Acanthamoeba Is an Evolutionary Ancestor of Macrophages: a Myth Or Reality? Ruqaiyyah Siddiqui Aga Khan University

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February 2012 Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality? Ruqaiyyah Siddiqui Aga Khan University

Naveed Ahmed Khan Aga Khan University

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Recommended Citation Siddiqui, R., Khan, N. (2012). Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality?. Experimental Parasitology, 130(2), 95-97. Available at: http://ecommons.aku.edu/pakistan_fhs_mc_bbs/16 Experimental Parasitology 130 (2012) 95–97

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Experimental Parasitology

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Minireview Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality? ⇑ Ruqaiyyah Siddiqui a, Naveed Ahmed Khan a,b, a Aga Khan University, Stadium Road, Karachi, Pakistan b School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, England, UK article info abstract

Article history: Given the remarkable similarities in cellular structure (morphological and ultra-structural features), Received 26 October 2011 molecular motility, biochemical physiology, ability to capture prey by phagocytosis and interactions with Received in revised form 17 November 2011 microbial pathogens, here we pose the question whether Acanthamoeba and macrophages are evolution- Accepted 19 November 2011 ary related. This is discussed in the light of evolution and functional aspects such as the astonishing Available online 28 November 2011 resemblance of many bacteria to infect and multiply inside human macrophages and amoebae in analogous ways. Further debate and studies will determine if Acanthamoeba is an evolutionary ancestor of Keywords: macrophages. Is this a myth or reality? Acanthamoeba Ó 2011 Elsevier Inc. All rights reserved. Evolution Macrophages

Contents

Acknowledgments ...... 96 References ...... 96

Dear Editor, kingdom, from marine sponges to insects and other lower and high- Acanthamoeba and macrophages share remarkable similarities in er invertebrates/vertebrates (Hanington et al., 2009), suggesting a their cellular structure (morphological and ultra-structural fea- common source, earlier in the evolution. The ability of amoebae to tures), molecular motility, biochemical physiology, ability to cap- distinguish between self and non-self is a pivotal one and is the root ture prey by phagocytosis and interactions with microbial of the immune system of many species (Janeway et al., 2001). pathogens (Fig. 1). Is it plausible that Acanthamoeba and macro- Recent work has shown that Acanthamoeba is the Trojan horse phages are evolutionary related? As opposed to higher animals that of the microbial world. With no real speciﬁcity, it is known to up- are highly complex, protists (single-celled organisms) are consid- take a variety of microbes including viruses (mimivirus, coxsacki- ered as ‘‘simple’’ organisms but much of complexity arose early in eviruses, adenoviruses, poliovirus, echovirus, enterovirus, evolution. Amoebae are unicellular protists that separated from vesicular stomatitis virus etc.), bacteria (Aeromonas, Bacillus, the tree leading to the emergence of metazoan over a billion years Bartonella, Burkholderia, Campylobacter, Chlamydophila, Coxiella, ago (Cosson and Soldati, 2008; Khan, 2009). Based on the ribosomal Escherichia coli, Flavobacterium, Helicobacter, Legionella, Listeria, RNA sequences, it is estimated that protists such as amoeba appear Staphylococcus, Mycobacterium, Pasteurella, Prevotella, Porphyro- near the base of eukaryotic evolution with strong similarity to fungi monas, Pseudomonas, Rickettsia, Salmonella, Shigella, Vibrio, etc.), and animals. A partial genome analysis of Acanthamoeba revealed protists (Cryptosporidium, Toxoplasma gondii) and yeast (Cryptococ- that it can eat and reproduce, crawl and phagocytose, form cysts cus, Blastomyces, Sporothrix, Histoplasma, Streptomyces, Exophiala, to wait out bad conditions, and organize itself internally much as etc.) (reviewed in Khan (2009)). Conversely, macrophage literally a human cell does (Anderson et al., 2005). The human body also in- translates to ‘‘big eaters’’. Being phagocytic cells, they are a major cludes cells that can crawl and phagocytose, such as macrophages. line of defence against invading microbes. The key property of Macrophage-like phagocytes occur throughout the animal the macrophage is phagocytosis, which is shared with Acantha- moeba. Phagocytosis probably appeared early in evolution (Delves

⇑ Corresponding author at: Aga Khan University, Stadium Road, Karachi, Pakistan. et al., 2006), evolving ﬁrst in unicellular eukaryotes. Fax: +92 21 3493 4294. The astonishing resemblance of many bacteria to infect and E-mail address: [email protected] (N.A. Khan). multiply inside human macrophages and amoebae in analogous

‘‘hyaloplasm’’, which is a clear form of ectoplasm, the ﬂow is di- verted towards the membrane whereupon the endoplasm is gelled to form ectoplasm. These transformations are quite clearly visible both in human macrophages and Acanthamoeba and exhibit remarkable similarity at the molecular level in structure, function and biochemical regulation of phagocytosis and cellular motility. Post-uptake, both Acanthamoeba and macrophages demonstrate a number of similarities in oxidative metabolism. For example, both

exhibit cyanide-insensitive O2 uptake and increased O2 consump- tion during phagocytosis by expressing a respiratory burst like oxi-

