GPR83 Antibody

What is GPR83 and where is it primarily expressed?

GPR83 (also known as JP05, GIR, GPR72) is a G-protein coupled receptor (GPCR) belonging to the family of seven-transmembrane domain receptors. It is highly expressed in specific brain regions, particularly the hippocampus, amygdala, prefrontal cortex, and hypothalamic nuclei, as well as in the spleen and thymus . Gene expression profiling in C57BL/6 mice has confirmed that Gpr83 is predominantly expressed in the brain, with moderate expression in the hypothalamus, while showing negligible expression in peripheral tissues such as liver, muscle, heart, testis, and adipose tissues .

In the brain's arcuate nucleus, GPR83 has been shown to colocalize with the ghrelin receptor (Ghsr1a) and agouti-related protein (AgRP), suggesting its involvement in metabolic regulation pathways . Its expression pattern indicates potential roles in both neurological functions and immune regulation.

What are the validated applications for GPR83 antibodies in research?

Based on current literature, GPR83 antibodies have been validated for several research applications:

Most commercially available antibodies target either the extracellular N-terminus, cytoplasmic domain, or C-terminus of GPR83 . For brain tissue analysis, IHC applications have been particularly informative, revealing GPR83 immunoreactivity in specific neuronal populations such as hippocampal dentate gyrus interneurons and cortical pyramidal neurons .

How should researchers design experiments to study GPR83's role in anxiety-related behaviors?

When designing experiments to study GPR83's role in anxiety-related behaviors, researchers should consider several methodological factors:

• Sex-specific effects: Studies have demonstrated significant sex differences in GPR83's influence on anxiety behaviors. Global knockout of GPR83 has minimal impact on anxiety-like behaviors in female mice but decreases anxiety-related behaviors in male mice . Therefore, both sexes should be included with sufficient statistical power to detect sex-specific effects.

• Brain region specificity: Local GPR83 knockdown produces region-specific effects. For example, knockdown in the basolateral amygdala (BLA) increases anxiety-related behaviors in female mice, while knockdown in the central amygdala (CeA) or nucleus accumbens (NAc) shows no significant effect . Use stereotaxic injections of lentiviral GPR83 shRNA to achieve ~50% knockdown in specific brain regions.

• Multiple behavioral assays: Different behavioral tests may yield varying results. Using both elevated plus maze (EPM) and open field tests is recommended, as some effects may be detected in one assay but not another. For example, BLA GPR83 knockdown affected behavior in the EPM but not in the open field test .

• Estrous cycle consideration: Consider controlling for or monitoring estrous cycle stages, as GPR83 expression in peripheral tissues is regulated during the estrus cycle in an estrogen and progesterone dependent manner .

• Stress exposure controls: Design protocols to minimize stress exposure that could confound results, particularly when studying anxiety-related behaviors.

What methods are most effective for visualizing GPR83 expression in brain tissue?

For optimal visualization of GPR83 expression in brain tissue, researchers should consider the following methodological approaches:

• Combined in situ hybridization with immunohistochemistry: This approach has been successfully used to demonstrate colocalization of GPR83 with other proteins such as Ghsr1a and AgRP in the arcuate nucleus . This technique allows precise cellular localization of GPR83 mRNA along with protein markers.

• Immunohistochemistry on fixed frozen sections: GPR83 antibodies targeting the extracellular domain have been effective for staining perfusion-fixed frozen mouse brain sections at dilutions of approximately 1:3000, followed by fluorescent secondary antibodies such as goat anti-rabbit-AlexaFluor-488 .

• Immunofluorescence counterstaining: Combine GPR83 immunostaining with DAPI nuclear counterstaining to better visualize cellular distribution patterns. This approach has revealed GPR83 immunoreactivity in hippocampal dentate gyrus interneurons and neurons of the cortical pyramidal layer .

• Control experiments: Include appropriate controls such as GPR83 knockout tissue or antibody preabsorption with immunizing peptide to confirm staining specificity.

• High-resolution confocal microscopy: For detailed subcellular localization, use confocal microscopy to distinguish between membrane and cytoplasmic expression of this GPCR.

How does GPR83 interact with the ghrelin receptor (Ghsr1a) and what experimental approaches best capture this interaction?

GPR83 has been shown to interact with the ghrelin receptor (Ghsr1a), with significant functional implications. To effectively study this interaction:

• Colocalization studies: In situ hybridization combined with immunohistochemistry has revealed that Gpr83 colocalizes with Ghsr1a in the arcuate nucleus . Researchers should use double-labeling techniques with specific antibodies or mRNA probes.

