SERCA2 protects against cisplatin-induced damage of auditory cells: Possible relation with alleviation of ER stress

AIMS

SERCA2, one of the P-type pumps encoded by gene ATP2A2, is the only calcium reflux channel of the endoplasmic reticulum (ER) and participates in maintaining calcium homeostasis. The present study was designed to explore SERCA2 expression pattern in auditory hair cells and the possible mechanism underlying the effects of SERCA2 on cisplatin-induced ototoxicity.

MAIN METHODS

The SERCA2 expression pattern in cochlea hair cells and HEI-OC1 cells was measured by Western blot (WB) and immunofluorescence staining. The apoptosis and its related factors were detected by TUNEL assay and WB. The expression levels of ER stress-related factors, ATF6, PERK, IRE1α, and GRP78, were measured via WB. As for the determination of SERCA2 overexpression and knockdown, plasmids and lentiviral vectors were constructed, respectively.

KEY FINDINGS

We found that SERCA2 was highly expressed in cochlea hair cells and HEI-OC1 cells. Of note, the level of SERCA2 expression in neonatal mice was remarkably higher than that in adult mice. Under the exposure of 30 μM cisplatin, SERCA2 was down-regulated significantly compared with the control group. In addition, cisplatin administration triggered the occurrence of ER stress and apoptosis. Those events were reversed by overexpressing SERCA2. On the contrary, SERCA2 knockdown could aggravate the above processes.

SIGNIFICANCE

The findings from the present study disclose, for the first time, that SERCA2 is abundantly expressed in cochlea hair cells, and the suppression of SERCA2 caused by cisplatin could trigger ER homeostasis disruption, thereby implying that SERCA2 might be a promising target to prevent cisplatin-induced cytotoxicity of hair cells.

SERCA2 dysfunction triggers hypertension by interrupting mitochondrial homeostasis and provoking oxidative stress

BACKGROUND AND AIM

Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) is critical in maintaining Ca2+ homeostasis. The cysteine 674 (C674) is the key redox regulatory cysteine in regulating SERCA2 activity, which is irreversibly oxidized in the renal cortex of hypertensive mice. We have reported that the substitution of C674 by serine causes SERCA2 dysfunction and increases blood pressure by induction of endoplasmic reticulum stress (ERS). This study is to explore whether the dysfunction of SERCA2 causes hypertension by interrupting mitochondrial homeostasis and inducing oxidative stress.

METHODS & RESULTS

We used heterozygous SERCA2 C674S gene mutation knock-in (SKI) mice, where one copy of C674 was substituted by serine to represent partial C674 oxidation. In renal proximal tubule (RPT) cells, the substitution of C674 by serine decreased mitochondrial Ca2+ content, increased mitochondrial membrane potential, ATP content, and reactive oxygen species (ROS), which could be reversed by ERS inhibitor 4-phenylbutyric acid or SERCA2 agonist CDN1163. In SKI RPT cells, the redox modulator Tempol alleviated oxidative stress, downregulated the protein expression of ERS markers and soluble epoxide hydrolase, upregulated the protein expression of dopamine D1 receptor, and reduced Na+/K+- ATPase activity. In SKI mice, SERCA2 agonists CDN1163 and [6]-Gingerol, or the redox modulator Tempol increased urine output and lowered blood pressure.

CONCLUSION

The irreversible oxidation of C674 is not only an indicator of increased ROS, but also further inducing oxidative stress to cause hypertension. Activation of SERCA2 or inhibition of oxidative stress is beneficial to alleviate hypertension caused by SERCA2 dysfunction.

CDN1163 alleviates SERCA2 dysfunction-induced pulmonary vascular remodeling by inhibiting the phenotypic transition of pulmonary artery smooth muscle cells

BACKGROUND AND PURPOSE

Substitution of Cys674 (C674) in the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) causes SERCA2 dysfunction which leads to activated inositol requiring enzyme 1 alpha (IRE1α) and spliced X-box binding protein 1 (XBP1s) pathway accelerating cell proliferation of pulmonary artery smooth muscle cells (PASMCs) followed by significant pulmonary vascular remodeling resembling human pulmonary hypertension. Based on this knowledge, we intend to investigate other potential mechanisms involved in SERCA2 dysfunction-induced pulmonary vascular remodeling.

EXPERIMENTAL APPROACH

Heterozygous SERCA2 C674S knock-in (SKI) mice of which half of cysteine in 674 was substituted by serine to mimic the partial irreversible oxidation of C674 were used. The lungs of SKI mice and their littermate wild-type mice were collected for PASMC culture, protein expression, and pulmonary vascular remodeling analysis.

RESULTS

SERCA2 dysfunction increased intracellular Ca2+ levels, which activated Ca2+-dependent calcineurin (CaN) and promoted the nuclear translocation and protein expression of the nuclear factor of activated T-lymphocytes 4 (NFAT4) in an IRE1α/XBP1s pathway-independent manner. In SKI PASMCs, the scavenge of intracellular Ca2+ by BAPTA-AM or inhibition of CaN by cyclosporin A can prevent PASMC phenotypic transition. CDN1163, a SERCA2 agonist, suppressed the activation of CaN/NFAT4 and IRE1α/XBP1s pathways, reversed the protein expression of PASMC phenotypic transition markers and cell cycle-related proteins, and inhibited cell proliferation and migration when given to SKI PASMCs. Furthermore, CDN1163 ameliorated pulmonary vascular remodeling in SKI mice.

CONCLUSIONS AND IMPLICATIONS

SERCA2 dysfunction promotes PASMC phenotypic transition and pulmonary vascular remodeling by multiple mechanisms, which could be improved by SERCA2 agonist CDN1163.

SERCA2 phosphorylation at the heart of the disease

Gonnot et al. [1] thoroughly investigated the regulatory role of glycogen synthase kinase 3 beta (GSK3β) in modulating cardiac isoform 2 of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA2) activity. They have found that in ischemic hearts of patients and mouse-GSK3β -mediated SERCA2 phosphorylation at serine 663 dampens the SERCA2 pump activity and induces Ca2+ overload which sensitizes towards myocardial ischemia-reperfusion (I/R) injury. The inhibition of serine 663 phosphorylation significantly increases SERCA2 activity and, by preventing cytosolic and mitochondrial Ca2+ overload, reduces cell death during reperfusion. Augmented SERCA2 activity also substantially improves excitation-contraction coupling in cardiomyocytes upon recovery from reperfusion injury. This study provides valuable insights into pathophysiological relevance of GSK3β -mediated SERCA2 phosphorylation in the context of heart diseases and paves the way for designing novel clinical therapeutic approaches to alleviate post infartion heart failure.

Loss of STIM2 in colorectal cancer drives growth and metastasis through metabolic reprogramming and PERK-ATF4 endoplasmic reticulum stress pathway

The endoplasmic reticulum (ER) stores large amounts of calcium (Ca2+), and the controlled release of ER Ca2+ regulates a myriad of cellular functions. Although altered ER Ca2+ homeostasis is known to induce ER stress, the mechanisms by which ER Ca2+ imbalance activate ER stress pathways are poorly understood. Stromal-interacting molecules STIM1 and STIM2 are two structurally homologous ER-resident Ca2+ sensors that synergistically regulate Ca2+ influx into the cytosol through Orai Ca2+ channels for subsequent signaling to transcription and ER Ca2+ refilling. Here, we demonstrate that reduced STIM2, but not STIM1, in colorectal cancer (CRC) is associated with poor patient prognosis. Loss of STIM2 causes SERCA2-dependent increase in ER Ca2+, increased protein translation and transcriptional and metabolic rewiring supporting increased tumor size, invasion, and metastasis. Mechanistically, STIM2 loss activates cMyc and the PERK/ATF4 branch of ER stress in an Orai-independent manner. Therefore, STIM2 and PERK/ATF4 could be exploited for prognosis or in targeted therapies to inhibit CRC tumor growth and metastasis.

Polyarginine Cell-Penetrating Peptides Bind and Inhibit SERCA2

Cell-penetrating peptides (CPPs) are short peptide sequences that have the ability to cross the cell membrane and deliver cargo. Although it is critical that CPPs accomplish this task with minimal off-target effects, such actions have in many cases not been robustly screened. We presently investigated whether the commonly used CPPs TAT and the polyarginines Arg9 and Arg11 exert off-target effects on cellular Ca2+ homeostasis. In experiments employing myocytes and homogenates from the cardiac left ventricle or soleus muscle, we observed marked inhibition of Ca2+ recycling into the sarcoplasmic reticulum (SR) following incubation with polyarginine CPPs. In both tissues, the rate of SR Ca2+ leak remained unchanged, indicating that protracted Ca2+ removal from the cytosol stemmed from inhibition of the SR Ca2+ ATPase 2 (SERCA2). No such inhibition occurred following treatment with TAT, or in preparations from the SERCA1-expressing extensor digitorum longus muscle. Experiments in HEK cells overexpressing individual SERCA isoforms confirmed that polyarginine incubation specifically inhibited the activity of SERCA2a and 2b, but not SERCA1 or 3. The attenuation of SERCA2 activity was not dependent on the presence of phospholamban, and ELISA-based analyses rather revealed direct interaction between the polyarginines and the actuator domain of the protein. Surface plasmon resonance experiments confirmed strong binding within this region of SERCA2, and slow dissociation between the two species. Based on these observations, we urge caution when employing polyarginine CPPs. Indeed, as SERCA2 is expressed in diverse cell types, the wide-ranging consequences of SERCA2 binding and inhibition should be anticipated in both experimental and therapeutic settings.

