Coculture of primary rat hepatocytes and nonparenchymal cells permits expression of insulin-like growth factor binding protein-3 in vitro.
In biological fluids, the insulin-like growth factors (IGFs) are associated with binding proteins (IGFBPs), which modify IGF distribution and action. Circulating IGFs are bound predominantly to IGFBP-3, of apparent hepatic origin, but regulation of IGFBP-3 has been difficult to dissect because of the lack of systems suitable for examining hepatic production of IGFBP-3 in vitro. In the present studies, IGFBP-3 expression was identified primarily in hepatic nonparenchymal cells, particularly Kupffer and sinusoidal endothelial cells. Coculture with hepatocytes enhanced the stability of nonparenchymal cells to express IGFBP-3 in vitro. IGFBP-3 in conditioned medium had apparent mol wt of 150-300 kilodaltons, suggesting formation of a ternary complex with IGFs and the acid-labile subunit. Expression and secretion of IGFBP-3 were hormonally responsive and strongly correlated (r = 0.79; P < 0.001), with 2- to 3-fold stimulation by added insulin or IGF-I (both P < 0.05), but not by added GH alone. Our findings suggest that GH may act indirectly to promote IGFBP-3 generation in vivo via increasing both the secretion of insulin and the hepatic production of IGF-I; in patients with diabetes mellitus, reduced circulating levels of IGFBP-3 despite high levels of GH may result from both insulin deficiency and inadequate hepatic production of IGF-I. Coculture of hepatic nonparenchymal and parenchymal cells should be useful for further analysis of the mechanism of IGFBP-3 regulation.
Villafuerte
B C
BC
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30303.
Koop
B L
BL
Pao
C I
CI
Gu
L
L
Birdsong
G G
GG
Phillips
L S
LS
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D002469:Cell Separation; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D017077:Culture Media, Conditioned; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004727:Endothelium / Q000378:metabolism; D015870:Gene Expression; D013006:Growth Hormone / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007700:Kinetics; D007728:Kupffer Cells / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D007328:Insulin; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone