Recombinant Macaca mulatta Urotensin-2 receptor (UTS2R)

What is Recombinant Macaca mulatta Urotensin-2 receptor (UTS2R)?

Recombinant Macaca mulatta Urotensin-2 receptor (UTS2R) is a G-protein-coupled receptor expressed predominantly in cardiovascular tissue that functions as the receptor for Urotensin-II (U-II), a vasoactive 'somatostatin-like' cyclic peptide. UTS2R is also known by several alternative names including GPR14, UTR, and UR-2-R. The protein consists of 389 amino acids in Macaca mulatta (Rhesus macaque) with a specific sequence structure that enables its binding to U-II with high affinity . This binding interaction is functionally coupled to calcium mobilization, triggering downstream signaling pathways that mediate various physiological responses, particularly in the cardiovascular system .

The recombinant form of this protein is produced through molecular cloning and expression techniques, allowing for detailed in vitro studies of receptor function, structure, and ligand interactions. The receptor plays a significant role in cardiovascular regulation, and its study in non-human primates provides valuable translational insights for human health and disease mechanisms.

What physiological roles does UTS2R play in non-human primates?

In non-human primates, UTS2R mediates several critical physiological functions, with particularly prominent roles in the cardiovascular system. When activated by its endogenous ligand Urotensin-II (U-II), the receptor triggers responses that significantly impact vascular tone and cardiac function .

Key physiological roles include:

• Potent vasoconstriction: U-II binding to UTS2R produces vasoconstriction that is approximately an order of magnitude more potent than endothelin-1, making it one of the most powerful mammalian vasoconstrictors identified . This effect is particularly pronounced in isolated arteries from non-human primates.

• Regulation of peripheral resistance: In vivo studies with anesthetized non-human primates have demonstrated that activation of UTS2R markedly increases total peripheral resistance .

• Cardiac function modulation: UTS2R activation is associated with profound cardiac contractile dysfunction in non-human primates, suggesting its involvement in regulating heart function .

• Glucose metabolism regulation: Research indicates that UTS2R plays a role in glucose metabolism and insulin resistance, suggesting potential involvement in metabolic regulation .

• Neurological and endocrine functions: The presence of UTS2R immunoreactivity in central nervous system and endocrine tissues suggests additional roles beyond the cardiovascular system, though these functions are less well characterized .

These physiological effects make UTS2R an important target for studying cardiovascular disease mechanisms and potential therapeutic interventions in both non-human primates and humans.

What methodologies are most effective for measuring UTS2R activation in vitro?

Several methodologies have been developed for measuring UTS2R activation in vitro, with the TGFα-shedding assay emerging as a particularly effective approach. This methodology enables sensitive detection of GPCR activation through monitoring of TGFα release:

TGFα-shedding assay protocol:

• Seed HEK293A cells in a 12-well culture plate

• Transfect cells using polyethylenimine (PEI) reagent (2.5 μl of 1 mg/ml per well) with:

  • UTS2R plasmids (100 ng per well)

  • Plasmids encoding alkaline phosphatase (AP)-tagged TGFα (AP-TGFα; 250 ng)

• Culture for 24 hours

• Harvest transfected cells and collect by centrifugation

• Suspend cells in Hank's Balanced Salt Solution (HBSS) containing 5 mM HEPES (pH 7.4)

• Seed in a 96-well plate

• Incubate for 30 minutes, then add test compounds

• Measure TGFα shedding as an indicator of receptor activation

For comprehensive functional characterization, this assay can be complemented with:

• Calcium mobilization assays: Since UTS2R activation is functionally coupled to calcium mobilization, fluorescent calcium indicators can be used to measure receptor activity .

• BRET/FRET-based assays: These techniques allow real-time monitoring of protein-protein interactions involved in UTS2R signaling.

• Co-expression with chimeric G-proteins: For initial screening and characterization of UTS2R function, chimeric Gα subunit proteins (mixture of Gα q/s, Gα q/i1, Gα q/i3, Gα q/o, Gα q/z, Gα q/12, Gα q/13, and Gα 16) can be co-expressed to determine G-protein coupling specificity .

