Jean-Christophe Deschemin

Astrocytes are thought to play a crucial role in brain iron homeostasis. How they accomplish this regulation in vivo is unclear. In a recent transcriptomic analysis, we showed that polysomalFtl1andFth1mRNAs, encoding the ferritin light (Ftl) and heavy (Fth) chains that assemble into ferritin, a critical complex for iron storage and reduction, are enriched in perisynaptic astrocytic processes as compared to astrocytic soma. These data suggested that ferritin translation plays a specific role at the perisynaptic astrocytic interface and is tighly regulated by local translation. Here, we used our recently describedAstroDot3D in situ methodology to study the density and localization of ferritin mRNAs in astrocytes in the hippocampus in three different contexts in which local or systemic iron overload has been documented: aging, the hepcidin knock‐out mouse model of hemochromatosis and the APP/PS1dE9 mouse model of Alzheimer's disease (AD). Our results showed that in wild type mice,Fth1mRNA density was higher thanFtl1and that both mRNAs were mostly distributed in astrocyte fine processes. Aging and absence of hepcidin caused an increasedFth1/Ftl1ratio in astrocytes and in the case of aging, led to a redistribution ofFth1mRNAs in astrocytic fine processes. In contrast, in AD mice, we observed a lowerFth1/Ftl1ratio.Fth1mRNAs became more somatic andFtl1mRNAs redistributed in large processes of astrocytes proximal to Amyloid beta (Aß) deposits. Hence, we propose that regulation of ferritin mRNA density and distribution in astrocytes contribute to iron homeostasis in physiology and pathophysiology. image

Significance: Adaptive thermogenesis is a metabolic switch that converts the metabolic status of fat tissue from energy conservation to energy release into heat, thereby significantly attenuating the energy burden of obesity and diabetes. It is well known that increased iron content and subsequent mitochondrial formation are required for thermogenic activation. However, no information is available on how iron is mobilized from storage sites into thermogenic fat. Here, we show that acute hypoxia and stress-erythropoiesis responses facilitate securing iron required for white-to-beige fat conversion. Our study revealed that hepcidin down-regulation is a fundamental mechanism required for beige fat development. It also suggests that systemic iron modulation could be a promising strategy to curb obesity and metabolic complications by augmenting adaptive thermogenesis.

Increased body iron stores and inflammation in adipose tissue have been implicated in the pathogenesis of insulin resistance (IR) and type 2 diabetes mellitus. However, the underlying basis of these associations are unclear. In order to assess this, we studied how IR and associated inflammation in adipose tissue developed in the presence of increased body iron stores. Male hepcidin knock-out ( Hamp1 ^-/- ) mice, which have increased body iron stores, and wild-type (WT) mice were fed a high-fat diet (HFD) for 12 and 24 weeks. Development of IR and metabolic parameters linked to this, insulin signaling in tissue, and inflammation and iron-related parameters in visceral adipose tissue were studied in these animals. HFD-feeding resulted in impaired glucose tolerance in both genotypes of mice. In response to the HFD for 24 weeks, Hamp1-/- mice gained less body weight and developed less IR than corresponding WT mice. This was associated with less lipid accumulation in the liver and decreased inflammation and lipolysis in the adipose tissue in the knock-out mice, than in the WT animals. Fewer macrophages infiltrated the adipose tissue in the knockout mice than in wild-type mice, with these macrophages exhibiting a predominantly anti-inflammatory (M2-like) phenotype. These observations suggest a novel role of hepcidin (central regulator of systemic iron homeostasis) in the development of inflammation in adipose tissue and insulin resistance, in response to a high-fat diet. CLINICAL PERSPECTIVES: Elevated body iron stores and inflammation in adipose tissue have been implicated in the pathogenesis of insulin resistance (IR) and type 2 diabetes mellitus. However, the underlying molecular mechanisms linking them are unclear. In response to high-fat diet (HFD)-feeding (to induce IR), mice that lacked hepcidin ( Hamp1 ^-/- ) (and hence had elevated body iron stores) gained less body weight and developed less insulin resistance than wild-type (WT) mice. Inflammation and infiltration of macrophages into adipose tissue of HFD-fed Hamp1 ^-/- mice were less than in WT mice, with the macrophages exhibiting an anti-inflammatory M2-like phenotype. These findings suggest a novel role of iron and hepcidin in HFD-induced inflammation in adipose tissue and development of insulin resistance. They raise the possibility that modulation of body iron may represent a potential way to inhibit these processes.

