HTR4 Antibody

What is HTR4 and what biological systems express this receptor?

HTR4 (5-hydroxytryptamine receptor 4) is a G protein-coupled receptor that stimulates cAMP production in response to serotonin (5-hydroxytryptamine). It's a glycosylated transmembrane protein expressed in both the central and peripheral nervous systems where it modulates neurotransmitter release . Within the central nervous system, HTR4 is primarily expressed in limbic structures including the hypothalamus, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus . In peripheral tissues, HTR4 is found in the gastrointestinal tract and heart . The receptor plays crucial roles in learning and memory, feeding control, and stress response, and can generate multiple splice variants with distinct C-terminal sequences .

What applications are HTR4 antibodies validated for in current research?

HTR4 antibodies have been validated for multiple research applications with varying recommended dilutions:

Most commercial antibodies are tested for reactivity with human, mouse, and rat samples, with some showing broader species reactivity including bovine, canine, equine, and monkey samples .

What positive controls should be used when validating HTR4 antibodies?

When validating HTR4 antibodies, researchers should consider the following positive controls based on validated data:

• For IHC: Human prostate hyperplasia tissue has shown consistent positive staining with HTR4 antibodies

• For IF/ICC: HeLa cells have demonstrated positive detection

• For Western blot: HepG2 cell lysates have been validated , as have Jurkat and COLO205 cell lysates

• For flow cytometry: Human THP-1 monocytic leukemia cells and rat PC12 cells have shown positive cell surface detection

Appropriate negative controls should include samples known not to express HTR4 or antibody pre-incubated with specific blocking peptides to demonstrate specificity .

What are the most effective fixation and antigen retrieval methods for HTR4 detection in tissue sections?

For optimal HTR4 detection in paraffin-embedded tissue sections, the following methods have proven effective:

• Recommended antigen retrieval: TE buffer pH 9.0 has been demonstrated to work well

• Alternative method: Citrate buffer pH 6.0 also works but may give different staining intensity

• Fixation compatibility: Both formalin-fixed and PFA-fixed paraffin-embedded sections have been successfully used

• Antibody concentration: For IHC applications, 7-17 μg/mL or dilutions of 1:50-1:500 depending on the specific antibody

For immunofluorescence on cultured cells, standard 4% PFA fixation protocols are generally effective. Special protocols for HTR4 antibody use in IHC and IF applications are available from some manufacturers .

How should samples be prepared for Western blot analysis of HTR4?

When preparing samples for Western blot analysis of HTR4, researchers should consider:

• Expected molecular weight range: While the calculated molecular weight of HTR4 is 44 kDa (388 amino acids), Western blots typically show bands in the 40-140 kDa range due to post-translational modifications, particularly glycosylation

• Sample preparation: As a membrane protein, care should be taken to use appropriate lysis buffers that effectively solubilize membrane proteins while preserving the native structure of HTR4

• Antibody dilution: Most HTR4 antibodies work optimally at 1:500-1:1000 dilutions for Western blot applications

• Controls: Include lysates from cells known to express HTR4 such as HepG2, Jurkat, or COLO205 cells

• Loading amount: Typical protein loading amounts range from 20-50 μg of total protein per lane, though this may need adjustment based on expression levels

What are the challenges in detecting specific HTR4 splice variants?

Detection of specific HTR4 splice variants presents several challenges:

• Multiple variants: The HTR4 gene generates ten different splice variants in humans, primarily with distinct C-terminal sequences

• Epitope selection: Antibodies targeting different regions will detect different subsets of variants. N-terminal antibodies (like those targeting amino acids 14-66 ) will detect most variants, while C-terminal antibodies may be variant-specific

• Size discrimination: The small size differences between some variants may be difficult to resolve by Western blot

• Functional similarity: The variants share similar pharmacological properties , making functional discrimination challenging

• Tissue-specific expression: Different splice variants may be preferentially expressed in different tissues

For variant-specific detection, researchers should select antibodies with carefully mapped epitopes and consider using RT-PCR alongside immunological methods to confirm variant identity.

How can HTR4 antibodies be used to study receptor trafficking and internalization?

