N-ACETYL-L-ORNITHINE DEACETYLASE IS AN ESSENTIAL FACT OR FOR THE ADAPTATION OF ENTAMOEBA HISTOLYTICA TO NITROSATIVE STRESS

Adaptation of the parasite Entamoeba histolytica to toxic level of NO may be essential for the establishment of chronic amebiasis and for the survival of parasite within the host. To obtain insight into the mechanism of adaptation to NO, E. histolytica trophozoites were selected in vitro by stepwise exposures to increasing amounts of NO donor S-Nitrosoglutathione (GSNO) up to a concentration of 110 µM. These NO adapted trophozoites (NAT) were more resistance to acute exposure of GSNO (350μM), to activated macrophages and have a better capability to invade porcine colon explants compared to wild-type trophozoites. The transcriptome of NAT was investigated by RNA-sequencing and it showed only a weak overlapping with the transcriptome of trophozoites exposed to acute NO stress. N-acetyl ornithine deacetylase (NAOD) was among the 208 genes that were up-regulated in NAT. NAOD catalyzes the deacylation of N²-acetyl-L-ornithine to yield ornithine and acetate. Immunofluorescence confocal microscopy using NAOD antibody showed that NAOD has a cytoplasmic location in wild type trophozoites and is present in both the cytoplasm and nucleus of NAT. Overexpression of NAOD confers a selective advantage to adaptation to NO. This selective advantage was also observed when a mutated form of NAOD, devoid of its catalytic activity, was overexpressed. We have also demonstrated that NAOD interacts with glyceraldehyde 3-phosphate dehydrogenase, a glycolytic enzyme recently associated with NO resistance in Leishmania spp.

This works emphasizes the ability of E.histolytica to adapt to toxic amount of NO. In addition, we identified NAOD as a new virulence factor involved in the adaptation of the parasite to nitrosative stress. This new function represents a potential target for the chemotherapy of amoebiasis.