mRNA Sequencing Reveals Upregulation of Glutathione S-Transferase Genes during Acanthamoeba Encystation

Unveiling the molecular architecture of the mitochondrial respiratory chain of Acanthamoeba castellanii

Acanthamoeba castellanii is a ubiquitous free-living amoeba that can cause severe infections in humans. Unlike most other organisms, A. castellanii possesses a "complete" mitochondrial respiratory chain, meaning it con-tains several additional enzymes that contribute to its metabolic versa-tility and survival in diverse environments. This review provides a com-prehensive overview of the mitochondrial respiratory chain in A. castellanii, focusing on the key alternative components in-volved in oxidative phosphorylation and their roles in energy metabo-lism, stress response, and adaptation to various conditions. The func-tional characterization of the alternative oxidase (AOX), uncoupling pro-tein (UCP), and alternative NAD(P)H dehydrogenases, highlight their roles in reducing oxidative stress, modulating proton gradients, and adapting to changes in temperature and nutrient availability. These pro-teins and systems serve a role in the survival of A. castel-lanii under stressful conditions such as starvation and cold con-ditions. Further knowledge of the respiratory chain of the amoeba has potential implications for understanding the evolution of mitochondrial respiration and developing new therapies for treating Acanthamoeba infections.

Effect of lead on photosynthetic pigments, antioxidant responses, metabolomics, thalli morphology and cell ultrastructure of Iridaea cordata (Rhodophyta) from Antarctica

Over the past decades, the concern about lead pollution in marine environments has increased due to its remarkable toxicity, even at low concentrations. Lead is one of the significant contaminants arising from human activities in Antarctica. However, its effects on polar photosynthetic organisms are poorly known. This work aims to evaluate the effects of two different environmental concentrations of lead (10 μg/L and 50 μg/L) on pigment content, antioxidant enzyme activities (catalase, superoxide dismutase, ascorbate peroxidase and glutathione-S-transferase), metabolome, thalli morphology and cell ultrastructure of the red seaweed Iridaea cordata (Turner) Bory from Terra Nova Bay (Ross Sea, Antarctica). The results highlighted that lead exposure decreased phycocyanin and phycoerythrin content, starting from 10 μg/L, while induced carotenoid accumulation at 50 μg/L. Catalase, ascorbate peroxidase, and superoxide dismutase activities generally increased after lead exposure and distinct biochemical features were identified in the control and treatment groups. Further lead-related effects on cell ultrastructure comprised floridean starch accumulation and plastoglobuli formation. Overall, our results suggested that the enhanced formation of reactive oxygen species in response to lead altered the photosynthetic pigment pattern, antioxidant defenses, metabolome and ultrastructure of I. cordata.

Mifepristone protects acetaminophen induced liver injury through NRF2/GSH/GST mediated ferroptosis suppression

Ferroptosis is a form of iron-dependent cell death that has attracted significant attention for its potential role in numerous diseases. Targeted inhibition of ferroptosis could be of potential use in treating diseases: such as drug induced liver injury (DILI). Ferroptosis can be antagonized by the xCT/GSH/GPX4, FSP1/CoQ10, DHODH/CoQ10, GCH1/BH4, and NRF2 pathways. Identifying novel anti-ferroptosis pathways will further promote our understanding of the biological nature of ferroptosis and help discover new drugs targeting ferroptosis related human diseases. In this study, we identified the clinically used drug mifepristone (RU486) as a novel ferroptosis inhibitor. Mechanistically, RU486 inhibits ferroptosis by inducing GSH synthesis pathway, which supplies GSH for glutathione-S-transferase (GST) mediated 4-HNE detoxification. Furthermore, RU486 induced RLIP76 and MRP1 export 4-HNE conjugate contributes to its anti-ferroptosis activity. Interestingly, RU486 induced GSH/GSTs/RLIP76&MRP1 anti-ferroptosis pathway acts independent of classic anti-ferroptosis systems: including xCT/GSH/GPX4, FSP1, DHODH, GCH1, SCD1 and FTH1. Moreover, NRF2 was identified to be important for RU486's anti-ferroptosis activity by inducing downstream gene expression. Importantly, in mouse model, RU486 showed strong protection effect on acetaminophen (APAP)-induced acute liver injury, evidenced by decreased ALT, AST level and histological recovery after APAP treatment. Interestingly, RU486 also decreased oxidative markers, including 4-HNE and MDA, and induced NRF2 activation as well as GSTs, MRP1 expression. Together, these data suggest NRF2/GSH/GST/RLIP76&MRP1 mediated detoxification pathway as an important independent anti-ferroptosis pathway act both in vitro and in vivo.

Editorial for the Special Issue "Advances in Acanthamoeba"

Some free-living amoebae can behave as opportunistic parasites, causing rare but dangerous diseases in humans and animals, primarily amoebic keratitis, with loss of vision, and encephalitis, which is almost always fatal [...].

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.

Encystation and Stress Responses under the Control of Ubiquitin-like Proteins in Pathogenic Amoebae

Amoebae found in aquatic and terrestrial environments encompass various pathogenic species, including the parasite Entamoeba histolytica and the free-living Acanthamoeba castellanii. Both microorganisms pose significant threats to public health, capable of inducing life-threatening effects on humans. These amoebae exist in two cellular forms: trophozoites and cysts. The trophozoite stage is the form used for growth and reproduction while the cyst stage is the resistant and disseminating form. Cysts occur after cellular metabolism slowdown due to nutritional deprivation or the appearance of environmental conditions unfavourable to the amoebae's growth and division. The initiation of encystation is accompanied by the activation of stress responses, and scarce data indicate that encystation shares factors and mechanisms identified in stress responses occurring in trophozoites exposed to toxic compounds derived from human immune defence. Although some "omics" analyses have explored how amoebae respond to diverse stresses, these studies remain limited and rarely report post-translational modifications that would provide knowledge on the molecular mechanisms underlying amoebae-specific stress responses. In this review, we discuss ubiquitin-like proteins associated with encystation and cell survival during oxidative damage. We aim to shed light on the signalling pathways involved in amoebic defence mechanisms, with a focus on their potential clinical implications against pathogenic amoebae, addressing the pressing need for effective therapies.