Silencing of hepcidin enforces the apoptosis in iron-induced human cardiomyocytes

Abstract

BackgroundIron is essential not only for erythropoisis but also for several bioenergetics’ processes in myocardium. Hepcidin is a well-known regulator of iron homeostasis. Recently, researchers identified low hepcidin was independently associated with increased 3-year mortality among systolic heart failure patients. In addition, our previous in vivo study revealed that the left ventricular mass index increased in chronic kidney disease patients with lower serum hepcidin. We hypothesize that hepcidin interacts with the apoptotic pathway of cardiomyocytes during oxidative stress conditions.MethodsTo test this hypothesis, human cardiomyocytes were cultured and treated with ferrous iron. The possible underlying signaling pathways of cardiotoxicity were examined following knockdown studies using siRNAs of hepcidin (siRNA1 was used as a negative control and siRNA2 was used to silence hepcidin).ResultsWe found that ferrous iron induces apoptosis in human cardiomyocytes in a dose-dependent manner. This iron-induced apoptosis was linked to enhanced caspase 8, reduced Bcl-2, Bcl-xL, phosphorylated Akt and GATA-4. Hepcidin levels increased in human cardiomyocytes pretreated with ferrous iron and returned to non-iron treated levels following siRNA2 transfection. In iron pretreated cardiomyocytes, the siRNA2 transfection further increased caspase 8 expression and decreased the expression of GATA-4, Bcl-2, Bcl-xL and phosphorylated Akt than iron pretreatment alone, but caspase 9 levels remained unchanged.ConclusionsOur findings suggest that hepcidin can rescue human cardiomyocytes from iron-induced apoptosis through the regulation of GATA-4/Bcl-2 and the extrinsic apoptotic pathway.

Balance of cardiac and systemic hepcidin and its role in heart physiology and pathology

“…Silencing hepcidin promotes apoptosis in cardiomyocytes, which suggests a protective role of hepcidin beyond iron regulation. 44 This is in terms with the observation that GATA-4, the transcription factor known for mediating cardiac hypertrophy and apoptosis, has a binding site in the hepcidin promoter, at least in liver cells. 45,46 Disturbance of the GATA-4-binding site downregulates hepcidin expression in response to IL-6, but not to BMP6.…”

“…During cardiac iron overload cardiac hepcidin protects cardiomyocytes against apoptosis. 44 Another protective role of cardiac hepcidin in hypoxia/ ischemia is the increase in ferritin levels. Hepcidin increases ferritin, which sequesters excess iron that might cause oxidative damage in cardiomyocytes not only during ischemia, but also during reperfusion.…”

Keeping heart homeostasis in check through the balance of iron metabolism

“…It reduces cardiomyocyte iron export by acting on FPN . Its loss is accompanied by serious heart dysfunction, and similarly to FPN, it also responds to cardiac iron load . Many studies suggest that cardiac hepcidin is upregulated during cardiac stress and injury, such as ischaemia, hypoxia, inflammation and mechanical stretch .…”

“…For example, cardiac hepcidin has been found to be responsible for reactive hypertrophy in Dahl salt‐sensitive rats . Furthermore, hepcidin regulates the level of hypertrophy in dilated cardiomyopathy but also reduces interstitial fibrosis and apoptosis which in turn preserves cardiac function . This is probably why knockdown of cardiac hepcidin is accompanied by dilated cardiomyopathy and low ejection fraction .…”

“…Increased iron import in remote myocardium influences cardiac remodelling, that is, dietary iron restriction reduces cardiac fibrosis and dilatation . On the other hand, cardiac hepcidin upregulation seems to protect the heart from damaging cardiac hypertrophy . Preserving fine iron protein balance seems to protect the heart during MI.…”