Problem 7 - Biochemistry

Question

Leptin is an adipocyte hormone that sends signals to the brain to "eat less" and "metabolize more." What is the explanation for why leptin injections cause weight loss in the strain of OB mutant mice, but leptin injections have no effect in the majority of obese people? Is this observation analogous to type 1 or type 2 diabetes? Explain.

Step-by-Step Solution

Answer

Answer: Leptin injections cause weight loss effects in OB mutant mice because they lack the gene responsible for producing leptin, leading to uncontrolled appetite and obesity. When given leptin injections, their bodies can respond to the effects of appetite suppression and increased energy expenditure, resulting in weight loss. In most obese people, however, they experience leptin resistance, where their brains become less sensitive to the effects of leptin. Administering leptin injections has little effect on weight loss in these individuals due to this resistance. The leptin resistance observed in the majority of obese individuals is more analogous to type 2 diabetes, where the body becomes resistant to the effects of insulin.

Step 1: Define Leptin and its effects

Leptin is a hormone produced by adipocytes (fat cells) that plays a crucial role in regulating energy intake and energy expenditure. The main actions of leptin are to suppress appetite and increase energy expenditure. When the body has sufficient energy stored in the form of fat, leptin signals the brain to reduce food intake and increase metabolism, thus maintaining energy balance.

Step 2: Explain the role of Leptin in OB mutant mice

OB mutant mice are genetically engineered mice lacking the gene responsible for producing leptin. As a result, these mice do not produce leptin, which leads to uncontrolled appetite, reduced energy expenditure, obesity, and insulin resistance. When OB mutant mice are given leptin injections, the leptin can exert its normal effects on appetite suppression and increased energy expenditure, leading to weight loss and improved metabolic health.

Step 3: Explain the role of Leptin in obese people

In the majority of obese people, the production and circulation of leptin are generally higher than in lean individuals. This phenomenon is known as leptin resistance, where the brain becomes less sensitive to the appetite-suppressing and metabolism-boosting effects of leptin. Due to this resistance, administering leptin injections to these individuals has little to no effect on weight loss, as their brains are unable to effectively respond to the additional leptin.

Step 4: Compare the observation with Type 1 and Type 2 Diabetes

Type 1 diabetes is an autoimmune condition in which the body attacks and destroys insulin-producing cells in the pancreas. The lack of insulin results in high blood sugar levels, and patients with type 1 diabetes need to take insulin injections to manage their blood glucose levels. On the other hand, type 2 diabetes is characterized by insulin resistance, where the body produces insulin but does not use it effectively, leading to high blood sugar levels. The leptin resistance observed in the majority of obese individuals is more analogous to type 2 diabetes. Just as the body in type 2 diabetes becomes resistant to the effects of insulin, the brain in obese individuals becomes resistant to the appetite-suppressing and metabolism-boosting effects of leptin. Therefore, the comparison of leptin resistance in obese individuals is more relevant to type 2 diabetes than type 1 diabetes.