Identification of Protein Arginine Methyltransferase 5 as a Regulator for Encystation of Acanthamoeba

Oxidase enzyme genes are differentially expressed during Acanthamoeba castellanii encystment

Acanthamoeba castellanii, a ubiquitous protozoan, is responsible for significant diseases such as Acanthamoeba keratitis and granulomatous amoebic encephalitis. A crucial survival strategy of A. castellanii involves the formation of highly resistant cysts during adverse conditions. This study delves into the cellular processes underpinning encystment, focusing on gene expression changes related to reactive oxygen species (ROS) balance, with a particular emphasis on mitochondrial processes. Our findings reveal a dynamic response within the mitochondria during encystment, with the downregulation of key enzymes involved in oxidative phosphorylation (COX, AOX, and NADHalt) during the initial 48 h, followed by their overexpression at 72 h. This orchestrated response likely creates a pro-oxidative environment, facilitating encystment. Analysis of other ROS processing enzymes across the cell reveals differential expression patterns. Notably, antioxidant enzymes, such as catalases, glutaredoxins, glutathione S-transferases, peroxiredoxins, and thioredoxins, mirror the mitochondrial trend of downregulation followed by upregulation. Additionally, glycolysis and gluconeogenesis are downregulated during the early stages in order to potentially balance the metabolic requirement of the cyst. Our study underscores the importance of ROS regulation in Acanthamoeba encystment. Understanding these mechanisms offers insights into infection control and identifies potential therapeutic targets. This work contributes to unraveling the complex biology of A. castellanii and may aid in combatting Acanthamoeba-related infections. Further research into ROS and oxidase enzymes is warranted, given the organism's remarkable respiratory versatility.

Biological characteristics and pathogenicity of Acanthamoeba

Acanthamoeba is an opportunistic protozoa, which exists widely in nature and is mainly distributed in soil and water. Acanthamoeba usually exists in two forms, trophozoites and cysts. The trophozoite stage is one of growth and reproduction while the cyst stage is characterized by cellular quiescence, commonly resulting in human infection, and the lack of effective monotherapy after initial infection leads to chronic disease. Acanthamoeba can infect several human body tissues such as the skin, cornea, conjunctiva, respiratory tract, and reproductive tract, especially when the tissue barriers are damaged. Furthermore, serious infections can cause Acanthamoeba keratitis, granulomatous amoebic encephalitis, skin, and lung infections. With an increasing number of Acanthamoeba infections in recent years, the pathogenicity of Acanthamoeba is becoming more relevant to mainstream clinical care. This review article will describe the etiological characteristics of Acanthamoeba infection in detail from the aspects of biological characteristic, classification, disease, and pathogenic mechanism in order to provide scientific basis for the diagnosis, treatment, and prevention of Acanthamoeba infection.

Stimulation of Acanthamoeba castellanii excystment by enzyme treatment and consequences on trophozoite growth

Acanthamoeba castellanii is a widespread Free-Living Amoeba (FLA) that can cause severe ocular or cerebral infections in immunocompetent and immunocompromised patients, respectively, besides its capacity to transport diverse pathogens. During their life cycle, FLA can alternate between a vegetative form, called a trophozoite, and a latent and resistant form, called a cyst. This resistant form is characterized by the presence of a cell wall containing two layers, namely the ectocyst and the endocyst, mainly composed of cellulose and proteins. In the present work, we aimed to stimulate Acanthamoeba castellanii excystment by treating their cysts with a cellulolytic enzyme, i.e., cellulase, or two proteolytic enzymes, i.e., collagenase and pepsin. While 11 days were necessary to obtain total excystment in the control at 27°C, only 48 h were sufficient at the same temperature to obtain 100% trophozoites in the presence of 25 U/mL cellulase, 50 U/mL collagenase or 100 U/mL pepsin. Additionally, more than 96% amoebae have excysted after only 24 h with 7.5 U/mL cellulase at 30°C. Nevertheless, no effect of the three enzymes was observed on the excystment of Balamuthia mandrillaris and Vermamoeba vermiformis. Surprisingly, A. castellanii trophozoites excysted in the presence of cellulase displayed a markedly shorter doubling time at 7 h, in comparison to the control at 23 h. Likewise, trophozoites doubled their population in 9 h when both cellulose and cellulase were added to the medium, indicating that Acanthamoeba cyst wall degradation products promote their trophozoite proliferation. The analysis of cysts in epifluorescent microscopy using FITC-lectins and in electron microscopy revealed a disorganized endocyst and a reduction of the intercystic space area after cellulase treatment, implying that these cellular events are preliminary to trophozoite release during excystment. Further studies would be necessary to determine the signaling pathways involved during this amoebal differentiation process to identify new therapeutic targets for the development of anti-acanthamoebal drugs.

