Roles of store-operated Ca2+ channels in regulating cell cycling and migration of human cardiac c-kit+ progenitor cells

Bradykinin-pretreated Human cardiac-specific c-kit+ Cells Enhance Exosomal miR-3059-5p and Promote Angiogenesis Against Hindlimb Ischemia in mice

BACKGROUND

Protection of cardiac function following myocardial infarction was largely enhanced by bradykinin-pretreated cardiac-specific c-kit+ (BK-c-kit+) cells, even without significant engraftment, indicating that paracrine actions of BK-c-kit+ cells play a pivotal role in angiogenesis. Nevertheless, the active components of the paracrine actions of BK-c-kit+ cells and the underlying mechanisms remain unknown. This study aimed to define the active components of exosomes from BK-c-kit+ cells and elucidate their underlying protective mechanisms.

METHODS

Matrigel tube formation assay, cell cycle, and mobility in human umbilical vein endothelial cells (HUVECs) and hindlimb ischemia (HLI) in mice were applied to determine the angiogenic effect of condition medium (CM) and exosomes. Proteome profiler, microRNA sponge, Due-luciferase assay, microRNA-sequencing, qRT-PCR, and Western blot were used to determine the underlying mechanism of the angiogenic effect of exosomes from BK-c-kit+.

RESULTS

As a result, BK-c-kit+ CM and exosomes promoted tube formation in HUVECs and the repair of HLI in mice. Angiogenesis-related proteomic profiling and microRNA sequencing revealed highly enriched miR-3059-5p as a key angiogenic component of BK-c-kit+ exosomes. Meanwhile, loss- and gain-of-function experiments revealed that the promotion of angiogenesis by miR-3059-5p was mainly through suppression of TNFSF15-inhibited effects on vascular tube formation, cell proliferation and cell migration. Moreover, enhanced angiogenesis of miR-3059-5p-inhibited TNFSF15 has been associated with Akt/Erk1/2/Smad2/3-modulated signaling pathway.

CONCLUSION

Our results demonstrated a novel finding that BK-c-kit+ cells enrich exosomal miR-3059-5p to suppress TNFSF15 and promote angiogenesis against hindlimb ischemia in mice.

Concanavalin A promotes angiogenesis and proliferation in endothelial cells through the Akt/ERK/Cyclin D1 axis

CONTEXT

Concanavalin A (Con A) exhibited multiple roles in cancer cells. However, the role of Con A in endothelial cells was not reported.

OBJECTIVE

Our present study investigated the potential angiogenic role of Con A in endothelial cells and ischaemic hind-limb mice.

MATERIALS AND METHODS

Human umbilical vein endothelial cells and Ea.hy926 cells were employed to determine the effect of Con A (0.3, 1, and 3 μg/mL) or vehicle on angiogenesis and cell proliferation with tube formation, ELISA, flow cytometry, EdU, and western blot. Hind-limb ischaemic mice were conducted to determine the pro-angiogenic effect of Con A (10 mg/kg) for 7 days.

RESULTS

Con A promoted tube formation to about three-fold higher than the control group and increased the secretion of VEGFa, PDGFaa, and bFGF in the medium. The cell viability was promoted to 1.3-fold by Con A 3 μg/mL, and cell cycle progression of G0G1 phase was decreased from 77% in the vehicle group to 70% in Con A 3 μg/mL, G2M was promoted from 15 to 19%, and S-phase was from 7 to 10%. Con A significantly stimulated phosphorylation of Akt and ERK1/2 and expression of cyclin D1 and decreased the expression of p27. These effects of Con A were antagonised by the PI3K inhibitor LY294002 (10 μM) and MEK pathway antagonist PD98059 (10 μM). Moreover, Con A (10 mg/kg) exhibited a repair effect in ischaemic hind-limb mice.

DISCUSSION AND CONCLUSIONS

This study will provide a new option for treating ischaemic disease by local injection with Con A.

Expanding the clinical and genetic spectrum of pathogenic variants in STIM1

INTRODUCTION/AIMS

Stromal interaction molecule 1 (STIM1) is a reticular Ca²⁺ sensor composed of a luminal and a cytosolic domain. Autosomal dominant mutations in STIM1 cause tubular aggregate myopathy and Stormorken syndrome or its variant York platelet syndrome. In this study we aimed to expand the features related to new variants in STIM1.