Translocation of IGF-1R in endoplasmic reticulum enhances SERCA2 activity to trigger Ca2+ER perturbation in hepatocellular carcinoma

The well-known insulin-like growth factor 1 (IGF1)/IGF-1 receptor (IGF-1R) signaling pathway is overexpressed in many tumors, and is thus an attractive target for cancer treatment. However, results have often been disappointing due to crosstalk with other signals. Here, we report that IGF-1R signaling stimulates the growth of hepatocellular carcinoma (HCC) cells through the translocation of IGF-1R into the ER to enhance sarco-endoplasmic reticulum calcium ATPase 2 (SERCA2) activity. In response to ligand binding, IGF-1Rβ is translocated into the ER by β-arrestin2 (β-arr2). Mass spectrometry analysis identified SERCA2 as a target of ER IGF-1Rβ. SERCA2 activity is heavily dependent on the increase in ER IGF-1Rβ levels. ER IGF-1Rβ phosphorylates SERCA2 on Tyr990 to enhance its activity. Mutation of SERCA2-Tyr990 disrupted the interaction of ER IGF-1Rβ with SERCA2, and therefore ER IGF-1Rβ failed to promote SERCA2 activity. The enhancement of SERCA2 activity triggered Ca2+ER perturbation, leading to an increase in autophagy. Thapsigargin blocked the interaction between SERCA2 and ER IGF-1Rβ and therefore SERCA2 activity, resulting in inhibition of HCC growth. In conclusion, the translocation of IGF-1R into the ER triggers Ca2+ER perturbation by enhancing SERCA2 activity through phosphorylating Tyr990 in HCC.

Termination codon readthrough of NNAT mRNA regulates calcium-mediated neuronal differentiation

Termination codon readthrough (TCR) is a process in which ribosomes continue to translate an mRNA beyond a stop codon generating a C-terminally extended protein isoform. Here, we demonstrate TCR in mammalian NNAT mRNA, which encodes NNAT, a proteolipid important for neuronal differentiation. This is a programmed event driven by cis-acting RNA sequences present immediately upstream and downstream of the canonical stop codon and is negatively regulated by NONO, an RNA-binding protein known to promote neuronal differentiation. Unlike the canonical isoform NNAT, we determined that the TCR product (NNATx) does not show detectable interaction with the sarco/endoplasmic reticulum Ca2+-ATPase isoform 2 Ca2+ pump, cannot increase cytoplasmic Ca2+ levels, and therefore does not enhance neuronal differentiation in Neuro-2a cells. Additionally, an antisense oligonucleotide that targets a region downstream of the canonical stop codon reduced TCR of NNAT and enhanced the differentiation of Neuro-2a cells to cholinergic neurons. Furthermore, NNATx-deficient Neuro-2a cells, generated using CRISPR-Cas9, showed increased cytoplasmic Ca2+ levels and enhanced neuronal differentiation. Overall, these results demonstrate regulation of neuronal differentiation by TCR of NNAT. Importantly, this process can be modulated using a synthetic antisense oligonucleotide.

Regulation of beige adipocyte thermogenesis by the cold-repressed ER protein NNAT

OBJECTIVE

Cold stimuli trigger the conversion of white adipose tissue into beige adipose tissue, which is capable of non-shivering thermogenesis. However, what process drives this activation of thermogenesis in beige fat is not well understood. Here, we examine the ER protein NNAT as a regulator of thermogenesis in adipose tissue.

METHODS

We investigated the regulation of adipose tissue NNAT expression in response to changes in ambient temperature. We also evaluated the functional role of NNAT in thermogenic regulation using Nnat null mice and primary adipocytes that lack or overexpress NNAT.

RESULTS

Cold exposure or treatment with a β3-adrenergic agonist reduces the expression of adipose tissue NNAT in mice. Genetic disruption of Nnat in mice enhances inguinal adipose tissue thermogenesis. Nnat null mice exhibit improved cold tolerance both in the presence and absence of UCP1. Gain-of-function studies indicate that ectopic expression of Nnat abolishes adrenergic receptor-mediated respiration in beige adipocytes. NNAT physically interacts with the ER Ca²⁺-ATPase (SERCA) in adipocytes and inhibits its activity, impairing Ca²⁺ transport and heat dissipation. We further demonstrate that NHLRC1, an E3 ubiquitin protein ligase implicated in proteasomal degradation of NNAT, is induced by cold exposure or β3-adrenergic stimulation, thus providing regulatory control at the protein level. This serves to link cold stimuli to NNAT degradation in adipose tissue, which in turn leads to enhanced SERCA activity.

CONCLUSIONS

Our study implicates NNAT in the regulation of adipocyte thermogenesis.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Lathyrol promotes ER stress-induced apoptosis and proliferation inhibition in lung cancer cells by targeting SERCA2

Lathyrol is a natural product isolated from the traditional Chinese medicine Semen Euphorbiae with unknown anti-tumor effects. We found that lathyrol had significant inhibitory effect on lung cancer cells by inducing apoptosis and inhibiting proliferation. Subsequently, we demonstrated for the first time that endoplasmic reticulum (ER) stress is a key anti-tumor mechanism of lathyrol. Furthermore, we found that lathyrol can induce ER stress in lung cancer cells by upregulating the protein expression levels of GRP78, PERK, p-eIF2α, CHOP, and ATF4, and the inhibitory effect of lathyrol on lung cancer cells was significantly reversed when cells were pretreated with ER stress inhibitor. In addition, we found that inhibition of SERCA2 resulted in depletion of the ER Ca²⁺ pool followed by a sustained increase in cytoplasmic Ca²⁺ levels, eventually leading to ER stress induced tumor cell apoptosis and proliferation inhibition. Lathyrol targeted SERCA2 to cause a significant upregulation of Ca²⁺ levels, and the inhibitory effect of lathyrol on lung cancer cells was significantly reversed after pretreatment with SERCA2 agonist. Taken together, our data suggest that lathyrol exerts its anti-tumor effect primarily by targeting SERCA2. Our findings highlight the potential for lathyrol as a new candidate drug for the treatment of lung cancer.

Insights into the role of intracellular calcium signaling in the neurobiology of neurodevelopmental disorders

Calcium (Ca²⁺) comprises a critical ionic second messenger in the central nervous system that is under the control of a wide array of regulatory mechanisms, including organellar Ca²⁺ stores, membrane channels and pumps, and intracellular Ca²⁺-binding proteins. Not surprisingly, disturbances in Ca²⁺ homeostasis have been linked to neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. However, aberrations in Ca²⁺ homeostasis have also been implicated in neuropsychiatric disorders with a strong neurodevelopmental component including autism spectrum disorder (ASD) attention-deficit hyperactivity disorder (ADHD) and schizophrenia (SCZ). While plasma membrane Ca²⁺ channels and synaptic Ca²⁺-binding proteins have been extensively studied, increasing evidence suggests a prominent role for intracellular Ca²⁺ stores, such as the endoplasmic reticulum (ER), in aberrant neurodevelopment. In the context of the current mini-review, we discuss recent findings implicating critical intracellular Ca²⁺-handling regulators such as the sarco-ER Ca²⁺ ATPase 2 (SERCA2), ryanodine receptors (RyRs), inositol triphosphate receptors (IP₃Rs), and parvalbumin (PVALB), in the emergence of ASD, SCZ, and ADHD.

Highly expressed SERCA2 triggers tumor cell autophagy and is a druggable vulnerability in triple-negative breast cancer

Chemoresistance remains a major obstacle to successful treatment of triple negative breast cancer (TNBC). Identification of druggable vulnerabilities is an important aim for TNBC therapy. Here, we report that SERCA2 expression correlates with TNBC progression in human patients, which promotes TNBC cell proliferation, migration and chemoresistance. Mechanistically, SERCA2 interacts with LC3B via LIR motif, facilitating WIPI2-independent autophagosome formation to induce autophagy. Autophagy-mediated SERCA2 degradation induces SERCA2 transactivation through a Ca²⁺/CaMKK/CREB-1 feedback. Moreover, we found that SERCA2-targeting small molecule RL71 enhances SERCA2-LC3B interaction and induces excessive autophagic cell death. The increase in SERCA2 expression predisposes TNBC cells to RL71-induced autophagic cell death in vitro and in vivo. This study elucidates a mechanism by which TNBC cells maintain their high autophagy activity to induce chemoresistance, and suggests increased SERCA2 expression as a druggable vulnerability for TNBC.

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.

