Orai1 Channel Inhibition Preserves Left Ventricular Systolic Function and Normal Ca ²⁺ Handling After Pressure Overload

Abstract

Background: Orai1 is a critical ion channel subunit, best recognized as a mediator of store-operated Ca 2+ 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 R91W 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 2+ 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 2+ signaling alterations (increased SOCE, decreased [Ca 2+ ] i transients amplitude and decay rate, lower SR Ca 2+ 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.

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

“…Furthermore, it has been shown that the STIM1/Orai1 complexes were enriched at N-cadherin-rich IDs sites over Cx43-rich sites in adult mice cardiomyocytes (Bonilla et al, 2019). We also noted occasional nuclear Orai1 labeling in isolated mice cardiomyocytes (Bartoli et al, 2020). Indeed, the location of Orai1/STIM1 complex in the nucleoplasm has been reported by other authors as well (Lee et al, 2018), suggesting Orai1 involvement in nucleoplasmic Ca 2+ regulation.…”

“…In contrast, heterozygous global Orai1-deficient mice did not present alteration of heart structure and function (Horton et al, 2014). Likewise, we have reported that cardiomyocytespecific dn-Orai1 R91W transgenic mice displayed normal cardiac electromechanical function and ECC despite reduced Orai1dependent SOCE (Bartoli et al, 2020), as recently confirmed in cardiomyocyte-specific and temporally inducible Orai1 knockout (KO) mouse line (Segin et al, 2020). Although in the later study, this was associated with reduced body weight and a downregulation of Orai3, STIM2, and store-operated Ca 2+ entry-associated regulatory factor (SARAF) transcript expression, those results suggested that Orai1 is not instrumental for the ECC and cardiac function at rest.…”

“…Increased Orai1 expression was also observed after ischemia/reperfusion in NRVMs ( Dominguez-Rodriguez et al, 2018 ). Several in vivo studies also found Orai1 mRNA and protein expression upregulation in mouse cardiac hypertrophic model induced by pressure and volume overload, such as transverse aortic constriction, abdominal aortic banding, chronic AngII infusion, or myocardial infarction ( Volkers et al, 2012 ; Dai et al, 2018 ; Bartoli et al, 2020 ; Segin et al, 2020 ). In right ventricular hypertrophy and dysfunction secondary to pulmonary hypertension, we also observed an increased Orai1 expression ( Sabourin et al, 2018 ).…”

“…In isolated adult ventricular cardiomyocytes from rats and mice, Orai1 has been located at the surface sarcolemma, with higher concentration at the intercalated disks (IDs) ( Volkers et al, 2012 ; Bonilla et al, 2019 ; Bartoli et al, 2020 ). Furthermore, it has been shown that the STIM1/Orai1 complexes were enriched at N-cadherin-rich IDs sites over Cx43-rich sites in adult mice cardiomyocytes ( Bonilla et al, 2019 ).…”

Lithium Reduces Migration and Collagen Synthesis Activity in Human Cardiac Fibroblasts by Inhibiting Store-Operated Ca2+ Entry

“…Consistent with the literature [ 8 ], our recent studies have demonstrated that Ca 2+ entry is a crucial signal that regulates the pro-fibrotic activity of human cardiac fibroblasts [ 9 , 10 ]. Among the various types of Ca 2+ entry through ion channels in the plasma membrane, the dysfunction of store-operated Ca 2+ entry has recently been found to be the key contributor to heart failure [ 11 , 12 , 13 , 14 ]. Cardiac fibroblasts isolated from patients with heart failure have been reported to possess an enhanced ability to synthesize collagen, which is related to the increase in Ca 2+ entry via elevation in store-operated Ca 2+ entry and the expression level of calcium release-activated calcium channel protein 1 (Orai1) [ 13 ].…”