METHODS

We performed a cross-sectional study of individuals harboring monoallelic STIM1 variants recruited at five tertiary centers involved in a study of inherited myopathies analyzed with a multigene-targeted panel.

RESULTS

We identified seven individuals (age range, 26-57 years) harboring variants in STIM1, including five novel changes: three located in the EF-hand domain, one in the sterile α motif (SAM) domain, and one in the cytoplasmatic region of the protein. Functional evaluation of the pathogenic variants using a heterologous expression system and measuring store-operated calcium entry demonstrated their causative role and suggested a link of new variants with the clinical phenotype. Muscle contractures, found in three individuals, showed variability in body distribution and in the number of joints involved. Three patients showed cardiac and respiratory involvement. Short stature, hyposplenism, sensorineural hearing loss, hypothyroidism, and Gilbert syndrome were variably observed among the patients. Laboratory tests revealed hyperCKemia in six patients, thrombocytopenia in two patients, and hypocalcemia in one patient. Muscle biopsy showed the presence of tubular aggregates in three patients, type I fiber atrophy in one patient, and nonspecific myopathic changes in two patients.

DISCUSSION

Our clinical, histological, and molecular data expand the genetic and clinical spectrum of STIM1-related diseases.

Pretreatment of cardiac progenitor cells with bradykinin attenuates H2O2-induced cell apoptosis and improves cardiac function in rats by regulating autophagy

Background

Previous studies have demonstrated that human cardiac c-Kit⁺ progenitor cells (hCPCs) can effectively improve ischemic heart disease. However, the major challenge in applying hCPCs to clinical therapy is the low survival rate of graft hCPCs in the host heart, which limited the benefit of transplanted hCPCs. Bradykinin (BK) is a principal active agent of the tissue kinin-kallikrein system. Our previous studies have highlighted that BK mediated the growth and migration of CPCs by regulating Ca²⁺ influx. However, the protective effect of BK on CPCs, improvement in the survival rate of BK-pretreated hCPCs in the infarcted heart, and the related mechanism remain elusive.

Methods

HCPCs were treated with H₂O₂ to induce cell apoptosis and autophagy, and different concentration of BK was applied to rescue the H₂O₂-induced injury detected by MTT assay, TUNEL staining, flow cytometry, western blotting, and mitoSOX assays. The role of autophagy in the anti-apoptotic effect of BK was chemically activated or inhibited using the autophagy inducer, rapamycin, or the inhibitor, 3-methyladenine (3-MA). To explore the protective effect of BK on hCPCs, 3-MA or BK-pretreated hCPCs were transplanted into the myocardial infarcted rats. An echocardiogram was used to determine cardiac function, H&E and Masson staining were employed to assess pathological characteristics, HLA gene expression was quantified by qRT-PCR, and immunostaining was applied to examine neovascularization using confocal microscopy.

Results

The in vitro results showed that BK suppressed H₂O₂-induced hCPCs apoptosis and ROS production in a concentration-dependent manner by promoting pAkt and Bcl-2 expression and reducing cleaved caspase 3 and Bax expression. Moreover, BK restrained the H₂O₂-induced cell autophagy by decreasing LC3II/I, Beclin1, and ATG5 expression and increasing P62 expression. In the in vivo experiment, the transplanted BK- or 3-MA-treated hCPCs were found to be more effectively improved cardiac function by decreasing cardiomyocyte apoptosis, inflammatory infiltration, and myocardial fibrosis, and promoting neovascularization in the infarcted heart, compared to untreated-hCPCs or c-kit^- cardiomyocytes (CPC^- cells).

Conclusions

Our present study established a new method to rescue transplanted hCPCs in the infarcted cardiac area via regulating cell apoptosis and autophagy of hCPCs by pretreatment with BK, providing a new therapeutic option for heart failure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02503-6.

Targeting Orai1-Mediated Store-Operated Ca2+ Entry in Heart Failure

The archetypal store-operated Ca²⁺ channels (SOCs), Orai1, which are stimulated by the endo/sarcoplasmic reticulum (ER/SR) Ca²⁺ sensor stromal interaction molecule 1 (STIM1) upon Ca²⁺ store depletion is traditionally viewed as instrumental for the function of non-excitable cells. In the recent years, expression and function of Orai1 have gained recognition in excitable cardiomyocytes, albeit controversial. Even if its cardiac physiological role in adult is still elusive and needs to be clarified, Orai1 contribution in cardiac diseases such as cardiac hypertrophy and heart failure (HF) is increasingly recognized. The present review surveys our current arising knowledge on the new role of Orai1 channels in the heart and debates on its participation to cardiac hypertrophy and HF.