Sigma-1 receptor attenuates osteoclastogenesis by promoting ER-associated degradation of SERCA2

Sigma-1 receptor (Sigmar1) is a specific chaperone located in the mitochondria-associated endoplasmic reticulum membrane (MAM) and plays a role in several physiological processes. However, the role of Sigmar1 in bone homeostasis remains unknown. Here, we show that mice lacking Sigmar1 exhibited severe osteoporosis in an ovariectomized model. In contrast, overexpression of Sigmar1 locally alleviated the osteoporosis phenotype. Treatment with Sigmar1 agonists impaired both human and mice osteoclast formation in vitro. Mechanistically, SERCA2 was identified to interact with Sigmar1 based on the immunoprecipitation-mass spectrum (IP-MS) and co-immunoprecipitation (co-IP) assays, and Q615 of SERCA2 was confirmed to be the critical residue for their binding. Furthermore, Sigmar1 promoted SERCA2 degradation through Hrd1/Sel1L-dependent ER-associated degradation (ERAD). Ubiquitination of SERCA2 at K460 and K541 was responsible for its proteasomal degradation. Consequently, inhibition of SERCA2 impeded Sigmar1 deficiency enhanced osteoclastogenesis. Moreover, we found that dimemorfan, an FDA-approved Sigmar1 agonist, effectively rescued bone mass in various established bone-loss models. In conclusion, Sigmar1 is a negative regulator of osteoclastogenesis, and activation of Sigmar1 by dimemorfan may be a potential treatment for osteoporosis in clinical practice.

Substitution of SERCA2 Cys674 aggravates cardiac fibrosis by promoting the transformation of cardiac fibroblasts to cardiac myofibroblasts

Sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) is vital to maintain intracellular calcium homeostasis, and its redox Cys⁶⁷⁴ (C674) is the key to regulating activity. Our goal was to investigate whether the redox state of SERCA2 C674 is critical for cardiac fibrosis and the mechanisms involved. Heterozygous SERCA2 C674S knock-in (SKI) mice, in which half of C674 was substituted by serine, were used to mimic the partial loss of the reactive C674 thiol in pathological conditions. In cardiac fibroblasts, the substitution of C674 thiol increased Ca²⁺ levels in cytoplasm and mitochondria, and intracellular ROS levels, and activated calcineurin/nuclear factor of activated T-lymphocytes (NFAT) pathway, increased the protein expression of profibrotic factors TGF beta 1 (TGF-β1), alpha smooth muscle actin, collagen I and collagen III, and promoted the transformation of cardiac fibroblasts to cardiac myofibroblasts, which could be reversed by calcineurin/NFAT inhibitor, SERCA2 agonist, or ROS scavenger. Activation of SERCA2 or scavenging ROS is beneficial to alleviate cardiac fibrosis caused by the substitution of C674. In conclusion, the partial loss of the reactive C674 thiol in the SERCA2 exacerbates cardiac fibrosis by activating the calcineurin/NFAT/TGF-β1 pathway to promote the transformation of cardiac fibroblasts to cardiac myofibroblasts, which highlights the importance of C674 redox state in maintaining the homeostasis of cardiac fibroblasts. SERCA2 is a potential therapeutic target for the treatment of cardiac fibrosis.

Substitution of the SERCA2 Cys674 reactive thiol accelerates atherosclerosis by inducing endoplasmic reticulum stress and inflammation

BACKGROUND AND PURPOSE

The cysteine⁶⁷⁴ (C674) thiol of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 is easily and irreversibly oxidized under atherosclerotic conditions. However, the contribution of the C674 thiol redox status in the development of atherosclerosis remains unclear. Our goal was to elucidate the possible mechanism involved.

EXPERIMENTAL APPROACH

Heterozygous SERCA2 C674S knock-in mice in which half of the C674 was substituted by serine⁶⁷⁴ (S674) were used to mimic the removal of the reactive C674 thiol which occurs under pathological conditions. Bone marrow-derived macrophages (BMDMs) and cardiac endothelial cells (ECs) were used for intracellular Ca²⁺ , macrophage adhesion, and protein expression analysis. The whole aorta and aortic root were isolated for histological analysis.

KEY RESULTS

Cell culture studies suggest the partial substitution of SERCA2 C674 increased intracellular Ca²⁺ levels and induced ER stress in both BMDMs and ECs. The release of pro-inflammatory factors and macrophage adhesion increased in SKI BMDMs. In ECs, the overexpression of S674 induced endothelial inflammation and promoted macrophage recruitment. SKI mice developed more severe atherosclerotic plaque and macrophage accumulation. Additionally, 4-phenyl butyric acid (PBA), an ER stress inhibitor, suppressed ER stress and inflammatory responses in BMDMs and ECs, and alleviate atherosclerosis in SKI mice.

CONCLUSIONS AND IMPLICATIONS

The substitution of SERCA2 C674 thiol accelerates the development of atherosclerosis by inducing ER stress and inflammation. Our findings highlight the importance of SERCA2 C674 redox state in the context of atherosclerosis and open up a novel therapeutic strategy to combat atherosclerosis.

SGLT2 inhibitor dapagliflozin reduces endothelial dysfunction and microvascular damage during cardiac ischemia/reperfusion injury through normalizing the XO-SERCA2-CaMKII-coffilin pathways

Background: Given the importance of microvascular injury in infarct formation and expansion, development of therapeutic strategies for microvascular protection against myocardial ischemia/reperfusion injury (IRI) is of great interest. Here, we explored the molecular mechanisms underlying the protective effects of the SGLT2 inhibitor dapagliflozin (DAPA) against cardiac microvascular dysfunction mediated by IRI. Methods: DAPA effects were evaluated both in vivo, in mice subjected to IRI, and in vitro, in human coronary artery endothelial cells (HCAECs) exposed to hypoxia/reoxygenation (H/R). DAPA pretreatment attenuated luminal stenosis, endothelial swelling, and inflammation in cardiac microvessels of IRI-treated mice. Results: In H/R-challenged HCAECs, DAPA treatment improved endothelial barrier function, endothelial nitric oxide synthase (eNOS) activity, and angiogenic capacity, and inhibited H/R-induced apoptosis by preventing cofilin-dependent F-actin depolymerization and cytoskeletal degradation. Inhibition of H/R-induced xanthine oxidase (XO) activation and upregulation, sarco(endo)plasmic reticulum calcium-ATPase 2 (SERCA2) oxidation and inactivation, and cytoplasmic calcium overload was further observed in DAPA-treated HCAECs. DAPA also suppressed calcium/Calmodulin (CaM)-dependent kinase II (CaMKII) activation and cofilin phosphorylation, and preserved cytoskeleton integrity and endothelial cell viability following H/R. Importantly, the beneficial effects of DAPA on cardiac microvascular integrity and endothelial cell survival were largely prevented in IRI-treated SERCA2-knockout mice. Conclusions: These results indicate that DAPA effectively reduces cardiac microvascular damage and endothelial dysfunction during IRI through inhibition of the XO-SERCA2-CaMKII-cofilin pathway.

Adipocyte-specific ablation of the Ca2+ pump SERCA2 impairs whole-body metabolic function and reveals the diverse metabolic flexibility of white and brown adipose tissue

OBJECTIVE

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) transports Ca²⁺ from the cytosol into the ER and is essential for appropriate regulation of intracellular Ca²⁺ homeostasis. The objective of this study was to test the hypothesis that SERCA pumps are involved in the regulation of white adipocyte hormone secretion and other aspects of adipose tissue function and that this control is disturbed in obesity-induced type-2 diabetes.

METHODS

SERCA expression was measured in isolated human and mouse adipocytes as well as in whole mouse adipose tissue by Western blot and RT-qPCR. To test the significance of SERCA2 in adipocyte functionality and whole-body metabolism, we generated adipocyte-specific SERCA2 knockout mice. The mice were metabolically phenotyped by glucose tolerance and tracer studies, histological analyses, measurements of glucose-stimulated insulin release in isolated islets, and gene/protein expression analyses. We also tested the effect of pharmacological SERCA inhibition and genetic SERCA2 ablation in cultured adipocytes. Intracellular and mitochondrial Ca²⁺ levels were recorded with dual-wavelength ratio imaging and mitochondrial function was assessed by Seahorse technology.

RESULTS

We demonstrate that SERCA2 is downregulated in white adipocytes from patients with obesity and type-2 diabetes as well as in adipocytes from diet-induced obese mice. SERCA2-ablated adipocytes display disturbed Ca²⁺ homeostasis associated with upregulated ER stress markers and impaired hormone release. These adipocyte alterations are linked to mild lipodystrophy, reduced adiponectin levels, and impaired glucose tolerance. Interestingly, adipocyte-specific SERCA2 ablation leads to increased glucose uptake in white adipose tissue while glucose uptake is reduced in brown adipose tissue. This dichotomous effect on glucose uptake is due to differently regulated mitochondrial function. In white adipocytes, SERCA2 deficiency triggers an adaptive increase in FGF21, increased mitochondrial UCP1 levels, and increased oxygen consumption rate (OCR). In contrast, brown SERCA2 null adipocytes display reduced OCR despite increased mitochondrial content and UCP1 levels compared to wild type controls.

CONCLUSIONS

Our data suggest causal links between reduced white adipocyte SERCA2 levels, deranged adipocyte Ca²⁺ homeostasis, adipose tissue dysfunction and type-2 diabetes.

