Orai1 Channel Inhibition Preserves Left Ventricular Systolic Function and Normal Ca Handling After Pressure Overload.
Bartoli Fiona,Bailey Marc A,Rode Baptiste,Mateo Philippe,Antigny Fabrice,Bedouet Kaveen,Gerbaud Pascale,Gosain Rajendra,Plante Jeffrey,Norman Katherine,Gomez Susana,Lefebvre Florence,Rucker-Martin Catherine,Ainscough Justin F X,Kearney Mark T,Bruns Alexander-Francisco,Shi Jian,Appleby Hollie L,Young Richard S,Shawer Heba M,Debant Marjolaine,Gomez Ana-Maria,Beech David J,Foster Richard,Benitah Jean-Pierre,Sabourin Jessica
BACKGROUND:Orai1 is a critical ion channel subunit, best recognized as a mediator of store-operated Ca entry (SOCE) in nonexcitable cells. SOCE has recently emerged as a key contributor of cardiac hypertrophy and heart failure but the relevance of Orai1 is still unclear. METHODS:To test the role of these Orai1 channels in the cardiac pathophysiology, a transgenic mouse was generated with cardiomyocyte-specific expression of an ion pore-disruptive Orai1 mutant (C-dnO1). Synthetic chemistry and channel screening strategies were used to develop 4-(2,5-dimethoxyphenyl)-N-[(pyridin-4-yl)methyl]aniline (hereafter referred to as JPIII), a small-molecule Orai1 channel inhibitor suitable for in vivo delivery. RESULTS:Adult mice subjected to transverse aortic constriction (TAC) developed cardiac hypertrophy and reduced ventricular function associated with increased Orai1 expression and Orai1-dependent SOCE (assessed by Mn influx). C-dnO1 mice displayed normal cardiac electromechanical function and cellular excitation-contraction coupling despite reduced Orai1-dependent SOCE. Five weeks after TAC, C-dnO1 mice were protected from systolic dysfunction (assessed by preserved left ventricular fractional shortening and ejection fraction) even if increased cardiac mass and prohypertrophic markers induction were observed. This is correlated with a protection from TAC-induced cellular Ca signaling alterations (increased SOCE, decreased [Ca] transients amplitude and decay rate, lower SR Ca load and depressed cellular contractility) and SERCA2a downregulation in ventricular cardiomyocytes from C-dnO1 mice, associated with blunted Pyk2 signaling. There was also less fibrosis in heart sections from C-dnO1 mice after TAC. Moreover, 3 weeks treatment with JPIII following 5 weeks of TAC confirmed the translational relevance of an Orai1 inhibition strategy during hypertrophic insult. CONCLUSIONS:The findings suggest a key role of cardiac Orai1 channels and the potential for Orai1 channel inhibitors as inotropic therapies for maintaining contractility reserve after hypertrophic stress.
Changes in STIM isoforms expression and gender-specific alterations in Orai expression in human heart failure.
Čendula R,Dragún M,Gažová A,Kyselovič J,Hulman M,Máťuš M
Store-operated calcium entry (SOCE) is one of regulatory mechanisms which regulates Ca2+ cycling in the heart. SOCE alterations in pathological conditions contribute to progression of heart failure and cardiac hypertrophy by multiple signaling pathways such as Cn/NFAT and CaMKII/MEF2. Several components mediating SOCE have been identified, such as STIM and Orai. Different isoforms of both Orai and STIM have been detected in animal studies, exhibiting distinct functional properties. This study is focused on the analysis of STIM and Orai isoforms expression in the end-stage human failing myocardium. Left ventricle samples isolated from 43 explanted hearts from patients undergoing heart transplant and from 5 healthy donor hearts were used to determine the mRNA levels of Orai1, Orai2 and Orai3, STIM1, STIM2 and STIM2.1 by qRT-PCR. The expression was further analyzed for connection with gender, related co-morbidities, pathoetiology, clinical data and biochemical parameters. We show that Orai1 expression is decreased by 30 % in failing myocardium, even though we detected no significant changes in expression of Orai2 or Orai3. Interestingly, this decrease in Orai1 was gender-specific and was present only in men, with no change in women. The ratio Orai1/Orai3 was significantly lower in males as well. The novel STIM2.1 isoform was detected both in healthy and failing human myocardium. In the end-stage heart failure, the expression of STIM2.1 was significantly decreased. The lower ratio of STIM2.1/STIM2 in failing hearts indicates a switch from SOCE-inhibiting STIM2.1 isoform to stimulatory STIM2.2. STIM1 mRNA levels were not significantly changed. These observed alterations in Orai and STIM expression were independent of functional heart parameters, clinical or biochemical patient characteristics. These results provide detailed insight into the alterations of SOCE regulation in human failing myocardium. Gender-specific change in Orai1 expression might represent a possible mechanism of cardioprotective effects of estrogens. The switch from STIM2.1 to STIM2.2 indicates an amplification of SOCE and could contribute to the hypertrophy development in the filing heart.
