Ca²⁺ driven by sarco (endo)plasmic reticulum Ca²⁺-ATPase (SERCA) and generating heat from ATP hydrolysis to be a promising strategy to counteract obesity and metabolic dysfunction. However, to the best of our knowledge, no experimental studies concerning the metabolic effects of pharmacologically targeting SERCA in human skeletal muscle cells have been reported. Thus, in the present study, we aimed to explore the effects of SERCA-activating compound, CDN1163, on energy metabolism in differentiated human skeletal muscle cells (myotubes).

Methods

In this study, we used primary myotube cultures derived from muscle biopsies of the musculus vastus lateralis and musculi interspinales from lean, healthy male donors. Energy metabolism in myotubes was studied using radioactive substrates. Oxygen consumption rate was assessed with the Seahorse XF24 bioanalyzer, whereas metabolic genes and protein expressions were determined by qPCR and immunoblotting, respectively.

Results

Both acute (4 ​h) and chronic (5 days) treatment of myotubes with CDN1163 showed increased uptake and oxidation of glucose, as well as complete fatty acid oxidation in the presence of carbonyl cyanide 4-(trifluromethoxy)phenylhydrazone (FCCP). These effects were supported by measurement of oxygen consumption rate, in which the oxidative spare capacity and maximal respiration were enhanced after CDN1163-treatment. In addition, chronic treatment with CDN1163 improved cellular uptake of oleic acid (OA) and fatty acid β-oxidation. The increased OA metabolism was accompanied by enhanced mRNA-expression of carnitine palmitoyl transferase (CPT) 1B, pyruvate dehydrogenase kinase (PDK) 4, as well as increased AMP-activated protein kinase (AMPK)^Thr172 phosphorylation. Moreover, following chronic CDN1163 treatment, the expression levels of stearoyl-CoA desaturase (SCD) 1 was decreased together with de novo lipogenesis from acetic acid and formation of diacylglycerol (DAG) from OA.

Conclusion

Altogether, these results suggest that SERCA activation by CDN1163 enhances energy metabolism in human myotubes, which might be favourable in relation to disorders that are related to metabolic dysfunction such as obesity and type 2 diabetes mellitus.

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CDN1163 induced an increase in glucose and fatty acid metabolism in primary human myotubes.

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Myotubes treated with CDN1163 showed lower intramyocellular lipid accumulation and higher rate of β-oxidation.

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AMPK activity was upregulated in CDN1163-treated myotubes.

Sarco/endoplasmic reticulum Ca2+ -ATPase 2b mediates oxidation-induced endoplasmic reticulum stress to regulate neuropathic pain

BACKGROUND AND PURPOSE

Neuropathic pain is a widespread health problem with limited curative treatment. Decreased sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA) expression has been reported in dorsal root ganglion (DRG) of animals suffering from neuropathic pain. We aimed to establish the relationship between SERCA expression and the pain responses and to elucidate the underlying molecular mechanism.

EXPERIMENTAL APPROACH

Neuropathic pain was modeled using rat chronic constriction injury (CCI). Ca²⁺ imaging and current clamp patch-clamp were used to determine cytosolic Ca²⁺ levels and action potential firing, respectively. Western blots, immunofluorescence staining and RT-PCR were used to quantitatively assess protein and mRNA expression, respectively. H&E staining and coupled enzyme assay were used to evaluate the nerve injury and SERCA2b activity, respectively.

KEY RESULTS

SERCA2b is the predominant SERCA isoform in rat DRG and its expression is decreased after CCI at mRNA, protein and activity levels. Whereas inhibiting SERCA with thapsigargin causes neuronal hyperexcitation, nerve injury, ER stress, satellite glial cell activation and mechanical allodynia, activating SERCA by CDN1163 or overexpressing SERCA2b in DRG after CCI produces long-term relief of mechanical and thermal allodynia with accompanied morphological and functional restoration through alleviation of ER stress. Furthermore, the downregulation of DRG SERCA2b in CCI rats is caused by increased production of reactive oxygen species (ROS) through Sp1-dependent transcriptional inhibition.

