The cAMP effectors PKA and Epac activate endothelial NO synthase through PI3K/Akt pathway in human endothelial cells

3',5'-Cyclic adenosine monophosphate (cAMP) exerts an endothelium-dependent vasorelaxant action by stimulating endothelial NO synthase (eNOS) activity, and the subsequent NO release, through cAMP protein kinase (PKA) and exchange protein directly activated by cAMP (Epac) activation in endothelial cells. Here, we have investigated the mechanism by which the cAMP-Epac/PKA pathway activates eNOS. cAMP-elevating agents (forskolin and dibutyryl-cAMP) and the joint activation of PKA (6-Bnz-cAMP) and Epac (8-pCPT-2'-O-Me-cAMP) increased cytoplasmic Ca²⁺ concentration ([Ca²⁺]_c) in ≤30% of fura-2-loaded isolated human umbilical vein endothelial cells (HUVEC). However, these drugs did not modify [Ca²⁺]_c in fluo-4-loaded HUVEC monolayers. In DAF-2-loaded HUVEC monolayers, forskolin, PKA and Epac activators significantly increased NO release, and the forskolin effect was reduced by inhibition of PKA (Rp-cAMPs), Epac (ESI-09), eNOS (L-NAME) or phosphoinositide 3-kinase (PI3K; LY-294,002). On the other hand, inhibition of CaMKII (KN-93), AMPK (Compound C), or total absence of Ca²⁺, was without effect. In Western blot experiments, Serine 1177 phosphorylated-eNOS was significantly increased in HUVEC by cAMP-elevating agents and PKA or Epac activators. In isolated rat aortic rings LY-294,002, but not KN-93 or Compound C, significantly reduced the vasorelaxant effects of forskolin in the presence of endothelium. Our results suggest that Epac and PKA activate eNOS via Ser 1177 phosphorylation by activating the PI3K/Akt pathway, and independently of AMPK or CaMKII activation or [Ca²⁺]_c increase. This action explains, in part, the endothelium-dependent vasorelaxant effect of cAMP.

Activation of PKA and Epac proteins by cyclic AMP depletes intracellular calcium stores and reduces calcium availability for vasoconstriction

AIMS

We investigated the implication of PKA and Epac proteins in the endothelium-independent vasorelaxant effects of cyclic AMP (cAMP).

MAIN METHODS

Cytosolic Ca(2+) concentration ([Ca(2+)]c) was measured by fura-2 imaging in rat aortic smooth muscle cells (RASMC). Contraction-relaxation experiments were performed in rat aortic rings deprived of endothelium.

KEY FINDINGS

In extracellular Ca(2+)-free solution, cAMP-elevating agents induced an increase in [Ca(2+)]c in RASMC that was reproduced by PKA and Epac activation and reduced after depletion of intracellular Ca(2+) reservoirs. Arginine-vasopressin (AVP)-evoked increase of [Ca(2+)]c and store-operated Ca(2+) entry (SOCE) were inhibited by cAMP-elevating agents, PKA or Epac activation in these cells. In aortic rings, the contractions induced by phenylephrine in absence of extracellular Ca(2+) were inhibited by cAMP-elevating agents, PKA or Epac activation. In these conditions, reintroduction of Ca(2+) induced a contraction that was inhibited by cAMP-elevating agents, an effect reduced by PKA inhibition and reproduced by PKA or Epac activators.

SIGNIFICANCE

Our results suggest that increased cAMP depletes intracellular, thapsigargin-sensitive Ca(2+) stores through activation of PKA and Epac in RASMC, thus reducing the amount of Ca(2+) released by IP3-generating agonists during the contraction of rat aorta. cAMP rise also inhibits the contraction induced by depletion of intracellular Ca(2+), an effect mediated by reduction of SOCE after PKA or Epac activation. Both effects participate in the cAMP-induced endothelium-independent vasorelaxation.

