Cyclic AMP-Rap1A signaling activates RhoA to induce α(2c)-adrenoceptor translocation to the cell surface of microvascular smooth muscle cells

Intracellular signaling by the second messenger cyclic AMP (cAMP) activates the Ras-related small GTPase Rap1 through the guanine exchange factor Epac. This activation leads to effector protein interactions, activation, and biological responses in the vasculature, including vasorelaxation. In vascular smooth muscle cells derived from human dermal arterioles (microVSM), Rap1 selectively regulates expression of G protein-coupled α(2C)-adrenoceptors (α(2C)-ARs) through JNK-c-jun nuclear signaling. The α(2C)-ARs are generally retained in the trans-Golgi compartment and mobilize to the cell surface and elicit vasoconstriction in response to cellular stress. The present study used human microVSM to examine the role of Rap1 in receptor localization. Complementary approaches included murine microVSM derived from tail arteries of C57BL6 mice that express functional α(2C)-ARs and mice deficient in Rap1A (Rap1A-null). In human microVSM, increasing intracellular cAMP by direct activation of adenylyl cyclase by forskolin (10 μM) or selectively activating Epac-Rap signaling by the cAMP analog 8-pCPT-2'-O-Me-cAMP (100 μM) activated RhoA, increased α(2C)-AR expression, and reorganized the actin cytoskeleton, increasing F-actin. The α(2C)-ARs mobilized from the perinuclear region to intracellular filamentous structures and to the plasma membrane. Similar results were obtained in murine wild-type microVSM, coupling Rap1-Rho-actin dynamics to receptor relocalization. This signaling was impaired in Rap1A-null murine microVSM and was rescued by delivery of constitutively active (CA) mutant of Rap1A. When tested in heterologous HEK293 cells, Rap1A-CA or Rho-kinase (ROCK-CA) caused translocation of functional α(2C)-ARs to the cell surface (~4- to 6-fold increase, respectively). Together, these studies support vascular bed-specific physiological role of Rap1 and suggest a role in vasoconstriction in microVSM.

Primary congenital anomalies of the coronary arteries and relation to atherosclerosis: an angiographic study in Lebanon

BACKGROUND

Most coronary artery anomalies are congenital in origin. This study angiographically determined the prevalence of different forms of anomalous aortic origins of coronary anomalies and their anatomic variation in a selected adult Lebanese population. Correlation between these anomalies and stenotic coronary atherosclerotic disease was also investigated.

METHODS

4650 coronary angiographies were analyzed for anomalous aortic origin. These anomalies were clustered in four main groups: anomalous left circumflex (LCX) coronary artery, anomalous right coronary artery, anomalous left main coronary artery and anomalous left anterior descending coronary artery.

RESULTS

Thirty four patients had anomalous aortic origin of coronary arteries. Of these, anomalous LCX coronary artery was the most common (19 of 34 patients). The second most common anomaly was anomalous RCA origin (9 of 34 patients.) The incidence of coronary stenosis in non-anomalous vessels was 50%. However, a significantly smaller percentage (17.46%; 6 of 34 patients) of anomalous vessels exhibited significant stenosis, reminiscent of atherosclerotic disease. Of these six vessels, five were LCX coronary artery arising from right coronary sinus or from early branch of right coronary artery. The sixth was right coronary artery arising from left coronary sinus.

CONCLUSION

The incidence of congenital coronary anomalies in Lebanon is similar to other populations where the most common is the LCX coronary artery. Isolated congenital coronary anomalies do not increase the risk of developing coronary stenosis or atherosclerosis. Angiographic detection of these anomalies is clinically important for coronary angioplasty or cardiac surgery.

Cyclic AMP acts through Rap1 and JNK signaling to increase expression of cutaneous smooth muscle alpha2C-adrenoceptors

Cold increases cutaneous vasoconstriction by unmasking the contractile activity of alpha(2C)-adrenoceptors (alpha(2C)-ARs) in vascular smooth muscle cells (VSMCs), which is mediated by the cold-induced mobilization of alpha(2C)-ARs from the transGolgi to the cell surface. The expression of alpha(2C)-ARs in human cutaneous VSMCs is under dual regulation by cyclic AMP: gene transcription is inhibited by cyclic AMP acting through protein kinase A but is increased by cyclic AMP acting through the exchange protein directly activated by cyclic AMP (EPAC) and the GTP-binding protein Rap1. Experiments were performed to further characterize the Rap1 signaling pathway. Forskolin (10 muM), the selective EPAC activator, 8-pCPT-2'-O-Me-cyclic AMP (CMC; 100 microM), or a constitutively active mutant of Rap1 (Rap1CA) increased the activity of c-Jun NH(2)-terminal kinase (JNK) in human cutaneous VSMCs. This was associated with the increased phosphorylation of c-Jun and activation of an activator protein (AP)-1 reporter construct, which were inhibited by the JNK inhibitor SP600125 (3 microM). Rap1CA increased the activity of an alpha(2C)-AR promoter-reporter construct, which was inhibited by SP600125 (3 microM) or by the mutation of an AP-1 binding site in the alpha(2C)-AR promoter. Furthermore, forskolin (10 microM) or CMC (100 microM) increased the expression of the alpha(2C)-AR protein, and these effects were inhibited by SP600125 (3 microM). Therefore, cyclic AMP increases the expression of alpha(2C)-ARs in cutaneous VSMCs by activating a novel Rap1 signaling pathway, mediated by the activation of JNK, AP-1, and the subsequent transcriptional activation of the alpha(2C)-AR gene. By increasing the expression of cold-responsive alpha(2C)-ARs, this pathway may contribute to enhanced cold-induced vasoconstriction in the cutaneous circulation, including Raynaud's phenomenon.

