Leptin Mouse
Description
Introduction to Leptin Mouse Models
Leptin mouse models are genetically modified or naturally occurring strains used to study the role of leptin in energy balance, obesity, and metabolic regulation. These models include:
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ob/ob mice: Lacks functional leptin due to mutations in the ob gene (leptin-deficient).
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db/db mice: Defective leptin receptor (LEPR) due to mutations in the db gene, leading to leptin insensitivity.
These models have revolutionized obesity research by elucidating leptin’s role in appetite regulation, energy expenditure, and insulin sensitivity .
Core Mouse Strains
| Feature | ob/ob Mice | db/db Mice |
|---|---|---|
| Genetic Defect | ob gene mutation (no leptin) | db gene mutation (non-functional LEPR) |
| Phenotype | Severe obesity, hyperphagia, diabetes | Obesity, hyperphagia, insulin resistance |
| Response to Leptin | Responsive (weight loss) | Non-responsive |
| Key Pathways Affected | NPY/AgRP suppression, α-MSH activation | Impaired JAK-STAT signaling |
Leptin-deficient ob/ob mice exhibit 4–6-fold higher adiposity than wild-type controls, while db/db mice show similar obesity but remain unresponsive to exogenous leptin .
Physiological Roles of Leptin in Mice
Leptin regulates energy balance through hypothalamic and peripheral mechanisms:
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Hypothalamic Signaling:
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Peripheral Effects:
Leptin Resistance in Obesity
In diet-induced obesity (DIO) mice, leptin resistance manifests as:
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Reduced leptin transport across the blood-brain barrier.
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Hyperactivation of mTOR in hypothalamic neurons, impairing leptin signaling .
Leptin Therapy Efficacy
| Model | Leptin Dose | Outcome | Reference |
|---|---|---|---|
| ob/ob mice | 5 μg/hr (SC) | 82.7% body fat loss | |
| DIO mice | 20 mg/kg (IP) | 30.5% fat loss (vs. 82.7% in lean mice) | |
| db/db mice | 5 μg/hr (SC) | No response |
Note: ob/ob mice show full responsiveness to leptin, while DIO mice exhibit partial resistance .
Mechanisms of Leptin Resistance
Recent studies identify:
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mTOR Hyperactivity: In obese mice, mTOR overactivation in hypothalamic neurons blocks leptin signaling. Inhibiting mTOR with rapamycin restores leptin sensitivity .
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Endothelial LEPR Deletion: Genetic deletion of LEPR in endothelial cells reduces leptin transcytosis into the brain, exacerbating obesity .
Measurement Techniques
| Method | Sensitivity | Sample Types | Application |
|---|---|---|---|
| Mouse Leptin ELISA | <25.4 pg/mL | Serum, plasma, tissue | Quantifying circulating leptin |
| Recombinant Leptin | 146 aa mature | In vivo/in vitro assays | Testing bioactivity in mouse models |
ELISA kits enable precise measurement of leptin levels in obese and lean mice, critical for assessing leptin resistance .
Leptin’s Role in Glucose Metabolism
In ob/ob mice, acute leptin administration:
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Rapidly improves glucose tolerance (15–60 minutes post-injection).
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Enhances hepatic insulin sensitivity via vagal/non-vagal pathways .
Leptin and Cardiovascular Health
Leptin promotes:
Product Specs
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Q&A
Experimental Design for Leptin Administration in Mice
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Q: What is the optimal dosing regimen for administering leptin to mice in experimental settings?
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A: The dosing regimen can vary based on the experimental design. For instance, a study administered 3 mg/kg body weight of recombinant mouse leptin to fasted non-obese male mice to determine the half-life of circulating leptin . Another study used intracerebroventricular injections of 5 μg leptin in 1.5 μl of PBS for central administration . The choice of dosing should align with the specific research objectives, such as studying leptin's effects on metabolism or appetite regulation.
Half-Life of Leptin in Mice
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Q: What is the half-life of leptin in mice, and how does it affect experimental design?