RAC1-Dependent ORAI1 Translocation to the Leading Edge Supports Lamellipodia Formation and Directional Persistence

Tumor invasion requires efficient cell migration, which is achieved by the generation of persistent and polarized lamellipodia. The generation of lamellipodia is supported by actin dynamics at the leading edge where a complex of proteins known as the WAVE regulatory complex (WRC) promotes the required assembly of actin filaments to push the front of the cell ahead. By using an U2OS osteosarcoma cell line with high metastatic potential, proven by a xenotransplant in zebrafish larvae, we have studied the role of the plasma membrane Ca²⁺ channel ORAI1 in this process. We have found that epidermal growth factor (EGF) triggered an enrichment of ORAI1 at the leading edge, where colocalized with cortactin (CTTN) and other members of the WRC, such as CYFIP1 and ARP2/3. ORAI1-CTTN co-precipitation was sensitive to the inhibition of the small GTPase RAC1, an upstream activator of the WRC. RAC1 potentiated ORAI1 translocation to the leading edge, increasing the availability of surface ORAI1 and increasing the plasma membrane ruffling. The role of ORAI1 at the leading edge was studied in genetically engineered U2OS cells lacking ORAI1 expression that helped us to prove the key role of this Ca²⁺ channel on lamellipodia formation, lamellipodial persistence, and cell directness, which are required for tumor cell invasiveness in vivo.

Knockdown of STIM1 expression inhibits non-small-cell lung cancer cell proliferation in vitro and in nude mouse xenografts

Stromal interaction molecule 1 (STIM1) is a calcium-sensing protein localized in the membrane of the endoplasmic reticulum. The expression of STIM1 has been shown to be closely associated with cell proliferation. The aim of the present study was to investigate the role of STIM1 in the regulation of cancer progression and its clinical relevance. The data demonstrated that the expression of the STIM1 was significantly higher in non-small-cell lung cancer (NSCLC) tissues than in benign lesions and was associated with advanced NSCLC T stage. Knockdown of STIM1 expression in NSCLC cell lines A549 and SK-MES-1 significantly inhibited cell proliferation and induces A549 and SK-MES-1 cell arrest at the G2/M and S phases of the cell cycle. Western blotting showed that the expression of cyclin-dependent kinase (CDK) 1 and CDK2 were reduced while knockdown of STIM1 expression. Furthermore, knockdown of STIM1 in NSCLC cells significantly reduced the levels of xenograft tumor growth in nude mice. These data indicate that aberrant expression of the STIM1 protein may contribute to NSCLC progression. Future studies should focus on targeting STIM1 as a novel strategy for NSCLC therapy.

Specific Upregulation of TRPC1 and TRPC5 Channels by Mineralocorticoid Pathway in Adult Rat Ventricular Cardiomyocytes

Whereas cardiac TRPC (transient receptor potential canonical) channels and the associated store-operated Ca²⁺ entry (SOCE) are abnormally elevated during cardiac hypertrophy and heart failure, the mechanism of this upregulation is not fully elucidated but might be related to the activation of the mineralocorticoid pathway. Using a combination of biochemical, Ca²⁺ imaging, and electrophysiological techniques, we determined the effect of 24-h aldosterone treatment on the TRPCs/Orai-dependent SOCE in adult rat ventricular cardiomyocytes (ARVMs). The 24-h aldosterone treatment (from 100 nM to 1 µM) enhanced depletion-induced Ca²⁺ entry in ARVMs, as assessed by a faster reduction of Fura-2 fluorescence decay upon the addition of Mn²⁺ and increased Fluo-4/AM fluorescence following Ca²⁺ store depletion. These effects were prevented by co-treatment with a specific mineralocorticoid receptor (MR) antagonist, RU-28318, and they are associated with the enhanced depletion-induced N-[4-[3,5-Bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl]-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2)-sensitive macroscopic current recorded by patch-clamp experiments. Molecular screening by qRT-PCR and Western blot showed a specific upregulation of TRPC1, TRPC5, and STIM1 expression at the messenger RNA (mRNA) and protein levels upon 24-h aldosterone treatment of ARVMs, corroborated by immunostaining. Our study provides evidence that the mineralocorticoid pathway specifically promotes TRPC1/TRPC5-mediated SOCE in adult rat cardiomyocytes.

