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Tissue fibrosis is characterized by excessive production, deposition, and contraction of the extracellular matrix (ECM). The second messenger cAMP has antifibrotic effects in fibroblasts from several tissues, including cardiac fibroblasts (CFs). Increased cellular cAMP levels can prevent the transformation of CFs into profibrogenic myofibroblasts, a critical step that precedes increased ECM deposition and tissue fibrosis. Here we tested two hypotheses: 1) myofibroblasts have a decreased ability to accumulate cAMP in response to G protein-coupled receptor (GPCR) agonists, and 2) increasing cAMP will not only prevent, but also reverse, the myofibroblast phenotype. We found that myofibroblasts produce less cAMP in response to GPCR agonists or forskolin and have decreased expression of several adenylyl cyclase (AC) isoforms and increased expression of multiple cyclic nucleotide phosphodiesterases (PDEs). Furthermore, we found that forskolin-promoted increases in cAMP or N(6)-phenyladenosine-cAMP, a protein kinase A-selective analog, reverse the myofibroblast phenotype, as assessed by the expression of collagen Iα1, α-smooth muscle actin, plasminogen activator inhibitor-1, and cellular contractile abilities, all hallmarks of a fibrogenic state. These results indicate that: 1) altered expression of AC and PDE isoforms yield a decrease in cAMP concentrations of cardiac myofibroblasts (relative to CFs) that likely contributes to their profibrotic state, and 2) approaches to increase cAMP concentrations not only prevent fibroblast-to-myofibroblast transformation but also can reverse the profibrotic myofibroblastic phenotype. We conclude that therapeutic strategies designed to enhance cellular cAMP concentrations in CFs may provide a means to reverse excessive scar formation following injury and to treat cardiac fibrosis.

The article Epac activation inhibits IL-6-induced cardiac myocyte dysfunction., Author(s): Huiling Jin[sup.1], Takayuki Fujita[sup.1], Meihua Jin[sup.1,2], Reiko Kurotani[sup.1,3], Yuko Hidaka[sup.1], Wenqian Cai[sup.1], Kenji Suita[sup.1], Rajesh Prajapati[sup.1], Chen Liang[sup.1], Yoshiki Ohnuki[sup.4], Yasumasa Mototani[sup.4], Masanari Umemura[sup.1], Utako Yokoyama[sup.1], Motohiko Sato[sup.1,5], Satoshi [...]

PKA phosphorylates multiple molecules involved in calcium ([Ca.sup.2+]) handling in cardiac myocytes and is considered to be the predominant regulator of β-adrenergic receptor-mediated enhancement of cardiac contractility; however, recent identification of exchange protein activated by cAMP (EPAC), which is independently activated by cAMP, has challenged this paradigm. Mice lacking Epac1 (Epac1 KO) exhibited decreased cardiac contractility with reduced phospholamban (PLN) phosphorylation at serine-16, the major PKA-mediated phosphorylation site. In Epac1 KO mice, intracellular [Ca.sup.2+] storage and the magnitude of [Ca.sup.2+] movement were decreased; however, PKA expression remained unchanged, and activation of PKA with isoproterenol improved cardiac contractility. In contrast, direct activation of EPAC in cardiomyocytes led to increased PLN phosphorylation at serine-16, which was dependent on PLC and PKCe. Importantly, Epac1 deletion protected the heart from various stresses, while Epac2 deletion was not protective. Compared with WT mice, aortic banding induced a similar degree of cardiac hypertrophy in Epac1 KO; however, lack of Epac1 prevented subsequent cardiac dysfunction as a result of decreased cardiac myocyte apoptosis and fibrosis. Similarly, Epac1 KO animals showed resistance to isoproterenol- and aging-induced cardiomyopathy and attenuation of arrhythmogenic activity. These data support Epac1 as an important regulator of PKA-independent PLN phosphorylation and indicate that Epac1 regulates cardiac responsiveness to various stresses., Introduction β-Adrenergic receptor (β-AR) signaling is well established as a primary defense mechanism against acute stress or changes in hemodynamic load; however, its role in cardiac pathogenesis, although studied extensively, [...]

Vascular smooth muscle cell (VSMC) migration and the subsequent intimal thickening play roles in vascular restenosis. We previously reported that an exchange protein activated by cAMP 1 (Epac1) promotes platelet-derived growth factor (PDGF)-induced VSMC migration and intimal thickening. Because basic fibroblast growth factor (bFGF) also plays a pivotal role in restenosis, we examined whether Epac1 was involved in bFGF-mediated VSMC migration. bFGF-induced lamellipodia formation and migration were significantly decreased in VSMCs obtained from Epac1.sup.-/- mice compared to those in Epac1.sup.+/+-VSMCs. The bFGF-induced phosphorylation of Akt and glycogen synthase kinase 3[beta] (GSK3[beta]), which play a role in bFGF-induced cell migration, was attenuated in Epac1.sup.-/--VSMCs. Intimal thickening induced by the insertion of a large wire was attenuated in Epac1.sup.-/- mice, and was accompanied by the decreased phosphorylation of GSK3[beta]. These data suggest that Epac1 deficiency attenuates bFGF-induced VSMC migration, possibly via Akt/GSK3[beta] pathways. Keywords: Exchange protein activated by cAMP 1, Intimal thickening, Basic fibroblast growth factor, Vascular smooth muscle cells, Migration, Author(s): Yuko Kato[sup.1,2], Utako Yokoyama[sup.1], Takayuki Fujita[sup.1], Masanari Umemura[sup.1], Tetsuo Kubota[sup.2] and Yoshihiro Ishikawa[sup.1] Introduction Intimal thickening that occurs after vascular injury resulting from percutaneous coronary intervention is a major [...]

Caveolin, a member of the membrane-anchoring protein family, accumulates various growth receptors in caveolae and inhibits their function. Upregulation of caveolin attenuates cellular proliferation and growth. However, the role of caveolin in regulating insulin signals remains controversial. Here, we demonstrate that caveolin potently enhances insulin receptor (IR) signaling when overexpressed in the liver in vivo. Adenovirus-mediated gene transfer was used to overexpress caveolin specifically in the liver of diabetic obese mice, which were generated with a high-fat diet. Expression of molecules involved in IR signaling, such as IR or Akt, remained unchanged after gene transfer. However, hepatic glycogen synthesis was markedly increased with a decrease in phosphoenolpyruvate carboxykinase protein expression. Insulin sensitivity was increased after caveolin gene transfer as determined by decreased blood glucose levels in response to insulin injection and fasting blood glucose levels. Glucose tolerant test performance was also improved. Similar improvements were obtained in [KKA.sup.y] genetically diabetic mice. Adenovirus-mediated over-expression of caveolin-3 in hepatic cells also enhanced IR signaling, as shown by increased phosphorylation of IR in response to insulin stimulation and higher glycogen synthesis at baseline. These effects were attributed mostly to increased insulin receptor activity and caveolin-mediated, direct inhibition of protein tyrosine phosphatase 1B, which was increased in obese mouse livers. In conclusion, our results suggest that caveolin is an important regulator of glucose metabolism that can enhance insulin signals. insulin receptor; diabetes mellitus doi:10.1152/ajpcell.00077.2009