Physiological Role In Transport Research Articles

Molecular Characterization of Zebrafish Oatp1d1 (Slco1d1), a Novel Organic Anion-transporting Polypeptide

The organic anion-transporting polypeptide (OATP/Oatp) superfamily includes a group of polyspecific transporters that mediate transport of large amphipathic, mostly anionic molecules across cell membranes of eukaryotes. OATPs/Oatps are involved in the disposition and elimination of numerous physiological and foreign compounds. However, in non-mammalian species, the functional properties of Oatps remain unknown. We aimed to elucidate the role of Oatp1d1 in zebrafish to gain insights into the functional and structural evolution of the OATP1/Oatp1 superfamily. We show that diversification of the OATP1/Oatp1 family occurs after the emergence of jawed fish and that the OATP1A/Oatp1a and OATP1B/Oatp1b subfamilies appeared at the root of tetrapods. The Oatp1d subfamily emerged in teleosts and is absent in tetrapods. The zebrafish Oatp1d1 is similar to mammalian OATP1A/Oatp1a and OATP1B/Oatp1b members, with the main physiological role in transport and balance of steroid hormones. Oatp1d1 activity is dependent upon pH gradient, which could indicate bicarbonate exchange as a mode of transport. Our analysis of evolutionary conservation and structural properties revealed that (i) His-79 in intracellular loop 3 is conserved within OATP1/Oatp1 family and is crucial for the transport activity; (ii) N-glycosylation impacts membrane targeting and is conserved within the OATP1/Oatp1 family with Asn-122, Asn-133, Asn-499, and Asn-512 residues involved; (iii) the evolutionarily conserved cholesterol recognition interaction amino acid consensus motif is important for membrane localization; and (iv) Oatp1d1 is present in dimeric and possibly oligomeric form in the cell membrane. In conclusion, we describe the first detailed characterization of a new Oatp transporter in zebrafish, offering important insights into the functional evolution of the OATP1/Oatp1 family and the physiological role of Oatp1d1.

Identification and quantification of differentially expressed proteins in plasma of spinocerebellar ataxia type 12

Spinocerebellar ataxia 12 (SCA12) is a unique dominant type of ataxia characterized by early and prominent action tremors, memory deficit, neuropathy, dysarthria, etc. The expansion of DNA triplet (CAG) repeats in 5′UTR of PPP2R2B gene appears to be the cause for the pathogenesis of the neurodegenerative disorder, SCA12. The objective of the current study was to identify the aberrantly expressed plasma proteins for their potential application in therapy or diagnosis/prognosis of SCA12. Sixty-two clinically suspected patients were assessed using International Co-operative Ataxia Rating Scale (ICARS) and genetic confirmation was done using PCR followed by DNA sequencing. Twenty patients who were genetically confirmed were included in the study. 2D-DIGE analyses of plasma proteins of SCA12 patients revealed 14 differentially expressed protein spots, which were confirmed as nine proteins by LC–MS/MS. The 6 downregulated and 3 upregulated proteins are known to have physiological role in transport (thyroxin and retinol to brain), lipid metabolism, memory, scavenging of free haemoglobin, etc. Altered expression of some of the proteins of interest, transthyretin, haptaglobin, apolipoprotein C-II, apolipoprotein C-III are indicative of clinical manifestations such as neuropathy, cognitive impairment and altered lipid metabolism in SCA12.