Role of the calcium toolkit in cancer stem cells

Cancer stem cells are a subpopulation of tumor cells that proliferate, self-renew and produce more differentiated tumoral cells building-up the tumor. Responsible for the sustained growth of malignant tumors, cancer stem cells are proposed to play significant roles in cancer resistance to standard treatment and in tumor recurrence. Among the mechanisms dysregulated in neoplasms, those related to Ca²⁺ play significant roles in various aspects of cancers. Ca²⁺ is a ubiquitous second messenger whose fluctuations of its intracellular concentrations are tightly controlled by channels, pumps, exchangers and Ca²⁺ binding proteins. These components support the genesis of Ca²⁺ signals with specific spatio-temporal characteristics that define the cell response. Being involved in the coupling of extracellular events with intracellular responses, the Ca²⁺ toolkit is often hijacked by cancer cells to promote notably their proliferation and invasion. Growing evidence obtained during the last decade pointed to a role of Ca²⁺ handling and mishandling in cancer stem cells. In this review, after a general overview of the concept of cancer stem cells we analyse and discuss the studies and current knowledge regarding the complex roles of Ca²⁺ toolkit and signaling in these cells. We highlight that numbers of Ca²⁺ signaling actors promote cancer stem cell state and are associated with cell resistance to current cancer treatments and thus may represent promising targets for potential clinical applications.

Bradykinin-mediated Ca2+ signalling regulates cell growth and mobility in human cardiac c-Kit+ progenitor cells

Our recent study showed that bradykinin increases cell cycling progression and migration of human cardiac c‐Kit⁺ progenitor cells by activating pAkt and pERK1/2 signals. This study investigated whether bradykinin‐mediated Ca²⁺ signalling participates in regulating cellular functions in cultured human cardiac c‐Kit⁺ progenitor cells using laser scanning confocal microscopy and biochemical approaches. It was found that bradykinin increased cytosolic free Ca²⁺ (Cai2+) by triggering a transient Ca²⁺ release from ER IP3Rs followed by sustained Ca²⁺ influx through store‐operated Ca²⁺ entry (SOCE) channel. Blockade of B2 receptor with HOE140 or IP3Rs with araguspongin B or silencing IP3R3 with siRNA abolished both Ca²⁺ release and Ca²⁺ influx. It is interesting to note that the bradykinin‐induced cell cycle progression and migration were not observed in cells with siRNA‐silenced IP3R3 or the SOCE component TRPC1, Orai1 or STIM1. Also the bradykinin‐induced increase in pAkt and pERK1/2 as well as cyclin D1 was reduced in these cells. These results demonstrate for the first time that bradykinin‐mediated increase in free Cai2+ via ER‐IP3R3 Ca²⁺ release followed by Ca²⁺ influx through SOCE channel plays a crucial role in regulating cell growth and migration via activating pAkt, pERK1/2 and cyclin D1 in human cardiac c‐Kit⁺ progenitor cells.

Quiescence status of glioblastoma stem-like cells involves remodelling of Ca2+ signalling and mitochondrial shape

Quiescence is a reversible cell-cycle arrest which allows cancer stem-like cells to evade killing following therapies. Here, we show that proliferating glioblastoma stem-like cells (GSLCs) can be induced and maintained in a quiescent state by lowering the extracellular pH. Through RNAseq analysis we identified Ca²⁺ signalling genes differentially expressed between proliferating and quiescent GSLCs. Using the bioluminescent Ca²⁺ reporter EGFP-aequorin we observed that the changes in Ca²⁺ homeostasis occurring during the switch from proliferation to quiescence are controlled through store-operated channels (SOC) since inhibition of SOC drives proliferating GSLCs to quiescence. We showed that this switch is characterized by an increased capacity of GSLCs’ mitochondria to capture Ca²⁺ and by a dramatic and reversible change of mitochondrial morphology from a tubular to a donut shape. Our data suggest that the remodelling of the Ca²⁺ homeostasis and the reshaping of mitochondria might favours quiescent GSLCs’ survival and their aggressiveness in glioblastoma.

