LEP

Leptin is a hormone secreted predominantly by adipose tissue, playing a pivotal role in regulating energy balance, appetite, and metabolism. It was first discovered in 1994, and since then, its involvement in the complex regulation of body weight and energy homeostasis has been the focus of extensive research. Leptin is sometimes referred to as the "satiety hormone" or the "starvation hormone," as it signals the brain about the body's energy reserves and influences hunger.Leptin acts primarily on the hypothalamus, a region of the brain involved in controlling appetite and energy expenditure. It binds to specific receptors (such as the leptin receptor, LepR) present on hypothalamic neurons, leading to the activation of various signaling pathways. These pathways modulate the production of neuropeptides, such as neuropeptide Y (NPY) and proopiomelanocortin (POMC), which regulate appetite and energy balance. In general, high leptin levels suppress appetite and stimulate energy expenditure, while low leptin levels promote hunger and reduce energy expenditure.Leptin levels in the body are proportional to the amount of adipose tissue, meaning that obese individuals typically have higher leptin levels than those of normal weight. However, despite increased leptin levels, many obese individuals exhibit "leptin resistance," a condition in which the brain becomes less responsive to leptin's appetite-suppressing effects. This resistance is believed to be one of the key factors contributing to the development of obesity and its associated metabolic disorders.Apart from its role in energy homeostasis, leptin also exerts effects on other physiological processes, such as immune function, bone metabolism, and reproduction. It has been shown to regulate the activation of immune cells, modulate bone formation and resorption, and influence reproductive function by affecting gonadotropin-releasing hormone secretion.In summary, leptin is a crucial hormone involved in maintaining energy balance, appetite control, and metabolism. Its dysregulation, particularly in the form of leptin resistance, contributes to the development of obesity and related metabolic disorders. Understanding the molecular mechanisms underlying leptin's actions and the factors that contribute to leptin resistance may help develop novel therapeutic strategies to combat obesity and its associated health complications.