A comparative study of myocardial molecular phenotypes of two tfr2β null mice: Role in ischemia/reperfusion

Abstract

Transferrin receptor 2 (Tfr2) is an iron-modulator transcribed in two isoforms, Tfr2α and Tfr2β. The latter is expressed in the heart. We obtained two mouse models with silencing of Tfr2β: one with a normal systemic iron amount (SIA), i.e. Tfr2-KI, and the other, i.e. LCKO-KI, with high SIA due to hepatic Tfr2α silencing. We aimed to assess whether Tfr2β might play a role in myocardial injury and whether Tfr2β silencing might modify proteins of iron metabolism, antioxidant, apoptotic and survival enzyme activities in the heart undergoing ischemia/reperfusion (I/R).Isolated hearts of wild-type (WT) and Tfr2-null mice were studied before or after an I/R protocol, and proteins/RNA analyzed by Western blot and/or quantitative PCR.Tfr2β increased in WT hearts subject to I/R, and both Tfr2β null mice hearts were protected against I/R injury (about 40% smaller infarct-size compared to WT hearts). RISK kinases (ERK1/2-AKT-PKCε)were found up-regulated after I/R in Tfr2-KI, whereas SAFE enzyme (Stat3) and GSK3β resulted phosphorylated during I/R in LCKO-KI hearts. While HO-1 and HIF-2a were high in both Tfr2β-null mice, Catalase and pro-apoptotic factors were upregulated only in LCKO-KI. Finally, Tfr2-KI hearts presented an increased Ferritin-H and a decreased Ferroportin1, whereas LCKO-KI hearts displayed an upregulation of Ferritin-L chain and DMT1/Hamp-RNA.In conclusion, Tfr2β isoform is involved in cardiac iron metabolism and its silencing leads to a protected phenotype (antioxidants, RISK and/or SAFE upregulation) against I/R challenging. Irondependent signals involved in cardioprotection seem to be positively affected by Tfr2β downregulation and subsequent Ferritins upregulation.

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

“…It exists in two isoforms, one of which is expressed in the heart and its downregulation is associated with heart protection during ischemia and reperfusion injury. 61 The downregulation of cardiac TFR2 is accompanied by increased ferritin and decreased FPN expression, which is similar to the effect of hepcidin. 61,62 However, data suggest that this action of TFR2-beta is realized through direct transcriptional modification of FPN, 62 which would make TFR2-beta an unlikely signaling candidate in inducing cardiac hepcidin during reperfusion injury.…”

“…61 The downregulation of cardiac TFR2 is accompanied by increased ferritin and decreased FPN expression, which is similar to the effect of hepcidin. 61,62 However, data suggest that this action of TFR2-beta is realized through direct transcriptional modification of FPN, 62 which would make TFR2-beta an unlikely signaling candidate in inducing cardiac hepcidin during reperfusion injury. It is interesting to notice the dichotomy between hepcidin and TFR2-beta in cardiac cells; myocardial injury increases expression of cardiac hepcidin and TFR2-beta, but hepcidin protects cardiomyocytes in this setting, whereas TFR2-beta overexpression has deleterious effect on heart function.…”

Keeping heart homeostasis in check through the balance of iron metabolism

“…Knockdown of TFR2‐beta protects rodent heart from I/R injury, and this might occur because of an increase in cellular antioxidative protection in the heart . It has to be mentioned that effects of cardiac hepcidin on similar cardiac metabolic pathways are opposite to TFR2, while loss of TFR2 is correlated with increased hepcidin expression . These data suggest a direct but inverse relationship between cardiac hepcidin and TFR2, though its importance is not known.…”

“…Iron overload can exacerbate cardiac hypertrophy and fibrosis in rodent models (Sukumaran Iron overload exacerbates). On the other hand, DMT1 (as well as TFR1) has been shown to be upregulated during ischaemia/reperfusion (I/R) injury and in remote myocardium after myocardial infarction . DMT1 upregulation in remote myocardium is related to myocardial remodelling via iron overload .…”

“…Its beta isoform is expressed in the heart and controls FPN transcriptional activity . Knockdown of TFR2‐beta protects rodent heart from I/R injury, and this might occur because of an increase in cellular antioxidative protection in the heart . It has to be mentioned that effects of cardiac hepcidin on similar cardiac metabolic pathways are opposite to TFR2, while loss of TFR2 is correlated with increased hepcidin expression .…”