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Research Article

Metformin promotes innate immunity through a conserved PMK-1/p38 MAPK pathway

, , , , , , , , , ORCID Icon, & ORCID Icon show all
Pages 39-48 | Received 08 Jun 2019, Accepted 24 Oct 2019, Published online: 28 Dec 2019

Figures & data

Figure 1. Metformin enhances pathogen resistance

(a) Metformin promotes innate immune response to P. aeruginosa PA14 compared to WT in a dose-dependent manner (*P< 0.05, log-rank test). (b) metformin (50 mM) did not delay the proliferation of P. aeruginosa PA14. (c) Metformin (50 mM) did not affect the colony-forming units (CFUs) of bacteria in WT worms after P. aeruginosa PA14 infection. These results are mean ± SD of three independent experiments, each involving 15 parallel groups. NS, no significance.
Figure 1. Metformin enhances pathogen resistance

Figure 2. Metformin promotes innate immunity through the p38 MAPK pathway

(a–i) PMK-1/p38 MAPK is involved in metformin-mediated innate immunity. Metformin (50 mM) enhanced resistance to P. aeruginosa PA14 in WT (N2) (a), daf-2(e1370) (c), mpk-1(n2521) (d), egl-30(n686) (e), dkf-2(ok1704)(f), fshr-1(ok778)mutants (g), but not in pmk-1(km25) mutants (b). *P< 0.05 versus worms + metformin (log-rank test). (h and i) Mutations in the components of the p38 MAPK pathway suppressed metformin-mediated resistance of worms to PA14. (h) nsy-1(ag3); (i) sek-1(ag1).
Figure 2. Metformin promotes innate immunity through the p38 MAPK pathway

Figure 3. Metformin activates p38 MAPK signaling in C. elegans

(a) The phosphorylation of p38 MAPK was elevated in WT worms (N2) exposed to metformin (50 mM). (b) The right panel shows quantification of phosphorylated p38 MAPK levels. These results are mean ± SD of three independent experiments performed in triplicate. *P< 0.05 vs E. coliOP50 (one-way ANOVA followed by a Student-Newman-Keuls test). (c) The mRNA levels of three p38 MAPK targets K08D8.5, lys-2, and F35E12.5 in worms exposed to metformin (50 mM). These results are mean ± SD of three independent experiments performed in triplicate. *P< 0.05 versus OP50 (one-way ANOVA followed by a Student-Newman-Keuls test). (d) Expression of K08D8.5p::GFP was up-regulated in WT worms, but not in worms subjected to pmk-1(km25) mutants, exposed to metformin (50 mM). (e) The right panel shows quantification of fluorescence intensity. These results are mean ± SD of three independent experiments performed in triplicate. *P< 0.05 versus OP50 (one-way ANOVA followed by a Student-Newman-Keuls test).
Figure 3. Metformin activates p38 MAPK signaling in C. elegans

Figure 4. Intestinal PMK-1 enhances resistance to pathogen infection after metformin treatment

(a) metformin (50 mM) did not increase resistance to P. aeruginosa PA14 infection in the intestine knockdown of pmk-1worms. However, RNAi of pmk-1 in hypodermis (b), muscle (c), and neuron (d), respectively, after metformin treatment did not prevent metformin action on promoting pseudomonas resistance. (e) Expression of pmk-1 under the intestinal-specific vha-6 promoter (AY102) restored resistance against P. aeruginosa PA14 infection in pmk-1(km25) mutants after treatment with metformin (50 mM) .*P< 0.05 versus worms + metformin (log-rank test). (f) Pre-treatment of AY102 worms with metformin (50 mM) restored the level of active PMK-1. (g) The right panel shows quantification of phosphorylated p38 MAPK levels. These results are mean ± SD of three independent experiments performed in triplicate. *P< 0.05 versus OP50 (one-way ANOVA followed by a Student-Newman-Keuls test).
Figure 4. Intestinal PMK-1 enhances resistance to pathogen infection after metformin treatment

Figure 5. Metformin protected mice against P. aeruginosa infection and increased p-p38 in the lung

(a) Metformin (200 mg/kg body weight) treated mice increases the resistance to P. aeruginosa PA14 infection compared with control mice. *P< 0.05 (log-rank test). (b) The p38 inhibitor SB202190 increased the susceptibility to P. aeruginosa PA14 infection compared with control mice *P< 0.05 (log-rank test) and suppressed the enhanced resistance to P. aeruginosa PA14 upon metformin (200 mg/kg body weight) treatment P =0.0512 (log-rank test). (c) Metformin (200 mg/kg body weight) significantly increased the levels of active PMK-1 in the lung. (d) The right panel shows quantification of phosphorylated p38 MAPK levels. These results are mean ± SD of three independent experiments performed in triplicate. *P< 0.05 versus control (one-way ANOVA followed by a Student-Newman-Keuls test).
Figure 5. Metformin protected mice against P. aeruginosa infection and increased p-p38 in the lung
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