Iron is required for the oxidative response of neutrophils to allow the production of reactive oxygen species (ROS). However, neutrophil function may be severely altered in conditions of iron overload, as observed in chronically transfused patients. Therefore, a tight regulation of neutrophil iron homeostasis seems to be critical for avoiding iron toxicity. Hepcidin is the key iron regulator in organisms; however, no studies have investigated its role in maintaining neutrophil iron homeostasis or characterized neutrophil function in patients with hereditary hemochromatosis (HH), a common iron overload genetic disorder that results from a defect in hepcidin production. To explore these issues, we studied 2 mouse models of iron overload: an experimentally induced iron overload model (EIO), in which hepcidin is increased, and a genetic HH model of iron overload with a deletion of hepatic hepcidin. We found that iron-dependent increase of hepatic hepcidin results in neutrophil intracellular iron trapping and consecutive defects in oxidative burst activity. In contrast, in both HH mouse models and HH patients, the lack of hepcidin expression protects neutrophils from toxic iron accumulation. Moreover, systemic iron overload correlated with a surprising neutrophil priming and resulted in a more powerful oxidative burst. Indeed, important factors in neutrophil priming and activation, such as tumor necrosis factor α (TNF-α), VCAM-1, and ICAM-1 are increased in the plasma of HH patients and are associated with an increase in HH neutrophil phagocytosis capacity and a decrease in L-selectin surface expression. This is the first study to characterize neutrophil iron homeostasis and associated functions in patients with HH.

Pulmonary iron excess is deleterious and contributes to a range of chronic and acute inflammatory diseases. Optimal lung iron concentration is maintained through dynamic regulation of iron transport and storage proteins. The iron-regulatory hormone hepcidin is also expressed in the lung. In order to better understand the interactions between iron-associated molecules and the hepcidin-ferroportin axis in lung iron balance, we examined lung physiology and inflammatory responses in two murine models of systemic iron-loading, either hepcidin knock-out (Hepc KO) or liver-specific hepcidin KO mice (Hepc KOliv), which do (Hepc KOliv) or do not (Hepc KO) express lung hepcidin. We have found that increased plasma iron in Hepc KO mice is associated with increased pulmonary iron levels, consistent with increased cellular iron uptake by pulmonary epithelial cells, together with an increase at the apical membrane of the cells of the iron exporter ferroportin, consistent with increased iron export in the alveoli. Subsequently, alveolar macrophages accumulate iron in a non-toxic form and this is associated with elevated production of ferritin. The accumulation of iron in the lung macrophages of hepcidin KO mice contrasts with splenic and hepatic macrophages which contain low iron levels as we have previously reported. Hepc KOliv mice with liver-specific hepcidin deficiency demonstrated same pulmonary iron overload profile as the Hepc KO mice, suggesting that pulmonary hepcidin is not critical in maintaining local iron homeostasis. In addition, the high iron load in the lung of Hepc KO mice does not appear to enhance acute lung inflammation or injury. Lastly, we have shown that intraperitoneal LPS injection is not associated with pulmonary hepcidin induction, despite high levels of inflammatory cytokines. However, intranasal LPS injection stimulates a hepcidin response, likely derived from alveolar macrophages, and alters pulmonary iron content in Hepc KO mice.

