Inflammasome activation in THP-1 target cells triggered by pathogenic Naegleria fowleri

Abstract

Naegleria fowleri, also known as the brain-eating amoeba, causes acute primary amoebic meningoencephalitis. During swimming and other recreational water activities, N. fowleri trophozoites penetrate the nasal mucosa and invade the olfactory bulbs, resulting in intense inflammatory reactions in the forebrain tissue. To investigate what kinds of inflammasome molecules are expressed in target cells due to N. fowleri infection, human macrophage cells (THP-1 cells) were co-cultured with N. fowleri trophozoites under the non-contact system, and consequently IL-1β production was estimated. By western blotting and ELISA analysis, the caspase-1 activation and IL-1β production from THP-1 cells and the culture supernatant were observed 3 hr after co-cultivation. In addition, the increased expression of ASC and NLRP3, which consist of inflammasome complex, was also observed 3 hr post co-cultivation. To confirm the caspase-1 activation and IL-1β production via NRLP3 inflammasome in THP-1 cells triggered by N. fowleri trophozoites, several inhibitors were pretreated on THP-1 cells. Results of the inhibition assay show that CA-074 (cathepsin B inhibitor), Glybenclamide (NRLP-3 molecule inhibitor) and Z-VAD-FMK (caspase-1 inhibitor) reduced the caspase-1 activation and IL-1β production from THP-1 cells. This study suggests that N. fowleri infection induces the NLRP3-inflammasome complex, which activates the caspase-1 and subsequently produces the IL-1β, thus resulting in inflammation.