title: Regulation of cardiac fibroblast collagen synthesis by adenosine: roles for Epac and PI3K.
abstract: Rat cardiac fibroblasts (CF) express multiple adenosine (ADO) receptors. Pharmacological evidence suggests that activation of A(2) receptors may inhibit collagen synthesis via adenylyl cyclase-induced elevation of cellular cAMP. We have characterized the signaling pathways involved in ADO-mediated inhibition of collagen synthesis in primary cultures of adult rat CF. ANG II stimulates collagen production in these cells. Coincubation with agents that elevate cellular cAMP [the ADO agonist, 5'-N-ethylcarboxamidoadensoine (NECA), and forskolin] inhibited the stimulatory effects of ANG II. However, direct stimulators and inhibitors of protein kinase A (PKA) did not alter ANG II-induced collagen synthesis, indicating that PKA does not mediate the inhibitory effects of NECA. Inhibitors of AMP-kinase (AMPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) do not alter NECA-inhibited collagen synthesis. However, activation of exchange factor directly activated by cAMP (Epac) mimicked the effects of NECA on ANG II-stimulated collagen synthesis. Inhibition of phosphoinositol-3 kinase (PI3K) reduced the inhibitory effects of NECA on ANG II-induced collagen synthesis, suggesting that NECA acts via PI3K. Furthermore, inhibition of PI3K also relieved the inhibitory effect of Epac activation on ANG II-stimulated collagen synthesis. Thus it appears that ADO activates the A(2)R-G(s)-adenylyl cyclase pathway and that the resultant cAMP reduces collagen synthesis via a PKA-independent, Epac-dependent pathway that feeds through PI3K.
authors.affiliation: Department of Medicine, University of California, La Jolla, CA, USA. fvillarr@ucsd.edu
authors.forename: Francisco
authors.initials: F
authors.lastname: Villarreal
authors.forename: Sara A
authors.initials: SA
authors.lastname: Epperson
authors.forename: Israel
authors.initials: I
authors.lastname: Ramirez-Sanchez
authors.forename: Katrina G
authors.initials: KG
authors.lastname: Yamazaki
authors.forename: Laurence L
authors.initials: LL
authors.lastname: Brunton
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D003094:Collagen / Q000096:biosynthesis*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D000241:Adenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D000804:Angiotensin II; D003094:Collagen; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020662:Guanine Nucleotide Exchange Factors; D019869:Phosphatidylinositol 3-Kinases; D018047:Receptors, Purinergic P1; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; C526973:Rapgef3 protein, rat