Urate transport capacity of glucose transporter 9 and urate transporter 1 in cartilage chondrocytes

Abstract

Chronic gouty arthritis, caused by a persistent increase in, and the deposition of, soluble uric acid (sUA), can induce pathological chondrocyte destruction; however, the effects of urate transport and intracellular sUA on chondrocyte functionality and viability are yet to be fully determined. Thus, the aim of the present study was to investigate the presence and functionality of a urate transport system in chondrocytes. The expression profiles of two primary urate reabsorptive transporters, glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1), in human articular cartilage and chondrocyte cell lines were examined via western blotting, reverse transcription-quantitative PCR, immunohistochemistry and immunofluorescence. Then, chondrocytes were incubated with exogenous sUA at increasing concentrations. Negative control assays were conducted via the specific knockdown of GLUT9 and URAT1 with lentiviral short hairpin (sh)RNAs, and by pretreatment with benzbromarone, a known inhibitor of the two transporters. Intracellular UA concentrations were measured using colorimetric assays. The expression levels of GLUT9 and URAT1 were determined in cartilage tissues and chondrocyte cell lines. Incubation of chondrocytes with sUA led to a concentration-dependent increase in intracellular urate concentrations, which was inhibited by GLUT9 or URAT1 knockdown, or by benzbromarone pretreatment (27.13±2.70, 44.22±2.34 and 58.46±2.32% reduction, respectively). In particular, benzbromarone further decreased the already-reduced intracellular UA concentrations in HC-shGLUT9 and HC-shURAT1 cells by 46.79±2.46 and 39.79±2.22%, respectively. Cells overexpressing GLUT9 and URAT1 were used as the positive cell control, which showed increased intracellular UA concentrations that could be reversed by treatment with benzbromarone. In conclusion, chondrocytes may possess an active UA transport system. GLUT9 and URAT1 functioned synergistically to transport UA into the chondrocyte cytoplasm, which was inhibited by specific gene knockdowns and drug-induced inhibition. These results may be fundamental in the further investigation of the pathological changes to chondrocytes induced by sUA during gouty arthritis, and identified UA transport processes as potential targets for the early control of chronic gouty arthritis.

Uric Acid Has Direct Proinflammatory Effects on Human Macrophages by Increasing Proinflammatory Mediators and Bacterial Phagocytosis Probably via URAT1

“…In this way, we describe for, the first time, that human macrophages express URAT1, a transmembrane protein that had been only reported in endothelial cells, adipocytes, and cartilage chondrocytes [5]. Notably, we found that URAT1 expression in macrophages decreased as uric acid concentration increased, which might partially explain the fact that TNF-alpha, TLR4, and CD11c expression reached a saturation point, which in turn led to a decrease their protein levels.…”

“…In humans, monosodium urate-also referred to as uric acid-is the end-product of purine metabolism [1]. Uric acid is mainly excreted in urine and then reabsorbed in epithelial cells of the proximal convoluted tubule by urate transporters, such as the urate anion transporter 1 (URAT1), a transmembrane protein highly expressed in endothelial cells, adipocytes, and cartilage chondrocytes [2][3][4][5].…”

SLC2A9 rs1014290 Polymorphism is Associated with Prediabetes and Type 2 Diabetes

“…Tese fndings indicate the GG genotype was signifcantly associated with lower blood UA levels and a lower risk of T2DM compared with the other two genotypes. GLUT9 [20] was once classifed as a glucose and/or fructose transporter and, although its transport activity is very low, GLUT9 has a large efect on glucose metabolism [7,21,22]. GLUT9 is upregulated in the liver and kidney tissues of diabetic mice and afects glucoseinduced insulin secretion in pancreatic β cells [6,[23][24][25].…”

“…GLUT9 [ 20 ] was once classified as a glucose and/or fructose transporter and, although its transport activity is very low, GLUT9 has a large effect on glucose metabolism [ 7 , 21 , 22 ]. GLUT9 is upregulated in the liver and kidney tissues of diabetic mice and affects glucose-induced insulin secretion in pancreatic β cells [ 6 , 23 – 25 ].…”

“…Original data-2. Genotyping and determination of gene polymorphisms were carried out with reference to the literature [ 20 ]. Genomic DNA extraction kit (Generay Biotechnology, Shanghai, China).…”