These methodologies provide complementary information about UTS2R function, allowing researchers to comprehensively characterize receptor activation, signaling, and pharmacological properties.

How do genetic variations in UTS2R affect receptor function and disease associations?

Genetic variations in UTS2R have significant impacts on receptor function and are associated with several pathological conditions, particularly metabolic and cardiovascular disorders. Research has revealed:

Key genetic variations and their functional consequences:

Researchers have generated and studied 110 missense mutants corresponding to human SNVs in the UTS2R gene to characterize their effects on receptor function . These studies have revealed that:

• Mutations in transmembrane domains often affect ligand binding affinity

• Mutations in intracellular loops can disrupt G-protein coupling

• Certain promoter region variations alter transcriptional regulation

The AC haplotype (-11640A and -8515C) in the UTS2R gene has been associated with higher plasma glucose levels 2 hours after a 75g oral glucose load in Hong Kong Chinese populations, suggesting its involvement in glucose metabolism regulation . This finding points to UTS2R's potential role in metabolic disorders like type 2 diabetes mellitus.

The dramatic upregulation of UTS2R expression (nearly 2,000-fold) observed in diabetic tissue compared to control nephrectomy tissue further supports its pathophysiological relevance . These findings collectively highlight UTS2R as an important genetic factor in metabolic and cardiovascular disease susceptibility.

How can computational approaches enhance UTS2R structure-function studies?

Computational approaches have become invaluable tools for studying UTS2R structure-function relationships, offering insights that complement experimental methods. Several computational techniques have proven particularly useful:

AlphaFold protein structure prediction:
AlphaFold has revolutionized GPCR structural biology by providing high-confidence predictions of UTS2R structure. In recent studies, researchers:

• Obtained the human UTS2R structure from the AlphaFold Protein Structure Database

• Trimmed the lid-like N-terminus region (residues 1-42) with low pLDDT scores to improve modeling quality

• Added hydrogen atoms to the trimmed receptor using the program Reduce

• Used this refined structural model for further analyses

Molecular docking simulations:
These approaches allow for the prediction of ligand-receptor interactions:

• Tools such as AutoDockFR have been used to dock ligands like remdesivir in the orthosteric pocket of UTS2R

• Parameters typically include 50 genetic algorithm evolutions and a maximum of 2,500,000 evaluations

• Docking poses are clustered (e.g., at 2 Å cutoff) and assessed based on criteria such as hydrogen bonding

• The predicted binding poses can be visualized and analyzed with tools like CueMol and PyMOL

Electronic rapid amplification of cDNA ends (e-RACE):
This computational approach has been used to re-annotate UTS2R gene structure:

• Using genomic DNA sequences flanking coding sequences as queries for BLAST searches

• Determining both 5'UTR and 3'UTR ends of the genes against EST databases

• This approach identified specific ESTs (e.g., BF513269 for the 5'UTR end and AA621666 for the 3'UTR end of human UTS2R)

These computational methods have helped researchers identify key amino acid residues essential for ligand binding, predict the effects of genetic variations, and better understand UTS2R's structural basis for function. The integration of these approaches with experimental data has significantly accelerated our understanding of this important receptor.

What are the implications of UTS2R's cardiovascular effects for drug development?

UTS2R's profound cardiovascular effects position it as a significant target for therapeutic intervention, though its development presents both opportunities and challenges:

Cardiovascular Effects with Therapeutic Relevance:

The exceptional potency of UTS2R activation makes it the most potent mammalian vasoconstrictor identified to date . This characteristic suggests antagonists could potentially be valuable for treating hypertension or other conditions characterized by excessive vasoconstriction. Conversely, selective activation might benefit conditions involving vascular insufficiency.

Despite these promising therapeutic avenues, the field faces challenges in developing compounds with optimal selectivity, potency, and pharmacokinetic properties. The high conservation of UTS2R across species facilitates translational research using non-human primate models, potentially accelerating the path from preclinical to clinical studies. Future development will likely focus on tissue-specific targeting to maximize therapeutic benefit while minimizing systemic side effects.

How does UTS2R function differ between species, and what are the implications for translational research?

