Suppression of store-operated calcium entry causes dilated cardiomyopathy of the Drosophila heart

Abstract

Store-operated Ca2+ entry (SOCE) is an essential Ca2+ signaling mechanism present in most animal cells. SOCE refers to Ca2+ influx that is activated by depletion of sarco/endoplasmic reticulum (S/ER) Ca2+ stores. The main components of SOCE are STIM and Orai. STIM proteins function as S/ER Ca2+ sensors, and upon S/ER Ca2+ depletion STIM rearranges to S/ER-plasma membrane junctions and activates Orai Ca2+ influx channels. Studies have implicated SOCE in cardiac hypertrophy pathogenesis, but SOCE's role in normal heart physiology remains poorly understood. We therefore analyzed heart-specific SOCE function in Drosophila, a powerful animal model of cardiac physiology. We show that heart-specific suppression of Stim and Orai in larvae and adults resulted in reduced contractility consistent with dilated cardiomyopathy. Myofibers were also highly disorganized in Stim and Orai RNAi hearts, reflecting possible decompensation or upregulated stress signaling. Furthermore, we show that reduced heart function due to SOCE suppression adversely affected animal viability, as heart specific Stim and Orai RNAi animals exhibited significant delays in post-embryonic development and adults died earlier than controls. Collectively, our results demonstrate that SOCE is essential for physiological heart function, and establish Drosophila as an important model for understanding the role of SOCE in cardiac pathophysiology.

SOCE in the cardiomyocyte: the secret is in the chambers

“…Whether the SR-microtubule connection is important structural support of the myocyte is not known. But, STIM1 −/− cardiomyocytes from several different models (mice and flies) exhibit myofibril derangement supporting the hypothesis that deletion of STIM1 might disrupt the microtubular lattice and destabilize myofibril integrity [ 73 , 75 ].…”

Analysis ofDrosophilacardiac hypertrophy by micro-computerized tomography for genetic dissection of heart growth mechanisms

“…Therefore, we next evaluated whether SOCE upregulation due to Stim CA and Orai CA expression affects heart contractility. Adult heart contractility was analyzed by intravital fluorescence imaging of animals with cardiomyocyte-specific tdTomato (CM-tdTom) expression (21; 44). As shown in Figure 5A-D, control hearts exhibited strong, consistent contractions with an average end diastolic dimension (EDD) of 65.17 ± 1.33 μm, average end systolic dimension (ESD) of 32.15 ± 0.83 μm, and average fractional shortening (FS) of 51 ± 0.85% (mean ± SEM).…”

“…Intravital fluorescence imaging of adult hearts was carried out using animals that express tdTomato under control of the cardiomyocyte-specific R94C02 (CM-tdTom) enhancer element (21) as previously described (44). Five-day old adult females were briefly anesthetized with CO 2 and adhered dorsal side down to a glass coverslip with Norland Optical Adhesive that was then cured with a 48-watt UV LED light source (LKE) for 60 seconds.…”

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

“…This was associated with ultrastructure alterations of sarcomeres, leading to reduced expression and impaired z-disc localization of calsarcin involved in the activation of calcineurin/nuclear factor of activated T cell (CaN/NFAT) hypertrophic pathway. In addition, inducible RNAi to specifically suppress Orai1 expression in the Drosophila heart resulted in significant delays in post-embryonic development, premature death in adults, and impaired cardiac function due to myofibril disorganization consistent with dilated cardiomyopathy ( Petersen et al, 2020 ).…”