• Heterodimerization assays: In vitro analyses have demonstrated that GPR83 forms heterodimers with Ghsr1a, which diminishes the activation of Ghsr1a by acyl-ghrelin . Appropriate techniques include:

  • Co-immunoprecipitation

  • Bioluminescence/fluorescence resonance energy transfer (BRET/FRET)

  • Proximity ligation assays

• Functional assessment: The biological significance of this interaction can be assessed using GPR83-deficient mice, which show potentiated orexigenic and adipogenic responses to ghrelin administration . Researchers should design experiments that compare ghrelin effects in wild-type versus GPR83 knockout models.

• Metabolic phenotyping: While GPR83 knockout mice display normal body weight and glucose tolerance on regular chow diets, they are protected from obesity and glucose intolerance when challenged with high-fat diets, despite showing hyperphagia and increased hypothalamic expression of AgRP, NPY, and Ghsr1a . This suggests complex metabolic regulatory mechanisms that should be investigated using:

  • Glucose tolerance tests

  • Insulin sensitivity assays

  • Food intake measurements

  • Body composition analysis

What are the methodological challenges in studying GPR83's role in T regulatory cell function?

Studying GPR83's role in T regulatory (Treg) cell function presents several methodological challenges that researchers should address:

How does antibody selection affect GPR83 detection in different experimental contexts?

The choice of GPR83 antibody significantly impacts experimental outcomes. Consider these technical aspects:

• Epitope selection: Commercial antibodies target different regions of GPR83, including:

  • Extracellular domain (N-terminus): Suitable for detecting cell surface expression and live cell applications

  • Cytoplasmic domain: Better for detecting total cellular GPR83

  • C-terminus: Often used for Western blot applications

• Species cross-reactivity: While many antibodies recognize human, mouse, and rat GPR83, the degree of reactivity varies. Some antibodies show broader cross-reactivity with species like cow, monkey, dog, and even Xenopus laevis . Verify species reactivity for your specific model organism.

• Application-specific considerations:

  • For immunohistochemistry on paraffin sections: Use antibodies validated for IHC-P at concentrations of approximately 9 μg/ml

  • For flow cytometry applications: Select antibodies validated for live cell surface detection

  • For Western blot: Use dilutions of approximately 1:400 for optimal detection in brain membrane preparations

• Validation methods: Confirm antibody specificity using:

  • GPR83 knockout tissues as negative controls

  • Peptide competition assays

  • Multiple antibodies targeting different epitopes

What are the optimal protocols for detecting changes in GPR83 expression under different metabolic conditions?

To effectively detect changes in GPR83 expression under different metabolic conditions, researchers should consider these methodological approaches:

• Quantitative RT-PCR for mRNA expression: Studies have shown that hypothalamic Gpr83 expression decreases in mice with diet-induced obesity compared to lean controls, and fasting for 12-36 hours results in a time-dependent decrease in expression . For optimal results:

  • Use the RNeasy kit for RNA extraction from sorted cell populations

  • Perform DNase digestion

  • Use Superscript II reverse transcriptase with a mix of oligo(dT) and random hexamer primers

  • Employ real-time PCR with SYBR Green and specific primers for GPR83

  • Include appropriate housekeeping genes (e.g., RPS9) for normalization

• Nutritional intervention protocols: To study regulation by nutrient availability:

  • Fast mice for varying periods (12, 24, or 36 hours)

  • Refeed with specific diets (high-fat or fat-free) for 6 hours

  • Process hypothalamic tissue for mRNA analysis

• Western blot analysis for protein levels: Use brain membrane preparations from different metabolic states with antibody dilutions of approximately 1:400 .

• Immunohistochemical analysis: Compare GPR83 staining intensity and distribution in brain sections from:

  • Diet-induced obese versus lean mice

  • Fasted versus fed states

  • Different dietary interventions

• Co-expression analysis: Combine GPR83 detection with markers for energy metabolism such as AgRP, NPY, and ghrelin receptor to understand context-dependent regulation.

How do we reconcile conflicting findings on GPR83's role in Treg cell function versus metabolic regulation?

The apparent disconnect between GPR83's roles in immune tolerance and metabolic regulation represents an important research challenge. To address these seemingly disparate functions:

• Tissue-specific knockout models: Generate conditional GPR83 knockout mice targeting either CNS or immune cell populations to dissect tissue-specific roles.

• Molecular interaction mapping: Identify common signaling pathways or molecular interactions between:

  • GPR83-Ghsr1a interaction in hypothalamic neurons

  • GPR83-mediated signals in T regulatory cells

• Integrated physiological studies: Design experiments examining both metabolic parameters and immune function in the same animals under various conditions (high-fat diet, inflammatory challenges).