Understanding interspecies differences in UTS2R structure and function is crucial for translational research. Key differences and similarities include:

Comparative UTS2R Characteristics Across Species:

Human UTS2R was initially thought to lack UTRs according to some database entries (NM_018949.1), but electronic rapid amplification of cDNA ends (e-RACE) approaches have identified specific EST sequences corresponding to both 5'UTR (BF513269) and 3'UTR (AA621666) ends of the gene . These regulatory regions may contribute to species-specific expression patterns.

The strong similarity in cardiovascular responses between humans and non-human primates makes Macaca mulatta an excellent model for studying UTS2R-mediated effects relevant to human health and disease. Studies showing that human U-II effectively constricts isolated arteries from non-human primates and produces similar in vivo effects on peripheral resistance and cardiac function support this translational value .

These interspecies comparisons highlight the importance of selecting appropriate animal models for UTS2R research, with non-human primates offering advantages for cardiovascular studies compared to more phylogenetically distant species.

What is the relationship between UTS2R and metabolic disorders like type 2 diabetes?

Recent research has established significant connections between UTS2R and metabolic regulation, particularly in the context of type 2 diabetes mellitus (T2DM). Several key findings illustrate this relationship:

UTS2R in Diabetes Pathophysiology:

• Dramatic expression changes: In human diabetic tissue, UTS2R expression is increased approximately 2,000-fold compared to control nephrectomy tissue (P<0.01), suggesting a significant role in diabetic pathophysiology .

• Genetic associations: Specific haplotypes in the UTS2R gene have been linked to altered glucose metabolism. The AC haplotype (-11640A and -8515C) in the UTS2R gene is associated with higher plasma glucose levels 2 hours after a 75g oral glucose load in Hong Kong Chinese populations .

• Insulin resistance connection: UTS2R has been reported to affect glucose metabolism and insulin resistance, which is a core pathological characteristic of patients with T2DM .

• Potential mechanisms: The receptor's effects on vascular function may contribute to altered tissue perfusion and glucose delivery. Additionally, direct effects on insulin signaling pathways have been proposed but require further investigation.

The mechanistic links between UTS2R and diabetes appear multifaceted, potentially involving:

• Vascular effects that alter blood flow to insulin-sensitive tissues

• Direct modulation of insulin signaling pathways

• Inflammatory processes that contribute to insulin resistance

• Alterations in pancreatic islet blood flow affecting insulin secretion

These findings suggest that UTS2R may represent a novel therapeutic target for metabolic disorders, particularly T2DM. Antagonizing UTS2R function might potentially improve insulin sensitivity and glucose homeostasis, though this hypothesis requires further investigation through targeted preclinical and clinical studies.

What challenges exist in developing selective UTS2R ligands for research and therapeutic applications?

Developing selective UTS2R ligands presents several significant challenges that researchers must overcome:

Structural complexity of the binding pocket: The UTS2R binding domain contains multiple interaction sites that contribute to ligand recognition and binding. Recent structural studies using AlphaFold and docking simulations have identified key amino acid residues that are essential for ligand binding, but the complex three-dimensional arrangement of these residues complicates rational drug design .

Selectivity challenges: Achieving selectivity for UTS2R over related GPCRs requires precise targeting of unique structural features. The orthosteric binding site shares some similarities with other peptide receptors, potentially leading to off-target effects. Studies have used docking simulations to identify compounds like remdesivir that can interact with UTS2R, but achieving high selectivity remains difficult .

Species differences in ligand responsiveness: Though UTS2R is relatively well-conserved across species, subtle structural differences can affect ligand binding and activation. This complicates translational research and necessitates careful validation across species.

Pharmacokinetic hurdles: Many peptide-based UTS2R ligands face challenges related to oral bioavailability, plasma stability, and blood-brain barrier penetration. Non-peptide small molecules may overcome some of these limitations but often show reduced potency or selectivity.

Target tissue selectivity: UTS2R is expressed in multiple tissues, including cardiovascular, renal, and central nervous system. Developing ligands that selectively target UTS2R in specific tissues while sparing others represents a substantial challenge for reducing side effects.