Comparative analysis of differentially expressed genes in Acanthamoeba after ingestion of Legionella pneumophila and Escherichia coli

Acanthamoeba spp. feeds on bacteria, fungi, and algae to obtain nutrients from the environment. However, several pathogens can survive and multiply in Acanthamoeba. Mechanisms necessary for the survival and proliferation of microorganisms in Acanthamoeba remain unclear. The object of this study was to identify effective factors for the survival of microorganisms in Acanthamoeba. Differentially expressed genes (DEGs) in A. castellanii infected by Legionella pneumophila or Escherichia coli were identified based on mRNA sequencing. A total of 2342 and 1878 DEGs were identified in Acanthamoeba with L. pneumophila and E. coli, respectively. Among these DEGs, 502 were up-regulated and 116 were down-regulated in Acanthamoeba infected by L. pneumophila compared to those in Acanthamoeba feed on E. coli. Gene ontology analysis showed that the genes encoded small GTPase-mediated signal transduction proteins in the biological process domain, intracellular proteins in the cellular component domain, and ATP binding proteins in the molecular function domain were up-regulated while integral components of membrane proteins in the cellular component domain were down-regulated in Acanthamoeba infected by Legionella compared to those in Acanthamoeba feed on E. coli. During endosymbiosis with Legionella, Acanthamoeba showed various changes in the expression of genes supposed to be involved in phagosomal maturation. Acanthamoeba infected by Legionella also showed high expression levels of aminotransferase, methyltransferase, and cysteine proteinase but low expression levels of RNA pseudouridine synthase superfamily protein and 2OG-Fe(II) oxygenase superfamily. These results provide directions for further research to understand the survival strategy of L. pneumophila in A. castellanii.

Free-living amoebae and squatters in the wild: ecological and molecular features

Free-living amoebae are protists frequently found in water and soils. They feed on other microorganisms, mainly bacteria, and digest them through phagocytosis. It is accepted that these amoebae play an important role in the microbial ecology of these environments. There is a renewed interest for the free-living amoebae since the discovery of pathogenic bacteria that can resist phagocytosis and of giant viruses, underlying that amoebae might play a role in the evolution of other microorganisms, including several human pathogens. Recent advances, using molecular methods, allow to bring together new information about free-living amoebae. This review aims to provide a comprehensive overview of the newly gathered insights into (1) the free-living amoeba diversity, assessed with molecular tools, (2) the gene functions described to decipher the biology of the amoebae and (3) their interactions with other microorganisms in the environment.

Encystation: the most prevalent and underinvestigated differentiation pathway of eukaryotes

Not long ago, protists were considered one of four eukaryote kingdoms, but recent gene-based phylogenies show that they contribute to all nine eukaryote subdomains. The former kingdoms of animals, plants and fungi are now relegated to lower ranks within subdomains. Most unicellular protists respond to adverse conditions by differentiating into dormant walled cysts. As cysts, they survive long periods of starvation, drought and other environmental threats, only to re-emerge when conditions improve. For protists pathogens, the resilience of their cysts can prevent successful treatment or eradication of the disease. In this context, effort has been directed towards understanding the molecular mechanisms that control encystation. We here firstly summarize the prevalence of encystation across protists and next focus on Amoebozoa, where most of the health-related issues occur. We review current data on processes and genes involved in encystation of the obligate parasite Entamoeba histolytica and the opportunistic pathogen Acanthamoeba. We show how the cAMP-mediated signalling pathway that controls spore and stalk cell encapsulation in Dictyostelium fruiting bodies could be retraced to a stress-induced pathway controlling encystation in solitary Amoebozoa. We highlight the conservation and prevalence of cAMP signalling genes in Amoebozoan genomes and the suprisingly large and varied repertoire of proteins for sensing and processing environmental signals in individual species.

DNA Methylation of Gene Expression in Acanthamoeba castellanii Encystation

Encystation mediating cyst specific cysteine proteinase (CSCP) of Acanthamoeba castellanii is expressed remarkably during encystation. However, the molecular mechanism involved in the regulation of CSCP gene expression remains unclear. In this study, we focused on epigenetic regulation of gene expression during encystation of Acanthamoeba. To evaluate methylation as a potential mechanism involved in the regulation of CSCP expression, we first investigated the correlation between promoter methylation status of CSCP gene and its expression. A 2,878 bp of promoter sequence of CSCP gene was amplified by PCR. Three CpG islands (island 1–3) were detected in this sequence using bioinformatics tools. Methylation of CpG island in trophozoites and cysts was measured by bisulfite sequence PCR. CSCP promoter methylation of CpG island 1 (1,633 bp) was found in 8.2% of trophozoites and 7.3% of cysts. Methylation of CpG island 2 (625 bp) was observed in 4.2% of trophozoites and 5.8% of cysts. Methylation of CpG island 3 (367 bp) in trophozoites and cysts was both 3.6%. These results suggest that DNA methylation system is present in CSCP gene expression of Acanthamoeba. In addition, the expression of encystation mediating CSCP is correlated with promoter CpG island 1 hypomethylation.

Identification and Characterization of Protein Arginine Methyltransferase 1 in Acanthamoeba castellanii

Protein arginine methyltransferase (PRMT) is an important epigenetic regulator in eukaryotic cells. During encystation, an essential process for Acanthamoeba survival, the expression of a lot of genes involved in the encystation process has to be regulated in order to be induced or inhibited. However, the regulation mechanism of these genes is yet unknown. In this study, the full-length 1,059 bp cDNA sequence of Acanthamoeba castellanii PRMT1 (AcPRMT1) was cloned for the first time. The AcPRMT1 protein comprised of 352 amino acids with a SAM-dependent methyltransferase PRMT-type domain. The expression level of AcPRMT1 was highly increased during encystation of A. castellanii. The EGFP-AcPRMT1 fusion protein was distributed over the cytoplasm, but it was mainly localized in the nucleus of Acanthamoeba. Knock down of AcPRMT1 by synthetic siRNA with a complementary sequence failed to form mature cysts. These findings suggested that AcPRMT1 plays a critical role in the regulation of encystation of A. castellanii. The target gene of AcPRMT1 regulation and the detailed mechanisms need to be investigated by further studies.