Leptin receptor isoforms expressed in human adipose tissue

Leptin and its structural gene, Ob, are exclusively expressed in adipose tissue. Leptin is secreted into the blood and is responsible for fat mass regulation via leptin receptors in the hypothalamus. This has been considered the major role of leptin, but leptin receptor isoforms are expressed not only in the brain but also in most other tissues in humans and rodents: heart, placenta, lung, liver, muscle, kidney, pancreas, spleen, thymus, prostate, testes, ovary, small intestine, and colon. This implicates leptin regulation in other systems apart from fat mass regulation, and leptin action has been demonstrated in human fetal development and reproductive development, liver metabolism, hematopoiesis, and insulin secretion. Four splice variants of the leptin receptor have been identified in humans: the long isoform huOb-R and the shorter isoforms B219.1 to B219.3. It is known that the long isoform has full intracellular signaling capacity, and is responsible for anorectic action in the hypothalamus. The roles of the other isoforms are yet to be elucidated. Here, we report the identification by reverse transcriptase-polymerase chain reaction (RT-PCR) of three leptin receptor isoforms coexpressed in human visceral adipose tissue: the long isoform huOb-R and the short isoforms huB219.1 and huB219.3. The possible roles of these isoforms are discussed.