Retinol mobilization from cultured rat hepatic stellate cells does not require retinol binding protein synthesis and secretion.
Retinol mobilization from retinyl esters stores of hepatic stellate cells (HSCs) is a key step in the regulation of mammalian retinol homeostasis, but the precise mechanisms of such a mobilization are still poorly understood. Using primary cultures of HSCs, we first demonstrated that HSCs expressed immunoreactivity against retinol-binding-protein (RBP) when cultured in a medium containing RBP but were unable to synthesize RBP transcripts and proteins. Using pulse and chase-type experiments, we demonstrated that radioactive retinol was released in culture medium without binding proteins. Inhibition of protein secretion by brefeldin A did not modify quantitatively retinol release. This data ruled out, for the first time, the direct involvement of RBP in retinol mobilization from HSCs. Moreover, HSCs co-cultured with primary isolated hepatocytes displayed an increase of retinol transfer from HSCs to hepatocytes when they established direct physical contacts, as compared with co-cultures without contact. Based on this latter data, a mechanism of retinol mobilization from HSCs via the hepatocytes using retinol transfer through cellular membranes is proposed.
Sauvant
P
P
Unité des Maladies Métaboliques et Micronutriments, Equipe Vitamines, Centre INRA Clermont-Ferrand-Theix, 63122, Saint-Genès Champanelle, France. patrick.sauvant@clermont.inra.fr
Sapin
V
V
Alexandre-Gouabau
M C
MC
Dodeman
I
I
Delpal
S
S
Quadro
L
L
Partier
A
A
Abergel
A
A
Colantuoni
V
V
Rock
E
E
Azaïs-Braesco
V
V
D000818:Animals; D001692:Biological Transport; D015415:Biomarkers; D015153:Blotting, Western; D002450:Cell Communication; D002469:Cell Separation / Q000379:methods; D002478:Cells, Cultured; D018920:Coculture Techniques; D004591:Electrophoresis, Polyacrylamide Gel; D015696:Gene Products, tat / Q000032:analysis; D022781:Hepatocytes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012177:Retinol-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism; D014801:Vitamin A / Q000378:metabolism*
D015415:Biomarkers; D015696:Gene Products, tat; D012333:RNA, Messenger; D012177:Retinol-Binding Proteins; D014801:Vitamin A