HTR4 antibodies are valuable tools for studying receptor trafficking and internalization:

• Surface vs. total staining: Antibodies targeting extracellular domains, such as those against the "2nd extracellular loop" , can be used in non-permeabilized cells to specifically detect surface receptors

• Live cell imaging: Search result #3 demonstrates "Cell surface detection of Serotonin receptor 4 in intact living rat pheochromocytoma (PC12) cells" using extracellular-targeted antibodies

• Trafficking dynamics: Antibodies can track changes in receptor localization following agonist treatment or other stimuli

• SNX27-mediated recycling: HTR4 surface levels depend on endocytic recycling from endosomes to the plasma membrane mediated by sorting nexin 27 (SNX27) . Antibodies can be used to monitor this process

• Quantification methods: Flow cytometry with extracellular-targeted antibodies provides quantitative measurement of surface receptor populations

For internalization studies, researchers should use antibodies targeting extracellular epitopes and compare staining patterns before and after agonist treatment.

What evidence links HTR4 dysfunction to COVID-19 symptoms, and how are antibodies helping investigate this connection?

Recent research has uncovered a direct link between SARS-CoV-2 infection and HTR4 dysfunction:

• Mechanism: SARS-CoV-2 spike (S) protein blocks sorting nexin 27 (SNX27)-mediated endocytic recycling of HTR4, reducing its surface levels

• Molecular interaction: The spike protein disrupts the interaction between SNX27 and Vps26A, a subunit of retromer essential for receptor recycling to the plasma membrane

• Experimental evidence: Using HTR4 antibodies in immunofluorescence analysis, researchers demonstrated that GFP-tagged spike protein (but not the binding-deficient T1238A mutant) significantly reduced surface HTR4 levels in both HEK293T and HeLa cells

• Clinical relevance: HTR4 deficiency has been linked to depression, anxiety, cognitive impairment, and loss of appetite—symptoms frequently observed in COVID-19 and long COVID patients

• Potential implications: This mechanism suggests that neuropsychiatric symptoms in COVID-19 patients may partially result from HTR4 deficiency, offering potential therapeutic targets

This research demonstrates how HTR4 antibodies can elucidate disease mechanisms beyond traditional receptor characterization.

How can HTR4 antibodies be used in studies of neuropsychiatric and neurodegenerative disorders?

HTR4 antibodies play crucial roles in studying neuropsychiatric and neurodegenerative conditions:

• Receptor level quantification: Western blot analysis can reveal altered HTR4 expression levels in brain tissues from patients with depression, anxiety, Alzheimer's disease, or Huntington's disease

• Distribution mapping: Immunohistochemistry with HTR4 antibodies can map changes in receptor distribution across brain regions in disease states

• Cellular localization: Immunofluorescence studies can reveal abnormal intracellular trafficking or localization of HTR4 in disease models

• Protein interactions: Immunoprecipitation with HTR4 antibodies can identify disease-specific protein interactions

• Disease mechanisms: As demonstrated in COVID-19 research, HTR4 antibodies can help elucidate how pathogenic processes disrupt receptor function

Low levels of HTR4 receptors are associated with numerous neuropsychiatric disorders including Alzheimer's disease, Huntington's disease, feeding disorders, and stress-related disorders such as anxiety and depression , making antibodies against this receptor valuable tools in neuropsychiatric research.

What methods should be used to validate the specificity of HTR4 antibodies?

Validating HTR4 antibody specificity requires multiple complementary approaches:

• Peptide competition: Pre-incubating the antibody with the immunizing peptide should abolish specific staining. This is demonstrated in search result #3, which shows elimination of signal when "Anti-5HT4 Receptor (HTR4) (extracellular) Antibody, preincubated with 5HT4 Receptor/HTR4 (extracellular) Blocking Peptide"

• Multiple applications: A specific antibody should show consistent results across multiple applications (WB, IHC, IF) with appropriate controls

• Size verification: In Western blots, bands should appear within the expected molecular weight range (40-140 kDa for HTR4)

• Sequence analysis: BLAST analysis of the immunogen peptide should confirm no homology with other human proteins

• Known positive controls: Testing in tissues or cells with confirmed HTR4 expression (e.g., human prostate hyperplasia tissue or HeLa cells )

• Multiple antibodies: Using antibodies targeting different epitopes of HTR4 should produce similar staining patterns if specific

Thorough validation is especially important for HTR4 due to its multiple splice variants and post-translational modifications.

What storage conditions and handling practices maximize HTR4 antibody performance and shelf-life?

Optimal storage and handling of HTR4 antibodies varies somewhat by formulation, but generally:

Following manufacturer-specific recommendations is important, as formulations vary between suppliers.

How do polyclonal and monoclonal HTR4 antibodies compare in research applications?

