Decreased expression and function of adipocyte hormone-sensitive lipase in subcutaneous fat cells of obese subjects

Decreased lipolytic effect of catecholamines in adipose tissue has repeatedly been demonstrated in obesity and may be a cause of excess accumulation of body fat. However, the mechanisms behind this lipolysis defect are unclear. The role of hormone-sensitive lipase was examined using abdominal subcutaneous adipocytes from 34 obese drug-free and otherwise healthy males or females and 14 non-obese control subjects. The enzyme catalyzes the rate-limiting step of the lipolysis pathway. The maximum lipolytic capacity of fat cells was significantly decreased in obesity when measured using either a non-selective beta-adrenergic receptor agonist (isoprenaline) or a phosphodiesterase resistant cyclic AMP analogue (dibutyryl cyclic AMP). Likewise, enzyme activity, protein expression, and mRNA of hormone-sensitive lipase were significantly decreased in adipocytes of obese subjects. The findings were not influenced by age or gender. The data suggest that a decreased expression of hormone-sensitive lipase in subcutaneous fat cells, which in turn causes decreased enzyme function and impaired lipolytic capacity of adipocytes, is present in obesity. Impaired expression of the hormone-sensitive lipase gene might at least in part explain the enzyme defect.