High-fat diet promotes colorectal carcinogenesis through SERCA2 mediated serine phosphorylation of Annexin A2

Colorectal cancer (CRC) is a highly common malignancy, being the third leading cause of cancer death worldwide. Recent epidemiological studies have indicated that carcinogenic effect of diet was mainly attributed to high-fat diets. To investigate the mechanism of high-fat diet-induced colorectal cancer, we systematically quantified the phosphoproteome in human HT-29 cells treated with sodium palmitate (PA). p-Annexin A2 (S26) was predicted to be specifically up-regulated by PA. We confirmed that PA-induced Annexin A2 phosphorylation at Ser26 in C57BL/6 J-Apc^Min/J mice fed with high-fat diet. Phosphorylation of Annexin A2 at Ser26 promotes PA-induced proliferation of HT-29 cells. Moreover, PA suppressed SERCA activity and SERCA2 expression was compensatorily increased. Mechanistically, SERCA2 can partially reverse Annexin A2 phosphorylation at Ser26 caused by PA through intracellular calcium release. Finally, SERCA2 knockdown inhibited high-fat diet-induced tumor growth and Annexin A2 phosphorylation at Ser26 in SCID mice. In all, our studies demonstrate that high-fat diet promotes colorectal carcinogenesis through SERCA2 mediated serine phosphorylation of Annexin A2.

Targeting the Ubiquitin-Proteasome System in Limb-Girdle Muscular Dystrophy With CAPN3 Mutations

LGMDR1 is caused by mutations in the CAPN3 gene that encodes calpain 3 (CAPN3), a non-lysosomal cysteine protease necessary for proper muscle function. Our previous findings show that CAPN3 deficiency leads to reduced SERCA levels through increased protein degradation. This work investigates the potential contribution of the ubiquitin-proteasome pathway to increased SERCA degradation in LGMDR1. Consistent with our previous results, we observed that CAPN3-deficient human myotubes exhibit reduced SERCA protein levels and high cytosolic calcium concentration. Treatment with the proteasome inhibitor bortezomib (Velcade) increased SERCA2 protein levels and normalized intracellular calcium levels in CAPN3-deficient myotubes. Moreover, bortezomib was able to recover mutated CAPN3 protein in a patient carrying R289W and R546L missense mutations. We found that CAPN3 knockout mice (C3KO) presented SERCA deficits in skeletal muscle in the early stages of the disease, prior to the manifestation of muscle deficits. However, treatment with bortezomib (0.8 mg/kg every 72 h) for 3 weeks did not rescue SERCA levels. No change in muscle proteasome activity was observed in bortezomib-treated animals, suggesting that higher bortezomib doses are needed to rescue SERCA levels in this model. Overall, our results lay the foundation for exploring inhibition of the ubiquitin-proteasome as a new therapeutic target to treat LGMDR1 patients. Moreover, patients carrying missense mutations in CAPN3 and presumably other genes may benefit from proteasome inhibition by rescuing mutant protein levels. Further studies in suitable models will be necessary to demonstrate the therapeutic efficacy of proteasome inhibition for different missense mutations.

Active nNOS Is Required for Grp94-Induced Antioxidant Cytoprotection: A Lesson from Myogenic to Cancer Cells

The endoplasmic reticulum (ER) chaperone Grp94/gp96 appears to be involved in cytoprotection without being required for cell survival. This study compared the effects of Grp94 protein levels on Ca²⁺ homeostasis, antioxidant cytoprotection and protein–protein interactions between two widely studied cell lines, the myogenic C2C12 and the epithelial HeLa, and two breast cancer cell lines, MDA-MB-231 and HS578T. In myogenic cells, but not in HeLa, Grp94 overexpression exerted cytoprotection by reducing ER Ca²⁺ storage, due to an inhibitory effect on SERCA2. In C2C12 cells, but not in HeLa, Grp94 co-immunoprecipitated with non-client proteins, such as nNOS, SERCA2 and PMCA, which co-fractionated by sucrose gradient centrifugation in a distinct, medium density, ER vesicular compartment. Active nNOS was also required for Grp94-induced cytoprotection, since its inhibition by L-NNA disrupted the co-immunoprecipitation and co-fractionation of Grp94 with nNOS and SERCA2, and increased apoptosis. Comparably, only the breast cancer cell line MDA-MB-231, which showed Grp94 co-immunoprecipitation with nNOS, SERCA2 and PMCA, increased oxidant-induced apoptosis after nNOS inhibition or Grp94 silencing. These results identify the Grp94-driven multiprotein complex, including active nNOS as mechanistically involved in antioxidant cytoprotection by means of nNOS activity and improved Ca²⁺ homeostasis.

Activation of UCP1-Independent Ca2+ Cycling Thermogenesis by Wireless Optogenetics

The identification of non-canonical UCP1-independent thermogenic mechanisms offers new opportunities to target such pathways to improve metabolic health. Based on our recent studies on Ca2+ futile cycling thermogenesis in beige fat, we applied the newly developed implantable wireless optogenetic system to activate Ca2+ cycling in an adipocyte-specific manner without external stimuli, i.e., fat-specific cold mimetics. Here, we describe the detailed methodology and application to the prevention of obesity.

Inactivation of SERCA2 Cys674 accelerates aortic aneurysms by suppressing PPARγ

BACKGROUND AND PURPOSE

Inactivation of Cys⁶⁷⁴ (C674) in the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) causes intracellular Ca²⁺ accumulation, which activates calcineurin-mediated nuclear factor of activated T-lymphocytes (NFAT)/NF-κB pathways, and results in the phenotypic modulation of smooth muscle cells (SMCs) to accelerate angiotensin II-induced aortic aneurysms. Our goal was to investigate the mechanism involved.

EXPERIMENTAL APPROACH

We used heterozygous SERCA2 C674S knock-in (SKI) mice, where half of C674 was substituted by serine, to mimic partial irreversible oxidation of C674. The aortas of SKI mice and their littermate wild-type mice were collected for RNA sequencing, cell culture, protein expression, luciferase activity and aortic aneurysm analysis.

KEY RESULTS

Inactivation of C674 inhibited the promoter activity and protein expression of PPARγ, which could be reversed by inhibitors of calcineurin or NF-κB. In SKI SMCs, inhibition of NF-κB by pyrrolidinedithiocarbamic acid (PDTC) or overexpression of PPARγ2 reversed the protein expression of SMC phenotypic modulation markers and inhibited cell proliferation, migration, and macrophage adhesion to SMCs. Pioglitazone, a PPARγ agonist, blocked the activation of NFAT/NF-κB, reversed the protein expression of SMC phenotypic modulation markers, and inhibited cell proliferation, migration, and macrophage adhesion to SMCs in SKI SMCs. Furthermore, pioglitazone also ameliorated angiotensin II-induced aortic aneurysms in SKI mice.

CONCLUSIONS AND IMPLICATIONS

The inactivation of SERCA2 C674 promotes the development of aortic aneurysms by disrupting the balance between PPARγ and NFAT/NF-κB. Our study highlights the importance of C674 redox status in regulating PPARγ to maintain aortic homeostasis.

Clioquinol inhibits cell growth in a SERCA2-dependent manner

Clioquinol has been reported to act as a potential therapy for neurodegenerative diseases and cancer. However, the underlying mechanism is unclear. We have previously reported that clioquinol induces S-phase cell cycle arrest through the elevation of calcium levels in human neurotypic SH-SY5Y cells. In this study, different types of cells were observed to detect if the effect of clioquinol on intracellular calcium levels is cell type-specific. The Cell Counting Kit-8 assay showed that clioquinol exhibited varying degrees of concentration-dependent cytotoxicity in different cell lines, and that the growth inhibition caused by it was not related to cell source or carcinogenesis. In addition, the inhibition of cell growth by clioquinol was positively associated with its effect on intracellular calcium content ([Ca²⁺ ]_i ). Furthermore, the elevation of [Ca²⁺ ]_i induced by clioquinol led to S-phase cell cycle arrest. Similar to our previous studies, the increase in [Ca²⁺ ]_i was attributed to changes in the expression levels of the calcium pump SERCA2. Comparison of expression levels of SERCA2 between cell lines showed that cells with high levels of SERCA2 were more sensitive to clioquinol. In addition, analysis using UALCAN and the Human Protein Atlas also showed that the expression of SERCA2 in the corresponding human tissues was similar to that of the cells tested in this study, suggesting potential in the application of clioquinol in the future. In summary, our results expand the understanding of the molecular mechanism of clioquinol and provide an important strategy for the rational use of clioquinol.

Yulink, predicted from evolutionary analysis, is involved in cardiac function

Background

The comparative evolutionary genomics analysis was used to study the functions of novel Ka/Ks-predicted human exons in a zebrafish model. The Yulink (MIOS, Entrez Gene: 54,468), a conserved gene from zebrafish to human with WD40 repeats at N-terminus, was identified and found to encode an 875 amino acid in human. The biological function of this Yulink gene in cardiomyocytes remains unexplored. The purpose of this study is to determine the involvement of Yulink in the functions of cardiomyocytes and to investigate its molecular regulatory mechanism.

Methods

Knockdown of Yulink was performed using morpholino or shRNA in zebrafish, mouse HL-1 cardiomyocytes, and human iPSC-derived cardiomyocytes. The expression levels of mRNA and protein were quantified by qPCR and western blots. Other methods including DNA binding, ligand uptake, agonists treatment and Ca²⁺ imaging assays were used to study the molecular regulatory mechanism by Yulink. Statistical data were shown as mean ± SD or mean ± standard error.

