Protective effects of the mechanistic target of rapamycin against excess iron and ferroptosis in cardiomyocytes

Abstract

Clinical studies have suggested that myocardial iron is a risk factor for left ventricular remodeling in patients after myocardial infarction. Ferroptosis has recently been reported as a mechanism of iron-dependent nonapoptotic cell death. However, ferroptosis in the heart is not well understood. Mechanistic target of rapamycin (mTOR) protects the heart against pathological stimuli such as ischemia. To define the role of cardiac mTOR on cell survival in iron-mediated cell death, we examined cardiomyocyte (CM) cell viability under excess iron and ferroptosis conditions. Adult mouse CMs were isolated from cardiac-specific mTOR transgenic mice, cardiac-specific mTOR knockout mice, or control mice. CMs were treated with ferric iron [Fe(III)]-citrate, erastin, a class 1 ferroptosis inducer, or Ras-selective lethal 3 (RSL3), a class 2 ferroptosis inducer. Live/dead cell viability assays revealed that Fe(III)-citrate, erastin, and RSL3 induced cell death. Cotreatment with ferrostatin-1, a ferroptosis inhibitor, inhibited cell death in all conditions. mTOR overexpression suppressed Fe(III)-citrate, erastin, and RSL3-induced cell death, whereas mTOR deletion exaggerated cell death in these conditions. 2',7'-Dichlorodihydrofluorescein diacetate measurement of reactive oxygen species (ROS) production showed that erastin-induced ROS production was significantly lower in mTOR transgenic versus control CMs. These findings suggest that ferroptosis is a significant type of cell death in CMs and that mTOR plays an important role in protecting CMs against excess iron and ferroptosis, at least in part, by regulating ROS production. Understanding the effects of mTOR in preventing iron-mediated cell death will provide a new therapy for patients with myocardial infarction. NEW & NOTEWORTHY Ferroptosis has recently been reported as a new form of iron-dependent nonapoptotic cell death. However, ferroptosis in the heart is not well characterized. Using cultured adult mouse cardiomyocytes, we demonstrated that the mechanistic target of rapamycin plays an important role in protecting cardiomyocytes against excess iron and ferroptosis.

Ferroptosis is programmed by the coordinated regulation of glutathione and iron metabolism by BACH1

“…Finally, we tried to examine whether or not the promotion of ferroptosis by BACH1 is involved in pathological changes in vivo . As there are several reports showing that ferroptosis is involved in ischemia-reperfusion injury in the heart (Baba et al, 2018, Fang et al, 2019, Gao et al, 2015), we used an AMI model based on left anterior descending coronary artery (LAD) ligation (Abarbanell et al, 2010, Shindo et al, 2016) (Fig 6A). In this model, Bach1 -/- mice showed less severe injuries than WT mice as judged by the post-operative survival rate and an evaluation of the cardiac function with echocardiography (Figs 6B, C and EV5A-C.…”

“…In addition, we showed that ferroptosis was involved in the pathology of not only ischemia-reperfusion injury (IRI) (Baba et al, 2018, Fang et al, 2019, Gao et al, 2015) but also AMI. The severity of AMI was improved by the iron chelator, DFX particularly in WT mice (Fig 7C-F).…”

“…Ferroptosis is a new form of programmed cell death caused by the iron-dependent accumulation of lipid hydroperoxide (Dixon et al, 2012, Yang et al, 2014). As a pathological cell death, ferroptosis causes various oxidative stress-related diseases, including ischemia-reperfusion injury (Baba et al, 2018, Fang et al, 2019, Gao et al, 2015, Linkermann et al, 2013, Linkermann et al, 2014) and neurodegenerative diseases (Chiang et al, 2017, Di Domenico et al, 2017). Ferroptosis also contributes to tumor suppression as a response induced by p53 and is important for organisms in preventing cancer (Jiang et al, 2015, Kim et al, 2016, Viswanathan et al, 2017, Yang et al, 2014).…”

Keeping heart homeostasis in check through the balance of iron metabolism

“…Decreased cellular supply with cystine can be caused by a variety of inducing factors some of which have been investigated in different cells including cardiomyocytes . The most investigated inducer of ferroptosis, named erastin, has been shown to cause ferroptosis in cardiomyocytes, similar to other cells . Lipid peroxidation observed during ferroptosis can be caused by excess iron, and this action is reversed by preserving the function of mechanistic target of rapamycin (mTOR) pathway in cardiomyocytes .…”

“…The most investigated inducer of ferroptosis, named erastin, has been shown to cause ferroptosis in cardiomyocytes, similar to other cells . Lipid peroxidation observed during ferroptosis can be caused by excess iron, and this action is reversed by preserving the function of mechanistic target of rapamycin (mTOR) pathway in cardiomyocytes . The protective role of mTOR is based on its ability to induce iron transport in and out of cardiomyocytes, although the details of this action are still unknown .…”