title: Adenosine A₁ receptors do not play a major role in the regulation of lipogenic gene expression in hepatocytes.
abstract: Activation of adenosine A₁ receptors was reported to promote fatty acid synthesis in AML-12 cells, by increasing the expression of SREBP-(1c) (sterol regulatory binding protein 1c) and FAS (fatty acid synthase). Since these findings have important therapeutic implications for the discovery of adenosine A₁ receptor agonists, further studies were undertaken to determine the expression and functional relevance of adenosine A₁ receptor in the liver. To that end, we used two classes of distinct adenosine A₁ receptor agonists: CPA (N⁶-cyclopentyl-adenosine), a full agonist and GS-9667 (2-{6-[((1R,2R)-2-hydroxycyclopentyl)-amino]purin-9-yl}(4S,5S,2R,3R)-5-[(2-fluorophenylthio)methyl]-oxolane-3,4-diol), a partial agonist. Treatment of AML-12 cells, HepG2 cells and primary human hepatocytes with either CPA or GS-9667 did not increase the gene expression of SREBP-(1c) or FAS. Furthermore, in AML-12 and HepG2 cells, CPA did not antagonize forskolin-stimulated cAMP production, a characteristic of adenosine A₁ receptor activation, indicating that these cells lack adenosine A₁ receptor function. Consistent with this finding, adenosine A₁ receptor gene expression was found to be very low and adenosine A₁ receptor protein levels were hardly detectable by radioligand binding assays in hepatic cell lines such as AML-12 and HepG2 as well as in both mouse and human liver tissues. Finally, acute treatment with adenosine A₁ receptor agonist GS-9667 had no significant effect on gene expression of both SREBP-(1c) and FAS in livers of Sprague Dawley rats. Taken together, our data suggest that the expression of adenosine A₁ receptor is too low to play a major role in the regulation of lipogenic gene expression in hepatocytes.
authors.affiliation: Department of Biology, Gilead Sciences, Inc., 7601 Dumbarton Circle, Fremont, CA 94555, USA. ming.yang@gilead.com
authors.forename: Ming
authors.initials: M
authors.lastname: Yang
authors.forename: Ruth
authors.initials: R
authors.lastname: Chu
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Chisholm
authors.forename: Holger
authors.initials: H
authors.lastname: Doege
authors.forename: Luiz
authors.initials: L
authors.lastname: Belardinelli
authors.forename: Arvinder K
authors.initials: AK
authors.lastname: Dhalla
mesh_terms: D058907:Adenosine A1 Receptor Agonists / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects; D008297:Male; D051379:Mice; D008875:Middle Aged; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043682:Receptor, Adenosine A1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000819:agonists / Q000378:metabolism; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D058907:Adenosine A1 Receptor Agonists; D012333:RNA, Messenger; D043682:Receptor, Adenosine A1; D011994:Recombinant Proteins; D051780:Sterol Regulatory Element Binding Protein 1; D064429:Fatty Acid Synthases