Results

The knockdown of yulink with three specific morpholinos in zebrafish resulted in cardiac dysfunctions with pericardial edema, decreased heart beats and cardiac output. The Yulink knockdown in mouse HL-1 cardiomyocytes disrupted Ca²⁺ cycling, reduced DNA binding activity of PPARγ (peroxisome proliferator-activated receptor gamma) and resulted in a reduction of Serca2 (sarcoplasmic reticulum Ca²⁺ ATPase 2) expression. Expression of Serca2 was up-regulated by PPARγ agonists and down-regulated by PPARγ-shRNA knockdown, suggesting that Yulink regulates SERCA2 expression through PPARγ in mouse HL-1 cardiomyocytes. On the other hand, YULINK, PPARγ or SERCA2 over-expression rescued the phenotypes of Yulink KD cells. In addition, knockdown of YULINK in human iPSC-derived cardiomyocytes also disrupted Ca²⁺ cycling via decreased SERCA2 expression.

Conclusions

Overall, our data showed that Yulink is an evolutionarily conserved gene from zebrafish to human. Mechanistically Yulink regulated Serca2 expression in cardiomyocytes, presumably mediated through PPARγ nuclear entry. Deficiency of Yulink in mouse and human cardiomyocytes resulted in irregular Ca²⁺ cycling, which may contribute to arrhythmogenesis.

Relative role of T-tubules disruption and decreased SERCA2 on contractile dynamics of isolated rat ventricular myocytes

AIMS

Ventricular myocytes (VM) depolarization activates L-type Ca2+ channels (LCC) allowing Ca2+ influx (ICa) to synchronize sarcoplasmic reticulum (SR) Ca2+ release, via Ca2+-release channels (RyR2). The resulting whole-cell Ca2+ transient triggers contraction, while cytosolic Ca2+ removal by SR Ca2+ pump (SERCA2) and sarcolemmal Na+/Ca2+ exchanger (NCX) allows relaxation. In diseased hearts, extensive VM remodeling causes heterogeneous, blunted and slow Ca2+ transients. Among remodeling changes are: A) T-tubules disorganization. B) Diminished SERCA2 and low SR Ca2+. However, those often overlap, hindering their relative contribution to contractile dysfunction (CD). Furthermore, few studies have assessed their specific impact on the spatiotemporal Ca2+ transient properties and contractile dynamics simultaneously. Therefore, we sought to perform a quantitative comparison of how heterogeneous and slow Ca2+ transients, with different underlying determinants, affect contractile performance.

METHODS

We used two experimental models: A) formamide-induced acute "detubulation", where VM retain functional RyR2 and SERCA2, but lack T-tubules-associated LCC and NCX. B) Intact VM from hypothyroid rats, presenting decreased SERCA2 and SR Ca2+, but maintained T-tubules. By confocal imaging of Fluo-4-loaded VM, under field-stimulation, simultaneously acquired Ca2+ transients and shortening, allowing direct correlations.

KEY FINDINGS

We found near-linear correlations among key parameters of altered Ca2+ transients, caused independently by T-tubules disruption or decreased SR Ca2+, and shortening and relaxation, SIGNIFICANCE: Unrelated structural and molecular alterations converge in similarly abnormal Ca2+ transients and CD, highlighting the importance of independently reproduce disease-specific alterations, to quantitatively assess their impact on Ca2+ signaling and contractility, which would be valuable to determine potential disease-specific therapeutic targets.

Pathways for Sensing and Responding to Hydrogen Peroxide at the Endoplasmic Reticulum

The endoplasmic reticulum (ER) has emerged as a source of hydrogen peroxide (H₂O₂) and a hub for peroxide-based signaling events. Here we outline cellular sources of ER-localized peroxide, including sources within and near the ER. Focusing on three ER-localized proteins-the molecular chaperone BiP, the transmembrane stress-sensor IRE1, and the calcium pump SERCA2-we discuss how post-translational modification of protein cysteines by H₂O₂ can alter ER activities. We review how changed activities for these three proteins upon oxidation can modulate signaling events, and also how cysteine oxidation can serve to limit the cellular damage that is most often associated with elevated peroxide levels.

Effects of Standardized Green Tea Extract and Its Main Component, EGCG, on Mitochondrial Function and Contractile Performance of Healthy Rat Cardiomyocytes

We recently showed that the long-term in vivo administration of green tea catechin extract (GTE) resulted in hyperdynamic cardiomyocyte contractility. The present study investigates the mechanisms underlying GTE action in comparison to its major component, epigallocatechin-3-gallate (EGCG), given at the equivalent amount that would be in the entirety of GTE. Twenty-six male Wistar rats were given 40 mL/day of a tap water solution with either standardized GTE or pure EGCG for 4 weeks. Cardiomyocytes were then isolated for the study. Cellular bioenergetics was found to be significantly improved in both GTE- and EGCG-fed rats compared to that in controls as shown by measuring the maximal mitochondrial respiration rate and the cellular ATP level. Notably, the improvement of mitochondrial function was associated with increased levels of oxidative phosphorylation complexes, whereas the cellular mitochondrial mass was unchanged. However, only the GTE supplement improved cardiomyocyte mechanics and intracellular calcium dynamics, by lowering the expression of total phospholamban (PLB), which led to an increase of both the phosphorylated-PLB/PLB and the sarco-endoplasmic reticulum calcium ATPase/PLB ratios. Our findings suggest that GTE might be a valuable adjuvant tool for counteracting the occurrence and/or the progression of cardiomyopathies in which mitochondrial dysfunction and alteration of intracellular calcium dynamics constitute early pathogenic factors.

Oxymatrine attenuates arsenic-induced endoplasmic reticulum stress and calcium dyshomeostasis in hepatic stellate cells

Background

Oxymatrine is the main bioactive component of Sophora flavescens. It exhibits various biological activities and has been used in various liver diseases, including hepatic fibrosis (HF). Hepatic stellate cells (HSCs) are the primary cell type involved during HF progression. Oxymatrine treatment could suppress the proliferation of HSCs and degrade the extracellular cell matrix (ECM), presumed to be associated with HF. However, the mechanism is still unknown.

Methods

NaAsO₂ induces HF in LX2 cells. Oxymatrine was used to treat NaAsO₂- induced LX2 cells. Then, the LX2 cell proliferation, apoptosis, ECM secretion protein, oxidative stress index, and intracellular calcium concentration were respectively measured. Furthermore, after knocking down GRP78 [endoplasmic reticulum (ER) chaperone BiP] or overexpressing of SERCA2 (ATPase sarcoplasmic/ER Ca²⁺ transporting 2) in NaAsO₂-induced LX2 cells, we detected the changes in ER stress and calcium homeostasis in LX2 cells.

Results

NaAsO₂ exposure promoted apoptosis, increased ECM secretion, produced ER stress, and disrupted calcium homeostasis, which could be attenuated by oxymatrine treatment. Furthermore, knockdown of GRP78 to alleviate ER stress, or overexpression of SERCA2 to restore intracellular calcium homeostasis can inhibit the NaAsO₂ effect.

Conclusions

Oxymatrine treatment could improve calcium homeostasis and attenuate ER stress to reverse NaAsO₂-induced HSC activation and ECM secretion, which are the significant phenotypes of HF. The ER stress and calcium homeostasis may be the therapeutic targets for HF.

LncRNA MEG3-210 regulates endometrial stromal cells migration, invasion and apoptosis through p38 MAPK and PKA/SERCA2 signalling via interaction with Galectin-1 in endometriosis

BACKGROUND

Endometriosis is a benign gynaecological disease with malignant characteristics that severely affects women's quality of life. Long noncoding RNA maternally expressed gene 3 (LncRNA MEG3) is a tumour suppressor that is downregulated in various cancer cells and tissues, and regulates multiple biological processes. Emerging studies have revealed that the interactions between MEG3 and proteins are involved in disease progression. Galectin-1 affects cell motility, signal transduction and vascularization, and is overexpressed in endometriosis. Our study is the first to explore the role of MEG3-210 transcript in endometriosis and to reveal the regulatory mechanism mediated by the interaction between MEG3-210 and Galectin-1.

MATERIALS AND METHODS

Endometrial tissues and sera from patients with endometriosis and controls were collected. qRT-PCR was performed to detect the expression of MEG3-210 in the endometrium and endometrial stromal cells (ESCs). The CCK-8 assay, the Transwell assay, flow cytometry and animal models were conducted to evaluate the functions of MEG3-210 in vitro and in vivo. Bioinformatic analysis, Western blot assays, RNA-pull down assays and RNA immunoprecipitation were used to explore the potential mechanism of MEG3-210 in endometriosis.

RESULTS

Our results showed that MEG3-210 expression was lower in the eutopic endometrium of women with endometriosis. MEG3-210 downregulation promoted ESCs migration, invasion, anti-apoptosis in vitro and growth of endometriotic lesions in vivo. Furthermore, MEG3-210 downregulation could activate p38 mitogen-activated protein kinase (p38 MAPK) and inhibit cAMP-dependent protein kinase A/sarcoplasmic reticulum Ca²⁺ ATPase 2 (PKA/SERCA2) signalling, which was mediated by Galectin-1. The protein levels of Galectin-1 in patients with endometriosis were elevated, and Galectin-1 siRNA could reduce the size of lesions.

CONCLUSION

MEG3-210 regulates ESCs through p38 MAPK and PKA/SERCA signalling via interaction with Galectin-1. The novel regulatory mechanism may provide new insights into drug therapy and the diagnosis of endometriosis.

