Interplay between adipose tissue and blood vessels in obesity and vascular dysfunction.

There is a close anatomical and functional relationship between adipose tissue and blood vessels. The crosstalk between these two organs is vital to both metabolic and vascular homeostasis. On the one hand, adipose tissue is highly vascularized, and maintenance of ample supply of blood flow is essential for both expansion and metabolic functions of adipose tissue. Vascular endothelium also secretes many factors to regulate adipogenesis and adipose tissue remodeling. On the other hand, almost all blood vessels are surrounded by perivascular adipose tissue (PVAT), which regulates vascular function by producing a large number of "vasocrine" molecules. Under the normal conditions, PVAT exerts its anti-contractile effects by release of vasorelaxants (such as adipocyte-derived relaxation factors and adiponectin) that promote both endothelium-dependent and -independent relaxations of blood vessels. However, PVAT in obesity becomes highly inflamed and induces vascular dysfunction by augmented secretion of vasoconstriction factors (such as the major components of renin-angiotensinogen-aldosterone system and superoxide) and pro-inflammatory adipokines (such as TNF-α and adipocyte fatty acid binding protein), the latter of which are important contributors to endothelial activation, vascular inflammation and neointimal formation. Furthermore, several adipocyte-derived adipokines impair vascular function indirectly, by acting in the brain to activate sympathetic nerve system (such as leptin) or by exerting their actions in major metabolic organs to induce vascular insulin resistance, which in turn aggravates endothelial dysfunction. Aberrant secretion of adipokines and other vasoactive factors in adipose tissue is a major contributor to the onset and progression of obesity-related metabolic and vascular complications.