Granulin-3 Antibody
Description
Definition and Biological Context
Granulin-3 (GRN-3) is a cysteine-rich peptide derived from proteolytic cleavage of progranulin (PGRN), a glycoprotein implicated in neurodevelopment, lysosomal function, and neurodegenerative diseases such as frontotemporal dementia (FTD) and Alzheimer’s disease (AD). The Granulin-3 antibody is a specialized tool designed to detect and study GRN-3 in biological systems, enabling insights into its role in disease mechanisms and protein interactions .
Key Applications of Granulin-3 Antibodies
Granulin-3 antibodies are critical for:
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Western Blot Analysis: Detecting GRN-3 and its precursor PGRN in lysates (e.g., HepG2 and HEK293T cell lines) .
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Functional Studies: Investigating GRN-3’s impact on lysosomal protease activity, stress responses, and neurodegenerative pathology .
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Therapeutic Research: Evaluating GRN-3’s role in amyloid-β (Aβ) aggregation and TDP-43 degradation, processes linked to AD and FTD .
GRN-3 in Lysosomal Dysregulation
Studies in C. elegans demonstrate that GRN-3 disrupts lysosomal aspartyl protease activity (e.g., ASP-3, ortholog of human Cathepsin D) even in the presence of full-length PGRN-1. Key data include:
| Strain | Lysosomal Aspartyl Protease Activity (% of WT) | Lysosome Size (μm²) |
|---|---|---|
| Wildtype (N2) | 100% | 1.2 ± 0.1 |
| pgrn-1(-) | 65% | 0.8 ± 0.1 |
| gran3 OE | 40% | 0.7 ± 0.1 |
| pg/gr (PGRN-1 + GRN-3) | 35% | 1.1 ± 0.1 |
Full-length PGRN-1 rescues lysosomal morphology but fails to restore protease activity in the presence of GRN-3, highlighting GRN-3’s dominant-negative effects .
GRN-3 and Amyloid-β Aggregation
GRN-3 accelerates Aβ42 fibril formation under both oxidized and reduced conditions, reducing neurotoxic oligomers:
| Condition | Aβ42 Fibril Formation Rate (Relative to Control) | Cellular Apoptosis (% Reduction) |
|---|---|---|
| Aβ42 alone | 1.0x | 0% |
| Aβ42 + Oxidized GRN-3 | 2.5x | 45% |
| Aβ42 + Reduced GRN-3 | 2.2x | 38% |
This suggests GRN-3 may mitigate Aβ toxicity by promoting fibrillization, though redox state influences efficacy .
GRN-3 Antibody Validation in Cellular Models
The Human Progranulin/PGRN Antibody (AF2420) detects both PGRN (~80 kDa) and GRN-2/3 (~6 kDa) in Western blots. Key validations include:
| Cell Line | PGRN Detection (80 kDa) | GRN-2/3 Detection (6 kDa) |
|---|---|---|
| HEK293T (Wildtype) | Yes | Yes |
| HEK293T (PGRN KO) | No | No |
| HepG2 | Yes | Yes |
This antibody is knockout-validated, confirming specificity for PGRN and its cleavage products .
Implications for Neurodegenerative Diseases
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FTD and Lysosomal Dysfunction: GRN-3 overexpression impairs TDP-43 degradation, exacerbating toxicity in neuronal models .
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AD Pathology: GRN-3’s interaction with Aβ42 provides a redox-sensitive mechanism for modulating amyloid aggregation .
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Therapeutic Targeting: Antibodies against GRN-3 could normalize lysosomal protease activity or Aβ fibril dynamics, though balancing GRN-3/PGRN ratios is critical .
Challenges and Future Directions
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Dose-Dependent Effects: GRN-3’s dual roles in inflammation and proteostasis require precise modulation to avoid unintended consequences .
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Redox Sensitivity: The functional impact of GRN-3 varies with oxidative state, complicating therapeutic strategies .
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Interactions with Other Granulins: GRN-3’s effects may synergize or antagonize those of other granulins (e.g., GRN-2), necessitating further study .
Product Specs
Constituents: 50% Glycerol, 0.01M Phosphate Buffered Saline (PBS), pH 7.4
Target Background
Q&A
What is Granulin-3 and why is it important in biological research?
Granulin-3 is one of several cysteine-rich, biologically active peptides derived from the cleavage of progranulin (PGRN), an evolutionarily conserved protein implicated in neurodevelopmental and neurodegenerative diseases. Granulin peptides accumulate with age and stress, making them particularly relevant for studying age-related disorders .
Granulin-3 has gained research importance due to its distinct biological functions, including:
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Inhibition of epithelial cell proliferation and induction of IL-8 secretion by epithelial cells
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Suppression of lysosomal aspartyl protease activity (particularly ASP-3/CTSD), even in the presence of intact full-length progranulin
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Impairing animal fitness, development rate, and stress response in model organisms
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Affecting the degradation of disease-relevant proteins like TDP-43
These functions suggest that not only absolute progranulin levels but also the balance between full-length progranulin and its cleavage products is crucial for regulating lysosomal biology and may represent a potential therapeutic intervention site .
How do Granulin-3 antibodies help in studying lysosomal functions?
Granulin-3 antibodies provide essential tools for investigating the complex relationship between Granulin-3 and lysosomal biology through multiple methodological approaches:
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Detection and quantification: Antibodies allow precise measurement of Granulin-3 levels in cellular lysates, enabling correlation between Granulin-3 abundance and lysosomal metrics. Using tag-specific antibodies (e.g., against RFP or FLAG tags), researchers can achieve picomolar sensitivity in quantifying both full-length progranulin and cleaved Granulin-3 peptides .
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Visualization of localization: Immunohistochemistry using Granulin-3 antibodies helps visualize its distribution relative to lysosomal markers.
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Protein-protein interaction studies: Immunoprecipitation experiments with Granulin-3 antibodies allow identification of binding partners that mediate its effects on lysosomes .
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Functional assessments: Antibodies can be used to track how Granulin-3 impacts various aspects of lysosomal function, including:
Studies in C. elegans demonstrated that while full-length progranulin can rescue the lysosome size defects caused by Granulin-3 overexpression, it cannot restore lysosomal aspartyl protease activity, suggesting distinct mechanisms of action for these proteins on different aspects of lysosomal biology .
What are the critical considerations when selecting Granulin-3 antibodies for research applications?
When selecting Granulin-3 antibodies for research, consider the following critical factors:
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Specificity: Choose antibodies validated for specificity against Granulin-3 versus other granulin peptides. Due to sequence homology between granulin domains, cross-reactivity is a significant concern .
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Application compatibility: Verify the antibody is validated for your specific applications (WB, IP, IHC-P). For example, some antibodies like EPR15864 are validated for multiple applications including immunoprecipitation, western blotting, and immunohistochemistry on paraffin-embedded samples .
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Species reactivity: Confirm the antibody recognizes your species of interest. Many commercial antibodies are raised against human Granulin-3 but may have variable cross-reactivity with other species .
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Target region: Consider whether the antibody targets full-length progranulin, specific granulin domains, or linker regions, as this affects what forms of the protein will be detected.
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Validation data: Review published validation data, including knockout controls, to ensure reliability. For instance, some antibodies have been knockout tested to confirm specificity .
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Compatible detection methods: For techniques like immunoprecipitation, specialized secondary detection reagents may be required to minimize detection of the heavy and light chains of the IP antibody .
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Working dilutions: Use recommended dilutions as starting points (e.g., 1
