The role of neutral lipases in human adipose tissue lipolysis

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Abstract
The aim of this article is to describe the relative roles of hormone sensitive lipase and adipose triglyceride lipase in human fat cell lipolysis. Until recently, only hormone sensitive lipase was considered important for the regulation of lipolysis within fat cells. Recent rodent studies have suggested that adipose triglyceride lipase may, however, be more important. The few human adipose triglyceride lipase studies that have been published point to species differences between humans and rodents. Selective inhibition of hormone sensitive lipase in human fat cells completely counteracts hormone-activated lipolysis, though there is a considerable (≫50%) residual nonhormonal (basal) lipolysis. In rodents, adipose triglyceride lipase enzyme activity is stimulated by a cofactor termed CGI-58. In the absence of CGI-58, lipase activity in fat cells is much higher for hormone sensitive lipase than adipose triglyceride lipase. Hormone sensitive lipase expression is regulated by obesity and body weight reduction (decreased and increased, respectively), but this is not the case for adipose triglyceride lipase. A role of adipose triglyceride lipase in human lipolysis is suggested by studies of gene polymorphisms. Two lipases the ‘old’ hormone sensitive lipase and the ‘new’ adipose triglyceride lipase are of importance for the regulation of lipolysis in rodent fat cells. In humans, adipose triglyceride lipase seems essential for maintaining basal lipolytic activity, while hormone sensitive lipase is the enzyme most responsive to stimulated lipolysis.