CONCLUSION AND IMPLICATIONS

Our findings reveal a novel pathway centering around SERCA2b as the key molecule underlying the mechanism of development and maintenance of neuropathic pain, and SERCA2b activators have the potential for therapeutic treatment of neuropathic pain.

Stimulation of Ca2+ -ATPase Transport Activity by a Small-Molecule Drug

The sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) hydrolyzes ATP to transport Ca2+ from the cytoplasm to the sarcoplasmic reticulum (SR) lumen, thereby inducing muscle relaxation. Dysfunctional SERCA has been related to various diseases. The identification of small-molecule drugs that can activate SERCA may offer a therapeutic approach to treat pathologies connected with SERCA malfunction. Herein, we propose a method to study the mechanism of interaction between SERCA and novel SERCA activators, i. e. CDN1163, using a solid supported membrane (SSM) biosensing approach. Native SR vesicles or reconstituted proteoliposomes containing SERCA were adsorbed on the SSM and activated by ATP concentration jumps. We observed that CDN1163 reversibly interacts with SERCA and enhances ATP-dependent Ca2+ translocation. The concentration dependence of the CDN1163 effect provided an EC50 =6.0±0.3 μM. CDN1163 was shown to act directly on SERCA and to exert its stimulatory effect under physiological Ca2+ concentrations. These results suggest that CDN1163 interaction with SERCA can promote a protein conformational state that favors Ca2+ release into the SR lumen.

Blinded, Multicenter Evaluation of Drug-induced Changes in Contractility Using Human-induced Pluripotent Stem Cell-derived Cardiomyocytes

Animal models are 78% accurate in determining whether drugs will alter contractility of the human heart. To evaluate the suitability of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for predictive safety pharmacology, we quantified changes in contractility, voltage, and/or Ca²⁺ handling in 2D monolayers or 3D engineered heart tissues (EHTs). Protocols were unified via a drug training set, allowing subsequent blinded multicenter evaluation of drugs with known positive, negative, or neutral inotropic effects. Accuracy ranged from 44% to 85% across the platform-cell configurations, indicating the need to refine test conditions. This was achieved by adopting approaches to reduce signal-to-noise ratio, reduce spontaneous beat rate to ≤ 1 Hz or enable chronic testing, improving accuracy to 85% for monolayers and 93% for EHTs. Contraction amplitude was a good predictor of negative inotropes across all the platform-cell configurations and of positive inotropes in the 3D EHTs. Although contraction- and relaxation-time provided confirmatory readouts forpositive inotropes in 3D EHTs, these parameters typically served as the primary source of predictivity in 2D. The reliance of these “secondary” parameters to inotropy in the 2D systems was not automatically intuitive and may be a quirk of hiPSC-CMs, hence require adaptations in interpreting the data from this model system. Of the platform-cell configurations, responses in EHTs aligned most closely to the free therapeutic plasma concentration. This study adds to the notion that hiPSC-CMs could add value to drug safety evaluation.

Current and Future Therapeutic Strategies for Limb Girdle Muscular Dystrophy Type R1: Clinical and Experimental Approaches

Limb girdle muscular dystrophy type R1 disease is a progressive disease that is caused by mutations in the CAPN3 gene and involves the extremity muscles of the hip and shoulder girdle. The CAPN3 protein has proteolytic and non-proteolytic properties. The functions of the CAPN3 protein that have been determined so far can be listed as remodeling and combining contractile proteins in the sarcomere with the substrates with which it interacts, controlling the Ca²⁺ flow in and out through the sarcoplasmic reticulum, and regulation of membrane repair and muscle regeneration. Even though there are several gene therapies, cellular therapies, and drug therapies, such as glucocorticoid treatment, AAV- mediated therapy, CRISPR-Cas9, induced pluripotent stem cells, MYO-029, and AMBMP, which are either in preclinical or clinical phases, or have been completed, there is no final cure. Inhibitors and small molecules (tauroursodeoxycholic acid, salubrinal, rapamycin, CDN1163, dwarf open reading frame) targeting ER stress factors that are thought to be effective in muscle loss can be considered potential therapy strategies. At present, little can be done to treat the progressive muscle wasting, loss of function, and premature mortality of patients with LGMDR1, and there is a pressing need for more research to develop potential therapies.

