Objective To study the molecular mechanism and regulatory effect of resistin on lipopolysaccharide (LPS)-induced interleukin (IL)-1β and tumor necrosis factor-α (TNF-α) expression through activation of peroxisome proliferator-activated receptor γ (PPARγ).
Methods An endotoxin-induced inflammation model was established by intraperitoneal injection of 5 mg/kg LPS in C57BL/6J mice, and the expression levels of resistin in mouse serum and spleen tissue were measured. Using resistin-treated RAW264.7 cells and C57BL/6J mice administered intraperitoneal injections as models, real-time quantitative PCR, Western blot, and ELISA were used to assess the mRNA and protein expression of PPARγ, total p65, phosphorylated p65, inhibitor of NF-κB alpha (IκBα), IL-1β, and TNF-α in LPS-induced RAW264.7 cells under conditions of resistin pretreatment or combined intervention with the PPARγ activator rosiglitazone or the inhibitor GW9662. Using C57BL/6J mice with intraperitoneal injection of 20 mg/kg LPS as a model, the effects of resistin on survival and serum IL-1β and TNF-α levels were evaluated.
Results After intraperitoneal injection of LPS, the mRNA and protein levels of resistin in the spleen of mice decreased by more than 80%, and the serum concentration dropped by 58%, which was statistically significant compared with the PBS control group (P < 0.001). Under pretreatment with 20 ng/mL resistin, the mRNA and relative protein expression levels of PPARγ in LPS-stimulated RAW264.7 cells increased from 0.58 ±0.07 and 0.34 ± 0.04 to 0.95 ± 0.03 and 1.78 ± 0.28, respectively, and further increased to 2.03 ± 0.16 and 2.82 ± 0.08 under the combined action of resistin and rosiglitazone, with statistically significant differences among the three treatments (P < 0.05). Resistin increased PPARγ mRNA and relative protein expression levels in LPS- and GW9662-treated RAW264.7 cells from 0.44 ± 0.06 and 0.43± 0.03 to 1.19± 0.08 and 0.55 ± 0.04, respectively, with statistically significant differences between the two groups (P < 0.05). Meanwhile, intracellular IL-1β mRNA levels decreased from 12.31 ± 1.50 to 7.45 ± 0.83, and cell culture supernatant protein levels dropped from (179.62 ± 9.27) pg/mL to (108.59 ± 17.32) pg/mL. Additionally, TNF-α mRNA levels declined from 3.41 ± 0.11 to 2.50 ± 0.04, while supernatant protein levels decreased from (1265.30 ± 154.78) pg/mL to （1025.96±45.41） pg/mL. Statistical comparisons between the two groups showed significant differences (P < 0.05), indicating that Retn partially inhibits GW9662's effect on promoting LPS-induced IL-1β and TNF-α expression. It was found that under the action of resistin, intracellular IκBα protein levels increased and p-p65/p65 expression decreased; meanwhile, IL-1β and TNF-α mRNA levels decreased by 24.7% and 26.9%, and protein expression levels decreased by 36.3% and 37.2%, respectively, with statistically significant differences compared with the LPS group (P < 0.05). Compared with the LPS-only treatment group, pretreatment with 25 μg/kg resistin reduced mouse serum IL-1β levels from (1616.66 ± 96.68) pg/mL to (1277.04 ± 27.73) pg/mL, TNF-α from (617.80 ± 145.54) pg/mL to (322.91 ± 129.50) pg/mL and IFN-γ from (12944.50 ± 90.69) pg/mL to (9222.84 ± 268.30) pg/mL, with all differences being statistically significant (P < 0.05); meanwhile, the 7-day survival rate of mice increased from 20% to 80%, which was statistically significant compared with the LPS group (P < 0.05).
Conclusion Intraperitoneal injection of LPS can lead to decreased resistin expression in the mouse spleen and human resistin can reduce LPS-induced IL-1β and TNF-α expression, as well as the mortality of LPS-induced shock mice by activating PPARγ and inhibiting NF-κB signaling.
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