Abstract:
:Leptin has been shown to activate multiple signaling molecules in cultured cells, including Janus kinase-2, STAT (signal transducer and activator of transcription) proteins, and mitogen-activated protein kinase, and to stimulate the DNA-binding activity of STAT3 in mouse hypothalamus. In this study, the activation of candidate leptin signaling molecules in the hypothalamus of normal rats in vivo was investigated. Fasted male Sprague-Dawley rats were injected iv with recombinant murine leptin or vehicle. Plasma leptin concentrations were determined at defined time points, and the phosphorylation of signaling proteins was assessed in hypothalamic lysates. There was a marked increase in plasma leptin concentration at 2 min and a gradual decline by 45 min after leptin injection. Immunoblotting analysis of hypothalamic lysates with a phosphospecific STAT3 antibody demonstrated a time-dependent stimulation of STAT3 tyrosine phosphorylation. STAT3 phosphorylation was first evident at 5 min and was maximal at 30 min after leptin injection. By contrast, leptin did not increase the phosphorylation of Janus kinase proteins, mitogen-activated protein kinase, or STAT1 and -5 despite abundant expression of these signaling molecules in the hypothalamus. These results differ from findings in cultured cells and in vitro systems. It remains unclear how signaling is propagated downstream from the leptin receptor to STAT3, but this may involve novel signaling intermediates.
journal_name
Endocrinologyjournal_title
Endocrinologyauthors
McCowen KC,Chow JC,Smith RJdoi
10.1210/endo.139.11.6301subject
Has Abstractpub_date
1998-11-01 00:00:00pages
4442-7issue
11eissn
0013-7227issn
1945-7170journal_volume
139pub_type
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