Localization of binding sites in the central nervous system for leptin (OB protein) in normal, obese (ob/ob), and diabetic (db/db) C57BL/6J mice.

Leptin (OB protein) fused to the FLAG epitope and a kinase recognition site was expressed in bacteria, immunopurified, and phosphorylated using [gamma-(33)p] ATP. The resulting probe was used to characterize the distribution of leptin binding sites within brain sections of normal, ob/ob, and db/db C57BL/6J male mice. Leptin binding sites were found in leptomeninges and choroid plexus. Leptin binding within the choroid plexus is slightly elevated in ob/ob mice when compared to normal males (p<0.05). Binding of leptin by the choroid plexus of db/db male mice is lower than in normal males (p<0.05), but normally distributed. Based on the association and dissociation rates of leptin binding on tissue sections, we estimate the KD of the choroid plexus site at 0.25x10(-9) M. From our results, we hypothesize that the binding of leptin to its site may cause the release or transport of uncharacterized factor(s) into the cerebral spinal fluid (CSF) to affect neuronal populations controlling feeding and metabolism.