Oxidative modification impairs SERCA activity in Drosophila and human cell models of Parkinson's disease

DJ-1 is a causative gene for familial Parkinson's disease (PD) with different functions, standing out its role against oxidative stress (OS). Accordingly, PD model flies harboring a mutation in the DJ-1β gene (the Drosophila ortholog of human DJ-1) show high levels of OS markers like protein carbonylation, a common post-translational modification that may alter protein function. To increase our understanding of PD pathogenesis as well as to discover potential therapeutic targets for pharmacological intervention, we performed a redox proteomic assay in DJ-1β mutant flies. Among the proteins that showed increased carbonylation levels in PD model flies, we found SERCA, an endoplasmic reticulum Ca²⁺ channel that plays an important role in Ca²⁺ homeostasis. Interestingly, several studies have supported the involvement of Ca²⁺ dyshomeostasis in PD. Thus, we decided to study the relation between SERCA activity and PD physiopathology. Our results showed that SERCA enzymatic activity is significantly reduced in DJ-1β mutant flies, probably as a consequence of OS-induced carbonylation, as well as in a human cell PD model based on DJ-1-deficiency. Indeed, higher carbonylation levels of SERCA were also observed in DJ-1-deficient cells compared to controls. In addition, the specific activator of SERCA, CDN1163, was also able to restore PD-related phenotypes in both familial PD models by increasing SERCA activity. Taken together, our results indicate that impaired SERCA activity due to oxidative modification may play a role in PD physiopathology. Furthermore, we demonstrate that therapeutic strategies addressing SERCA activation could be beneficial to treat this disease as shown for CDN1163.

Pharmacological activation of SERCA ameliorates dystrophic phenotypes in dystrophin-deficient mdx mice

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder characterized by progressive muscular weakness because of the loss of dystrophin. Extracellular Ca2+ flows into the cytoplasm through membrane tears in dystrophin-deficient myofibers, which leads to muscle contracture and necrosis. Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) takes up cytosolic Ca2+ into the sarcoplasmic reticulum, but its activity is decreased in dystrophic muscle. Here, we show that an allosteric SERCA activator, CDN1163, ameliorates dystrophic phenotypes in dystrophin-deficient mdx mice. The administration of CDN1163 prevented exercise-induced muscular damage and restored mitochondrial function. In addition, treatment with CDN1163 for 7 weeks enhanced muscular strength and reduced muscular degeneration and fibrosis in mdx mice. Our findings provide preclinical proof-of-concept evidence that pharmacological activation of SERCA could be a promising therapeutic strategy for DMD. Moreover, CDN1163 improved muscular strength surprisingly in wild-type mice, which may pave the new way for the treatment of muscular dysfunction.

Restoration of Sarcoplasmic Reticulum Ca2+ ATPase (SERCA) Activity Prevents Age-Related Muscle Atrophy and Weakness in Mice

Sarcopenia has a significant negative impact on healthspan in the elderly and effective pharmacologic interventions remain elusive. We have previously demonstrated that sarcopenia is associated with reduced activity of the sarcoplasmic reticulum Ca²⁺ ATPase (SERCA) pump. We asked whether restoring SERCA activity using pharmacologic activation in aging mice could mitigate the sarcopenia phenotype. We treated 16-month male C57BL/6J mice with vehicle or CDN1163, an allosteric SERCA activator, for 10 months. At 26 months, maximal SERCA activity was reduced 41% in gastrocnemius muscle in vehicle-treated mice but maintained in old CDN1163 treated mice. Reductions in gastrocnemius mass (9%) and in vitro specific force generation in extensor digitorum longus muscle (11%) in 26 versus 16-month-old wild-type mice were also reversed by CDN1163. CDN1163 administered by intra-peritoneal injection also prevented the increase in mitochondrial ROS production in gastrocnemius muscles of aged mice. Transcriptomic analysis revealed that these effects are at least in part mediated by enhanced cellular energetics by activation of PGC1-α, UCP1, HSF1, and APMK and increased regenerative capacity by suppression of MEF2C and p38 MAPK signaling. Together, these exciting findings are the first to support that pharmacological targeting of SERCA can be an effective therapy to counter age-related muscle dysfunction.

