REDD1 deletion and treadmill running increase liver hepcidin and gluconeogenic enzymes in male mice.

The iron-regulatory hormone hepcidin is transcriptionally up-regulated by gluconeogenic signals. Recent evidence suggeststhat increases in circulating hepcidin may decrease dietary iron absorption following prolonged exercise, however evidence is limited on whether gluconeogenic signals contribute to post-exercise increases in hepcidin. Mice with genetic knockout of regulated in development and DNA response-1 (REDD1) display greater glycogen depletion following exercise, possibly indicating greater gluconeogenesis. The objective of the present study was to determine liver hepcidin, markers of gluconeogenesis and iron metabolism in REDD1 knockout and wild-type mice following prolonged exercise. Twelve-week-old male REDD1 knockout and wild-type mice were randomised to rest or 60 min treadmill running with 1, 3 or 6 h recovery (n = 5-8/genotype/group). Liver gene expression of hepcidin (Hamp) and gluconeogenic enzymes (Ppargc1a, Creb3l3, Pck1, Pygl) were determined by qRT-PCR. Effects of genotype, exercise and their interaction were assessed by two-way ANOVAs with Tukey's post-hoc tests, and Pearson correlations were used to assess the relationships between Hamp and study outcomes. Liver Hamp increased 1- and 4-fold at 3 and 6 h post-exercise, compared to rest (P-adjusted < 0⋅009 for all), and was 50% greater in REDD1 knockout compared to wild-type mice (P = 0⋅0015). Liver Ppargc1a, Creb3l3 and Pck1 increased with treadmill running (P < 0⋅0001 for all), and liver Ppargc1a, Pck1 and Pygl were greater with REDD1 deletion (P < 0⋅02 for all). Liver Hamp was positively correlated with liver Creb3l3 (R = 0⋅62, P < 0⋅0001) and Pck1 (R = 0⋅44, P = 0⋅0014). In conclusion, REDD1 deletion and prolonged treadmill running increased liver Hamp and gluconeogenic regulators of Hamp, suggesting gluconeogenic signalling of hepcidin with prolonged exercise.

Mild to Moderate Food Deprivation Increases Hepcidin and Results in Hypoferremia and Tissue Iron Sequestration in Mice.

BACKGROUND: Short-term starvation and severe food deprivation (FD) reduce dietary iron absorption and restricts iron to tissues, thereby limiting the amount of iron available for erythropoiesis. These effects may be mediated by increases in the iron regulatory hormone hepcidin; however, whether mild to moderate FD has similar effects on hepcidin and iron homeostasis is not known. OBJECTIVES: To determine the effects of varying magnitudes and durations of FD on hepcidin and indicators of iron status in male and female mice. METHODS: Male and female C57BL/6J mice (14 wk old; n = 170) were randomly assigned to consume AIN-93M diets ad libitum (AL) or varying magnitudes of FD (10%, 20%, 40%, 60%, 80%, or 100%). FD was based on the average amount of food consumed by the AL males or females, and food was split into morning and evening meals. Mice were euthanized at 48 h and 1, 2, and 3 wk, and hepcidin and indicators of iron status were measured. Data were analyzed by Pearson correlation and one-way ANOVA. RESULTS: Liver hepcidin mRNA was positively correlated with the magnitude of FD at all time points (P < 0.05). At 3 wk, liver hepcidin mRNA increased 3-fold with 10% and 20% FD compared with AL and was positively associated with serum hepcidin (R = 0.627, P < 0.0001). Serum iron was reduced by ∼65% (P ≤ 0.01), and liver nonheme iron concentrations were ∼75% greater (P ≤ 0.01) with 10% and 20% FD for 3 wk compared with AL. Liver hepcidin mRNA at 3 wk was positively correlated with liver Bmp6 (R = 0.765, P < 0.0001) and liver gluconeogenic enzymes (R = >0.667, P < 0.05) but not markers of inflammation (P > 0.05). CONCLUSIONS: FD increases hepcidin in male and female mice and results in hypoferremia and tissue iron sequestration. These findings suggest that increased hepcidin with FD may contribute to the disturbances in iron homeostasis with undernutrition.