Metoprolol alleviates arginine vasopressin-induced cardiomyocyte hypertrophy by upregulating the AKT1-SERCA2 cascade in H9C2 cells

Background

Arginine vasopressin (AVP) is elevated in patients with heart failure, and the increase in the AVP concentration in plasma is positively correlated with disease severity and mortality. Metoprolol (Met) is a beta blocker that is widely used in the clinic to treat pathological cardiac hypertrophy and to improve heart function. However, the specific mechanism by which Met alleviates AVP-induced pathological cardiac hypertrophy is still unknown. Our current study aimed to evaluate the inhibitory effects of Met on AVP-induced cardiomyocyte hypertrophy and the underlying mechanisms.

Methods

AVP alone or AVP plus Met was added to the wild type or AKT1-overexpressing rat cardiac H9C2 cell line. The cell surface areas and ANP/BNP/β-MHC expressions were used to evaluate the levels of hypertrophy. Western bolting was used to analyze AKT1/P-AKT1, AKT2/P-AKT2, total AKT, SERCA2, and Phospholamban (PLN) expression. Fluo3-AM was used to measure the intracellular Ca²⁺ stores.

Results

In the current study, we found that AKT1 but not AKT2 mediated the pathogenesis of AVP-induced cardiomyocyte hypertrophy. Sustained stimulation (48 h) with AVP led to hypertrophy in the H9C2 rat cardiomyocytes, resulting in the downregulation of AKT1 (0.48 fold compared to control) and SERCA2 (0.62 fold), the upregulation of PLN (1.32 fold), and the increase in the cytoplasmic calcium concentration (1.52 fold). In addition, AKT1 overexpression increased the expression of SERCA2 (1.34 fold) and decreased the expression of PLN (0.48 fold) in the H9C2 cells. Moreover, we found that Met could attenuate the AVP-induced changes in AKT1, SERCA2 and PLN expression and decreased the cytoplasmic calcium concentration in the H9C2 cells.

Conclusions

Our results demonstrated that the AKT1-SERCA2 cascade served as an important regulatory pathway in AVP-induced pathological cardiac hypertrophy.

Role of TG2-Mediated SERCA2 Serotonylation on Hypoxic Pulmonary Vein Remodeling

Sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) pumps take up Ca2+ from the cytoplasm to maintain the balance of intracellular Ca2+. A decline in expression or activity of SERCA results in persistent store-operated calcium entry (SOCE). In cardiomyocytes as well as vascular smooth muscle cells (SMCs), SERCA2 acts as an important regulator of calcium cycling. The purpose of this study is to identify and better understand the role of transglutaminases2 (TG2) as a key factor involved in SERCA2 serotonination (s-SERCA2) and to elucidate the underlying mechanism of action. Human pulmonary venous smooth muscle cell in normal pulmonary lobe were isolated and cultured in vitro. Establishment of hypoxic pulmonary hypertension model in wild type and TG2 knockout mice. SERCA2 serotonylation was analyzed by co-(immunoprecipitation) IP when the TG2 gene silenced or overexpressed under normoxia and hypoxia in vivo and in vitro. Intracellular calcium ion was measured by using Fluo-4AM probe under normoxia and hypoxia. Real-time (RT)-PCR and Western blot analyzed expression of TG2, TRPC1, and TRPC6 under normoxia and hypoxia. Bioactivity of cells were analyzed by using Cell Counting Kit (CCK)-8, flow cytometry, wound healing, RT-PCR, and Western blot under PST-2744 and cyclopiazonic acid. We confirmed that 1) hypoxia enhanced the expression and activity of TG2, and 2) hypoxia increased the basal intracellular Ca2+ concentration ([Ca2+]i) and SOCE through activating TRPC6 on human pulmonary vein smooth muscle cells (hPVSMC). Then, we investigated the effects of overexpression and downregulation of the TG2 gene on the activity of SERCA2, s-SERCA2, basal [Ca2+]i, and SOCE under normoxia and hypoxia in vitro, and investigated the activity of SERCA2 and s-SERCA2 in vivo, respectively. We confirmed that SERCA2 serotonylation inhibited the activity of SERCA2 and increased the Ca2+ influx, and that hypoxia induced TG2-mediated SERCA2 serotonylation both in vivo and in vitro. Furthermore, we investigated the effect of TG2 activity on the biological behavior of hPVSMC by using an inhibitor and agonist of SERCA2, respectively. Finally, we confirmed that chronic hypoxia cannot increase vessel wall thickness, the right ventricular systolic pressure (RVSP), and right ventricular hypertrophy index (RVHI) of vascular smooth muscle-specific Tgm2−/− mice. These results indicated that hypoxia promoted TG2-mediated SERCA2 serotonylation, thereby leading to inhibition of SERCA2 activity, which further increased the calcium influx through the TRPC6 channel. Furthermore, tissue-specific conditional TG2 knockout mice prevents the development of pulmonary hypertension caused by hypoxia. In summary, we uncovered a new target (TG2) for treatment of chronic hypoxic pulmonary hypertension (CHPH).

Inactivation of cysteine 674 in the SERCA2 accelerates experimental aortic aneurysm

Sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) is vital to maintain intracellular calcium homeostasis. SERCA2 cysteine 674 (C674) is highly conservative and its irreversible oxidation is upregulated in human and mouse aortic aneurysms, especially in smooth muscle cells (SMCs). The contribution of SERCA2 and its redox C674 in the development of aortic aneurysm remains enigmatic. Objective: Our goal was to investigate the contribution of inactivation of C674 to the development of aortic aneurysm and the mechanisms involved. Approach and results: Using SERCA2 C674S knock-in (SKI) mouse line, in which half of C674 was substituted by serine 674 (S674) to represent partial irreversible oxidation of C674 in aortic aneurysm, we found that in aortic SMCs the replacement of C674 by S674 resulted in SMC phenotypic modulation. In SKI SMCs, the increased intracellular calcium activated calcium-dependent calcineurin, which promoted the nuclear translocation of nuclear factor of activated T-lymphocytes (NFAT) and nuclear factor kappa-B (NFκB), while inhibition of calcineurin blocked SMC phenotypic modulation. Besides, the replacement of C674 by S674 accelerated angiotensin II-induced aortic aneurysm. Conclusions: Our results indicate that the inactivation of C674 by causing the accumulation of intracellular calcium to activate calcineurin-mediated NFAT/NFκB pathways, resulted in SMC phenotypic modulation to accelerate aortic aneurysm, which highlights the importance of C674 redox state in the development of aortic aneurysms.

High shear stress amplitude in combination with prolonged stimulus duration determine induction of osteoclast formation by hematopoietic progenitor cells

To date, it is unclear how fluid dynamics stimulate mechanosensory cells to induce an osteoprotective or osteodestructive response. We investigated how murine hematopoietic progenitor cells respond to 2 minutes of dynamic fluid flow stimulation with a precisely controlled sequence of fluid shear stresses. The response was quantified by measuring extracellular adenosine triphosphate (ATP), immunocytochemistry of Piezo1, and sarcoplasmic/endoplasmic Ca²⁺ reticulum ATPase 2 (SERCA2), and by the ability of soluble factors produced by mechanically stimulated cells to modulate osteoclast differentiation. We rejected our initial hypothesis that peak wall shear stress rate determines the response of hematopoietic progenitor cells to dynamic fluid shear stress, as it had only a minor correlation with the abovementioned parameters. Low stimulus amplitudes corresponded to activation of Piezo1, SERCA2, low concentrations of extracellular ATP, and inhibition of osteoclastogenesis and resorption area, while high amplitudes generally corresponded to osteodestructive responses. At a given amplitude (3 Pa) and waveform (square), the duration of individual stimuli (duty cycle) showed a strong correlation with the release of ATP and osteoclast number and resorption area. Collectively, our data suggest that hematopoietic progenitor cells respond in a viscoelastic manner to loading, since a combination of high shear stress amplitude and prolonged duty cycle is needed to trigger an osteodestructive response. PLAIN LANGUAGE SUMMARY: In case of painful joints or missing teeth, the current intervention is to replace them with an implant to keep a high-quality lifestyle. When exercising or chewing, the cells in the bone around the implant experience mechanical loading. This loading generally supports bone formation to strengthen the bone and prevent breaking, but can also stimulate bone loss when the mechanical loading becomes too high around orthopedic and dental implants. We still do not fully understand how cells in the bone can distinguish between mechanical loading that strengthens or weakens the bone. We cultured cells derived from the bone marrow in the laboratory to test whether the bone loss response depends on (i) how fast a mechanical load is applied (rate), (ii) how intense the mechanical load is (amplitude), or (iii) how long each individual loading stimulus is applied (duration). We mimicked mechanical loading as it occurs in the body, by applying very precisely controlled flow of fluid over the cells. We found that a mechanosensitive receptor Piezo1 was activated by a low amplitude stimulus, which usually strengthens the bone. The potential inhibitor of Piezo1, namely SERCA2, was only activated by a low amplitude stimulus. This happened regardless of the rate of application. At a constant high amplitude, a longer duration of the stimulus enhanced the bone-weakening response. Based on these results we deduce that a high loading amplitude tends to be bone weakening, and the longer this high amplitude persists, the worse it is for the bone.