Estrogen increases smooth muscle expression of α2C-adrenoceptors and cold-induced constriction of cutaneous arteries

Raynaud's phenomenon, which is characterized by intense cold-induced constriction of cutaneous arteries, is more common in women compared with men. Cold-induced constriction is mediated in part by enhanced activity of α2C-adrenoceptors (α2C-ARs) located on vascular smooth muscle cells (VSMs). Experiments were therefore performed to determine whether 17β-estradiol regulates α2C-AR expression and function in cutaneous VSMs. 17β-Estradiol (0.01–10 nmol/l) increased expression of the α2C-AR protein and the activity of the α2C-AR gene promoter in human cultured dermal VSMs, which was assessed following transient transfection of the cells with a promoter-reporter construct. The effect of 17β-estradiol was associated with increased accumulation of cAMP and activation of the cAMP-responsive Rap2 GTP-binding protein. Transient transfection of VSMs with a dominant-negative mutant of Rap2 inhibited the 17β-estradiol-induced activation of the α2C-AR gene promoter, whereas a constitutively active mutant of Rap2 increased α2C-AR promoter activity. The effects of 17β-estradiol were inhibited by the estrogen receptor (ER) antagonist, ICI-182780 (1 μmol/l), and were mimicked by a cell-impermeable form of the hormone (estrogen:BSA) or by the selective ER-α receptor agonist 4,4′,4‴-(4-propyl-[1H]-pyrazole-1,3,5-triyl)tris-phenol (PPT; 10 nmol/l) or the selective ER-β receptor agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; 10 nmol/l). Therefore, 17β-estradiol increased expression of α2C-ARs by interacting with cell surface receptors to cause a cAMP/Rap2-dependent increase in α2C-AR transcription. In mouse tail arteries, 17β-estradiol (10 nmol/l) increased α2C-AR expression and selectively increased the cold-induced amplification of α2-AR constriction, which is mediated by α2C-ARs. An estrogen-dependent increase in expression of cold-sensitive α2C-ARs may contribute to the increased activity of cold-induced vasoconstriction under estrogen-replete conditions.

Distinct cAMP signaling pathways differentially regulate alpha2C-adrenoceptor expression: role in serum induction in human arteriolar smooth muscle cells

The physiological role of alpha(2)-adrenoceptors (alpha(2)-ARs) in cutaneous, arteriolar, vascular smooth muscle cells (VSMs) is to mediate cold-induced constriction. In VSMs cultured from human cutaneous arterioles, there is a selective increase in alpha(2C)-AR expression after serum stimulation. In the present study, we examined the cellular mechanisms contributing to this response. Serum induction of alpha(2C)-ARs was paralleled by increased expression of cyclooxygenase-2 (COX-2), increased release of prostaglandins, and increased intracellular concentration of cAMP. Inhibition of COX-2 by acetyl salicylic acid (1 mM), NS-398 (5 microM), or celecoxib (3 microM) abolished the increase in cAMP and markedly reduced alpha(2C)-AR induction in response to serum stimulation. The cAMP agonists, forskolin (10 microM), isoproterenol (10 microM), and cholera toxin (0.1 microg/ml) each dramatically increased expression of alpha(2C)-ARs in human cutaneous VSMs. The A-kinase inhibitor H-89 (2 microM) inhibited phosphorylation of cAMP response element binding protein, but not the increase in alpha(2C)-AR expression in response to these agonists. cAMP-dependent but A-kinase independent signaling can involve activation of guanine nucleotide exchange factors for the GTP-binding protein, Rap. Indeed, pull-down assays demonstrated Rap1 activation by serum and forskolin in VSM. Transient transfections using alpha(2C)-AR promoter-luciferase reporter construct demonstrated that Rap1 increased reporter activity, whereas the A-kinase catalytic subunit decreased reporter activity. These results indicate that cAMP signaling can have dual effects in cutaneous VSMs:activation of alpha(2C)-AR transcription mediated by Rap1 GTPase and suppression mediated by A-kinase. The former effect predominates in serum-stimulated VSMs leading to a COX-2, cAMP, and Rap 1-dependent increase in alpha(2C)-AR expression. Such increased expression of alpha(2C)-ARs may contribute to enhanced cold-induced vasoconstriction and Raynaud's phenomenon.

