Orai1-mediated I (CRAC) is essential for neointima formation after vascular injury

Orai1 Participates in Coronary Artery Dysfunction Caused by Hypertension via Regulating Smooth Muscle Cell Phenotype Transformation

Hypertension plays a critical role in the development of vascular remodeling and atherosclerosis. STIM/Orai1 proteins mediate store-operated Ca2+ entry (SOCE), which is one of the cellular Ca2+ signaling machinery involved in the pathological process of cardiovascular remodeling. However, the role and mechanism of Orai1/Orai1 mediated SOCE in coronary artery dysfunction caused by hypertension remain incompletely elucidated. The present study aimed to investigate the role of the Orai1/NFAT/calcineurin signaling pathway in hypertension-induced coronary vasoconstriction impairment utilizing spontaneous hypertension rats (SHRs) and coronary arterial smooth muscle cells (CASMCs) exposed to high hydrostatic pressure (180 mmHg). Here, we found that agonists (5-HT, U46619, and ET-1) induced coronary artery constriction that was significantly reduced in SHRs compared with Wistar rats. The SOCE inhibitors SKF96365 and 2-APB also significantly inhibited coronary artery constriction in both SHRs and Wistar rats; only the inhibitory effect of low concentrations (50 μM) of 2-APB on SHRs was weaker than that of Wistar rats. Hypertension/high hydrostatic pressure (180 mmHg) induced phenotypic transformation of CASMCs, with an increase in the expression of STIM1/Orai1, Calcineurin-NFAT2, and the synthetic phenotypic marker protein OPN, and a decrease in the contractile phenotypic marker protein SMMHC. The intervention of Orai1/Orai1 mediated SOCE (overexpression with ad-Orai1, inhibition of SOCE channel with BTP2 or downregulation with Orai1 siRNA) regulated STIM1, Calcineurin-NFAT2 expression, and contraction/synthesis phenotypic markers. Together, these findings suggest that hypertension leads to coronary vascular dysfunction via the upregulation of Orai1, which is required for the phenotypic transformation of VSMCs by activating the Calcineurin-NFAT signaling pathway.

VSMC-specific TRPC1 deletion attenuates angiotensin II-induced hypertension and cardiovascular remodeling

Transient receptor potential canonical 1 (TRPC1) channel, a Ca2+-permeable ion channel widely expressed in vasculature, has been reported to be involved in various cardiovascular disorders. However, the pathophysiological function of vascular smooth muscle cell (VSMC)-derived TRPC1 in hypertension and hypertensive cardiovascular remodeling remains to be defined. In this study, we found increased TRPC1 expression in both angiotensin II (AngII)-treated VSMCs and aortas from AngII-infused mice. VSMC-specific TRPC1 deficiency strikingly attenuated AngII-induced vasoconstriction, hypertension, vascular remodeling, and cardiac hypertrophy. Mechanistically, AngII activated enhancer of zeste homolog 2 (EZH2) to stimulate TRPC1 expression, induced calcium influx and phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK-ERK), which in turn triggered VSMC proliferation and migration and exacerbated hypertension and cardiovascular remodeling. Treatment with EZH2 inhibitor reduced VSMC proliferation and migration and alleviated vasoconstriction and hypertension in AngII-infused mice. Together, we revealed the pathogenic role of the EZH2-TRPC1-MEK/ERK pathway in AngII-induced hypertension and cardiovascular damage. TRPC1 or EZH2 inhibition may represent a desirable therapeutic target for the treatment of hypertension. KEY MESSAGES: AngII activates AT1R-EZH2-TRPC1 pathway in VSMCs and aortas of hypertensive mice. TRPC1 promotes VSMC proliferation and migration via MEK/ERK signaling. Inhibition of TRPC1 or EZH2 alleviates hypertension and cardiovascular remodeling.

Inositol 1,4,5-Trisphosphate Receptors Regulate Vascular Smooth Muscle Cell Proliferation and Neointima Formation in Mice

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation is involved in many types of arterial diseases, including neointima hyperplasia, in which Ca2+ has been recognized as a key player. However, the physiological role of Ca2+ release via inositol 1,4,5-trisphosphate receptors (IP3Rs) from endoplasmic reticulum in regulating VSMC proliferation has not been well determined.

METHODS AND RESULTS

Both in vitro cell culture models and in vivo mouse models were generated to investigate the role of IP3Rs in regulating VSMC proliferation. Expression of all 3 IP3R subtypes was increased in cultured VSMCs upon platelet-derived growth factor-BB and FBS stimulation as well as in the left carotid artery undergoing intimal thickening after vascular occlusion. Genetic ablation of all 3 IP3R subtypes abolished endoplasmic reticulum Ca2+ release in cultured VSMCs, significantly reduced cell proliferation induced by platelet-derived growth factor-BB and FBS stimulation, and also decreased cell migration of VSMCs. Furthermore, smooth muscle-specific deletion of all IP3R subtypes in adult mice dramatically attenuated neointima formation induced by left carotid artery ligation, accompanied by significant decreases in cell proliferation and matrix metalloproteinase-9 expression in injured vessels. Mechanistically, IP3R-mediated Ca2+ release may activate cAMP response element-binding protein, a key player in controlling VSMC proliferation, via Ca2+/calmodulin-dependent protein kinase II and Akt. Loss of IP3Rs suppressed cAMP response element-binding protein phosphorylation at Ser133 in both cultured VSMCs and injured vessels, whereas application of Ca2+ permeable ionophore, ionomycin, can reverse cAMP response element-binding protein phosphorylation in IP3R triple knockout VSMCs.

CONCLUSIONS

Our results demonstrated an essential role of IP3R-mediated Ca2+ release from endoplasmic reticulum in regulating cAMP response element-binding protein activation, VSMC proliferation, and neointima formation in mouse arteries.

Orai1/STIMs modulators in pulmonary vascular diseases

Calcium (Ca2+) is a secondary messenger that regulates various cellular processes. However, Ca2+ mishandling could lead to pathological conditions. Orai1 is a Ca2+channel contributing to the store-operated calcium entry (SOCE) and plays a critical role in Ca2+ homeostasis in several cell types. Dysregulation of Orai1 contributed to severe combined immune deficiency syndrome, some cancers, pulmonary arterial hypertension (PAH), and other cardiorespiratory diseases. During its activation process, Orai1 is mainly regulated by stromal interacting molecule (STIM) proteins, especially STIM1; however, many other regulatory partners have also been recently described. Increasing knowledge about these regulatory partners provides a better view of the downstream signalling pathways of SOCE and offers an excellent opportunity to decipher Orai1 dysregulation in these diseases. These proteins participate in other cellular functions, making them attractive therapeutic targets. This review mainly focuses on Orai1 regulatory partners in the physiological and pathological conditions of the pulmonary circulation and inflammation.

Vascular polycystin proteins in health and disease

PKD1 (polycystin 1) and PKD2 (polycystin 2) are expressed in a variety of different cell types, including arterial smooth muscle and endothelial cells. PKD1 is a transmembrane domain protein with a large extracellular N-terminus that is proposed to act as a mechanosensor and receptor. PKD2 is a member of the transient receptor potential (TRP) channel superfamily which is also termed TRPP1. Mutations in the genes which encode PKD1 and PKD2 lead to autosomal dominant polycystic kidney disease (ADPKD). ADPKD is one of the most prevalent monogenic disorders in humans and is associated with extrarenal and vascular complications, including hypertension. Recent studies have uncovered mechanisms of activation and physiological functions of PKD1 and PKD2 in arterial smooth muscle and endothelial cells. It has also been found that PKD function is altered in the vasculature during ADPKD and hypertension. We will summarize this work and discuss future possibilities for this area of research.

