LEP
LEP encodes leptin, an adipose-derived hormone that regulates energy balance by inhibiting hunger. Genetic leptin deficiency causes severe early-onset obesity, though most common obesity is characterized by leptin resistance.
Key Takeaways
- •LEP encodes leptin, the body’s primary "satiety hormone" secreted by adipose tissue.
- •Leptin communicates the size of fat stores to the hypothalamus to inhibit hunger and stimulate energy expenditure.
- •Leptin resistance, rather than deficiency, is the hallmark of common obesity.
- •Falling leptin levels during fasting trigger the "starvation response," slowing metabolism and increasing appetite.
Basic Information
- Gene Symbol
- LEP
- Full Name
- Leptin
- Also Known As
- OBOBS
- Location
- 7q32.1
- Protein Type
- Peptide Hormone (Adipokine)
- Protein Family
- Type I Cytokine Family
Related Isoforms
Key SNPs
Common variant (-2548G/A) associated with altered leptin expression, circulating levels, and susceptibility to obesity.
Overview
The LEP gene (originally called the *ob* gene) encodes leptin, a 16-kDa cytokine-like hormone. Secreted primarily by white adipose tissue, leptin circulates in the blood at levels directly proportional to total body fat mass. It serves as an adipostatic signal, informing the brain of the body’s long-term energy reserves.
Leptin acts by binding to its receptor (LEPR) in the arcuate nucleus of the hypothalamus. It activates POMC neurons (which suppress appetite) and inhibits AgRP/NPY neurons (which drive hunger). This dual action establishes a "lipostat" that maintains stable body weight. Beyond appetite, leptin regulates the onset of puberty, immune function, and bone metabolism.
Conceptual Model
A simplified mental model for the pathway:
Leptin is the body’s long-term energy status report; when it is high, the brain stops the drive to seek more fuel.
Core Health Impacts
- • Appetite suppression: The primary signal for systemic satiety and reduced food intake.
- • Energy expenditure: Stimulates the sympathetic nervous system to increase basal metabolic rate.
- • Reproductive onset: A permissive signal required for the initiation of puberty and normal fertility.
- • Immune modulation: Regulates T-cell function and bridges metabolism with the immune system.
- • Bone metabolism: Exerts complex control over bone density via central and peripheral pathways.
Upstream Regulators
Adipose Tissue Mass Activator
The primary driver; leptin secretion is directly proportional to total fat storage.
Insulin Activator
Stimulates leptin production after meals to signal immediate energy availability.
Glucocorticoids Activator
Cortisol and other stress hormones can chronically increase leptin gene expression.
Inflammation (LPS/TNF) Activator
Acute inflammatory triggers can transiently stimulate leptin secretion.
Fasting Inhibitor
Rapidly suppresses leptin production independent of changes in fat mass.
Downstream Targets
LEPR (Leptin Receptor) Activates
The long isoform (LEPRb) activates the JAK2/STAT3 signaling pathway in the brain.
POMC Neurons Activates
Stimulates neurons that produce alpha-MSH, a potent appetite suppressor.
AgRP / NPY Neurons Inhibits
Suppresses the neurons that normally drive intense hunger and fuel seeking.
TRH Activates
Stimulates thyroid-releasing hormone to maintain a high metabolic rate.
Role in Aging
Leptin levels and sensitivity change dramatically with age, shifting the body toward fat accumulation and metabolic slowing.
Leptin Resistance
Aging is often accompanied by hypothalamic leptin resistance, where the brain no longer "sees" the satiety signal, leading to late-life obesity.
Sarcopenic Obesity
The breakdown of the leptin-insulin axis contributes to the loss of muscle mass paired with increased visceral fat in the elderly.
Thymic Involution
Falling leptin sensitivity may accelerate the age-related shrinking of the thymus, weakening the immune system (immunosenescence).
Starvation Defense
Leptin is the primary mediator of the longevity-promoting effects of caloric restriction; low leptin tells the body to prioritize repair over growth.
Disorders & Diseases
Congenital Leptin Deficiency
Rare recessive mutations leading to undetectable leptin. Causes extreme hyperphagia (uncontrollable hunger) and morbid obesity from early infancy.
