Attenuation of In Vitro and In Vivo Virulence Is Associated with Repression of Gene Expression of AIG1 Gene in Entamoeba histolytica

Work with me here: variations in genome content and emerging genetic tools in Entamoeba histolytica

Entamoeba histolytica is the causative agent of amoebiasis, a significant source of morbidity and mortality in developing nations. Despite this, E. histolytica is understudied, leading to few treatment options and a poor understanding of pathogenesis. Genetic tools have historically been limited. By applying modern approaches, it was recently revealed that the genome is aneuploid. Interestingly, gene expression levels do not correlate with ploidy, potentially highlighting the importance of RNAi in gene regulation. Characterization of the RNAi pathway has led to potent tools for targeted gene knockdown, and the advent of RNAi-based forward genetics. CRISPR/Cas tools for editing the endogenous genome are an exciting possibility on the horizon. We celebrate the gains that have made E. histolytica tractable and anticipate continued advances.

Theoretical Study of Sphingomyelinases from Entamoeba histolytica and Trichomonas vaginalis Sheds Light on the Evolution of Enzymes Needed for Survival and Colonization

The path to survival for pathogenic organisms is not straightforward. Pathogens require a set of enzymes for tissue damage generation and to obtain nourishment, as well as a toolbox full of alternatives to bypass host defense mechanisms. Our group has shown that the parasitic protist Entamoeba histolytica encodes for 14 sphingomyelinases (SMases); one of them (acid sphingomyelinase 6, aSMase6) is involved in repairing membrane damage and exhibits hemolytic activity. The enzymatic characterization of aSMase6 has been shown to be activated by magnesium ions but not by zinc, as shown for the human aSMase, and is strongly inhibited by cobalt. However, no structural data are available for the aSMase6 enzyme. In this work, bioinformatic analyses showed that the protist aSMases are diverse enzymes, are evolutionarily related to hemolysins derived from bacteria, and showed a similar overall structure as parasitic, free-living protists and mammalian enzymes. AlphaFold3 models predicted the occupancy of cobalt ions in the active site of the aSMase6 enzyme. Cavity blind docking showed that the substrate is pushed outward of the active site when cobalt is bound instead of magnesium ions. Additionally, the structural models of the aSMase6 of E. histolytica showed a loop that is absent from the rest of the aSMases, suggesting that it may be involved in hemolytic activity, as demonstrated experimentally using the recombinant proteins of aSMase4 and aSMase6. Trichomonas vaginalis enzymes show a putative transmembrane domain and seem functionally different from E. histolytica. This work provides insight into the future biochemical analyses that can show mechanistic features of parasitic protists sphingomyelinases, ultimately rendering these enzymes potential therapeutic targets.

Avirulent UG10 Entamoeba histolytica mutant derived from HM-1:IMSS strain shows limited genome variability and aberrant 5-methyl cytosine genomic distribution

Entamoeba histolytica, an intestinal parasite of global significance, poses substantial health risks with its associated high morbidity and mortality rates. Despite the current repertoire of molecular tools for the study of gene function in, the regulatory mechanisms governing its pathogenicity remain largely unexplored. This knowledge gap underscores the need to elucidate key genetic determinants orchestrating cellular functions critical to its virulence. Previously, our group generated an avirulent strain, termed UG10, with the same genetic background as the HM1:IMSS strain. UG10 strain, despite showing normal expression levels of well-known virulence factors, was unable to perform in-vitro and in-vivo activities related to amoebic virulence. In this study, we aimed to uncover the genome-wide modifications that rendered the avirulent phenotype of the UG10 strain through whole-genome sequencing. As a complementary approach, we conducted Methylated DNA Immunoprecipitation coupled with sequencing (MeDIP-seq) analysis on both the highly virulent HM1:IMSS strain and the low-virulence UG10 strain to uncover the genome-wide methylation profile. These dual methodologies revealed two aspects of the UG10 avirulent strain. One is the random integration of fragments from the ribosomal gene cluster and tRNA genes, ranging from 120 to 400 bp; and secondly, a clear, enriched methylation profile in the coding and non-coding strand relative to the start codon sequence in genes encoding small GTPases, which is associated with the previously described avirulent phenotype. This study provides the foundation to explore other genetic and epigenetic regulatory circuitries in E. histolytica and novel targets to understand the pathogenic mechanism of this parasite.

