Impairment of liver GH receptor signaling by fasting.
Fasting causes a state of GH resistance responsible for low circulating IGF-I levels. To investigate whether this resistance may result from alterations in the GH signaling pathway, we determined the effects of fasting on the GH transduction pathway in rat liver. Forty-eight-hour fasted or fed male rats were injected with recombinant rat GH via the portal vein. Liver was removed 0 and 15 min after injection. Although GH stimulated Janus kinase 2 (JAK2) phosphorylation in all animals, this was severely blunted in fasted animals. Similarly, the phosphorylation of the GH receptor, although observed in both fasted and fed rats after GH injection, was markedly reduced in fasted rats. A rapid signal transducer and activator of transcription 5 (STAT5) tyrosine phosphorylation was also induced in the liver of fed animals in response to GH. In contrast, in fasted rats only a slight phosphorylated STAT5 signal was observed. The inhibitory effect of fasting on these GH signaling molecules occurred without changes in their protein content. Furthermore, the impairment of the JAK-STAT pathway in fasted animals was associated with increased liver suppressor of cytokine signaling 3 mRNA levels. Although glucocorticoids, which are increased by fasting, may cause GH resistance, adrenalectomy failed to prevent alterations in the JAK-STAT pathway caused by fasting. In conclusion, the GH resistance induced by fasting is associated with impairment of the JAK-STAT signaling pathway. This might contribute to the decrease in liver IGF-I production observed in fasting.
Beauloye
Váronique
V
Unité de Diabétologie et Nutrition, Université Catholique de Louvain, B-1200 Brussels, Belgium.
Willems
Bertrand
B
de Coninck
Virginie
V
Frank
Stuart J
SJ
Edery
Marc
M
Thissen
Jean-Paul
JP
D000315:Adrenalectomy; D000818:Animals; D015152:Blotting, Northern; D004268:DNA-Binding Proteins / Q000378:metabolism; D005215:Fasting / Q000502:physiology*; D053614:Janus Kinase 2; D008099:Liver / Q000502:physiology*; D008297:Male; D008894:Milk Proteins; D010766:Phosphorylation; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D017208:Rats, Wistar; D011986:Receptors, Somatotropin / Q000502:physiology*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; C507927:Jak2 protein, rat; D053614:Janus Kinase 2