Common Obesity
Characterized by high circulating leptin but impaired hypothalamic response (leptin resistance), similar to insulin resistance in T2D.
Lipodystrophy
Disorders of fat storage that lead to very low leptin, causing severe metabolic damage because the brain thinks the body is starving.
Hypothalamic Amenorrhea
Very low leptin (due to excessive exercise or low body fat) signals the brain to shut down the reproductive system to save energy.
Interventions
Supplements
Shown in some animal models to help restore hypothalamic leptin sensitivity.
Deficiency is linked to impaired leptin signaling and worsened metabolic inflammation.
Zinc deficiency can reduce circulating leptin levels and impair the satiety response.
Lifestyle
Consistent high-quality sleep is the most effective way to maintain healthy leptin levels and prevent ghrelin-driven hunger.
Can help "reset" leptin sensitivity by providing periods of low-leptin signal duration.
Acute cold stress transiently lowers leptin while activating thermogenesis to burn fat.
High fructose intake is a primary driver of hepatic and hypothalamic leptin resistance.
Medicines
Recombinant human leptin approved for patients with lipodystrophy or congenital leptin deficiency.
Bypass leptin resistance by using a parallel satiety pathway (incretins) to reduce appetite.
Pramlintide can synergize with endogenous leptin to improve the satiety signal in the brain.
Lab Tests & Biomarkers
Activity Markers
Standard measure; levels >30 ng/mL in the presence of obesity are diagnostic of leptin resistance.
A rising ratio is a hallmark of worsening adipose tissue dysfunction and metabolic syndrome.
Hormonal Interactions
Ghrelin Direct Antagonist
The "hunger hormone" from the stomach; it competes with leptin for control of the arcuate nucleus.
Insulin Post-Prandial Synergist
Works with leptin to signal the brain that energy is abundant and growth programs can proceed.
Thyroid Hormone (T3) Metabolic Effector
Leptin ensures T3 levels remain high enough to maintain thermogenesis.
Deep Dive
Network Diagrams
The Hypothalamic Satiety Relay
Leptin Negative Feedback & Resistance
Activation Mechanics: The Hypothalamic Switch
Leptin signals through the long form of the leptin receptor (LEPRb), which is concentrated in the arcuate nucleus of the hypothalamus. This receptor is part of the class I cytokine receptor family and signals via the JAK2/STAT3 pathway.
When leptin binds, it recruits and activates the kinase JAK2. JAK2 then phosphorylates the receptor, creating a docking site for the transcription factor STAT3. Once activated, STAT3 moves into the nucleus to drive a transcriptional “re-wiring” of the brain. It upregulates POMC, which produces alpha-MSH to signal fullness, and simultaneously downregulates AgRP and NPY, which are the neurons that create the intense, primal drive to eat.
The Mechanism of Leptin Resistance
In common obesity, the body produces massive amounts of leptin, but the brain behaves as if it is starving. This is hypothalamic leptin resistance.
The primary molecular “brake” is a protein called SOCS3. When leptin signaling is chronically high (as in obesity), the cell upregulates SOCS3 as a negative feedback mechanism. SOCS3 binds to the leptin receptor and prevents JAK2 from signaling. A second brake, PTP1B, dephosphorylates JAK2 to shut down the signal. In obesity, these brakes are permanently “on,” effectively disconnecting the brain from the fat stores and causing the body to defend an ever-higher weight set-point.
The Starvation Response: Fasting and Leptin
Leptin’s most powerful evolutionary role is not to prevent obesity, but to signal when the body is starving. When you stop eating, your leptin levels fall much faster than your fat stores do.
This drop in leptin is the “master alarm” for the starvation response. The brain senses the falling leptin and immediately slows down the metabolism (via the thyroid), shuts off the reproductive system (amenorrhea), increases stress hormones (cortisol), and triggers an obsession with food. This is why it is so difficult to maintain large amounts of weight loss: the body perceives the lower leptin levels as a life-threatening fuel shortage.
Relevant Research Papers
Links go to PubMed (abstracts are public); some papers also offer free full text via PMC or the publisher.
The landmark discovery of the leptin gene, transforming our understanding of body weight regulation.
The first clinical proof that leptin is the definitive satiety signal in humans.