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The GLUT9 transporter, coded by the SLC2A9 gene, is one of the key proteins enabling the trasnfer of uric acid across the membrane in epithelial cells of the proximal tubule. In humans, this protein is naturally expressed in two variants: long (GLUT9L) and short (GLUT9S), which differ from one another by their N-terminus sequence. Each of these isoforms is localized on a different pole of the epithelial cell. The signal sequence/motif responsible for this difference is presumed to be located in the aforementioned N-terminus domain. Numerous allelic variants influencing the transport properties of the protein have also been described. The first aim of this thesis is to verify the influence of a newly discovered variant, characterized by substituting of valine for leucine in the 114th position (V114L, in the short form its corresponding variant V85L) on the ability to transport uric acid. Second aim is to verify the influence of mutations in selected motifs, which could be responsible for the localization of the protein, thus also changing its transport properties. Two dileucine motifs 12LGL14 and 33LL34 and one tyrosine motif 84YIKA87 were tested. Functional studies using 14 C radiolabeled urate demonstrated significant decrease of transport ability for the V114L/V85L allelic variant in both...

There are localised proteins (so-called urate transporters) in the renal proximal tubules and in the intestine, which excrete and reabsorb uric acid. Polymorphisms in the genes coding these proteins can result in the disruption of the transport function and development of hyperuricemia and gout. However the serum level of uric acid is also determined by other factors which include the intake of exogenous purines in food, synthesis of endogenous purines and degradation of nucleic acids, but also certain conditions. In 250 patients with primary hyperuricemia and gout we used Sanger sequencing to analyse the exons and adjacent intron regions in ten genes coding urate transporters: ABCG2, ABCC4, SLC2A9, SLC22A12, SLC22A11, SLC22A13, SLC17A1, SLC17A3, SLC22A6 and SLC22A8. We examined a possible connection between the identified genetic variants and primary hyperuricemia and gout based on a comparison of allele frequencies with the European population, according to topological models, according to programs predicting the functional impacts of variants and searches in specialised literature. We also took into account the conclusions of functional studies analysing the impact of nonsynonymous variants in the ABCG2 and SLC2A9 genes. We also focused on the effect of the concomitant occurrence of several...

Uric acid excretion disorders are the most common cause of primary dysuricemia. The kidneys eliminate two-thirds of uric acid production and the other third is eliminated in the gastrointestinal tract. Renal reabsorption and secretion occur through the polarised epithelial cells in the proximal tubules. Uric acid transporters are expressed on these cell membranes. Reabsorption deficiency leads to hypouricemia and elevated fraction excretion associated with urolithiasis, nephrolithiasis or acute renal injury. Decreased uric acid secretion in the kidneys and small intestine leads to hyperuricemia, which develops into gout in 10% of individuals. Genome wide association studies detected a strong effect of SLC22A12 (URAT1), SLC2A9 (GLUT9) reabsorbing transporters and ABCG2 (ABCG2) secreting transporter on uric acid serum concentration variability. This thesis aimed to map out urate transporter allelic variants in a cohort of primary dysuricemia patients and identification of the variants causing defective uric acid excretion. Six non-synonymous variants were described in SLC22A12 (URAT1) and SLC2A9 (GLUT9) genes in hypouricemic individuals, which had not been identified previously in any population studies. Significant decreases in uric acid transport have been demonstrated experimentally in vitro,...