Scrutinizing science to save lives: uncovering flaws in the data linking L-type calcium channels blockers to CRAC channels and heart failure

Hypertension is estimated to affect almost 1 billion people globally and significantly increases risk of myocardial infarction, heart failure, stroke, retinopathy and kidney disease. One major front line therapy that has been used for over 50 years involves L-type Ca 2+ channel blockers (LCCBs). One class of LCCBs is the dihydropyridine family, with amlodipine being widely prescribed regardless of gender, race, ethnicity or age. In 2020, Johnson et al. 7 reported that all LCCBs significantly increased the risk of heart failure, and attributed this effect to non-canonical activation of store-operated Ca 2+ entry. A major approach on which they based many of their arguments was to measure cytosolic Ca 2+ using the fluorescent Ca 2+ indicator dye fura-2. We recently demonstrated that amlodipine is highly fluorescent within cells and overwhelms the fura-2 signal, precluding the use of the indicator dye with amlodipine 24 . Our meta-analyses and prospective real world study showed that dihydropyridines were not associated with an increase in heart failure, likely explained by the lack of consideration by Johnson et al. 7 of well-known confounding factors such as age, race, obesity, prior anti-hypertensive treatment or diabetes 24 . Trebak and colleagues have responded to our paper with a forthright and unwavering defence of their work 27 . In this paper, we carry out a forensic dissection of Johnson et al., 7 and conduct new experiments that address directly points raised by Trebak et al. 27 . We show that there are major flaws in the design and interpretation of their key experiments, that fura-2 cannot be used with amlodipine, that there are fundamental mathematical misunderstandings and mistakes throughout their study leading to critical calculations on heart failure that are demonstrably wrong, and several of their own results are inconsistent with their interpretation. We therefore believe the study by Johnson et al. 7 is flawed at many levels and we stand by our conclusions.

Store-Operated Ca2+ Entry in Fibrosis and Tissue Remodeling

Fibrosis is a pathological condition characterized by excessive tissue deposition of extracellular matrix (ECM) components, leading to scarring and impaired function across multiple organ systems. This complex process is mediated by a dynamic interplay between cell types, including myofibroblasts, fibroblasts, immune cells, epithelial cells, and endothelial cells, each contributing distinctively through various signaling pathways. Critical to the regulatory mechanisms involved in fibrosis is store-operated calcium entry (SOCE), a calcium entry pathway into the cytosol active at the endoplasmic reticulum-plasma membrane contact sites and common to all cells. This review addresses the multifactorial nature of fibrosis with a focus on the pivotal roles of different cell types. We highlight the essential functions of myofibroblasts in ECM production, the transformation of fibroblasts, and the participation of immune cells in modulating the fibrotic landscape. We emphasize the contributions of SOCE in these different cell types to fibrosis, by exploring the involvement of SOCE in cellular functions such as proliferation, migration, secretion, and inflammatory responses. The examination of the cellular and molecular mechanisms of fibrosis and the role of SOCE in these mechanisms offers the potential of targeting SOCE as a therapeutic strategy for mitigating or reversing fibrosis.

Betulinaldehyde inhibits vascular remodeling by regulating the microenvironment through the PLCγ1/Ca2+/MMP9 pathway

BACKGROUND

Vascular remodeling plays a crucial role in the pathogenesis of several cardiovascular diseases (CVDs). Unfortunately, current drug therapies offer limited relief for vascular remodeling. Therefore, the development of innovative therapeutic strategies or drugs that target vascular remodeling is imperative. Betulinaldehyde (BA) is a triterpenoid with diverse biological activities, but its effects on vascular remodeling remain unclear.

OBJECTIVE

This study aimed to investigate the role of BA in vascular remodeling and its mechanism of action, providing valuable information for future applications of BA in the treatment of CVDs.

METHODS

Network pharmacology was used to predict the key targets of BA in vascular remodeling. The effect of BA on vascular remodeling was assessed in a rat model of balloon injury using hematoxylin and eosin staining, Masson staining, immunohistochemistry staining, and Western blotting. A phenotypic transformation model of vascular smooth muscle cells (VSMCs) was induced by platelet-derived growth factor-BB, and the functional impacts of BA on VSMCs were assessed via CCK-8, EdU, Wound healing, Transwell, and Western blotting. Finally, after manipulation of phospholipase C gamma1 (PLCγ1) expression, Western blotting and Ca²⁺ levels determination were performed to investigate the potential mechanism of action of BA.

RESULTS

The most key target of BA in vascular remodeling, matrix metalloproteinase 9 (MMP9), was identified through network pharmacology screening. Vascular remodeling was alleviated by BA in vivo and its effects were associated with decreased MMP9 expression. In vitro studies indicated that BA inhibited VSMC proliferation, migration, phenotypic transformation, and downregulated MMP9 expression. Additionally, BA decreased PLCγ1 expression and Ca²⁺ levels in VSMCs. However, after pretreatment with a phospholipase C agonist, BA's effects on down-regulating the expression of PLCγ1 and Ca²⁺ levels were inhibited, while the expression of MMP9 increased compared to that in the BA treatment group.

CONCLUSION

This study demonstrated the critical role of BA in vascular remodeling. These findings revealed a novel mechanism whereby BA mediates its protective effects through MMP9 regulation by inhibiting the PLCγ1/Ca²⁺/MMP9 signaling pathway. Overall, BA may potentially be developed into a novel medication for CVDs and may serve as a promising therapeutic strategy for improving recovery from CVDs by targeting MMP9.

Contribution of calcium dysregulation to impaired coronary artery contraction in Zucker diabetic fatty rats

Diabetic coronary artery injury is closely associated with Ca²⁺ dysregulation, although the underlying mechanism remains unclear. This study explored the role and mechanism of Ca²⁺ handling in coronary artery dysfunction in type 2 diabetic rats. Zucker diabetic fatty (ZDF) rats were used as the type 2 diabetes mellitus model. The contractility of coronary artery rings induced by KCl, CaCl₂ , 5-HT and U46619 was significantly lower in ZDF rats than in Zucker lean rats. Vasoconstriction induced by 5-HT and U46619 was greatly inhibited by nifedipine. However, in the presence of 1 μM nifedipine or in the Ca²⁺ -free KH solution containing 1 μM nifedipine, there was no difference in the vasoconstriction between Zucker lean and ZDF rats. Store-operated calcium channels (SOCs) were not involved in coronary vasoconstriction. The downregulation of contractile proteins and the upregulation of synthesized proteins were in coronary artery smooth muscle cells (CASMCs) from ZDF rats. Metformin reversed the reduction of vasoconstriction in ZDF rats. Taken together, L-type calcium channel is important for regulating the excitation-contraction coupling of VSMCs in coronary arteries, and dysregulation of this channel contributes to the decreased contractility of coronary arteries in T2DM.

STIM/Orai Inhibition as a Strategy for Alleviating Diabetic Erectile Dysfunction Through Modulation of Rat and Human Penile Tissue Contractility and in vivo Potentiation of Erectile Responses

BACKGROUND

Stromal interaction molecule (STIM)/Orai calcium entry system appears to have a role in erectile dysfunction (ED) pathophysiology but its specific contribution to diabetic ED was not elucidated.

AIM

To evaluate STIM/Orai inhibition on functional alterations associated with diabetic ED in rat and human penile tissues and on in vivo erectile responses in diabetic rats.

METHODS

Rat corpus cavernosum (RCC) strips from nondiabetic (No DM) and streptozotocin-induced diabetic (DM) rats and human penile resistance arteries (HPRA) and corpus cavernosum (HCC) from ED patients undergoing penile prosthesis insertion were functionally evaluated in organ chambers and wire myographs. Erectile function in vivo in rats was assessed by intracavernosal pressure (ICP) responses to cavernous nerve electrical stimulation (CNES). Expression of STIM/Orai elements in HCC was determined by immunofluorescence and immunoblot.

MAIN OUTCOME MEASURES

Functional responses in RCC, HCC and HPRA and STIM/Orai protein expression in HCC. In vivo erectile responses to CNES.

RESULTS

Inhibition of Orai channels with YM-58483 (20 µM) significantly reduced adrenergic contractions in RCC but more effectively in DM. Thromboxane-induced and neurogenic contractions were reduced by STIM/Orai inhibition while defective endothelial, neurogenic and PDE5 inhibitor-induced relaxations were enhanced by YM-58483 (10 µM) in RCC from DM rats. In vivo, YM-58483 caused erections and attenuated diabetes-related impairment of erectile responses. YM-58483 potentiated the effects of PDE5 inhibition. In human tissues, STIM/Orai inhibition depressed adrenergic and thromboxane-induced contractions in ED patients more effectively in those with type 2 diabetes. Diabetes was associated with increased expression of Orai1 and Orai3 in ED patients.

CLINICAL TRANSLATION

Targeting STIM/Orai to alleviate diabetes-related functional alterations of penile vascular tissue could improve erectile function and potentiate therapeutic effects of PDE5 inhibitors in diabetic ED.

STRENGTHS AND LIMITATIONS

Improving effects of STIM/Orai inhibition on diabetes-related functional impairment was evidenced in vitro and in vivo in an animal model and validated in human tissues from ED patients. Functional findings were complemented with expression results. Main limitation was low numbers of human experiments due to limited human tissue availability.

