The irresistible biology of resistin.

Fuel sources have historically triggered many battles throughout the globe and will likely continue to do so. The design of biological systems is no different. Adipose tissue holds the richest energy sources and exerts substantial influence on the organism. While this fundamental truth has eluded scientists for a long time, it is now clear that adipocytes have established effective communication networks and gained control over important trade routes to maintain their influential status. To this end, these innocent-looking cells appear to utilize two main tools: fatty acids and polypeptide hormones. It is likely that they have additional, yet unknown, signaling mechanisms. It has been known for some time that obesity is associated with insulin resistance and diabetes. Yet how and why these problems are so closely linked at the molecular level has not been clear. As in most such cases, lack of knowledge led to many conspiracy theories — my favorite one being that agents produced by fat cells affect metabolic control at other sites. An example of such an agent is the inflammatory cytokine TNF-α, which is produced in excess in obesity and causally linked to insulin resistance (1). Many other such agents have now been added to this list, although unlike TNF-α, some do not mediate adverse effects on metabolism. In fact, some, such as leptin and adiponectin, work to improve the metabolic status of their fellow organs (2).