Lipocalin 2 alleviates iron toxicity by facilitating hypoferremia of inflammation and limiting catalytic iron generation

Abstract

Iron is an essential transition metal ion for virtually all aerobic organisms, yet its dysregulation (iron overload or anemia) is a harbinger of many pathologic conditions. Hence, iron homeostasis is tightly regulated to prevent the generation of catalytic iron (CI) which can damage cellular biomolecules. In this study, we investigated the role of iron-binding/trafficking innate immune protein, lipocalin 2 (Lcn2, aka siderocalin) on iron and CI homeostasis using Lcn2 knockout (KO) mice and their WT littermates. Administration of iron either systemically or via dietary intake strikingly upregulated Lcn2 in the serum, urine, feces, and liver of WT mice. However, similarly-treated Lcn2KO mice displayed elevated CI, augmented lipid peroxidation and other indices of organ damage markers, implicating that Lcn2 responses may be protective against iron-induced toxicity. Herein, we also show a negative association between serum Lcn2 and CI in the murine model of dextran sodium sulfate (DSS)-induced colitis. The inability of DSS-treated Lcn2KO mice to elicit hypoferremic response to acute colitis, implicate the involvement of Lcn2 in iron homeostasis during inflammation. Using bone marrow chimeras, we further show that Lcn2 derived from both immune and non-immune cells participate in CI regulation. Remarkably, exogenous rec-Lcn2 supplementation suppressed CI levels in Lcn2KO serum and urine. Collectively, our results suggest that Lcn2 may facilitate hypoferremia, suppress CI generation and prevent iron-mediated adverse effects.

Ectopic Expression of Innate Immune Protein, Lipocalin-2, in Lactococcus lactis Protects Against Gut and Environmental Stressors

“…Lcn2 primarily controls the gut bacterial overgrowth by limiting its iron uptake and also mediates facilitation of the hypoferremia during inflammation 12 . Additionally, Lcn2 serve as an indispensable factor for proper neutrophil migration, adhesion, and function 50 .…”

“…Our findings suggested that the beneficial effects of Lactis Lcn2 could be potentially explained, at least in part, by the augmented survival or colonization ability of the probiotic L. lactis that express Lcn2. Nevertheless, we could not rule out the possibility that exogenous Lcn2 may also provide mucoprotective effects to the host via: (i) mitigating gut dysbiosis such as preventing the bloom of Enterobacteriaceae (e.g., E. coli ) 4, 10 , (ii) restricting luminal iron and the labile iron pool 12 , thus attenuating iron-induced oxidative stress, (iii) serving as an epithelial survival factor 52 and promote wound healing 53, 54 . Further prolonged survival may also enhance the generation of L. lactis derived soluble, effector molecules, which can diminish gut inflammation.…”

“…Previously, we have shown that fecal Lcn2 is a dynamic, sensitive and non-invasive biomarker of gut inflammation 3 . Among its diverse physiological functions, one well-established role of Lcn2 is to sequester bacterial siderophores, such as enterobactin (Ent) and thus limit the growth of iron-dependent bacteria 4, 10–12 . In addition, Lcn2 also plays a role in facilitating the hypoferremia of inflammation and suppressing the generation of catalytic iron 12 .…”

“…Among its diverse physiological functions, one well-established role of Lcn2 is to sequester bacterial siderophores, such as enterobactin (Ent) and thus limit the growth of iron-dependent bacteria 4, 10–12 . In addition, Lcn2 also plays a role in facilitating the hypoferremia of inflammation and suppressing the generation of catalytic iron 12 . Such mechanisms suggest that the upregulation of Lcn2 during intestinal or systemic inflammation may mediate alterations in the gut microbiota, particularly during IBD 13–15 .…”

Modulation of urinary siderophores by the diet, gut microbiota and inflammation in mice

“…Total iron levels were estimated using a standard curve generated with the iron AA standard (Ricca Chemical Company). Serum TIBC and catalytic iron was analyzed as described in detail elsewhere [19, 20]. Transferrin saturation was calculated as serum total iron/TIBC × 100 [21].…”