Hepatocellular heme oxygenase 1 deficiency does not affect inflammatory hepcidin regulation in mice

Hepcidin is an iron regulatory peptide hormone that is secreted from hepatocytes and inhibits iron efflux from tissues to plasma. Under inflammatory conditions, hepcidin is transcriptionally induced by IL-6/STAT3 signaling and promotes hypoferremia, an innate immune response to infection. If this pathway remains unresolved, chronic overexpression of hepcidin contributes to the anemia of inflammation, a common medical condition. Previous work showed that carbon monoxide (CO) releasing drugs (CORMs) can attenuate inflammatory induction of hepcidin. Because CO is physiologically generated during heme degradation by heme oxygenase 1 (HO-1), an IL-6-inducible enzyme with anti-inflammatory properties, we hypothesized that hepatocellular HO-1 may operate as a physiological feedback regulator of hepcidin that resolves inflammatory signaling. To address this, we generated and analyzed hepatocyte-specific HO-1 knockout (Hmox1(Alb-Cre)) mice. We show that these animals mount appropriate hepcidin-mediated hypoferremic response to LPS-induced inflammation, with kinetics similar to those of control Hmox1(fl/fl) mice. Likewise, primary hepatocytes from Hmox1(Alb-Cre) and Hmox1(fl/fl) mice exhibit similar degree and kinetics of hepcidin induction following IL-6 treatment. We conclude that hepatocellular HO-1 has no physiological function on hepcidin regulation by the inflammatory pathway.