Recombinant Human 2-oxoglutarate receptor 1 (OXGR1)

What is OXGR1 and what are its alternative nomenclatures in scientific literature?

OXGR1 (2-oxoglutarate receptor 1) is a G protein-coupled receptor located on the surface membranes of certain cells. In the scientific literature, it is also referred to as GPR80, GPR99, P2RY15, P2Y15, cysteinyl leukotriene receptor E (CysLT E), and cysteinyl leukotriene receptor 3 (CysLT3) . The protein is reported to have a molecular mass of approximately 38.3 kilodaltons . OXGR1 functions by binding specific ligands, thereby activating and triggering pre-programmed cellular responses .

What are the primary ligands for OXGR1?

OXGR1 has been shown to be activated by multiple ligands:

• α-ketoglutarate (the dianionic form of α-ketoglutaric acid)

• Itaconate (the dianionic form of itaconic acid)

• Cysteinyl-containing leukotrienes, including:

  • Leukotriene E4 (LTE4)

  • LTC4

  • LTD4

It's important to note that at physiological pH levels (>7) found in animal tissues, α-ketoglutaric acid and itaconic acid exist predominantly in their dianionic forms (α-ketoglutarate and itaconate), which are the active ligands for OXGR1 .

What tissue distribution patterns does OXGR1 exhibit?

OXGR1 shows distinct tissue expression patterns that correlate with its various physiological functions:

• Kidney: Expressed in cortical connecting tubule and collecting duct Type B intercalated cells

• Male reproductive system: Highly expressed in testis and smooth muscle of the epididymis

• Other tissues: Expression has been detected in various other tissues, though the testis shows particularly high expression levels according to early studies

What are effective methods for detecting OXGR1 in experimental samples?

Multiple approaches can be used to detect OXGR1 in research settings:

Many commercial anti-OXGR1 antibodies are available from suppliers, offering specificity for human, mouse, and rat orthologs .

How can researchers establish functional OXGR1 expression systems?

Researchers have successfully employed several expression systems to study OXGR1:

• HEK293T cells: Useful for protein production and basic signaling studies. Expression typically results in a multi-band pattern on immunoblotting, consistent with receptor multimerization .

• Xenopus oocytes: Effective for electrophysiology and calcium uptake studies. When expressing N-terminal MYC-tagged wildtype OXGR1 in oocytes, researchers have demonstrated AKG-responsive Ca²⁺ uptake .

• Mouse models: Both global and tissue-specific OXGR1 knockout models have been developed to study physiological functions .

When establishing these systems, verification of expression through Western blotting and surface localization via confocal microscopy is essential to confirm functional receptor expression .

How can researchers measure OXGR1 activation and downstream signaling?

Several methodological approaches can assess OXGR1 activation:

• Calcium uptake assays: OXGR1-expressing Xenopus oocytes exhibit AKG-responsive Ca²⁺ uptake, which can be measured to assess receptor functionality .

• Signaling pathway analysis: Upon AKG binding, OXGR1 signals through Protein Kinase C (PKC) to promote the chloride-bicarbonate exchanger Pendrin .

• Physiological readouts: In mouse models, OXGR1 activation can be assessed through:

  • Measurement of epididymal fluid acid-base balance

  • Analysis of sperm maturation parameters

  • Evaluation of renal bicarbonate handling

What role does OXGR1 play in male reproductive physiology?

OXGR1 has been identified as a critical regulator of sperm maturation:

• OXGR1 is highly expressed in the smooth muscle of the epididymis, with expression levels decreasing with aging and heat stress .

• Studies using global OXGR1 knockout and epididymis-specific OXGR1 knockout mouse models have demonstrated that this receptor is essential for epididymal sperm maturation by regulating acid-base homeostasis in renal tubular fluid .

• AKG supplementation (2% in drinking water) has been shown to significantly reduce sperm malformation rates in the epididymis and increase sperm capacitation and spontaneous acrosome reaction rates in aging mice .

• Similar beneficial effects were observed in heat stress mouse models, though AKG supplementation was less effective at improving sperm capacitation in heat-stressed animals .