Chronic but not acute pharmacological activation of SERCA induces behavioral and neurochemical effects in male and female mice

Intracellular calcium (Ca²⁺) homeostasis is a vital process to nerve cell survival and function with an intricate regulatory network. It is well established that the endoplasmic reticulum (ER) is a major intraneuronal Ca²⁺ storage and that the sarco/endoplasmic reticulum (SR/ER) calcium (Ca²⁺)-ATPase (SERCA) pump is a key regulator of cytosolic Ca²⁺ levels. SERCA pumps play a critical role in brain pathophysiology, thus SERCA comprises an emerging pharmacological target for the treatment of brain diseases. Interestingly, preclinical studies in rodents suggest that chronic pharmacological activation of SERCA2 by the quinoline derivative CDN1163 comprises a potential pharmacotherapeutic target in Alzheimer's and Parkinson's diseases. As little is known about the behavioral and neurochemical consequences of CDN1163 administration, in the current study we investigated the potential effects of acute (i.e., at 1 h) and chronic (i.e., 17 days) CDN1163 administration (i.e., 10 mg/kg and 20 mg/kg; intraperitoneally) on locomotor activity and relevant affective behaviors, as well as on monoaminergic neurotransmission in naïve C57BL/6J mice of both sexes. Interestingly, chronic, but not acute, CDN1163 administration induced anxiogenic and depressive-like behavioral effects in mice, as assessed in the open field (OF) test and the forced swim test (FST), respectively. In addition, chronic CDN1163 administration induced sustained sex- and brain region-dependent noradrenergic and serotonergic neurochemical effects ex vivo. Taken together, present findings support the critical role of SERCA-dependent Ca²⁺ handling in regulating behavior and neurochemical activity, and further highlight the need to consider sex in the development of SERCA-targeting pharmacotherapies for the treatment of debilitating brain disorders.

TRPV4 contributes to ER stress: Relation to apoptosis in the MPP+-induced cell model of Parkinson's disease

AIMS

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder. Its molecular mechanism is still unclear. Endoplasmic reticulum (ER) stress has been highlighted in PD. Transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium cation channel. A defined role for TRPV4 in PD has not been reported. The purpose of the present research was to investigate the molecular mechanisms by which TRPV4 regulates ER stress induced by the 1-methyl-4-phenylpyridinium ion (MPP⁺) in PC12 cells.

MAIN METHODS

PC12 cells were pretreated with the TRPV4-specific antagonist HC067047 or transfected with TRPV4 siRNA followed by treatment with MPP⁺. Cell viability was measured by the CCK-8 Assay. The expression of TRPV4, sarco/endoplasmic reticulum Ca²⁺-ATPase 2 (SERCA2), glucose-regulated protein 78 (GRP78), glucose-regulated protein 94 (GRP94), C/EBP homologous protein (CHOP), procaspase-12, and tyrosine hydroxylase (TH) was detected by western blot and RT-PCR.

KEY FINDINGS

The expression of TRPV4 was upregulated, while cell viability was decreased by MPP⁺, which was reversed by HC067047. The ER stress common molecular signature SERCA2 was depressed by MPP⁺. Moreover, MPP⁺ induced upregulation of GRP78, GRP94, CHOP, and decrease in procaspase-12 and TH. HC067047 and TRPV4 siRNA reversed MPP⁺-induced ER stress and restored TH production.

