Functional Characterization of Tyrosine Transporters in fibroblast from Healthy Controls and Schizophrenic Patients

Sammanfattning: ABSTRACTCultured human fibroblasts offer an advantageous system to investigate the amino acid transport properties without confounding the affects of disease state and its treatment in many systemic psychiatric disorders. In previous studies, fibroblast cells have been used to investigate the tyrosine transport across plasma membranes in patients with schizophrenia and autism with out characterizing the particular amino acid transporters.The importance of the major tyrosine transporters (system-L and system-A) was investigated in this study. Systemic functional characterization of tyrosine transport in fibroblasts from healthy controls and patients with schizophrenia, with respect to the system-L isoforms (LAT1, LAT2, LAT3, and LAT4) was performed.Ten (n=10) fibroblast cell lines from healthy controls and ten (n=10) from patients with schizophrenia were included in this study. Transport and uptake of [14-C] L-tyrosine in fibroblasts was measured using the cluster tray method in the absence and presence of different specific inhibitors. The maximal transport capacity, Vmax and the affinity constant of the tyrosine-binding site, Km, of LAT1 isoform were determined.The results of this study showed that tyrosine transport in fibroblasts is facilitated mainly by the system-L and LAT1 isoform is involved in 90% of total tyrosine uptake. LAT2 isoform seems to be functionally weak in uptake of tyrosine, as not more than 3% could be contributed by it. LAT3 and LAT4 contributed around 7%. System-A (ATA2 isoform) contributed around 10%. Alanine consequently inhibited the tyrosine transport by up to 60%. Tyrosine uptake and kinetics did not differ between patients and controls at the LAT1 isoform. Moreover, the affinity of LAT1 isoform for tyrosine was higher when compared to system-L. LAT1 is also involved in around 51% of uptake of alanine.In conclusion, the present thesis, confirms the presence of system-L with its isoform LAT1 as a main transporter of tyrosine in human fibroblast cells. The competition between tyrosine and alanine to get transported is shown to probably exist mainly at LAT1 isoform. Aberrant tyrosine transport observed in previous studies in patients with schizophrenia is probably not linked to the LAT1 isoform. This study gave further importance and established fibroblast cells as a suitable experimental model for studying amino acid transport properties in humans.Key words: Fibroblasts, Tyrosine and alanine transport, System-L, LAT1, LAT2, LAT3, LAT4, Schizophrenia, Precursor of Dopamine.