Mutation of a conserved Asp (D98) in the rat serotonin (5HT) transporter (rSERT) to Glu (D98E) led to decreased 5HT transport capacity, diminished coupling to extracellular Na+ and Cl-, and a selective loss of antagonist potencies (cocaine, imipramine, and citalopram but not paroxetine or mazindol) with no change in 5HT Km value. D98E, which extends the acidic side chain by one carbon, affected the rank-order potency of substrate analogs for inhibition of 5HT transport, selectively increasing the potency of two analogs with shorter alkylamine side chains, gramine, and dihydroxybenzylamine. D98E also increased the efficacy of gramine relative to 5HT for inducing substrate-activated currents in Xenopus laevis oocytes, but these currents were noticeably dependent on extracellular medium acidification. I-V profiles for substrate-independent and -dependent currents indicated that the mutation selectively impacts ion permeation coupled to 5HT occupancy. The ability of the D98E mutant to modulate selective aspects of substrate recognition, to perturb ion dependence as well as modify substrate-induced currents, suggests that transmembrane domain I plays a critical role in defining the permeation pathway of biogenic amine transporters.

The mechanisms responsible for the uptake and cellular processing of the endogenous cannabinoid anandamide are not well understood. We propose that anandamide uptake may occur via a caveola/lipid raft-related endocytic process in RBL-2H3 cells. Inhibitors of caveola-related (clathrin-independent) endocytosis reduced anandamide transport by ϳ50% compared with the control. Fluorescein derived from fluorescently labeled anandamide colocalized with protein markers of caveolae at early time points following transport. In this study, we have also identified a yet unrecognized process involved in trafficking events affecting anandamide following its uptake. Following uptake of [ 3 H]anandamide by RBL-2H3 cells, we found an accumulation of tritium in the caveolin-rich membranes. Inhibitors of both anandamide uptake and metabolism blocked the observed enrichment of tritium in the caveolin-rich membranes. Mass spectrometry of subcellular membrane fractions revealed that the tritium accumulation observed in the caveolin-rich membrane fraction was not representative of intact anandamide, suggesting that following metabolism by the enzyme fatty acid amide hydrolase (FAAH), anandamide metabolites are rapidly enriched in caveolae. Furthermore, HeLa cells, which do not express high levels of FAAH, showed an accumulation of tritium in the caveolin-rich membrane fraction only when transfected with FAAH cDNA. Western blot and immunocytochemistry analyses of RBL-2H3 cells revealed that FAAH was localized in intracellular compartments distinct from caveolin-1 localization. Together, these data suggest that following uptake via caveola/lipid raft-related endocytosis, anandamide is rapidly metabolized by FAAH, with the metabolites efficiently recycled to caveolin-rich membrane domains.

A facilitated transport process that removes the endogenous cannabinoid anandamide from extracellular spaces has been identified. Once transported into the cytoplasm, fatty acid amide hydrolase (FAAH) is responsible for metabolizing the accumulated anandamide. We propose that FAAH contributes to anandamide uptake by creating and maintaining an inward concentration gradient for anandamide. To explore the role of FAAH in anandamide transport, we examined anandamide metabolism and uptake in RBL-2H3 cells, which natively express FAAH, as well as wild-type HeLa cells that lack FAAH. RBL-2H3 and FAAH-transfected HeLa cells demonstrated a robust ability to metabolize anandamide compared with vector-transfected HeLa cells. This activity was reduced to that observed in wild-type HeLa cells upon the addition of the FAAH inhibitor methyl arachidonyl fluorophosphonate. Anandamide uptake was reduced in a dose-dependent manner by various FAAH inhibitors in both RBL-2H3 cells and wild-type HeLa cells. Anandamide uptake studies in wild-type HeLa cells showed that only FAAH inhibitors structurally similar to anandamide decreased anandamide uptake. Because there is no detectable FAAH activity in wild-type HeLa cells, these FAAH inhibitors are probably blocking uptake via actions on a plasma membrane transport protein. Phenylmethylsulfonyl fluoride, a FAAH inhibitor that is structurally unrelated to anandamide, inhibited anandamide uptake in RBL-2H3 cells and FAAH-transfected HeLa cells, but not in wild-type HeLa cells. Furthermore, expression of FAAH in HeLa cells increased maximal anandamide transport 2-fold compared with wild-type HeLa cells. These results suggest that FAAH facilitates anandamide uptake but is not solely required for transport to occur.

CLU and MS4A4A eSNPs may at least partly explain the LOAD risk association at these loci. CLU and ABCA7 may harbor additional strong eSNPs. These results have implications in the search for functional variants at the novel LOAD risk loci.

BackgroundMicroRNAs (miRNAs) represent a growing class of small non-coding RNAs that are important regulators of gene expression in both plants and animals. Studies have shown that miRNAs play a critical role in human cancer and they can influence the level of cell proliferation and apoptosis by modulating gene expression. Currently, methods for the detection and measurement of miRNA expression include small and moderate-throughput technologies, such as standard quantitative PCR and microarray based analysis. However, these methods have several limitations when used in large clinical studies where a high-throughput and highly quantitative technology needed for the efficient characterization of a large number of miRNA transcripts in clinical samples. Furthermore, archival formalin fixed, paraffin embedded (FFPE) samples are increasingly becoming the primary resource for gene expression studies because fresh frozen (FF) samples are often difficult to obtain and requires special storage conditions. In this study, we evaluated the miRNA expression levels in FFPE and FF samples as well as several lung cancer cell lines employing a high throughput qPCR-based microfluidic technology. The results were compared to standard qPCR and hybridization-based microarray platforms using the same samples.ResultsWe demonstrated highly correlated Ct values between multiplex and singleplex RT reactions in standard qPCR assays for miRNA expression using total RNA from A549 (R = 0.98; p < 0.0001) and H1299 (R = 0.95; p < 0.0001) lung cancer cell lines. The Ct values generated by the microfluidic technology (Fluidigm 48.48 dynamic array systems) resulted in a left-shift toward lower Ct values compared to those observed by ABI 7900 HT (mean difference, 3.79), suggesting that the microfluidic technology exhibited a greater sensitivity. In addition, we show that as little as 10 ng total RNA can be used to reliably detect all 48 or 96 tested miRNAs using a 96-multiplexing RT reaction in both FFPE and FF samples. Finally, we compared miRNA expression measurements in both FFPE and FF samples by qPCR using the 96.96 dynamic array and Affymetrix microarrays. Fold change comparisons for comparable genes between the two platforms indicated that the overall correlation was R = 0.60. The maximum fold change detected by the Affymetrix microarray was 3.5 compared to 13 by the 96.96 dynamic array.ConclusionThe qPCR-array based microfluidic dynamic array platform can be used in conjunction with multiplexed RT reactions for miRNA gene expression profiling. We showed that this approach is highly reproducible and the results correlate closely with the existing singleplex qPCR platform at a throughput that is 5 to 20 times higher and a sample and reagent usage that was approximately 50-100 times lower than conventional assays. We established optimal conditions for using the Fluidigm microfluidic technology for rapid, cost effective, and customizable arrays for miRNA expression profiling and validation.