dase system which is responsible for stimulated O2 uptake during phagocytosis leading to O2 formation. Thus phagocytosis in Acanthamoeba exhibits many similarities to the macrophages Fig. 1. Transmission electron micrographs showing Acanthamoeba castellanii including increased cyanide-insensitive O uptake during phagocy- belonging to the T4 genotype and an alveolar macrophage (taken from Khan, 2 N.A., 2008. Emerging Protozoan Pathogens. Taylor & Francis (Eds.), p. 384. ISBN: tosis; stoichiometric conversion of O2 to oxidants to kill ingested 978-0-415-42864-4). bacteria; exhibiting a direct relationship between the number of phagocytic vesicles produced per cell and the extent of oxidant production and the presence of a b-type cytochrome in phagolys- ways and by using the same mechanisms at the transcriptional, osomal membranes suggesting that the enzyme complexes post-transcriptional and cellular levels indicates that amoebae responsible for the respiratory burst in both Acanthamoeba and and human macrophages have comparable properties that allow macrophages are analogous which highlights a possible evolution- the bacteria to carry out their infection in both hosts. This concept ary relationship (reviewed in Khan, 2009). Similar to macrophages is further strengthened with the finding that Acanthamoeba resem- which use an NADPH oxidase to produce bactericidal superoxide, bles human macrophages in many ways, particularly in their cell Acanthamoeba has a superoxide-generating NADPH oxidase surface receptors and phagocytic activity (Yan et al., 2004). For (Anderson et al., 2005). Overall, much of our understanding of example, the viability and intracellular growth of Legionella pneu- the cytoskeleton, cell motility, engulfment using pseudopodia, mophila within Acanthamoeba and human macrophages is shown invagination, phago-lysosome formation, re-cycling of membrane to be dependent on corresponding genes including icmT, icmR, and the underlying mechanisms comes from studies on Acantha- icmQ, icmP, icmO, icmM, icmL, icmK, icmE, icmC, icmD, icmJ and icmB moeba (Khan, 2009). The similarities of these processes at the mor- (Segal and Shuman, 1999). More recent studies have shown that phological, molecular, biochemical details and at the functional- the Dot/Icm type IV secretion system is required by L. pneumophila level are outstanding. for intracellular proliferation within human macrophages and It may seem far-fetched to propose that Acanthamoeba may Acanthamoeba (Al-Khodor et al., 2008) by evading the default have had an evolutionary relationship with macrophages, given endocytic pathway in both hosts (Segal and Shuman, 1999). The some of the dissimilarities. For example, the ability of Acantha- Dot/Icm type IV secretion system is required for secretion of effec- moeba to live freely in the environment and to differentiate into tors to maintain integrity of the Legionella-containing phagosome. a cyst stage under nutrient-deprived conditions is not observed The PmrA/PmrB two-component system of L. pneumophila that has in macrophages. On the other hand, macrophages are produced a global effect on gene expression is required for the intracellular by cellular differentiation of monocytes suggesting that the under- proliferation of L. pneumophila within human macrophages and lying mechanisms may be common. Notably, Acanthamoeba exhib- Acanthamoeba (Al-Khodor et al., 2009). At the same time, absence its increased number of mitochondria during its active trophozoite of the heavy metal efflux gene island in L. pneumophila was re- stage as compared with the dormant cyst stage. Interestingly, pre- quired neither for survival nor replication inside Acanthamoeba vious findings suggest that an increased number of mitochondria castellanii or human macrophages (Kim et al., 2009). Likewise, correlate with activation of macrophages (Cohn and Benson, invasion of Mycobacterium spp. into A. castellanii or macrophages 1964; Cohn et al., 1965). The availability of the Acanthamoeba gen- showed notable similarities at the transcriptional and post-transla- ome, in addition to micro RNA profiles will lead to a more complete tional level (Danelishvili et al., 2007). Such findings are being doc- understanding at the genetic level as well as its’ interaction with umented for a variety of pathogens and this has led to speculations other microbes. These studies will shed light on the possible evolu- that Acanthamoeba is a training ground for microbial organisms to tionary relationship between macrophages and Acanthamoeba and become successful human and animal pathogens to evade macro- whether this is a myth, or reality. phage-mediated killing (Salah et al., 2009), but whether the two distinct hosts (Acanthamoeba and macrophages) have had an evo- Acknowledgments lutionary relationship remains unknown. Both Acanthamoeba and macrophages uptake microbes via The authors declare (1) no conflicts of interests for the submit- phagocytosis. This is an actin-dependent process involving the ted work; (2) no financial relationships with commercial entities polymerization of monomeric G-actin into filamentous F-actin that might have an interest in the submitted work; (3) no spouses, resulting in pseudopod formation and cell motility. To this end, partners, or children with relationships with commercial entities much of our understanding of the structure and function of the ac- that might have an interest in the submitted work; and (4) no tin, myosin, profiling, and actin-binding proteins come from non-financial interests that may be relevant to the submitted work. Acanthamoeba and it has long been studied as a model eukaryotic cell with emphasis on the actin cytoskeleton (reviewed in Khan, References 2009). At the cellular-level, two convertible states of cytoplasm are observed in Acanthamoeba and macrophages, i.e., endoplasm Al-Khodor, S., Price, C.T., Habyarimana, F., Kalia, A., Abu Kwaik, Y., 2008. A Dot/Icm- and ectoplasm. Endoplasm (seen at the cell center, hence the translocated ankyrin protein of Legionella pneumophila is required for name) is fluid, while ectoplasm under the cell membrane is gel- intracellular proliferation within human macrophages and protozoa. Molecular Microbiology 70 (4), 908–923. lated and comparatively static. During active locomotion, endo- Al-Khodor, S., Kalachikov, S., Morozova, I., Price, C.T., Abu Kwaik, Y., 2009. The PmrA/ plasm flows forwards. As the fluid endoplasm reaches the PmrB two-component system of Legionella pneumophila is a global regulator R. Siddiqui, N.A. Khan / Experimental Parasitology 130 (2012) 95–97 97

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