Both polyclonal and monoclonal HTR4 antibodies have specific advantages and limitations:

Polyclonal HTR4 Antibodies:

• Recognize multiple epitopes, potentially offering higher sensitivity

• Often work well in multiple applications (WB, IHC, IF, ELISA)

• May detect multiple splice variants more effectively

• Show broader species cross-reactivity (e.g., "Bovine, Canine, Equine, Human, Mammals, Monkey, Porcine, Rabbit" )

• Batch-to-batch variation may require reoptimization

Monoclonal HTR4 Antibodies:

• Offer higher specificity for a single epitope

• Provide better reproducibility between experiments

• Recombinant monoclonal antibodies (like product #85083-1-PBS ) offer "unrivalled batch-to-batch consistency, easy scale-up, and future security of supply"

• May have more restricted species reactivity

• Some monoclonals like "5-HTR4 (D8O5K) Rabbit mAb" have been validated for endogenous level detection

For critical quantitative applications, monoclonal or recombinant antibodies may offer better reproducibility, while polyclonal antibodies might be preferred for applications requiring detection of multiple variants or enhanced sensitivity.

How are HTR4 antibodies being used to investigate the receptor's role in gastrointestinal function?

HTR4 plays significant roles in gastrointestinal function, and antibodies are key tools in this research:

• Expression mapping: HTR4 antibodies in IHC studies help map receptor distribution throughout the GI tract

• Enteric nervous system studies: Immunofluorescence with HTR4 antibodies helps characterize serotonergic signaling in the enteric nervous system

• Motility regulation: HTR4 antibodies help investigate how this receptor regulates GI motility, with implications for functional GI disorders

• Therapeutic development: HTR4 antibodies are used to validate target engagement of HTR4-targeted therapeutics for GI disorders

• Experimental models: Search result #3 references research on "Effects of sacral nerve electrical stimulation on 5‐HT and 5‐HT3AR/5‐HT4R levels in the colon and sacral cord of acute spinal cord injury rat models," demonstrating the use of HTR4 antibodies in neurogenic bowel dysfunction research

The gastrointestinal applications of HTR4 antibodies complement the more extensively studied neuropsychiatric applications.

What techniques are being developed to improve detection of low-abundance HTR4 in tissue samples?

For detecting low-abundance HTR4 in tissues, researchers are employing several advanced techniques:

• Signal amplification systems: Tyramide signal amplification (TSA) and polymer-based detection systems significantly enhance sensitivity for IHC and IF applications

• Optimized antigen retrieval: Fine-tuning of antigen retrieval conditions with TE buffer pH 9.0 or citrate buffer pH 6.0 improves epitope accessibility

• High-sensitivity antibody formats: Recombinant antibody technology provides consistently high-affinity reagents

• Multiplex imaging: Combining HTR4 antibodies with markers for specific cell types or subcellular compartments provides contextual information even with low signal

• Digital pathology tools: Advanced image analysis algorithms help extract quantitative data from subtle staining patterns

• Proximity ligation assays: These techniques can amplify signals from antibody-antigen interactions through rolling circle amplification when studying protein-protein interactions involving HTR4

These approaches are particularly important when studying brain regions where HTR4 expression may be physiologically low or in pathological conditions where receptor levels are reduced.

How can researchers distinguish between different HTR4 phosphorylation states using antibodies?

Distinguishing HTR4 phosphorylation states is challenging but methodologically important:

• Phospho-specific antibodies: While not explicitly mentioned in the search results, development of antibodies specifically targeting known phosphorylation sites on HTR4 would be the most direct approach

• 2D gel electrophoresis: Combining this with Western blotting using HTR4 antibodies can separate phosphorylated forms based on charge differences

• Phosphatase treatment: Comparing HTR4 detection before and after phosphatase treatment can reveal phosphorylation-dependent mobility shifts

• Co-immunoprecipitation: Using HTR4 antibodies for immunoprecipitation followed by phospho-specific detection can identify receptor phosphorylation status

• Mass spectrometry: Immunoprecipitation with HTR4 antibodies followed by mass spectrometry analysis can identify and quantify specific phosphorylation sites

• Functional correlation: Combining phosphorylation studies with trafficking analysis (as in search result #5) can reveal how phosphorylation affects receptor recycling and surface expression

Understanding HTR4 phosphorylation is particularly relevant given its role in receptor desensitization, internalization, and signaling pathway selection.