Despite these challenges, progress is being made through:

• Advanced computational approaches to better understand receptor structure

• High-throughput screening against focused compound libraries

• Structure-activity relationship studies to optimize lead compounds

• Development of allosteric modulators that may offer improved selectivity

These efforts are critical for developing both research tools to better understand UTS2R biology and potential therapeutic agents targeting conditions ranging from cardiovascular disease to metabolic disorders.

What are the key considerations when designing experiments to study UTS2R function?

When designing experiments to study UTS2R function, researchers should consider several critical factors to ensure robust and reproducible results:

Expression system selection: Different cellular backgrounds can significantly influence UTS2R expression, trafficking, and signaling. HEK293A cells are commonly used for recombinant expression studies , but researchers should consider whether this heterologous system adequately reflects the receptor's native environment. Primary cells from relevant tissues may provide more physiologically relevant contexts but present challenges in transfection efficiency and standardization.

Receptor construct design: When creating recombinant UTS2R constructs, researchers must carefully consider:

• Whether to include epitope tags and their potential impact on receptor function

• The importance of the N-terminal domain (residues 1-42), which has been identified as having low confidence in structural predictions

• The need for codon optimization based on the expression system

Control experiments:

• Positive controls using known UTS2R ligands like human Urotensin-II

• Negative controls with inactive receptor mutants or in the absence of ligand

• Vehicle controls to account for solvent effects

• Specificity controls using related receptors to confirm selectivity

Readout system selection: Different assay systems measure distinct aspects of receptor function:

• TGFα-shedding assays for receptor activation

• Calcium mobilization assays for signaling pathway engagement

• Binding assays to directly measure ligand-receptor interactions

• Downstream functional assays for physiological responses

G-protein coupling analysis: UTS2R can potentially couple to multiple G-protein subtypes, affecting downstream signaling. Co-expression with chimeric Gα subunit proteins (Gα q/s, Gα q/i1, Gα q/i3, etc.) helps determine coupling specificity .

Statistical considerations:

• Power analysis to determine appropriate sample sizes

• Accounting for batch effects and experimental variability

• Selection of appropriate statistical tests based on data distribution

• Consideration of multiple testing corrections when performing high-throughput experiments

By carefully addressing these considerations, researchers can design more robust experiments that yield reliable and interpretable data about UTS2R function in various contexts.

How should researchers interpret conflicting data regarding UTS2R function in different experimental models?

Interpreting conflicting data regarding UTS2R function across different experimental models requires a systematic approach that considers multiple factors:

Source of biological variation:

• Species differences: UTS2R function may vary between species despite sequence homology. For example, while UTS2R shows potent vasoconstrictor effects in non-human primates that mirror human responses , results from more evolutionarily distant species may diverge significantly.

• Tissue-specific effects: UTS2R expression and signaling can vary dramatically between tissues. The nearly 2,000-fold increased expression in diabetic tissue compared to control nephrectomy tissue illustrates how pathological conditions can dramatically alter receptor levels in a tissue-specific manner.

• Genetic background effects: Different genetic backgrounds may influence UTS2R function through modifier genes. Studies have identified specific haplotypes in the UTS2R gene associated with altered glucose metabolism , suggesting genetic context matters.

Methodological considerations:

• Assay sensitivity differences: The TGFα-shedding assay may detect receptor activation with different sensitivity than calcium mobilization assays or other functional readouts .

• Receptor expression levels: Variations in receptor density can shift dose-response relationships and alter apparent efficacy/potency.

• Experimental conditions: Buffer composition, temperature, presence of serum proteins, and other variables can affect ligand binding and receptor function.

Resolution approaches:

• Direct comparison studies: When conflicting data exists, design studies that directly compare different models under identical conditions.

• Multimodal assessment: Employ multiple complementary assays (binding, signaling, functional) to build a comprehensive picture of receptor activity.

• Dose-response relationships: Complete dose-response curves often reveal nuances missed by single-concentration experiments.

• Molecular determinants analysis: Investigate specific residues or domains involved in observed differences through mutagenesis studies. The creation and characterization of 110 missense mutants corresponding to human SNVs in the UTS2R gene provides valuable data for understanding how specific mutations affect function .