The biguanide metformin is used for its antidiabetic effect for many years but how metformin acts remains poorly understood and controversial. AMP-activated protein kinase (AMPK), a protein kinase that plays a key role in maintaining energy homeostasis, is assumed to be one of the prime targets of metformin. However, since our demonstration that AMPK is not required for the beneficial effects of metformin on the control of glycemia, the list of AMPK-independent actions of metformin is rapidly increasing. Given the conflicting results on the effects of metformin we sought, using our genetic mouse models deficient in the catalytic subunits of AMPK, to determine whether this kinase is involved in the effects of metformin on the expression of the iron-regulatory hormone hepcidin, as recently proposed. Here we demonstrate, using different approaches, either isolated hepatocytes that lack AMPK, or direct AMPK activators, that, AMPK activation is not necessary for metformin to inhibit BMP6-induced hepcidin gene expression. These results may shed new lights on the increasingly recognized AMPK-independent metformin’s molecular action, an important area of current research.

Iron is both an essential and a potentially toxic element, and its systemic homeostasis is controlled by the iron hormone hepcidin. Hepcidin binds to the cellular iron exporter ferroportin, causes its degradation, and thereby diminishes iron uptake from the intestine and the release of iron from macrophages. Given that hepcidin‐resistant ferroportin mutant mice show exocrine pancreas dysfunction, we analysed pancreata of aging hepcidin knockout (KO) mice. Hepcidin and Hfe KO mice were compared with wild‐type (WT) mice kept on standard or iron‐rich diets. Twelve‐month‐old hepcidin KO mice were subjected to daily minihepcidin PR73 treatment for 1 week. Six‐month‐old hepcidin KO mice showed cytoplasmic acinar iron overload and mild pancreatitis, together with elevated expression of the iron uptake mediators DMT1 and Zip14. Acinar atrophy, massive macrophage infiltration, fatty changes and pancreas fibrosis were noted in 1‐year‐old hepcidin KO mice. As an underlying mechanism, 6‐month‐old hepcidin KO mice showed increased pancreatic oxidative stress, with elevated DNA damage, apoptosis and activated nuclear factor‐κB (NF‐κB) signalling. Neither iron overload nor pancreatic damage was observed in WT mice fed iron‐rich diet or in Hfe KO mice. Minihepcidin application to hepcidin KO mice led to an improvement in general health status and to iron redistribution from acinar cells to macrophages. It also resulted in decreased NF‐κB activation and reduced DNA damage. In conclusion, loss of hepcidin signalling in mice leads to iron overload‐induced chronic pancreatitis that is not seen in situations with less severe iron accumulation. The observed tissue injury can be reversed by hepcidin supplementation. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cystic Fibrosis (CF) is a frequent and lethal autosomal recessive disease caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Patients with CF suffer from chronic infections and severe inflammation, which lead to progressive pulmonary and gut diseases. Recently, an expanding body of evidence has suggested that iron homeostasis was abnormal in CF with, in particular, systemic iron deficiency and iron sequestration in the epithelium airway. The molecular mechanisms responsible for iron dysregulation and the relationship with inflammation in CF are unknown. We assessed the impact of CFTR deficiency on systemic and tissue iron homeostasis as well as inflammation in wildtype and CFTR knockout (KO) mice. First, in contrast to the systemic and intestinal inflammation we observed in the CFTR KO mice, we reported the absence of lung phenotype with regards to both inflammation and iron status. Second, we showed a significant decrease of plasma ferritin levels in the KO mice, as in CF patients, likely caused by a decrease in spleen ferritin levels. However, we measured unchanged plasma iron levels in the KO mice that may be explained by increased intestinal iron absorption. These results indicate that in CF, the lung do not predominantly contributes to the systemic ferritin deficiency and we propose the spleen as the major organ responsible for hypoferritinemia in the KO mouse. These results should provide a better understanding of iron dysregulation in CF patients where treating or not iron deficiency remains a challenging question.