SIGNIFICANCE

TRPV4 functions upstream of ER stress induced by MPP⁺ and holds promise as a prospective pharmacotherapy target for PD.

Channels that Cooperate with TRPV4 in the Brain

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective Ca²⁺-permeable cation channel that is a member of the TRP channel family. It is clear that TRPV4 channels are broadly expressed in the brain. As they are expressed on the plasma membrane, they interact with other channels and play a crucial role in nervous system activity. Under some pathological conditions, TRPV4 channels are upregulated and sensitized via cellular signaling pathways, and this can cause nervous system diseases. In this review, we focus on receptors that cooperate with TRPV4, including large-conductance Ca²⁺-activated K⁺(BKca) channels, N-methyl-D-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors (AMPARs), inositol 1,4,5-trisphosphate receptors (IP3Rs), ryanodine receptors (RyRs), aquaporin 4 (AQP4), and other potential cooperative receptors in the brain. The data demonstrate how these channels work together to cause nervous system diseases under pathological conditions. The aim of this review was to discuss the receptors and signaling pathways related to TRPV4 based on recent data on the important physiological functions of TRPV4 channels to provide new clues for future studies and prospective therapeutic targets for related brain diseases.

A Role for SERCA Pumps in the Neurobiology of Neuropsychiatric and Neurodegenerative Disorders

Calcium (Ca²⁺) is a fundamental regulator of cell fate and intracellular Ca²⁺ homeostasis is crucial for proper function of the nerve cells. Given the complexity of neurons, a constellation of mechanisms finely tunes the intracellular Ca²⁺ signaling. We are focusing on the sarco/endoplasmic reticulum (SR/ER) calcium (Ca²⁺)-ATPase (SERCA) pump, an integral ER protein. SERCA's well established role is to preserve low cytosolic Ca²⁺ levels ([Ca²⁺]_cyt), by pumping free Ca²⁺ ions into the ER lumen, utilizing ATP hydrolysis. The SERCA pumps are encoded by three distinct genes, SERCA1-3, resulting in 12 known protein isoforms, with tissue-dependent expression patterns. Despite the well-established structure and function of the SERCA pumps, their role in the central nervous system is not clear yet. Interestingly, SERCA-mediated Ca²⁺ dyshomeostasis has been associated with neuropathological conditions, such as bipolar disorder, schizophrenia, Parkinson's disease and Alzheimer's disease. We summarize here current evidence suggesting a role for SERCA in the neurobiology of neuropsychiatric and neurodegenerative disorders, thus highlighting the importance of this pump in brain physiology and pathophysiology.

CETSA beyond Soluble Targets: a Broad Application to Multipass Transmembrane Proteins

Demonstration of target binding is a key requirement for understanding the mode of action of new therapeutics. The cellular thermal shift assay (CETSA) has been introduced as a powerful label-free method to assess target engagement in physiological environments. Here, we present the application of live-cell CETSA to different classes of integral multipass transmembrane proteins using three case studies, the first showing a large and robust stabilization of the outer mitochondrial five-pass transmembrane protein TSPO, the second being a modest stabilization of SERCA2, and the last describing an atypical compound-driven stabilization of the GPCR PAR2. Our data demonstrated that using modified protocols with detergent extraction after the heating step, CETSA can reliably be applied to several membrane proteins of different complexity. By showing examples with distinct CETSA behaviors, we aim to provide the scientific community with an overview of different scenarios to expect during CETSA experiments, especially for challenging, membrane bound targets.

Protein Misfolding and ER Stress in Huntington's Disease

Increasing evidence in recent years indicates that protein misfolding and aggregation, leading to ER stress, are central factors of pathogenicity in neurodegenerative diseases. This is particularly true in Huntington's disease (HD), where in contrast with other disorders, the cause is monogenic. Mutant huntingtin interferes with many cellular processes, but the fact that modulation of ER stress and of the unfolded response pathways reduces the toxicity, places these mechanisms at the core and gives hope for potential therapeutic approaches. There is currently no effective treatment for HD and it has a fatal outcome a few years after the start of symptoms of cognitive and motor impairment. Here we will discuss recent findings that shed light on the mechanisms of protein misfolding and aggregation that give origin to ER stress in neurodegenerative diseases, focusing on Huntington's disease, on the cellular response and on how to use this knowledge for possible therapeutic strategies.

