Hyperuricemia Cell Models for Research

Hyperuricemia, defined as serum uric acid > 6.8 mg/dL, affects approximately 21% of the general population in the United States and up to 25% in some developing countries (WHO, 2023). It is a major risk factor for gout, which has a global prevalence of 1-4% and is increasing. Chronic hyperuricemia is also associated with hypertension, chronic kidney disease, metabolic syndrome, and cardiovascular events. The economic burden is substantial, with gout alone costing billions annually in healthcare and lost productivity. Early intervention and targeted therapies are critical, making hyperuricemia a key area for drug development.

Hyperuricemia is ideal for mechanistic studies due to its well-defined metabolic pathways and genetic components. The uric acid transport system involves multiple transporters (URAT1, GLUT9, ABCG2) and enzymes (XDH). Public datasets such as the UK Biobank and genome-wide association studies (GWAS) provide extensive genetic data. Open questions include the precise regulation of uric acid excretion and the molecular mechanisms linking hyperuricemia to comorbidities. Gene-edited cell models allow researchers to dissect these pathways in a controlled environment, facilitating target validation and drug screening.

• • Uric acid is the end product of purine metabolism. Key steps:
• • Purine nucleotides are broken down to hypoxanthine.
• • Xanthine oxidase (XOD) converts hypoxanthine to xanthine and then to uric acid.
• • Uric acid is excreted via the kidneys (two-thirds) and intestines (one-third).
• • Renal excretion involves glomerular filtration, reabsorption (URAT1, GLUT9), and secretion (ABCG2).
• • Overproduction (e.g., high purine diet, genetic defects) or underexcretion (e.g., impaired renal function) leads to hyperuricemia.

Data from ClinVar and GWAS studies.

• • Hyperuricemia is not a classic oncogenic pathway but involves metabolic and inflammatory signaling:
• • Uric acid activates the NLRP3 inflammasome, leading to IL-1β production and inflammation.
• • Hyperuricemia induces oxidative stress, activating MAPK and NF-κB pathways.
• • Urate transporters are regulated by hormones (insulin, angiotensin II) and transcription factors (HNF4α, PPARγ).
• • In renal cells, uric acid upregulates renin-angiotensin system, contributing to hypertension.
• • Key nodes: NLRP3, IL-1β, MAPK, NF-κB, and urate transporters.

Organoids derived from kidney or intestinal tissues offer 3D architecture and better mimic physiological transport. They are valuable for studying urate handling and drug responses.

• • Uricase-knockout mice: lack functional uricase, leading to hyperuricemia and gout-like symptoms.
• • Potassium oxonate-induced hyperuricemia in rats: inhibits uricase, causing rapid increase in serum uric acid.
• • Genetically engineered mouse models (GEMMs) with mutations in SLC22A12 or ABCG2 to study transporter function.
• • Humanized mice expressing human urate transporters for drug testing.
• • Patient-derived xenografts (PDX) are less common for hyperuricemia but used for cancer-related studies.

• • CRISPR-Cas9 gene editing enables precise modification of urate metabolism genes. Isogenic cell lines with knockout or knock-in mutations are essential for studying gene function and drug responses. For example:
• • URAT1 (SLC22A12) knockout in HK-2 cells to study urate reabsorption.
• • ABCG2 knockout in Caco-2 cells to model intestinal excretion defects.
• • XDH knockout in HepG2 cells to reduce uric acid production.
• • Point mutations (e.g., R406W in URAT1) introduced to mimic familial renal hypouricemia.

These sequence-verified models are commercially available and accelerate research by providing consistent, reproducible systems. They are used for target validation, drug screening, and mechanistic studies.

• • Knockout and knock-in lines validate the role of genes in uric acid metabolism. For instance:
• • SLC22A12 knockout in renal cells reduces urate uptake, confirming its role in reabsorption.
• • ABCG2 knockout in intestinal cells impairs urate efflux, linking it to hyperuricemia.
• • CRISPR screens can identify novel regulators of urate transport by targeting all genes in the genome.

• • Isogenic pairs (wild-type vs. knockout) are used to screen compounds that inhibit or activate urate transporters. For example:
• • URAT1 inhibitors (e.g., lesinurad) are tested in URAT1-expressing cells.
• • Resistance mechanisms to urate-lowering drugs can be studied by generating resistant cell lines via CRISPR.
• • High-throughput screening with gene-edited cells identifies new therapeutic candidates.

CRISPR-based synthetic lethality screens can identify genes that, when knocked out, are lethal only in hyperuricemic conditions. This can reveal new drug targets. Additionally, gene-edited cells are used to discover biomarkers for early detection of renal dysfunction or gout.