Modulation of store-operated calcium entry and nascent adhesion by p21-activated kinase 1

Calcium mobilization is necessary for cell movement during embryonic development, lymphocyte synapse formation, wound healing, and cancer cell metastasis. Depletion of calcium in the lumen of the endoplasmic reticulum using inositol triphosphate (IP3) or thapsigargin (TG) is known to induce oligomerization and cytoskeleton-mediated translocation of stromal interaction molecule 1 (STIM1) to the plasma membrane, where it interacts with the calcium release-activated calcium channel Orai1 to mediate calcium influx; this process is referred to as store-operated calcium entry (SOCE). Furthermore, aberrant STIM1 or SOCE regulation is associated with cancer cell motility and metastasis. The p21-activated kinases (PAKs), which are downstream effectors of GTPases, reportedly regulate cytoskeletal organization, protrusive activity, and cell migration. Although cytoskeletal remodeling apparently contributes to calcium mobilization via SOCE, and vice versa, the mechanisms by which they regulate each other remain unclear. In this study, we aimed to characterize whether PAK1 modulates calcium mobilization and STIM1 localization. Our data demonstrate that PAK1 interacts with STIM1 in vitro and that this interaction was enhanced by treatment with a nascent adhesion inducer, such as phorbol 12,13-dibutyrate (PDBu). Under basal conditions, both proteins appeared to primarily colocalize in the cytosol, whereas treatment with PDBu induced their colocalization to vinculin-positive peripheral adhesions. Downregulation of PAK1 activity via chemical inhibitors or by PAK1 shDNA expression impaired STIM1-mediated calcium mobilization via SOCE. Based on these findings, we propose that PAK1 interacts with STIM1 to regulate calcium mobilization and the formation of cellular adhesions.

A molecular mechanism underlying cell movement may contribute to the aggressive migration of metastatic tumor cells. A team led by Ki-Duk Song at Chonbuk National University, Jeonju-si, and Joong-Kook Choi at Chungbuk National University, Cheongju in South Korea investigated the function of a protein called p21-activated kinase 1 (PAK1). PAK1 is known to contribute to the reorganization of cellular structure. The researchers determined that it directly interacts with molecular machinery that controls the storage and release of stockpiled calcium ions at the periphery of the cell where migration takes place. These ions play an important role in enabling cell movement and attachment, and the researchers showed that they could disrupt cellular calcium ion accumulation by switching off the gene encoding PAK1. They now aim to investigate how this mechanism contributes to cancer cell migration.

Calcium-dependent potassium channels control proliferation of cardiac progenitor cells and bone marrow-derived mesenchymal stem cells

KEY POINTS

Ex vivo proliferated c-Kit⁺ endogenous cardiac progenitor cells (eCPCs) obtained from mouse and human cardiac tissues have been reported to express a wide range of functional ion channels. In contrast to previous reports in cultured c-Kit⁺ eCPCs, we found that ion currents were minimal in freshly isolated cells. However, inclusion of free Ca²⁺ intracellularly revealed a prominent inwardly rectifying current identified as the intermediate conductance Ca²⁺ -activated K⁺ current (KCa3.1) Electrical function of both c-Kit⁺ eCPCs and bone marrow-derived mesenchymal stem cells is critically governed by KCa3.1 calcium-dependent potassium channels. Ca²⁺ -induced increases in KCa3.1 conductance are necessary to optimize membrane potential during Ca²⁺ entry. Membrane hyperpolarization due to KCa3.1 activation maintains the driving force for Ca²⁺ entry that activates stem cell proliferation. Cardiac disease downregulates KCa3.1 channels in resident cardiac progenitor cells. Alterations in KCa3.1 may have pathophysiological and therapeutic significance in regenerative medicine.