CONCLUSIONS

STIM/Orai inhibition alleviated alterations of functional responses in vitro and improved erectile responses in vivo in diabetic rats, potentiating the effects of PDE5 inhibition. STIM/Orai inhibition was validated as a target to modulate functional alterations of human penile vascular tissue in diabetic ED where Orai1 and Orai3 channels were upregulated. STIM/Orai inhibition could be a potential therapeutic strategy to overcome poor response to conventional ED therapy in diabetic patients. Sevilleja-Ortiz A, El Assar M, García-Gómez B, et al. STIM/Orai Inhibition as a Strategy for Alleviating Diabetic Erectile Dysfunction Through Modulation of Rat and Human Penile Tissue Contractility and in vivo Potentiation of Erectile Responses. J Sex Med 2022;19:1733-1749.

Ca2+ -activated Cl- channels (TMEM16A) underlie spontaneous electrical activity in isolated mouse corpus cavernosum smooth muscle cells

Penile detumescence is maintained by tonic contraction of corpus cavernosum smooth muscle cells (CCSMC), but the underlying mechanisms have not been fully elucidated. The purpose of this study was to characterize the mechanisms underlying activation of TMEM16A Ca2+ -activated Cl- channels in freshly isolated murine CCSMC. Male C57BL/6 mice aged 10-18 weeks were euthanized via intraperitoneal injection of sodium pentobarbital (100 mg.kg-1 ). Whole-cell patch clamp, pharmacological, and immunocytochemical experiments were performed on isolated CCSM. Tension measurements were performed in whole tissue. TMEM16A expression in murine corpus cavernosum was confirmed using immunocytochemistry. Isolated CCSMC developed spontaneous transient inward currents (STICs) under voltage clamp and spontaneous transient depolarizations (STDs) in current clamp mode of the whole cell, perforated patch clamp technique. STICs reversed close to the predicted Cl- equilibrium potential and both STICs and STDs were blocked by the TMEM16A channel blockers, Ani9 and CaCC(inh)-A01. These events were also blocked by GSK7975A (ORAI inhibitor), cyclopiazonic acid (CPA, sarcoplasmic reticulum [SR] Ca2+- ATPase blocker), tetracaine (RyR blocker), and 2APB (IP3 R blocker), suggesting that they were dependent on Ca2+ release from intracellular Ca2+ stores. Nifedipine (L-type Ca2+ channel blocker) did not affect STICs, but reduced the duration of STDs. Phenylephrine induced transient depolarizations and transient inward currents which were blocked by Ani9. Similarly, phenylephrine induced phasic contractions of intact corpus cavernosum muscle strips and these events were also inhibited by Ani9. This study suggests that contraction of CCSM is regulated by activation of TMEM16A channels and therefore inhibition of these channels could lead to penile erection.

Chronic reduction of store operated Ca2+ entry is viable therapeutically but is associated with cardiovascular complications

Loss of function mutations in store-operated Ca²⁺ entry (SOCE) are associated with severe paediatric disorders in humans, including combined immunodeficiency, anaemia, thrombocytopenia, anhidrosis and muscle hypotonia. Given its central role in immune cell activation, SOCE has been a therapeutic target for autoimmune and inflammatory diseases. Treatment for such chronic diseases would require prolonged SOCE inhibition. It is, however, unclear whether chronic SOCE inhibition is viable therapeutically. Here we address this issue using a novel genetic mouse model (SOCE hypomorph) with deficient SOCE, nuclear factor of activated T cells activation, and T cell cytokine production. SOCE hypomorph mice develop and reproduce normally and do not display muscle weakness or overt anhidrosis. They do, however, develop cardiovascular complications, including hypertension and tachycardia, which we show are due to increased sympathetic autonomic nervous system activity and not cardiac or vascular smooth muscle autonomous defects. These results assert that chronic SOCE inhibition is viable therapeutically if the cardiovascular complications can be managed effectively clinically. They further establish the SOCE hypomorph line as a genetic model to define the therapeutic window of SOCE inhibition and dissect toxicities associated with chronic SOCE inhibition in a tissue-specific fashion. KEY POINTS: A floxed stromal interaction molecule 1 (STIM1) hypomorph mouse model was generated with significant reduction in Ca²⁺ influx through store-operated Ca²⁺ entry (SOCE), resulting in defective nuclear translocation of nuclear factor of activated T cells, cytokine production and inflammatory response. The hypomorph mice are viable and fertile, with no overt defects. Decreased SOCE in the hypomorph mice is due to poor translocation of the mutant STIM1 to endoplasmic reticulum-plasma membrane contact sites resulting in fewer STIM1 puncta. Hypomorph mice have similar susceptibility to controls to develop diabetes but exhibit tachycardia and hypertension. The hypertension is not due to increased vascular smooth muscle contractility or vascular remodelling. The tachycardia is not due to heart-specific defects but rather seems to be due to increased circulating catecholamines in the hypomorph. Therefore, long term SOCE inhibition is viable if the cardiovascular defects can be managed clinically.

Multiphasic changes in smooth muscle Ca2+ transporters during the progression of coronary atherosclerosis

Ischemic heart disease due to macrovascular atherosclerosis and microvascular dysfunction is the major cause of death worldwide and the unabated increase in metabolic syndrome is a major reason why this will continue. Intracellular free Ca²⁺ ([Ca²⁺]_i) regulates a variety of cellular functions including contraction, proliferation, migration, and transcription. It follows that studies of vascular Ca²⁺ regulation in reductionist models and translational animal models are vital to understanding vascular health and disease. Swine with metabolic syndrome (MetS) develop the full range of coronary atherosclerosis from mild to severe disease. Intravascular imaging enables quantitative measurement of atherosclerosis in vivo, so viable coronary smooth muscle (CSM) cells can be dispersed from the arteries to enable Ca²⁺ transport studies in native cells. Transition of CSM from the contractile phenotype in the healthy swine to the proliferative phenotype in mild atherosclerosis was associated with increases in SERCA activity, sarcoplasmic reticulum Ca²⁺, and voltage-gated Ca²⁺ channel function. In vitro organ culture confirmed that SERCA activation induces CSM proliferation. Transition from the proliferative to a more osteogenic phenotype was associated with decreases in all three Ca²⁺ transporters. Overall, there was a biphasic change in Ca²⁺ transporters over the progression of atherosclerosis in the swine model and this was confirmed in CSM from failing explanted hearts of humans. A major determinant of endolysosome content in human CSM is the severity of atherosclerosis. In swine CSM endolysosome Ca²⁺ release occurred through the TPC2 channel. We propose a multiphasic change in Ca²⁺ transporters over the progression of coronary atherosclerosis.

The airway smooth muscle sodium/calcium exchanger NCLX is critical for airway remodeling and hyperresponsiveness in asthma

The structural changes of airway smooth muscle (ASM) that characterize airway remodeling (AR) are crucial to the pathogenesis of asthma. During AR, ASM cells dedifferentiate from a quiescent to a proliferative, migratory, and secretory phenotype. Calcium (Ca²⁺) is a ubiquitous second messenger that regulates many cellular processes, including proliferation, migration, contraction, and metabolism. Furthermore, mitochondria have emerged as major Ca²⁺ signaling organelles that buffer Ca²⁺ through uptake by the mitochondrial Ca²⁺ uniporter and extrude it through the Na⁺/Ca²⁺ exchanger (NCLX/Slc8b1). Here, we show using mitochondrial Ca²⁺-sensitive dyes that NCLX only partially contributes to mitochondrial Ca²⁺ extrusion in ASM cells. Yet, NCLX is necessary for ASM cell proliferation and migration. Through cellular imaging, RNA-Seq, and biochemical assays, we demonstrate that NCLX regulates these processes by preventing mitochondrial Ca²⁺ overload and supporting store-operated Ca²⁺ entry, activation of Ca²⁺/calmodulin-dependent kinase II, and transcriptional and metabolic reprogramming. Using small animal respiratory mechanic measurements and immunohistochemistry, we show that smooth muscle-specific NCLX KO mice are protected against AR, fibrosis, and hyperresponsiveness in an experimental model of asthma. Our findings support NCLX as a potential therapeutic target in the treatment of asthma.

