Evolutionary Conservation of Vertebrate Blood-Brain Barrier Chemoprotective Mechanisms in Drosophila

Department of Anesthesia and Perioperative Care, San Francisco General Hospital, and Department of Pharmaceutical Chemistry, University of California at San Francisco, San Francisco, California 94143, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 04/2009; 29(11):3538-50. DOI: 10.1523/JNEUROSCI.5564-08.2009
Source: PubMed

ABSTRACT Pharmacologic remedy of many brain diseases is difficult because of the powerful drug exclusion properties of the blood-brain barrier (BBB). Chemical isolation of the vertebrate brain is achieved through the highly integrated, anatomically compact and functionally overlapping chemical isolation processes of the BBB. These include functions that need to be coordinated between tight diffusion junctions and unidirectionally acting xenobiotic transporters. Understanding of many of these processes has been hampered, because they are not well mimicked by ex vivo models of the BBB and have been experimentally difficult and expensive to disentangle in intact rodent models. Here we show that the Drosophila melanogaster (Dm) humoral/CNS barrier conserves the xenobiotic exclusion properties found in the vertebrate vascular endothelium. We characterize a fly ATP binding cassette (ABC) transporter, Mdr65, that functions similarly to mammalian xenobiotic BBB transporters and show that varying its levels solely in the Dm BBB changes the inherent sensitivity of the barrier to cytotoxic pharmaceuticals. Furthermore, we demonstrate orthologous function between Mdr65 and vertebrate ABC transporters by rescuing chemical protection of the Dm brain with human MDR1/Pgp. These data indicate that the ancient origins of CNS chemoprotection extend to both conserved molecular means and functionally analogous anatomic spaces that together promote CNS selective drug partition. Thus, Dm presents an experimentally tractable system for analyzing physiological properties of the BBB in an intact organism.

