The Effect of Exogenous Melatonin or Luzindole on NLRP3 Inflammasome Activation and Endogenous Melatonin Synthesis
Subsequently, we showed that administration of melatonin dramatically decreased the protein expressions of NLRP3, mature IL-1β and caspase 1(p20), lowered the productions of IL-1β and IL-18 in comparison with those in vehicle-treated WT mice following OVA challenge (Figures 6A–F). Importantly, NLRP3 inflammasome activity was not significantly different between vehicle-treated and luzindole-treated TLR2−/− mice post OVA challenge (Figures 6A–F). These data suggested that melatonin elicited its effect on NLRP3 inflammasome activity via TLR2 signaling, when TLR2 was deficient, blocking the effect of melatonin had null effect on NLRP3 inflammasome activity.
Figure 6  The effect of exogenous melatonin or luzindole on NLRP3 inflammasome activation and endogenous melatonin synthesis. (A) Representative blots showing the protein expression of NLRP3, mature IL-1β, pro-IL-1β, and caspase1(p20) in lung homogenate. (B–D) Relative band densities of NLRP3 and caspase1(p20) were analyzed by normalizing to GAPDH, relative band densities of IL-1β was analyzed by normalizing to pro-IL-1β. (E,F) The levels of IL-1β, IL-18 in BALF were detected by ELISA. (G) Representative blots showing the levels of AANAT and ASMT in lung homogenate. (H,I) Relative band densities of AANAT and ASMT were analyzed by normalizing to GAPDH. (J,K) The level of 5-HT in BALF and melatonin in the lung homogenate were detected by ELISA. *p < 0.05, **p < 0.01, ***p < 0.001. Finally, we found that treatment of melatonin resulted in dramatic increase in the protein expression of ASMT, marked elevation in the levels of 5-HT and melatonin, while did not affect the AANAT expression in comparing with vehicle-treated WT mice (Figures 6G–K). The protein expression of ASMT in lung tissues, the levels of 5-HT in BALF and melatonin in lung homogenate in melatonin-treated WT mice were comparable to that in vehicle-treated TLR2−/− mice post OVA challenge. However, TLR2−/− mice treated with luzindole showed notably reduced expressions of both AANAT and ASMT (Figures 6G–I), and lowered the level of melatonin in lung homogenate but not 5-HT in BALF in comparison with that of vehicle-treated TLR2−/− mice following OVA challenge (Figures 6J,K). Therefore, our study suggested that administration of melatonin further promoted endogenous melatonin biosynthesis, while treatment of luzindole significant inhibited endogenous melatonin synthesis in TLR2−/− mice.