Restoration of SERCA ATPase prevents oxidative stress-related muscle atrophy and weakness

Molecular targets to reduce muscle weakness and atrophy due to oxidative stress have been elusive. Here we show that activation of Sarcoplasmic Reticulum (SR) Ca²⁺ ATPase (SERCA) with CDN1163, a novel small molecule allosteric SERCA activator, ameliorates the muscle impairment in the CuZnSOD deficient (Sod1^-/-) mouse model of oxidative stress. Sod1^-/- mice are characterized by reduced SERCA activity, muscle weakness and atrophy, increased oxidative stress and mitochondrial dysfunction. Seven weeks of CDN1163 treatment completely restored SERCA activity and reversed the 23% reduction in gastrocnemius mass and 22% reduction in specific force in untreated Sod1^-/- versus wild type mice. These changes were accompanied by restoration of autophagy protein markers to the levels found in wild-type mice. CDN1163 also reversed the increase in mitochondrial ROS generation and oxidative damage in muscle tissue from Sod1^-/- mice. Taken together our findings suggest that the pharmacological restoration of SERCA is a promising therapeutic approach to counter oxidative stress-associated muscle impairment.

Altered sarco(endo)plasmic reticulum calcium adenosine triphosphatase 2a content: Targets for heart failure therapy

Sarco(endo)plasmic reticulum calcium adenosine triphosphatase is responsible for transporting cytosolic calcium into the sarcoplasmic reticulum and endoplasmic reticulum to maintain calcium homeostasis. Sarco(endo)plasmic reticulum calcium adenosine triphosphatase is the dominant isoform expressed in cardiac tissue, which is regulated by endogenous protein inhibitors, post-translational modifications, hormones as well as microRNAs. Dysfunction of sarco(endo)plasmic reticulum calcium adenosine triphosphatase is associated with heart failure, which makes sarco(endo)plasmic reticulum calcium adenosine triphosphatase a promising target for heart failure therapy. This review summarizes current approaches to ameliorate sarco(endo)plasmic reticulum calcium adenosine triphosphatase function and focuses on phospholamban, an endogenous inhibitor of sarco(endo)plasmic reticulum calcium adenosine triphosphatase, pharmacological tools and gene therapies.

The SERCA2: A Gatekeeper of Neuronal Calcium Homeostasis in the Brain

Calcium (Ca²⁺) ions are prominent cell signaling regulators that carry information for a variety of cellular processes and are critical for neuronal survival and function. Furthermore, Ca²⁺ acts as a prominent second messenger that modulates divergent intracellular cascades in the nerve cells. Therefore, nerve cells have developed intricate Ca²⁺ signaling pathways to couple the Ca²⁺ signal to their biochemical machinery. Notably, intracellular Ca²⁺ homeostasis greatly relies on the rapid redistribution of Ca²⁺ ions into the diverse subcellular organelles which serve as Ca²⁺ stores, including the endoplasmic reticulum (ER). It is well established that Ca²⁺ released into the neuronal cytoplasm is pumped back into the ER by the sarco-/ER Ca²⁺ ATPase 2 (SERCA2), a P-type ion-motive ATPase that resides on the ER membrane. Even though the SERCA2 is constitutively expressed in nerve cells, its precise role in brain physiology and pathophysiology is not well-characterized. Intriguingly, SERCA2-dependent Ca²⁺ dysregulation has been implicated in several disorders that affect cognitive function, including Darier's disease, schizophrenia, Alzheimer's disease, and cerebral ischemia. The current review summarizes knowledge on the expression pattern of the different SERCA2 isoforms in the nervous system, and further discusses evidence of SERCA2 dysregulation in various neuropsychiatric disorders. To the best of our knowledge, this is the first literature review that specifically highlights the critical role of the SERCA2 in the brain. Advancing knowledge on the role of SERCA2 in maintaining neuronal Ca²⁺ homeostasis may ultimately lead to the development of safer and more effective pharmacotherapies to combat debilitating neuropsychiatric disorders.

