Recombinant Mouse P2Y purinoceptor 4 (P2ry4)

What is the structure and functional profile of mouse P2Y4 receptors compared to human and rat orthologs?

Mouse P2Y4 receptor is a G protein-coupled receptor with seven transmembrane spanning regions, consisting of 361 amino acids. It shares 95% amino acid identity with rat P2Y4 and 82% with human P2Y4 . P2Y4 receptors couple primarily to Gq proteins, activating phospholipase C (PLC), leading to inositol 1,4,5-trisphosphate (IP3) production and subsequent Ca2+ release from intracellular stores .

Species differences are significant:

• Mouse P2Y4 is equally activated by ATP and UTP

• Human P2Y4 is primarily a UTP-selective receptor

• Rat P2Y4 shows similar pharmacology to mouse P2Y4

Antagonist sensitivity also varies between species, with mouse and human P2Y4 being sensitive to PPADS (IC50 ≈ 10.5 μM and 9.6 μM respectively), while rat P2Y4 shows low sensitivity to this antagonist (IC50 >100 μM) .

Which tissues express P2Y4 receptors in mice and how can this expression be detected?

P2Y4 mRNA in mice has been detected in multiple tissues using reverse transcription and polymerase chain reaction (RT-PCR):

In the brain, P2Y4 shows enriched expression in specific regions :

• Neural crest cells during development

• Neuronal precursors during differentiation

• Type 2b neural stem cells in adult hippocampus

Detection methods for P2Y4 expression include:

• RT-PCR for mRNA detection across tissues

• In situ hybridization for spatial expression patterns

• Immunohistochemistry with validated antibodies

• Generation of reporter mouse lines (similar to P2rx4-tdTomato mice)

What expression systems are recommended for functional studies of recombinant mouse P2Y4?

Multiple expression systems have been validated for recombinant mouse P2Y4 studies:

Methodological recommendations:

• For calcium imaging: Use stable cell lines with consistent receptor expression levels

• For electrophysiology: Use Cs-aspartate containing electrodes (3-8 MΩ) in HEPES-buffered extracellular medium

• For binding studies: COS-7 cells have shown high expression levels for related receptors

How can functional activity of recombinant mouse P2Y4 receptors be quantitatively measured?

Multiple complementary approaches can be used:

Calcium Mobilization Assays:

• Load cells with ratiometric (Fura-2) or single-wavelength (Fluo-4) calcium indicators

• Measure fluorescence changes following receptor stimulation

• Quantify peak amplitude, duration, and oscillation frequency

• Can detect different patterns of calcium signaling (sustained vs. oscillatory)

Electrophysiological Measurements:

• Whole-cell patch clamp recordings in expression systems

• Typical parameters: EC50 values for ATP at mouse P2Y4 ≈ 2.3 μM

• Compare responses to different agonists as percentage of maximum ATP response

• Measure current-voltage relationships to confirm channel properties

Inositol Phosphate Accumulation:

• Pre-label cells with [3H]inositol

• Measure accumulation of IP3 following receptor activation

• Use LiCl to inhibit inositol phosphate degradation for cumulative measurements

G-protein Coupling Analysis:

• Use pertussis toxin to differentiate between Gq and Gi coupling

• Measure cAMP levels to detect potential coupling to Gs/Gi proteins

• PKC modulation affects calcium signaling patterns (frequency and spike width)

What is the detailed pharmacological profile of mouse P2Y4 and how does it compare to other P2Y subtypes?

Agonist Profile for Mouse P2Y4:

Antagonist Profile:

Species Differences:

• For rat P2Y4: α,β-meATP is an antagonist (IC50 = 4.6 μM)

• For human P2Y4: PPADS IC50 = 9.6 μM

P2Y Subtype Comparison:

• P2Y1: Prefers ADP > ATP; inhibited by suramin

• P2Y2: Responds equally to ATP and UTP

• P2Y6: Prefers UDP

• P2Y12-14: Couple primarily to Gi proteins (vs. Gq for P2Y4)

What genetic approaches can be used to investigate P2Y4 function in mouse models?

Knockout Strategies:

• Conventional P2Y4 knockout mice show phenotypes related to:

  • Improved glucose tolerance and insulin sensitivity

  • Protection against myocardial infarction

  • Increased adiponectin secretion

  • Decreased cardiac inflammation

TALEN-Mediated Gene Disruption:

• Transcription activator-like effector nuclease (TALEN) has been used for targeted disruption of P2Y4

• Left and right TALEN pairs (50 pg each) can be injected to disrupt gene function

• DNA sequencing confirms target gene disruption

• Phenotypic analysis at relevant developmental stages

siRNA Knockdown:

• Effective for in vitro studies

• Transfection of P2Y4-specific siRNAs reduces receptor expression

• Verify knockdown by western blot or qPCR

• Functional consequences can be measured by calcium imaging or other assays

Reporter Strategies:

• Generation of P2Y4 reporter mice (similar to P2rx4-tdTomato mice)

• Crossing with cell-specific reporter lines to identify cellular expression

• Combined with functional studies to correlate expression with physiological roles

What is known about the role of P2Y4 receptors in neuronal development and differentiation?