Basal Vascular Smooth Muscle Cell Tone in eNOS Knockout Mice Can Be Reversed by Cyclic Stretch and Is Independent of Age

Introduction and Aims: Endothelial nitric oxide synthase (eNOS) knockout mice develop pronounced cardiovascular disease. In the present study, we describe the alterations in aortic physiology and biomechanics of eNOS knockout and C57Bl/6 control mice at 2–12 months of age, including a thorough physiological investigation of age and cyclic stretch-dependent VSMC contractility and aortic stiffness.

Methods and Results: Peripheral blood pressure and aortic pulse wave velocity were measured in vivo, and aortic biomechanical studies and isometric contractions were investigated ex vivo. Age-dependent progression of aortic stiffness, peripheral hypertension, and aortic contractility in eNOS knockout mice was absent, attenuated, or similar to C57Bl/6 control mice. Voltage-gated calcium channel (VGCC)-dependent calcium influx inversely affected isometric contraction and aortic stiffening by α₁-adrenergic stimulation in eNOS knockout mice. Baseline aortic stiffness was selectively reduced in eNOS knockout mice after ex vivo cyclic stretch exposure in an amplitude-dependent manner, which prompted us to investigate cyclic stretch dependent regulation of aortic contractility and stiffness. Aortic stiffness, both in baseline conditions and after activation of vascular smooth muscle cell (VSMC) contraction, was reduced with increasing cyclic stretch amplitude. This cyclic stretch dependency was attenuated with age, although aged eNOS knockout mice displayed better preservation of cyclic stretch-dependency compared to C57Bl/6 control mice. Store operated calcium entry-medicated aortic stiffening as induced by inhibiting sarcoplasmic reticulum calcium ATPase pumps with 10 µM CPA was most pronounced in the aorta of aged mice and at low cyclic stretch amplitude, but independent of eNOS. Basal aortic tonus and VSMC depolarization were highly dependent on eNOS, and were most pronounced at low cyclic stretch, with attenuation at increasing cyclic stretch amplitude.

Conclusion: eNOS knockout mice display attenuated progression of arterial disease as compared to C57Bl/6 control mice. Basal VSMC tone in eNOS knockout mice could be reduced by ex vivo exposure to cyclic stretch through stretch-dependent regulation of cytosolic calcium. Both baseline and active aortic stiffness were highly dependent on cyclic stretch regulation, which was more pronounced in young versus aged mice. Other mediators of VSMC contraction and calcium handling were dependent on cyclic stretch mechanotransduction, but independent of eNOS.

STIMulating blood pressure

The protein STIM1 helps to maintain membrane coupling sites in smooth muscle cells that regulate arterial contractility and blood pressure.

Mitofusin-2 Negatively Regulates Melanogenesis by Modulating Mitochondrial ROS Generation

Inter-organellar communication is emerging as one of the most crucial regulators of cellular physiology. One of the key regulators of inter-organellar communication is Mitofusin-2 (MFN2). MFN2 is also involved in mediating mitochondrial fusion–fission dynamics. Further, it facilitates mitochondrial crosstalk with the endoplasmic reticulum, lysosomes and melanosomes, which are lysosome-related organelles specialized in melanin synthesis within melanocytes. However, the role of MFN2 in regulating melanocyte-specific cellular function, i.e., melanogenesis, remains poorly understood. Here, using a B16 mouse melanoma cell line and primary human melanocytes, we report that MFN2 negatively regulates melanogenesis. Both the transient and stable knockdown of MFN2 leads to enhanced melanogenesis, which is associated with an increase in the number of mature (stage III and IV) melanosomes and the augmented expression of key melanogenic enzymes. Further, the ectopic expression of MFN2 in MFN2-silenced cells leads to the complete rescue of the phenotype at the cellular and molecular levels. Mechanistically, MFN2-silencing elevates mitochondrial reactive-oxygen-species (ROS) levels which in turn increases melanogenesis. ROS quenching with the antioxidant N-acetyl cysteine (NAC) reverses the MFN2-knockdown-mediated increase in melanogenesis. Moreover, MFN2 expression is significantly lower in the darkly pigmented primary human melanocytes in comparison to lightly pigmented melanocytes, highlighting a potential contribution of lower MFN2 levels to higher physiological pigmentation. Taken together, our work establishes MFN2 as a novel negative regulator of melanogenesis.

STIM1-dependent peripheral coupling governs the contractility of vascular smooth muscle cells

Peripheral coupling between the sarcoplasmic reticulum (SR) and plasma membrane (PM) forms signaling complexes that regulate the membrane potential and contractility of vascular smooth muscle cells (VSMCs). The mechanisms responsible for these membrane interactions are poorly understood. In many cells, STIM1 (stromal interaction molecule 1), a single-transmembrane-domain protein that resides in the endoplasmic reticulum (ER), transiently moves to ER-PM junctions in response to depletion of ER Ca²⁺ stores and initiates store-operated Ca²⁺ entry (SOCE). Fully differentiated VSMCs express STIM1 but exhibit only marginal SOCE activity. We hypothesized that STIM1 is constitutively active in contractile VSMCs and maintains peripheral coupling. In support of this concept, we found that the number and size of SR-PM interacting sites were decreased, and SR-dependent Ca²⁺-signaling processes were disrupted in freshly isolated cerebral artery SMCs from tamoxifen-inducible, SMC-specific STIM1-knockout (Stim1-smKO) mice. VSMCs from Stim1-smKO mice also exhibited a reduction in nanoscale colocalization between Ca²⁺-release sites on the SR and Ca²⁺-activated ion channels on the PM, accompanied by diminished channel activity. Stim1-smKO mice were hypotensive, and resistance arteries isolated from them displayed blunted contractility. These data suggest that STIM1 – independent of SR Ca²⁺ store depletion – is critically important for stable peripheral coupling in contractile VSMCs.

Physiological Functions of CRAC Channels

Store-operated Ca2+ entry (SOCE) is a ubiquitous Ca2+ signaling pathway that is evolutionarily conserved across eukaryotes. SOCE is triggered physiologically when the endoplasmic reticulum (ER) Ca2+ stores are emptied through activation of inositol 1,4,5-trisphosphate receptors. SOCE is mediated by the Ca2+ release-activated Ca2+ (CRAC) channels, which are highly Ca2+ selective. Upon store depletion, the ER Ca2+-sensing STIM proteins aggregate and gain extended conformations spanning the ER-plasma membrane junctional space to bind and activate Orai, the pore-forming proteins of hexameric CRAC channels. In recent years, studies on STIM and Orai tissue-specific knockout mice and gain- and loss-of-function mutations in humans have shed light on the physiological functions of SOCE in various tissues. Here, we describe recent findings on the composition of native CRAC channels and their physiological functions in immune, muscle, secretory, and neuronal systems to draw lessons from transgenic mice and human diseases caused by altered CRAC channel activity.

STIM1 is a core trigger of airway smooth muscle remodeling and hyperresponsiveness in asthma

Airway remodeling and airway hyperresponsiveness are central drivers of asthma severity. Airway remodeling is a structural change involving the dedifferentiation of airway smooth muscle (ASM) cells from a quiescent to a proliferative and secretory phenotype. Here, we show up-regulation of the endoplasmic reticulum Ca2+ sensor stromal-interacting molecule 1 (STIM1) in ASM of asthmatic mice. STIM1 is required for metabolic and transcriptional reprogramming that supports airway remodeling, including ASM proliferation, migration, secretion of cytokines and extracellular matrix, enhanced mitochondrial mass, and increased oxidative phosphorylation and glycolytic flux. Mechanistically, STIM1-mediated Ca2+ influx is critical for the activation of nuclear factor of activated T cells 4 and subsequent interleukin-6 secretion and transcription of pro-remodeling transcription factors, growth factors, surface receptors, and asthma-associated proteins. STIM1 drives airway hyperresponsiveness in asthmatic mice through enhanced frequency and amplitude of ASM cytosolic Ca2+ oscillations. Our data advocates for ASM STIM1 as a target for asthma therapy.

Cross-Talk between Mechanosensitive Ion Channels and Calcium Regulatory Proteins in Cardiovascular Health and Disease

Mechanosensitive ion channels are widely expressed in the cardiovascular system. They translate mechanical forces including shear stress and stretch into biological signals. The most prominent biological signal through which the cardiovascular physiological activity is initiated or maintained are intracellular calcium ions (Ca²⁺). Growing evidence show that the Ca²⁺ entry mediated by mechanosensitive ion channels is also precisely regulated by a variety of key proteins which are distributed in the cell membrane or endoplasmic reticulum. Recent studies have revealed that mechanosensitive ion channels can even physically interact with Ca²⁺ regulatory proteins and these interactions have wide implications for physiology and pathophysiology. Therefore, this paper reviews the cross-talk between mechanosensitive ion channels and some key Ca²⁺ regulatory proteins in the maintenance of calcium homeostasis and its relevance to cardiovascular health and disease.