STIM1 and STIM2 cooperatively regulate mouse neutrophil store-operated calcium entry and cytokine production.
Clemens Regina A,Chong Joshua,Grimes Derayvia,Hu Yongmei,Lowell Clifford A
Neutrophils are key effector cells of the innate immune system. Calcium-dependent signaling pathways initiated by store-operated calcium entry (SOCE) are known to regulate neutrophil activation; however, the precise mechanism of this process remains unclear. STIM1 and STIM2 are calcium-sensing molecules that link calcium depletion of the endoplasmic reticulum with opening of plasma membrane calcium channels. Although a role for STIM1 in neutrophil SOCE and activation has been established, the function of STIM2 is unknown. Here we use mice with conditional ablation of and/or to investigate the role of STIM2 in neutrophil activation. We demonstrate that loss of STIM2 results in decreased SOCE, particularly at lower doses of agonists. Reactive oxygen species (ROS) production, degranulation, and phagocytosis are normal in the absence of STIM2, suggesting STIM1 is the dominant calcium sensor required for classical short-term neutrophil responses. However, neutrophil cytokine production required STIM2, but not STIM1, at least in part as a result of redox regulation of cytokine gene expression. In vivo loss of STIM2 results in lower cytokine levels and protection from mortality in a mouse model of systemic inflammatory response syndrome. These data, combined with previous studies focusing on STIM1, define distinct but cooperative functions for STIM1 and STIM2 in modulating neutrophil bactericidal and cytokine responses.
Oxidative stress facilitates cell death by inhibiting Orai1-mediated Ca entry in brain capillary endothelial cells.
Yamamura Hideto,Suzuki Yoshiaki,Asai Kiyofumi,Imaizumi Yuji,Yamamura Hisao
Biochemical and biophysical research communications
Brain capillary endothelial cells (BCECs) form the blood-brain barrier (BBB) and play an essential role in the regulation of its functions. Oxidative stress accumulates excessive reactive oxygen species (ROS) and facilitates the death of BCECs, leading to a dysfunctional BBB. However, the mechanisms underlying the death of BCECs under oxidative stress remain unclear. In the present study, the effects of oxidative stress on cell viability, ROS production, intracellular Ca concentration, and protein expression were examined using a cell line derived from bovine BCECs, t-BBEC117. When t-BBEC117 cells were exposed to oxidative stress induced by hydrogen peroxide (HO, 10-100 μM), cell growth was inhibited in a dose-dependent manner. Oxidative stress by 30 μM HO increased the production of ROS and its effects were blocked by the ROS scavenger, 10 mM N-acetyl-l-cysteine (NAC). In addition, oxidative stress reduced store-operated Ca entry (SOCE) and this decrease was recovered by NAC or the Orai channel activator, 5 μM 2-aminoethyl diphenylborinate (2-APB). The siRNA knockdown of Orai1 revealed that Orai1 was mainly responsible for SOCE channels and its activity was decreased by oxidative stress. However, the protein expression of Orai1 and STIM1 was not affected by oxidative stress. Oxidative stress-induced cell death was rescued by 2-APB, NAC, or the STIM-Orai activating region. In conclusion, oxidative stress reduces Orai1-mediated SOCE and, thus, facilitates the death of BCECs.
Hydrogen peroxide is a critical regulator of the hypoxia-induced alterations of store-operated Ca entry into rat pulmonary arterial smooth muscle cells.
Chen Tao-Xiang,Xu Xiao-Ya,Zhao Zhao,Zhao Fang-Yu,Gao Yi-Mei,Yan Xiao-Hong,Wan Yu
American journal of physiology. Lung cellular and molecular physiology
To investigate the association between store-operated Ca entry (SOCE) and reactive oxygen species (ROS) during hypoxia, this study determined the changes of transient receptor potential canonical 1 (TRPC1) and Orai1, two candidate proteins for store-operated Ca (SOC) channels and their gate regulator, stromal interaction molecule 1 (STIM1), in a hypoxic environment and their relationship with ROS in pulmonary arterial smooth muscle cells (PASMCs). Exposure to hypoxia caused a transient Ca spike and subsequent Ca plateau of SOCE to be intensified in PASMCs when TRPC1, STIM1, and Orai1 were upregulated. SOCE in cells transfected with specific short hairpin RNA (shRNA) constructs was almost completely eliminated by the knockdown of TRPC1, STIM1, or Orai1 alone and was no longer affected by hypoxia exposure. Hypoxia-induced SOCE enhancement was further strengthened by PEG-SOD but was attenuated by PEG-catalase, with correlated changes to intracellular hydrogen peroxide (HO) levels and protein levels of TRPC1, STIM1, and Orai1. Exogenous HO could mimic alterations of the interactions of STIM1 with TRPC1 and Orai1 in hypoxic cells. These findings suggest that TRPC1, STIM1, and Orai1 are essential for the initiation of SOCE in PASMCs. Hypoxia-induced ROS promoted the expression and interaction of the SOC channel molecules and their gate regulator via their converted product, HO.