These findings suggest that the AKG/OXGR1 signaling pathway in smooth muscle regulates local microenvironmental acid-base homeostasis, which influences sperm maturation .

How is OXGR1 implicated in renal pathophysiology?

OXGR1 has been identified as a candidate disease gene for calcium oxalate nephrolithiasis (kidney stones) and nephrocalcinosis:

• Exome sequencing has revealed rare heterozygous OXGR1 missense variants (including c.371T>G, p.L124R) that cosegregate with calcium oxalate nephrolithiasis and/or nephrocalcinosis in an autosomal dominant inheritance pattern .

• In the distal nephron, OXGR1 responds to its ligand AKG by stimulating the chloride-bicarbonate exchanger Pendrin, which also regulates transepithelial calcium transport in cortical connecting tubules .

• Functional studies using Xenopus oocytes demonstrated that wildtype OXGR1 mediates AKG-responsive Ca²⁺ uptake, while disease-associated variants showed impaired AKG-dependent Ca²⁺ uptake, indicating a loss-of-function mechanism .

• Statistical analysis has shown that rare, potentially deleterious OXGR1 variants are significantly enriched in nephrolithiasis/nephrocalcinosis patients compared to ExAC controls (χ²=7.117, p=0.0076) .

These findings establish rare dominant loss-of-function OXGR1 variants as a novel etiology of recurrent calcium oxalate nephrolithiasis and nephrocalcinosis .

What metabolic roles has OXGR1 been implicated in beyond reproduction and kidney function?

As a receptor for α-ketoglutarate, a key intermediate in the tricarboxylic acid (TCA) cycle, OXGR1 serves as an important metabolic sensor. Research has shown that OXGR1 activation through AKG has regulatory roles in:

• Extending lifespan

• Maintaining intestinal health

• Reducing the risk of obesity

• Activating macrophages

These diverse functions highlight OXGR1's potential importance in integrating metabolic signals with cellular responses across multiple physiological systems.

How should researchers approach the functional characterization of OXGR1 variants?

When characterizing OXGR1 variants, particularly those associated with disease states, a systematic approach is recommended:

• Expression verification: Confirm comparable expression levels between wildtype and variant OXGR1 through Western blotting .

• Subcellular localization assessment: Use confocal microscopy to verify proper surface localization of variant proteins .

• Functional assays: Employ calcium uptake assays in expression systems such as Xenopus oocytes to evaluate AKG-responsive signaling .

• pH dependence studies: Test variants under different pH conditions (e.g., pH 5 and 7.4) to fully characterize functional defects, as some variants may show pH-dependent impairment .

• Co-expression studies: When studying OXGR1's interaction with partners like Pendrin, consider that some experimental systems may lack essential components for the complete signaling pathway .

What considerations are important when studying OXGR1 regulation of Pendrin activity?

The regulation of Pendrin by OXGR1 presents specific methodological challenges:

When investigating this pathway, researchers should consider:

• The potential requirement for additional signaling components

• The influence of the cellular microenvironment

• Species-specific variations in signaling pathways

• Alternative experimental systems that better recapitulate the native cellular context

What strategies can enhance the study of OXGR1 as a therapeutic target?

For researchers investigating OXGR1 as a potential therapeutic target, several approaches may prove valuable:

• Structure-function studies: Investigating the binding pocket of OXGR1 through molecular modeling and mutagenesis to understand ligand interactions.

• Selective agonist/antagonist development: Developing compounds that selectively target OXGR1 without affecting related receptors.

• Therapeutic supplementation strategies: Based on findings that AKG supplementation improves sperm parameters in aging and heat-stressed mice , similar supplementation approaches could be explored for kidney stone prevention.

• Biomarker development: Evaluating AKG levels or OXGR1 expression patterns as potential biomarkers for conditions such as male infertility or kidney stone risk.

• Genetic screening: Implementing OXGR1 variant screening in patients with recurrent calcium oxalate kidney stones to identify those who might benefit from targeted therapies .