Ameliorated biomechanical properties of carotid arteries by puerarin in spontaneously hypertensive rats

BACKGROUND

An emerging body of evidence indicates that puerarin (PUE) plays an important role in the treatment of angina pectoris, myocardial ischemia-reperfusion injury, hypertension and other cardiovascular diseases, but how PUE affects the vascular remodeling of hypertensive rats has not been reported yet. This study aimed to investigate the effect and mechanism of PUE on carotid arteries of spontaneously hypertensive rats (SHR) to provide the basis for the clinical application of PUE.

METHODS

Thirty male SHR and six male Wistar Kyoto rats (WKY) aged 3 months were used in this study, SHR rats were randomly divided into 5 groups, PUE(40 or 80 mg/kg/d, ip) and telmisartan (TELMI) (30 mg/kg/d, ig) were administrated for 3 months. We use DMT myography pressure-diameter system to investigate biomechanical properties of carotid arteries, 10 μM pan-classical transient receptor potential channels (TRPCs) inhibitor SKF96365, 200 nM specific TRPC6 inhibitor SAR7334 and 100 μM Orai1 inhibitor ANCOA4 were used in the mechanical test.

RESULTS

PUE can significantly decrease systolic and diastolic blood pressure, long-term administration of PUE resulted in a mild reduction of thickness and inner diameter of carotid artery. PUE ameliorate NE-response and vascular remodeling mainly through inhibiting TRPCs channel activities of VSMC.

CONCLUSION

PUE can ameliorate biomechanical remodeling of carotid arteries through inhibiting TRPCs channel activities of VSMC in spontaneously hypertensive rats.

ORAI1 Ca2+ Channel as a Therapeutic Target in Pathological Vascular Remodelling

In the adult, vascular smooth muscle cells (VSMC) are normally physiologically quiescent, arranged circumferentially in one or more layers within blood vessel walls. Remodelling of native VSMC to a proliferative state for vascular development, adaptation or repair is driven by platelet-derived growth factor (PDGF). A key effector downstream of PDGF receptors is store-operated calcium entry (SOCE) mediated through the plasma membrane calcium ion channel, ORAI1, which is activated by the endoplasmic reticulum (ER) calcium store sensor, stromal interaction molecule-1 (STIM1). This SOCE was shown to play fundamental roles in the pathological remodelling of VSMC. Exciting transgenic lineage-tracing studies have revealed that the contribution of the phenotypically-modulated VSMC in atherosclerotic plaque formation is more significant than previously appreciated, and growing evidence supports the relevance of ORAI1 signalling in this pathologic remodelling. ORAI1 has also emerged as an attractive potential therapeutic target as it is accessible to extracellular compound inhibition. This is further supported by the progression of several ORAI1 inhibitors into clinical trials. Here we discuss the current knowledge of ORAI1-mediated signalling in pathologic vascular remodelling, particularly in the settings of atherosclerotic cardiovascular diseases (CVDs) and neointimal hyperplasia, and the recent developments in our understanding of the mechanisms by which ORAI1 coordinates VSMC phenotypic remodelling, through the activation of key transcription factor, nuclear factor of activated T-cell (NFAT). In addition, we discuss advances in therapeutic strategies aimed at the ORAI1 target.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

More Than Just Simple Interaction between STIM and Orai Proteins: CRAC Channel Function Enabled by a Network of Interactions with Regulatory Proteins

The calcium-release-activated calcium (CRAC) channel, activated by the release of Ca2+ from the endoplasmic reticulum (ER), is critical for Ca2+ homeostasis and active signal transduction in a plethora of cell types. Spurred by the long-sought decryption of the molecular nature of the CRAC channel, considerable scientific effort has been devoted to gaining insights into functional and structural mechanisms underlying this signalling cascade. Key players in CRAC channel function are the Stromal interaction molecule 1 (STIM1) and Orai1. STIM1 proteins span through the membrane of the ER, are competent in sensing luminal Ca2+ concentration, and in turn, are responsible for relaying the signal of Ca2+ store-depletion to pore-forming Orai1 proteins in the plasma membrane. A direct interaction of STIM1 and Orai1 allows for the re-entry of Ca2+ from the extracellular space. Although much is already known about the structure, function, and interaction of STIM1 and Orai1, there is growing evidence that CRAC under physiological conditions is dependent on additional proteins to function properly. Several auxiliary proteins have been shown to regulate CRAC channel activity by means of direct interactions with STIM1 and/or Orai1, promoting or hindering Ca2+ influx in a mechanistically diverse manner. Various proteins have also been identified to exert a modulatory role on the CRAC signalling cascade although inherently lacking an affinity for both STIM1 and Orai1. Apart from ubiquitously expressed representatives, a subset of such regulatory mechanisms seems to allow for a cell-type-specific control of CRAC channel function, considering the rather restricted expression patterns of the specific proteins. Given the high functional and clinical relevance of both generic and cell-type-specific interacting networks, the following review shall provide a comprehensive summary of regulators of the multilayered CRAC channel signalling cascade. It also includes proteins expressed in a narrow spectrum of cells and tissues that are often disregarded in other reviews of similar topics.

Long Non-coding RNA PEBP1P2 Suppresses Proliferative VSMCs Phenotypic Switching and Proliferation in Atherosclerosis

Long non-coding RNAs (lncRNAs) play a crucial role in the growth of vascular smooth muscle cells (VSMCs), the dysfunction of which is closely associated with the initiation and progression of cardiovascular diseases (CVDs). Abnormal phenotypic switching and proliferation of VSMCs constitute a significant event in the progression of atherosclerosis. The present study identified a novel lncRNA, PEBP1P2, which serves as a valuable regulator of VSMCs in phenotypic transformation and proliferation. The expression of PEBP1P2 was remarkably decreased in proliferating VSMCs and pathological arteries when using a balloon injury model of rats. Furthermore, we found that PEBP1P2 represses proliferation, migration, and dedifferentiation during phenotype switching in VSMCs induced by platelet-derived growth factor BB (PDGF-BB). Mechanistically, cyclin-dependent kinase 9 (CDK9) was confirmed to be the direct target of PEBP1P2, which was proven to mediate phenotypic switching and proliferation of VSMCs and was rescued by PEBP1P2. Then, we explored the clinical significance, as we observed the decreased expression of PEBP1P2 in the serum of coronary heart disease (CHD) patients and human advanced carotid atherosclerotic plaques. Finally, PEBP1P2 overexpression distinctly suppressed neointima formation and VSMC phenotypic switching in vivo. Taken together, PEBP1P2 inhibits proliferation and migration in VSMCs by directly binding to CDK9, implying that it may be a promising therapeutic target for the treatment of proliferative vascular diseases.

L-type Ca2+ channel blockers promote vascular remodeling through activation of STIM proteins

Voltage-gated L-type Ca2+ channel (Cav1.2) blockers (LCCBs) are major drugs for treating hypertension, the preeminent risk factor for heart failure. Vascular smooth muscle cell (VSMC) remodeling is a pathological hallmark of chronic hypertension. VSMC remodeling is characterized by molecular rewiring of the cellular Ca2+ signaling machinery, including down-regulation of Cav1.2 channels and up-regulation of the endoplasmic reticulum (ER) stromal-interacting molecule (STIM) Ca2+ sensor proteins and the plasma membrane ORAI Ca2+ channels. STIM/ORAI proteins mediate store-operated Ca2+ entry (SOCE) and drive fibro-proliferative gene programs during cardiovascular remodeling. SOCE is activated by agonists that induce depletion of ER Ca2+, causing STIM to activate ORAI. Here, we show that the three major classes of LCCBs activate STIM/ORAI-mediated Ca2+ entry in VSMCs. LCCBs act on the STIM N terminus to cause STIM relocalization to junctions and subsequent ORAI activation in a Cav1.2-independent and store depletion-independent manner. LCCB-induced promotion of VSMC remodeling requires STIM1, which is up-regulated in VSMCs from hypertensive rats. Epidemiology showed that LCCBs are more associated with heart failure than other antihypertensive drugs in patients. Our findings unravel a mechanism of LCCBs action on Ca2+ signaling and demonstrate that LCCBs promote vascular remodeling through STIM-mediated activation of ORAI. Our data indicate caution against the use of LCCBs in elderly patients or patients with advanced hypertension and/or onset of cardiovascular remodeling, where levels of STIM and ORAI are elevated.

