Metabolism of Adipose Tissue

Metabolism of Adipose Tissue

Introduction

Adipose tissue plays a central role in energy homeostasis by storing excess energy as triglycerides and mobilizing it when needed. It also functions as an endocrine organ, secreting hormones and cytokines (adipokines) that influence systemic metabolism. The two main types of adipose tissue are white adipose tissue (WAT) and brown adipose tissue (BAT), each with distinct metabolic functions.

White Adipose Tissue (WAT)

Functions:

- Energy storage in the form of triglycerides.

- Releases free fatty acids during energy demand via lipolysis.

- Secretes adipokines such as leptin, adiponectin, and resistin.

Key Processes:

- Lipogenesis:

  - Stimulated by insulin during the fed state.

  - Involves uptake of glucose and fatty acids, which are esterified into triglycerides.

- Lipolysis:

  - Triggered by catecholamines (epinephrine, norepinephrine), cortisol, and fasting.

  - Hormone-sensitive lipase (HSL) breaks down triglycerides into free fatty acids and glycerol.

  - Free fatty acids are transported to liver and muscle for β-oxidation.

- Regulation:

  - Insulin inhibits lipolysis and promotes fat storage.

  - Glucagon has a minimal direct effect on adipocytes but supports lipolysis via hepatic glucose production.

Brown Adipose Tissue (BAT)

- Rich in mitochondria and involved in non-shivering thermogenesis.

- Contains uncoupling protein 1 (UCP1), which dissipates the proton gradient to generate heat instead of ATP.

- More active in neonates and may contribute to thermoregulation in adults.

Endocrine Functions of Adipose Tissue

- Leptin: Regulates appetite and energy expenditure by acting on the hypothalamus.

- Adiponectin: Enhances insulin sensitivity and fatty acid oxidation.

- Resistin: Linked to insulin resistance.

- Dysregulation of adipokines is associated with obesity, insulin resistance, and metabolic syndrome.

Clinical Relevance

Alterations in adipose tissue metabolism play a major role in metabolic disorders such as obesity, type 2 diabetes, and cardiovascular disease. Targeting adipose tissue function and signaling is a key strategy in metabolic disease management.

Conclusion

Adipose tissue is not just a passive energy depot but an active regulator of systemic metabolism. Its metabolism is dynamically controlled by nutritional status and hormonal signals, making it central to energy balance and metabolic health.

References

1. Guyton and Hall Textbook of Medical Physiology, 14th Edition

2. Lehninger Principles of Biochemistry, 7th Edition

3. Lippincott Illustrated Reviews: Biochemistry, 7th Edition