CCL2 is Upregulated by Decreased miR-122 Expression in Iron-Overload-Induced Hepatic Inflammation

Abstract

Background/aims: Iron overload (IO) is accompanied by hepatic inflammation. The chemokine (C-C motif) ligand 2 (CCL2) mediates inflammation, and its overexpression is associated with IO. However, whether IO results in CCL2 overexpression in the liver and the underlying mechanisms are unclear.

Methods: We subjected mice to IO by administering intraperitoneal injections of dextran-iron or by feeding mice a 3% dextran-iron diet to observe the effects of IO on miR-122/CCL2 expression through real-time qPCR and Western blot analysis. We also used indicators, including the expression of the inflammatory cytokine, the inflammation score based on H&E staining and the serum content of ALT and AST to evaluate the effects of IO on hepatic inflammation. Meanwhile, we observed the effects of vitamin E on IO-induced hepatic inflammation. In cells, we used 100 µΜ FeSO4 or 30 µΜ Holo-Tf to produce IO and observed the roles of miR-122 in regulating CCL2 expression by using miR-122 mimics or inhibitors to overexpress or inhibit miR-122. Then, we used a dual-luciferase reporter assay to prove that miR-122 regulates CCL2 expression through direct binding to its complementary sequence in the CCL2 mRNA 3'UTR.

Results: IO induces the downregulation of miR-122 and the upregulation of CCL2, as well as inflammatory responses both in vitro and in vivo. Although IO-induced oxidative stress is eliminated by the antioxidant vitamin E, IO-induced hepatic inflammation still exists, which probably can be explained by the fact that vitamin E has no effects on the miR-122/CCL2 pathway. In in vitro experiments, the overexpression and inhibition of miR-122 significantly reduced and increased CCL2 expression, respectively. The dual-luciferase reporter assay indicates that miR-122 binds CCL2 mRNA 3'UTR.

Conclusion: We propose the roles of miR-122/CCL2 in IO-induced hepatic inflammation. Our studies should provide a new clue for developing clinical strategies for patients with IO.

Keywords: Chemokine (C-C motif) ligand 2 (CCL2); Hepatic inflammation; Iron overload; miR-122.