A Prolonged Bout of Running Increases Hepcidin and Decreases Dietary Iron Absorption in Trained Female and Male Runners.

BACKGROUND: Declines in iron status are frequently reported in those who regularly engage in strenuous physical activity. A possible reason is increases in the iron regulatory hormone hepcidin, which functions to inhibit dietary iron absorption and can be induced by the inflammatory cytokine interleukin-6 (IL-6). OBJECTIVES: The current study aimed to determine the impact of a prolonged bout of running on hepcidin and dietary iron absorption in trained female and male runners. METHODS: Trained female and male collegiate cross country runners (n = 28, age: 19.7 ± 1.2 y, maximal oxygen uptake: 66.1 ± 6.1 mL $\cdot$ kg -1$\cdot$ min-2, serum ferritin: 21.9 ± 13.3 ng/mL) performed a prolonged run (98.8 ± 14.7 min, 21.2 ± 3.8 km, 4.7 ± 0.3 min/km) during a team practice. Participants consumed a stable iron isotope with a standardized meal 2 h postrun and blood was collected 1 h later. The protocol was repeated 2 wk later except participants abstained from exercise (rest). RBCs were collected 15 d after exercise and rest to determine isotope enrichment. Differences between exercise and rest were assessed by paired t tests and Wilcoxon matched-pairs signed rank tests. Data are means ± SDs. RESULTS: Plasma hepcidin increased 51% after exercise (45.8 ± 34.4 ng/mL) compared with rest (30.3 ± 27.2 ng/mL, P = 0.0010). Fractional iron absorption was reduced by 36% after exercise (11.8 ± 14.6 %) compared with rest (18.5 ± 14.4 %, P = 0.025). Plasma IL-6 was greater after exercise (0.660 ± 0.354 pg/mL) than after rest (0.457 ± 0.212 pg/mL, P < 0.0001). Exploratory analyses revealed that the increase in hepcidin with exercise may be driven by a response in males but not females. CONCLUSIONS: A prolonged bout of running increases hepcidin and decreases dietary iron absorption compared with rest in trained runners with low iron stores. The current study supports that IL-6 contributes to the increase in hepcidin with prolonged physical activity, although future studies should explore potential sex differences in the hepcidin response.This trial was registered at Clinicaltrials.gov as NCT04079322.

Iron deficient diets modify the gut microbiome and reduce the severity of enteric infection in a mouse model of S. Typhimurium-induced enterocolitis.

Enteric infections are widespread in infants and children living in low-resource settings. Iron availability in the gastrointestinal tract may modify the gut microbiome and impact the incidence and severity of enteropathy. This study was designed to determine the effect of an iron-deplete compared to an iron-rich environment in the lower intestine on the gut microbiome, and whether iron availability in the lower intestine affects the host immune response and severity of enteric infection in young mice. Weanling C57BL/6 female mice were fed an iron deficient (Fe-, <6 ppm iron) or an iron fortified (Fe+, 300 ppm iron) diet for 6 weeks. Mice were pretreated with streptomycin prior to oral inoculation of Salmonella enterica subspecies enterica serovar Typhimurium to induce enteric infection (Sal+) or saline control (Sal-). Cecal iron concentrations were 55-fold greater with Fe+Sal- compared to Fe-Sal-. Microbiome sequencing revealed shifts in gut microbiota with dietary iron and enteric infection. There was ∼30% more S. Typhimurium in the cecum of Fe+Sal+ compared to Fe-Sal+. Plasma hepcidin increased with dietary iron and enteric infection, but was greatest in Fe+Sal+. Plasma lipocalin-2 and spleen size relative to bodyweight were greater in Fe+Sal+ compared to Fe+Sal-, Fe-Sal- and Fe-Sal+, and Fe+Sal+ lost more bodyweight compared to Fe-Sal+. Unabsorbed iron in the lower intestine modifies the gut microbiome and promotes a more severe enteropathy. These findings could suggest the need for alternative iron supplementation strategies in areas where enteric infection are common.