Cloning and characterization of a human leptin receptor using a biologically active leptin immunoadhesin

Abstract

Leptin, the product of the ob gene, is a hormone secreted by fat cells which is primarily involved in the regulation of body weight. We have generated a leptin immunoadhesin (leptin-IgG) which was more potent than leptin alone at reducing body weight and food intake when injected into ob/ob mice. This molecule was used to identify high affinity binding sites on human embryonic 293 kidney cells and subsequently to isolate a cDNA encoding the leptin receptor from this cell line by expression cloning. This receptor corresponds to the short form of the recently isolated leptin receptor. Analysis of the expression pattern of the two forms of receptor by Northern blot, in situ hybridization and quantitative PCR showed that the receptor is expressed in most tissues but that the long form is prevalent in the hypothalamus.

Comparing effects of leptin and insulin on glucose metabolism in skeletal muscle: evidence for an effect of leptin on glucose uptake and decarboxylation

“…Under conditions of clamped glycaemia, 7 leptin increases insulin sensitivity in normal rats both under fasting conditions and in the presence of hyperinsulinaemia; these effects do not appear to be dependent on altered body weight. It is also important to notice that the leptin receptor or its splice variants have so far been identi®ed in many different tissues including skeletal muscle, 8 which may be a possible target site for leptin action. It was recently shown that leptin stimulates glucose transport and glycogen synthesis in C 2 C 12 myotubes, 9 in opposition to previous ®ndings that leptin impairs insulin signaling, that is, insulin receptor autophosphorylation and insulin-receptor substrate (IRS)-1 phosphorylation in rat-1 ®broblasts, NIH3T3 cells 10 and HepG2 cells.…”

Pivotal role of leptin in insulin effects

“…Analysis of the expression pattern of the two forms (long and short) of leptin receptors by Northern blot, in situ hybridization and quantitative PCR showed that the receptors are expressed in most tissues (brain, testes, ovary, kidney, spleen, intestines, brown and white adipose tissues, heart, lung, liver, skeletal muscle, and adrenals (14,18)), with the long form being prevalent in the hypothalamus (18), in addition to also being found in the medulla of the adrenal, the inner zone of the medulla of the kidney (16,18), pancreatic islets (19), and fat tissue (18).…”

“…Skeletal muscle and adipose tissue are the most important sites of postprandial glucose disposal, and in these tissues the stimulation of glucose uptake, glycogen synthesis and lipid synthesis are the main effects of insulin. The leptin receptor has been identified in muscle and in adipose tissue (14,18), a fact that makes these tissues possible target sites for the action of leptin.…”

“…It has been speculated that circulating factors derived from adipose tissue impair insulin signaling in the skeletal muscle cell. In addition, it was recently demonstrated that a short form of the Ob-R is expressed in this tissue (14,18). Previous studies have reported that daily intraperitoneal injections of leptin for 28 days produce a significant dose-dependent reduction in glycemia and insulinemia in ob/ ob mice but not in lean mice (1), and also caused a reduction in body weight when injected intracerebroventricularly into rats fasted for 24 h (30).…”

“…Since the identification of the OB protein receptor in adipocytes (14,18), it has been speculated that leptin might also exert an autocrine effect. However, very few data are available regarding this issue.…”