Abnormal Ca2+ handling contributes to the impairment of aortic smooth muscle contractility in Zucker diabetic fatty rats

Vascular dysfunction is a common pathological basis for complications in individuals affected by diabetes. Previous studies have established that endothelial dysfunction is the primary contributor to vascular complications in type 2 diabetes (T2DM). However, the role of vascular smooth muscle cells (VSMCs) in vascular complications associated with T2DM is still not completely understood. The aim of this study is to explore the potential mechanisms associated with Ca²⁺ handling dysfunction and how this dysfunction contributes to diabetic vascular smooth muscle impairment. The results indicated that endothelium-dependent vasodilation was impaired in diabetic aortae, but endothelium-independent vasodilation was not altered. Various vasoconstrictors such as phenylephrine, U46619 and 5-HT could induce vasoconstriction in a concentration-dependent manner, such that the dose-response curve was parallel shifted to the right in diabetic aortae, compared to the control. Vasoconstrictions mediated by L-type calcium (Cav1.2) channels were attenuated in diabetic aortae, but effects mediated by store-operated calcium (SOC) channels were enhanced. Intracellular Ca²⁺ concentration ([Ca²⁺]_i) in VSMCs was detected by Fluo-4 calcium fluorescent probes, and demonstrated that SOC-mediated Ca²⁺ entry was increased in diabetic VSMCs. VSMC-specific knockout of STIM1 genes decreased SOC-mediated and phenylephrine-induced vasoconstrictive response in mice aortae. Additionally, Orai1 expression was up-regulated, Cav1.2 expression was downregulated, and the phenotypic transformation of diabetic VSMCs was determined in diabetic aortae. The overexpression of Orai1 markedly promoted the OPN expression of VSMCs, whereas SKF96365 (SOC channel blocker) reversed the phenotypic transformation of diabetic VSMCs. Our results demonstrated that the vasoconstriction response of aortic smooth muscle was weakened in type 2 diabetic rats, which was related to the downregulation of the Cav1.2 channel and the up-regulation of the SOC channel signaling pathway.

Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

A new selective pharmacological enhancer of the Orai1 Ca2+ channel reveals roles for Orai1 in smooth and skeletal muscle functions

Store operated calcium (Ca²⁺) entry is an important homeostatic mechanism in cells, whereby the release of Ca²⁺ from intracellular endoplasmic reticulum stores triggers the activation of a Ca²⁺ influx pathway. Mediated by Orai1, this Ca²⁺ influx has specific and essential roles in biological processes as diverse as lactation to immunity. Although pharmacological inhibitors of this Ca²⁺ influx mechanism have helped to define the role of store operated Ca²⁺ entry in many cellular events, the lack of isoform specific modulators and activators of Orai1 has limited our full understanding of these processes. Here we report the identification and synthesis of an Orai1 activity enhancer that concurrently potentiated Orai1 Ca²⁺ -dependent inactivation (CDI). This unique enhancer of Orai1 had only a modest effect on Orai3 with weak inhibitory effects at high concentrations in intact MCF-7 breast cancer cells. The Orai1 enhancer heightened vascular smooth muscle cell migration induced by platelet-derived growth factor and the unique store operated Ca²⁺ entry pathway present in skeletal muscle cells. These studies show that IA65 is an exemplar for the translation and development of Orai isoform selective agents. The ability of IA65 to activate CDI demonstrates that agents can be developed that can enhance Orai1-mediated Ca²⁺ influx but avoid the cytotoxicity associated with sustained Orai1 activation. IA65 and/or future analogues with similar Orai1 and CDI activating properties could be fine tuners of physiological processes important in specific disease states, such as cellular migration and immune cell function.

Pathophysiological Significance of Store-Operated Calcium Entry in Cardiovascular and Skeletal Muscle Disorders and Angiogenesis

Store-Operated Ca²⁺ Entry (SOCE) is an important Ca²⁺ influx pathway expressed by several excitable and non-excitable cell types. SOCE is recognized as relevant signaling pathway not only for physiological process, but also for its involvement in different pathologies. In fact, independent studies demonstrated the implication of essential protein regulating SOCE, such as STIM, Orai and TRPCs, in different pathogenesis and cell disorders, including cardiovascular disease, muscular dystrophies and angiogenesis. Compelling evidence showed that dysregulation in the function and/or expression of isoforms of STIM, Orai or TRPC play pivotal roles in cardiac hypertrophy and heart failure, vascular remodeling and hypertension, skeletal myopathies, and angiogenesis. In this chapter, we summarized the current knowledge concerning the mechanisms underlying abnormal SOCE and its involvement in some diseases, as well as, we discussed the significance of STIM, Orai and TRPC isoforms as possible therapeutic targets for the treatment of angiogenesis, cardiovascular and skeletal muscle diseases.

Phosphate-induced ORAI1 expression and store-operated Ca2+ entry in aortic smooth muscle cells

Compromised renal phosphate elimination in chronic kidney disease (CKD) leads to hyperphosphatemia, which in turn triggers osteo-/chondrogenic signaling in vascular smooth muscle cells (VSMCs) and vascular calcification. Osteo-/chondrogenic transdifferentiation of VSMCs leads to upregulation of the transcription factors MSX2, CBFA1, and SOX9 as well as tissue-nonspecific alkaline phosphatase (ALPL) which fosters calcification by degrading the calcification inhibitor pyrophosphate. Osteo-/chondrogenic signaling in VSMCs involves the serum- and glucocorticoid-inducible kinase SGK1. As shown in other cell types, SGK1 is a powerful stimulator of ORAI1, a Ca²⁺-channel accomplishing store-operated Ca²⁺-entry (SOCE). ORAI1 is stimulated following intracellular store depletion by the Ca²⁺ sensor STIM1. The present study explored whether phosphate regulates ORAI1 and/or STIM1 expression and, thus, SOCE in VSMCs. To this end, primary human aortic smooth muscle cells (HAoSMCs) were exposed to the phosphate donor β-glycerophosphate. Transcript levels were estimated by qRT-PCR, protein abundance by western blotting, ALPL activity by colorimetry, calcification by alizarin red S staining, cytosolic Ca²⁺-concentration ([Ca²⁺]_i) by Fura-2-fluorescence, and SOCE from increase of [Ca²⁺]_i following re-addition of extracellular Ca²⁺ after store depletion with thapsigargin. As a result, β-glycerophosphate treatment increased ORAI1 and STIM1 transcript levels and protein abundance as well as SOCE in HAoSMCs. Additional treatment with ORAI1 inhibitor MRS1845 or SGK1 inhibitor GSK650394 virtually disrupted the effects of β-glycerophosphate on SOCE. Moreover, the β-glycerophosphate-induced MSX2, CBFA1, SOX9, and ALPL mRNA expression and activity in HAoSMCs were suppressed in the presence of the ORAI1 inhibitor and upon ORAI1 silencing. In conclusion, enhanced phosphate upregulates ORAI1 and STIM1 expression and store-operated Ca²⁺-entry, which participate in the orchestration of osteo-/chondrogenic signaling of VSMCs. KEY MESSAGES: • In aortic SMC, phosphate donor ß-glycerophosphate upregulates Ca²⁺ channel ORAI1. • In aortic SMC, ß-glycerophosphate upregulates ORAI1-activator STIM1. • In aortic SMC, ß-glycerophosphate upregulates store-operated Ca²⁺-entry (SOCE). • The effect of ß-glycerophosphate on SOCE is disrupted by ORAI1 inhibitor MRS1845. • Stimulation of osteogenic signaling is disrupted by MRS1845 and ORAI1 silencing.