Drug Interactions With the Ca2+-ATPase From Sarco(Endo)Plasmic Reticulum (SERCA)

The sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) is an intracellular membrane transporter that utilizes the free energy provided by ATP hydrolysis for active transport of Ca²⁺ ions from the cytoplasm to the lumen of sarco(endo)plasmic reticulum. SERCA plays a fundamental role for cell calcium homeostasis and signaling in muscle cells and also in cells of other tissues. Because of its prominent role in many physiological processes, SERCA dysfunction is associated to diseases displaying various degrees of severity. SERCA transport activity can be inhibited by a variety of compounds with different chemical structures. Specific SERCA inhibitors were identified which have been instrumental in studies of the SERCA catalytic and transport mechanism. It has been proposed that SERCA inhibition may represent a novel therapeutic strategy to cure certain diseases by targeting SERCA activity in pathogens, parasites and cancer cells. Recently, novel small molecules have been developed that are able to stimulate SERCA activity. Such SERCA activators may also offer an innovative and promising therapeutic approach to treat diseases, such as heart failure, diabetes and metabolic disorders. In the present review the effects of pharmacologically relevant compounds on SERCA transport activity are presented. In particular, we will discuss the interaction of SERCA with specific inhibitors and activators that are potential therapeutic agents for different diseases.

A new target for Alzheimer's disease: A small molecule SERCA activator is neuroprotective in vitro and improves memory and cognition in APP/PS1 mice

Amongst the cellular cacophony of altered signals in Alzheimer's disease (AD), disrupted Ca²⁺ homeostasis and consequential endoplasmic reticulum (ER) stress signals have been recognized as key determinants of neuron fate. This altered Ca²⁺ state is accompanied by a failing sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump, which has been recognized as a causal feature of the underlying disease state. Repair of the Ca²⁺ dyshomeostasis represents a putative drug target via alleviation of ER stress and rescue of injured neurons, effectively modifying the AD state. Herein, we report a small molecule SERCA activator that rescues brain cells and raises ER Ca²⁺ in vitro, and shows efficacy in the APP/PS1 double transgenic mouse model of Alzheimer's disease. These results support SERCA activation as a therapeutic target for AD.

Direct detection of SERCA calcium transport and small-molecule inhibition in giant unilamellar vesicles

We have developed a charge-mediated fusion method to reconstitute the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) in giant unilamellar vesicles (GUV). Intracellular Ca²⁺ transport by SERCA controls key processes in human cells such as proliferation, signaling, and contraction. Small-molecule effectors of SERCA are urgently needed as therapeutics for Ca²⁺ dysregulation in human diseases including cancer, diabetes, and heart failure. Here we report the development of a method for efficiently reconstituting SERCA in GUV, and we describe a streamlined protocol based on optimized parameters (e.g., lipid components, SERCA preparation, and activity assay requirements). ATP-dependent Ca²⁺ transport by SERCA in single GUV was detected directly using confocal fluorescence microscopy with the Ca²⁺ indicator Fluo-5F. The GUV reconstitution system was validated for functional screening of Ca²⁺ transport using thapsigargin (TG), a small-molecule inhibitor of SERCA currently in clinical trials as a prostate cancer prodrug. The GUV system overcomes the problem of inhibitory Ca²⁺ accumulation for SERCA in native and reconstituted small unilamellar vesicles (SUV). We propose that charge-mediated fusion provides a widely-applicable method for GUV reconstitution of clinically-important membrane transport proteins. We conclude that GUV reconstitution is a technological advancement for evaluating small-molecule effectors of SERCA.