Ceruloplasmin deficiency does not induce macrophagic iron overload: lessons from a new rat model of hereditary aceruloplasminemia

Abstract

Hereditary aceruloplasminemia (HA), related to mutations in the ceruloplasmin (Cp) gene, leads to iron accumulation. Ceruloplasmin ferroxidase activity being considered essential for macrophage iron release, macrophage iron overload is expected, but it is not found in hepatic and splenic macrophages in humans. Our objective was to get a better understanding of the mechanisms leading to iron excess in HA. A clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR associated protein 9 (Cas9) knockout of the Cp gene was performed on Sprague-Dawley rats. We evaluated the iron status in plasma, the expression of iron metabolism genes, and the status of other metals whose interactions with iron are increasingly recognized. In Cp 2/2 rats, plasma ceruloplasmin and ferroxidase activity were absent, together with decreased iron concentration and transferrin saturation. Similarly as in humans, the hepatocytes were iron overloaded conversely to hepatic and splenic macrophages. Despite a relative hepcidin deficiency in Cp 2/2 rats and the loss of ferroxidase activity, potentially expected to limit the interaction of iron with transferrin, no increase of plasma non-transferrin-bound iron level was found. Copper was decreased in the spleen, whereas manganese was increased in the plasma. These data suggest that the reported role of ceruloplasmin cannot fully explain the iron hepatosplenic phenotype in HA, encouraging the search for additional mechanisms.-

Genetic and Clinical Heterogeneity in Thirteen New Cases with Aceruloplasminemia. Atypical Anemia as a Clue for an Early Diagnosis

“…Since macrophages are key cells in iron recycling, a macrophage iron overload would be expected in ACP. Conversely, iron accumulation is usually observed in hepatocytes/liver ( Figure 1) rather than in macrophages/spleen in affected patients, suggesting that additional pathophysiologic roles of CP are probably involved [17]. Specifically, it has been reported that GPI-anchored CP can also modulate the interaction between ferroportin and hepcidin [18][19][20], the master regulator of systemic iron homeostasis [21].…”

Copper Homeostasis in Mammals, with Emphasis on Secretion and Excretion. A Review

“…Clearly, Cu in the bloodstream is also bound to proteins other than ceruloplasmin and potentially also to non-protein molecules. Humans and mice with no ceruloplasmin in the circulation survive fairly well overall, although not without some complications involving both Cu and Fe metabolism [54][55][56][57]. In Wilson disease (with no functional ATP7B to incorporate Cu into ceruloplasmin), there still is Cu in the blood, and subjects lead relatively normal lives as long as they are treated with chelators to remove the excess Cu [3].…”

Advances in Genome Editing and Application to the Generation of Genetically Modified Rat Models

“…Hereditary aceruloplasminemia is a genetic disease characterized by progressive iron overload (liver and brain) and is related to mutations in the ceruloplasmin (CP) gene. In contrast to Cp KO mice, Cp KO rats mimic the human phenotype with hepatosplenic iron load and could be more appropriate for providing information to understand and treat the disease (Kenawi et al, 2019).…”