• Mediator identification: The ligand for GPR83 remains unclear. Identified as a receptor for PEN (a neuropeptide produced from proSAAS) , but other potential ligands may exist. Use techniques such as:

  • Receptor internalization assays

  • Calcium mobilization assays

  • β-arrestin recruitment

  • G-protein activation studies

• Translational approaches: Examine human samples (brain tissue, peripheral blood mononuclear cells) for correlations between GPR83 expression and metabolic or immune parameters.

What are the most promising experimental approaches to identify and characterize the physiological ligand(s) for GPR83?

As a relatively recently deorphanized receptor, identifying and characterizing GPR83's physiological ligands remains an active research area:

• Candidate ligand screening: Test known neuropeptides and hormones for activation of GPR83, focusing on:

  • PEN (a neuropeptide from proSAAS) has been identified as a ligand acting through G(i)- and G(q)-alpha-mediated pathways

  • Neuropeptide Y-related peptides, given GPR83's homology to NPY receptors

  • Glucocorticoid-regulated factors, given GPR83's identification as a glucocorticoid-induced receptor (GIR)

• Functional assays to confirm ligand activity:

  • G-protein coupling assays (GTPγS binding)

  • Second messenger measurements (cAMP, calcium)

  • β-arrestin recruitment

  • Receptor internalization

• Structure-activity relationship studies: Once candidate ligands are identified, generate analogs to map the pharmacophore and optimize binding/activity.

• Tissue-specific ligand hunting: Screen tissue extracts from regions with high GPR83 expression (brain, thymus, spleen) for activating factors.

• In vivo confirmation: Validate identified ligands through administration to wild-type versus GPR83 knockout mice, examining physiologically relevant readouts such as:

  • Food intake

  • Anxiety-related behaviors

  • T regulatory cell induction

  • Glucocorticoid responses

This comprehensive understanding of GPR83 ligand biology will be crucial for developing potential therapeutic approaches targeting this receptor system.

How should researchers account for sex differences when studying GPR83's role in anxiety and metabolism?

Sex differences significantly impact GPR83 function and should be carefully considered in experimental design:

• Baseline differences: Female wild-type mice tend to display lower baseline levels of anxiety compared to males, which impacts the detection of GPR83-related effects . When designing anxiety studies:

  • Include both sexes with sufficient sample sizes

  • Consider that female mice may show resistance to certain anti-anxiety treatments due to floor effects

  • Analyze males and females separately before pooling data

• Different behavioral assays: Some assays may be more sensitive for detecting effects in one sex versus the other:

  • Elevated plus maze has shown sex-specific effects of GPR83 manipulation

  • Open field tests may be less sensitive for detecting anxiety-related phenotypes in females

  • Consider using multiple behavioral paradigms including novelty suppressed feeding and marble burying

• Hormonal influence: GPR83 expression in peripheral tissues is regulated during the estrous cycle in an estrogen and progesterone dependent manner . Experimental designs should:

  • Track estrous cycle stages through vaginal cytology

  • Consider ovariectomy with hormone replacement to control hormonal variables

  • Analyze data with respect to estrous cycle stage

• Brain region specificity: The effect of local GPR83 knockdown may differ between sexes in specific brain regions. For example, knockdown in the basolateral amygdala increases anxiety in females . Use stereotaxic techniques for region-specific manipulations in both sexes.

• Metabolic phenotyping: While metabolic phenotypes of GPR83 knockout have been studied primarily in male mice , extending these studies to females is essential to understand potential sex-specific metabolic regulation.

What evidence supports targeting GPR83 for obesity and metabolic disorders?

Several lines of evidence suggest GPR83 as a potential therapeutic target for obesity and metabolic disorders:

• Expression regulation in obesity: Hypothalamic Gpr83 expression is decreased in mice with diet-induced obesity compared to lean controls , suggesting a possible role in the pathophysiology of obesity.

• Fasting-feeding regulation: Hypothalamic Gpr83 expression decreases in a time-dependent manner during fasting (12-36h) and increases following refeeding with either high-fat or fat-free diets , indicating responsiveness to nutritional status.

• Protection against diet-induced obesity: GPR83 knockout mice show:

  • Normal body weight and glucose tolerance on regular chow diet

  • Protection from obesity and glucose intolerance when challenged with a high-fat diet

  • This protection occurs despite hyperphagia and increased hypothalamic expression of orexigenic factors (AgRP, NPY, Hcrt, Ghsr1a)

• Ghrelin signaling modulation: GPR83 forms heterodimers with the ghrelin receptor (Ghsr1a), diminishing its activation by acyl-ghrelin. In GPR83-deficient mice, the orexigenic and adipogenic effects of ghrelin are potentiated , suggesting GPR83 as a natural brake on ghrelin signaling.

• Colocalization with metabolic regulators: In the arcuate nucleus, GPR83 colocalizes with the ghrelin receptor and agouti-related protein , placing it within a well-established network of energy homeostasis regulation.