Dietary Iron Is Necessary to Support Proliferative Regeneration after Intestinal Injury

Abstract

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.

Keywords: intestinal injury; intestinal proliferation; iron; tissue repair; wound healing.

FIGURE 1

Iron levels are elevated in IBD tissue compared with normal tissue. ICP-MS measurement of total iron in IBD and normal tissue. n = 5 per group, 15 total. Data represent the mean ± SEM. ∗∗∗P < 0.001 compared with respective bars. IBD, inflammatory bowel disease; ICP-MS, inductively coupled plasma mass spectrometry.

FIGURE 2

Iron levels increase during DSS-induced colonic injury and is necessary for wound healing. (A) Time course with histology score (left y-axis, blue) and total tissue iron (right y-axis, red) of 350 ppm iron diet mice on 3% DSS and during recovery (n = 5 mice per time point, 80 total). (B) Labile iron as measured via flow cytometry by FerroOrange staining. (C) Representative H&E images of colon section at days 0, 7, 10, and 14. (D) Kaplan–Meier survival curve and (E) histological score of mice fed 350 ppm and 5 ppm iron diet on 3% DSS and during recovery (n = 5 per group per time point, 75 total). (F) Representative H&E colon sections during recovery phase between 350 ppm and 5 ppm iron diet mice. (G) Representative EdU-stained proximal to distal Swiss-rolled mucosal small intestine and colon sections and respective quantifications of 350 ppm and 5 ppm iron diet mice at basal, inflammatory, and recovery stages of DSS experiment (n = 3–5 per group, 23 total). (H) Red blood cell count measurements during the recovery phase at day 10 (n = 5 per group, 10 total). Data represent the mean ± SEM. ∗P < 0.05, ∗∗P < 0.01, and ∗∗∗P < 0.001 compared with respective bars. DSS, dextran sulfate sodium; EdU, 5-ethynyl-2'-deoxyuridine; H&E, hematoxylin & eosin.

FIGURE 3

Iron increases in the epithelial compartment after biopsy wound and helps facilitate wound closure. (A) Schematic of endoscopic biopsy wound model. (B) Total iron levels of wounds at 24 and 72 h after biopsy (n = 5 per time point, 15 total). (C) Labile iron levels measured by quantification of FerroOrange via flow cytometry (n = 5 per time point, 15 total). (D) Representative images of wound at 24 and 72 h after biopsy in mice fed 350 ppm and 5 ppm iron. (E) Wound closure percentage between mice fed 350 ppm and 5 ppm iron (n = 10 per group, 20 total). (F) Red blood cell count measurements at 72 h (n = 5 per group, 10 total) ∗P < 0.05, ∗∗P < 0.01, and ∗∗∗P < 0.001 compared with respective bars.

FIGURE 4

Low dietary iron decreases intestinal proliferation after injury. (A) Schematic of irradiation injury model. (B) Relative weight changes after irradiation (n = 3–8 per group per time point, 26 total). (C) Red blood cell count measurements at day 4 (n = 5 per group, 10 total). (D) Red blood cell count measurements at day 4 (n = 5 per group, 10 total). (E and F) Representative EdU-stained corpus and antrum or (G and H) representative EdU-stained small intestine and colon sections and respective quantifications at time points indicated after irradiation (n = 2–4 per group, 24 total). Data represent the mean ± SEM. ∗P < 0.05, ∗∗P < 0.01, and ∗∗∗P < 0.001 compared with respective bars. EdU, 5-ethynyl-2'-deoxyuridine.

FIGURE 5

Low dietary iron does not alter epithelial cell types. (A) Representative H&E images of small intestine and colon sections of mice fed 350 ppm and 5 ppm iron diet. Panel of cell type markers measured by qPCR in (B) small intestine or (C) colon of mice fed 350 ppm and 5 ppm iron diet (n = 5 per group, 10 total). H&E, hematoxylin & eosin.

FIGURE 6

Intestinal stem cell compartment maintains iron levels after low-iron diet. (A) Duodenal organoid formation efficiency in mice fed 350 ppm and 5 ppm iron diet (n = 5 per group, 10 total). FTH1 staining in the (B) small intestine and (C) colon sections of mice fed 350 ppm and 5 ppm iron diet at basal conditions or during (D) the inflammatory (E) recovery stage. FTH1, ferritin heavy chain 1.