Anatomic localization of alternatively spliced leptin receptors (Ob-R) in mouse brain and other tissues

Abstract

Leptin's effects are mediated by interactions with a receptor that is alternatively spliced, resulting in at least five different murine forms: Ob-Ra, Ob-Rb, Ob-Rc, Ob-Rd, and Ob-Re. A mutation in one splice form, Ob-Rb, results in obesity in mice. Northern blots, RNase protection assays, and PCR indicate that Ob-Rb is expressed at a relatively high level in hypothalamus and low level in several other tissues. Ob-Ra is expressed ubiquitously, whereas ObRc, -Rd, and -Re RNAs are only detectable using PCR. In hypothalamus, Ob-Rb is present in the arcuate, ventromedial, dorsomedial, and lateral hypothalamic nuclei but is not detectable in other brain regions. These nuclei are known to regulate food intake and body weight. The level of Ob-Rb in hypothalamus is reduced in mice rendered obese by gold thioglucose (GTG), which causes hypothalamic lesions. The obesity in GTG-treated mice is likely to be caused by ablation of Ob-Rb-expressing neurons, which results in leptin resistance.Leptin, a hormone secreted by adipocytes, regulates the size of the adipose tissue mass while affecting satiety and energy metabolism (1-3). Leptin has pleiotypic effects on a number of organ systems and affects reproduction, metabolism, and glucose homeostasis (4-6). Leptin is more potent when given centrally versus peripherally suggesting that some of its effects are mediated via direct actions on receptors in brain (refs. 3 and 7; unpublished data). The leptin receptor, Ob-R, is alternatively spliced, and five different splice forms of the receptor have been identified (8, 9). One form of the receptor, Ob-Rb, is mutant in C57BL͞Ks db͞db mice (9, 10). Both reverse transcription-PCR and RNase protection assays indicate that this splice form is expressed at a relatively high level in hypothalamus, suggesting that leptin interacts with neurons in this brain region (9, 11).The Ob-Rb receptor is different from other forms of the receptor in that it has a long cytoplasmic region with consensus amino acid sequences involved in receptor binding to JAK tyrosine kinases (9). JAK tyrosine kinases are required for signal transduction of receptors in the Ob-R class (12). The cytoplasmic region of Ob-Rb also contains a motif required for binding of the Stat3 transcription factor, a known substrate of JAKs (8, 13). Injections of leptin in vivo result in a dose-dependent activation of Stat3 in hypothalamus within 15 min in wild-type and ob mice but not in db mice (13). The other forms of Ob-R have truncated cytoplasmic regions and presumably cannot by themselves activate JAKs or Stats.In aggregate, these data suggest that leptin's effects are mediated, in part, via binding to the Ob-Rb isoform of the receptor in the hypothalamus. Here we define the tissue distribution of the different Ob-R isoforms in mice and use in situ hybridization to localize the different receptor isoforms in mouse brain and other tissues. We also report the exon and intron boundaries of the different splice forms. Finally, the levels of Ob-Rb are quantitated in mutant mic...

New insights into sympathetic regulation of glucose and fat metabolism

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Regulation of corticotropin-releasing factor and urocortin 2/3 mRNA by leptin in hypothalamic N39 cells

“…The short-form Ob-Rs, Ob-Ra and Ob-Rc, contribute to transport of leptin into the brain [3]. The long-form Ob-R, Ob-Rb, is abundantly expressed in the ARC, PVN, VMH, and lateral hypothalamic area [16,17,41]. Leptin activates STAT3 with Jak2.…”

Leptin induces migration and invasion of glioma cells through MMP‐13 production

“…Either overexpression or lack of leptin can result in phenotypic abnormalities, such as obesity (Hsing et al 2007) or hypertension (Tumer et al 2007). Leptin elicits its effects by interacting with specific receptors (ObR), which are found in many tissues with several spliced forms (Fei et al 1997). The long isoform of leptin receptor (ObRl) has signaling characteristics while other shorter spliced variants (ObRt) are thought to serve mainly as leptin transporters or to 4 GLIA- mediate leptin degradation (Uotani et al 1999).…”