ABSTRACT

Endogenous c-Kit⁺ cardiac progenitor cells (eCPCs) and bone marrow (BM)-derived mesenchymal stem cells (MSCs) are being developed for cardiac regenerative therapy, but a better understanding of their physiology is needed. Here, we addressed the unknown functional role of ion channels in freshly isolated eCPCs and expanded BM-MSCs using patch-clamp, microfluorometry and confocal microscopy. Isolated c-Kit⁺ eCPCs were purified from dog hearts by immunomagnetic selection. Ion currents were barely detectable in freshly isolated c-Kit⁺ eCPCs with buffering of intracellular calcium (Ca²⁺_i ). Under conditions allowing free intracellular Ca²⁺ , freshly isolated c-Kit⁺ eCPCs and ex vivo proliferated BM-MSCs showed prominent voltage-independent conductances that were sensitive to intermediate-conductance K⁺ -channel (KCa3.1 current, I_KCa3.1 ) blockers and corresponding gene (KCNN4)-expression knockdown. Depletion of Ca²⁺_i induced membrane-potential (V_mem ) depolarization, while store-operated Ca²⁺ entry (SOCE) hyperpolarized V_mem in both cell types. The hyperpolarizing SOCE effect was substantially reduced by I_KCa3.1 or SOCE blockade (TRAM-34, 2-APB), and I_KCa3.1 blockade (TRAM-34) or KCNN4-knockdown decreased the Ca²⁺ entry resulting from SOCE. I_KCa3.1 suppression reduced c-Kit⁺ eCPC and BM-MSC proliferation, while significantly altering the profile of cyclin expression. I_KCa3.1 was reduced in c-Kit⁺ eCPCs isolated from dogs with congestive heart failure (CHF), along with corresponding KCNN4 mRNA. Under perforated-patch conditions to maintain physiological [Ca²⁺ ]_i , c-Kit⁺ eCPCs from CHF dogs had less negative resting membrane potentials (-58 ± 7 mV) versus c-Kit⁺ eCPCs from control dogs (-73 ± 3 mV, P < 0.05), along with slower proliferation. Our study suggests that Ca²⁺ -induced increases in I_KCa3.1 are necessary to optimize membrane potential during the Ca²⁺ entry that activates progenitor cell proliferation, and that alterations in KCa3.1 may have pathophysiological and therapeutic significance in regenerative medicine.

TRPC1/TRPC3 channels mediate lysophosphatidylcholine-induced apoptosis in cultured human coronary artery smooth muscles cells

The earlier study showed that lysophosphatidylcholine (lysoPC) induced apoptosis in human coronary artery smooth muscle cells (SMCs); however, the related molecular mechanisms are not fully understood. The present study investigated how lysoPC induces apoptosis in cultured human coronary artery SMCs using cell viability assay, flow cytometry, confocal microscopy, and molecular biological approaches. We found that lysoPC reduced cell viability in human coronary artery SMCs by eliciting a remarkable Ca2+ influx. The effect was antagonized by La3+, SKF-96365, or Pyr3 as well as by silencing TRPC1 or TRPC3. Co-immunoprecipitation revealed that TRPC1 and TRPC3 had protein-protein interaction. Silencing TRPC1 or TRPC3 countered the lysoPC-induced increase of Ca2+ influx and apoptosis, and the pro-apoptotic proteins Bax and cleaved caspase-3 and decrease of the anti-apoptotic protein Bcl-2 and the survival kinase pAkt. These results demonstrate the novel information that TRPC1/TRPC3 channels mediate lysoPC-induced Ca2+ influx and apoptosis via activating the pro-apoptotic proteins Bax and cleaved caspase-3 and inhibiting the anti-apoptotic protein Bcl-2 and the survival kinase pAkt in human coronary artery SMCs, which implies that TRPC1/TRC3 channels may be the therapeutic target of lysoPC-induced disorders such as atherosclerosis.

TRPC3-mediated Ca2+ signals as a promising strategy to boost therapeutic angiogenesis in failing hearts: The role of autologous endothelial colony forming cells

