Liang Huiqing,Li Huixian,Li Fangjiang,Xiong Xiaobo,Gao Yang
Background: Heart failure (HF) is the ultimate transformation result of
various cardiovascular diseases. Mitochondria-mediated cardiomyocyte apoptosis has
been uncovered to be associated with this disorder.
Objective: This study mainly delves into the mechanism of the anti-arrhythmic drug
amiodarone on mitochondrial toxicity of cardiomyocytes.
Methods: The viability of H9c2 cells treated with amiodarone at 0.5, 1, 2, 3, and 4 μM
was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
assay, and Sigmar1 expression was examined by quantitative real-time PCR (qRTPCR).
After transfection, the viability, apoptosis, reactive oxygen species (ROS) level,
mitochondrial membrane potential (MMP), and potassium voltage-gated channel
subfamily H member 2 (KCNH2) expression in H9c2 cells were assessed by MTT, flow
cytometry, ROS assay kit, mitochondria staining kit, and Western blot.
Results: Amiodarone at 1-4 μM notably weakened H9c2 cell viability with IC50 value of
2.62 ± 0.43 μM. Amiodarone at 0.5-4 μM also evidently suppressed the Sigmar1 level
in H9c2 cells. Amiodarone repressed H9c2 cell viability and KCNH2 level and triggered
apoptosis, ROS production and mitochondrial depolarization, while Sigmar1 upregulation
reversed its effects. Moreover, KCNH2 silencing neutralized the combined
modulation of amiodarone and Sigmar1 up-regulation on H9c2 cell viability, apoptosis,
and ROS production.
Conclusion: Amiodarone facilitates the apoptosis of H9c2 cells by restraining Sigmar1
expression and blocking KCNH2-related potassium channels.
Sigma Non-Opioid Intracellular Receptor 1 (SigmaR1) is a member of the sigma family of receptors that interacts with a variety of psychotomimetic drugs and is involved in a wide range of cellular and physiological functions. Despite its increasing importance in human physiology and disease, the subcellular localization of SigmaR1 and its molecular function remain poorly defined. Using endogenous tagging and cell fractionation, we show that SigmaR1 is a type II integral ER membrane protein that is specifically enriched at ER sheets. A short region at the N-terminus of SigmaR1 promotes its ER-sheet localization. Importantly, our biochemical studies demonstrate that SigmaR1 directly interacts with components of the translocon complex including TRAPα and Nicalin. In addition, we found that a β-barrel at the C-terminal of SigmaR1 binds phosphatidylcholine (PC), and the binding of PC strengthens the association of SigmaR1 with the translocon complex. SigmaR1 knockout systematically impaired cellular protein and lipid homeostasis, resulting in accumulation of lipid droplets in hepatocytes. Collectively, we propose that SigmaR1 is an auxiliary translocon factor that binds lipids to regulate protein and lipid droplet homeostasis, which may underlie the broad and vital roles of SigmaR1 in physiology and disease.
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