P2Y4 plays a critical role in neuronal development through multiple mechanisms:

Expression in Neuronal Precursors:

• Expression peaks during neuronal differentiation from embryonic stem cells

• Transiently increases during differentiation after loss of pluripotency (Oct4) but before terminal differentiation

Glutamatergic Neuron Specification:

• P2Y4-Gq signaling axis induces glutamatergic markers

• UTP stimulation increases vesicular glutamate transporter expression

• siRNA knockdown of P2Y4 inhibits UTP-dependent induction of glutamatergic neurons

• Detected predominantly in type 2b neural stem cells in adult hippocampus

Head Development:

• P2Y4 is required for head organizer formation during neural induction in Xenopus

• Disruption results in small head phenotype and reduced expression of head organizer genes (dkk1, cerberus)

• Reduction in neural crest marker expression (snail1, hairy2b) at neurula stage

• TALEN-mediated knockout disrupts anterior neural development

Mechanism of Action:

• P2Y4 receptor activation induces calcium signaling in neural progenitors

• Required for proper neural crest cell formation and migration

• May regulate cell proliferation to maintain progenitor cells in an undifferentiated state

How does P2Y4 function in cardiovascular health and glucose metabolism?

P2Y4 has emerged as an important regulator of both cardiovascular function and glucose homeostasis:

Cardiovascular Protection:

• P2Y4 knockout mice show protection against myocardial infarction

• Smaller infarcts in the left anterior descending coronary artery ligation model

• Significant decrease in cardiac inflammation and permeability

• Higher levels of cardioprotective adiponectin correlate with increased cardiac adipose tissue

N178T Polymorphism Effects:

• Loss-of-function variant in human P2Y4 receptor

• Located in the second extracellular loop

• Less frequent in coronary artery disease patients than in controls

• Associated with:

  • Reduced cardiac severity scores (jeopardy and Gensini)

  • Lower resting heart rates

  • Reduced plasma NT-proBNP levels

  • Lower fasting glucose concentration

Glucose Metabolism:

• P2Y4 knockout mice show:

  • Significantly improved glucose tolerance

  • Enhanced insulin sensitivity

  • These effects are dependent on adiponectin (not observed in adiponectin/P2Y4 double-KO mice)

• P2Y4 receptors can regulate Cl- and K+ channels and intracellular Ca2+ signaling in pancreatic ducts

Therapeutic Implications:

• P2Y4 antagonists may have applications in treating:

  • Myocardial infarction

  • Type 2 diabetes

  • Insulin resistance

What methods are available to study the structural aspects of P2Y4 receptors?

Computational Approaches:

• Homology modeling based on related P2Y receptor crystal structures

• Molecular dynamics simulations to study receptor flexibility and ligand interactions

• AlphaFold/ColabFold predicted structural models, especially valuable when experimental structures are unavailable

Mutagenesis Studies:

• Site-directed mutagenesis to identify key residues for ligand binding or receptor function

• Mutation types include:

  • Reduction of side chain size (e.g., to Ala) to reduce ligand interactions

  • Introduction of bulkier side chains (e.g., to Trp) to create steric hindrance

  • Charge alterations to disrupt electrostatic interactions

Structural Comparison:

• Comparison with experimental structures of related receptors (e.g., P2X4)

• Focus on conserved residues and binding pockets

• Analysis of species differences in key binding regions

Functional Validation:

• Patch-clamp recordings of mutant receptors

• Calcium imaging to assess functionality of mutants

• Binding studies with labeled agonists/antagonists

• Assessment of agonist/antagonist potency alterations in mutants

While no crystal structure of P2Y4 has been reported, insights can be gained from structures of related receptors combined with careful functional studies of mutant receptors.

How can differential Ca2+ signaling patterns mediated by P2Y4 be analyzed and interpreted?

P2Y4 activation generates complex calcium signaling patterns that can be analyzed through multiple approaches:

Calcium Oscillation Analysis:

• P2Y4 activation typically produces oscillatory Ca2+ responses

• Key parameters to measure:

  • Oscillation frequency

  • Spike amplitude

  • Spike width (duration)

  • Time to first peak

  • Pattern sustainability

Regulatory Mechanisms:

• PKC modulation affects P2Y receptor calcium signaling:

  • PKC activation decreases oscillation frequency for P2Y1

  • Both PKC activation and inhibition decrease spike width for P2Y2/4, suggesting multiple opposing feedback mechanisms

  • Plasma membrane Ca2+ entry required for negative PKC feedback on P2Y1 but not for P2Y2/4

Analytical Approaches:

• Real-time imaging with high temporal resolution (>1 Hz)

• Single-cell analysis to capture heterogeneity

• Automated analysis software to quantify oscillation parameters

• Pharmacological dissection using channel blockers and pathway inhibitors

Physiological Relevance:

• Different patterns of calcium signaling can encode specific cellular responses

• Oscillation frequency may determine which downstream pathways are activated

• Understanding these patterns helps interpret P2Y4-specific functions in different cell types

What are the current challenges in developing selective pharmacological tools for P2Y4 research?

Subtype Selectivity:

• High sequence similarity between P2Y receptor subtypes complicates selective tool development

• Limited structural information specific to P2Y4

• Need to distinguish from closely related P2Y2 which shares similar agonist profile

Species Differences:

• Significant pharmacological differences between human, mouse, and rat P2Y4 orthologues

• Mouse/rat P2Y4 activated equally by ATP and UTP, while human P2Y4 is UTP-selective

• Species-dependent antagonist sensitivity (e.g., PPADS effective at mouse/human but not rat P2Y4)

Binding Site Characterization:

• Limited information on precise binding sites for P2Y4 agonists and antagonists

• Need for systematic mutagenesis studies similar to those for P2X receptors

• Requirement for robust expression systems that maintain proper receptor folding and function

Design Strategy Recommendations:

• Focus on extracellular loop regions where sequence divergence is greatest

• Target allosteric sites rather than orthosteric sites for greater selectivity

• Develop antibody-based approaches for selectivity when small molecules fail

• Use complementary genetic approaches (siRNA, CRISPR) to validate pharmacological findings