Binding of a pure I-125-monoiodoleptin analog to mouse tissues: a developmental study

The preparation of a pure I-125-labeled monoiododerivative of mouse leptin is described. This radiolabeled analog has been used to characterize and lo calize central and peripheral leptin binding sites (Ob-R) of the mouse at d ifferent stages of its development. The affinity values found in membrane h omogenates of various mouse tissues are similar and range between 0.1 and 0 .3 nM, indicating that all the Ob-R isoforms have a similar affinity. Lepti n binding sites are highly expressed at the membrane level in lung, intesti ne, kidney, liver, and skin and to a lesser degree in stomach, heart, and s pleen. Brain, thymus, and pancreas homogenates are devoid of any specific b inding. The distribution of mouse Ob-R has also been explored by autoradiog raphy and dipping techniques on whole mouse sections. In lung, leptin bindi ng sites are located at the pulmonary parenchyma and at the bronchiolar epi thelial level. Binding sites are expressed all along the digestive tract fr om the tongue to the rectum (esophagus. stomach, intestine, colon, and rect um). In muscular visceral structures (stomach, intestine, and bladder) the binding is mainly present in the lamina propria. During development, leptin receptors are early expressed in the liver, kidney, and bone. In the lung, the Ob-R level increased gradually from birth to adulthood where the expre ssion is maximal. By contrast, leptin receptors located in the medulla of t he kidney remain remarkably constant all along the development. A broad sig nal is present in cartilage and bone particularly in vertebrae, limb, and r ibs. Interestingly, leptin receptors are barely detectable in the mouse bra in except in the choroid plexus and leptomeninges, whereas in the rat brain leptin binding sites are located in the thalamus, the piriform cortex, the cerebellum (at the granular and molecular cell layer), and the pineal glan d. (C) 2000 Elsevier Science Inc. All rights reserved.