The origin and purpose of layers of subcutaneous adipose tissue in pigs and man

Abstract

Adipose tissue exists in many locations or depots that differ from one another based on numerous and various characteristics. The unique "layered" anatomical feature of subcutaneous adipose tissue (SAT) in man and the pig is reviewed and discussed. The origin of fetal pig adipose tissue subcutaneous layers is reviewed before the onset of adipogenesis and after the overt adipogenesis. Furthermore, the distinguishing characteristics of developing outer SAT layer (OSQ) and middle SAT layer (MSQ) in pigs are reviewed. These characteristics include adipocyte hypertrophy, metabolism and genetic regulation. The MSQ layer is the major layer in the pig and expands to the greatest degree in obesity and growth. Abdominal SAT in man is composed of deep SAT (dSAT) and superficial SAT (sSAT) layers. Clearly, dSAT expands disproportionally more than sSAT with increasing obesity in Caucasian males which precipitates a number of human pathologies associated with increased adiposity. We reviewed the considerable evidence that demonstrates the distinction between sSAT and dSAT which includes higher levels of saturated fatty acids (FAs) and greater levels of lipolysis in dSAT. Furthermore, dSAT expresses more metabolic and inflammatory genes. Studies comparing visceral adipose tissue (VAT) and dSAT indicate that both depots are implicated in insulin resistance (IR) and other human pathologies. Epigenetic studies of MSQ and dSAT have begun to indicate a role for DNA methylation in gene regulation of these depots. Further studies of dSAT and MSQ are warranted as they are clearly a major manifestation of obesity.

Keywords: adipose tissue; development and metabolism; layers; man; pigs.