Dietary Iron Is Necessary to Support Proliferative Regeneration after Intestinal Injury.

BACKGROUND: Tissue repair and regeneration in the gastrointestinal system are crucial for maintaining homeostasis, with the process relying on intricate cellular interactions and affected by micro- and macro-nutrients. Iron, essential for various biological functions, plays a dual role in tissue healing by potentially causing oxidative damage and participating in anti-inflammatory mechanisms, underscoring its complex relationship with inflammation and tissue repair. OBJECTIVE: The study aimed to elucidate the role of low dietary iron in gastrointestinal tissue repair. METHODS: We utilized quantitative iron measurements to assess iron levels in inflamed regions of patients with ulcerative colitis and Crohn's disease. In addition, 3 mouse models of gastrointestinal injury/repair (dextran sulfate sodium-induced colitis, radiation injury, and wound biopsy) were used to assess the effects of low dietary iron on tissue repair. RESULTS: We found that levels of iron in inflamed regions of both patients with ulcerative colitis and Crohn's disease are elevated. Similarly, during gastrointestinal repair, iron levels were found to be heightened, specifically in intestinal epithelial cells across the 3 injury/repair models. Mice on a low-iron diet showed compromised tissue repair with reduced proliferation. In standard diet, epithelial cells and the stem cell compartment maintain adequate iron stores. However, during a period of iron deficiency, epithelial cells exhaust their iron reserves, whereas the stem cell compartments maintain their iron pools. During injury, when the stem compartment is disrupted, low iron levels impair proliferation and compromise repair mechanisms. CONCLUSIONS: Low dietary iron impairs intestinal repair through compromising the ability of epithelial cells to aid in intestinal proliferation.

Myeloid Hif2α is not essential to maintain systemic iron homeostasis.

Dietary consumption serves as the primary source of iron uptake, and erythropoiesis acts as a major regulator of systemic iron demand. In addition to intestinal iron absorption, macrophages play a crucial role in recycling iron from senescent red blood cells. The kidneys are responsible for the production of erythropoietin (Epo), which stimulates erythropoiesis, whereas the liver plays a central role in producing the iron-regulatory hormone hepcidin. The transcriptional regulator hypoxia-inducible factor (HIF)2α has a central role in the regulation of Epo, hepcidin, and intestinal iron absorption and therefore plays a crucial role in coordinating the tissue crosstalk to maintain systemic iron demands. However, the precise involvement of Hif2α in macrophages in terms of iron homeostasis remains uncertain. Our study demonstrates that deleting Hif2α in macrophages does not disrupt the expression of iron transporters or basal erythropoiesis. Mice lacking Hif2α in myeloid cells exhibited no discernible differences in hemodynamic parameters, including hemoglobin concentrations and erythrocyte count, when compared with littermate controls. This similarity was observed under conditions of both dietary iron deficiency and acute erythropoietic demand. Notably, we observed a significant increase in the expression of iron transporters in the duodenum during iron deficiency, indicating heightened iron absorption. Therefore, our findings suggest that the disruption of Hif2α in myeloid cells does not significantly impact systemic iron homeostasis under normal physiologic conditions. However, its disruption induces adaptive physiologic changes in response to elevated iron demand, potentially serving as a mechanism to sustain increased erythropoietic demand.

Modulation of the HIF2α-NCOA4 axis in enterocytes attenuates iron loading in a mouse model of hemochromatosis.

Intestinal iron absorption is activated during increased systemic demand for iron. The best-studied example is iron deficiency anemia, which increases intestinal iron absorption. Interestingly, the intestinal response to anemia is very similar to that of iron overload disorders, as both the conditions activate a transcriptional program that leads to a hyperabsorption of iron via the transcription factor hypoxia-inducible factor 2α (HIF2α). However, pathways for selective targeting of intestine-mediated iron overload remain unknown. Nuclear receptor coactivator 4 (NCOA4) is a critical cargo receptor for autophagic breakdown of ferritin and the subsequent release of iron, in a process termed ferritinophagy. Our work demonstrates that NCOA4-mediated intestinal ferritinophagy is integrated into systemic iron demand via HIF2α. To demonstrate the importance of the intestinal HIF2α/ferritinophagy axis in systemic iron homeostasis, whole-body and intestine-specific NCOA4-/- mouse lines were generated and assessed. The analyses revealed that the intestinal and systemic response to iron deficiency was not altered after disruption of intestinal NCOA4. However, in a mouse model of hemochromatosis, ablation of intestinal NCOA4 was protective against iron overload. Therefore, NCOA4 can be selectively targeted for the management of iron overload disorders without disrupting the physiological processes involved in the response to systemic iron deficiency.

Colorectal cancer cells utilize autophagy to maintain mitochondrial metabolism for cell proliferation under nutrient stress.

Cancer cells reprogram cellular metabolism to maintain adequate nutrient pools to sustain proliferation. Moreover, autophagy is a regulated mechanism to break down dysfunctional cellular components and recycle cellular nutrients. However, the requirement for autophagy and the integration in cancer cell metabolism is not clear in colon cancer. Here, we show a cell-autonomous dependency of autophagy for cell growth in colorectal cancer. Loss of epithelial autophagy inhibits tumor growth in both sporadic and colitis-associated cancer models. Genetic and pharmacological inhibition of autophagy inhibits cell growth in colon cancer-derived cell lines and patient-derived enteroid models. Importantly, normal colon epithelium and patient-derived normal enteroid growth were not decreased following autophagy inhibition. To couple the role of autophagy to cellular metabolism, a cell culture screen in conjunction with metabolomic analysis was performed. We identified a critical role of autophagy to maintain mitochondrial metabolites for growth. Loss of mitochondrial recycling through inhibition of mitophagy hinders colon cancer cell growth. These findings have revealed a cell-autonomous role of autophagy that plays a critical role in regulating nutrient pools in vivo and in cell models, and it provides therapeutic targets for colon cancer.

Hepatic hepcidin/intestinal HIF-2α axis maintains iron absorption during iron deficiency and overload.

Iron-related disorders are among the most prevalent diseases worldwide. Systemic iron homeostasis requires hepcidin, a liver-derived hormone that controls iron mobilization through its molecular target ferroportin (FPN), the only known mammalian iron exporter. This pathway is perturbed in diseases that cause iron overload. Additionally, intestinal HIF-2α is essential for the local absorptive response to systemic iron deficiency and iron overload. Our data demonstrate a hetero-tissue crosstalk mechanism, whereby hepatic hepcidin regulated intestinal HIF-2α in iron deficiency, anemia, and iron overload. We show that FPN controlled cell-autonomous iron efflux to stabilize and activate HIF-2α by regulating the activity of iron-dependent intestinal prolyl hydroxylase domain enzymes. Pharmacological blockade of HIF-2α using a clinically relevant and highly specific inhibitor successfully treated iron overload in a mouse model. These findings demonstrate a molecular link between hepatic hepcidin and intestinal HIF-2α that controls physiological iron uptake and drives iron hyperabsorption during iron overload.