TMX2 Is a Crucial Regulator of Cellular Redox State, and Its Dysfunction Causes Severe Brain Developmental Abnormalities

The redox state of the neural progenitors regulates physiological processes such as neuronal differentiation and dendritic and axonal growth. The relevance of endoplasmic reticulum (ER)-associated oxidoreductases in these processes is largely unexplored. We describe a severe neurological disorder caused by bi-allelic loss-of-function variants in thioredoxin (TRX)-related transmembrane-2 (TMX2); these variants were detected by exome sequencing in 14 affected individuals from ten unrelated families presenting with congenital microcephaly, cortical polymicrogyria, and other migration disorders. TMX2 encodes one of the five TMX proteins of the protein disulfide isomerase family, hitherto not linked to human developmental brain disease. Our mechanistic studies on protein function show that TMX2 localizes to the ER mitochondria-associated membranes (MAMs), is involved in posttranslational modification and protein folding, and undergoes physical interaction with the MAM-associated and ER folding chaperone calnexin and ER calcium pump SERCA2. These interactions are functionally relevant because TMX2-deficient fibroblasts show decreased mitochondrial respiratory reserve capacity and compensatory increased glycolytic activity. Intriguingly, under basal conditions TMX2 occurs in both reduced and oxidized monomeric form, while it forms a stable dimer under treatment with hydrogen peroxide, recently recognized as a signaling molecule in neural morphogenesis and axonal pathfinding. Exogenous expression of the pathogenic TMX2 variants or of variants with an in vitro mutagenized TRX domain induces a constitutive TMX2 polymerization, mimicking an increased oxidative state. Altogether these data uncover TMX2 as a sensor in the MAM-regulated redox signaling pathway and identify it as a key adaptive regulator of neuronal proliferation, migration, and organization in the developing brain.

The role of desmin alterations in mechanical electrical feedback in heart failure

AIM

Mechanoelectric feedback (MEF) was related to malignant arrhythmias in heart failure (HF). Desmin is a cytoskeleton protein and could be involved in MEF as a mechanoelectrical transducer. In this study, we will discuss the role of desmin alterations in mechanical electrical feedback in heart failure and its mechanisms.

METHODS

We used both an in vivo rat model and an in vitro cardiomyocyte model to address this issue. For the in vivo experiments, we establish a sham group, an HF group, streptomycin (SM) group, and an MDL-28170 group. The occurrence of ventricular arrhythmias (VA) was recorded in each group. For the in vitro cardiomyocyte model, we established an NC group, a si-desmin group, and a si-desmin + NBD IKK group. The expression of desmin, IKKβ, p-IKKβ, IKBα, p-NF-κB, and SERCA2 were detected in both in vivo and in vitro experiments. The content of Ca²⁺ in cytoplasm and sarcoplasmic were detected by confocal imaging in vitro experiments.

RESULTS

An increased number of VAs were found in the HF group. SM and MDL-28170 can reduce desmin breakdown and the number of VAs in heart failure. The knockdown of desmin in the cardiomyocyte can activate the NF-κB pathway, decrease the level of SERCA2, and result in abnormal distribution of Ca²⁺. While treatment with NF-κB inhibitor can elevate the level of SERCA2 and alleviate the abnormal distribution of Ca²⁺.

SIGNIFICANCE

Overall, desmin may participate in MEF through the NF-κB pathway. This study provides a potential therapeutic target for VA in HF.

Impact of oxidative posttranslational modifications of SERCA2 on heart failure exacerbation in young patients with non-ischemic cardiomyopathy: A pilot study

Background

Oxidative posttranslational modifications (OPTM) impair the function of Sarcoplasmic/endoplasmic reticulum (SR) calcium (Ca²⁺) ATPase (SERCA) 2 and trigger cytosolic Ca²⁺ dysregulation. We investigated the extent of OPTM of SERCA2 in patients with non-ischemic cardiomyopathy (NICM).

Methods and results

Endomyocardial biopsy (EMB) was obtained in 40 consecutive patients with NICM. Total expression and OPTM of SERCA2, including sulfonylation at cysteine-674 (S-SERCA2) and nitration at tyrosine-294/295 (N-SERCA2), were examined by immunohistochemical analysis. S-SERCA2 increased in the presence of late gadolinium enhancement on cardiac magnetic resonance imaging. S-SERCA2/SERCA2 and N-SERCA2/SERCA2 correlated with cardiac fibrosis evaluated by Masson’s trichrome staining of EMB. SERCA2 expression modestly increased in parallel with an upward trend in OPTM of SERCA2 with aging. This tendency became prominent only in patients aged >65 years. OPTM of SERCA2 positively correlated with brain natriuretic peptide (BNP) values only in patients aged ≤65 years. Composite major adverse cardiac events (MACE) increased more in the high OPTM group of younger patients; however, MACE-free survival was similar irrespective of the extent of OPTM in older patients.

Conclusions

OPTM of SERCA2 correlate with myocardial fibrosis in NICM. In younger patients, OPTM of SERCA2 correlate with elevated BNP and increased composite MACE.

Darier disease: first molecular study of a Portuguese family

Background

Darier disease (DD) is a rare autosomal dominant condition characterized by skin lesions. Additionally, a wide range of neuropsychiatric symptoms is frequently reported in DD patients. This genodermatosis relies on mutations in the ATPase sarcoplasmic/endoplasmic reticulum Ca²⁺ transporting 2 (ATP2A2) gene, which encodes an ATPase responsible for pumping Ca²⁺ from the cytosol to the lumen of the ER.

Objective

Herein we studied the molecular aspect of a two-generation Portuguese family with DD history with clinical variability.

Methods

All exons and intron-exon borders of genomic ATP2A2, as well as coding ATP2A2, were sequenced. Relative levels of SERCA2 mRNA and protein were quantified by qPCR and western blotting, respectively.

Results

The c.1287+1G > T variant was identified in all affected individuals, whereas the unaffected individual was shown to carry the wild-type ATP2A2 sequence in both alleles. This variant leads to the skipping of full exon 10, which consequently generates a frameshift originating a premature STOP codon in exon 11 (p.V395 = fs*19). Although the mutant mRNA seems to partially escape degradation, results suggest synthesis inhibition or immediate degradation of the mutant protein. Neuropsychiatric and other occurrences affecting certain patients are also reported.

Conclusion

This is the first study of DD in Portugal, the variant identified, previously described in a single Japanese patient, may be considered a pathogenic mutation, and haploinsufficiency the mechanism underlying DD pathology in these patients. This study also highlights the co-occurrence of neuropsychiatric features in DD.

N-acetyl-seryl-aspartyl-lysyl-proline treatment protects heart against excessive myocardial injury and heart failure in mice

Myocardial infarction (MI) in mice results in cardiac rupture at 4-7 days after MI, whereas cardiac fibrosis and dysfunction occur later. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has anti-inflammatory, anti-fibrotic, and pro-angiogenic properties. We hypothesized that Ac-SDKP reduces cardiac rupture and adverse cardiac remodeling, and improves function by promoting angiogenesis and inhibiting detrimental reactive fibrosis and inflammation after MI. C57BL/6J mice were subjected to MI and treated with Ac-SDKP (1.6 mg/kg per day) for 1 or 5 weeks. We analyzed (1) intercellular adhesion molecule-1 (ICAM-1) expression; (2) inflammatory cell infiltration and angiogenesis; (3) gelatinolytic activity; (4) incidence of cardiac rupture; (5) p53, the endoplasmic reticulum stress marker CCAAT/enhancer binding protein homology protein (CHOP), and cardiomyocyte apoptosis; (6) sarcoplasmic reticulum Ca2+ ATPase (SERCA2) expression; (7) interstitial collagen fraction and capillary density; and (8) cardiac remodeling and function. Acutely, Ac-SDKP reduced cardiac rupture, decreased ICAM-1 expression and the number of infiltrating macrophages, decreased gelatinolytic activity, p53 expression, and myocyte apoptosis, but increased capillary density in the infarction border. Chronically, Ac-SDKP improved cardiac structures and function, reduced CHOP expression and interstitial collagen fraction, and preserved myocardium SERCA2 expression. Thus, Ac-SDKP decreased cardiac rupture, ameliorated adverse cardiac remodeling, and improved cardiac function after MI, likely through preserved SERCA2 expression and inhibition of endoplasmic reticulum stress.

Immunolocalization of calcium sensing and transport proteins in the murine endolymphatic sac indicates calciostatic functions within the inner ear

An exceptionally low calcium (Ca²⁺) concentration in the inner ear endolymph ([Ca²⁺]_endolymph) is crucial for proper auditory and vestibular function. The endolymphatic sac (ES) is believed to critically contribute to the maintenance of this low [Ca²⁺]_endolymph. Here, we investigated the immunohistochemical localization of proteins that are presumably involved in the sensing and transport of extracellular Ca²⁺ in the murine ES epithelium. Light microscopic and fluorescence immunolabeling in paraffin-embedded murine ES tissue sections (male C57BL/6 mice, 6–8 weeks old) demonstrated the presence of the calcium-sensing receptor CaSR, transient receptor potential cation channel subtypes TRPV5 and TRPV6, sarco/endoplasmic reticulum Ca²⁺-ATPases SERCA1 and SERCA2, Na⁺/Ca²⁺ exchanger NCX2, and plasma membrane Ca²⁺ ATPases PMCA1 and PMCA4 in ES epithelial cells. These proteins exhibited (i) membranous (apical or basolateral) or cytoplasmic localization patterns, (ii) a proximal-to-distal labeling gradient within the ES, and (iii) different distribution patterns among ES epithelial cell types (mitochondria-rich cells (MRCs) and ribosome-rich cells (RRCs)). Notably, in the inner ear membranous labyrinth, CaSR was exclusively localized in MRCs, suggesting a unique role of the ES epithelium in CaSR-mediated sensing and control of [Ca²⁺]_endolymph. Structural loss of the distal ES, which is consistently observed in Meniere’s disease, may therefore critically disturb [Ca²⁺]_endolymph and contribute to the pathogenesis of Meniere’s disease.