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A: The half-life of circulating leptin in mice has been determined to be approximately 40.2 minutes . This information is crucial for designing experiments involving exogenous leptin administration, as it helps predict how long leptin levels will remain elevated in the bloodstream.
Leptin Resistance and Obesity Models
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Q: How do mouse models, such as the db/db mice, contribute to understanding leptin resistance and obesity?
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A: db/db mice are a valuable model for studying obesity and leptin resistance due to their spontaneous mutations in the leptin receptor gene, leading to receptor inactivation . These mice are used to explore the mechanisms of leptin resistance and obesity, providing insights into potential therapeutic targets.
Genotyping db/db Mice
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Q: What methods are available for genotyping db/db mice, and what are their advantages?
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A: A quick and reliable method for genotyping db/db mice involves a three-step process using tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) . This method is advantageous due to its simplicity, high sensitivity, and reproducibility, requiring minimal tissue samples.
Data Analysis and Contradiction Resolution
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Q: How can researchers resolve contradictions in data from different leptin studies in mice?
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A: Contradictions in data can arise from differences in experimental design, such as dosing regimens, mouse strains, or housing conditions . Resolving these contradictions involves careful analysis of study methodologies and consideration of how these factors might influence outcomes. Meta-analyses or systematic reviews can also help synthesize findings across studies.
Advanced Research Questions: Leptin and Neural Circuits
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Q: How can mouse models be used to study the neural circuits involved in leptin-mediated appetite regulation?
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A: Modern mouse genetics and neuromodulation techniques allow researchers to dissect the neural circuits that govern appetite and metabolism. By using techniques like intracerebroventricular leptin injections, researchers can explore how leptin interacts with specific brain regions to regulate feeding behavior .
Methodological Considerations for Leptin Studies
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Q: What are some key methodological considerations when designing studies involving leptin administration in mice?
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A: Key considerations include the choice of mouse strain, dosing regimen, method of administration (e.g., intraperitoneal vs. intracerebroventricular), and housing conditions (e.g., group vs. single housing) . Additionally, ensuring accurate measurement of leptin levels and metabolic outcomes is crucial for interpreting results.
Implications for Human Obesity Research
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Q: How do findings from mouse models of leptin deficiency or resistance translate to human obesity research?
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A: While leptin deficiency is rare in humans, mouse models provide valuable insights into the mechanisms of leptin action and resistance. These insights can inform the development of leptin-based therapies or strategies to improve leptin sensitivity in humans .
Product Science Overview
Leptin was first identified in 1994 through the cloning of the mouse and human leptin genes . The protein product of the obese gene, leptin, was found to be a key regulator of energy balance. Mice with mutations in the obese gene that block the synthesis of leptin exhibit obesity, diabetes, reduced activity, decreased metabolism, and lower body temperature .
Leptin is primarily synthesized and secreted by white adipose tissue (WAT), which is now recognized as an active endocrine organ. WAT secretes a variety of hormones, collectively known as adipokines or adipocytokines, which have autocrine, paracrine, or endocrine effects on metabolic processes both in the periphery and the central nervous system (CNS) .
Initially considered an anti-obesity hormone due to its role in maintaining body weight, leptin has since been found to have significant effects on glycemic control and cognitive function . Leptin deficiency (hypoleptinemia) and leptin resistance (hyperleptinemia) are characterized by dysfunctional leptin signaling, leading to systemic metabolic defects, including obesity and diabetes .
Recombinant mouse leptin is produced using E. coli expression systems. The recombinant protein is often used in research to study leptin’s role in various physiological processes. It is typically purified to a high degree, with a purity of over 97% as determined by SDS-PAGE under reducing conditions . The endotoxin level is kept below 1.0 EU per 1 μg of protein, ensuring its suitability for biological assays .
Recombinant leptin is used in various research applications, including cell proliferation assays, where it has been shown to stimulate the proliferation of BaF3 mouse pro-B cells transfected with human leptin receptors . It is also used to study the effects of leptin on energy balance, metabolism, and cognitive function .