Soluble adenylyl cyclase links Ca2+ entry to Ca2+/cAMP-response element binding protein (CREB) activation in vascular smooth muscle

Ca²⁺-transcription coupling controls gene expression patterns that define vascular smooth muscle cell (VSMC) phenotype. Although not well understood this allows normally contractile VSMCs to become proliferative following vessel injury, a process essential for repair but which also contributes to vascular remodelling, atherogenesis and restenosis. Here we show that the Ca²⁺/HCO₃^--sensitive enzyme, soluble adenylyl cyclase (sAC), links Ca²⁺ influx in human coronary artery smooth muscle cells (hCASMCs) to 3',5'-cyclic adenosine monophosphate (cAMP) generation and phosphorylation of the transcription factor Ca²⁺/cAMP response element binding protein (CREB). Store-operated Ca²⁺ entry (SOCE) into hCASMCs expressing the FRET-based cAMP biosensor H187 induced a rise in cAMP that mirrored cytosolic [Ca²⁺]. SOCE also activated the cAMP effector, protein kinase A (PKA), as determined by the PKA reporter, AKAR4-NES, and induced phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and CREB. Transmembrane adenylyl cyclase inhibition had no effect on the SOCE-induced rise in cAMP, while sAC inhibition abolished SOCE-generated cAMP and significantly reduced SOCE-induced VASP and CREB phosphorylation. This suggests that SOCE in hCASMCs activates sAC which in turn activates the cAMP/PKA/CREB axis. sAC, which is insensitive to G-protein modulation but responsive to Ca²⁺, pH and ATP, may therefore act as an overlooked regulatory node in vascular Ca²⁺-transcription coupling.

A calcium/cAMP signaling loop at the ORAI1 mouth drives channel inactivation to shape NFAT induction

ORAI1 constitutes the store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel crucial for life. Whereas ORAI1 activation by Ca²⁺-sensing STIM proteins is known, still obscure is how ORAI1 is turned off through Ca²⁺-dependent inactivation (CDI), protecting against Ca²⁺ toxicity. Here we identify a spatially-restricted Ca²⁺/cAMP signaling crosstalk critical for mediating CDI. Binding of Ca²⁺-activated adenylyl cyclase 8 (AC8) to the N-terminus of ORAI1 positions AC8 near the mouth of ORAI1 for sensing Ca²⁺. Ca²⁺ permeating ORAI1 activates AC8 to generate cAMP and activate PKA. PKA, positioned by AKAP79 near ORAI1, phosphorylates serine-34 in ORAI1 pore extension to induce CDI whereas recruitment of the phosphatase calcineurin antagonizes the effect of PKA. Notably, CDI shapes ORAI1 cytosolic Ca²⁺ signature to determine the isoform and degree of NFAT activation. Thus, we uncover a mechanism of ORAI1 inactivation, and reveal a hitherto unappreciated role for inactivation in shaping cellular Ca²⁺ signals and NFAT activation.

ORAI1 constitutes the store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel, but how this channel is turned off through Ca²⁺-dependent inactivation (CDI) remained unclear. Here the authors identify a spatially-restricted Ca²⁺/cAMP signaling crosstalk critical for mediating CDI which in turn regulates cellular Ca²⁺ signals and NFAT activation.

LncRNA analysis of lung tissues after hUC-MSCs and FTY720 treatment of lipopolysaccharide-induced acute lung injury in mouse models

Acute lung injury (ALI), a persistent lung inflammatory response syndrome, may evolve into acute respiratory distress syndrome (ARDS). Characterized by rapid onset, critical features, and a complex etiology, ALI remains a challenging critical respiratory disease. Recently, mesenchymal stem cells (MSCs) have provided a new solution for the treatment of ALI. We built a lipopolysaccharide (LPS)-induced ALI model in mice. After treatment with human umbilical cord mesenchymal stem cells (hUC-MSCs), FTY720, or a combination of hUC-MSCs and FTY207, the lung inflammatory response was apparently attenuated. To understand the mechanism underlying MSCs treatment of ALI at the genetic level, significant differentially expressed long non-coding RNAs (lncRNAs) between the treatment and model groups were analyzed using microarray technology. Moreover, genetic gene prediction, gene ontology (GO) analysis, pathway analysis, and transcription factor (TF) prediction were carried out. The results showed that a total of 66 lncRNAs were differentially expressed in all three treatment groups, including 8 up-regulated and 58 down-regulated lncRNAs. LncRNA A_30_P01029806 and A_30_P01029194, which were down-regulated, were involved in the signaling pathways closely related to ALI. Through further TF analysis, we identified several significant TFs which lay a foundation for revealing the mechanism underlying lncRNAs treatment of ALI. LncRNA A_30_P01029806 and A_30_P01029194 may serve as candidate biomarkers in the diagnosis and treatment of ALI.

ORAI channels in cellular remodeling of cardiorespiratory disease

Cardiorespiratory disease, which includes systemic arterial hypertension, restenosis, atherosclerosis, pulmonary arterial hypertension, asthma, and chronic obstructive pulmonary disease (COPD) are highly prevalent and devastating diseases with limited therapeutic modalities. A common pathophysiological theme to these diseases is cellular remodeling, which is contributed by changes in expression and activation of ion channels critical for either excitability or growth. Calcium (Ca²⁺) signaling and specifically ORAI Ca²⁺ channels have emerged as significant regulators of smooth muscle, endothelial, epithelial, platelet, and immune cell remodeling. This review details the dysregulation of ORAI in cardiorespiratory diseases, and how this dysregulation of ORAI contributes to cellular remodeling.

Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction

Protease activated receptor 2 (PAR2) is a G-protein coupled receptor that contributes to prostate fibrosis and lower urinary tract symptoms (LUTS). In addition to fibrosis, aberrant smooth muscle tone in the prostate has been hypothesized to play a role. We therefore examined PAR2 expression in primary human prostate smooth muscle cells (PSMC) and studied the downstream signaling effects of PAR2 activation. Signaling pathways involved in the process were assessed using the PAR2 activating peptide SLIGKV-NH2. We show that PAR2 is expressed in PSMC and that PAR2 activation mediates a biphasic elevation in intracellular Ca²⁺ and phosphorylation of myosin light chain 20 (MLC20), causing cellular contraction as assessed in a gel contraction assay. Intracellular Ca²⁺ flux was inhibited by a phosphoinositide hydrolysis inhibitor, U73122, showing a requirement for phospholipase C β (PLCβ) activation. PSMC expressed mRNA for L-type voltage dependent Ca²⁺ channels (VDCC) as well as Ca²⁺ release activated channels (CRAC), a hitherto unreported finding. Secondary intracellular Ca²⁺ oscillations were abrogated only by BTP2, the CRAC channel inhibitor, but not by nifedipine, an inhibitor of VDCC. These data suggest that, PAR2 activation and subsequent Ca²⁺ entry through CRAC channels are important mechanisms in prostate smooth muscle contraction.

Kv channels and vascular smooth muscle cell proliferation

Kv channels are present in virtually all VSMCs and strongly influence contractile responses. However, they are also instrumental in the proliferative, migratory, and secretory functions of synthetic, dedifferentiated VSMCs upon PM. In fact, Kv channels not only contribute to all these processes but also are active players in the phenotypic switch itself. This review is focused on the role(s) of Kv channels in VSMC proliferation, which is one of the best characterized functions of dedifferentiated VSMCs. VSMC proliferation is a complex process requiring specific Kv channels at specific time and locations. Their identification is further complicated by their large diversity and the differences in expression across vascular beds. Of interest, both conserved changes in some Kv channels and vascular bed-specific regulation of others seem to coexist and participate in VSMC proliferation through complementary mechanisms. Such a system will add flexibility to the process while providing the required robustness to preserve this fundamental cellular response.

Study of the Endogenous CRAC Channel Using shRNA-Mediated Gene Silencing

The Ca²⁺ release-activated Ca²⁺ (CRAC) current is a major signaling event in non-excitable cells whereby Ca²⁺ store depletion activates Ca²⁺ entry across the plasma membrane from the extracellular space. Stromal interaction molecule 1 (STIM1) and Orai1 proteins are the key molecular players of the CRAC channel. Previous studies have linked activity of this channel to many physiological functions, and dysregulation of the CRAC channel has been associated with various diseases. In the absence of inducible tissue-specific knockout mice, in vivo knockdown studies examining the endogenous function of CRAC channel proteins, STIM1 and Orai1, are a challenge. In this chapter, we describe a lentiviral delivery system of shRNA-mediated gene silencing that has proven successful in studying the endogenous CRAC channel in vivo.

ORAI Calcium Channels

In this review article, we discuss the different gene products and translational variants of ORAI proteins and their contribution to the makeup of different native calcium-conducting channels with distinct compositions and modes of activation. We also review the different modes of regulation of these distinct calcium channels and their impact on downstream cellular signaling controlling important physiological functions.