Rho Kinase Mediates Cold-Induced Constriction of Cutaneous Arteries

Cold-induced vasoconstriction in cutaneous blood vessels is mediated in part by increased activity of vascular smooth muscle α2-adrenoceptors (VSM α2-ARs). In mouse cutaneous arteries, α2C-ARs are normally silent at 37°C but mediate cold-induced augmentation of α2-AR responsiveness. In transfected HEK293 cells, this functional rescue is mediated by cold-induced translocation of α2C-ARs from the Golgi to the plasma membrane. Experiments were performed to determine the role of Rho/Rho kinase signaling in this process. Inhibition of Rho kinase (fasudil, Y27632 or H-1152) did not affect constriction of isolated mouse tail arteries to the α2-AR agonist UK 14 304 at 37°C but dramatically reduced the augmented responses to the agonist at 28°C. After Rho kinase inhibition, cooling no longer increased constriction evoked by α2-AR stimulation. Cooling (to 28°C) activated Rho in VSM cells and increased the calcium sensitivity of constriction in α toxin-permeabilized arteries. Stimulation of α2-ARs in VSM cells had no effect on Rho activity or calcium sensitivity at 37°C or 28°C. In HEK293 cells transfected with α2C-ARs, cooling (to 28°C) stimulated the translocation of α2C-ARs to the plasma membrane and this effect was prevented by inhibition of Rho kinase, using fasudil or RNA interference. Consistent with inhibition of the spatial rescue of α2C-ARs, fasudil inhibited α2-AR–mediated mobilization of calcium in tail arteries at 28°C but not 37°C. Therefore, cold-induced activation of Rho/Rho kinase can mediate cold-induced constriction in cutaneous arteries by enabling translocation of α2C-ARs to the plasma membrane and by increasing the calcium sensitivity of the contractile process.

Regulation of alpha(2)-adrenoceptors in human vascular smooth muscle cells

This study analyzed the regulation of alpha2-adrenoceptors (alpha2-ARs) in human vascular smooth muscle cells (VSMs). Saphenous veins and dermal arterioles or VSMs cultured from them expressed high levels of alpha2-ARs (alpha2C > alpha2A, via RNase protection assay) and responded to alpha2-AR stimulation [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK-14,304, 1 microM)] with constriction or calcium mobilization. In contrast, VSMs cultured from aorta did not express alpha2-ARs and neither cultured cells nor intact aorta responded to UK-14,304. Although alpha2-ARs (alpha2C >> alpha2A) were detected in aortas, alpha2C-ARs were localized by immunohistochemistry to VSMs of adventitial arterioles and not aortic media. In contrast with aortas, aortic arterioles constricted in response to alpha2-AR stimulation. Reporter constructs demonstrated higher activities for alpha2A- and alpha2C-AR gene promoters in arteriolar compared with aortic VSMs. In arteriolar VSMs, serum increased expression of alpha2C-AR mRNA and protein but decreased expression of alpha2A-ARs. Serum induction of alpha2C-ARs was reduced by inhibition of p38 mitogen-activated protein kinase (MAPK) with 2 microM SB-202190 or dominant-negative p38 MAPK. UK-14,304 (1 microM) caused calcium mobilization in control and serum-stimulated cells: in control VSMs, the response was inhibited by the alpha2A-AR antagonist BRL-44408 (100 nM) but not by the alpha2C-AR antagonist MK-912 (1 nM), whereas after serum stimulation, MK-912 (1 nM) but not BRL-44408 (100 nM) inhibited the response. These results demonstrate site-specific expression of alpha2-ARs in human VSMs that reflects differential activity of alpha2-AR gene promoters; namely, high expression and function in venous and arteriolar VSMs but no detectable expression or function in aortic VSMs. We found that alpha2C-ARs can be dramatically and selectively induced via a p38 MAPK-dependent pathway. Therefore, altered expression of alpha2C-ARs may contribute to pathological changes in vascular function.

Accumulation of diflubenzuron in bolti fish Orechromis niloticus

Orechromis niloticus fingerlings were exposed to the insect growth inhibitor diflubenzuron 1-(2,6-Difluorobenzoyl)3-(4-chlorophenyl)urea for 21 days. Diflubenzuron was introduced to the aquariums where fish were maintained at the beginning of the experiment, then its level in water, gills and liver was detected after 1, 7, 14 and 21 days. The fish accumulated diflubenzuron 76 and 99 times greater than the water content when kept in an ambient concentration of 2.5 and 5 mg/l, respectively, indicating a low bioaccumulation potential. Some degradation products of diflubenzuron were found mainly in liver and water.