Human Mutations in SLC2A9 (Glut9) Affect Transport Capacity for Urate

Area of Science:

• Biochemistry and Molecular Biology
• Physiology
• Genetics

Background:

• Solute carrier family 2, member 9 (SLC2A9), or Glut9, is a urate transporter crucial for regulating serum uric acid levels.
• Mutations in Glut9 are linked to familial hypouricemia and influence serum urate concentrations.
• Glut9's role in urate homeostasis makes it a significant factor in conditions like gout and hyperuricemia.

Purpose of the Study:

• To systematically analyze the functional consequences of known human Glut9 mutants.
• To elucidate the transport characteristics and cellular behavior of Glut9 variants.
• To gain insights into the structure-function relationship of the Glut9 urate transporter.

Main Methods:

• Functional characterization of Glut9 mutants using 14C-urate uptake assays in Xenopus laevis oocytes.
• Electrophysiological analysis via two-electrode voltage clamp (TEVC) to measure urate currents.
• Assessment of protein expression and localization using immunostaining and biotinylation techniques.

Main Results:

• Most Glut9 variants exhibited reduced urate transport activity.
• Mutants displayed distinct behaviors: poor expression/activity or normal expression with reduced activity.
• Specific mutations like C210F showed decreased transport, while N333S indicated altered urate affinity, potentially within the binding pocket.

Conclusions:

• Glut9 is a key regulator of serum urate, and its mutations significantly impact transport function.
• Understanding Glut9 mutant behavior provides insights into urate homeostasis and potential therapeutic targets.
• This research reinforces Glut9's potential as a therapeutic target for hyperuricemia treatments.