Role of adrenomedullin system in lipid metabolism and its signaling mechanism in cultured adipocytes.
We investigated the levels of adrenomedullin (AM) system during the process of preadipocyte differentiation and its role in lipid metabolism and cellular signaling mechanism in differentiated adipocytes. We cultured rat preadipocytes and measured the following during the process of differentiation: two molecular forms of AM in the culture medium using a specific immunoradiometric assay and gene expression of AM and its receptor component using RT-PCR analysis. In differentiated adipocytes, we measured the effects of AM on the intracellular cAMP level, lipolysis, glucose incorporation, and the protein levels. Two molecular forms of AM were secreted into the medium, and the AM-mature/AM-total ratio was increased after 6 days of differentiation. Cultured rat preadipocytes highly expressed the genes of AM and its receptor components at day 1, and they increased at day 10. Administration of AM to preadipocytes increased the number of Oil Red O-positive adipocytes and spectrophotometric absorbance of Oil Red O. AM dose dependently increased cAMP level and lipolysis, and its effect was blocked by CGRP(8-37). Isoproterenol increased lipolysis, and AM had additive effects on isoproterenol-induced lipolysis. KT5720 and U0126 significantly inhibited the AM-induced lipolysis, whereas KT5720, but not U0126, significantly inhibited the isoproterenol-induced lipolysis. AM increased glucose incorporation and its effect was blocked by wortmannin. Western blot analysis revealed that AM increased phospho PKA, ERK, and Akt. These results indicate that AM and its receptor component are highly expressed in cultured adipocytes and may play a role in lipid metabolism via a different signaling pathway.
Iemura-Inaba
Chikako
C
Dept. of Hypertension and Cardiorenal Medicine, Dokkyo Univ. School of Medicine, Mibu, Tochigi 321-0293, Japan.
Nishikimi
Toshio
T
Akimoto
Kazumi
K
Yoshihara
Fumiki
F
Minamino
Naoto
N
Matsuoka
Hiroaki
H
D017667:Adipocytes / Q000378:metabolism* / Q000502:physiology; D053607:Adrenomedullin / Q000502:physiology*; D000818:Animals; D001391:Azo Compounds; D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis / Q000235:genetics; D006152:Cyclic GMP / Q000096:biosynthesis / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D050356:Lipid Metabolism / Q000502:physiology*; D008066:Lipolysis / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D058261:Receptor Activity-Modifying Proteins; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*
D001391:Azo Compounds; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D058261:Receptor Activity-Modifying Proteins; D018015:Receptors, Calcitonin Gene-Related Peptide; D053607:Adrenomedullin; D000242:Cyclic AMP; C011049:oil red O; D006152:Cyclic GMP; D005947:Glucose