The octapeptide-repeat surface protein of Entamoeba nuttalli is a novel virulence factor that promotes adherence to host cells

Entamoeba nuttalli is genetically the closest to Entamoeba histolytica, the causative agent of human amebiasis, and its natural host is Macaca species. A unique E. nuttalli specific surface protein (PTORS) containing 42 repeats of octapeptide was identified by comparative genomic analysis of Entamoeba species. We aimed to elucidate the function of this protein. When trophozoites from various E. nuttalli strains were examined by immunofluorescence microscopy and flow cytometry using a PTORS-specific monoclonal antibody, only a limited proportion of trophozoites were stained, indicating that the protein was not commonly expressed in all E. nuttalli trophozoite. The proportion of trophozoites expressing PTORS increased after passage in hamster livers, suggesting that the protein functions in the virulence of trophozoites in the liver tissue. Single-cell analysis revealed that in the cluster including trophozoites with PTORS gene expression, genes of virulence-related proteins were also upregulated. Trophozoites of E. histolytica transfected with PTORS showed enhanced adherence and subsequent phagocytic activity towards human Jurkat cells, independent of the lectin. E. histolytica trophozoites expressing PTORS formed larger liver abscesses in hamsters. These results demonstrate that PTORS is a novel virulence factor in Entamoeba species.

Genes differentially expressed between pathogenic and non-pathogenic Entamoeba histolytica clones influence pathogenicity-associated phenotypes by multiple mechanisms

Recently, two genes involved in amoebic liver abscess formation in a mouse model were identified by their differential expression of non-pathogenic (A1np) and pathogenic (B2p) clones of the Entamoeba histolytica isolate HM:1-IMSS. While overexpression of a gene encoding the metallopeptidase EhMP8-2 reduces the virulence of the pathogenic clone B2p, overexpression of the gene ehi_127670 (ehhp127), encoding a hypothetical protein, increases the virulence of the non-pathogenic clone A1np, while silencing this gene in the pathogenic B2p reduces virulence. To understand the role of both molecules in determining the pathogenicity of E. histolytica, silencing, and overexpression transfectants were characterized in detail. Silencing of ehmp8-2, of the homologous gene ehmp8-1, or both in non-pathogenic A1np trophozoites significantly altered the transcript levels of 347, 216, and 58 genes, respectively. This strong change in the expression profiles caused by the silencing of ehmp8-1 and ehmp8-2 implies that these peptidases regulate the expression of numerous genes. Consequently, numerous phenotypic characteristics, including cytopathic, hemolytic, and cysteine peptidase activity, were altered in response to their silencing. Silencing of ehhp127 in pathogenic B2p trophozoites did not affect the expression of other genes, whereas its overexpression in non-pathogenic A1np trophozoites results in an altered expression of approximately 140 genes. EhHP127 is important for trophozoite motility, as its silencing reduces, while its overexpression enhances movement activity. Interestingly, the specific silencing of ehhp127 also significantly affects cytopathic, cysteine peptidase, and hemolytic activities. All three molecules characterized in this study, namely EhMP8-1, EhMP8-2, and EhHP127, are present in amoeba vesicles. The results show that ehmp8-2 and ehhp127 are not only differentially expressed between pathogenic and non-pathogenic amoebae, but that they also significantly affect amoeba pathogenicity-associated phenotypes by completely different mechanisms. This observation suggests that the regulation of amoeba pathogenicity is achieved by a complex network of molecular mechanisms rather than by single factors.