Transferrin (Tf) Mediated Protection of the Liver Against Fas-Induced Injury Requires Tf-Receptor Type 2 and Is Modulated by Baseline Plasma Iron Levels.

Abstract

Transferrin (Tf) plays a central role in iron transport and metabolism. In addition, we showed that Tf interferes with programmed cell death. Specifically, Tf counteracted Fas-induced liver injury by down-regulating pro-apoptotic and up-regulating anti-apoptotic signals; those signals were further modified by iron. Surprisingly, the data suggested, that the Tf effect was not mediated by Tf-receptor type 1 (TfR1, CD71). Here, we investigated in murine models a possible role of TfR type 2 (TfR2) in Tf-mediated hepatoprotection. TfR2 is prominently expressed on hepatocytes. Male and female C57BL6, BALB/c, SVJ/129 mice, and mice with deletion of TfR2 (TfR2Y245X) were used. Mice were injected intraperitoneally with agonistic anti-Fas MAB (aFas) Jo2, 0.08 mg/g of body weight and treated with saline (controls) or human ApoTf at 0.1 mg/mouse at 48, 24, and 1 hour before, and 1 hour after aFas injection. Plasma iron and aspartate-aminotransferase (AST) levels were determined at 0, 6, 12, 24, 48 hours and 7 days after aFas. The magnitude of AST rises differed significantly between strains and were less striking in male than in female mice in response to the same per body weight doses of aFas. C57BL6 mice showed the smallest AST increments as compared to BALB/c or SVJ/129 mice. The highest AST levels occurred in female SVJ/129 mice (8934±1833 U/L) versus 3912±1280 U/L in female BALB/c, and 660±159 U/L in female C57BL6 mice. The corresponding baseline plasma iron levels (male and female) were 240–290, 220–270, and 140–170 ug/dL, respectively. Changes in iron levels were biphasic and most pronounced in female mice. In C57BL6, for example, iron decreased from 148±13 ug/dL to 73±8 ug/dL (p<0.02) at 6 hours, followed by an increase to 282±30 ug/dL (p<0.02) at 48 hours after aFas injection. The plasma iron decline preceded the increase in AST levels, which peaked at 12–24 hours. This pattern suggested an early utilization of iron in Fas signaling and a subsequent release of iron from injured cells. A comparison of plasma iron levels in wild type (WT) mice and mice heterozygous (HT) or homozygous (HO) for TfR2 deletion showed the highest levels (217±11 in males and 297±11 in females [p<0.001]) in HO mice, intermediate levels (180±11 in males, and 199±7 in females [p=NS]) in HT, and the lowest levels (157±4 in males, and 159±14 in females [p=NS]) in WT mice. As observed in controls, aFas injection resulted in a decline in plasma iron followed by a rise in AST in all genotypes. However, while pre-treatment with Tf almost completely prevented AST rises in WT mice (134±30 U/L versus 500±28 U/L in male [p<0.02], and 167±66 U/L versus 675±173 U/L [p<0.02] in female Tf-treated and saline treated controls, respectively), there was no significant protection in HT (521±351 versus 782±666 U/L in male, and 645±98 versus 515±69 U/L in females [p=NS]) and HO (352±100 versus 236±32 U/L in male, and 585±214 versus 604±41 U/L [p=NS]) Tf-treated and saline treated mice, respectively. These results support the hypothesis that the hepatoprotective effect of Tf against Fas-mediated apoptosis is dependent upon functional TfR2 expression. Rises in plasma AST levels, related to Fas-induced hepatic injury, were strain and gender dependent, and were accompanied by changes in blood plasma iron concentrations. The data suggest that Tf would be useful as a cytoprotective agent in recipients of cytotoxic therapy.