Geriatric Polytrauma-Cardiovascular and Immunologic Response in a Murine Two-Hit Model of Trauma

BACKGROUND

The aims of the present study were to establish a clinically relevant two-hit model with trauma/hemorrhage followed by sepsis in older mice and investigate age-dependent cardiovascular and immunologic specificities under these conditions.

MATERIALS AND METHODS

In aged mice (12, 18, and 24 mo old), a femur fracture followed by hemorrhage was induced. After resuscitation, animals were monitored for 72 h before sepsis was induced. Vital signs were monitored during shock. Systemic interleukin (IL)-6 levels were measured daily. Expression of sarcoplasmic or endoplasmic reticulum calcium ATPase (SERCA) and IL-6 receptor were analyzed in heart, lung, and liver tissues.

RESULTS

After induction of shock, mean arterial pressure decreased significantly in all groups (12 mo, P < 0.001; 18 mo, P < 0.001; 24 mo, P = 0.013). Compared with younger animals, 24-mo old mice were not able to adequately compensate for hypovolemia by an increase of heart rate (P = 0.711). Expression of SERCA2 (P = 0.002) and IL-6 receptor on myocytes (P = 0.037), lung (P = 0.005), and liver (P = 0.009) tissues were also lowest in this group. Systemic IL-6 values showed the most distinct posttraumatic response in 24-mo-old mice (P = 0.016). Survival rate decreased significantly with increased age (P = 0.005).

CONCLUSIONS

The increased mortality rate in older animals was associated with a limited compensatory physiological response and a more distinct immunologic reaction after trauma and sepsis. A decreased SERCA2 expression and missing feedback loops due to a reduced density of organ bound immune receptors might represent possible explanations for the observed age-dependent differences.

DP71 and SERCA2 alteration in human neurons of a Duchenne muscular dystrophy patient

Cognitive deficit has been identified in one third of patients affected by Duchenne Muscular Dystrophy, primarily attributed to loss of the short Dp71 dystrophin, the major brain dystrophin isoform. In this study, we investigated for the first time the Dp71 and Dp71-associated proteins cellular localization and expression in human neurons obtained by differentiation from induced pluripotent stem cell line of a patient affected by cognitive impairment. We found structural and molecular alterations in both pluripotent stem cell and derived neurons, reduced Dp71 expression, and a Ca²⁺ cytoplasmic overload in neurons coupled with increased expression of the SERCA2 pump in the dystrophic neurons. These results suggest that the reduction of Dp71 protein in the Duchenne muscular dystrophy neurons leads to alterations in SERCA2 and to elevated cytosolic Ca²⁺ concentration with consequent potential disruption of the dystrophin proteins and Dp71-associated proteins.

Exendin-4 Plays a Protective Role in a Rat Model of Spinal Cord Injury Through SERCA2

BACKGROUND/AIMS

Current therapies for spinal cord injury (SCI) have limited efficacy, and identifying a therapeutic target is a pressing need. Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) plays an important role in regulating calcium homeostasis, which has been shown to inhibit apoptosis. Exendin-4 has been shown to inhibit the apoptosis of nerve cells in SCI, which can also improve SERCA2 expression. In this study, we sought to determine whether exendin-4 plays a protective role in a rat model of SCI via SERCA2.

METHODS

To investigate the effects of exendin-4 on SCI, a rat model of SCI was induced by a modified version of Allen's method. Spinal cord tissue sections from rats and western blot analysis were used to examine SERCA2 expression after treatment with the long-acting glucagon-like peptide 1 receptor exendin-4 or the SERCA2 antagonist 5(6)-carboxyfluorescein diacetate N-succinimidyl ester (CE). Locomotor function was evaluated using the Basso Beattie Bresnahan locomotor rating scale and slanting board test.

RESULTS

Cell apoptosis was increased with CE treatment and decreased with exendin-4 treatment. Upregulation of SERCA2 in female rats with SCI resulted in an improvement of motor function scores and histological changes.

CONCLUSION

These findings suggest that exendin-4 plays a protective role in a rat model of SCI through SERCA2 via inhibition of apoptosis. Existing drugs targeting SERCA2 may be an effective therapeutic strategy for the treatment of SCI.

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.

HDAC Inhibition Improves the Sarcoendoplasmic Reticulum Ca2+-ATPase Activity in Cardiac Myocytes

SERCA2a is the Ca²⁺ ATPase playing the major contribution in cardiomyocyte (CM) calcium removal. Its activity can be regulated by both modulatory proteins and several post-translational modifications. The aim of the present work was to investigate whether the function of SERCA2 can be modulated by treating CMs with the histone deacetylase (HDAC) inhibitor suberanilohydroxamic acid (SAHA). The incubation with SAHA (2.5 µM, 90 min) of CMs isolated from rat adult hearts resulted in an increase of SERCA2 acetylation level and improved ATPase activity. This was associated with a significant improvement of calcium transient recovery time and cell contractility. Previous reports have identified K464 as an acetylation site in human SERCA2. Mutants were generated where K464 was substituted with glutamine (Q) or arginine (R), mimicking constitutive acetylation or deacetylation, respectively. The K464Q mutation ameliorated ATPase activity and calcium transient recovery time, thus indicating that constitutive K464 acetylation has a positive impact on human SERCA2a (hSERCA2a) function. In conclusion, SAHA induced deacetylation inhibition had a positive impact on CM calcium handling, that, at least in part, was due to improved SERCA2 activity. This observation can provide the basis for the development of novel pharmacological approaches to ameliorate SERCA2 efficiency.

The cardioprotective effect of rosmarinic acid on acute myocardial infarction and genes involved in Ca2+ homeostasis

Acute myocardial infarction (AMI) is a common cause of hospitalisation and high mortality due to lethal arrhythmias. Sarcoplasmic reticulum Ca2+ ATPase (SERCA2) and ryanodine receptor (RyR2) regulate the cytosolic Ca2+ ion concentration. Rosmarinic acid (RA) is one of the most common caffeic esters in Rosmarinus officinalis. The present study was conducted to test the hypothesis whether RA can protect cardiac function against AMI and arrhythmias induced by isoproterenol through the regulatory effect of SERCA2 and RyR2 gene expression. To this aim, male Sprague-Dawley rats were allocated into in vivo and ex vivo studies and received RA (10, 15, and 30 mg/kg; 14 days). AMI was induced by two consecutive subcutaneous injections of 100 mg/kg isoproterenol. Blood pressure (BP), heart rate, electrocardiography (ECG) parameters, plasma levels of cardiac biomarkers, and antioxidative enzymes were evaluated (in vivo study). Cardiac functions were measured in isolated hearts using Langendorff set up. Gene expressions of SERCA2 and RyR2 were measured in left ventricular heart. Isoproterenol administration showed a significant decline in BP, QRS voltage, activities of antioxidant enzymes, cardiac function, and gene expressions of SERCA2 and RyR2. The results also indicated a significant increase in heart rate, ST-elevation, cardiac biomarkers, and antioxidant enzymes. RA at 30 mg/kg dosage showed the best effect on the improvement of the mentioned factors. This study suggests that RA has potent cardioprotective effects against AMI and arrhythmia, which may be due to its ability to enhance expression of plasma antioxidant enzymes and genes involved in Ca2+ homeostasis SERCA2 and RyR2. The protective role of RA is also possibly related to its antiadrenergic effects.

Therapeutic Benefit and Gene Network Regulation by Combined Gene Transfer of Apelin, FGF2, and SERCA2a into Ischemic Heart

Despite considerable advances in cardiovascular disease treatment, heart failure remains a public health challenge. In this context, gene therapy appears as an attractive approach, but clinical trials using single therapeutic molecules result in moderate benefit. With the objective of improving ischemic heart failure therapy, we designed a combined treatment, aimed to simultaneously stimulate angiogenesis, prevent cardiac remodeling, and restore contractile function. We have previously validated IRES-based vectors as powerful tools to co-express genes of interest. Mono- and multicistronic lentivectors expressing fibroblast growth factor 2 (angiogenesis), apelin (cardioprotection), and/or SERCA2a (contractile function) were produced and administrated by intramyocardial injection into a mouse model of myocardial infarction. Data reveal that combined treatment simultaneously improves vessel number, heart function parameters, and fibrosis prevention, due to FGF2, SERCA2a, and apelin, respectively. Furthermore, addition of SERCA2a in the combination decreases cardiomyocyte hypertrophy. Large-scale transcriptome analysis reveals that the triple treatment is the most efficient in restoring angiogenic balance as well as expression of genes involved in cardiac function and remodeling. Our study validates the concept of combined treatment of ischemic heart disease with apelin, FGF2, and SERCA2a and shows that such therapeutic benefit is mediated by a more effective recovery of gene network regulation.