Leptin signaling in the hypothalamus during chronic central leptin infusion.
Using a rat model of chronic central leptin infusion in which neuropeptide Y neurons develop leptin resistance, we examined whether leptin signal transduction mechanism in the hypothalamus is altered during central leptin infusion. Adult male rats were infused chronically into the lateral cerebroventricle with leptin (160 ng/h) or vehicle via Alzet pumps for 16 d. In the leptin-infused group, the initial decrease in food intake was followed by a recovery to their preleptin levels by d 16, although food intake remained significantly lower than in artificial cerebrospinal fluid controls; and body weight gradually decreased reaching a nadir at d 11 and remained stabilized at lower level thereafter. Phosphorylated leptin receptor and phosphorylated signal transducer and activator of transcription-3 (p-STAT3) remained elevated in association with a sustained elevation in DNA-binding activity of STAT3 in the hypothalamus throughout 16-d period of leptin infusion. However, phosphorylated Janus kinase-2 was increased during the early part of leptin infusion but remained unaltered on d 16. Although hypothalamic suppressors of cytokine signaling-3 (SOCS3) mRNA levels were increased throughout leptin infusion, SOCS3 protein levels were increased only on d 16. This study demonstrates a sustained elevation in hypothalamic leptin receptor signaling through Janus kinase-STAT pathway despite an increased expression of SOCS3 during chronic central leptin infusion. We propose that an alteration in leptin signaling in the hypothalamus through pathways other than STAT3 and/or a defect in downstream of STAT3 signaling may be involved in food intake recovery seen after an initial decrease during chronic central leptin infusion.
Pal
Rekha
R
Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Sahu
Abhiram
A
D000273:Adipose Tissue / Q000033:anatomy & histology / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D004435:Eating / Q000187:drug effects; D004822:Epididymis / Q000033:anatomy & histology / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D007031:Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007276:Injections, Intraventricular; D007328:Insulin / Q000097:blood; D053614:Janus Kinase 2; D020738:Leptin / Q000097:blood* / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000378:metabolism*; D009765:Obesity / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000235:genetics; D054411:Receptors, Leptin; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors
D001786:Blood Glucose; D004268:DNA-Binding Proteins; D007328:Insulin; D020738:Leptin; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; C491410:Socs3 protein, rat; C494088:Stat3 protein, rat; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; C507927:Jak2 protein, rat; D053614:Janus Kinase 2