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    • "Insect midgut is rich in ABC transporters, whose action, therefore, likely prevents permethrin to reach its target sites [8]. Furthermore, insects possess protective neural barriers (e.g. a layer of glially derived epithelial cells), where ABC transporters likely play an important role in the exchange of molecules [12, 13]. In particular, inhibition of P-gp in Schistocerca gregaria has been shown to increase brain uptake of different drugs [13]. "
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    ABSTRACT: Background: Proteins from the ABC family (ATP-binding cassette) represent the largest known group of efflux pumps, responsible for transporting specific molecules across lipid membranes in both prokaryotic and eukaryotic organisms. In arthropods they have been shown to play a role in insecticide defense/resistance. The presence of ABC transporters and their possible association with insecticide transport have not yet been investigated in the mosquito Anopheles stephensi, the major vector of human malaria in the Middle East and South Asian regions. Here we investigated the presence and role of ABCs in transport of permethrin insecticide in a susceptible strain of this mosquito species. Methods: To identify ABC transporter genes we obtained a transcriptome from untreated larvae of An. stephensi and then compared it with the annotated transcriptome of Anopheles gambiae. To analyse the association between ABC transporters and permethrin we conducted bioassays with permethrin alone and in combination with an ABC inhibitor, and then we investigated expression profiles of the identified genes in larvae exposed to permethrin. Results: Bioassays showed an increased mortality of mosquitoes when permethrin was used in combination with the ABC-transporter inhibitor. Genes for ABC transporters were detected in the transcriptome, and five were selected (AnstABCB2, AnstABCB3, AnstABCB4, AnstABCmember6 and AnstABCG4). An increased expression in one of them (AnstABCG4) was observed in larvae exposed to the LD50 dose of permethrin. Contrary to what was found in other insect species, no up-regulation was observed in the AnstABCB genes. Conclusions: Our results show for the first time the involvement of ABC transporters in larval defense against permethrin in An. stephensi and, more in general, confirm the role of ABC transporters in insecticide defense. The differences observed with previous studies highlight the need of further research as, despite the growing number of studies on ABC transporters in insects, the heterogeneity of the results available at present does not allow us to infer general trends in ABC transporter-insecticide interactions.
    Parasites & Vectors 07/2014; 7(1):349. DOI:10.1186/1756-3305-7-349 · 3.43 Impact Factor
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    • "A BBB-like function has been shown in the larval brain that is carried out by perineural glia that ensheath the optic lobes, central brain, and ventral nerve cord of the larval CNS (Mayer et al., 2009). Furthermore, a role for ABC family transporters localized to this fly BBB, specifically MDR65, the fly homolog of human MDR1/p-glycoprotein, has been documented to show orthologous function in exclusion of xenobiotics from the larval brain (Mayer et al., 2009). Localization of dMRP in the larval brain remains to be investigated in greater detail. "
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    ABSTRACT: Methylmercury (MeHg) is a ubiquitous and persistent neurotoxin that poses a risk to human health. While the mechanisms of MeHg toxicity are not fully understood, factors that contribute to susceptibility are even less well known. Studies of human gene polymorphisms have identified a potential role for the multidrug resistance-like protein (MRP/ABCC) family, ATP-dependent transporters, in MeHg susceptibility. MRP transporters have been shown to be important for MeHg excretion in adult mouse models, but their role in moderating MeHg toxicity during development has not been explored. We therefore investigated effects of manipulating expression levels of MRP using a Drosophila development assay. Drosophila MRP (dMRP) is homologous to human MRP1-4 (ABCC1-4), sharing 50% identity and 67% similarity with MRP1. A greater susceptibility to MeHg is seen in dMRP mutant flies, demonstrated by reduced rates of eclosion on MeHg-containing food. Furthermore, targeted knockdown of dMRP expression using GAL4>UAS RNAi methods demonstrates a tissue-specific function for dMRP in gut, Malpighian tubules, and the nervous system in moderating developmental susceptibility to MeHg. Using X-ray synchrotron fluorescence imaging (XFI), these same tissues were also identified as the highest Hg-accumulating tissues in fly larvae. Moreover, higher levels of Hg are seen in dMRP mutant larvae compared to a control strain fed an equivalent dose of MeHg. In sum, these data demonstrate that dMRP expression, both globally and within Hg-targeted organs, has a profound effect on susceptibility to MeHg in developing flies. Our findings point to a potentially novel and specific role for dMRP in neurons in the protection against MeHg. Finally, this experimental system provides a tractable model to evaluate human polymorphic variants of MRP and other gene variants relevant to genetic studies of mercury-exposed populations.
    Toxicological Sciences 05/2014; 140(2). DOI:10.1093/toxsci/kfu095 · 3.85 Impact Factor
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    • "mdr50 and the least effect was by mdr65, suggesting that mdr49 and mdr50 could be having a more direct role in polyQ-mediated pathogenesis. This can also be related to the functional differences between these genes (Mayer et al. 2009; Ricardo and Lehmann 2009). On comparing the observations , it was found that mdr65-RNAi background showed a significant decrease in mild phenotype just like mdr49-RNAi and mdr50-RNAi. "
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    ABSTRACT: Trinucleotide CAG repeat disorders are caused by expansion of polyglutamine (polyQ) domains in certain proteins leading to fatal neurodegenerative disorders and are characterized by accumulation of inclusion bodies in the neurons. Clearance of these inclusion bodies holds the key to improve the disease phenotypes, which affects basic cellular processes such as transcription, protein degradation and cell signaling. In the present study, we show that P-glycoprotein (P-gp), originally identified as a causative agent of multidrug resistant cancer cells, plays an important role in ameliorating the disease phenotype. Using a Drosophila transgenic strain which expresses a stretch of 127-Glutamine repeats, we demonstrate that enhancing P-gp levels reduces eye degeneration caused by expression of polyQ, whereas reducing it increases the severity of the disease. Increase in polyQ inclusion bodies represses the expression of mdr genes, suggesting a functional link between P-gp and polyQ. P-gp up-regulation restores the defects in the actin organization and precise array of the neuronal connections caused by inclusion bodies. β-catenin homologue, Armadillo, also interacts with P-gp and regulates the accumulation of inclusion bodies. These results thus show that P-gp and polyQ interact with each other, and changing P-gp levels can directly affect neurodegeneration.
    Genetics 09/2013; 195(3). DOI:10.1534/genetics.113.155077 · 5.96 Impact Factor
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