MECHANISMS IN ENDOCRINOLOGY: White, brown and pink adipocytes: the extraordinary plasticity of the adipose organ

Abstract

In mammals, adipocytes are lipid-laden cells making up the parenchyma of the multi-depot adipose organ. White adipocytes store lipids for release as free fatty acids during fasting periods; brown adipocytes burn glucose and lipids to maintain thermal homeostasis. A third type of adipocyte, the pink adipocyte, has recently been characterised in mouse subcutaneous fat depots during pregnancy and lactation. Pink adipocytes are mammary gland alveolar epithelial cells whose role is to produce and secrete milk. Emerging evidence suggests that they derive from the transdifferentiation of subcutaneous white adipocytes. The functional response of the adipose organ to a range of metabolic and environmental challenges highlights its extraordinary plasticity. Cold exposure induces an increase in the 'brown' component of the organ to meet the increased thermal demand; in states of positive energy balance, the 'white' component expands to store excess nutrients; finally, the 'pink' component develops in subcutaneous depots during pregnancy to ensure litter feeding. At the cell level, plasticity is provided not only by stem cell proliferation and differentiation but also, distinctively, by direct transdifferentiation of fully differentiated adipocytes by the stimuli that induce genetic expression reprogramming and through it a change in phenotype and, consequently function. A greater understanding of adipocyte transdifferentiation mechanisms would have the potential to shed light on their biology as well as inspire novel therapeutic strategies against metabolic syndrome (browning) and breast cancer (pinking).

Adipose Tissue–Derived Stem Cells From Obese Subjects Contribute to Inflammation and Reduced Insulin Response in Adipocytes Through Differential Regulation of the Th1/Th17 Balance and Monocyte Activation

“…Far from being a mere repository of fat mass, the AT is perhaps the most plastic organ of the body, capable of meeting the evolutionarily conserved need of storing energy/nutrients during periods of plenty but also of acting as a thermogenic organ (27). Such plasticity, associated with lifestyle changes in nutrition and physical activity in the population worldwide, has led to the current epidemics of obesity (28).…”

Mitochondrial Turnover

“…The morphological and molecular responses of white fat depots to a range of environmental conditions highlight its extraordinary plasticity (32). This primary response is the reversible interconversion of brown and white adipocytes in response to adrenergic signaling.…”

RBM4-MEF2C network constitutes a feed-forward circuit that facilitates the differentiation of brown adipocytes

“…Two major types of adipocytes, white and brown adipocytes (BAs), were identified in mammals based on their macroscopic appearance. 1 Obesity depends on an increase in the mass of white adipose tissues (WATs) that store energy in the form of triglycerides (TGs). In contrast, brown adipose tissues (BATs) dissipate fatty acids in the form of heat to maintain the body temperature, 2 which implies their therapeutic potential for combating obesity.…”