Lactobacillus johnsonii L531 Ameliorates Salmonella enterica Serovar Typhimurium Diarrhea by Modulating Iron Homeostasis and Oxidative Stress via the IRP2 Pathway

Salmonella enterica serovar Typhimurium (S. Typhimurium) has evolved mechanisms to evade the host's nutritional immunity and thus promote bacterial growth by using the iron in the host. However, the detailed mechanisms of S. Typhimurium induce dysregulation of iron homeostasis and whether Lactobacillus johnsonii L531 can alleviate the iron metabolism disorder caused by S. Typhimurium has not been fully elucidated. Here, we show that S. Typhimurium activated the expression of iron regulatory protein 2 (IRP2), transferrin receptor 1, and divalent metal transporter protein 1 and suppressed the expression of iron exporter ferroportin, which resulted in iron overload and oxidative stress, inhibiting the key antioxidant proteins NF-E2-related factor 2, Heme Oxygenase-1, and Superoxide Dismutase in vitro and in vivo. L. johnsonii L531 pretreatment effectively reversed these phenomena. IRP2 knockdown inhibited iron overload and oxidative damage induced by S. Typhimurium in IPEC-J2 cells, while IRP2 overexpression promoted iron overload and oxidative damage caused by S. Typhimurium. Interestingly, the protective effect of L. johnsonii L531 on iron homeostasis and antioxidant function was blocked following IRP2 overexpression in Hela cells, demonstrating that L. johnsonii L531 attenuates disruption of iron homeostasis and consequent oxidative damage caused by S. Typhimurium via the IRP2 pathway, which contributes to the prevention of S. Typhimurium diarrhea in mice.

Automated summary

Salmonella enterica serovar Typhimurium (S. Typhimurium) has evolved mechanisms to evade the host's nutritional immunity and promote bacterial growth by using host iron. However, the detailed mechanisms of S. Typhimurium-induced dysregulation of iron homeostasis and the potential alleviative effect of Lactobacillus johnsonii L531 on iron metabolism disorder caused by S. Typhimurium remains unclear. In this study, it was found that S. Typhimurium activated the expression of iron regulatory protein 2 (IRP2) and other iron-related proteins while suppressing the expression of iron exporter ferroportin, resulting in iron overload and oxidative stress. Pretreatment with L. johnsonii L531 effectively reversed these effects. Knockdown of IRP2 inhibited iron overload and oxidative damage induced by S. Typhimurium, while overexpression of IRP2 promoted these effects. Furthermore, the protective effect of L. johnsonii L531 on iron homeostasis and antioxidant function was blocked by IRP2 overexpression, indicating that L. johnsonii L531 attenuates disruption of iron homeostasis and oxidative damage caused by S. Typhimurium via the IRP2 pathway, contributing to the prevention of S. Typhimurium diarrhea in mice.