Endothelial progenitor cells (EPCs) are a sub-population of bone marrow-derived mononuclear cells that are released in circulation to restore damaged endothelium during its physiological turnover or rescue blood perfusion after an ischemic insult. Additionally, they may be mobilized from perivascular niches located within larger arteries' wall in response to hypoxic conditions. For this reason, EPCs have been regarded as an effective tool to promote revascularization and functional recovery of ischemic hearts, but clinical application failed to exploit the full potential of patients-derived cells. Indeed, the frequency and biological activity of EPCs are compromised in aging individuals or in subjects suffering from severe cardiovascular risk factors. Rejuvenating the reparative phenotype of autologous EPCs through a gene transfer approach has, therefore, been put forward as an alternative approach to enhance their therapeutic potential in cardiovascular patients. An increase in intracellular Ca²⁺ concentration constitutes a pivotal signal for the activation of the so-called endothelial colony forming cells (ECFCs), the only known truly endothelial EPC subset. Studies from our group showed that the Ca²⁺ toolkit differs between peripheral blood- and umbilical cord blood (UCB)-derived ECFCs. In the present article, we first discuss how VEGF uses repetitive Ca²⁺ spikes to regulate angiogenesis in ECFCs and outline how VEGF-induced intracellular Ca²⁺ oscillations differ between the two ECFC subtypes. We then hypothesize about the possibility to rejuvenate the biological activity of autologous ECFCs by transfecting the cell with the Ca²⁺ -permeable channel Transient Receptor Potential Canonical 3, which selectively drives the Ca²⁺ response to VEGF in UCB-derived ECFCs.

Bradykinin regulates cell growth and migration in cultured human cardiac c-Kit+ progenitor cells

Bradykinin is a well-known endogenous vasoactive peptide. The present study investigated the bradykinin receptor expression in human cardiac c-Kit⁺ progenitor cells and the potential role of bradykinin in regulating cell cycling progression and mobility. It was found that mRNA and protein of bradykinin type 2 receptors, but not bradykinin type 1 receptors, were abundant in cultured human cardiac c-Kit⁺ progenitor cells. Bradykinin (1-10 nM) stimulated cell growth and migration in a concentration-dependent manner. The increase of cell proliferation was related to promoting G0/G1 transition into G2/M and S phase. Western blots revealed that bradykinin significantly increased pAkt and pERK1/2 as well as cyclin D1, which were countered by HOE140 (an antagonist of bradykinin type 2 receptors) or by silencing bradykinin type 2 receptors. The increase of pAkt, pERK1/2 and cyclin D1 by bradykinin was prevented by the PI3K inhibitor Ly294002, the PLC inhibitors U73122 and neomycin, and/or the PKC inhibitor chelerythrine and the MAPK inhibitor PD98059. Our results demonstrate the novel information that bradykinin promotes cell cycling progression and migration in human cardiac c-Kit⁺ progenitor cells via activating PI3K, PLC, PKC, cyclin D1, pERK1/2, and pAkt.

Complex phenotypes associated with STIM1 mutations in both coiled coil and EF-hand domains

Dominant mutations in STIM1 are a cause of three allelic conditions: tubular aggregate myopathy, Stormorken syndrome (a complex phenotype including myopathy, hyposplenism, hypocalcaemia and bleeding diathesis), and a platelet dysfunction disorder, York platelet syndrome. Previous reports have suggested a genotype-phenotype correlation with mutations in the N-terminal EF-hand domain associated with tubular aggregate myopathy, and a common mutation at p.R304W in a coiled coil domain associated with Stormorken syndrome. In this study individuals with STIM1 variants were identified by exome sequencing or STIM1 direct sequencing, and assessed for neuromuscular, haematological and biochemical evidence of the allelic disorders of STIM1. STIM1 mutations were investigated by fibroblast calcium imaging and 3D modelling. Six individuals with STIM1 mutations, including two novel mutations (c.262A>G (p.S88G) and c.911G>A (p.R304Q)), were identified. Extra-neuromuscular symptoms including thrombocytopenia, platelet dysfunction, hypocalcaemia or hyposplenism were present in 5/6 patients with mutations in both the EF-hand and CC domains. 3/6 patients had psychiatric disorders, not previously reported in STIM1 disease. Review of published STIM1 patients (n = 49) confirmed that neuromuscular symptoms are present in most patients. We conclude that the phenotype associated with activating STIM1 mutations frequently includes extra-neuromuscular features such as hypocalcaemia, hypo-/asplenia and platelet dysfunction regardless of mutation domain.