Molecular Determinants for STIM1 Activation During Store- Operated Ca2+ Entry

BACKGROUND

STIM/ORAI-mediated store-operated Ca2+ entry (SOCE) mediates a myriad of Ca2+-dependent cellular activities in mammals. Genetic defects in STIM1/ORAI1 lead to devastating severe combined immunodeficiency; whereas gain-offunction mutations in STIM1/ORAI1 are intimately associated with tubular aggregate myopathy. At molecular level, a decrease in the Ca2+ concentrations within the lumen of endoplasmic reticulum (ER) initiates multimerization of the STIM1 luminal domain to switch on the STIM1 cytoplasmic domain to engage and gate ORAI channels, thereby leading to the ultimate Ca2+ influx from the extracellular space into the cytosol. Despite tremendous progress made in dissecting functional STIM1-ORAI1 coupling, the activation mechanism of SOCE remains to be fully characterized.

OBJECTIVE AND METHODS

Building upon a robust fluorescence resonance energy transfer assay designed to monitor STIM1 intramolecular autoinhibition, we aimed to systematically dissect the molecular determinants required for the activation and oligomerization of STIM1.

RESULTS

Here we showed that truncation of the STIM1 luminal domain predisposes STIM1 to adopt a more active conformation. Replacement of the single transmembrane (TM) domain of STIM1 by a more rigid dimerized TM domain of glycophorin A abolished STIM1 activation. But this adverse effect could be partially reversed by disrupting the TM dimerization interface. Moreover, our study revealed regions that are important for the optimal assembly of hetero-oligomers composed of full-length STIM1 with its minimal STIM1-ORAI activating region, SOAR.

CONCLUSIONS

Our study clarifies the roles of major STIM1 functional domains in maintaining a quiescent configuration of STIM1 to prevent preactivation of SOCE.

Essential role for smooth muscle cell stromal interaction molecule-1 in myocardial infarction

OBJECTIVES

Stromal interacting molecule-1 (STIM1) plays a role in coordinating calcium signaling in different cell types. The increase or deletion of STIM1 expression in cardiomyocyte causes cardiac complication. Moreover, the deletion of STIM1 in endothelial cell causes vascular endothelial dysfunction. However, the disruption of STIM1 in smooth muscle cells (SMC) has no effect on endothelial function but protects vascular function when mice are infused with angiotensin-II. Nevertheless, the role of SMC-STIM1 in acute and chronic myocardial infarction (MI) induced by acute ischemia-reperfusion injury and permanent coronary artery occlusion is unknown.

METHODS AND RESULTS

Stim1 were generated and crossed into the SM22α-Cre backgrounds. SM22α-Cre causes deletion of STIM1 floxed genes in adult SMC (Stim1). Control and Stim1 mice were subjected to acute ischemia-reperfusion injury. Hearts were then harvested and incubated with triphenyltetrazolium chloride to determine the infarct size. In control mice which are subjected to ischemia-reperfusion, the heart developed a significant infarct associated with an increase in STIM1 expression. Interestingly, the infarct size was substantially reduced in Stim1 mice. The protection in Stim1 mice against ischemia-reperfusion injury involves the modulation of endoplasmic reticulum stress, apoptosis, oxidative stress, protein kinase B, and mitogen-activated protein (MAP) kinase (ERK1/2 and p38) signaling, and inflammation. Furthermore, in another model of chronic MI induced by permanent coronary artery occlusion, SMC-STIM1 disruption significantly reduced myocardial infarct size and improved cardiac function.

CONCLUSION

Our results provide new evidence that SMC-STIM1 disruption is a novel mechanism that protects the heart from MI through reduction of endoplasmic reticulum stress, oxidative stress, MAP-Kinase, apoptosis, and inflammation.

On the Role of Store-Operated Calcium Entry in Acute and Chronic Neurodegenerative Diseases

In both excitable and non-excitable cells, calcium (Ca²⁺) signals are maintained by a highly integrated process involving store-operated Ca²⁺ entry (SOCE), namely the opening of plasma membrane (PM) Ca²⁺ channels following the release of Ca²⁺ from intracellular stores. Upon depletion of Ca²⁺ store, the stromal interaction molecule (STIM) senses Ca²⁺ level reduction and migrates from endoplasmic reticulum (ER)-like sites to the PM where it activates the channel proteins Orai and/or the transient receptor potential channels (TRPC) prompting Ca²⁺ refilling. Accumulating evidence suggests that SOCE dysregulation may trigger perturbation of intracellular Ca²⁺ signaling in neurons, glia or hematopoietic cells, thus participating to the pathogenesis of diverse neurodegenerative diseases. Under acute conditions, such as ischemic stroke, neuronal SOCE can either re-establish Ca²⁺ homeostasis or mediate Ca²⁺ overload, thus providing a non-excitotoxic mechanism of ischemic neuronal death. The dualistic role of SOCE in brain ischemia is further underscored by the evidence that it also participates to endothelial restoration and to the stabilization of intravascular thrombi. In Parkinson's disease (PD) models, loss of SOCE triggers ER stress and dysfunction/degeneration of dopaminergic neurons. Disruption of neuronal SOCE also underlies Alzheimer's disease (AD) pathogenesis, since both in genetic mouse models and in human sporadic AD brain samples, reduced SOCE contributes to synaptic loss and cognitive decline. Unlike the AD setting, in the striatum from Huntington's disease (HD) transgenic mice, an increased STIM2 expression causes elevated synaptic SOCE that was suggested to underlie synaptic loss in medium spiny neurons. Thus, pharmacological inhibition of SOCE is beneficial to synapse maintenance in HD models, whereas the same approach may be anticipated to be detrimental to cortical and hippocampal pyramidal neurons. On the other hand, up-regulation of SOCE may be beneficial during AD. These intriguing findings highlight the importance of further mechanistic studies to dissect the molecular pathways, and their corresponding targets, involved in synaptic dysfunction and neuronal loss during aging and neurodegenerative diseases.

The Complex Role of Store Operated Calcium Entry Pathways and Related Proteins in the Function of Cardiac, Skeletal and Vascular Smooth Muscle Cells

Cardiac, skeletal, and smooth muscle cells shared the common feature of contraction in response to different stimuli. Agonist-induced muscle's contraction is triggered by a cytosolic free Ca²⁺ concentration increase due to a rapid Ca²⁺ release from intracellular stores and a transmembrane Ca²⁺ influx, mainly through L-type Ca²⁺ channels. Compelling evidences have demonstrated that Ca²⁺ might also enter through other cationic channels such as Store-Operated Ca²⁺ Channels (SOCCs), involved in several physiological functions and pathological conditions. The opening of SOCCs is regulated by the filling state of the intracellular Ca²⁺ store, the sarcoplasmic reticulum, which communicates to the plasma membrane channels through the Stromal Interaction Molecule 1/2 (STIM1/2) protein. In muscle cells, SOCCs can be mainly non-selective cation channels formed by Orai1 and other members of the Transient Receptor Potential-Canonical (TRPC) channels family, as well as highly selective Ca²⁺ Release-Activated Ca²⁺ (CRAC) channels, formed exclusively by subunits of Orai proteins likely organized in macromolecular complexes. This review summarizes the current knowledge of the complex role of Store Operated Calcium Entry (SOCE) pathways and related proteins in the function of cardiac, skeletal, and vascular smooth muscle cells.

A dual mechanism promotes switching of the Stormorken STIM1 R304W mutant into the activated state

STIM1 and Orai1 are key components of the Ca²⁺-release activated Ca²⁺ (CRAC) current. Orai1, which represents the subunit forming the CRAC channel complex, is activated by the ER resident Ca²⁺ sensor STIM1. The genetically inherited Stormorken syndrome disease has been associated with the STIM1 single point R304W mutant. The resulting constitutive activation of Orai1 mainly involves the CRAC-activating domain CAD/SOAR of STIM1, the exposure of which is regulated by the molecular interplay between three cytosolic STIM1 coiled-coil (CC) domains. Here we present a dual mechanism by which STIM1 R304W attains the pathophysiological, constitutive activity eliciting the Stormorken syndrome. The R304W mutation induces a helical elongation within the CC1 domain, which together with an increased CC1 homomerization, destabilize the resting state of STIM1. This culminates, even in the absence of store depletion, in structural extension and CAD/SOAR exposure of STIM1 R304W leading to constitutive CRAC channel activation and Stormorken disease.

Stormorken syndrome is associated with the R304W mutation in STIM1, which is a Calcium sensor in the endoplasmic reticulum. Here authors use FRET and electrophysiology to show that R304W induces STIM1 conformational extension by a dual mechanism resulting in constitutive activation of Ca2+ channels.