PKA and Epac activation mediates cAMP-induced vasorelaxation by increasing endothelial NO production

Vascular relaxation induced by 3',5'-cyclic adenosine monophosphate (cAMP) is both endothelium-dependent and endothelium-independent, although the underlying signaling pathways are not fully understood. Aiming to uncover potential mechanisms, we performed contraction-relaxation experiments on endothelium-denuded and intact rat aorta rings and measured NO levels in isolated human endothelial cells using single cell fluorescence imaging. The vasorelaxant effect of forskolin, an adenylyl cyclase activator, was decreased after selective inhibitor of protein kinase A (PKA), a cAMP-activated kinase, or L-NAME, an endothelial nitric oxide synthase (eNOS) inhibitor, only in intact aortic rings. Both selective activation of PKA with 6-Bnz-cAMP and exchange protein directly activated by cAMP (Epac) with 8-pCPT-2'-O-Me-cAMP significantly relaxed phenylephrine-induced contractions. The vasorelaxant effect of the Epac activator, but not that of the PKA activator, was reduced by endothelium removal. Forskolin, dibutyryl cAMP (a cAMP analogue), 6-Bnz-cAMP and 8-pCPT-2'-O-Me-cAMP increased NO levels in endothelial cells and the forskolin effect was significantly inhibited by inactivation of both Epac and PKA, and eNOS inhibition. Our results indicate that the endothelium-dependent component of forskolin/cAMP-induced vasorelaxation is partially mediated by an increase in endothelial NO release due to an enhanced eNOS activity through PKA and Epac activation in endothelial cells.

Trans-resveratrol simultaneously increases cytoplasmic Ca(2+) levels and nitric oxide release in human endothelial cells

SCOPE

The aim of this study was to investigate whether the dietary polyphenol trans-resveratrol (t-Resv) increases [Ca(2+)](c) in endothelial cells, leading to a simultaneous augmentation of nitric oxide (NO) biosynthesis.

METHODS AND RESULTS

We have separately and simultaneously measured [Ca(2+)](c) and NO in human endothelial cells using the Ca(2+) indicator fura-2 and the NO-sensitive fluorescent probe 4,5-diaminofluorescein. In ∼30% of cells, t-Resv (30 μM) induced an increase in [Ca(2+)](c) with a transient as well as sustained component and a simultaneous increase in NO biosynthesis. This effect was reduced by non-selective Ca(2+) channel blockers, inhibition of intracellular Ca(2+) release, inhibition of endothelial nitric oxide synthase (eNOS) and, to a lesser extent, inhibition of extracellular signal-regulated kinase 1/2 (ERK 1/2) or 5' adenosine monophosphate-activated protein kinase (AMPK). t-Resv did not modify in vitro eNOS activity, suggesting that the observed stimulation of NO generation proceeds via mobilisation of Ca(2+) and not through direct effects on eNOS.

CONCLUSION

We therefore show, for the first time, that t-Resv induces a concentration-dependent, simultaneous increase in [Ca(2+)](c) and NO biosynthesis that could be linked to its endothelium-dependent vasorelaxant effect. Under the assumption that t-Resv exhibits similar behaviour in human blood vessels in vivo, the pharmacological properties described here may contribute to the beneficial cardiovascular effects of this polyphenol by improving endothelial function.

[Locomotion and gait disorders]

INTRODUCTION

Human beings are characterised by the specialisation of certain functions, such as language or the ability to walk. We have achieved this capacity thanks to the development of multiple connections among different areas of the central and peripheral nervous system, together with adaptation of the musculoskeletal system. These are all essential to be able to walk correctly and to keep our balance.

DEVELOPMENT

Gait disorders are currently receiving a great deal of attention in neurology departments, and this fact is directly related to the phenomenon of the ageing of the population, since it is a pathology that is particularly prevalent among the elderly. One of the fundamental mainstays in the study of these disorders is being able to distinguish between the different clinical gait patterns and their classification according to the neural system that has been damaged. Observation, the use of different manoeuvres in the examination and the search for other associated clinical signs all enable us reach a good diagnostic approximation, which will later be confirmed with more specific complementary techniques.

CONCLUSIONS

From the therapeutic point of view, an early multidisciplinary intervention by the neurologist, primary care, specialists in rehabilitation and physiotherapists improves patients' quality of life and lowers the rate of associated comorbidity and mortality, which also results in a reduction in spending on community health resources.

Calculation of the wetting parameter from a cluster model in the framework of nanothermodynamics

The critical wetting parameter omega(c) determines the strength of interfacial fluctuations in critical wetting transitions. In this Brief Report, we calculate omega(c) from considerations on critical liquid clusters inside a vapor phase. The starting point is a cluster model developed by Hill and Chamberlin in the framework of nanothermodynamics [Proc. Natl. Acad. Sci. USA 95, 12779 (1998)]. Our calculations yield results for omega(c) between 0.52 and 1.00, depending on the degrees of freedom considered. The findings are in agreement with previous experimental results and give an idea of the universal dynamical behavior of the clusters when approaching criticality. We suggest that this behavior is a combination of translation and vortex rotational motion (omega(c)=0.84).