Tissue Specificity: Store-Operated Ca2+ Entry in Cardiac Myocytes

Calcium (Ca²⁺) is a key regulator of cardiomyocyte contraction. The Ca²⁺ channels, pumps, and exchangers responsible for the cyclical cytosolic Ca²⁺ signals that underlie contraction are well known. In addition to those Ca²⁺ signaling components responsible for contraction, it has been proposed that cardiomyocytes express channels that promote the influx of Ca²⁺ from the extracellular milieu to the cytosol in response to depletion of intracellular Ca²⁺ stores. With non-excitable cells, this store-operated Ca²⁺ entry (SOCE) is usually easily demonstrated and is essential for prolonging cellular Ca²⁺ signaling and for refilling depleted Ca²⁺ stores. The role of SOCE in cardiomyocytes, however, is rather more elusive. While there is published evidence for increased Ca²⁺ influx into cardiomyocytes following Ca²⁺ store depletion, it has not been universally observed. Moreover, SOCE appears to be prominent in embryonic cardiomyocytes but declines with postnatal development. In contrast, there is overwhelming evidence that the molecular components of SOCE (e.g., STIM, Orai, and TRPC proteins) are expressed in cardiomyocytes from embryo to adult. Moreover, these proteins have been shown to contribute to disease conditions such as pathological hypertrophy, and reducing their expression can attenuate hypertrophic growth. It is plausible that SOCE might underlie Ca²⁺ influx into cardiomyocytes and may have important signaling functions perhaps by activating local Ca²⁺-sensitive processes. However, the STIM, Orai, and TRPC proteins appear to cooperate with multiple protein partners in signaling complexes. It is therefore possible that some of their signaling activities are not mediated by Ca²⁺ influx signals, but by protein-protein interactions.

Electrically Induced Calcium Handling in Cardiac Progenitor Cells

For nearly a century, the heart was viewed as a terminally differentiated organ until the discovery of a resident population of cardiac stem cells known as cardiac progenitor cells (CPCs). It has been shown that the regenerative capacity of CPCs can be enhanced by ex vivo modification. Preconditioning CPCs could provide drastic improvements in cardiac structure and function; however, a systematic approach to determining a mechanistic basis for these modifications founded on the physiology of CPCs is lacking. We have identified a novel property of CPCs to respond to electrical stimulation by initiating intracellular Ca²⁺ oscillations. We used confocal microscopy and intracellular calcium imaging to determine the spatiotemporal properties of the Ca²⁺ signal and the key proteins involved in this process using pharmacological inhibition and confocal Ca²⁺ imaging. Our results provide valuable insights into mechanisms to enhance the therapeutic potential in stem cells and further our understanding of human CPC physiology.

Store-operated Ca(2+) entry in rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS), the most common pediatric soft tissue sarcoma, has an intrinsic or early-acquisition of resistance to chemo- and radiation therapy. Molecular determinants pivotal for RMS migration, metastatic invasion, cell proliferation, and survival are incompletely identified. Migration and cell proliferation were shown to correlate with cytosolic Ca(2+) activity ([Ca(2+)]i). Store-operated Ca(2+)-entry (SOCE) that increases intracellular [Ca(2+)] is accomplished by Orai1, a pore-forming ion channel unit, the expression of which is stimulated by the transcription factor NFκB. The present study explored the expression of Orai1 and its regulators STIM1 and NFκB in human rhabdomyosarcoma cell lines and analyzed their impact on cell proliferation and migration. For the study human rhabdomyosarcoma cell lines RD (embryonal) and RH30 (alveolar) were analyzed for Orai1, STIM1, and NFκB transcription by RT-PCR and their corresponding proteins in Western blot. [Ca(2+)]i was detected via Fura-2 fluorescence and SOCE - resulting from [Ca(2+)]i increase following store depletion with extracellular Ca(2+) removal and inhibition of the sarcoendoplasmatic reticular Ca(2+) ATPase - detected with thapsigargin. Cell migration was analyzed in transwell and mitotic cell death with the clonogenic assay. In summary, Orai1, STIM1, and NFκB are expressed in embryonal (RD) and alveolar (RH30) rhabdomyosarcoma. SOCE inhibitor BTP2, Orai1 inhibitor 2-APB, or NFκB inhibitor wogonin virtually abrogated (BTP2, 2-APB) or significantly reduced (wogonin) SOCE. Moreover, SOCE inhibitors 2-APB and BTP2 and wogonin significantly inhibited migration and proliferation of both, RD and RH30 cells. These results suggest that Orai1 signaling is involved in SOCE into rhabdomyosarcoma cells thus contributing to migration, invasion and proliferation.