By systematically evaluating these factors, researchers can better interpret seemingly conflicting data and develop a more nuanced understanding of UTS2R biology across different experimental contexts.

How are emerging technologies advancing our understanding of UTS2R function?

Emerging technologies are revolutionizing UTS2R research, providing unprecedented insights into receptor structure, function, and therapeutic potential:

AI-based protein structure prediction: Tools like AlphaFold have transformed our ability to model UTS2R structure. Researchers have successfully used AlphaFold to predict UTS2R structure and identify key binding residues, as demonstrated in studies examining remdesivir-UTS2R interactions . This approach overcomes traditional limitations in obtaining crystal structures of GPCRs, which are notoriously difficult to crystallize due to their flexible transmembrane domains.

Advanced molecular docking: Sophisticated docking tools like AutoDockFR with genetic algorithm approaches enable more accurate prediction of ligand-receptor interactions. These computational methods allow for the screening of large compound libraries and the identification of novel UTS2R ligands with improved selectivity profiles .

CRISPR-Cas9 genome editing: This technology facilitates precise modification of UTS2R genes in cellular and animal models, enabling:

• Creation of knockout models to study receptor function

• Introduction of specific mutations corresponding to human polymorphisms

• Generation of reporter systems for studying receptor expression and trafficking

Single-cell transcriptomics: This approach reveals cell-type-specific expression patterns of UTS2R, providing insights into its distribution across tissues and potential roles in specific cell populations. This is particularly valuable given UTS2R's presence in diverse tissues including cardiovascular, nervous system, and endocrine tissues .

Cryo-electron microscopy (Cryo-EM): Recent advances in Cryo-EM resolution now enable structural determination of GPCRs in various conformational states, potentially revealing the molecular basis of UTS2R activation and signaling.

Biased ligand development: Modern pharmacological approaches aim to develop ligands that selectively activate specific UTS2R signaling pathways, potentially separating beneficial effects from adverse ones.

These technological advances are rapidly expanding our understanding of UTS2R biology and creating new opportunities for targeting this receptor in various disease states, from cardiovascular disorders to metabolic conditions like type 2 diabetes .

What are the most promising areas for future UTS2R research?

Several high-potential research directions are emerging in the UTS2R field, offering opportunities for significant scientific and therapeutic advances:

Metabolic disease connections: The established link between UTS2R and glucose metabolism opens promising research avenues. The dramatic upregulation (approximately 2,000-fold) of UTS2R expression in diabetic tissue warrants further investigation into:

• Mechanisms underlying this upregulation

• Functional consequences for insulin signaling and glucose homeostasis

• Potential for UTS2R-targeted interventions in type 2 diabetes

Cardiovascular disease applications: As the most potent mammalian vasoconstrictor identified , UTS2R's role in cardiovascular pathophysiology represents a significant opportunity:

• Development of UTS2R antagonists for hypertension and heart failure

• Investigation of UTS2R in pulmonary hypertension pathogenesis

• Exploration of UTS2R involvement in atherosclerosis progression

Pharmacogenomic personalization: The identification of functional UTS2R genetic variants and haplotypes associated with metabolic phenotypes suggests potential for:

• Developing genetic screening approaches to identify individuals likely to benefit from UTS2R-targeted therapies

• Understanding how genetic variation modifies disease risk and progression

• Creating personalized medicine approaches based on UTS2R genotype

Cross-species comparative biology: Studying UTS2R across species from its evolutionary origins in fish to its functions in primates offers insights into:

• Evolutionary conservation and divergence of UTS2R signaling

• Translational relevance of animal models for human UTS2R biology

• Novel functional roles that may be more prominent in specific species

Tissue-specific signaling mechanisms: Understanding how UTS2R signaling varies across tissues presents opportunities for:

• Developing tissue-targeted therapeutic approaches

• Identifying tissue-specific signaling partners and regulatory mechanisms

• Elucidating the basis for tissue-specific pathologies related to UTS2R dysfunction

These research directions leverage current findings while addressing key knowledge gaps, potentially leading to both fundamental discoveries about receptor biology and novel therapeutic strategies for conditions ranging from cardiovascular disease to metabolic disorders.