Oatp58Dc contributes to blood-brain barrier function by excluding organic anions from the Drosophila brain

Abstract

The blood-brain barrier (BBB) physiologically isolates the brain from the blood and, thus, plays a vital role in brain homeostasis. Ion transporters play a critical role in this process by effectively regulating access of chemicals to the brain. Organic anion-transporting polypeptides (Oatps) transport a wide range of amphipathic substrates and are involved in efflux of chemicals across the vertebrate BBB. The anatomic complexity of the vascularized vertebrate BBB, however, creates challenges for experimental analysis of these processes. The less complex structure of the Drosophila BBB facilitates measurement of solute transport. Here we investigate a physiological function for Oatp58Dc in transporting small organic anions across the BBB. We used genetic manipulation, immunocytochemistry, and molecular techniques to supplement a whole animal approach to study the BBB. For this whole animal approach, the traceable small organic anion fluorescein was injected into the hemolymph. This research shows that Oatp58Dc is involved in maintaining a chemical barrier against fluorescein permeation into the brain. Oatp58Dc expression was found in the perineurial and subperineurial glia, as well as in postmitotic neurons. We specifically targeted knockdown of Oatp58Dc expression in the perineurial and subperineurial glia to reveal that Oatp58Dc expression in the perineurial glia is necessary to maintain the barrier against fluorescein influx into the brain. Our results show that Oatp58Dc contributes to maintenance of a functional barrier against fluorescein influx past the BBB into the brain.

Barrier mechanisms in the Drosophila blood-brain barrier

“…The Drosophila genome encodes eight Oatp transporters, two of which have enriched transcript number in the Drosophila brain ( Oatp58Dc and Oatp74D ; http://flyatlas.org/ ). Seabrooke and O'Donnell ( 2013 ) have recently shown that Oatp58Dc is expressed in the PG, SPG and post-mitotic neurons, and is required specifically in PG cells for maintaining chemical protection of the brain from fluorescein. In the absence of Oatp58Dc, levels of hemolymph-injected fluorescein are higher in the brains of Oatp58Dc Drosophila brains.…”

“…Eight potential SLC21 (Oatp) transporters have been identified in Drosophila (Seabrooke and O'Donnell, 2013 ). Of these eight, four are expressed in the Drosophila head or brain ( Oatp30B, Oatp33Ea, Oatp58Dc , and Oatp74D ; http://flyatlas.org/ ; Torrie et al, 2004 ; Seabrooke and O'Donnell, 2013 ).…”

“…Eight potential SLC21 (Oatp) transporters have been identified in Drosophila (Seabrooke and O'Donnell, 2013 ). Of these eight, four are expressed in the Drosophila head or brain ( Oatp30B, Oatp33Ea, Oatp58Dc , and Oatp74D ; http://flyatlas.org/ ; Torrie et al, 2004 ; Seabrooke and O'Donnell, 2013 ). According to the data in DeSalvo et al ( 2014 ), Oatp30B is primarily expressed in neurons, however, Meyer et al ( 2014 ) suggested a glial role for Oatp30B in neural lamella integrity and CNS shape.…”

“…Oatp33Ea shows very low expression in all cell types of the adult brain; as its expression was previously shown in the fly head, Oatp33Ea may therefore localize to the fat bodies of the head rather than the brain. As mentioned above, the organic anion transporter Oatp58Dc is expressed in the PG, SPG and post-mitotic neurons of the Drosophila CNS; however, its function was shown to be specifically required in the PG layer of the BBB (Seabrooke and O'Donnell, 2013 ). This suggests a novel role for the PG in regulating organic anion access to the brain.…”

Multidrug transporters and organic anion transporting polypeptides protect insects against the toxic effects of cardenolides

“…Given their conserved biological function, members of the Mdr and Oatp families are prime candidates for adaptive evolution (Dobler et al, 2015; Petschenka and Agrawal, 2016). Together with work showing the protective effects of Mdrs and Oatps against plant-derived toxins and pesticides (Dermauw and Van Leeuwen, 2014; Seabrooke and O’Donnell, 2013; Torrie et al, 2004), these findings have led to the hypothesis that the broad-substrate Mdrs and Oatps might have a general role in excluding plant toxins at the gut membrane and BBB, and in excreting toxins at the Malpighian tubules (Dobler et al, 2015). The high level of amino acid sequence conservation across animals suggests that these transporters could provide some resistance against cardenolides in most insects.…”