Cardiac‐Specific Deletion of Orai3 Leads to Severe Dilated Cardiomyopathy and Heart Failure in Mice

Abstract

Background Orai3 is a mammalian‐specific member of the Orai family (Orai1‒3) and a component of the store‐operated Ca 2+ entry channels. There is little understanding of the role of Orai channels in cardiomyocytes, and its role in cardiac function remains unexplored. Thus, we developed mice lacking Orai1 and Orai3 to address their role in cardiac homeostasis. Methods and Results We generated constitutive and inducible cardiomyocyte‐specific Orai3 knockout (Orai3 cKO ) mice. Constitutive Orai3‐loss led to ventricular dysfunction progressing to dilated cardiomyopathy and heart failure. Orai3 cKO mice subjected to pressure overload developed a fulminant dilated cardiomyopathy with rapid heart failure onset, characterized by interstitial fibrosis and apoptosis. Ultrastructural analysis of Orai3‐deficient cardiomyocytes showed abnormal M‐ and Z‐line morphology. The greater density of condensed mitochondria in Orai3‐deficient cardiomyocytes was associated with the upregulation of DRP1 (dynamin‐related protein 1). Cardiomyocytes isolated from Orai3 cKO mice exhibited profoundly altered myocardial Ca 2+ cycling and changes in the expression of critical proteins involved in the Ca 2+ clearance mechanisms. Upregulation of TRPC6 (transient receptor potential canonical type 6) channels was associated with upregulation of the RCAN1 (regulator of calcineurin 1), indicating the activation of the calcineurin signaling pathway in Orai3 cKO mice. A more dramatic cardiac phenotype emerged when Orai3 was removed in adult mice using a tamoxifen‐inducible Orai3 cKO mouse. The removal of Orai1 from adult cardiomyocytes did not change the phenotype of tamoxifen‐inducible Orai3 cKO mice. Conclusions Our results identify a critical role for Orai3 in the heart. We provide evidence that Orai3‐mediated Ca 2+ signaling is required for maintaining sarcomere integrity and proper mitochondrial function in adult mammalian cardiomyocytes.

The SOCE Machinery: An Unbalanced Knowledge between Left and Right Ventricular Pathophysiology

“…A more dramatic cardiac phenotype emerged when Orai3 is removed in adult mice using a tamoxifen-inducible Orai3 cKO mouse, indicating that the loss of cardiac Orai3 is critical for LV function. In a pathological state, Orai3 cKO mice subjected to pressure overload (2 weeks post-TAC) developed a fulminant dilated cardiomyopathy with rapid HF, characterized by interstitial fibrosis and apoptosis [ 86 ]. This has also been confirmed in vivo in two models of adaptive hypertrophy by infusion of isoproterenol for 15 days or by AAB for 28 days in rats.…”

STIM and Orai Mediated Regulation of Calcium Signaling in Age-Related Diseases

“…The same group also showed that oxidative stress reduced SOCE in hippocampal neurons and that knockdown of Orai1 was protective against glutathione depletion ( Henke et al, 2013 ). In support of these studies, several of the cardiomyocyte-specific KO and overexpression models of STIM and Orai proteins show significant mitochondrial structural abnormalities correlating with reductions in mitochondrial function and alternations in mitochondrial quality control ( Collins et al, 2014 ; Correll et al, 2015 ; Collins et al, 2019 ; Segin et al, 2020 ; Gammons et al, 2021 ). Silva-Rojas et al examined gain of function mutations in both STIM1 and Orai1 and found that this resulted in increased SOCE and promoted abnormal Ca 2+ handling and mitochondrial activity.…”

“…More recently, the physiological role of Orai3 has been interrogated in the heart using a cardiomyocyte-specific deletion. Gammons et al ( Gammons et al, 2021 ) showed that both constitutive and inducible cardiomyocyte-specific deletion of Orai3 develop a phenotype consistent with dilated cardiomyopathy, with increased fibrosis, increased mortality, ultrastructural changes in mitochondria, increased mitochondrial fission, and abnormal sarcomeric structure; highlighting a potentially important regulatory role of Orai3 in the heart.…”

Isoform-Specific Properties of Orai Homologues in Activation, Downstream Signaling, Physiology and Pathophysiology

“…Loss of Orai3 expression has been reported to lead to ventricular dysfunction progressing to dilated cardiomyopathy and heart failure. Orai3 is required for proper heart function, maintains intact sarcomere formation and mitochondrial function [ 164 ] ( Table 6 ).…”